Wednesday, November 3, 2004

8:05 a.m.









Hilton Washington, D.C. North

620 Perry Parkway

Gaithersburg, Maryland




Call to Order 3

Conflict of Interest Statement 5

Update on Previous Meeting Discussions/

Introduction to the Topics of This Meeting 7

Topic 1: Pharmacogenetics of Irinotecan

Introduction 30

Scientific and Clinical Evidence 49

Current and Future Perspectives on

Irinotecan Pharmacogenetics 76

Clinical Utilities of Genotyping 113

Committee Discussions and Recommendations 143

Open Hearing 166

Topic 2: Drug-Drug Interaction Concept

Paper: Issues Related to CYPs, Transporter-

and Induction-based Interactions and

Multiple Inhibitor Drug Interaction


Conflict of Interest Statement 206

Relevant Principles on Drug Interaction

Concept Paper 209

A Scientific Perspective 255

Induction-Based Interactions 269

Multiple Inhibitor Studies 323

Committee Discussions and Recommendations 345




[8:05 a.m.]

DR. VENITZ: Okay; good morning, everyone.

Welcome to the Clinical Pharmacology Subcommittee

meeting. We have a full agenda for today, and

before we proceed with our agenda, I would like to

go around the table and for every person sitting on

this table to introduce him or herself, please.

Gerry, do you want to go ahead?

MR. MIGLIACCIO: Gerry Migliaccio,

vice-president, global quality operations, Pfizer.

DR. BLASCHKE: Terry Blaschke, Stanford


DR. BARRETT: Jeff Barrett, Childrens

Hospital, Philadelphia.

DR. CAPPARELLI: Edmund Capparelli,

University of California, San Diego.

DR. DAVIDIAN: Marie Davidian, North

Carolina State University.

DR. DERENDORF: Hartmut Derendorf,

University of Florida.

DR. GIACOMINI: Kathy Giacomini,



University of California, San Francisco.

DR. HALL: Steve Hall, Indiana University

School of Medicine.

DR. JUSKO: William Jusko, University at


DR. VENITZ: Jurgen Venitz, Virginia

Commonwealth University.

MS. SCHAREN: Hilda Scharen, FDA Center

for Drugs, executive secretary.

DR. MCLEOD: Howard McLeod, Washington


DR. SADEE: Wolfgang Sadee, Ohio State


DR. WATKINS: Paul Watkins, University of

North Carolina.

DR. RAHMAN: Atiko Rahman, FDA.

DR. WILLIAMS: Grant Williams, oncology

drugs, FDA.

DR. PAZDUR: Richard Pazdur, oncology

drugs, FDA.

DR. LESKO: Larry Lesko, Office of

Clinical Pharmacology and Biopharmaceutics at FDA.



DR. VENITZ: Thank you, everyone.

Our next step is to review the conflict of

interest statement, and Ms. Scharen is going to do

that for us.

MS. SCHAREN: Good morning. The following

announcement addresses the issue of conflict of

interest and is made a part of the record to

preclude even the appearance of such at this


Based on the submitted agenda and all

financial interests reported by the subcommittee

participants, it has been determined that all

interest in firms regulated by the Center for Drug

Evaluation and Research present no potential for an

appearance of conflict of interest with the

following exceptions: in accordance with 18 USC

208(b)(3), the following participants have been

granted waivers: Dr. Paul Watkins has been granted

a waiver for consulting with the sponsor and a

competitor on unrelated matters. He has received

less than $10,001 per year from the sponsor and

between $10,000 to $50,000 per year from the



competing firm.

Dr. Kathleen Giacomini has been granted a

waiver because her spouse is a member of the

speakers bureaus for the sponsor and a competitor.

He lectures on matters unrelated to the issues to

be discussed at this meeting. He receives less

than $10,001 per year from the sponsor and between

$10,001 and $50,000 per year from the competing


Dr. Edmund Capparelli has been granted a

waiver for unrelated consulting for the sponsor.

He receives less than $10,001 per year. A copy of

the waiver statements may be obtained by submitting

a written request to the agency's Freedom of

Information Office, Room 12-A-30 of the Parklawn

Building. In addition, Dr. William Jusko has been

recused from participating in this portion of the


We would like to note that Dr. Paul

Fachler is participating in this meeting as

nonvoting industry representative acting on behalf

of regulated industry. Dr. Fachler's role in this



meeting is to represent industry interests in

general and not any one particular company. Dr.

Fachler is employed by Teva Pharmaceuticals.

In the event that the discussions involve

any other products or firms not already on the

agenda for which an FDA participant has a financial

interest, the participants are aware of the need to

exclude themselves from such involvement, and their

exclusion will be noted for the record. With

respect to all other participants, we ask in the

interests of fairness that they address any current

or previous financial involvement with any firm

whose product they may wish to comment upon.

Thank you.

DR. VENITZ: Thank you, Hilda.

Our first agenda item is Dr. Lesko, who is

going to bring us up to date on the outcomes of our

previous meetings and who is going to set the stage

for the next day and a half.


DR. LESKO: Thank you, Dr. Venitz and good

morning, everybody, and welcome to our fourth Clin



Pharm Subcommittee meeting of the Advisory

Committee for Pharmaceutical Sciences. And I'd

like to say that we've been looking forward to

today's meeting, and I think we have three

interesting topics that we will be looking for your

input and discussion of as we move forward with

these particular areas.

Following the first couple of meetings,

there was some interest in sort of stepping back

and reflecting and recapping on some of the topics

that have been previously presented to the

subcommittee and in particular to reflect upon the

value of the meeting in terms of what FDA has

accomplished with the input from the committee.

And what I'm going to do now is summarize the

topics that we've discussed at prior meetings along

with some of the status of the projects that we've

brought before the Committee.

Let me first say that again, we have some

new members on the Committee, so this will be very

helpful, I think, for those individuals, but this

Committee was established in May of 2002, and in



putting the Committee together, we selected

individuals with very specific expertise in broad

areas of clinical pharmacology that was

cross-applicable across many of the therapeutic

areas that clinical pharmacology deals with, and

those three areas were pharmacogenomics,

pharmacometrics and pediatrics, three broad areas,

but as we've seen with the past meetings, various

subtopics that are of interest to clinical

pharmacology. The three prior meetings occurred in

October 2002, April 2003 and last November.

I'll begin with some of the topics that we

covered during these meetings, and you'll see that

the topics were not confined to one or another of

the advisory committees. We've used our meetings

in a continuous fashion as the projects unfolded,

and the first topic that we actually brought before

the Committee was a methodology for identifying

patient subgroups at risk for toxicity. These are

the subgroups that represent specific or special

populations such as those with renal impairment.

And what we did in the early meeting was



propose a quantitative method that was based upon a

number of features that we thought would be

beneficial, not only the mean exposure of the drug

in test populations such as the renal impaired

population and reference populations like the

healthy volunteers, but also, we proposed a method

that looked at the distribution of exposure values,

and then, from that distribution and comparing

those two distribution curves, identified a

critical cutoff value at the high end of the

distribution curve based on the exposure response


What we are trying to get at here is a

cutoff value above which the risk of toxicity was

unacceptable from a clinical perspective. In

addition, we showed how we could calculate the

probably of a clinically significant response

beyond that cutoff, and we proposed a standardized

decision tree for dosing adjustments.

The summary points of our discussion was

that we linked population PK with clinical outcomes

through examples with unresolved questions. We



discussed exposure response methodologies, using

modeling and simulations of adverse event

probabilities through drug-drug interactions. We

also discussed in some of our earlier meetings

decisional analysis based on exposure response

methods for assessing QT risk in special


These were intended to be examples of the

methodology, and inherent in those examples was

some methodological questions and issues that we

brought before the Committee for discussion.

So what did all of this lead to? Well,

the status of this project was that we've currently

implemented this methodology in our NDA reviews.

The methods we proposed to the Committee or a

variant of them as we went through the process are

routinely used in the quantitative analysis of

exposure response data for efficacy and safety.

The primary impact of the topic and the Committee's

recommendations have been for us in the office, we

use these methodologies and recommendations to

formulate our dosing adjustments that we recommend



for inclusion in the package insert or in the

product label.

So we really went to several methods then

from our discussions here, selecting each of them

on a case-by-case basis, depending on the question

and the issues. That was the identification of

patient subgroups at risk.

We also brought another methodology that

was intended to do basically the same thing, and

that was the utility function for optimizing dosing

strategies. The summary points associated with

this topic was that we had proposed the utility

function as a methodology based on the probability

of either an adverse event or the absence of

toxicity taking into account the magnitude of harm

if the adverse or toxicity occurs.

We worked on this project for some period

of time, and the status at the moment is that we've

postponed further development, not that it wasn't a

worthwhile project, but the underlying approach was

difficult for us in implementation. Underneath

this approach was assigning relative weights to the



value of the efficacy versus the value of the

toxicity, each of which can range from marginal to

significant, and thereby defining a therapeutic

index for the drug.

One of the ways you define these

endpoints, if you will, upper and lower limits of

acceptability and the relative benefit-risk is to

ask clinicians, which we did. We also searched

literature and looked for applications, and we

found that the approach for our purposes in

regulatory decision making was unsatisfactory

because of the difficulty in defining targets and

penalties for different measures of the utility


That being said, the method certainly has

merit, and we have seen this in terms of drug

development. It certainly has merit in its

application to the selection of doses to be used in

clinical trials during the drug development

process, and we know of examples where this is, in

fact, done by sponsors. But for our purposes, at

this point in time, we have not been able to



implement it as a regulatory, quantitative tool for

decision making.

The next topic that we had before the

Committee was using exposure response relationships

in the pediatric decision tree, which is an

appendix to our exposure-response guidance that was

released to the public in April of 2003. What we

had is summary points from these discussions, which

cover two of our meetings, was a proposal for the

design of a pediatric database to effectively

extract new knowledge from the in-house studies.

This was a data mining exercise, so that we could

use the information to update our pediatric

decision tree, which right now, is used

conventionally across our therapeutic areas.

We asked the Committee to comment and

recommend the highest priority questions or queries

from this database assuming that we could establish

it, and some of the things we presented to the

Committee using the database at the time was a

model for pediatric clearance in order to predict

it, which took into account age, adult PK and




We subsequently proposed a systematic

pediatric research project that was fairly

ambitious. We wanted to evaluate the trends in

exposure response with age, using the information

that we had in house. We wanted to develop a

standardized approach for use across therapeutic

areas for population PK studies, and we wanted to

develop a computer-aided pediatric template for

study design that we can use during the IND process

in designing studies in collaboration with a


So the status of this project, following

our deliberations at the Committee, is that it's

ongoing. The progress on the database itself has

been limited for a variety of reasons. We had

difficulty accessing data in our files because of

the nonuniformity in the way data comes in. Some

of it is electronic; some of it is manual. It

became a laborious process to assemble this data,

and it's still in an ongoing mode.

The other issue that we found in mining



our database was the availability of standard PK

and PD information. It was heterogeneous. We

could not easily take everything that we had

received in the files and assemble it into a

database that would be consistent across the

submissions. So it was a major work effort for us

to begin, but we have begun, although it's not a

complete project by any means.

We had proposed to the Committee a

pediatric research project, as I said, and this was

funded by CDER in June. I have June 2003. It

actually is 2004. Last couple of months, we

received money from the Center to fund this

project. It's being headed by Dr. Peter Lee, and

we've just begun to get going on the project.

We've hired four scientists under a contract.

We've established a steering committee for this

research. It has commenced, and we have some

12-month milestones.

So the input, the project are all ongoing,

and we're looking forward to sharing the results of

that project with the Committee as we move forward



into next year.

The next topic that we covered in the

early meetings was the genetic polymorphism of

TMPT. The summary points from this discussion

included a presentation on the scientific and

clinical evidence that linked three different TMPT

genotypes with the incidence of myelosuppression.

What we discussed was a general framework for

consideration of analytical validation, clinical

validity and clinical utility for improving

benefit-risk and pharmacogenomics.

The third summary point was the discussion

that we had in front of this Committee related to

the revision of the label of 6-mercaptopurine that

would include dosing adjustments based on genotype

and the more rich information on what we know to be

the case with regard to polymorphism of TPMT.

The status of this project is that with

the input of this Committee and our Pediatric

Oncology Subcommittee, the project is in essence

complete. Both committees, if you recall some of

the discussion that we had at this Committee,



recommend a revision of the label of 6-mp to

include TPMT information in various sections of the

label. Negotiations with the sponsor of these

products are basically complete, and the updated

label for both of the thiopurines will be available

in early 2005.

The next topic that was really a new topic

back in April of 2003 was our evaluation and

labelling of drug interactions of NMEs, an

important topic because we were just beginning the

initiation of the revision of our in vitro and in

vivo guidances for industry on drug interactions.

And a summary of what we presented at the Committee

was an in vitro drug interaction decision tree for

CYP enzymes and associated label language that

would go with that decision tree. We discussed

some of the scientific basis for policy decisions

related to NDA review, label language and class

distinctions for drug interactions, and we

discussed some specific drug-drug interaction

studies involving transporters, specifically PGP

and, by extension, some of the other transporters



that are sort of on the front edge of the drug

interaction area.

The status of this topic is that it's

complete in many ways, although we have a little

bit more work to do, but the revision of the

guidance, which was the process that was behind the

topic we brought before the Committee is nearly

complete. The working group has been working on

this for some time, and we're getting close to

finalizing that guidance, which would be an update

of our current in vitro and in vivo drug

interaction guidances.

Furthermore, the topic that we've

discussed here has been included as a topic and

discussion point in the office's GRP drug-drug

interaction map and cross-labeling map, so again,

we try to transfer the knowledge and information

that we've learned through this Committee to

day-to-day practice in terms of IND and NDA


A year ago, we introduced another new

topic. It was the end of phase 2-A meetings, and



we had a very useful discussion on the topic. We

had as a background, if you remember, the concept

paper on the end of phase 2-A meeting, and what we

presented was the principles of the concept, and we

received again a significant input on the goals,

the process, the obstacles and the metrics of

success of the end of phase 2-A meeting.

With regard to the concept paper, we have

worked on the development of a guidance for

industry on the end of phase 2-A guidance. We

anticipate this guidance will be a final guidance,

in that it's not necessarily a controversial

guidance. We like to get it out fairly soon.

However, the status is ongoing, and over

the past year, we've had at least four significant

end of phase 2-A meetings. These had to do with

the questions that we had in the concept paper.

They involved a fair amount of modeling and

simulation. In one case, we have a disease state

model that came out of the meeting that was very

useful for simulating phase 2-B and 3 trials. And

by all indications, these meetings have been a



success, both by comments we've received from the

sponsors and by comments we've received from the

medical divisions with whom we coordinate these


So we're very optimistic about this

process as a so-called critical path activity that

has the potential to impact the efficiency, the

informational content of the drug development


As I say, the deliberations were very

helpful to us in writing a draft guidance for

industry on the end of phase 2-A meeting. It's

undergone internal review, and for all practical

purposes, it's complete. There is a process to

release a guidance, and that would probably take us

through the first quarter of 2005, when we make

that guidance public.

Another topic we discussed before the

Committee was the quantitative analysis of QT. The

summary points that we presented to the Committee

was some approaches using modeling and simulation

and also metrics for assessing QTC interval



prolongation. If you recall, the metrics that we

talked about were pros and cons of maximal change

from baseline area under the QTC time curve, et

cetera. And we asked for input from the Committee

on these methodologies that we could begin to apply

in the review of QT studies within the NDA


Status of this is still ongoing. There's

a lot of current discussion on standardization of

both study design and data analysis of these kinds

of studies. We've made recommendations and

presentations that have stemmed from our discussion

here at the Advisory Committee to the CDER QT

working group, who was favorably impressed by what

we delivered in terms of a quantitative approach to

assessing the risk of QT.

We also discussed drug interactions

involving somewhat unrecognized and

underappreciated potential drug interactions

involving CYP2B6 and 2C8. The summary of our

presentation and discussion here at the Committee

was that we sort of took an inventory of our



current understanding of inhibition reactions in

particular that are based mechanistically on the

2C8 and 2B6 pathways.

We discussed some of the reliability of

the in vitro and vivo associations of these drug

interactions, similar to what we do for the more

common CYP enzymes to see to what degree these in

vitro studies can be a guide to the need to do

clinical studies, and if we do clinical studies,

what are the model drugs? So we did present some

examples to the Committee with model drugs, and

I've listed a few of them there asking for comment

on the methodology and the use of the information.

So the status of this project is ongoing.

The input was seriously considered in the context

of our CDER working group on drug-drug

interactions, and there's probably a good chance

we'll be discussing more of this in subsequent

Committee meetings.

So anyway, that in a nutshell is what

we've brought before the Committee as topics. I

think you can see how they fit into those three



broad areas of pharmacogenetics, pharmacometrics

and pediatrics. We've branched out into the

drug-drug interaction area as the need arose for us

to bring this to a public discussion.

So my reflections on the first three

meetings as we move into our next one is that the

topics we've brought before you as an advisory

committee have been challenging. We recognize they

have been diverse. They've been as diverse as the

expertise of the membership.

Just so you appreciate how we bring topics

to the Committee, we try to select topics that are

relatively new and important to NDA reviews such as

the quantitative methods. You've noticed that they

are not usually drug-specific, because we bring

general topics that are cross-applicable across

many therapeutic areas. We've brought topics to

the Committee that I think are cutting-edge

science, the drug interaction area in particular

with transporters and some of the new CYP enzymes

are areas that we have a lot of issues to resolve

in terms of what we would recommend to drug



sponsors and their drug development programs.

And finally, some of the topics we've

brought here had an element of controversy, because

they were new, and I would say in our

pharmacogenetic area, we've had a lot of good

discussion and clarity about the integration of

pharmacogenetics into product labels and into the

assessment of benefit risks.

So in short, a compliment to the

Committee. The value of this Committee has been

tremendous. I think it's the only committee that

has dealt with those topics. It has given us

significant guidance on decisions we have to make

in terms of the specific areas that we've brought

forward, and it has had a very significant

influence on our clinical pharmacology program at


And finally, many committees do vote.

Usually, this is characteristic of committees in

which specific drugs are brought forward for voting

on one issue or another associated with that. We

haven't done that very much in this Committee. The



nature of our topics really haven't lent themselves

to voting, because they are more general. We

anticipate we will be doing more of that, including

some of the topics that we will bring before you

today, but the primary benefit is not the voting,

necessarily; the primary benefit that we've

received is the copious notes that we've been able

to take and the benefit that we've had from the

discussion of the Committee.

So for all of this, I would thank you for

your service to the FDA and service to the public

as members of this Committee and, frankly, look

forward to further very interesting discussions

with you all.

I will pause at this point, and it looks

like if there's any questions, I'd be happy to

answer those. I'll turn it back to the Chair

before I move on to a specific topic.

DR. VENITZ: Thank you, Larry.

Any comments or questions by Committee


I'm interested in the end of phase 2



status. What are the metrics of success that

you're considering right now to evaluate whether

this program is going to be a success?

DR. LESKO: Yes, the metrics of success

really have been a questionnaire that we're

preparing to send to the company. We also call the

company to try to get feedback on what we did as a

process and what recommendations we gave them in

terms of value. We interact both with the clinical

group at sponsors. We work with the

biostatisticians and the clin pharm folks as well

as the regulatory folks at the various companies.

We also survey the medical division that

we coordinate the meeting with to see if what we

brought to the table in terms of the quantitative

methods was perceived to have value, and then,

finally, we have, in one form or another, a

debriefing of the internal team that worked on that

preparation for the end of phase 2-A meeting to get

back into lessons learned and see what we can do


What has it all meant? I think we need to



have more experience with it, but as I said in my

remarks, I think the feedback we've gotten both

from the company and the internal participants has

been very encouraging for us to go forward. These

have not been small efforts. We're somewhat

overwhelmed by the effort that goes into preparing

for these meetings in the short time frame that we

have, and it is very resource-intensive, so it's

important to us to actually get good metrics of

success, and we're going to be collecting those,

and I'd like to share that, maybe, with the

Committee at some point in time.

DR. VENITZ: And I was exactly going to

encourage you to do that, because as you remember,

the discussion that we had, even though the

Committee was very much in favor of this

initiative, there was concern about resource

allocation and so on, so you really have to

demonstrate that there is a value in doing this.

DR. LESKO: Exactly, and I remember those

comments exactly. And there was no rebuttal to

those. We just had to get into it and try it, and



indeed, we have gotten into it and tried it. But,

you know, aside from what the impact was on drug

development, the impact on us in FDA being able to

work together in a quantitative way to discuss drug

development and benefit risk in a way that you can

put on the table in terms of a model and do a lot

of what-if scenarios has really been good for us,

and I think it's, again, made us a stronger group

within the agency aside from whatever impact it had

on drug development.

It's oftentimes spoken about in the

context of critical path now, which came out this

past March of one of the leading initiatives of the

critical path project that has the potential to

influence in a positive way the drug development

process so--

DR. VENITZ: Thank you. Any other

comments, questions?

[No response.]

DR. VENITIZE: Then why don't you proceed

with the topics for the next day and a half?

DR. LESKO: Okay; so, now, switching to



the topics for the next day and a half, we're

bringing three projects, topics, to the Committee.

The first of those this morning is going to be in

the area of pharmacogenetics. Specifically, we're

going to be discussing the scientific and clinical

evidence that surrounds the UGT1A1 polymorphism and

its relationship to the pharmacogenetics of


This afternoon, we're going to bring to

the Committee a topic in the area of drug-drug

interactions. We'll be talking about metabolism

and transporter-based interactions, and again, this

is a relative topic to the revised guidance for

industry on the on-drug interactions. And thirdly,

we're going to bring to the Committee a topic from

the world of pharmacometrics, but it also is from

the world of the critical path.

We're beginning to focus on specific

critical path activities that we would like to

advance, and tomorrow, we'll be talking about one

that deals with the greater use of biomarkers

within the context of drug development and their



systematic progression to potential surrogate

markers. We'll primarily be talking about the

project and the project plans in the latter area

but not necessarily on any specific biomarker in

any given therapeutic area but a more general plan

that we hope to get input on as we move forward

with it.

So those are the three topics, and I think

what I'll do now is really launch into the first

topic, but I want to pull up the slides for that.

So the first topic of the morning is the

pharmacogenetics of Irinotecan. And we'll be

talking about the scientific and clinical impact of

UGT polymorphism. And my role up here right now is

to present a background to the topic and then turn

it over to the individual presenters that we've

scheduled for the morning prior to the discussion

with the Committee.

I'll start out with the labeling

regulations that apply to both new and to

previously-approved drugs, and the labeling

regulations are that if evidence is available to



support the safety and effectiveness of the drug

only in selected subgroups of the larger population

with the disease, the labeling shall describe the

evidence and identify specific tests needed for

selection and monitoring of patients who need the

drug. Obviously, this is not pharmacogenetic

specific but certainly I think encompasses

pharmacogenetic testing and information.

Pharmacogenetic information on drug labels

in general is not anything new. There's no current

barriers to including this information in product

labels. Many of you, I'm sure, are familiar with

examples of Herceptin, which is probably one of the

most well-known examples of pharmacogenetic

information on product labels. That is one example

of where a test and a drug therapy are used in

conjunction with one another.

If one were to survey the PDR and look at

package inserts over the years, about 35 percent of

the approved drugs have pharmacogenetic information

in the label. That doesn't necessarily mean that

that information is clinically important or



clinically relevant. Much of it is descriptive,

and much of it doesn't really translate into what

physicians would do in clinical practice having

that information in hand.

On the other hand, this is reflecting many

years of pharmacogenetics in terms of the

well-known biomarkers of cytochrome enzymes, and

it's only now that I think we're beginning to see

evidence that some of these enzymes are clinically

important and ought to be considered more seriously

in dosing of approved drugs.

A couple of other examples: Thioridazine

is a previously-approved drug, and if you look at

the package insert for that, there's a black box

warning in there that warns physicians and patients

that they ought to avoid this drug in 2D6 poor

metabolizers because of the toxicity risk

associated with poor metabolism, and Thioridazine,

of course, is a 2D6 substrate.

Atomoxetine is an example of a relatively

new drug for attention deficit disorder. There was

information from the clinical development plan



about the relationship between pharmacogenetics,

specifically poor metabolizers and extensive

metabolizers and clinical outcomes in terms of

efficacy and safety. This was information that

both the sponsor and the agency agreed is

worthwhile to put in the label, and in fact, we

included it in the label in seven different

sections, ranging from the laboratory test section

to the clinical pharmacology section. However,

there was no reason to require or suggest that a

test would have to be done prior to using the drug.

Cetuximab is a drug that was approved that

includes genomic information and particularly tumor

genomics about receptor positivity. This drug is

an EGFR inhibitor, and there's some general in

there about the relationship between the drug and

its pharmacology and its receptor positivity from a

mechanism standpoint. Again, there was no

recommendation to require a test prior to

prescribing the drug.

Finally, as I mentioned in my opening

remarks, we have discussed before the Committee



6-mercaptopurine and azathioprine, and these

labels, for all intents and purposes have been

updated to include the polymorphism information in

multiple sections. That was deemed important.

With regard to the outcome of the 6MP and

TMPT polymorphism, in many ways, it was a step in a

general framework for assessing the

pharmacogenetics of approved drugs. We are trying

to create a structure for that type of discussion

as we look at approved drugs that may benefit in

terms of the inclusion of pharmacogenomic

information, so we start out in this case with the

absence of information in the label, which was then

discussed at the Clin Pharm Subcommittee as well as

the Pediatric Oncology Subcommittee.

The new labeling, as I said, has been

revised in consultation with FDA and includes, now,

data on increased risk of severe myelosuppression

associated with genotypes of TMPT. So we think the

label has been updated with useful information for

clinicians and patients as they weigh their options

of using TMPT testing to guide along with other



adjunctive tools and clinical information to guide

the treatment of 6MP.

The general process that we've tried to

create as a general framework for assessing

pharmacogenetics, particularly of

previously-approved drugs, where we don't have the

benefit of new drug development plans and

prospective trials, is to think about the general

process of approaching the assessment of

pharmacogenetics and its value in inclusion on


In this meeting, we wouldn't mind having

comments on this. It's not one of the specific

questions, but I think we need to think about a

general process where we develop the appropriate

questions. What is the question we're asking of a

pharmacogenetic test or a piece of information? We

try to capture the relevant evidence. Oftentimes,

that comes from the published literature. You'll

see today how we try to abstract and summarize in a

sort of meta-analysis the scientific and clinical

evidence that allows us to go forward and make a




We think it's important to evaluate the

quality of the studies, and that's what we've done

in this case of 6MP as well as the Irinotecan we'll

talk about. We look at the overall strength of the

evidence from the individual studies, and we

consider other factors in the relabeling decision

that has to do with test availability, test

performance and things of that sort, and then,

finally, we move to the specific language for the


So it's a general framework that we walk

through as we think about this drug or that drug or

the next drug where pharmacogenetic information may

possibly be pertinent to the improvement of

benefit-risk or dosing.

Now, today, you're going to hear about the

current understanding of pharmacogenetics and

neutropenia with regard to Irinotecan. What I've

summarized in this table is on the left-hand side,

groups that begin with all of the patients and then

moving over from left to right the prevalence of



genotypes and the risk of toxicity that we

currently feel is the case. And this comes from

the data of one paper that's been published by

Innocenti in 2004, and what this shows basically is

that all patients have a relative risk of 10

percent of developing grade three/grade four


Breaking down the general population, we

have a subgroup that represents the 7/7 genotype

for UGT. Prevalence of that genotype is

approximately 10 percent. The relative risk of

toxicity, that is to say, the penetrance of

toxicity is 50 percent. Patients that are

heterozygous, prevalence of 40 percent with a

relative risk of toxicity of 12.5 percent, and at

least in this study, patients that were 6-6 had a

prevalence of 50 percent and a relative risk of

toxicity of zero percent.

So you see more of that data, but this is

the compelling data I think that facilitated

bringing this before the Committee. So we see the

potential for a test for UGT testing in this figure



that oftentimes is used to represent the value of

pharmacogenetics. And basically, we're looking at

patients with the same diagnoses that require this

drug for its approved indication and an overall

risk of 10 percent for neutropenia.

We know, however, in this general

population is a mixture of people with different

genotypes, and the value of the tests and the way

we'd like to consider this is what would this test

bring to the table as an adjunct piece of

information to use this drug in the most optimal

way? We have on the top the profile for the high

risk patient that we could identify with a genomic

test. Not all of those patients identified, as

you'll see, will develop frame toxicity. We have a

middle group that represents those at moderate

risk, and we have the bottom group based on the

data I've showed you that has a relatively low


So I think the goal of pharmacogenetics in

general and in this case specifically is to try to

differentiate and discern the differences between



patients who otherwise would be perceived to be

those patients with the same disease and the same

indication for the drug and bring that

differentiation as a tool to the clinical practice

for improving benefit-risk and drug and dose


So that's the context for what we want to

do this morning. So we'll begin with a discussion

of the scientific and clinical evidence that links

the UGT polymorphism with severe neutropenia.

We'll discuss, then, the role that testing can play

in identifying patients predisposed to severe


Now, I want to share with you that we have

had very positive interactions with the sponsor on

this topic. The sponsor is committed to providing

informative and understandable labeling as is the

FDA for all its drug products. Both agree that

information on UGT polymorphism and the risk of

toxicity on the label is of great importance. Both

sponsor and FDA agree to update the label to fully

inform prescribers and patients about




However, in this discussion today, we're

not going to get into what the label will say or

what the specific wording will say. We'll be

talking primarily about the scientific and clinical

evidence and the strength of evidence and the

questions that we've brought before the Committee.

I'll say this once now, just to sort of

create a framework for what you're going to hear.

We'll go back to the questions, obviously, near the

end of the morning. But basically, we're going to

ask is the clinical and scientific evidence that

you'll hear sufficient to demonstrate that

homozygous genotypes, the 7/7 genotypes, are at

significantly greater risks for developing

neutropenia and/or acute and delayed diarrhea from


We're going to ask based upon what is

known on this relationship between Irinotecan

containing regimens and toxicity three

subquestions: do we know enough to recommend the

starting dose of the drug in the single agent and



combination therapy? What would be the risks and

benefits of the recommended starting dose? And if

we need more information, what is the appropriate

study to evaluate dosing in these types of


We'll ask how information about genotype

can be used in combination with bilirubin. This

is, like a lot of genetic tests, not the end all

and be all, but it's an adjunct piece of

information that, used in conjunction with other

indicators like bilirubin, can be used to improve

clinical decision making.

And finally, you'll see some information

where we're going to ask is the measurement of the

genotype sufficiently robust in terms of its

clinical sensitivity and specificity to be used as

a response predictor test for Irinotecan dosing?

So those are the questions and my

introduction. I could pause and turn it over to

the chair, or we can launch into the next


DR. VENITZ: Any quick questions or



comments by the Committee before we start off on

the first topic?

DR. SINGPURWALLA: I hesitate to raise

these questions because I'm new here to this

Committee, but I'd like to draw your attention--I'd

like to go to that particular chart, where you had

prevalence and risk of toxicity. If I were to

understand correctly, the purpose of this chart is

to show that patients who are 7/7, and I don't know

what that means, have a 50 percent risk of


DR. LESKO: That is correct.

DR. SINGPURWALLA: There are two concerns

I have. One is why is the 10 percent prevalence

important? Because if you know the patient is 7/7,

then, the risk of toxicity is 50 percent. So the

fact that there are only 10 percent of individuals

who are of that particular category is not

relevant, unless you are giving the drug blindly,

without taking into consideration the

characteristics of them. So that's the first

question I want to ask.



DR. LESKO: Okay.

DR. SINGPURWALLA: Then, I have a comment

to make, and I'm not sure if this is appropriate,

but there's something called Simpson's Paradox that

arises in these particular contexts. And I'm

wondering if that has been taken into account.

DR. LESKO: Well, let's go to the first

question. I think in the first question, what I've

showed is that in the overall population, and you

use that term blinded. If you're blinded, and we

were all sitting around the room as potential

patients, the overall risk of toxicity is 10

percent. The question is which of the one out of

10 people are going to be most at risk for that


Without a test, you wouldn't know that.

You could obviously use other information that's

available on the drug and currently is in the label

regarding age or bilirubin levels. What the

genomic tests would do is to begin to differentiate

those people in the room, those 10 people around

the table that would be more at risk than the 10



percent risk for the general population, because

you're teasing out, obviously, the people that

would have a very low risk or no risk at all and

identifying those with a higher risk.

So if we took the general population,

subdivided it by genotype, then, the overall risk

would be 10 percent. It's only a reference mark.

I didn't mean to say more about it than that.

However, in this group of patients identified by a

genotype, by a test, the risk is much higher. It's

about 50 percent.

And what you'll hear in some of the

presentations is the likelihood ratio and relative

risk of developing this adverse event in that

defined subset by the genomic test, so that's the

relevance of the test and comparing it to the

current situation without and the future situation

with a test.

DR. SINGPURWALLA: Yes, but I'm still not

clear. If there is a 7/7 patient, I'm sorry; you

wouldn't blindly give the drug to anybody, any

person who shows up at random. You'd find out if



that is a 7/7 and then act accordingly; isn't that


DR. LESKO: Well, clinically, I'd think

you'd want to do that, because that would have a

role in making your decision to give the drug, what

dose to give and to consider other choices, but you

need something to identify that patient, and

currently, that information is not contained in the

package insert to guide the physician to make that


DR. SINGPURWALLA: I see. So now, given

that that is the case, then, I would strongly

encourage you to look at this notion, this concept

of Simpson's Paradox before you arrive at a 10

percent risk for patients overall.

DR. LESKO: Can you tell me what Simpson's

Paradox is?


DR. SINGPURWALLA: Well, yes, what is good

for--a drug is good for men, and a drug is good for

women, but a drug is not good for the population as

a whole. That's the paradox. Okay; some of your



statisticians will help you with that.

DR. LESKO: Okay.

DR. SINGPURWALLA: If not, I'll charge you

a fantastic consulting fee and help you.

DR. LESKO: Sounds good. I don't know if

you'd be on our advisory committee.


DR. SADEE: Larry, I have a comment, maybe

a different type of question that's brought up by

this polymorphism for Irinotecan.

The optimal dose, unquote, optimal dose

has been derived before these considerations, and

that includes a patient population that's really

inappropriate to calculate the optimal dose. So

what would be the position of the FDA to--in new

trials, where you combine Irinotecan? Do you go by

the old optimal dose, unquote, that included a

patient population that really shouldn't have been


So the question would be how do we define

optimal dose in future trials to the normal

population, which is the inverse of saying what is



the optimal dose for those people who are at high


DR. LESKO: Right; yes, I don't think we

have the data to make that call. We'd like to know

the answer to that question, but I don't think we

have enough information to say what the optimal

dose would be for these subtypes. I'm not sure we

have enough information to talk about the optimal

dose for any of the patient groups.

However, we're going to discuss that as we

get further into the morning. In fact, I think

that's one of the questions we'll talk about: in

the absence of credible information to discern the

dose, what type of study and what type of study

design would be appropriate? And I think you'll

hear about some of the ongoing studies that will be

along those lines. So maybe we can leave that as a

partial answer and wait for the rest of the


DR. VENITZ: Thank you, Dr. Lesko.

Then, our first speaker on that topic is

Dr. Atik Rahman. He's going to review for us the



clinical evidence of the role of UGT1A1 in


DR. RAHMAN: Good morning. I am Atik

Rahman, the acting deputy director of the Division

of Pharmaceutical Evaluation I, the Office of

Clinical Pharmacology and Biopharmaceutics. I'm

also the chair of the OCPB Pharmacogenetic Working


This morning, you have already heard from

Dr. Lesko regarding the approach that we took with

6MP and thiopurine methyltransferase enzyme. The

pharmacogenetics of thiopurine methyltransferase,

TMPT enzyme, and 6MP toxicity was discussed by the

Advisory Committee of the Pharmaceutical Sciences

in November of 2001. Subsequently, the topic was

also discussed by this Committee on April 23 and

also by the Oncology Drug Advisory Committee,

Pediatric Subcommittee on July 15 of 2003.

I will briefly discuss or update the

Committee on 6MP label modifications that resulted

from the Committee's deliberations and the FDA

interaction with the manufacturer of Purenithol. I



will follow that with the scientific and the

clinical evidence from the literature that we have

in the agency to demonstrate a relationship between

UGT1A enzyme polymorphism and its association with

Irinotecan toxicity.

6MP is inactivated by TPMT. TPMT is a

polymorphic enzyme. Ninety percent of the

caucasian and African-American population have

normal gene and normal enzyme activity. Ten

percent of the population have intermediate enzyme

activity, resulting from one deficient TPMT allele,

and one in 300 has low or no TPMT activity because

of two deficient allele in their gene.

There is a strong correlation between

genotype and phenotype, which is expressed as

either TPMT enzyme activity or as the levels of

6-thioguanine nucleotides in red blood cells.

A clinical study showed that 100 percent

of the homozygous patients required 6MP dose

reduction to prevent toxicity, compared to 35

percent of heterozygous and 7 percent wild type

patients. Currently, prospective trials are



ongoing to evaluate appropriate dose of 6MP in

acute lymphoblastic leukemia patients.

6MP is given with other myelosuppressive

therapy in the treatment of acute lymphoblastic

leukemia or ALL. Literature information indicated

a potential benefit of reducing the dose of 6MP in

patients with low to intermediate TPMT enzyme

activity. This reduction of approximately 50

percent 6MP dose in heterozygous and approximately

80 percent 6MP dose reduction in homozygous

patients allowed other myelosuppressive agents to

be given in full dose with 6MP during the entire

course of therapy.

Most of ALL protocol now avoid radiation

with 6MP because of the higher incidences of brain

tumors observed in TPMT-deficient patients in

previous trials.

Based on the advice of the advisory

committees and the manufacturer of Purinethol, Tiva

collaborated to include the information on TPMT

polymorphism and its relationship with 6MP toxicity

in the package insert of Purinethol. A new



subsection is included in the clinical pharmacology

section to describe the metabolism of 6MP and TPMT


In the warning section, bone marrow

toxicity subsection includes a warning for

substantial dose reduction for homozygous TPMT

deficient patients. Information on the

availability of genetic tests is indicated in the

precaution section.

The availability of the test is mentioned

in the dosage and administration section of the

label, and substantial dose reduction is indicated

for patients with TPMT deficiency. In the future,

we hope to provide specific dosing recommendations

for both the homozygous and the heterozygous TPMT

deficient patients for 6MP therapy.

Now, I al provide you with the scientific

and clinical evidence that relates Irinotecan

pharmacogenetics with toxicity. Irinotecan is

indicated as a first line therapy in combination

with 5-fluorouracil and leucovorin for colorectal

cancer patients. The drug is also indicated as a



single agent for patients with metastatic

colorectal carcinoma, whose disease has recurred or

progressed after initial 5-fluorouracil-based


Two phased randomized controlled

multinational clinical trials show that Irinotecan

in combination with 5-fluorouracil and leucovorin

increased the survival in first line colorectal

cancer patients compared to Irinotecan alone or

5-fluorouracil alone. Two multicenter randomized

clinical trials show significant increase in

survival for colorectal cancer patients whose

disease has recurred or progressed after prior

5-fluorouracil therapy.

Irinotecan is metabolized by

carboxyesterases to SN38, a metabolite which is

1,000 times more potent than the parent drug. SN38

is glucuronidated in the liver by UDP glucuronol

transferase family of enzymes, predominantly by

UGT1A1, and eliminated via biliary route.

Deficiency of UGT1A1 results in increased SN38

levels in plasma and in bone marrow cells, causing



hematologic and nonhematologic toxicities. These

toxicities result in dose delay, dose reduction and

hospitalization and even sometimes in deaths.

UGT1 gene is located on chromosome 2 and

contains at least 13 different promoter axons which

are spliced to common axons 2 through 5. UGT1A1 is

an isoform that is associated with bilirubin

glucuronidation. The isoenzyme has more than 30

variant alleles. UGT1A1*28 is a variant allele

that contains seven TA repeats in that TATA box of

the promoter region instead of six TA repeats.

Today, we will focus on UGT1A1*28 variant

only, because the agency believes that we have the

most mature data on this variant's association with

Irinotecan toxicity. I will use the term 7/7

genotype to refer to UGT1A1*28 variant in my


Fischer et al studied the relationship

between UGT1A1*28 genotype and estradiol

glucuronidation mediated by UGT1A1 enzyme. Liver,

kidney, lung and intestinal tissues were tested for

UGT1A1, 1A6 and 2B7 isoenzymes. In the 7/7



genotype liver samples, the apparent Micholas

Mentin constant KM was not altered, but the V-max

was altered, compared to 6/6 wild type liver

samples. Liver samples with 7/7 genotype had a

fourfold lower activity of the enzyme compared to

the samples with normal gene expressions, as shown

in this bar plot.

As you have already heard, that in the

caucasian population, the frequency of homozygous

deficient 7/7 genotype is approximately 10 percent,

with a range from 5 to 15 percent. The

heterozygous 6/7 genotype is approximately 40


This slide illustrates the relationship

between the risk of severe neutropenia and diarrhea

and SN38 exposure. These data are from the phase

2-3 studies of Irinotecan in which weekly doses of

100 to 150 milligrams per meter square were

administered to patients with colorectal cancer.

In absence of individual PK data in these studies,

mean AUC data from earlier studies were used.

