Targeting HIV attachment and entry for therapy

Peptide inhibitors against influenza virus

Influenza A virus is a particularly problematic virus because of its ability to cause high levels of morbidity on a global scale within a remarkably short period of time. It also has the potential to kill very large numbers of people as occurred in the Spanish influenza pandemic in 1918. Options for antiviral therapy are limited because of the paucity of available drugs and the rapid mutation rate of the virus leading to the emergence of drug-resistant strains. The current H1N1 pandemic and potential threats posed by other strains highlight the need to develop novel therapeutic and prophylactic strategies. Here, we summarize the current state and recent developments of peptide-based inhibitors of influenza A virus.

Quantifying the relationship between HIV-1 susceptibility to CCR5 antagonists and virus affinity for antagonist-occupied co-receptor

Previous studies have demonstrated that HIV-1 develops resistance to CCR5 antagonists by gaining the ability to use drug-occupied co-receptor. However, the effects of CCR5 antagonists on the affinity of virus-co-receptor interactions have been difficult to quantify. We developed a pharmacological model for allosteric interaction at G-protein coupled receptors to analyze the effect of different CCR5 antagonists on infection by three laboratory adapted viruses with low, moderate and high susceptibility to the inhibitors. Infection data for these viruses fitted a model in which susceptibility to inhibition by CCR5 antagonists was directly related to fold reduction in virus affinity for CCR5. Dissociation constants for CCR5 antagonists calculated from the modeled data were consistent with values obtained by standard methods, suggesting that this approach can quantify pharmacologically relevant changes in co-receptor:ligand affinity in the context of infection of whole cells by authentic HIV-1 particles.

Expression of a modified form of CD4 results in the release of an anti-HIV factor derived from the Env sequence

We have studied the inhibitory effect of a CD4 chimera (CD4epsilon15) on HIV replication. This chimera is retained in the endoplasmic reticulum and traps the HIV envelope precursor gp160, preventing its maturation. Retroviral expression of the chimera strongly inhibited HIV replication even when it is expressed by only a minority of the T cell population. This protective effect on bystander nontransduced cells is mediated by a soluble factor that we identified as a fragment of HIV gp120 envelope protein and accordingly, we named this factor Env-derived antiviral factor (EDAF). Biochemical and immunoreactivity data show that EDAF is comprised of the gp120 C3-C5 regions and indeed, a recombinant protein bearing this sequence reproduces the anti-HIV properties of EDAF. Surprisingly, three tryptic peptides derived from EDAF are homologous but not identical with the corresponding sequences of the HIV isolate used to generate EDAF. We propose that EDAF results from an alternative intracellular processing of the Env protein provoked by its association to CD4epsilon15 and the selection of the best fitted Env protein sequences contained within the HIV isolate. The presence of EDAF improves the therapeutic potential of the CD4epsilon15 gene and it opens new possibilities for antiviral treatment and vaccine development.

Inhibitors of HIV-1 attachment. Part 3: A preliminary survey of the effect of structural variation of the benzamide moiety on antiviral activity

1-(4-Benzoylpiperazin-1-yl)-2-(1H-indol-3-yl)ethane-1,2-dione (1a) has been characterized as an inhibitor of HIV-1 attachment that interferes with the interaction of viral gp120 with the host cell receptor CD4. In previous studies, the effect of indole substitution pattern on antiviral activity was probed. In this Letter, the effect of structural variation of the benzamide moiety is described, a study that reveals the potential or the phenyl moiety to be replaced by five-membered heterocyclic rings and a restricted tolerance for the introduction of substituents to the phenyl ring.

Reduction of CCR5 with low-dose rapamycin enhances the antiviral activity of vicriviroc against both sensitive and drug-resistant HIV-1

Vicriviroc (VCV) is a chemokine (C-C motif) receptor 5 (CCR5) antagonist with potent anti-HIV activity that currently is being evaluated in phase III clinical trials. In the present study, donor CCR5 density (CCR5 receptors/CD4 lymphocytes) inversely correlated with VCV antiviral activity (Spearman's correlation test; r = 0.746, P = 0.0034). Low doses of the transplant drug rapamycin (RAPA) reduced CCR5 density and enhanced VCV antiviral activity. In drug interaction studies, the RAPA/VCV combination had considerable antiviral synergy (combination indexes of 0.1-0.04) in both multicycle and single-cycle infection of lymphocytes. The synergy between RAPA and VCV translated into dose reduction indexes of 8- to 41-fold reductions for RAPA and 19- to 658-fold reductions for VCV. RAPA enhanced VCV antiviral activity against both B and non-B clade isolates, potently suppressing clade G viruses with reported reduced sensitivities to VCV and to the licensed CCR5 antagonist maraviroc. Importantly, RAPA reduction of CCR5 density in lymphocytes sensitized VCV-resistant strains to VCV, inhibiting virus production by approximately 90%. We further demonstrated the role of CCR5 density on VCV activity against resistant virus in donor lymphocytes and in cell lines expressing varying CCR5 densities. Together, these results suggest that low doses of RAPA may increase the durability of VCV-containing regimens in patients by enhancing VCV viral suppression, by allowing the use of lower doses of VCV with reduced potential for toxicity, and by controlling emerging VCV-resistant variants.