Hepatitis B virus quasispecies susceptibility to entecavir confirms the relationship between genotypic resistance and patient virologic response

Evolution and diversity of the hepatitis B virus genome: Clinical implications

Hepatitis B virus (HBV) infection remains a significant global health burden. The genetic variation of HBV is complex. HBV can be divided into nine genotypes, which show significant differences in geographical distribution, clinical manifestations, transmission routes and treatment response. In recent years, substantial progress has been made through various research methods in understanding the development, pathogenesis, and antiviral treatment response of clinical disease associated with HBV genetic variants. This progress provides important theoretical support for a deeper understanding of the natural history of HBV infection, virus detection, drug treatment, vaccine development, mother-to-child transmission, and surveillance management. This review summarizes the mechanisms of HBV diversity, discusses methods used to detect viral diversity in current studies, and the impact of viral genome variation during infection on the development of clinical disease.

Switching to tenofovir alafenamide for nucleos(t)ide analogue-experienced patients with chronic hepatitis B: week 144 results from a real-world, multi-centre cohort study

BACKGROUND

Tenofovir alafenamide (TAF) may be preferable to other nucleos(t)ide analogues (NA) regarding outcomes against chronic hepatitis B virus (HBV) infection.

AIMS

To evaluate the longer term virological/biochemical effectiveness of TAF and the renal safety of sequential therapy to TAF in real-world settings METHODS: This multi-centre, retrospective cohort study included consecutive adult patients who were switched from other NAs to TAF. We assessed the virological and biochemical responses up to 144 weeks. We performed sensitivity analyses for a subgroup with chronic kidney disease (CKD) at baseline.

RESULTS

We analysed the data of 391 patients with chronic hepatitis B previously treated with entecavir (ETV) (n = 174), tenofovir disoproxil fumarate (TDF) (n = 116) or an NA combination (n = 101) for ≥ 24 months. HBV DNA <10 IU/ml at week 144 was found for 99% of patients, regardless of prior NA regimen or HBV DNA level at baseline. For patients who switched from TDF to TAF, total, low-density lipoprotein, high-density lipoprotein cholesterol and triglycerides were significantly increased after the switch. Patients who switched from a nucleotide analogue to TAF had an improved estimated glomerular filtration rate, although the rate of hypophosphataemia (<2.5 mg/dl) remained 9.7% at week 144. The virological and biochemical responses of patients with CKD were similar to the overall results.

CONCLUSIONS

Switching to TAF remained effective and safe for up to 3 years. Given the increasing comorbidities related to ageing, it will be important to carefully follow the change in the lipid levels of patients with a prior TDF-based regimen.

Hepatitis B Virus Genotype G: The Odd Cousin of the Family

With a widespread distribution but low prevalence worldwide, the hepatitis B virus (HBV) genotype G (HBV/G) is a recently described genotype for which the origin and biology are poorly understood. Some unique features make HBV/G the most peculiar of all genotypes. In this review, we reflect on the major milestones in HBV/G research, highlighting the main aspects of its discovery, molecular epidemiology, and virological and clinical characteristics. We also illustrate common pitfalls in the routine detection, which may lead to underestimated rates of HBV/G infection. Large-scale analysis of data from dozens of articles was further performed, with the aim of gaining comprehensive insights into the epidemiological aspects of HBV/G. Finally, we point out recent findings on HBV/G origins and discuss new perspectives regarding the evolutionary history of HBV/G and the plausibility of an African geographic re-emergence of this genotype.

Entecavir resistance in a patient with treatment-naïve HBV: A case report

Among nucleos(t)ide analogue therapies for hepatitis B virus (HBV) treatment, entecavir (ETV) and tenofovir disoproxil fumarate (TDF)/tenofovir alafenamide are associated with the lowest rate of drug resistance. ETV is a drug requiring at least three substitutions in the reverse transcriptase (RT) domain to develop resistance, which is a rare occasion in treatment-naïve patients. However, pre-existing or acquired single mutations in the RT domain could lead to a virological breakthrough, after viral suppression. The present case report describes a 58-year-old female patient with hepatitis B virus (HBV) and high viral load who started HBV treatment with ETV. After 85 weeks of treatment, HBV-DNA declined to 0 IU/ml and remained undetectable for 3 years. However, after that period of time, the HBV-DNA rebounded, followed by the rise of liver enzymes (aspartate aminotransferase and alanine transaminase). Only the substitution M204I was detected in the HBV polymerase region. The patient was then switched to TDF treatment, achieving normalization of the liver enzymes and a decline in HBV-DNA levels. The present case report suggests that nucleoside-naïve patients should be cautiously monitored for resistance, even more than biochemically (transaminases, bilirubin) and virologically (HBV-DNA), even if complete HBV suppression is achieved.

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.

Molecular cloning and phenotypic analysis of drug-resistance mutants with relevant S-region variants of HBV for a patient during 189-month anti-HBV treatment

BACKGROUND

A unique chronic hepatitis B patient was followed over 189 months of nucleoside/nucleotide analogue (NA) therapies with the analysis of multiple drug-resistance HBV mutants.

METHODS

Clonal sequencing (≥20 clones/sample) was performed on sera sampled at 41 time points, and the phenotypic features of eight representative mutants were analysed.

RESULTS

Lamivudine (LAM)-, adefovir dipivoxil (ADV)-, entecavir (ETV)- and repeat ADV-resistance mutants emerged upon individual sequential NA monotherapy. The efficacy of NA combination rescue therapies ranked as LAM+ADV < ETV+ADV < ETV+ tenofovir disoproxil fumarate (TDF). Specifically, LAM+ADV and ETV+ADV suppressed viral loads to <100 IU/ml for a long period of time, either with or without late stage HBV DNA fluctuations. Furthermore, ETV+TDF suppressed the viral load to <10 IU/ml. During the LAM+ADV and ETV+ADV combination therapies, ETV-resistance mutants dominated at most time points, and multidrug-resistance (MDR) mutants that harboured LAM-, ETV- and ADV-resistance mutations were intermittently detected. Interestingly, the rtA181T-causative sW172stop to sW172non-stop mutation transition was observed at HBV DNA fluctuations. In a phenotypic analysis, two MDR strains had cross-resistance to LAM, ETV and ADV, and a lower susceptibility to TDF (<10-fold decrease compared with the wild-type strain). In contrast, the natural replication capacity was inversely associated with the number of primary resistant mutations which would limit MDR mutant development.

CONCLUSIONS

Taken together, viral drug susceptibility, replication capacity, and perhaps immunological adaptation may play coordinated roles in the fitness of drug-resistance mutants. ETV+TDF therapy is the preferred option for treating chronic hepatitis B patients with multiple drug failure.

Hepatitis B virus mutation pattern rtL180M+A181C+M204V may contribute to entecavir resistance in clinical practice

Background and Aims: Entecavir (ETV) resistance of hepatitis B virus (HBV) conventionally requires rt184, 202, or 250 mutations plus lamivudine-resistance mutation (rtM204V/I ± L180M). This study aimed to clarify whether rtL180M+A181C+M204V mutations may contribute to HBV ETV resistance.

Methods: Serum samples were collected from 22,009 patients who underwent resistance testing in Beijing 302 Hospital from 2007 to 2016. HBV reverse transcriptase (RT) gene was screened by direct sequencing and verified by clonal sequencing. Phenotypic analysis was performed for evaluating replication capacity and drug susceptibility.

