Biotech Values

[DewDiligence]

VRUS Reports HCV Monotherapy Data for PSI-7851

[PSI-7851 is a polymerase inhibitor positioned as VRUS’ wholly-owned follow-up to R7128 (the drug licensed to Roche and being tested in the all-oral INFORM-1 study). PSI-7851 is rather similar to IDIX’s IDX184: the former is a uridine nucleotide analog while the latter is a guanosine nucleotide analog.

As discussed in prior threads (e.g. #msg-39720566), 3-day monotherapy studies of HCV polymerase inhibitors do not provide much useful data other than safety because: i) 3 days is too short a duration for these drugs to reach steady-state concentrations; and ii) efficacy (SVR rate) will depend on the performance of the drug in a cocktail with interferon and ribavirin.]

http://finance.yahoo.com/news/Pharmasset-Reports-Positive-prnews-4290719138.html?x=0&.v=1

›PSI-7851 achieves a 1 log(10) reduction in HCV RNA after 3 days of monotherapy - No discontinuations or serious adverse events reported

Conference call at 8:00 AM ET today

Friday July 31, 2009, 7:00 am EDT

PRINCETON, N.J., July 31 /PRNewswire-FirstCall/ -- Pharmasset, Inc. (Nasdaq: VRUS ) reported today positive preliminary results from its phase I clinical trial of PSI-7851 for the treatment of hepatitis C (HCV). PSI-7851 is a second generation nucleotide polymerase inhibitor of HCV.

PSI-7851 Phase 1 Multiple Ascending Dose Study Overview

In June 2009, Pharmasset initiated a phase 1 multiple ascending dose study with PSI-7851. The trial was conducted at two US centers, as a blinded, randomized, and placebo-controlled study, in 30 patients chronically infected with HCV genotype 1. The primary objective was to assess the safety, tolerability, and pharmacokinetics of PSI-7851 after once-daily (QD) dosing for 3 days. The secondary objective was to assess antiviral activity by measuring the change in HCV RNA. Patients were randomized to receive either PSI-7851 (8 patients per cohort) or placebo (2 patients per cohort). Three dose cohorts of PSI-7851 (50mg QD, 100mg QD, 200mg QD) were evaluated.

PSI-7851 Antiviral Activity Summary

Preliminary Antiviral Response Observed Following PSI-7851 Administered as Monotherapy for 3 Days
--------------------------------------------------------------------------
Dose N Mean Change in HCV RNA at Day 3
(Log(10))
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50mg QD 8 -0.49
100mg QD 8 -0.61
200mg QD 8 -1.01
Placebo 6 -0.03
--------------------------------------------------------------------------

PSI-7851 demonstrated potent antiviral activity with a mean HCV RNA decrease of -0.49 log(10) IU/mL, -0.61 log(10) IU/mL and -1.01 log(10) IU/mL in patients receiving 50mg QD, 100mg QD, and 200mg QD, respectively.

PSI-7851 Pharmacokinetic and Safety Summary

Pharmacokinetics were similar between healthy subjects in the single ascending dose study and HCV infected patients in the multiple ascending dose study. PSI-7851 was generally safe and well tolerated across all cohorts with no discontinuations. There were no serious adverse events and no dose-related trends in adverse events or laboratory abnormalities.

"We are very encouraged by the preliminary efficacy and safety data with PSI-7851, our second generation nucleotide analog," said Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "The data from these first three cohorts demonstrate that we have achieved our goal of identifying a nucleotide analog with good efficacy that can be administered once daily at a low milligram dose. Given these characteristics and the potential benefits of nucleotide analogs over other classes of HCV direct acting antivirals, we continue to believe that PSI-7851 could become a key component of any future combination treatment regimen for HCV."

Conference Call and Webcast

Members of Pharmasset's management team will host a conference call today, Friday, July 31, 2009, at 8:00 a.m. ET to discuss the preliminary results of the multiple ascending dose trial with PSI-7851. Investors may listen to the webcast of the conference call live on the "Events & Presentations" section of Pharmasset's website, www.pharmasset.com. Alternatively, investors may listen to the call by dialing [phone] from locations in the U.S. and [phone] from outside the U.S. The webcast replay will be available for at least 72 hours following the call.

About PSI-7851

PSI-7851 is a uridine nucleotide analog currently in development for the treatment of chronic HCV infection. PSI-7851 has demonstrated potent in vitro anti-HCV activity with EC(90) values of 31 +/- 12 nM, which is approximately 15-fold more potent than Pharmasset's first generation nucleoside polymerase inhibitor, RG7128 (formerly known as R7128). In vitro studies of PSI-7851 have not shown evidence of any mitochondrial or other cellular toxicities that may be associated with some nucleoside analogs. Like RG7128, PSI-7851 has demonstrated pan genotype activity in vitro.

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 on the development of oral therapeutics for the treatment of hepatitis C virus (HCV) and, secondarily, on the development of Racivir® for the treatment of human immunodeficiency virus (HIV). Our research and development efforts focus on nucleos(t)ide 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. RG7128, a nucleoside analog for chronic HCV infections, is in a Phase 2b clinical trial in combination with Pegasys® plus Copegus® and is also in INFORM studies, the first series of studies designed to assess the potential of combinations of small molecules without Pegasys® and Copegus® to treat chronic HCV. These clinical studies are being conducted through a strategic collaboration with Roche. Our other clinical stage candidates are PSI-7851, an unpartnered, next generation HCV nucleotide analog which recently began Phase 1 clinical studies and Racivir, for the treatment of HIV, which has completed a Phase 2 clinical trial.‹