1

 

                DEPARTMENT OF HEALTH AND HUMAN SERVICES

 

                      FOOD AND DRUG ADMINISTRATION

 

                CENTER FOR DRUG EVALUATION AND RESEARCH

 

 

 

 

 

 

 

 

 

 

                   ANTIVIRAL DRUGS ADVISORY COMMITTEE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                         Friday, March 11, 2005

 

                               8:00 a.m.

 

 

 

 

 

 

 

                             Salons A and B

                Hilton Washington DC North/Gaithersberg

                           620 Perry Parkway

                         Gaithersburg, Maryland

                                                                 2

 

                        P A R T I C I P A N T S

 

      Janet A. Englund, M.D., Chair

 

      Anuja M. Patel, M.P.H., Executive Secretary

 

      Committee Members:

 

      John A. Bartlett, M.D.

      Victor G. DeGruttola, Sc.D.

      Douglas G. Fish, M.D.

      John G. Gerber, M.D.

      Richard H. Haubrich, M.D.

      Victoria A. Johnson, M.D.

      Robert J. Munk, Ph.D. (Consumer Representative)

      Lynn A. Paxton, M.D., M.P.H.

      Kenneth E. Sherman, M.D., Ph.D.

      Eugene Sun, M.D. (Industry Representative)

      Maribel Rodriguez-Torres, M.D.

      Lauren V. Wood, M.D.

      Ronald G. Washburn, M.D.

 

      Special Government Employee Consultants (Voting):

 

      Samuel K. So, M.D., B.S.

      Kathleen Schwarz, M.D.

 

      Government Employee Consultants (Voting):

 

      Beth P. Bell, M.D., M.P.H.

      Ronald Herbert, D.V.M., Ph.D.

      Leonard B. Seeff, M.D.

 

      SGE Patient Representative (Voting)

 

      Brett Grodeck

 

      FDA Participants:

 

      Mark J. Goldberger, M.D., M.P.H., CDER

      Debra B. Birnkrant, M.D., CDER

      Linda L. Lewis, M.D., CDER

      James G. Farrelly, Ph.D., CDER

                                                                 3

 

                            C O N T E N T S

 

      Call to Order and Opening Remarks,

         Janet Englund, M.D., Chair                              4

 

      Conflict of Interest Statement, Anuja Patel, M.P.H.

         Executive Secretary, FDA                                7

 

      Overview of Issues, Debra B. Birnkrant, M.D.,

          Director, DAVDP                                       10

 

      Sponsor Presentation:

 

      Introduction, Elliott Sigal, M.D., Ph.D.                  16

 

      Background, Richard Colonno, Ph.D.                        20

 

      Nonclinical Safety, Lois Lehman-McKeeman, Ph.D.           28

 

      Clinical Efficacy and Safety, Evren Atillasoy, M.D.       37

 

      Resistance, Richard Colonno, Ph.D.                        58

 

      Pharmacovigilance and Summary, Donna Morgan Murray,

      Ph.D.                                                     70

 

      Questions from the Committee                              77

 

      FDA Presentation:

 

      Carcinogenicity Issues, James G. Farrelly, Ph.D..        108

 

      Clinical Issues, Linda L. Lewis, M.D.                    119

 

      Discussion                                               151

 

      Advisory Committee Discussion of Questions

                Question 1:                                    185

                Question 2:                                    202

                Question 3:                                    204

                Question 4:                                    221

                Question 5:                                    235

                Question 6:                                    267

 

                                                                 4

 

  1                      P R O C E E D I N G S

 

  2                Call to Order and Opening Remarks

 

  3             DR. ENGLUND:  Good morning.  Welcome,

 

  4   everyone.  My name is Janet Englund.  I am the

 

  5   acting chairperson today and I would like to

 

  6   welcome you to the Antiviral Drugs Advisory

 

  7   Committee.

 

  8             Today we are going to discuss the new drug

 

  9   application 21-797 and 21-798 for entecavir tablets

 

 10   and entecavir oral solution, respectively, by

 

 11   Bristol-Myers Squibb Company.  These drugs are

 

 12   proposed for the treatment of patients with chronic

 

 13   hepatitis B infection.

 

 14             With that, I would like to call the

 

 15   meeting to order and introduce the committee

 

 16   members.  In fact, I will have you introduce

 

 17   yourselves because that would be better.  I would

 

 18   like to just remind everyone on this committee that

 

 19   this is being transcribed and so, before you speak,

 

 20   you are going to need to identify yourself but, for

 

 21   now, if we could just start maybe with Dr. Sun and

 

 22   just introduce yourself and your affiliation.

 

 23             DR. SUN:  Eugene Sun, Abbott Laboratories.

 

 24             DR. GERBER:  John Gerber, University of

 

 25   Colorado Health Sciences Center.

 

                                                                 5

 

  1             DR. WASHBURN:  Ron Washburn, Shreveport VA

 

  2   and LSU.

 

  3             DR. FISH:  Douglas Fish, Albany Medical

 

  4   College, Albany, New York.

 

  5             DR. HERBERT:  Ron Herbert, National

 

  6   Institutes of Environmental Health Sciences and the

 

  7   National Toxicology Program.

 

  8             DR. SHERMAN:  Ken Sherman, University of

 

  9   Cincinnati.

 

 10             DR. JOHNSON:  Victoria Johnson, University

 

 11   of Alabama at Birmingham.

 

 12             DR. PAXTON:  Lynn Paxton, Centers for

 

 13   Disease Control and Prevention.

 

 14             DR. WOOD:  Lauren Wood, National Cancer

 

 15   Institute.

 

 16             MR. GRODECK:  Brett Grodeck, patient

 

 17   representative.

 

 18             MS. PATEL:  Anuja Patel, Executive

 

 19   secretary for the Antiviral Drugs Advisory

 

                                                                 6

 

  1   Committee, the Food and Drug Administration.

 

  2             DR. ENGLUND:  I am Janet Englund, from

 

  3   Children's Hospital and University of Washington,

 

  4   in Seattle.

 

  5             DR. DEGRUTTOLA:  Victor DeGruttola,

 

  6   Harvard School of Public Health.

 

  7             DR. BARTLETT:  I am John A. Bartlett, from

 

  8   Duke University.

 

  9             DR. HAUBRICH:  Richard Haubrich,

 

 10   University of California in San Diego.

 

 11             DR. MUNK:  Bob Munk, consumer

 

 12   representative.

 

 13             DR. SEEFF:  Leonard Seeff, Liver Disease

 

 14   Branch, NIDDK, National Institutes of Health.

 

 15             DR. BELL:  Beth Bell, Centers for Disease

 

 16   Control and Prevention.

 

 17             DR. SCHWARZ:  Kathy Schwarz, Johns Hopkins

 

 18   University.

 

 19             DR. FARRELLY:  Jim Farrelly, Division of

 

 20   Antiviral Drugs, FDA.

 

 21             DR. LEWIS:  Linda Lewis, Division of

 

 22   Antiviral Drugs, FDA.

 

 23             DR. BIRNKRANT:  Debbie Birnkrant, Division

 

 24   Director, Division of Antiviral Drugs, Food and

 

 25   Drug Administration.

 

                                                                 7

 

  1             DR. ENGLUND:  And Dr. Mark Goldberger,

 

  2   from the FDA, will be joining us momentarily.  At

 

  3   this point I would like to have Anuja Patel read

 

  4   for us the conflict of interest statement.

 

  5                  Conflict of Interest Statement

 

  6             MS. PATEL:  Thank you.  The following

 

  7   announcement addresses the issue of conflict of

 

  8   interest and is made part of the record to preclude

 

  9   even the appearance of such at this meeting.  Based

 

 10   on the submitted agenda and all financial interests

 

 11   reported by the committee participants, it has been

 

 12   determined that all interests in firms regulated by

 

 13   the Center for Drug Evaluation and Research present

 

 14   no potential for an appearance of a conflict of

 

 15   interest, with the following exceptions:

 

 16             In accordance with 18 USC Section

 

 17   208(b)(3), full waivers have been granted to the

 

 18   following participants, Dr. Johnson for her

 

 19   employer's contract with a federal agency to

 

                                                                 8

 

  1   provide virology laboratory support for the adult

 

  2   AIDS clinical trials group.  The contract is funded

 

  3   for greater than $300,000 per year.  Dr. Gerber for

 

  4   consulting on unrelated matters for the sponsor and

 

  5   a competitor.  He receives less than $10,001 per

 

  6   year per firm.  Dr. Bartlett for serving on

 

  7   speakers bureaus for two competitors.  He receives

 

  8   greater than $10,000 from one firm and between

 

  9   $5,001 to $10,000 per year from the other.  Dr.

 

 10   Sherman for serving on speakers bureaus for two

 

 11   competitors.  He receives from $5,001 to $10,000 a

 

 12   year from each firm.  Dr. Munk for consulting on

 

 13   unrelated matters for a competitor.  He receives

 

 14   less than $10,001 a year.

 

 15             Dr. Schwarz has been granted waivers under

 

 16   (b)(3) and 21 USC 355(n)(4) for her employer's

 

 17   grant to study competing products.  Each grant is

 

 18   funded for less than $100,000 per firm per year.

 

 19   Dr. Haubrich has been granted a (b)(3) waiver for

 

 20   consulting on unrelated matters for a competitor

 

 21   and the sponsor.  He receives less than $10,001 per

 

 22   year per firm.  Brett Grodeck has been granted a

 

                                                                 9

 

  1   355(n)(4) waiver for owning stock in a competitor,

 

  2   valued at less than $5,001.  Because the stock in a

 

  3   competitor does not exceed $25,000, 5 CFR

 

  4   2640.202(a)(2) exception applies and a (b)(3)

 

  5   wavier is not required.  Dr. DeGruttola has been

 

  6   granted a (b)(3) waiver for consulting on unrelated

 

  7   matters for two competitors.  He receives less than

 

  8   $10,001 a year from each firm.

 

  9             A copy of the waiver statements may be

 

 10   obtained by submitting a written request to the

 

 11   agency's Freedom of Information Office, Room 12A-30

 

 12   of the Parklawn Building.

 

 13             In the event that the discussions involve

 

 14   any other products or firms not already on the

 

 15   agenda for which an FDA participant has a financial

 

 16   interest, the participants are aware of the need to

 

 17   exclude themselves from such involvement and their

 

 18   exclusion will be noted for the record.

 

 19             We would also like to note that Dr. Sun

 

 20   has been invited to participate as an industry

 

 21   representative, acting on behalf of the regulated

 

 22   industry.  Dr. Sun is employed by Abbott

 

                                                                10

 

  1   Laboratories.

 

  2             With respect to all other participants, we

 

  3   ask in the interest of fairness that they address

 

  4   any current or previous financial involvement with

 

  5   any farm whose products they may wish to comment

 

  6   upon.  Thank you.

 

  7             DR. ENGLUND:  Thank you, everyone.  With

 

  8   that done, I would like to introduce Dr. Debra

 

  9   Birnkrant who will now proceed to give us an

 

 10   overview of the issues and our plan for today.

 

 11                        Overview of Issues

 

 12             DR. BIRNKRANT:  Good morning.  I would

 

 13   also like to welcome our advisory committee members

 

 14   and consultants to this meeting.

 

 15             Today, as was mentioned, we will be

 

 16   discussing the new drug application for the tablet

 

 17   and solution formulations for entecavir for the

 

 18   treatment of chronic hepatitis B infection.

 

 19             The last time this committee met to

 

 20   discuss a similar topic was back in 2002 when we

 

 21   presented the new drug application for adefovir,

 

 22   and on the second day of that meeting we discussed

 

                                                                11

 

  1   general drug development for hepatitis B.  Today's

 

  2   meeting gives us another opportunity to discuss

 

  3   this serious problem.

 

  4             The next two slides were downloaded from

 

  5   cdc.gov.  This slide shows the geographic

 

  6   distribution of chronic hepatitis B infection.

 

  7   What you can see in red are high andemic areas in

 

  8   Africa and Asia with hepatitis B prevalence at a

 

  9   rate more than 8 percent, and this is considered

 

 10   high.  In gold we have medium prevalence areas, and

 

 11   in green we have low prevalence areas, such as the

 

 12   United States, excluding Alaska.  In the high

 

 13   prevalence areas the lifetime risk of acquiring

 

 14   hepatitis B infection approaches 60 percent and is

 

 15   acquired mainly during childhood, whereas in the

 

 16   low prevalence areas the lifetime risk is much

 

 17   lower and occurs in adolescents, adults and

 

 18   well-defined risk groups.

 

 19             This slide shows hepatitis B incidence by

 

 20   year through the years 1966 through 2000 in the

 

 21   United States.  What this is dramatic for is the

 

 22   decline in hepatitis B occurring soon after

 

                                                                12

 

  1   licensure of hepatitis B vaccine.  You can see that

 

  2   the incidence drops dramatically over the years in

 

  3   the late '80s and beyond after public health

 

  4   programs adopted hepatitis B vaccination.

 

  5             Although we see this dramatic decrease in

 

  6   the United States of acute hepatitis B it still

 

  7   remains a major problem.  It has been estimated

 

  8   that chronic hepatitis B infection affects 350-400

 

  9   million subjects worldwide and approximately 1.25

 

 10   million subjects in the United States.  It accounts

 

 11   for, it is estimated, approximately one million

 

 12   deaths per year due to complications of the

 

 13   disease, namely cirrhosis and hepatocellular

 

 14   carcinoma.  The treatment options are quite

 

 15   limited.  As you can see, there are only three at

 

 16   this point, interferon, lamivudine and adefovir

 

 17   dipivoxil.

 

 18             I will briefly touch on the pros and cons

 

 19   of these therapies.  Interferon is used in a

 

 20   limited patient population, however, it is used for

 

 21   a definite period of time and in the limited

 

 22   population the effect is durable.  However, the

 

                                                                13

 

  1   side effect profile is somewhat limiting.  With

 

  2   interferon we see flu-like syndrome, depression,

 

  3   alopecia and exacerbation of autoimmune disorders.

 

  4             Lamivudine, a nucleoside analog, is much

 

  5   better tolerated, however, subjects taking

 

  6   lamivudine develop resistance at a rate approaching

 

  7   20 percent per year.

 

  8             Adefovir dipivoxil, a prodrug of adefovir,

 

  9   a nucleotide analog, was approved in 2002.  It is

 

 10   active against lamivudine-resistant virus, and is

 

 11   tolerated well except for nephrotoxicity that

 

 12   appears in decompensated patients, more so, and

 

 13   other advanced patients such as those undergoing

 

 14   transplant.

 

 15             Let's turn now to today's subject, that

 

 16   is, entecavir.  Entecavir is also a nucleoside

 

 17   analog.  It has activity against HBV polymerase,

 

 18   and in vitro it inhibits lamivudine-resistant virus

 

 19   at concentrations 8-32-fold greater than that

 

 20   required for wild type virus.

 

 21             Its antiviral activity has been

 

 22   demonstrated in established animal models.  In

 

                                                                14

 

  1   woodchuck, hepatitis virus infected woodchucks with

 

  2   that disease, 67 percent treated with entecavir

 

  3   survived 3 years compared to a 4 percent survival

 

  4   rate in infected historic controls.  So, it appears

 

  5   quite active in this established animal model.

 

  6             Now I will describe pertinent nonclinical

 

  7   pharm/tox findings briefly.  There was an increased

 

  8   incidence of tumors in rodent carcinogenicity

 

  9   studies.  Lung tumors were observed at low

 

 10   multiples of entecavir exposure relative to humans

 

 11   and it is thought that these tumors may be species

 

 12   specific.  Other tumors occurred at much higher

 

 13   multiples of entecavir exposure relative to humans.

 

 14   This topic will be discussed extensively by

 

 15   Bristol-Myers Squibb and Dr. Farrelly of the Food

 

 16   and Drug Administration.  What we have to keep in

 

 17   mind here is that the animal data needs to be

 

 18   interpreted in the context of the clinical data,

 

 19   the severity of the disease and the available

 

 20   treatment options.       Turning to the clinical

 

 21   studies, I would like to commend Bristol-Myers

 

 22   Squibb for their drug development program for

 

                                                                15

 

  1   entecavir.  They studied a wide population in

 

  2   e-antigen positive, e-antigen negative and

 

  3   lamivudine-resistant subjects.  Their trials were

 

  4   multicenter and multinational, using an active

 

  5   control, lamivudine.  The endpoints used were

 

  6   similar to other approved therapies.

 

  7             At today's advisory committee meeting we

 

  8   will be asking you to discuss the clinical trial

 

  9   data in the context of these animal carcinogenicity

 

 10   findings and the implications for human use.  In

 

 11   addition, we will be asking you to discuss the

 

 12   adequacy of the proposed pharmacovigilance study.

 

 13   We will also pose a question related to pediatric

 

 14   usage.

 

 15             If in the afternoon session when questions

 

 16   are posed you vote that this drug should be

 

 17   approved, we will then proceed to discuss labeling

 

 18   implications and further post-marketing studies.

 

 19             With that, I would like to just briefly

 

 20   review the agenda.  Following my comments,

 

 21   Bristol-Myers Squibb will present.  This will be

 

 22   followed by a break.  Then FDA will present and the

 

                                                                16

 

  1   presentations will be discussed prior to lunch.  At

 

  2   one o'clock there is an open public hearing.

 

  3   Following that hearing, we will continue the

 

  4   discussion and then pose our questions to the

 

  5   advisory committee.  Thank you very much.

 

  6             DR. ENGLUND:  Thank you very much.  Now I

 

  7   think we would like to begin with the sponsor

 

  8   presentation by Bristol-Myers Squibb.

 

  9                       Sponsor Presentation

 

 10                           Introduction

 

 11             DR. SIGAL:  Thank you, Dr. Englund and

 

 12   members of the committee and FDA.  Good morning.  I

 

 13   am Elliott Sigal.  I am head of research and

 

 14   development and chief scientific officer for

 

 15   Bristol-Myers Squibb.  Today it is our pleasure to

 

 16   bring you data on entecavir for the treatment of

 

 17   patients with chronic hepatitis B infection.