Despite the limited data, logistic regression



analysis suggested that the risk of severe

neutropenia and diarrhea increases with SN38


The first article that I'd like to present

today is a clinical study that was conducted at the

University of Chicago by Dr. Mark Ratain and his

group. The article was published in the Journal of

Clinical Oncology this year. This was a

prospective study in 66 solid tumor or lymphoma

patients. The study evaluated the association

between the prevalence of severe toxicity and

UGT1A1 genetic variation.

The patients received 350 milligram per

meter square dose of Irinotecan every three weeks.

This is an approved dosing regimen for single agent

Irinotecan therapy. Toxicity was assessed during

cycle 1. Fischer's exact test was used to relate

genotype with pharmacokinetic parameters,

pretreatment bilirubin and absolute neutrophil


I'd like to mention some of the highlights

of this study. The study has certain unique



features compared to the other studies that I'm

going to present subsequently. This is a

prospective trial with an adequate number of

patients who had 7/7 genotype. The study is clean

in terms of not having any contribution in toxicity

from other agents. Sometimes, it's hard to pin

down the culprit for toxicity in combination

regimen chemotherapy trials.

The onset of toxicity was rapid with the

first cycle of therapy. The PK assessment was

reliable, being conducted in a lab that has

pioneered an assay for this complex and unstable


There was a significant difference in the

dose normalized AUC exposure between 7/7 genotype

and 6/6 genotype patients. A significant

difference was also noted between 6/7 and 6/6

genotype patients. This is a combined data set,

including 66 patients from the Innocenti study and

20 patients from another phase one study conducted

in the same institute, using 300 milligram per

meter square dose of Irinotecan.



This slide shows the relationship between

the maximal decrease in absolute neutrophil count

ANC as a function of SN38 exposure. Patients with

6/6 genotype are shown in blue. Those with 6/7

genotype are shown in green. And patients with the

7/7 genotype are shown in red. The square symbols

are the mean ANC nadirs and SN38 AUCs for the three

subgroups. The data were log-transformed and fit

using linear regression models. The blue line

shows the predicted curve for 6/6 and 6/7 genotypic

groups, and the red line shows the predicted curve

for the 7/7 patients.

The 7/7 genotype has a greater effect on

the ANC nadir versus SN38 AUC relationship compared

to the 6/6 and 6/7 genotypes. For the same AUC,

the 7/7 genotypes show a lower ANC nadir.

Overall, the study showed 50 percent of

the 7/7 genotype patients had grade four

neutropenia compared to 12.5 percent heterozygous

patients, and no wild type patients had grade four

neutropenia. There is a significant difference in

the exposure to SN38 between the



homozygous-deficient 7/7 patients and the 6/6

genotype patients as shown in the previous slide.

Also, the pretreatment bilirubin levels between the

7/7 and the combined 6/7 and 6/6 genotype patients

was significant.

The prevalence of grade four neutropenia

and grade three diarrhea in the overall

population--sorry, the prevalence of grade four

neutropenia was 9.5 percent, and the grade four--or

the severe diarrhea was 5 percent in this study.

Notable in this study, one patient died of

neutropenia-related sepsis who had 7/7 genotype and

had the highest total bilirubin level.

In the study, the grade four neutropenia

was significantly higher in 7/7 patients compared

with 6/7 and 6/6 patients. The relative risk for

grade four neutropenia for 7/7 patients was 9.3.

Only three patients in this study had grade three

diarrhea. One was a 7/7 patient, and the two

others were patients with 6/7 genotype. None of

the patients with 6/6 genotype had severe diarrhea.

The study conclusively established an association



between genotype and neutropenia.

This is a prospective phase two study

designed to evaluate the influence of UGT1A1

polymorphism on the toxicity profile, on the

response rate and on the overall survival in 95

colorectal cancer patients treated with four

Irinotecan containing regimens. Irinotecan

regimens were 350 milligram per meter square every

three weeks; 80 milligram per meter square weekly;

or 180 milligram per meter square biweekly.

Toxicity was evaluated during the entire duration

of treatment. No PK samples were collected.

Various statistical tests were applied to assess

the differences between the categorical variables

and between the related or unrelated continuous


Logistic regression was used as a

multivariate method to assess of genotype

independently predicted toxicities. I will not

present any efficacy data from this trial.

Neutropenia and diarrhea in this table

includes both grade three and grade four



toxicities. Forty percent, four out of 10 7/7

genotype patients had grade three/four neutropenia

compared to 15 percent patients with normal

alleles. Seventy percent of the patients with 7/7

genotype had severe diarrhea compared to 17 percent

patients with normal alleles. The cumulative dose

of Irinotecan received by 7/7 genotype patients was

1,398 milligrams per meter square, compared with

1,725 milligrams per meter square received by

patients with 6/6 allele.

The prevalence of grade 3/4 neutropenia

and diarrhea in the overall population was 21

percent and 31 percent respectively. Notable is

the incidence of diarrhea, which was higher in this

trial compared to what we have seen with other

Irinotecan-based trials.

Both univariate and multivariate analysis

showed statistically significant association

between appearance of diarrhea and 7/7 genotype

compared with 6/6 genotype. Hematologic toxicities

increased from 6/6 patients to 7/7 homozygous

patients from 15 to 40 percent but didn't achieve



statistical significance. Cumulative dose of

Irinotecan received by 7/7 patients were lower than

the dose received by 6/6 patients because of the

dose reduction that was necessary for the

appearance of severe diarrhea. This study

demonstrated a significant relationship between

genotype and severe diarrhea. The statement by the

author of this article shows a need for

genetic-based chemotherapy treatments for cancer


This is the third study that I'm going to

talk in detail about. This is a retrospective

study of 75 metastatic colorectal cancer patients

receiving two common Irinotecan containing

combination regimens. Irifufol regimen contains 85

milligram per meter square weekly Irinotecan, given

with 1,200 milligram per meter square weekly

infusional 5-fluorouracil plus 100 milligram per

meter square bolus leucovorin. Folfiri regimen

contained 180 milligram per meter square biweekly

Irinotecan given with 2,500 milligram per meter

square infusion of 5-fluorouracil and 400 milligram



per meter square leucovorin. No PK samples were

collected in the study. Kruskal-Wallis test was

used to assess the statistical difference among the

three populations.

Seventy-one percent of the 7/7 patients,

five out of seven, compared with 10 percent 6/6

patients, three out of 31, had grade 3/4

neutropenia. Sixty percent of the 7/7 patients had

neutropenic fever compared to no 6/6 patients

suffering from neutropenic fever. Neutropenic

fever was associated only with patients who carried

at least one deficient allele of UGT1A1.

Irinotecan courses had to be delayed in

five out of seven patients in the 7/7 group

compared with 21 out of 35 in 6/7 and 10 out of 31

in 6/6 group. 100 percent of the 7/7 patients

whose therapy had to be delayed for toxicity had to

be hospitalized compared with no 6/6 patients with

delayed therapy requiring hospitalization.

The prevalence of grade 3/4 neutropenia

and diarrhea in the overall population was 30

percent and 7 percent respectively. There was no



association between genotype and diarrhea because

of the low frequency of diarrhea in this trial.

There was a strong correlation between genotype and

grade 3/4 neutropenia. 100 percent of the 7/7

patients who had severe neutropenia needed delayed

therapy and hospitalization compared to none of the

6/6 patients who had neutropenia and/or diarrhea.

The authors mentioned in this article that

hematologic and digestive toxic events were not due

to 5-fluorouracil because all of the patients had

5-fluorouracil dose adjusted individually to avoid

severe 5-fluorouracil toxicity.

Literature includes other adequately-sized

studies that I'd like to summarize for the

Committee. These are the two PK studies that

evaluated the effect of variant alleles on

Irinotecan disposition. Mathijssen's study

evaluated a number of genes associated with the

metabolism, transport, and disposition of

Irinotecan. UGT1A1 genotype did not correlate with

Irinotecan disposition. Notable, there were only

two UGT1A1*28 patients in this study.



On the other hand, Paoluzzi's study showed

a significant decrease in the exposure ration of

the SN38 glucuronide to SN38, indicating a

reduction in the formation of the SN38 glucuronide

in 7/7 patients.

Font, et al., published a phase two study

evaluating the activity of docetaxel and Irinotecan

in 51 non small cell lung cancer patients.

Irinotecan 70 milligram per meter square was

administered with 25 milligram per meter square

docetaxel. The study did not see any correlation

between genotype and toxicity. The overall

incidence of grade 3/4 neutropenia and grade 3

diarrhea in this study was low. Also, the dose of

Irinotecan used in the study was 70 milligrams,

compared to 100 to 125 milligram per meter square

dose used in combination studies of Irinotecan.

A retrospective analysis of 118 Japanese

patients who received Irinotecan containing regimen

showed that UGT1A1*28 genotype was a significant

predictor of severe toxicity. In this analysis, 55

percent of the patients, irrespective of genotype,



who had grade 4 neutropenia also had grade 3/4

diarrhea, and 73 percent of the patients who had

grade 3/4 diarrhea also had grade 3/4 neutropenia.

Sai et al in Japan conducted a PK study to

evaluate the relationship between SN38 PK and

UGT1A1 haplotype. UGT1A1*28 was associated with

reduced SN38 glucuronide to SN38 area under the

curve ratio and increased total bilirubin.

Iyer, et al., published a prospective PK

study in 20 patients that related genotype with

reduced SN38 glucuronidation rates and lower

absolute neutrophil counts in 7/7 patients compared

to 6/6 genotype patients.

In the evaluation of the clinical data

provided to the agency for the approval of this

drug, certain predictive factors were related to

increased toxicities. These are observations only

and not statistically powered data that allowed the

agency to recommend a reduced starting dose of

camptazar for patients equal to or older than 65

years; patients who received prior pelvic or

abdominal radiotherapy, patients whose performance



status was two, and patients with increased

bilirubin levels.

The reduction was by only one level. That

is for the 350 milligram per meter square every

three weeks regimen, the starting dose will be 300

milligram per meter square. Similarly, if the

normal starting dose is 125 milligrams per meter

square weekly, the predictive factors will

recommend a dose of 100 milligrams per meter

square. If the patients tolerated the reduced

starting dose, the dose in the next cycle is

increased to the standard dose.

In the geriatric use section of the label

we have the statement the starting dose of

camptizar in patients 70 years and older for once

every three week dosage schedule should be 300

milligram per meter square, a 50 milligram per

meter square reduction from the standard dose.

Based on the scientific and clinical evidence

available in the current literature, the agency

believes that genotype is a predictive factor for

Irinotecan dose limiting toxicity. The agency also



believes that SN38 level is a likely predictive

factor for toxicity.

Based on Innocenti's article, UGT1A1

polymorphism information will help to reduce the

overall incidence of grade four neutropenia from 10

percent to 5.7 percent, almost a 50 percent

reduction in the incidence of grade four

neutropenia. Irinotecan can be given as a weekly,

biweekly or every three weeks regimen. One of the

regimens may be more appropriate for the 7/7

genotype patients. Genotype testing, combined with

bilirubin levels and other predictive factors shown

in the previous slide, will allow the physicians to

select Irinotecan therapy more judiciously in the

high risk patients. Alternate therapy, either in

the first line or in the second line setting, may

be a choice for the 7/7 genotype patients.

I'd like to thank my colleagues from the

Office of Clinical Pharmacology and

Biopharmaceutics, Dr. Larry Lesko, Dr. Shiew-Mei

Huang, and Dr. Felix Frueh for helping me out with

this presentation. I'd like to thank my colleagues



from the Division of Pharmaceutical Evaluation I

for helping me out with or for providing the PK

analysis of the Innocenti's and the Phase I data.

They are Dr. Roshni Ramchandani, Dr. Yanning Wang,

Dr. Brian Booth, and Dr. Joga Gobburu. I'd like to

thank my boss, Dr. Mehul Mehta, for giving me the

time to prepare for this meeting, and last but not

least, I'd like to thank my colleagues from the

Division of Oncology Drug Products, Dr. Grant

Williams and Dr. Richard Pazdur, for challenging me

to translate the principles of clinical

pharmacology, especially pharmacogenetics, to

clinical practice and clinical use.

Thank you.

DR. VENITZ: Thank you, Atik.

Any questions or comments by Committee


And what I'd like to do is after each of

the presentations, give everybody an opportunity to

ask questions for clarification. We have a whole

hour reserved from 11:00 to 12:00 to discuss the

specific questions that Dr. Lesko wants us to




So, any specific questions?

DR. GIACOMINI: Yes, I had a couple of


Was race specifically or ethnicity

specifically looked at in any of the studies that

you reviewed?

DR. RAHMAN: I would say no, because the

Japanese study included only the Japanese

population, and the other studies in Europe and the

United States included only the caucasian

population. So we at this time don't know the

prevalence in blacks, in the African-American

population, or in other populations. I think the

polymorphism is less prevalent in the Asian

population. Dr. Howard McLeod might correct me on


DR. MCLEOD: There is ethnic variation for

the frequency both of the 6 and 7 allele but also

the presence of either five repeats or eight

repeats seem to be more common in the, I think, the

racial minority groups found in the United States.



The impact of those other alleles is not completely

clear, although Dr. Ratain may address that in his


DR. GIACOMINI: Okay; and as a followup to

that, then, maybe you can explain it to me: what

is the difference? I mean, you've called it the

star--I think, is it 28 haplotype versus 7/7. What

is in the haplotype besides the promoters? Are

there some other snips in the haplotype, and what

are they? And are they functional in any way?

DR. RAHMAN: Dr. Howard McLeod?

DR. MCLEOD: It's a genotype, Kathy, not

haplotype. Star-28 is the name that was stuck on

the 7/7 repeat, so folks that are homozygous for

the 7/7 genotype are called star-28 by the powers

that be in determining a nomenclature for UGT1A1.

DR. GIACOMINI: So it's not like there's

any other snip in there.

DR. MCLEOD: Correct.

DR. GIACOMINI: It's just simply not.

DR. RAHMAN: Can I clarify that a little

bit? Actually, that was not an appropriate term,



but there was a haplotype study that has been

published by Dr. Margaret Eng's group that are

associating star-28 with other variant alleles,

star-60 and others, and there is a paper out on

that. So I kind of was alluding to that, that in

that study, the number of star-28 patients,

homozygous patients, were low, and they were

associated with other risk factors.

DR. GIACOMINI: Okay; but we can assume

when somebody says star-28, they mean the 7/7;

they're homozygous, they mean the 7/7 genotype.

DR. RAHMAN: Seven, yes.

DR. GIACOMINI: Okay; one other question:

in terms of mechanism, I didn't see you quote any,

you know, like a reporter assay or something in

which we're seeing a transcription rate difference

between the 7, some biochemical mechanism which

supports what you're seeing clinically in terms of

that. Are there biochemical data like that?

Mark's saying yes. You can't talk, Mark.

DR. MCLEOD: In the--I don't know if

everybody received--there was a packet that we



received of light reading. Within that is a number

of papers addressing those issues, including a

paper from Dr. Boiler Scripps that looked at both

the racial issue as well as the promoter variance

in terms of luciferase assays, seeing this stepwise

inverse relationship between length of the TA

repeat and the amount of transcript that's


DR. GIACOMINI: Okay; thank you.

DR. VENITZ: Go ahead.

DR. HALL: Can you give some idea as your

part of the agency as to your views on why, you

know, you know, several or a significant number of

the 6/6s get the toxicity, and a significant number

of the 7/7s don't get any toxicity? Do you have

some kind of rationalization for this?

DR. RAHMAN: As I've shown in this, in my

presentation that the toxicity in the 6/6s

definitely lower than 7/7 patients. As you can

see, 71 percent versus 10 percent. In one of the

studies, none of the 6/6 patients had toxicity. So

I'm not sure if there is a significant--the



statement that you made, there is a significant

toxicity in 6/6 patients is really true. But there

is toxicity in the 6/6 patients also, and that

could be attributed to not only Irinotecan

depending on the studies if there were a

combination of regimens used. It could be also

attributed to the others. But it also could be

attributed to Irinotecan.

DR. HALL: So have you considered other

mechanisms other than this 1A1 polymorphism as a

contributor to the toxicities?

DR. RAHMAN: Yes; as I've shown that other

predictive factors have been associated for

predicting the toxicity, like the bilirubin levels

is one of the predictors that has been kind of

alluded to being related to toxicity

DR. HALL: But bilirubin would be

metabolized by the enzymes. So they would be

somewhat correlated.


DR. HALL: Other enzymes? Other genes,




DR. RAHMAN: There are papers out in the

public domain which are trying to associate other

UGT1A1 enzyme, and the factors that could also

contribute is the sensitivity of the individual

patients to specific neutropenia or to severe

diarrhea, and that is something I am not aware of

the magnitude of. But there is an understanding

that some of the patients might be overly sensitive

to a certain kind of regimen compared to the

others, even that don't carry any of the homozygous

deficient alleles.


DR. BARRETT: I had a question about the

prevalence rates in your responses both in the

grade 3 diarrhea and in the neutrophil count. It

seems that there's quite a bit of interstudy

variability, and I know in your pooled analysis,

you were basing this on mean data, but is there

any--and now, with the Innocenti PK information

available, you really could use some of that

information to back-project some of the individual

variance in those models. Is that going to happen?



DR. RAHMAN: So, first of all, I'm trying

to address the question about finding differences

in the neutropenia and diarrhea in different

studies. What happens is that in certain trials,

the patients were allowed to take premedication for

diarrhea, so that might have helped. It is

approved in the label for using of loperamide and

other agents for controlling of diarrhea.

Now, there are two components of diarrhea.

One is the early phase diarrhea, and the other is

the late phase diarrhea. I have kind of focused on

Innocenti's article, because that truly was trying

to address these toxicity issues. And their study

was trying to look for diarrhea as well. However,

the incidence was pretty low.

Now, we are exploring the pharmacogenetics

of this drug. However, we're trying to see if SN38

could be a good predictor or could add on to to

come to a kind of dose for 6/7 and 7/7 patients,

but this is still in the earliest stage, and I

think we need some more solid data to show the

relationship and then can make a difference.



DR. SADEE: The star-28 genotype is

associated with Jorbert's syndrome.

DR. RAHMAN: Right.

DR. SADEE: And so my question is how

often is this diagnosed, and what is the

correlation between having a patient diagnosed with

Jorbert's syndrome and toxicity? So, in other

words, could we substitute a genotyping with a

diagnosis for Jorbert's Syndrome?

DR. RAHMAN: I haven't come across any

article to address that question.

DR. VENITZ: Larry?

DR. LESKO: Yes, just on the last

question, you know, another way to think about this

is as an adjunct test. You could actually think of

tests being done in parallel. If you think of a

screening test, you're screening an entire

population with or without an elevated bilirubin.

You could increase, I think, the sensitivity of a

UGT test by maybe screening people that signal by

their high bilirubin that they may be at potential

risk for the genotype.



So either in parallel or in serial, I

think you could enhance the value of the test by

thinking of it as an adjunct to the current

information that somebody would have. When you

look at--getting back to the prevalence issue, when

you look at prevalence of Jolbert's syndrome as a

function of the ethnic or racial group and the

prevalence of the UGT, there are some parallelisms


In a review article that appeared last

year, the range of prevalence of UGT was anywhere

from 2 to 3 percent in Asian populations; up to 23

percent in blacks and Africans. So that's sort of

the 2 to 23 percent range that people have reported

for the prevalence of the polymorphism.

I was going to maybe add this other

information, because Atik showed the slide, and it

was shown as average values, but we were looking at

the question Steven Hall raised about the 6/6s

becoming toxic and the 7/7s not, but I think what

we have here is a probabilistic issue that if you

look at the variability in SN38 area under curve in



each of the genotypes, there's clear distinctions

based on mean values. However, the low end of the

6/6 area under curve and the high end of the SN38

area under curve for the 7/7s does overlap.

So I think what we're seeing, then, is

some risk in the 6/6 homozygous and some lack of

risk in the other people as one possible

explanation. I think another explanation is that

in most of these cases, more than the target allele

was not looked at, so there could be other alleles

that would be predisposing individuals to risks

that weren't measured, perhaps because of, you

know, the ethnic or racial background. But these

are some of the possible reasons anyway, but

certainly, the pharmacokinetic explanation seems to

make sense based on what we know about area under

curves related to nadirs of neutrophils.

DR. MCLEOD: Back to Dr. Sadee's question:

in the prospective study in the GI intergroup

throughout North America, the N9741 study,

Jolbert's syndrome was one of the flags in the

inclusion criteria or exclusion criteria. Yet, we



had an 8 percent frequency of the 7/7 genotype.

But just kind of highlights the lack of diagnosis

of Jolbert's syndrome, because it is a subclinical

benign hyperbilirubinemia syndrome.

It's out there, and so, plenty of people

are getting this drug without that diagnosis,

because it's not something that's really evaluated

in common practice.

DR. WATKINS: I was the only--as the only

hepatologist here, I'd just reiterate that it's a

subclinical diagnosis that can be brought out by

fasting and certain other conditions, like certain

protease inhibitors.

But in the studies that have looked at, I

believe, even the majority of 7/7s have bilirubins

within normal limits, so it would not be a

surrogate. I guess one question is how much does

the genotyping add in a multiple regression if you

include in serum bilirubin, which I haven't heard,

but I'm sure someone is going to address it.

DR. SINGPURWALLA: Your slide 15,

retrospective analysis, you showed two pictures,



one on the left, my left, and one on the right.

You have predicted versus observed. How did you

get the predicted?

DR. RAHMAN: Okay; the predicted line came

from the regression analysis.

DR. SINGPURWALLA: So the predicted is

based on the observed data.

DR. RAHMAN: Right.

DR. SINGPURWALLA: I'm curious why you

didn't fit a straight line. I know if you fit a

straight line--

DR. RAHMAN: Right.

DR. SINGPURWALLA: --it would go out, but

why did you choose that particular form?

DR. RAHMAN: It was done by our

pharmacometric folks, and they have got a better

understanding of the modeling that they did. And I

think they thought that this was the appropriate

regression to use rather than a linear regression.

DR. SINGPURWALLA: I understand, but there

were three points, and you can draw all kinds of




DR. RAHMAN: Yes, that's true. Actually,

the intent was to show that there is a relationship

that we have seen, but it's very soft at this time,

as I've said, because these are all the mean values

that we are lumping together; it's not the

individual ones, which would have given us a much

better fit. And also, in large clinical trials,

the PK is not collected.

So we kind of lumped them together and had

only three reliable mean values that we could do

something with predictions.

DR. SINGPURWALLA: So rather than saying

predicted, you should really say fitted.

DR. RAHMAN: Fitted.

DR. SINGPURWALLA: Because when you say

predicted, I'm thinking of some theory that tells

you what's the probability.

DR. RAHMAN: Right, right.

DR. SINGPURWALLA: As the dose increases.

DR. RAHMAN: Right.


DR. CAPPARELLI: Yes, I just wanted to



echo a little bit of what Dr. Watkins was saying,

and one of the studies you mentioned that there was

an evaluation of bilirubin levels as well as

genotype, and you'd expect them to be, you know,

highly correlated, and one of the questions is

what's the independent component that the genotype

is going to give in conjunction with the fact that

there is some induceability of this enzyme, and so,

genotype may not fully predict especially, and a

single genotype differential may not predict.

The other sort of related question that I

have is has there been any look at inducers of

CYP3A? Because the APC metabolite actually

represents a larger portion of the compound that

ends up in urine and feces. And so, if that goes

by 3A4, again, you may have some differential there

as well as if you have some inducers, you may have

some confounding of the genotype.

DR. RAHMAN: One thing I can tell you is

that there are studies going on, I think, which

Pfizer will present showing that they are looking

at, besides UGT1A1*28, other genetic factors and



other 3A4, 3A5 to show if--to see if they have any

association with the toxicity. So there are

studies going on. That's how far I know. But I

have not reviewed or looked at any articles

focusing on that.

And also, Dr. Ratain's and Dr. Howard's

group are looking at all these various factors in

association with toxicity for Irinotecan.

DR. DAVIDIAN: My comment just pertained

to Nozer's comment a minute ago. This is a

logistic regression, right? Is that what was done?


DR. DAVIDIAN: I think it was a logistic


DR. RAHMAN: Right.

DR. DAVIDIAN: So this is just the fitted

probability curve.

DR. RAHMAN: Right.

DR. DAVIDIAN: Was this based on these

three mean values? Or was it based on--or are you

just showing the mean values on the plots?

DR. RAHMAN: It is based on the three mean




DR. DAVIDIAN: And that's all.

DR. RAHMAN: Right.

DR. DAVIDIAN: Oh, okay.

DR. VENITZ: Okay; Atik, let me ask you

one final question for my clarification: the

Innocenti study is the only one that's a single

agent study. All the other studies are


DR. RAHMAN: That is correct.

DR. VENITZ: So that is really the only

study that allows us to look at Irinotecan as

opposed to the contribution that other

chemotherapeutic agents might play--

DR. RAHMAN: That is true.

DR. VENITZ: --in toxicity.

DR. RAHMAN: As far as I know, that is the

only prospective study that was actually conducted

to address this association of genotype with

Irinotecan toxicity. So this was kind of--this was

a focused study looking at these specific issues,

which was based on another phase one trial which



they conducted early on with 20 patients, so they

kind of, you know, expanded on that and moved on to

do this prospective trial to address the issue.

DR. VENITZ: But all the other studies

that you reviewed either prospective or

retrospective in nature, they involved other agents

as well.

DR. RAHMAN: Yes, like in the four

different regimens in the second trial that I

talked about, Markelos' trial, I think they had one

arm with a few patients who received a single

agent, Irinotecan, and then the other arms. So

there are blips of single agent here and there, but

the other studies definitely had other components

besides single agent trials.

DR. VENITZ: Okay; if there are no more

questions, then I thank you.

Our next presenter is Dr. Parodi. He is

the director of clinical pharmacogenomics at

Pfizer, and he's going to give us the Pfizer


DR. PARODI: Good morning.



I would like to thank Dr. Lesko, Dr.

Rahman for inviting Pfizer to participate in this

meeting. I would like also to acknowledge my

colleagues Dr. Mark Morrison and Dr. Akitunde Belo,

who are here to answer any questions that may be in

regards to clinical or pharmacokinetic issues

during the meeting.

During this presentation, we would like to

reiterate the commitment of Pfizer to the safety of

all of our products. In addition, we would like to

talk about how we are applying pharmacogenetics at

Pfizer. At Pfizer, pharmacogenetics is getting

important information during the whole drug

development process, from early discovery research

through development and through the safety and

efficacy of our marketed products.

Today's discussion is around Irinotecan, a

cytotoxic agent that has been proven to be an

effective therapeutic choice for patients with

metastatic colorectal cancer and colorectal cancer

in general. Since the late nineties, there have

been several publications reporting a relationship



between Irinotecan's safety and genotype. We have

kept abreast of these publications, and we have

provided for the Advisory Committee a summary of

those published reports in the background document.

We will review this data, and we will

present to a highlight of what Pfizer is doing to

continue to expand the database regarding the

Irinotecan pharmacogenomics. We will also talk

about how we're working in collaboration with the

FDA to provide useful information in the label that

may refer to this particular genotype.

We believe this forum is going to be an

important meeting, where we can share our views and

our ideas about the subject and present activities

that we are currently undertaking to address these

issues. I would like to outline how

pharmacogenomics is being used at Pfizer. At

Pfizer, we use pharmacogenomics as a generic term

which also encompasses what may be traditionally

called pharmacogenetics. We use disease genetics

to select targets. We use the knowledge of the

variation of our targets to improve the safety and



efficacy profile of our drug candidates. And in

some cases, we are using the genetic variation to

define subpopulations for conducting proof of

concept studies.

For our marketed products, we are also

looking into the effect that genetic variation has

on the safety and efficacy of our drugs. Today,

we're focusing on the effect of genetic variation

on the safety and efficacy of Irinotecan.

We have been interested in this area since

the first studies that were reported reporting the

relationship between Irinotecan safety and

genotype. Later, Dr. Ratain, who has been a leader

in this effort, will address and present his ideas

on the subject.

During recent years, we have supported and

sponsored many clinical trials that contain a

pharmacogenomics component. We will go through a

detailed list of the projects we are supporting or

sponsoring later in the presentation. Most

recently, we have engaged in a collaboration with a

company in Germany called Epidaurus to explore the



significant variation of transporters in

metabolizing genes in pharmacogenomics.

Today, we will focus on our knowledge of

the variation in the genes involved in the

Irinotecan disposition and metabolism. This is a

representation of the genes involved in Irinotecan

metabolism, taking into account only what's going

on in the gastrointestinal lumen, where we have

more information. We have very little information

regarding the genes involved in the disposition of

both Irinotecan and its metabolites, both at bone

marrow level or at tumor level.

In general, we can say that the mechanism

for disposition and metabolism of Irinotecan is

complex, and it involves several genes. We want to

also note that all of these genes are very

polymorphic, and those polymorphisms are known to

be functional. As pointed out earlier, there is a

great deal of variability in the frequency of the

different alleles of these genes in the different

ethnic groups, which makes extrapolations from one

ethnic group to another very difficult.



The UGT1A1 polymorphisms are probably the

best known, but information is constantly being

accumulated about the polymorphisms in other genes.

As recently as a couple of weeks ago, there has

been a couple of reports reporting on novel

polymorphisms in the carboxylesterase genes.

Our discussion today will focus on one of

these genes, UGT1A1, in particular, one snip in one

of these genes, and we would like to address the

relevance of the published data associating that

polymorphism, specifically what has been called the

7/7 or star-28 polymorphism, in regards to

neutropenia and diarrhea.

By now, you are familiar with these

studies. We have basically conducted an extensive

review of the published literature and have

selected these studies which are full papers,

because they provide the frequencies of diarrhea

and neutropenia as well as the frequencies of

genotypes for the UGT1A1 gene.

Something we would like to note is that

these studies contain a rather small number of



individuals included in the studies. Given the low

frequency of the 7/7 genotype, very few patients in

this group have been actually included in these


Again, all studies don't include the same

type of cancer patients. Two of these studies

include only colorectal cancer patients, while the

other three include primarily lung cancer patients.

Probably more significantly is the issue that these

studies all use different dosing regimens, both in

the intensity of the dose of Irinotecan and the

schedule, and more significantly yet, the inclusion

of 5-fluorouracil, a known agent that causes


Although there are many differences in

these studies, we have attempted to look at the

data in a comprehensive way. So we realize that

this data can be interpreted from multiple

perspectives, so what I'm going to provide for you

in the next few slides is a statistical analysis of

the data. All of the analysis has been done based

on the raw data presented in those papers and are



unadjusted for any known factors.

First, we would like to look at the rate

of neutropenia in the UGT1A1 7/7 patients compared

to the rate of neutropenia in the group containing

the 6/6 plus the 6/7 patients. A simple look at

this table tells us that the frequency of

neutropenia in the 7/7 patients is higher than the

frequency of neutropenia in this other group. In

order to establish a comparison between the

different rates recorded in the studies, we

calculated the odds ratios and the 95 percent

confidence intervals as represented by this

statistic to quantify the association between

genotype and neutropenia.

The odds ratios vary from study to study

and have very wide confidence intervals. Based on

the 95 percent confidence intervals, the odds ratio

was statistically significant in three out of the

four studies.

Without adjusting for known risk factors,

this univariate analysis shows a statistically

significant association between UGT1A1 7/7 genotype



and neutropenia, although we note that the

association varies among studies with odds ratios

between 2.5 and 16.7. This variability could be

due to the small sample size, differences in the

dosing schedules and the contribution of

5-fluorouracil to neutropenia; the fact that we are

not controlling for known factors such as baseline

bilirubin levels, age, performance status, and

prior pelvic radiation; and indeed, differences in

the population's treatment, both from the ethnic

perspective and also from the tumor type.

In a similar fashion, we have done the

same analysis for diarrhea, grade three plus. In

this case, we have included the Font study, because

the Font study reports the rates of diarrhea for

the different genotypes. It was not included in

the analysis of neutropenia because Font did not

provide the data for neutropenia separately in his


Again, we would like to note that this

analysis has been done without adjusting for known

factors, and if we look at the diarrhea rate



between the 7/7 genotype and the group of 6/6 plus

6/7, simple inspection of the rates shows that it's

difficult to draw a general conclusion. Here

again, we calculate the odds ratios and 95 percent

confidence intervals as a representative statistic

to quantify the association between genotype and

severe diarrhea.

The odds ratios vary from study to study

and have wide confidence intervals, and based on

the 95 percent confidence intervals, we can say

that two out of five studies were statistically


In summary, we have performed a

comprehensive review of the published literature

and selected publications that provided genotypes

and rates for neutropenia and diarrhea in

Irinotecan-treated patients. Although there are

significant differences among studies, we analyzed

the data without adjustments using odds ratios and

confidence intervals as a representative statistic.

We conclude that there is a statistically

significant association of UGT1A1 genotype in the



development of neutropenia. The association of

genotype in diarrhea is not as consistent among


Now, if we want to translate this

association data to a predictive performance of a

test, we need to assess multiple parameters. We

have used the same published rates for neutropenia

in genotypes used for the association analysis to

calculate the test performance parameters.

The following analysis assumes that the

genotyping test is 100 percent accurate for the

detection of UGT1A1 7/7, 6/6 and 6/7 genotype. We

have calculated the performance parameters based on

the reported rates in the publications that were

examined previously for neutropenia.

First, we look at the clinical

sensitivity. The clinical sensitivity can be

interpreted as the probability that those patients

that have neutropenia will have the 7/7 genotype.

We note that the clinical sensitivity varies from

15 percent or 0.15 to 50 percent.

Probably for our discussion, it's more



important to look at the predicted values.

Ideally, we would like to have a test with high

predicted values, maybe approaching 100 percent

possibly. Under the assumption that we know that a

patient has the 7/7 UGT1A1 genotype, the overall

probability that the patient will develop

neutropenia will be about 50 percent.

These values are not highly predictive for

developing neutropenia. Given that we cannot

accurately predict the development of neutropenia,

we have to be cautious when balancing the risk for

neutropenia and the benefit of treatment.

Neutropenia is generally manageable, and dosing

reductions for all UGT1A1 patients would result in

unnecessary reductions for 50 percent of the

patients, and the outcome is unknown.

We think that this data furnishes a

provocative signal hinting at the biology and

provides guidance for additional ongoing research

in this area. We recognize the importance of this

data that has been collected so far, but we also

feel that more research is necessary. As mentioned



earlier, we have many ongoing sponsor and supported

trials that investigate the UGT1A1 and other

genetic factors and their association with severe

neutropenia and diarrhea. In parallel, we have

ongoing discussions with the FDA to understand the

implications of the published data and what may be

an appropriate use of this data in the Camptosar


These are the sponsored or supported

studies that include Irinotecan-treated patients

and that have a pharmacogenomics component. These

studies may address some of the limitations of

previous published studies, in particular, sample

size, the analysis of multiple genetic factors, the

possibility for controlling for known factors, and

the inclusion of current standard of care regimens

for first line metastatic cancer or colorectal

cancer patients FOLFIRI and FOLFOX.

Although most of these studies are

ongoing, we would like to highlight that study

N9741 is finished, and the NCCTG has almost

completed an analysis of pharmacogenomics data for



15 polymorphic markers on 10 genes. A publication

is planned in the near future by the NCCTG.

The future looks very promising. The data

from these studies will provide important new

information in addition to other efforts and other

studies that are being conducted by other

investigators. We hope that from these studies, we

can better define the magnitude and strength of the

association between UGT1A1 and safety; we can also

identify other potential covariants of severe

neutropenia and diarrhea, and as the data matures

from the ongoing studies, we look forward to

providing additional information for health care

providers and patients to aid their treatment


I would like to acknowledge a large team

of Pfizer colleagues who have worked together to

provide this presentation this morning. Thank you.

DR. VENITZ: Thank you.

Any questions, comments by Committee


Can I ask you to go back to your slide



where you discuss the performance of the test? You

focus on the sensitivity. Would you care to

discuss the specificity and the negative predictive


DR. PARODI: The clinical specificity

basically gives the overall probability that given

that a patient has neutropenia, does not have

neutropenia, will not have a 7/7 positive test. In

general, the clinical specificity seems quite high.

The negative predicted value gives a probability

that given that the test is negative for 7/7, what

is the probability that that patient will not

develop neutropenia?

The overall values that you see there are

averages. They are not weighted averages. We feel

that a negative predicted value is relatively high

and much better than the positive predicted value.

DR. VENITZ: So would it be fair, based on

this analysis, then, to say if you did the test on

a large number of patients, you may not necessarily

predict neutropenia with a 50 percent sensitivity,

but if your star-28 is negative, you have a very



small chance of developing neutropenia?

DR. PARODI: Certainly, if you get a

negative value--a negative test for 7/7, you have a

high probability of not developing neutropenia than

if you had a positive value for 7/7; basically, a

50 percent chance of developing neutropenia is

equivalent to a toss-up.

DR. VENITZ: Right, but that's from your

perspective the bad thing, but the good thing is,

on the other hand, if you have a negative test,

you're unlikely, very unlikely, to develop

neutropenia; is that correct?

DR. PARODI: That is correct, but overall,

given the incidence of neutropenia, the likelihood

that you will develop neutropenia anyways is low.

DR. VENITZ: Any other questions?


DR. SINGPURWALLA: Yes, I was just looking

at your first slide where you had the odds ratios

and the confidence limits around the odds ratios.

DR. PARODI: Which one? For neutropenia

or diarrhea?



DR. SINGPURWALLA: Well, let's just take

that one.


DR. SINGPURWALLA: I can't pronounce all

these things.

DR. PARODI: Oh, me neither.

DR. SINGPURWALLA: So let me try and

understand the objective of this slide from a

layperson's point of view.

DR. PARODI: Right.

DR. SINGPURWALLA: If I was 7-7, and if I

took this medication, then, it appears that there

is a 50 percent chance that I'll get an adverse

reaction; is that correct?

DR. PARODI: That is correct. You have a

higher probability of having an adverse reaction.

DR. SINGPURWALLA: And if I was either a

6/6 or a 6/7, I have a lower probability.

DR. PARODI: That is correct.

DR. SINGPURWALLA: If I pool all those

numbers, I find the answers to be 50 percent

probability and 25 percent probability roughly, if



I just add everything now.

DR. PARODI: Yes, yes.

DR. SINGPURWALLA: So I'd still be scared

if I had a 25 percent chance of an adverse


DR. PARODI: Yes, and you should be.

DR. SINGPURWALLA: Is that the point

you're making?

DR. PARODI: The point we're trying to

make is we try to really provide--we'd have liked

to have done a meta-analysis of this data. Given

the differences, significant differences in these

studies, it's really unfair to pool all this data

together in a meta-analysis exercise. So we are

basically presenting this data in a tabular form,

using a calculated statistic as a comparator

between studies, because not all studies reported

the same statistic, as Dr. Rahman indicated. I

mean, some people used one statistic; some the


So it made the tabulation and the

comparison between studies a little bit difficult




DR. SINGPURWALLA: I see your point, but

look at the confidence limits. They're so wild.

DR. PARODI: The confidence limits are

very wide, and that is primarily due possibly to

the fact that these are very small sample sizes.

DR. SINGPURWALLA: That's right.

Therefore, it makes sense to pool them.

DR. PARODI: It makes sense to pool them,

but, I mean, we're doing this in a highly

abstracted way, because I think pooling the data is

really not warranted. This is basically an

exercise, and also, we have not adjusted for known

factors, because it is difficult to extract from

the policy literature what was the performance

status of the patient, what was the baseline

bilirubin. All of these adjustments will have to

be made, since these are known covariants in the

incidence of neutropenia.

DR. SINGPURWALLA: Can I suggest that you

consider the use of prior odds and the posterior

odds in these kinds of studies?



DR. PARODI: Can you be more explicit?

DR. SINGPURWALLA: Well, prior odds are

you put prior distributions on these ratios, and

you compute the aposterior using these.

DR. PARODI: Okay; prior probabilities



DR. PARODI: We could do something like


DR. PAZDUR: I wanted to bring up some

clinical issues here, and perhaps I realize that

the company Pfizer kind of got this drug from

Pharmacia, who did most of the development on this,

and feel free, obviously, to discuss these with

your clinical colleagues--

DR. PARODI: Right.

DR. PAZDUR: --if they have an issue with

this. But I think it's very important for the

Committee here to understand the clinical

development of this drug, and obviously, we'll be

talking about an effect on dose reduction and

potentially a potential reduction in efficacy. And



I wanted to give the Committee some idea about how

the dose of this drug was selected on either

schedule. There's two schedules on the product

label: a weekly schedule times four and then an

every three weeks schedule.

How is that dose selected in the 1990s

here? And that has carried us forward here

throughout the entire clinical development, and I

was wondering if you could give us some idea: how

did you get this dose? What was it based on?

DR. PARODI: I would like to defer to one

of my colleagues to answer that particular


MR. MORRISON: Okay; thank you. I'm Mark

Morrison. I'm the medical team leader for

Camptosar in the U.S. I've been with Pfizer, so I

don't have first hand experience of the development

at Pharmacia; however, the dose was arrived at by

the standard mechanism of looking at MTD and

pushing the dose up to the MTD and then backing

down to a tolerable dose just below MTD. So it was

a standard development.



DR. PAZDUR: Well, I guess the point that

I wanted to bring out here, when the dose was

selected, we were looking in a 5-FU refractory

population, and the dose was being looked at in

terms of response rate here, okay, which was

relatively modest. We were looking at 15 percent

response rate. And the point that I want to bring

out is what is the relationship that the company

has with dose and a clinical outcome of an impact

on survival? Because here again, if we talk about

perhaps changing the dose, you have to be cognizant

about any missing data that we have on a dose and

the ultimate clinical outcome and what is that

level of certainty that we have regarding that

dose, the package insert dose and clinical outcome?

