Insights into the mechanism of inhibition of CXCR4: identification of Piperidinylethanamine analogs as anti-HIV-1 inhibitors.

The cellular entry of HIV-1 into CD4(+) T cells requires ordered interactions of HIV-1 envelope glycoprotein with C-X-C chemokine receptor type 4 (CXCR4) receptors. However, such interactions, which should be critical for rational structure-based discovery of new CXCR4 inhibitors, remain poorly understood. Here we first determined the effects of amino acid substitutions in CXCR4 on HIV-1NL 4 - 3 glycoprotein-elicited fusion events using site-directed mutagenesis-based fusion assays and identified 11 potentially key amino acid substitutions, including D97A and E288A, which caused >30% reductions in fusion. We subsequently carried out a computational search of a screening library containing ∼604,000 compounds, in order to identify potential CXCR4 inhibitors. The computational search used the shape of IT1t, a known CXCR4 inhibitor, as a reference and employed various algorithms, including shape similarity, isomer generation, and docking against a CXCR4 crystal structure. Sixteen small molecules were identified for biological assays based on their high shape similarity to IT1t, and their putative binding modes formed hydrogen bond interactions with the amino acids identified above. Three compounds with piperidinylethanamine cores showed activity and were resynthesized. One molecule, designated CX6, was shown to significantly inhibit fusion elicited by X4 HIV-1NL 4 - 3 glycoprotein (50% inhibitory concentration [IC50], 1.9 µM), to inhibit Ca(2+) flux elicited by stromal cell-derived factor 1α (SDF-1α) (IC50, 92 nM), and to exert anti-HIV-1 activity (IC50, 1.5 µM). Structural modeling demonstrated that CX6 bound to CXCR4 through hydrogen bond interactions with Asp97 and Glu288. Our study suggests that targeting CXCR4 residues important for fusion elicited by HIV-1 envelope glycoprotein should be a useful and feasible approach to identifying novel CXCR4 inhibitors, and it provides important insights into the mechanism by which small-molecule CXCR4 inhibitors exert their anti-HIV-1 activities.

A conserved hydrogen-bonding network of P2 bis-tetrahydrofuran-containing HIV-1 protease inhibitors (PIs) with a protease active-site amino acid backbone aids in their activity against PI-resistant HIV.

In the present study, GRL008, a novel nonpeptidic human immunodeficiency virus type 1 (HIV-1) protease inhibitor (PI), and darunavir (DRV), both of which contain a P2-bis-tetrahydrofuranyl urethane (bis-THF) moiety, were found to exert potent antiviral activity (50% effective concentrations [EC50s], 0.029 and 0.002 µM, respectively) against a multidrug-resistant clinical isolate of HIV-1 (HIVA02) compared to ritonavir (RTV; EC50, >1.0 µM) and tipranavir (TPV; EC50, 0.364 µM). Additionally, GRL008 showed potent antiviral activity against an HIV-1 variant selected in the presence of DRV over 20 passages (HIVDRV(R)P20), with a 2.6-fold increase in its EC50 (0.097 µM) compared to its corresponding EC50 (0.038 µM) against wild-type HIV-1NL4-3 (HIVWT). Based on X-ray crystallographic analysis, both GRL008 and DRV showed strong hydrogen bonds (H-bonds) with the backbone-amide nitrogen/carbonyl oxygen atoms of conserved active-site amino acids G27, D29, D30, and D30' of HIVA02 protease (PRA02) and wild-type PR in their corresponding crystal structures, while TPV lacked H-bonds with G27 and D30' due to an absence of polar groups. The P2' thiazolyl moiety of RTV showed two conformations in the crystal structure of the PRA02-RTV complex, one of which showed loss of contacts in the S2' binding pocket of PRA02, supporting RTV's compromised antiviral activity (EC50, >1 µM). Thus, the conserved H-bonding network of P2-bis-THF-containing GRL008 with the backbone of G27, D29, D30, and D30' most likely contributes to its persistently greater antiviral activity against HIVWT, HIVA02, and HIVDRV(R)P20.

Delayed emergence of HIV-1 variants resistant to 4'-ethynyl-2-fluoro-2'-deoxyadenosine: comparative sequential passage study with lamivudine, tenofovir, emtricitabine and BMS-986001.

BACKGROUND: 4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) contains an ethynyl moiety and the 3'-hydroxyl and exerts highly potent activity against various HIV type-1 (HIV-1) strains including multi-drug-resistant variants. METHODS: Comparative selection passages against EFdA, lamivudine (3TC), tenofovir disoproxil fumarate (TDF), emtricitabine (FTC) or BMS-986001 (Ed4T) were conducted using a mixture of 11 highly multi-drug-resistant clinical HIV-1 isolates (HIV11MIX) as a starting virus population. RESULTS: Before selection, HIV11MIX was sensitive to EFdA with a 50% inhibitory concentration (IC50) of 0.032 µM, less susceptible to TDF and Ed4T with IC50s of 0.57 and 2.6 µM, respectively, and highly resistant to 3TC and FTC with IC50s>10 µM. IC50s of TDF against HIV11MIX exposed to EFdA and TDF for 17 (HIV11MIX(EFdA-P17)) and 14 (HIV11MIX(TDF-P14)) passages were 8 and >10 µM, respectively, while EFdA remained active against HIV11MIX(EFdA-P17) and HIV11MIX(TDF-P14) with IC50s of 0.15 and 0.1 µM, respectively. Both selected variants were highly resistant against zidovudine, 3TC, Ed4T and FTC (IC50 values >10 µM). CONCLUSIONS: The present data demonstrate that HIV11MIX developed resistance more rapidly against 3TC, FTC, TDF and Ed4T than against EFdA and that EFdA remained substantially active against TDF- and EFdA-selected variants. Thus, EFdA has a favourable resistance profile and represents a potentially promising new-generation nucleoside reverse transcriptase inhibitor.