The hepatitis B virus M539V polymerase variation responsible for 3TC resistance also confers cross-resistance to other nucleoside analogues.

A variant of hepatitis B virus (HBV) containing a Met-to-Val substitution (M539V) in the YMDD motif of the polymerase nucleoside-binding domain exhibited resistance to the cytosine analogue lamivudine (3TC). To determine if the mutation responsible for the M539V polymerase variant affected the sensitivity of the virus to other nucleoside analogues, we constructed a tetracycline-responsive cell line, HepAD79. This cell line is stably transfected with a cDNA copy of the pregenomic RNA of an HBV genome containing an A-to-G mutation in the first position of the polymerase gene codon 539. This mutation results in a Met-to-Val substitution at amino acid 539 of the polymerase. When grown under the proper conditions, HepAD79 cells produced HBV RNA, contained HBV DNA associated with immature core particles and released core-associated HBV DNA into the medium. The M539V polymerase variant produced in this cell line was approximately 26-fold less sensitive to the antiviral effects of 3TC than wild-type virus. In addition, this variant demonstrated decreased sensitivity to the cytosine analogues FTC and ddC, as well as the thymidine analogue AZT.