Resistance to adefovir dipivoxil therapy associated with the selection of a novel mutation in the HBV polymerase

Dynamic changes of HBV quasispecies and deletion patterns in a chronic hepatitis B patient

Hepatitis B virus (HBV) infection is a dynamic process during which molecular variants are selected continuously to adapt to changes. In addition to drug resistant mutations, sequential antiviral therapy may also lead to the selection of deleted mutants. To investigate this process, the following samples were collected from a patient who failed lamivudine therapy and then was switched to adefovir dipivoxil. HBV DNA was sequenced at two separate regions; a 1 kb region of reverse transcriptase (RT) and a 1.5 kb region encompassing the C gene and part of the preS gene. Sequence analysis of the RT region showed that the prevailing lamivudine resistant mutations were reduced after switching to adefovir dipivoxil, and ultimately the mutations were undetectable. Quasispecies distribution and deletion patterns in the C and preS regions were also different between the two antiviral therapies. In lamivudine-treated samples, wild-type strains (57.7%) were dominant and deletions in the preS region were observed. However, in the subsequent therapy involving adefovir dipivoxil, a virus population harboring 81 and 96 bp deletions (86%) in the C gene prevailed. Both major deletions encompassed T- and B-cell epitopes. Meanwhile, the frequencies of the preS deletions decreased significantly, except for the 129 bp deletion. Notably, the presence of 81, 96, and 129 bp deletions was always accompanied with some nucleotide substitutions. In conclusion, the prevalence of deletions at the C gene epitopes accompanied with the gradual disappearance of lamivudine resistance mutations may contribute to the survival of HBV under sequential antiviral therapy.

Hepatitis B virus variants

HBV replicates through reverse transcription of an RNA intermediate; the inherent lack of proofreading causes a high mutation frequency. Mutations in the precore and core promoter regions that abolish or reduce the production of hepatitis B e antigen occur most commonly. Patients with these HBV variants remain viremic and can develop progressive liver disease. Mutations in the core promoter region are associated with an increased risk of hepatocellular carcinoma. Exogenous selection pressure might favor certain mutations. Mutations in the HBV polymerase that confer resistance to nucleoside and nucleotide analog treatments are a major barrier to the success of therapy for hepatitis B. The development of antiviral drug resistance negates the initial treatment response and can lead to hepatitis flares and hepatic decompensation. Prompt addition of another drug to which the virus is not cross-resistant is required. Mutations in the HBV surface protein that facilitate escape from host immunity are responsible for the failure of immune prophylaxis in infants who received HBV vaccine and in liver transplant recipients who received hepatitis B immune globulin.

Quantitative detection of the M204V hepatitis B virus minor variants by amplification refractory mutation system real-time PCR combined with molecular beacon technology

Mutations in the highly conserved tyrosine-methionine-aspartate-aspartate (YMDD) motif are frequently associated with resistance to antivirals and represent a major concern in the treatment of hepatitis B virus (HBV) infection. Conventional methods fail to detect minority populations of drug-resistant viral quasispecies if they represent less than 25% of the total sample virus population. The amplification refractory mutation system real-time PCR (ARMS RT-PCR) was combined with molecular beacon technology using the LightCycler system. The samples from HBV patients selected for assay evaluation included (i) 57 samples from treatment-naïve patients for biological discriminatory ability (cutoff) estimation, (ii) 12 samples from patients with treatment failure that were M204V positive by sequencing, and (iii) 13 samples from patients with treatment failure that were negative for mutation at codon 204 by sequencing. The discriminatory ability of the assay was 0.25% when tested with laboratory-synthesized DNA target sequences. The median mutant-to-wild-type ratio for samples from naive patients tested positive for the wild type and for mutant variants was 0.01% (5th and 95th percentiles = 0.0001 and 0.04%, respectively). A value of 0.04% was selected as the biological cutoff of the assay of clinical samples. In all samples M204V positive by sequencing (12/12), the mutant variant was detected as the predominant population (range, 82.76 to 99.43%). Interestingly, in 5 (38%) of 13 samples negative by sequencing, the M204V variant was detected at a ratio above the biological cutoff (0.05 to 28%). The assay represents an efficient technique for the early detection and quantification of M204V variants before mutant strains emerge to dominate the population.

[Antiviral efficacy of lamivudine/adefovir combination therapy in chronic hepatitis b patients with resistance to lamivudine and adefovir consecutively]

BACKGROUND/AIMS

The aim of this study was to elucidate the antiviral efficacy of lamivudine (LMV)-adefovir (ADV) combination therapy in chronic hepatitis B patients who showed resistance to LMV and ADV consecutively.

METHODS

A retrospective review was performed in eighteen patients with chronic hepatitis B who developed virologic breakthroughs during LMV-ADV sequential mono-therapy and treated with LMV-ADV combination therapy.

RESULTS

The median duration of follow up was 17 months (range, 6-27) after the start of LMV-ADV combination therapy. Mean HBV DNA level in log10 IU/mL was 6.08+/-0.95, 4.05+/-1.66, 3.17+/-1.58, 3.18+/-2.16, and 2.35+/-1.52 at 0, 3, 6, 12, and 24 months, respectively. Sixteen patients (88.9%) showed HBV DNA reduction below detection limit (<20,000 IU/mL). HBeAg seroconversion was observed in one patient (7.1%) after 8 months of combination therapy. Virologic breakthrough occurred in only one patient after 21 months of combination therapy. Viral rebound occurred in two patients at 12 months and 14 months of combination therapy. Normalization of serum ALT was achieved in twelve patients (66.7%). Primary non-response was observed in two cases (11.1%).

CONCLUSIONS

LMV-ADV combination treatment was effective in 88.9% of patients with resistance to LMV and ADV in a short-term follow up. It may be applied as a bridge therapy until another effective antiviral regimen becomes available.

