PSI-7977 plus Standard Therapy Cures 100% of Genotype 2-3 Hepatitis C Patients

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Pharmasset's investigational hepatitis C virus (HCV) polymerase inhibitor PSI-7977 combined with pegylated interferon/ribavirin cured 100% of people with HCV genotype 2 and 3 in the Phase 2b PROTON trial; sustained response results for hard-to-treat genotype 1 patients are expected later this year.

Below is an edited excerpt from a press release issued by Pharmasset describing the study and its findings.

Pharmasset Announces Final SVR Data from PROTON trial with PSI-7977 in Subjects Infected with Hepatitis C Infection Genotype 2 or 3

-- 24 out of 24 subjects with HCV genotype 2 or 3 achieved an SVR after 12 weeks of treatment with PSI-7977 400mg QD and pegylated interferon and ribavirin

-- SVR12 results from PROTON in HCV genotype 1 subjects are expected in second half of 2011

Princeton, NJ-- July 20, 2011 -- Pharmasset, Inc. (Nasdaq: VRUS) announced today the final sustained virologic response (SVR) results from its phase 2b PROTON study with PSI-7977 dosed once daily in combination with peginterferon alfa 2a and ribavirin (Peg-IFN/RBV) in subjects with hepatitis C virus (HCV) genotype 2 or 3 who have not been treated previously. Twenty-four out of twenty-four subjects (100%) who completed treatment achieved an SVR, defined as HCV RNA below the limit of detection (<15 IU/ml) 24 weeks after the completion of treatment. No subject exhibited breakthrough on treatment or relapse after treatment.

Twenty-five treatment-naive subjects with HCV genotype 2 or 3 were enrolled in an open-label arm of the PROTON trial, receiving PSI-7977 400mg QD [once-daily] with Peg-IFN/RBV for 12 weeks, with no Peg-IFN/RBV follow-up. At the European Association for the Study of the Liver (EASL) in April 2011, Dr J. Lalezari presented interim results from this arm showing that 24 out of 24 subjects achieved an SVR12, defined as HCV RNA below the limit of detection (<15 IU/ml) 12 weeks after the completion of treatment. The combination was generally safe and well tolerated with one subject discontinuing treatment after day 1 and was lost to follow up. Overall PSI-7977 with Peg-IFN/RBV demonstrated potent viral suppression in subjects with HCV genotype 2 or 3 over 12 weeks of treatment.

Pharmasset anticipates reporting the SVR12 results from the PROTON trial in genotype 1 HCV subjects in the second half of 2011.

About the PROTON Trial

The Phase 2b PROTON trial enrolled 121 subjects infected with HCV genotype 1 who have not been treated previously. The primary endpoint of the trial will be the assessment of safety and tolerability of PSI-7977 in combination with Peg-IFN/RBV over 12 weeks with response-guided therapy allowing discontinuation of Peg-IFN/RBV at week 24. The trial was conducted in the U.S. Subjects were randomized (2:2:1) into one of 3 arms:

In addition, 25 treatment-naive subjects with HCV genotype 2 or 3 were enrolled in a fourth, open-label arm, receiving PSI-7977 400mg QD with Peg-IFN/RBV for 12 weeks, with no Peg-IFN/RBV follow-up. Subjects were followed for an additional 24 weeks after discontinuation of all therapy to assess SVR.

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed to discovering, developing, and commercializing novel drugs to treat viral infections. Pharmasset's primary focus is the development of oral therapeutics for the treatment of hepatitis C virus (HCV) infection. Our research and development efforts are focused on nucleoside/tide analogs, a class of compounds which act as alternative substrates for the viral polymerase, thus inhibiting viral replication. We currently have three clinical-stage product candidates advancing in trials in various populations. Our pyrimidine, PSI-7977, an unpartnered uracil nucleotide analog, is currently under study in four Phase 2b trials in patients with HCV genotypes 1 through 6, including abbreviated duration interferon and interferon-free regimens. Our purine, PSI-938, an unpartnered guanosine nucleotide analog, recently reported safety and efficacy data from 14 days of monotherapy as well as 14 days in combination with the pyrimidine, PSI-7977. An SVR-endpoint study of the purine-pyrimidine combination is anticipated to begin in the third quarter of 2011. Mericitabine (RG7128) continues in three Phase 2b trials and one interferon-free trial being conducted through a strategic collaboration with Roche.

7/26/11

Source

Pharmasset. Pharmasset Announces Final SVR Data from PROTON trial with PSI-7977 in Subjects Infected with Hepatitis C Infection Genotype 2 or 3. Press release. July 20, 2011.