MR. MORRISON: That's actually something

that we proposed to look at going back into the

databases. What we do know, in the first line

setting, we use a combination of bolus IFL is that

with dose reduction after cycle one and follow them

out, each group is dose-reduced, and you do see a

slight trend for a difference in efficacy; however,



it's not statistically significant, so that you'd

have to come to the conclusion that the overall

efficacy at the end of the day was very similar,

because both wind up being dose-reduced more.

We do need to look at that in the

single-agent setting going back to the second line

studies. One thing I'd like to point out, if we go

back to the probability slide, looking at negative

predictive value, I think a very important point to

make in looking at the label, the incidence of

grade four neutropenia would be expected if you

average the two trials, which isn't statistically

valid, because they're two different populations,

but it comes out to about 18 percent.

So the negative predicted value tells you

that you have a 17 percent chance of having the

effect or an 83 percent chance of not having the

effect, and that's what we know to begin with. So

the test actually is more indicative of the

standard population. The positive predictive value

of 50 percent gives us added information that these

patients are at increased risk over the general



population; however, we would like a test with a

positive predictive value of 90 or 95 percent.

So what other factors are coming into

play? Is it the carboxylesterase, for example? Is

it transporters? Camptosar itself is present in

micromolar concentrations versus SN38 in nanomolar


So given the difference in efficacy

between the two compounds, they're both present at

therapeutic concentrations, and UGT is important

for SN38 much more so than for Camptosar, and the

carboxylesterase may be a very important factor.

We don't know whether it is; upcoming data from our

clinical trials will hopefully give us an answer,

and likewise, transporters in the bone marrow and

in the gut and in the liver may help us unwind the

story of selectivity and look at the therapeutic

index and try to figure out what combination of

factors might give us a positive predictive value

greater than 90 percent.

So we're striving to do that, and we will

have data available in the near future from a



number of trials that Dr. Parodi has mentioned to

try to improve on that ratio.

DR. PAZDUR: Just one last question. We

spent a lot of time on this slide. I've seen it

put up now three or four times, and it addresses

severe neutropenia. However, you know, if you ask

medical oncologists that actually use this drug, if

you ask them what are the top 10 toxicities with

Irinotecan, one to nine would be diarrhea,

diarrhea, diarrhea, diarrhea, diarrhea, diarrhea,

diarrhea, diarrhea.

So is it really a fair--just to look at

neutropenia here, are we really missing something

by not really looking at what is the most

clinically relevant toxicity, and that is either

diarrhea alone which leads to the hospitalization

or, more importantly, diarrhea in the presence of

severe neutropenia, which generally is very

problematic and is usually associated with the

deaths that we have seen on this drug?

So I would like to make sure that the

Committee understands, you know, the clinical



relevance of neutropenia that we're talking about

here. Severe neutropenia in oncology circles, we

deal with on a daily basis here. The real toxicity

with this drug that we should be paying attention

to is diarrhea and severe diarrhea that will lead

to the patient's hospitalization.

One last question, just to give the

Committee an idea of kind of the softness on the

dosing on this drug. If one would take a look at

the single agent use of Irinotecan before it went

into combinations, at the labeled doses of 125

milligrams per meter squared, how many people could

actually be maintained on that full dose?

MR. MORRISON: I think the dose intensity

for the various drugs ranges from about 70 to 80


DR. PAZDUR: Okay; but how many people

would require dose reductions, I'm asking


MR. MORRISON: By cycle two, I know in the

IFL data, for example, in first line--

DR. PARODI: Single agent.



MR. MORRISON: Yes, single agent, I don't

have that figure.

DR. PARODI: It's usually the majority,

usually a high, high number of people.

MR. MORRISON: And if I could comment on

the diarrhea issue, this is something we're

absolutely looking at, and we're very concerned

about neutropenia occurring in the presence of

diarrhea when we've got endothelium or epithelium

is compromised. And we would like to see what

correlates with diarrhea, and I think more

importantly, we're urging the medical community to

use the infusional regimen of 5-FU, which has been

shown to cause less diarrhea and actually seems to

be more efficacious.

So we're actually advocating use of the

FOLFERI regimen, which is a two-day infusion of

5-FU preceded by a bolus of 5-FU, and the

Irinotecan and 5-FU are given once every two weeks.

So that seems to be a much more tolerable regimen;

requires less dose reduction; and appears to be

more efficacious, and we are looking at these same



pharmacogenomic correlates for UGT and a whole host

of other genes with that regimen in our ongoing


DR. WATKINS: Just a quick point, which is

obvious to everybody, I'm sure, on the panel here.

But as a newcomer, it obviously would be very nice

if the genomic DNA and the clinical data was

available on the patients who went through the

studies back in the early nineties, that would

greatly be to patients' benefits. And I guess

since you started off the talk talking about

Pfizer's global role in pharmacogenetics and as a

leader in R&D, is Pfizer now routinely collecting

genomic DNA and creating databases and bank so that

when such questions come up in the future for

drugs, you can very quickly go back and--


DR. WATKINS: --verify these rather than

doing large phase four studies?

DR. PARODI: Absolutely. We have a very

large commitment in the company to

pharmacogenomics, including systematic collection



of DNA samples, and we are actually developing the

right infrastructure to store and retain this

valuable asset for future investigations.

MR. MORRISON: And we're actually looking

at this not just in terms of Camptosar, but we're

looking at genes involved in a number of other

compounds as well. We're looking at genes involved

in metastasis; for example, in a protocol that

we're just getting ready to launch, we're going to

have tumor samples from the primary tumor and from

liver metastases in a neoadjutant program.

So we're looking at genes that are

involved in invasion metastasis and responsive

therapy, so we're trying to look at everything

across the gamut.

One thing I neglected to mention was we're

also looking very carefully at bilirubin levels,

and we do have in our label a statement concerning

data looking at bilirubin in the normal range,

even. In the range of 1.0 to 1.5 milligrams per

deciliter, there is a significant increase in

toxicity. And that is within the label, and it's



brought to clinicians' attention.

And this is statistically significant

compared to patients with bilirubins less than 1,

so we're very concerned about this. And we would

like to see how bilirubin correlates with UGT, and

maybe Luis can comment more on that, because I know

in the analysis by Dr. Innocenti, that was


DR. VENITZ: Steve.

DR. HALL: Yes, I noticed on your initial

slide talking about the metabolism of the drug and

its metabolites that only the UGT1A1 was mentioned.

And that seems to be the theme so far.

Now, there's a growing literature, and

Kathy's just done a literature search here on the

computer that, you know, other UGTs are involved,

and in your own materials that you supplied to us,

there was a study from the Foxchase Cancer

Institute, I think, that implicated for sure the

1A7 UGT also as a contributor.

So I wondered if you had any information

on the impact of the other UGTs, and secondly, I



noticed in the list of genes that you plan to look

for in the studies you listed again in your

materials, there were no other UGTs mentioned, and

I wondered if that was something that in the

short-term, you would be able to get some concrete

insight into rather than in the longer-term


DR. PARODI: I think we have, as I

indicated, sponsored the N9741 study, which has

established a collection of DNA samples from

Irinotecan-treated patients. And maybe there is an

opportunity in using those samples to investigate

other candidate genes that may be associated with


In our earlier studies, we had not

collected a DNA sample from the earlier

registration studies, but as I indicated in another

slide, we had on the other collaborative studies

that we're conducting right now, we are collecting

samples for future analysis. So if we wanted an

answer about, well, what about UGT1A7, I think a

more immediate answer can come from maybe



genotyping those samples from the 9741 and getting

an answer.

Maybe Dr. McLeod would like to comment on


DR. MCLEOD: In the context of several of

the GI intergroup studies which I am involved in as

well as several others in this room, Dr. Ratain,

Dr. Giacomini, we have tried to take a drug pathway

approach that does not focus on any one particular

element of the disposition of the drug. And so,

missing from this slide here is also many of the

pharmacodynamic markers that are starting to come

out of the some of the screening systems we have.

And so, taking this pseudoholistic

approach as much as our knowledge lets us, we're

trying to understand these issues. So any genes

that come out of these screens are fair game and

hopefully will complement the additional data

that's available.

DR. SADEE: I just want to bring up the

issue of how we use genotype and also as a question

on this. Obviously, and just looking at the 6 and



7 alleles for the gene, including the enzyme, we

will have three genotypes. One is you get both

7/7; that's homozygous for one; and then, you have

homozygous for 6/6; and then, you have the third

population that's heterozygous.

Now, you have chosen, in most of your

slides, to combine the homozygous 6/6 with the

heterozygous 6/7. And in this particular case,

it's very likely that there is additional

functional polymorphism in this gene. So you have

a much greater chance for a large variety in the

heterozygous population that you included with the

6/6 or the 6/6 and the 6/7. They're very

different. And you also have, in the 6/7

population, clinical symptoms for--suggesting that

this is truly, again, a different population.

So my question is how do we deal with, if

we make dosage recommendations, and we have one

population where it's very uncertain; we have one

population--that would be the heterozygous

population; one where it's--and the two others are

more certain, I would say, or we have better




So can we actually combine them, those

populations, heterozygous and homozygous, and would

that be a basis of making decisions along the lines

of dosages?

DR. PARODI: The reason which we combined

6/6 and 6/7s was basically because we saw that

those groups, at least in the reported data,

behaved almost equivalently. So from the phenotype

that we're looking at was almost indistinguishable.

So that was the reason why we--of course, when

you--I take your point that even within one of

these genotypes, like the--even including the 7/7,

it can be genetically very heterogeneous, because

any of these groups can be genetically


But from the point of view of the

phenotype, it certainly made sense to us to combine

6/6 and 6/7s and compare that to the 7/7s.

DR. LESKO: Yes, it's really two questions

with regard to the information provided. The first

is thinking about risk factors separately versus



complements. You mentioned there appears to be a

relationship, albeit imperfect, between

pretreatment bilirubin levels and the level of

toxicity and neutropenia, and that's consistent

with the literature. There's been several articles

that have pointed in that direction with modest

predictive values, let's say.

However, if I were to--and this may be

something that's worth calculating--if I were to

take individuals with certain preexisting bilirubin

levels and then add to it as a complement the

genotype information, would I then increase

predictive value in terms of my risk of toxicity,

my individual risk of toxicity, to the point where

it would be higher than it is?

That would be sort of the one question,

and one could go back and look at that, I'm sure,

with the data in the files, and taken together,

those two indicators, I think, would give a pretty

good indication of an individual's risk of

developing toxicity.

The second question is with regard to



dosing. I mean, from our discussions, it's clear

that dosing in the label is based upon some

clinical studies, but there's also, as I recall,

some dose reductions recommended in the label. And

I don't have it in front of me, but I think elderly

was one of those. And there's some measure of dose

reduction in the elderly. And I'd wondered if

there's any information on either--well, the

information on what was used to lower that dose,

and is there any exposure data in elderly that

would be related to the exposure you would see in


In other words, I'm trying to draw an

analogous situation between lowering the dose in

terms of elderly, because they have a certain

exposure of SN38 area under curve and then

comparing that to the area under curve that we see

in the genotypes and see if there's any logic to

using that as a guide to what dosing reductions

would be done.

DR. PARODI: If I can answer the first

question, and maybe Dr. Morrison can answer the



second, with regard to the correlation between

baseline bilirubin levels and the neutropenia,

actually, the Innocenti paper models this

correlation and actually, in the electronic version

of the paper, they offer to deposit the data at the

publicly available genomics database.

I have checked the database, and it was

not publicly available yet. So it might become

available. And then, once that data is available,

we could attempt the modeling. They report a

multivariate analysis adding a genotype with

baseline bilirubin, and in their modeling, both

genotype, baseline bilirubin and sex were

determinants of the correlation.

MR. MORRISON: Regarding the second

question, I can't comment on exposure to Irinotecan

or SN38; however, the decision to use clinical

judgment to perhaps decrease the dose level in the

elderly was based on an increase in late diarrhea

that was seen in that population.

DR. PAZDUR: But didn't Upjohn do a study?

Perhaps Dr. McGovren could comment on this, on the



elderly, and it had a PK component?

DR. MCGOVREN: Yes, yes.

DR. PAZDUR: And I believe I was one of

the authors on that.


DR. VENITZ: Would you introduce yourself,


DR. MCGOVREN: For various reasons, that

data has been a long time being put into a report

form, and--

DR. PAZDUR: Yes, I know that.

DR. MCGOVREN: And in fact, that data will

be filed with the agency very soon. Age is

probably not the best example to go into here,

because in fact, in that study that you

participated in, there really was no association

between age and diarrhea or age and PK.

DR. VENITZ: Can you introduce yourself

for the record?

DR. MCGOVREN: I'm sorry; it's Pat

McGovren from clin pharm group at Pfizer.

DR. PAZDUR: And for the record, that long



time was how many years?

DR. MCGOVREN: It was probably about five

or six years, yes.

DR. VENITZ: Okay; thank you.

DR. MCGOVREN: For the record, do you want

to indicate what that gesture means?


DR. VENITZ: Speaking about the record, I

think it's time for a break. We'll take a break

until 10:45 and reconvene for the Committee

discussion. So at 10:45, we'll reconvene.


DR. VENITZ: Okay; welcome back, everyone.

Our next and last speaker for our first topic is

Dr. Mark Ratain. He is one of the authors of the

paper that was discussed in detail earlier on, and

he's going to give us his perception and

perspective as to how to use the test for


DR. RATAIN: Good morning. Thank you. I

very much appreciate the opportunity to speak here.

I want to thank Dr. Lesko and Rahman from FDA for



inviting me. I really want to thank Pfizer and

their predecessor companies for providing drug for

my trials. Actually, it goes back into the early

nineties with our initial trial. And I thank the

indulgence of the Advisory Committee.

Some of you are totally overexposed to

Irinotecan already.


DR. RATAIN: And that goes long before

this particular meeting.

Now, I've been working on this drug since

the early 1990s, and I was specifically asked today

to speak to you as a clinician, as a medical

oncologist, and how I would see from with obviously

a biased view how this test could be used to

enhance the treatment of patients.

So, many of you have seen a poster child

before. The poster child is the one on the right

here, 6-mercaptopurine. And you're very familiar

with this, as was alluded to in the important work

that's been done by many, particularly the group at

St. Jude, and this is a figure from the Nature



Reviews cancer paper by Mary Relling and her

colleague showing the relationship of TMPT

polymorphisms to the therapeutic index of

6-mercaptopurine in children with acute leukemia.

Now, here's another poster child. This is

from pharm GKB. This is the Website of the NIH

pharmacogenetics research network, and this was our

poster child. This was the first pathway that went

up. This is a pathway that some members of this

advisory committee have agonized over, and I would

urge you to take a look at it. It is a clickable

interface. And in theory, it should get you the

data that you're looking for; at least that's what

we're told. Some of us have actually been able to

retrieve the data out of this database.

But I think it's pretty clear that this is

a very complex drug. You see the parent drug here.

The parent drug is inactive. The only way the

parent drug becomes active is when it's hydrolyzed

by carboxylesterases, and there are

carboxylesterases within cells. So you can, if you

expose cells to Irinotecan and the cells contain



carboxylesterases, the drugs will get hydrolyzed to

SN38 and become activated. But by itself, it is

inactive. And the primary enzyme responsible for

the hydrolysis is CES-2.

Irinotecan is also a substrate, as shown

here, for CYP-3A. Both CYP-3A4 and CYP-3A5,

although CYP-3A5 has a relatively minor role; the

major oxidative metabolite is APC. That is formed

only by CYP-3A4, and I will add we have looked at

CYP-3A polymorphisms in our studies. We have not

been able to correlate it with anything.

SN38 is a substrate for glucuronasil

transferases. As far as the glucuronasil

transferases that are expressed in the liver,

UGT1A1 far and away is the most important enzyme.

There is probably a minor contribution of UGT1A9.

We have not been able to demonstrate any role for

UGT1A6 in the metabolism of SN38.

And there are other UGT1s that are

expressed in the gut, particularly UGT1A7 and

UGT1A10 that do have the capability of

glucuronidating SN38.



And finally, SN38 as well as the parent

drug and the glucuronide are all substrates for a

variety of transporters, and we are actively

looking at the relationship of polymorphisms in

these transporters to the pharmacokinetics and

toxicity of the drug. We have not been able to

find any relationship between polymorphisms and

MDR1 or ABCB1 and clinical outcomes, but we have

some preliminary data that was presented at the

American Society for Clinical Oncology meeting this

year on a polymorphism in ABCC2, also known as

MRP2, and the pharmacokinetics plasma

concentrations of parent drug as well as APC and

SN38 glucuronide, and we currently have some work

in progress looking at possible relationships of

subtleties such as haplotypes and other clinical

outcomes, but that is all work in progress that has

not even undergone any internal statistical review.

So I really want to focus you on the

subject of today, UGT1A1. Because as you've heard,

this is a polymorphism that, one, is common, and

two, for which there have been multiple studies.



Now, this is a study, and I can't remember whether

this was a pharmacy or an Upjohn study, the mass

balance study of Irinotecan. And I think that this

paper, published in Drug Metabolism and Disposition

in 2000, gives you some idea of what happens to the


And in a mass balance study, 55 percent of

the drug is found, is excreted as parent drug.

Nine percent is SN38; 3 percent is SN38

glucuronide. Only 11 percent is this oxidative

metabolite APC. Only 1.5 percent as NPC, another

oxidative metabolite. So as far as metabolites,

you can see that this pathway, down SN38 and SN38

glucuronide is pretty important, but also, there's

a lot of parent drug that comes out unchanged,

which does make you wonder about the importance of

polymorphisms and transporters.

Now, as you've heard, Irinotecan is a

cytotoxic agent approved in the United States for

metastatic colorectal cancer. It is usually

administered these days in combination with 5-FU,

and I will add is also active in many other



malignant diseases, and it's commonly used

off-label for other solid tumors.

Its usage is definitely limited by

toxicity, both actual toxicity and perceived

toxicity. The toxicities include life-threatening

neutropenia and associated infection. This appears

to be most common on the every three week schedule.

And the other major toxicity, clearly the one that

is more problematic when it occurs, is severe or

life-threatening diarrhea, requiring parenteral

fluids and/or hospitalization, and this occurs

primarily on the schedule, the weekly schedule,

which consists of four weeks on, two weeks off.

And in our hands, at least, this diarrhea

really is not very common on the every three week

schedule. So clearly, we have different

pharmacodynamics going on on these two different

schedules. And so, it is very important not to

lump studies together, particularly when looking at

the diarrhea, because of the schedule-dependent

effects, as well as the confounding issue of

concomitant drugs such as 5-FU, which commonly



causes diarrhea.

Now, I think from a clinician's

perspective, Irinotecan is one of many FDA-approved

choices for metastatic colorectal cancer. And the

discussion to date has focused on if one chooses to

give Irinotecan, what does one do? And I think

from a clinician's perspective, one has to also ask

the question: might genotyping help the clinician

decide among the various choices?

So for first-line therapy, you have 5-FU,

which nowadays is always given with leucovorin,

folinic acid, a modulator of 5-FU, Irinotecan,

oxaliplatin, which is a platinum analogue that has

a totally different mechanism of action from any of

the other approved drugs; capecitabine, which is an

oral fluoroprimadine and is very similar to 5-FU,

and bevacizumab, Genentech's monoclonal antibody

against veg-F. And these are all approved for

first-line therapy in various combinations.

For second-line therapy, one has a choice

of Irinotecan, oxaliplatin, 5-FU with leucovorin,

or cetuximab, the monoclonal antibody against EGFR



marketed by Inclone and Bristol-Myers-Squibb. So

again, one has many choices.

So how might clinicians choose among

various choices? Well, one is clearly personal

experience. Two is interpretation of phase three

data; three, marketing influences; four,

reimbursement; five is a very controversial piece,

chemosensitivity testing. There was a recent story

in the Wall Street Journal suggesting that this

should be done. The American Society for Clinical

Oncology has reviewed this and really, there are no

good data as to how one might use chemosensitivity

testing in an infectious disease kind of model to

decide among treatments. And then, the one we're

talking about today, genotyping, whether one can

predict toxicity or one can predict activity or

efficacy. These might influence how a clinician

would choose among the various options.

So I want to review with you some of the

clinical data, so you can see the dilemma. So this

is a study from the North Central Cancer Treatment

Group, and this was a prospective randomized study,



three different regimens: N9741. And you see that

two of the regimens, IFL and IROX, included

Irinotecan, and one regimen, FOLFOX4, did not

include Irinotecan.

And this study demonstrated that the two

Irinotecan regimens were both--that FOLFOX4 was

superior to IFL, p value 0.0001, and that IROX was

superior to IFL, so that the conclusion of many

clinicians from this study was that FOLFOX4, a

regimen that does not contain Irinotecan, was the

preferred first-line therapy.

Here is a more recent study from the New

England Journal of Medicine. This regimen used

IFL. This is a regimen that was shown to be

inferior in the previous study, and combined it

with Genentech's monoclonal antibody, bevacizumab,

and this study showed that IFL plus bevacizumab is

superior to IFL, and this study led to the approval

of bevacizumab for the first-line treatment of

metastatic colorectal cancer. And the label does

not say in combination with this IFL regimen; the

label says in combination with any 5-FU



leucovorin-containing regimen.

So again, the clinician is still

struggling with what to do. The only published

data is in combination with IFL here.

And then, there is this trial by

Tournigand, a European trial, published in the

Journal of Clinical Oncology this year. This was a

randomized trial that compared FOLFIRI, an

Irinotecan-containing regimen, to FOLFOX, a regimen

that does not contain Irinotecan. Prospective

randomized trial; 113 patients per arm, and then,

second line patients crossed over to the

alternative therapy.

And what this study showed was that

basically, for first-line therapy, the two

regimens, the Irinotecan and the non-Irinotecan

regimen, were comparable from the standpoint of

response rate. Again, bringing the clinician back

to wonder what's appropriate first-line therapy?

And when one looks at survival, again, you get the

same survival no matter what you start with.

So the clinicians treating colorectal



cancer need all the help they can get.

Now, Oncoscreen, a German company, has

taken advantage of this dilemma and is marketing a

commercial test for UGT1A1 genotyping, and you can

go to www.oncoscreen.com, I think, and you can

read--part of it's in German, and part of it's in

English, and part of it's in misspelled

English--about the side effects of Irinotecan, also

known as CPT11, and polymorphisms in the promoter

region of UGT1A1. And it gives you the address,

and you can send blood here. I've never tried, and

I have no idea how well they're doing, but they've

taken advantage of this opportunity to actually

market the test.

And this is the data from our study, the

Innocenti study that you've heard about, shown in

greater granularity. And this was 66 patients

enrolled prospectively as you've heard. And the

study was powered around trying to show a trend, a

significant trend, 6/6, 6/7, 7/7, although the

original study design was powered to look for

diarrhea, which at the time we started the study,



we did not understand the schedule dependent

differences in the diarrhea, and so, we ended up

looking at neutropenia as the endpoint.

As you've also heard, there are other

polymorphisms: allele 5 and allele 8. Allele 5

has been suggested to have higher glucuronidating

activity than a 6, and allele 8 has been suggested

to have lower glucuronidating activity than the 7.

And in response to the question previously asked

about ethnicity, the study was primarily caucasian,

not exclusively caucasian. I believe there were

one or two Asian patients, and there were certainly

some African-American patients in the study, but

there were certainly not enough within any

population subgroup to stratify for that.

And you see that there was a significant

trend with the 7/7s having a lower absolute

neutrophil count nadir than the other two groups,

with the 6/7 being intermediate, but clearly, the

difference between 7/7 and 6/7 is greater than the

difference between 6/7 and 6/6.

I will also add that if you want to



translate absolute neutrophil count nadir to grades

of neutropenia, grade three neutropenia is less

than 1,000. That's probably not clinically

significant, although it can affect subsequent

dosing. It might result in delays of treatment if

you develop grade three neutropenia.

Grade four neutropenia is an absolute

neutrophil count nadir of less than 500, and a

patient who has grade four neutropenia, who

develops a fever, is essentially automatically

admitted to a hospital and treated with parenteral

antibiotics. And so, it is very common to get

fevers when you're neutropenic, and so, that that

is a real morbidity and a real cost issue.

So others have addressed the issue of

sensitivity and specificity, and I'm just going to

again go through our data, and again, this is a

single study: 350 milligrams per meter squared

every three weeks and looking at grade four

neutropenia, the clinically significant

neutropenia, this is the extreme, less than 500.

And again, we agree with the Pfizer analysis. The



sensitivity is 50 percent of patients who have

grade four neutropenia who are 7/7. Specificity:

95 percent of patients who do not have grade four

neutropenia are not 7/7.

And the positive predictive value: 50

percent of patients who are 7/7 have grade four

neutropenia, and the negative predictive value, 95

percent of patients who are not 7/7 do not have

grade four neutropenia.

Now, let's put this into the context of

without testing and with testing. Without testing,

100 percent of patients are treated, and 10 percent

have grade four neutropenia. If you chose not to

treat the 7/7 patients, with testing, 90 percent of

patients are treated, and approximately 5 percent

would have grade four neutropenia. You would have

a 5 percent absolute reduction. You would test 20

to protect one.

So I put out what is my bias but I believe

is still hypothesis that pharmacogenetic testing

will improve outcomes in metastatic colorectal

cancer. That's really what we're here to discuss.



And I believe it will allow the clinician to select

a drug regimen based on patients' genetic, and now,

we're talking germ-line polymorphisms, genetic

characteristics, that this will lead to reduced

toxicity and potentially will lead to increased

efficacy, something that we've not previously

talked about.

My opinion is that sufficient data exist

to recommend that patients who are homozygous for

the star-28, the 7/7, should not receive Irinotecan

at standard doses. Some might say that you could

treat at standard dose and accept greater toxicity.

Some might say you could reduce the dose. I

believe that these patients would be most

appropriately treated with an alternative regimen

such as an oxaliplatin-based regimen that has the

same survival outcome as an Irinotecan-based

regimen. I cannot sit here and recommend reduced

dose, because we have no clinical data to show that

patients treated with 7/7 at a reduced dose have

comparable activity and comparable survival

outcomes to patients treated with alternative




On the other hand, the optimal treatment

of patients who are at reduced risk of Irinotecan

toxicity star-one, star-one, or 6/6 is unclear.

Should they be treated with standard

Irinotecan-based regimens? Should they be treated

with high-dose Irinotecan-based regimens? There's

one European study that took patients treated with

standard dose, escalated patients who did not have

significant toxicity; they escalated them up from

350 per meter square to 500 per meter square. It's

a single-arm study, but it's got the highest single

agent response rate of any study in the literature,

and so that this may be an opportunity to reexplore

dose in a low-risk group of patients representing

50 percent of patients that are candidates for this


Or is oxaliplatin the best regimen for

these patients? We have no data to support that,

particularly for the low-risk patients.

I want to contrast this with other drugs

and other polymorphisms, because I think this is a



great opportunity to use pharmacogenetics to

individualize treatment of colorectal cancer. And

this is Bob Diazio's Website, www.dpdenzyme.com,

where you can learn about screening patients for

DPD enzyme deficiency. Oncoscreen also offers this


What do we know about this test? And

here, you see the Oncoscreen Website, and it says

this test is supported by the German health

insurance companies. Actually, the German health

insurance companies initially--the German oncology

group initially recommended this test and then

retracted the recommendation, which is kind of

interesting. There's a history there.

And the most common mutation in DPD is an

exon 14-skipping mutation. This has an allelic

frequency of approximately 1 percent. The star-7

polymorphism has an allelic frequency of

approximately 35 percent. So there's a big

difference in allelic frequency here. DPD testing,

if you test this exon 14-skipping mutation, and

your endpoint is grade four, life threatening 5-FU



toxicity, without the test, all patients would get

treated, and approximately 3 percent of patients

have this toxicity. So only 3 percent of patients

have grade four toxicity from 5-FU as a single


With the test, you would treat 98 percent

of patients, and approximately 2 percent of

patients will still have toxicity, a 1 percent

absolute reduction. You would test 100 to protect

one, so much lower efficiency of this test.

And then, there's another important

polymorphism that may predict for toxicity and

efficacy of fluoroprimadines, and that's a

polymorphic repeat sequence in the thymidylate

synthase gene that has been suggested to affect

translational efficiency but not gene expression.

And this is quite polymorphic.

Here, you see the population distribution

of this 28-base pair repeat. This is data from

Howard McLeod's group. And you see that the three

repeat is more common than the two repeat, and that

there's also a four repeat present in African




So with parting words: oncology is widely

anticipated to be the best model for demonstrating

the clinical importance of pharmacogenetics as it

relates to germ line polymorphisms. Colorectal

cancer is an important model, because of the large

number of active agents. We have candidate genes,

candidate polymorphisms and abundant clinical data.

And I want to thank my colleagues in the

PAR group, pharmacogenetics of anticancer agents

research group. I want to thank my colleagues in

the PGRN, pharmacogenetics research network, those

sitting here today, those I've collaborated with,

and those who have had to sit through far too many

discussions of Irinotecan.

So, thank you.

DR. VENITZ: Thank you, Dr. Ratain.

Any questions or comments by the Committee

before we start our overall discussion?


DR. WATKINS: Just a question about the

UGT1A7, which is in the gut, and we've heard that



diarrhea is probably a bigger issue than

neutropenia. What work has been done looking at

UGT1A1 polymorphisms and diarrhea?

DR. RATAIN: It's a very difficult

problem, because there are definitely polymorphism

1A7 that have shown to be functional that are

strongly linked to UGT1A1, because it's all one

gene. And, in fact, the linkage in UGT1A1 goes

five prime at least down to UGT1A9. So to actually

distinguish the independent effect from 1A7 from

1A1 requires a very large study.

One would not--since 1A7 is not expressed

in the liver, one would not expect it to have a

significant effect on the plasma pharmacokinetics

or on the neutropenia, but it certainly is a

candidate gene for gastrointestinal toxicity. But

we really need a lot more data, because this really

will require haplotype based analyses of the whole

UGT1 gene.

DR. SADEE: Mark, this comes back to my

earlier question about dosage escalation in

populations. You mentioned that here that in



patients who are apparently protected against the

cytotoxic effects, you can go to higher doses and

get higher efficiencies. So I think that really

sets an important example to pursue that.

Do you have any other examples where that

has been pursued, so rather than looking at the

negative side, one would look where you want to

avoid things. You exploit the patients that really

should get a different dose.

DR. RATAIN: Well, I mean, you know, there

have been some studies in oncology where patients

sometimes get intraindividual dose escalation, but

there's really not a large data set on that. I

mean, Dr. Pazdur may have some comments.

DR. VENITZ: Howard?

DR. MCLEOD: Mark, we heard from Dr.

Rahman's talk about how the current package insert

includes data on age and bilirubin and some other

factors that I'm forgetting, public radiation and

one other thing, as risk factors and with a need

for dose reduction.

I wonder if you could put the 7/7 genotype



into the context of those existing risk factors.

DR. RATAIN: Well, we've looked at age in

our data set, and we have not found at least in our

study of 66 patients a significant impact of age.

So I would say from the standpoint of neutropenia,

genotype is certainly more important than that.

Bilirubin, in our hands, is a pretty good poor

man's genotype, but this is a single institution

where the bilirubin is collected in a standard way.

Once you get into multiple laboratories, and

bilirubin is tested at various times of the day

with various degrees of fasting, you're going to

really obscure the relationship between genotype

and bilirubin.

And so, I think that yes, patients with

higher bilirubins, particularly if it's

unconjugated, are very likely to be 7/7, because

many patients within the normal range of bilirubin

are 7/7. So, but I think even there are some

subtleties. I think again, patients with very low

bilirubins probably are not 7/7, and I've used that

in my clinical practice to help determine dosing in



the absence of an approved test.

DR. GIACOMINI: Yes, Mark, in your study

in which you documented the neutropenia, did you

also measure pharmacokinetically the SN38, and was

it higher in those patients with the 7/7?

DR. RATAIN: Yes, we did measure SN38.

SN38 is higher in the 7/7. SN38 correlated with

neutropenia. As I said, we have some evidence that

polymorphisms in ABCC2 through our collaboration

with Deanna Krebs may relate to the

pharmacokinetics of SN38 glucuronide, which makes

it difficult to interpret SN38 to SN38 glucuronide

ratios, which we previously assumed to reflect

solely glucuronidation. It quite possibly is

determined by both glucuronidation as well as


DR. GIACOMINI: Let me ask a followup on

the bilirubin thing. Does bilirubin actually

competitively inhibit the glucuronidation of the

SN38 to SN30 mechanistically? Is it a competitive

inhibition, so when the levels of bilirubin are

low, it's telling you two things, one, about the



genotype but also about just direct

competitive-competitive inhibition?

DR. RATAIN: You're asking me does

bilirubin inhibit--


DR. RATAIN: We've not looked at that. I

don't know of any data. I would not expect it to.

And there is certainly some evidence not for--it's

possible that SN38 could inhibit bilirubin

glucuronidation if the levels are pretty low, but

there are certainly examples of other drugs,

particularly the protease inhibitors, that inhibit

UGT1A1 and do competitively inhibit bilirubin


DR. GIACOMINI: Okay; but you wouldn't

expect the bilirubin and the high bilirubin levels

to be inhibiting the SN38.

DR. RATAIN: Not in--not in--I don't think

so; I mean, Dr. Watkins would have a better feel

for that.

DR. DERENDORF: I'd like to come back to

your mass balance slide. If I understood it right,



only about 9 percent of the parent drug gets

converted to the SN38. So what do we know about

the other metabolites?

DR. RATAIN: Would you like for me to put

that back up?

DR. DERENDORF: Yes, you can. It's the

number five.

DR. RATAIN: Messed it up; sorry.

So, this is the mass balance slide you

were referring to. And I'm sorry--

DR. DERENDORF: Only 9 percent gets

converted to the SN38, right?

DR. RATAIN: Well, 9 percent is found as

SN38, and 3 percent is found as SN38 glucuronide.

DR. DERENDORF: Oh, okay.

DR. RATAIN: And again, this is a limited

number of subjects. These subjects were not

genotyped, but approximately 12 percent, I think

it's fair to say, goes down that pathway. I think

that's a reasonable estimate. And you see 55

percent in this study was--the parent drug was

excreted unchanged. About 12 percent is oxidative



metabolites, metabolites known to be formed by

CYP3A, and then, we don't know the rest of this.

And again, I was not an author of this study; just

presenting it for perspective.

DR. WATKINS: Just to address that issue

of can bilirubin itself interfere with the

glucuronidation of SN38 or any other drug, in

theory, that's possible. It certainly works the

other way around. There are some drugs that will

inhibit glucuronidation in patients who have a

genetic predisposition of Jolbert's. But I'm

unaware of any studies that have looked the other

way, so I don't think I can address that.

But the question I wanted to ask myself,

one of the concerns with using genotypes of the

host as opposed to the tumor in cancer chemotherapy

is the fact that genotype and phenotype don't

always go together, particularly in an ill cancer

patient on multiple drugs with cytokines, and

certainly, if their liver is completely replaced by

tumor, genotype is irrelevant.

And one of the very unique things here is



this particular phase two enzyme has an endogeneous

substrate, so in effect, you have a phenotype

measurement. And my assumption up until what you

just said was that that endogeneous probe for

UGT1A1 was not very good. But what you're saying

at your institution, it's in fact very good.

DR. RATAIN: There are two studies that

address this. There's our study that within a

single institution, all patients were on a research

protocol; the bilirubins were collected at, you

know, in a fairly consistent way just by nature of

our research practice, and it looked pretty good.

There's also a study that I was a coauthor on that

relates to a Pfizer study in which a large data set

was analyzed, and bilirubin really wasn't a very

good predictor, and this was just published in the

Journal of Clinical Oncology this year by Meierhard

is the first author, and the company may want to

elaborate on that further.

DR. WATKINS: Because if I can just follow

up, I mean, the key question is what does

genotyping add to the existing tool kit of the



oncologist? And my assumption in all the

background reading was that it adds a significant

amount. If an alternative is just standardizing

indirect bilirubin measurements, that's another

option that could be considered, I think.

DR. RATAIN: Again, you know, from an

analytical perspective, there's a gray zone, and it

doesn't--bilirubin doesn't, you know, in a large

data set may not correlate as well as something

that is a discrete answer like a 7/7 genotype. I

think also, it might be tough to distinguish 6/6s

from the 6/7s, and I think that the 6/6s are

potentially appropriate candidates for phase four

clinical trials looking at higher doses of

Irinotecan which I think is another important

reason to find a way to get this test in the hands

of the clinical oncologists and the research

oncologists to help further explore the

dose-response of this drug.

DR. HALL: So in part to follow on from

that, then, in your hands, what would your

recommendation be for the heterozygotes? Are they



to be treated or given an alternative?

DR. RATAIN: I would see no reason not to

treat the heterozygotes, given the data today.

DR. MCLEOD: One of the things you

commented on was that neutropenia is an important

toxicity, and I certainly second that. And during

the discussion, hopefully, we will elaborate on

that more, because it's a common problem that is

less of a worry but probably more of a problem to

the patients.

The question I have for you is you made

the comment that you thought the 7/7 patients

maybe--might represent a data set that should get a

different drug, oxilaplatin or something like that.

But with the current state-of-the-art and the one

for probably the foreseeable future is that every

colorectal cancer patient at a decent center will

get Irinotecan. If they don't get it first line,

they will get it second line.

And so, we can't really avoid the issue

that Irinotecan is going to appear. This is a real

drug for colon cancer. And they're going to get it



at some point, first line, second line, third line.

So it would be worthwhile, either now get your

comments or in the discussion, trying to think

about that issue, because the drug is approved in

both these settings, and so, we do have the remit

to actually talk about it in first line, second

line, et cetera.

DR. RATAIN: Well not everybody gets it

second line. There's some patients--

DR. MCLEOD: Not everybody does, but they


DR. RATAIN: What I'm saying is if--some

patients don't get to second line. If you were to

give Irinotecan first line and have a grade five, a

fatal event, they won't get to second line. So you

would say, ideally, the clinician would like to

reserve the more toxic drug for second line rather

than first line.

DR. MCLEOD: But I totally agree with your

thinking behind it. I'm just--we can't avoid it.

I mean, the patients that make it through first

line because they didn't get Irinotecan, and they



were 7/7, the selection now, you've just taken one

drug off the table. It's now either single agent

Irinotecan or Irinotecan and bevacizumab, whatever.

We may not be able to come up with those

things, because like you said, there is no

prospective studies. But certainly, it is an

important issue.

DR. RATAIN: You know, I think as you

think about it as a clinician, you know, if you

have a discussion with a patient, and you sit down

with them, and you talk about Irinotecan versus

oxaliplatin as first line therapy, when you talk

about Irinotecan, you have to talk about

neutropenia, diarrhea, which can be severe,

life-threatening or even fatal. And as you talk

about oxaliplatin, you have to talk about

neurotoxicity that can be persistent.

And, you know, patients have to make

choices, and I think being able to inform patients

about their relative risk, particularly of the

toxicity that scares a lot of both patients and

clinicians, which is the neutropenia/diarrhea



complex, I think, is useful, and I think if one

could reassure a clinician that their patient is at

relatively low risk of these toxicities of

Irinotecan, a clinician would be more interested in

prescribing Irinotecan first line.

And so, I think that this actually is

helpful, very helpful to the clinician and I think

potentially very helpful to the sponsor who is

marketing the drug.

DR. BARRETT: You mentioned the lack of

prior appreciation of the scheduled dependence on

diarrhea, and I wondered, back on your

recommendations as far as not reducing the dose,

would you feel the same with neutropenia and the

diarrhea? And I guess the followup question there

is most of this data has been summarized outside of

the time dependency, so do you feel if that kind of

information is brought to light through either dose

reduction in the context of managing toxicities

that you could perhaps devise a schedule for one

toxicity versus another?

DR. RATAIN: Well, the diarrhea is a lot



messier to model; no pun intended. And the

neutropenia is pretty well correlated with plasma

SN38 exposure, and we can understand that both in

the context of these studies as well as in the

context of other studies, anticancer agents and


The diarrhea is not fully understood, and

we've tried to model it in the past to somehow try

to model biliary excretion of SN38, and we have one

study that actually came up with a surrogate

endpoint, or, actually, biomarker would probably be

a better term for it, which was the CPT11AUC times

the SNC38AUC over the SN38 glucuronide AUC.

But it's very complicated. I think that

the thing one is most concerned about is the

neutropenia/diarrhea complex and particularly in

the context of schedules that are more frequent

than the every three weeks, which is where you see

this problem.

DR. VENITZ: Mark, as you know, the

Committee is asked to review the evidence to see

whether we would concur with the recommendation to



include pharmacogenetic testing. I'd like to know

what the competition is. In other words, I'd like

to know right now what is being done to come up

with a starting dose. How do you choose a starting

dose for Irinotecan with the information right now

without genetic testing?

DR. RATAIN: Right now, people just rely

on clinical evidence, which is one size fits all

based on body surface area, even though body

surface area has been shown not to correlate with

the pharmacokinetics of this drug.

DR. VENITZ: Followup question: how do

they adjust the dose once the patient is being put

on Irinotecan?

DR. RATAIN: I think clinicians do it to

some extent by the package insert and some extent

by their personal experience.

DR. VENITZ: Okay; thanks.

Larry, I think you had the last question

and then maybe frame the questions for the

Committee so we can start the questions.

