HBV clinical isolates expressing adefovir resistance mutations show similar tenofovir susceptibilities across genotypes B, C and D
Background & Aims
Hepatitis B virus (HBV) genotypes can influence clinical outcomes as well as response to antiviral therapy. This study evaluated the tenofovir (TFV) susceptibility of HBV genotype B, C and D clinical isolates with adefovir resistance-associated mutations (ADV-R).
Full-length HBV isolates from patients infected with genotype B, C and D virus had rtA181T, rtA181V, rtN236T, rtA181T + rtN236T and rtA181V + rtN236T mutations introduced by site-directed mutagenesis. Phenotypic analyses were performed in HepG2 cells and susceptibility to TFV and ADV were assessed.
Clinical HBV isolates containing rtA181T, rtA181V or rtN236T as single mutants remained sensitive to TFV across genotypes B, C and D. Clinical isolates containing the rtA181T + rtN236T double mutant remained sensitive to TFV in genotype D but exhibited reduced susceptibility to TFV in genotypes B and C. Viruses containing the double mutant rtA181V + rtN236T in genotypes B and D exhibited reduced susceptibility to TFV with EC50 fold changes (FC) of 3.8 and 2.5, respectively, while genotype C viruses containing rtA181V + rtN236T either remained sensitive (FC = 1.3) or exhibited reduced susceptibility to TFV (FC = 2.9) depending on the isolate. All rtA181V + rtN236T isolates conferred reduced susceptibility to ADV (FC values 2.3–4.2).
Genotype B, C and D isolates with single ADV resistance mutations remained fully sensitive to TFV, while the double mutants rtA181T + rtN236T and rtA181V + rtN236T exhibited either no change or low-level reduced susceptibility to TFV across genotypes. These results are consistent with the clinical efficacy observed with tenofovir disoproxil fumarate (TDF) treatment across all genotypes in vivo and the limited impact of ADV-R mutations on TDF therapy.