Danoprevir, a small-molecule NS3/4A protease inhibitor for the potential oral treatment of HCV infection

Danoprevir (ITMN-191; RG-7227), under development by InterMune Inc and Roche Holding AG, is a promising, potent NS3/4A protease inhibitor for the oral treatment of HCV infection. Preclinical data demonstrated that danoprevir binds with high affinity and dissociates slowly from the HCV NS3 protease, allowing high liver drug exposure with only modest plasma drug exposure. A phase Ib, 'IFN-free' clinical trial demonstrated that danoprevir, combined with the HCV polymerase inhibitor RG-7128 (Pharmasset Inc/Roche Holding AG), was effective in reducing HCV-RNA levels in a large proportion of treatment-naive patients with HCV infection and in approximately half of previously non-responsive patients with HCV-1 infection, without resistance or safety concerns. In a phase IIb trial in treatment-naive patients with HCV-1 infection, danoprevir plus pegylated IFN alpha 2a and ribavirin resulted in undetectable levels of HCV-RNA in the majority of patients, without any evidence of viral resistance; however, the high-dose danoprevir arm was prematurely terminated because of grade 4 ALT elevations. Phase I trials have also demonstrated that ritonavir boosting improved the pharmacokinetic profile of danoprevir; therefore, at the time of publication, a phase IIb trial to evaluate ritonavir-boosted, low-dose danoprevir in combination with RG-7128 was planned.