Gilead Sciences says its new HIV drug tenofovir alafenamide fumarate (TAF) will shortly enter late-stage development after encouraging results in phase II testing.
The new drug is a chemical variant of Gilead's successful HIV drug Viread (tenofovir disoproxil fumarate) that has been designed to overcome some of the side effects of its parent, notably renal impairment and bone thinning.
In the phase II study, Gilead's four-drug HIV therapy Stribild, which contains Viread 300mg as well as elvitegravir, cobicistat and emtricitabine - was compared to TAF 10mg plus the other three drugs in the same doses in treatment-naïve HIV patients.
The TAF-based regimen achieved the same virologic responses as Stribild - with viral load falling to less than 50 copes/ml of blood in 87 and 90 per cent of patients, respectively.
On the key issue of tolerability however Gilead's new drug performed significantly better, with a reduced tendency to cause reductions in bone mineral density (BMD) in the spine and hip and blood markers of kidney damage after 24 weeks of treatment.
"These interim findings are encouraging and warrant advancing this TAF-containing single tablet regimen into phase III development," commented Norbert Bischofberger, Gilead's chief scientific officer.
Gilead also noted that TAF is also being studied in a second phase II trial comparing the combination of TAF, Johnson & Johnson's Prezista (darunavir), cobicistat and emtricitabine in a single tablet to Gilead's Truvada (emtricitabine and tenofovir disoproxil fumarate) plus Prezista and cobicistat, dosed as individual components.
The study is fully enrolled and 24-week results will be available in the first half of 2013, said the company.
The active component of Viread - first launched in 2001 - has been a massively successful drug for Gilead, featuring as a component in all five of its marketed HIV drugs which collectively achieved sales of just over $2bn in the third quarter of 2012.
The patent on tenofovir disoproxil fumarate is due to start expiring in 2018, so Gilead is hoping to develop new regimens based on TAF as a 'patent cliff' mitigation strategy.