Search

Background: Current antiretroviral therapy against human immunodeficiency virus (HIV-1) reduces viral load and thereby prevents viral spread, but it cannot eradicate proviral genomes from infected cells. Cells in immunological sanctuaries as well as cells producing low levels of virus apparently contribute to a reservoir that maintains HIV persistence in the presence of highly active antiretroviral therapy. Thus, accelerated elimination of virus producing cells may represent a complementary strategy to control HIV infection. Here we sought to exploit HIV protease (PR) related cytotoxicity in order to develop a strategy for drug induced killing of HIV producing cells. PR processes the viral Gag and Gag-Pol polyproteins during virus maturation, but is also implicated in killing of virus producing cells through off-target cleavage of host proteins. It has been observed previously that micromolar concentrations of certain non-nucleoside reverse transcriptase inhibitors (NNRTIs) can stimulate intracellular PR activity, presumably by enhancing Gag-Pol dimerization., Results: Using a newly developed cell-based assay we compared the degree of PR activation displayed by various NNRTIs. We identified inhibitors showing higher potency with respect to PR activation than previously described for NNRTIs, with the most potent compounds resulting in ~2-fold increase of the Gag processing signal at 250 nM. The degree of enhancement of intracellular Gag processing correlated with the compound's ability to enhance RT dimerization in a mammalian two-hybrid assay. Compounds were analyzed for their potential to mediate specific killing of chronically infected MT-4 cells. Levels of cytotoxicity on HIV infected cells determined for the different NNRTIs corresponded to the relative degree of drug induced intracellular PR activation, with CC50 values ranging from ~0.3 μM to above the tested concentration range (10 μM). Specific cytotoxicity was reverted by addition of PR inhibitors. Two of the most active compounds, VRX-480773 and GW-678248, were also tested in primary human cells and mediated cytotoxicity on HIV-1 infected peripheral blood mononuclear cells., Conclusion: These data present proof of concept for targeted drug induced elimination of HIV producing cells. While NNRTIs themselves may not be sufficiently potent for therapeutic application, the results provide a basis for the development of drugs exploiting this mechanism of action.

The success of highly active antiretroviral therapy (HAART) for HIV-1 infection has sparked interest in mechanisms by which the virus can persist despite effectively suppressive therapy. Latent HIV-1 reservoirs established early during infection not only prevent sterilizing immunity but also represent a major obstacle to virus eradication. When HIV-1 gains a foothold in the immunologic memory or in certain inaccessible compartments of the human body, it cannot be easily purged by HAART and is able to replenish systemic infection on treatment interruption. Because latently infected cells are indistinguishable from uninfected cells, deliberate activation of latent infection combined with intensified HAART seems to be the best strategy to combat latent infection. Initial hypothesis-driven clinical trials did not achieve their ultimate goal, although they provided valuable insight for the design of future eradication protocols. A more detailed understanding of the basic mechanisms underlying the establishment and long-term maintenance of HIV-1 reservoirs will be critical in developing new eradication approaches.