 

 18             As you heard from Dr. Birnkrant, this

 

 19   disease affects well over actually a million people

 

 20   in the United States and accounts for approximately

 

 21   5,000 deaths here a year.  Outside the United

 

 22   States another 400 million people are chronically

 

                                                                17

 

  1   infected with hepatitis B so it represents a

 

  2   worldwide public health issue of great importance.

 

  3             We, at Bristol-Myers Squibb, have

 

  4   concluded, based on the data you will hear today,

 

  5   that entecavir represents an important therapeutic

 

  6   advance.  Our application is being considered first

 

  7   here, in the U.S., but we have filed in Europe and

 

  8   in China, and intend to file elsewhere around the

 

  9   world as part of a larger global commitment.

 

 10             All new therapies present a need to assess

 

 11   both benefits and risks.  Years ago, knowing this

 

 12   compound to be a nucleoside analog, we

 

 13   intentionally completed and analyzed rodent

 

 14   carcinogenicity studies before initiating a Phase

 

 15   III program.  Then we continued to explore the

 

 16   mechanisms of these rodent findings and we

 

 17   collaborated with health authorities around the

 

 18   world on how to characterize clinical benefit.  The

 

 19   goal has been to determine benefits seen in the

 

 20   clinic and weigh those against the potential for

 

 21   risk raised by nonclinical studies.

 

 22             Entecavir has clinical benefits based on

 

                                                                18

 

  1   its antiviral potency and these are superior

 

  2   suppression of viral replication; a favorable

 

  3   resistance profile; and improvement in both liver

 

  4   histology and in biochemical abnormalities.  To

 

  5   establish all of this we conducted an extensive

 

  6   Phase III program, the first in this field with an

 

  7   active comparator.  As the sponsor, we concluded

 

  8   that the benefits in the clinic, including the

 

  9   resistance profile, outweigh the potential seen of

 

 10   risk in nonclinical studies and entecavir, to us,

 

 11   represents an important therapeutic option for

 

 12   patients with chronic hepatitis B infection.

 

 13             However, as with any new medicine, an

 

 14   assessment of benefit-risk at the time of approval

 

 15   can only be an estimate.  Therefore, our company is

 

 16   committed to further defining therapeutic benefits

 

 17   and to understanding any potential human risk with

 

 18   entecavir.

 

 19             To accomplish this we have submitted to

 

 20   FDA draft pharmacovigilance plans, approaches and

 

 21   observational studies that we plan to conduct to

 

 22   allow for a continuous benefit-risk assessment once

 

                                                                19

 

  1   entecavir is available for patients.  For the

 

  2   medical community these studies will advance the

 

  3   overall scientific knowledge about this disease.

 

  4   Bristol-Myers Squibb has a history of antiviral

 

  5   clinical research in the treatment of patients with

 

  6   HIV infection.  Now with entecavir we are expanding

 

  7   that commitment to advance the medical science of

 

  8   chronic hepatitis B infection.

 

  9             Furthermore, let me say that our efforts

 

 10   in the marketplace will be directed to ensure the

 

 11   appropriate use of this new medicine.  We will

 

 12   create a U.S. field organization solely dedicated

 

 13   to entecavir.  It will combine medical

 

 14   professionals and representatives who will be

 

 15   specifically trained in chronic hepatitis B.  Their

 

 16   focus will be on a relatively small number of

 

 17   physicians, 3,500, that provide care for nearly all

 

 18   the U.S. patients treated for chronic hepatitis B.

 

 19   This focused approach will ensure high quality

 

 20   interaction with prescribing physicians and

 

 21   appropriate use of entecavir for patients.

 

 22             Dr. Rich Colonno will now begin the data

 

                                                                20

 

  1   presentation.  Dr. Englund, two of our speakers

 

  2   fell ill over the last 36 hours so you will see a

 

  3   few different names on the program.  One of our

 

  4   internal hepatologists, Dr. Atillasoy, will be the

 

  5   one presenting our clinical data.  Dr. Colonno?

 

  6                            Background

 

  7             DR. COLONNO:  Good morning.  Sorry for the

 

  8   confusion.  Entecavir is under review for the

 

  9   proposed indication shown here, the treatment of

 

 10   chronic hepatitis B disease in adults with evidence

 

 11   of liver inflammation.  The usual dose will be 0.5

 

 12   mg daily and a higher 1.0 mg dose is proposed for

 

 13   patients who are lamivudine-refractory.

 

 14             Our presentation will follow the outline

 

 15   shown on this slide, covering nonclinical safety,

 

 16   clinical efficacy, clinical safety, resistance and

 

 17   pharmacovigilance.  We have been assisted in

 

 18   evaluating our data by a number of experts who are

 

 19   listed on the next slide.  These consultants,

 

 20   covering hepatology, health policy, toxicology,

 

 21   pathology and biostatistics, are here and available

 

 22   to the committee.

 

 23             Dr. Birnkrant and Dr. Sigal outlined the

 

 24   disease burden and consequences of chronic HBV

 

 25   infection.  Only about 10-30 percent of people

 

                                                                21

 

  1   currently affected with HBV go on to develop a

 

  2   chronic infection.  But the millions who do, it is

 

  3   sometimes decade-long process that for a

 

  4   substantial number of patients ends with cirrhosis,

 

  5   liver failure, hepatocellular carcinoma, transplant

 

  6   or death.

 

  7             This is a viral disease and the clinical

 

  8   course of liver injury is driven by the continuous

 

  9   replication of the virus perpetuating a cycle of

 

 10   inflammation.  HBV is not inherently cytopathic but

 

 11   liver cells support a continuous cycle of viral

 

 12   replication that triggers the inflammatory response

 

 13   that over time leads to fibrosis, cirrhosis and

 

 14   liver cancer.  HBV has recently been designated a

 

 15   carcinogen, in recognition that HBV-induced

 

 16   hepatocellular carcinoma is the fifth most frequent

 

 17   single type of cancer.

 

 18             It has now been shown that the outcome of

 

 19   this long course of chronic infection with HBV is

 

                                                                22

 

  1   not just caused by the initial infection but is

 

  2   related to the degree of continued viral

 

  3   replication.  This was supported by a prospective

 

  4   Taiwan cohort study in which three key points

 

  5   emerged:  The incidence of hepatocellular carcinoma

 

  6   and liver cirrhosis correlated with baseline HBV

 

  7   DNA levels.  The higher the baseline, the higher

 

  8   the incidence.  Two, persisting elevation of the

 

  9   viral load over time has the greatest impact on

 

 10   hepatocellular carcinoma risk.  Viral load

 

 11   predicted risk of future hepatocellular carcinoma

 

 12   independent of e-antigen status and serum ALT

 

 13   levels.

 

 14             The concept that viral replication drives

 

 15   disease process is depicted in the schematic shown

 

 16   on this slide.  Viral replication, monitored by

 

 17   serum HBV DNA levels, drives the downstream

 

 18   inflammation, measured by ALT levels and by

 

 19   histology assessments.  These were our week 48

 

 20   endpoints, and we will be referring to this

 

 21   simplified schematic later in our presentation.

 

 22             Currently, three drugs are approved to

 

                                                                23

 

  1   treat chronic hepatitis B infection, interferon,

 

  2   lamivudine and adefovir.  Interferon is an

 

  3   immunomodulator while adefovir and lamivudine are

 

  4   antivirals whose demonstrated antiviral activity

 

  5   led to their approval.  In their clinical studies

 

  6   both lamivudine and adefovir were shown to be

 

  7   superior to placebo using the endpoints of liver

 

  8   histology, viral suppression and ALT normalization

 

  9   at week 48.  They decreased viral load, the first

 

 10   stage of the schema, and interrupted the process

 

 11   measured by ALT and histology, in the center

 

 12   section.  Beyond the week 48 data points,

 

 13   lamivudine has now shown superiority to placebo in

 

 14   affecting some of the long-term outcomes seen in

 

 15   the far right-hand slide of the schema,

 

 16   characterized as disease progression.

 

 17             In the recent landmark paper by Liaw et

 

 18   al., lamivudine treatment was prospectively

 

 19   compared with placebo in patients with compensated

 

 20   cirrhoses who are at greatest risk for disease

 

 21   progression, including HCC and worsening cirrhosis.

 

 22   With lamivudine treatment by 32 months the rate of

 

                                                                24

 

  1   disease progression was significantly reduced

 

  2   relative to placebo, 8 percent versus 18 percent.

 

  3   This study confirmed the hypothesis that effective

 

  4   antiviral therapy results in a better long-term

 

  5   clinical outcome than indicated by the week 48

 

  6   histology, virology and ALT endpoints.

 

  7             The study also pointed out that a

 

  8   development of resistance to a particular antiviral

 

  9   therapy limits its benefit.  By the end of the

 

 10   study roughly half of the lamivudine-treated

 

 11   patients who had developed lamivudine resistance,

 

 12   or YMDD virus, and these patients had twice the

 

 13   percentage of disease progression when compared to

 

 14   those where the virus remained fully susceptible,

 

 15   11 percent versus 5 percent respectively.

 

 16             So, while lamivudine is effective and

 

 17   lacks the tolerability concerns of interferon and,

 

 18   unlike adefovir, does not require careful

 

 19   monitoring of renal function, resistance impacts

 

 20   the ability of lamivudine to deliver long-term

 

 21   benefits.  While the study confirmed that antiviral

 

 22   treatment provides benefit, it also suggested that

 

                                                                25

 

  1   a more effective antiviral with both greater

 

  2   potency and less resistance will be more

 

  3   efficacious in preventing downstream clinical

 

  4   disease.

 

  5             This morning you will see that entecavir,

 

  6   by the accepted and proven histologic, virologic

 

  7   and biochemical endpoints of our studies, was

 

  8   superior to lamivudine.  We will demonstrate that

 

  9   entecavir is effective, safe and well tolerated;

 

 10   has excellent potency and very low rates of

 

 11   resistance; and maintains future options because it

 

 12   doesn't select for lamivudine or adefovir

 

 13   resistance and is, therefore, an important advance

 

 14   in therapy for chronic HBV disease.

 

 15             The activity of entecavir results from its

 

 16   being a cyclopentyl guanosine analog.  It is a

 

 17   selective and potent inhibitor of HBV replication.

 

 18   It has no significant activity against HIV.  The

 

 19   selectivity contributes to its safety since it is a

 

 20   poor substrate for sailor DNA polymerases and does

 

 21   not inhibit human mitochondrial or gamma

 

 22   polymerase.  Its potency reflects the fact that it

 

                                                                26

 

  1   inhibits all three functional activities of the HBV

 

  2   polymerase, priming, DNA-dependent synthesis and

 

  3   reverse transcription.  It is also a function of a

 

  4   highly efficient conversion of entecavir to its

 

  5   active form entecavir triphosphate, seen

 

  6   consistently in a wide variety of cell types.

 

  7             Entecavir undergoes rapid and efficient

 

  8   phosphorylation by sailor enzymes at low

 

  9   concentrations, and can be detected within one

 

 10   hour.  Once formed, the intracellular half-life of

 

 11   entecavir triphosphate is approximately 15 hours.

 

 12   With an EC                                                50 of 4 nM it

is the most potent inhibitor

 

 13   of hepatitis B virus.  Entecavir is greater than

 

 14   300 times more potent than either of the available

 

 15   agents, lamivudine or adefovir, or two newer agents

 

 16   under development dibividine[?] and tenofovir.

 

 17             Animal models of HBV have been developed

 

 18   using woodchucks and ducklings and entecavir

 

 19   demonstrated impressive potency in these systems as

 

 20   well.  The woodchuck model is of particular

 

 21   importance because it has been predictive of the

 

 22   efficacy and safety of drugs subsequently used in

 

                                                                27

 

  1   humans to treat hepatitis B virus.  The antiviral

 

  2   susceptibility of the woodchuck hepatitis B virus,

 

  3   or WHBV, is similar to the human virus.  In this

 

  4   model greater than 95 percent of chronically

 

  5   infected animals will development HCC and die, and

 

  6   less than 5 percent will survive to age 4.

 

  7             In our study, animals standard established

 

  8   chronic infection were dosed with entecavir at 0.5

 

  9   mg/kg, a dose that results in exposure levels of

 

 10   approximating the exposure in humans with the 1 mg

 

 11   dose.  The drug was initially administered daily

 

 12   for 2 months and then weekly for a total of 14-36

 

 13   months.  In both groups entecavir treatment

 

 14   resulted in viral DNA levels being reduced by as

 

 15   much as 8 logs to undetectable levels.  The

 

 16   reductions were sustained for up to 3 years, with

 

 17   no evidence of virologic rebound or resistance.

 

 18             The study compared the improvement in

 

 19   survival versus historical controls, shown in grey.

 

 20   The 11 woodchucks, represented by the yellow bars,

 

 21   started treatment at 8 months of age as soon as a

 

 22   chronic infection was verified.  They had 4-year

 

                                                                28

 

  1   HCC-free survival of 50 percent and 80 percent

 

  2   respectively for the 14- and 36-month treatment

 

  3   groups.  The non-concurrent historical control had

 

  4   a survival rate of 4 percent.  Although the numbers

 

  5   of animals were small, these results were of high

 

  6   statistical significance.  Surviving animals were

 

  7   also shown to have no histological evidence of HCC

 

  8   development upon subsequent examination.

 

  9             In summary, the nonclinical data and the

 

 10   expected benefit of antiviral treatment supported

 

 11   going forward with development of entecavir for

 

 12   treatment of chronic HBV infection.  As with any

 

 13   drug being developed for long-term chronic dosing

 

 14   in humans, the carcinogenicity potential of

 

 15   entecavir was evaluated in lifelong dosing studies

 

 16   in rats and mice.  Dr. Lois Lehman-McKeeman will

 

 17   now present this data.

 

 18                        Nonclinical Safety

 

 19             DR. LEHMAN-MCKEEMAN:  Today's discussion

 

 20   of the nonclinical safety of entecavir is focused

 

 21   on the rodent carcinogenicity studies.  Entecavir

 

 22   was identified as a carcinogenic hazard in rats and

 

                                                                29

 

  1   mice, and the benefit-risk evaluation for entecavir

 

  2   must consider this risk identified in animals

 

  3   relevant to the human clinical benefit.

 

  4             For background on the rodent data, I will

 

  5   briefly describe the design, conduct and

 

  6   interpretation of these studies.  Rodent

 

  7   carcinogenicity studies are lifetime studies,

 

  8   typically 2 years, and group sizes are large with

 

  9   50-60 animals per sex per group.  Dose selection is

 

 10   critical, and highest dosage is expected to

 

 11   represent a maximum tolerated dose, or MTD.  The

 

 12   simplest definition of an MTD is a dose that causes

 

 13   no more than a 10 percent decrease in body weight

 

 14   gain relative to controls.  The lower dosages

 

 15   studied, typically 2 additional levels, are

 

 16   selected to be some fraction of the MTD or some

 

 17   multiple of the relevant human clinical exposure.

 

 18             At the end of the study all tissues are

 

 19   evaluated microscopically for tumors.  Several

 

 20   tissues in rats and mice are prone to spontaneous

 

 21   tumor development.  For example, in mice there was

 

 22   a relatively high background rate of tumors in

 

                                                                30

 

  1   liver and lung, while in rats liver, pituitary and

 

  2   mammary gland tumors occurred at high spontaneous

 

  3   rates.  So, finding tumors in animals, including

 

  4   controls, is not surprising and we rely on

 

  5   statistical methods and an understanding of

 

  6   historical control tumor rates to identify those

 

  7   that are drug related.

 

  8             Statistical significance in rodent tumors

 

  9   is established by sequentially testing for a linear

 

 10   dose-dependent trend starting with all dose groups.

 

 11   Tumor incidence is adjusted for survival and the

 

 12   time and cause of death and the level of

 

 13   statistical significance varies with whether a

 

 14   tumor is common or rare.  The more common the

 

 15   tumor, the more rigorous the statistical analysis.

 

 16   When the results identify a positive trend, data

 

 17   are reanalyzed by dropping the highest dose and

 

 18   repeating the test.  This cycle is repeated until

 

 19   no significant trend is observed.

 

 20             With that as an overview on rodent

 

 21   carcinogenicity studies, let's review the results

 

 22   for entecavir.  These results have been reviewed

 

                                                                31

 

  1   with the FDA's Executive Carcinogenicity Assessment

 

  2   Committee, or CAC, and the full CAC and a number of

 

  3   tumor sites were concluded to be relevant to human

 

  4   safety.

 

  5             Entecavir-induced tumors followed two

 

  6   distinct patterns.  The first pattern was observed

 

  7   in tissues that showed preneoplastic changes, that

 

  8   is, sites were early changes, consistent with the

 

  9   increased likelihood of tumor development, were

 

 10   observed.  The only site that showed this pattern

 

 11   was the mouse lung.

 

 12             The second pattern of increased tumors was

 

 13   in tissues that showed no evidence of preneoplastic

 

 14   changes and occurred at high exposure multiples

 

 15   relative to anticipated human exposure.  These

 

 16   tumors included liver carcinomas in male mice;

 

 17   vascular tumors in female mice; gliomas in male

 

 18   rats; and gliomas, liver adenomas and skin fibromas

 

 19   in female rats.

 

 20             In addition to listing the tumor sites,

 

 21   let's look at the incidences observed in these

 

 22   studies.  Entecavir was dosed to mice across a dose

 

                                                                32

 

  1   range of 0.004 mg/kg to 4 mg/kg.  To orient you to

 

  2   this slide, the dosages are shown in the top line

 

  3   and the exposure multiples are noted below the

 

  4   dosages representing the comparison of the plasma

 

  5   area under the curve in mice relative to human

 

  6   exposure at the 0.5 mg or 1 mg dose.  The exposures

 

  7   are presented as those in the males, followed by

 

  8   the females.  4 mg/kg was an MTD and this dose

 

  9   represented at least a 40-fold multiple over the

 

 10   human exposure at 1 mg.

 

 11             The mouse lung is a major target organ for

 

 12   tumor development following entecavir treatment.

