Development of Three Antiretroviral Drugs Halted

Given the effectiveness of current combination ART, it has become increasingly difficult for new drugs to demonstrate superiority to existing therapies in clinical trials.

In July, Merck announced that it was discontinuing development of its investigational CCR5 antagonist vicriviroc for treatment of HIV infection. Last January, the company announced that it would not seek approval of vicriviroc for treatment-experienced individuals. At the 2010 Conference on Retroviruses and Opportunistic Infections (CROI) last February, researchers reported that in the VICTOR trials, vicriviroc did not demonstrate noninferiority to an optimized background regimen plus placebo for this population.

This summer, the company announced that it has also decided to stop testing the drug for treatment-naive HIV patients, again due to unimpressive Phase II study results. All ongoing clinical trials of vicriviroc were terminated and participants were transitioned to other drugs. The company did not indicate whether it plans to pursue research on vicriviroc for other potential indications.

In related news, the Australian biotechnology company Avexa announced in May that it has stopped development of its investigational nucleoside reverse transcriptase inhibitor (NRTI) apricitabine after failing to find a licensing partner. While apricitabine demonstrated potent antiviral activity and good tolerability in a Phase IIb trial, its twice-daily dosing schedule puts it at a disadvantage compared with once-daily NRTIs such as abacavir (Ziagen) and tenofovir.

Finally, in June, Utah-based Myrexis (formerly Myriad Pharmaceuticals) said it is ending development of the HIV maturation inhibitor bevirimat, once known as PA-457 and renamed MPC-4326 when Myriad purchased it from Panacos in 2009. Bevirimat demonstrated promising activity in early studies, but the tablet formulation had poor bioavailability and response rates were lower than expected. Researchers later determined that HIV with specific genetic polymorphisms (variations) was more likely to respond, but about one-third of treatment-naive HIV patients showed decreased susceptibility to the drug. Myrexis indicated that it will suspend work on this class of HIV drugs and focus instead on cancer therapies.

Liz Highleyman (liz@black-rose.com) is a freelance medical writer based in San Francisco.