Antiviral Activities and Cellular Toxicities of Modified 2′,3′-Dideoxy-2′,3′-Didehydrocytidine Analogues

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Abstract
The antiviral efficacies and cytotoxicities of 2′,3′- and 4′-substituted 2′,3′-didehydro-2′,3′-dideoxycytidine analogs were evaluated. All compounds were tested (i) against a wild-type human immunodeficiency virus type 1 (HIV-1) isolate (strain xxBRU) and lamivudine-resistant HIV-1 isolates, (ii) for their abilities to inhibit hepatitis B virus (HBV) production in the inducible HepAD38 cell line, and (iii) for their abilities to inhibit bovine viral diarrhea virus (BVDV) production in acutely infected Madin-Darby bovine kidney cells. Some compounds demonstrated potent antiviral activities against the wild-type HIV-1 strain (range of 90% effective concentrations [EC 90 s], 0.14 to 5.2 μM), but marked increases in EC 90 s were noted when the compounds were tested against the lamivudine-resistant HIV-1 strain (range of EC 90 s, 53 to >100 μM). The β- l -enantiomers of both classes of compounds were more potent than the corresponding β- d -enantiomers. None of the compounds showed antiviral activity in the assay that determined their abilities to inhibit BVDV, while two compounds inhibited HBV production in HepAD38 cells (EC 90 , 0.25 μM). The compounds were essentially noncytotoxic in human peripheral blood mononuclear cells and HepG2 cells. No effect on mitochondrial DNA levels was observed after a 7-day incubation with the nucleoside analogs at 10 μM. These studies demonstrate that (i) modification of the sugar ring of cytosine nucleoside analogs with a 4′-thia instead of an oxygen results in compounds with the ability to potently inhibit wild-type HIV-1 but with reduced potency against lamivudine-resistant virus and (ii) the antiviral activity of β- d -2′,3′-didehydro-2′,3′-dideoxy-5-fluorocytidine against wild-type HIV-1 (EC 90 , 0.08 μM) and lamivudine-resistant HIV-1 (EC 90 = 0.15 μM) is markedly reduced by introduction of a 3′-fluorine in the sugar (EC 90 s of compound 2a, 37.5 and 494 μM, respectively).