 

 13   Lung tumors are common in mice.  There was a 12

 

 14   percent incidence of tumors in the control males in

 

 15   this study.

 

 16             Entecavir increased the incidence of lung

 

 17   adenomas with a statistical increase in tumors,

 

 18   here noted in yellow, observed at the 0.4 mg/kg

 

 19   dose in males.  This dose is 3-5 times higher than

 

 20   human clinical exposure.  Lung adenomas were

 

 21   further increased at the 2 higher dosages and at 4

 

 22   mg/kg entecavir increased the incidence of lung

 

                                                                33

 

  1   carcinomas.

 

  2             In female mice lung tumors occur at a

 

  3   higher spontaneous rate than in males, with a

 

  4   background incidence of 20 percent in this study.

 

  5   Entecavir increased pulmonary tumors in female mice

 

  6   but the statistical significance was noted only at

 

  7   the highest dose.

 

  8             Other toxicology studies indicated that

 

  9   entecavir elicited unique changes in the mouse

 

 10   lung, and we conducted experiments to define these

 

 11   changes and to determine whether they were linked

 

 12   to the increased susceptibility to tumor

 

 13   development.  The results showed preneoplastic

 

 14   changes in the mouse lung that consisted of

 

 15   increased numbers of macrophages and Type II

 

 16   pneumocyte hyperplasia.  Cell proliferation is a

 

 17   recognized risk factor for tumor development and

 

 18   entecavir caused a sustained proliferation of Type

 

 19   II pneumocytes.  Most mouse lung tumors arise from

 

 20   Type II pneumocytes and these cells were identified

 

 21   as the progenitor cells for entecavir-induced lung

 

 22   tumors as well.  The increased numbers of

 

                                                                34

 

  1   macrophages was required to support the

 

  2   proliferation of the Type II pneumocytes and

 

  3   entecavir increased the number of alveolar

 

  4   macrophages in the lung because it was chemotactic

 

  5   for mouse monocytes.

 

  6             In contrast to the mouse, no similar

 

  7   changes were observed in the lungs of rats, dogs or

 

  8   monkeys treated with entecavir.  Finally, although

 

  9   entecavir was chemotactic for mouse monocytes, it

 

 10   was not chemotactic for human monocytes, suggesting

 

 11   that an accumulation of macrophages in the human

 

 12   lung would be unlikely to occur.  The results

 

 13   suggest that entecavir causes unique effects in the

 

 14   mouse lung and lung tumors observed in mice may be

 

 15   species specific.

 

 16             The second presentation of entecavir-

 

 17   induced tumors in mice was in organs that, unlike

 

 18   the lung, showed no evidence of preneoplastic

 

 19   change.  In males entecavir increased the incidence

 

 20   of liver carcinomas and in females entecavir

 

 21   increased the incidence of vascular tumors,

 

 22   specifically hemangiomas.  In both cases there was

 

                                                                35

 

  1   no dose response relationship noted, with tumors

 

  2   observed only at the highest dosage.

 

  3             We have not explored mechanisms underlying

 

  4   the high dose tumor findings on an organ by organ

 

  5   basis, but we have looked at whether a common mode

 

  6   of action may contribute to tumor development.

 

  7   Entecavir is phosphorylated to entecavir

 

  8   triphosphate, the active form that inhibits viral

 

  9   replication, and we determined that, likely by

 

 10   competing for phosphorylation as depicted here,

 

 11   entecavir disrupts deoxynucleotide triphosphate

 

 12   pools, dNTP pools, in male mouse liver.  Data in

 

 13   the scientific literature demonstrates that such

 

 14   perturbations disrupt the fidelity of DNA synthesis

 

 15   and repair.  We conclude that changes in the dNTP

 

 16   pools may explain tumor findings, particularly when

 

 17   there is a high dose response for tumor

 

 18   development.

 

 19             Moving on to rats, in Sprague-Dawley rats

 

 20   entecavir was dosed to males at dosages up to 1.4

 

 21   mg/kg or to females at dosages up to 2.6 mg/kg.

 

 22   The 4 dosage levels are noted here along with the

 

                                                                36

 

  1   exposure multiples as were presented on the mouse

 

  2   slides relative to the 0.5 mg or 1 mg clinical

 

  3   dose.  Maximum exposures were at least 35 times

 

  4   human exposure in male rats or 24 times human

 

  5   exposure in female rats.  In rats all tumors

 

  6   observed were consistent with the second pattern of

 

  7   tumor presentation, that is, no evidence of

 

  8   development of preneoplastic change.

 

  9             In males and females entecavir increased

 

 10   the incidence of gliomas with statistical

 

 11   significance only at the highest dosage.  In

 

 12   females entecavir increased the incidence of liver

 

 13   adenomas and skin fibromas.  As determined in mice,

 

 14   we have postulated that the dNTP pool perturbations

 

 15   resulting from high doses of entecavir that

 

 16   overwhelm the strict regulation of nucleotide

 

 17   metabolism may explain entecavir-induced tumors in

 

 18   rats.

 

 19             Carcinogenicity studies in rodents

 

 20   identify whether a compound is a carcinogenic

 

 21   hazard.  In the absence of data in humans it is

 

 22   assumed that carcinogenic effects in rodents

 

                                                                37

 

  1   suggest a possible carcinogenic risk in humans.

 

  2   However, to extrapolate these findings to humans

 

  3   other relevant data, such as genetic toxicity and

 

  4   species differences in biological response, along

 

  5   with dose-response relationships and exposure

 

  6   comparisons, are important considerations that may

 

  7   increase or decrease the likelihood of human cancer

 

  8   risk.  For entecavir there is evidence suggesting a

 

  9   unique biological response in the mouse lung and

 

 10   mouse lung tumors may be species specific.

 

 11             Extrapolation of the other tumor findings

 

 12   is more difficult, but the weight of evidence

 

 13   suggests that human risk is minimal because rodent

 

 14   tumors were observed at dosages that greatly exceed

 

 15   human clinical exposure.

 

 16             Dr. Evren Atillasoy will now review the

 

 17   benefit of entecavir as determined from the Phase

 

 18   III clinical trials.

 

 19                   Clinical Efficacy and Safety

 

 20             DR. ATILLASOY:  Thank you and good

 

 21   morning.  The entecavir clinical development

 

 22   program is comprehensive and assesses the efficacy

 

                                                                38

 

  1   and safety of entecavir for the treatment of

 

  2   chronic hepatitis B infection.  The experience was

 

  3   broad with major disease patterns well represented.

 

  4   Studies addressed hepatitis B e-antigen positive

 

  5   patients and e-negative disease, and assessed

 

  6   entecavir in lamivudine-refractory as well as

 

  7   nucleoside-naive patients.

 

  8             The global program recruited patients from

 

  9   5 continents in over 30 countries.  Separate

 

 10   programs are in progress in China and Japan.  The

 

 11   studies that contribute to the NDA review provide

 

 12   analyzed data on approximately 1,500

 

 13   entecavir-treated patients.  Entecavir is the first

 

 14   nucleoside program to be evaluated for HBV using an

 

 15   active comparator, lamivudine, which was the only

 

 16   approved HBV nucleoside at the time that the

 

 17   program was initiated.

 

 18             The map of the clinical program

 

 19   illustrates the sense of the size, breadth and

 

 20   complexity.  The core of the program is represented

 

 21   by the green box and includes the three Phase III

 

 22   studies you will be hearing about today.  Small

 

                                                                39

 

  1   studies in special populations include experiences

 

  2   in liver transplant patients, co-infected

 

  3   HIV-positive patients and decompensated patients,

 

  4   the trial which we are still actively enrolling.

 

  5             Two long-term rollover studies provide for

 

  6   prolonged observation and data collection.  Study

 

  7   901, at the bottom left, provides an ongoing

 

  8   treatment option for those patients in whom

 

  9   long-term treatment is appropriate.  Study 049 is a

 

 10   post-treatment observational study, designed to

 

 11   collect long-term safety and efficacy information.

 

 12   All Phase III patients have the opportunity to

 

 13   enroll in these trials.  These data in 049 have not

 

 14   yet been analyzed.

 

 15             Dose selection for entecavir anticipated

 

 16   that lamivudine-refractory patients would require a

 

 17   higher dose than naive patients because of the

 

 18   higher EC                                              50 of

lamivudine-resistant virus in vitro.

 

 19   An earlier proof of principle study testing doses

 

 20   over a range from 0.5 mg to 1 mg daily hinge on

 

 21   overlapping responses for the highest doses of 0.5

 

 22   mg and 1 mg daily.  Therefore, these doses were

 

                                                                40

 

  1   used as the highest ones tested in dose selection

 

  2   studies, 0.5 mg in naive patients, in yellow on the

 

  3   left graph, and 1 mg refractory patients, in orange

 

  4   on the right graph.  The lamivudine control is

 

  5   represented in blue in both graphs.

 

  6             A dose response was demonstrated in each

 

  7   population, with the greatest responses occurring

 

  8   at the two highest doses with diminishing

 

  9   incremental benefit at the last increase.

 

 10   Entecavir 0.5 mg daily and 1 mg daily were taken

 

 11   forward as the doses to be tested for Phase III for

 

 12   naive and refractory patients respectively.

 

 13             Clinical efficacy--Phase III included

 

 14   trials in three disease settings, nucleoside-naive

 

 15   e-antigen positive patients, nucleoside e-antigen

 

 16   negative patients and lamivudine refractory

 

 17   e-antigen positive patients.  The definition of

 

 18   lamivudine refractory was that patients must have

 

 19   clinical failure after at least 6 months of

 

 20   lamivudine, or earlier failure with the

 

 21   confirmation of lamivudine-resistant virus.

 

 22   Clinical failure was defined as detectable viremia

 

                                                                41

 

  1   using the bDNA assay.  Today's presentation of

 

  2   clinical results will be by treatment population

 

  3   rather than study number.

 

  4             Lets turn to study design across Phase

 

  5   III.  Patients were screened and randomized 1:1 to

 

  6   either entecavir or lamivudine in a double-blind

 

  7   fashion and were treated for a minimum of 52 weeks.

 

  8   Lamivudine-refractory patients who were required to

 

  9   have breakthrough viremia while on lamivudine were

 

 10   switched on treatment day 1 directly from

 

 11   lamivudine to blinded study drug without a period

 

 12   either of overlap or washout.  Liver biopsies were

 

 13   obtained at baseline and at week 48 for assessment

 

 14   of the primary efficacy endpoint, histologic

 

 15   improvement.  Patient management at week 52 was

 

 16   based on lab results using data from the week 48

 

 17   visit, with results of the 24 follow-up period

 

 18   presented in the briefing document that you have.

 

 19             Inclusion criteria, let's talk about these

 

 20   for the three studies.  Inclusion criteria required

 

 21   that patients needed to have compensated liver

 

 22   disease, together with an elevated ALT, or were

 

                                                                42

 

  1   required to have detectable viremia by bDNA.  The

 

  2   different virologic characteristics of the

 

  3   e-antigen positive and e-antigen negative disease

 

  4   patients resulted in different minimal requirements

 

  5   for enrollment by HBV DNA.

 

  6             The baseline demographics of each study

 

  7   population are consistent with the characteristics

 

  8   expected for the patient population.  In the

 

  9   presentations that follow results for the naive

 

 10   e-antigen positive patients will appear on the left

 

 11   of the slide.  In the middle you will see data for

 

 12   the naive e-antigen negative patients and on the

 

 13   furthest right you will see results for the

 

 14   lamivudine-refractory e-antigen positive

 

 15   population.  Within each study the

 

 16   entecavir/lamivudine study groups were well matched

 

 17   for demographic characteristics.

 

 18             Turning to baseline HBV characteristics,

 

 19   these are also expected to differ according to the

 

 20   pattern of disease studied.  Again, within each

 

 21   study the entecavir/lamivudine treatment groups

 

 22   were well matched for baseline HBV disease

 

                                                                43

 

  1   characteristics.  Looking across studies, HBV

 

  2   e-antigen positive patients, whether

 

  3   nucleoside-naive or lamivudine-refractory, had mean

 

  4   HBV DNA values that were approximately 2 logs

 

  5   higher than the mean value for the e-antigen

 

  6   negative population.

 

  7             Finally baseline histology across the

 

  8   studies showed a higher mean necroinflammatory

 

  9   score, using Knodell, than nucleoside-naive

 

 10   subjects.  Only a minority had biopsy evidence for

 

 11   cirrhosis as classified by Knodell fibrosis score

 

 12   of 4.  This is because participants were selected

 

 13   to have compensated liver disease.

 

 14             Patient disposition--patient disposition

 

 15   for the first 48 weeks across the three studies

 

 16   demonstrates high retention rates, with at least 94

 

 17   percent of entecavir-treated patients completing 48

 

 18   weeks of treatment in each of the three studies.

 

 19   Lamivudine retention rates ranged from 87-95

 

 20   percent, with the lowest rate in the

 

 21   lamivudine-refractory study.

 

 22             In all three studies, paired biopsies were

 

                                                                44

 

  1   scored using a single reader, who was Dr. Zachary

 

  2   Goodman.  Dr. Zachary Goodman was blinded to drug

 

  3   assignment as well as the temporal sequence of the

 

  4   paired biopsies.  Dr. Goodman also read the

 

  5   biopsies for lamivudine and adefovir registrational

 

  6   programs.

 

  7             Overall, paired baseline and week 48

 

  8   biopsies were available for efficacy assessment in

 

  9   88 percent of patients.  Histologic improvement at

 

 10   week 48 as compared to baseline is the primary

 

 11   efficacy endpoint in these trials.  Histologic

 

 12   improvement was defined as at least a 2-point

 

 13   reduction in the Knodell necroinflammatory score

 

 14   with no concurrent worsening in Knodell fibrosis.

 

 15             In order for a biopsy pair to be

 

 16   evaluable, the baseline sample must have had enough

 

 17   tissue pathologically and it also must have had a

 

 18   necroinflammatory score of at least 2, and 89

 

 19   percent of patients had a baseline biopsy that fit

 

 20   these criteria and constitute the evaluable

 

 21   baseline histology cohort.  Patients from the

 

 22   evaluable cohort who had missing or inadequate week

 

                                                                45

 

  1   48 specimens were considered to have no

 

  2   improvement.  Therefore, the primary analysis for

 

  3   histologic improvement is analogous to a

 

  4   non-completer or equal failure analysis but is

 

  5   applied to the evaluable cohort rather than the

 

  6   all-treated population.

 

  7             The nucleoside-naive studies were designed

 

  8   with two-stage testing.  The first test was for

 

  9   non-inferiority and, if that was met, then

 

 10   superiority was tested.  Non-inferiority is

 

 11   established if the lower confidence limit is above

 

 12   minus 10 percent.  Superiority is met if the lower

 

 13   confidence limit is above zero.  In comparing two

 

 14   active treatments it was expected that differences

 

 15   in histologic improvement, a downstream endpoint,

 

 16   might take longer than 48 weeks to emerge.

 

 17   Nevertheless, at week 48 entecavir 0.5 mg daily was

 

 18   superior to lamivudine 100 mg daily for histologic

 

 19   improvement in both nucleoside-naive populations.

 

 20   Entecavir achieved a 72 percent response rate in

 

 21   naive e-antigen positive patients and a 70 percent

 

 22   response rate in the naive e-negative population.

 

 23             Looking to the study in

 

 24   lamivudine-refractory patients, this was designed

 

 25   for superiority.  Two independent co-primary

 

                                                                46

 

  1   endpoints were evaluated because histologic

 

  2   response hadn't been characterized in this

 

  3   population previously.  The first co-primary

 

  4   endpoint is histologic improvement, as we have

 

  5   discussed.  The second is a composite reflecting

 

  6   both virologic response and hepatic inflammation as

 

  7   measured by serum ALT.  Entecavir 1 mg daily was

 

  8   superior to continued lamivudine 100 mg daily for

 

  9   both co-primary endpoints, and 55 percent achieved

 

 10   the endpoint of histologic improvement; likewise,

 

 11   55 percent achieved an HBV DNA below the detection

 

 12   of the bDNA assay, together with an ALT less than

 

 13   1.25 times the upper limit of normal.  Changes in

 

 14   fibrosis are expected to follow changes in

 

 15   necroinflammation.  While the primary endpoint,

 

 16   histologic improvement, assessed primarily

 

 17   necroinflammation, secondary histologic endpoints

 

 18   included an assessment of changes in fibrosis using

 

 19   the Ishak scoring system.

 

 20             The numbers in the circles along the zero

 

 21   line represent the proportions with no change,

 

 22   while the bars above and below the line represent

 

 23   the proportions with improvement and worsening

 

 24   respectively.  In the two naive studies entecavir

 

 25   and lamivudine are comparable.  This is not

 

                                                                47

 

  1   unexpected as week 48 is relatively an early time

 

  2   point for assessing this downstream endpoint,

 

  3   especially when comparing two active treatments.

 

  4   The effect of large differences, however, can be

 

  5   seen in lamivudine-refractory patients.  Here

 

  6   entecavir was superior to lamivudine for

 

  7   improvement in fibrosis.  The distribution of

 

  8   responses in entecavir-treated patients mirrors

 

  9   that in the naive studies and 34 percent had

 

 10   improvement while only 11 percent worsened while on

 

 11   entecavir.  This compares to only 16 percent

 

 12   improvement and 26 percent worsening for continued

 

 13   lamivudine.

 

 14             Non-histologic secondary endpoints were

 

 15   also assessed at week 48.  These included

 

 16   virologic, biochemical and serologic endpoints. 

 

                                                                48

 

  1   These assessments are all used routinely in the

 

  2   clinical management of patients with chronic HBV.

 

  3   Treatment comparisons were made using a

 

  4   non-completer or equal failure analysis, and all

 

  5   treated patients were counted in the denominator.

