Inhibitors of viral entry.

The entry of viruses into target cells involves a complex series of sequential steps, with opportunities for inhibition at every stage. Entry inhibitors exert their biological properties by inhibiting protein-protein interactions either within the viral envelope (Env) glycoproteins or between viral Env and host-cell receptors. The nature of resistance to entry inhibitors also differs from compounds inhibiting enzymatic targets due to their different modes of action and the relative variability in Env sequences both temporally and between patients. Two drugs that target HIV-1 entry, enfuvirtide and maraviroc, are now licensed for treatment of HIV-1 infection. The efficacy of these drugs validates entry as a point of intervention in viral life cycles and, in the context of HIV treatment, contributes to the growing armamentarium of antivirals which, in multidrug combinations, can effectively inhibit viral replication and prevent disease progression.

HIV-1 coreceptor use in triple-class treatment-experienced patients: baseline prevalence, correlates, and relationship to enfuvirtide response.

OBJECTIVE: We wished to assess, in heavily treatment-experienced patients, the prevalence of and baseline characteristics associated with HIV-1 coreceptor use and their relationship to responses to enfuvirtide treatment. METHODS: Samples were obtained from participants in phase 3 studies of enfuvirtide. Multiple logistic regression and analysis of covariance were performed on data for baseline coreceptor use, virological and immunological response, and changes in coreceptor use during treatment. RESULTS: Baseline envelopes were phenotyped for 724 patients; 50% harbored R5 strains, 48% harbored dual/mixed (D/M) strains, and 2% harbored X4 strains. D/M strains were associated with significantly lower CD4(+) cell counts but comparable viral loads, compared with R5 strains (P=.0005). Virological and immunological responses to enfuvirtide-based treatment showed no correlation with baseline coreceptor use. Changes in virus tropism from D/M to R5 strains during treatment were common, particularly in patients who received enfuvirtide (27%, vs. 14% who received no enfuvirtide; P<.05). CONCLUSION: At baseline, D/M strains were associated with lower CD4(+) cell counts but similar viral loads, compared with R5 strains, and were common across CD4(+) cell count strata. The comparable virological and immunological responses and bias toward shifts from D/M to R5 strains in patients who received enfuvirtide support its use in triple-class treatment-experienced patients and its study as a therapeutic partner for coreceptor-binding inhibitors.

T-1249 retains potent antiretroviral activity in patients who had experienced virological failure while on an enfuvirtide-containing treatment regimen.

BACKGROUND: T-1249 is a 39-amino acid synthetic peptide fusion inhibitor (FI) shown to preserve antiretroviral activity in vitro against human immunodeficiency virus (HIV) isolates that have decreased susceptibility to enfuvirtide (ENF). METHODS: A 10-day phase 1/2 study of the safety and antiretroviral activity of T-1249 was conducted in 53 HIV-1-infected adults with detectable viremia while on an ENF-containing treatment regimen. RESULTS: From FI-naive baseline levels, the geometric mean (GM) decrease in susceptibility to ENF was 116.3-fold, and the GM decrease in susceptibility to T-1249 was 2.0-fold. Patients continued to administer their failing treatment regimen but replaced ENF with T-1249 at a dose of 192 mg/day. T-1249 was generally well tolerated; injection site reactions, which were generally mild, were the most commonly reported adverse event (64% of patients). The median change from levels of HIV-1 RNA at baseline to levels on day 11 was -1.26 log(10) copies/mL (95% confidence interval, -1.40 to -1.09 log(10) copies/mL); on day 11, a decrease from baseline HIV-1 RNA levels of >/=1.0 log(10) copies/mL was seen in 73% of patients. Antiretroviral activity, as measured by levels of HIV-1 RNA, was not predicted by baseline susceptibility to T-1249 or to ENF; genotypic substitutions that emerged during T-1249 treatment were identified in virus from some patients. CONCLUSIONS: These results indicate that FIs constitute an expanding class of antiretroviral agents with the potential to be sequenced.

Characterization of determinants of genotypic and phenotypic resistance to enfuvirtide in baseline and on-treatment HIV-1 isolates.

BACKGROUND: Enfuvirtide (ENF) is the first of a novel class of drugs that block HIV gp41-mediated viral fusion to host cells. Viruses with mutations at positions 36-38 in HIV-1 gp41 and/or reduced susceptibility to ENF have been selected both in vitro and in vivo. METHODS: An analysis of baseline and on-treatment ENF susceptibility in virus samples from Phase II clinical trial patients treated with ENF as functional monotherapy for 28 days (TRI-003) or in combination with oral antiretrovirals for >/= 48 weeks (T20-205, T20-206 and T20-208). Population sequencing identified amino acid (aa) substitutions at positions 36-45 of gp41 in plasma HIV-1. ENF susceptibility of virus isolates was tested in the cMAGI assay and viral DNA was sequenced for selected isolates. RESULTS: HIV-1 gp41 aa 36-45 were highly conserved in virus from ENF-naive patients, except for a 15% incidence of N42S which did not reduce sensitivity to ENF. Virus from patients experiencing viral load rebound exhibited reduced susceptibility to ENF and substitutions in gp41 aa 36-45. The most common substitutions observed on treatment were at positions 36, 38, 40, 42 and 43. On-treatment changes in the phenotypic susceptibility of virus isolates to ENF were generally associated with genotypic changes in aa 36-45. There was a relatively lower incidence of ENF resistance in patients with baseline sensitivity to more oral antiretrovirals in comparison to patients sensitive to fewer antiretrovirals. CONCLUSIONS: These data identify the importance of HIV-1 gp41 aa 36-45 in the emergence of resistance to ENF.