Gilead Sciences, Inc announced that a phase-II clinical trial of its investigational integrase inhibitor-based, once-daily, fixed-dose 'Quad' regimen of elvitegravir, GS 9350 and Truvada (emtricitabine and tenofovir disoproxil fumarate) for the treatment of HIV-1 infection met its primary objective. The ongoing study of 71 HIV-infected, antiretroviral treatment-naïve adults compares the Quad with Atripla (efavirenz 600 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg). Based on 24-week data, efficacy of the Quad met the statistical criteria of non-inferiority as compared to Atripla based on the proportion of subjects with HIV RNA levels (viral load) of less than 50 copies/mL. Discontinuation rates due to adverse events were comparable in both arms of the study. Full study results will be submitted for presentation at a scientific meeting in early 2010.

Elvitegravir is Gilead's investigational HIV integrase inhibitor. GS 9350 is Gilead's investigational pharmacoenhancing or 'boosting' agent, being developed to increase blood levels of certain medicines, including elvitegravir, and allows for once-daily dosing.

Gilead is also studying GS 9350 as a stand-alone boosting agent for other antiretrovirals, in particular, protease inhibitors. A phase-II clinical trial evaluating the safety and efficacy of GS 9350-boosted atazanavir compared to ritonavir-boosted atazanavir, each in combination with Truvada, is ongoing. The phase-II study involves 79 HIV-infected, antiretroviral treatment-naïve adults. The study met its primary objective of achieving HIV RNA levels (viral load) of less than 50 copies/mL at 24 weeks of treatment. GS 9350-boosted atazanavir and Truvada had similar efficacy to ritonavir-boosted atazanavir and Truvada. Discontinuation rates due to adverse events were comparable in both arms of the study. Ritonavir is currently the only agent used to boost HIV therapy. Results from this study will also be submitted for presentation at a scientific meeting in early 2010.

The GS 9350 phase-II study is a double-blind, multicenter, randomized (2:1), active-controlled 48-week clinical trial evaluating the safety and efficacy of GS 9350-boosted atazanavir (n=50) compared to ritonavir-boosted atazanavir (n=29), each in combination with Truvada, in HIV-infected treatment-naïve adults with HIV RNA levels (viral load) greater than or equal to 5,000 copies/mL and CD4 cell counts greater than 50 cells/mm3. Entry criteria required that patients did not have nucleoside reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor or primary protease inhibitor resistance mutations, as defined by International AIDS Society-USA guidelines, and no prior use of antiretroviral treatments.

The study is ongoing. Secondary endpoints will include the proportion of patients with HIV RNA levels (viral load) less than 50 copies/mL at 48 weeks of treatment, and the safety and tolerability of the two treatment regimens through 48 weeks of treatment. After week 48, subjects will continue to take blinded study drug until treatment assignments have been unblinded, at which point all subjects will be given the option to participate in an open-label rollover extension and receive GS 9350-boosted atazanavir and Truvada.

Elvitegravir is an HIV integrase inhibitor. Unlike other classes of antiretroviral agents, integrase inhibitors interfere with HIV replication by blocking the ability of the virus to integrate into the genetic material of human cells.

GS 9350 is Gilead's proprietary potent mechanism-based inhibitor of cytochrome P450 3A (CYP3A), an enzyme that metabolizes drugs in the body.

Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes innovative therapeutics in areas of unmet medical need.