 

  6             Results for virologic endpoints

 

  7   demonstrate superiority for entecavir in all three

 

  8   populations studied.  The proportion of patients

 

  9   achieving an HBV DNA less than 400 copies/mL by PCR

 

 10   is presented here as a function of time on

 

 11   treatment, and 69 percent of naive e-antigen

 

 12   positive patients treated with entecavir achieved

 

 13   an HBV DNA of less than 400 copies/mL as compared

 

 14   to 38 percent for lamivudine, an absolute

 

 15   difference of 31 percentage points.

 

 16             The lower baseline viremia and e-antigen

 

 17   negative patients is associated with higher rates

 

 18   of viral suppression.  Here, 91 percent of

 

 19   entecavir-treated patients achieved an HBV DNA less

 

 20   than 400 copies as compared to 73 percent for

 

 21   lamivudine, an absolute difference of 18 percentage

 

 22   points.  In both populations there is an early

 

                                                                49

 

  1   separation response, with superiority for entecavir

 

  2   as early as week 24.  This was the first time point

 

  3   in which a PCR measurement was taken.

 

  4             In the lamivudine-refractory population

 

  5   entecavir was also superior to continued

 

  6   lamivudine, with early separation during the first

 

  7   24 weeks of treatment, and 21 percent of

 

  8   entecavir-treated patients achieved an HBV DNA less

 

  9   than 400 copies.

 

 10             An additional way of assessing virologic

 

 11   response is looking at the mean log reduction in

 

 12   HBV DNA from baseline.  For this analysis results

 

 13   depend upon the characteristics of the population

 

 14   studied and the HBV DNA used.  The maximum

 

 15   reduction possible for a particular population

 

 16   depends on the starting baseline values for those

 

 17   individuals.  In a responder the endpoint will

 

 18   reflect the lower limit of detection for an assay.

 

 19   Therefore, comparisons of this endpoint across

 

 20   different populations must account for differences

 

 21   in baseline characteristics and HBV DNA assay.

 

 22             Entecavir is superior to lamivudine across

 

                                                                50

 

  1   all three populations.  Naive e-antigen positive

 

  2   patients who started out with an HBV DNA of 9.7

 

  3   logs in wild type virus demonstrate--so that

 

  4   entecavir demonstrates its full potential with a

 

  5   mean decrease of nearly 7 logs at week 48,

 

  6   differing by 1.5 logs or 30-fold from lamivudine.

 

  7   In the e-negative population the 5-log decrease for

 

  8   entecavir approximates the maximal change possible

 

  9   given the lower starting HBV DNA and the PCR limit

 

 10   of quantitation at 2.5 logs, or 300 copies/mL.  In

 

 11   the lamivudine-refractory population entecavir

 

 12   achieves a substantial 5.1-log decrease in HBV DNA.

 

 13             Viral suppression also leads to reduced

 

 14   hepatic inflammation as judged by ALT.  Here,

 

 15   entecavir is superior to lamivudine for

 

 16   normalization of ALT in all three populations.  As

 

 17   expected, the largest treatment difference is seen

 

 18   in the refractory population.

 

 19             Reduced viral replication may also induce

 

 20   an immunologic response resulting in HBe antigen

 

 21   seroconversion.  The precise biology of this

 

 22   interaction is poorly understood.  In the naive

 

                                                                51

 

  1   e-antigen population entecavir and lamivudine are

 

  2   comparable for seroconversion with response rates

 

  3   of 21 and 18 percent respectively.

 

  4             In summary, across the three Phase III

 

  5   studies entecavir is consistently superior to

 

  6   lamivudine for histologic improvement, virologic

 

  7   response and ALT normalization.  For the four key

 

  8   endpoints across the three studies there were 11

 

  9   efficacy comparisons.  Entecavir demonstrates

 

 10   statistical superiority to lamivudine in 9 of these

 

 11   11, with confidence intervals for treatment

 

 12   differences lying to the right of zero.  The two

 

 13   seroconversion endpoints favor entecavir

 

 14   numerically and establish non-inferiority with

 

 15   confidence intervals lying above the minus 10

 

 16   boundary.  In addition, the mean log reduction is

 

 17   consistently superior for entecavir, ranging from

 

 18   5-7 logs across the three populations.

 

 19             Let's move to safety.  The clinical

 

 20   profile of entecavir has been extensively

 

 21   characterized.  The format for the safety

 

 22   presentation will differ slightly from that of the

 

                                                                52

 

  1   efficacy presentation.  These analyses use

 

  2   augmented patient cohorts and integrate data across

 

  3   studies in order to increase the sensitivity to

 

  4   possible safety signals.

 

  5             The nucleoside-naive lamivudine-refractory

 

  6   populations are considered separately, primarily

 

  7   because the exposure to entecavir differs with

 

  8   dose.  The safety cohort includes patients from 10

 

  9   analyzed Phase II and Phase III studies.  For the

 

 10   Phase III populations mean treatment duration was 5

 

 11   weeks longer for entecavir-treated naive patients

 

 12   and 17 weeks longer for entecavir-treated

 

 13   refractory patients.  The follow-up observations

 

 14   were consistently longer for entecavir than for

 

 15   lamivudine across all populations.

 

 16             Follow-up is defined as the period of

 

 17   post-treatment follow-up during which no

 

 18   alternative HBV therapy was given.  Its duration

 

 19   was shorter in refractory patients as compared to

 

 20   naive patients due to earlier initiation of

 

 21   alternative therapy or early enrollment into an

 

 22   entecavir rollover trial.  Observation periods for

 

                                                                53

 

  1   the safety cohort are expanded to include

 

  2   open-label treatment and post-treatment observation

 

  3   on alternate HBV therapy.

 

  4             The safety presentation is divided into

 

  5   three sections, general safety, hepatic safety and

 

  6   malignant neoplasms.  General safety analyses

 

  7   provide standard assessments for rates of clinical

 

  8   adverse events and laboratory abnormalities.  All

 

  9   analyses use data from all treated patients in the

 

 10   selected studies.  Analyses are cumulative from the

 

 11   first day of dosing through the last contact with

 

 12   each patient.  Therefore, year 2 data are included

 

 13   for some patients.

 

 14             Rates for three standard safety

 

 15   assessments--discontinuations due to an adverse

 

 16   event, serious adverse events and deaths, were low

 

 17   for both treatments across both populations.  The

 

 18   types of serious events reported for entecavir and

 

 19   lamivudine were comparable, and no individual

 

 20   serious adverse event occurred in more than one

 

 21   percent of patients.  None of the events leading to

 

 22   death was considered related to study drug.

 

 23             In terms of adverse events, on treatment

 

 24   adverse events were generally mild to moderate in

 

 25   severity and were common, reflecting the long

 

                                                                54

 

  1   duration of study observation.  The frequencies of

 

  2   individual events and the types and distribution of

 

  3   these events were comparable for both treatment

 

  4   groups across both populations.

 

  5             Hepatic safety--hepatic safety focuses on

 

  6   hepatic flares because these can represent an

 

  7   important clinical risk in the treatment of

 

  8   hepatitis B regardless of the specific therapy

 

  9   which is used.  ALT flares were defined as

 

 10   increases in ALT greater than 10 times the upper

 

 11   limit of normal and 2 times the patient's own

 

 12   reference value.  The reference value was the

 

 13   baseline value for on-treatment flares.  For

 

 14   off-treatment flares the reference was the lower of

 

 15   the baseline or the end of treatment value.

 

 16             Rates for on- and off-treatment flares are

 

 17   consistently less than 10 percent for entecavir.

 

 18   Of note, the median time from stopping therapy to

 

 19   an off-treatment flare is substantially longer for

 

                                                                55

 

  1   entecavir.  The delayed time course for

 

  2   off-treatment flares for entecavir may be related

 

  3   to the extent of virologic suppression achieved on

 

  4   treatment.

 

  5             ALT flares are frequently asymptomatic.  A

 

  6   deterioration in hepatic function can, however,

 

  7   occur without ALT changes that meet this flair

 

  8   definition.  Therefore, we performed analyses to

 

  9   identify individuals meeting flair criteria who had

 

 10   associated relevant laboratory abnormalities or

 

 11   relevant hepatic clinical events, or those who had

 

 12   a serious hepatic adverse event without meeting

 

 13   flair criteria.  These events were infrequent among

 

 14   both naive and refractory patients, with the number

 

 15   of individual cases summarized here.

 

 16             Safety surveillance of the entecavir

 

 17   development program involved the assessment of

 

 18   comparative incidences for new or recurrent

 

 19   malignancy diagnoses in entecavir- and

 

 20   lamivudine-treated subjects.  Use of the larger

 

 21   safety cohort database increases sensitivity in

 

 22   this analysis of events that are infrequent.  A new

 

                                                                56

 

  1   diagnosis or a new recurrence of malignancy was

 

  2   counted from the time of first study dose to the

 

  3   time of the last patient contact regardless of

 

  4   whether the event was diagnosed on or post

 

  5   treatment.  In the safety cohort the

 

  6   entecavir/lamivudine treatment groups differed in

 

  7   size and the duration of observation.

 

  8             Event rates are presented as incidences of

 

  9   patients diagnosed per 1,000 patient-years of

 

 10   observation.  Hepatocellular carcinoma is the

 

 11   single most frequent type of cancer identified, not

 

 12   unexpectedly, due to the underlying HBV disease.

 

 13   Incidences across the treatment groups are

 

 14   comparable whether assessed for any malignancy, any

 

 15   malignancy excluding non-melanoma skin tumors or

 

 16   the category of great interest, non-hepatocellular

 

 17   carcinoma, non-skin malignancies.

 

 18             Further analyses in the entecavir program

 

 19   demonstrate that the distribution of new or

 

 20   recurrent non-skin malignancy diagnoses over time

 

 21   is comparable for entecavir and lamivudine.  In

 

 22   both treatment groups the greatest number of new

 

                                                                57

 

  1   diagnoses occurred between weeks 24 and 48.  This

 

  2   temporal clustering may reflect tumors that were

 

  3   latent at the time of study enrollment.  There is

 

  4   an apparent leveling off for new diagnoses after

 

  5   week 48.

 

  6             In order to establish a comparative

 

  7   context for the observed tumor rates in the

 

  8   development program, Bristol-Myers Squibb provided

 

  9   grants to two independent research groups.  These

 

 10   groups identified cohorts of chronic HBS antigen

 

 11   positive patients within their established

 

 12   databases.  The results are provided in the two

 

 13   right-hand columns.  The Taiwan cohort had been

 

 14   prospectively identified as part of an established

 

 15   cancer incidence study which started in 1991 and is

 

 16   sponsored by the Taiwan Ministry of Health.  The

 

 17   rates of malignancy in the entecavir-lamivudine

 

 18   arms are comparable to the Taiwan and the Kaiser

 

 19   observational cohorts.

 

 20             In summary, the safety profile of

 

 21   entecavir is consistently comparable to that of

 

 22   lamivudine.  Also, the safety of entecavir is

 

                                                                58

 

  1   comparable across the nucleoside-naive and

 

  2   lamivudine-refractory populations, and across the

 

  3   two doses of 0.5 mg and 1 mg daily.  Importantly,

 

  4   the malignancy incidences among approximately 1,500

 

  5   entecavir-treated patients are comparable among

 

  6   those observed in the lamivudine-treated control

 

  7   group.  Dr. Richard Colonno will now present the

 

  8   resistance profile for entecavir.

 

  9                            Resistance

 

 10             DR. COLONNO:  Thank you.  For all

 

 11   antivirals there is a direct relationship between

 

 12   potent viral suppression and absence of viral

 

 13   resistance emergence because viruses require a

 

 14   minimal threshold level of replication to select

 

 15   for resistant variants.  Sustained suppression of

 

 16   viral DNA undetectable levels in the woodchuck

 

 17   model, described earlier, resulted in the absence

 

 18   of virologic rebound and no evidence of resistance

 

 19   over the 14- and 36-month treatment periods.

 

 20             To ascertain whether the potent and

 

 21   sustained suppression of viral replication achieved

 

 22   by entecavir in our clinical studies results in a

 

                                                                59

 

  1   favorable resistance profile, a comprehensive

 

  2   resistance evaluation was conducted that included

 

  3   both in vitro and in vivo studies, along with

 

  4   characterization of over 1,500 clinical samples

 

  5   from entecavir-treated patients.

 

  6             In vitro studies showed entecavir

 

  7   susceptibility was reduced when viruses contained

 

  8   the two primary lamivudine-resistant substitutions,

 

  9   a leucine thymodin[?] change at residue 180 and a

 

 10   methionine to valine or isoleucine change at

 

 11   residue 204.  Despite this reduction, entecavir

 

 12   remains greater than 50-fold more potent than

 

 13   adefovir against lamivudine-resistant viruses.

 

 14   There was no cross-resistance between entecavir and

 

 15   adefovir since adefovir-resistant viruses

 

 16   containing resistant substitutions at residues 181

 

 17   or 236 remain fully susceptible to entecavir.

 

 18             During Phase II studies two extensively

 

 19   pretreated patients, designated as patient A and

 

 20   patient B, exhibited virologic rebounds on

 

 21   entecavir therapy.  Following at least 76 weeks of

 

 22   entecavir, virologic rebounds noted in two patterns

 

                                                                60

 

  1   of genotypic resistance emergence were identified.

 

  2   Entecavir resistance emergence in patient A

 

  3   required two additional substitutions, an

 

  4   isoleucine change at residue 169 and a valine

 

  5   substitution at residue 250.  Patient B needed

 

  6   glycine and isoleucine substitutions at residues

 

  7   184 and 202 respectively, along with a subsequent

 

  8   change at residue 169.  In both cases these changes

 

  9   occurred in the background of preexisting

 

 10   lamivudine-resistant substitutions.  Both isolates

 

 11   were growth impaired and remained fully susceptible

 

 12   to adefovir.

 

 13             The impact of substitutions at each of

 

 14   these four residues of entecavir's susceptibility

 

 15   are shown on this slide.  Recombinant viruses

 

 16   containing the indicated substitutions at residues

 

 17   169, 184 and 202 alone had no significant impact on

 

 18   entecavir's susceptibility relative to wild type

 

 19   virus, while a change at residue 250 reduced

 

 20   entecavir's susceptibility levels by less than

 

 21   10-fold, about the same as when

 

 22   lamivudine-resistant substitutions alone are

 

                                                                61

 

  1   present.

 

  2             The 169 substitution appears to act as a

 

  3   secondary mutation and did not further reduce

 

  4   entecavir's susceptibility in the

 

  5   lamivudine-resistant viruses.  However, when

 

  6   lamivudine-resistant substitutions are combined

 

  7   with the entecavir-resistant substitutions at

 

  8   residues 184, 202 and 250 significantly higher

 

  9   levels of entecavir resistance are observed.

 

 10   Presence of multiple entecavir-resistant

 

 11   substitutions further decreased entecavir's

 

 12   susceptibility levels.

 

 13             An extensive resistance monitoring program

 

 14   was undertaken.  In the nucleoside-naive trials all

 

 15   available entecavir-treated e-antigen positive and

 

 16   two-thirds of randomly selected e-antigen negative

 

 17   patients were genotyped at study entry and at week

 

 18   48, a total of 550 pairs of patient samples.  For

 

 19   the lamivudine-refractory population all available

 

 20   patient samples were genotyped.  All emerging

 

 21   changes identified were tested for their potential

 

 22   impact on entecavir susceptibility.

 

 23             In addition, samples from all patients

 

 24   experiencing a virologic rebound, defined as any

 

 25   greater than or equal to 1 log increase from nadir

 

                                                                62

 

  1   identified by PCR, were genotyped and subjected to

 

  2   population phenotyping to determine if they

 

  3   harbored circulating viruses resistant to study

 

  4   drug.  In nucleoside-naive patients treated with

 

  5   entecavir there was no evidence of genotypic or

 

  6   phenotypic resistance by week 48.

 

  7             The figure plots the distribution of

 

  8   patients with the HBV DNA levels indicated at study

 

  9   entry and at week 48 for both entecavir and

 

 10   lamivudine.  The size of each circle corresponds to

 

 11   the percentage of patients and each column of

 

 12   circles adds up to 100 percent.  And, 81 percent of

 

 13   entecavir-treated patients achieved viral DNA

 

 14   levels of less than 300 copies/mL, represented by

 

 15   the bottom circle, compared to only 57 percent for

 

 16   lamivudine-treated patients.  Overall, 88 percent

 

 17   of patients, represented by the bottom two circles

 

 18   in each case, achieved viral DNA reductions below

 

 19   1,000 copies/mL on entecavir by week 48.

 

 20             Genotyping identified 76 emerging changes

 

 21   but no distinctive patterns were observed, and no

 

 22   change was present in more than three isolates,

 

 23   representing 0.6 percent of those treated.

 

 24   Phenotypic analysis of these emerging changes show

 

 25   that their presence did not result in a significant

 

                                                                63

 

  1   decrease in entecavir susceptibility.  There were

 

  2   11 virologic rebounds on the entecavir arms of

 

  3   these studies compared to 88 rebounds on lamivudine

 

  4   therapy.

 

  5             This slide shows the origin and frequency

 

  6   of rebounds by study.  When genotyped, nearly all

 

  7   of the observed virologic rebounds on lamivudine

 

  8   therapy coincided with the emergence of resistance

 

  9   substitutions at residues 180 and 204, yielding a

 

 10   confirmed resistance frequency of 8-18 percent by

 

 11   week 48.  In contrast, none of the entecavir

 

 12   virologic rebounds observed in nucleoside-naive

 

 13   patients could be attributed to emergence of

 

 14   resistance.

 

 15             A close examination of the individual

 

 16   patient profiles showed that all 11 patients

 

                                                                64

 

  1   exhibiting a rebound on entecavir had at least a

 

  2   3-log reduction in viral DNA levels and 7 of the 11

 

  3   had greater than a 5-log reduction.  Most

 

  4   importantly, all patients had viral populations

 

  5   that were full susceptible to entecavir at the time

 

  6   of rebound, and there was no evidence of emerging

 

  7   genotypic changes that reduced entecavir

 

  8   susceptibility.