DR. LESKO: Okay; thanks.



Yes, Mark, and I think you may have

answered this in the last couple of minutes, but I

was looking at the relationships that Atik had

presented looking at the probability of neutropenia

and diarrhea respectively as a function of SN38

area under the curve.

They're remarkably similar, although they

were based upon mean data. So the question is is

there an indirect benefit in reducing the risk of

severe diarrhea from paying more attention to,

let's say, the neutropenic problem? In other

words, do they go together, and to what degree do

they go together?

DR. RATAIN: Yes, there's certainly an

association of the two, but they don't always go

together. But a patient with neutropenia is more

likely to have diarrhea and vice versa.

DR. VENITZ: Good. Thank you. We

appreciate your comments.

Larry, why don't you frame your questions

for us?

DR. LESKO: How about if we bring them up



on a slide?

DR. VENITZ: That's fine.

DR. LESKO: I'll just scroll through


Okay; so, as the time proceeds, I'll

scroll through the individual questions, but the

first question that we have for the committee

discussion is regarding the scientific and clinical

evidence that we're all aware of at this point. So

the question is is the evidence presented

sufficient to demonstrate that the homozygous

star-28 genotypes or 7/7s, as we call them, are at

significantly greater risk for developing a,

neutropenia, and b, the acute and delayed diarrhea

that we've heard about as an adverse event?

DR. VENITZ: And you would like for us to

vote on this?


DR. VENITZ: So as far as the Committee is

concerned, any comments, discussion items for FDA

before we vote? And by the way, the vote is going

to be by voice vote. I'm going to call your



individual names, and you're going to have to tell

me whether you're a yes, no or abstain for the

individual questions as we go along.


DR. VENITZ: Nozer.

DR. SINGPURWALLA: Would you consider

removing the word significantly?

DR. LESKO: What would you suggest as an

alternative? Just--are you thinking of it because

it's a statistical--how would you convey a small

risk versus a large risk?

DR. SINGPURWALLA: Well, I'm not sure if I

could subscribe to the view that the risk is

significantly larger.

DR. LESKO: Could we use markedly greater?

Clinically important?

DR. SINGPURWALLA: I made my point.

DR. LESKO: I think the question is

intended to convey a magnitude of risk. If we want

to say clinically important, markedly, I think it's

fine. I think it conveys the same thing.

DR. SINGPURWALLA: You mean you insist on



an adjective?

DR. LESKO: I think a qualifier would


DR. VENITZ: Any further comments?

DR. SADEE: Are we to consider these two

together, A plus B, or A separate from B?

DR. LESKO: I think we need to, based on

the way the evidence was presented today, it's

probably better to consider them separately.

DR. VENITZ: So we'll have two votes.

We'll have one on neutropenia and one on diarrhea.


DR. VENITZ: Any other comments before I

call for the vote?

[No response.]

DR. VENITZ: Okay; then, the first

question is is there sufficient evidence of a

greater risk of developing neutropenia. And as I

said, you have three choices: yes, no or abstain.

So let me go down my list.

Dr. Barrett?




DR. VENITZ: Dr. Capparelli?


DR. VENITZ: Dr. D'Argenio?


DR. VENITZ: Dr. Davidian?


DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: That doesn't count.

DR. VENITZ: Dr. Hall?

DR. HALL: Yes.

DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. Singpurwalla?


DR. VENITZ: And Dr. Watkins.


DR. VENITZ: Okay; then, the second part



of that question is is there sufficient evidence to

substantiate a significantly greater risk for the

delayed diarrhea and acute delayed diarrhea? Oh,

before--I'm a yes, too. So we have unanimous.

Okay; second question, then, what about

diarrhea? Does the Committee feel there is

evidence to support significantly the increased


Dr. Barrett?


DR. VENITZ: Dr. Capparelli?

DR. CAPPARELLI: No, not yet.

DR. VENITZ: Dr. D'Argenio?


DR. VENITZ: Dr. Davidian?


DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?




DR. VENITZ: Dr. McLeod?

DR. MCLEOD: No at the moment, but the

data looks like there's something there.

DR. VENITZ: That counts as a no.

Dr. Sadee?


DR. VENITZ: Dr. Singpurwalla?


DR. VENITZ: Dr. Watkins?


DR. VENITZ: And I would add my no, but it

does appear not only that there might be something

but it may be limited to patients that have

colorectal cancer; in other words, diarrhea may not

be present in patient populations that don't have


Okay; any other comments about question

number one? So we have a unanimous vote on the

first part, and we have an almost unanimous part on

the second part of that question.

Okay; Larry, you want to present us with

the second part of this question?



DR. LESKO: Yes, I think on this second

question, if I can propose that the way this is

worded, it's not in a sense a votable question,

because I think we're looking for discussion; for

example, what would be the risks and benefit, what

is an appropriate study design, and it strikes me

that it doesn't lend itself to a vote. So if I can

propose that we look at this question and address

the questions that are posed on the slide in a

discussion context as opposed to a voting context,

I think that would be useful to us.

DR. VENITZ: Okay; then, I open the


DR. GIACOMINI: Yes, one of the things I

didn't see, and I don't even know who I'm

addressing this to, this question to, but did we

ever see any data and, like, Kaplan-Meyer curves?

I don't even know if--Kaplan-Meyer curves, where

they've factored, you know, where they've looked at

survival data over time and then genotypes, put

them in categories, like the people with the star-7

genotype or the star-28 genotype are they having a



better survival or worse survival?

Can I ask Mark, or is he not allowed to

talk? Can I ask this to Mark? He can't talk?

DR. VENITZ: Yes, you may.

DR. GIACOMINI: Mark, I mean, just to get

an idea of the benefit to--

DR. RATAIN: There are no published data.

Dr. McLeod has a data set that may provide some

insight into the answer to your question.

DR. GIACOMINI: Oh; Howard? I guess what

I'm trying to do is get a feel--

DR. MCLEOD: Yes, there are no published

data on colorectal. There are two studies included

in the papers from--provided by Pfizer that looked

at the UGT1A1*28 genotype and survival. They were

both in the context of non-small lung cancer, if I

recall correctly. And one of the studies found

that the 7/7 genotype group from the star-28

homozygotes had a poorer survival. The other study

didn't separate the groups quite the same way, but

the group that contained the 7/7 genotypes had an

improved survival.



Now, neither of them met statistical

significance. They were all 0.06, 0.07 type

things; small studies, no covariance; I mean, a lot

of different issues. So my interpretation is we

really don't know the effect of UGT1A1 on survival.

In the context of colorectal cancer, there

is sufficient data, in my mind, to show that any

one study is not really going to have the full

answer on patient survival. So if you look at

patient survival for the impact of first-line

therapy is confounded by the presence of good

second-line therapy, good third-line therapy, et

cetera. And the Chornagon study demonstrated that.

Didn't matter what you gave first from what Mark

showed. If you gave the other one second, then, it

was a wash in the end.

And so, in the context of response, there

is some data that UGT1A1 may have an influence on

response, although the numbers were small and not

definitive. But there was no impact on time to

progression or survival, and so, it's inferior

data. It's as good as we have at the moment.



There are large studies in the cooperative groups

that are going to be able to address this in a much

more aggressive fashion because of sample size.

So I don't really know the answer. It

appears there may be an influence on response, but

there certainly does not appear to be an influence

on time to disease progression, so time until the

tumor grows again, or survival influence.


DR. BARRETT: In thinking about dosing

this agent, I'm struck with Dr. Pazdur's original

comments when he talked about the fragility of the

original dose selection of this compound and the

modest response rate. So while I think most of the

discussion is focused on managing toxicities, the

loss of efficacy looms very high with this

compound. But I guess the other curious thing I

had in my mind is do we have any of the historical

data in which dose reductions were, in fact,

monitored where you could look at the

responsiveness of these markers or responses as far

as diarrhea and neutropenia go relative to a dose



reduction, so you can get some sense of, you know,

how, in fact, responsive those toxicities are to

dose reduction?

DR. MCLEOD: So that would be dose

reduction regardless of the cause?


DR. RAHMAN: I'd just like to comment on

something that we have in the package insert

already. We have data on 100 milligram per meter

square weekly dose, 125 milligram per meter square

weekly dose, and 150 milligrams per meter square

weekly dose, and what we have seen is that there is

not a whole lot of differences in the response

rates, although numbers are very small, so you

cannot do a cross-study comparison here.

But the observation that we have from the

package, and also, it is in the package insert is

that the survival, median survival across those

dosage groups is not a whole lot different so is

not the response rates.

DR. PAZDUR: The additional point is that

we do not know the relationship between response



rate as a surrogate for survival in this situation.

I would like to point out that this drug had in the

5-FU refractory disease population a 15 percent

response rate, yet it was able to show an overall

survival advantage compared to best supportive care

in two trials, which indicates to me that perhaps

disease stabilization or some influence on time to

progression is far more important than simply tumor

reduction size.

DR. VENITZ: Dr. Williams?

DR. WILLIAMS: I think one of the most

important questions to answer is what you're going

to base your dose selection on for the 7/7s. Mark

suggested, you know, not treating them as one

option, but obviously, you are going to have to

treat them. You cannot base it on a survival

observation. You just don't have enough patients

to make that observation.

So you're going to have to decide what to

select a dose on, and your new study, perhaps,

that's going to be done to look at dosing in that

population. So what are you going to base it on?



I was sort of interested with Mark, would you base

it on a targeted dose of AUC of SN38? That's a

little unsettling, because the slide that Atik

showed suggested that even with the same AUC, these

patients had a higher degree of myelosuppression.

You know, they were having grade four neutropenia

all along the bottom of that graph up and down the

AUC spectrum, so that's a little mysterious, and

then, you ask, well how about from the

pharmacodynamic standpoint for the tumor? Is the

tumor equally sensitive to the same AUC of SN38?

So, I mean, I think you're going to have

to target something. You can't, you know, you just

can't look retrospectively at toxicity, and I'd be

interested in what the Committee thinks when you do

this new study to try to individualize dosing for

these patients, what are you going to target?

DR. RAHMAN: I'd like to make a comment

about the starting dose. What I have shown in my

presentation that there is already a nice algorithm

for a starting dose for standard therapy and

continuous therapy and dose modification based on



toxicities in the package insert. And as I have

mentioned that we have some predictive factors

already in the package insert which are bilirubin

levels, prior radiation therapy, performance

status. Those are already indicating, recommending

a dose level lower than the standard dose as a

starting dose.

And then, if the patients do not have any

complication with that, the package insert allows

to go up to the standard dose and then move on with

that. So here is the starting dose that we can be

thinking about that can we do anything different

for the UGT1A1 patient, 7/7 patient, I mean?

DR. MCLEOD: And to follow up on that, I

wonder if maybe Dr. Morrison or one of the Pfizer

team could comment on whether dose reduction is a

covariant in terms of outcome, time to progression,

whatever your favorite is, coming back to try to

get at Jeff's initial question.

MR. MORRISON: Maybe if I could defer to

Pat to comment on that, because this was actually

before my time.



DR. MCLEOD: Lucky Pat.

DR. MCGOVREN: Yes, I don't have an

answer. It has not been modeled. So I don't

know--I think that the various risk factors were

arrived at very empirically, and dose reduction was

not done in any systematic way.

DR. MCLEOD: Well, Atik clearly and

correctly mentions that there is a range of doses

that seem to be equal. Those patients may have

declared themselves as being different not only in

their sensitivity to the drug but also for other

factors, and so we can't say that just because we

can start low, that means that people who are

sensitive will still do well.

DR. PAZDUR: But there is an inherent bias

in looking at the data that patients that may get

the dose reduction are poor performance status or

other issues that lend themselves to poor either

responses or poor survival outcomes. I think it's

clear, though, you know, having worked with this

drug before I came to the agency and have had a

long history, I think it would be fair to say that



we do not have a really good handle on what is the

dose in its relationship to the eventual outcome.

You know, could we have achieved a similar

outcome with a reduced dose? Remember, this drug

was developed in a time when oncology had the

mantra more is better, more is better, more is

better, and we kind of were hitting toward what is

the absolute highest dose that we could deliver,

and this is common in many of the oncology drugs

that we have developed over the past decade, and

now, we're trying to step back and ask this

question, which is very difficult to do.

You know, should we look at, for example,

at these patients that have this genetic mutation

to do just simply a phase one study, as we

suggested, sometimes through the company to take a

look at what would be the appropriate dose,

starting out at an artificially dose reduction and

seeing actually what the dose, because we really

don't have a good handle, even in the general

population, of what is a dose response for this

drug. And we're basing it on toxicity, basically,



and that's--we have to be realistic on the

development of this drug. That's how it happened

over the past decade.

DR. VENITZ: Let me make a--

DR. MCGOVREN: Yes, go ahead.

DR. VENITZ: --followup comment that gets

to item number B. I think right now, the concern

is that if you reduce the dose, we might compromise

efficacy. Well, but can you not turn that argument

around? If you improve tolerability and compliance

on a long-term treatment, don't delay treatment as

a result of a lower dose, you might actually

improve efficacy, not just compromise it. So to

me, I don't know which way to go. As you pointed

out, this drug was developed under the paradigm of

an MTD.

So by actually backing off of the dose,

you might get improved efficacy just by keeping

more patients on drug.

DR. MCGOVREN: Yes, none of the trials, I

don't think, were large enough to actually dissect

out the efficacy in patients who started at the



standard dose and continued on the standard dose

until their tumor progressed versus patients who

started with the standard dose, were dose-reduced

because of toxicity and then continued on a reduced

dose versus those who started on a reduced dose

because they had a risk factor at the time they

went on treatment, performance status or whatever,

and then continued on that reduced dose or even had

that dose reduced because they couldn't take the -1

level dose.

So it's just very difficult to tease out

of the available trials all of these factors which,

of course, complicates how do you design to

determine the appropriate dose for the 7/7s?

DR. VENITZ: Then maybe let me focus the

Committee on the third part of this question: what

would be needed, what would need to be done in

order to figure out what to do with those patients

in terms of coming up with a starting dose for

patients that are 7/7 genotypes?

DR. SINGPURWALLA: Jurgen? As an outsider

looking at this, the question is what is an



appropriate study.

Now, I can't answer that question as to

what is an appropriate study, but one thought goes

through my mind: electrical engineers use control

theory to control the movement of something or to

control the behavior of something. Has any thought

been given to using a similar kind of a paradigm in

this particular business? You start with a certain

dose; you make a prediction as to what the effect

of the dose will be; then, you observe the actual

outcome and make a correction subsequent to that

and keep on doing it in some kind of a filtering


That is a suggestion that I would like to

put forward.

DR. MCLEOD: There are study designs that

have used a variation on that theme, both in terms

of trying to reduce the number of patients required

to study in early evaluation and also try to make

them more rapid. They've had variable success, and

in the end, we've kind of fallen back to the status

quo. But people are certainly aware of sort of



iterative-type processes. We just haven't figured

out how to do them very well.

DR. SINGPURWALLA: Well, I'm surprised

that you've said you've fallen back, because

control theory is one of the most successful

applications of process control, which is really a

part of this, and I'm surprised why the study

failed or why they regressed.

DR. MCLEOD: Well, it's a very successful

theory in many industries. Biomedicine is not one

of the areas where it has been a blazing success.

And so, I think with the greater understanding of

systems biology, it will be successful.

Currently, the endpoints that we talk

about in phase one are incredibly crude, and crude

endpoints don't lend themselves to intricate

approaches such as what you described.

DR. SINGPURWALLA: Are these studies

published? Is there any way I can read up on them?

DR. MCLEOD: Certainly.

DR. WILLIAMS: Let me sort of restate my

question earlier. I think from a practical



standpoint, certainly, you could do a phase one

study in these patients, right? And I think the

question would be that's probably what you should

do, right? Do a phase one study in the 7/7s; you

find a reasonable toxicity.

But then, what are you going to use to

provide yourself with the assurance you're in the

right place? Will it be that you have the AUC that

everybody else had with SN38? Would that provide

you assurance, or would there be some other route?

So I guess I'm just throwing out the possibility

that you would do a normal type phase one study

looking at toxicity and pharmacokinetics.

But then, what would you do, you know, to

assure yourself that you're where you want to be?

DR. VENITZ: Marie?

DR. DAVIDIAN: I just wanted to bring up,

related to that, there's been some recent work in

the statistical literature by Peter Fall, who is at

M.D. Anderson, and I was just wondering if any of

his work would be relevant in looking at toxicity

and efficacy jointly?



DR. WILLIAMS: I mean, I wonder, you know,

in this setting, do you think that--I guess the

only thing you could look at would be response rate

in that kind of setting. I don't know--we have to

talk to the statisticians, whether you could really

study enough patients to do that.

DR. DAVIDIAN: I agree.

DR. VENITZ: Just a followup to your, I

guess, subquestion here. I think that's the only

way you can approach it with what we know right

now. Doing a phase one dose escalation study and

see what area do you accomplish? What's the

corresponding dose?

DR. PAZDUR: But we really don't have a

good pharmacodynamic relationship between any

parameter and efficacy, either if one tries to look

at response rate or any other clinical endpoint

with this drug, and we have to be realistic about

that. And I think also, it depends on what type of

dose reduction that we're talking about with these

7/7 patients. If we're talking about a 75 percent

dose reduction, that could be quite problematic.



If all we're talking about is a 25 percent

dose reduction, I would feel a little more


DR. WILLIAMS: Let me push back to my boss

here. But what if it was a 25 percent dose

reduction, and you had the same AUC? Would that

help you? That's what I'm sort of trying to get


DR. PAZDUR: Yes, but we don't know as far

as that would involve some comparison here, but we

don't know, basically, that AUC correlates with

response rate or doesn't.

DR. MCLEOD: And Atik's data says that AUC

is not AUC in terms of risk of neutropenia.

DR. WILLIAMS: For these patients, anyway,

right? There somehow seems to be a little bit of a

difference in these particular patients'

sensitivity to AUC than the other patients. That's

what I took away from this graph.

DR. PAZDUR: But, Grant, I think that

would give you a degree of some comfort here to

have some parameter that you're achieving.



DR. VENITZ: Final words, Larry?

DR. LESKO: If we're thinking of dosing

adjustments, whether it's a drug in oncology or

not, we generally try to bring a quantitative

analysis to the probability of an adverse event

based on exposure, whether it's a renally-impaired

patient or whether it's a drug interaction, and

depending on the outcome of that analyses, we would

reduce the dose to achieve similar area under

curve. This is pretty much how labels are derived

in terms of dosing adjustments for specific


So that concept isn't all that foreign.

It's actually the first principles of the way that

drugs work. So I think in any study that would be

conducted, the area under curve of the species that

has been shown to correlate with neutropenia to

date, which is the SN38 area under curve, would be

extremely important to measure and then use as a

guide along with other measures to determine what

the appropriate dose would be.;

I also think you don't necessarily need a



prospective study. There are many studies

discussed today, and not knowing the details of all

of them, one could imagine that a study would be

conducted in which efficacy or safety would guide

the treatment and then having some genotype

information in a retrospective fashion to associate

the dose that was given and the appropriate outcome

that was previously decided upon would be an

extremely powerful correlation to have, coupled

with area under curve to figure out what the right

dose reduction ought to be.

MR. BELLO: Hello. My name is Akintunde

Bello. I work for Pfizer clinical sciences. We

just thought it's interesting and important to

point out that there is actually a study that's

going to be starting shortly that's actually

looking at different doses and will be looking at

genotyping as well as exposure, PK exposure for

various moieties related to CPT11. So this is work

that's ongoing. There's a study that's forthcoming

and may give us the answers that we're looking for.

DR. VENITZ: Howard?



DR. MCLEOD: In the context of the

cooperative groups, this issue has also come up,

not just so much from a regulatory standpoint but

from a clinical trial standpoint, and I'm wondering

whether Dr. Ratain would be able at this point to

comment on some of the discussion that's going on

in the context of these patient genotypes. It may

be too early for that, Mark, but if you want to

comment, here's an invitation.

DR. VENITZ: Are you willing, Mark?

DR. MCLEOD: And if I put you on the spot,

I'll buy you a beer.

DR. RATAIN: Thank you.

Yes, the CLGB has a study in

development--CLGB is Cancer and Leukemia Group

B--in which patients will be genotyped; patients

with 6/6 genotype will be enrolled in a trial to

establish the safety or potential safety of higher

doses, as high as 500 milligrams per meter squared,

based on the evidence from this European trial that

some patients can tolerate 500 milligrams per meter

squared, and the hypothesis that these are 6/6




And if, indeed, we can establish that, the

next step would be a prospective randomized trial

in the 6/6 genotype patients of 500 versus the

standard 350.

I also, since I'm up here, I thought I

would follow up on some of the previous comments

about the pharmacodynamics of the activity. I

don't think we know what correlates with activity.

I think there is a fair amount of evidence that

it's not the SN38 AUC, and in fact, in a study that

we've completed and is in press in Clinical

Pharmacology and Therapeutics, we have modulated

the pharmacokinetics of Irinotecan with cyclosporin

A as an inhibitor of transport and also inhibits

CYP3A as well as phenobarbital is an inducer of

glucuronidation, and activity is preserved in some

patients despite very, very low SN38 AUCs.

So I would not recommend that one titrates

dosing to--from an efficacy perspective to

particular SN38 AUC. I think that is useful to

guide neutropenia considerations but not from the



standpoint of efficacy.

DR. VENITZ: Okay; Larry, you want to move

along to the next--

DR. LESKO: Yes, I'll just say the next

two questions are obviously up there, and the first

is not, I don't believe, a voting question, but

nevertheless, it would be useful, again, to have

some discussion of a context. Some of this has

been covered already, I think, in the prior

discussions, but if there's any other remaining

comments on the question number three in terms of

how a genotype could be complementary to

preexisting information on risk and how it might be

integrated into predelivery of the drug or

simultaneous delivery of the drug would be


Question four refers to some of the terms

we had about performance and probability content

information of a test, and one of the things that

hasn't been discussed is the relative value of the

expressions of a performance of a genomic test to

clinicians in terms of understanding. We've heard



sensitivity, specificity, predictive value, odds

ratio. There is one other, and that is the

likelihood ratio, all of which are used in the

literature to different degrees for these tests as

screening tests, basically, and any discussion or

comment people have on the relative value of these

different tests in conveying the probabilistic

nature of these genomic tests would be useful.

DR. VENITZ: Okay; then, I start with any

comments to question number three. How would you

incorporate PG information?

DR. WATKINS: Well, the point I made

before is that this is, to my knowledge, a unique

situation where you've got a

xenobiotic--polymorphic, xenobiotic metabolizing

enzyme that has an endogeneous substrate. So one

of the biggest concerns in using host genotypic

information to predict dose, particularly to

escalate dose in the 6/6 individuals is that in

fact, there might be a nongenetic factor or

additional polymorphisms that would make that

person susceptible.



But in this case, you have an endogeneous

marker. You've got indirect bilirubin, which is a

safety valve. So if you're missing environmental

reasons or other snips, the bilirubin should go up,

with the caveat that in total liver failure, serum

bilirubin only rises about a milligram and a half

per deciliter per day, so this would not be a

sensitive measure of acute changes.

So, apropos question number three, I think

the main unique situation here is there is an

endogenous, built-in marker for the rare

individual, or it doesn't matter how rare, the

individual that would be 6/6 genotype but in fact

would have low activity.

DR. VENITZ: Any other comments to

question number three?

DR. MCLEOD: Just to follow up on that,

Paul, I mean, it should be a surrogate marker,

biomarker, bilirubin, but, I mean, from some of the

data that was presented and some of the discussion,

it doesn't seem to be a good biomarker. I mean,

genotypes seem to offer something beyond the



current approaches. And I know there are

approaches out there where you give a single dose

of rifampin and then six hours later take a

bilirubin level, look at induction or induction but

the increase in glucuronidation. And there's other

tests like that.

But in terms of something that could be

used in clinical practice, baseline bilirubin in

the context of multiple centers, from what Mark

described in his JCO paper, wasn't a good marker.

But yet, genotype wouldn't be influenced by those

things. So genotype wouldn't be the answer, but it

seems like an achievable answer.

DR. WATKINS: No, and I think the overall

data is that bilirubin is not as good a marker as

genotyping in this case. That wasn't the point I

was making this time, which was the comforting

thing is there's a built-in marker for someone

who's very deficient in UGT1A1 but genotypes as

having normal activity. So there's a built-in

safety valve, which is really unique, to my

knowledge, to this situation, which is very



reassuring and, I think, makes it easier to go

ahead and push genotyping, knowing that there's a

safety factor involved.

That wasn't implying bilirubin is better;

it's just a safety valve here.

DR. VENITZ: Steve?

DR. HALL: I think one of the features of

the UGTs is they don't have a high degree of

specificity, you know. So maybe the 1A1 is a major

determinant of bilirubin conjugation, but many

others contribute a small part, and in the absence

of one, they kind of all contribute something to

the remaining activity.

So I don't think it would be surprising

that the bilirubin wouldn't work as a good index of

the enzyme, and I think the 1A family of the UGTs

is complex. They're all this single locus. They

have highly related polymorphisms that probably all

contribute in some part to the overall bilirubin

thing. So I don't think it's likely to be the

surrogate for that single enzyme defect.

DR. BARRETT: I think if the question is



how to use this information relative to the other

factors, I mean, you have a clear idea with the

bilirubin and these other factors in conjunction

with genotype as far as the directionality goes

with Irinotecan, so as far as using it, I mean, I

think there is a practical guidance that could come

out of this, independent of the fact that it's not

a perfect correlate.

So, you know, where you are today in terms

of your understanding of this polymorphism, there

is a directionality there. Whether or not people

use it is another thing. I mean, I think the

comment from Dr. Raitan was very interesting. You

know, for the most part, there is a default to

what's in the label as far as dosing guidance, but

there's still a lot of empiricism. So the extent

to which you can provide educated information to

that empiricism, you should do it.

DR. VENITZ: Okay; then, let's move on


DR. SADEE: Since you bring that topic up,

I have to agree. Clearly, we have, for the star-28



allele, we have good information that it does make

a difference. But what is missing is the

information on what is the variability within these

genotypes? And I don't think it's all that

difficult to get. In fact, while we're listening

to it, motivated to maybe look into this and maybe

provide definitive numbers as to in a population of

500 people, when you look at 1,000 alleles, how

often do you see that one is less than the other?

And what's the variability within this one


I see this again and again with

pharmacogenetics that translate into clinical

trials, where there's a single genotype that's been

isolated; for instance, the LPR for the serotonin

transporter. And every single clinical study is

using this, and there isn't even evidence that it

does make a difference in where the gene is really


So I think in this case, there's very good

evidence that we have a clear difference. We still

haven't defined here how much does this difference



really cover of what's actually happening in the

body? And so, I would like to really see that we

take the first step, and we have all agreed that

there is a correlation already with neutropenia,

but the second step must be--we must have

quantitative information: how often is this

predictive? How soft is this information? And I

think this needs to be clarified.

DR. VENITZ: Okay; then, last question,

Larry, do you want us to vote on this, question

number four?


DR. VENITZ: Okay; so, first, let's have a

discussion on do we believe as a Committee that

current test has sufficient sensitivity and

specificity to be used. And I'm assuming response

predictor means toxic response predictor.

DR. LESKO: Yes, it does, and if there's

any discussion of the question or other measures we

haven't brought up to the Committee, that would be

appreciated as well.

DR. VENITZ: Let me start making my



comment first. Obviously, the numbers that we've

seen, that both Dr. Raitan and the Pfizer group has

presented, the positive predictive value looks

pretty low: 50 percent. The negative predictive

value, 83 to 90 percent, very high. So now, we

have to use my favorite concept of the utility

concept. In other words, we have to use judgment,

not just statistics.

So is a 50 percent positive predictive

value, is that something that we deem clinically

important? In other words, is that enough

assurance for a patient and/or a health care

provider to start treatment or vice versa? Is a

negative predictive value of saying I'm 90 percent

certain that with a 6/6, you're not going to

develop neutropenia, is that comforting enough?

And in my assessment, it is, based on clinical

judgment, not based on the statistics empirically

per se.

DR. PAZDUR: Could I just ask a question

before we go on? And maybe this is to Larry or

Atik: the meaning of this question, are you trying



to implicate in this question that all patients,

before they go on Irinotecan, should have their

status known? Is that what we're after here?

DR. LESKO: That's a different question.

I don't think that's the question we were intending

to ask. It was more directed towards if, as a

physician, I'm going to treat a patient, and I'm

going to use this test, I have to have some

information about what the test conveys in terms of


I think we heard about the sensitivity and

specificity, and then, we moved to predictive

values and odds ratios, so it's, for example, the

question on the likelihood ratio would be if I

tested positive, I would have a ninefold greater

chance of becoming neutropenic. That's what the

likelihood ratio would say for this. Now, what

would that mean to the clinician in terms of, a,

using the drug; monitoring the patient; using a

lower dose; making other decisions, coupled with

the knowledge of the bilirubin or other preexisting

risk factors?



And I think it's important not to take the

test in isolation in making these decisions but

coupled with and complementary to the other

information that would normally be at the disposal

of the patient and the physician to make a

decision. So I don't know if that answered the

question. I don't think it's asking is there a

need to prerequisite do the test before deciding to

give the drug, but it certainly would seem to be

useful, very useful a priori information.

DR. WILLIAMS: One of the points we had

discussed internally was to look at the current

label and some of the information that suggested

you might want to dose-reduce based on these

things, such as age, et cetera. And realizing

that--thinking about, I wonder what the basis of

that was?

So some things, we may have put in the

label. You might wonder about how strong the

evidence was there. I don't know if that relates

to this. It seems to a little bit.

DR. VENITZ: Howard?



DR. MCLEOD: My followup question, the

reason I asked Mark that question is is there

performance data for these other factors, for

bilirubin, prior pelvic radiation, performance--

DR. PAZDUR: It's very poor.


DR. PAZDUR: And a lot of this has to do

with how the clinical trials were done that led to

the registration of the trials, because what we put

in the labeling usually reflects the patient

eligibility of the clinical trial that was done.

For example, age was put in the label because the

European trial restricted entry based on age.

Whether or not that would occur now, I don't know,

and we've heard from Pat that that probably doesn't

make a lot of sense, and we need to revisit this.

So the data on this are probably not as

robust as what we're seeing here, to be honest with


DR. BARRETT: You're going to appreciate

you framing the question, because if I had to

answer number four the way it's written, I would



say no. However, if you said to me would I vote

for a test in which the negative predictive value

was greater than 90 percent as far as an aid to

dosing, I would say yes.

DR. VENITZ: Larry?

DR. LESKO: Yes, another way we tried to

think about this question is really the question

that we're trying to ask: are we trying to rule in

a risk or rule out a risk? And I think that really

reflects on the usefulness of the predictive

values. If we're trying to rule out a potential

risk with a high specificity, that would seem

valuable to know that in terms of making judgments

about the therapy with the drug as opposed to

trying to rule in someone with toxicity. It gives

an indication, but it's a little bit softer because

of those predicted values.

So I think there's a context for these

tests that have to be what is the question we're


DR. VENITZ: Well the positive predictive

value in my mind is so low because you have low



prevalence. It is only an average 10 to 20 percent

of neutropenia. So you have to have a very

specific, I mean, very, very sensitive test to have

a high positive predictive value.

DR. LESKO: Well, the other question is

you're exactly right: the predictive value is a

function of the prevalence, and we know that's

relatively low. Another way to think about the

question is how does it perform in the context of

other tests that are used routinely in

therapeutics, in particular in oncology, where some

of the predictive values are down around 10


Another way to ask the question is what is

the predictive value in sensitivity and specificity

if I want to detect a variant allele, namely, a 6/7

or a 7/7 patient? Now, you have a prevalence of

about 50 percent, and then, you begin to look at

predictive values; they're probably moving up on

the positive side to 85 or 90 percent at that

point, with a 50 percent prevalence.

DR. VENITZ: When you've seen Mark present



that it takes 20 patients tested in order to avoid

one bout of toxicity relative to TMPT, where it

takes 100 patients that need to be screened.

DR. LESKO: It was 300 to find one in the

TMPT, so this is fairly efficient.

DR. VENITZ: Any additional comments in

terms of question four before we vote?


DR. SINGPURWALLA: I was not sure whether

you wanted some kind of a reaction to odds ratio

versus likelihood ratio. Is that correct?

DR. LESKO: Yes, I think that would be

useful, because both are used in the field of

testing, of screening tests, and we'd like to hear

what the Committee thinks or what you think about


DR. SINGPURWALLA: Well, perhaps I'm

wrong, and maybe Marie can correct me, but I

thought that the likelihood ratio is, in fact, the

odds ratio when the model is a binomial model. So

I think they are the same thing. And I was

wondering why you wanted a comment on the



distinction between the two.

DR. LESKO: Because I'm not a



DR. SINGPURWALLA: Okay; so, here is my

contribution to this meeting: they are the same



DR. VENITZ: Any other comments,

statistical or not?

DR. WILLIAMS: Another comparison that

might be of interest is the design of a phase one

oncology study. We usually consider, you know, you

have one toxicity in three patients, and then,

maybe you should look at a little more; or you have

less than that, it's okay; you have more than that,

it's not.

Well, here, I think 50 percent is--of

grade four toxicity, it is kind of interesting.

That really is above what we would say is the MTD,

and so, to that extent, you might consider it's

relevant. You're getting a patient population here



saying is above the MTD. So from that extent, you

might consider it relevant.

DR. VENITZ: Okay; any other comments

before we call for the vote?

[No response.]

DR. VENITZ: Okay; so, we are voting on

question number four. The only friendly amendment,

predictor means toxic response predictor, right?

Because we're not talking about efficacy.

Okay; so, you have three choices: yes,

no, or abstain, and I'm going to call your name.

Dr. Barrett.


DR. VENITZ: That's a yes but, right?

DR. BARRETT: Yes but.

DR. VENITZ: Okay; Dr. Capparelli?


DR. VENITZ: Dr. D'Argenio?


DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Abstain?



Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?

DR. HALL: Yes.

DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. Singpurwalla?

DR. SINGPURWALLA: I'm afraid I have to


DR. VENITZ: The statisticians abstain.

DR. SINGPURWALLA: Well, I'll make a

comment that if somebody starts with a yes, there

is a high probability that the yeses will--


DR. VENITZ: Okay; Dr. Watkins?

DR. WATKINS: I'm going to abstain. I

mean, we've all agreed that the test predicts

neutropenia, but this is somewhere between that



answer and do we think all oncologists should be

doing it, and I'm just not sure where the question

really is in that spectrum, so I'm abstaining.

DR. VENITZ: Okay; so I'm going to vote

yes, so we have three abstentions and nine yes, for

a total of 12.

And I think that does conclude our morning

session, so I appreciate you all's contribution.

We'll take a break until 1:00 for the open

public hearing, and the Committee members have a

room for lunch reserved in the restaurant right

here in the hotel, Martindale's.

[Whereupon, at 12:12 p.m., the meeting

recessed for lunch, to reconvene at 1:00 p.m.]

- - -




[1:08 p.m.]

DR. VENITZ: Our next agenda item is the

open hearing, and we do have one letter submitted

by Dr. Rowling, a member of the Committee who was,

unfortunately, not able to attend. She submitted a

letter for your information that is attached to

your packages and will be posted on the Website.

Other than that, we have nobody here for

public hearing.

Then, our next order of business is

conflict of interest statement.



The following announcement addresses the

issue of conflict of interest with respect to this

meeting and is made a part of the record to

preclude even the appearance of such.

Based on the agenda, it has been

determined that the topics of today's meeting are

issues of broad applicability, and there are no

products being approved. Unlike issues before a



subcommittee in which a particular product is

discussed, issues of broader applicability involve

many industrial sponsors and academic institutions.

All special Government employees have been screened

for their financial interest as they may apply to

the general topics at hand.

To determine if any conflict of interest

existed, the agency has reviewed the agenda and all

relevant financial interests reported by the

meeting participants. The Food and Drug

Administration has granted general matter waivers

to the special Government employees participating

in this meeting who require a waiver under Title

18, United States Code, Section 208. A copy of the

waiver statements may be obtained by submitting a

written request to the agency's Freedom of

Information Office, Room 12A30 of the Parklawn


Because general topics impact so many

entities, it is not practical to recite all

potential conflicts of interest as they apply to

each member, consultant and guest speaker. FDA



acknowledges that there may be potential conflicts

of interest, but because of the general nature of

the discussions before the subcommittee, these

potential conflicts are mitigated.

With respect to FDA's invited industry

representative, we would like to disclose that Dr.

Paul Fachler and Dr. Gerald Migliaccio are

participating in this meeting as nonvoting industry

representatives acting on behalf of regulated

industry. Dr. Fachler's and Mr. Migliaccio's role

at this meeting is to represent industry interests

in general and not any one particular company.

Dr. Fachler is employed by Teva

Pharmaceuticals USA, and Mr. Migliaccio is employed

by Pfizer. In the event that the discussions

involve any other products or firms not already on

the agenda for which FDA participants have a

financial interest, the participant's involvement

and their exclusion will be noted for the record.

With respect to all of the participants,

we ask in the interest of fairness that they

address any current or previous financial



involvement with any firm whose product they may

wish to comment upon.

Thank you.

DR. VENITZ: Thank you, Hilda.

The second topic of today's meeting is in

regards of drug-drug interaction and will be

introduced by Dr. Shiew-Mei Huang, who is the

deputy director for sciences of the Office of

Clinical Pharmacology and Biopharmaceutics.

DR. HUANG: Thank you, Jurgen.

Good afternoon. Before I talk about

relevant principles of drug interaction concept

paper that is published as part of the background

information for this Committee's discussion, I'd

like to briefly summarize some of the publication

and discussion that happened to lead to a revision

of this guidance.

Back in 1997 and 1999, we in CDER, with

CBER, published two guidance documents for

industry: the 1997 on in vitro drug interactions

and 1999 on in vivo drug interactions, focusing on

study design, data analysis, and recommendations



for labeling. Subsequent to the publication of

these two guidance documents, we had various public

workshops discussing different topics related to

drug interactions.

We also had a lot of internal discussions,

including CDER-wide scientific round discussions.

There is one example of publication on one of the

public workshop, and you have heard from Dr. Lesko.

We have various internal documents. Some of them

are published, such as the good review practices,

where we have included important drug interaction

questions to ask during the review of the

applications. And we also have drafted a MAP,

which is Manual for Policy Procedures about

cross-labeling and also about in vitro evaluation

of drug interactions.

PhRMA has published a white paper last

year on general drug interaction issues, and as Dr.

Lesko summarized earlier this morning that this

advisory group, the Advisory Committee for

Pharmaceutical Sciences and the Clinical

Pharmacology Subcommittee, at a meeting last year



in April, we discussed the proposal of classifying

CYP3A inhibitors, and we also touched upon PGP

inhibition-based interactions, and in November, we

talked about some of the emerging important

enzymes, such as CYP2B6 and 2CA and their role in

the evaluation of drug interactions.

So based on these discussions, the CDER

working group with the contribution from CBER, we

have drafted an interaction guidance, which is in

internal review right now. And this will be

published soon as a draft for comments, and when

the guidance is finalized, this will replace the

two in vitro and in vivo guidance documents

currently posted on the Internet, where we have

updated information and recommendations on drug

interaction evaluation.

We also have this guidance to address some

of the recent labeling rule change. In 2000, we

had published a proposed rule about professional

labeling of prescription drugs. The final rule

will be published soon, with accompanying various

guidance documents to talk about various segments



of the labeling.

So I'd like to talk about some of the

principles that we discussed and the drug

interaction concept paper which was released for

discussion purposes only.

In this concept paper, we stress the

importance that metabolism and drug interaction

information to benefit-risk assessment for new

molecular entities prior to market approval. We

have learned our lessons from recent U.S. market

withdrawal from 1998 to 2003. Note that this table

was constructed prior to the withdrawal of Vioxx,

so we did not include Vioxx in the table.

However, if you look at these 10 drugs

that were withdrawn between 1998 and 2001, where

they had been approved between 1985 and 1999, these

10 drugs with different characteristics and use;

there are some antihistamine or cholesterol

lowering. But if you look at these, the risks,

five of the 10 drugs, the risk of drug interaction

has contributed to withdrawal. And out of these

five drugs, if we look at Terfenadine, Astemizole,



Cisapride, Cerivastatin, these are substrates of

cytokine p450 enzymes or other enzymes or

transporters, while Mibefradil is an inhibitor of

CYP enzymes, PGP and possibly other transporters.

So these examples demonstrate that it is

important to evaluate other drugs' effect on the

new molecular entity and the new molecular entity's

effect on other drugs. We have a recent example

where a new molecular entity is a CYP3A inducer,

and the risk of drug interaction has contributed to

that drug's nonapproval. So again, we want to

stress it's important to evaluate inhibition-based

interaction as well as induction-based interaction.

Second principle I'd like to talk about in

the concept paper is to talk about an integrated

approach to evaluate drug interaction in vitro, in

vivo, specific and population pharmacokinetic

studies where when you look at the totality of data

to estimate the potential for drug interaction, and

this, hopefully, will reduce the number of

unnecessary studies and to optimize our knowledge.

In the concept paper, we discuss that for



the evaluation of metabolic interactions, as far as

evaluating the new molecular entity as an

inhibitor, we said it's important to study the five

major CYP enzymes: 1A2, 2C9, 2C19, 3A and 2D6. As

far as evaluating as an inducer, since the 2D6 has

not been shown to be inducible, here, we're

stressing the importance to study the other four

major CYP enzymes.

