1. 1 Resistance and Tropism - Maraviroc Lisa K. Naeger, Ph.D. Division of Antiviral Products Food and Drug Administration April 24, 2007 FDA Antiviral Advisory Committee Meeting

2. 2 Maraviroc Resistance and Tropism Novel Target –host receptor Unique Resistance Issues –resistance to MVC –tropism switching –outgrowth of CXCR4-tropic virus

3. 3 Baseline Analyses Studies 1027 and 1028 Genotypic susceptibility scores (GSS) and phenotypic susceptibility scores (PSS) were balanced across treatment groups –median GSS = 1 –median PSS = 2 Heavily treatment-experienced population 67% had overall susceptibility scores <2 30% had one potentially active drug in their OBT 14% had no potentially active drug in their OBT

4. 4 Tropism at Baseline 2560 screened; 56% were CCR5-tropic 90% of enrolled subjects had CCR5- tropic virus at Baseline – 4% had Dual-mixed tropic virus – 5% had non-typable virus

5. 5 Why Did Subjects Fail MVC Treatment in Studies 1027 and 1028? CCR5 to CXCR4 co-receptor switch through virus mutation Outgrowth of MVC resistant CCR5-tropic viruses Outgrowth of CXCR4-tropic viruses undetected at baseline Resistance to Optimized Background Therapy Host CCR5 genotype

6. 6 FDA Censored Dataset for “As- Treated” Analyses FDA Censored: Subjects who Discontinued while suppressed (<400 copies/mL) Discontinued with >400 copies/mL between Baseline and Week 4 Discontinued between Baseline and Week 8 with at least 0.5 log decrease and no rebound (previous ≥2 log decrease with 1 log increase) Overall Number of subjects in Pfizer virology dataset1050 Overall number of subjects in virology dataset from FDA 962 FDA Censored 88 Studies 1027 and 1028

7. 7 Tropism at Failure

8. 8 Tropism at Time of Failure Percentage of Virologic Failures (>400 copies/mL) with CCR5-tropic and CXCR4-tropic virus at Week 24 Tropism MVC QD n=154 MVC BID n=143 Placebo n=146 CCR547%34%84% Dual-Mixed 31%43%8% CXCR412%14%1% NR/NP10% 8%

9. 9 Resistance to Optimized Background Therapy

10. 10 Responders (<400 copies/mL) by Susceptibility Score at Baseline Overall Susceptibility Score

11. 11 Optimized Background in Treatment Failures QD N=154 BID N=143 Placebo N=143 % No Susceptible Drugs at Baseline 29% 27% % Changes in OBT on therapy 43%42%46%

12. 12 Enfuvirtide Use in Treatment Failures QD N=154 BID N=143 Placebo N=143 ENF Use 45% ENF Resistance Mutations at Failure 71%52%74%

13. 13 Overall Susceptibility Scores of Treatment Failures by Tropism OSS CXCR4-tropic n=29 CCR5-tropic n=163 Dual/Mixed n=94 All n=320 0-180%55%63%60% 217%24%23% ≥33%19%11%15%

14. 14 Virology Sub-Studies Comprehensive analysis requested –Treatment failures and/or –Change in HIV co-receptor tropism

15. 15 Failure with CCR5-Tropic Virus: Determine maraviroc susceptibility in cell culture Nucleotide sequence analysis of the gp120 region to identify amino acid substitutions Nucleotide sequence analysis of protease and RT regions

16. 16 Failure with CXCR4-Tropic Virus: Baseline and on-treatment clonal evaluation of virus to determine the relative number of CXCR4-tropic and CCR5-tropic viral isolates. Nucleotide sequence analysis of the gp120 region to identify amino acid changes that may contribute to a co-receptor switch to CXCR4 Phylogenetic analysis to determine the relationship of emerging CXCR4-tropic virus to the CCR5-tropic virus at baseline Nucleotide sequence analysis of protease and RT

17. 17 Virology Subgroup Analysis Selected 267 subjects on blinded therapy from Studies 1027 and 1028 38 failures with CCR5-tropic virus (13 MVC: 25 PLC) 20 failures with CXCR4- tropic virus (16 MVC: 4 PLC)

18. 18 Virology Subgroup Analysis Selected 267 subjects on blinded therapy from Studies 1027 and 1028 38 failures with CCR5-tropic virus (13 MVC: 25 PLC) 20 failures with CXCR4- tropic virus (16 MVC: 4 PLC)

19. 19 Subjects Failing with CCR5-Tropic Virus Virus from 2 subjects had 3-fold shifts in MVC susceptibility at failure All other subjects on maraviroc had EC 50 FC values <2-fold within the normal range of the Monogram assay (0.32-1.95)

20. 20 Subjects Failing with CCR5-Tropic Virus Viruses from 5 subjects showed evidence of a lower plateau in maximum percentage inhibition All had novel amino acid changes in the V3 loop at time of failure

21. 21 Genotypic Changes on Maraviroc in gp120 V3 loop sequences were heterogeneous with multiple substitutions Changes at either amino position 13 or 26 were seen in the V3 loop in 5/5 subjects with MVC-associated lower plateaus in MPI

