rtE218G, a novel hepatitis B virus mutation with resistance to adefovir dipivoxil in patients with chronic hepatitis B

Summary.  Antiviral therapy is a potentially successful approach for the treatment of patients with Hepatitis B virus (HBV) infection. One antiviral agent is the nucleoside analogue adefovir dipivoxil (ADV). Its efficiency is compromised by the emergence of drug‐resistant HBV mutants. Although three major ADV‐resistant mutations of HBV are known, rtA181T/V and rtN236T, HBV mutations associated with ADV resistance have not been fully identified. We analyzed DNA sequences that covered a 244 base pair region of the HBV polymerase gene from patients with clinical manifestations of ADV resistance. A novel pattern of amino acid substitutions in HBV polymerase was detected in 26 out of 86 patients. This mutant exhibited a substitution of glycine for glutamic acid at residue 218 (rtE218G). Transient transfection of the HBV replication‐competent construct including the rtE218G mutation was performed in HepG2 cells in order to determine the relevance of this mutation to ADV resistance. Phenotypic analyses demonstrated that the rtE218G mutation could independently confer resistance to ADV in vitro, with a 50% inhibitory concentration (IC50) 5.5‐fold higher than wild‐type HBV. RtE218G‐mutated HBV also showed a decreased replication capacity in vitro, equal to 87% of wild‐type HBV. The present study showed that the rtE218G mutation may be a novel ADV‐resistant mutation. Further work will focus on resistance surveillance and cross‐resistance analyses, and the molecular mechanisms involved.