We know it's important to study other

drugs' effect on the new molecular entity, so it's

important to evaluate the metabolic profile of the

new molecular entity. We think it's important to

evaluate those five CYP enzymes, but when none of

these enzymes are found to be responsible for the

metabolism, it may be important to evaluate other

CYP enzymes such as CYP2B6, 2C8, rarely 2E1 or

other phase two metabolizing enzymes.

This morning, we have discussed how the

genetic variation would affect a drug with a

substrate for UGT1A1. Unless we know this drug is

metabolized by UGT, we probably won't know how the

genetic component would affect its metabolism and



its clinical response.

As far as inhibition, we have included an

appendix to talk about how to evaluate in vitro,

and we have indicated one parameter to look at

possibility of in vivo inhibition based on in vitro

data is to look at the I over KI, I as the

concentration of an inhibitor, which we like to use

a CMAX at a steady state at a highest dose and

compare to a KI of get a five major CYP enzymes.

The PhRMA paper indicated I over KI of 1

or 0.1. More than 1 is likely to be an inhibitor.

We did not specifically indicate what ratios,

although we did mention when the I and the KI were

separated by a very large--such as 50, then, it's

not likely to have an interaction. However, we

also indicated that we could rank order the in

vitro data to determine and prioritize the in vivo


For example, this is one new molecular

entity. And here, the five major CYPs are

evaluated. We like to look at the KI value.

Sometimes, we don't have the KI values, because



when you have very high concentration, you still

don't see inhibition. Sometimes, IC50 will be

expressed as higher than the concentration being

evaluated. So in this case, if you look at I and

KI, you would say, well, this is a very likely

event, and this one falls into probable, and this

may not be likely.

In order for us to--we don't have a

definite number to work with, I over KI ratios, so

the suggestion would be to look at the KI in rank

order, and you probably want to evaluate the CYP

that's most potently inhibited first in vivo. If

the results are negative, then, you wouldn't have

to evaluate the other that's less potently

inhibited, but if the results are positive, we

couldn't extrapolate, and we need to evaluate the

other CYP enzymes.

As far as induction, we have a new message

in the concept paper. We say that induction can be

addressed with in vitro methodology. In our

previous guidance documents, we mention that

induction can only be evaluated in vivo as a



technology for evaluation has not--there's

insufficient data to support a use of in vitro. So

we said we would look at the induction data based

on in vivo at this point.

I have mentioned earlier, it is important

to evaluate CYP1A2, 2C9, 2C19 and 3A. However, we

are suggesting that the initial in vitro evaluation

can be done with 1A2 and 3A. Part of the reason we

thought the 3A could be coinduced with 2C9 and

2C19, so if the results from CYP3A is negative,

then, you don't have to evaluate 2C9 and 2C19. Dr.

LeCluyse is going to show us some data to support

that argument later.

Again, we say negative results may

preclude in vivo evaluation of the other important

CYPs that we have mentioned that are important to

evaluate in a submission. Unlike the inhibition

study where we only say a positive control is

optional, for induction, we say a positive control

is recommended. For example, if you're evaluating

CYP3A, we think it's important--we could use

revamping as a positive control.



We think it's very important, since our

recommendation is if the data is negative, then,

you don't have to do in vivo. If it's positive,

then, you need to do an in vivo study. So it's

important how we define when it's positive. The

original concept paper, we said we can either use a

40 percent of positive control as a cutoff or

twofold of the negative control.

With subsequent discussion that when we

look at both 3A and 1A2, there may be too much

false positive if we use the twofold negative, so

we have dropped it right now, and we are

discussing, we are asking the Committee to comment

on the appropriateness of using a 40 percent of

positive control to suggest a possible induction,

and this 40 percent number was based on the PhRMA

white paper.

Ever since we have started to discuss the

appropriateness of using in vitro induction

methodology to evaluate induction, we have received

quite a few comments. Well, then, it's now a need

to conduct in vitro inductions for all new



molecular entities. And our answer is no.

However, it's important to address induction. You

can either use in vitro or in vivo. It's important

to address, but you don't necessarily have to use

in vitro, but it may be a good approach to start

with in vitro. And then, if the results are

negative, then, you're done, but if it's positive,

then, you continue. This is sort of what I just

said. Positive in vitro needs to be followed with

in vivo.

And I want to mention that induction can

be part of evaluation of in vivo inhibition

studies. Oftentimes, we have seen inhibition

studies carried out with Midazolam when we're

evaluating the possibility of inhibition of CYP3A

with Midazolam. And when the sponsor conducted a

study with multiple dose, multiday evaluation, when

the results are negative, you could claim that this

is not an inhibitor. At the same time, you could

also say it's not an inducer.

Study design data analysis is key and

should be well thought out so that we can provide



important information for proper labeling. In our

concept paper, we said we need to design a study to

maximize seeing an effect. And we said that when

you are starting with an inhibitor, we'd like to

use the highest dose, shortest-dosing interval of

an inhibitor.

A common question is always, well, if we

are evaluating inhibitor effect using ketaconazole

to evaluate a CYP3A inhibition, should we use 400

or 200 milligrams? Many of our submissions use

multiple doses. And so, the question is really

whether what is the dose level that should be


The literature data has many studies using

400 or 200 milligrams. However, they have varied

study design. The difference in study length,

timing of coadministration or different

populations, so it's difficult to compare

intrastudy. And that's why later on, I will show a

study where we compare within study, where the

subject was given both 200 and 400 and make a

direct comparison.



However, in one literature data, one

publication has shown that ketoconazole CMAX

concentration appeared to show a correlation with

the inhibition effect on Midazolam. If you look at

the AUC ratio where Midazolam was given with

ketoconazole versus when it's given alone, you can

see the ratio increase as ketoconazole levels


This study was conducted only with one

dose of ketoconazole, but this is the initial base

of our recommendation to sponsors that we should

use a higher dose of ketoconazole when conducting

interaction studies, however, we did include a

study to evaluate 200 versus 400 milligrams of

ketoconazole as part of a collaborative research

and development collaboration with Indiana

University, and Dr. Steve Hall is the principal

investigator for the collaboration.

And this is a preliminary result that was

shown from that study, where Midazolam, after IV

and oral were compared when it's given together

with 200 milligram dose of ketoconazole or 400



milligrams of ketoconazole given for six or seven

days. You can see that after IV administration,

the extent of interaction is smaller as compared to

oral. It's about fourfold after the 400 milligram

dose, and it's about threefold after the 200

milligram dose.

After oral administration, the extent of

interaction is much higher. The AUC ratio is about

15 after the 400 milligram dose; it's about tenfold

after the 200 milligram ketoconazole dose. So

based on the literature data and the study

comparison that I just showed you demonstrate that

CYP3A inhibition after ketoconazole is dose

dependent with 400 milligram dose having a higher

effect than a 200 milligram dose. And we believe

that inhibition studies with ketoconazole should be

conducted at a 400 milligram dose.

However, we have seen in many applications

that a study is already being done with 200

milligram doses. So questions always come up:

well, if you're already studying at 200 milligrams,

do you need to conduct another study with 400? And



there are several cases where the sponsor went back

and conducted a 400 milligram dose, and it showed a

difference. The 400 milligram produced a higher

extent of interaction.

There is also a case where a 200 milligram

dose was already demonstrated to have a very large

extent of interaction and is likely to result in a

contraindication. In that need, may not need to

have an additional study, because if you already

know what 400 milligram results will--data will

result in what kind of labeling; it's probably very

similar. It's a contraindication. So in that

case, you don't need to conduct another study. We

need to look at the results and other information

such as exposure response before we automatically

request an additional study.

What about other study design issues?

This one was not directly addressed in the concept

paper, but it was frequently asked: can we use the

cocktail approach where, in vivo, a mixture of pro

substrates for three to five of the major CYP

enzymes were given together with the new molecular



entity to evaluate the new molecular entity as an

inhibitor or inducer?

We say yes, they can be used if they are

properly designed; probes are specific; they do not

interact with each other, and there are a

sufficient number of subjects that are used in the

evaluation and if the results are negative, then,

we could preclude further evaluation. However,

many of these cocktail studies used a ratio such as

metabolic ratio in the urine or plasma level, and

it's difficult to extrapolate to assess what would

be the extent of interaction, unlike the studies

that we used where you look at AUC ratios, where

you know it's a fivefold increase or a tenfold

increase. In that case, then, we may need

additional evaluation to provide some quantitative


And again, we have seen cases where some

of the older cocktails were used, and one of the

probes may not be specific, and it may interact

with one of the--it also affect the other CYP. The

other--the data from the other CYPs can still be



used, and it could be used in combination of other

in vitro-in vivo data. It could still provide

useful information. Again, we don't automatically

throw away data from a study just because it's not

well designed and certain parts of a design.

Again, the design issue, we were often

asked what kind of substrates or inhibitors or

inducers that should be used both in vivo and in

vitro? What concentrations of substrates should be

used in vitro? We've been asked so many questions,

and this happened always in a sponsor meeting. So

the working group thought it would be good if we

can provide tables in the concept paper on some of

the proven or good in vivo and in vitro probe

substrates, inhibitor inducers.

Earlier, we thought this may be too

proscriptive, and the tables may be outdated

frequently. And we thought we could address it by

using a Web link so we can provide more frequent

updates of the tables than the guidance itself.

And this is just one example of in vivo

probes that we have included in the concept paper.



You can see, in addition to the five major CYPs, we

also included information on 2B6, 2C8, since these

are emerging, and 2E1, and you can see that in some

of the well-defined polymorphic enzymes such as

2C9, 2C19 and 2D6, we also think that the

evaluation of pharmacokinetics in poor metabolites

of those enzymes and compare that to the extensive

metabolizer, and this could be done in lieu of a

drug interaction study.

We also indicated that for 1A2, since we

couldn't find a good inducers, since omeprazole has

not been consistently providing induction effect

based on some of the criteria that we mentioned in

our table that made these drugs onto the list, so

we provided that perhaps the pharmacokinetic

evaluation of smokers versus nonsmokers could be

conducted in lieu of an induction study.

And this, I already mentioned, that the

kinetic evaluation in poor metabolizer or smokers

can be used, and we also mentioned, we put a

statement that it may be important to evaluate

interaction based on a pathway in poor metabolizers



of enzymes, of the other pathway, which is

considered to be major and the extensive

metabolizer. For example, if the drug is a

substrate for both CYP2D6 and 3A, then, in poor

metabolizer, the CYP3A may be an important pathway,

and you may want to consider the evaluation of that


In addition, based on information that we

know about herb, dietary supplement interactions,

juice, food interactions, we thought it's important

to also start to look at the protocols, and we

provided some sample language that should be

included in a clinical protocol when we evaluate

drug interaction, so that when we look at the

interaction results, they're not compromised by the

unknown factors that are contributed by these other


The concept paper not only discussed

metabolism-based drug interactions, but it also

included transporter-based drug interactions,

although right now, we focus only on PGP-based

interactions. In our concept paper, we mentioned



that if a new molecular entity is an inhibitor of

PGP in vitro, then, we think a clinical study using

digoxin may be appropriate. And we have discussed

this in the April meeting last year, and this was

just a summary of some of the data that are

presented at that time.

This is the digoxin plasma AUC or

steady-state concentration that's the ratio when

it's given with these drugs or without. And you

can look at some of the known inhibitors of PGP:

quinidine, retonavir, verapamil, has increased the

ratio to 1.5 to 2.5-fold. Here, grapefruit juice,

aprepitant did not show an interaction.

The known inducers of PGP, St. John's

wort, rifampin, has shown to reduce the plasma

concentration by 20 to 30 percent. And we'd like

to ask the Committee to comment on this point


So we talk about the new molecular entity

as an inhibitor. What about it as a substrate?

And we thought it's important to discuss it with

the status of its CYP3A, whether it's a CYP3A



substrate or not. So we said in a concept paper if

a new molecular entity is a substrate for PGP and

CYP3A, and we have a lot of cases like this, then,

the clinical study with a dual inhibitor or a

multi-inhibitor may be appropriate. We just put in

ritonavir as an example, because ritonavir affects

multiple pathways, and here, we're just using

example data from vardenafil labeling, where you

see the AUC ratio of vardenafil when it's given

with these compounds as compared to when it's given

by itself.

And you can look at ritonavir, indinavir,

ketoconazole. Vardenafil is a CYP3A substrate, and

you can look at the strong CYP3A substrates have

shown a large degree of interaction. It's more

than tenfold, and here, ketoconazole is only given

as 200.

The moderate inhibitor, I will explain

about in the classification on CYP3A inhibitors

later, but erythromycin has shown a little bit

lower than fivefold increase in vardenafil.

This should show even these three



compounds are classified as strong 3A inhibitors,

but they did show some differential effect. And

so, there's a possibility that ritonavir, because

of its effect on other pathways, in addition to PGP

and other transporters that contributed to a much

larger effect on the substrate.

So we say if a new molecular entity is a

substrate of PGP but not a substrate of 3A, then, a

clinical study with regular known PGP inhibitor may

be appropriate. Again, it's hard to differentiate,

because some of the compounds that are listed here

are also 3A inhibitors, but they're not as strong

an inhibitor.

And here, this is the same table I have

listed earlier with digoxin, so you can see one of

these PGP inhibitors could be used when we have a

new molecular entity which is a substrate of PGP

but not 3A. So we're asking the Committee to

consider whether CYP3A status should be a key

factor when we decide what kind of inhibition study

to conduct, when the drug is a PGP substrate and

also whether we have sufficient data to recommend



routine evaluation of PGP interaction if a

substrate, if a drug is a substrate of PGP.

Finally, the last issues regarding study

design: we put in some statement in the concept

paper about the use of multiple inhibitors or

multiple impaired system. When we evaluate the

possibility of a serious adverse events such as we

use the QT prolongation to assess the probability

of trassar DuPont's, we have recommended in the QT

concept paper, actually, it's an ICH document right

now, to use perhaps a strong inhibitor of the major


In addition, we have seen examples where

either the reviewer has recommended or the sponsor

has conducted that multiple inhibitors--this is

different than multi-inhibitor. It's a multiple

inhibitors to attack different pathways or, using

one inhibitor for one pathway in poor metabolizers

of the other pathway in the evaluation.

And we have examples such as

telithromycine. An inhibitor such as ketoconazole

was used in the evaluation of a QT prolongation to



obtain maximum exposure. We also have cases where

a strong inhibitor was used, for example, when we

evaluated vardenafil. A separate study prior to

the QT evaluation was conducted to estimate what

the maximum exposure that's attainable with a

strong inhibitor; then, use that information to

design a high dose study to evaluate QT


Finally, though not directly related to

this issue, we think the use of multiple inhibitors

of one pathway is also important. Particularly,

right now, we're talking about possibility of

classifying CYP3A inhibitors to moderate inhibitors

and possibly monoinhibitors. That was suggested in

the PhRMA position paper, and we have research

ongoing again with Indiana University, looking at

multiple moderate inhibitors' effect, whether they

would be additive or synergistic or producing an

effect like you're giving a strong inhibitor.

Next point I'd like to stress is this is

the same point that we have stressed in the

previous guidance in 1999, that it's important to



establish a therapeutic equivalency boundary for

the new molecular entity, so we will be able to

interpret the extent of interaction based on

interaction studies and what to put in the


And here, I am going to present a

hypothetical case where we use combined data from

different applications. This new molecular entity

was given with ketoconazole, a strong 3A inhibitor.

This new molecular entity is a 3A substrate. And

you look at the CMAX increased by fourfold.

The moderate inhibitors: erythromycin,

verapamil, increased by threefold. The AUC showed

similar effect. I put CMAX here because one of the

adverse events was believed to be related to a

maximum concentration.

And we look at exposure response data,

where from the safety and efficacy database, we try

to relate the exposure to one of the endpoints for

efficacy, and one of the endpoints was adverse

events. Here, I simplified the outcome. Actually,

we have several endpoints for both efficacy and



safety. And based on the data, between 15 and 60,

the exposure, consider that the drug will be

efficacious and safe. However, because of

ketoconazole's effect, it's varied. It's very

large. We think it's important to advise against

abusing strong inhibitors with this drug.

For moderate inhibitors, if you approve

the dose of 15 and 30, since if you give 30

milligrams, and the moderate inhibitors will

increase the exposure to outside the safe and

effective exposure range. So we would recommend to

use a lower dose.

My final point is that labeling language

needs to be useful and needs to be consistent. In

our concept paper, where we said that if a drug has

been determined to be a sensitive substrate or a

CYP3A substrate with a narrow therapeutic range,

and I'll explain a definition later, and it does

not need to be tested with all strong or moderate

inhibitors of 3A in order to warn about it in the


And in the concept paper, we gave



examples. We have many tables. And one table is,

well, strong, examples of strong 3A inhibitors or

moderate CYP3A inhibitors. Here, the strong 3A

inhibitors, we have included. The definition is

any substrate, any--if an inhibitor, if that caused

more than fivefold increase in the area under the

curve of a CYP3A substrate. And that's not limited

to Midazolam, then, we listed it as a strong


The PhRMA paper specifically talks about

Midazolam. But since there are many strong CYP3A

inhibitors, we do not have Midazolam data, and we

think it's important to include these strong

inhibitors in the table, since we do have

information from the other.

The moderate inhibitors, we have similar

definition with a PhRMA white paper, except we

added some specifics. We said that a moderate

inhibitor is one that caused a more than two but

less than fivefold increase in area under the curve

of a sensitive substrate. It has to be a sensitive

substrate, and the inhibitor needs to be given at



the highest dose and lowest, shortest dosing

interval, so that we won't misclassify a strong

inhibitor because a study was conducted with a low

dose, a long dosing interval, or it's not--it was

conducted not with a sensitive substrate, so you

may underestimate the extent of interaction and

therefore misclassify.

And one example I've already shown that

even the study was only conducted with ketoconazole

for a strong inhibitor but it does not prevent us

from labeling it with other strong inhibitors. And

for moderate inhibitors, even only done with

erythromycin and verapamil, we will be able to

label with the other additional moderate


In the concept paper, we also mentioned

that if a drug has been determined to be a strong

inhibitor of 3A, it does not need to be tested with

all sensitive substrates or substrates here

specific about CYP3A with a narrow therapeutic

range. And in the concept paper, we included

examples of sensitive substrates or substrates with



a narrow therapeutic range.

This is a new definition. The PhRMA white

paper did not discuss a sensitive substrate in the

definition. And here, we defined that sensitive

substrates are drugs that AUC will increase

fivefold or more with an inhibitor. It doesn't

have to be a strong inhibitor; any inhibitor.

A CYP3A substrate with a narrow

therapeutic range: this would be applicable to

drugs that are not a sensitive substrate. However,

the increase in exposure because of

coadministration with a CYP3A inhibitor may result

in serious safety concerns, such as trussar DuPont,

so you can see there are quite a few drugs:

cisapride, astemizole, terfenadine; these were

removed from the market but are included in the

table just for illustration purposes.

An example of a labeling based on this

table would be--I'm using telithromycin as a case.

This drug, when, it's given with Midazolam,

increased the area under the curve by sixfold, so

in definition, it's a strong inhibitor. So in the



labeling, we said telithromycin is a strong

inhibitor of the cytochrome p4503A, and we also

said the use of simvastatin and other statins here

concomitantly with telithromycin should be avoided.

We also said that the use of telithromycin

is contraindicated with cisapride and pimozide.

And you will notice, based in the information in

the summary of our study, we did not evaluate all

of these drugs that are listed here. For sensitive

substrates, we only evaluated with simvastatin, but

it does not prevent us from listing other sensitive


For substrates, CYP3A substrates with

narrow therapeutic range, the pimozide was not

evaluated. But again, because of what we classify

it as a substrate with narrow therapeutic range, we

put it in our labeling. Right now, we have various

discussions on how to label strong inhibitors; what

sensitive substrates to put in the labeling when we

are evaluating one, and we may come up with a

different list. Therefore, we think it's important

that we publish the labels and constantly update it



so that we have consistency among the labeling of

different drugs.

So in summary, we think metabolism drug

interaction is key to benefit-risk assessment, and

I think based on today's discussion, we probably

will add some transporter information as well. An

integrated approach may reduce the number of

necessary studies and optimize our knowledge.

Study design data analysis is important and

information for proper labeling, and we have

devoted many pages of our concept paper on study

design, and we've also added an appendix on the

conditions of in vitro evaluation: what are the

study design and data analysis issues?

The thing we need to establish,

therapeutic equivalency boundaries, so we can have

proper interpretation of the clinical outcome and

put it into a useful information in the labeling,

and we have added tables of classification of CYP3A

inhibitors, substrates, to hopefully that we have

consistent and useful labeling.

And I'd like to acknowledge the drug



interaction working group. It consisted of many

members from our office, the Office of Clinical

Pharmacology and Biopharmaceutics; from individuals

outside our office, the Office of Pharmaceutical

Science; individuals from CBER; some of them have

joined us after the reorganization and also from

the Office of Medical Policy.

I think my time is up. Do you want to

take any clarification questions?

DR. VENITZ: Thank you.

Any comments or clarification questions

for Shiew-Mei by the Committee?

DR. JUSKO: I have one.

DR. VENITZ: Go ahead.

DR. JUSKO: Shiew-Mei, that was very clear

and impressive. With the study of the ketoconazole

interaction that you showed, I didn't see that

using 400 milligram ketoconazole was that much

better than 200, and I would have come to the same

conclusions with either dose. Why are you so firm

on 400, where there may be some additional negative

aspects as opposed to 200?



DR. HUANG: The example, since we use a

sensitive substrate with Midazolam, you probably

can see, well, 200 milligrams already gives you a

tenfold increase, and we probably will classify to

say not to use it together with some more sensitive

substrate already.

If the exposure response data are such

that, then, you don't need to do another study.

However, we have a lot of compounds where CYP3A is

part of the pathway. So in that case, the results

are not clear cut. We did have one example where a

threefold and fivefold difference, from these two

different doses, and it would make a difference.

For example, one of the examples that I showed you,

the moderate inhibitor and strong inhibitors, one

shows fourfold; one shows threefold, and we do have

a different proposal for labeling, because

depending on the compound's exposure response,

fourfold increase is going to take you outside that

safe and effective exposure range; then, you would

contraindicate. But if it's threefold, it may

still be within the range, and you can either using



a dose reduction in the labeling to address that


So for less sensitive substrates, the

difference, three to fourfold or versus one to

twofold, it will make a difference in the proposal

and the labeling.

DR. GIACOMINI: Do I have that--yes,

Shiew-Mei, that was an excellent and very clear

presentation. I just have a couple of comments

related, of course, to transporters and how we have

to begin thinking of not really metabolism but more

metabolic pathways, which would include maybe an

influx transporter, the enzyme and then an eflux

transporter, which may be all part of a pathway.

So when you've indicated here, and you've

got particularly sensitive substrates, and you have

examples of inhibitors, and many of these are

dirty; they'll inhibit different things along the

pathway, and I think it would be helpful in this

paper at some point to at least indicate what may

be a dual substrate and a dual inhibitor, and are

you planning to do that dual, triple, whatever?



DR. HUANG: There are a lot of

publications that did suggest this, and what we

want to put in the guidance is where it's going to

be useful in the study design or in the labeling,

what's going to be translated to a clinical

setting. So any information that may not be

helpful; for example, if we say we evaluate this

drug as an MRP substrate, and we know it's both

CYP3A and MRP.

However, we really couldn't recommend to a

sponsor a certain type of study to conduct besides

a PGP. We do have some proposals; or we don't know

what to do with the data, and how would that help

prescribing a physician or health care provider's?

Then, we don't think that that will belong to the

guidance. It will belong to the literature, and we

have enough information to make a recommendation

under this case, what should you do in your study

design? Then, we will include that in the


DR. GIACOMINI: I mean, I agree with you.

I hear what you're saying, but it seems to me like



if somebody has done some kind of an inhibition

study, they may make an interpretation; they're

going to use that to make some kind of an

interpretation, and you're focused mostly on the

interpretation as it relates to the dose of the

drug. But I'm just wondering about even a

mechanistic interpretation by at least indicating

that certain substances may, certain compounds may

be inhibitors of both a transporter and an enzyme,

that some caution in the--especially, you're going

to extrapolate, right? Because you're going to say

well, now, that we showed this, you better be

careful for all of these, all of these compounds,

which may also be substrates of CYP3A4 when, in

fact, the transporter was the bigger part of the

interaction, and that wasn't--

DR. HUANG: Yes, well, I would welcome the

Committee's discussion, because I did have some

question to see what other transporter that should

be evaluated. But you will notice, even we put all

the tables, when we want to translate one study to

the others and put in the labeling, we only provide



some very specific information. For example, we

say ketoconazole, an inhibitor, and whatever

happens with that result, you can translate to the


When a study was conducted such as a

cyclosporin study, and with rosovostatin, when we

couldn't translate that in the labeling, we only

said when cyclosporin increased rosovostatin by

sevenfold, and therefore, the initial dose should

be this, and we do not translate that to others.

So until we know more, then, I think we

will be able to put in the table and put in the

guidance you're suggesting.

DR. DERENDORF: I'm very happy to see that

induction is addressed, and that was overdue in

both in vitro and in vivo. Now, in the in vitro

part, I have a question: it says if 40 percent of

positive controls suggest possible induction

potential, does that mean, first of all, 40 percent

of what? What will be the measure? And the

positive control will be defined, because

otherwise, you can change, you know, the percentage



based on your control.

DR. HUANG: Yes, you will hear more from

the subsequent speakers, but I can say in our

guidance, we--sorry, concept paper, we did

recommend that, for example, with CYP3A, you look

at revamping induction, and we use the enzyme

activity, the fold increase in enzyme activity. So

if it's increased tenfold, then, 40 percent would

be fourfold.

DR. DERENDORF: With respect to the in

vivo, you have the classification of strong and

moderate with two and fivefold increases in

exposure. If we apply that to induction, would

that mean that a fivefold decrease in exposure

would also be the border between moderate and


DR. HUANG: Well, we did propose that at

the April Committee meeting last time, and the

comments from all of you was that we don't have

sufficient data to indicate which one is a strong

inducer, and we just don't have the information.

But I'll be happy to revisit that if the Committee



thinks it's proper that we do that.

DR. HALL: Yes, could you comment

on--you've done a really good job of talking about

when to conclude something is an inhibitor, but

when it came to concluding that it was not an

inhibitor, you somewhat skirted around that. And I

think, you know, there are clearly labeling

advantages to being able to conclude it's not. You

mentioned you have no recommendation, but the

former working group did come up with a


And it seems like that would be an

important thing to address.

DR. HUANG: Well, I'd love to hear the

Committee's recommendation. The PhRMA white paper,

as far as inhibition, it says if I over KI ratio is

more than 1, it's likely; if it's between 0.1 and

1, it's probable, and I believe it's--when it's

less than 0.1, it's at least--well, I don't

remember the exact words, but it's not likely. And

we do have, we have cases where the ratio of 0.1,

you still see some interactions.



So it is difficult to say--I mean, rare

occasions to say that it directly translates,

especially for 3A, since the inhibition, I mean,

the induction could happen--I'm sorry, fall back;

inhibition could also happen in the GI tract. So

when you use the equation, you might be able to

come up, to derive an equation to say, well, 0.1,

it's going to result in very small extent of


But if you consider the other components

in the GI and also the uncertainty of the

concentration in the hepatocyte as compared to what

we are using right now, plasma concentration, and

that's why we are using a more conservative

approach. We did not use exactly 0.1, although we

did mention when you have a large gap between I and

KI, and we put in the numbers and say if it's

fiftyfold, then, it's not likely there's

interaction. I know it's a very conservative


And that's why we're proposing perhaps we

could use a rank order evaluation. Any time in



doubt, you probably want to study with the one with

the strongest inhibition, that is, the smallest KI.

And if the in vitro data, in vivo also show no

interaction, then, you do not have to do the other

studies. If there are other alternative

approaches, the working group will be very willing

to listen to the suggestion.

DR. SADEE: Shiew-Mei, I have a comment

and maybe a question about HIV therapy, which takes

advantage of many of the agents that you have shown

to be interacting, so we expect a lot of

interactions. Now, in that case, physicians use

retonavir to, in fact, as a dosage sparing agent;

in other words, you block probably PGP; you block

3A4 and a number of other cytochromes by adding

retonavir; then, you systematically adduce the

other agents because of that knowledge.

Unfortunately, these patients are also

given statins. They're given antineoplastic

agents, antidepressants, you name it. So this is

the inverse usage of the information of inhibitors,

and it appears to me that it has tremendous effect



on the adverse effects that are pretty prevalent in

HIV patients. So is this something you also want

to look at, or I was personally very surprised to

hear these relatively nonchalant views of the

inhibitors to spare other agents, whereas, to me,

it would induce a lot more problems.

DR. HUANG: Yes, you mentioned kalitra,

which is a combination of retonavir and lopinavir,

and a low dose of retonavir was used to increase

the exposure of lopinavir to its HIV therapeutic

effect. In that case, there's no difference in how

we treat the evaluation of kalitra as an inhibitor

or inducer if it's submitted today. So we have the

package included many interaction studies based on

that we already know retonavir is a CYP3A

inhibition, and there are many studies that were

conducted because of the nature of the HIV therapy,

and many of these studies, the results were

summarized in a table format, and there's also

certain for kalitra, I think most of the study

results were summarized in tables. I don't think

there's extrapolation of the conducted study.



And this is true for most of the HIV

therapy. When you submit a new molecular entity,

this drug's effect on others will be evaluated as a

standard procedure almost the same as what we have

described in the concept paper. If you're going to

evaluate multiple inhibitors, how that would

effect, and I think there's some ongoing research

project that we hope to conduct using modeling and

simulation and just see how different the various

inhibitors or various pathways will result in an

extent of drug interaction.

And the study that we're conducting with

Indiana, and it's only a very first step to looking

at multiple inhibitors of one substrate, how would

that conduct? How would that compare to a

simulation outcome? And what you envision is much

more complex.

DR. WATKINS: You know, that was a great

presentation, and I think it's a great idea to try

to merge the two old documents and come up with new

guidelines, but I suspect to industry, it's not

going to be reassuring that the reason to do this



is that we can now Web link the different

substrates that could change week to week is sort

of the implication.

But I think the document then needs to

stress the fact that unfortunately, this is still a

work in progress. We really haven't refined the

probes, for instance, for PGP and the issues Cathy

was bringing up of separating out transport from

metabolism and the interactions of transport and

metabolism. And the last thing you would want is

with the publication of this guidance for upper

management in a major pharmaceutical company to

feel that this had been solved and that the

scientists could be put onto other projects,

because there's so much work left to do in the


DR. HUANG: Right, we--the idea of the Web

link tables is, I think, because the last guidance

was published in 1999, and this is not likely to be

finalized until 2005. So it's a six-year gap. And

with the Web link, I think we can do maybe more

frequent than every six years.



DR. REYNOLDS: I just wanted to address

the ritonavir issue. When a company is evaluating

an HIV droug, and ritonavir will be part of the

regimen, we really consider the drug plus ritonavir

the drug. So if the drug will be given alone, or

if it will be given with ritonavir, we expect them

to look at it both ways, and we consider the

interactions very seriously.

DR. SADEE: On that also, interactions

with statins, for instance, which are very often

given or metabolized and transported by very

similar gene products.

DR. REYNOLDS: Right, so we would expect

to understand the interaction of the protease

inhibitor plus ritonavir on the statin.

DR. BLASCHKE: I think coming back to

Wolfgang's point, as you're saying, I think,

virtually all patients who are getting a protease

inhibitor for HIV are also getting ritonavir, and

what I think it speaks to is probably the

importance--and they're also getting these multiple

other drugs, whether they're statins or CNS active



drugs and so forth, and it probably really speaks

to the importance of most drugs in which we think

there's any possibility of using that in

HIV-positive patients, that the ritonavir should be

one of the drugs that is studied rather than some


DR. VENITZ: One comment: as you know,

I'm very much in favor of using this approach to

minimize the amount of studies that need to be

done. One concern that I have, and I mentioned

that before, is whenever you talk about dose

adjusting based on either inhibition or induction

data, you're basically trying to match areas under

the curve or something like that for the parent


What you don't necessarily consider, and I

suggest you incorporate that in your paper, in your

guidance, the change in the metabolite profile.

You're reducing the dose. It's not the same as

inhibiting a particular pathway. You all of a

sudden have a metabolite in higher concentrations

than it would be, okay? So I'm not sure whether



that's relevant for specific drugs, but it may well

be, depending on whether the metabolite contributes

to activity, meaning safety or efficacy.

But it's something that I haven't seen in

any of the documents that you've provided us.

DR. REYNOLDS: Correct, yes.

DR. VENITZ: Okay; any other comments or


[No response.]

DR. VENITZ: Then, thank you, Shiew-Mei,

and our next speaker is Dr. Keith Gottesdiener from

Merck, who's going to give us the scientific


DR. GOTTESDIENER: Thanks very much for

inviting me here today. Before I start, I'd just

like to also let you know that many Merck

colleagues helped me to put this talk together, and

I just wanted to acknowledge some of the people who

had actually worked on this talk as well.

It's a real pleasure to be here today.

I'm in charge of early development and clinical

pharmacology at Merck, and to a great extent, what



I do or a major part of what I do every day, every

month, every year is really looking at this

question from inside the industry as opposed as to

from outside. Of course, the FDA is very

interested that the packages we put together and we

submit for registration of a drug be complete.

In a sense, I get to do that sometimes

months and years ahead of the FDA, and it's really

my job to really make sure that package is robust

and to try to put it together. And so, in a sense,

I think that both myself and the people in the

industry who do these kinds of things have a very

unique perspective. We get to see a lot of

compounds that never really make it past this

evaluation stage as well as those that actually go

forward to filing, and I hope I'll share some of my

thoughts with you today.

I can assure you that senior management

does not think that this problem is solved yet

today, and I'll point out some of the issues. I

wasn't able to really participate in the last

meeting where you talked about induction, but some



of the questions that came up to Shiew-Mei are

exactly very similar to the kinds of questions that

I would pose as well: how difficult it is

sometimes to do this in a real life situation.

So what I'm going to do is talk just a

minute about the approach to assessing drug

interactions. I'll talk about the many areas of

agreement with the concept paper that exist, which

I really have to applaud. It's a real step

forward. I'll mention a couple of areas where I

think there's really some further discussion, and I

just pick three today: induction, transporters,

and this issue of multiple inhibitors, multiple


I'm not going to cover specific comments

on the concept paper. I do have many. I've shared

some of them with Shiew-Mei as well. The study

designs, the tables, et cetera; when that comes out

as a draft guidance, I'm sure I'll have plenty of

opportunity to comment, and nor was I going to

spend much time talking about specific comments on

the questions to the Committee.



What I wanted to do was focus on the

approach to some of these issues. When I think

about approaching, assessing drug interactions, I'm

really probably saying this slide or two, I'm

probably talking to the wrong audience. I often

have to explain to people what the approach is.

But clearly, the issue is how should we adjust the

dose of a substrate drug in the presence of an

interacting drug? And which DDIs and which drug

interactions to study, how to answer that question?

And clearly, we're moving from the past,

when this choice was largely empirical by the

likelihood of coadministration, clinical

consequences of the interaction towards a

science-driven approach, particularly where

feasible. You know, we're using preclinical in

vitro studies to determine in vivo studies, in vivo

studies using probe substrates and really robust

study designs. But clearly, I think there's ideas

where the science is evolving and the necessary

tools and the probes are still lacking.

We also think it's important, again, like



the FDA, that there be prespecified criteria to

compare the PK or PD measures to the drug in the

presence and the absence of the interacting drug,

and clearly, this is based on the safety and the

efficacy profile of the substrate drug, the

therapeutic index, the clinical context of the use

of the drug, which I think actually is quite

important and very hard to capture in the guidance

and the concentration and response data for the

substrate, which is obviously something this

Committee is very interested in, and so are we.

One thing, though, I do want to emphasize

is often, this is not clearly positive or negative.

It's very difficult if something is or is not an

inhibitor; it does or does not have a clinically

relevant effect on one drug or another, and

actually, probably, the one comment I'd make about

the questions today, it will probably be the only

one, is the questions are really framed as

either-or. If it is an inhibitor, this is what you

should do.

And in many cases, I think the guidance



the Committee is going to give, and it's going to

be quite interesting; my problem is trying to

decide is it an inhibitor or not in many ways, and

I know that the FDA struggles with that very

question. For the NCE or the NME, the data is

often quite limited; concentration response info is

always better for efficacy than it is for safety,

and I still think there's many areas for probe

substrates, where there really isn't much

consensus, even though I think we've come quite

far. And as I'll point out today, induction in

particular is problematic.

But let me talk first about all the good

points. I think that the integrated and scientific

approach is clearly the right step forward. I

think we've made a lot of progress and clarity on

CYP interactions, especially the in vitro-in vivo

correlations and the clarity on the substrates,

inhibitors or inducers, though I do have to

comment: somehow, simvostatin is on the list of

sensitive inhibitors twice, and I didn't know if

that was a hint from the agency to Merck or not or



whether it was just a typo.

I'd certainly agree with the use of PK in

poor metabolizers where appropriate. I think the

robust study designs is really important, and in

many ways, I applaud the efforts and the question,

the slides that Shiew-Mei showed, for example, on

doing a ketoconazole interaction study. Having

read that literature for many, many years and

struggling with that issue day by day, the issue of

whether you're going to do 200 and 400, whether

you're going to dose one day, three days, five days

or a week, those are real issues that have real

impact on how the results come, and it's all too

easy to pick a study design that really will, in a

sense, manipulate the result so that it comes out

the way you'd like it to rather than the way it's

most scientifically correct.

So I think really, we're going to be in

much better shape as we start to look at robust

designs and receive, you know, gain a little bit of

clarity on which ones really give us the best




I also applaud useful and consistent

labeling language. Part of my job is to read to

every new label that comes out and see what the FDA

says about every new drug, and I understand the

desire to be consistent, really quite hard in the

field of drug interactions, and I'm always so

struck about how difficult that is. And of course,

then, I also get to compare it to what happens in

the EU and the rest of the world, where a whole new

variety of approaches come forward as well.

So I think that this is a real step

forward, but I do think there still needs some

discussion on how to label moderate inhibitors, how

to define sensitive CYP substrates, and I must

admit: all the devil is in the details. So while

I agree with the principles the FDA has said, it's

really going to be what's in the tables and how

it's translated into labeling language, I think,

that I'm going to be very curious to see.

So let me talk now about some of the

issues that I think are worth discussing, where I'm

not sure I fully agree with the concept paper or



some of the issues that you may grapple with today.

And I think about things very, very practically.

You know, where are we today with in vitro

predictions of in vivo drug-drug interactions? And

I think ready for prime time. You know, we really

understand where we are; things related to CYP

inhibition, particularly for the five major CYPs.

I think almost ready for prime time are

some of the PGP interactions, UGT and some of the

other CYPs, I won't talk about them today, and CYP

induction. And there, actually, I think there are

some issues with the tools we can use in vitro, but

I also think there's many more issues actually in

the in vivo studies that follow, because in the

end, as I look at this, it isn't only an interest;

it isn't only of interest to me to try to predict

from in vitro what is going to happen in vivo, but

there's also the issue of how do I interpret what

happened in vivo, obviously, into something that's

useful, so that we can actually use the drug


And then, I really think that many things



are not ready for prime time, though I applaud the

science moving forward. Most transporters, to me,

still are in this gray, murky area where I have a

very difficult time understanding how to use them.

And I'll also point out some of my difficulties

with multiple paths of inhibition as well.

So induction, I don't have to talk to you

about. There's a lot of concerns for induction.

Mostly, it's related to the reduction in

therapeutic efficacy. Auto-induction is also a big

concern; rarely the imbalance between toxification

and detoxification. It's dose and time dependent.

The study designs become really quite important

here. It's dependent on clearance and route of

administration. Again, a study design issue, and I

should also point out it's a concern with both

initiation and discontinuation of an interacting


We have many models or many tools now to

talk about CYP induction, and animal models were

previously used. You know, it wasn't that long ago

that that happened. When I arrived at Merck nine



years ago, the only way we really assessed

induction was by doing high dose, short-term

studies in rodents instead of looking at liver

weights and science of induction.

You know, nine years is a very short time.

And today, we're talking about, really, a whole new

category of tools. Dr. LeCluyse is going to talk

about that. But clearly, those were poor

predicters. We looked at those, and we shrugged,

and we went ahead into the clinic, and we had no

idea what to do with the information.

Nowadays, the in vitro models are much

better: the assays, the primary culture of human

hepatocytes, and they're very, very--clearly, very,

very helpful in the selection of drug candidates.

And in fact, in many ways, that's where their most

helpful nature is. We rule out enormous numbers of

candidates, because they're really positive in

these assays overall.

But I will also tell you it isn't always

that easy. It sounds like it's great: you set a

criteria; you cross off a drug candidate, and you



move on. As targets become more complex, the

chemistry becomes more complex; the size of

molecules increases, more and more whole areas of

structures actually carry some risk of induction.

So in many cases, we're not able to cross off those

candidates, and we have to bring them forward into

the clinic.

But the problem I have is still is it

quantitative in vitro-in vivo prediction possible

for induction? And I think there's many factors

that complicate that in vitro-in vivo

extrapolation, particularly inter-individual

variability; plasma protein binding; multiple

mechanisms as well.

Now, I wanted to share with the Committee

some idea of what I actually see as a

vice-president of clinical, you know, pharmacology,

drug development. This is the kid of data I see.

These are hypothetical drugs. None of them is

real. But they're all based on drugs that actually

have made it into the clinic. And as you start to

look at this, you can see some of the things that



come forward and some of the complexities.

