Dynamics of lamivudine-resistant hepatitis B virus strains in patients with entecavir rescue therapy

Revisiting HBV resistance to entecavir with a phenotypic approach

Treatment adaptation after hepatitis B virus (HBV) treatment failure relies on genotypic resistance testing. However, the results of such tests are not always consistent with treatment response. These discrepancies may be due to differences in resistance levels between isolates with the same genotypic resistance testing profiles. We explored this hypothesis by investigating six cases of entecavir treatment failure with an integrative strategy combining genotypic and phenotypic resistance testing, medical record review and therapeutic drug monitoring. Among isolates with genotypic reduced susceptibility to entecavir, one displayed a higher level of resistance to entecavir (mean fold change in entecavir IC₅₀ of 1 508 ± 531 vs. 318 ± 53, p = 0.008). This isolate harbored a substitution (rt250L) at a position reported to be associated with resistance (rt250V). Reversion to wild-type amino acid at this position partially restored susceptibility to entecavir, confirming that the rt250L mutation was responsible for the high level of resistance to entecavir. This is the first description of entecavir treatment failure associated with selection of the rt250L mutation without other entecavir resistance mutations. One isolate with genotypic resistance to entecavir, harboring the rt173L mutation, displayed a lower level of resistance than the other, harboring the rt202G mutation (mean fold change of 323 ± 124 vs. 6 036 ± 2 100, p = 0.20). These results suggest that isolates harboring the rt250L mutations should be considered resistant to entecavir, whereas isolates harboring the rt173L mutations should be considered to display reduced susceptibility to entecavir. An integrative approach to antiviral drug resistance in HBV would provide a more accurate assessment of entecavir treatment failures and help to improve the accuracy of genotypic testing algorithms.

Present and Future Therapies for Chronic Hepatitis B

Chronic hepatitis B (CHB) remains the leading cause of liver-related morbidity and mortality across the world. If left untreated, approximately one-third of these patients will progress to severe end-stage liver diseases including liver failure, cirrhosis, and hepatocellular carcinoma (HCC). High level of serum HBV DNA is strongly associated with the development of liver failure, cirrhosis, and HCC. Therefore, antiviral therapy is crucial for the clinical management of CHB. Current antiviral drugs including nucleoside/nucleotide analogues (NAs) and interferon-α (IFN-α) can suppress HBV replication and reduce the progression of liver disease, thus improving the long-term outcomes of CHB patients. This chapter will discuss the standard and optimization antiviral therapies in treatment-naïve and treatment-experienced patients, as well as in the special populations. The up-to-date advances in the development of new anti-HBV agents will be also discussed. With the combination of the current antiviral drugs and the newly developed antiviral agents targeting the different steps of the viral life cycle or the newly developed agents modulating the host immune responses, the ultimate eradication of HBV will be achieved in the future.

Deep sequencing of hepatitis B surface antigen gene in the preserved umbilical cords in immunoprophylaxis failure against mother-to-child HBV transmission

BACKGROUND

Vaccine escape mutants (VEMs) are one of the causes of breakthrough infections in the mother-to-child transmission of hepatitis B virus (HBV). We hypothesized that VEMs existing as minor populations in the maternal blood are associated with breakthrough infections in children. We sought to determine whether VEMs exist as minor populations in the preserved umbilical cords of children with breakthrough infections.

CASE PRESENTATION

Two families (Family 1: three children, Family 2: two children) were enrolled. Despite immunoprophylaxis, a breakthrough infection occurred in two Family 1 children and two Family 2 children. Preserved umbilical cords, serum, and nails were used for the HBV DNA analysis. To detect VEMs, we performed direct and deep sequencing of hepatitis B surface antigen gene. The direct sequencing showed that there were no VEMs in the serum of the children or mother of Family 1 and family 2, but it identified a G145A mutant in the nails of the mother of Family 2. In Family 1, deep sequencing detected a T143S mutant as a minor population (1.7-2.0%) in the umbilical cords and serum of all three children and in the serum of the mother. A T126A mutant was also detected in the umbilical cord (9.2%) and serum (7.0%) of the first-born child of Family 1. In Family 2, the deep sequencing showed no VEMs in the umbilical cords, but it detected D144A (2.5%) and G145A (11.2%) mutants in the serum of the 2nd-born child.

