Profile: Pharmasset, Inc. (VRUS.O)

Pharmasset, Inc. (Pharmasset), incorporated on June 8, 2004, is a clinical-stage pharmaceutical company engaged in discovering, developing, and commercializing drugs to treat viral infections. Its primary focus is on the development of nucleoside/tide analogs as oral therapeutics for the treatment of chronic hepatitis C virus (HCV) infection and secondarily, on the development of Racivir for the treatment of human immunodeficiency virus (HIV) infection. Nucleoside/tide analogs are a class of compounds, which act as alternative substrates for the viral polymerase, thus inhibiting viral replication. As of September 30, 2009, the Company had three clinical-stage product candidates, two of which it is developing itself and one of which the Company is developing with a strategic partner. It is also advancing a series of preclinical candidates in preparation for clinical development.

Pharmasset’s three clinical stage product candidates are RG7128, PSI-7851 and Racivir. RG7128, formerly R7128, is a first generation HCV nucleoside polymerase inhibitor, which the Company is developing through a strategic collaboration with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche). RG7128 is in a Phase IIb clinical trial in combination with Pegasys (pegylated interferon) plus Copegus (ribavirin) and completed INFORM-I, a study designed to investigate the combination of two oral, direct acting antivirals (DAAs) in the absence of pegylated interferon and ribavirin. Both of these studies are being conducted by Roche. PSI-7851 is a second generation HCV nucleotide polymerase inhibitor, which has completed two phase I studies providing adequate safety and efficacy data to support initiation of a Phase IIa clinical trial. Racivir, which is developed for the treatment of HIV in combination with other approved HIV drugs, has completed a Phase II clinical trial.

In addition, the Company also nominated PSI-352938 (PSI-938) and PSI-352879 (PSI-879) as third generation nucleotide development candidates for the treatment of HCV, each of which could potentially be used in combination with its nucleoside/tides, RG7128 or PSI-7851. PSI-938 and PSI-879 are purine nucleotide analog inhibitors of HCV polymerase that are in preclinical studies required for submission of an investigational new drug (IND) application with the United States Food and Drug Administration (FDA) or equivalent foreign regulatory application. It continue to research nucleoside/tide analogs (both pyrimidines and purines) with the intention of identifying additional product candidates that can potentially be used in combination with its nucleoside/tides, RG7128 and PSI-7851, in combination with other classes of designated approving authorities (DAAs), or with pegylated interferon and/or ribavirin for the treatment of HCV.

The Company competes with Novartis/Human Genome Sciences, Vertex, Merck and Three Rivers Pharmaceuticals.