Anti-hepatitis B virus activity in vitro of combinations of tenofovir with nucleoside/nucleotide analogues

BACKGROUND

Long-term management of some chronic hepatitis B patients might require combination therapy using drugs with distinct resistance profiles to sustain viral suppression and to reduce the resistance-associated failure. Tenofovir disoproxil fumarate (TDF), approved for hepatitis B virus (HBV) and HIV-1 treatment, is active against wildtype HBV and HBV containing YMDD mutations, which confer resistance to emtricitabine (FTC), lamivudine (3TC) and telbivudine (LdT) and contribute to entecavir (ETV) resistance. We therefore evaluated the in vitro anti-HBV activity of tenofovir (TFV), the active parent drug of TDF, combined with FTC, 3TC, ETV, LdT and adefovir (AFV).

METHODS

The anti-HBV activities of the compounds were tested using the AD38 cell line that expresses wild-type HBV from a tetracycline-controllable promoter. Intracellular HBV DNA levels were quantified using real-time PCR assay and cytotoxicities were assessed with XTT assays. The antiviral data of the drug combinations were evaluated using MacSynergy analyses on the basis of the Bliss independence model as well as isobologram analyses on the basis of the Loewe additivity theory.

RESULTS

All drug combinations tested, FTC+TFV, 3TC+TFV, ETV+TFV, LdT+TFV and AFV+TFV, showed additive antiviral interactions as analysed by MacSynergy. Isobologram analyses revealed that these combination pairs were additive, with the exception of FTC+TFV, which demonstrated slight synergistic activity. No cytotoxic or antagonistic effects were observed with any of the combinations tested.

CONCLUSIONS

The combination of TFV with FTC, 3TC, ETV, LdT or AFV had additive to slightly synergistic anti-HBV effects in vitro. These results support the use of TDF as a component in combination regimens with currently available anti-HBV nucleoside analogues.

Evolution of hepatitis B virus polymerase mutations in a patient with HBeAg-positive chronic hepatitis B virus treated with sequential monotherapy and add-on nucleoside/nucleotide analogues

BACKGROUND

Nucleoside/nucleotide analogues are a fundamental tool for the treatment of chronic hepatitis B virus (HBV). Sequential anti-HBV treatment might lead to the selection of mutations.

OBJECTIVE

This report aimed to analyze the genetic evolution of the reverse-transcriptase (RT) gene of viral quasispecies in a patient with hepatitis B e antigen (HBeAg)-positive chronic HBV who received, sequentially, lamivudine (LAM), adefovir dipivoxil (ADV), and ADV + telbivudine (LDT) combination treatment over a total of 108 weeks.

METHODS

A 20-year-old Chinese man presented to Huashan Hospital, Fudan University, Shanghai, People's Republic of China, with hepatitis B surface antigen-positive and HBeAg-positive chronic HBV and was sequentially treated with LAM 100 mg/d for 18weeks,ADV 10mg/d for 68weeks, and ADV 10mg/d + LDT 600 mg/d combination treatment for 22 weeks. Compliance was monitored every 4 weeks using a pill count. For genotypic analysis, the RT region of the polymerase gene from the serum of this patient was amplified, cloned, and sequenced. Fifty clones with HBV insert were selected for sequencing at weeks 0 (baseline), 18, 22, 60, 70, 86, and 108.

RESULTS

The rtM204V/L LAM-resistance mutation was detected in 4.4% (2/45) of clones prior to LAM treatment. At week 18 during LAM treatment, the rtM204I mutation became predominant, being present in 79.5% (35/44) of clones. The rtM204I mutation was associated with compensatory mutations (rtL180M and rtT184L). A total of 9.1% (4/44) of the clones harbored the rtL180M + rtT184L + rtM204I mutations. Two new mutations, rtL229V and rtV191I, were detected in 75.0% (33/44) and 11.4% (5/44) of clones, respectively. At week 22 during ADV treatment, LAM-resistance mutations (rtL180M, rtT184L, rtM204I, rtV191I, and rtL229V) were not detected. At week 86 during ADV therapy, the rtN236T ADV-resistance mutation was detected in 58.8% (20/34) of clones. A total of 20.6% (7/34) of the clones harbored the rtK212T + rtM250L mutation, and rtA181V was found in 2.9% (1/34) of the clones. At week 108, after the patient had been receiving ADV + LDT combination therapy for 22 weeks, rtS202G and rtI269T had emerged, representing 28.9% (13/45) and 8.9% (4/45), respectively, of the viral population during ADV + LDT combination treatment. We also detected several polymorphic sites,including rtF221Y, rtS223A, rtI224V, rtN238H, rtL267Q, and rtQ271M, during the sequential treatment. After 22 weeks of combination treatment, HBV DNA count was decreased to less than the lower limit of quantitation (<200 copies/mL).

CONCLUSIONS

This report identified HBV mutations that escaped the antiviral pressure of LAM, ADV, and ADV + LDT in this patient and provided insight into the process of mutation selection through genotypic analysis during antiviral treatment. Mutations selected under sequential treatments of LAM, ADV, and ADV + LDT can lead to a series of compensatory mutations, which partially restore the level of viral replication. ADV administered in combination with LDT appeared to be effective in this selected case with clinical or virologic resistance to sequential treatment with LAM and ADV.

