GS-7977
On March 6, 2012 interim results from an arm of the ELECTRON phase 2 study were released at the Conference on Retroviruses and Opportunistic Infections (CROI). This particular arm treated HCV genotype 1, prior null responders—the hardest group to retreat—with GS-7977 (HCV polymerase inhibitor) plus ribavirin (RBV) (no interferon (PEG)). The arm enrolled 10 patients who were treated for 12 weeks with GS-7977 plus ribavirin. Of the nine patients who were HCV RNA undetectable at the end of treatment, eight patients relapsed within 4 weeks post treatment. One patient who did achieve SVR12 had favorable predictors of successful response—female, Caucasian, IL28B CC genotype and a low fibrosis score.
Comments: This is very disappointing news in the light of all of the positive stories about GS-7977/RBV therapy (without interferon) that have been released. But it is important to keep in mind a couple of important issues when interpreting these results:
The null responder population is and will be the most difficult to treat population. GS-7977 plus ribavirin in genotypes 2 and 3 has cure rates in phase 2 studies of up to 100% and HCV genotype 1 treatment-naïve patients in phase 2 studies have had up to 91% cure rates.
In this difficult to treat population there is most likely a need to add another direct acting antiviral (DAA) or treat for a longer period of time. Gilead has an entire portfolio of other DAAs that can be combined with GS-7977 including GS-9256—HCV protease inhibitor, and GS-9190—HCV polymerase inhibitor.
There are two other interferon-free collaborations of GS-7977 with other pharmaceutical companies:
BMS’s daclatasvir—NS5A inhibitor with GS-7977 with and without RBV, and
Tibotec’s TMC435—HCV protease inhibitor with and without RBV.
The bottom line is not to give up hope—we will get to the 100% cure rates for genotypes 1, 2, 3, 4, 5, and 6 eventually—it’s just a matter of finding the right combination of drugs and the optimal treatment durations—that’s what clinical trials are all about.
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