CENTER FOR DRUG EVALUATION AND
`RESEARCH
`
`
`APPLICATION NUMBER:
`208341Orig1s000
`
`MICROBIOLOGY/VIROLOGY REVIEW(S)
`
`
`
`
`
`
`
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341
`SDN: 000
`DATE REVIEWED: 03/17/2015
`
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`NDA#: 208341
`
`Serial #: 000
`
`Reviewer's Name(s): Lisa K. Naeger, Ph.D.
`
`Sponsor’s Name and Address:
`Gilead Sciences, Inc
`333 Lakeside Drive
`
`Foster City, CA 94404
`
`Initial Submission Dates:
`
`Correspondence Date: October 28, 2015
`CDER Receipt Date: October 28, 2015
`Assigned Date: October 29, 2015
`Review Complete Date: March 29, 2016
`PDUFA Date: June 28, 2016
`
`Amendments:
`
`SDN
`
`Date Submitted
`
`Date Received
`
`Date Assigned
`
`Related/Supporting Documents:
`
`IND115670, IND106739, NDA204671
`
`Velpatasvir (GS-5816)
`
`Sofosbuvir (GS-7977)
`
`Names
`
`Structures
`
`
`
`Chemical
`Names
`
`
`
`
`
`(S)— lsopropyl 2—((S)—
`W"
`(((2R,3R,4R,5R)—5—(2,4—dioxo—
`
`3,4-dihydropyrimidin—1 (2H)—y| )-4-
`
`fluoro-3-hydroxy-4-
`methyltetrahydrofuran-Z-
`yl)methoxy)(phenoxy)
`
`phosphorylamino) propanoate
`
`
`
`Molecular
`
` C22H29FN309P
`C49H54N308
`formula
`
`Molecular
`wei ht
`
`
`
`
`
`Drug category: Antiviral
`
`Reference ID: 3909418
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`Indication: Fixed-dose combination of velpatasvir, a hepatitis C virus (HCV) NS5A
`inhibitor and sofosbuvir, an HCV nucleotide analog NS5B polymerase inhibitor and is
`indicated for the treatment of chronic hepatitis C (CHC)
` infection
`
`Dosage Form/Route of administration: Oral
`
`Dispensed: Rx
`
`Abbreviations: BVDV, bovine viral diarrhea virus; BL, baseline; DAA, direct acting
`antiviral; EC50, effective concentration at 50%; FC, fold-change; FDA, Food and Drug
`Administration; FDC, fixed-dose combination; GT, genotype; HBV, hepatitis B virus;
`HCV, hepatitis C virus; HIV, human immunodeficiency virus; IC50, inhibitory
`concentration at 50%; IFN, recombinant human interferon; LDV, ledipasvir; NGS, next
`generation sequencing; NRTIs, nucleoside reverse transcriptase inhibitors; PBL,
`peripheral blood lymphocytes; PDVF, protocol defined virologic failure; PI, NS3/4A
`protease inhibitor; P/R, pegylated interferon/ribavirin; RBV, ribavirin; RSV, respiratory
`syncytial virus; SDM, site-directed mutants; SOF, sofosbuvir; SVR, sustained virologic
`response; SVR12, sustained virologic response at 12 week after end of treatment; VEL,
`velapatasvir; WT, wild-type
`
`TABLE OF CONTENTS
`
`1
`
`2
`
`3
`4
`
`5
`6
`
`Executive Summary………………………………………………..........Page 3
`
`Recommendations
`1.1
`Recommendations on Approvability………………………........Page 8
`1.2
`Recommendation on Phase 4 Commitments………………….Page 8
`Summary of Virology Assessments
`2.1
`Non-Clinical Virology……………………………………………...Page9
`2.2
`Clinical Virology ……………………………………………….….Page 10
`Administrative signatures………………………………..........................Page 13
`Virology Review
`4.1
`Important Milestones in Development……………………….....Page 14
`4.2
`Methodology…………………………………………………….....Page 14
`4.3
`Prior FDA Reviews……………………………………………......Page 15
`4.4
`State of antivirals used for the indication...………....................Page 15
`4.5
`Non-Clinical Virology ……………………………………………..Page17
`4.6
`Clinical Studies………………………………………………….....Page 43
`4.7
`Clinical Virology………………………………………………........Page 47
`Conclusion……………………………………………………………..……Page 66
`Package Insert
`6.1
`Applicant-Proposed……………………......................................Page 68
`6.2
`FDA-Proposed ……………………...........................................Page 73
`
`Reference ID: 3909418
`
`2
`
`(b) (4)
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`EXECUTIVE SUMMARY
`
`This NDA for a fixed-dose combination (FDC) of velpatasvir (VEL) and and the approved
`NS5B nucleotide analog inhibitor sofosbuvir (SOF), seeks an indication with and without
`ribavirin (RBV) for the treatment of adult patients with chronic HCV infection. From a
`virology perspective, this application for SOV/VEL is approvable.