Prevention and management of drug resistance for antihepatitis B treatment

Emergence of drug resistance in antiviral therapy for chronic hepatitis B negates treatment benefits. There is a lower chance for emergence of resistance for drugs with rapid and potent viral suppression and a high genetic barrier for resistant mutations. Measurement of viral load at 24 weeks' treatment to aid decision making is mandatory for patients receiving drugs that are associated with a higher resistance rate. Combination treatment with drugs that belong to different groups is associated with a lower chance of resistance. To ensure better control of viral replication in patients with drug resistance, the addition of another drug without an overlapping resistance profile should be given as early as possible, preferably at the time when genotypic resistance emerges. With such strategies, most patients can be maintained in clinical remission. However, because of the mechanism of viral persistence, research efforts should continue to anticipate and prevent the emergence of multidrug-resistant strains.

Antiviral resistance and hepatitis B therapy

The management of chronic hepatitis B currently rests with long-term therapy using oral nucleoside analogs. The major limitation of long-term therapy is antiviral resistance. Antiviral resistance is due to the high rate of mutations that can occur during hepatitis B virus (HBV) replication and the selection of these mutants due to a replication advantage in the presence of the antiviral agent. Indeed, high rates of antiviral resistance have been found with long-term use of lamivudine, in up to 76% of patients treated for 5 years or more. Rates of antiviral resistance are lower with adefovir therapy, approximately 30% at 5 years. Newer more potent nucleoside analogs (tenofovir and entecavir) have proven to have much lower rates of antiviral resistance (<1% after 2 years in treatment-naïve subjects), but the long-term rates of resistance have yet to be fully defined. The appearance of these viral mutations (genotypic resistance) is usually followed by rises in HBV DNA levels (virological breakthrough) and then by rises in serum aminotransferase levels (biochemical breakthrough). The appearance of antiviral resistance can be accompanied by a transient but occasionally severe exacerbation of the underlying liver disease which in some instances has led to acute liver failure. Combinations of nucleoside analogs may offer an approach to preventing antiviral resistance, but the efficacy and safety of this approach have yet to be shown. A future research priority is to identify new agents active against HBV that target different steps in the viral life-cycle and might provide effective means to circumvent the antiviral resistance of nucleoside analogs.

Adefovir dipivoxil resistance patterns in patients with lamivudine-resistant chronic hepatitis B

Background

Lamivudine (3TC)-resistant chronic hepatitis B patients demonstrated a higher rate of adefovir dipivoxil (ADV) resistance compared with nucleoside-naive patients. This study describes ADV mutation patterns in 3TC-resistant patients treated with ADV+3TC or ADV monotherapy, investigating whether mutations selected during 3TC therapy predispose to ADV resistance. Risk factors for ADV resistance were also evaluated.

Methods

A total of 60 3TC-experienced patients were treated with (or switched to) ADV monotherapy (30 patients) or ADV+3TC combination therapy (30 patients), and followed for at least 12 months. In all patients the hepatitis B virus reverse transcriptase (RT) region was amplified and directly sequenced before initiating ADV. The RT sequence was reevaluated for virological breakthrough patients and phenotypic analysis was performed for several patients.

Results

In total, 14 (23%) patients showed virological breakthrough (10/30 on ADV monotherapy and 4/30 on ADV+3TC). ADV resistance mutations (rtA181V/T and rtN236T) were detected alone or in combination for 11/14 patients, whereas novel substitutions were present in 3 patients. Before ADV treatment, apart from 3TC resistance signature mutations, additional changes were found, including the rtA181T mutation, which was already present in 2/14 ADV-resistant patients.

Conclusions

Although most patients showed virological breakthrough because of the well known rtA181V/T and rtN236T substitutions, more complex patterns were also found. ADV monotherapy, dose reduction and suboptimal virological response after 48 weeks of therapy were significantly associated with ADV resistance.

Immunopathogenesis of hepatitis B persistent infection: implications for immunotherapeutic strategies

It has been shown that cellular immunity, especially by cytotoxic T lymphocytes (CTLs), NK cells and NK-T cells, plays a central role in the control of virus infection. In addition, CD4+ T cells facilitate both CTL and B-cell responses. Hyporesponsiveness of HBV-specific T cells in peripheral blood has been shown in patients with chronic HBV infection. Interferon and nucleos(t)ide analogs, such as lamivudine, adefovir, entecavir and tenofovir, are the currently available treatments. Unfortunately, the efficacy of nucleos(t)ide analogs is limited by viral reactivation by the emergence of escaped mutants in cases of prolonged treatment. Therefore, immunotherapy is one of the significant options to eradicate or control HBV replication without drugs. The aim of immunotherapies is to decrease the levels of viral replication and to eradicate infected hepatocytes. For this reason, new strategies for immunotherapies by vaccination target not only the induction or stimulation of CD4+ and CD8+ T cell responses, but also the induction of proinflammatory cytokines capable of controlling viral replication. We will review the immunopathogenesis of persistent HBV infection, especially focusing on the mechanisms of immune suppression. Then we will review the immunotherapy for HBV persistent infection.

Transfusion of autologous cytokine-induced killer cells inhibits viral replication in patients with chronic hepatitis B virus infection

Adoptive immune transfer plays an important role in clearance of hepatitis B virus (HBV) in chronic hepatitis B (CHB) patients. However, it is unclear whether cytokine-induced killer (CIK) cells could suppress HBV replication in CHB patients, especially if drug resistance develops. In this study, functional CIK cells were efficiently generated from 21 CHB patients and were transfused in an autologous manner. We found that CIK cells from the CHB patients displayed substantial proliferation and function. Administration of the CIK cells closely correlated with the decrease in the serum HBV load and improvement in liver function in some patients. The virological response rate in patients with baseline serum alanine aminotransferase (ALT) levels of >40 U/L was higher than that in patients with baseline serum ALT levels of < or = 40 U/L. Moreover, patients who had HBeAg loss or showed seroconversion generally had baseline serum ALT levels of >40 U/L. No serious side effects were observed. This protocol represents an alternative immune therapeutic strategy for the disease.

