Gilead Sciences, announced detailed 48-week results from two phase 3 studies (Studies 104 and 111) evaluating its investigational once-daily single tablet regimen containing tenofovir alafenamide (TAF) for the treatment of HIV-1 infection in treatment-naïve adults.

A regimen of elvitegravir 150 mg, cobicistat 150 mg, emtricitabine 200 mg and TAF 10 mg (E/C/F/TAF) was found to be statistically non-inferior to Gilead's Stribild (containing elvitegravir 150 mg, cobicistat 150 mg, emtricitabine 200 mg and tenofovir disoproxil fumarate 300 mg), based on percentages of patients with HIV-1 RNA levels less than 50 copies/mL. A second analysis found that patients receiving the TAF regimen also had significantly better renal and bone laboratory parameters than those treated with Stribild. The data were presented in two late-breaker presentations (Sessions O-10 and O-11) at the 22nd Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle.

TAF is a novel nucleotide reverse transcriptase inhibitor (NRTI) that has demonstrated high antiviral efficacy at a dose 10 times lower than Gilead's Viread (tenofovir disoproxil fumarate, TDF), as well as improved renal and bone laboratory parameters in clinical trials.

"Long-term renal and bone health have been ongoing concerns, especially as people with HIV live longer and remain on antiretroviral treatment for greater periods of time," says Paul Sax, MD, a Clinical Director at Brigham and Women's Hospital, Professor of Medicine at Harvard Medical School and the lead researcher of the E/C/F/TAF safety analysis. "These results show that a TAF-based single tablet regimen has the potential to help address the needs of appropriate HIV patients facing life-long antiretroviral therapy."

In the combined analyses of Studies 104 and 111, a total of 1,733 treatment-naïve adults with HIV were randomised to receive E/C/F/TAF or Stribild. At 48 weeks, 92.4 per cent (n=800/866) of patients taking E/C/F/TAF and 90.4 per cent (n=784/867; CI -0.7 per cent to +4.7 per cent, p=0.13) of patients taking Stribild achieved HIV RNA levels less than 50 copies/mL (Abstract 113LB/Wohl). These analyses found that the rate of virologic success between the two regimens was similar across patient subgroups (age, gender, race, baseline HIV-1 RNA level and baseline CD4 count). Discontinuations due to adverse events were low in both treatment arms (0.9 per cent (n=8) for E/C/F/TAF vs. 1.5 per cent (n=13) for Stribild), with the most common side effects being diarrhoea, nausea, headache and upper respiratory tract infection.

"TAF delivers high levels of tenofovir directly to HIV-infected cells," said David Wohl, MD, Associate Professor of Medicine, Division of Infectious Diseases, University of North Carolina at Chapel Hill and lead author of the E/C/F/TAF efficacy analysis. "This means that patients benefit from high efficacy at a remarkably low dose."

A separate, in-depth analysis investigated the effect of the two regimens on laboratory parameters of kidney, bone and plasma lipid levels (Abstract 143LB/Sax). To examine kidney function, multiple tests of glomerular and tubular function were conducted, all of which statistically favored the E/C/F/TAF regimen. This included a statistically significant difference in the median change in estimated glomerular filtration rate (eGFR) from baseline to week 48, favoring the TAF-based regimen (-6.6 mL/min for E/C/F/TAF vs. -11.2 mL/min for Stribild, p<0.001). The analysis also found that bone mineral density (BMD) was reduced significantly more among patients taking Stribild compared to patients taking E/C/F/TAF (spine: -2.86 vs. -1.30, p<0.001; hip: -2.95 vs. -0.66, p<0.001). Finally, patients on E/C/F/TAF had higher plasma lipid values than patients on Stribild, which appeared to be consistent with the changes seen with other non-TDF based regimens.

"Given its high efficacy and favourable renal and bone safety profile, Gilead believes E/C/F/TAF represents an important evolution in the treatment of HIV," says Norbert W. Bischofberger, Gilead's executive vice president, research and development and chief scientific officer. "We look forward to the opportunity to offer patients this and other next-generation, TAF-based therapies that have the potential to improve HIV treatment."

