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Pharmasset Starts Phase 3 Trials of PSI-7977 Without Interferon

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Pharmasset, Inc. announced this week that it has begun a Phase 3 program of studies of its hepatitis C virus (HCV) polymerase inhibitor PSI-7977 taken once-daily in combination with ribavirin but not pegylated interferon. These trials will enroll previously untreated people with HCV genotype 2 or 3, and patients with any genotype who cannot use interferon.

The advent of direct-acting antiviral agents is revolutionizing hepatitis C treatment, but current approved regimens still require pegylated interferon, which is expensive can cause potentially debilitating side effects. Better-tolerated all-oral regimens are therefore a priority.

As reported this past summer, PSI-7977 combined with pegylated interferon/ribavirin cured 100% of people with HCV genotypes 2 and 3 in the Phase 2b PROTON trial. When used without interferon, early studies have shown that PSI-7977 works well with ribavirin and with its companion polymerase inhibitor PSI-938.

Below is an edited excerpt from a recent company press release describing the forthcoming clinical trials.

Pharmasset Announces the Initiation of an Interferon-Free Phase 3 Program with PSI-7977 for HCV

Princeton, N.J. -- November 1, 2011 -- Pharmasset, Inc. (Nasdaq: VRUS) today announced the initiation of a Phase 3 program with the hepatitis C virus (HCV) nucleotide analog, PSI-7977. This pivotal program will evaluate a 12-week, all-oral, interferon-free regimen of PSI-7977 and ribavirin [RBV] in patients with HCV, independent of viral genotype or their ability to take interferon therapy.

"After recent discussions with Health Authorities, we are excited to be initiating the first of a series of pivotal studies to explore an interferon-free regimen of PSI-7977 in broad populations of individuals with HCV," said Michael Rogers, PhD, Pharmasset's Chief Development Officer.

The first trial, FISSION, will enroll approximately 500 treatment-naive patients with HCV genotype [GT] 2 or 3, and will evaluate the safety and efficacy of a 12-week interferon-free regimen of PSI-7977 and ribavirin compared to 24 weeks of pegylated interferon and ribavirin. The primary endpoint of the study is sustained virologic response 12 weeks after the completion of treatment (SVR12).

Pharmasset plans to initiate a second 12-week duration, interferon-free Phase 3 trial, POSITRON, in early 2012. This trial will enroll approximately 225 patients with HCV genotype 2 or 3 who cannot take interferon.

In mid-2012, Pharmasset intends to initiate a third 12-week duration, interferon-free Phase 3 trial, NEUTRINO. This trial will enroll patients who cannot take interferon, and will include patients with HCV regardless of viral genotype, including those with HCV genotype 1. The final study design will be based on emerging data from ELECTRON and from PSI-7977 plus RBV-containing arms in the ongoing QUANTUM study.

"Based on encouraging results to date, we have selected an IFN-free regimen of PSI-7977/RBV for our registrational program," said Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "We continue to believe that interferon remains the greatest impediment to care for a majority of the millions of individuals living with HCV. PSI-7977 has demonstrated high cure rates, without viral resistance, and across HCV genotypes; we hope to confirm these benefits in these registrational studies."

About FISSON

FISSION will be conducted at more than 100 centers in the U.S., Europe and other territories. The trial will enroll approximately 500 treatment-naive patients with HCV genotype 2 or 3 into one of two open-label regimens:

  • PSI-7977 400 mg QD with ribavirin for 12 weeks
  • The current standard-of-care for HCV GT2/3, pegylated interferon and ribavirin for 24 weeks

The study will include patients with and without cirrhosis, and will enroll a greater proportion of patients with HCV genotype 3, who are less likely to achieve an SVR with the currently available therapy, pegylated interferon and ribavirin. The primary endpoint of the trial will be SVR12. Enrollment is anticipated to begin by the end of 2011.

About POSITRON

POSITRON will be conducted at more than 100 centers in the US, Europe and other territories. The trial will enroll patients with HCV genotype 2 or 3 who cannot take interferon into one of two blinded regimens:

  • PSI-7977 400 mg QD with ribavirin for 12 weeks
  • Placebo PSI-7977 and placebo ribavirin

POSITRON will enroll approximately 225 patients with or without cirrhosis. The primary endpoint of the trial will be SVR12. Enrollment is anticipated to begin in the first quarter of 2012.

About NEUTRINO

NEUTRINO will enroll approximately 280 patients who cannot take interferon. The study will be conducted at more than 100 centers in the U.S., Europe and other territories. The final design of the trial will be based on emerging data from ongoing studies, including ELECTRON and QUANTUM. We anticipate the study will enroll patients with HCV regardless of viral genotype, and including those with HCV GT1. Enrollment is anticipated to begin in mid-2012.

Pharmasset anticipates submitting data from all three phase 3 trials in the second half of 2013 to support the marketing approval of PSI-7977 in the U.S. and European Union.

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 initiating an interferon-free, Phase 3 program in patients with HCV genotypes 1, 2 and 3 and continues to be evaluated in five Phase 2b trials in patients with all HCV genotypes. Our purine, PSI-938, an unpartnered guanosine nucleotide analog, is being studied in QUANTUM, a Phase 2b interferon-free trial of PSI-7977 and/or PSI-938 in patients with all HCV genotypes. Mericitabine (RG7128) continues in development through a strategic collaboration with Roche.

11/4/11

Source

Pharmasset, Inc. Pharmasset Announces the Initiation of an Interferon-Free Phase 3 Program with PSI-7977 for HCV. Press release. November 1, 2011.