. By FACS analysis we demonstrate that rapamycin (RAPA), a drug that disrupts IL-2 receptor signaling, reduces CCR5 surface expression on T cells at concentrations as low as 1 nM. In addition, lower concentrations of RAPA (0.01 nM) were sufficient to reduce CCR5 surface expression on maturing monocytes. PCR analysis on peripheral blood mononuclear cells (PBMCs) showed that RAPA interfered with CCR5 expression at the transcriptional level. Reduced expression of CCR5 on PBMCs cultured in the presence of RAPA was associated with increased extracellular levels of macrophage inflammatory protein (MIP)-1␣ and MIP-1␤. In infectivity assays, RAPA suppressed the replication of R5 strains of HIV-1 both in PBMC and macrophage cultures. In total PBMC cultures, RAPA-mediated inhibition of CCR5-using strains of HIV-1 occurred at 0.01 nM, a concentration of drug that is Ϸ10 3 times lower than therapeutic through levels of drug in renal transplant recipients. In addition, RAPA enhanced the antiviral activity of the CCR5 antagonist TAK-779. These results suggest that low concentrations of RAPA may have a role in both the treatment and prevention of HIV-1 infection.

HIV necessitates host factors for successful completion of its life cycle. Mammalian target of rapamycin (mTOR) is a conserved serine/threonine kinase that forms two complexes, mTORC1 and mTORC2. Rapamycin is an allosteric inhibitor of mTOR that selectively inhibits mTORC1. Rapamycin interferes with viral entry of CCR5 (R5)-tropic HIV and with basal transcription of the HIV LTR, potently inhibiting replication of R5 HIV but not CXCR4 (X4)-tropic HIV in primary cells. The recently developed ATP-competitive mTOR kinase inhibitors (TOR-KIs) inhibit both mTORC1 and mTORC2. Using INK128 as a prototype TOR-KI, we demonstrate potent inhibition of both R5 and X4 HIV in primary lymphocytes (EC50 < 50 nM), in the absence of toxicity. INK128 inhibited R5 HIV entry by reducing CCR5 levels. INK128 also inhibited both basal and induced transcription of HIV genes, consistent with inhibition of mTORC2, whose activity is critical for phosphorylation of PKC isoforms and, in turn, induction of NF-κB. INK128 enhanced the antiviral potency of the CCR5 antagonist maraviroc, and had favorable antiviral interactions with HIV inhibitors of reverse transcriptase, integrase and protease. In humanized mice, INK128 decreased plasma HIV RNA by >2 log10 units and partially restored CD4/CD8 cell ratios. Targeting of cellular mTOR with INK128 (and perhaps others TOR-KIs) provides a potential strategy to inhibit HIV, especially in patients with drug resistant HIV strains.

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 ϳ 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.chemokine receptor 5 antagonists ͉ coreceptor density ͉ HIV resistance ͉ vicriviroc resistance ͉ maraviroc H ighly active antiretroviral therapy (HAART) has improved treatment of HIV-1 infected individuals considerably (1). However, the success of current therapies is limited by the emergence of drug-resistant strains, the need for sustained adherence to complex regimens, and the potential for drug toxicity (2, 3). The two new antiretroviral classes of integrase and entry inhibitors may help overcome some of the current limitations of HAART (4, 5). Entry inhibitors are especially attractive because they target HIV at the earliest step of the viral cycle and are effective against strains resistant to inhibitors of protease and reverse transcriptase. Entry inhibitors interfere with HIV binding to CD4 receptor (attachment inhibitors) or chemokine (C-C motif) receptor 5 (CCR5)/chemokine (C-X-C-motif) receptor 4 (CXCR4) coreceptors (coreceptor antagonists) or by preventing fusion between cellular and viral membranes (fusion inhibitors) (5). Currently, the fusion inhibitor T-20 (enfuvirtide) and the CCR5 antagonist maraviroc (Selzentry) are the only licensed entry inhibitors (6, 7). The CCR5 antagonist vicriviroc (VCV) presently is in phase III clinical trials (8). Coreceptor CCR5 antagonists inhibit CCR5-tropic HIV-1 (referred to as ''R5 HIV-1'') strains, which are responsible for most transmissions and generally are present throughout the course of infection. In nor...

Non-toxic concentrations of IM inhibit HIV-1 by blocking viral gene expression mediated by the cellular factor P-TEFb. The drug is effective against wild-type and drug-resistant strains of HIV-1. IM may help control replication of HIV-1 in patients by disrupting a step of the HIV-1 cycle that is not being targeted in current antiretroviral treatments.