I picked five drugs where the mouse

five-day study was actually negative, okay, just to

sort of get that off the table. You can see the

human PXR data, the mRNA data. Those are percent

activity of a rifampin control at 10 micromolar;

the enzyme activity in human hepatocytes, and I put

over on the side something that I also think is

important is really what the CMAX concentration was

in the clinic. Sometimes, that's a predicted

value; sometimes, it's an actual value when we get

into the clinic, and we understand efficacy.

And you can see, if you looked at any one

of these drugs here, the question about should we

or shouldn't we do an in vivo induction study is

really quite difficult. Now, I wish I could tell

you what these five drugs were. More importantly,

I wish I could tell you what the results of, for

example, Midazolam studies were for those five

drugs. Many of them have not progressed far enough

in the clinic to have that evaluation, but this is

the kind of data we grapple with every single day.



And the question I ask myself is which

ones really need an in vivo study? And I don't

really know. So at present, I could probably only

say that we can predict a likelihood of CYP

induction; highly possible on one hand; less likely

on others. And I kind of gave some examples of

things where at least they fell into the possible

range going forward, and most likely, we would have

done an in vivo study to follow up what's going on.

I should also point that clinical data

does sometimes help. For example, we see--often,

we see evidence of autoinduction, which helps to

clarify the issue in a particular clinical dose.

But I think once again, it really depends to some

degree on what kind of exposures one has in the

clinic, and that helps in some ways to really

interpret the data.

Now, of course, I think that's the easy

part. I think the hard part is actually

interpreting an in vivo study. I think there's

less consensus on probe substrates, their clinical

interpretation. I wasn't here for the Committee



deliberations last time about the issue of

induction, but I find these questions quite


And this is just a slide showing the

percent of baseline exposure for a variety of known

inducers. I don't think you have to pay attention

to the specific data. Many of these were studied

on numerous occasions. But this is the effect on

oral Midazolam. And I look at this data, and I'm

asking myself really, is this where we think the

bar should be? This is just about a fivefold

decrease, or should the bar be here? We know the

glucocorticoids and St. John's worts do have

clinical effects on certain drugs, or where should

it be?

And in the end, I still struggle with

really the interpretation of induction, whether

it's the in vitro or in vivo going forward. Now,

more recently, the role of transporters has been

recognized, and I think there's clear examples of

transporter-mediated drug interactions. A couple

of years ago, I don't think I would have actually



said that there were clear examples. I would have

said hypothetical or potential examples.

And I certainly think the understanding of

peak lack of protein is advanced greatly. But the

in vitro methods are not really standardized, and

they're not really quite as available as we'd like.

And I think a quantitative in vitro prediction of

in vivo relevance is still quite difficult. And of

course, it's complicated by the fact that the

transporters really are just not an issue of

metabolism but also absorption, tissue

distribution, excretion; as someone said earlier,

the whole pathways can be involved as one is

looking at this influx, eflux, et cetera.

Now, probably peak lack of protein is the

best study, and I don't have to say much to this

particular Committee about that. But even there,

the in vitro methodologies are not quite what I

would like. The transgenic MDR naga mice are a

very powerful tool, but we have numerous examples

where the human and rodent differences occur.

The in vitro tools are clearly becoming



more sophisticated, but some of the PGP substrates

don't follow simple kinetics. There's a lot of

overlapping substrates between PGP and CYP3A4, many

inhibitors affect both, and of course, there's the

issue of other transporters as well. The tools are

most useful to identify PGP substrates. We can

certainly identify PGP inhibitors, but it's still

comparatively laborious and time consuming to do


And what might I, as a clinical

pharmacologist, actually get as an evaluation of a

PGP substrate? This is a paragraph, actually, from

a real drug. I changed the numbers once again to

make it a little hypothetical, but you can read

this. What we see is what happens in the MDR mice.

We can look at transport ratios going back and

forth. I have a B to A ratio from the two sides of

1.7. I'm not really sure if that's a substrate or

not; what should I do with that particular data?

Now, if an in vivo study is indicated, and

I've told you I struggle with what that actually,

you know, how do I actually decide that, I think



for assessing a potential PGP inhibitor, digoxin

clearly is a suitable probe. I do think that most

other probe PGP substrates are less than ideal.

But I've borrowed a slide from Shiew-Mei

just to talk about some of the difficulties I have

about thinking about assessing PGP substrates.

This is the same slide that Shiew-Mei showed

before. These are all PGP inhibitors, and you can

see in vardenafil what the tremendous difference

there might be between all those, and of course,

part of the difference is that ritonavir, as we

pointed out, oops, doesn't work, ritonavir, as we

pointed out, clearly is an inhibitor not only of

PGP but of CYP3A4, but in this particular case,

it's also an inhibitor of 2C9, which is probably

the other pathway by which vardenafil is actually


And you can see there's a widely divergent

variation in terms of the results one would see.

I'm not sure here that I think that that's really

the kind of data I'd like to be generating to help

understand how to extrapolate datas to new




I think the situation in terms of

inhibitors and doing a study on a substrate with an

inhibitor is even worse. If you look at the

compounds that we have that are inhibitors, there's

quinidine, ritonavir, verapamil, cyclosporin, okay?

These are all very difficult compounds to work

with. We don't use quinidine in volunteers. We

really think it carries too much risk. Ritonavir,

as I've already mentioned, is a 3A4 PGP substrate,

inhibits 2C9.

We've had studies where we've seen

tremendous induction of UGTs, a whole variety.

Some have gone up, some have gone down. In the

end, when we do studies with ritonavir, what we do

is we conclude this is what ritonavir does and

nothing else, because we really just don't know how

to interpret the individual data.

Verapamil, also very complicated; similar

on PGP and CYP3A4, but we stopped using it in our

clinical trials. When we gave it to volunteers,

Dr. Vago in the back there who used to be at Merck



did studies for us where we showed that we clearly

saw, you know, PR lengthening in all of our healthy

volunteers, and we just really thought that the

risk-benefit really wouldn't allow us to do that.

And of course, cyclosporin has myriad

effects. The interpretation is difficult, but it

carries a significant risk to volunteers, and we've

been unwilling to do more than single dose studies

in volunteers because of the effects it has on the

kidney and on immunosuppression. As a matter of

fact, this is very real to me. Last Friday, Merck

spent a couple of hours, a whole crowd trying to

design a study requested by the agency to really

try to understand the effect of a model PGP

inhibitor, cyclosporin, on one of our drugs, and we

just found it almost impossible to design a study

that we thought would really be able to answer the

question without significant patient risk.

Other transporters are far less

standardized and available. Many cell-based

systems contain multiple transporters, making it

hard to interpret in vitro. There's few



well-defined substrates and inhibitors. The

correlations are difficult. Many of the

interactions can't even be linked to a single

transporter system. And we just don't know how to

generalize these.

So I think that in general, my feeling

about other transporters are that the science

doesn't support an in vitro-in vivo correlation.

Clearly, we're moving that way. I have high hopes

that five years from now, if I stood in front of

the Committee, I'd have a different answer, but

this is what I think today.

Now, I wanted to just close and talk a

little bit about the multiple inhibitors, multiple

impaired. Just like with induction, Dr. LeCluyse

is going to be talking about that; someone is going

to be giving a presentation about this as well, and

I think there's some really elegant work there.

But I have to admit, I'm not a big fan of this

particular approach. I understand the agency's

desire for higher exposures when evaluating QTC

issues, which I think is probably the primary



driver for many of these studies.

But the new hurdle for QTC is very, very

stringent. And we certainly agree, I certainly

agree that the margins are critical. But the real

question I ask myself is for how many of the drugs

that are coming forward are extraordinary efforts

justified? And of course, not everybody would

agree with me that some of the things that we're

doing with multiple inhibitors are truly

extraordinary efforts.

But I want to just lead you through a

little bit about how this actually works in

practice you can understand why I take that

approach. First of all, the QTC effects of many

inhibitors are not well-characterized. That's a

solvable problem. And again, I hope that in a

couple of years, we'll know that ketoconazole and

itriconazole and, you know cyclosporin or whatever

we're going to use in these studies, ritonavir

really has no effect on QTC that could mess up

these definition QTC studies.

But the important thing to realize is



while the industry agrees with all the agencies

around the world that these studies are important,

these studies are extremely costly and difficult to

do, and the carrot to the industry, okay, is the

fact that if we do these right, and we get an

answer that really satisfies the agency that this

drug does not have a QTC effect, we really need

that information to prevent us from doing

extraordinary efforts in terms of monitoring in

phase three. So it kind of puts a limit on when we

need to really have this data to be most useful in

terms of designing a QTC study.

If it isn't available for us at the end of

a phase 2B study, honestly, it's much less valuable

to us overall. And so, we have to work hard to get

that in. Now, what do we have to do to do a

multiple pathway study? In most cases, we have to

do a clinical study first to really define the in

vivo metabolic pathways. It takes nine months to

set up, six months to analyze. We need clinical

data on each inhibitor separately, really, to

understand the usefulness to increase PK exposures.



We have to get that data, we have to model it to

make a prediction what is going to happen when we

look at multiple pathways.

And in most cases, I would argue, you

actually need to test the concomitant

administration of the inhibitors before the QTC

study because of the issue of safety and

tolerability. These studies are not really done at

sites that are really set up to carefully evaluate

sort of phase one type issues, and in many cases,

you'll be giving a new exposure to drug that no one

has ever seen before.

And of course, these QTC studies get quite

complex if people feel dizzy or nauseous or vomit,

have diarrhea, okay? I have to tell you: I am

senior management, but if I went back and said we

couldn't complete our QTC study and that a million

or two dollars are really down the drain because

people were unable to tolerate the drug, I would

not be well received. And so, we have to do that

stuff as well.

Special populations also are needed in



some cases, and I think there are some elegant

studies, like the telithromycin study, because

recruiting those particular people is really quite

difficult and time consuming as well.

Now, to make it even worse, those are

logistics issues. This is what I might see,

actually, from a particular drug where we're

considering a multiple pathway. And this is,

again, patterned after a real drug. In vitro data

incident that 3A4 plays the major role, but there's

10 percent from four other CYPs. What inhibitors

should we use? How should we actually design such

a study?

And lastly, I also question are we really

as smart as we think? Despite all our knowledge,

can we really predict the effects of inhibition of

multiple pathways? And I just wanted to give one

example of some data that will be presented at

ASCPT the next year about a study we were asked to

do, which I think was actually a very good study to

request, so I certainly support it, but one where

it showed me that I was a lot less smart than I



thought I might have been.

Aprepitant is a moderate CYP inhibitor.

It's used in combination with 5HT3 antagonists, and

dolasetron is a 5HT3 antagonist we had not studied

in our clinical program. It's metabolized by 2D6,

with 3A4 being an important pathway. And because

of the concern of QTC prolongation with the

dolasetron, we did a study at the agency's request

to conduct an aprepitant interaction study in 2D6

extensive in poor metabolizers.

All of the data that we had would have

suggested we should have had a remarkable effect.

And in that study, as you can see from that data,

if you take a look at what happens with dolasetron,

with aprepitant, APR, and dolasetron together, we

were able to show, in fact, yes, poor metabolizers

do have higher levels. But closing off the CYP3A4

route with a moderate inhibitor really had no

important effect at all on the levels. Very

reassuring in this particular case, but clearly not

what we would have predicted overall.

So overall, I think that we really are



making a lot of progress. I very much applaud the

efforts of this Committee and the FDA, and I think,

though, that we're really not there yet in all of

the things going forward, and this is sort of my

summary of what's ready today and what I hope will

be ready in the future.

Thank you very much for your patience.

DR. VENITZ: Thank you.

Any comments or questions?

[No response.]

DR. VENITZ: Thank you again.

Our next speaker is Dr. LeCluyse. He is

the chief scientific officer of CellzDirect, Inc.,

and he's going to talk about induction.

DR. LECLUYSE: Excuse me while we do a

technology switch here.


DR. LECLUYSE: It worked.

Okay; I also would like to thank the

Committee for this opportunity to speak to you.

The way I interpret my role in all of this is that

I think I'm supposed to condense this labyrinth of



information that's out there on nuclear receptor

biology and what it all means in terms of human

gene regulation, P450 induction and how to do in

vitro screening for that.

So with that task in mind, let me start

out by just first putting up the questions that

it's my understanding that we are asked to address,

and this is very limited as compared to a number of

issues that Keith brought up and addressed in terms

of the in vitro-in vivo correlations, et cetera,

and some of the complications associated with that.

So I am specifically going to focus on

these questions that were placed in the paper or at

least suggested in the papers, questions that need

to be addressed, such as if a drug's induction

effect on 3A4 in vitro is negative, then, it is

acceptable to not recommend any in vivo studies

with substrates of 3A, 2C9, 2B6 and 2C19, yes or


Also, the other question that was meant to

be addressed today is if the in vitro induction or

increase in enzyme activity is more than 40 percent



of the positive control, then, there is a need to

recommend an in vivo induction study, yes or no?

I'm going to focus predominantly on this first

question, because I think that's the one that's

most complicated and involves a little bit more of

a mechanistic understanding of what our current

understanding of regulatory of the human liver

genes, and this, you could argue, is as much of a

philosophical one.

So before we can address that specific

question, especially the first one, let's start off

by first reviewing the enzyme induction in humans

as we currently understand it or as observed in the


So, for example, if you take compounds,

and certainly, this is not a complete or

comprehensive list, but it serves to represent the

point that for most drugs that are known to cause

clinically significant drug interactions, and

that's the point, our current understanding of

which CYPs are involved in their interaction is

pretty evident these days, especially by the number



of drugs that we use as probes as well as the in

vitro data to support that.

We also know the relevant plasma

concentrations at which we see a clinically

significant interaction event. And then, also,

now, we're very much aware of the particular

pathways that mediate these events. And notice

that for the most part, these center around three

receptors, namely, CAR, PXR and the AHR. And I'll

go into much greater detail on those in a second.

Another way to look at this is if you

actually look at the inducible P450 enzymes in

human liver, with the exception of CYP1A, which is

predominantly induced by aromatic hydrocarbons,

some dietary components and cigarette smoking and

with the exception of 2E1, which is basically

induced by solvents and drugs like isoniazid but

mostly involves a mechanism of stabilizing protein

and RNA, for the most part, the rest of these often

are induced by compounds represented by the

anticonvulsants, antibiotic rifampin, et cetera,

suggesting that there is some overlap or



commonality in their mechanism of regulation.

It's now fairly apparent that especially

for the regulation of the human hepatic enzymes,

that there's three major receptors that are

involved: predominantly the aral hydrocarbon

receptor, the AH receptor; constitutive androstane

receptor or CAR; and the pregnane X receptor, PXR.

And there's three main points that I want

to basically draw from this particular slide:

number one, each of these receptors contains a

ligand or drug binding domain which determines,

basically, which drugs are going to activate it,

and also, they contain a DNA-binding domain, which

determines which DNA sequences or response elements

that they're going to bind to upon activation by


Now, the other point I want to bring out

is that these all form heterodymers with other

proteins, and for the most part, the AH receptor is

distinct, in the sense that it partners with a

protein called the aral hydrocarbon receptor

nuclear translocase protein. I didn't name it. It



was given that name a long time ago. The acronym

AHRNTP is given to that.

On the other hand, CAR and PXR both

heterodimarize with another receptor called RXR,

but basically, it's gratuitous in its function

here. It's predominantly driven by--it's the

partner CAR and PXR. Now, the other point I want

to make is that upon activation, each of these

nuclear receptors induces a number of genes, not

just a single subfamily or, you know, a limited

class of genes, but, for example, upon activation

of PXR, you're upregulating a number of phase one

enzymes; also, transporters as well as phase two

enzymes as well as others, including the

carboxylesterases, by the way.

So bear in mind that also, CAR and PXR

share a number of these target genes in common.

So, for example, 2B is upregulated by both CAR and

PXR; 3A4 and the 2Cs, beginning to suggest that

there are some common regulatory mechanisms of

these genes by these nuclear receptors. And we

actually understand now enough about the particular



promoter region sequences and the response elements

that are in the promoters of these genes to explain

mechanistically now that they can be and ought to

be coregulated by activators of these receptors.

So our first evidence for coregulation

that we observed in my lab, and we've been looking

at this for over a decade, I would hate to admit

now; basically, our first evidence was a study that

we set out to do to explore the effect of 14

different compounds that were known to induce 3A4

to various extents, either in vivo or in vitro, and

our intention was to relate that to their PXR

activation profiles.

Now, interestingly, when we extended those

studies to include 2B6 activity, we basically found

something very interesting, which is summarized in

these tables over here. So if you basically look

at the most potent or the strongest inducers of 3A,

you'll notice that clotrimazole, rifampin and

ritonavir are also very potent inducers of 2B6 in

this particular case.

Notice also in the 2B6 column that there



is a couple of others, including phenotone and

phenobarbital that are strong 2B6 inducers, but

they're either moderate or weak inducers of 3A;

however, upon more extensive evaluation, even these

compounds are known to induce 3A, here again

showing some common regulatory mechanisms.

Now, if we extend these studies to include

CYP2C9, we also find very similar profiles; for

example, potent inducers of 3A and 2B6 also induce

2C9. Now, this is represented nicely in this

particular slide, where we looked at the

coregulation of CYP2C9 and 3A4 by avasomid, which

we discovered to be a very potent PXR activator.

It's also been shown to interact clinically with

warfarin and midazolam and digoxin.

You can see here in two separate donors,

if you look at 2C9 versus 3A4 in hepatocytes from

one particular donor how the response concentration

curves basically are almost superimposeable. Also,

in a second donor, the same situation, suggesting

here common regulatory mechanisms via PXR in this

particular case.



Now, if we extend these studies to include

additional inducers of 2B6 and 3A, but then, look

at the induction now of multiple 2Cs, including

2C8, 2C9 as well as 2C19, in this particular case,

we're looking at RNA, not activity, but it still

exhibits the point that I want to make that

basically, all these compounds that are inducers of

2B6 and 3A via activation of CAR and PXR also

upregulate the three 2C enzymes.

The other point I want to make is that the

most efficacious inducers are actually

transactivators of these 2C9 genes have a tendency

to be rifampin and/or phenobarbital in all three


And finally, the other point that I want

to make, because it's going to play a role in terms

of why we're proposing looking at a limited number

of endpoints is if you actually look at the

induction of 2C9, it's basically between two and

threefold, with even the most potent inducers,

positive controls, if you will, suggesting that

it's actually not a very sensitive target gene if



you're trying to actually elucidate the induction

potential of a particular drug, and since we've now

discovered that there's a lot more coregulation

between these genes, we propose a more

mechanism-driven type screening strategy than what

has typically been proposed in the past.

So in essence, what this boils down to is

we think we're at a point now where we understand

the regulatory mechanisms of the relevant human

P450 genes to where we can now do a more

mechanism-driven screening strategy with a goal to

screen efficacious activators of these particular

dominant nuclear receptors and these clinically

relevant induction events where we propose

screening protocol using a sensitive endpoint for

each nuclear receptor being the goal with the

premise that potent activators of each of these

individual nuclear receptors will induce a number

of target genes but differentially.

So for example, potent PXR activators will

induce 3A, 2B, the 2Cs, even some of the phase 2

enzymes like 1A1, UGT1A1, transporters like MDR1,



but 3A4 is the most sensitive. Likewise, potent

CAR activators will induce a number of these same

genes that overlap with PXR, but 2B6 is the most

sensitive. And then, finally, potent AH receptor

agonists will induce 1A2, phase two enzymes such as

UGT1A1, GSTs. But 1A2 is the most sensitive in

terms of screening for that.

So, finally, an example protocol that we

would advocate, and we currently use, is to treat

human hepatocytes. That's a given with our

protocol. Treat with a new drug at three to four

relevant concentrations, especially where

clinically relevant concentrations are known; treat

for one to three days; include positive controls,

which is very important in terms of making

appropriate comparisons, so, for example, the most

robust 1A, 2B and 3A inducers ought to be used for

positive controls, in our opinion, where some sort

of maximum is obtained that's possible with the

particular preparations of cells.

Now, one has the ability to measure RNA,

certainly, protein as well as enzyme activity. We



would advocate that the enzyme activity is probably

the best representation of the induction response.

Protein content is semiquantitative at best, and

the relationship between RNA content and enzyme

activity is still yet to be completely

characterized, although I think we're nearly there.

And finally, the last point here is that a

major CYP target gene for each nuclear receptor

ought to be the focus of these initial screens; so,

for example, looking at CYP1A2 as an endpoint for

AH receptor agonists, 3A4 for PXR, and possibly 2B6

for CAR, although all 2B6 inducers and CAR

activators that we've come across thusfar also turn

out to be inducers of 3A4.

So finally, one other point that I want to

make in terms of looking beyond enzyme activities,

in this particular case, where we're looking at a

mechanism-based inhibitor such as ritonavir, if you

limit yourself to looking at enzyme activities,

which is the case in this particular study, where

we evaluated seven different inducers of 3A, you

can see that if you only evaluate things on the



enzyme activity, which is normalized enzyme

activity to the negative control, here, you can see

that ritonavir actually knocked out the activity

significantly in these microsomal assays that we

did. And as we all know, ritonavir is one of the

most potent mechanism-based inhibitors that we've

come across.

However, if you actually were to look at

its effects at the ability to upregulate 3A4 gene

expression at the RNA level, you'd find that

ritonavir is every bit as efficacious as positive

control rifampin at that level, suggesting that

it's actually a very potent PXR activator and


So finally, some of the other important

factors to consider in terms of study design: the

interdonor differences in the control and basal

activity between preparations of hepatocytes can

often be a caveat. We suggest that that's why it's

important to compare it to a positive control

rather than fold over a negative control. We also

believe that it's possible that depending on how



high the basal activity is, it may exclude some

preparations of hepatocytes from maybe being

appropriate for induction studies.

Also, the relevant concentration range of

your drug is important, focused on plasma and

tissue concentrations; appropriate choice and

concentration of a positive control is an important

consideration; certainly, the major species

differences have to be acknowledged in terms of

nuclear receptor activation as well as induction of

specific P450s, so for example, it still surprises

me that some of the studies that I come across

where dexamethasone is still used as a positive

control in human hepatocytes, it's a very potent

inducer, as is PCN in for rodents, but there's

about an order of magnitude difference between

dexamethasone's ability to induce the 3A enzymes in

human hepatocytes compared to, let's say, a

positive control like rifampin.

Also, the expression of the data in the

relevant endpoints is very critical, and that's

been also an issue that's been addressed and



relating that to a positive control. Exposure time

is important, especially for the particular

subforms that you might be evaluating, shorter for

CYP1A, for example; longer for 3A; and then,

finally, one must bear in mind that solvent effects

on P450 expression and activity are observed.

DMSO, for example, is an activator of PXR itself at

sufficiently high concentrations, and also some of

the alcohols are known to even inhibit some of the


And finally, just in summary of the key

points: our mechanistic understanding of enzyme

induction in human liver has increased markedly in

the past decade. Most inducible human P450s, UGTs

and transporters involved in DDIs are regulated by

a few receptors, namely PXR, AH receptor and CAR.

Screening for potential inducers during drug

development, in my opinion, can be achieved using a

single, selective and sensitive target gene for

each of these nuclear receptors through following a

3A4, 1A2 and/or 2B6, and activity data from in

vitro induction studies for a new drug should be



normalized to a negative control, compared to an

appropriate positive control at appropriate

concentration, considered significant when they are

greater than or equal to 40 percent of the positive

control, and that's actually a question that I'd be

interested to hear others' opinion on that and also

complemented with protein or RNA data if time

dependent inhibition is involved.

So, with that, I'll be happy to answer any

other questions that you may have.

DR. VENITZ: Thank you, Ed.

Any questions for Dr. LeCluyse?

Go ahead.

DR. HALL: Ed, one of the biggest concerns

with hepatocyte work has always been the

preparation, the treatment, the handling, and the

sort of somewhat unique capabilities of one group

versus another group in just the way the

hepatocytes work. Do you believe that is now

sufficiently robust that this can be done

independent of supplier, source of the liver,

they're all going to work?



And if they are going to work, how many do

you have to use in order to come up with a reliable


DR. LECLUYSE: Yes, that's an excellent

question, and I think that's been part of the

historical issues with the use of hepatocytes is

depending on whose hands the studies are conducted

in, you can get some variability. And I think that

goes back to how important the study design is and

the appropriate use of the positive controls as

markers or indicators of whether the studies have

been appropriately done, and I think, you know, I

think John is going to maybe discuss that a little

bit more in terms of those criteria, but I think

we're there now to where we can start stipulating

those issues and at least minimize poor results.

And personally, I think you're pretty much

going to have a good indication as to whether your

drug stands a possibility of being an inducer in

three to four preparations of hepatocytes. So I

think if you get--certainly, in this case, where

we're talking about negatives, if you haven't seen



induction in three preparations of hepatocytes

where you've gotten adequate and sufficient

induction with a positive control, then, I think

you can pretty much rule that out so--

DR. HALL: So to sort of follow up that,

the 40 percent number seems reasonable, but is this

40 percent N statistically significantly different?

I mean, if you had a 0 of 40 and an 80 percent

change, is that okay, or how would you deal with

that issue?

DR. LECLUYSE: Is that between donors--

DR. HALL: Yes.

DR. LECLUYSE: --you're talking about?

Yes, and it is very possible that you may get that

kind of variability, although it may not be that

significant, but, you know, certainly, you may get,

in some donors, and it may be on the border; less

than 40, certainly.

And I think to me, it's more about the

potential. So if you've got one donor where you

exhibit greater than 40 percent induction, then,

that's letting you know that your compound



certainly exhibits the appropriate properties; that

it's likely or stands a chance of inducing, at

least assuming that your study was designed around

appropriate, you know, in vivo or physiologically

relevant concentrations, it stands a chance of


So, you know, I mean, we can go into a

long dissertation about why it may be lower or

higher in certain donors, but certainly, if you see

it in a single donor, then, you know, greater than

40 percent, then, that's telling you what you need

to know, I would argue, so--

DR. SADEE: My question is a little bit

along the same lines. You have a basal activity of

transcription of all of these genes, which is

usually reduced, and those are a whole set of other

transcription factors like the HNF transcription

factor family, and if you have a high expression of

those, your induction will be percentagewise much

lower. So in vitro, you apparently exclude those

where you have high basal activity.

But I wonder whether, in extrapolating,



then, the data you obtain with hepatocytes in vitro

which have minimal basal activity to the in vivo

situation, that you're not somehow exaggerating the

importance of induction compared to the situation

where you have reasonably high basal activity,

which may be more prevalent in the in vivo

situation, and variability actually comes more from

basal rather than from induced activity in vivo.

DR. LECLUYSE: Yes, I mean, I think

obviously, that's a very good point. In fact, the

one thing I like personally about the use of human

hepatocytes is you do get some feel for what that

range may be in the clinic, because I think they

are representative of true donors. And so, you

know, here, again, to me, it's more about getting

an indication as to whether you should--whether a

compound is going to stand a chance to be an

inducer in an in vivo setting and about whether

you're going to get a negative or not, not about

what do you do when you get to a positive? I mean,

that could be another whole discussion we could

have, which I'm happy to engage in.



But you know--

DR. SADEE: Do you have any information on

the interaction between, let's say, HNF4-alpha with

a CAR, or are they additive, or do you have any

feeling for this?

DR. LECLUYSE: Yes, they're supportive.

You may be aware of Richard Kim's data as well as

that of others now that suggests that there are a

number of transcription factors as well as

cofactors that are supportive or even necessary for

a normal induction event to occur. And so, it's

almost the equivalent or the way I look at it is

all of these factors are necessary to drive the

car, so in other words, in order for you to get in

your car and drive down the street, you have to

know that your engine is working, the tires are

okay, et cetera, et cetera.

So without any of those things, you may

not get very far, either, but what's driving the

bus, basically, or what's critically driving it is

these nuclear receptors. So something like

HNF4-alpha, as well as other cofactors and



transcription factors, are necessary for just the

normal events to occur. If anything, that argues

the point of why human hepatocytes are a relevant

model, because they retain their normal profiles of

those factors, cofactors, transcription factors

that I think is actually written in the concept

paper as to why cell lines, for example, might be


But you're exactly right: I mean, all

those things that just go into factoring maybe some

of the donor differences in how the hepatocytes and

in vitro setting respond, they're also operative in

vivo, so, you know, like I say, to me, what I like

about it is that it's probably more reflective of

what you're likely to run into in vivo.

DR. WATKINS: Ed, as you know, I'm a big

fan of cultured human hepatocytes, but there are

some practical issues as an academician. We find

it very hard to get human livers. And I don't know

if that's been solved by cryopreservation, but

clearly, it's, I think, a limited resource that's

very expensive if you talk about doing all these



validations and multiple, you know, with multiple

donors' hepatocytes and doing multiple experiments.

And, of course, there are problems when

you culture human hepatocytes, which is they no

longer have canaliculi, so all the canalicular

transporters presumably just spread out over the

basolateral membrane. So some of the theoretical

advantages of having the relevant cell with the

relevant transporters, I think, is gone, and I

would imagine can be deceptive.

So one of the questions is now that you've

whittled it down to basically two relevant

receptors or maybe three with two endpoints, I

mean, wouldn't the first step be some sort of in

vitro transcription factor activation or transgenic

mouse or something to actually look at the effect

of your compound on the transcription factors

directly rather than marching right into human


DR. LECLUYSE: Well, yes, in fact,

exactly. What you've described is exactly

generally what industry is doing is they're



starting with the least common denominator, which

is the nuclear receptors. And whether their

compounds either bind to or transact or activate

the nuclear receptor, you know, these reporter

assays, as you know, full well, people are using

fairly extensively.

But the relationship between nuclear

receptor activation and a reporter assay and how

that translates to, then, an hepatocyte assay and

then, further yet, in vivo is still, I think, a

long ways from being clear. I actually view them

as nice, complementary tools. I mean, you're going

to get a lot of information from using both to

complement one another, in my opinion.

But back to your point, Paul, about the

availability of resources. You know, that has been

limiting for both industrial scientists as well as

academic to do these kinds of studies, and we're

slowly making headway on that both in terms of more

sensitive assays, where we can do maybe what used

to could only be done in a petri dish, we could now

do in multiwell plates, much more high throughput




We are, I think, on the cusp of being able

to understand the relationship of the RNA, level,

changes in RNA levels with those of activities, so

that allows you to even make these much more rapid

throughput assays much more amenable to less

material being used and all those things. And

also, you mentioned cryohepatocytes. There are

batches of cryohepatocytes now that are available

to do these studies, so you can basically stock up

on those, if you will, or have better access to

whole donors where they would be available to

multiple investigators or multiple departments

within the same institution or company.

And that's oftentimes what companies have

turned to now is just buying whole lots of

cryopreserved hepatocytes that do plate out and are

inducible and respond well to positive controls to

doing their screening. In our understanding of

what makes a good cryobatch of hepatocytes that

will then attach has advanced significantly, too,

from years ago, so--



DR. WATKINS: If I could follow up, I

mean, I think the data undoubtedly exists, and you

may have it, but it would be awfully nice to see

stories of drugs that were positive for the in

vitro transcription assays, and you went into

hepatocytes and more negative or vice versa and

then went into man, and it turned out hepatocytes

were the right answer and well worth the resources

and, you know, provided all this additional


I just have not seen that kind of data put

together that would at least from my perspective

justify recommending human hepatocytes as somehow

muscling to the front and an assessment of

potential drug interactions.

DR. LECLUYSE: Let me tell you off the top

of my head the reason for it is remember, these

nuclear receptor assays only evaluate a single

pathway at a time, and we actually do not have a

good assay for human CAR that's similar to the

reporter assays that exist for PXR. And we do, for

a fact, know that there are compounds that



induce--that are 3A4 in human hepatocytes actually

to the same degree as rifampin that show up as

negative in a PXR assay.

So I think, you know, like I say, the

technology just needs to come along a little bit

further. I don't disagree with you. I mean, I

think we're getting there. I just think we're not

quite there yet, so in this particular case, I

think hepatocytes are going to cover more of your

bases, more of the signalling pathways, cofactors

that we just described, nuclear receptors,

alternative pathways and even working in synergy

all exist together in a human hepatocyte system


DR. DERENDORF: Yes, I'd like to come back

to my previous comment. I'm a little uncomfortable

with that clean cut cutoff of 40 percent as a

threshold for significance or relevance,

particularly we need to define what we're

measuring. We need to define what is an

appropriate positive control. We need to define

what concentrations should we look at, what time



point. And I think unless we do that and have a

correlation with, if it's really meaningful, that

40 percent seems arbitrary.

DR. LECLUYSE: Yes, and that's honestly

been the ongoing debate over the last, I would

argue, couple of years. And by the way, I think we

have defined all those other parameters that you've

mentioned, and now, it's just, and this is where

I'd like to open the floor for discussion, and I

think that's part of what the point is is how

comfortable are we with that 40 percent mark? I

think that's--I would argue that's where we need to

focus. I mean, there's other things that have been

brought up around hepatocytes and doing these in

vitro studies where I think is more away from the


But I think those kinds of issues are

valid points that still need to be up for

discussion somewhat so--

DR. GIACOMINI: I think I just wanted to

echo what Paul said about the transporters not

really being in place in the hepatocytes. I don't



know if this is still the best system, you know, to

test for inducing the nuclear receptors.

The other comment I had was we've tried

making constructs, you know, reporter constructs

and then transfecting them into hepatocytes. Have

you tried that kind of--so that you get a more

quantitative readout at the end of the, you know,

comparative quantitative readout?

DR. LECLUYSE: Right, yes, no, actually,

we do that, too. I mean, we basically, you know, I

should qualify this: my academic lab does

do--takes all those measures. In fact, you do get

normal disposition of human CAR using the primary

cell versus these, you know, the immortalized cell

lines, where CAR translocates constituitively to

the nucleus, as you're aware.

So, yes, certainly, you know, here again,

you're still using primary hepatocytes to get to

the answer. And I think the complementary tool

here, again, of following endogeneous gene

expression with your reporter assays is probably

even the best way to do those particular



assessments, I would advocate, so--

DR. STRONG: I think generally, at least

in our guidance, we do accept the fact, though,

that this issue of induction of 3A4, if we see

that's negative, that we probably don't have to

worry about C92C19. My concern, though, comes back

to the same issue that I think is really pertinent

today, and that is what's the way we define an

inducer and not inducer, the 40 percent?

In fact, what I did was one of the slides

that you showed with the comparison between 2B6 and

3A4 with the number of compounds, I looked at

phenytoin which is a strong CAR inducer, and

compared it to rifampin. When you do that, it

shows that the induction of 3A4 defined by the 40

percent rule, phenytoin is not an inducer.

And so, the question is what's going on

here? Well, I think it comes back again, and some

folks have alluded to it, is the hepatocyte

experiment and the hepatocytes themselves. I think

all of us agree that you can find hepatocytes that

have been induced to their maximum, and you see



very little additional induction. And if you look

at the particular figure he showed, the basal

activity in that set of experiments with the 14

compounds, whatever they were, it was considerably

higher than what you saw, say, in the 2B6. So it

may be just experimental design.

And again, I think this is a question that

we have to really grapple with if we're going to

use hepatocytes for induction. Maybe we need to

define better some parameters with respect to the

hepatocytes we're using.

I wanted to make one other comment off the

subject, but I think it's great. I think again, we

believe that enzyme activity is still a gold

standard. On the other hand, Ed brought up the

issue of ritonavir, an inducer and inhibitor, and

how some of these other measurements like MR8 can

come in and add additional information.

Another way to look at that, though, is

that we're looking at mechanism-based inhibitors.

And in most of these drugs, when you're doing your

inhibitor study, you'll already know that your



compound is or is not a mechanistically-based

inhibitor, so that you can put a red flag up with

regards to induction studies.

DR. VENITZ: Ed, I have two questions:

how do--your CYP induction, how does that compare

to UGT inductions? Have you looked at that at all?

DR. LECLUYSE: Yes, in fact, I don't know

if you got my background slides, but I did include

some UGT1A1 data in there, too, and basically, as

you may be aware, UGT1A1 is unusual in the sense

that it's regulated by all three receptors. And

so, activators of those three receptors will induce

UGT1A1 in human hepatocyte preparations, according

to the potency of the compound, and there, it's the

compound's ability to activate those nuclear


So, you know, here again, you see the most

potent induction of UGT1A1 with things like

rifampin, phenobarbital, and also activators of the

AH receptor like 3-methylclanthrine, homeprizole.

DR. VENITZ: The second thing: can you

help predict hepatic enzyme induction for GI enzyme



induction, 3A4?

DR. LECLUYSE: Well, that's an interesting

point, because that's also a debated issue

currently right now, and the fact that the gut

enzymes are regulated by other factors that are

unique to the gut--now, bear in mind that the

profiles of these nuclear receptors are

tissue-specific, so you will find PXR, for example,

in the gut. And so, inducers of hepatic 3A or

activators of PXR will induce hepatic target genes

as well as the gut.

But there's other things going on in the

gut that are not operative in the liver and vice

versa, like with the vitamin D receptor, for

example. So there are additional mechanisms that

might be operative in the gut that may cause

upregulation of transporters of P450s that you

wouldn't observe in just an hepatocyte model, for

example, so--

DR. VENITZ: Any other questions or


[No response.]



DR. VENITZ: Then thank you again.

DR. LECLUYSE: Thank you.

DR. VENITZ: Shiew-Mei?

DR. HUANG: About the 40 percent, I just

wanted to throw this question out. Initially, we

got this from the PhRMA paper, although I know that

there is still discussion on whether this is too

high a value; should we be more conservative, 20,

25, or 30 percent. But I think the cut-off should

be supported by data, and as John mentioned that

based on some of the existing data, perhaps 40

percent is too high a cutoff.

And so, I was going to say in our concept

paper, we recommend the evaluation of 3A along with

2C9, 2C19, and we have not included 2B6 or UGT1A1,

although this will be some time to come. So I

thought perhaps it's important maybe we consider to

have different cutoffs depending on what

information we would like to get from 3A. If you

want the information of the certain cutoff to

support that, if 3A data is negative, then, we

don't have to do 2C9, 2C19. Perhaps 40 percent



would be sufficient.

But if you're going to include 2B6 or

UGT1A1, then, perhaps there's a different cutoff.

And I'd like to see what your opinion, really,

because I think it's data-driven. We need to know

very carefully what data we have.

DR. LECLUYSE: Well, I can look at it from

a number of different perspectives, Shiew-Mei. And

I'd like to hear the panel's views on these, too,

because the one issue is, you know, just the views

on enzyme induction as an event in itself,

especially the clinical relevance of it as an

event. Now, I can tell you that I have my own

opinion on the chronic activation of these nuclear

receptors by not only drugs but any xenobiotic can

be an issue, especially the more potent ones, and

that you would want to stay away from those. But,

you know, that would be like the rifampin type


So the question is like where do you start

worrying about it, you know, where you're more in

the gray zone or where are you comfortable saying



that it's a negative result, which also can be

interpreted as a not significant enough of a result

is another way I look at it, because, you know--so

the assumption is if you've done everything else

right, and at the optimal concentration, your drug

or a particular drug never induces more than 40

percent of your positive control like a rifampin.

What's going to be the clinical outcome of that?

Is it really going to be noticed above and beyond,

you know, the normal distribution of the

population, et cetera, et cetera? I mean, we've

had these discussions before.

And so, you know, but that's different

than asking the question, does it have a potential

to cause an interaction, you know? And so, I think

that's where the debate really lies. And, you

know, I could argue both ends of the argument,

depending on how conservative you want to be. So,

you know, I think that's--I'd like to hear the

agency's view on that as well as the panel's view

on that so--

DR. SINGPURWALLA: I'm surprised that our



chairman on the matter of cut-off, our chairman has

not raised his pet issue, namely utilities. Is

there no discussion of utilities in these cut-off


DR. VENITZ: He's not really dealing with

clinical yet. This is purely in vitro. The

utility has something to do with what happens if

this turns out to be clinically relevant.

DR. SINGPURWALLA: Factored in subsequent

to utilities.


DR. SADEE: I still have just a quick

comment that we haven't mentioned that, for

instance, CAR consists of multiple, multiple

isoforms, spliced isoforms. And so, that not only

changes between tissues but also between

individuals and the splices contain 14 different

proteins that are all differentially expressed,


Do you consider this as a potentially

problematic factor, or is it a factor that could

account for the finding that sometimes, you find an



adoption, sometimes, not?

DR. LECLUYSE: Yes, I think that's an

excellent point. I mean, that's sort of where our

current understanding leads us to believe that

variability in things like the particular receptor

and differences in the cofactors that even regulate

these receptors all factor into some of these

interindividual differences. Bear in mind that

even with 3A4 or the difference between 3A activity

baseline that we brought up that you've got 3A5

contributing to the baseline activity that's not

really very inducible compared to 3A4.

So you've got all these things operative

in vivo, and that, here again, goes back to the

point that we raised again: while I like human

hepatocytes, and it's probably more indicative of

all these factors, now, I don't think we have a

complete understanding as to what the--whether

there's an individual subpopulation of individuals

that are going to be maybe on one extreme of the

spectrum or another.

Interestingly, as you may be aware, that



the known polymorphisms for these receptors suggest

that for PXR, anyway, that most of them don't

really have a functional relevance. Now, CAR, on

the other hand, seems to show a lot more

variability in a lot of different ways, including

the expression levels. It seems to be more

susceptible to shifts, ebbs and flows, you know, in

a person's social life, you know, genetic makeup,

et cetera, et cetera, whereas PXR, for whatever

reason, through evolution, it's pretty stable.

