In Vitro Phenotypic Characterization of Hepatitis C Virus NS3 Protease Variants Observed in Clinical Studies of Telaprevir

Telaprevir is a linear, peptidomimetic small molecule that inhibits hepatitis C virus (HCV) replication by specifically inhibiting the NS3·4A protease. In phase 3 clinical studies, telaprevir in combination with peginterferon and ribavirin (PR) significantly improved sustained virologic response (SVR) rates in genotype 1 chronic HCV-infected patients compared with PR alone. In patients who do not achieve SVR after treatment with telaprevir-based regimens, variants with mutations in the NS3·4A protease region have been observed. Such variants can contribute to drug resistance and limit the efficacy of treatment. To gain a better understanding of the viral resistance profile, we conducted phenotypic characterization of the variants using HCV replicons car-rying site-directed mutations. The most frequently observed (significantly enriched) telaprevir-resistant variants, V36A/M, T54A/S, R155K/T, and A156S, conferred lower-level resistance (3- to 25-fold), whereas A156T and V36MR155K conferred higher-level resistance (>25-fold) to telaprevir. Rarely observed (not significantly enriched) variants included V36I/L and I132V, which did not confer resistance to telaprevir; V36C/G, R155G/I/M/S, V36AT54A, V36LR155K, T54SR155K, and R155TD168N, which conferred lower-level resistance to telaprevir; and A156F/N/V, V36AR155K/T, V36MR155T, V36A/ MA156T, T54AA156S, T54SA156S/T, and V36MT54SR155K, which conferred higher-level resistance to telaprevir. All telaprevir-resistant variants remained fully sensitive to alpha interferon, ribavirin, and HCVNS5B nucleoside and nonnucleo-side polymerase inhibitors. In general, the replication capacity of telaprevir-resistant variants was lower than that of the wild-type replicon