Hepatitis B virus quasispecies susceptibility to entecavir confirms the relationship between genotypic resistance and patient virologic response.
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.
Baldick
Carl J
CJ
Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492, USA. joe.baldick@bms.com
Eggers
Betsy J
BJ
Fang
Jie
J
Levine
Steven M
SM
Pokornowski
Kevin A
KA
Rose
Ronald E
RE
Yu
Cheng-Fang
CF
Tenney
Daniel J
DJ
Colonno
Richard J
RJ
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
D000998:Antiviral Agents; D004279:DNA, Viral; D019259:Lamivudine; C413685:entecavir; D006147:Guanine