Results: Classical ETV-resistance mutations of HBV were detected in 1252 patients who were receiving ETV therapy. The rtA181C mutation was detected with rtL180M+M204V mutations in 18 lamivudine-experienced ETV-treated patients, and the emergence of the mutations was associated with virological breakthrough or inadequate virological response to ETV. Patient-derived representative rtA181C-containing mutants, rtL180M+A181C+M204V, rtL180M+A181C+M204V+M250V, and rtL180M+A181C+S202G+M204V, exhibited 45.7%, 25.9%, and 25.0% replication capacity and 85.6-, 356.1-, and 307.1-fold decreased susceptibility to ETV respectively compared to the wild-type strain, while the three mutants remained sensitive to tenofovir (TDF). Artificial elimination of rtA181C largely restored the rtL180M+A181C+M204V mutant’s sensitivity to ETV. Molecular modelling of viral RT binding to ETV showed that the rtL180M+A181C+M204V mutant had a less stable conformation compared to rtL180M+M204V mutant. In clinical practice, undetectable serum HBV DNA was achieved in two of five longitudinally followed rtA181C-positive patients who received switching-to TDF therapy, but not in the other three who received add-on adefovir therapy during observation.

Conclusions: Both clinical and experimental data support rtL180M+A181C+M204V as a novel non-classical ETV-resistance mutation pattern.

Discovery of the Novel Entecavir-Resistant Hepatitis B Virus Reverse Transcriptase A181C Substitution From an Integrated Genotypic Analysis

Entecavir (ETV) is a first-line therapy for chronic hepatitis B virus (HBV), demonstrating potent suppression of HBV DNA and a high barrier to viral resistance. Previous studies revealed that ETV-resistant (ETVr) HBV DNA resulted from substitutions in the HBV reverse transcriptase (RT) at positions rtT184, rtS202, or rtM250 in combination with lamivudine resistance (LVDr) substitutions rtM204I/V±rtL180M. In vitro, viral variants exhibit varying degrees of ETV susceptibility and replication capacity depending on specific resistance substitutions. To explore the potential for additional pathways to ETVr, HBV RT sequences from 982 evaluable patients enrolled in 17 ETV clinical studies were analyzed. Thirty novel emergent substitutions at amino acid positions not previously associated with HBV nucleos(t)ide drug resistance were observed in at least 2 patients and were identified in patient-derived HBV with a wild-type, LVDr, or ETVr RT sequence. Phenotypic analysis of these substitutions indicated that they had no effect on ETV susceptibility. Phenotypic analysis was also performed on patient-derived HBV RT sequences from 10 LVD-naive and 13 LVD-experienced patients with virologic breakthrough and emergent novel substitutions while on ETV treatment. One LVD-experienced patient-derived HBV RT harboring LVDr substitutions rtL180M+rtM204V with rtA181C displayed reduced ETV susceptibility (122-fold greater than wild-type HBV) and remained susceptible to adefovir and tenofovir. HBV harboring the rtA181C substitution without LVDr substitutions rtL180M+rtM204V remained susceptible to inhibition by ETV, adefovir, and tenofovir, although cross-resistance to LVD and telbivudine was observed. Conclusion: An integrated genotypic analysis of HBV RT sequences from patients with chronic HBV treated with ETV led to the discovery of the novel ETVr substitution rtA181C. This substitution was always detected in combination with LVDr substitutions rtL180M+rtM204V in ETV-treated patients.

Novel stable HBV producing cell line systems for expression and screening antiviral inhibitor of hepatitis B virus in human hepatoma cell line

Chronic hepatitis B virus (HBV) infection is currently a major public health burden. Therefore, there is an urgent need for the development of novel antiviral inhibitors. The stable HBV-producing cell lines of genotype D are widely used to investigate the HBV life cycle and to evaluate antiviral agents. However, stable HBV-producing cell lines of different genotypes do not exist. To construct more convenient and efficient novel cell systems, stable cell lines of genotypes A, B, and C were established using a full-length HBV genome sequence isolated from chronic HBV patients in human hepatoma HepG2 cells. Novel HBV clones were identified and stable HBV-producing cell lines derived from these clones were constructed. HBV replication activities demonstrated time-dependent expression, and the novel cell lines were susceptible to several antiviral inhibitors with no cytotoxicity. Furthermore, infectious viruses were produced from these cell lines. In conclusion, we have established novel stable HBV-producing cell line systems of genotypes A, B, and C. These systems can provide valuable tools for screening antiviral agents and analyzing viral phenotypes in vitro.

Pediatric hepatitis B treatment

Although the introduction of hepatitis B vaccine has been contributing to the reduction in the prevalence of hepatitis B virus (HBV) carriers worldwide, the treatment of children with chronic HBV infection is a challenge to be addressed. HBeAg seroconversion, which induces low replication of HBV, is widely accepted as the first goal of antiviral treatment in children with chronic hepatitis B. However, spontaneous HBeAg seroconversion is highly expected in children with chronic HBV infection. Therefore, the identification of children who need antiviral treatment to induce HBeAg seroconversion is essential in the management of chronic HBV infection. Guidelines and experts' opinion show how to identify children who should be treated and how to treat them. If decompensated cirrhosis is absent, interferon-alpha is the first-line antiviral treatment. Nucleos(t)ide analogues (NAs), such as lamivudine, adefovir, entecavir and tenofovir, are also available for the treatment of children, although the approval age differs among them. If decompensated cirrhosis is present, NAs are the first-line antivirals. When the emergence of drug-resistant HBV variants is taken into consideration, entecavir (approved for age 2 years or older) and tenofovir (age 12 years or older), which have high genetic barriers, will play a central role in the treatment of HBV infection. However, the optimal duration of NA treatment and adverse events of long-term NA treatment remain unclear in children. In resource-constrained countries and regions, the financial burden of visiting hospitals, receiving routine blood examination and purchasing antiviral drugs is heavy. Moreover, there is no clear evidence that the induction of HBeAg seroconversion by antiviral treatment prevents the progression of liver disease to cirrhosis and hepatocellular carcinoma in children with chronic HBV infection. It is thus imperative to clarify the clinical impact of antiviral treatment in children with HBV infection.

Randomized, controlled trial of entecavir versus placebo in children with hepatitis B envelope antigen-positive chronic hepatitis B

This ongoing, randomized phase III study assesses the safety and efficacy of entecavir versus placebo in nucleos(t)ide-naïve children (2 to <18 years) with hepatitis B envelope antigen (HBeAg)-positive chronic hepatitis B (CHB). Blinded treatment was administered for a minimum of 48 weeks. After week 48, patients with HBeAg seroconversion continued blinded treatment; those without switched to open-label entecavir. The primary endpoint was HBeAg seroconversion and HBV DNA <50 IU/mL at week 48. A total of 180 patients were randomized (2:1) and treated. Baseline median age was 12 years, with approximately 50% of children ages >12 to <18, and 25% each ages ≥2 to ≤6 and >6 to ≤12. Rates for the primary endpoint at week 48 were significantly higher with entecavir than placebo (24.2% [29 of 120] vs. 3.3% [2 of 60]; P = 0.0008). Furthermore, higher response rates were observed with entecavir compared with placebo for the key week 48 secondary endpoints: HBV DNA <50 IU/mL (49.2% [59 of 120] vs. 3.3% [2 of 60]; P < 0.0001); alanine aminotransferase normalization (67.5% [81 of 120] vs. 23.3% [14 of 60]; P < 0.0001); and HBeAg seroconversion (24.2% [29 of 120] vs. 10.0% [6 of 60]; P = 0.0210). Among entecavir-randomized patients, there was an increase in all efficacy endpoints between weeks 48 and 96, including an increase from 49% to 64% in virological suppression. The cumulative probability of emergent entecavir resistance through years 1 and 2 of entecavir was 0.6% and 2.6%, respectively. Entecavir was well tolerated with no observed differences in adverse events or changes in growth compared with placebo.

