Prevalence, viral replication efficiency and antiviral drug susceptibility of rtQ215 polymerase mutations within the hepatitis B virus genome☆
Received 13 February 2009; received in revised form 22 April 2009; accepted 27 April 2009. published online 27 May 2009.
Background/Aims
The rtQ215S mutation in the hepatitis B virus (HBV) polymerase has been described as a secondary mutation associated with resistance to lamivudine (LAM) and adefovir (ADV). We aimed at assessing the prevalence of substitutions at rtQ215 of the HBV polymerase and determining the molecular and functional consequences using phenotypic analyses in vitro.
Methods
The polymerase region was directly sequenced in HBV isolates from a cohort of 249 HBV genotype D-infected patients from Iran (174 males/ 75 females, 194 treatment-naı¨ve/ 55 LAM-treated). Replication-competent HBV constructs containing the naturally occurring rtQ215H, rtQ215P and rtQ215S mutations were generated, and compared to wild-type, LAM- (rtM204I, rtL180M/rtM204V) and ADV-resistant (rtN236T) clones.
Results
In an Iranian cohort of 249 HBV infected patients, 14.5% (36/249) showed mutations in the rtQ215 locus, namely 6.8% rtQ215S, 3.6% rtQ215P and 4.1% rtQ215H. The frequency of rtQ215 substitutions was higher in LAM-treated than treatment-naı¨ve patients (25% vs. 11%), but not associated with clinical complications. In phenotypic assays, rtQ215S, rtQ215P and rtQ215H constructs showed equivalent levels of viral replication as wild-type HBV, whereas LAM- and ADV-resistant mutants had significantly impaired replicative capacities. Furthermore, rtQ215S, rtQ215P and rtQ215H harbouring constructs remained susceptible towards treatment with LAM or ADV in vitro.
Conclusions
Our study reveals that rtQ215 substitutions in the HBV polymerase frequently occur in chronic hepatitis B, even without exogenous selection pressures. As these substitutions do neither impair the viral replication efficiency nor susceptibility to LAM or ADV in vitro, rtQ215 substitutions likely represent background polymorphisms rather than resistance mutations with clinical implications.
☆ C.T. and F.T. have received research grants from Novartis and Bristol-Myers Squibb. The other authors who have taken part in this study declared that they do not have anything to disclose with respect to this manuscript.
ABSTRACT