CONCLUSIONS

VEMs were present as minor populations in the preserved umbilical cords of children with breakthrough infections. The VEMs did not become major populations after the breakthrough infections. The evolution of VEMs from a minor form to a major form might not be a prerequisite for breakthrough infections in mother-to-child transmission.

How viral genetic variants and genotypes influence disease and treatment outcome of chronic hepatitis B. Time for an individualised approach?

Chronic hepatitis B virus (HBV) infection remains a global problem. Several HBV genotypes exist with different biology and geographical prevalence. Whilst the future aim of HBV treatment remains viral eradication, current treatment strategies aim to suppress the virus and prevent the progression of liver disease. Current strategies also involve identification of patients for treatment, namely those at risk of progressive liver disease. Identification of HBV genotype, HBV mutants and other predictive factors allow for tailoured treatments, and risk-surveillance pathways, such as hepatocellular cancer screening. In the future, these factors may enable stratification not only of treatment decisions, but also of patients at risk of higher relapse rates when current therapies are discontinued. Newer technologies, such as next-generation sequencing, to assess drug-resistant or immune escape variants and quasi-species heterogeneity in patients, may allow for more information-based treatment decisions between the clinician and the patient. This article serves to discuss how HBV genotypes and genetic variants impact not only upon the disease course and outcomes, but also current treatment strategies. Adopting a personalised genotypic approach may play a role in future strategies to combat the disease. Herein, we discuss new technologies that may allow more informed decision-making for response guided therapy in the battle against HBV.

HBV quasispecies composition in Lamivudine-failed chronic hepatitis B patients and its influence on virological response to Tenofovir-based rescue therapy

The present study sought to evaluate the structure of HBV quasispecies in Lamivudine (LMV)-failed chronic hepatitis B (CHB) patients and its impact in defining the subsequent virological responses to Tenofovir (TDF)-based rescue-therapy. By analyzing HBV clones encompassing reverse transcriptase (RT) and surface (S) region from LMV-failed and treatment-naïve CHB patients, we identified 5 classical and 12 novel substitutions in HBV/RT and 9 substitutions in immune-epitopes of HBV/S that were significantly associated with LMV failure. In silico analysis showed spatial proximity of some of the newly-identified, mutated RT residues to the RT catalytic centre while most S-substitutions caused alteration in epitope hydrophobicity. TDF administration resulted in virological response in 60% of LMV-failed patients at 24-week but non-response in 40% of patients even after 48-weeks. Significantly high frequencies of 6 S-substitutions and one novel RT-substitution, rtH124N with 6.5-fold-reduced susceptibility to TDF in vitro, were noted at baseline in TDF non-responders than responders. Follow-up studies depicted greater evolutionary drift of HBV quasispecies and significant decline in frequencies of 3 RT and 6 S-substitutions in responder-subgroup after 24-week TDF-therapy while most variants persisted in non-responders. Thus, we identified the HBV-RT/S variants that could potentially predict unfavorable response to LMV/TDF-therapy and impede immune-mediated viral clearance.

Lamivudine-resistant rtL180M and rtM204I/V are persistently dominant during combination rescue therapy with entecavir and adefovir for hepatitis B

Adefovir (ADV) sequential monotherapy was included in the 2005 Asia-Pacific guidelines for the management of patients with lamivudine (LAM) resistance. However, following the development of ADV resistance, the proportion of resistant variants during combined rescue therapy with ADV and entecavir (ETV) were unknown. The present study characterized the dynamics of resistant variants in patients with chronic hepatitis B (CHB) and LAM-resistant variants during antiviral therapy consisting of ADV monotherapy followed by ADV-ETV combination therapy. A total of 3 patients were selected from a cohort of 55 patients with CHB due to developing ADV resistance. The patients had been previously treated with LAM (100 mg daily) for 21–24 months. At the initiation of sequential monotherapy with ADV, LAM-resistant variants (rtM204V/I and rtL180M) were detected in the three patients. These patients developed ADV resistance during 19–30 months of ADV sequential monotherapy, and then switched their antiviral regimen to ADV-ETV combination therapy. During ADV monotherapy and ADV-ETV combination therapy, the patients were monitored every 3 months for the first year of therapy, and then every 6 months thereafter. A total of 30 serum samples were collected from the patients throughout the monitoring period. In total, 10 mutants that were associated with commonly-used antiviral drugs were detected by pyrosequencing. During ADV sequential monotherapy, LAM-resistant variants were gradually decreased, whereas ADV-resistant rtA181V/T and rtN236T variants gradually increased in the viral population. During 30–41 months of ADV-ETV combination therapy, viral load reduction was 2.59–3.28 log₁₀ copies/ml; ADV-resistant variants rtA181T/V and rtN236T were undetectable following 11–24 months of combination therapy; and rtL180M and rtM204I/V remained dominant in the viral population. In conclusion, the results of the present study suggested that, in patients with LAM and ADV-resistant variants that developed during LAM-ADV sequential monotherapy, ETV-ADV combination therapy may partially inhibit the replication of HBV DNA; however, LAM-resistant rtL180M and rtM204I/V variants remained predominant following 30–41 months combination therapy.

