Pharmasset has entered into a clinical collaboration agreement with Tibotec Pharmaceuticals to evaluate in a phase II study the safety and efficacy of PSI-7977 in combination with TMC435, for the treatment of chronic hepatitis C virus (HCV).

This phase II study will evaluate the potential to achieve sustained virologic response 12 weeks post-treatment with an all oral, once-daily, interferon-free treatment regimen in patients infected with genotype 1 HCV.  The study will assess the safety, pharmacokinetics and pharmacodynamics of 12 and 24 weeks of PSI-7977 in combination with TMC435, with and without ribavirin, in patients infected with HCV genotype 1 who had a prior null response to peginterferon alfa and ribavirin treatment. The study is planned to start in the second half of 2011.

"PSI-7977 is now being studied in interferon-free combinations with each of the three leading classes of direct-acting antivirals: Tibotec's protease inhibitor, Bristol-Myers Squibb's NS5a inhibitor and our own nucleotide, PSI-938. This advances one of our key goals at Pharmasset: to develop our nucleotide analogs as the backbone of interferon-free HCV therapy,” said Bill Symonds, PharmD, Pharmasset's senior vice president of clinical pharmacology and translational medicine.