`
`SOF/VEL is indicated for the treatment of GT1, 2, 3, 4, 5, and 6 HCV infections. The
`recommended treatment regimen for patients without cirrhosis and patients with
`compensated cirrhosis (Child-Pugh A) is 12 weeks of SOF/VEL. The recommended
`treatment regimen for patients with decompensated cirrhosis (Child-Pugh B and C) is 12
`weeks of SOF/VEL + RBV. This virology review supports adding a footnote to the
`Dosage and Administration Table to consider adding RBV to 12 week SOF/VEL for GT3
`subjects with compensated cirrhosis, because relapse rates were higher overall in this
`population and the consequences of failure with resistance to all NS5A inhibitors and
`potentially SOF for the cirrhotic population are significant. GT3 subjects with
`compensated cirrhosis treated with 12 weeks SOF/VEL had a relapse rate of 9%
`compared to 2% for GT3 subects without cirrhosis. Importantly, relapse rates were
`much higher (33%) in GT3 compensated cirrhotic subjects who had baseline NS5A
`resistance-associated polymorphisms (RAPs). Furthermore, all the GT3 virologic
`failures with compensated cirrhosis had the Y93H NS5A resistance substitution at
`failure, which confers high-level resistance to all current NS5A inhibitors and may
`compromise future treatment options. Thus, it is important to optimize chances of
`virologic success for this advanced patient population. The data support adding RBV to
`12 weeks SOF/VEL to optimize SVR12 rates in GT3 patients with compensated
`cirrhosis.
`
`Sofosbuvir (SOF) is a uridine nucleotide analog inhibitor of the HCV NS5B RNA-
`dependent RNA polymerase, which is required for viral replication. Specifically, the SOF
`prodrug is hydrolyzed by cellular esterases to a uridine analog monophosphate that is
`subsequently converted by cellular kinases to uridine analog triphosphate. The uridine
`analog is incorporated into HCV RNA by the NS5B polymerase and acts as a chain
`terminator. Velpatasvir (VEL) is an inhibitor of the HCV NS5A protein, which is required
`for viral replication. Resistance selection experiments in cell culture and cross-resistance
`studies indicate velpatasvir targets NS5A as its mode of action.
`
`SOF and VEL have antiviral activity against HCV genotypes (GT) 1, 2, 3, 4, 5, and 6.
`The EC50 values for SOF range from 15 to 264 nM against laboratory replicons and the
`EC50 values for VEL range from 0.004 to 0.130 nM. Against clinical isolates, median
`EC50 values range from 29 - 102 nM and 0.002 – 0.024 nM for SOF and VEL,
`respectively.
`
`Velpatasvir was not antagonistic in reducing HCV RNA levels in replicon cells when
`combined with sofosbuvir or IFN-α, RBV, a HCV NS3/4A protease inhibitor, the HCV
`NS5A inhibitor, ledipasvir, or HCV NS5B non-nucleoside inhibitors, GS-9190 or GS-
`9669.
`
`In cell culture, HCV replicons with reduced susceptibility to sofosbuvir were selected in
`cell culture for genotypes 1b, 2a, 2b, 3a, 4a, 5a, and 6a. Reduced susceptibility to
`
`Reference ID: 3909418
`
`3
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`sofosbuvir was associated with the NS5B substitution S282T in all replicon genotypes
`examined. An M289L substitution developed along with the S282T substitution in
`genotype 2a, 5 and 6 replicons. Site-directed mutagenesis of the S282T substitution in
`replicons of genotypes 1 to 6 conferred 2- to 18-fold reduced susceptibility to sofosbuvir.
