VX-950, a novel hepatitis C virus (HCV) NS34A protease inhibitor, exhibits potent antiviral activities in HCV replicon cells

The NS34A serine protease of hepatitis C virus (HCV) is essential for viral replication and therefore has been one of the most attractive targets for developing specific antiviral agents against HCV. VX-950, a highly selective, reversible, and potent peptidomimetic inhibitor of the HCV NS34A protease, is currently in clinical development for the treatment of hepatitis C. In this report, we describe the in vitro characterization of anti-HCV activities of bVX-950 in subgenomic HCV replicon cells. Incubation with VX-950 resulted in a time-and dose-dependent reduction of HCV RNA and proteins in replicon cells. Moreover, following a 2-week incubation with VX-950, a reduction in HCV RNA levels of 4.7 log was observed, and this reduction resulted in elimination of HCV RNA from replicon cells, since there was no rebound in replicon RNA after withdrawal of the inhibitor. The combination of VX-950 and alpha interferon was additive to moderately synergistic in reducing HCV RNA in replicon cells with no significant increase in cytotoxicity. The benefit of the combination was sustained over time: a 4-log(10) reduction in HCV RNA level was achieved following a 9-day incubation with VX-950 and alpha interferon at lower concentrations than when either VX-950 or alpha interferon was used alone. The combination of VX-950 and alpha interferon also suppressed the emergence of in vitro resistance mutations against VX-950 in replicon cells.