Selection and characterization of hepatitis C virus replicons dually resistant to the polymerase and protease inhibitors HCV-796 and boceprevir (SCH 503034)

HCV-796 is a nonnucleoside inhibitor of the hepatitis C virus (HCV) nonstructural protein 5B (NS5B) polymerase, and boceprevir is an inhibitor of the NS3 serine protease. The emergence of replicon variants resistant to the combination of HCV-796 and boceprevir was evaluated. Combining the inhibitors greatly reduced the frequency with which resistant colonies arose; however, some resistant replicon cells could be isolated by the use of low inhibitor concentrations. These replicons were approximately 1,000-fold less susceptible to HCV-796 and 9-fold less susceptible to boceprevir. They also exhibited resistance to anthranilate nonnucleoside inhibitors of NS5B but were fully sensitive to inhibitors of different mechanisms: a pyranoindole, HSP90 inhibitors, an NS5B nucleoside inhibitor, and pegylated interferon (Peg-IFN). The replicon was cleared from the combination-resistant cells by extended treatment with Peg-IFN. Mutations known to confer resistance to HCV-796 (NS5B C316Y) and boceprevir (NS3 V170A) were present in the combination-resistant replicons. These changes could be selected together and coexist in the same genome. The replicon bearing both changes exhibited reduced sensitivity to inhibition by HCV-796 and boceprevir but had a reduced replicative capacity.