Pooled analysis of amino acid changes in the HBV polymerase in patients from four major adefovir dipivoxil clinical trials

Molecular and Genetic Characterization of Hepatitis B Virus (HBV) among Saudi Chronically HBV-Infected Individuals

The study aimed to characterize the genotype and subgenotypes of HBV circulating in Saudi Arabia, the presence of clinically relevant mutations possibly associated with resistance to antivirals or immune escape phenomena, and the possible impact of mutations in the structural characteristics of HBV polymerase. Plasma samples from 12 Saudi Arabian HBV-infected patients were analyzed using an in-house PCR method and direct sequencing. Saudi patients were infected with mainly subgenotype D1. A number of mutations in the RT gene (correlated to antiviral resistance) and within and outside the major hydrophilic region of the S gene (claimed to influence immunogenicity and be related to immune escape) were observed in almost all patients. Furthermore, the presence of mutations in the S region caused a change in the tertiary structure of the protein compared with the consensus region. Clinical manifestations of HBV infection may change dramatically as a result of viral and host factors: the study of mutations and protein-associated cofactors might define possible aspects relevant for the natural and therapeutic history of HBV infection.

Early dynamic changes of quasispecies in the reverse transcriptase region of hepatitis B virus in telbivudine treatment

BACKGROUND

Telbivudine (LdT) - a synthetic thymidine β-L-nucleoside analogue (NA) - is an effective inhibitor for hepatitis B virus (HBV) replication. The quasispecies spectra in the reverse transcriptase (RT) region of the HBV genome and their dynamic changes associated with LdT treatment remains largely unknown.

METHODS

We prospectively recruited a total of 21 treatment-naive patients with chronic HBV infection and collected sequential serum samples at five time points (baseline, weeks 1, 3, 12, and 24 after LdT treatment). The HBV RT region was amplified and shotgun-sequenced by the Ion Torrent Personal Genome Machine (PGM)® system. We reconstructed full-length haplotypes of the RT region using an integrated bioinformatics framework, including de novo contig assembly and full-length haplotype reconstruction. In addition, we investigated the quasispecies' dynamic changes and evolution history and characterized potential NAs resistant mutations over the treatment course.

RESULTS

Viral quasispecies differed obviously between patients with complete (n = 8) and incomplete/no response (n = 13) at 12 weeks after LdT treatment. A reduced d_N/d_S ratio in quasispecies demonstrated a selective constraint resulting from antiviral therapy. The temporal clustering of sequential quasispecies showed different patterns along with a 24-week observation, although its statistic did not differ significantly. Several patients harboring pre-existing resistant mutations showed different clinical responses, while NAs resistant mutations were rare within a short-term treatment.

CONCLUSION

A complete profile of quasispecies reconstructed from in-depth shotgun sequencing may has important implications for enhancing clinical decision in adjusting antiviral therapy timely.

Hepatitis B virus mutation pattern rtA181S+T184I+M204I may contribute to multidrug resistance in clinical practice: Analysis of a large cohort of Chinese patients

The study aimed to characterize the prevalence and virological features of the rtA181S + T184I + M204I mutant in a large cohort of patients with chronic HBV infection. In total, 22,009 nucleoside/nucleotide analog-treated patients who underwent resistance testing at the Fifth Medical Center of Chinese PLA General Hospital between 2007 and 2016 were enrolled. Serum samples were collected for HBV reverse-transcriptase gene sequencing. Phenotypic analysis of the viral replication capacity and drug susceptibility was performed. The rtA181S mutation was detected in 0.82% (180/22,009) of samples. rtA181S-positive patients had significantly higher lamivudine (LAM), adefovir (ADV), and entecavir (ETV) exposure than rtA181S-negative patients. Of 180 rtA181S-positive patients, 42 had no coexistent resistance mutations, 34 had coexisting LAM-resistance mutation (LAMr), 17 had coexisting ADV-resistance mutation (ADVr), and 86 had coexisting ETV-resistance mutation (ETVr), and one had ADVr + ETVr. rtA181S + T184I + M204I occurred in 79.1% (68/86) of patients with rtA181S + ETVr and 37.8% (68/180) of all rtA181S-positive patients. Longitudinal analysis of the clinical course of resistant mutant evolution for four representative cases showed that rtA181S + T184I + M204I developed in all patients who had received LAM/telbivudine ± ADV and was receiving ETV or ADV + ETV. Compared with wild-type, the rtA181S + T184I + M204I mutant had 53.7% lower replication capacity and >1000-, 3.9-, and 383.3-fold greater LAM, ADV, and ETV resistance, respectively, but remained sensitive to tenofovir. Artificial elimination of rtA181S from the rtA181S + T184I + M204I mutant restored viral susceptibility to ADV but decreased viral replication capacity. Our study presented the first evidence that HBV rtA181S + T184I + M204I mutation had features of multidrug-resistance that contributed to resistance to both nucleoside and nucleotide analogs.

Characterization and Clinical Significance of Natural Variability in Hepatitis B Virus Reverse Transcriptase in Treatment-Naive Chinese Patients by Sanger Sequencing and Next-Generation Sequencing

Mutations in hepatitis B virus (HBV) reverse transcriptase (RT) are associated with nucleos(t)ide analogue (NA) resistance during long-term antiviral treatment. However, the characterization of mutations in HBV RT in untreated patients has not yet been well illustrated. The objective of this study was to investigate the characterization and clinical significance of natural variability in HBV RT in treatment-naive patients. HBV RT sequences were analyzed in 427 patients by Sanger sequencing and in 66 patients by next-generation sequencing. Primary or secondary NA resistance (NA^r) mutations were not found, except A181T in RT (rtA181T) by Sanger sequencing, but they were detected by next-generation sequencing. Mutations were found in 56 RT amino acid (aa) sites by Sanger sequencing, 36 of which had mutations that could lead to changes in B or T cell epitopes in the RT or S protein. The distribution of mutations was diverse in different sections within the RT region. Multiple mutations showed significant association with HBV DNA, HBsAg, HBeAg, age, and severity of liver fibrosis. Mutations at rt251, rt266, rt274, rt280, rt283, rt284, and rt286 were found most in the advanced liver disease (ALD) group by next-generation sequencing. The present study demonstrates that next-generation sequencing (NGS) was more suitable than Sanger sequencing to monitor NA^r mutations at a low rate in the treatment-naive patients, and that mutations in the RT region might be involved in the progression to ALD.

Potential resistant mutations within HBV reverse transcriptase sequences in nucleos(t)ide analogues-experienced patients with hepatitis B virus infection

This study was performed to analyze the potential resistant mutations within HBV reverse transcriptase (RT) sequences against nucleos(t)ide analogues (NA). HBV DNA RT region spanning from amino acid 169 to 250 was amplified and sequenced from 435 HBV patients who experienced NA treatment. Among study’s cohort, genotypes B and C infected patients were 55.9% and 44.1%, respectively. Mutations were recorded in 54.7% (238/435) patients at 22 positions. Genotype C displayed significant higher frequency of potential NA resistant mutations than genotype B (63.0% vs. 48.1%, P = 0.003). Moreover, eight mutation sites, including 180, 181, 191, 200, 202, 221, 229 and 224, in genotype C showed significant higher frequencies than in genotype B. In contrast, mutation at site 236 was more common in genotype B. Notably, 11 mutations at position 169, 202, 250, 173, 180, 200, 207, 214, 237, 242 and 245 coexisted with M204I or V. Substitutions at nine non-classical mutation sites (191, 207, 213, 218, 221, 224, 229, 238 and 242) were detected in patients with virological breakthrough. Particularly, tenofovir (TDF) resistance was observed in one patient undergoing TDF monotherapy and experienced several NA treatment before. These results might provide clinical useful information under antiviral therapy.

