Pharmasset shares continue rise on PhIII plan for interferon-free PSI-7977

Shares of Pharmasset continued their meteoric rise yesterday as investors warmed to the news that the biotech has mapped out its march through the clinic to a new, interferon-free hep C treatment application. Pharmasset launched a late-stage study combining its lead treatment, PSI-7977, with ribavirin to see how the combo fares against a regimen of ribavirin and interferon. And the biotech ($VRUS) has whipped up a slate of late-stage trials for PSI-7977, a darling of the investment community, which clearly comprehends the blockbuster market that awaits any hepatitis C treatment that doesn't require injections of interferon.

This new study will start enrolling patients before the end of the year, with two other studies in 2012 designed to build a package of data for regulators, laying the groundwork for a possible approval in 2013. That sounds just right to investors, who helped push up Pharmasset shares more than 10% as the biotech's stock continued a surge that has seen shares triple in value over the course of the year. A similar spike was triggered by Pharmasset's recent decision to expand a study for PSI-7977.

Why the excitement? Taking interferon out of the treatment equation for hepatitis C is now the next big game changer in the field. At FierceBiotech's recent executive breakfast in Boston, Vertex research chief Peter Mueller told me that interferon is "terrible stuff." Some patients can't handle the side effects and all of them would prefer a simple oral regimen with no injections required. Now all the developers in the field have their eye on that ball, including Vertex, and the investment community has been quick to pick up on the implications. Pharmasset, though, has a very careful, clear Phase III strategy set up for 2012, putting the developer at the head of the pack.

Pharmasset has laid out plans for three registration studies. The first, dubbed FISSION, will enroll about 500 treatment-naive patients and split them between an arm for PSI-7977 and ribavirin and a separate arm for pegylated interferon and ribavirin. The primary endpoint of the study is sustained virologic response 12 weeks after treatment is completed. A second 12-week trial will launch in early 2012, enrolling 225 patients unable to take interferon. A third 12-week trial is slated to begin in mid-2012. The final study design will be based on emerging data from ongoing studies.

- read the press release on their Phase III program
- here's the story from Bloomberg