In vitro susceptibilities of wild-type or drug-resistant hepatitis B virusto (-)-beta-D-2,6-diaminopurine dioxolane and 2 '-fluoro-5-methyl-beta-L-arabinofuranosyluracil

Prolonged treatment of chronic hepatitis B virus (HBV) infection with lamiv udine ([-]-beta -L-2 ' ,3 ' -dideoxy-3 ' thiacytidine) or famciclovir may s elect for viral mutants that are drug resistant due to point mutations in t he polymerase gene. Determining whether such HBV mutants are sensitive to n ew antiviral agents is therefore important. We used a transient transfectio n system to compare the sensitivities of wild-type HBV and four lamivudine- and/or famciclovir-resistant HBV mutants to adefovir [9- (2-phosphonyl-met hoxyethyl)-adenine; PMEA] and the nucleoside analogues (-)-beta -D-2, 6-dia minopurine dioxolane (DAPD) and 2 ' -fluoro-5-methyl-beta -L-arabinofuranos yluracil (L-FMAU). The drug-resistant mutants contained amino acid substitu tions in the polymerase protein. We found that the M5501 and M550V plus L52 6M substitutions, which confer lamivudine resistance, did not confer cross- resistance to adefovir or DAPD, but conferred cross-resistance to L-FMAU. T he M550V substitution in isolation conferred a similar phenotype to M5501, except that it did not confer significant resistance to L-FMAU. The L526M s ubstitution, which is associated with famciclovir resistance, conferred cro ss-resistance to L-FMAU but not to adefovir or DAPD. Inhibition of HBV secr etion by DAPD, L-FMAU, and adefovir did not always correlate with inhibitio n of the generation of intracellular HBV replicative intermediates, suggest ing that these analogs may preferentially inhibit specific stages of the vi ral replication cycle.