Hepatitis B virus rtA181T/sW172non-stop mutation may increase resistance fold to adefovir- and entecavir-resistant mutants compared to rtA181T/sW172* mutation

The study aimed to characterize rtA181T/sW172stop (*) and rtA181T/sW172non-stop mutations of hepatitis B virus (HBV). Total of 22,009 patients who visited Beijing 302 Hospital from 2007 to 2016 were enrolled. These patients all received nucleos(t)ide analogues (NAs) treatment and their serum samples were collected for sequence analysis of HBV reverse-transcriptase (RT) and S regions. The rtA181T mutation was detected in 5.37% (1182/22,009) of the patients' samples. The rtA181T-causative sW172*, sW172non-stop (sW172 L/S), and mixed sW172*/non-stop mutations occupied 82.91%, 7.70%, and 9.39%, respectively. The patients with rtA181T/sW172non-stop mutants had a higher HBV DNA level compared to those with rtA181T/sW172* mutants. 44.33% (524/1182) rtA181T-positive samples were detected with signature drug-resistant mutations, including 325 with adefovir-resistant mutation rtA181V/N236T, 57 with lamivudine-resistant mutation rtM204V/I, 99 with entecavir-resistant mutation rtM204V/I plus rt184/202/250 substitution(s), and 43 with multidrug-resistant mutation rtA181V/N236T + rtM204V/I ± rt184/202/250 substitution(s). The rtA181T/sW172non-stop mutation had a higher ratio of coexistence with adefovir-resistant mutation compared to rtA181T/sW172* mutation (42.86% vs. 24.59%, P < 0.05). rtA181T/sW172S + rtN236T and rtA181T/sW172L + rtN236T mutants exhibited higher HBV DNA production and adefovir resistance fold than that of rtA181T/sW172* + rtN236T mutant (98.02% and 85.5% vs. 42.1% in HBV DNA production, and 7.38-fold and 5.49-fold vs. 3.69-fold in half maximal effective concentration of wild-type strain); rtA181T/sW172L + rtS202G + rtM204V strain exhibited higher HBV DNA production and entecavir resistance fold than that of rtA181T/sW172* + rtS202G + rtM204V strain (50.98% vs. 34.49%, 524.00-fold vs. 69.33-fold). In conclusion, rtA181T/sW172non-stop mutation may increase resistance fold of adefovir- and entecavir-resistant mutants compared to rtA181T/sW172* mutation and might influence clinical presentation of NAs-treated patients.

No detectable resistance to tenofovir disoproxil fumarate in HBeAg+ and HBeAg- patients with chronic hepatitis B after 8 years of treatment

A major hurdle in the long-term treatment of chronic hepatitis B (CHB) patients is to maintain viral suppression in the absence of drug resistance. To date, no evidence of resistance to tenofovir disoproxil fumarate (TDF) has been observed. A cumulative evaluation of CHB patients who qualified for resistance surveillance over 8 years of TDF treatment was conducted. Patients in studies GS-US-174-0102 (HBeAg-) and GS-US-174-0103 (HBeAg+) were randomized 2:1 to receive TDF or adefovir dipivoxil (ADV) for 48 weeks followed by open-label TDF through year 8. Population sequencing of HBV pol/RT was attempted for all TDF-treated patients at baseline and, annually if viremic, at discontinuation, or with addition of emtricitabine. Overall, 88/641 (13.7%) patients qualified for sequence analysis at one or more time points. The percentage of patients qualifying for sequence analysis declined over time, from 9 to 11% in years 1-2 to <4% over years 3-8. Forty-one episodes of virologic breakthrough (VB) occurred throughout the study, with most (n=29, 70%) associated with nonadherence to study medication. Fifty-nine per cent of VB patients with an opportunity to resuppress HBV achieved HBV DNA resuppression. A minority of patients who qualified for sequencing had polymorphic (41/165, 24.8%) or conserved (17/165, 10.3%) site changes in pol/RT, with six patients developing lamivudine and/or ADV resistance-associated mutations. No accumulation of conserved site changes was detected. The long-term treatment of CHB with TDF monotherapy maintains effective suppression of HBV DNA through 8 years, with no evidence of TDF resistance or accumulation of conserved site changes.

A strong conservative tendency in HBV transcriptase (RT): a majority of natural RT mutations derived from the S gene

BACKGROUND & AIMS

Little is known about natural mutations in the HBV reverse transcriptase (RT) region. Our study aimed to characterize the natural RT mutation along the natural course of chronic Hepatitis B (CHB).

METHODS

Sixty CHB patients (immune-tolerant phase, IT, n = 20; immune-active phase, IA, n = 20 and inactive carriers phase, IC, n = 20) were selected from the Focal study, including 25 subjects with median 18 months follow-up. Mutations were evaluated at both RT and main S protein encoding region by clone-based sequencing.

RESULTS

The HBV RT quasispecies had significant lower heterogeneity in IT than IA and IC phases (P < 0.05), but not between IA and IC phases (P > 0.05). Limited heterogeneity over time was further confirmed in a longitudinal study. Locations of RT mutations were primarily located in the interdomians and the lowest in functional domains in each phase. Mutations in human leukocyte antigen (HLA) I epitopes (IT, 0.95%; IA, 1.31%; IC, 1.28%, P < 0.05) and HLA II epitopes (IT, 0.70%; IA, 0.90%; IC, 1.45%, P < 0.01) varied significantly over time. More frequent mutations were detected in the ORF of S gene from the same clones (HBsAg vs. RT: IT, 75 vs. 45; IA, 83 vs. 64; IC, 80 vs. 65). The majority of RT mutations were shared with genetic changes in the main S gene.

CONCLUSIONS

Our findings suggested that HBV RT showed a strong conservative tendency and a majority of their natural mutations were derived from the same genetic changes in the S gene.

Antiviral efficacy of entecavir versus entecavir plus adefovir for hepatitis B virus rtA181V/T mutants alone

BACKGROUND/AIMS

Hepatitis B virus (HBV) rtA181V/T mutants developed by long-term nucleos(t) ide analogue therapy are known to present cross-resistance for other nucleos (t) ide analogues, except entecavir (ETV). Some studies reported that HBV rtA181V/T mutants could induce cross-resistance to ETV and showed incomplete response as well as persistence of HBV DNA, despite rescue therapy by ETV. This study aimed to investigate the antiviral efficacy of ETV monotherapy and ETV plus adefovir (ADV) as rescue therapy for HBV rtA181V/T single mutation.

PATIENTS AND METHODS

A total of 30 patients who received ETV alone (1.0 mg/day, n = 16) or ETV plus ADV (10.0 mg/day, n = 14) over 48 weeks between April 2008 and October 2011 were enrolled. Virological, biochemical, and serological response at 48 weeks of rescue therapy were investigated retrospectively.

RESULTS

No significant difference in baseline characteristics was observed between the ETV group and the ETV plus ADV group. Virological response showed complete response (62.5 vs. 42.9%), partial response (6.3 vs. 28.6%), non-response (25.0 vs. 28.6%), and virological breakthrough (6.3 vs. 0%) in the two groups, respectively. Virological response did not statistically differ between both groups (P = 0.278). No significant difference in the mean reduction of serum HBV DNA and biochemical response was observed between both groups (4.3 ± 2.9 vs. 4.1 ± 1.8 log 10 IU/ml; P = 0.294 and 88.9 vs. 100%; P = 1.000, respectively). In addition, no significant difference in HBeAg loss or seroconversion was observed between the two groups (26.7 vs. 28.6%; P = 1.000).

CONCLUSIONS

ETV monotherapy and ETV plus ADV therapy were clinically effective and comparable as rescue therapy for HBV rtA181V/T mutants alone.

Tenofovir disoproxil fumarate has a substantial efficacy against multidrug-resistant strains of hepatitis B virus

BACKGROUND & AIMS

To evaluate the efficacy of tenofovir in chronic hepatitis B (CHB) patients with adefovir resistance (ADF-R) and suboptimal response to adefovir (ADF-S).

METHODS

Nucleos(t)ide analogue (NA)-naïve patients and patients with previous adefovir failure receiving tenofovir therapy for at least 6 months were included in the study. Biochemical and virological tests were obtained at baseline and 3-month intervals in the first year and every 6 months thereafter. The primary outcome measure was complete virological response (CVR) (HBVDNA < 20 IU/ml). CVR rates were calculated by Kaplan-Meier analysis, and a multivariate Cox proportional hazard model was generated to find out factors independently associated with CVR.

RESULTS

A total of 165 patients (118 men, mean age 42 ± 12, 64 HBeAg(+) ) were included in the study. There were 105 patients in NA-naïve, 32 patients in ADF-S and 28 patients in ADF-R groups. All patients in the ADF-R group had multidrug resistance patterns. Mean duration of tenofovir treatment was 29 ± 14 months. CVR rates in NA-naïve, ADF-S and ADF-R groups were 65% vs. 75% vs. 58% at 12th month, 77% vs. 87% vs. 79% at 24th month and 83% vs. 94% vs. 79% at 36th month respectively. According to multivariate Cox regression model, HBeAg positivity (HR = 0.56, 95%CI 0.36-0.86, P = 0.008), high baseline HBVDNA level (HR = 0.64, 95%CI 0.55-0.74, P < 0.001) and ADF-R (HR = 0.47, 95%CI 0.28-0.81, P = 0.006) were independent predictors for CVR. Seven patients encountered mild renal dysfunction and were managed by dose adjustments.

CONCLUSION

CVR rates during the follow-up show that tenofovir has a decreased, yet still potent in vivo efficacy against multidrug-resistant strains of HBV.

