Chinical and phenotipic analyses of untypical adefovir-resistanence-associated mutation rtN238T of hepatitis B virus

Abstract

Objective To identify clinical prevalence of untypical adefovir-resistant mutations of hepatitis B virus (HBV), and to analyze their phenotypic characteristics. Methods 1741 patients with chronic HBV infection were evolved. Untypical adefovir-resistant mutations were analyzed by direct sequencing. Longitudinal analysis was performed by clonal sequencing. Wild-type and mutant HBV genomic amplicons were constructed into pTriEx-HBV 1.1 vector and transfected into HepG2 cells. The replication capacity and the 50% effective concentration of drugs (EC50) were calculated. Results Patients treated with adefovir alone were more likely to develop rtN238T mutation than those treated with other nucleos(t)ide drugs (χ2=17.10, P<0.01). The patient received adefovir for 47 months, and then viral rebound and biochemical breakthrough occurred with detection of rtN238T + A181V and rtN238T mutation. Switching-to entecavir therapy suppressed HBV DNA and ALT to an undetectable level and converted all viruses into wild type ones. The reulsts of viral replication capacity showed that rtN238T+ A181V strain was higher than rtA181V strain (t=9.54, P<0.01). Compared to the wild type virus, rtN238T+ A181V variant was relatively less susceptible to adefovir. Conclusions rtN238T mutation conferred no resistance to ADV but enhanced natural replication capacity, hence it might represent a novel compensatory drug-resistant mutation for adefovir. Key words: Hepatitis B virus; Mutation; Drug resistance