Human immunodeficiency virus type 1 (HIV-1) continues to spread, principally by heterosexual sex, but no vaccine is available. Hence, alternative prevention methods are needed to supplement educational and behavioural-modification programmes. One such approach is a vaginal microbicide: the application of inhibitory compounds before intercourse. Here, we have evaluated the microbicide concept using the rhesus macaque 'high dose' vaginal transmission model with a CCR5-receptor-using simian-human immunodeficiency virus (SHIV-162P3) and three compounds that inhibit different stages of the virus-cell attachment and entry process. These compounds are BMS-378806, a small molecule that binds the viral gp120 glycoprotein and prevents its attachment to the CD4 and CCR5 receptors, CMPD167, a small molecule that binds to CCR5 to inhibit gp120 association, and C52L, a bacterially expressed peptide inhibitor of gp41-mediated fusion. In vitro, all three compounds inhibit infection of T cells and cervical tissue explants, and C52L acts synergistically with CMPD167 or BMS-378806 to inhibit infection of cell lines. In vivo, significant protection was achieved using each compound alone and in combinations. CMPD167 and BMS-378806 were protective even when applied 6 h before challenge.

Impacts of mutations at position E138 (A/G/K/Q/R/V) alone or in combination with M184I in HIV-1 reverse transcriptase (RT) were investigated. We also determined why E138K is the most prevalent nonnucleoside reverse transcriptase inhibitor mutation in patients failing rilpivirine (RPV) therapy. Recombinant RT enzymes and viruses containing each of the above-mentioned mutations were generated, and drug susceptibility was assayed. Each of the E138A/G/K/Q/R mutations, alone or in combination with M184I, resulted in decreased susceptibility to RPV and etravirine (ETR). The maximum decrease in susceptibility to RPV was observed for E138/R/Q/G by both recombinant RT assay and cell-based assays. E138Q/R-containing enzymes and viruses also showed the most marked decrease in susceptibility to ETR by both assays. The addition of M184I to the E138 mutations did not significantly change the levels of diminution in drug susceptibility. These findings indicate that E138R caused the highest level of loss of susceptibility to both RPV and ETR, and, accordingly, E138R should be recognized as an ETR resistance-associated mutation. The E138K/Q/R mutations can compensate for M184I in regard to both enzymatic fitness and viral replication capacity. The favored emergence of E138K over other mutations at position E138, together with M184I, is not due to an advantage in either the level of drug resistance or viral replication capacity but may reflect the fact that E138R and E138Q require two distinct mutations to occur, one of which is a disfavorable G-to-C mutation, whereas E138K requires only a single favorable Gto-A hypermutation. Of course, other factors may also affect the concept of barrier to resistance.

Upon the initiation of highly active antiretroviral therapy (HAART) for the treatment of HIV infection, the level of viral RNA in the blood rapidly decays in at least two distinct phases (12, 28), according to the death rates of cells that were already infected before treatment began. First-phase decay occurs during the first 7 to 10 days of treatment and has a half-life of 0.9 to 1.6 days (6,28,29), reflecting the death rate of productively infected CD4 ϩ T cells. The slower second phase occurs over a period of weeks and exhibits a half-life of approximately 14 days (28), corresponding to the turnover rate of long-lived infected cells. Second-phase sources of virus are believed to include cells of the monocyte/macrophage lineage and may also include infected resting CD4 ϩ T cells carrying unintegrated DNA (preintegration latent cells), follicular dendritic cells harboring intact virions, infected CD4 ϩ T cells that are not cleared by the host immune response, and an as-yet-unidentified cell type (4,12,17,28,30). An extremely slow third phase of decay is detectable by more sensitive assays and has a half-life estimated to range from months to years (7, 11). The viremia in this phase is believed to result from the reactivation of latently infected CD4 ϩ T cells (11, 40) or low-level ongoing replication (8, 14, 32), or both (35).Recent clinical trials with the first clinically approved HIV-1 integrase (IN) inhibitor, raltegravir (RAL), have yielded promising results. The phase II Merck protocol 004 part II trial (22, 23) and the phase III STARTMRK trial (20) compared the activity of RAL to that of the nonnucleoside reverse transcriptase inhibitor (NNRTI) efavirenz (EFV), each as part of standard combination therapy in drug-naïve HIV-1-infected individuals. While both drugs showed equal efficacy for the long-term suppression of the viral load, the limit of detection was reached more rapidly with RAL. This has been attributed to levels of virus production from second-phase sources that were 70% lower with RAL-based treatment than with EFV-based treatment (26).Several hypotheses may explain these unique viral load decay dynamics. They include differences in the time until drug bioavailability, differences in drug potency, a role for cells latently infected preintegration, the greater penetration of certain drugs into sanctuary sites, the stage of viral replication targeted, and the IN inhibitor-induced accumulation of unintegrated viral DNA (15,23,26,33,34). On the basis of the mathematical modeling of viral load decay, it has been proposed that the clinical observations can be explained by the effect of RAL on cells latently infected preintegration (26). These models also suggest that differences in drug potency might play a minor role but are inconsistent with a role for sanctuary sites (26). The mathematical models of viral load decay prepared by others suggest that the stage of viral replication targeted by RAL versus that targeted by EFV can explain the clinical trial results but are inconsistent with roles for ...