Performance of LigAmp assay for sensitive detection of drug-resistant hepatitis B virus minor variants in comparison with standard nucleotide sequencing

BACKGROUND AND OBJECTIVES

A virus population often exists as a complex mixture of genetic populations. Antiviral-resistant mutants could be circulating as minority variants in the mixed virus population that are not detected by standard sequencing methods. The role of minor drug-resistant variants and clinical outcome is slowly evolving and there is a need to employ sensitive methods for detection of minority variants that emerge as dominant species and subsequently affect the antiviral efficacy. This study was intended to develop a technique called the ligation amplification assay (LigAmp) to identify minor drug-resistant variants of hepatitis B virus (HBV).

METHODS

A LigAmp HBV assay was developed and clinical samples were tested from chronic hepatitis B subjects on antiviral treatment. Nucleotide sequencing of HBV reverse transcriptase (rt) region was performed and the results were compared with LigAmp assay. The performance of LigAmp assay was validated by clonal sequencing. Virological response was measured using HBV DNA levels and the results were correlated with antiviral-resistant mutations detected by sequencing and LigAmp assays.

RESULTS

A total of 80 reactions of LigAmp assay were performed for rtM204V and rtM204I (ATT) mutant detection. Samples were obtained from 40 chronic hepatitis B subjects. Among these subjects, rtM204V and rtM204I (ATT) mutations were identified by standard sequencing in 10 (25%) and 12 (30%) subjects, respectively. LigAmp detected both rtM204V and rtM204I (ATT) mutations in 13 (32.5%) subjects, rtM204I mutation in 12 (30%) subjects and rtM204V mutation in 1 (2.5%) subject, respectively. LigAmp detected primary resistant mutants in 69.4% of lamivudine non-responders while sequencing detected resistant mutations in only 55.6% subjects (p < 0.001).

CONCLUSIONS

This data shows significantly higher sensitivity of LigAmp for detection of minority rtM204V and rtM204I (ATT) mutations over standard sequencing. Therefore, LigAmp has potential clinical utility for appropriate monitoring and tailoring of HBV therapy.

Current and future antiviral drug therapies of hepatitis B chronic infection

Despite significant improvement in the management of chronic hepatitis B virus (HBV) it remains a public health problem, affecting more than 350 million people worldwide. The natural course of the infection is dynamic and involves a complex interplay between the virus and the host’s immune system. Currently the approved therapeutic regimens include pegylated-interferon (IFN)-α and monotherapy with five nucleos(t)ide analogues (NAs). Both antiviral treatments are not capable to eliminate the virus and do not establish long-term control of infection after treatment withdrawal. IFN therapy is of finite duration and associates with low response rates, liver decompensating and numerous side effects. NAs are well-tolerated therapies but have a high risk of drug resistance development that limits their prolonged use. The imperative for the development of new approaches for the treatment of chronic HBV infection is a challenging issue that cannot be over-sided. Research efforts are focusing on the identification and evaluation of various viral replication inhibitors that target viral replication and a number of immunomodulators that aim to restore the HBV specific immune hyporesponsiveness without inducing liver damage. This review brings together our current knowledge on the available treatment and discusses potential therapeutic approaches in the battle against chronic HBV infection.

Microarray-based genotyping and detection of drug-resistant HBV mutations from 620 Chinese patients with chronic HBV infection

Background

Research has shown that hepatitis B virus (HBV) genotypes are closely linked to the clinical manifestations, treatment, and prognosis of the disease.

Objective

To study the association between genotype and drug-resistant HBV mutations in 620 Chinese patients with chronic HBV infection.

Methods

HBV DNA levels were determined using real-time quantitative PCR in plasma samples. Microarrays were performed for the simultaneous detection of HBV genotypes (HBV/B, C, and D) and drug-resistance-related hotspot mutations. A portion of the samples analyzed using microarrays was selected randomly and the data were confirmed using direct DNA sequencing.

Results

Most samples were genotype C (471/620; 76.0%), followed by genotype B (149/620; 24.0%). Among the 620 patient samples, 17 (2.7%) had nucleotide analogs (NA) resistance-related mutations. Of these, nine and eight patients carried lamivudine (LAM)-/telbivudine (LdT)-resistance mutations (rtL180M, rtM204I/V) and adefovir (ADV)-resistance mutations (rtA181T/V, rtN236T), respectively. No patients had both lamivudine (LAM)- and either adefovir (ADV) or entecavir (ETV) resistance mutations. Additionally, out of the 620 patient samples, 64.0% (397/620) were also detected with the precore stop-codon mutation (G1896A) by microarray assay.

Conclusion

The results of the current study revealed that the prevalence of nucleotide analogs (NA)-resistance in Chinese hospitalized HBV-positive patients was so low that intensive nucleotide analogs (NA)-resistance testing before nucleotide analog (NA) treatment might not be required. In addition, the present study suggests that chronic HBV patients with genotype C were infected with fitter viruses and had an increased prevalence of nucleotide analogs (NA)-resistance mutations compared to genotype B virus.

Variations and mutations in the hepatitis B virus genome and their associations with clinical characteristics

Hepatitis B virus (HBV) infection is major global issue, because chronic HBV infection is strongly associated with liver cancer. HBV spread worldwide with various mutations and variations. This variability, called quasispecies, is derived from no proof-reading capacity of viral reverse transcriptase. So far, thousands of studies reported that the variety of genome is closely related to the geographic distribution and clinical characteristics. Recent technological advances including capillary sequencer and next generation sequencer have made in easier to analyze mutations. The variety of HBV genome is related to not only antigenicity of HBs-antigen but also resistance to antiviral therapies. Understanding of these variations is important for the development of diagnostic tools and the appropriate therapy for chronic hepatitis B. In this review, recent publications in relation to HBV mutations and variations are updated and summarized.

The rtA181S mutation of hepatitis B virus primarily confers resistance to adefovir dipivoxil

The study aimed to clarify clinical significance of hepatitis B virus (HBV) rtA181S mutation in Chinese HBV-infected patients. A total of 18 419 patients with chronic HBV infection from Beijing 302 Hospital were investigated. HBV complete reverse transcriptase region of polymerase was screened by direct sequencing, and the results were verified by clonal sequencing. Replication-competent mutant and wild-type HBV genomic amplicons were constructed and transfected into the HepG2 cells and cultured in the presence or absence of serially diluted nucleos(t)ide analogues. Intracellular HBV replicative intermediates were quantitated for calculating the 50% effective concentration of the drug (EC(50)). The rtA181S was detected in 98 patients with 12 kinds of mutational patterns. Genotype C and genotype B HBV infection occupied 91.8% and 8.2% in rtA181S-positive patients, in contrast to 84.6% and 15.4% in rtA181S-negative patients (P < 0.01). All rtA181S-positive patients had received nucleos(t)ide analogues. rtA181S was detected in multiple patients with virologic breakthrough. Phenotypic analysis of patient-derived viral strains showed that rtA181S, rtA181S+N236T, rtN236T and rtA181V strains had 68.5%, 49.9%, 71.4% and 66.2% of natural replication capacity of wild-type strain, and 3.7-fold, 9.8-fold, 7.9-fold and 5.6-fold increased EC(50) to adefovir dipivoxil (ADV). The rtA181S strain remained susceptible to lamivudine, entecavir and tenofovir, and ADV susceptibility was restored after the mutation was eliminated through site-directed mutagenesis. Rescue therapy with entecavir or combination therapy was effective in rtA181S-related ADV-refractory patients. The rtA181S mutation confers moderate resistance to ADV. It could be induced by either lamivudine or ADV and contribute ADV treatment failure.

Antiviral efficacy of adefovir dipivoxil in the treatment of chronic hepatitis B subjects from Indian subcontinent

Adefovir is one of the therapeutic options for the treatment of chronic hepatitis B. A total of 30 adefovir-experienced subjects with the median treatment duration of 12 (interquartile range (IQR) 6-18) months were studied. Virological response was measured by hepatitis B virus deoxyribonucleic acid (HBV DNA) levels. HBV reverse transcriptase (rt) domains were sequenced for the identification of resistance mutations. Among the 30 subjects, two (7%) showed virological response and 19 (63%) were non-responders. The virological response for the remaining nine (30%) subjects was not determined. On sequence analysis, two subjects were identified with rtI169L and rtA181V mutation after 9 months and 18 months of adefovir treatment, respectively. Though the frequencies of adefovir resistance mutations are low, a large majority of subjects showed non-response. Therefore, adefovir in the management of HBV should be used judiciously.