`HCV genotype 1a, 1b, 2a, 3a, 4a, 5a, and 6a replicon variants with reduced
`susceptibility to velpatasvir were also selected in cell culture. Selected viruses
`developed amino acid substitutions at NS5A resistance-associated positions 24, 28, 30,
`31, 32, 58, 92, and 93. Phenotypic analysis of site-directed mutagenesis mutant
`replicons of the selected NS5A substitutions showed that single and double
`combinations of L31V and Y93H/N in genotype 1a, the combination of L31V +Y93H in
`genotype 1b, Y93H/S in genotype 3a, and L31V and P32A/L/Q/R in genotype 6
`conferred greater than 100-fold reduction in velpatasvir susceptibility. In the genotype
`2a replicon, the single mutants F28S and Y93H showed 91-fold and 46-fold reduced
`susceptibility to VEL, respectively. The single mutant Y93H conferred 3-fold reduced
`susceptibility to VEL in genotype 4a replicons. Combinations of these NS5A
`substitutions often showed greater reductions in susceptibility to velpatasvir than single
`substitutions alone.
`
`Clinical Virology Assessment of ASTRAL Trials
`For the FDA resistance analyses (see also the independent analysis of the next
`generation sequencing data by Virology Reviewer Eric Donaldson, Ph.D.), subjects who
`died, experienced an AE while serum HCV RNA was undetectable, or were lost to
`follow-up in the ASTRAL trials were removed from the analyses. Thus, 3 GT1a subjects
`in ASTRAL 1 and 16 GT3 subjects in ASTRAL 3 were censored for the FDA resistance
`analysis. The prevalence of baseline NS5A RAPs (any change at amino acid positions
`24, 28, 30, 31, 58, 92 and 93) at a sensitivity threshold of 15% of the viral population
`was assessed in the ASTRAL trials. Analyses were performed to assess the effect of
`baseline NS5A RAPS and cirrhosis on relapse rates. In addition, the NS5A resistance-
`associated substitutions that emerged in virologic failures were examined.
`
`ASTRAL 1 and 2
`In the ASTRAL 1 and 2 studies of subjects with GT1, 2, 4, 5, and 6, the prevalence of
`baseline NS5A RAPs was 18% (38/211) in subjects with GT1a HCV infection and 31%
`(42/134) in subjects with GT1b HCV infection. The most prevalent NS5A RAPs in GT1a
`were at positions M28 (5%) and H58 (7%). The most prevalent NS5A RAPs in GT1b
`were at positions 30 (8%), 31 (7%), 58 (9%) and 93 (10%). The prevalence of baseline
`NS5A RAPs in subjects with GT2 HCV infection was 60% (233/387). The most prevalent
`GT2 NS5A RAPs were L31M (51%) and K24R/T/Q (17%). The prevalence of baseline
`NS5A RAPs in subjects with GT4, GT5, and GT6 infection was 63% (73/115), 9% (3/35),
`and 83% (35/42), respectively. The predominant polymorphisms were at positions 28, 30
`and 58 in GT4 and at positions 24, 28, 30 and 58 in GT6.
`
`There were only 2 GT1 virologic failures in ASTRAL 1 and there were no virologic
`failures in ASTRAL 2. Thus, for GT2, GT4, GT5 and GT6 subjects, SVR12 rates were
`100% with or without the presence of baseline NS5A RAPs. Since there were only 2
`GT1 virologic failures, the effect of baseline NS5A polymorphisms was not assessed for
`GT1 subjects in ASTRAL 1.
`
`Reference ID: 3909418
`
`4
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`GT1 Virologic Failures
`There were 2 GT1 virologic failures who relapsed; one with GT1a and one with GT1c/h.
`The GT1a relapser had low level Q30R at baseline detectable with next generation
`sequencing (NGS) below the 15% threshold and had emergent Y93N at failure with an
`805-fold reduced susceptibility to VEL. The GT1c/h relapse had cirrhosis and baseline
`NS5A RAPs Q30R, L31M and H58P (above 15% threshold). This subject had emergent
`L24M/T, L31I/V and Y93H substitutions with 763-fold reduced susceptibility to VEL.
`Neither subject had baseline or emergent NS5B nucleoside analog inhibitor resistance
`substitutions.
`
`ASTRAL 3
`In ASTRAL-3, a study of GT3 subjects both with and without compensated cirrhosis, the
`prevalence of NS5A RAPs at baseline was 21% (115/551) with the most prevalent NS5A
`RAPs at positions A30 (11%) and Y93H (6%).
`
`The effect of the presence of baseline NS5A RAPs on relapse rates in subjects with GT3
`HCV infection following 12-week SOF/VEL or 24-week SOF/RBV treatment were
`examined in ASTRAL 3. The overall relapse rate for the SOF/VEL 12 week treatment
`arm was 4% (11/275) compared to 15% (40/260) for the comparator SOF/RBV 24 weeks
`treatment arm. In the SOF/VEL arm, the relapse rate for subjects with baseline NS5A
`RAPs was 7% (4/56) compared to 3% (7/218) for subjects without RAPs. As expected,
`the presence of NS5A RAPs did not affect the relapse rates (15-16%) in the SOF/RBV
`arm because of the absence of an NS5A inhibitor in the treatment regimen.