CONCLUSION

In childhood CHB, entecavir demonstrated superior antiviral efficacy to placebo with a favorable safety profile. These results support the use of entecavir as a therapeutic option in children and adolescents with CHB.

A novel method for nucleos(t)ide analogues susceptibility assay of hepatitis B virus by viral polymerase transcomplementation

Nucleos(t)ide analogues (NUCs) susceptibility assay is important for the study of hepatitis B virus (HBV) drug resistance. The purpose of susceptibility assay is to test the sensitivity of a specific HBV variant to NUCs in vitro, by which assesses if and to what extent the mutant virus is resistant to a specific NUC. Among the existing susceptibility assay methods, stable cell line expressing the specific variant is one of the commonly used assessment systems based on its high repeatability. However, establishment of stable cell lines expressing individual variant is laborious and time-consuming. In the present study, we developed a novel strategy for rapidly establishing HBV replicating stable cell lines. We first established an acceptor cell line stably transfected with a polymerase-null HBV 1.1mer genome DNA, then lentiviruses expressing different mutant HBV polymerases were transduced into the acceptor cell line respectively. Stable cell lines replicating HBV DNA with the trans-complemented HBV polymerases were established by antibiotics selection. Lamivudine and entecavir susceptibility data from these polymerase-complementing cell lines were validated by comparing with other assays. Taken together, this transcomplementation strategy for establishment of stable cell lines replicating HBV DNA with clinically isolated HBV polymerase provides a new tool for NUC susceptibility assay of HBV.

Monotherapy for hepatitis B infection: a review of treatment options

Chronic hepatitis B (CHB) is a global health problem, causing liver failure, cirrhosis and hepatocellular carcinoma. CHB treatment aims to prevent liver-related complication. The treatment of CHB infection includes monotherapy with either interferons (IFNs) or nucleos(t)ide (NUC) analogs. IFNs have moderate antiviral effects, and their use is limited by side effects. With the availability of NUCs, IFN-intolerant and decompensated cirrhotic patients began to be treated. Lamivudine and telbivudine, nucleoside analogs, have low genetic barrier to resistance. Adefovir, a nucleotide analog, has moderate potency and potential nephrotoxicity. Entecavir and tenofovir, with their high potency, high genetic barrier to resistance and favorable safety profile are the standard of care in CHB treatment. Long-term use of NUCs with maintained viral suppression results in a decrease in liver-related complications.

Entecavir allows an unexpectedly high residual replication of HBV mutants resistant to lamivudine

BACKGROUND

Entecavir is an efficient inhibitor of HBV reverse transcriptase (RT) and widely used for therapy of chronic hepatitis B. Entecavir treatment of HBV patients with lamivudine-resistant viral strains, however, often fails, but the mechanism of cross-resistance development is not fully understood.

METHODS

Using non-linear regression models, dose-response curves of cloned HBV strains from patients pre-treated with RT inhibitors were established in human hepatoma cell lines after transfection with HBV genomes containing HBV polymerase genes from patient isolates. 50% and 90% inhibitory concentrations (IC50 and IC90) and corresponding antiviral resistance factors (RF50 and RF90) were calculated.

RESULTS

The entecavir dose-response curve of lamivudine-resistant HBV RT mutants rtM204 for the replication of HBV decreased less than expected with increasing drug dose. Remarkably, due to the flat dose-response curves, RF90 values against entecavir of samples with rtM204 substitutions were up to 30× higher than their RF50 values.

CONCLUSIONS

The unexpectedly high IC90 indicates a strong residual replication capacity of lamivudine-resistant HBV rtM204 variants under entecavir therapy, although IC50 values are initially within the therapeutic range of entecavir. This characteristic favours rapid selection of additional mutants with overt resistance against entecavir. Thus, the current phenotypic resistance assays should include determination of IC90.

Is increasing the dose of Entecavir effective in partial virological responders?

OBJECTIVE

To analyze the effect of increasing Entecavir (ETV) dosage in patients with chronic hepatitis B (CHB) who partially responded to ETV after 1 year.

METHODS

Twenty-three hepatitis B e antigen (HBeAg)-positive and 36 HBeAg-negative patients with CHB were treated with ETV 0.5 mg daily. After 1 year of the treatment, those with detectable hepatitis B virus (HBV-DNA) were randomized to either ETV 0.5 mg or 1 mg daily. The resistance to ETV was excluded. Both groups received ETV for 3 years. The groups were compared in aspects of undetectable DNA.

RESULTS

Group 1 was given 0.5 mg ETV and included 32 patients (20 HBeAg-negative and 12 HBeAg-positive). Group 2 was given 1 mg ETV and consisted of 27 patients (16 HBeAg-negative and eleven HBeAg-positive). Group 2 had more effective suppression of HBV-DNA while both groups had comparable rates of HBeAg loss (58% and 63% for group 1 and group 2, respectively) and alanine transaminase (ALT) normalization at the end of 4 years.

CONCLUSION

Increasing ETV dose from 0.5 mg to 1 mg after 1 year of ETV treatment may provide an effective suppression of viral replication.

Is increasing the dose of Entecavir effective in partial virological responders?

OBJECTIVE

To analyze the effect of increasing Entecavir (ETV) dosage in patients with chronic hepatitis B (CHB) who partially responded to ETV after 1 year.

METHODS

Twenty-three hepatitis B e antigen (HBeAg)-positive and 36 HBeAg-negative patients with CHB were treated with ETV 0.5 mg daily. After 1 year of the treatment, those with detectable hepatitis B virus (HBV-DNA) were randomized to either ETV 0.5 mg or 1 mg daily. The resistance to ETV was excluded. Both groups received ETV for 3 years. The groups were compared in aspects of undetectable DNA.

RESULTS

Group 1 was given 0.5 mg ETV and included 32 patients (20 HBeAg-negative and 12 HBeAg-positive). Group 2 was given 1 mg ETV and consisted of 27 patients (16 HBeAg-negative and eleven HBeAg-positive). Group 2 had more effective suppression of HBV-DNA while both groups had comparable rates of HBeAg loss (58% and 63% for group 1 and group 2, respectively) and alanine transaminase (ALT) normalization at the end of 4 years.

CONCLUSION

Increasing ETV dose from 0.5 mg to 1 mg after 1 year of ETV treatment may provide an effective suppression of viral replication.

Randomized comparison of tenofovir disoproxil fumarate vs emtricitabine and tenofovir disoproxil fumarate in patients with lamivudine-resistant chronic hepatitis B

BACKGROUND & AIMS

Tenofovir disoproxil fumarate (TDF) is active against lamivudine-resistant hepatitis B virus (HBV) infection, but data to support its clinical efficacy in this setting are limited.

METHODS

In a prospective, double-blind, 96-week trial, patients were randomly assigned (1:1) to groups given TDF (300 mg, n = 141) or a combination of emtricitabine (FTC, 200 mg; n = 139) and TDF (300 mg, FTC/TDF). Patients were hepatitis B e antigen (HBeAg)-positive or HBeAg-negative, with levels of HBV DNA ≥3 log10 IU/mL and lamivudine resistance mutations (HBV polymerase or reverse transcriptase amino acid substitutions rtM204I/V ± rtL180M by INNO-LiPA Multi-DR v3; Innogenetics, Inc, Alpharetta, GA). The primary end point was proportion with HBV DNA <69 IU/mL (Roche COBAS Taqman assay; Roche Molecular Systems, Inc, Pleasanton, CA).

