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Resistance and Tropism - Maraviroc

Lisa K. Naeger, Ph.D.

Division of Antiviral ProductsFood and Drug Administration

April 24, 2007 FDA Antiviral Advisory Committee Meeting

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Maraviroc Resistance and Tropism

• Novel Target–host receptor

• Unique Resistance Issues–resistance to MVC–tropism switching –outgrowth of CXCR4-tropic virus

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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

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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

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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

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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 dataset 1050

Overall number of subjects in virology dataset from FDA

962

FDA Censored 88

Studies 1027 and 1028

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Tropism at Failure

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Tropism at Time of Failure

Percentage of Virologic Failures (>400 copies/mL) with CCR5-tropic and CXCR4-tropic virus at Week 24

TropismMVC QD

n=154MVC BID

n=143Placebo n=146

CCR5 47% 34% 84%Dual-Mixed 31% 43% 8%

CXCR4 12% 14% 1%

NR/NP 10% 10% 8%

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Resistance to Optimized Background Therapy

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

0

10

20

30

40

50

60

70

80

90

0 1 2 3+

MVC QDMVC BIDPlacebo

Overall Susceptibility Score

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Optimized Background in Treatment Failures

QDN=154

BIDN=143

PlaceboN=143

% No SusceptibleDrugs at Baseline

29% 29% 27%

% Changes inOBT on therapy

43% 42% 46%

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Enfuvirtide Use inTreatment Failures

QDN=154

BIDN=143

PlaceboN=143

ENF Use 45% 45% 45%ENF Resistance Mutations at Failure

71% 52% 74%

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Overall Susceptibility Scores of Treatment Failures by Tropism

OSSCXCR4-tropic

n=29CCR5-tropic

n=163Dual/Mixed

n=94All

n=320

0-1 80% 55% 63% 60%

2 17% 24% 23% 23%

≥3 3% 19% 11% 15%

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Virology Sub-Studies

Comprehensive analysis requested –Treatment failures and/or

–Change in HIV co-receptor tropism

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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

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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

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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)

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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)

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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 EC50 FC values <2-fold within the normal range of the Monogram assay (0.32-1.95)

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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

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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

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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

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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

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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)

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Clonal EvaluationOne subject:

192 pre-treatmentclones

48 on-treatmentclones

Pink = R5Green = X4Blue = dual/mixed

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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.

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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

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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?

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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

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CD4+ Cell Counts Mean (median) Change in CD4 counts from Baseline

LOCF24

Tropism at Failure QD

N=154BID

N=143PlaceboN=146

R5 123 (93)N=72

128 (110)N=48

38 (11)N=122

CXCR4 60 (33)N=18

52 (31)N=20

76N=1

Dual-Mixed 47 (25)N=48

63 (58)N=61

43 (14)N=11

NR/NP 70 (70)N=16

99 (103)N=14

63 (29)N=12

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Follow-Up on Failures with CXCR4-Tropic Virus

• Viral load

• CD4+ cell counts

• HIV co-receptor tropism

• AIDS defining events

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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# DecreasedCD4+ cells

Mean changeCD4+ cells

20 35% (7) 50% (10) -21

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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

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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

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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?

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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

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Back-Up Slides

Lisa K. Naeger, Ph.D.

Division of Antiviral ProductsFood and Drug Administration

April 24, 2007 FDA Antiviral Advisory Committee Meeting

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Failures with 32 Deletion/WT or CCR5 Promoter Haplotypes

QD BID Placebo

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)