22. 22 Role of the V3 Loop Amino Acid Substitutions in MVC Resistance Site-Directed Mutagenesis In 2 subjects –Mutating amino acids in baseline clones resulted in the MVC resistance phenotype of <95% MPI –Back-mutation of the amino acid changes of the failure clones resulted in a MVC-sensitive phenotype

23. 23 Some Subjects had No Phenotypic Markers of MVC Resistance 7 subjects receiving MVC showed no phenotypic markers of MVC resistance 5/7 had evidence of reduced susceptibility to 1 or more drugs in OBT at screening and/or failure

24. 24 Virology Subgroup Analysis Selected 267 subjects on blinded therapy from Studies 1027 and 1028 38 failures with CCR5-tropic virus (13 MVC: 25 PLC) 20 failures with CXCR4- tropic virus (16 MVC: 4 PLC)

25. 25 Clonal Evaluation One subject: 192 pre-treatment clones 48 on-treatment clones Pink = R5 Green = X4 Blue = dual/mixed

26. 26 20 Treatment Failure Subjects with CXCR4-Tropic Virus 14 subjects –CXCR4-tropic ‘on-treatment’ clones shared a common ancestor with a pre-treatment CXCR4- tropic virus. 6 subjects –CXCR4-tropic ‘on-treatment’ clones were genetically distinct from both the ‘pre-treatment’ and ‘on- treatment’ R5 population. –The V3 loop sequences differed by 7-17 amino acid residues from the nearest R5 sequence on the phylogenetic tree.

27. 27 Greatest Proportion of MVC Failures had Dual-Mixed or CXCR4-Tropic Virus Mutation from a CCR5 progenitor - Tropism switch Outgrowth of undetected CXCR4- virus at screening

28. 28 Why Did Subjects Fail Treatment in MVC Studies 1027 and 1028? Outgrowth of CXCR4-using viruses not detected at screening CCR5-using viruses: some are resistance to MVC Resistance to OBT CCR5 receptor genotype?

29. 29 What is the Outcome of Failures who had CXCR4-Tropic Virus Emerge on MVC Treatment? Evolution to a CXCR4-utilizing HIV may result in a more virulent virus Concern that MVC use will result in worse outcomes for patients because of outgrowth of CXCR4-tropic virus

30. 30 CD4+ Cell Counts Mean (median) Change in CD4 counts from Baseline LOCF24 Tropism at Failure QD N=154 BID N=143 Placebo N=146 R5123 (93) N=72 128 (110) N=48 38 (11) N=122 CXCR460 (33) N=18 52 (31) N=20 76 N=1 Dual-Mixed47 (25) N=48 63 (58) N=61 43 (14) N=11 NR/NP70 (70) N=16 99 (103) N=14 63 (29) N=12

31. 31 Follow-Up on Failures with CXCR4-Tropic Virus Viral load CD4+ cell counts HIV co-receptor tropism AIDS defining events

32. 32 Follow-Up Data (n=20) 2/3 had changed tropism back to CCR5 or dual-mixed For the subjects with CCR5- or dual/mixed-tropic virus at end of follow-up, the median time to last follow-up was approximately 5 months (range 18 days to 8 months). In contrast, the follow-up time for the subjects who remained CXCR4-tropic at the last follow-up visit was one month or less (median time was approximately 11 days). Number # X4-tropic Virus at Follow-up # Decreased CD4+ cells Mean change CD4+ cells 2035% (7)50% (10)-21

33. 33 Follow-Up Data (n=20) Viral loads remained similar to the value at treatment failure No new category C AIDS-defining events were reported 4 subjects went on a new ARV treatment –viral loads decreased –CD4 + cell count increased

34. 34 Tropism Summary ~50-60% subjects failed with CXCR4- or dual/mixed-tropic virus in the MVC arms Prominent reason for failure in these studies was outgrowth of a minor CXCR4-tropic virus population not detected at screening

35. 35 Resistance Summary Maraviroc treatment failure with CCR5-tropic virus also occurred –phenotypic and genotypic resistance to MVC –resistance to Optimized Background Therapy CCR5 host receptor genotype?

36. 36 Maraviroc Resistance Lower plateaus in MPI were detected in viruses from 5 subjects failing maraviroc regimens Changes in the V3 sequence of gp160 correlated with the presence of lower plateaus and maraviroc resistance

37. 37 Back-Up Slides Lisa K. Naeger, Ph.D. Division of Antiviral Products Food and Drug Administration April 24, 2007 FDA Antiviral Advisory Committee Meeting

38. 38 Failures with  32 Deletion/WT or CCR5 Promoter Haplotypes QDBIDPlacebo D32/WT 8% (13/154)3% (5/143)6% (9/143) WT/WT 84% (130/154)89% (127/143)85% (122/143) P1 46% (71/154)41% (59/143)46% (31/143) P4 11% (17/154)12% (17/143)12% (143) P1/P4 33% (51/143)34% (49/143)31% (45/143)