Dynamics of Hepatitis B Virus Resistance to Lamivudine

Abstract

Lamivudine was the first approved inhibitor of hepatitis B virus (HBV) reverse transcriptase (RT). Lamivudine resistance develops in 53% to 76% of patients after 3 years of treatment. We extensively characterized the dynamics of HBV quasispecies variant populations in four HBV-infected patients who developed lamivudine resistance. Virological breakthrough was preceded by 2 to 4 months by the emergence of quasispecies variants bearing amino acid substitutions at RT position 204, i.e., within the YMDD catalytic motif (rtM204V/ I). Three patients had a gradual switch from a YMDD variant population at baseline to a 100% lamivudineresistant variant population, whereas the remaining patient had a fluctuating pattern of resistance variant dynamics. Careful analysis of amino acid substitutions located outside domain C of HBV RT, including those known to partially restore replication capacities in vitro, showed that the in vivo replication of HBV variants is driven by multiple forces, including intrinsic replicative advantages conferred by mutations accumulating outside domain C and the changing environment in which these variants replicate. Our findings also suggest that individual treatment optimization will require sensitive methods capable of detecting the emergence of viral resistance before the relevant variants acquire optimal replicative capacities. Hepatitis B virus (HBV) infection is a major public health problem, with approximately 350 million individuals chronically infected worldwide (19). Chronic HBV carriers are exposed to a risk of complications, such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma, of which HBV is currently the most frequent cause (13). Up to one million people die every year from complications of HBV infection (19).HBV infection is characterized by high levels of virus production and turnover (28, 39), whereas the HBV reverse transcriptase (RT), like the human immunodeficiency virus (HIV) RT, is an error-prone enzyme lacking 3Ј-5Ј-exonuclease proofreading capacity (3,14). As a result, HBV, like other viruses with error-prone polymerases, such as HIV, hepatitis C virus, and poliovirus, has a quasispecies distribution in infected individuals (14). This means that HBV circulates as a complex mixture of genetically distinct but closely related variants that are in equilibrium at a given time point of infection in a given replicative environment. The quasispecies distribution of HBV implies that any newly generated mutation conferring a selective advantage to the virus in a given replicative environment will allow the corresponding viral population to overtake the other variants, following a classical Darwinian evolutionary process (10).Treatment of chronic hepatitis B is aimed at driving viral replication to the lowest possible level, and thereby to halt the progression of liver disease and prevent the onset of complications. However, HBV infection cannot be fully eradicated, because of covalently closed circular proviral DNA persistence in host cells. The first HBV RT inhibit...

Selection of a Multiple Drug-Resistant Hepatitis B Virus Strain in a Liver-Transplanted Patient

“…A detailed clonal HBV genome analysis was performed on sequential serum samples throughout the course of the disease, as it was recently done in four patients who failed lamivudine therapy 29 . These data allowed to show the complex evolution of the viral quasi-species under the different antiviral pressures.…”

Comparison of ligase detection reaction and real-time PCR for detection of low abundant YMDD mutants in patients with chronic hepatitis B

“…These resistant variants initially represent a minority of the quasispecies and gradually replace the wild-type YMDD variants [10] . Detection of low abundant lamivudine-resistant mutants in the background of wild-type HBV as early as possible is helpful for virological follow-up and diagnosis of resistance in the clinical setting.…”

“…Clinical breakthrough was observed 2 wk-7 mo after the emergence of YMDD mutations [8][9][10] , causing considerable morbidity and mortality in those patients [20][21][22][23][24] .…”

“…Initially, YMDD mutants consist of minor populations. They gradually replace the wildtype virus, reaching a 100% lamivudine-resistant variant population, and this replacement occurs in parallel with the increase in HBV DNA load [10] . Sensitive methods for early detection of lamivudine-resistant mutants will be helpful for physicians to make clinical decisions in treatment of patients with HBV infection.…”

“…Resistance is associated with mutations in the highly conserved tyrosine-methionineaspartate-aspartate (YMDD) motif of the reverse transcriptase, which is part of the catalytic site of the HBV polymerase [7] . Viological breakthrough and alanine transaminase (ALT) elevation have been shown to occur 2-28 wk and 12-31 wk after the emergence of YMDD mutants, respectively [8][9][10] . Initially, YMDD mutants consist of minor populations.…”