It's pretty amazing what we've been able to do to

try to vary PXR expression in human hepatocytes,

and you can imagine we've done everything that's

possible to vary its expression. It's fairly

stable. It's almost like a housekeeping gene, in

that sense.

Whereas, CAR can be variable. So, I mean,

I think--but the net results is over the course of

looking at three to four donors for the same drug

at the same concentrations, you know, we generally

get a good clue as to whether a compound is likely

to induce or not so--



DR. VENITZ: Okay; last question.

DR. JUSKO: It looks very promising that

this type of screen using human hepatocytes would

allow one to anticipate enzyme induction for

multiple CYPs. But this is partly based on the

premise found with rifampicin and anticonvulsants

that these drugs are a bit ubiquitous in inducing

many CYPs. Has the reverse type of literature

review been done to see how many drugs may induce

one CYP and not others? I notice in your list, you

have CLZ as an inducer of CYP3A4. Does it induce

the other CYPs?

How many sort of false negatives, or I'm

not sure which way it's going to go, how many

misleading results will there be because of the

lack of ubiquitousness of this kind of thing?

DR. LECLUYSE: Yes, well, actually, I was

hoping early in my academic career that that was

exactly the case. So then, we could get excited

about these unique kind of compounds that were very

selective or specific inducers. When I first

started my career, I hate to admit, again, that it



was over a decade ago. We kind of went into this

with this biased impression that there's, like, 1A

inducers, there's 2B inducers, there's 3A inducers,

suggesting that there's, you know, some distinction

between them.

And one of the first things I became

disappointed in is the fact that the human doesn't

seem to operate that way so much. In fact, for

whatever reason, the receptors have evolved to

where generally, if you have inducers of 3A, you

always see induction of 2C9. And same way with 2B.

I don't know why it is, but it seems to be the


So we've been out there searching. I

honestly have been looking for compounds that will

just selectively induce particular subfamilies of

the human P450s and not come across--and a lot of

that data, admittedly, you know, partly due to time

but partly due to proprietary nature, et cetera,

you know, we've not come across over the, you know,

years and years we've been doing this of compounds

that are that selective.



And it kind of makes sense. I mean, you

know, the other thing I didn't get to do, and it's

part of my background slides, I actually have,

like, some of the promoter sequences for all the

promoters of the 2C promoters, 2B and 3A, and what

they share in common, and it begins to make sense

why they are coregulated and why it would be very

difficult to come up with a compound that

selectively induces any one of these, because on a

molecular level, it just wouldn't make sense that

it would happen, number one, because of the

overlapping specificity of the nuclear receptors

themselves and the fact that they share a lot of

commonality in their DNA binding domains.

So basically, they're meant to kind of

overlap and to crosstalk on these specific

isoforms, so--

DR. VENITZ: Okay; thank you again.

Our last presentation, right, for today,

is Dr. Reynolds. Kellie is in the Office of

Clinical Pharmacology and Biopharmaceutics, and she

is a team leader in Division Three.



DR. REYNOLDS: I just have a brief

presentation to open up a topic that's been

mentioned in two other talks today. It's a topic,

I think, that's been bounced around at several

other meetings, so we finally want to bring it to

the Committee for you to discuss.

The term that's used is multiple inhibitor

studies, and it really does refer to a lot more

than just multiple inhibitor studies. That's just

the terminology we've used. So I just want to

address what we're actually talking about, why we

think we need this information or may need this

information in some cases and how we might collect

the information.

So what we're actually referring to are

studies that are conducted to determine the effects

of a new molecular entity at the maximum exposure

that's likely in patients. And by effect, we mean

adverse effect.

And there's several different reasons we

might need this information. The primary reason is

to define the safety at the top of the exposure



response curve for adverse effects. And the

example that is brought up most often is for QT

prolongation. So this is actually mentioned in the

ICH draft document for the clinical evaluation of

QT prolongation, and there's also similar wording

in our draft concept paper for drug interactions.

So it mentions that if there aren't any

safety concerns, it may be useful to look at the

effect of the drug at substantial multiples of the

anticipated maximum therapeutic exposure, and if

you can't get to that exposure by giving higher

doses of the drug, you may do different types of

inhibition studies.

And another reason we may need this

information is to really just define what the worst

case scenario is for the drug. There are numerous

reasons that patients might be exposed to elevated

drug concentrations above what was observed in

clinical trials. It may be due to drug

interactions, genetic polymorphisms of the drug

metabolizing enzymes, renal impairment; it could be

hepatic impairment or multiple combinations of



these factors.

So there are several different ways that

we can get this information. We can give a higher

dose of the new molecular entity, if that's

possible. We can give the drug with a high dose of

a potent enzyme inhibitor. We can give multiple

inhibitors if the drug is metabolized by different

enzymes. If it's a drug that's metabolized by an

enzyme that has different genotypes, we can give it

with poor metabolizers to help higher

concentrations, or we can combine these factors,

and that's why these are called multiple inhibitor

studies. You may give the drug to patients with

renal impairment in combination with an enzyme

inhibitor, or you may give it to 2D6 poor

metabolizers in combination with a 3A4 inhibitor.

But there are some special considerations

for the studies. We need to consider what safety

data are available, both in animals and in humans.

Do the safety data actually support the conduct of

the studies? And we also need to consider the

relevance of the high exposure: what is the



expected dose in the clinic? Have higher doses

already been given? Did they start out looking at

a much higher dose and then settle on a lower dose?

What are the expected concomitant

medications? Is it likely that inhibitors will be

given with the drug? And that's an important

consideration. And also, what is the target


So there's several steps in the process:

first, if you're going to do a multiple inhibitor

study, you need to know the effect of individual

factors by themselves first, and then, you can

simulate the effect of the multiple factors. And

if there are safety concerns, it's probably a good

idea to study lower doses first to see what the

actual fold increase in concentration is before you

actually give a higher dose with the potent

inhibitor. And so, it is multiple step process

that would take quite a bit of time.

And there are not a lot of examples. We

don't have a whole lot of data on this. And I

guess that's probably one of the concerns. But we



did find two examples. The first example is for

repaglinide, and this drug is a substrate for

CYP2CA and CYP3A4. And there was an interaction

study conducted in 12 healthy subjects. It was a

four-way crossover study. They received the

repaglinide either with placebo, itraconazole,

which is a 3A4 inhibitor; gemfibrozil, which is a

2C8 inhibitor; and also, the combination of

itraconazole and gemfibrozil.

And you can see that there was an increase

in the effect. When we gave it with itraconazole,

there was a 41 percent increase in the AUC. With

the gemfibrozil, there was a 712 percent increase.

And with itraconazole, it was almost a 20-fold,

with itraconazole plus gemfibrozil, both

inhibitors, it was almost a 20-fold increase in


Another example is telithromycin, and this

example is actually in the label. This drug is a

substrate for CYP3A4. Thirteen percent of the dose

is excreted unchanged in the urine, but that may

serve as a compensatory elimination pathway when



metabolic clearance is impaired. So if you give

ketoconazole with telithromycin, there is a 95

percent increase in the AUC, and in patients with

severe renal impairment, there's about a 90 percent

increase compared to normal, healthy volunteers.

And very limited data is just from two

subjects. But in two subjects with severe renal

impairment who are also given ketaconazole, the AUC

increased four to fivefold compared to normal

volunteers who did not receive ketaconazole.

So in summary, just to prepare for the

questions that we have, what we're referring to

here when we say multiple inhibitor studies is any

studies where we're trying to determine the effect

of the new molecular entity; its adverse effects at

the maximum exposure possible. And we think it may

be important in some cases to consider this,

because some patients may be exposed to the

worst-case scenario. We want to define what that

is and evaluate what happens there.

And the way we can evaluate it in some

cases, just a single factor will be enough to do



this. And in some cases, we may need multiple

factors. But there are a lot of different

unanswered questions that we need to consider for

this: first, how practical is the approach? It

does take a lot of different steps, and if you need

the answer at a certain point in drug development,

you need to get all the information prior to

conducting the study.

Are there certain cases where we think we

need this information and other places where it may

not be necessary? And do we actually have enough

information about the effect of multiple factors to

make a specific recommendation? I guess that's

kind of the same as are we smart enough? Do we

really know what we're doing here?

And there are just limited data. There's

probably one or two other examples that we have,

other than the two that I showed here. And is the

general recommendation acceptable, or do we need to

make it more specific? There are some general

recommendations in the ICH guidance and also in the

concept paper. Do we need to be more specific



about when we actually think we need to make the


And also, is there a possible role of

population pharmacokinetics for determining what

the effect of multiple factors would be? If we

actually enroll patients who have the multiple

factors on board into the clinical trials, with

appropriate population pharmacokinetics, we may be

able to determine what the effect is.

And so, there are going to be two

questions posed to the Committee regarding this:

first, is it acceptable to recommend this under

certain circumstances, and also, if we do recommend

this, what other issues should be considered first?

DR. VENITZ: Thank you, Kellie.

Any quick questions or comments?

As I said, we will discuss the individual

questions at the full discussion after the break.

Are there any quick comments or questions to the



DR. HALL: Could you clarify, is there



sort of an agenda that would lead you to include

this in this drug interaction guidance? It seems

to me that it's not truly in the spirit of the

overall document, that it's a separate issue. Is

there some reason that you believe it should be in


DR. REYNOLDS: I think--well, one reason,

Shiew-Mei may be able to address it better, just

because it's been talked about a lot, and it seems

because it does involve drug interactions, and it

does involve specific study design concerns, that's

one reason it is in here. It is a little bit

different from the rest of the tone of the

document, though. If Shiew-Mei wants to provide

more insight--


DR. BARRETT: You mentioned that on the

why was to define the worst case scenario. But

under what conditions would you say you need to

define the worst-case scenario? What properties of

a drug would lead you to say that I need to know




DR. REYNOLDS: I think it really would

depend on what we know about the safety of the

drug. I mean, if we feel like there are situations

where patients may be exposed to higher

concentrations than they were exposed to in the

clinical trials, and we have special concerns about

the drug, then, maybe one situation. It would

depend on, like, in phase two, what the dose

finding was, whether they actually ended up

settling on the highest dose they looked at or

whether they actually looked at doses several fold

lower and settled on one of the lower doses.

DR. VENITZ: Larry?

DR. LESKO: Yes, just in the context of

Kellie's presentation, the adverse event that comes

up often and is spoken about in this context is QTC

prolongation. Now, the question would be what else

is there beyond that that would be sort of a

characteristic of this concern about multiple

inhibition? I don't think it would be dry mouth,

for example, or things of that sort, of course.

So we have to sort of think about when is



this concern a legitimate concern. And one thing

that wasn't mentioned is how we ought to be

thinking about the exposure-response relationship

that we do know about prior to making the decision

on these multiple inhibitors, and how does that

factor into the decision? That is to say, how can

modeling and simulation play a role here based on

an analysis of the data that's contained within the

clinical trial program, to look at worst case

scenario and simulate its settings as a

prerequisite to doing something live.

DR. VENITZ: Any other questions or



DR. WATKINS: Being responsive to the

ethical concerns of putting together combinations

of drugs or medical conditions like renal failure

with another inhibitor, would this be proposed

during drug development as--I'm just curious--as

this is something you have to do to establish

safety in patients that may be out there, or would

be you either have to fess up and put in bold,



black letters that ketaconazole shouldn't be given

with this drug in people with renal failure based

on what we know, unless the company is willing to

do this study to see if that could be removed from

the label or both?

DR. REYNOLDS: We're certainly not to the

point yet where we're saying you have to do that.

We haven't said that to anyone, as far as I know.

And as far as whether or not there may be

situations where there need to be special warnings

in the label, I think that's going to be very


DR. WATKINS: Because my interpretation is

that Merck was being asked to do something that

they felt they couldn't do, not that this was

something that you wanted to do and couldn't do.

DR. GOTTESDIENER: Could I respond to

that? The answer is Merck has not yet been asked

to do that for a specific compound. There are

other members of industry who have told me that

they have been asked to do that, specifically in

relationship to a QTC study, or at least it's been




In at least the one case I know the

details of, the company was able to convince the

agency that in the end, it really didn't make a lot

of sense, because again, this is anecdotal, so I'm

not sure I'm capturing everything, but the idea was

that the particular risk of QTC effects for that

particular drug appeared a little more remote than

most, and I think in fact, the agency must have

made a decision that in this particular case, the

risk-benefit of going to those high doses didn't

quite exist.

I do think that the issue of, though, how

high you're going to go in the QTC studies is

something that every company faces every day, and I

think as mentioned, there are many ways to get

those kind of margins overall. But it's clear that

there are situations where without these kinds of

what I still call extraordinary efforts, it may or

may not be possible to do so, and then, I think the

question is what are--as Dr. Lesko said, what is it

you're worried about, and how concerning is that



issue overall?

I think Merck, as well as other companies,

would say that if there were a very specific issue

that needed to be addressed to use a drug safely,

such an approach might very well make sense. But I

personally believe that those examples are very far

and in between.

DR. VENITZ: Anything else?

[No response.]

DR. VENITZ: Okay; then, let's take our

last break for today. We'll reconvene at 4:00, and

the Committee will discuss the 11 questions put in

front of us.


DR. VENITZ: All right; our final task for

today is to work through 11 questions that Dr.

Huang has put in front of us. And the way I'd like

to manage that, I'd like for Shiew-Mei to introduce

each question with help of at least one of our

Committee members, and then, have a brief

discussion before we vote. And just like we did

this morning, I'm going to have to go around the



table, make a voice--collect voice votes and then

tabulate them.

So, Shiew-Mei, go ahead.

DR. HUANG: All right; thanks, Jurgen.

Our first question: the next few

questions will be related to inhibition of CYP

enzymes and transporters, so the first question is

related to inhibition of CYP enzymes.

So based on what we have said in the

concept paper, we say five major CYPs are important

to evaluate for inhibition. So if a new molecular

entity is not an inhibitor of the five major CYPs,

based on in vitro data, then, there is no need to

conduct in vivo interaction studies based on these


DR. HALL: So could you define "not"?


DR. HUANG: I mean, one approach is to use

the I over KI ratio, and the other one is to use

the rank order. The approach I have mentioned, we

do not say it very clearly on. We didn't

specifically say if I over KI ratio is 0.1, then,



there is no need to inhibit, although we did

mention if the ratio is 0.02, you definitely do not

need to evaluate. And further, we have talked

about using a rank order. If a more potent or

smaller KI were used, you don't see any inhibition

in vivo, then, you do not have to do the others.

DR. HALL: But the rank order, you have to

do a study in vivo, right, based on the rank order

approach so--

DR. HUANG: Right, so if we use our

definition, we could vote; you could answer a

question based on our ratio, I over KI, of 0.02, or

you can--at 0.1. So maybe when you answer, you can

say yes for 0.1, no for 0.02 if we come down to

that it's a critical issue. That would be very

helpful for us also.

DR. VENITZ: So we do allow yes buts? Is

that what you're saying?

DR. HUANG: No, I'm saying since Steve,

Dr. Hall, has asked me to define what in vitro

data, and we always look at I over KI, and I we

have defined as CMAX at steady state at a highest



dose, projected CMAX, and it's a total

concentration, not free concentration, versus KI.

So sometimes, we use IC50 when KI is not available.

And so, currently, it could be interpreted

that we set in our concept paper a ratio of 0.02 or

lower. We would not need a study. And I think Dr.

Hall is bringing up another issue. Perhaps that

number is too conservative. Maybe we should look

at 0.1. So I would recommend that you could amend

your answer to say I would say yes if the ratio is

0.02. But it's better if it's 0.1.

DR. SADEE: So, let me clarify. I'm not

quite sure. Then, there's no need to conduct in

vivo interaction studies. Does that also include,

well, PGP or--

DR. HUANG: No, just CYP interaction


DR. SADEE: So if we know about a compound

that is metabolized by these enzymes, but we--we

would have to know that there's no other possible--

DR. HUANG: Here, we're talking about--the

guidance talks about the effects of a new molecular



entity on others; also, others on this enzyme. And

right now, we're talking about the effect of this

new molecular entity on others.

DR. SADEE: Okay.

DR. CAPPARELLI: Just a clarification of

downstream from that, making the answer no. If I

recall, there's pathways, then, though, to screen

in population approaches or potentially other

modalities rather than a straight, you know, in

vivo study of a specific substrate.

DR. HUANG: Yes, I'd like to clarify.

This is only one approach. So you could use

population kinetics or other specific studies to

say there is no interaction. But I'm saying we

could extrapolate from in vitro when using I over

KI ratio. When there is no inhibition, then, we do

not have to do a study in vivo.

One of the comments that I've heard from

outside FDA is that the drug may affect

transporters, and that indirectly affects

metabolism. And so, that's one of the reason there

is some suggestion that even though it shows a drug



may not affect this CYP enzyme, but if through

affecting transporters, they may still affect the

CYP enzymes. So that's one of the reasons

everyone's throwing the question.

DR. VENITZ: So how do I vote if I believe

that in vitro trumps in vivo? In other words, if I

have evidence in vitro that there is no inhibition,

that there is no necessity for an in vivo study,

how should I vote? Because I think that's what

most of us agree with, but I'm not sure how to


DR. HUANG: Well, you're saying most

people agree?

DR. VENITZ: No, I'm saying I'm not sure

how I can vote on your question, but I know what I

believe: I believe that if you have in vitro

evidence that there is no inhibition, that there

shouldn't be any necessity or any need to do an in

vivo study.

DR. HUANG: Right, for inhibition, yes.

DR. VENITZ: If that's what I believe, how

should I vote on this question?





DR. SADEE: But I think you have to add

there, there's no need to conduct in vivo

interaction studies based on these CYPs targeting

only these CYPs.

DR. VENITZ: That's what it says.

DR. SADEE: Okay; well, if it's clear--

DR. VENITZ: Okay; so everybody then

understands the question.

Okay; then, let me randomize the way we

vote, because I was advised by our statistician

that I was biasing the Committee.


DR. VENITZ: So let's start with Dr.


DR. WATKINS: I agree with that statement

as a general statement. I could think of specific

instances where even if you didn't show inhibition,

it might be prudent to do an in vivo interaction

study. And the other thing is just to emphasize

that the devil is in the details. For instance,



we've talked about, Shiew-Mei, it's standard, I

believe, within industry to use two different

substrates for 3A4 and in vitro studies, a big one,

a little one, reflecting the fact that it can act

like two different enzymes.

And since that survived through the Basil

consensus and the PhRMA document, there would have

to be new data, I would think, to take it out of

the FDA's guidance now, which then leads to the

problem what do you do with that information if one

substrate group inhibits and one doesn't?

I mean, those sorts of details, I think,

will come back as industry response. But as a

general statement, yes.

DR. VENITZ: Dr. Sadee?

DR. SADEE: I think I agree with it with

some hesitation, you know, that it doesn't state

that you don't need to do in vivo interaction

studies. It's just that you don't need to do it

for that reason. So if I understand that

correctly, my answer is yes.

DR. VENITZ: Dr. McLeod?




DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. Hall?

DR. HALL: Yes.

DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: I'll abstain as a

statistician here who doesn't have the expertise to


DR. VENITZ: Okay; fair.

Dr. D'Argenio?


DR. VENITZ: Dr. Capparelli?


DR. VENITZ: Dr. Blaschke?


DR. VENITZ: Dr. Barrett?




DR. VENITZ: And I would add my yes, but I



DR. VENITZ: --I don't like the way you

define absence of inhibition in vitro. 0.02 to me

is too conservative.

DR. HUANG: Okay; before I go to the next

question, I just want to clarify: in our concept

paper, we did recommend to use two different CYP3A

substrates, and if either of them shows positive,

then, this, then, you would need to do an in vivo


The next three questions are related to

PGP transporter, and this was a very statement from

the April discussion of this Committee that if a

new molecular entity is an inhibitor of PGP in

vitro, then, there is a need to conduct an in vivo

study using digoxin or other suitable substrates.

DR. VENITZ: Okay, any discussion?

DR. DERENDORF: I think we have to define





DR. GIACOMINI: Shiew-Mei, are we going to

use the same I over KI in the same way, in the same

spirit that we do?

DR. HUANG: Well, for the PGP, what we

have seen, at least, in the submissions is you use

the in vitro system such as CAPO2 or other system

where you look at A to B--or, I'm sorry, this is an

inhibitor, so you'd look at the effect on digoxin,

a labeled digoxin transport, and when there is an

effect, which we do not define, but you could look

at, such as quinidine effect, as a positive


I mean, we did not specify the detail in

this guidance, but if the Committee thinks it will

help to have a detailed appendix just like we have

for the CYP enzyme, we could do that. We have not

done it, because as we have heard earlier, there

are different ways of conducting it. There's not a

standardized way, although based on the digoxin

study, we often can conclude that this drug is an

inhibitor of PGP, based on its effects on digoxin

or other substrates transport.



DR. DERENDORF: But you need some

quantitative cutoff here, some quantitative cutoff

to make that decision whether it is or it is not.

So what would that be?

DR. HUANG: Okay; we have not specifically

stated, but usually, when we have this submission,

it will say this is an inhibitor, based on either a

statistically pure t-test. I mean, that's what we

have seen in the submission, to show there is a

difference in the transport, A to B, B to A for the

digoxin or compared to a quinidine effect, and it's

comparable, or maybe a certain percentage of it.

DR. DERENDORF: But that wouldn't really

be consistent with the first approach, because

there, we standardize it to the I, to the

concentration that we have, so I think we need to

do that as well.

DR. HUANG: Okay.

DR. GIACOMINI: I mean at least be

measuring in the therapeutic range, you know,

somewhere in the therapeutic range and then look at

the inhibition then.



DR. HUANG: I'm sorry; for some reason

standing here, it's hard to hear.

DR. GIACOMINI: So I'm just saying, I'm

just agreeing with Hartmut that in fact, it's good

to at least standardize that in some way. So I

like your idea of comparing, having a comparison

with quinidine and dig, that comparison, but I also

like the idea of, you know, making sure you're in

the therapeutic range, where you're seeing an

inhibition in and around this. I kind of like I

over KI as being just sort of a guidance.

DR. HUANG: Okay; so, should I amend the

question so that it would be similar to the first

one, that we are going to recommend something on in

vitro data? We probably will use I over KI, the

ratio, and suggest, say, for example, with--this is

what you see, and compare to a standard. Then,

based on that, we'll come to this question.

So I guess the recommendation is we have

something in our concept paper, in the guidance.

DR. HALL: I think staying away from the

phrase therapeutic range would be good, because at



this point, they have no idea what the therapeutic

range would be at this point in the history of the

drug, right?

DR. WATKINS: The other part of that is

the choice of probe, and I think if you say digoxin

or other suitable substrate, everyone will do

digoxin until there are other suitable substrates

in the document. And, you know, it's a dilemma,

because digoxin may be the best substrate, but we

know it's transported by other transporters.

Furthermore, you give, you know, a tenth

of a milligram, and it all gets in. So it gets by

an absorption MDR-1 gene product, p-glycoprotein.

So there's some intuitive disconnect about using a

digoxin, and you're clearly not evaluating the

intestinal component, and whether something else

like fexofenadine would be better; you know,

unfortunately, we still don't know the answers to

it, and that's the reservation that I have at this

stage about recommending, you know, an in vitro-in

vivo algorithm. But I don't know the alternative;

I don't know what else to do.



DR. VENITZ: And that's exactly the reason

I'm going to vote against this question. I don't

think the science is there yet. I don't think we

know necessarily which in vitro transporter--not

transporter but probe substance to use. I'm not

sure whether digoxin is the most informative

clinical substrate, so maybe in a couple of years,

we'll know that. Right now, I don't think we can

make the same jump that we make in terms of your

question one.

DR. HUANG: Yes, in the current

submissions, we have seen studies done with digoxin

and fexofenadine.

DR. GIACOMINI: Can I comment on that

also, on the digoxin?

DR. VENITZ: Absolutely.

DR. GIACOMINI: I mean, digoxin, there's

multiple lines of evidence, certainly, that it's a

PGP substrate: cell culture, knockout mouse;

there's a quinidine interaction that's gone

through--in my mind, it goes through sort of all of

the tiers in terms of levels of evidence in terms



of whether it is, it's not metabolized, so it's an

ideal substrate to use, and then, the specific

inhibitors, even if they have studies of the

drug-drug interaction in a knockout mouse, which

they're looking at quinidine-dig interaction, and

the quinidine-dig interaction doesn't occur in the

knockout mouse, and it does occur in the wild-type


So that, again, suggests that that

particular interaction is pretty--

DR. VENITZ: I don't doubt that digoxin is

an in vitro and in vivo PGP substrate.


DR. VENITZ: It's just that the main thing

that we're concerned about is PGP as it relates to

drug absorption, and I don't think that's where the

major--where digoxin has a problem. Digoxin has a

variability of 70 to 90 percent.

DR. GIACOMINI: Right, right.

DR. VENITZ: So I don't think that's the

best in vivo substrate to find out whether some in

vitro inhibitor is actually going to change



protease inhibitor absorption. That's my concern.


DR. VENITZ: So I'm not doubting that

digoxin is a PGP substrate, but I don't think we're

testing for absorption interactions, which are the

ones that I'm personally most concerned about.

DR. GIACOMINI: But then, in the absence

of that, I mean, if you don't put something in the

guidance, then, even a dig study isn't even done at

this point, because this is a recommendation to say

that we need a clinical study. If you've got a PGP

substrate inhibitor, your enemy is that PGP


Should you carry out a clinical study with


DR. VENITZ: Maybe in a couple of years,

we'll find fexofenadine or some other model

substrate is a better one. Maybe we'll find better

ways of assessing the in vitro potential to


DR. BARRETT: I think the original

intention of this was to be purposely vague so that



you would have a little bit of freedom to define it

as you saw fit. So, you know, even though the

original comment was to standardize between the

first two questions, it may be written okay as far

as the spirit of being able to recommend, assuming

the sponsor has done some studies here, not to do

an in vivo study, assuming they have some

compelling data on the in vitro side.

DR. SADEE: Your concern may be mostly

related to bioavailability, but this also relates

to other endpoints, such as do you get your drugs

into lymphocytes in HIV patients, and that may be a

very large effect. You cannot assess this with

pharmacokinetics necessarily.

So is that--you're only talking here about

an in vivo study that includes measurement of drug

levels in plasma and area under the curve; is that



DR. SADEE: And if you have that, say, you

know certain target tissues, you would not

necessarily consider that--



DR. HUANG: Right, right, and just to

remind the committee that there is some

recommendation from the April meeting that digoxin

even is not the perfect substrate for PGP for all

the reasons we just heard, because of the clinical

significance on the change in digoxin, and that

was, at that time, digoxin was proposed as one

substrate to consider if the drug is a PGP

inhibitor. I know not everyone from that committee

was here today, are here today.

DR. VENITZ: Okay; any other comments,


Then, let's go the opposite way. So, Dr.

Barrett, you go first this time.


DR. VENITZ: Okay; Dr. Blaschke?


DR. VENITZ: Dr. Capparelli? Oops; sorry.

DR. CAPPARELLI: Took my spot.

DR. VENITZ: I'm going alphabetically

according to the seating order.

DR. BLASCHKE: My answer is yes, but I



would also just comment that I think that there's

been a couple of important points made, and that if

a drug is a PGP inhibitor, there may be a lot of

other kinds of clinical studies that might fall out

of that, as was suggested, perhaps those that

affect drug transport into cells, et cetera. But I

think this is an appropriate place to start.

DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain.

DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. Watkins?

DR. WATKINS: Yes, if it is further

quantified what degree of inhibition and at what


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?

DR. HALL: Yes.

DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. McLeod?




DR. VENITZ: Dr. Sadee?

DR. SADEE: Abstain.

DR. VENITZ: Dr. Watkins?

DR. WATKINS: Yes, and just to comment, I

was glad Shiew-Mei clarified that, because I

remember when the first guidances were put

together, the point was made that the FDA has to be

concerned about safety and should not be dictating

science, and in that sense, digoxin is a very

relevant interaction. A lot of people on it;

neurotherapeutic index. And so, it's a reasonable

substrate from that aspect, although

scientifically, it's not perfect, so yes.

DR. VENITZ: All right; and my last vote

is a no, which according to my count, gets us two

noes, three abstains and eight yeses.


DR. HUANG: Yes; the next question is

about a new molecular entity as a substrate for

PGP, and I need to clarify this here. When we have

the concept, when we have the guidance, we would



talk about how do you determine as a substrate, and

this would be one of the ways is to look at one of

cell systems and look at A to B, B to A, base

lateral to applicable transport and look at the

difference between these two.

And so, if you determine it to be a

substrate in vitro, and actually, the next two

questions are related: number one is to consider

the CYP3A status in making the recommendation, and

then, number two, the question is whether it's

proper to evaluate PGP-based interaction when the

new molecular entity is a substrate. So they could

be commented together. And when you say yes and

no, I think it's probably more informative to also

discuss the examples we used here, whether these

are appropriate examples to give.

DR. VENITZ: Any comments?

DR. GIACOMINI: Yes, so, in terms of three

and four, when you conduct a clinical study, what

we would be interested in at that point when a

clinical study is conducted is since this is the

substrate is what the inhibitor is, what inhibitor



to use in a clinical study. And since, of course,

this is one of those cases where we're going to

have to use an inhibitor that's going to be an

inhibitor, probably, of a transporter and an

enzyme, PGP and CYP3A4, for example, something like

that; so I guess I want to say that from my point

of view, three and four are hard to pull apart, you

know, because I don't see that I could pick an

inhibitor for three that didn't work for four. So

I would lump the two together, whether your NME is

a substrate of PGP alone or whether it is a

substrate of PGP and a CYP 3 and 4.

DR. HUANG: One of the reasons I did that,

because if this drug is a substrate of 3A, when we

assess interaction, we would recommend to use a

strong inhibitor.


DR. HUANG: The inhibitor that we

recommend in question three, four, they're not

strong 3 inhibitors.

DR. GIACOMINI: Okay; okay.

DR. HALL: So I guess it again comes down



to the details of whether such--whether there are

such inhibitors that can be used in some sense

ethically in these types of studies, and, you know,

ritonavir, for sure, there are concerns with it.

We've heard cyclosporin, verapamil, there are

concerns with those that the IRBs commonly express,

and so, in practice, I think there are some issues

with this.

I think, you know, the general principle

of the question, I don't think people would

disagree with. But whether you can execute that on

a large scale is another issue. And I'm not

convinced that these are reasonable choices of

inhibitors to be used for these types of questions.

DR. HUANG: Yes, one standard for us to be

putting on something the guidance to make a

recommendation is we have to have something that is

a general inhibitor that we will agree to, and it

can be used in a study. So if none of these are

practical inhibitors, then, we probably would not

be able to put that in the guidance or




DR. VENITZ: And that means we should vote

no, right?

DR. HUANG: If we couldn't think of any,

or we could put in a general statement instead of

putting the examples if these are not--well, one

question is we have to agree that when we found

that a drug is a substrate, then, we would

routinely conduct a study in vivo. That was one of

the important questions.

DR. VENITZ: Any other comments?

Go ahead, Terry.

DR. BLASCHKE: Well, just a comment about

the ritonavir. I think single dose ritonavir,

Steve, would not be a concern; certainly not a

multiple dose study with ritonavir, but certainly,

I think a single dose study with ritonavir would

not be a safety concern.

DR. HALL: Would that work, though, to get

the full interactive effect of ritonavir?

DR. BLASCHKE: We've done single-dose

studies with ritonavir looking at interactions, and

it's certainly a potent inhibitor even with a



single 400-milligram dose, yes.

DR. CAPPARELLI: But there still is a

specificity issue with ritonavir. In terms of

depending on the compound that you're looking at,

it's not just 3A and PGP, so you still have those

issues of what's, you know, how do you apply the

results that you get.

DR. WATKINS: Can I--yes, just I realized

it was helpful to me to think about, you know, why

we're being asked these questions. So with

digoxin, you know have a PGP inhibitor. You go to

a digoxin study. If it's a negative interaction

study, unfortunately, it doesn't mean you won't

inhibit PGP in the intestine and other things. But

here, I think the implication is if you have a

substrate for both PGP and 3A4, and you don't have

an interaction with ritonavir, you can stop. There

are no more rocks to turn over. That's the end of

the drug interaction considerations.

And I actually agree with that. But I

think that's the question. And then, the next

thing is if it's a PGP substrate but not 3A4, of



course, you could do ritonavir again. But being a

little more specific, again, sticking with

clinically relevant interactions, you do the

cyclosporin study. If that's negative; you're

done. You don't have to do anything else. And I

think I agree with that, too.

DR. HUANG: Yes, one of the reasons we put

in cyclosporin here for discussion, because it

affects a lot of transporters, not just PGP. And

so, as you said, if you do a study, and it's

negative, it's a very good information.

DR. WATKINS: With a positive control,

obviously. You've got some other probe; you're

showing that cyclosporin got in the right place in

the right concentrations, et cetera, but--

DR. HUANG: Right, right.

DR. VENITZ: So is this question, then,

supposed to read if the NME is not a substrate for

PGP and not a substrate for 3A4, no clinical study

will have to be done? Because I think that's what

I heard you say, Paul, right?

DR. WATKINS: Yes, I think we already



decided that, didn't we? I mean--oh, I guess no,

we didn't. You're right, no, no, we didn't decide


DR. VENITZ: We talked about inhibitors;

we didn't talk about substrates.

DR. WATKINS: That's true.

DR. VENITZ: So are we here saying if the

in vitro is negative, stop; no further clinical

study? Are we saying if the in vitro is positive,

a clinical study has to be conducted? Because

that's the way I read this question.

DR. HUANG: Right, but Paul was going one

step further: if it's a substrate, and you did a

study with a cyclosporin or ritonavir, then, you're

pretty confident that other future transporter

inhibitors will not have an effect. It's just

cyclosporin and ritonavir inhibits a lot of

pathways, not just PGP.

DR. WATKINS: In other words, it doesn't

matter that it's not specific; it's just the

maximum way to knock out those two pathways. And

if that has no effect, and the study is done right,



you're done. You don't have to do anything else.

DR. BARRETT: Shiew-Mei, it strikes me

when I look at the questions that there's a

decision tree that's going to fall out of this,

assuming that the yeses and noes fall in the right

path. And if you could superimpose history on top

of what you're going to come up with at the end of

this, is there some idea of the sensitivity and

specificity of what that kind of a proposal would

look like, or can you do a kind of scenario testing

to this? I mean, you have the benefit of looking

back on a lot of development programs that have

made it to market.

So if you look at the decision tree based

on, you know, taking away those kinds of studies,

you know, would you arrive at the right--where you

think you want to be, I guess, with this kind of a


DR. HUANG: I think this will be the

beginning of gathering some information. I don't

think we are at the stage yet that once you did a

study, if it's a positive, what else do you need to



do? I mean, with the cyclosporin study, if it's a

positive, you probably will report this in the

labeling. If it's negative, you could say a lot of

things that it does not affect, and probably, the

other PGP inhibitors will not be able to--

DR. BARRETT: You know, I know you're

laying this out prospectively. This is something

we want to put forward as, you know, moving

forward, but if you applied this kind of an

approach back to historical agents, where you had

the benefit of in vitro signals and in vivo

studies, you know, I just wonder where you think we

would end up. Do you have that kind of

information, or has the working group looked at any

of that?

DR. HUANG: We started to construct a

decision tree based on in vitro and how that

compares with digoxin; then, we decide whether to

do an in vivo. But once we reach an in vivo, we

haven't had enough information to say what to do.

For CYP3A inhibition, it's very easy. We

say if there's no interaction with medazolam, you



stop. If it does, then, you continue with other

sub, like, sensitive substrates or other

coadministered drugs. And we do have that layout

in our good review practices.

For PGP, we don't have that, partly

because many of the inhibitors that we're talking

about are not specific for just PGP, but I would be

happy to have any input from the Committee members.

DR. VENITZ: Are we ready to vote?

Go ahead.

DR. JUSKO: When I look back at your

slides and look at the severity of the

interactions, the first question we examined looked

at digoxin AUCs and the presence of quinidine, and

there's a 2.5-fold increase in AUC. So it's a

moderate interaction. The ritonavir interaction is

extremely strong, a 50-fold change, it looks like

to me.

But for question four, the single

interaction, it goes back to about a 2.5-fold, so

some consideration needs to be made upon what we're

going to learn and how important these interactions



are, and it looks like number three there is a very

important one; but going back to number two and

number four, they're not quite so important that we

need to do these clinical studies.

DR. HUANG: When you say number two,

number four, you mean the questions?

DR. JUSKO: The degree of interaction

demonstrated in previous studies in relation to the

benefit gained from doing these kinds of studies.

DR. HUANG: Okay; as mentioned earlier,

digoxin, because it's a high bioavailability and

others, so the extent of interaction may not be as

great. But we know for digoxin, 2.5-fold increase

is definitely important. And so far, since it's

probably the best substrate that we have as far as

PGP specificity is concerned and also the clinical

significance that the change in digoxin is

important; that's why we recommended it.

But if you're talking about the drug as a

PGP substrate, then, we don't know yet. Perhaps

the ritonavir and cyclosporin will have a very high

degree of interaction, cyclosporin and rosuvistat,



and that's one other transporter, has sevenfold

increase. So it depends on the substrate that

we're talking about right now. We're talking about

the new molecular entity as a substrate, so

depending on its kinetic or disposition

characteristic, you probably will have much higher

extent of interaction compared to digoxin.

I use digoxin just because it's what we

have. If you look at fexofenadine or others, those

are nonpure PGP substrates. You might see a

different extent of interaction.

DR. VENITZ: That's exactly the problem I

have with both of those questions. I don't know

anything about the NME. I don't know anything

about the degree of absorption. If it's 90 percent

absorbed, PGP, it's probably not particularly


DR. HUANG: But we did see--we don't know

the mechanism of interaction, but we know about


DR. VENITZ: I understand.

DR. HUANG: But for ritonavir and



vardenafil, we have 50-fold increase. Cyclosporin

and rosuvistat, we have sevenfold. So we're seeing

a great degree of interaction, possibly because of

some transporters.

DR. VENITZ: But you don't know whether

it's based on the fact that they're PGP substrates

is my point, so you're using some in vitro tests

that may have nothing to do with the interaction

that you're going to find when you look at

ritonavir interaction.

DR. HUANG: If they're a substrate of PGP,

we know ritonavir and cyclosporin, they do inhibit.

DR. VENITZ: Right, but it could be that

by giving ritonavir, something else is going on.

They did it in--

DR. HUANG: Correct.

DR. VENITZ: Okay; the second question or

concern that I have, what is the exposure response,

and what's the side effects or the negative utility

that--what are the stakes, basically? I mean,

here, you're not looking at the effect of the drug

on something else but of something else on the




DR. HUANG: Correct.

DR. VENITZ: So unless you know that, I'm

not sure whether you can give it a clear-cut yes or

no answer.

DR. HUANG: Right; we definitely put that

into consideration when we interpret a drug

interaction. For a drug that's a substrate of 3A,

we don't ask what is the exposure response before

we recommend an interaction study. We want to look

at interaction, what is the maximum effect of

interaction, and then, see whether they're within

that exposure response or not. And we don't say

that this drug has a very wide therapeutic range;

therefore, you do not need to study an interaction.

DR. VENITZ: But I think we know more

about 3A-4 interactions than we knew about PGP


DR. HUANG: Okay.

DR. VENITZ: That's my--

DR. HUANG: All right.

DR. VENITZ: Any other--



DR. CAPPARELLI: I still have a question

on the yield on number three, and, you know, if you

really look at 3A substrates, are you really going

to catch anything extra by doing a ritonavir

interaction study? In other words, are there

examples where doing these interaction studies

surprises you and shows you no interaction?

Because the single dose PK is not going to reflect

what's going to happen in any clinical situation;

in other words, it will show you sort of the

maximal effect of wiping out a lot of systems, but

it's not going to tell you--you know, I'm wondering

if it's going to tell you enough to really justify

that study versus doing something more specific and

moving on from there.

DR. HUANG: Right. But doing a single

dose study might be able to tell us whether there's

a pharmacokinetic interaction, and we may not be

able to assess a dynamic or other additional

response. We know that.

DR. VENITZ: Okay; are we ready for a




Then, let's start with Dr. Watkins:

question number three.

DR. WATKINS: Yes; do them one at a time,

or should I do four with that?

DR. VENITZ: Do both of them.

DR. WATKINS: I would say yes to both, and

the only suggestion I would have, and I understand

the problem probably with doing it, is having been

involved with certain drug approvals, often, the

interpretation of guidelines differs not only from

company to company but even within the agency.

So I would suggest rewording. It says

that you should do this. I would say that if you

do this, and it's negative, you don't have to do

anything else; I mean, just to clarify what I think

is really the essence of the message that will get

upper management and pharmaceutical companies very

excited about the work they don't have to do.

DR. VENITZ: Okay; Dr. Sadee?

DR. SADEE: So, what am I voting for?

DR. VENITZ: Three and four.

DR. SADEE: Well, as it stands, on three,



I have to abstain, and four, I say no.

DR. VENITZ: Okay; Dr. McLeod?

DR. MCLEOD: Three yes, four no.

DR. VENITZ: Dr. Jusko?

DR. JUSKO: Three yes, four no.

DR. VENITZ: Dr. Hall?

DR. HALL: Three yes, four yes.

DR. VENITZ: Dr. Giacomini?