Clinical implications of hepatitis B virus mutations: Recent advances

Hepatitis B virus (HBV) infection is a major cause of acute and chronic hepatitis, and of its long-term complications. It is the most variable among DNA viruses, mostly because of its unique life cycle which includes the activity of error-prone enzyme, reverse transcriptase, and the very high virion production per day. In last two decades, numerous research studies have shown that the speed of disease progression, reliability of diagnostic methods and the success of antiviral therapy and immunization are all influenced by genetic variability of this virus. It was shown that mutations in specific regions of HBV genome could be responsible for unwanted clinical outcomes or evasion of detection by diagnostic tools, thus making the monitoring for these mutations a necessity in proper evaluation of patients. The success of the vaccination programs has now been challenged by the discovery of mutant viruses showing amino acid substitutions in hepatitis B surface antigen (HBsAg), which may lead to evasion of vaccine-induced immunity. However, the emergence of these mutations has not yet raised concern since it was shown that they develop slowly. Investigations of HBV genetic variability and clinical implications of specific mutations have resulted in significant advances over the past decade, particularly in regard to management of resistance to antiviral drugs. In the era of drugs with high genetic barrier for resistance, on-going monitoring for possible resistance is still essential since prolonged therapy is often necessary. Understanding the frequencies and clinical implications of viral mutations may contribute to improvement of diagnostic procedures, more proper planning of immunization programs and creating the most efficient therapeutic protocols.

Nucleoside/nucleotide analog inhibitors of hepatitis B virus polymerase: mechanism of action and resistance

Hepatitis B virus (HBV) polymerase and human immunodeficiency virus (HIV) reverse transcriptase are structurally related. However, the HBV enzyme has a protein priming activity absent in the HIV enzyme. Approved nucleoside/nucleotide inhibitors of the HBV polymerase include lamivudine, adefovir, telbivudine, entecavir and tenofovir. Although most of them target DNA elongation, guanosine and adenosine analogs (e.g. entecavir and tenofovir, respectively) also impair protein priming. Major mutational patterns conferring nucleoside/nucleotide analog resistance include the combinations rtL180M/rtM204(I/V) (for lamivudine, entecavir, telbivudine and clevudine) and rtA181V/rtN236T (for adefovir and tenofovir). However, development of drug resistance is very slow for entecavir and tenofovir. Novel nucleoside/nucleotide analogs in advanced clinical trials include phosphonates similar to adefovir or tenofovir, and new tenofovir derivatives with improved pharmacological properties.

Screening and identification of a novel adefovir dipivoxil resistance associated mutation, rtN236V, of HBV from a large cohort of HBV-infected patients

BACKGROUND

The study aimed to clarify whether rtN236V mutation of HBV derived from adefovir dipivoxil (ADV)-refractory patients was associated with drug resistance.

METHODS

A total of 18,419 patients from Beijing 302 Hospital were investigated. HBV complete reverse transcriptase region of polymerase was screened by direct sequencing and verified by clonal sequencing if necessary. Replication-competent wild-type and mutant HBV genomic amplicons were constructed, transfected into HepG2 cells and cultured in the presence or absence of serially diluted nucleoside/nucleotide analogues. Intracellular HBV replicative intermediates were quantitated for calculating the 50% effective concentration of drug.

RESULTS

rtN236V was detected in six ADV-refractory patients; signature ADV-resistant mutations rtA181V and rtN236T were detected in 1,311 patients. rtN236V mutants emerged predominantly with virological breakthrough in the clinical course of the six patients. Phenotypic analysis of the mutants from two patients was performed. rtN236V mutants from patient 1 and patient 2 exhibited 3.90-fold and 3.10-fold decreased susceptibility to ADV, respectively, compared to the wild-type virus; by contrast, rtN236T mutants from the patients had 4.50-fold and 4.75-fold decreased susceptibility, respectively. Both mutants had a relatively lower viral replication capacity compared to wild-type virus in the absence of antivirals and remained susceptible to lamivudine, entecavir and tenofovir disoproxil fumarate. In clinical practice, switching to entecavir rescue therapy suppressed HBV DNA to an undetectable level and normalized alanine aminotransferase level for both patients.

CONCLUSIONS

rtN236V was a novel infrequently occurring ADV-resistance-associated mutation. It conferred a moderate resistance to ADV with relatively lower natural replication capacity.

Mutation profiling of the hepatitis B virus strains circulating in North Indian population

AIMS

The aim of this study was to investigate the genomic mutations in the circulating Hepatitis B virus strains causing infection in the Indian population. Further, we wanted to analyze the biological significance of these mutations in HBV mediated disease.

METHODS

222 HBsAg positive patients were enrolled in the study. The genotype and mutation profile was determined for the infecting HBV isolate by sequencing overlapping fragments. These sequences were analyzed by using different tools and compared with previously available HBV sequence information. Mutation Frequency Index (MFI) for the Genes and Diagnosis group was also calculated.

RESULTS

HBV Genotype D was found in 55% (n = 121) of the patient group and genotype A was found in 30% (n = 66) of samples. The majority (52%) of the HBV-infected individuals in the present study were HBeAg-negative in all the age groups studied. Spontaneous drug associated mutations implicated in resistance to antiviral therapy were also identified in about quarter of our patients, which is of therapeutic concern. The MFI approach used in the study indicated that Core peptide was the most conserved region in both genotypes and Surface peptide had highest mutation frequency. Few mutations in X gene (T36A and G50R) showed high frequency of association with HCC. A rare recombinant strain of HBV genotype A and D was also identified in the patient group.

CONCLUSIONS

HBV genotype D was found out to be most prevalent. More than half of the patients studied had HBeAg negative disease. Core region was found to be most conserved. Drug Associated mutations were detected in 22% of the patient group and T36A and G50R mutations in X gene were found to be associated with HCC.

Analysis of potential antiviral resistance mutation profiles within the HBV reverse transcriptase in untreated chronic hepatitis B patients using an ultra-deep pyrosequencing method

The potential antiviral resistance mutations within hepatitis B virus (HBV) reverse transcriptase (RT) region for nucleos(t)ide analogues (NA) are not well known. Especially, the effect of pre-existing antiviral drug resistance mutations in untreated patients in comparison to the resistance developed after treatment is not still clear. Sixteen naive chronic hepatitis B patients were studied. None of the patients had received NA treatment prior to the serum samples being collected. Forty-two potential NA resistance (NAr) mutation sites were screened by ultra-deep pyrosequencing (UDPS). After therapy, mutations conferring treatment resistance were detected by LiPA. Serum samples taken before treatment showed no classic primary or compensatory/secondary drug resistance mutations. However, NAr mutations found in 6 isolates (37.5%) involved 7 positions including rtL91I, rtT128I, rtQ215P, rtF221Y, rtN238D, rtC256S, and rtI266G. Substitutions at 3 NAr mutation sites (rtT128I, rtN238D, and rtC256S) were detected in 3 unresponsive patients developing drug resistance after NA treatment. One patient with rtI266G mutation also developed drug resistance after lamivudine (LAM) therapy. However, the relationship between rtI266G mutation and NA drug resistance was not previously reported. These results suggest that association of potential mutations besides the primary and secondary/compensatory resistance mutations should be investigated. Investigation of NAr mutations before treatment may be important for the success of the treatment.

Rapid detection of hepatitis B virus variants associated with lamivudine and adefovir resistance by multiplex ligation-dependent probe amplification combined with real-time PCR

Drug-resistant mutations of hepatitis B virus (HBV) are the major obstacles to successful therapy for chronic hepatitis B infection. Although there are many methods for detecting the antiviral drug-resistant mutations of HBV, their applications are restricted because of their shortcomings, such as low sensitivity, the time required, and the high cost. For this study, a multiplex ligation-dependent probe real-time PCR (MLP-RT-PCR) method was developed to simultaneously detect lamivudine (LAM)- and adefovir (ADV)-resistant HBV mutants (those with the mutations rtM204V/I, rtA181V/T, and rtN236T). The new method combined the high-throughput nature of multiplex ligation-dependent probe amplification (MLPA) with the rapid and sensitive detection of real-time PCR. In this report, MLP-RT-PCR was evaluated by detecting drug-resistant mutants in 116 patients with chronic hepatitis B infection. By MLP-RT-PCR analysis, LAM-resistant mutations were detected in 41 patients (35.3%), ADV-resistant mutations were detected in 17 patients (14.7%), and LAM- and-ADV-resistant mutations were detected in 5 patients (4.3%). Based on the results of MLP-RT-PCR, the mutations rtM204V, rtM204I, rtA181T, rtA181V, and rtN236T were 95.7% (111/116 patients), 98.3% (114/116 patients), 99.1% (115/116 patients), 98.3% (114/116 patients), and 99.1% (115/116 patients) concordant, respectively, with those of direct sequencing. The MLP-RT-PCR assay was more sensitive than direct sequencing for detecting mutations with low frequencies. Four samples containing the low-frequency (<10%) mutants were identified by MLP-RT-PCR and further confirmed by clonal sequencing. MLP-RT-PCR is a rapid and sensitive method that enables the detection of multidrug-resistant HBV mutations in clinical practice.