Evolution of entecavir-resistant hepatitis B virus during entecavir and adefovir dipivoxil combination therapy

The emergence of entecavir (ETV) resistance is rare, particularly in a longitudinal study. The aim of the present study was to characterize the evolution of ETV-resistant variants during antiviral therapy using entecavir monotherapy followed by ETV-adefovir dipivoxil (ADV) combination therapy. The study included a prospective cohort of 53 consecutive chronic hepatitis B (CHB) patients. During the 60-month period of ETV therapy, 2 patients exhibited ETV resistance and their medical records were comprehensively reviewed. A total of 25 consecutive serum samples were regularly collected from the 2 patients. All the samples were used to characterize the evolution of the polymerase gene mutations using pyrosequencing. The linkage of the variants was analyzed from 87 reverse transcriptase sequences of 3 selective samples using clone sequencing. The 2 patients presented with viral breakthrough during ETV monotherapy. In patient A, the rtL180M, rtS202G and rtM204V mutant variants were detected using pyrosequencing prior to virological breakthrough. Although the viral load declined following the administration of ADV, the ETV-resistant variants were persistently dominant in the viral populations. In patient B, the rtL180M, rtM204I and rtM204V mutants were present in ~70, 30 and 10% of the viral populations, respectively, at the time of study entry. In addition, rtT184F was present in ~20% of the viral population during virological breakthrough, at month 24. The rtL180M, rtT184F and rtM204V were predominant during the combination treatment. Clonal analysis further revealed that the rtS202G or rtT184F was in all cases co-localized with rtL180M and rtM204V in any single virus isolate clone. The results of the present study indicate that the addition of ADV therapy with ETV for treating ETV-resistant mutation may not inhibit the replication of ETV-resistant variants that developed previously in lamivudine-treated CHB patients.

Delayed Reduction of Hepatitis B Viral Load and Dynamics of Adefovir-Resistant Variants during Adefovir plus Entecavir Combination Rescue Therapy

OBJECTIVE

Entecavir (ETV) added to adefovir (ADV) is recommended in the consensus for management of patients with ADV resistance. However, little attention has been focused on the delayed reduction of HBV DNA and dynamics of ADV-resistant variants during ADV-ETV combination rescue therapy in the clinical setting. We characterized the dynamics of viral load and resistant variants in nucleos(t)ide analogues (NAs)-naïve chronic hepatitis B (CHB) patients during antiviral treatment with ADV monotherapy followed by ADV-ETV combination therapy.

METHODS

A cohort of 55 CHB patients was enrolled in this study. Three NAs-naïve patients developed ADV-resistant variants during 24-33 months of ADV monotherapy, and then switched to ADV-ETV combination therapy. Thirty-five serial serum samples from these three patients were regularly collected during treatment. Ten mutants associated with commonly used antiviral drugs were detected by pyrosequencing.

RESULTS

HBV DNA decreased to the lowest level during ADV monotherapy at 6-18 months, with a decrease of 0.95-5.51 log10 copies/mL, whereas rtA181V or rtN236T gradually increased with extended therapy. HBV DNA decreased to below the detectable level during ADV-ETV combination therapy at 21-24 months, with a decrease of 4.19-4.65 log10 copies/mL. Resistant rtA181V and rtN236T were undetectable after 21-24 months of combination therapy. Moreover, no LAM-resistant rtM204I/V or ETV-resistant variants were detected during the 27-36 months of combination therapy.

CONCLUSION

Although ADV-resistant variants were suppressed, viral load reduction was delayed during ADV-ETV combination rescue therapy in patients with ADV-resistant HBV. The quantification of resistant variants by pyrosequencing may facilitate monitoring of antiviral therapy.