RESULTS

Patient groups were well matched for demographic and disease characteristics, including region (60% from Europe), HBV genotype (45% genotype D), HBeAg status (47% HBeAg-positive), and duration of lamivudine treatment (mean, 3.8 years). At week 96 of treatment, 89.4% of patients in the TDF group and 86.3% in the FTC/TDF group had levels of HBV DNA <69 IU/mL (P = .43). HBeAg loss and seroconversion did not differ between groups; only 1 patient (0.7%) in the FTC/TDF group lost hepatitis B surface antigen. Treatment was well tolerated; confirmed renal events (creatinine increase of ≥0.5 mg/dL [>44 umol/L], creatinine clearance <50 mL/min, or level of PO4 <2 mg/dL [<0.65 mmol/L]) were generally mild and infrequent (<1%). Small reductions (<2%) in mean bone mineral density of hip and spine were detected by dual-energy x-ray absorptiometry in both groups. No TDF resistance developed through 96 weeks of treatment.

CONCLUSIONS

TDF alone is safe and effective for treatment of patients with lamivudine-resistant, chronic HBV infection. Clinical Trials.gov No, NCT00737568.

Adefovir and Lamivudine Combination Therapy in Patients with Entecavir-Resistant Chronic Hepatitis B: Antiviral Responses and Evolution of Mutations

<b><i>Objective:</i></b> This study was designed to prospectively evaluate the antiviral responses and evolution of resistance mutations during adefovir (ADV) plus lamivudine (LMV) therapy in patients with entecavir (ETV)-resistant hepatitis B virus (HBV) infection. <b><i>Methods:</i></b> Twenty chronic hepatitis B (CHB) patients who had been receiving ETV for more than 6 months and developed virologic breakthrough due to ETV resistance were consecutively enrolled. <b><i>Results:</i></b> Patients received ADV plus LMV therapy for 12 months. The baseline mean serum HBV DNA level was 5.59 ± 1.28 log₁₀ IU/ml. The rtT184L/I/A/F (50%), rtS202G (25%) and mixed ETV-resistant mutations (25%) were detected at enrollment. The mean reduction in serum HBV DNA levels from baseline to 12 months was -2.3 ± 1.06 log₁₀ IU/ml (p<i> <</i> 0.001). Seventeen patients were followed up for the full 12 months, and complete virologic response (HBV DNA <20 IU/ml) was observed in 4 patients (23.5%). Among the remaining 13 patients who still had detectable HBV DNA, 7 patients showed disappearance of ETV-resistant mutations or reduction of the proportion of ETV-resistant mutants. An ADV- and LMV-resistant mutant (rtA181T) emerged in 2 patients (11.7%). <b><i>Conclusions:</i></b> ADV plus LMV combination therapy suppresses ETV-resistant mutants in the viral population and significantly reduces serum HBV DNA levels in ETV-resistant CHB patients.

Nucleoside plus nucleotide analogs and cessation of hepatitis B immunoglobulin after liver transplantation in chronic hepatitis B is safe and effective

BACKGROUND

After orthotopic liver transplantation (OLT) in chronic hepatitis B (HBV), adequate prophylaxis for recurrence of HBV in the graft is mandatory.

OBJECTIVES

Evaluate safety of HBV prophylaxis with tenofovir and emtricitabine (TDF/FTC) after cessation of hepatitis B immunoglobulin (HBIG) after OLT in chronic HBV.

STUDY DESIGN

In 17 consecutive patients after OLT in chronic HBV we started TDF/FTC after cessation of HBIG. All had received HBIG >6 months. 15/17 were HBsAg negative and 16/17 had undetectable HBV-DNA.

RESULTS

After mean follow-up of 2 years 16/17 patients were alive, one died due to urosepsis. All 16 with undetectable HBV-DNA remained HBV-DNA negative. From 15 HBsAg negative patients at start, in one seroconversion to positive HBsAg occurred, without detectable HBV-DNA. Liver biochemistry remained within the normal ranges. There were no cases of drug discontinuation. No major side effects were reported. TDF/FTC use saves €16,262/year over standard-of-care (HBIG+LAM). This prospective follow-up study shows that in liver transplantation for chronic hepatitis B, after initial treatment including HBIG for at least 6 months combined with or followed by (dual) nucleos(t)ide analog therapy, TDF/FTC provides adequate prophylaxis against recurrent HBV infection without major side effects and leads to substantial cost savings over a regimen with HBIG.

CONCLUSION

Combined prophylaxis with TDF/ETV nucleoside plus nucleotide analogs and cessation of immunoglobulin after liver transplantation in chronic hepatitis B is safe and effective.

Two-step evolution of the hepatitis B drug-resistant mutations in a patient who developed primary entecavir resistance

AIM

Few cases of primary entecavir resistance in chronic hepatitis B patients have been reported to date. The serial profiling of the HBV polymerase gene mutations from a treatment-naive patient who developed drug resistance after 32 months of entecavir therapy is presented here.

DESIGN

Serum samples were collected at multiple time points from before the start of therapy to virological and biochemical breakthrough. The evolution of the hepatitis B virus polymerase gene mutations was analysed with commercial line probe assay and pyrosequencing.

RESULTS

Drug resistance mutation analysis by pyrosequencing revealed a two-step process in the selection of drug resistance. The patient had a good initial response to entecavir 0.5 mg/day. A partially resistant HBV strain first emerged as the predominant species from as early as 2 weeks. After a period of non-compliance to therapy, there was virological breakthrough, which resolved on restarting entecavir. Shortly after, there was secondary failure of entecavir therapy, caused by a new resistant strain carrying all three mutations required.

CONCLUSION

In this patient, pre-existence of minor population of partially resistant viral strains and treatment non-compliance probably contributed to his development of primary entecavir resistance.

Virologic responses to add-on adefovir dipivoxil treatment versus entecavir monotherapy in children with lamivudine-resistant chronic hepatitis B

PURPOSE

The aim of the study was to compare the virologic response to adefovir (ADV) add-on therapy with switching to entecavir (ETV) monotherapy in children and adolescents with chronic hepatitis B (CHB) who have developed lamivudine (LAM) resistance during LAM treatment.

METHODS

Twenty-seven consecutive patients with CHB who had developed LAM resistance during LAM treatment were included. Of these 27 patients, 8 patients were treated with the addition of ADV to ongoing LAM and 8 patients were treated by switching to ETV monotherapy and each of these 16 patients were compared with the 11 patients who were treated by switching to ADV alone, as a historical control. Therapeutic responses to treatment were evaluated at 12, 24, 36, and 48 weeks from the initiation of therapy by measuring the decrement of hepatitis B virus (HBV)-DNA titers.

RESULTS

The therapeutic period for HBV-DNA titer decrement (>2  log(10) IU/mL) was significantly shorter in both the LAM+ADV group and the ETV group than in the ADV group (P = 0.008); however, there was no significant difference between the LAM+ADV group and the ETV group. The rate of virologic response, defined as decrement in HBV-DNA titer to undetectable levels at 24 weeks, was significantly higher in both the LAM+ADV group and the ETV group than in the ADV group (P = 0.029).

CONCLUSIONS

Both the LAM+ADV combination therapy and ETV monotherapy exhibited significantly more effective virologic responses compared to the ADV monotherapy in children and adolescents with LAM-resistant CHB, although there was no significant difference between the LAM+ADV group and the ETV group.

Long-term continuous entecavir therapy in nucleos(t)ide-naïve chronic hepatitis B patients

BACKGROUND & AIMS

We determined the antiviral potency and viral resistance rate after 4 years of continuous entecavir treatment in patients with chronic hepatitis B (CHB) infection.