Characterization of antiviral resistance mutations among the Eastern Indian Hepatitis B virus infected population

Background

Antiviral therapy using nucleos(t)ide analogues (NAs) is an effective control measure of chronic hepatitis B virus (HBV) infection; however they need long term treatment. Presence of drug-resistance mutations may get in the way of the efficacy of antiviral therapy. Our study was aimed at defining the prevalence of HBV drug-resistance in HBVrt region in a population of 147 HBsAg positive patients.

Findings

HBV/D has shown multiple types of HBVrt mutations both among treatment naïve (65.0%, 13 of 20 HBV/D) and treated patients (56.2%, 9 of 16 HBV/D). In additional, several mutations, with a suggested role in drug resistance, were detected among the treatment naïve as well as the treated patients. The mutations reported to be involved in reduction of drug effectiveness, was common among non-responders to therapy as well as among the naïve patients. Notably, classical antiviral resistance mutations (rtL80I/V-rtI169T-rtV173L-rtL180M-rtA181T/V/S-rtT184A/S/G/C-rtA194T-rtS202C /G/I -rtM204V/I-rtN236T-rtM250V) were not detected.

Conclusion

The prevalence of putative NAr mutations among non responders to therapy suggests that they might have role in reduced efficacy of currently available antivirals and requires further investigations.

Impact of rtI233V mutation in hepatitis B virus polymerase protein and adefovir efficacy: Homology modeling and molecular docking studies

Adefovir is an adenosine analogue approved by the Food and Drug Administration for the treatment of chronic hepatitis B. Mutations occurring in the hepatitis B virus (HBV) reverse transcriptase (rt) domains are shown to confer resistance to antiviral drugs. The role of the rtI233V mutation and adefovir resistance remains contradictory. In this study, it was attempted to evaluate the impact of putative rtI233V substitution on adefovir action by homology modeling and docking studies. The HBVrt nucleotide sequence containing rtI233V mutation was obtained from the treatment-naive chronic hepatitis B subject. The three dimensional model of HBV polymerase/rt was constructed using the HIV-1rt template (PDB code: 1RTD A) and the model was evaluated by the Ramachandran plot. Autodock was employed to dock the HBV polymerase/rt and adefovir. The modelled structure showed the amino acid rtI233 to be located away from the drug interactory site. The substitution of isoleucine to valine did not appear to affect the catalytic sites of the protein. In addition, it does not alter the conformation of bent structure formed by residues 235 to 240 that stabilizes the binding of dNTPs. Therefore, it was predicted that rtI233V substitution may not independently affect the antiviral action of adefovir and incoming dNTP binding.

Prevalence and significance of Hepatitis B reverse transcriptase mutants in different disease stages of untreated patients

AIMS

Hepatitis B virus (HBV) reverse transcriptase (RT) mutants, which have not been well characterized according to different disease stages. This study aimed to characterize the profiles of naturally occurring mutations in the HBV RT region and their associated clinical outcomes.

METHODS

HBV RT region mutations and genotypes were determined by PCR-direct sequencing and compared with p-distance model.

RESULTS

Among 467 consecutive eligible patients (262 chronic hepatitis B patients, 105 cirrhotic patients and 100 hepatocellular carcinoma patients), the nucleos(t)ide analogues-related mutations (rtI169T, rtV173L, rtL180M, rtA181T, rtS202C, rtM204I/V, rtN236T) were found. The p-distance value reached a peak in the age of 20-30 years in the CHB patients and in the age of 40-45 years in the cirrhotic patients and hepatocellular carcinoma patients. The naturally occurring mutation, rtS106C mutation was higher in chronic hepatitis B patients (14/100, 14.0%) and cirrhotic patients (14/100, 14.0%) than that in hepatocellular carcinoma patients (4/100, 4.0%, P = 0.013). And the rtD134E/G/N/S mutations were also higher in chronic hepatitis B patients (22/100, 22.0%) and cirrhotic patients (21/100, 21.0%) than that in hepatocellular carcinoma patients (10/100, 10.0%, P = 0.021 and P = 0.032 respectively). The mutation frequencies in A-B interdomain were higher in cirrhotic patients (101/1900, 5.3%) than that in hepatocellular carcinoma patients (68/1900, 3.6%) (P = 0.009).

CONCLUSIONS

The nucleos(t)ide analogues-related mutations do exist in treatment naive patients with different disease stages. rtS106C, rtD134E/G/N/S and A-B interdomain mutations may be associated with necro-inflammation, immune response and cirrhosis development at ages older than 40.

Comparison of the Mechanisms of Drug Resistance among HIV, Hepatitis B, and Hepatitis C

Human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) are the most prevalent deadly chronic viral diseases. HIV is treated by small molecule inhibitors. HBV is treated by immunomodulation and small molecule inhibitors. HCV is currently treated primarily by immunomodulation but many small molecules are in clinical development. Although HIV is a retrovirus, HBV is a double-stranded DNA virus, and HCV is a single-stranded RNA virus, antiviral drug resistance complicates the development of drugs and the successful treatment of each of these viruses. Although their replication cycles, therapeutic targets, and evolutionary mechanisms are different, the fundamental approaches to identifying and characterizing HIV, HBV, and HCV drug resistance are similar. This review describes the evolution of HIV, HBV, and HCV within individuals and populations and the genetic mechanisms associated with drug resistance to each of the antiviral drug classes used for their treatment.

Factors influencing inadequate or suboptimal response to adefovir with or without genotypic resistance

The aim of the study was to explore the factors in inadequate-responders to treatment with adefovir (ADV) with or without genotypic resistance. The reverse-transcriptase (RT) gene of hepatitis B virus (HBV) was sequenced in 161 patients with inadequate-response to ADV and analyzed for HBV genotypes using a phylogenetic approach. Seventy-six patients (47.2%) were found to carry the rtA181V/T/S or rtN236T residue substitution, and most of them had viral rebound. In the patients with viral rebound and ADV genotypic resistance, 19 (25.7%) showed rtA181V/T/S + rtN236T substitutions. In the other patients, it was found that HBV genotypes and cirrhosis influenced the selection of ADV-resistant positions by univariate analysis and multiple logistic regression analysis. The rtN236T was more frequent in patients with genotype B, and the rtA181V/T/S was more common in patients with genotype C (χ(2)  = 11.543, P = 0.001). Multiple logistic regression analysis showed that the rtN236T and time resistant strains occurred during ADV-treatment were statistically significant for influencing rtA181 variation types (P = 0.007 and P = 0.024, respectively), and the occurrence of rtA181T was found to be significantly earlier than rtA181V. In conclusion, genotypic resistance was not detected in the majority of primary nonresponders to ADV when compared to the patients with viral rebound. The different HBV genotypes influence the selection of ADV-resistant mutation positions. The rtA181T occurs more frequently in patients with the rtN236T and it occurs earlier when compared to the rtA181V. These findings suggest that early judgment of adequate response and making a decision for interference in patients treated with ADV are of importance in clinical practice.

Analysis of mutations in the reverse transcriptase domain of HBV polymerase in adefovir-resistant HBV patients

AIM: To study the characteristics of the B domain of the HBV polymerase gene in adefovir-resistant HBV patients.

METHODS: One hundred and seven patients with chronic hepatitis B treated with adefovir (ADV) (including 73 ADV-naïve patients and 34 LAM-resistant patients) at our hospital were selected. The B-C regions of the RT and S genes were amplified by PCR using specific primers flanking these regions. The PCR products were directly analyzed by sequencing. The differences in nucleotide and amino acid sequences and mutation patterns of the RT region were classified using Chromas2.0 software. HBV genotypes were analyzed using Clustalx1.81.msw.

RESULTS: Of the 107 patients, 36 had rtA181V mutation, 43 had rtA181T, 47 had rtN236T, 20 had rtM204I/V ± rtL180M, and 12 had other ADV - related mutations. In ADV-naïve patients, 27 (36.99%) had rtA181V/T, 14 (19.18%) had rtN236T, 28 (38.36%) had rtA181V/T + rtN236T, and 4 (5.48%) had other mutations. In LAM-resistant patients, 21 (61.76%) had rtA181V/T, 2 (5.88%) had rtN236T, 3 (8.82%) had rtA181V/T + rtN236T, and 8 (23.53%) had other mutations. rtA181T/V and rtN236T mutations were not detected in 12 patients, but they had rtA181S/C (2 cases), rtV214I/A (3 cases), rtQ215H (1 case), or rtH/N238S/T/R/A/K (6 cases), which are ADV resistance-related mutations.

