Pharmasset, Inc. (Nasdaq: VRUS), announced today sustained virologic response (SVR) results from its phase 2b PROTON study with PSI-7977 400 mg dosed once daily in combination with peginterferon alfa 2a and ribavirin (Peg-IFN/RBV) in subjects with hepatitis C virus (HCV) genotype 1 who have not been treated previously. 43 out of 44 (98%) evaluable subjects achieved an SVR12, defined as HCV RNA below the limit of detection (<15 IU/mL) 12 weeks after the completion of treatment. All enrolled subjects will be followed to determine SVR24, the primary efficacy endpoint of the study.
Ninety five treatment-naive patients with HCV genotype 1 were enrolled into two open-label arms of the PROTON trial, receiving either PSI-7977 200 mg QD (N=48) or 400 mg QD (N=47) for 12 weeks. Individuals in both arms received Peg-IFN/RBV for 24 weeks and were followed post-treatment to assess SVR12. Twenty-six subjects were enrolled in a placebo control arm and are receiving 48 weeks of Peg-IFN/RBV. Results from this study through the SVR12 endpoint are scheduled to be presented as part of a Presidential Plenary Session at the American Association for the Study of Liver Diseases (AASLD) meeting on Tuesday, November 8, 2011."I am very pleased with the results of this study which clearly demonstrate the benefit of the 400 mg dose of PSI-7977 with only 24 weeks of interferon for all subjects," stated Dr. Eric Lawitz, the study's principal investigator. "HCV therapy is becoming overly complex, and the elimination of 24 weeks of interferon and ribavirin as well as all response guided criteria for patients with HCV genotype 1 would be a welcomed simplification."
At the European Association for the Study of the Liver (EASL) in April 2011, Dr. David Nelson presented interim results from the PROTON trial showing that 43 out of 47 subjects receiving the 400 mg dose of PSI-7977 achieved an eRVR, defined as HCV RNA below the limit of detection (<15 IU/ml) at week 4 through week 12. Of those not achieving eRVR, 3 discontinued therapy early due to unrelated adverse events and 1 was lost to follow-up, as previously reported. Notably, one of these individuals went on to achieve an SVR12 in spite of the shortened course of therapy. The combination of PSI-7977, pegylated interferon and ribavirin was generally safe and well tolerated.