 

  9             From this comprehensive analysis we

 

 10   conclude that there was no evidence of emerging

 

 11   genotypic or phenotypic resistance to entecavir in

 

 12   any of the nucleoside-naive patients by week 48, a

 

 13   result that is most likely due to the high degree

 

 14   of sustained viral suppression observed.  We

 

 15   continue to monitor these patients for resistance

 

 16   in subsequent treatment years.

 

 17             Let us now turn to the

 

 18   lamivudine-refractory patient population where

 

 19   previous studies indicated that entecavir

 

 20   resistance emergence can occur.  Similar to

 

 21   nucleoside-naive patients, entecavir was highly

 

 22   effective in lamivudine-refractory patients

 

                                                                65

 

  1   enrolled in study 026 and in the 1 mg arm of study

 

  2   014.

 

  3             The figure again plots the distribution of

 

  4   lamivudine-refractory patients having the HBV DNA

 

  5   levels indicated at study entry, week 24 and week

 

  6   48.  While reductions were somewhat less than those

 

  7   observed in nucleoside-naive patients, 22 percent

 

  8   of entecavir-treated patients achieved viral DNA

 

  9   reductions below 300 copies/mL by week 48.  There

 

 10   was a clear trend of sustained and increasing

 

 11   reductions from week 24 to week 48, and superiority

 

 12   to continued lamivudine therapy.

 

 13             As part of our comprehensive resistance

 

 14   evaluation, all patients, regardless of treatment

 

 15   arm, were genotyped at study entry and week 48.

 

 16   There were 5 virologic rebounds among the

 

 17   lamivudine-refractory patients treated with

 

 18   entecavir.

 

 19             The figure plots the HBV DNA levels for

 

 20   the first two patients, labeled 1 and 2.  Both

 

 21   exhibited only modest reductions in HBV DNA levels

 

 22   on entecavir therapy.  Evidence of entecavir

 

                                                                66

 

  1   resistance substitutions at residue 184 were noted

 

  2   in both patients and population phenotypes

 

  3   indicated a 15-19-fold decrease in entecavir

 

  4   susceptibility, consistent with resistance

 

  5   emergence.

 

  6             In contrast, the three other patients,

 

  7   labeled 3, 4 and 5, all experienced at least a

 

  8   4-log reduction in viral DNA levels and further

 

  9   reductions following rebound either on continued

 

 10   therapy or off treatment, with no evidence of

 

 11   genotypic or phenotypic changes beyond those

 

 12   expected for lamivudine-resistant viruses.

 

 13             Based on this evaluation, only two

 

 14   patients or one percent of lamivudine-refractory

 

 15   patients treated with entecavir experienced

 

 16   virologic rebound due to resistance by week 48.

 

 17   Entecavir-resistant substitutions were, however,

 

 18   noted in 12 entecavir-treated patients by week 48,

 

 19   all with a background of lamivudine-resistant

 

 20   substitutions.  These patients continue to be

 

 21   monitored for virologic rebounds in subsequent

 

 22   years.  Emerging substitutions at 14 other residues

 

                                                                67

 

  1   were also identified, but none were present in more

 

  2   than 3 patients or reduced entecavir susceptibility

 

  3   beyond those expected for lamivudine-resistant

 

  4   viruses.

 

  5             An unexpected finding was that lamivudine

 

  6   can preselect for entecavir-resistant

 

  7   substitutions.  This was further supported by the

 

  8   observation that lamivudine-treated patients showed

 

  9   evidence of emerging changes at residues 169 and

 

 10   184 in study 026.  Among the greater than 360

 

 11   lamivudine-refractory patients genotyped, at least

 

 12   22 had detectable changes at entecavir-resistant

 

 13   substitutions at study entry.  Nine were randomized

 

 14   to an entecavir treatment arm, where two progressed

 

 15   to have resistance-induced virologic rebounds

 

 16   described earlier.  Only 2/9 patients were able to

 

 17   reduce viral DNA levels below 300 copies/mL.  This

 

 18   observation, along with the other results described

 

 19   in this presentation, indicate that extended use of

 

 20   lamivudine will not only select for the primary

 

 21   lamivudine-resistant substitutions at 180 and 204,

 

 22   but can also select for a number of secondary

 

                                                                68

 

  1   substitutions that can significantly reduce

 

  2   entecavir susceptibility and clinical efficacy.

 

  3             This slide summarizes our current

 

  4   understanding of the entecavir resistance profile

 

  5   at week 48.  There was no evidence of genotypic or

 

  6   phenotypic resistance in any studied

 

  7   nucleoside-naive patients treated with entecavir.

 

  8   Entecavir did not select for lamivudine-resistant,

 

  9   or entecavir-resistant substitutions, or other

 

 10   novel substitutions that result in decreased

 

 11   entecavir susceptibility and there were no

 

 12   virologic rebounds due to resistance.

 

 13             Among the patients having primary

 

 14   lamivudine-resistant substitutions at residues 180

 

 15   and 204, 7 percent exhibited emerging

 

 16   entecavir-resistant substitutions while on

 

 17   entecavir therapy, and only 1 percent of

 

 18   lamivudine-refractory patients exhibited a

 

 19   virologic rebound due to resistance by week 48.

 

 20   The preexistence of entecavir-resistant

 

 21   substitutions appears to be a marker for decreased

 

 22   efficacy and potential virologic rebound.

 

 23             In summary, the potent and sustained

 

 24   suppression of viral replication by entecavir

 

 25   likely accounts for the absence of resistance

 

                                                                69

 

  1   emergence in nucleoside-naive patients.  An

 

  2   extensive analysis of nucleoside-naive patients

 

  3   showed no evidence or resistance.  Entecavir was

 

  4   also effective in lamivudine-refractory patients

 

  5   where only 1 percent of patients experienced a

 

  6   virologic rebound due to resistance by week 48.

 

  7   Substitutions correlated with entecavir resistance

 

  8   were identified at primary residues 184, 202 and

 

  9   250 and the secondary residue 169.

 

 10   Lamivudine-resistant substations are a prerequisite

 

 11   for achieving high level entecavir resistance and

 

 12   lamivudine treatment can preselect for some

 

 13   entecavir-resistant substitutions.

 

 14             We conclude that this virologic profile

 

 15   provides critical information to physicians

 

 16   regarding the placement of entecavir in the

 

 17   armamentarium of drugs available to treat chronic

 

 18   hepatitis B infection.  Dr. Donna Morgan Murray

 

 19   will now conclude our presentation with

 

                                                                70

 

  1   pharmacovigilance and final summary.

 

  2                  Pharmacovigilance and Summary

 

  3             DR. MORGAN MURRAY:  As you have heard this

 

  4   morning, the entecavir clinical development program

 

  5   was extensive.  It was the largest HBV program

 

  6   conducted to date and the only antiviral HBV

 

  7   program to use an active comparator in Phase III

 

  8   trials.  That comparator was lamivudine, the only

 

  9   agent available at the time of initiation of the

 

 10   trials and the most common HBV therapy used to

 

 11   date.

 

 12             Entecavir demonstrated substantial

 

 13   clinical benefit in Phase III and was superior to

 

 14   lamivudine in the prespecified primary endpoint of

 

 15   improved histology.  Entecavir was also superior to

 

 16   lamivudine in most of the secondary endpoints.

 

 17             Based on the rodent tumor findings,

 

 18   entecavir is a rodent carcinogen.  The lung tumors

 

 19   appear to be species specific, and the other tumors

 

 20   occur at high exposure multiples.  The

 

 21   investigative data submitted to the carcinogenicity

 

 22   assessment committee do not definitively eliminate

 

                                                                71

 

  1   a risk for humans.  With more than 2,300 patients

 

  2   treated with entecavir, there is no safety signal

 

  3   related to malignancy in the clinical development

 

  4   program.  While this is reassuring, we recognize

 

  5   that the observation period is short.

 

  6             As Dr. Sigal mentioned, we are committed

 

  7   to continuously assessing the benefit versus risk

 

  8   profile of entecavir, and have proposed a

 

  9   post-marketing pharmacovigilance plan with three

 

 10   main components.  In addition to routine

 

 11   post-marketing surveillance, the pharmacovigilance

 

 12   plan also includes real-time monitoring of special

 

 13   events, specifically malignancies and hepatic

 

 14   events.  We have designed special questionnaires to

 

 15   aid in collecting follow-up information for reports

 

 16   of both malignancies and hepatic events.  We will

 

 17   periodically review post-marketing and clinical

 

 18   trial adverse event data, using quarterly aggregate

 

 19   frequency reports, and we will review these events

 

 20   of special interest.

 

 21             There are three ongoing long-term safety

 

 22   studies and we have proposed an additional large,

 

                                                                72

 

  1   prospective, randomized safety study to be

 

  2   conducted post-marketing.  First let's review the

 

  3   ongoing studies.

 

  4             The clinical development program included

 

  5   one- to two-year treatment studies and long-term

 

  6   safety studies with careful observation for the

 

  7   development of malignancies.  Responders from the

 

  8   Phase II/III trials were encouraged to enroll in an

 

  9   observational study that was aimed to gather safety

 

 10   data off treatment.  Malignancy was the primary

 

 11   focus of this observational study.  Some patients

 

 12   from the Phase II treatment studies were eligible

 

 13   to enroll in open-label treatment studies, and

 

 14   these patients were also encouraged to enroll in

 

 15   the observational study.

 

 16             To date, more than 80 percent of patients

 

 17   from Phase III have enrolled in at least one of the

 

 18   long-term safety studies, and the observational

 

 19   study has more than 400 patients enrolled, with the

 

 20   expectation that we will enroll up to 1,500

 

 21   patients and all patients will be followed for 5

 

 22   years.  In addition to the ongoing studies, we

 

                                                                73

 

  1   propose initiating a large safety study post

 

  2   approval.

 

  3             Given the limitations of pre-approval

 

  4   clinical studies, we recognize that we cannot rule

 

  5   out a cancer risk in patients treated with

 

  6   entecavir.  Pre-approval studies do not provide

 

  7   sufficient numbers of patients to rule out such

 

  8   uncommon events.  We considered several options for

 

  9   further assessment and concluded that a randomized,

 

 10   prospective study would permit rigorous analysis of

 

 11   these events of special interest--mortality,

 

 12   neoplasms and progression of liver disease.

 

 13             The draft protocol for this study calls

 

 14   for patients to be randomized 1:1 to entecavir

 

 15   versus another standard of care nucleoside or

 

 16   nucleotide; to be stratified as naive or previously

 

 17   treated; and to be followed for at least 5 years.

 

 18   It is our intent to engage an external, independent

 

 19   data safety monitoring board to conduct periodic

 

 20   reviews of the data from this study.

 

 21             We propose to conduct the study globally

 

 22   and to recruit patients via their own physicians. 

 

                                                                74

 

  1   Patients who are starting a new HBV therapy or are

 

  2   changing their therapy will be eligible to enroll.

 

  3   We expect to enroll a total of 12,500 patients.  We

 

  4   will report annually on rates of all-cause

 

  5   mortality, malignancy and progression of liver

 

  6   disease.  While other common nucleosides also have

 

  7   rodent tumor findings, and the benefit-risk

 

  8   assessment was favorably concluded based on the

 

  9   serious nature of the disease, such as AZT for HIV,

 

 10   few have been the subject of the rigorous

 

 11   assessment that we propose here.

 

 12             However, the proposed study does have

 

 13   several challenges.  First, the planned primary

 

 14   analysis is intent-to-treat and, as patients will

 

 15   inevitably switch therapies over the course of the

 

 16   study, the primary analysis may be confounded.

 

 17   However, we will not limit our review of the data

 

 18   to this analysis and we will look at the data in

 

 19   several different ways.

 

 20             Second, there may be limited ability to

 

 21   detect treatment group differences for events of

 

 22   variable latency.  Since all patients will be

 

                                                                75

 

  1   studied for at least 5 years, and many may well be

 

  2   studied for up to 8 years, we should detect a

 

  3   signal if there is an increased risk.

 

  4             Third, the study is designed to detect

 

  5   differences in overall malignancy rates and in

 

  6   rates of HCC, but is not designed to detect

 

  7   treatment group differences for individual

 

  8   malignancy types.

 

  9             Finally, attrition will occur but this

 

 10   does not mean that patients will be lost to

 

 11   follow-up.  We will implement tactics to enhance

 

 12   follow-up, and we have developed strategies to

 

 13   address these challenges listed on this slide, and

 

 14   conclude that the proposed study will provide

 

 15   important data on both the benefits of entecavir

 

 16   and on further risk assessment.

 

 17             Adequate data exist to demonstrate the

 

 18   substantial benefit of entecavir over existing

 

 19   therapies.  Entecavir provides superior viral

 

 20   suppression in both nucleoside-naive and

 

 21   lamivudine-refractory patients.  Specifically,

 

 22   treatment with entecavir resulted in up to a 7-log

 

                                                                76

 

  1   decrease in HBV DNA.

 

  2             Entecavir results in superior

 

  3   normalization of ALT in both nucleoside-naive and

 

  4   lamivudine-refractory patients.  Up to 78 percent

 

  5   of patients achieve normal ALT.

 

  6             Entecavir also provides superior

 

  7   improvement in histology in both nucleoside-naive

 

  8   and lamivudine-refractory patients.  Treatment with

 

  9   entecavir resulted in up to 72 percent reduction in

 

 10   necroinflammation.

 

 11             Entecavir has a favorable resistance

 

 12   profile compared to lamivudine.  As you heard from

 

 13   Dr. Colonno, no resistance substitutions emerged in

 

 14   nucleoside-naive patients and resistance

 

 15   substitutions were uncommon in

 

 16   lamivudine-refractory patients.

 

 17             Given the demonstrated superiority of

 

 18   entecavir in viral suppression, ALT normalization

 

 19   and improved histology, and the favorable

 

 20   resistance profile both in nucleoside-naive and

 

 21   lamivudine-refractory patient populations,

 

 22   long-term benefits of entecavir might include a

 

                                                                77

 

  1   reduction in disease progression, such as lower

 

  2   rates of liver failure, liver cancer, liver

 

  3   transplant and liver-related deaths.

 

  4             We conclude that the demonstrated benefits

 

  5   of entecavir represent an important treatment

 

  6   advance for HBV infection.  The demonstrated

 

  7   benefits of entecavir against HBV, a known

 

  8   carcinogen, are indeed substantial and outweigh the

 

  9   theoretical risk posed by the rodent tumor data.

 

 10   Thank you for you attention this morning.

 

 11                   Questions from the Committee

 

 12             DR. ENGLUND:  Thank you very much, Dr.

 

 13   Murray.  I would like to thank the Bristol-Myers

 

 14   Squibb people for a very clear, concise and timely

 

 15   presentation.  It was very nice.  Thank you.

 

 16             This is the time that we are going to open

 

 17   up for questions to the panel, but I would like to

 

 18   caution people that the questions are supposed to

 

 19   be directly related to the information presented

 

 20   today.  We will have discussion time later on but

 

 21   if there are clarifications or questions about

 

 22   specific points related to the presentation we just

 

                                                                78

 

  1   heard, now is the time to begin so I will open it

 

  2   to the panel for questions.  Dr. DeGruttola?

 

  3             DR. DEGRUTTOLA:  Yes, I have two

 

  4   questions.  The presentations mentioned that the

 

  5   studies in dogs and rats did not find an increased

 

  6   risk of lung cancer associated with entecavir.  I

 

  7   was wondering how long those studies had gone on;

 

  8   were they powered to be able to detect such an

 

  9   effect?  Then, regarding the post-marketing study

 

 10   to try to determine an effect on cancer in humans,

 

 11   I was wondering what the power will be in that

 

 12   study; what magnitudes of effects is the study

 

 13   powered to detect?

 

 14             DR. MORGAN MURRAY:  First I will ask Dr.

 

 15   Lois Lehman-McKeeman to address your first question

 

 16   about the duration of studies in dogs and rats.

 

 17             DR. LEHMAN-MCKEEMAN:  I will speak to the

 

 18   rats first because they were, in fact, one of the

 

 19   species used in the lifetime carcinogenicity study.

 

 20   So, in two years, for the lifetime of the rat,

 

 21   there were no tumors in the lung that developed.

 

 22             The dog the studies were not conducted to

 

                                                                79

 

  1   be carcinogenicity studies; they were chronic

 

  2   toxicology studies and they were three months in

 

  3   duration.  However, what we understand about the

 

  4   lung lesion in the mouse is that it develops very

 

  5   quickly and the early preneoplastic change that I

 

  6   described occurs within the first two weeks of

 

  7   dosing.  In the course of a three-month study in

 

  8   dogs we saw no early preneoplastic change.

 

  9             DR. DEGRUTTOLA:  Thank you.

 

 10             DR. MORGAN MURRAY:  And for your second

 

 11   question about the power of our post-marketing

 

 12   study to detect differences, Dr. Phil Pierce will

 

 13   address that.

 

 14             DR. PIERCE:  The primary goal of the large

 

 15   safety trial is to investigate the potential

 

 16   treatment effect on the development of non-HCC

 

 17   malignancies.  First we had to establish what the

 

 18   background rate in this population is, and we

 

 19   utilized the data from the Taiwan cohort that was

 

 20   presented, as well as the background rates that we

 

 21   saw in the BMS studies.

 

 22             The background rate was approximately 4

 

                                                                80

 

  1   non-HCC cancers over 1,000 patient-years of

 

  2   follow-up.  We estimated from that that there would

 

  3   be 16 non-HCC malignant events per 1,000

 

  4   patient-years per arm over 5 years.  Also, the

 

  5   total accrual of time will be 65,000 patient-years.

 

  6   Our study was designed to show a 30 percent

 

  7   increased risk of malignancy.  That translates into

 

  8   5 additional cancers per 1,000 patient-years over

 

  9   the 16 that I mentioned earlier.  I believe BMS

 

 10   concludes this is a reasonable assessment of that

 

 11   risk.

