THE M539V POLYMERASE VARIANT OF HUMAN HEPATITIS-B VIRUS DEMONSTRATES RESISTANCE TO 2'-DEOXY-3'-THIACYTIDINE AND A REDUCED ABILITY TO SYNTHESIZE VIRAL-DNA

The cytosine analog 2'-deoxy-3'-thiacytidine (3TC) has been shown to b e an effective treatment for chronic hepatitis B virus (HBV) infection . However, several liver transplant patients who were undergoing treat ment with 3TC for HBV infection experienced a breakthrough of virus wh ile on 3TC. The predominant virus found in these patients' sera contai ned either a valine or isoleucine for the methionine in the highly con served YMDD nucleotide binding site in the HBV polymerase. To determin e the biological relevance of the Met-to-Val substitution, we mutated a plasmid that contained a cDNA copy of the HBV pregenomic RNA such th at when virus replication occurred during transient transfection of He pG2 cells, an M539V polymerase variant was produced. We found that in transiently transfected cells, this variant was approximately 330-fold less sensitive to the antiviral effects of 3TC and produced 7-fold le ss viral DNA than the wild type.