Abstract 1113 Mechanistic studies of incorporation of activated Islatravir by HIV-1 reverse transcriptase mutants

Islatravir, or 4′-ethynyl-2-fluoro-2′-deoxyadenosine (EFdA), is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that can potently inhibit human immune deficiency virus-1 as demonstrated by the results from multiple late-stage clinical trials by Merck, Inc. Once transported into human cells, EFdA is converted into its active form, EFdA 5'-triphophate (EFdA-TP), by cellular kinases. EFdA-TP can act as an immediate chain terminator, by interacting with the hydrophobic pocket of HIV-1 reverse transcriptase (HIV-1 RT) through the 4′-ethynyl group of EFdA, and also as a delayed chain terminator, allowing only for incorporation of a few more nucleotides after EFdA-TP incorporation. NRTI and NNRTI treatments often select for a variety of HIV-1 RT mutants that can drastically decrease the treatment effectiveness. Here, using pre-steady state kinetics, we investigated the impact of two treatment associated HIV-1 RT mutations, M184V and F227C in the aforementioned EFdA-TP interacting hydrophobic pocket. M184V is associated with NRTI drugs lamivudine and emtricitabine while F227C is connected with doravirine, a NNRTI drug used in combination therapy with NRTIs. We found that with M184V, the incorporation efficiency of EFdA-TP is about 50% of that of dATP. In contrast, F227C incorporates EFdA-TP about 50% more efficient than dATP. Together, our kinetic results indicate that these HIV-1 RT mutations that have been found detrimental to other anti-HIV treatments, have only a moderate impact on the effectiveness of EFdA-TP. This project is financially supported by a research grant from Merck Investigator Studies Program of Merck, Inc.