Abstract
Duck hepatitis B virus (DHBV) was used as a model in the search for antiviral compounds against hepatitis B. The triphosphate of 3′-fluoro-2′,3′-dideoxythymidine (FLT) inhibits DHBV DNA polymerase in vitro. The aim of this investigation was to evaluate the in vivo inhibitory effect of FLT on DHBV in ducks. Four DHBV-positive ducklings were treated with FLT by intraperitoneal injections of 25 mg kg−1, two times daily for 17 days. No decrease of DHBV DNA in serum was observed. Therefore, it was investigated if FLT could be efficiently phosphorylated in duck liver.
From DHBV-infected and non-infected duck livers protein extracts were prepared and partially purified by ion-exchange chromatography. Only one enzyme with thymidine (and deoxycytidine) kinase activity was found, corresponding to thymidine kinase 2 (i.e. the mitochondrial type of deoxynucleoside kinase). In contrast to extracts from duck spleen, the liver extracts showed a very low capacity to phosphorylate FLT, and this may explain the failure of FLT to prevent DHBV replication in vivo. These results suggest that new nucleoside analogues designed for treatment of hepatitis B should be evaluated with respect to phosphorylation by enzymes from non-dividing liver cells.