Inhibition of hepatitis B virus by a novel L-nucleoside, 2'-fluoro-5-methyl-beta-L-arabinofuranosyl uracil

2'-Fluoro-5-methyl-beta-L-arabinofuranosyl uracil (L-FMAU) was discovered to have potent antiviral activity against hepatitis B virus (HBV), L-FMAU was more potent than its D-enantiomer and produced dose-dependent inhibition of the viral DNA replication in 2.2.15 cells (human HepG2 cells with the HBV genome), with a 50% inhibitory concentration of 0.1 mu M. There was no inhibitory effect on HBV transcription or protein synthesis, In the 2.2.15 cell system, L-FMAU did not show any toxicity up to 200 mu M, whereas the D-enantiomer was toxic, with a 50% inhibitory concentration of 50 mu M. Repeated treatments of HepG2 cells with L-FMAU at a 1 mu M concentration for 9 days did not result in any decrease in the total mitochondrial DNA content, suggesting that a mode of toxicity similar to that produced by 2',3'-dideoxycytidine is unlikely, Also at concentrations as high as 200 mu M, L-FMAU did not adversely affect mitochondrial function as determined by lactic acid production by L-FMAU-treated hepatoma cells, L-FMAU was metabolized in the cells to its mono-, di-, and triphosphates. A dose-dependent inhibition of HBV DNA synthesis by L-FMAU triphosphate was observed in the DNA polymerase assays with isolated HBV particles, suggesting that the mode of action of this compound could involve viral polymerase. However, L-FMAU was not incorporated into the cellular DNA, Considering the potent inhibition of the viral DNA synthesis and the nontoxicity of L-FMAU towards the host DNA synthetic machinery, this compound should be further explored for development as an anti-HBV drug.