METHODS

The cumulative rates of undetectable hepatitis B virus DNA (HBV DNA;<2.6 log(10) copies/ml), hepatitis B e antigen (HBeAg) seronegativity, seroconversion, alanine aminotransferase (ALT) normalization, and entecavir signature mutations were calculated in 474 nucleos(t)ide-naïve CHB patients (HBeAg-positive: 47%) on continuous entecavir treatment for 4 years.

RESULTS

Median age was 47 years and follow-up period was 2.4 years, with 403, 281, 165, and 73 patients followed-up for at least 1, 2, 3, and 4 years, respectively. Incremental increases were observed in the rates of undetectable HBV DNA, HBeAg seroclearance and seroconversion, and ALT normalization, reaching 96%, 42%, 38% and 93%, respectively, by the fourth year. In all, 100% and 93% of patients negative and positive for HBeAg, respectively, had undetectable HBV DNA at year 4. Of 165 patients, HBV DNA was detectable in nine patients after 3 years. Multivariate analysis identified HBV DNA level (≤7.6 log(10) copies/ml, OR=15.8; 95% CI=43.1-79.9, P=0.001) as an independent predictor of undetectable HBV DNA at year 3. Five patients experienced virological breakthrough including two (0.4%) who developed entecavir-resistance mutations.

CONCLUSIONS

Continuous treatment of nucleos(t)ide-naïve CHB patients with entecavir over 4 years was associated with 96% chance of undetectable HBV DNA and only 0.4% chance of emerging entecavir-resistant mutations.

Entecavir: a review of its use in the treatment of chronic hepatitis B in patients with decompensated liver disease

The oral deoxyguanosine nucleoside analogue entecavir (Baraclude®) has potent activity against hepatitis B virus (HBV) and a high genetic barrier to resistance. This article reviews the clinical efficacy and tolerability of entecavir in the treatment of chronic hepatitis B in patients with decompensated liver disease, as well as summarizing its pharmacological properties. Entecavir 1 mg/day was more effective than adefovir dipivoxil 10 mg/day in the treatment of patients with chronic hepatitis B and decompensated liver disease, according to the results of a randomized, open-label, multicentre trial. Patients were either nucleos(t)ide naive or lamivudine experienced. The reduction from baseline in HBV DNA levels at week 24 (primary endpoint) was significantly greater with entecavir than with adefovir dipivoxil. The proportion of patients with HBV DNA levels of <300 copies/mL was also significantly greater with entecavir than with adefovir dipivoxil at weeks 24, 48 and 96, as was the proportion of patients with ALT normalization. Entecavir 0.5 or 1 mg/day, tenofovir disoproxil fumarate 300 mg/day and a fixed-dose combination of emtricitabine/tenofovir disoproxil fumarate 200 mg/300 mg per day were effective in the treatment of chronic hepatitis B in patients with decompensated liver disease, according to the 48-week analysis of a randomized, double-blind, multicentre trial, primarily designed to examine tolerability endpoints. In this trial, over one-third of patients had received previous therapy with lamivudine for ≥6 months. The efficacy of entecavir in treatment-naive patients with HBV-related decompensated cirrhosis did not significantly differ from that seen in patients with chronic hepatitis B or compensated cirrhosis (compensated group), according to the results of a prospective, nonrandomized study. After 6 or 12 months of entecavir treatment, there were no significant differences between the decompensated and compensated groups in virological, biochemical or serological endpoints. In patients with decompensated cirrhosis, significant improvements from baseline in liver function were seen after 12 months of entecavir therapy. Oral entecavir was generally well tolerated in patients with chronic hepatitis B and decompensated liver disease, with most of the reported treatment-emergent adverse events consistent with decompensated liver disease. In the trial primarily designed to examine tolerability endpoints, there was no significant difference between patients receiving entecavir and those receiving tenofovir disoproxil fumarate with or without emtricitabine in terms of the proportion of patients experiencing tolerability failure or the proportion of patients with confirmed increases in serum creatinine levels of ≥0.5 mg/dL above baseline or confirmed serum phosphorus levels of <2.0 mg/dL at week 48 (co-primary endpoints). It has been suggested that the risk of lactic acidosis associated with oral nucleos(t)ide analogue therapy is increased in patients with highly impaired liver function. However, only one case of lactic acidosis was reported among entecavir recipients across two clinical trials in patients with chronic hepatitis B and decompensated liver disease. Moreover, small studies found that the risk of lactic acidosis was not increased in patients with chronic hepatitis B and decompensated liver disease who received entecavir, compared with patients with non-HBV decompensated liver disease. In conclusion, entecavir is a valuable agent for the first-line treatment of chronic hepatitis B in patients with decompensated liver disease.

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.

Response to tenofovir monotherapy in chronic hepatitis B patients with prior suboptimal response to entecavir

Both entecavir (ETV) and tenofovir (TDF) are potent antiviral agents for hepatitis B virus (HBV). Suboptimal response (SOR) following antiviral therapy is associated with an increased risk of subsequent treatment failure and viral resistance. It remains unclear whether switching to TDF is a reasonable approach in patients with SOR to ETV treatment. This study was aimed to determine how HBV patients with SOR to ETV respond to TDF monotherapy. Data of patients with SOR to ETV (failure to achieve >1 log(10) HBV-DNA reduction during the last 24 weeks of ETV treatment) who were switched to TDF monotherapy during 2005 and 2010 were reviewed. Treatment adherence was assessed by pill-count. Fourteen patients (2.9%) were identified from a total cohort of 482 ETV-treated patients. All 14 patients were Chinese and were infected with HBV genotype C (71%) or B (29%). Nine patients were men, and the median age was 41.5 years (19-64). Twelve were treatment naïve (one lamivudine- and one peginterferon-experienced patient); 85.7% were HBeAg positive. The median baseline HBV-DNA was 7.55 (5.30-9.40) log(10) copies/mL, and 57% had abnormal serum alanine aminotransferase (ALT) levels. Precore and/or basal core promoter mutations were detected in four patients, whereas no genotypic resistance was detected at baseline and before switching to TDF. The median duration of ETV treatment was 64.5 (26-126) weeks. The median HBV-DNA at the time of switching to TDF was 3.69 (3.00-4.90) log(10) copies/mL. The median HBV-DNA reduction from baseline and during the last 6-month observation period prior to switching to TDF was 4.04 (0.51-6.06) log(10) and 0.43 (-0.09-1.13) log(10) copies/mL, respectively. After the switching to TDF, all 14 patients (100%) achieved undetectable HBV-DNA and ALT normalization within a median duration of 30 weeks. In 12 patients who were HBeAg positive, HBeAg seroconversion was observed in two patients after TDF treatment of 75- and 84-weeks duration. There was no virological breakthrough observed after switching to TDF with a median follow-up period of 50 (24-160) weeks. TDF treatment was safe and well tolerated. In conclusion, suboptimal response to ETV is rare (approximately 3%). TDF monotherapy is safe and very effective in the management of HBV patients with SOR to ETV.

Phenotypic assay of a hepatitis B virus strain carrying an rtS246T variant using a new strategy

Phenotypic assays of hepatitis B virus (HBV) play an important role in research related to the problem of drug resistance that emerges during long-term nucleot(s)ide therapy in patients with chronic hepatitis B. Most of the phenotypic assay systems that are available currently rely on the transfection of recombinant replication-competent HBV DNA into hepatoma cell lines. Cloning clinical HBV isolates using conventional digestion-and-ligation techniques to generate replication-competent recombinants can be very difficult because of the sequence heterogeneity and unique structure of the HBV genome. In this study, a new strategy for constructing an HBV 1.1× recombinant was developed. The core of this strategy is the "fragment substitution reaction" (FSR). FSR allows PCR fragments to be cloned without digestion or ligation, providing a new tool for cloning fragments or genomes amplified from serum HBV DNA, and therefore making the assay of HBV phenotypes more convenient. Using this strategy, a phenotypic assay was performed on an HBV strain carrying an rtS246T variant isolated from a patient with chronic hepatitis B that was only responsive partially to entecavir therapy. The results indicated that this strain is sensitive to entecavir in vitro.

