Identification of a novel small-molecule inhibitor of the HIV-1 reverse transcriptase activity with a non-nucleoside mode of action.

Background: Human immunodeficiency virus-1 (HIV-1) is the causative agent of acquired immunodeficiency syndrome, which is a major global health problem. Although combination antiretroviral therapy (cART) successfully expands the lifespan of HIV-1-infected patients, long-term cART often increases drug resistance and adverse effects. Therefore, efforts are ongoing to develop novel anti-HIV-1 drugs.

Methods: The anti-HIV-1 activities of compounds were investigated using TZM-bl reporter cell line, A3.01 T cell line, and peripheral blood mononuclear cells infected with several HIV-1 strains, including wild type and drug-resistance associated mutants. Next-generation sequencing analysis and in silico molecular docking studies were employed to determine the mode of action of the compound.

Results: We identified a small-molecule inhibitor consisting of a thiadiazole core appended to two pyrazoles (BPPT), which exerted a highly potent inhibitory effect on HIV-1 infectivity, with a half-maximal effective concentration (EC₅₀) of 60 nM, without causing cytotoxicity. In experiments with various HIV-1 strains and cell types, the potency of BPPT was found to be comparable to that of commercial antiretroviral agents (azidothymidine, nevirapine, and others). Further analysis of the mode of action demonstrated that BPPT is a novel type of HIV-1 non-nucleoside reverse transcriptase inhibitor (NNRTI). Analysis of viruses harboring drug-resistance-associated mutations showed that BPPT was potent against G190A (C or S) mutations in reverse transcriptase (RTase), exhibiting high-level resistance to other NNRTIs. Next-generation sequencing analysis of long-term treatment with BPPT displayed an RTase mutation profile different from that in the case of established NNRTIs. Given these data, in silico molecular docking studies demonstrated the molecular mechanism underlying the BPPT-mediated inhibition of RTase.

Conclusion: Our data suggest that BPPT is a novel small-molecule inhibitor of HIV-1 RTase and could serve as a promising chemical scaffold to complement or replace conventional treatments, particularly for overcoming resistance associated with the G190 mutation.