While scanning the CROI 2010 abstracts during my six-hour plane ride to San Francisco, the thought occurred to me that we may be witnessing the winding down of the HIV drug development process.
Historically, CROI has been a high-profile event during which pharmaceutical companies would showcase their up-and-coming investigational antiretroviral agents. Not anymore.
At this conference, the number of clinical trials of novel antiretroviral agents could be counted on one hand: Gilead's "quad" tablet, elvucitabine, vicriviroc and the ViiV integrase inhibitor S/GSK1349572. There were a few interesting antiretroviral agents presented, but never has there been such a wide gap between the number of investigational pre-clinical antiretroviral agents and the compounds that are actually moving through clinical development.
There appear to be several reasons for this phenomenon. First and foremost, the bar for antiretroviral drug development has been raised to a very high level. Current combination therapy is not perfect, but about 80% of patients reach an undetectable viral load with minimal or manageable side effects. Furthermore, co-formulation of frontline antiretroviral therapy is becoming the standard, so a promising first-line agent without an already-established potential antiretroviral partner is at a disadvantage.
On the other end of the treatment spectrum, for an investigational agent looking for a niche among treatment-experienced patients, there is not a clear path forward to regulatory approval. For example, as Myles Helfand discussed in his blog, data presented at this meeting detailed the failure of the CCR5 inhibitor vicriviroc to outperform placebo in a salvage trial. The failure was not because of a lack of potency or side effects, but rather was related to the fact that the majority of patients in the placebo arm had more than two active agents in their optimized background regimen.
The misfortune that befell vicriviroc may have a chilling effect on future salvage trials. An ethical study design which would allow a potential salvage drug to demonstrate efficacy has yet to be articulated.
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