Combination therapy of lamivudine and hepatitis B vaccine for chronic hepatitis B: an analysis of 39 cases

AIM: To investigate the therapeutic efficacy of combination therapy of LAM plus hepatitis B (HB) vaccine for chronic HBV-infected patients.

METHODS: A total of 79 chronic HBV-infected patients CHB were enrolled in the study, and randomized to receive either LAM monotherapy (n = 40) or combination therapy of LAM and HB vaccine (n = 39). In the combination therapy group, 100 mg/d of LAM was administered as a baseline therapy, and 20 μg of HB vaccine was injected subcutaneously every two weeks starting at the 13th week after LAM administration, 12 times in total.

RESULTS: After 52 weeks' treatment, the rate of ALT normalization in HBeAg⁺ patients was significantly higher in combination therapy group than in the monotherapy group (93.3% vs 78.1%, P = 0.026). After 24 weeks' treatment, the HBV DNA negativity rate in HBeAg⁺ patients was significantly higher in combination therapy group than in monotherapy group (93.3% vs 43.8%, P < 0.05), and rates of HBeAg loss or HBeAg seroconversion in HBeAg⁺ patients were not remarkably different between monotherapy group and combination group, as well as the rates of ALT normalization or HBV DNA seroconversion in HBeAg^- patients between the monotherapy group and combination group. At the same time, no adverse effects with the use of HB vaccine were observed in all the patients treated with the combination therapy.

CONCLUSION: Combination therapy of LAM and HB vaccine is a safe and effective way to enhance the rate of ALT normalization and HBV DNA negativity, especially in HBeAg⁺ patients.

On-treatment monitoring of adefovir therapy in chronic hepatitis B: virologic response can be assessed at 24 weeks

Patients with chronic hepatitis B (CHB) who will and those who will not respond to adefovir (ADV) monotherapy need to be identified at an early stage in order to adjust treatment and prevent future development of antiviral resistance. In a single-centre cohort study, we investigated 76 CHB patients [50% hepatitis B e antigen (HBeAg)-positive] treated with long-term ADV monotherapy. During a median follow-up of 122 (24-185) weeks, 42 (55%) patients achieved virologic response (VR), defined as HBV-DNA levels <10(3) copies/mL, and 10 patients (13%) developed genotypic ADV resistance. Independent baseline predictors of VR were HBeAg negativity [hazard ratio (HR) 2.98; 95% confidence interval (CI) 1.24-7.19; P = 0.02], high alanine aminotransferase (ALT) levels (HR 1.11; 95% CI 1.05-1.18; P = 0.001), and low HBV-DNA levels (HR 0.56; 95% CI 0.41-0.75; P < 0.001). HBV-DNA at week 24 demonstrated a higher predictive value for VR than HBV-DNA at week 48. Important predictors of genotypic resistance were presence of cirrhosis (HR 6.54; 95% CI 1.39-30.9; P = 0.018), and not achieving VR during treatment (HR 6.60; 95% CI 1.35-32.4; P = 0.008). Patients without VR at week 24 already demonstrated a trend towards the emergence of ADV resistance (P = 0.07). HBV-DNA at week 24 was a better on-treatment predictor of VR than HBV-DNA at week 48, and ADV-resistant mutations developed more frequently in patients without VR at week 24. Therefore, our study suggests that virologic response to ADV therapy can be assessed at 24 weeks, instead of the generally recommended 48 weeks.

Spontaneous HBeAg seroconversion and loss of hepatitis B virus DNA after acute flare due to development of drug resistant mutants during entecavir monotherapy

AIMS

Patients with chronic hepatitis B virus (HBV) infection under entecavir (ETV) treatment develop resistant mutants with viral rebound. Here, we report an interesting case of spontaneous loss of HBV-DNA and seroconversion following an acute flare after the development of ETV-resistant mutants. This patient received ETV after lamivudine breakthrough.

METHODS

Cloning and sequence analysis of the HBV reverse transcriptase (RT) region were performed with seven samples during ETV therapy. In addition, two full-length HBV genomes derived from samples before and after the emergence of ETV resistance were sequenced.

RESULTS

ETV resistant mutants appeared at week 228, with virological and biochemical rebound at the same time. Unexpectedly, HBeAg seroconversion occurred 8 weeks later. The viral load decreased and became undetectable from week 252. Analysis of HBV isolates in the patient at week 124 revealed that wild-type HBV was predominant at that time and ETV resistant mutants were not found among 20 clones. Interestingly, a new mutant type with rtL180M+rtT184L was found alongside rtL180M+rtT184L+rtM204V/I at week 228 and appeared to develop independently, according to the sequence analysis. In contrast to the previously identified ETV resistant mutants, it did not carry the rtM204V/I mutations.

CONCLUSION

The data presented here indicates that the flare following the emergence of ETV resistant mutants may reflect immune-mediated control of HBV infection, leading to a spontaneous loss of HBV-DNA and seroconversion.

Complex dynamics of hepatitis B virus resistance to adefovir

In patients with hepatitis B e antigen-negative chronic hepatitis B, adefovir dipivoxil administration selects variants bearing reverse transcriptase rtN236T and/or rtA181V/T substitutions in 29% of cases after 5 years. The aim of this study was to characterize the dynamics of adefovir-resistant variant populations during adefovir monotherapy in order to better understand the molecular mechanisms underlying hepatitis B virus resistance to this class of nucleotide analogues. Patients included in a 240-week clinical trial of adefovir monotherapy who developed adefovir resistance-associated substitutions were studied. The dynamics of hepatitis B virus populations were analyzed over time, after generating nearly 4,000 full-length reverse transcriptase sequences, and compared with the replication kinetics of the virus during therapy. Whatever the viral kinetics pattern, adefovir resistance was characterized by exclusive detection of a dominant wild-type, adefovir-sensitive variant population at baseline and late and gradual selection by adefovir of several coexisting resistant viral populations, defined by the presence of amino acid substitutions at position rt236, position rt181, or both. The gain in fitness of one or the other of these resistant populations during adefovir administration was never associated with the selection of additional amino acid substitutions in the reverse transcriptase.