`
`Relapse rates were higher for subjects with cirrhosis in both treatment arms; 9% (7/80)
`for the SOF/VEL arm and 29% (23/78) for the SOF+RBV arm. For subjects without
`cirrhosis, relapse rates were 2% for both subjects with and without NS5A RAPs.
`However, for cirrhotic subjects treated with SOF/VEL for 12 weeks, relapse rates were
`higher for subjects with NS5A RAPs (33%; 3/9) than subjects without RAPs (6%; 4/71).
`
`Four subjects (9%) in the SOF/VEL arm with 1 baseline NS5A RAP relapsed (1 with
`A30K and 3 with Y93H). Specifically, one non-cirrhotic subject with the Y93H
`polymorphism at baseline relapsed (8%; 1/13), but both cirrhotic subjects with the Y93H
`polymorphism relapsed (100%; 2/2). The fourth relapse subject in the SOF/VEL 12
`Week arm had the A30K polymorphism at baseline. Thus overall, relapse rates in the
`SOF/VEL 12 Week arm were 20% (3/15) for GT3 subjects with the Y93H polymorphism
`and 4% (1/28) for subjects with an A30K polymorphism at baseline.
`
`GT3 Virologic Failures with Compensated Cirrhosis
`In ASTRAL 3, there were 11 GT3 virologic failures in the SOF/VEL 12 week arm
`compared to 38 relapsers in the SOF+ RBV 24 week arm. In the SOF/VEL arm, one
`failure subject (Subject 01069-62225) had GT3a HCV infection at screening but had
`GT1a HCV infection at virologic failure as determined by NS5B sequencing. This
`indicates reinfection and not a relapse of the original GT3a virus. This subject did not
`have NS5A or NS5B baseline polymorphisms or post-treatment substitutions. As stated
`above, 4 of the the relapsers in the SOF/VEL arm had baseline NS5A RAPs (3 had
`Y93H and 1 had A30K). Eight of the 11 relapsers had emergent NS5A resistance-
`associated substitutions; all 8 had emergent Y93H (1 from a mixture at baseline), 1 had
`emergent P58L at 2% frequency and 1 had emergent A30V at 12% frequency. In total,
`
`Reference ID: 3909418
`
`5
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`10 of the 11 failures had Y93H at failure. If the subject who is suspected of being
`reinfected is removed from the analysis, then all 10 relapsers had Y93H at failure.
`
`ASTRAL 4
`In ASTRAL-4, a study in GT1, 2, 3, 4, 5, and 6 subjects with decompensated cirrhosis, 8
`GT1 and 2 GT3a subjects were censored for the FDA resistance analysis, because they
`died or were lost to follow-up. The prevalence of NS5A RAPs at baseline was 24%
`(48/198), 60% (6/10), 11% (4/37), and 63% (5/8) in GT1, GT2, GT3, and GT4 HCV
`subjects, respectively. The prevalence of NS5A RAPs in GT1 subjects was balanced
`across the 3 treatment arms. There were no subjects with GT5 HCV infection and only 1
`subject with GT6 infection in the SOF/VEL 24 Week arm who had a baseline NS5A
`RAP.
`
`The effect of the presence of baseline NS5A RAPs on relapse rates in subjects with GT1
`and GT3 HCV infection following 12-week SOF/VEL, 24-week SOF/VEL or 12-week
`SOF/VEL+RBV treatment were examined. Relapse rates were 0% for subjects with
`GT2, GT4 and GT6, so there was no effect of the presence of baseline NS5A RAPs in
`this study for these genotypes.
`
`Genotype 1: Effect of Baseline NS5A RAPs on Relapse Rates
`For GT1 subjects, the overall relapse rates were lower for the 12-week SOF/VEL + RBV
`arm (2%; 1/66) compared to 8% (5/65) and 4% (3/68) for the SOF/VEL 12-week and 24-
`week treatment arms, respectively. In the 12-week SOF/VEL + RBV arm, relapse rates
`were 0% (0/17) for subjects with NS5A RAPs compared to 2% (1/49) for subjects with no
`NS5A RAPs. In comparison, in the 12-week SOF/VEL arm, the relapse rate for subjects
`with baseline NS5A RAPs was 17% (2/12) compared to 6% (3/52) for subjects without
`RAPs. In the 24-week SOF/VEL arm, the relapse rate for subjects with NS5A RAPs was
`11% (2/19) compared to 2% (1/48) for subjects without RAPs. Therefore in this patient
`population, the SOF/VEL + RBV for 12 weeks treatment option is more effective and
`reduces relapse rates compared to the other 2 tested treatments. This is especially
`seen for subjects with NS5A RAPs where relapse rates were 0% for the RBV containing
`arm compared to 17% and 11% for the 12-week and 24-week SOF/VEL regimens,
`respectively.
