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-fluoro-2′- deoxyadenosine (EFdA), which has potent activity against wild-type and multidrug-resistant HIV-1 strains. When CEM cells were exposed to 0.1 μM [³H]EFdA or [³H]3′-azido-2′,3′- dideoxythymidine (AZT) for 6 h, the intracellular EFdA-triphosphate (TP) level was 91.6 pmol/10⁹ cells, while that of AZT was 396.5 pmol/10 ⁹ cells. When CEM cells were exposed to 10 μM [³H]EFdA, the amount of EFdA-TP increased by 22-fold (2,090 pmol/10⁹ cells), while the amount of [³H]AZT-TP increased only moderately by 2.4-fold (970 pmol/10⁹ cells). The intracellular half-life values of EFdA-TP and AZT-TP were ∼17 and ∼3 h, respectively. When MT-4 cells were cultured with 0.01 μM 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 μM AZT were 55 and 9.2%, respectively. The 50% inhibitory concentration values of EFdA-TP against human polymerases α, β, and γ were >100 μM, >100 μM, and 10 μM, respectively, while those of ddA-TP were >100 μM, 0.2 μM, and 0.2 μM, 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.