The effect of analogues of both 2',3'-dideoxy-3'-fluorothymidine (FddThd) [2',3'-dideoxy-3'-fluorouridine (
FddUrd), 2',3'-dideoxy-3'-fluoro-5-chlorouridine (
FddClUrd), 2',3'-dideoxy-3'- fluoro-5-bromouridine (
FddBrUrd) and 2',3'-dideoxy-3'-fluoro-5-bromovinyluridine (FddBVUrd)] and
2',3'-dideoxy-3'-fluorocytidine (FddCyt) [2',3'-dideoxy-3'-fluoro-5-fluorocytidine (FddFCyt), 2',3'-dideoxy-3'-fluoro-5-chlorocytidine (FddClCyt), 2',3'-dideoxy-3'-fluoro-5-methylcytidine (FddMeCyt), 2',3'-dideoxy-3'-fluoro-5-ethylcytidine (FddEtCyt), 2',3'-dideoxy-3'-chloro-5-methylcytidine (ClddMeCyt), 2',3'-dideoxy-3'-amino-5-methylcytidine (AmddMeCyt), 2',3'-dideoxy-3'-azido-5- methylcytidine (AzddMeCyt) and arabinosyl-5-methylcytosine (AraMeCyt)] were tested for their potential
antiviral activity in vitro using the human
hepatoblastoma cell line, Hep G2 2.2.15, which was transfected with a vector containing hepatitis B virus (HBV). It was found that FddThd, FddMeCyt, FddEtCyt, ClddMeCyt, AmddMeCyt and AraMeCyt display
cytostatic activity at concentrations (CD50 values) between 0.54 (FddMeCyt) and 3.93 microM (FddEtCyt), while
FddUrd,
FddClUrd,
FddBrUrd, FddBVUrd, FddCyt, FddFCyt, FddClCyt and AzddMeCyt do not affect cell growth at concentrations of up to 25 microM. Among the
thymidine analogues tested, FddThd is the most effective
antiviral agent: at a concentration of 0.03 microM a more than 90% reduction of HBV
DNA synthesis was measured. On the other hand, the
antiviral indexes displayed by
FddClUrd,
FddBrUrd and FddBVUrd are higher than tht of FddThd;
FddUrd was completely inactive. The most powerful
antiviral agents in the group of
cytidine analogues tested in vitro were FddMeCyt (more than 90% reduction of HBVDNA synthesis at 0.10 microM) and ClddMeCyt (0.10 microM); FddClCyt, FddEtCyt, AmddMeCyt and AraMeCyt were of intermediate activity. None of the negligible
antiviral activity was determined for
FddUrd, FddCyt, FddFCyt and AzddMeCyt. FddThd and FddMeCyt displayed in vivo an
antiviral effect in the duck/duck HBV (DHBV) animal system. Administration of 10 or 20 mg/kg (total daily dose) of FddThd and 5 or 10 mg/kg of FddMeCyt (i.m. daily) to ducks infected with DHBV for 12 days blocked virus production. Termination of treatment with FddThd of infected animals led to reappearance of the virus in the serum though at lower levels. The in vitro and the in vivo data suggest that FddThd and FddMeCyt might be promising
antiviral agents for the treatment of
infection caused by HBV in humans.