CONCLUSION

Our results suggest that adefovir administration selects poorly fit preexisting or emerging viral populations with low-level adefovir resistance, which subsequently compete to fill the replication space. Viral kinetics depends on the initial virological response to adefovir. Lamivudine add-on restores some antiviral efficacy, but adefovir-resistant variants remain predominant. Whether these adefovir resistance-associated substitutions may confer cross-resistance to tenofovir in vivo will need to be determined.

Management and prevention of drug resistance in chronic hepatitis B

The management of hepatitis B virus resistance to antivirals has evolved rapidly in recent years. The definition of resistance is now well established, with the importance of partial response and the improvement of assays to detect genotypic resistance and virological breakthrough. Data on phenotypic resistance have allowed to define the cross-resistance profile for the main resistant mutants, providing a rationale for treatment adaptation. Clinical studies have shown that an early treatment intervention in case of a virological breakthrough or a partial response with the addition of a second drug having a complementary cross-resistance profile allows one to maintain the majority of patients in clinical remission. The prevention of resistance should rely on the use of the most potent antivirals with a high genetic barrier to resistance as a first-line therapy. The future perspectives are to design strategies to hasten the HBsAg clearance, which should become a new treatment endpoint, to prevent drug resistance and to decrease the incidence of complications of chronic hepatitis B.

[Hepatitis B in patients with HIV infection]

Chronic hepatitis B virus infection affects approximately 10% of HIV-infected patients. There are an estimated 4 million patients with HIV/HBV coinfection. HIV infection has a deleterious effect on the natural history of chronic hepatitis B and increases the risk of progression to cirrhosis and terminal liver disease. Since the widespread use of highly active antiviral therapy (HAART), liver disease has emerged as one of the main causes of morbidity and mortality in HIV-positive patients. Therefore, all patients with HIV/HBV coinfection should be evaluated for treatment of hepatitis B, independently of the CD4 lymphocyte count. Six drugs are currently authorized for the treatment of chronic hepatitis B: standard interferon-alpha (2a and 2b), pegylated interferon alpha-2a, lamivudine, adefovir, entecavir and telbivudine. Other drugs with activity against HBV, such as tenofovir and emtricitabine, are used for the treatment of HIV infection. In patients not requiring HAART, treatment of hepatitis B should preferably consist of drugs without activity against HIV, such as pegylated interferon or adefovir. In contrast, in patients requiring HAART, a combination of drugs with activity against both viruses should be used, such as lamivudine, emtricitabine and tenofovir, with the aim of achieving maximal viral suppression and avoiding the development of resistance. Patients with HIV/HBV coinfection require periodic clinical and virological monitoring. Patients with cirrhosis should undergo ultrasonography and alphafetoprotein determination every 6 months for the early detection of hepatocellular carcinoma.

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.

Current treatment indications and strategies in chronic hepatitis B virus infection

The optimal approach to the management of several marginal cases with chronic hepatitis B virus (HBV) infection is controversial. Serum HBV DNA and aminotransferase levels, and the degree of necroinflammation and fibrosis determine the therapeutic decisions. All patients with elevated aminotransferase (> twice the upper limit of normal) and serum HBV DNA above 20 000 IU/mL should be treated. Liver biopsy is important for therapeutic decisions in cases with mild aminotransferase elevations and serum HBV DNA below 20 000 IU/mL. Chronic HBV patients who do not receive treatment should be followed for life. There are seven agents licensed for chronic hepatitis B: standard and pegylated interferon-alpha, lamivudine, adefovir, entecavir, telbivudine and tenofovir. One-year courses with pegylated interferon-alpha induce sustained off-therapy remission in 30%-32% of patients with HBeAg-positive chronic hepatitis B and in a smaller proportion of patients with HBeAg-negative chronic hepatitis B. Oral antivirals achieve initial on-therapy responses in the majority of patients, but are intended as long-term therapies. Viral suppression has favourable effects on patients’ outcome and modifies the natural course of the disease. Viral resistance, however, is the major drawback of long-term oral antiviral therapy. Lamivudine monotherapy is associated with the highest and entecavir monotherapy with the lowest resistance rate so far. There has been no resistance to tenofovir, but after only 18 mo of treatment to date. The optimal first-line anti-HBV therapy with the best long-term cost/benefit ratio remains unclear. If oral antiviral agents are used, compliance should always be ascertained and HBV DNA levels should be regularly tested.

LB80380: a promising new drug for the treatment of chronic hepatitis B

Hepatitis B virus is a significant cause of liver cirrhosis and hepatocellular carcinoma in patients with chronic infection. Higher levels of viral load are associated with increased risk of developing liver-related complications. The current available oral therapies suppress viral replication through their action on the hepatitis B virus polymerase. As treatment with oral nucleoside/nucleotide analogues is associated with the development of drug-resistant mutations, there is continuing research for newer and more potent antiviral agents to reduce the chance of drug resistance. LB80380, a prodrug, is an oral nucleotide analogue that inhibits viral replication by incorporation into the viral DNA. Antiviral activity against wild-type virus and virus with drug-resistant mutations was demonstrated in Phase II trials, with significant reduction of viral load in patients treated with LB80380. LB80380 was also shown to be safe and well tolerated.

