Gilead Sciences, Inc.,a biopharmaceutical company, reported 48-week results from a phase 2 study (Study 102) evaluating an investigational once-daily single tablet regimen containing tenofovir alafenamide (TAF) for the treatment of HIV-1 infection. At 48 weeks, a regimen of elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/TAF 10 mg was found to be similar to Stribild (elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg) based on the percentage of patients with HIV RNA levels less than 50 copies/mL, and was associated with more favorable renal and bone safety markers. These findings were presented at the 53rd Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC 2013) in Denver.

“These results suggest that TAF has the potential to be an important advance for people living with HIV,” said Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital, Boston, Professor of Medicine at Harvard Medical School, and an investigator for Study 102. “In this study, the TAF-based regimen matched Stribild’s high viral suppression and demonstrated a favorable safety profile with respect to renal and bone changes.”

In Study 102, 170 HIV-positive treatment-naïve adult patients were randomized (2:1) to receive the investigational TAF-based regimen or Stribild. At 48 weeks, 88.4 percent (n=99/112) of patients taking TAF and 87.9 percent (n=51/58) of patients taking Stribild achieved HIV RNA (viral load) less than 50 copies/mL, based on the FDA snapshot algorithm (intent-to-treat analysis; stratum-adjusted difference between TAF and Stribild: -1.0 per cent, p=0.84, 95 per cent CI for the difference: -12.1 per cent, 10.0 per cent). No drug resistance was observed in patients receiving the TAF-based regimen.

Both regimens were generally well tolerated. There were no treatment-related serious adverse events. There were numeric differences in laboratory abnormalities of renal and bone markers, which favored the TAF-based regimen. There was a statistically significant difference in the median change in estimated glomerular filtration rate (eGFR) from baseline to week 48, with eGFR decreasing by -5.5 mL/min in the TAF arm compared to a decline of -10.0 mL/min in the Stribild arm (p=0.041). Additionally, there was a significantly smaller median percentage decrease in bone mineral density from baseline to week 48 for the TAF-based regimen compared to Stribild (-1.00 vs. -3.37 (p<0.001) for the lumbar spine and -0.62 vs. -2.39 (p<0.001) for the hip). There were no pathological bone fractures in either arm of the study.

“Based on these positive results, we believe that TAF has the potential to become a key component of next-generation single tablet regimens in HIV therapy,” said Norbert W. Bischofberger, Gilead’s executive vice president, research and development and chief scientific officer. “We are now completing enrollment of two phase 3 clinical trials comparing a TAF-based regimen to Stribild in patients new to HIV treatment, and look forward to sharing initial results from these large-scale studies by the end of 2014.”

Study 102 is a randomized, double-blind 48-week clinical trial evaluating the efficacy and safety of a once-daily single tablet regimen containing elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/TAF 10 mg (n=112) compared to Stribild (elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg) (n=58) among HIV-1 infected treatment-naïve adults with HIV RNA levels greater than or equal to 5,000 copies/mL, CD4 cell counts greater than 50 cells/mm3 and estimated creatinine clearance of at least 70 mL/min. Bone mineral density was assessed in all patients by DEXA scans at baseline and at 24 and 48 weeks of treatment. The primary endpoint of the study is the percentage of patients with HIV RNA levels less than 50 copies/mL at week 24, per the FDA snapshot algorithm. Secondary endpoints include the proportion of patients who achieve viral load of less than 50 copies/mL at week 48, and changes in HIV-1 RNA and in CD4 cell count from baseline to weeks 24 and 48.

At baseline, patients receiving the TAF-based regimen had a median HIV RNA of 4.55 log10 copies/mL and median CD4 cell count of 385 cells/mm3. Patients receiving Stribild had a median HIV RNA of 4.58 log10 copies/mL and median CD4 cell count of 397 cells/mm3. At week 48, mean CD4 cell count increases from baseline were 177 cells/mm3 in the TAF arm and 204 cells/mm3 for Stribild (p=0.41).

Discontinuations due to adverse events were similar in both treatment arms (3.6 percent for TAF vs. 0 percent for Stribild), and the frequency and nature of adverse events was also similar. The most common adverse events occurring in at least 10 per cent of TAF patients were nausea (21 per cent for TAF vs. 12 per cent for Stribild), diarrhea (16 percent vs. 16 per cent), upper respiratory tract infection (15 per cent vs. 21 percent), fatigue (14 per cent vs. 9 percent), headache (10 per cent vs. 14 per cent) and cough (10 per cent vs. 10 per cent).

The incidence of laboratory abnormalities (Grades 3-4) was 25 percent in the TAF arm and 17 per cent for Stribild. Grades 3-4 laboratory abnormalities occurring in at least 5 per cent of patients in either treatment arm were LDL (low-density lipoprotein or “bad” cholesterol), elevated creatine phosphokinase and neutropenia.

There were no discontinuations due to renal events and no cases of proximal renal tubulopathy in either arm. Additional exploratory markers of proximal renal tubulopathy, measuring impaired absorption and secretion of proteins caused by damage to the proximal tubule, favored the TAF-based regimen. At 48 weeks of treatment, the change from baseline in the ratio of urine retinol binding protein to creatinine for the TAF-based regimen was -0.1 µg/g compared to +20.7 µg/g for Stribild (p=0.001), and the change from baseline in the ratio of urine ß-2 microglobulin to creatinine for the TAF-based regimen and Stribild was -33.6 µg/g and +0.4 µg/g, respectively (p=0.008).

Tenofovir alafenamide (TAF) is a nucleotide reverse transcriptase inhibitor (NtRTI). It is a novel prodrug of tenofovir. Phase 1b dose-ranging studies identified a dose of TAF that is ten times lower than Viread® (tenofovir disoproxil fumarate) and provided greater reduction in viral load. The smaller milligram dose of TAF may enable the development of new fixed-dose combinations and single tablet regimens for HIV therapy that are not feasible with Viread.

Elvitegravir is a member of the integrase inhibitor class of antiretroviral compounds. Integrase inhibitors interfere with HIV replication by blocking the ability of the virus to integrate into the genetic material of human cells. Elvitegravir 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.

Cobicistat is Gilead’s proprietary potent mechanism-based inhibitor of cytochrome P450 3A (CYP3A), an enzyme that metabolizes drugs in the body. Unlike ritonavir, cobicistat acts only as a pharmacoenhancing or “boosting” agent and has no antiviral activity.

Elvitegravir/cobicistat/emtricitabine/TAF and elvitegravir and cobicistat as single agents are investigational products and their safety and efficacy have not yet been established.

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