Characterization of the antiviral effect of 2 ',3 '-dideoxy-2 ', 3 '-didehydro-beta-L-5-fluorocytidine in the duck hepatitis B virus infection model

A novel L-nucleoside analog of deoxycytidine, 2',3'-dideoxy-2',3'-didehydro -beta-L-5-fluorocytidine (beta-L-Fd4C), was recently shown to strongly inhi bit hepatitis B virus (HBV) replication in the 2.2.15 cell line. Therefore, its antiviral activity was evaluated in the duck HBV (DHBV) infection mode l. Using a cell-free system for the expression of the DHBV polymerase, beta -L-Fd4C-TP exhibited a concentration-dependent inhibition of dCTP incorpora tion into viral minus-strand DNA with a 50% inhibitory concentration of 0.2 mu M which was lower than that of other tested deoxycytidine analogs, i.e. , lamivudine-TP, ddC-TP, and beta-L-FddC-TP. Further analysis showed that b eta-L-Fd4C-TP is likely to be a competitive inhibitor of dCTP incorporation and to cause premature DNA chain termination. In primary duck hepatocyte c ultures infected in vitro, beta-L-Fd4C administration exhibited a long-last ing inhibitory effect on viral DNA synthesis but could not clear viral cova lently closed circular DNA (CCC DNA). Results of short-term antiviral treat ment in experimentally infected ducklings showed that beta-L-Fd4C exhibited the most potent antiviral effect, followed by beta-L-FddC, lamivudine, and ddC. Longer administration of beta-L-Fd4C induced a sustained suppression of viremia (>95% of controls) and of viral DNA synthesis within the liver. However, the persistence of trace amounts of viral CCC DNA detected only by PCR was associated with a recurrence of viral replication after drug withd rawal. In parallel, beta-L-Fd4C treatment suppressed viral antigen expressi on within the liver and decreased intrahepatic inflammation and was not ass ociated with any sign of toxicity. Our data, therefore, demonstrate that in the duck model of HBV infection, beta-L-Fd4C is a potent inhibitor of DHBV reverse transcriptase activity in vitro and suppresses viral replication i n the liver in vivo.