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 carrying 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 V36M+R155K 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, V36A+T54A, V36L+R155K, T54S+R155K, and R155T+D168N, which conferred lower- level resistance to telaprevir; and A156F/N/V, V36A+R155K/T, V36M+R155T, V36A/M+A156T, T54A+ A156S, T54S+A156S/T, and V36M+ T54S+R155K, which conferred higher- level resistance to telaprevir. All telaprevir- resistant variants remained fully sensitive to alpha interferon, ribavirin, and HCV NS5B nucleoside and nonnucleoside polymerase inhibitors. In general, the replication capacity of telaprevir- resistant variants was lower than that of the wildtype replicon.