 

 12             Slide 1-520, please.  I gave you a lot of

 

 13   numbers with that and I want to show the expected

 

 14   events in the untreated population over the 5

 

 15   years.  The rate that I mentioned for the non-skin,

 

 16   non-HCC cancers is 16 as the expected rate and we

 

 17   would have a power to detect, with this sized

 

 18   population, an increase of 5 over that 16.  The

 

 19   additional benefit of this study is that we will

 

 20   also be able to analyze the impact on the other

 

 21   events of interest which, obviously because of the

 

 22   large size of those, we are adequately powered to

 

                                                                81

 

  1   show whether we have an impact on the rates of HCC

 

  2   and on the progression to cirrhosis.

 

  3             DR. DEGRUTTOLA:  Thank you.

 

  4             DR. ENGLUND:  Thank you.  Dr. Washburn?

 

  5             DR. WASHBURN:  It is very interesting that

 

  6   the study drug is chemotactic for mouse monocytes

 

  7   but not human monocytes.  I wonder if there is any

 

  8   work that can be shared that would discuss some

 

  9   mechanism of that difference.  Does it relate to

 

 10   complement activation, or a macrophage chemotactic

 

 11   peptide, or other?  The question is of potential

 

 12   relevance in the carcinogenicity of disease.

 

 13             DR. MORGAN MURRAY:  Dr. Lehman-McKeeman

 

 14   will address that.

 

 15             DR. LEHMAN-MCKEEMAN:  At this point in

 

 16   time we don't know the molecular basis of that

 

 17   difference.  What we know is that based on the fact

 

 18   that macrophages were accumulating in the lung and

 

 19   were not proliferating to accumulate, we looked

 

 20   specifically for a chemotactic event and we tested

 

 21   that in some standard in vitro systems.  When we

 

 22   did that work, there is clear chemotactic activity

 

                                                                82

 

  1   to the mouse with no effect in the human at all.

 

  2             Now, to go further, we have looked, in

 

  3   doing some investigative work, at whether or not

 

  4   altering macrophage recruitment alters the

 

  5   progression of this lesion.  To do that, we have

 

  6   looked at a CCR2 knockout, so chemokine receptor to

 

  7   a knockout animal, and we found that that mouse

 

  8   does, indeed, have a very different response to the

 

  9   drug.  It is no unequivocal proof that this is

 

 10   mediated through CCR2, but it suggests that it

 

 11   plays a role.

 

 12             I want to add one other factor though, and

 

 13   that is that the lesion that we see involves

 

 14   accumulation of macrophages but, based on our

 

 15   assessment, those macrophages don't appear to be

 

 16   activated.  They are simply accumulating.

 

 17             DR. WASHBURN:  Thank you.

 

 18             DR. ENGLUND:  Dr. Fish?

 

 19             DR. FISH:  I didn't hear my name earlier

 

 20   in the disclosure statement and I just need to add

 

 21   that though I signed the disclosure waiver, I have

 

 22   been on the speakers bureau for the sponsor and two

 

                                                                83

 

  1   competitors.

 

  2             The question that I have is on the study

 

  3   were there pregnancies and, if so, the outcomes of

 

  4   those pregnancies in entecavir-treated patients?

 

  5             DR. MORGAN MURRAY:  I am going to try out

 

  6   Dr. Brett-Smith's voice here.  So, Helena?

 

  7             DR. BRETT-SMITH:  The studies were

 

  8   designed that if pregnancy was determined to occur

 

  9   during the course of the study the patient was to

 

 10   immediately stop study drug.  Indeed, pregnancies

 

 11   do occur.  The majority of these actually resulted

 

 12   in elective termination of pregnancies.

 

 13             If we could show slide 5-79, this includes

 

 14   the various treatment combinations that have been

 

 15   used across our entire program to date with

 

 16   entecavir alone, lamivudine alone, entecavir in

 

 17   combination with lamivudine, for the initial period

 

 18   of the 901 long-term rollover study and also in

 

 19   placebo.

 

 20             As you can see, the majority of

 

 21   pregnancies identified resulted in elective

 

 22   termination.  There was a small number of

 

                                                                84

 

  1   spontaneous abortions.  There have been 6 live

 

  2   births.  The 4 outcomes that are listed as

 

  3   "unknown" are progressions that are currently under

 

  4   way and for which we are actively pursuing

 

  5   follow-up on those deliveries.

 

  6             With respect to the live births, across

 

  7   those live births there were no reported defects in

 

  8   5 out of the 6 cases.  There was, indeed, 1 live

 

  9   birth where the mother had received entecavir 0.5

 

 10   mg for a total of 44 weeks but the diagnosis of the

 

 11   pregnancy was made at approximately week 7 of

 

 12   gestation.  That had a fairly complicated history.

 

 13   The child was born with what has been reported to

 

 14   us as a severe cerebral cortex defect.

 

 15   Unfortunately, despite repeated contact with the

 

 16   site, the family has not wished to provide us with

 

 17   further data.

 

 18             The details of the early pregnancy are a

 

 19   little complex so let me walk you through those.

 

 20   The patient had discontinued entecavir immediately

 

 21   at the time that pregnancy was diagnosed, as I

 

 22   said, about week 7.  The patient then experienced

 

                                                                85

 

  1   what was clinically diagnosed as a spontaneous

 

  2   abortion and was told by the gynecologist that no

 

  3   fetus had been present.  A subsequent ultrasound

 

  4   actually did reveal a live fetus, but in the

 

  5   interim entecavir had been briefly restarted by the

 

  6   clinician for 2 weeks and the moment the ultrasound

 

  7   became available it was discontinued.  So, that

 

  8   represents the sum of our experience to date in the

 

  9   program with pregnancy.

 

 10             DR. ENGLUND:  Dr. Haubrich?

 

 11             DR. HAUBRICH:  It is clear that emergence

 

 12   of viral resistance to therapy is dependent on the

 

 13   degree of viral suppression and, clearly, drugs

 

 14   that have greater suppression will have less

 

 15   emergence of resistance.  It is also clear from

 

 16   extensive experience in AZT that after 15-20 years

 

 17   of nucleoside therapy we are still identifying new

 

 18   mutations.  So, perhaps I didn't follow it well,

 

 19   but if you could clarify the emergence of mutations

 

 20   that may have occurred with entecavir.  Although

 

 21   they may not lead to phenotypic susceptibility

 

 22   since the number of mutations is few at this point,

 

                                                                86

 

  1   you know, they may in the future be defined when

 

  2   greater numbers of samples are available.

 

  3             So, just a comment that it is clear that

 

  4   the resistance profile is better with greater

 

  5   suppression, but it seems a little premature to be

 

  6   saying that there is no resistance that develops on

 

  7   therapy when the number of specimens is low and it

 

  8   may be a bit early.  So, if you could comment on

 

  9   that I would appreciate it.

 

 10             DR. MORGAN MURRAY:  I will ask Dr. Colonno

 

 11   to comment but first I would like to note that the

 

 12   original NDA and the safety update--at that time we

 

 13   only had 48-week data available and that is the

 

 14   only data that have been submitted for review.  But

 

 15   very recently we did complete the analysis on

 

 16   patients who have been treated for two years and

 

 17   Dr. Colonno can perhaps share those data as well.

 

 18             DR. COLONNO:  Let me just deal with the

 

 19   first part first in terms of the number of

 

 20   mutations, just to give you a sense of what

 

 21   mutations were found.

 

 22             Can I have slide 1-315, please?  This is a

 

                                                                87

 

  1   list of all the mutations that have been found or

 

  2   identified in all patients examined that have taken

 

  3   entecavir--as you can see, a very wide range.  The

 

  4   vast, vast majority of these, again, have occurred

 

  5   at polymorphic sites.  We call them new emerging

 

  6   substitutions because they have not been described

 

  7   previously at those particular sites.

 

  8             Again, I will point out that these

 

  9   mutations do not occur in any more than three

 

 10   patients.  Most of these occur in a single patient,

 

 11   again, representing less than one percent.  We have

 

 12   tested all of these different mutations and

 

 13   substitutions not only by themselves but also in

 

 14   the context of their preexisting clinical

 

 15   background and, as you can see by the EC                                 

                                                                50s that are

 

 16   present, they really do not alter the normal wild

 

 17   type susceptibility.

 

 18             Now if I can just move to your statement,

 

 19   which I think is a correct one and, again, as a

 

 20   virologist having worked in resistance for many,

 

 21   many years, there is no such thing as no

 

 22   resistance.  So, we have gone out to the second

 

                                                                88

 

  1   year, and this is real-time data and the data

 

  2   continues to come in, and I would like to just

 

  3   share with you some very encouraging data for the

 

  4   second year.

 

  5             This is the second year data as it

 

  6   currently stands.  On the left-hand side, again,

 

  7   are the bubble charts and the first thing I want to

 

  8   point out is this is study 022 where we have the

 

  9   most data.  You can see that the continued

 

 10   progression in decreasing DNA from week 48 to 96,

 

 11   where we have 65 undetectable now, we continue to

 

 12   drive viral load down with 81 percent of patients

 

 13   now with undetectable virus.

 

 14             That correlates with the table on the

 

 15   right where, again, despite the fact that we have

 

 16   treated now for 2 years, we have a very similar

 

 17   profile to what we saw in year 1.  In year 2 we

 

 18   have a total of 7 rebounds, virologic rebounds

 

 19   using the definition I described earlier but,

 

 20   again, looking at their genotypes and phenotypes we

 

 21   see no evidence of any genotypic or phenotypic

 

 22   resistance.  So, out to 2 years in the

 

                                                                89

 

  1   nucleoside-naive population with that type of viral

 

  2   suppression we have not observed any resistance to

 

  3   entecavir.

 

  4             DR. ENGLUND:  Dr. Johnson, do you have a

 

  5   specific question about that?

 

  6             DR. JOHNSON:  Victoria Johnson, University

 

  7   of Alabama at Birmingham.  As a virologist and

 

  8   viral resistance person, I share concerns that

 

  9   despite the elegant data presented, given this

 

 10   compound's potency, as you realize, two years may

 

 11   not be enough, and I want to just ask is this part

 

 12   of the pharmacovigilance monitoring plan?  That is

 

 13   one question.

 

 14             The second question is, if you can go to

 

 15   your second to last slide of your previous

 

 16   presentation--

 

 17             DR. MORGAN MURRAY:  Let me answer your

 

 18   first question first around the pharmacovigilance

 

 19   plan.  Several of our studies are ongoing, as I had

 

 20   mentioned, and in all of the ongoing clinical

 

 21   studies we do continue to monitor for resistance.

 

 22   Acknowledging that the pharmacovigilance plan is

 

                                                                90

 

  1   very large, we will have many centers and it will

 

  2   be usual practice, we feel it will be impossible

 

  3   for us to get resistance data on all of the 12,500

 

  4   patients.  But what we do propose is to have a

 

  5   sub-study, a subset of patients, a center in the

 

  6   U.S., a center, you know, here and there that we

 

  7   will get much more data including resistance data.

 

  8   I will let Dr. Colonno address your second point.

 

  9             DR. COLONNO:  We will continue to look for

 

 10   resistance until we find it.  Again, there is

 

 11   always going to be resistance at some point.  But

 

 12   the key point of this slide, which we don't have

 

 13   with HIV, unfortunately, even with combination

 

 14   therapy, is the ability to drive viral load down by

 

 15   6 or 7 logs, 8 logs in some cases and to maintain

 

 16   that for a very long period of time.  Those viruses

 

 17   require a minimal amount of replication to give

 

 18   rise to resistance.  So, we are encouraged.  Again,

 

 19   that is not to say there will never be resistance

 

 20   but we are highly encouraged with that kind of

 

 21   suppression and with the limited ability of the

 

 22   virus to actually replicate that a large amount of

 

                                                                91

 

  1   resistance will all of a sudden come up.  We will

 

  2   continue to monitor these patients for the

 

  3   foreseeable future.

 

  4             Another interesting point is that these

 

  5   particular patients do not give rise to any

 

  6   evidence of resistance substitutions being

 

  7   selected.  We know lamivudine resistance is a

 

  8   stepping stone to becoming clinically relevant

 

  9   resistance to entecavir.  But the fact that we,

 

 10   again in that population, see none of those changes

 

 11   really coming up again is encouraging but, again,

 

 12   it is only two-year data for a large number of

 

 13   patients, but not a tremendous amount, so we will

 

 14   continue to monitor in subsequent years.

 

 15             DR. JOHNSON:  My second question is on

 

 16   your second to last slide, just for clarification.

 

 17             DR. COLONNO:  My second to last slide?

 

 18             DR. JOHNSON:  Yes, from your earlier

 

 19   presentation.  It was called summary of viral

 

 20   resistance data at week 48.  So, just to clarify,

 

 21   and I think part of this got answered, the title is

 

 22   week 48 but the bottom data are presented on two

 

                                                                92

 

  1   patients who had greater than 76 weeks.

 

  2             DR. COLONNO:  Those two patients were from

 

  3   the Phase II study.  They are not included here;

 

  4   they were Phase II.

 

  5             DR. JOHNSON:  So, they are different than

 

  6   the two on this slide that are on the bottom?

 

  7             DR. COLONNO:  These two are from the Phase

 

  8   III evaluation.

 

  9             DR. JOHNSON:  At week 48?

 

 10             DR. COLONNO:  At week 48.

 

 11             DR. JOHNSON:  And that is different than

 

 12   the other two patients you described with virologic

 

 13   rebound resistance?

 

 14             DR. COLONNO:  That is correct.  One was in

 

 15   the 015 study which was a transplant study, and the

 

 16   other one was in 014.

 

 17             DR. JOHNSON:  But they appear to select

 

 18   the same signature mutations?

 

 19             DR. COLONNO:  They select the same

 

 20   signature mutations.  Those three mutations appear

 

 21   to be the key primary resistance markers for

 

 22   entecavir.

 

 23             DR. ENGLUND:  Dr. Sherman?

 

 24             DR. SHERMAN:  The presentation indicated

 

 25   that phosphorylation was required for this product.

 

                                                                93

 

  1   Could you comment on any data you have regarding

 

  2   interactions with anti-retrovirals that also

 

  3   require phosphorylation in vitro?  I know you have

 

  4   limited in vivo HIV-positive patients, but is there

 

  5   any pharmacokinetic analysis and any issues of

 

  6   changes in resistance to HIV or susceptibility

 

  7   because of the interaction?

 

  8             DR. MORGAN MURRAY:  I will let Dr. Colonno

 

  9   follow up on that.

 

 10             DR. COLONNO:  We have done an extensive

 

 11   analysis of the interactions because it is a

 

 12   nucleoside analog and there are many nucleoside

 

 13   analogs that are used in HIV, interactions based on

 

 14   the phosphorylation patterns of these various

 

 15   combinations.  What I can tell you is that because

 

 16   the concentration of entecavir is so low relative

 

 17   to other nucleoside analogs and the efficiency is

 

 18   so high, when one does in vitro cell culture

 

 19   combination studies to look for the effect of

 

                                                                94

 

  1   entecavir on the antiviral potency of the HIV

 

  2   nucleoside analogs, or in the opposite direction in

 

  3   the presence of the HIV and RTIs and does it have

 

  4   an impact on entecavir activity, we find, using

 

  5   concentrations of both sets of compounds up to five

 

  6   times their C                                                     max,

clinical Cmax, we see no

 

  7   interactions whatsoever; no antagonism; and no

 

  8   decrease in the activity.  Again, that is a big

 

  9   plus for entecavir because entecavir is very

 

 10   selective for hepatitis B and so it literally also

 

 11   can be used in a co-infected patient but not having

 

 12   to worry about any kind of selective pressure on

 

 13   HIV.

 

 14             DR. ENGLUND:  I am going by the order that

 

 15   I saw the hands come up, which may be wrong, and we

 

 16   are only going to have time for about four or five

 

 17   more questions.  But the first question was Mr.

 

 18   Grodeck's.

 

 19             MR. GRODECK:  In terms of marketing

 

 20   antivirals, one of the biggest games I have seen

 

 21   pharmaceutical companies play is the sequencing

 

 22   game--my drug should come before your drug.  In

 

                                                                95

 

  1   your description of the resistance profile of

 

  2   entecavir, it seems to me that you are setting up

 

  3   the drug to be positioned as a first-line

 

  4   treatment.  Is that your position?  How does it fit

 

  5   in terms of the range of other treatments available

 

  6   to chronic hepatitis B patients today?

 

  7             DR. MORGAN MURRAY:  I will ask Dr.

 

  8   Dienstag to comment on how entecavir might fit into

 

  9   current treatment guidelines and the physicians'

 

 10   armamentarium.  I will just remind you, from our

 

 11   data, that we have demonstrated that entecavir is

 

 12   superior to lamivudine.  We have substantial

 

 13   benefits in both nucleoside-naive and

 

 14   lamivudine-refractory patients.

 

 15             DR. DIENSTAG:  Jules Dienstag,

 

 16   Massachusetts General Hospital.  I think if we

 

 17   consider hepatitis B a viral disease, then the drug

 

 18   that suppresses HBV most profoundly is likely to

 

 19   have the most benefit.  That has been shown in this

 

 20   study for histology, biochemical markers and

 

 21   especially for the profundity of suppression of HBV

 

 22   DNA.  In almost 90 percent of patients you can

 

                                                                96

 

  1   achieve an undetectable level of HBV DNA, which no

 

  2   other antiviral comes close to at this point.

 

  3             So, it is not unreasonable to suggest that

 

  4   this would be a first-line therapy.  When you add

 

  5   the resistance profile and when you consider the

 

  6   potential that, for example, a drug like lamivudine

 

  7   sets you up for lamivudine resistance in the future

 

  8   and also sets you up for resistance to any other

 

  9   nucleoside, it makes sense to start with this drug.

 

 10   It is a very reasonable suggestion.

 

 11             DR. ENGLUND:  Dr. Paxton, did you get your

 

 12   question answered?