CONCLUSION: The major ADV resistance-related mutations are rtA181T/V and rtN236T in ADV-naïve patients, and rtA181V/T in LAM-resistant patients.

Discrepancy of potential antiviral resistance mutation profiles within the HBV reverse transcriptase between nucleos(t)ide analogue-untreated and -treated patients with chronic hepatitis B in a hospital in China

Little is known about the discrepancy of the potential antiviral resistance mutation profiles within the hepatitis B virus (HBV) reverse transcriptase (RT) between nucleos(t)ide analogue (NA)-untreated and -treated patients with chronic hepatitis B. Full-length HBV RT sequences from 59 NA-treated and 105 NA-untreated Chinese patients were amplified and sequenced. Forty-two potential NA resistance (NAr) mutation sites were screened within these 164 RT sequences. The NAr mutation prevalence and frequency in the NA-treated group were significantly higher than those in the NA-untreated one (P < 0.001, respectively). The classical primary drug resistance and secondary/compensatory mutations were only detected at seven sites (rtL80, rtI169, rtL180, rtA181, rtT184, rtM204, and rtN236) in NA-treated patients. The non-classical putative NAr and pre-treatment mutations were observed at 22 sites (rtT38, rtN/S53, rtL82, rtL/I91, rtN/Y124, rtH126, rtT128, rtN/D134, rtN139, rtR153, rtV191, rtV207, rtS213, rtV214, rtE218, rtY/F221, rtV/I224, rtL229, rtI233, rtN/H238, rtR242, and rtS/C256) in both groups. Substitutions at seven non-classical mutation sites were of interest due to either detection only in patients with virologic breakthrough (rtL82 and rtV214), or potential ties with HBV genotypes (rtV191 and rtL229), or coexistence with rtM204I/V (rtL229), or increased mutation trends after NA-treatment (rtT128, rtV207, and rtN/H238). In conclusion, NA treatment not only constitutes a major selection factor for the primary and secondary/compensatory NAr mutations but also drives the changes of some of the putative NAr mutation sites, most of which are the genotype-independent RT sites (rtL82, rtT128, rtV191, rtV207, rtV214, rtL229, and rtN/H238). Their antiviral resistance potential calls for further investigations.

Antiviral therapies: focus on hepatitis B reverse transcriptase

Hepatitis B virus (HBV) is the etiologic agent of mankind's most serious liver disease. While the availability of a vaccine has reduced the number of new HBV infections, the vaccine does not benefit the approximately 350 million people already chronically infected by the virus. Most of the drugs approved by the FDA for the treatment of hepatitis B target the reverse transcriptase (RT or P gene product) and are nucleoside RT inhibitors (NRTIs) that suppress viral replication. However, prolonged monotherapies directed against a single target result in the emergence of viral resistance. HBV genotypic differences affect NRTI resistance, and because the reading frames of the S (surface antigen) and P genes partially overlap, genomic differences that affect the surface of the virus may also alter the viral polymerase sequence, function and drug susceptibility. The scope of this review is to assess the effects of HBV genotypic variation on the development of drug resistance to NRTIs. Some RT residues that vary among different genotypes are in the vicinity of residues that mutate and give rise to NRTI resistance. Interactions between these amino acids can help explain the effect of HBV genotype on the development of NRTI resistance during antiviral therapies, and might help in the design of improved therapeutic strategies.

The rtL229 substitutions in the reverse transcriptase region of hepatitis B virus (HBV) polymerase are potentially associated with lamivudine resistance as a compensatory mutation

BACKGROUND

It remains unclear whether hepatitis B virus (HBV) reverse-transcriptase (RT) rtL229 substitutions influence HBV drug resistance.

OBJECTIVE

The study was to investigate the association of HBV rtL229 substitutions with viral resistance to lamivudine (LAM).

STUDY DESIGN

Entire HBV RT genes were amplified by nested PCR and sequenced from sera of 6000 nucleos(t)ide analog-experienced patients with chronic HBV infection. The incidence and clinic relevance of rtL229 substitutions were analyzed. Replication-competent viral amplicons which harbored HBV genomes of wild-type, rtM204I, or rtM204I in conjunction with various rtL229 substitutions (rtL229F/W/M/V) were constructed. The amplicons were transfected into HepG2 cells for phenotyping of replication capacity and susceptibility to nucleos(t)ide analogs.

RESULTS

The rtL229 substitutions were detected in 6.57% (394/6000) of patients. Individual substitution incidences were 2.77%, 0.97%, 0.83% and 0.55% for rtL229V, rtL229F, rtL229M and rtL229W, respectively. The incidence of rtL229 substitutions was significantly higher in LAM-experienced patients (341/4220, 8.1%) than in LAM-naïve patients (53/1780, 3.0%), and were independently associated with genotypic LAM resistance (77.9% vs. 21.2%, OR 8.806, 95%CI 6.345-12.223) and low viral replication (HBV DNA <1000IU/mL) (4.60% vs. 24.2%, OR 0.478, 95%CI 0.254-0.898). Representative cases follow-up showed that rtL229F developed subsequent to rtM204I emergence during LAM treatment and regressed with rtM204I after LAM withdrawal. Functionally, rtL229F did not confer reduced susceptibility to LAM, but could restore replication capacity of rtM204I strain.

CONCLUSION

The rtL229 substitutions were potentially associated with LAM resistance in Chinese patients and rtL229F had characteristics of a compensatory mutation of rtM204I mutant.

Large-scale survey of naturally occurring HBV polymerase mutations associated with anti-HBV drug resistance in untreated patients with chronic hepatitis B

Drug resistance is a major limitation for the long-term efficacy of antiviral therapy with nucleos(t)ide analogues (NAs) in chronic hepatitis B (CHB). Antiviral resistance mutations may pre-exist in the overall viral population of untreated patients. We aimed to assess the prevalence of such hepatitis B virus (HBV) variants in a large cohort of NAs-naïve patients with CHB and to explore possible association with viral and host variables. Serum samples from 286 NAs-naïve consecutive patients with CHB were tested for serum HBV-DNA, and 255 of them having HBV-DNA > 1000 IU/mL were further analysed for drug resistance mutations by INNO-LiPA HBV DRv2/v3. NAs-naïve patients analysed were mainly men (73%), Caucasians (85%), hepatitis B e Antigen (HBeAg) negative (79%) and genotype D (69%), with a mean age of 43.2 ± 13.4 years. HBV mutations associated with antiviral drug resistance were detected in 13 (5%) patients: three patients infected with HBV genotype C had the rtM204V + rtL180M mutations associated with lamivudine (LMV) resistance. Four patients had the rtI233V mutation that may reduce sensitivity to adefovir, and three patients had the rtM250L/V mutation typical of entecavir resistance. LMV compensatory mutations rtL80V and rtV173L were seen in two and one patients, respectively. No relationship was seen between presence of resistant or compensatory mutations and HBV-DNA levels, HBeAg/anti-HBe status or previous IFN therapy. These results confirm that HBV mutations, which confer resistance against currently available anti-HBV NAs, may already exist in patients who have never received the drug.

Profile of HBV antiviral resistance mutations with distinct evolutionary pathways against nucleoside/nucleotide analogue treatment among Chinese chronic hepatitis B patients

BACKGROUND

Antiviral drug-resistant HBV mutants under a variety of treatment protocols are complex and only partly understood. Here, a population-based cross-sectional study was performed to analyse the profile of resistance mutations in distinct evolutionary pathways refractory to different nucleoside/nucleotide analogues (NAs).

METHODS

Serum samples of 199 chronic hepatitis B patients undergoing NA treatment from five hospitals in four northern cities of China were obtained between January 2007 and July 2009. The genotypic resistance of HBV in these samples was characterized. The full-length HBV reverse transcriptase region was amplified, sequenced and analysed with particular focus on the following NA-resistant changes: rtL80, rtI169, rtV173, rtL180, rtA181, rtT184, rtA194, rtS202, rtM204, rtN236 and rtM250.

