Activity against human immunodeficiency virus type 1, intracellular metabolism, and effects on human DNA Polymerases of 4′-ethynyl-2-fluoro-2′-deoxyadenosine

We examined the intracytoplasmic anabolism and kinetics of antiviral activity against human immunodeficiency virus type 1 (HIV-1) of a nucleoside reverse transcriptase inhibitor, 4'-ethynyl-2-fiuoro-2'-deoxyadenosine (EFdA), which has potent activity against wild-type and multidrug-resistant HIV-1 strains. When CEM cells were exposed to 0.1 mu M [H-3]EFdA or [H-3]3'-azido-2',3'-dideoxythymidine (AZT) for 6 h, the intracellular EFdA-triphosphate (TP) level was 91.6 pmol/10(9) cells, while that of AZT was 396.5 pmol/10(9) cells. When CEM cells were exposed to 10 mu M [(3)HEFdA, the amount of EFdA-TP increased by 22-fold (2,090 pmol/10(9) cells), while the amount of [H-3]AZT-TP increased only moderately by 2.4-fold (970 pmol/10(9) cells). The intracellular half-life values of EFdA-TP and AZT-TP were similar to 17 and similar to 3 h, respectively. When MT-4 cells were cultured with 0.01 mu M EFdA for 24 h, thoroughly washed to remove EFdA, further cultured without EFdA for various periods of time, exposed to HIV-1(NL4-3),and cultured for an additional 5 days, the protection values were 75 and 47%, respectively, after 24 and 48 h with no drug incubation, while those with 1 mu M AZT were 55 and 9.2%, respectively. The 50% inhibitory concentration values of EFdA-TP against human polymerases alpha, beta, and gamma were >100 mu M, >100 mu M, and 10 mu M, respectively, while those of ddA-TP were >100 mu M, 0.2 mu M, and 0.2 mu M, respectively. These data warrant further development of EFdA as a potential therapeutic agent for those patients who harbor wild-type HIV-1 and/or multidrug-resistant variants.