Telbivudine, a nucleoside analog inhibitor of HBV polymerase, has a different in vitro cross-resistance profile than the nucleotide analog inhibitors adefovir and tenofovir

Telbivudine, a nucleoside analog inhibitor of the viral polymerase of hepatitis B virus (HBV), has been approved for the treatment of chronic HBV infection, along with the nucleoside inhibitors lamivudine and entecavir, and the nucleotide inhibitors adefovir and tenofovir. The resistance profiles of these agents were investigated via drug treatment of HepG2 cells stably transfected with wild-type or mutant HBV genomes bearing known resistance mutations. Telbivudine was not active against HBV strains bearing lamivudine mutations L180M/M204V/I but remained active against the M204V single mutant in vitro, potentially explaining the difference in resistance profiles between telbivudine and lamivudine. Against HBV genomes with known telbivudine-resistance mutations, M204I and L80I/M204I, telbivudine, lamivudine and entecavir lost 353- to >1000-fold activity whereas adefovir and tenofovir exhibited no more than 3-5-fold change. Conversely, against HBV cell lines expressing adefovir resistance mutations N236T and A181V, or the A194T mutant associated with resistance to tenofovir, telbivudine remained active as shown by respective fold-changes of 0.5 (N236T) and 1.0 (A181V and A194T). These in vitro results indicate that nucleoside and nucleotide drugs have different cross-resistance profiles. The addition of telbivudine to ongoing adefovir therapy could provide effective antiviral therapy to patients who develop adefovir resistance.

Advances in the diagnosis and treatment of hepatitis B

PURPOSE OF REVIEW

Hepatitis B virus is responsible for much morbidity and mortality worldwide. Although the armament of drugs licensed for its treatment grows, it is increasingly apparent that the efficacy of these drugs is dependent upon much more that their pharmacology.

RECENT FINDINGS

A better understanding of the natural history of chronic hepatitis B infection together with recent advances in the molecular biology of antiviral resistance have given added dimensions to physicians' decision-making thought processes.

SUMMARY

The present review outlines the recent advances in diagnostic testing that enable a better understanding of an individual patient's phase of illness and also how such information can update treatment choices better. In the second part of this review, the licensed therapies and their relative merits are discussed, as is their role in managing resistance to antiviral therapy.

Adefovir for Chronic Hepatitis B Treatment: Identification of Virological Markers Linked to Therapy Response

Background

HBV variants rtA181V/T, rtN236T and rtI233V, which confer resistance to adefovir dipivoxil (ADV), are not detected in many non-responding patients. Virological characteristics useful for predicting response have not been clearly elucidated. We determined pre-treatment virological markers to predict non-response and possible emergence of new variants during therapy.

Methods

This longitudinal study included 41 patients with chronic hepatitis B virus (HBV) infection receiving ADV monotherapy or ADV plus lamivudine (3TC). A fragment of HBV polymerase including catalytic domains was analysed for ADV-resistant variants.

Results

Complete virological response (CVR; HBV DNA<2.5 log10 copies/ml) was observed in 15 (36.6%) patients and partial virological response (PVR; HBV DNA<4 log10 copies/ml) in 23 (56.1%) patients. On multivariate analyses, hepatitis B e antigen (HBeAg) status was independently associated with CVR (hazard ratio [HR]=0.27, P=0.002) and PVR (HR=0.21, P<0.001) and viral genotype with CVR (HR=0.13, P=0.01). Predictive values for HBeAg were 88% for PVR in HBeAg-negative and 79% for non-CVR in HBeAg-positive patients. Predictive values for viral genotype were 93% for non-CVR and 72% for non-PVR for genotype A. On sequencing, variant rt217R (associated with subgenotype A2) was predictive of non-CVR (100%) and non-PVR (72.7%); the rtS219A variant emerged during therapy in three non-PVR patients. Both positions are located in a region likely to be related to the substrate union site, as predicted by our structural model of the HBV polymerase.

Conclusions

Virological pretreatment characteristics (HBeAg, viral genotype and rtL217R polymorphism) are potentially associated with ADV response. HBV polymerase structural modelling has provided a hypothesis to explain the molecular mechanism for ADV resistance associated with rtR217.

Telbivudine for the treatment of hepatitis B disease

Chronic hepatitis B affects approximately 350 million individuals worldwide leading to approximately 500,000 deaths annually. Current therapy includes immune modulators such as IFN-α and the oral antiviral agents, nucleoside analogs such as lamivudine and entecavir, and nucleotide analogs such as adefovir and tenofovir. Recently, telbivudine was approved in the USA for treatment of HBV disease. It is a synthetic nucleoside analog of thymidine that requires phosphorylation to convert to the active triphosphate form. Telbivudine is rapidly absorbed with a long half-life allowing for once-daily dosing. Clinical trials have demonstrated superior antiviral efficacy compared with lamivudine. Telbivudine has shown good correlations between antiviral efficacy at 24 weeks and a favorable outcome at 2 years. Telbivudine is well-tolerated, although monitoring for myopathies is recommended. Telbivudine resistance rates were lower compared with lamivudine. Telbivudine is an option for monotherapy in naive patients or for use in combination therapy in the treatment of chronic hepatitis B.

Predictive factors associated with the progression to hepatic failure caused by lamivudine-resistant HBV

The aims of this study were to select the patients with a potential for progression to hepatic failure due to lamivudine-resistant HBV and to standardize the treatment for patients with lamivudine-resistant HBV. Patients (n = 47) with reactivated hepatitis due to lamivudine-resistant HBV were classified into two groups, with and without potential for progression to hepatic failure, according to the criteria using the data of serum bilirubin level and prothrombin activity after the reactivated hepatitis. Multivariate analysis showed that prothrombin activity at the initiation of lamivudine therapy was related to the deterioration of the liver function after the emergence of lamivudine-resistant HBV (P = 0.0025, 95%CI 0.8269-0.9601). We assume that earlier additional or substitutive treatment with other antiviral agent, such as adefovir dipivoxil, should be recommended when the lamivudine-resistant HBV is detected in patients with the history of decompensated liver disease before the administration of lamivudine, even when hepatitis has not been reactivated yet.