RESULTS

Among 199 HBV isolates, 30 (15.08%) and 169 (84.92%) were genotypes B and C, respectively, and 65 (32.66%) harboured NA-resistant mutations. The prevalence of mutations at rtM204 was 34.33% in 134 patients who had received or who had been exposed to lamivudine-based therapy. Five cases of rtN236 mutations were detected exclusively among 75 patients receiving adefovir-dipivoxil-based therapies. A total of 19 cases of multidrug resistance rtA181 mutations were observed in those with lamivudine-, adefovir-dipivoxil- or telbivudine-based treatment (186 cases), but not in those undergoing entecavir treatment (13 cases). Mutations were not found at rtI169, rtT184, rtA194 or rtS202. rtM204 mutations (27 rtM204I, 15 rtM204V and 5 rtM204I/V cases) were detected at the highest frequency among 65 mutants (72.30% [47/65]) and found to display 16 combination mutation patterns, in which rtM204I and rtM204V were significantly associated with rtL80I/V and rtL180M, respectively (P<0.01).

CONCLUSIONS

One-third of the studied population harboured NA-resistant HBV with complicated mutation patterns. Monitoring HBV genotypic resistance mutation markers and patterns is therefore shown to be beneficial for optimizing antiviral therapies and for avoiding clinical deterioration.

Genotypic resistance profile of hepatitis B virus (HBV) in a large cohort of nucleos(t)ide analogue-experienced Chinese patients with chronic HBV infection

The study investigated the hepatitis B virus (HBV) genotypic resistance profile in 1803 nucleos(t)ide analogue (NA)-experienced Chinese patients with chronic HBV infection. Serum HBV DNA was extracted, and the reverse transcriptase region was analysed by a high-sensitive direct PCR sequencing and verified by clonal sequencing if necessary. Drug-resistant mutations were detected in 560 of the 1803 patients, including 214 of 490 patients who received lamivudine (LAM), 35 of 428 patients who received adefovir (ADV), five of 18 patients who received telbivudine and 306 of 794 patients who received various sequential/combined NA therapies. ADV-resistant mutations were detected in 36 of 381 patients who received LAM and then switched-to ADV in contrast to one of 82 patients who received ADV add-on LAM. Entecavir (ETV)-resistant mutations were detected not only in LAM- and ETV-treated patients but also in LAM-treated ETV-naïve patients. Double mutations rtM204I and rtL180M were detected more frequently in genotype C than in genotype B virus, and patients infected with this mutant had higher alanine transaminase levels than those infected with mutant containing the rtM204I substitution alone. Multidrug-resistant HBV strains were identified in eight patients, including two novel strains with mutational patterns rtL180M + A181V + S202G + M204V + N236T and rtL180M + S202G + M204V + N236T. The results provide new information on HBV genotypic resistance profiles in a large cohort of Chinese patients with chronic HBV infection and may have important clinical implication for HBV drug resistance management in China.

Antiviral resistance mutations and genotype-associated amino acid substitutions in treatment-naïve hepatitis B virus-infected individuals from the Indian subcontinent

BACKGROUND/AIMS

Antiviral resistance is a major challenge to the treatment currently available for hepatitis B virus (HBV). In this study, mutations that may affect the antiviral efficacy in treatment-naïve HBV-infected individuals were analyzed.

METHODS

Ninety-seven treatment-naïve HBV-infected individuals were included in this study. HBV reverse transcriptase (rt) domains were sequenced and nucleotide differences were compared to GenBank wild-type sequences. Furthermore, HBV genotypes, subgenotypes and subtypes were determined by analyzing surface gene sequences.

RESULTS

An adefovir-related rtI233V mutation was identified in 4 subjects. The rtS213T lamivudine and entecavir refractory mutant was presented in 3 individuals. Altogether, drug-related, atypical and novel HBVrt amino acid substitutions were seen in 73 positions. The HBV genotypes A, C, D and G were depicted in 15, 21, 60 and 1 individuals, respectively. There were 17 HBVrt amino acid substitutions that are associated with certain genotypes of HBV. Mutations in HBVrt corresponded to established surface gene mutations in 9 patients.

CONCLUSION

This data shows that antiviral-resistant HBV strains do exist in treatment-naïve individuals in this region. Further studies are essential to characterize the role of HBVrt amino acid substitutions in response to anti-HBV therapy.

Safety and efficacy of entecavir for the treatment of chronic hepatitis B

Entecavir is a cyclopentyl deoxyguanosine analog that was approved for the treatment of the hepatitis B virus (HBV) in 2005. In Phase III trials, it showed potent HBV suppression with drops of 6- to 7-log copies/mL in HBV DNA at 1 year. In addition, rates of genotypic resistance in nucleos(t)ide-naïve patients are low, reaching only 1.2% after 6 years. Safety and efficacy have been established in compensated cirrhosis and HIV-coinfected patients. Studies in decompensated cirrhosis also show efficacy. Because of potent viral suppression and a large genetic barrier to resistance, entecavir is now a first-line choice in most HBV treatment guidelines and has become an integral part of the HBV treatment armamentarium.

Variable influence of mutational patterns in reverse-transcriptase domain on replication capacity of hepatitis B virus isolates from antiviral-experienced patients

BACKGROUND

Various mutations in reverse-transcriptase domain (RT) of hepatitis B virus (HBV) polymerase may develop during antiviral therapy. The influence of these mutational patterns on HBV replication capacity remains to be fully clarified.

METHODS

Nine clones containing complete HBV genomes were isolated from 5 patients with chronic hepatitis B who had received antiviral treatment. Viral replication capacity was measured by quantitation of HBV replicative intermediates using vector-free transfer of paired mutant and wild-type HBV genomes into human hepatoma cell lines HepG2 and Huh7. HBV pgRNA was quantitated by real-time PCR and Southern blot analysis.

RESULTS

A real-time PCR assay with high sensitivity and small variation was developed for quantitation of HBV replicative intermediates. Compared to wild-type counterpart, mutant rtL217P produced 1.98-fold higher replicative intermediate level, and mutant rtM204I+rtL217P increased the replicative intermediate level to 1.20 fold. Other mutational patterns (rtV173M, rtA181S/V, rtM204I, rtQ215H, rtL229M, rtN238H, rtV84M+rtA181S+rtM204I, rtV84M+rtM204I, rtA181S+rtM204I, rtA181V+rtL229M, rtQ215H+rtN238H) reduced viral replication capacity to different extents.

CONCLUSIONS

The study offers a practical measurement assay and novel information for replication features of mutant strains; especially, rtL217P substitution likely represents an energetic replication-compensatory mutation.

Hepatitis B virus (HBV) subgenotypes C2 and B2 differ in lamivudine- and adefovir-resistance-associated mutational patterns in HBV-infected Chinese patients

We aimed to study the prevalence and clinical implications of hepatitis B virus (HBV) subgenotypes in Chinese patients. A total of 4,300 patients, mainly from northern China, were enrolled, including 182 patients with acute hepatitis B and 4,118 patients with chronic HBV infection who had been exposed to nucleoside or nucleotide analogs. HBV genotypes/subgenotypes were determined by direct sequencing of the HBV S/Pol region. The prevalence rates were 0.40% for HBV/B1, 14.30% for HBV/B2, 0.25% for HBV/B3, 0.35% for HBV/B4, 1.05% for HBV/C1, 81.72% for HBV/C2, 0.93% for HBV/C3, 0.16% for HBV/C4, and 0.84% for HBV/D. In chronic HBV infection, patients with HBV/B2 were younger and had lower ΗBeAg positive rates than patients with HBV/C2. The incidence of lamivudine-resistant mutations was significantly higher in HBV/C2 compared to HBV/B2 (27.9% versus 19.8%; P<0.01), and the significant difference was observed only for rtM204I and not rtM204V. In addition, compensatory mutations were more frequently detected in HBV/C2. The incidence of adefovir-resistant mutations was similar between the two subsets, but HBV/C2 inclined to show rtA181V (3.6% for C2 versus 0.9% for B2; P<0.01), while HBV/B2 inclined to show rtN236T (4.5% for versus 2.5% for C2; P<0.01). The ratios of HBV/B2 to HBV/C2 infection were 1.7 (110/65), 5.7 (2,653/463), 7.5 (520/69), 8.0 (48/6), and 15.3 (183/12) for acute hepatitis B, chronic hepatitis B, liver cirrhosis, acute-on-chronic liver failure, and hepatocellular carcinoma, respectively. In conclusion, HBV/C2 and HBV/B2, two prevalent subgenotypes, differ in lamivudine- and adefovir-resistance-associated mutational patterns. HBV/C2-infected patients are more likely to have disease progression than HBV/B2-infected ones.

Monitoring of therapy in patients with chronic hepatitis B virus

OBJECTIVE

The aims of this study were to evaluate therapy with lamivudine (LAM) and adefovir dipivoxil (ADV) monotherapy in chronic hepatitis B virus (HBV)-infected patients with frequent measurements of DNA levels, to characterize HBV genotypes, and to determine the emergence of nucleos(t)ide analogue mutants before and during the therapy by direct-sequencing the reverse transcriptase region and by INNO-LiPA HBV DR v3.

