Gilead Sciences, Inc. announced preclinical data and results from two phase I studies for GS 9350, an investigational compound being developed as a pharmacoenhancing agent (booster) to increase blood levels and allow once-daily dosing for certain medicines, including Gilead's investigational HIV integrase inhibitor, elvitegravir. These data suggest that GS 9350 has significant and selective pharmacoenhancing ability, no antiviral activity against HIV and differentiated biological properties in vitro compared to ritonavir, currently the only drug used to boost certain HIV treatments, including protease inhibitors.

Study results also show that GS 9350 effectively boosts elvitegravir, when both drugs are dosed as part of a single tablet complete fixed-dose regimen with Truvada (emtricitabine 200 mg and tenofovir disoproxil fumarate 300 mg). These data were presented today during an oral session at the 16th Conference on Retroviruses and Opportunistic Infections (CROI) in Montreal.

"These data represent the first major step forward in Gilead's clinical development of a new integrase-based, single tablet, once-daily regimen for HIV," said Norbert Bischofberger, PhD, executive vice president, research and development and chief scientific officer, Gilead Sciences. "Results also indicate that GS 9350 holds promise as a stand-alone alternative to ritonavir for patients receiving boosted HIV protease inhibitor-based treatment regimens."

A boosting agent is used to increase the blood levels of certain antiretroviral drugs prescribed to treat HIV infection. Gilead is developing GS 9350 to enable once-daily dosing for elvitegravir, which is currently being evaluated in combination with ritonavir-boosted HIV protease inhibitors, in comparison to twice-daily raltegravir, in a phase III clinical trial among treatment-experienced HIV patients. The company plans to initiate a Phase II study of the complete single tablet fixed-dose regimen containing elvitegravir, GS 9350 and Truvada in treatment-naïve patients in the second quarter of this year. Currently, the only available single tablet regimen for the treatment of HIV is Atripla® (efavirenz 600 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg), which is jointly marketed in the United States by Gilead and Bristol Myers-Squibb Company.

Gilead is also examining GS 9350's potential to boost HIV protease inhibitors, which are used in many HIV treatment regimens. Gilead has initiated a pharmacokinetic study of GS 9350 that will assess its ability to boost atazanavir, one of the most widely prescribed HIV protease inhibitors.

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. Elvitegravir, also known as GS 9137 or JTK 303, was licensed by Gilead from Japan Tobacco Inc. (JT) in March 2005. Under the terms of Gilead's agreement with JT, Gilead has exclusive rights to develop and commercialize elvitegravir in all countries of the world, excluding Japan, where JT retains rights. Elvitegravir is an investigational therapy and has not yet been determined safe or efficacious in humans.

Truvada, a combination of Emtriva and Viread, is indicated in combination with other antiretroviral agents (such as non-nucleoside reverse transcriptase inhibitors or protease inhibitors) for the treatment of HIV-1 infection in adults.

It is not recommended that Truvada be used as a component of a triple nucleoside regimen.

Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes innovative therapeutics in areas of unmet medical need. The company's mission is to advance the care of patients suffering from life-threatening diseases worldwide.