2′-Deoxy-4′-C-ethynyl-2-halo-adenosines active against drug-resistant human immunodeficiency virus type 1 variants

One of the formidable challenges in therapy of infections by human immunodeficiency virus (HIV) is the emergence of drug-resistant variants that attenuate the efficacy of highly active antiretroviral therapy (HAART). We have recently introduced 4′-ethynyl-nucleoside analogs as nucleoside reverse transcriptase inhibitors (NRTIs) that could be developed as therapeutics for treatment of HIV infections. In this study, we present 2′-deoxy-4′-C-ethynyl-2-fluoroadenosine (EFdA), a second generation 4′-ethynyl inhibitor that exerted highly potent activity against wild-type HIV-1 (EC₅₀ ∼ 0.07 nM). EFdA retains potency toward many HIV-1 resistant strains, including the multi-drug resistant clone HIV-1_{A62V/V75I/F77L/F116Y/Q151M}. The selectivity index of EFdA (cytotoxicity/inhibitory activity) is more favorable than all approved NRTIs used in HIV therapy. Furthermore, EFdA efficiently inhibited clinical isolates from patients heavily treated with multiple anti-HIV-1 drugs. EFdA appears to be primarily phosphorylated by the cellular 2′-deoxycytidine kinase (dCK) because: (a) the antiviral activity of EFdA was reduced by the addition of dC, which competes nucleosides phosphorylated by the dCK pathway, (b) the antiviral activity of EFdA was significantly reduced in dCK-deficient HT-1080/Ara-C^r cells, but restored after dCK transduction. Further, unlike other dA analogs, EFdA is completely resistant to degradation by adenosine deaminase. Moderate decrease in susceptibility to EFdA is conferred by a combination of three RT mutations (I142V, T165R, and M184V) that result in a significant decrease of viral fitness. Molecular modeling analysis suggests that the M184V/I substitutions may reduce anti-HIV activity of EFdA through steric hindrance between its 4′-ethynyl moiety and the V/I184 β-branched side chains. The present data suggest that EFdA, is a promising candidate for developing as a therapeutic agent for the treatment of individuals harboring multi-drug resistant HIV variants.