Impact of hepatitis B e antigen-suppressing mutations on the replication efficiency of entecavir-resistant hepatitis B virus strains

Hepatitis B e antigen (HBeAg)-negative hepatitis B commonly requires long-term treatment with nucleos(t)ide analogues aiming at persistently suppressing hepatitis B virus (HBV) replication to halt progression of liver disease and prevent complications. Entecavir (ETV) is widely used in HBeAg-negative hepatitis B, but distinct HBV polymerase mutations can confer resistance against ETV, in conjunction with lamivudine resistance. Precore (PC) and basal core promoter (BCP) mutations that underlie HBeAg-negativity enhance replication of lamivudine-resistant mutants. To comprehensively analyse the impact of PC or BCP mutations on viral replication of ETV-resistant HBV mutants, replication-competent HBV constructs were generated harbouring lamivudine resistance (rtM204V/rtL180M, rtM204I) plus ETV resistance (rtS202G, rtS202I or rtT184G) on wild-type (WT)-, PC- and BCP-backgrounds. Functional consequences on viral fitness and susceptibility to antivirals were assessed in vitro. The presence of any ETV resistance drastically reduced viral replication when compared to WT HBV. In rtS202G mutants (plus lamivudine resistance), addition of either PC or BCP mutations moderately enhanced the reduced replication, without reaching WT HBV levels. In rtS202I or rtT184G mutants, PC and BCP mutations did not significantly improve viral fitness. All ETV-resistant constructs, independently of PC or BCP mutations, showed resistance towards ETV and lamivudine, but remained susceptible to tenofovir. Our data demonstrate that HBeAg-suppressing PC or BCP mutations cannot restore the strongly reduced replicative capacity of ETV-resistant HBV mutants to WT level, although they moderately increase replication of rtS202G combination mutants. ETV resistance thereby differs from lamivudine resistance alone, corroborating that ETV is in short term a safe option for HBeAg-negative patients.

Nucleoside/nucleotide analogues in the treatment of chronic hepatitis B

The current available agents for the treatment of chronic hepatitis B (CHB) include immunomodulatory agents, such as interferon-α and pegylated interferon-α, and oral nucleoside/nucleotide analogues (NAs), including lamivudine, adefovir, telbivudine, entecavir and tenofovir. The NAs work mainly by inhibiting hepatitis B virus (HBV) DNA polymerase activity and thus suppress HBV replication. Oral NAs have become the mainstay of CHB treatment, mainly due to their profound viral suppressive effects and also due in part to the ease of single daily dosing and lack of significant side effects. One major drawback of NA therapy is the development of drug resistance mutations with long-term treatment. Lamivudine, the first oral NA approved for CHB patients, is associated with high rates of drug resistance, with resultant virological relapse and biochemical flare. Fortunately, newer and more potent NAs, such as entecavir and tenofovir, have very low resistance rates, with potent and durable viral suppression. This review is aimed at the current developments in NAs for CHB treatment, detailing the mechanisms of antiviral activity of the different agents, the efficacy of viral suppression, the achievement of treatment endpoints, the development of drug resistance and the optimal strategies for using these drugs.

Three years of continuous entecavir therapy in treatment-naïve chronic hepatitis B patients: VIRAL suppression, viral resistance, and clinical safety

OBJECTIVES

We aimed to determine the antiviral potency, viral resistance rate, and clinical safety of 3-year continuous entecavir treatment.

METHODS

We determined the cumulative rates of undetectable hepatitis B virus DNA (HBV DNA) levels (< 12 IU/ml), hepatitis B e antigen (HBeAg) seroconversion, alanine aminotransferase (ALT) normalization, and entecavir signature mutations (using the sensitive line probe assay) and monitored any side effects for 222 treatment-naïve chronic hepatitis B (CHB) patients (40.5% HBeAg positive) on continuous entecavir treatment for 3 years.

RESULTS

The median age and follow-up duration were 45 years and 25.1 months, respectively. In all, 222, 188, and 101 patients had been followed up for at least 1, 2, and 3 years, respectively. There were incremental increases in the rates of HBV DNA undetectability, HBeAg seroconversion, and ALT normalization reaching to 92.1, 43.9, and 90.4% at year 3, respectively. In all, 100 and 76.5% of patients with baseline HBV DNA levels < and ≥ 8 logs copies/ml, respectively, had undetectable HBV DNA at year 3. The cumulative rate of entecavir-resistant mutations was 1.2% at year 3. Three patients experienced virologic breakthrough, one with resistance development, one with subsequent HBeAg seroconversion, and one with subsequent decline in HBV DNA. Two patients with baseline rt204I mutations responded to entecavir treatment. There were no serious adverse events.

CONCLUSIONS

Using very sensitive HBV DNA and viral resistance assays, continuous entecavir treatment for treatment-naïve CHB patients for 3 years was associated with >90% chance of undetectable HBV DNA and only 1.2% chance of emergence of entecavir-resistant mutations.

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.

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: from diagnosis to treatment

During the next few decades, vaccination against hepatitis B virus (HBV) will dramatically change the epidemiological profile of this worldwide infection especially when Heath Policies encourage including HBV vaccination program for the newborns. However, it is still estimated that more than 2000millions living people have met HBV. Symptomatic hepatitis with jaundice is less frequent than asymptomatic infection; however, as much as 350millions of individuals remain chronically infected by HBV. In these cases, the need for efficient antiviral therapy remains clear when a viral replication is observed to control the risk of progression and the need for liver transplantation, which represents the only end-stage treatment. Indeed, patients having chronic hepatitis B (CHB) can now be successfully treated using nucleos(t)ide analogs (NA) or pegylated interferon (PEG-IFN). Therefore, beside vaccination, prevention of the progression of the disease to cirrhosis and liver decompensation, leading to end-stage liver disease and/or to hepatocellular carcinoma, by inhibiting viral replication seems to represent the best approach to improve survival. At last but not least, co-morbidities and other viral infections, leading also to chronic liver cirrhosis or liver inflammation such as the specific satellite delta virus (HDV), human immunodeficency virus (HIV) and/or hepatitis C (HCV) virus, are able to accelerate the progression and have to be taken in account. Interestingly, in treated infection, the dogma of the irreversibility of the liver fibrosis, when the cirrhosis is constituted, is tumbling down. In this review, we will focus on the clinical, virological and therapeutic aspects of hepatitis B infection in order to expose the proposals to follow-up and treat HBV-infected patients and the prevention of drug-resistant HBV mutants that frequently arise, leading to treatment failure and progression to liver disease.

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.

Efficacy of switching to entecavir monotherapy in Japanese lamivudine-pretreated patients

BACKGROUND AND AIMS

To assess the efficacy of switching Japanese chronic hepatitis B patients from lamivudine monotherapy to entecavir 0.5 mg/day.

METHODS

A retrospective analysis was conducted on 134 patients switched to entecavir between September 2006 and February 2008 for 6 months or more. Patients were divided into three groups based on viral load at entecavir switching point (baseline < 2.6, 2.6-5.0 and > 5.0 log(10) copies/mL).

