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

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

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

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.

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 th