MATERIALS AND METHODS

A total of 15 chronic HBV patients were analysed: 11 were treated with ADV and four were treated with LAM.

RESULTS

Viral genotype was determined, showing the presence of genotype D (73%) in 11 patients and genotype A (27%) in four patients. In the viral response to treatment, three patients developed substitutions at rtM204I associated with LAM resistance and one of these patients presented rtM204V/I plus rtL180M mutation. In contrast, of the 11 patients treated with ADV, three patients developed mutations (rtN236T; rtA181V; rtA181V plus rtN236T). With regard to this case, the same results were observed by INNO-LiPA HBV DR v3 and direct sequencing, but by direct sequencing we detected an extra mutation rtQ215S that was present in two patients: one patient who was on treatment with LAM had an rtQ215S mutation in addition to an rtM204I, and the second patient treated with ADV had rtA181V.

CONCLUSION

Direct sequence analysis is an essential tool to optimize therapeutic management of HBV chronic infection in clinical practice to choose the appropriate nucleos(t)ide analogues and to detect extra mutations that are not included in the commercial kit.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

While 25 compounds have been formally licensed for the treatment of HIV infection (AIDS), only seven licensed products are currently available for the treatment of chronic hepatitis B virus (HBV) infection: interferon-α, pegylated interferon-α, lamivudine, adefovir (dipivoxil), entecavir, telbivudine and tenofovir (disoproxil fumarate). In contrast to the treatment of HIV infections where the individual drugs are routinely used in combination, for the treatment of chronic HBV infection the individual drugs are generally used in monotherapy. In principle, combination drug therapy should allow reducing the likelihood of drug-resistant development.

Hepatitis B virus drug resistance in HIV-1-infected patients taking lamivudine-containing antiretroviral therapy

A cross-sectional study was conducted in HIV-1-infected patients receiving lamivudine-containing antiretroviral therapy (ART) to determine the prevalence and risk factors of hepatitis B virus drug resistance (HBV-DR). HBV DNA and HBV genotypic resistance test were performed. Patients were categorized into two groups: with and without HBV-DR. There were 84 patients with a mean age (standard deviation [SD]) of 42.2 (10.2) years and 77% were males. Median (range) duration of ART and lamivudine use was 46 (3-177) and 40 (3-140) months, respectively. Median (range) CD4 cell count was 352 (49-790) cells/mm(3). Of all, 19 (23%) had HBV-DR with a median (range) HBV DNA of 2.56 x 10(7) (2.54 x 10(3)-11 x 10(7)) IU/mL. In univariate analysis, there were no differences in age, gender, ART regimen, liver function test, anti-HBc antibody, anti-HCV antibody between the two groups. Patients with HBV-DR had a higher proportion of positive HBeAg (68.4% versus 3.8%, p < 0.001). In multivariate analysis, positive HBeAg (odds ratio [OR) 16.64; 95% confidence interval [CI], 3.31-83.60] and duration of lamivudine use [per 6-month increment, OR 1.24; 95% CI, 1.06-1.36] were significant risk factors for HBV-DR. All 19 patients with HBV-DR had lamivudine resistance with the mutations as follows: M204V/I (95%), L180M/A181T (95%), L80V/I (47%), V173L (32%), and N236T (21%). Of these, 95%, 84%, 84%, and 0% of patients had HBV-DR to telbivudine, entecavir, adefovir, and tenofovir, respectively. HBV-DR is common in HBV/HIV-1 coinfected patients receiving lamivudine-containing ART without tenofovir. Positive HBeAg and longer duration of lamivudine use are risk factors for HBV-DR. In addition to lamivudine resistance, cross-resistance to other anti-HBV drugs is also frequently observed.

Characterization of potential antiviral resistance mutations in hepatitis B virus reverse transcriptase sequences in treatment-naïve Chinese patients

Full-length hepatitis B virus (HBV) reverse transcriptase (RT) sequences were amplified and sequenced among 192 nucleos(t)ide analogue (NA)-naïve Chinese patients with chronic hepatitis B. Deduced amino acids (AAs) at 42 previously reported potential NA resistance (NAr) mutation positions in RT region were analyzed. Patients were found with either B-genotype (28.65%) or C-genotype (71.35%) infections. Rt53, rt91, rt124, rt134, rt221, rt224, rt238 and rt256 were identified as B- and C-genotype-dependent polymorphic AA positions. AA substitutions at 11 classical NAr mutation positions, i.e. rt80, rt169, rt173, rt180, rt181, rt184, rt194, rt202, rt204, rt236 and rt250, were not detected. However, potential NAr mutations were found in 30.73% (59/192) isolates, which involved 18 positions including rt53, rt207, rt229, rt238 and rt256, etc. The concomitant AA changes of HBsAg occurred in 16.67% (32/192) isolates including sG145R mutation. One-third of mutation positions were located in functional RT domains (e.g. rt207 and rt233), A-B interdomains (overlapping HBsAg 'a' determinant and showing most concomitant immune-associated mutations) and non-A-B interdomains (e.g. rt191 and rt213), respectively. Genotypes B and C each showed several preferred positions to mutate. These results might provide insights into understanding the evolution and selection basis of NAr HBV strains under antiviral therapy.

Prevalence, viral replication efficiency and antiviral drug susceptibility of rtQ215 polymerase mutations within the hepatitis B virus genome

BACKGROUND/AIMS

The rtQ215S mutation in the hepatitis B virus (HBV) polymerase has been described as a secondary mutation associated with resistance to lamivudine (LAM) and adefovir (ADV). We aimed at assessing the prevalence of substitutions at rtQ215 of the HBV polymerase and determining the molecular and functional consequences using phenotypic analyses in vitro.

METHODS

The polymerase region was directly sequenced in HBV isolates from a cohort of 249 HBV genotype D-infected patients from Iran (174 males/75 females, 194 treatment-nai ve/ 55 LAM-treated). Replication-competent HBV constructs containing the naturally occurring rtQ215H, rtQ215P and rtQ215S mutations were generated, and compared to wild-type, LAM- (rtM204I, rtL180M/rtM204V) and ADV-resistant (rtN236T) clones.

RESULTS

In an Iranian cohort of 249 HBV infected patients, 14.5% (36/249) showed mutations in the rtQ215 locus, namely 6.8% rtQ215S, 3.6% rtQ215P and 4.1% rtQ215H. The frequency of rtQ215 substitutions was higher in LAM-treated than treatment-nai ve patients (25% vs. 11%), but not associated with clinical complications. In phenotypic assays, rtQ215S, rtQ215P and rtQ215H constructs showed equivalent levels of viral replication as wild-type HBV, whereas LAM- and ADV-resistant mutants had significantly impaired replicative capacities. Furthermore, rtQ215S, rtQ215P and rtQ215H harbouring constructs remained susceptible towards treatment with LAM or ADV in vitro.

CONCLUSIONS

Our study reveals that rtQ215 substitutions in the HBV polymerase frequently occur in chronic hepatitis B, even without exogenous selection pressures. As these substitutions do neither impair the viral replication efficiency nor susceptibility to LAM or ADV in vitro, rtQ215 substitutions likely represent background polymorphisms rather than resistance mutations with clinical implications.

Antiviral resistance and impact on viral replication capacity: evolution of viruses under antiviral pressure occurs in three phases

Resistance development is a major obstacle to antiviral therapy, and all active antiviral agents have shown to select for resistance mutations. Aspects of antiviral resistance development are discussed for specific compounds or drug classes in the previous chapters, while this chapter provides an overview regarding the evolution of different viruses (HIV, HBV, HCV, and Influenza) under pressure of antiviral therapy. Virus replication is an error prone process resulting in a large number of variants (quasispecies) in patients. Resistance evolution under suboptimal therapy can be schematically distinguished into three phases. (1) preexisting variants less sensitive to the respective drug are selected from the quasispecies population, (2) outgrowing variants acquire additional mutations increasing their resistance, and (3) compensatory mutations accumulate to overcome the generally reduced replicative capacity of resistant variants. Successful therapy should be aimed at suppression of all existing viral variants, thus preventing selection of minority species and their subsequent evolution. This implies that the amount of mutations required for first escape to the viral regimen (genetic barrier) should be larger than the expected number of mutations present in viruses in the quasispecies. Accordingly, combination therapy can achieve complete inhibition of replication for most HIV, HBV, and Influenza infected patients without resistance development. However, resistant viruses can become selected under circumstances of suboptimal antiviral therapy and these resistant viruses can be transmitted. Proper use of drugs and worldwide monitoring for the presence and spread of drug resistant viruses are therefore of utmost importance.