RESULTS

At baseline, detection of lamivudine-resistant virus was highest in patients with higher hepatitis B virus (HBV) DNA (76% vs 23% in > or = 2.6 and < 2.6 log(10) copies/mL, respectively), and in patients with longest previous exposure to lamivudine (52%, 28% and 24% for > 3 years, 1-3 years and < 1 year, respectively). Two years after entecavir switching, HBV DNA suppression to less than 2.6 log(10) copies/mL was achieved in 100% (32/32), 92% (12/13) and 44% (4/9) of patients in the less than 2.6, 2.6-5.0 and more than 5.0 log(10) copies/mL baseline groups, respectively. Alanine aminotransferase (ALT) normalization occurred in 76-96% and 90-100% of patients following 1 and 2 years of entecavir treatment, respectively. One patient (2.6-5.0 log(10) copies/mL) with lamivudine-resistant mutants at baseline developed entecavir resistance at week 48 during follow up.

CONCLUSION

Switching to entecavir 0.5 mg/day achieves or maintains undetectable HBV DNA levels and ALT normalization over 2 years, especially in patients with viral load less than 5.0 log(10) copies/mL.

Antiviral effect of entecavir in chronic hepatitis B: influence of prior exposure to nucleos(t)ide analogues

BACKGROUND & AIMS

Entecavir is a potent inhibitor of viral replication in nucleos(t)ide analogue (NA)-naïve chronic hepatitis B patients, but data on the efficacy in NA-experienced subjects are limited.

METHODS

In a multi-center cohort study we investigated 161 chronic hepatitis B patients (34% NA-experienced) treated with entecavir monotherapy.

RESULTS

During a median follow-up of 11 (3-23)months, 82 (79%) of 104 NA-naïve patients achieved virologic response (VR), defined as HBV DNA <80IU/ml, and none of the patients (0%) developed genotypic entecavir-resistance. VR was demonstrated in 31 (54%) of 57 NA-experienced patients during a median follow-up of 12 (3-31)months. Patients with lamivudine-resistant mutations at the start of entecavir monotherapy had a reduced probability of achieving VR compared to lamivudine-naïve patients (HR 0.14; 95% CI 0.04-0.58; p=0.007). Antiviral efficacy was not decreased by prior treatment with lamivudine when lamivudine-resistance had never developed (HR 0.81; 95% CI 0.43-1.52; p=0.52). Prior adefovir therapy without development of adefovir-resistance (HR 0.84; 95% CI 0.43-1.64; p=0.61) and presence of adefovir-resistance (HR 0.86; 95% CI 0.27-2.71; p=0.80) did not influence antiviral response to entecavir. Switching to a tenofovir-containing treatment regimen resulted in viral load decline in patients with entecavir-resistance associated mutations.

CONCLUSIONS

Entecavir proved to be efficacious in NA-naïve patients. The antiviral efficacy of entecavir was not influenced by prior treatment with adefovir or presence of adefovir-resistance. Entecavir should not be used in patients with previous lamivudine-resistance, yet it may still be an option in lamivudine-experienced patients in case lamivudine-resistance never developed.

Entecavir for the long-term treatment of chronic hepatitis B

Hepatitis B virus is a major cause of chronic liver disease worldwide and is associated with an increased risk of hepatocellular carcinoma, progressive hepatic fibrosis and end-stage liver disease. Suppression of HBV replication is recognized as the primary on-treatment goal of antiviral therapy, as reduction of serum HBV DNA to low or undetectable levels is highly likely to have a positive impact on long-term clinical outcomes in HBV-associated chronic liver disease. Entecavir is an oral nucleoside analogue that effectively inhibits HBV polymerase, resulting in rapid viral suppression. Long-term data on patients receiving entecavir for chronic hepatitis B have demonstrated high potency, a low incidence of antiviral drug resistance and good tolerability, making entecavir an ideal first-line agent for the treatment of chronic hepatitis B.

Mechanistic characterization and molecular modeling of hepatitis B virus polymerase resistance to entecavir

Background

Entecavir (ETV) is a deoxyguanosine analog competitive inhibitor of hepatitis B virus (HBV) polymerase that exhibits delayed chain termination of HBV DNA. A high barrier to entecavir-resistance (ETVr) is observed clinically, likely due to its potency and a requirement for multiple resistance changes to overcome suppression. Changes in the HBV polymerase reverse-transcriptase (RT) domain involve lamivudine-resistance (LVDr) substitutions in the conserved YMDD motif (M204V/I ± L180M), plus an additional ETV-specific change at residues T184, S202 or M250. These substitutions surround the putative dNTP binding site or primer grip regions of the HBV RT.

Methods/Principal Findings

To determine the mechanistic basis for ETVr, wildtype, lamivudine-resistant (M204V, L180M) and ETVr HBVs were studied using in vitro RT enzyme and cell culture assays, as well as molecular modeling. Resistance substitutions significantly reduced ETV incorporation and chain termination in HBV DNA and increased the ETV-TP inhibition constant (K_i) for HBV RT. Resistant HBVs exhibited impaired replication in culture and reduced enzyme activity (k_cat) in vitro. Molecular modeling of the HBV RT suggested that ETVr residue T184 was adjacent to and stabilized S202 within the LVDr YMDD loop. ETVr arose through steric changes at T184 or S202 or by disruption of hydrogen-bonding between the two, both of which repositioned the loop and reduced the ETV-triphosphate (ETV-TP) binding pocket. In contrast to T184 and S202 changes, ETVr at primer grip residue M250 was observed during RNA-directed DNA synthesis only. Experimentally, M250 changes also impacted the dNTP-binding site. Modeling suggested a novel mechanism for M250 resistance, whereby repositioning of the primer-template component of the dNTP-binding site shifted the ETV-TP binding pocket. No structural data are available to confirm the HBV RT modeling, however, results were consistent with phenotypic analysis of comprehensive substitutions of each ETVr position.

Conclusions

Altogether, ETVr occurred through exclusion of ETV-TP from the dNTP-binding site, through different, novel mechanisms that involved lamivudine-resistance, ETV-specific substitutions, and the primer-template.

Mechanism of entecavir resistance of hepatitis B virus with viral breakthrough as determined by long-term clinical assessment and molecular docking simulation

The mechanism by which entecavir resistance (ETVr) substitutions of hepatitis B virus (HBV) can induce breakthrough (BT) during ETV therapy is largely unknown. We conducted a cross-sectional study of 49 lamivudine (LVD)-refractory patients and 59 naïve patients with chronic hepatitis B. BT was observed in 26.8% of the LVD-refractory group during weeks 60 to 144 of ETV therapy. A line probe assay revealed ETVr substitutions only in the LVD-refractory group, i.e., in 4.9% of patients at baseline, increasing to 14.6%, 24.4%, and 44.8% at weeks 48, 96, and 144, respectively. Multivariate logistic regression analysis adjusted for age, gender, HBV DNA levels, and LVD resistance (LVDr) (L180M and M204V, but not M204I) indicated that T184 substitutions and S202G (not S202C) were a significant factor for BT (adjusted odds ratio [OR], 141.12, and 95% confidence interval [CI], 6.94 to 2,870.20; OR, 201.25, and 95% CI, 11.22 to 3608.65, respectively). Modeling of HBV reverse transcriptase (RT) by docking simulation indicated that a combination of LVDr and ETVr (T184L or S202G) was characterized by a change in the direction of the D205 residue and steric conflict in the binding pocket of ETV triphosphate (ETV-TP), by significantly longer minimal distances (2.2 A and 2.1 A), and by higher potential energy (-117 and -99.8 Kcal/mol) for ETV-TP compared with the wild type (1.3 A; -178 Kcal/mol) and LVDr substitutions (1.5 A; -141 Kcal/mol). Our data suggest that the low binding affinity of ETV-TP for the HBV RT, involving conformational change of the binding pocket of HBV RT by L180M, M204V plus T184L, and S202G, could induce BT.