 

 13             DR. PAXTON:  Yes, it was.  Thank you.

 

 14             DR. ENGLUND:  Dr. Wood, or were you first,

 

 15   Dr. Seeff or Dr. Schwarz?

 

 16             DR. SCHWARZ:  I have two questions

 

 17   relative to future applications of entecavir.  You

 

 18   said that in the animal carcinogenicity models in

 

 19   the organ involved with the tumor there were

 

 20   ETV-induced dNTP pool perturbations.  In either the

 

 21   animal studies or in the human studies, was there

 

 22   evidence of peripheral blood lymphocytes--the same

 

                                                                97

 

  1   phenomenon occurring in peripheral blood

 

  2   lymphocytes that might be a useful non-invasive

 

  3   surrogate marker for malignant potential?

 

  4             Then the second question is I assume in

 

  5   these lifetime exposure studies that the drug was

 

  6   not started in the immediate newborn period.  So,

 

  7   at what age of the animal was it started, and can

 

  8   you make an educated guess about the human

 

  9   equivalent age?

 

 10             DR. MORGAN MURRAY:  I will ask Dr.

 

 11   Lehman-McKeeman to address the data that we have in

 

 12   animals around dNTP pool perturbations and also

 

 13   about the rodent studies.  I will just comment that

 

 14   we do not have any human data around dNTP pool

 

 15   perturbations.  As Dr. Lehman-McKeeman will

 

 16   describe, these perturbations in animals occur at

 

 17   much higher doses than we administer in humans.

 

 18             DR. LEHMAN-MCKEEMAN:  I will actually

 

 19   address the second question first for you.  The

 

 20   studies that are conducted in rodents basically

 

 21   start when they are approximately 5-6 weeks of age.

 

 22   For perspective, that is when a rodent reaches

 

                                                                98

 

  1   sexual maturity.  So, in a 2-year life span, if I

 

  2   had to extrapolate, I will just say at sexual

 

  3   maturity so it would be roughly teenage.

 

  4             To your first question about the dNTP

 

  5   pools, in the work that we did we specifically

 

  6   looked at target organ effects related to

 

  7   carcinogenicity.  So, we specifically looked at the

 

  8   liver and we don't have any data on another system.

 

  9   Those analyses are actually quite, I will say,

 

 10   difficult to do, as it were, simply because the

 

 11   pools themselves are really quite fleeting.  So, it

 

 12   really is prohibitive for us to collect more then

 

 13   one sample and we targeted the liver.  However,

 

 14   what we know, based on the work we have done, is

 

 15   that that is a high dose phenomenon.  So, at

 

 16   dosages where we saw carcinogenic activity we saw

 

 17   perturbations in pools, and at a dose below a

 

 18   carcinogenic effect we did not seriously disrupt

 

 19   pools.  So, I think it is a function, again, of the

 

 20   maximum tolerated dosage that we are administering

 

 21   in the carcinogenicity studies.

 

 22             DR. ENGLUND:  Dr. Wood?

 

 23             DR. WOOD:  My question has to do with

 

 24   analysis of rates of malignant neoplasms according

 

 25   to ethnicity.  This is related to the fact that I

 

                                                                99

 

  1   believe I read that Asians have a higher

 

  2   pharmacokinetic exposure to entecavir and I was

 

  3   wondering whether or not an analysis had been done

 

  4   on that basis.

 

  5             DR. MORGAN MURRAY:  I will ask Dr.

 

  6   Brett-Smith to come up again.  I will try and spare

 

  7   her voice a bit and comment that while we have not

 

  8   seen PK differences on the basis of race in

 

  9   particular, the differences that we do detect are

 

 10   related to weight more than to race.  Dr.

 

 11   Brett-Smith, on the malignancies?

 

 12             DR. BRETT-SMITH:  At this point we have

 

 13   chosen not to look at any subpopulations in terms

 

 14   of the overall rates in malignancies because the

 

 15   total numbers remain low, and we believe that the

 

 16   rates would be sort of unreliably variable.  That

 

 17   may become an option later in terms of the

 

 18   pharmacovigilance.

 

 19             DR. ENGLUND:  Dr. Seeff?

 

 20             DR. SEEFF:  I thought that the efficacy

 

 21   data that were presented were fairly impressive but

 

 22   there are a couple of questions that I just need

 

 23   some clarification on.  Perhaps you presented them

 

 24   and I missed them.

 

 25             The primary endpoint for your study was

 

                                                               100

 

  1   histologic using the Knodell score.  I gather that

 

  2   this is not unusual; this is fairly routine.  Is

 

  3   this the 18-point HAI score?

 

  4             DR. MORGAN MURRAY:  Yes.

 

  5             DR. SEEFF:  In other words, the drop for

 

  6   example from 10 points to 8 points would represent

 

  7   an endpoint having been achieved.

 

  8             DR. MORGAN MURRAY:  Correct.

 

  9             DR. SEEFF:  What was the average drop?  Do

 

 10   you know what the average decline in points was,

 

 11   just to get a sense of how much improvement there

 

 12   was in histology?  Do you have those data by any

 

 13   chance?  I mean, you have the percentage of people

 

 14   who achieved a 2-point reduction, but what I am

 

 15   interested in knowing is by how much of a

 

 16   reduction.

 

 17             DR. MORGAN MURRAY:  Dr. Brett-Smith?

 

 18             DR. BRETT-SMITH:  Yes, we do have data and

 

 19   I can present it for you if we can show slide 2-66.

 

 20   Overall, in the naive patients it was approximately

 

 21   a 4-point drop in the mean score, and in the

 

 22   refractory patients it was approximately a 3-point

 

 23   drop.

 

 24             DR. SEEF:  That is fine.  Thank you.  The

 

 25   second thing is your secondary endpoints,

 

                                                               101

 

  1   essentially a reduction in HBV viral load and

 

  2   normalization of ALT, do you have a composite score

 

  3   taking into account the virologic, histologic,

 

  4   biochemical reduction?  Do we have a score of using

 

  5   those three parameters?

 

  6             DR. MORGAN MURRAY:  Dr. Brett-Smith?

 

  7             DR. SEEFF:  And is it the same between

 

  8   entecavir and lamivudine for example?

 

  9             DR. BRETT-SMITH:  If I can just repeat the

 

 10   factors that you are interested in, you are

 

 11   interested in combining histology with virology--

 

 12             DR. SEEFF:  And with biochemical response.

 

 13             DR. BRETT-SMITH:  With ALT.

 

 14             DR. SEEF:  ALT.

 

 15             DR. BRETT-SMITH:  Those three.  We have

 

 16   looked at a number of ways of combining virology

 

 17   with ALT.  I will ask my colleagues to confirm

 

 18   whether we have yet completed the analysis

 

 19   combining with histology.  I do not have that at

 

 20   this time.

 

 21             DR. MORGAN MURRAY:  So, we will confer

 

 22   during the break and see if we can quickly pull

 

 23   something together to answer that.

 

 24             DR. ENGLUND:  Last question, Dr. So?

 

 25             DR. SO:  There is a common belief by many

 

                                                               102

 

  1   clinicians that, you know, if you have e-antigen

 

  2   seroconversion you pretty much, you know, have a

 

  3   good response and you might be cured.  So, I notice

 

  4   that earlier in this handout to us, the committee

 

  5   members, you did describe some follow-up on the

 

  6   patients in your study 22 where they have so-called

 

  7   complete response.  Some of the patients were taken

 

  8   off drugs.  Do you have two-year follow-up

 

  9   information regarding how many of those patients

 

 10   have so-called sustained response and what

 

                                                               103

 

  1   sustained response means?

 

  2             DR. MORGAN MURRAY:  I will ask Dr.

 

  3   Brett-Smith to comment, and I need to make the

 

  4   statement that in the NDA and the NDA update we

 

  5   only had the 48-week data so, again, these data

 

  6   have not been submitted for review.

 

  7             DR. BRETT-SMITH:  I heard a two-part

 

  8   question there.  Let me just clarify.  I heard

 

  9   first for patients who, at the end of year one,

 

 10   went off dosing--you were interested in the

 

 11   sustained response off treatment.

 

 12             DR. SO:  Right.

 

 13             DR. BRETT-SMITH:  Also, did I hear an

 

 14   interest in what happens to the portion of partial

 

 15   responders who have a virologic response--

 

 16             DR. SO:  No, I am just interested in your

 

 17   so-called complete responders.

 

 18             DR. BRETT-SMITH:  Let me first summarize

 

 19   for you the design of the studies at the week 52

 

 20   endpoint.  A clinical decision was made based on

 

 21   laboratory results from week 48 as to the

 

 22   management of the patient, which was simply a

 

                                                               104

 

  1   management algorithm that was modeled on guidance

 

  2   at the time and it differs for each population.  In

 

  3   the e-antigen positive population we required, in

 

  4   order to go off therapy, that patients have lost

 

  5   e-antigen and have an HBV DNA less than the bDNA

 

  6   assay level of detection, so less than 0.7.  In the

 

  7   e-negative population patients had to meet the

 

  8   virologic requirement of bDNA less than LOQ, and

 

  9   they had to have an ALT less than 1.25 times the

 

 10   upper limit of normal.  In the refractory antigen

 

 11   positive patients we again required that the

 

 12   patients achieve the virologic endpoint in

 

 13   association with e-loss.  In that last group there

 

 14   were very small numbers of patients going off

 

 15   treatment, therefore, we will not discuss that

 

 16   further; the numbers were substantially small.

 

 17             With respect to the two naive patient

 

 18   populations, if we could show slide 2-380, the

 

 19   studies were designed to follow people out to 24

 

 20   weeks of off-treatment follow-up.  If during that

 

 21   time patients went on alternative therapy or into

 

 22   the rollover study they were considered failures to

 

                                                               105

 

  1   maintain that endpoint.  These represent the

 

  2   respective percentages in the naive e-antigen

 

  3   positives on the left, 82 percent for entecavir and

 

  4   73 percent for lamivudine, who maintained their

 

  5   study-defined response rate at week 24 off

 

  6   treatment.  Likewise, in the naive e-antigen

 

  7   negative population we had 48 percent for entecavir

 

  8   and 35 percent for lamivudine.

 

  9             DR. SO:  But I don't think you answered my

 

 10   question.  How many of those patients who were off

 

 11   treatment actually were followed up, like actually

 

 12   48 weeks off treatment, are still off treatment?

 

 13   You know, it could be very misleading for a lot of

 

 14   clinicians when you say sustained response, not

 

 15   knowing, you know, for how many of those patients

 

 16   actually their histologic improvement was

 

 17   sustained?  Was the virologic improvement sustained

 

 18   at 48 weeks?  So, I feel that the 24-week off

 

 19   treatment, so-called sustained response, could be

 

 20   misleading.

 

 21             DR. BRETT-SMITH:  Point taken, 24 weeks is

 

 22   what had been agreed upon with regulatory

 

                                                               106

 

  1   authorities in the design of the original study.

 

  2   All patients are encouraged to enroll on completion

 

  3   of the original study in the 049 long-term rollover

 

  4   study which remains currently enrolling at this

 

  5   time and has not undergone its initial analysis.

 

  6             DR. SO:  Just one last question, how does

 

  7   your company plan to talk to those clinicians who

 

  8   say, you know, if my patient seroconverted--these

 

  9   are naive patients before treatment, if they

 

 10   seroconverted I am planning to stop the treatment?

 

 11   How do you plan to advise those clinicians?

 

 12             DR. MORGAN MURRAY:  Our current proposed

 

 13   labeling reflects how the studies were conducted,

 

 14   and in that regard, for those patients who were

 

 15   determined to be responders therapy was stopped at

 

 16   48 weeks and they were monitored.  Patients who

 

 17   were partial responders continued on therapy.  Our

 

 18   current trials cannot define the definitive

 

 19   duration of dosing for entecavir, which is in

 

 20   general in flux for HBV therapy.  Dr. Dienstag, do

 

 21   you have any further comments?

 

 22             DR. DIENSTAG:  Jules Dienstag, Mass.

 

                                                               107

 

  1   General Hospital.  No one really knows what the

 

  2   sustained responsiveness or the durability of an

 

  3   e-antigen response is, but in the experience we

 

  4   have for interferon, lamivudine and adefovir if a

 

  5   person maintains that serologic response for 6

 

  6   months after stopping therapy the durability is 80

 

  7   percent.  That is the experience in Asia and in the

 

  8   West.  I assume that that will be repeated in this

 

  9   experience but that remains to be seen.

 

 10             DR. ENGLUND:  Thank you, everyone, for

 

 11   asking questions, answering questions.  We will now

 

 12   take a 15-minute break.  We will be back at 10:25

 

 13   to resume the FDA portion of this morning's

 

 14   presentation.

 

 15             [Brief recess]

 

 16             DR. ENGLUND:  Thank you.  Welcome back

 

 17   from coffee.  We are now going to have an FDA

 

 18   presentation led by Dr. James Farrelly, the

 

 19   pharmacology team leader, and he will begin his

 

 20   presentation.

 

 21                         FDA Presentation

 

 22                      Carcinogenicity Issues

 

 23             DR. FARRELLY:  Good morning.  My name is

 

 24   Jim Farrelly.  I am the pharmacology team leader in

 

 25   the Division of Antiviral Drugs.

 

                                                               108

 

  1             Today our purpose is to present some of

 

  2   the data relating to the genetic toxicity and the

 

  3   animal carcinogenicity of entecavir.  Entecavir is

 

  4   a nucleoside analog and, as such, is a member of a

 

  5   class of molecules which are in general expected to

 

  6   be genetically toxic.  Its 5-prime hydroxyl can be

 

  7   phosphorylated to the nucleotide triphosphate and

 

  8   as a guanosine triphosphate analog can be

 

  9   incorporated into the growing DNA chain.  It has

 

 10   the three-prime hydroxyl group and is, therefore,

 

 11   not an obligate chain terminator as are many other

 

 12   nucleoside analogs.

 

 13             However, after incorporation of entecavir

 

 14   into the growing DNA chain, it halts DNA synthesis

 

 15   after the addition of a small number of subsequent

 

 16   bases.  Its mechanism of action is essentially as a

 

 17   chain terminator, which is consistent with its

 

 18   being a clastogenic compound or having the ability

 

 19   to break chromosomes.  Indeed, entecavir has been

 

                                                               109

 

  1   shown to be clastogenic in an in vitro assay in

 

  2   human lymphocytes.

 

  3             It is negative in a number of genetic

 

  4   toxicity tests both in vitro and in vivo.  These

 

  5   include an Ames test, an in vitro assay in Chinese

 

  6   hamster ovary cells, in the Syrian hamster embryo

 

  7   cell transformation assay, and in an in vivo rat

 

  8   micronucleus assay, and in an unscheduled DNA

 

  9   synthesis assay.  In general, most of the battery

 

 10   of genotoxicity tests can be used only for hazard

 

 11   identification.  They are not used for risk

 

 12   assessment but have indicated that entecavir can be

 

 13   a possible genetic toxicity hazard.

 

 14             In an effort to place the results of the

 

 15   genetic toxicity studies into perspective, one can

 

 16   compare the outcome of the studies used to evaluate

 

 17   entecavir with the outcome of the studies used to

 

 18   evaluate the genetic toxicity of the three entities

 

 19   approved for the treatment of hepatitis B.  The

 

 20   three are adefovir, lamivudine and interferon.

 

 21             Adefovir is a nucleotide analog rather

 

 22   than a nucleoside analog, and was found to be

 

                                                               110

 

  1   mutagenic and to induce chromosomal aberrations in

 

  2   two in vitro genetic toxicology studies.

 

  3   Lamivudine, or 3GC, is a nucleoside analog and was

 

  4   found to be mutagenic in two in vitro assays as

 

  5   well.  Interferon was not an active genetic toxin.

 

  6   Since it is a protein one would not expect

 

  7   interferon to be positive in the screening battery

 

  8   used to test for genetic toxicity.  However, most

 

  9   of the nucleoside analogs approved as antiviral

 

 10   antigens are positive in genetic toxicology

 

 11   batteries of tests.

 

 12             Now, as is usual for a drug that is going

 

 13   to be administered chronically to humans, entecavir

 

 14   was evaluated in two-year carcinogenicity studies

 

 15   in rats and mice.  The design and outcome of the

 

 16   study in rats can be seen in the next slide where

 

 17   the data for male rats are shown.

 

 18             Entecavir was administered by gavage to

 

 19   rats at four doses, 0.003, 0.02, 0.2 and 1.4

 

 20   mg/kg/day.  They were administered for 96 weeks.

 

 21   There were two identical vehicle controls in the

 

 22   study.  The doses in male rats represent the human

 

                                                               111

 

  1   equivalent exposure of much less than 1, 0.3, 5 and

 

  2   35 times the clinical dose at the 1 mg proposed

 

  3   clinical dose, which you see under MHD.

 

  4             In male rats at an exposure 35-fold that

 

  5   in the clinic entecavir caused the appearance of a

 

  6   low level but significant incidence of brain

 

  7   gliomas.  A no-level of tumors was seen, or very

 

  8   low level, at 5-fold the exposure, and below no

 

  9   significant number of tumors was seen in the study.

 

 10             The next slide shows the results in female

 

 11   rats.  As can be seen from this slide, entecavir

 

 12   was administered at doses of 0.01, 0.06, 0.4 or 2.6

 

 13   mg/kg/day for two years.  Dosing was again by

 

 14   gavage and drug groups as well as two identical

 

 15   vehicle control groups were treated for 104 weeks.

 

 16   As can be seen in the slide, entecavir again

 

 17   induced the appearance of brain gliomas at the high

 

 18   dose.  It also induced the appearance of skin

 

 19   fibromas at the high dose, and increased the

 

 20   incidence of liver tumors at the high dose from 1-8

 

 21   adenomas and from 0-3 carcinomas.  The exposure to

 

 22   entecavir at the high dose in which these tumors

 

                                                               112

 

  1   were seen was approximately 24-fold higher for

 

  2   females than that measured in the clinic at the 1

 

  3   mg dose.

 

  4             Mention should be made regarding the

 

  5   exposure multiples at which tumors were seen in the

 

  6   study.  Although a multiple of 24 in exposure is a

 

  7   high multiple of the human exposure, it should be

 

  8   remembered that there were no significant induction

 

  9   or increase in tumors at the 4-fold for females and

 

 10   5-fold level for males.  The real cutoff,

 

 11   therefore, is somewhere between the high dose and

 

 12   the next lower dose, and the no-observed effect for

 

 13   tumors was at the 4- and 5-fold human dose.

