Inhibition Mechanism of EFdA, a Highly Potent Inhibitor of HIV Reverse Transcriptase [abstract]
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The nucleoside 4'-ethynyl-2-fluoro-deoxyadenosine (EFdA) is one of the most potent antiretroviral nucleosides yet described, inhibiting replication of wild-type and multidrug-resistant HIV-1 strains in vitro (PBMC cells) with an EC50 as low as 50 pM. Our laboratory works in collaboration with academic, government and pharmaceutical industry laboratories, to characterize the mechanism of action of EFdA, and help develop it as a therapeutic for the treatment of HIV-infected patients, and as a topical microbicide to minimize sexual transmission of HIV. We have recently shown that the potency of antiviral activity stems in part from a mechanism of action not shown by any of the clinically used nucleoside antiretrovirals. Unlike other Reverse Transcriptase (RT) inhibitors, EFdA has a 3'-OH group which is necessary for nucleotide incorporation, yet it acts as a chain-terminator of retroviral DNA synthesis. Using biochemical techniques, we have determined that EFdA is incorporated very efficiently into the nascant viral DNA chain and blocks the incorporation of incoming nucleotides by stopping the translocation/movement of RT. Therefore, we have dubbed EFdA as a Translocation-Defective RT Inhibitor (TDRTI). A pilot collaborative study spearheaded by collaborators Parniak and Corb demonstrated that EFdA treatment of Rhesus Macaques resulted in a 2-3 log decrease in simian immunodeficiency virus (SIV) within seven days; these levels declined to undetectable levels (5-log reduction) within 2 months and essentially remained so for the duration of therapy. Hence, EFdA is a highly potent HIV RT inhibitor with in vitro and in vivo antiviral activities that warrant further development of the compound as a potential therapeutic for individuals harboring wild-type and/or multi-drug resistant HIV-1.