Based on initial data from Studies 104 and 111 announced in September 2014, Gilead filed a New Drug Application for E/C/F/TAF with the US Food and Drug Administration on November 5, 2014. Under the Prescription Drug User Fee Act, the agency has set a target action date of November 5, 2015. If approved, E/C/F/TAF would be Gilead's first single tablet regimen to contain TAF. A Marketing Authorization Application (MAA) in the European Union for E/C/F/TAF was fully validated on December 23, 2014. Review of the MAA by the European Medicines Agency is being conducted under the centralised licencing procedure, which, when finalised, provides one marketing authorisation in all 28 member states of the European Union.

In addition to Studies 104 and 111, several other E/C/F/TAF study results were presented this week at CROI. Notably, these include an open-label 48-week study (Study 112) supporting the efficacy and safety of E/C/F/TAF for use among HIV-infected patients with mild-to-moderate renal impairment (CrCL = 30mL/min) (Abstract 795/Pozniak). The study included 242 virologically suppressed patients whose treatment regimens were switched from both TDF- and non-TDF-containing regimens to E/C/F/TAF. The study found that 92 per cent of study participants remained virologically suppressed at week 48. There was no significant change in eGFR compared to baseline, and significant improvements were observed in other markers of renal function, including proximal renal tubular laboratory parameters and decreased proteinuria (UPCR >200 mg/g) and albuminuria (UACR= 30mg/g). Improvements in BMD (hip and spine) were also observed from baseline to week 48 (median percent change of 0.9 per cent and 1.9 per cent, respectively). Finally, lipid values among patients taking non-TDF-containing regimens prior to the study decreased, while fasting lipids increased among those who were taking TDF-containing regimens prior to study enrollment.

Twenty-four-week data from another phase 3 study (Study 106) of E/C/F/TAF in treatment-naïve adolescents also were presented (Abstract 953/Bennett). Two other studies on emergent resistance in treatment-naïve adult and adolescent patients taking E/C/F/TAF (Abstracts 6/Margot and 952/Porter) were presented February 21-22 at the International HIV Drug Resistance Workshop, an affiliated pre-conference workshop.

E/C/F/TAF is an investigational product and has not been determined to be safe or efficacious.

Studies 104 and 111, originally planned for 96 weeks but recently extended to 144 weeks, are randomised, double-blind, controlled phase 3 trials conducted among 1,733 treatment-naïve adults living with HIV. At study enrollment, 15 per cent of subjects were women, 43 percent were non-white and 23 per cent had viral loads =100,000 copies/mL. Patients were randomised 1:1 to receive a single tablet regimen of E/C/F/TAF or Stribild. Baseline median CD4 counts were 404 cells/µL for patients in the E/C/F/TAF arm and 406 cells/µL for those in the Stribild arm. The primary endpoint was Week 48 virologic response by FDA Snapshot Algorithm in a pre-specified analysis of the combined studies.

The primary endpoint was met, as E/C/F/TAF was non-inferior to Stribild, with respect to the proportion of patients having HIV RNA less than 50 copies/mL at Week 48. Median change in CD4 count at Week 48 was 211 cells/µL in the E/C/F/TAF arm vs. 181 cells/µL in the Stribild arm (p=0.024). Virologic failure with resistance occurred in 0.8 per cent in the E/C/F/TAF arm and 0.6 per cent in the Stribild arm.

There were no reports of proximal renal tubulopathy (including Fanconi Syndrome) in either arm. No single adverse event led to discontinuation of more than one subject on E/C/F/TAF. The most commonly reported adverse events (any grade) were: diarrhoea (17 per cent vs. 19 per cent), nausea (15 per cent vs. 17 per cent), headache (14 per cent vs. 13 per cent) and upper respiratory infection (11 per cent vs. 13 per cent) in the E/C/F/TAF and Stribild arms, respectively.

The studies are ongoing in a blinded fashion. After week 96, patients will continue to take their blinded study drug until treatment assignments have been unblinded, at which point all will be given the option to participate in an open-label rollover extension and receive E/C/F/TAF.