`
`Genotype 3: Effect of Baseline NS5A RAPs on Relapse Rates
`For GT3 subjects, the overall relapse rates were much higher than those seen with GT1
`subjects. However, relapse rates were lower for GT3 subjects in the 12-week SOF/VEL
`+ RBV arm (15%; 2/13) compared to 46% (6/13) and 45% (5/11) for the SOF/VEL 12-
`week and 24-week treatment arms, respectively. In the 12-week SOF/VEL arm, the
`relapse rate for subjects with NS5A RAPs was 33% (1/3) compared to 50% (5/10) for
`subjects without RAPs. In the 24-week SOF/VEL arm, the relapse rate for subjects with
`NS5A RAPs was 100% (1/1) compared to 40% (4/10) for subjects without RAPs. In the
`12-week SOF/VEL + RBV arm, there were no subjects with NS5A RAPs, so no
`comparison could be made to the 15% (2/13) relapse rate for subjects without NS5A
`RAPs.
`
`The data in ASTRAL 4 support the SOF/VEL + RBV 12 week regimen as the more
`effective treatment option for GT1 and GT3 decompensated subjects. These data also
`
`Reference ID: 3909418
`
`6
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`inform us that treatment for GT3 compensated cirrhotic patients might be improved by
`the addition of RBV to the 12 Week SOF/VEL regimen.
`
`ASTRAL 4 Virologic Failures with Decompensated Cirrhosis
`There were 9 total GT1 virologic failures in all the arms; 5 in the SOF/VEL 12 week arm,
`1 in the SOF/VEL 12 week + RBV arm and 3 in the SOF/VEL 24 week arm. Four of the
`GT1 relapsers had baseline NS5A RAPs (Q30Q/H + Y93Y/H, Y93Y/H, L31M, and R30Q
`+ Y93Y/H). Six of the 9 relapsers had emergent NS5A resistance-associated
`substitutions; all 6 had Y93H or N at failure. Other emergent substitutions included
`Q30H/R, L31M/V and H58D. The one GT1 virologic failure in the 12 week SOF/VEL +
`RBV arm had no NS5A or NS5B resistance substitutions at baseline or failure.
`
`There were 13 total GT3 virologic failures in all the arms; 6 in the SOF/VEL 12 week
`arm, 2 in the SOF/VEL 12 week + RBV arm and 5 in the SOF/VEL 24 week arm. Two of
`the GT3 relapsers had baseline NS5A RAPs (P58A or Y93H). Twelve of the 13
`relapsers had emergent NS5A resistance-associated substitutions and all 13 had Y93H
`at failure. Other emergent substitutions included M28T/V, S38P/Y and H58T. The 2
`GT3 virologic failures in the 12 week SOF/VEL + RBV arm had S38P + Y93H and M28V
`+ Y93H emerge at failure.
`
`Consideration for Adding RBV to SOF/VEL 12 Weeks for GT3 Compensated
`Cirrhotics
`Because of the concern for the consequences of virologic failure with development of
`Y93H in all failures and loss of subsequent treatment options, we pushed for a
`consideration for adding RBV to 12 week SOF/VEL in the GT3 compensated cirrhotic
`population. Specifically we were concerned for those with baseline NS5A RAPs, but did
`not have enough data to support screening all patients for NS5A RAPs before treatment
`with SOF/VEL. Our virology proposal to the review team was to add a footnote to Table
`1 in Section 2, Dosage and Administration stating “SOF/VEL + RBV for 12 weeks can be
`considered for GT3 patients with compensated cirrhosis [see Clinical 14 and
`Microbiology 12.4].
`
`The benefits of our consideration included: 1) relapse rates could be reduced for GT3
`patients with compensated cirrhosis who could take RBV. Based on a bridging
`assessment by the statistical reviewer, Karen Qi, Ph.D., relapse rates of 9% for GT3
`cirrhotics could be reduced to 2-3% with the addition of RBV, 2) relapse rates are 33%
`(3/9) for compensated cirrhotic subjects with baseline NS5A RAPs, so adding RBV
`would be a better option for these subjects and it would not be necessary to screen for
`RAPs and 3) adding RBV could reduce failure with the Y93H resistance substitution.
