The amino acid substitutions rtP177G and rtF249A in the reverse transcriptase domain of hepatitis B virus polymerase reduce the susceptibility to tenofovir

Long term antiviral therapy with nucleoside/nucleotide analogs have been routinely used to treat chronic hepatitis B virus (HBV) infection but may lead to the emergence of drug-resistant viral mutants. However, the HBV resistance mutations for tenofovir (TDF) remain controversial. It is speculated that the genetic barrier for TDF resistance may be high for HBV. We asked whether selected amino acid substitutions in HBV polymerase may reduce susceptibility to TDF. A series of amino acids in HBV polymerase were selected based on bioinformatics analysis for mutagenesis. The replication competence and susceptibility to TDF of the mutated HBV clones were determined both in vitro and in vivo. nineteen mutations in HBV polymerase were included and impaired the replication competence of HBV genome in different degrees. The mutations at rtL77F (sS69C), rtF88L (sF80Y), and rtP177G (sR169G) also significantly affected HBsAg expression. The HBV mutants with rtP177G and rtF249A were found to have reduced susceptibility to TDF in vitro with a resistance index of 2.53 and 12.16, respectively. The testing in in vivo model based on the hydrodynamic injection revealed the antiviral effect of TDF against wild type and mutated HBV genomes and confirmed the reduced the susceptibility of mutant HBV to TDF. (C) 2012 Elsevier B.V. All rights reserved.