title: Hepatitis B virus quasispecies susceptibility to entecavir confirms the relationship between genotypic resistance and patient virologic response.
abstract: OBJECTIVE
  The efficacy of anti-viral therapy for chronic hepatitis B virus (HBV) is lost upon the emergence of resistant virus. Using >500 patient HBV isolates from several entecavir clinical trials, we show that phenotypic susceptibility correlates with genotypic resistance and patient virologic responses.
  
  
  METHODS
  The full-length HBV or reverse transcriptase gene was amplified from patient sera, sequenced, and cloned into an HBV expression vector. Entecavir susceptibilities of individual virus clones and patient quasispecies populations were analyzed in conjunction with the sequenced resistance genotype and the patient's virologic response.
  
  
  RESULTS
  Entecavir susceptibility decreased approximately 8-fold for isolates with various constellations of lamivudine resistance substitutions. The spectrum of additional substitutions that emerged during therapy at residues rtT184, rtS202, or rtM250 displayed varying levels of entecavir susceptibility according to the specific resistance substitutions and the proportion of resistant variants in the quasispecies. Phenotypic analyses of samples associated with virologic breakthrough confirmed the role of these residue changes in entecavir resistance. Additional longitudinal phenotypic analyses showed that decreased susceptibility correlated with both genotypic resistance and increased circulating HBV DNA.
  
  
  CONCLUSIONS
  HBV phenotypic analysis provides additional insight as part of a resistance monitoring program that includes genotypic analysis and quantification of circulating virus.
authors: Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492, USA. joe.baldick@bms.com
authors: Carl J
authors: CJ
authors: Baldick
authors: Betsy J
authors: BJ
authors: Eggers
authors: Jie
authors: J
authors: Fang
authors: Steven M
authors: SM
authors: Levine
authors: Kevin A
authors: KA
authors: Pokornowski
authors: Ronald E
authors: RE
authors: Rose
authors: Cheng-Fang
authors: CF
authors: Yu
authors: Daniel J
authors: DJ
authors: Tenney
authors: Richard J
authors: RJ
authors: Colonno
mesh_terms: D000998:Antiviral Agents / Q000627:therapeutic use*; D004279:DNA, Viral / Q000097:blood*; D016903:Drug Monitoring / Q000379:methods; D024882:Drug Resistance, Viral / Q000235:genetics*; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D005838:Genotype; D006147:Guanine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D006509:Hepatitis B / Q000097:blood / Q000188:drug therapy*; D006515:Hepatitis B virus / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D019259:Lamivudine / Q000627:therapeutic use; D008137:Longitudinal Studies; D009154:Mutation / Q000235:genetics; D010641:Phenotype
chemical_list: D000998:Antiviral Agents; D004279:DNA, Viral; D019259:Lamivudine; C413685:entecavir; D006147:Guanine