How to diagnose and treat hepatitis B virus antiviral drug resistance in the liver transplant setting

1. Hepatitis B virus variants with antiviral drug-resistant mutations and/or hepatitis B immune globulin-resistant mutations are the main cause of hepatitis B virus reinfections post-liver transplant. 2. Early diagnosis of antiviral drug resistance and prompt initiation of rescue therapy are important in preventing hepatitis flares and hepatic decompensation. 3. Virologic breakthrough is the first indication of antiviral drug resistance. 4. Genotypic resistance testing should be performed when possible to avoid unnecessary modification of treatment in patients who do not have confirmed antiviral drug resistance and to permit appropriate selection of rescue therapy in those who have confirmed antiviral drug resistance. 5. Choice of rescue therapy requires knowledge of the past history of hepatitis B virus treatments and virologic response to those treatments, patterns of mutations detected at the time of virologic breakthrough, and in vitro cross-resistance data. 6. Occurrence of antiviral drug resistance can be reduced by the use of the most potent nucleos(t)ide analogue(s) with the highest genetic barrier to resistance, emphasis of medication compliance, and close monitoring of virologic response.

[Treatment of chronic hepatitis B]

SUMMARY

In recent years, marked progress has been made in the treatment of chronic hepatitis B. Several agents have been approved: interferon alpha-(IFN), pegylated interferon alpha2a (PEG-IFN alpha2a), lamivudine, adefovir, entecavir, telbivudine and recently, tenofovir. Each drug has advantages and limitations. IFN and PEG-IFN alpha2a have the advantage of inducing a sustained virologic response after a defined, limited course of treatment. However, these drugs are only effective in a minority of patients and have frequent side effects. Analogues have the advantage of being administered orally, with good safety profiles and a potent antiviral effect. However, these drugs need to be administered indefinitely since withdrawal of therapy is generally associated with reactivation, and a sustained response is uncommon except in HBeAg positive patients who develop HBe seroconversion. In case of HBe seroconversion, therapy should usually be continued for at least another 24 weeks. The efficacy of lamivudine is limited by the emergence of lamivudine-resistant HBV. Adefovir is associated with a moderate incidence of resistance but its antiviral effect is not optimal. Entecavir has shown to be more effective with a favourable safety profile and a low incidence of resistance. Telbivudine is more potent and has a lower rate of resistance than lamivudine but the resistance rate is significantly higher than other approved drugs. Tenofovir has a potent antiviral effect with a good resistance profile. The future of chronic hepatitis B therapy appears to be different drug combinations. Normally the advantage of drug combinations versus monotherapy should be additive or synergistic antiviral effects and a decrease in viral resistance. Unfortunately, there are few data available and none of the evaluated analogue combinations have been shown to be better than monotherapy. The only combination which has shown a synergistic effect is of pegylated interferon alpha2a with lamivudine. Therefore, combinations of pegylated interferon with the most potent analogues need to be evaluated. The ultimate goal of therapy is HBsAg seroconversion which is more often observed with interferon. Indeed, quantification of serum HBsAg will be a useful tool to predict the treatment outcome. More potent drugs and new combinations as well as understanding the mechanisms of viral resistance should be evaluated to improve the efficacy of treatment.

Understanding the molecular basis of HBV drug resistance by molecular modeling

Despite the significant successes in the area of anti-HBV agents, resistance and cross-resistance against available therapeutics are the major hurdles in drug discovery. The present investigation is to understand the molecular basis of drug resistance conferred by the B and C domain mutations of HBV-polymerase on the binding affinity of five anti-HBV agents [lamivudine (3TC, 1), adefovir (ADV, 2), entecavir (ETV, 3), telbivudine (LdT, 4) and clevudine (l-FMAU, 5)]. In this regard, homology modeled structure of HBV-polymerase was used for minimization, conformational search and induced fit docking followed by binding energy calculation on wild-type as well as on mutant HBV-polymerases (L180M, M204V, M204I, L180M+M204V, L180M-M204I). Our studies suggest a significant correlation between the fold resistances and the binding affinity of anti-HBV nucleosides. The binding mode studies reveals that the domain C residue M204 is closely associated with sugar/pseudosugar ring positioning in the active site. The positioning of oxathiolane ring of 3TC (1) is plausible due the induced fit orientation of the M204 residue in wild-type, and further mutation of M204 to V204 or I204 reduces the final binding affinity which leads to the drug resistance. The domain B residue L180 is not directly close ( approximately 6A) to the nucleoside/nucleoside analogs, but indirectly associated with other active-site hydrophobic residues such as A87, F88, P177 and M204. These five hydrophobic residues can directly affect on the incoming nucleoside analogs in terms of its association and interaction that can alter the final binding affinity. There was no sugar ring shifting observed in the case of adefovir (2) and entecavir (3), and the position of sugar ring of 2 and 3 is found similar to the sugar position of natural substrate dATP and dGTP, respectively. The exocyclic double bond of entecavir (3) occupied in the backside hydrophobic pocket (made by residues A87, F88, P177, L180 and M204), which enhances the overall binding affinity. The active site binding of LdT (4) and l-FMAU (5) showed backward shifting along with upward movement without enforcing M204 residue and this significant different binding mode makes these molecules as polymerase inhibitors, without being incorporated into the growing HBV-DNA chain. Structural results conferred by these l- and d-nucleosides, explored the molecular basis of drug resistance which can be utilized for future anti-HBV drug discovery.