Entecavir: a review of its use in chronic hepatitis B

Entecavir (Baraclude), a nucleoside analogue, is rapidly phosphorylated to the active intracellular 5'-triphosphate form that inhibits replication of hepatitis B virus (HBV). Oral entecavir is approved in the US, EU and several countries worldwide for the treatment of chronic HBV infection in adults (> or =16 years of age) with evidence of active viral replication and persistently elevated serum ALT and/or AST levels, and/or histological evidence of active disease. In several randomized, double-blind, multicentre trials, oral entecavir was an effective and generally well tolerated treatment in nucleoside-naive and lamivudine-refractory adult patients with chronic HBV infection, irrespective of whether patients were hepatitis B e antigen (HBeAg)-positive or -negative. Furthermore, it was more efficacious, associated with a lower risk of resistance, and more cost effective than lamivudine in these patient populations, with both drugs having a similar tolerability profile. In the EARLY trial, entecavir was significantly more effective than and as well tolerated as adefovir dipivoxil therapy in nucleoside-naive patients. In addition, in a double-blind, multicentre trial, entecavir plus lamivudine-based highly active antiretroviral therapy (HAART) was more effective than placebo plus lamivudine-based HAART in patients co-infected with HBV and HIV. Although the exact position of entecavir relative to other agents, such as tenofovir disoproxil fumarate and adefovir dipivoxil, for the treatment of chronic HBV infection remains to be fully determined, an important aspect in this positioning is the emergence of drug resistance. Hence, entecavir therapy provides a valuable first-line option in nucleoside-naive patients with chronic HBV infection and is a useful alternative in lamivudine-refractory patients.

Treatment of hepatitis B virus-infected patients: utility of therapeutic recommendations in developing countries

BACKGROUND

The treatment of individuals infected with hepatitis B virus (HBV) is a complex issue in practical settings, despite the explosion of new and effective antiviral agents.

OBJECTIVE

To assess the scope and limitations of ongoing treatment guidelines against HBV from a global perspective.

METHODS

Present therapeutic guidelines against HBV have been discussed with emphasis on their value in developing countries that harbor about 90% of the total number of global patients who are infected with HBV.

RESULTS/CONCLUSION

Treatment of HBV-infected patients should be appropriately followed up and healthcare delivery systems should be able to combat treatment-induced adverse side effects. Current therapeutic guidelines should be optimized based on the socio-economic conditions of developing countries.

Variations in the large surface protein gene of hepatitis B virus in vivo: a longitudinal study and application

AIM: To develop a method for longitudinal study of variations in the large surface protein gene of hepatitis B virus (HBV) in vivo and apply it to the investigation of the dynamics of HBV quasispecies.

METHODS: Two HBV carriers were included in the study. Patient 1 was a 38-year-old male who received no anti-virus therapy before and during the longitudinal study, while patient 2 was a 22-year-old female who received continuous adefovir dipivoxil (ADV) therapy during the one-year longitudinal study. Serum samples were collected from the two patients over the longitudinal period. Nucleic acids were extracted from the serum samples and used as templates to amplify the HBV large surface protein gene. The resulting PCR products were cloned into the pMD18-T vector and sequenced. Variation analysis was performed using sequence alignment tools to characterize and evaluate the dynamic changes of HBV quasispecies.

RESULTS: Of 24 large surface protein gene sequences (10 from patient 1 and 14 from patient 2) analyzed, two from patient 2 contained a 30-nt deletion in PreS2 coding region. Online HBV genotype analysis showed that all the 24 sequences belonged to genotype C. The divergence values (DA, DB and DC) of HBV large surface protein gene from patient 1 were 0.29, 0.16 and 0.23, respectively, while those from patient 2 were 0.80, 2.30 and 1.82, respectively. The 'a' determinant region was perfectly identical among the 10 sequences from patient 1. In patient 2, G145R mutation was found in two sequences (29%) at the beginning and in six sequences (86%) at the end of the study. Four point mutations also were noted in the 'a' determinant region of one sequence from patient 2 at the end of the study.

CONCLUSION: Our results support the quasispecies distribution of HBV inside human hosts. It is feasible to use divergence values DA, DB and DC to characterize and evaluate the dynamic changes of HBV quasispecies. ADV therapy may increase the diversity of HBV quasispecies and thereby raise the risk of developing drug resistance.

Two cases of development of entecavir resistance during entecavir treatment for nucleoside-naive chronic hepatitis B

BACKGROUND

Entecavir (ETV) is a potent nucleoside analogue against hepatitis B virus (HBV), and emergence of drug resistance is rare in nucleoside-naive patients because development of ETV resistance (ETVr) requires at least three amino acid substitutions in HBV reverse transcriptase. We observed two cases of genotypic ETVr with viral rebound and biochemical breakthrough during ETV treatment of nucleoside-naive patients with chronic hepatitis B (CHB).

RESULTS

Case 1: A 44-year-old HBeAg-positive man received ETV 0.1 mg/day for 52 weeks and 0.5 mg/day for 96 weeks consecutively. HBV DNA was 10.0 log(10) copies/ml at baseline, declined to a nadir of 3.1 at week 100, and rebounded to 4.5 at week 124 and 6.7 at week 148. Alanine aminotransferase (ALT) level increased to 112 IU/l at week 148. Switching to a lamivudine (LVD)/adefovir-dipivoxil combination was effective in decreasing HBV DNA. Case 2: A 47-year-old HBeAg-positive man received ETV 0.5 mg/day for 188 weeks. HBV DNA was 8.2 log(10) copies/ml at baseline, declined to a nadir of 2.9 at week 124, and then rebounded to 4.7 at week 148 and 6.4 at week 160. ALT level increased to 72 IU/l at week 172. The ETVr-related substitution (S202G), along with LVD-resistance-related substitutions (L180M and M204V), was detected by sequence analysis at week 124 in both case 1 and case 2.

CONCLUSIONS

ETVr emerged in two Japanese nucleoside-naive CHB patients after prolonged therapy and incomplete suppression and in one patient after <0.5 mg of dosing. ETV patients with detectable HBV DNA or breakthrough after extended therapy should be evaluated for compliance to therapy and potential emergence of resistance.

Ultrasensitive genotypic detection of antiviral resistance in hepatitis B virus clinical isolates

Amino acid substitutions that confer reduced susceptibility to antivirals arise spontaneously through error-prone viral polymerases and are selected as a result of antiviral therapy. Resistance substitutions first emerge in a fraction of the circulating virus population, below the limit of detection by nucleotide sequencing of either the population or limited sets of cloned isolates. These variants can expand under drug pressure to dominate the circulating virus population. To enhance detection of these viruses in clinical samples, we established a highly sensitive quantitative, real-time allele-specific PCR assay for hepatitis B virus (HBV) DNA. Sensitivity was accomplished using a high-fidelity DNA polymerase and oligonucleotide primers containing locked nucleic acid bases. Quantitative measurement of resistant and wild-type variants was accomplished using sequence-matched standards. Detection methodology that was not reliant on hybridization probes, and assay modifications, minimized the effect of patient-specific sequence polymorphisms. The method was validated using samples from patients chronically infected with HBV through parallel sequencing of large numbers of cloned isolates. Viruses with resistance to lamivudine and other l-nucleoside analogs and entecavir, involving 17 different nucleotide substitutions, were reliably detected at levels at or below 0.1% of the total population. The method worked across HBV genotypes. Longitudinal analysis of patient samples showed earlier emergence of resistance on therapy than was seen with sequencing methodologies, including some cases of resistance that existed prior to treatment. In summary, we established and validated an ultrasensitive method for measuring resistant HBV variants in clinical specimens, which enabled earlier, quantitative measurement of resistance to therapy.