Anti-hepatitis B virus activity and metabolism of 2′,3′-dideoxy-2′,3′-didehydro-β-L(-)-5-fluorocytidine

2',3'-Dideoxy-2',3'-didehydro-beta-L(-)-5-fluorocytidine [L(-)Fd4C] was found to be at least 10 times more potent than beta-L-2',3'-dideoxy-3'-thiacytidine [L(-)SddC; also called 3TC, or lamivudine]against hepatitis B virus (HBV) in culture. Its cytotoxicity against HepG2 growth in culture was also greater than that of L(-) SddC (3TC), There was no activity of this compound against mitochondrial DNA synthesis in cells at concentrations up to 10 mu M The dynamics of recovery of virus from the medium of cells pretreated with equal drug concentrations were slower with L(-)Fd4C than with L(-)SddC (3TC). L(-)Fd4C could be metabolized to mono-, di-, and triphosphate forms. The degree of L(-)Fd4C phosphorylation to the 5'-triphosphate metabolite was higher than the degree of L(-)SddC (3TC) phosphorylation when equal extracellular concentrations of the two drugs were used. The apparent K-m of L(-)Fd4C: phosphorylated metabolites formed intracellularly was higher than that for L(-)SddC (3TC), This may be due in part to a difference in the behavior of L(-)Fd4C and L(-)SddC (3TC) towards cytosolic deoxycytidine kinase, Furthermore, L(-)Fd4C 5'-triphosphate was retained longer within cells than L(-)SddC (3TC) 5'-triphosphate. L(-)Fd4C 5'-triphosphate inhibited HBV DNA polymerase in competition with dCTP with a K-i of 0.069 +/- 0.015 mu M. Given the antiviral potency and unique pharmacodynamic properties of L(-)Fd4C, this compound should be considered for development as an expanded-spectrum anti-HBV drug.