The High Genetic Barrier of EFdA/MK-8591 Stems from Strong Interactions with the Active Site of Drug-Resistant HIV-1 Reverse Transcriptase

Summary 4ʹ-Ethynyl-2-fluoro-2ʹ-deoxyadenosine (EFdA/MK-8591), a nucleoside reverse transcriptase inhibitor (NRTI) under clinical trials, is a potent and promising long-acting anti-HIV type 1 (HIV-1) agent. EFdA and its derivatives possess a modified 4ʹ-moiety and potently inhibit the replication of a wide spectrum of HIV-1 strains resistant to existing NRTIs. Here, we report that EFdA and NRTIs with a 4ʹ-ethynyl- or 4ʹ-cyano-moiety exerted activity against HIV-1 with an M184V mutation and multiple NRTI-resistant HIV-1s, whereas NRTIs with other moieties (e.g., 4ʹ-methyl) did not show this activity. Structural analysis indicated that EFdA and 4ʹ-ethynyl-NRTIs (but not other 4ʹ-modified NRTIs), formed strong van der Waals interactions with critical amino acid residues of reverse transcriptase. Such interactions were maintained even in the presence of a broad resistance-endowing M184V substitution, thus potently inhibiting drug-resistant HIV-1 strains. These findings also explain the mechanism for the potency of EFdA and provide insights for further design of anti-HIV-1 therapeutics.