 

 14             The results of the mouse carcinogenicity

 

 15   study were more complicated.  In the next slide it

 

 16   is shown that male mice were treated in a similar

 

 17   manner as were the rats.  The doses of entecavir

 

 18   used actually in both the males and the females

 

 19   were the same on a milligram per kilogram per day

 

 20   basis. The doses were 0.004, 0.04, 0.4 and 4

 

 21   mg/kg/day.

 

 22             As seen here, entecavir caused a

 

                                                               113

 

  1   dose-related increase in common bronchoalveolar

 

  2   adenomas in the males, significant at the three

 

  3   higher doses.  The lowest of the three doses

 

  4   produced an exposure only 3-fold higher than the

 

  5   clinical exposure.  Also increased in the males was

 

  6   the incidence of hepatocellular carcinoma at the

 

  7   high dose, going from 1 in one of the controls to 8

 

  8   at the high dose.  The exposure in the latter case

 

  9   was 42-fold higher than the clinical exposure.  For

 

 10   the hepatocellular carcinomas no increase was seen

 

 11   at an exposure 40-fold the clinical dose, very low;

 

 12   not significant.

 

 13             The next slide shows the female mice in

 

 14   which entecavir induced a significant increase in

 

 15   the lung tumors only at the high dose, giving an

 

 16   exposure in the animal study 40-fold the exposure

 

 17   in the clinic.  There was no significant increase

 

 18   at 11-fold the exposure.  Also in female mice there

 

 19   was an increase in ovarian and uterine vascular

 

 20   tumors, again at the high dose.  If one combined

 

 21   all the vascular tumors, as is commonly done, there

 

 22   was a significant increase in combined hemangiomas

 

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  1   and hemangiosarcomas at the high dose.

 

  2             We have heard the sponsor make a good case

 

  3   for the proposition that the pulmonary tumors seen

 

  4   in the mouse are mouse specific.  No cellular

 

  5   proliferation was seen in the lungs of rats and no

 

  6   lung tumors in rats, as well as no cellular

 

  7   proliferation in the dog and monkey studies.  If,

 

  8   indeed, the tumors were mouse specific the outcome

 

  9   would be that the only tumors seen in the two

 

 10   studies were at the high dose only.

 

 11             Again, putting the results of the

 

 12   carcinogenicity studies into perspective with the

 

 13   other approved regimens for hepatitis B, no

 

 14   carcinogenicity studies were carried out with

 

 15   interferon.  Studies were carried out with adefovir

 

 16   and lamivudine; they were not carcinogenic.

 

 17   However, because of kidney toxicity in the

 

 18   carcinogenicity studies, the exposures of the

 

 19   animals in the adefovir studies relative to the

 

 20   clinical exposures were 10-fold for mice and 4-fold

 

 21   for rats.  The maximum tolerated dose cannot go any

 

 22   higher than those.  So, if entecavir was examined

 

                                                               115

 

  1   only at those exposures, it would have been

 

  2   positive only for the lung tumors in mice and for

 

  3   no other tumor types.

 

  4             The exposures in lamivudine studies were

 

  5   high relative to the exposures in the clinic, up to

 

  6   34-fold in the mice and 200-fold in the rats.  At

 

  7   those exposures the entecavir results would have

 

  8   been at least identical to those which we have seen

 

  9   in these studies.  However, many nucleoside analogs

 

 10   approved as antivirals have been positive in

 

 11   carcinogenicity studies.

 

 12             The results of the two carcinogenicity

 

 13   studies were presented to the CDER Executive

 

 14   Carcinogenicity Assessment Committee, which we call

 

 15   the executive CAC, as well as to the full CAC for

 

 16   evaluation.  The CDER CAC committees were formed in

 

 17   the late 1980s to examine the protocols of

 

 18   carcinogenicity studies, as well as to examine the

 

 19   outcomes of the same studies.  The committees were

 

 20   founded so that the interpretation of the

 

 21   carcinogenicity data would not be inconsistent

 

 22   depending on which division reviewed them.  Two

 

                                                               116

 

  1   committees exist, the executive CAC, as I said, and

 

  2   the full CAC.

 

  3             The executive CAC consists of four

 

  4   members, the associate director for

 

  5   pharmacology/toxicology in the center; one

 

  6   permanent expert in the evaluation of

 

  7   carcinogenicity studies; the supervisor whose

 

  8   division is presenting the data; and another

 

  9   supervisor from another division chosen on a

 

 10   rotating roster.  The executive CAC meets every

 

 11   Tuesday and evaluates a great number of protocols

 

 12   and studies in a year, usually somewhere between

 

 13   150 and 200 either protocols or carcinogenicity

 

 14   studies in a year.

 

 15             The next slide shows the makeup of the

 

 16   full CAC which is empowered to review the studies

 

 17   when members of the executive CAC cannot

 

 18   unanimously agree on the interpretation of the

 

 19   data, or when requested by the sponsor of the drug.

 

 20   The full CAC consists of the associate director for

 

 21   the center; three associate directors for the

 

 22   offices; and each of the supervisors from the

 

                                                               117

 

  1   individual divisions in the center.  The full CAC

 

  2   is a fairly large committee and meets only rarely.

 

  3   In fact, the meeting for this drug was the first

 

  4   one in over a year for the full CAC.

 

  5             Both the executive CAC and the full CAC

 

  6   agreed that the tumors seen in the studies were

 

  7   probably relevant to a safety evaluation for

 

  8   humans.  The full CAC in general voted that the

 

  9   tumors seen in the carcinogenicity studies were

 

 10   relevant to human safety evaluation.

 

 11             The questions asked of the committee were

 

 12   does the CAC agree that the lung tumors in mice

 

 13   were relevant to human safety evaluation?  The

 

 14   committee voted yes, 16; no/probably not, 2; and 2

 

 15   answered they don't know.

 

 16             Does the CAC agree that, one, the liver

 

 17   tumors in male mice and, two, the vascular tumors

 

 18   in female mice are relevant to human safety

 

 19   evaluation?  The vote was 17 yes; 3 no.

 

 20             Does the CAC agree that, one,

 

 21   hepatocellular adenomas and carcinomas in female

 

 22   rats, two, the skin fibromas in female rats and,

 

                                                               118

 

  1   three, the brain gliomas in male and female rats

 

  2   are relevant to human safety evaluation?  The

 

  3   answer was yes, 17; 3 no.

 

  4             Now, in our division many carcinogenic

 

  5   nucleoside and nucleotide analogs have been

 

  6   approved for the treatment of viral diseases.

 

  7   Among these are ganciclovir which gives rodent

 

  8   tumors at very low doses relative to the human

 

  9   exposure; zidovudine; abacavir and cidofovir.

 

 10   Cidofovir causes palpable mammary adenocarcinomas

 

 11   in rats after as few as six weekly doses and is

 

 12   closely related in chemical structure to adefovir.

 

 13   Some of the reverse transcriptase inhibitors as

 

 14   well as the HIV protease inhibitors are positive

 

 15   for animal carcinogenicity.  Other drugs, such as

 

 16   8-methoxy psoralen, which has been approved for the

 

 17   treatment of psoriasis, are carcinogens.  In fact,

 

 18   this compound has been identified as a human

 

 19   carcinogen in epidemiology studies.  Dr. Linda

 

 20   Lewis will continue the division presentation.

 

 21   Thank you.

 

 22                         Clinical Issues

 

 23             DR. LEWIS:  Good morning.  My name is

 

 24   Linda Lewis, and I was the lead clinical reviewer

 

 25   for the entecavir review team.  I would like to

 

                                                               119

 

  1   give you the perspectives of the entire team on our

 

  2   review of entecavir for the treatment of chronic

 

  3   hepatitis B.

 

  4             My presentation is outlined in this slide.

 

  5   First I will go over a little bit of the

 

  6   development program for entecavir, which you have

 

  7   heard presented earlier by Bristol-Myers Squibb.

 

  8   Then I would like to go over the results of our

 

  9   reviews of the efficacy, safety and

 

 10   virology/resistance data that were contained in the

 

 11   NDA submission.  At that point I will turn my

 

 12   discussion to an assessment of the risk-benefit of

 

 13   entecavir and the applicant's proposed

 

 14   pharmacovigilance plan.  I will end the

 

 15   presentation with a preview of the questions that

 

 16   we would like the advisory committee to consider

 

 17   later this afternoon.

 

 18             As you heard this morning, the treatment

 

 19   options for chronic hepatitis B are somewhat

 

                                                               120

 

  1   limited.  Interferon was approved for treatment of

 

  2   hepatitis B in 1992.  Its requirement for

 

  3   parenteral administration and its significant side

 

  4   effect profile have somewhat limited its use.

 

  5   Lamivudine was the first effective oral therapy,

 

  6   and it was approved in 1998.  Its usefulness has

 

  7   been limited by the predictable emergence of

 

  8   resistance in relatively short periods of time.  A

 

  9   most recent addition, adefovir, was approved in

 

 10   2002.  It has known renal toxicity that may limit

 

 11   its use in some populations.

 

 12             The entecavir development program included

 

 13   a diverse patient population.  The clinical studies

 

 14   were drawn from multinational sites in North and

 

 15   South America, Europe and Asia.  Among these

 

 16   studies, patients from the United States made up

 

 17   about 10 percent of the pivotal trials.  The

 

 18   entecavir studies were made up of about 20 percent

 

 19   women.  There was a good mix of Asian and non-Asian

 

 20   patients in the populations.  However, Black or

 

 21   African American patients were under-represented in

 

 22   the clinical trials, making up only 2 percent of

 

                                                               121

 

  1   the pivotal studies.  The development program

 

  2   enrolled patients at different stages of disease

 

  3   and treatment.  Although there is a study in

 

  4   progress, the data were insufficient to review the

 

  5   use of entecavir in patients with decompensated

 

  6   liver disease during this review cycle.

 

  7             BMS submitted study reports and electronic

 

  8   data sets for the four key studies that they have

 

  9   mentioned in their presentation earlier.  To go

 

 10   over these again, study 022 was the Phase III study

 

 11   enrolling nucleoside-naive, e-antigen positive

 

 12   adults.  Study 027 enrolled nucleoside-naive

 

 13   e-antigen negative adults.  Both of these studies

 

 14   used a dose of 0.5 mg of entecavir given once

 

 15   daily.  Study 026 enrolled patients with persistent

 

 16   HBV viremia despite lamivudine treatment.  These

 

 17   are termed lamivudine-refractory subjects.

 

 18   Patients in this study were e-antigen positive and

 

 19   received a dose of 1 mg of entecavir given once

 

 20   daily.

 

 21             In order to expand the safety database for

 

 22   lamivudine-refractory patients we included in our

 

                                                               122

 

  1   review patients from study 014, the dose-finding

 

  2   study in that patient population, and used the

 

  3   cohorts that received either 1 mg of entecavir or

 

  4   the standard dose of lamivudine. As has been

 

  5   pointed out, all of the pivotal trials were

 

  6   compared to the standard dose of currently approved

 

  7   lamivudine.

 

  8             For all of the Phase III studies, studies

 

  9   022, 027 and 026, the primary endpoint was the

 

 10   overall histologic improvement in liver biopsy

 

 11   after 48 weeks of treatment.  This histologic

 

 12   improvement was defined as greater than or equal to

 

 13   a 2-point decrease in the Knodell necroinflammatory

 

 14   score, with no worsening in the Knodell fibrosis

 

 15   score compared to the baseline biopsy.  A series of

 

 16   secondary endpoints were also evaluated and

 

 17   included a number of virologic, serologic,

 

 18   biochemical and composite endpoints.

 

 19             The applicant also submitted data from

 

 20   several important studies in special populations.

 

 21   These included study 015.  This was a small pilot

 

 22   trial in post-liver transplant patients who had

 

                                                               123

 

  1   recurrent hepatitis B.  Study 038 enrolled a cohort

 

  2   of HIV/HBV co-infected patients.  Study 048

 

  3   compares the use of entecavir to adefovir in

 

  4   patients we decompensated liver disease.  This

 

  5   study is still enrolling and the data were not

 

  6   sufficient for us to conduct any meaningful interim

 

  7   analysis during this review cycle.  In these

 

  8   studies histologic endpoints were not used.  They

 

  9   relied on a series of virologic, serologic and

 

 10   biochemical endpoints.

 

 11             Now I would like to turn to the efficacy

 

 12   review of entecavir.  You will probably notice in

 

 13   these slides that many of our slides look very

 

 14   similar to those presented by the applicant earlier

 

 15   this morning.

 

 16             The FDA statistical review, conducted by

 

 17   Dr. Tom Hammerstron, confirmed the applicant's

 

 18   primary efficacy analysis.  A review of secondary

 

 19   efficacy analyses, using the virologic, serologic

 

 20   and biochemical endpoints, was also in agreement

 

 21   with BMS's conclusions.  Multiple sensitivity

 

 22   analyses and subgroup analyses were performed and

 

                                                               124

 

  1   all supported the primary analysis.

 

  2             This table displays the results of the

 

  3   primary efficacy analysis and some of the other

 

  4   histologic endpoints for each of the Phase III

 

  5   studies, study 022, 027 and 026.  The top line of

 

  6   the study shows the primary analysis, the overall

 

  7   histologic improvement after 48 weeks.  As you can

 

  8   see, in each of the three studies entecavir

 

  9   performed better than lamivudine in each study, as

 

 10   highlighted--these are supposed to be pink I don't

 

 11   know exactly how it projects.

 

 12             The next two lines display the two

 

 13   individual components that make up the overall

 

 14   histologic improvement score.  Again, you can see

 

 15   that patients receiving entecavir achieved that

 

 16   endpoint significantly more often than those who

 

 17   received lamivudine.  The last line of the study

 

 18   shows the secondary histologic endpoint of the

 

 19   Ishak fibrosis score.  This is another method of

 

 20   evaluating liver histology.  In this analysis

 

 21   entecavir was superior to lamivudine only in the

 

 22   lamivudine-refractory study, study 026.  In the

 

                                                               125

 

  1   treatment-naive studies the proportion of patients

 

  2   achieving an improvement in their Ishak fibrosis

 

  3   score was similar across the treatment arms.

 

  4             This table displays some of the

 

  5   sensitivity analyses that were done by our

 

  6   statistical reviewers.  The top line is a carryover

 

  7   from the previous slide and shows the primary

 

  8   analysis.  In the primary analysis the only

 

  9   subjects who had evaluable baseline biopsies were

 

 10   included in the analysis.  Subjects with missing or

 

 11   inadequate week 48 biopsies were counted as

 

 12   treatment failures.  The sensitivity analyses, done

 

 13   by Dr. Hammerstron, included a series of different

 

 14   methods to impute the missing data for each of the

 

 15   Phase III studies.  I am going to show you just two

 

 16   of the many analyses that he did.

 

 17             In FDA sensitivity analysis C, missing or

 

 18   inadequate baseline or week 48 biopsies were

 

 19   excluded from the analysis.  In this analysis, in

 

 20   study 022, the results were similar between

 

 21   entecavir and lamivudine and this is due primarily

 

 22   to the fact that more patients in the lamivudine

 

                                                               126

 

  1   arm were excluded because they did not have week 48

 

  2   biopsies.  In the other two studies, again,

 

  3   entecavir achieved the primary endpoint

 

  4   significantly more often than patients who received

 

  5   lamivudine.

 

  6             In sensitivity analysis D, this analysis

 

  7   includes all patients who were treated, not just

 

  8   those who had evaluable biopsies, but missing or

 

  9   inadequate week 48 biopsies were still counted as

 

 10   failures.  Although the numbers are lower for all

 

 11   of these analyses, the difference between entecavir

 

 12   and lamivudine remains evident in each of the three

 

 13   pivotal trials.

 

 14             This slide displays some of the analyses

 

 15   of secondary virologic, serologic and biochemical

 

 16   endpoints for the three pivotal trials.  Again, the

 

 17   significant values are highlighted in the pink

 

 18   cells.  In the Phase III studies a greater

 

 19   proportion of patients receiving entecavir than

 

 20   lamivudine achieved an HBV DNA PCR less than 400

 

 21   copies/mL.  Similarly, patients who received

 

 22   entecavir had a greater mean log decrease in PCR

 

                                                               127

 

  1   from baseline to week 48 than did patients who

 

  2   received lamivudine.  In the two studies that

 

  3   included e-antigen positive patients, studies 022

 

  4   and 026, the proportions of patients who had a

 

  5   seroconversion were roughly the same.  You will

 

  6   notice that in study 026 a relatively small number

 

  7   of patients actually met this criteria.  Finally,

 

  8   in terms of the proportion of patients who reached

 

  9   a normalized ALT, again, entecavir was shown to be

 

 10   superior to lamivudine in each of the three pivotal

 

 11   trials.

 

 12             We also conducted a number of subgroup

 

 13   analyses for baseline covariates of demographic or

 

 14   disease characteristics.  The treatment effect of

 

 15   the primary endpoint was comparable for the

 

 16   covariates gender, race, age, geographic region,

 

 17   HBV subtype, baseline ALT, baseline bDNA or PCR, or

 

 18   by prior treatment with lamivudine or interferon.

 

 19             Similarly, more limited subgroup analyses

 

 20   were performed to assess some of the key secondary

 

 21   endpoints.  The treatment effect measured by the

 

 22   proportion of patients of subjects who achieved a

 

                                                               128

 

  1   normalization of HBV DNA or those who achieved a

 

  2   viral load less than 400 copies/mL at weeks 24 and

 

  3   48 were similar according to gender, race and age.

 

  4             This slide displays a composite of the

 

  5   subgroup analysis for the Phase III studies.  I

 

  6   really show you this for pattern recognition more

 

  7   than to display any kind of specific results.  This

 

  8   slide plots the mean difference in treatment effect

 

  9   for the primary endpoint between entecavir and

 

 10   lamivudine, with 95 percent confidence intervals,

 

 11   for the three pivotal trials.  This cluster

 

 12   rep