`The presence of the Y93H resistance substitution has consequences for future treatment
`options with NS5A inhibitors. The cons of this approach are that 1) there are no phase 3
`data for GT3 cirrhotics with RAPs in the 12 Week SOF/VEL + RBV arm, 2) there would
`be potentially unnecessary RBV use in some patients, and 3) GT/subtype at screening
`would be required to determine if a patient was GT3 even though SOF/VEL has efficacy
`against GTs 1-6.
`
`The justification for adding the consideration footnote include:
` Phase 2 data showing the increase in SVR12 rate with RBV (88% (23/26) to 96%
`(25/26).
`
`Reference ID: 3909418
`
`7
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
` Cirrhosis is a continuum from compensated to decompensated so results in
`decompensated can inform treatment for compensated.
` Results from ASTRAL 4 in decompensated patients show better SVR rates with
`RBV in both GT3 subjects (46% without compared to 15% with RBV) and GT1
`subjects (8% without and 2% with RBV).
`
`1. RECOMMENDATIONS
`
`1.1. Recommendation and Conclusion on Approvability
`
`This supplemental NDA for the fixed-dose combination of velpatasvir (VEL) and
`sofosbuvir (SOF) is approvable with respect to virology
`
`1.2. Recommendation on Phase IV (Post-Marketing) Commitments,
`Agreements, and/or Risk Management Steps, if Approvable.
`
`The sponsor should submit the protocol and study results of the study
`cirrhotic patients where SOF/VEL +/- RBV treatments are being compared.
`
` of GT3
`
`Reference ID: 3909418
`
`8
`
`(b) (4)
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`2. SUMMARY OF OND VIROLOGY ASSESSMENTS
`
`2.1 Non-Clinical Virology
`
`Sofosbuvir (SOF) is a nucleotide prodrug of 2’-deoxy-2’-fluoro-2’-C-methyluridine
`monophosphate that is converted to the active uridine triphosphate form (GS-461203)
`within the hepatocyte. In a biochemical assay, GS-461203 inhibited the RNA
`polymerase activity of recombinant NS5B from HCV genotypes 1b, 2a, 3a and 4a with
`IC50 values ranging from 0.7 to 2.6 µM. SOF had EC50 values ranging from 14-110 nM
`in stable full-length replicon cells of genotype 1a, 1b, 2a, 3a and 4a; and chimeric GT1b
`Con-1 replicons carrying NS5B coding sequences from genotypes 2b, 5a, or 6a. The
`median EC50 values of sofosbuvir against chimeric replicons encoding NS5B sequences
`from clinical isolates were 62 nM for genotype 1a (range 29-128 nM; N=67), 102 nM for
`genotype 1b (range 45-170 nM; N=29), 29 nM for genotype 2 (range 14-81 nM; N=15)
`and 81 nM for genotype 3a (range 24-181 nM; N=106). The EC50 values of sofosbuvir
`against genotype 1a and 2a viruses were 30 and 20 nM, respectively.
`
`Velpatasvir (VEL; GS-5816) inhibits HCV replication by inhibiting NS5A protein activity.
`This is supported by resistance selection of substitutions in the NS5A protein in cell
`culure, the clinical resistance profile with NS5A resistance-associated subtitutions
`emerging in virologic failures, cross-resistance studies with other NS5A inhibitors, and
`studies showing VEL does not inhibit HCV enzymes.
`
`VEL demonstrated antiviral activity in multiple HCV replicon cell lines against major HCV
`genotypes/subtypes including 1a, 1b, 2a, 2b, 3a, 4a, 5a, 6a and 6e. In HCV replicon
`antiviral assays, VEL has EC50 values of 0.012 nM and 0.015 nM against GT1a and
`GT1b replicons, respectively, with no cytotoxicity observed at the highest concentrations
`tested (CC50 value >44,400 nM; selectivity indices of >3,000,000). VEL had EC50 values
`of 0.009 nM, 0.014 nM, 0.008 nM, 0.012 nM and 0.009 nM for genotype 2a (JFH-1), 2a
`(J6), 2b, 3a and 4a NS5A, respectively. The activity of VEL was not significantly different
`between L31 (JFH-1 strain) or M31 (J6 strain) forms of NS5A for GT2 HCV. VEL
`demonstrated antiviral activity against genotypes 5a, 6a and 6e with EC50 values of
`0.075 nM, 0.006 nM, and 0.13 nM, respectively. Furthermore, VEL has activity against
`infectious HCV in cell culture with an EC50 value of 0.008 nM. In the presence of 40%
`human serum, VEL potency against the genotype 1a HCV replicon was reduced 13.3-
`fold. This serum binding shift was within the range of several other tested HCV inhibitors
`including the first generation NS5A inhibitor ledipisvir.
