Background: Suppression of viral replication with nucleoside/nucleotide inhibitors has been shown to greatly improve the outcome of chronic HBV infection. β-l-nucleoside analogues, especially β-l-deoxycytidine derivatives represent one of the most efficient groups of antiretroviral compounds. We recently described that hydroxylation of the amino group of these β-l-deoxycytidine derivatives preserved their strong HBV inhibitory activity in vitro, but strongly reduced their cytotoxicity. From this new group of compounds we selected β-l-2',3'-didehydro-2',3'-dideoxy-N(4)-hydroxy-5-fluorocytidine (l-Hyd4FC) for a first in vivo investigation. The aim of this study was to determine the antiviral activity of l-Hyd4FC in HBV-infected human liver chimeric urokinase plasminogen activator (uPA)/SCID mice.
Methods: Stably infected animals (median 6×10(7) HBV DNA/ml) were injected daily with either l-Hyd4FC (50 mg/kg) or saline as controls. Mice treated with lamivudine served to compare the in vivo antiviral potency of l-Hyd4FC. Virological changes were determined by quantitative PCR.
Results: Treatment with l-Hyd4FC for 4 weeks induced a 2-log reduction of viraemia, while a median 1.5-log decline was achieved with lamivudine. Intrahepatically, l-Hyd4FC induced a median eightfold decline of viral activity (relaxed circular DNA/covalently closed circular DNA), and threefold reduction of pregenomic RNA/GAPDH levels. No significant decline of subgenomic HBV transcripts, as well as of circulating hepatitis B e antigen and hepatitis B surface antigen was detected. Maintenance of human serum albumin concentrations throughout the study, negative TUNEL staining and occurrence of viral rebound after drug withdrawal indicated that l-Hyd4FC was not toxic in human hepatocytes.
Conclusions: Administration of l-Hyd4FC in uPA/SCID mice harbouring HBV-infected human hepatocytes demonstrated the high antiviral potency of this drug in vivo. Such characteristics make l-Hyd4FC a good candidate for further investigations a as potential HBV therapeutic agent.