DR. GIACOMINI: Three yes, four yes, and I

like Paul's suggestion.

DR. VENITZ: Okay; Dr. Derendorf?

DR. DERENDORF: Three yes, four yes.

DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain and abstain.

DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain to both.

DR. VENITZ: Dr. Capparelli?

DR. CAPPARELLI: Three no and four no.

DR. VENITZ: Dr. Blaschke?

DR. BLASCHKE: Three yes and four yes as

amended by Paul.

DR. VENITZ: Dr. Barrett?



DR. BARRETT: Three no, four no.

DR. VENITZ: And I have no on three and no

on four. So we've got seven on question number

three; we've got seven, yes; four, no; two abstain.

Is that right? On question number four, six yes;

five no; and two abstain.


DR. HUANG: This question is trickier,

because right now, we say for inhibition

interactions, focus on the five major CYPs and

their emerging data on the importance of CYP2B6,

2CA, UGT1A1 and possibly other drugs. So this is

more of asking whether there are other CYPs that

seem important, because we know there are quite a

few drugs that are a substrate of 2CA. So whether

it's important to evaluate the inhibition

potential, of the other drugs, when you answer, you

could include others or maybe a specific set, only

certain CYPs that are important to evaluate right


DR. VENITZ: Any comments?

DR. WATKINS: One of the issues in the Bay



Call litigation is whether 2CA inhibitions should

have been routinely part of drug development back

in the, I guess, the midnineties, and it would

certainly seem, for those who don't know,

gemfibrizol inhibiting 2CA appears to be a relevant

mechanism for the rabdomyalisis there. And it

would seem to me if you knew and demonstrated that

your drug was largely metabolized by 2CA, it would

now be incomprehensible why you wouldn't do

interactions at least with gemfibrizol.

So certainly, for 2CA, it would seem to me

that should be part of the guidance.

DR. HUANG: We actually have a case where

we did recommend a study with gemfibrizol with a

2CA substrate. And now, the question is if a new

molecular comes in, do we need to ask routine

evaluation of in vivo interaction with CYP2CA


DR. WATKINS: So for clarification, are

you saying when there's no evidence from in vitro

studies that it's metabolized by 2CA?

DR. HUANG: Yes, right now, we're talking



about the effect of new molecular entity on others.

If this new molecular entity is a CYP2CA substrate,

because they're not the substrate of the other five

major CYPs, and 2CA is a major substrate, then, we

would recommend a study with the two CYP2CA

inhibitors that based on literature data.

But my question right now is if a new

molecular entity, when we evaluate its ability to

affect other drugs, do we routinely ask to evaluate


DR. WATKINS: I think I understood it

correctly, and my answer would be yes, that that's

a relevant pathway for certain statins and already

has a track record of problems. It's Taxol's major

pathway; rosyglydazone; it would make sense to me

to incorporate that into the document.

DR. HUANG: So we would add to the five

major CYPs perhaps CYP2C8?

DR. WATKINS: I would say so, yes.

DR. VENITZ: What would be your UGT1A1

inhibitor that you would recommend be studied?

DR. HUANG: Right, actually, I would not,



but this is thrown out as a question partly because

we haven't seen significant interaction. I think

earlier on, there was a question about UGT1A1

inhibition or actually this morning about

irinotecan. I don't think we have seen an

inhibitor which can deplete the activity as much as

a poor metabolizer status that would cause the

depletion of the UGT activity, so we have not

putting that as a recommendation of evaluating a

drug's ability to inhibit UGT1A1.

DR. VENITZ: You want to take it off the

question, then?

DR. HUANG: We could, unless there are


DR. MCLEOD: Is it known how many

companies are not currently screening for these

three? Because many companies are already looking

at these three because of the known polymorphisms

and trying to predict risk.

DR. HUANG: For a new molecular entity as

a substrate of these, yes. This has been done.

But as routinely to evaluate its ability to inhibit



these, no, not consistently. And the latter one is

my question.

DR. MCLEOD: Right, thank you.

DR. SADEE: I think that clearly, we

should be somehow going on record to say that the

potential for interaction should be assessed.

Whether we would want to recommend for all these

three genes and their products to recommend

clinical drug interaction studies, that's a

different question. But I think we need to go

forward and say these are important potential

factors in drug-drug interaction.

So in particular, if we don't have any

inhibitors, it would appear to be difficult to

recommend at this point clinical studies.

DR. VENITZ: Larry?

DR. LESKO: Yes, I just wanted to make

sure I understood Paul's comments, because I don't

think this fits the Bay Call situation, because the

question, as Shiew-Mei's asking it, is if I have a

drug that is a substrate for these enzymes, not a

substrate affected by another drug for these



enzymes. So, in other words, if the enemy was a

substrate for these enzymes, would you want to do

clinical studies based on the in vitro? Isn't that

what you just said?


DR. LESKO: Okay; could you just rephrase

that so I understand the question?

DR. HUANG: Well, in our guidance, we

actually said as a substrate, it's important to

study other than the five major CYPs, because if

there are not substrates for those five major CYPs,

you need to evaluate, for example, 2B6, 2C8 and

others and UGT 1A1. You need to know if it's a UGT

substrate, so later on, we can see the variation in

genetics, how that affects the pharmacokinetics.

But right now, I'm asking whether it's

prudent to recommend routine evaluation of a new

molecular entity's ability to inhibit--that's not

the same as the substrate--to inhibit these


DR. LESKO: Yes. That's my point. Bay

Call didn't inhibit gemfibrozil. It was the other



way around.

DR. HUANG: No, no, no, but Bay Call,

cerebrostatin is being found to be a substrate of

CYP2C8 and other transporters and UGT. So

gemfibrozil would affect the part of the

interaction of gemfibrozil and cerefostatin could

be through CYP2C8.

DR. LESKO: Well, creating the scenario,

the scenario is the cerebrostatin is the new

molecular entity, and the question is does that

affect the metabolism of other previously-approved

substrates for these enzymes?

DR. HUANG: Right; it would not.


DR. HUANG: But to come back to Paul's

question, now, with a new molecular entity such as

cerebrostatin, if we have, if we know that it's a

CYP2CA substrate, based on the new concept paper,

we would have recommended a gemfibrozil type of

study. We did have that statement in our guidance,

our concept paper. We have said that if it's a




DR. LESKO: Right.

DR. HUANG: But as an inhibitor, okay, if

cerevosin is right here, other drug that's being

approved which may affect its, okay, say it's 2CA

or many of these glydazones, they're CYP2CA

substrates. So if another NME that we're

reviewing, should we ask that it be evaluated as an

inhibitor of CYP2CA, because they may interact with

many of the glydazones?

DR. LESKO: Yes; it's just two different


DR. HUANG: But I'm asking this question,

not the other question.

DR. LESKO: The new molecular entity could

be the so-called offending drug, or it could be


DR. HUANG: Yes, offending drug.


DR. HUANG: We're only talking about

offending drug here.

DR. LESKO: All right; it's the offender.




DR. WATKINS: And just, Larry, because

it's getting late, and I'm getting confused, too,

about the two different things, but it would be

like if somebody developed a new gemfibrozil which

was an inhibitor of 2C8, and that appears to have

contributed to the recall of Bay Call because of a

drug interaction, and so, we already have a

precedent that caused a serious problem, it only

makes sense to me to included 2C8 inhibition in

the, you know, the next test tube and the line of,

you know, recombinant enzymes.

DR. GIACOMINI: It says clinical study.

It's not whether to put it in the test tube.

DR. WATKINS: All right; so you meant in

terms of coming up with specific probes for 2C8,

for instance?

DR. HUANG: Yes, and I'm actually asking a

general question: should we evaluate the other

pathway besides the five major CYPs?

DR. WATKINS: Okay; because that's the way

she rephrased the question is that we know 3A4, you

know, 1A2, et cetera. Should we be adding 2B6 and



2C8 all the way back to everything? And my answer

is yes, that should be done, and I think an in vivo

study should be done if there's evidence of

inhibiting 2C8 in vivo. So I'm just going to carry

it, like, 3A4 through the whole process. That's

what I meant, anyway.

See, I realize this says just clinically


DR. HUANG: But it's clear based on what

you said.

DR. WATKINS: Whereas 1A1 and 2B6, I

think, is much less clear, but 2C8, there's a track


DR. HUANG: Thank you.

DR. HALL: I think given, of course, that

it passes the test of your definition of not or



DR. HALL: So if the I over KI ratio is a

certain number, then, whether we have other

inhibitors of 1A1 or not, the new entity would be a

good inhibitor of 1A1 predicted from that in vitro



study, correct?

DR. HUANG: 1A1? You're talking about


DR. HALL: The UGT1A1, for example.


DR. HALL: So, you know, in 2B6, even

though there's not many 2B6 substrates that are

sufficient, if you were to coadminister it with

one, you would be concerned if the I over KI ratio,

however we define it, is sufficient.

DR. HUANG: Right.

DR. HALL: So I don't see why these would

be special. You would simply treat them just like


DR. HUANG: Right. One of the reasons we

put it this here, in order for us to put in a

guidance, we need to have probe substrates,

inhibitor, inducers to recommend. So if we have a

good probe to recommend, then, we would put it in

the guidance. If we don't have a good probe--we're

talking about metabolizing enzymes, not the

transporters--then, we usually do not. But we did



put in 2CA, 2B6 substrates and inducers. I don't

think we have an inhibitor for 2B6 yet based on our

discussion in November. But I know what you're--I

understand your comments.

DR. SADEE: But I think there needs to be

another qualifier here. Those are minor

cytochromes in terms of quantity, and if a compound

is a substrate for 2C8, let's say, and it's also a

good substrate for 3A4, then, it doesn't make any

sense to study this in further detail. So it needs

to be said that the evidence suggests that there

are substrates and that this is the major pathway

of metabolism.

DR. HUANG: Correct, correct.

DR. VENITZ: Okay; are we ready for a


Okay; then, I think I'm going to start

with Dr. Barrett.


DR. VENITZ: Dr. Blaschke.

DR. BLASCHKE: As amended, yes.

DR. VENITZ: Dr. Capparelli?




DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain.

DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?

DR. HALL: Yes.

DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. Watkins?


DR. VENITZ: And I put my yes in, so we

have 11 yes, no noes and two abstains.

DR. HUANG: Jurgen, can I clarify, because



I have heard some say yes with the amendment. So I

assume the amendment was based on Dr. Watkins'

comment that we consider 2C8? And the others are

just as-is, correct?


DR. HUANG: Okay.

DR. SADEE: What about the other--it has

to be the major metabolic pathway.

DR. HUANG: Right; that's on the substrate

side. Here, we're talking about inhibitor.


DR. HUANG: The next question is related

to the transporters. We said does the current

evidence support recommendations that drug

interactions based on other transporters, such as

OATP or MRP, be recommended for clinical study

during drug development? And I believe because the

answers from questions 2, 3, and 4 are relatively

positive, so I guess we could move on to this one.

If those were negative, then, we wouldn't ask this

question, because PGP is much more developed a




So I would go ahead and ask number six.

DR. GIACOMINI: I think it's hard to do

this at the end of the day, to present all of the

evidence to suggest that something might be

clinically relevant for us to begin to put this in

the guidance. So I have some thoughts about it,

but it's--there are some other transporters:

OATP1B1 in particular is one that we should be

thinking about.

And what is the evidence there? Well,

there's good evidence, first of all, in cell

culture that OATP1B1 and the statins, interacts

with the statins. There is a genetic polymorphism

in OATP1B1 that has now been shown in three or four

clinical studies that when that transporter is

polymorphic, pravostatin levels then go up. So

there's polymorphism evidence; there is in vitro

cell culture evidence; there is drug-drug


Now, these are, again, not clean. So you

take a drug like pravastatin. It interacts with

OATP1B1. It's not a CYP substrate. And when you



give it with cyclosporin, which is dirty, you get a

profound eightfold increase in the area under the

curve. Similarly, pitavostatin, which is another

one which is primarily--it's not a CYP substrate.

It's primarily a transporter thing. When you give

pitavostatin, when you give cyclosporin with

pitavostatin, you see, like, a four and a half fold

increase in area under the curve. So they're

increasing clinical drug-drug interactions showing

or suggesting highly that OATP1B1 is involved, and

then, there's genetic data.

So it's one that I think we should

certainly be considering as part of this guidance.

That's one that you're asking me to present at

5:00. And then, the other area, which I don't know

how the Committee feels about this, is just renal

transport interaction. So I had read the 1997

guidance, and there's nothing in there about--at

least I didn't see anything in there about renal

transport interactions, and there are known

probenecid versus penicillin, even therapeutic

interactions that people use those two drugs



together, actually, to enhance the effects of


So if I have some thoughts about, you

know, if a compound is secreted or if your in vitro

studies are suggesting that they're interacting

with some of these OATs, kidney-specific OATs,

particularly OAT1 and OAT3 or kidney-selective

OCTs, OCT2, which is only in the kidney, then, you

may want to consider doing a probenecid interaction

study for the N ions, and then, for a CAT ion, you

might want to consider doing, for example, a

somatadine interaction, if that's--so those are

renal transport points, and I think it would be

appropriate to mention, at least in this guidance.

It's drug-drug interactions that should only

concern the liver.

DR. HUANG: And just to clarify, so if

we--I mean, we do have certain studies that we look

at the competition of ectosecretion on renal

levels, although the labeling only states the

drugs. We do not extrapolate to other

transporters, and we do not currently name the



transporters. Do you think we're at the stage to

name the transporters when we report this type of


DR. GIACOMINI: Well, okay, so, for OAT3,

there's a knockout mouse that when the OAT3 is

knocked out, the cephalosporin renal elimination

goes way down. So you've got knockout mouse

studies, and then, you have studies showing, you

know, certain affinities for OAT3. So those are

the two levels that you have for OAT3.

For OAT1, there's not a knockout mouse.

You just have cell culture evidence. And you know

that these anines are interacting.

DR. MCLEOD: Kathy, do you think it needs

to be so specific, though, in the language?

Because you've identified several different

families where it's important. There will be more

coming. You didn't mention the transporters, which

from your own work and others, are also going to be

important. I almost think, like, that the language

needs to be more general, saying transporters, any

transporter that's shown to be--any drug that's



shown to be a substrate for a transporter needs to

be followed up if it's a main route of transport;

if there's some data.

Because if we get into the point where it

has to be a--only a named transporter on the list,

even if you have it on the Web, and it's dynamic,

you know, it's too new--the field is moving too

fast for this guidance to be changing every couple

of minutes.

DR. GIACOMINI: Yes; I guess what I did

when Shiew-Mei asked me to consult was I just

looked for the most compelling examples, not the

ones that, you know, the field is moving fast, and

I think we would be changing every week. But the

statin interactions are pretty strong; in

particular, the statin interactions with OATP1B1

look pretty compelling right now. And then, of

course, the renal transport interactions, which

have been historically around for so many years are

more or less compelling.

But again, I feel like the--I, personally,

feel like it would be nice if people saw the papers



and got the irinotecan book, you know, something

like that on some of these so that they could see

the evidence themselves.

DR. MCLEOD: And I've had the benefit of

seeing you present this data and others.


DR. MCLEOD: And there is very good data

for a lot of these.


DR. MCLEOD: So I think you're right that

these are at least on people's radar screens.


DR. MCLEOD: I think the companies, most

of the big companies, you know, it is on their


DR. GIACOMINI: Yes, it is, but I don't

know whether it's ready for this guidance.

DR. HUANG: Just for information, we do

have--we have seen in vitro data or animal data on

various transporters. So the question from our

reviewers is are we ready to recommend a followup

when it's shown to be a substrate or an inhibitor?



And that's why I put in this question. And these

are real-time review questions.

DR. VENITZ: And I guess my sense is I

think we are ahead of the science. I mean, here,

you're setting rules for large regulated industry,

and I don't think we're there yet. So maybe if you

come back in a year or two years from now, we'll

have more information. That's my personal opinion.

We'll have more information. But right now, I

can't agree with that.

DR. GIACOMINI: And I think he can't agree

with it, because we didn't have the time to

present, although you didn't see the papers and all

of that, so you have to look at that and see where

the evidence is. But we just didn't have time to,

because there is, on one of them, at least, there's

more and more compelling evidence, but I agree.

DR. LESKO: Yes, one of the questions I

have is how do you translate information in a sort

of cutting edge area into a label? I mean, with

the CYP enzymes that we're quite familiar with,

there's studies done in vitro; there's studies done



in vivo, and then, we label compounds with

information about drugs that were not studied,

necessarily, but are part of a class of 3A

substrates that are sensitive or modestly sensitive

or something like that. So the value of the

information becomes larger in magnitude, because

you can extrapolate.

My question then becomes, in this area of

transporters, when you say this cephalosporin or

that cephalosporin, is it then only that

interaction that's of relevance? I.e., can you go

beyond that to say, well, it isn't just the two

drugs I studied in the clinical study, but it also

would apply to this drug and that drug and other

drugs. Do we know enough about the information to

get more out of the study than simply two drugs

interact; that is leveraging the information for

the package insert?

DR. BARRETT: I come back to Howard's

point here, though. I don't know that we need this

level of granularity. I mean, I think if you

rephrase this in a more open fashion, and you don't



need to tell your child don't put your hand on the

stove if you told him not to put it in the

fireplace. So I don't know that you need to do


DR. DERENDORF: Well, I also think that it

really depends. I think the general answer to that

is very, very difficult, and coming back to what

was said earlier about the exposure response

relationship, if there is a likelihood that this

may be relevant, that depending on the PKPD

properties of the compound, it's a different story

than when I have a very safe compound, am I really,

you know, if it happens or not, it's nice to know,

but it really wouldn't make that much of a


So I think that needs to enter the

decision tree, too, at some point.

DR. VENITZ: Any other comments?

Okay; ready for the vote, Dr. Watkins?

DR. WATKINS: I know it's a tough one. I

mean, it's so clear that transporters and uptake

transporters are going to be so important in the



disposition of drugs. And to come back to Bay

Call, there was some evidence of OATP inhibition

and things. But unfortunately, the science is so

new, there aren't good probes or understanding of

regulation-specific inducers. So I think anything

more than just encouraging, you know, more research

in the area is very hard at this stage. So I don't

know whether that's a yes or a no.

I guess it's a no, because, well, I guess

we don't even have--oh, there it is, yes, because

you're saying clinical study, and I don't think we

really have the tools to clinically study it other

than maybe pravacol for 1OATP, so I guess I'm no.


Dr. Sadee?

DR. SADEE: I agree with the principle

that wherever you find a single gene product to be

important in drug-drug interactions, it is

essential to study it further. And the evidence is

beginning to appear, but I cannot see that we can

prescribe clinical studies at this point. So I

would like to abstain, but I like a more general



approach here.

DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Jusko?

DR. JUSKO: On one hand, it seems highly

advisable that if a drug is following a certain

pathway, it's the major pathway, that any

interactions with it should be studied. But we

haven't been given enough evidence for this whole

arena for me to say yes as yet, so I'm going to say


DR. VENITZ: Dr. Hall?

DR. HALL: I think I would go with a no as

well given the context that others have already


DR. VENITZ: Dr. Giacomini?

DR. GIACOMINI: I'm going to go with a yes

that there are specified transporters that we could

be looking--requiring clinical studies on and

drugs, specific drugs.

DR. VENITZ: Dr. Derendorf?

DR. DERENDORF: I go with a no unless



there is evidence that there is a high likelihood,

so not as a general recommendation.

DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain.

DR. VENITZ: Dr. Capparelli?

DR. CAPPARELLI: For the specific

transporters listed there, I would have to say no,

but I think that the issue of putting a general

statement in would be highly recommended.

DR. VENITZ: Dr. Blaschke?

DR. BLASCHKE: I would agree with that. I

think there should be something in there about

transporters, something that can be updated.

DR. VENITZ: And Dr. Barrett?


DR. VENITZ: And I would put my no in with

the recommendation to maybe come back at a future

meeting and talk about specific transporters and

probe substrates, probe inhibitors.

DR. HUANG: One clarifying question, when



Dr. Watkins says maybe with the exception of

prevastat and OATP1B1, is that--did you say that


DR. WATKINS: Maybe. Was it intelligent?

I can't remember.


DR. HUANG: That's all right.

DR. WATKINS: I mean, that's why I'm sort

of torn with this. I mean, there is the pravacol

example, so there's a probe, but I don't know the

studies that have validated it. I think as Kathy

said, we really haven't heard much about

transporters here, so, you know, I'm all for

clinical study of these things, and that's all I

can say right now.

DR. HUANG: Okay, thanks.

DR. VENITZ: Okay; the final vote is three

yes, seven no, and three abstain.

DR. HUANG: The next questions are related

to induction.

Okay; so there are two questions: one of

them is on--maybe I'll go to question A first,



because that's how it was presented: if a new

molecular entity induction effect on CYP3A in vitro

is negative, and it's acceptable not to recommend

in vivo studies, not only just CYP3A but also 2C9,

2C19 and 2B6; if you do not agree with 2B6, we

could take it out, because right now, we're only

recommending the major CYPs: 1A2, 3A2, 2C9, 2C19.


DR. WATKINS: If I could just ask for

clarification from John, actually: you were saying

that phenytoin was negative, at least in one human

hepatocyte induction study, and you thought that

was because the hepatocytes might have been

maximally induced, in which case the positive

control would have been negative?

I mean, my question is, and maybe I should

put in a context, because I've talked to Shiew-Mei.

What we're really voting on here is the concept

that every single drug ever developed from here on

either is given to people and probes either singly

or in a cocktail are done to see if they induce it.

And if you don't want to do that, you can do



cultured human hepatocytes and see whether the

induction is 40 percent of a positive control, and

if it's not, then, you don't have to do those


And since the clinical studies are further

in development and requires a lot of drug and

everything, what it's basically saying is every

single drug ever developed from now on, you can

correct me if I'm overstating the case, has to go

through a human hepatocyte study at some point in

its development. Practically, I think that would

be the outcome.

And the concern that I have is just that

I'm unaware of the data that would really

standardize this thing as being a routine part in

drug development, and we heard about all of the

different cells, and if the liver is ischemic, the

pericentral hepatocytes are gone, and you just have

the periportal hepatocytes, and maybe people can

cryopreserve a whole bunch of hepatocytes from 50

different donors, so genetic polymorphisms is

important, and you can refreeze the same aliquot,



and it will all be standardized, and it will all

make sense.

But from my perspective, I have just not

seen any data to suggest it's that robust. Now,

that would be acceptable in my opinion because I

think it is the best single test for induction if

it weren't such a precious resource to us

academicians. I mean, I don't know how industry is

getting all these to do all these studies. I just

know that we academic people have a very hard time

getting them.

So I think there's a cost of, you know, of

doing this, and so, that's the basis of what I'm

saying. You mentioned that there is a clear

clinical significant drug interaction with

phenotone. It's on a short list of drugs where

induction is really important, and didn't you say

that it was negative in a human hepatocyte culture


DR. STRONG: Yes, this was in some data

that Ed had in his slide. You know, I think in

most studies, you'll find that it would meet that



40 percent criteria. I think what I was pointing

out was design of experiment is very careful, you

have to be very careful with; i.e., these

particular hepatocytes appeared to, you know, be

induced with their background or basal activity for

three or four was very high, compared to, say, even

looking at the figure A, which was the 2B6.

So what I was talking about was I still

don't know what number quantitatively would be good

myself, and I think that's what we're trying to

discuss here. I think a lot of it may be just due

to the particular hepatocytes you're using and the

design of the study.

You were mentioning, you know, the

availability. You know, that's a question I don't

know either myself. Certainly, folks here in PhRMA

would know. I agree with you that they're

expensive, but--

DR. WATKINS: Well the price is going to

go way up.

DR. HUANG: Right.

DR. WATKINS: --if we endorse this,




DR. HUANG: I'd like to clarify. The in

vitro methodology is only one additional method

that we think that could be used to evaluate

induction, but it's not required to have hepatocyte

studies done. It obviously can be achieved through

in vivo study. It could be a specific study; it

could be a cocktail study; it could be a population

study. We're just adding an additional tool that

we think is acceptable to study.

So it's important to the issue that you

raised, but this is only one additional tool. So

with that, I would like to amend my question:

based on the mechanism of induction that we have

heard through various nuclear receptors, I would

like to say if the induction in 3A is negative,

which could be in vitro or in vivo, that we do not

need to assess 2C9 or 2C19, because they would have

been coinduced. So if a negative 3A could prevent

us from conducting an additional study about 2C9 or

2C19, that's my question.

So it could be a different, because of the



mechanism of induction, so I'm amending my

question, number eight. Number seven is specific

about in vitro methods, so we can come back later,

but I'd like to amend my question, so that we don't

have to be considering the appropriateness of the

hepatocyte preparation.

DR. HALL: I think again, we have to

discuss the not or the negative part, how that's

defined. And I think, you know we could define it

rigorously like Dr. LeCluyse did, which

incorporated many aspects, including RNA

quantitation, which is quite rigorous and would be

comforting, I think. But that's an enormous

burden, then, I think, on the industry to not only

procure all the hepatocytes but to do all the other

parts to that that would make it a water-tight

conclusion that it's negative.

So I think again, it's one of those

questions where you really have to state what being

negative means. What would you accept as being


DR. HUANG: So what about if we have



conducted an in vivo study with medazolam, and it

shows no change in medazolam AUCs with this new

molecular entity? Could we say that you do not

need to investigate whether this drug also induced

2C9 or 2C19? And perhaps you're hinging on the in

vitro data to make that conclusion. I'm doing an

additional leap of--not leap of faith; if you look

at mechanism of induction. If they're coinduced.

DR. JUSKO: When you do inhibition

studies, you very nicely take into account an I

over KI ratio. These in vitro induction studies

lend themselves to calculating EC50 values for the

induction, and in addition, you can bring in a CMAX

for the exposures, expected exposures in animals or

humans. It seems like these kinds of quantitative

indices are needed to augment this kind of


DR. MCLEOD: We were presented with data

showing that hitting the nuclear receptor caused

induction of 3A4 and 2C9 and a bunch of others. I

didn't remember seeing any data saying that that's

the only mechanism for inducing 2C9, 2C19, and



whatever else you want to write up there.

So do you have any data to share with us

to help on the voting how--if there are any other

realistic mechanisms of induction? Because it

seems like there's got to be something else.

DR. HUANG: Maybe Dr. LeCluyse can address

based on in vitro. But I think the information was

that if you induce 3A through PXR, if the 2C9 and

2C19 through PXR, then, you would have seen it.

But as for other mechanisms, so far, we don't have

a drug which is a pure CAR--

DR. MCLEOD: I'm thinking of false

negatives, basically.

DR. HUANG: Right, we don't have a drug.

So far, we don't have a drug that's based on in

vitro data to show that's the case. Until we have

a drug which is a pure CAR receptor effective,

then, for now, then, I don't think we'll see a

false negative.

DR. LECLUYSE: So basically your concern

is is there something that might be missing

mechanistically, and is it as simple as we portray



it as these three nuclear receptors, which is

really what I'm proposing. And we have come, you

know, round and round with this ourselves over the

years. We've asked ourselves the same questions:

is it as simple as if you don't see a compound

activating CAR or PXR, is it sufficient to exclude

any other possible mechanism?

And what's interesting is that seeing all

the evidence to date, not only our own but out

there in the literature, including if you look at

all the observed, clinically significant drug

interactions that are due to induction, and to me,

that's the question, I think, that's at hand, you

can explain every one of those through these three

nuclear receptors. And I think, you know, I think

Wolfgang brought up a point about some of these

other cofactors and some of these other

transcription factors that are involved in just

normal gene regulation, and, you know, whether it's

basal expression or induced expression, they play a


But the question was the clinically



relevant drug interactions that have been observed

in those events could all be explained by these

three nuclear receptors or these three receptors.

And it seems at least for the human P450 enzymes

that they're regulated by these three receptors and

can be explained through these.

So, you know, we're convinced to, like,

here I say our evidence as well as others that

you're pretty much covering all your bases or most

of your bases through these mechanisms; that at

this point in time, that's where the science is at.

DR. MCLEOD: Thanks. You're on the


DR. BARRETT: Shiew-Mei, instead of maybe

considering whether or not this test is adequately

sensitive to protect against induction of the other

CYPs, I just wonder if this guidance needs the

burden of having that statement in it, because I

think if you don't have it, it's going to be up to

the sponsor to investigate induction where they

think it's appropriate.

If they see CYP3A4 not involved as an



inducer, they're not going to do those studies.

However, you may see, either with population

analyses or otherwise, some evidence for induction,

and in that case, they're going to have to

investigate it.

I mean, I understand the spirit of trying

to reduce the redundant studies or eliminate

unnecessary or noninformative ones, but this seems

to be an additional burden to the guidance that

maybe it doesn't need.

DR. WATKINS: Sorry, and then, I will shut

up, but there are things called gratuitous

inducers; there's things that induce pathways that

aren't involved in their own metabolism; so just

that it's not a 3A substrate doesn't mean that it

couldn't induce, you know, bind and activate PXR.

Let me give a hypothetical example:

there's a drug that there's been no induction study

in two animal models and an in vitro, you know,

PXR, you know, binding and transcriptional assay;

there's no effect at all. The question is

what--show me the data that the human hepatocyte,



cultured human hepatocytes is going to add

significantly to the decision making of whether an

in vivo study should be done there. I mean, what

is the human hepatocyte--I mean, just where is this

data that this is going to be worth this precious

resource on an industrial scale?

Relatively early in development, which is

where I would do it if this guidance came out, and

right at lead candidate selection is when I'd try

to do a cultured hepatocyte study just to know what

was, you know, coming down the line. And it just

strikes me that I've not seen this data. I mean,

for instance, all the drugs that are known to be

clinically relevant inducers, say, through PXR, and

the whole list of drugs that aren't at all, like

niphetapine, for instance, is a PXR ligand,

activates PXR, but there's no drug interaction that

I'm aware of that's due to niphetpaine inducing

metabolism through PXR. And Ed, you may know about


But where is the data that really

critically evaluates the added value of early human



hepatocyte studies for induction? We know the

receptors; we should be able to see whether they

bind them and activate them, and that should be the

initial step, and if it's negative, I want the data

that going to human hepatocytes is adding the

enormous costs and resource that that represents.

DR. VENITZ: Okay; Shiew-Mei, why don't

you rephrase the question so we can vote on it?

Because you were going to make an amendment, if I

remember correctly.

DR. HUANG: Yes, although no committee

members have commented on in vivo. If in vivo 3A

shows negative induction, and we should--

DR. VENITZ: Should say in vitro or in



DR. VENITZ: Okay; so what we're voting on

is question eight with the addition of in vitro or

in vivo.

DR. HUANG: And I would just comment on

2C9 and 2C19. If a new molecular entity induction

effect on CYP3A in vitro or in vivo is negative, it



is acceptable to not recommend any studies with

substrates of 2C9 and 2C19.

DR. VENITZ: Okay; I think we are starting

with Dr. Barrett this time.


DR. VENITZ: Dr. Blaschke?

DR. BLASCHKE: As rephrased, I think it's

acceptable. I'd say yes.

DR. VENITZ: Dr. Capparelli?

DR. CAPPARELLI: In the definition, in the

rephrasing of it, if there is no in vivo or in

vitro indication of inhibition, then, I would say

yes. So there's the situation where you may mask

induction by having inhibition as well.

DR. HUANG: We're talking about induction


DR. CAPPARELLI: No, I understand.

DR. HUANG: Oh, okay.

DR. CAPPARELLI: But, like, with

ritonavir, if you gave a drug that induced but also

inhibited, you may miss it in a 3A screen, and it

may still have an impact on induction if it's not



inhibiting the 2C system.

DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain.

DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?

DR. HALL: I think as rephrased, then, I

agree with what Paul is saying, but this doesn't

say anything about hepatocytes. It could equally

well be a reporter system. So in that context, I

think I would say yes.

DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. Watkins?



DR. WATKINS: I'm just getting irritable,

but I feel like saying no at this point. But I

think the qualification--


DR. WATKINS: --is if you know that it

acts through PXR, if you know that, at least from

the evidence I know, then, demonstrating it does

one of these things in vivo, you know, gives you

your answer. You don't have to test for all of


So if that means my answer is yes, then,

it's yes.


DR. VENITZ: You tell me.

DR. WATKINS: I still think that the human

hepatocytes is hooked in here somewhere into this,

but, I mean, they only go together if they're all

being activated by PXR. And it sounds like all the

data makes that acceptable. So the real issue is

does your drug activate PXR? And then, you can see

whether it induces one of these and assume the rest

go along. But there has to be that PXR link, I




DR. VENITZ: I think that would be a yes.

DR. WATKINS: Yes, that's a yes.

DR. VENITZ: Okay; I'll throw my yes in,

and we have three abstains, one no, and eight

yeses, okay?

Then, question number seven, Shiew-Mei?

DR. HUANG: Question number seven is early

on clarified by Dr. LeCluyse. When we say that the

in vitro induction, and here, we look at increase

in enzyme activity, is more than 40 percent of the

positive control, and the 40 percent could be any

of the three with a preparation, so the mean value

could be lower than 40 percent, but it's any one of

them, because you need to have them all lower than

40 percent before you would declare it's negative.

So with that clarification, the question

is is 40 percent the proper positive control?

DR. VENITZ: Okay; any questions or


DR. SADEE: But if you have an inhibitor,

ritonavir again, you get a decrease, so--



DR. HUANG: Yes, in our guidance, we

actually have some provision. You need to look at

the inhibition. If there's a mechanism-based

inhibition, then, you look at mRNA and other

parameters in addition to enzyme activity. So that

would have taken care of this.

DR. GIACOMINI: Is this the human

hepatocyte again for--


DR. GIACOMINI: It absolutely is. So it

sets it as a standard, then.

DR. HUANG: This is, yes.

DR. GIACOMINI: Like not a reporter or

anything like that assay.

DR. HUANG: Here it's human hepatocyte.


DR. VENITZ: Hartmut?

DR. DERENDORF: It needs to be related to

a concentration, as Dr. Jusko pointed out, some

EC52P concentration term in there.

DR. HUANG: Yes, here in the appendix of

the concept paper, we recommended if we know the



concentration that we expected using tenfold or up

to 100-fold of concentration. So you have a

spectrum of concentration because of sometime, you

see an expected U-shaped or inverted-U effect, so

we need to look at various concentrations. So we

did have some detail in the concept paper about

what concentration to use.

And right now, this question, we're

looking at the maximum, maximum induction, and we

did not take into account EC52, even as it was

discussed. But this particular criterion was based

on that.

DR. SADEE: But in the human hepatocytes,

you then have to screen for those that have low

basal activity in order to get a high percentage.

Is that correct or--

DR. HUANG: Yes, our only recommendation

is that you need to have positive control, and

positive control needs to work. And we did put in

a reference value in the guidance on what should we

expect when certain concentrations of rifampin are

incubated with this particular system. What should



we expect to see? And only when those values are

valid, then, we will consider this next step.

DR. VENITZ: Any other comments?

Okay; then, I think, Dr. Watkins, you're

the one to go first.

DR. WATKINS: Now, I'll say no.

You know, the implication here is that

human hepatocytes have been widely standardized,

and companies can sprout all up and come up with a

reliable 40 percent estimate and a cost-effective

way that will be like an Ames test and yes-no

determining the subsequent development, and I have

just not seen any data that supports that, so no.

DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. McLeod?


DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. Hall?

DR. HALL: I would like to say yes. I'm

not sure about the 40 percent, and the details are



important, but in principle, yes.

DR. VENITZ: Okay; Dr. Giacomini?


DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. D'Argenio?

DR. D'ARGENIO: Abstain.

DR. VENITZ: Dr. Capparelli?


DR. VENITZ: Dr. Blaschke?


DR. VENITZ: Dr. Barrett?


DR. VENITZ: And I throw my no in.

Seven noes, three yes, and two


DR. HUANG: The last two questions: as

related to the multiple inhibitor studies, and it's

a long question. We say is it acceptable to

recommend that under certain conditions, and in



particular, when we're evaluating QT prolongation

effect, it's important to determine the maximum

exposure of new molecular entities. Actually,

these are in the ICH guidance on QT. It was the

detail that we're asking for recommendation.

The maximum exposure, it's probably not

what we should be discussing for this guidance. I

mean, the comment should be for the other guidance.

But with that guidance recommendation, how would we

achieve the maximum exposure? We can do that with

a single inhibitor or multiple inhibitor, so this

would be the focus of discussion when there is more

than one pathway or under multiple impaired

conditions, such as renal impairment plus

co-administration of an inhibitor.

DR. VENITZ: A couple of comments: I'm

still not sure that you can't predict this based on

the individual interactions that you know, and

then, use modeling and simulations to predict what

the maximum exposure would be.

Number two, you obviously would want to do

this for drugs where the stakes are high, meaning



you're really worried about toxic effects. Well,

those are probably the ones that you ethically

couldn't do a study like this unless you reduce the

dose. Well, if you reduce the dose, then, you have

to have some idea about what to expect; in other

words, you have to do modeling and simulations to

figure out how to adjust your dose.

And the last thing is to do those kinds of

studies logistically to me is a nightmare, and I'm

not sure what you're gaining. Are you just making

up for lack of dose finding in phase two or phase

one where you didn't push the dose enough to

achieve some toxicity that you can identify? So I

don't see any purpose.

DR. HUANG: Is that the Committee


DR. VENITZ: Only speaking for myself.


DR. VENITZ: Any other comments?

[No response.]

DR. VENITZ: Are you ready for the vote?

Looks like it's late.



Okay; then, we're voting on question

number nine, and I think we're starting with Dr.



DR. VENITZ: Dr. Blaschke?


DR. VENITZ: Dr. Capparelli?


DR. VENITZ: Dr. D'Argenio?


DR. VENITZ: Dr. Davidian?

DR. DAVIDIAN: Abstain.

DR. VENITZ: Dr. Derendorf?


DR. VENITZ: Dr. Giacomini?


DR. VENITZ: Dr. Hall?


DR. VENITZ: Dr. Jusko?


DR. VENITZ: Dr. McLeod?




DR. VENITZ: Dr. Sadee?


DR. VENITZ: Dr. Watkins?


DR. VENITZ: It looks like I'm speaking

for the Committee, so I'm a no.

So we've got 12 noes and one abstention.

DR. HUANG: So we probably do not need to

ask about question number 10.

Originally, we were asking whether should

we consider individual factors first and then

recommend a study or after the modeling and

simulation. But since the answer is no, the only

final question, is there any other issues that we

should have been addressed in the concept paper?

We have heard comments that transporter-related

issues; we probably need an additional discussion

before we have some more general discussion, more

general recommendation or guidance.

But are there other areas where the

science is mature that we have not included in our

concept paper?



DR. VENITZ: Any suggestions, comments for

Dr. Huang?

DR. HALL: I notice one thing: it's not

so much something to add but maybe something to

think about taking out. You mentioned stimulation

several times, and to the best of my knowledge,

there are no examples of clinical drug interactions

due to stimulation. Maybe the guys at Merck have

some more information on that, because they've

worked on it, but that seems to be just an

unnecessary burden, I think.

DR. DERENDORF: I hope that this guidance

doesn't end up as a checklist with all kinds of

studies that are required independent of if they're

really needed or not from a response point of view.

I think each drug is different, and each

interaction has a different significance, and that

needs to be considered somewhere. And just to do a

study to do a study isn't good enough. So there

needs to be some flexibility based on the

individual drug.

DR. VENITZ: And I'd like to recommend



that as far as the process is concerned that

perhaps you could review with the Committee at a

future meeting not just the guidance per se but the

decision making process that is part of it, because

part of the issues that I think most of us had

wrestled with when you forced us to vote is to put

those questions in perspective, and I think some of

the votes may have gotten different results if we

had seen how that fits into the overall scheme,

such as recommendations for further process.

DR. JUSKO: Many years ago, Craig Brader

did some very nice drug interaction studies looking

at diuretics and their effects and found that it

was the drug in the urine that best represented the

biophase for the action of the diuretics and that

drug interactions, when looked at from the

viewpoint of plasma concentrations, were misleading

in terms of the clinical relevance of such


So perhaps something could be added to the

guidance about what may be the relevant biophase

for the activity of the drug and include that in



the measurements in the context of drug

interactions. The whole guidance speaks to drug

interactions in the pharmacokinetic sense, and of

course, probably in the next decade, you'll be

getting to drug interactions and pharmacodynamics.

DR. VENITZ: Any further comments?

Then let me turn the podium over to Dr.

Lesko, who is going to wrap up the meeting for

today, right?

DR. LESKO: Thank you. I'll do that right

from my seat here, and I'm sure I wouldn't be very

popular if I take more than 30 seconds, given the

hour of the day, to wrap up. So I'm going to be

kind and thank the Committee that we don't need to

ask for any recounts on any of the votes.


DR. LESKO: However, the discussion today

was extremely helpful to us, and we really

appreciate your thoughtfulness and the quality of

your discussions and questions, and we left here, I

think, achieving the goals that we set out for

early this morning.



So I want to express your appreciation for

today and the hard work that you've done and look

forward to another exciting and high quality

discussion tomorrow on our biomarker topic that

we'll be bringing to the Committee.

DR. VENITZ: Thank you, and then, one last

announcement: the Committee members, we are going

to meet for dinner at 6:30 in the hotel restaurant

right next door, so hopefully, we will see you all.

If not, we will see you tomorrow, bright-eyed,

bushy-tailed at 8:00 for the second part of this.

[Whereupon, at 5:33 p.m., the meeting was

recessed, to reconvene on Thursday, November 4,


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