`
`Cell-based analyses of an extensive collection of NS5A genetic polymorphisms
`(residues 28, 30, 31, 44, 56, 58, 62, 92, and 93 that play critical roles in determining
`susceptibility to NS5A inhibitors) showed that VEL is equally effective against the
`majority of polymorphisms (≥89%) existing within genotypes 2a, 2b, 3a and 4a. VEL
`maintains consistent antiviral activity against a broad range of NS5A polymorphisms
`existing in these HCV genotypes/subtypes.
`
`VEL does not have inhibitory activity against a related flavivirus, bovine viral diarrhea
`virus, or unrelated viruses including respiratory syncytial virus, hepatitis B virus and
`human immunodeficiency virus.
`
`Reference ID: 3909418
`
`9
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`The antiviral activity and cellular toxicity of VEL was tested in combination with IFN-α,
`RBV, and a panel of Gilead Sciences’ clinical stage drug candidates including GS-9451
`(an NS3/4A protease inhibitor), ledipisvir (GS-5885, an NS5A inhibitor), GS-9190 and
`GS-9669 (two non-nucleoside NS5B inhibitors), and GS-6620 and GS-7977 (two
`nucleotide analog NS5B inhibitors). There was no antiviral antagonism of VEL in
`combination with any of these tested compounds. Furthermore, no cellular toxicity was
`observed when VEL was combined with any of the inhibitors at concentrations tested in
`the antiviral combinations experiments.
`
`Importantly, the replicon resistance selection studies conducted in GT1a and GT1b
`confirmed that VEL resistance maps to the NS5A protein, supporting the premise that
`NS5A is the antiviral target of VEL. In GT1a HCV replicon cells, NS5A substitutions
`L31V and Y93H were most frequently selected by VEL and conferred 129- and 1,004-
`fold resistance, respectively. Q30K, L31M and Y93N were selected less frequently and
`conferred 8-, 15-, and 2,926-fold, respectively, to VEL. Both Y93H and Y93N displayed
`>1,000-fold decreased susceptibility to VEL. Single substitutions Q30H and Q30R did
`not emerge in the cell culture resistance selection. Double mutants, including
`combinations of Q30H, Q30R or L31V with Y93H or Y93N, were observed at a low
`frequency.
`
`In GT1b HCV replicon cells, only double substitutions were identified. Y93H was
`identified in each of the clones, but always emerged as a “double mutant” together with
`other NS5A substitutions, including L28M, L31F, L31M, L31V, or Q54H. The single
`Y93H substitution and other NS5A single substitutions showed less than 2-fold
`resistance to VEL. However, once these substitutions were combined with Y93H,
`increases in VEL resistance were observed. The L31V/Y93H double mutant, the most
`frequently selected in these studies, conferred 986-fold resistance to VEL. The other
`double mutants, L31M/Y93H, L31F/Y93H and L28M/Y93H, conferred 68-, 27- and 5-fold
`decreased VEL susceptibility, respectively.
`
`Against a panel of clinically significant NS5A inhibitor resistant mutants in GT1, VEL
`showed less than or equal to 2-fold reduced antiviral activity against GT1a Q30H and
`Q30R mutants, as well as the GT1b Y93H resistant mutant. GT1a mutants M28T, L31M
`and Y93C showed 6- to 12-fold reduced susceptibility to VEL. VEL had less activity
`against GT1a mutant Y93H, with an EC50 value of 6.7 nM. Colony reduction assays
`provided evidence that VEL has an improved resistance barrier across genotypes 1 to 4
`relative to another NS5A inhibitor, daclatasvir (DCV).
`
`2.2
`
`Clinical Virology
`
`Virology Assessment of ASTRAL Trials
`For the FDA resistance analyses (see also the independent analysis of the next
`generation sequencing data by Virology Reviewer Eric Donaldson, Ph.D.), subjects who
`died, experienced an AE while undetectable, or were lost to follow-up in the ASTRAL
`trials were removed from the analyses. Thus, 3 GT1a subjects in ASTRAL 1 and 16 GT3
`subjects in ASTRAL 3 were censored for the FDA resistance analysis. The prevalence
`of baseline NS5A RAPs (any change at amino acid positions 24, 28, 30, 31, 58, 92 and
`93) at a sensitivity threshold of 15% of the viral population was assessed in the ASTRAL
`trials. Analyses were performed to assess the effect of baseline NS5A RAPS and
`
`Reference ID: 3909418
`
`10
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DATE REVIEWED: 03/17/2015
`Virology Reviewer: Lisa K. Naeger, Ph.D.