Despite some limitations, an 8-week off and on intermittent treatment regimen appeared clinically safe over 96 weeks while sparing half of the drug exposure.

These results suggest that CCR5 density levels in HIV-1 patients may impact the activity of T-20 against R5 strains and that therapeutic approaches to alter CCR5 density may potentiate T-20.

The CCR5 chemokine receptor plays a pivotal role in human immunodeficiency virus type 1 (HIV-1) infection. Several studies have suggested that CCR5 density levels in individuals are rate limiting for infection. In addition, CCR5 density levels influence the antiviral activity of the HIV-1 fusion inhibitor enfuvirtide (T-20) against R5 strains. In the present study we demonstrate that rapamycin (RAPA), a drug approved for the treatment of renal transplantation rejection, reduces CCR5 density levels on CD4 T cells and inhibits R5 HIV-1 replication. In addition, RAPA increased the antiviral activity of T-20 against R5 strains of the virus in a cell-cell fusion assay and as shown by quantification of early products of viral reverse transcription. Medianeffect analysis of drug interaction between RAPA and T-20 in infectivity assays using donor peripheral blood mononuclear cells demonstrated that the RAPA-T-20 combination is synergistic against R5 strains of HIV-1 and this synergy translates into T-20 dose reductions of up to ϳ33-fold. Importantly, RAPA effects on replication levels and T-20 susceptibility of R5 strains of HIV-1 were observed at drug concentrations that did not inhibit cell proliferation. These results suggest that low concentrations of RAPA may potentiate the antiviral activity of T-20 against R5 strains of HIV-1, which are generally present throughout the course of infection and are less sensitive to T-20 inhibition than are X4 strains.The fusion inhibitors mark the beginning of a new era in the management of human immunodeficiency virus type 1 (HIV-1) disease. With a unique mechanism of action they represent a new fourth class of antiretrovirals. Enfuvirtide (T-20) has been shown to exert potent antiretroviral activity and is approved for treatment in combination with other antiretrovirals in treatment-experienced patients with evidence of virus replication despite ongoing antiretroviral therapy (22, 23).HIV-1 entry is mediated by the HIV envelope glycoproteins gp120 and gp41. Upon binding of gp120 to CD4 and a cellular coreceptor (usually CCR5 or CXCR4), conformational changes occur in both the gp120 and gp41 subunits. Within gp41, the fusion peptide region becomes exposed and inserts into the cell membrane. Additional conformational changes result in the formation of a trimeric antiparallel coiled-coil structure between the HR-1 and HR-2 regions of gp41. The formation of the six-helix bundle is believed to bring the viral and cell membranes together and lead to viral entry (14, 42).T-20 acts by binding to the HR-1 region of gp41, thereby preventing the interaction between the HR-1 and HR-2 domains of gp41 that is required for virus/host membrane fusion (3,19). It is thought that T-20 can target the viral envelope only during a kinetic window that opens by CD4 and/or coreceptor binding and closes with the coalescence of HR-1 and HR-2 domains of gp41 forming a final six-helix bundle structure (1,7,14,20,27,32). Although T-20 blocks fusion of both R5 and X4 strains of HIV-1, X4 strains are overall m...

This paper describes selected modification and structure-activity relationship of the small molecule HIV-1 inhibitor, 4-benzoyl-1-[(4-methoxy-1H-pyrrolo[2,3-b]pyridin-3-yl)oxoacetyl]-2-(R)-methylpiperazine (BMS-378806). The results revealed: i) that both the presence and configuration (R vs. S) of the 3-methyl group on the piperazine moiety are important for the antiviral activity, with the 3-(R)-methyl derivatives showing the highest activity; ii) that the electronegativity of the C-4 substituent on the indole or azaindole ring seems to be important for the activity, with a small, electron-donating group such as a fluoro or a methoxy group showing enhanced activity, while a nitro group diminishes the activity; iii) that the N-1 position of the indole ring is not eligible for modification without losing activity; and iv) that bulky groups around the C-4 position of the indole or azaindole ring diminish the activity, probably due to steric hindrance in the binding. We found that a synthetic bivalent compound with two BMS-378806 moieties being tethered by a spacer demonstrated about 5-fold enhanced activity in an nM range against HIV-1 infection than the corresponding monomeric inhibitor. But the polyacrylamide-based polyvalent compounds did not show inhibitory activity at up to 200 nM.