r anti-HCV activity conferred by double resistance-associated substitutions was approximately equal to the product of that for the individual substitutions. In cell-based protease assays, an NS3 Q80K substitution did not reduce HCV sensitivity to boceprevir. In addition, the decreased sensitivity to boceprevir observed with R155K was not further decreased when combined with either Q80K or Q80R.
In Clinical Studies
An as-treated, pooled genotypic resistance analysis was conducted for subjects who received four weeks of PegIntron/REBETOL followed by VICTRELIS 800 mg three times daily in combination with PegIntron/REBETOL in two Phase 3 studies, SPRINT-2 and RESPOND-2. Among VICTRELIS-treated subjects who did not achieve a sustained virologic response, and for whom samples were analyzed, 53% had one or more specific post-baseline, treatment-emergent NS3 protease domain amino acid substitutions detected by a population-based sequencing assay (Table 8). Nearly all of these substitutions have been shown to reduce boceprevir anti-HCV activity in cell culture or biochemical assays. Among VICTRELIS-treated subjects who did not achieve SVR and for whom post-baseline samples were analyzed, 31% of PegIntron/REBETOL-responsive subjects, as defined by greater than or equal to 1-log10 decline in viral load at Treatment Week 4 (end of 4-week PegIntron/REBETOL lead-in period), had detectable treatment-emergent substitutions, compared to 68% of subjects with less than 1-log10 decline in viral load at Treatment Week 4. Clear patterns of boceprevir treatment-emergent substitutions in the NS3 helicase domain or NS4A coding regions of the HCV genome were not observed.
Table 8 Pooled Analysis of Treatment-Emergent NS3 Protease Domain Amino Acid Substitutions Detected Among VICTRELIS-Treated Subjects in SPRINT-2 and RESPOND-2 Who Did Not Achieve a Sustained Virologic Response (SVR) Subjects Infected with HCV Genotype 1a Subjects Infected with HCV Genotype 1b
>10% of VICTRELIS treated subjects who did not achieve SVR V36M, T54S, R155K T54A, T54S, V55A, A156S, I/V170A
<1% to 10% of VICTRELIS treated subjects who did not achieve SVR V36A, T54A, V55A, V55I, V107I, R155T, A156S, A156T, V158I, D168N, I/V170T, I/V170F V36A, V36M, T54C, T54G, V107I, R155K, A156T, A156V, V158I, I/V170T, M175L
Persistence of Resistance-Associated Substitutions
Data from an ongoing, long-term follow-up study of subjects who did not achieve SVR in Phase 2 trials with VICTRELIS, with a median duration of follow-up of approximately 2 years, indicate that HCV populations harboring certain post-baseline, VICTRELIS-treatment-emergent substitutions may decline in relative abundance over time. However, among those subjects with available data, one or more VICTRELIS-treatment-emergent substitutions remained detectable with a population-based sequencing assay in 25% of subjects after 2.5 years of follow-up. The most common NS3 substitutions detected after 2.5 years of follow-up were T54S and R155K. The lack of detection of a substitution based on a population-based assay does not necessarily indicate that viral populations carrying that substitution have declined to a background level that may have existed prior to treatment. The long-term clinical impact of the emergence or persistence of boceprevir-resistance-associated substitutions is unknown. No data are available regarding the efficacy of VICTRELIS among subjects who were previously exposed to VICTR |