`
`cirrhosis on relapse rates. In addition, the NS5A resistance-associated substitutions that
`emerged in virologic failures at relapse were examined.
`
`ASTRAL 1 and 2
` In the ASTRAL 1 and 2 studies of subjects with GT1, 2, 4, 5, and 6, the prevalence of
`baseline NS5A RAPs was 18% (38/211) in subjects with GT1a HCV infection and 31%
`(42/134) in subjects with GT1b HCV infection. The most prevalent NS5A RAPs in GT1a
`were at positions M28 (5%) and H58 (7%). The most prevalent NS5A RAPs in GT1b
`were at positions 30 (8%), 31 (7%), 58 (9%) and 93 (10%). The prevalence of baseline
`NS5A RAPs in subjects with GT2 HCV infection was 60% (233/387). The most prevalent
`GT2 NS5A RAPs were L31M (51%) and K24R/T/Q (17%). The prevalence of baseline
`NS5A RAPs in subjects with GT4, GT5, and GT6 infection was 63% (73/115), 9% (3/35),
`and 83% (35/42), respectively. The predominant polymorphisms were at positions 28, 30
`and 58 in GT4 and at positions 24, 28, 30 and 58 in GT6.
`
`There were only 2 GT1 virologic failures in ASTRAL 1 and there were no virologic
`failures in ASTRAL 2. Thus, for GT2, GT4, GT5 and GT6 subjects, SVR12 rates were
`100% with or without the presence of baseline NS5A RAPs. Since there were only 2
`GT1 virologic failures, the effect of baseline NS5A polymorphisms were not assessed for
`GT1 subjects in ASTRAL 1.
`
`GT1 Virologic Failures
`There were 2 GT1 virologic failures who relapsed; one with GT1a and one with GT1c/h.
`The GT1a relapse had low level Q30R detectable with next generation sequencing
`(NGS) below the 15% threshold and had emergent Y93N at failure with an 805-fold
`reduced susceptibility to VEL. The other GT1c/h subject had cirrhosis and baseline
`NS5A RAPs Q30R, L31M and H58P (above 15% threshold). This subject had emergent
`L24M/T, L31I/V and Y93H with 763-fold reduced susceptibility to VEL. Neither subject
`had baseline or emergent NS5B nucleoside analog inhibitor resistance substitutions.
`
`ASTRAL 3
`In ASTRAL-3, a study of GT3 subjects both with and without compensated cirrhosis, the
`prevalence of NS5A RAPs at baseline was 21% (115/551) with the most prevalent NS5A
`RAPS at positions A30 (11%) and Y93H (6%).
`
`The effect of the presence of baseline NS5A RAPs on relapse rates in subjects with GT3
`HCV infection following 12-week SOF/VEL or 24-week SOF/RBV treatment were
`examined in ASTRAL 3. The overall relapse rate for the SOF/VEL 12 week treatment
`arm was 4% (11/275) compared to 15% (40/260) for the SOF/RBV 24 weeks treatment
`arm. In the SOF/VEL arm, the relapse rate for subjects with baseline NS5A RAPs was
`7% (4/56) compared to 3% (7/218) for subjects without RAPs. As expected, the
`presence of NS5A RAPs did not affect the relapse rates (15-16%) in the SOF/RBV arm
`because of the absence of an NS5A inhibitor in the treatment regimen.
`
`Relapse rates were higher for subjects with cirrhosis in both treatment arms; 9% (7/80)
`for the SOF/VEL arm and 29% (23/78) for the SOF+RBV arm. For subjects without
`cirrhosis, relapse rates were 2% for both subjects with and without NS5A RAPs. For
`cirrhotic subjects treated with SOF/VEL for 12 weeks, relapse rates were higher for
`subjects with NS5A RAPs (33%; 3/9) than subjects without RAPs (6%; 4/71).
`
`Reference ID: 3909418
`
`11
`
`

`

`DIVISION OF ANTIVIRAL PRODUCTS (HFD-530) VIROLOGY REVIEW
`NDA: 208341 SDN: 000
`DA