I make this prediction after carefully rereading the transcript of the Pharmasset shareholder analyst call from 11/1/11. There was a lot of excitement when Pharmasset announced a 91% SVR12 for GT1 HCV in their PROTON study. What I think was missed by many is the fact that they achieved this result with triple therapy consisting of PSI-7977/peg-interferon/ribavirin. Now they have two ongoing phase II studies, ATOMIC and ELECTRON, that are supposed to advance their potential treatments for the HCV GT1 patients. The ATOMIC study is to determine if 12 week triple therapy in GT1 patients "...without 12 week Peg as a follow-on would achieve the same high response rate." The ELECTRON study was designed to "...determine the impact of reducing the total number of injections of interferon that would be necessary to retain the same high SVR." There upcoming phase III registration studies consist of FISSION, POSITRON ad NEUTRINO. The FISSION study will evaluate 12 weeks of PSI-7977/RBV in GT2/3 patients. The POSITRON study will evaluate 12 weeks of PSI-7977/RBV in GT2/3 patients that cannot take interferon. And the NEUTRINO study will test PSI-7977/RBV in patients, regardless of genotype, that cannot take interferon.
The bottom line is that Pharmasset has not been able to come up an effective regimen to treat GT1 HCV without including interferon injections. Apparently, they are aware of this so they will only test their oral regimen in GT1 patients that cannot take interferon. They might have better luck in their upcoming QUANTUM study that will treat HCV patients regardless of genotype and interferon tolerance using various combinations of PSI-938, PSI-7977 and ribavirin for 12 to 24 weeks. But results of that study are a long way off.