PSI-879 nominated as second development candidate for treating HCV infection

Pharmasset, Inc. (Nasdaq: VRUS) announced today the nomination of PSI-352879 (PSI-879) as a second development candidate from two series of purine analogs for the treatment of chronic hepatitis C virus (HCV) infection. PSI-879 is a proprietary nucleotide analog polymerase inhibitor of HCV that is being advanced into studies required for submission of an Investigational New Drug (IND) application with the FDA or equivalent foreign regulatory application.

"PSI-879 employs a different prodrug technology than our lead purine nucleotide, PSI-938. We plan to submit an IND for PSI-938 in the first quarter of 2010" stated Michael Otto, PhD, Pharmasset's Chief Scientific Officer. "We now are in a position to have two opportunities to develop a purine and pyrimidine nucleoside/tide combination. We believe in addition to being used in combination, our nucleoside/tide analogs also have the potential to be combined with other classes of direct acting antivirals for HCV."

Preclinical data demonstrate that purine nucleotide analogs have many of the benefits of pyrimidine nucleoside/tide analogs, such as RG7128 and PSI-7851, by demonstrating in vitro activity across multiple genotypes, a higher barrier to resistance than other classes of HCV small molecules in development, and the potential to be combined with other direct acting antivirals targeting HCV. In addition, these purine analogs are also active against the S282T resistant variant selected in vitro by the pyrimidine analogs and are metabolized to the active triphosphate form through a different phosphorylation pathway than the pyrimidines. Given these characteristics, purine and pyrimidine analogs have the potential to be combined as part of a future treatment regimen.