Small-molecule effectors of hepatitis B virus capsid assembly give insight into virus life cycle

The relationship between the physical chemistry and biology of self-assembly is poorly understood, but it will be critical to quantitatively understand infection and for the design of antivirals that target virus genesis. Here we take advantage of heteroaryldihydropyrimidines (HAPs), which affect hepatitis B virus (HBV) assembly, to gain insight and correlate in vitro assembly with HBV replication in culture. Based on a low-resolution crystal structure of a capsid-HAP complex, a closely related series of HAPs were designed and synthesized. These differentially strengthen the association between neighboring capsid proteins, alter the kinetics of assembly, and give rise to aberrant structures incompatible with a functional capsid. The chemical nature of the HAP variants correlated well with the structure of the HAP binding pocket. The thermodynamics and kinetics of in vitro assembly had strong and predictable effects on product morphology. However, only the kinetics of in vitro assembly had a strong correlation with inhibition of HBV replication in HepG2.2.15 cells; there was at best a weak correlation between assembly thermodynamics and replication. The correlation between assembly kinetics and virus suppression implies a competition between successful assembly and misassembly, small molecule induced or otherwise. This is a predictive and testable model for the mechanism of action of assembly effectors.

New paradigms for the treatment of chronic hepatitis B

The main goals of chronic hepatitis B treatment should be the long-term suppression of viral replication to minimize disease progression and the risk for the development of hepatocellular carcinoma. Treatment end-points, depending on surrogate markers alone, in particular hepatitis B e-antigen seroconversion, may not be ideal for patients who acquire the disease early in life. Currently-available drugs include interferons and oral nucleoside/nucleotide analogs. Although interferon therapy provides a finite treatment period, a significant proportion of patients may not respond, and long-term outcome is inconclusive. Long-term efficacy has been demonstrated for both lamivudine and adefovir. However, prolonged nucleoside/nucleotide analog therapy is associated with the emergence of drug-resistant mutations. Therefore, nucleoside/nucleotide analogs with a high genetic barrier and potent antiviral activity, such as entecavir, should be used to reduce the chance of developing drug-resistant mutations. Drugs with a low genetic barrier, including lamivudine and telbivudine, should be used in conjunction with early testing for antiviral response. This can predict favorable outcomes in the long term. The early detection of drug-resistant mutations should prompt clinicians to either add or switch to another agent with a different drug-resistance profile. There are currently no treatment models in the use of combination or sequential therapy in treatment-naïve patients. To date, long-term treatment appears to be the most effective option. Despite recent advances made with better understanding on the natural history of chronic hepatitis B infection and with newer antiviral drugs available, challenges remain with respect to treatment criteria, treatment end-points, and duration of treatment.

Treatment of chronic hepatitis B: recommendations from an Italian workshop

The changing scenario of hepatitis B virus therapy has encouraged the organisation of a workshop, endorsed by three Italian scientific societies, aimed at defining the current recommendations for hepatitis B virus treatment. Liver histology and stage of disease remain fundamental for treatment decisions; interferon and nucleoside/nucleotide analogues-based therapy represent different strategies for different phases of the hepatitis B virus disease. The recommendations defined: new and lower cut-off of hepatitis B virus-DNA for eligibility to therapy according to disease stage, how to optimise the use of nucleoside/nucleotide analogues and to individualise the monitoring of response and what to do with treatment failures. Specific recommendations have also been given for cirrhosis patients, those immune suppressed and co-infected with HIV and other hepatitis viruses.

Antiviral effects of lamivudine, emtricitabine, adefovir dipivoxil, and tenofovir disoproxil fumarate administered orally alone and in combination to woodchucks with chronic woodchuck hepatitis virus infection

Adefovir dipivoxil (ADV) and tenofovir disoproxil fumarate (TDF) are nucleotide analogs that inhibit the replication of wild-type hepatitis B virus (HBV) and lamivudine (3TC)-resistant virus in HBV-infected patients, including those who are coinfected with human immunodeficiency virus. The combination of ADV or TDF with other nucleoside analogs is a proposed strategy for managing antiviral drug resistance during the treatment of chronic HBV infection. The antiviral effect of oral ADV or TDF, alone or in combination with 3TC or emtricitabine (FTC), against chronic woodchuck hepatitis virus (WHV) infection was evaluated in a placebo-controlled study in the woodchuck, an established and predictive model for antiviral therapy. Once-daily treatment for 48 weeks with ADV plus 3TC or TDF plus FTC significantly reduced serum WHV viremia levels from the pretreatment level by 6.2 log(10) and 6.1 log(10) genome equivalents/ml serum, respectively, followed by TDF plus 3TC (5.6 log(10) genome equivalents/ml), ADV alone (4.8 log(10) genome equivalents/ml), ADV plus FTC (one survivor) (4.4 log(10) genome equivalents/ml), TDF alone (2.9 log(10) genome equivalents/ml), 3TC alone (2.7 log(10) genome equivalents/ml), and FTC alone (2.0 log(10) genome equivalents/ml). Individual woodchucks across all treatment groups also demonstrated pronounced declines in serum WHV surface antigen, characteristically accompanied by declines in hepatic WHV replication and the hepatic expression of WHV antigens. Most woodchucks had prompt recrudescence of WHV replication after drug withdrawal, but individual woodchucks across treatment groups had sustained effects. No signs of toxicity were observed for any of the drugs or drug combinations administered. In conclusion, the oral administration of 3TC, FTC, ADV, and TDF alone and in combination was safe and effective in the woodchuck model of HBV infection.

Review article: current antiviral therapy of chronic hepatitis B

BACKGROUND

The long-term goals of therapy for chronic hepatitis B are to reduce serum HBV DNA to low or undetectable levels and ultimately reduce or prevent the development of cirrhosis and hepatocellular carcinoma.

AIM

To review the current treatment of chronic hepatitis B, with a focus on diagnosis and management of resistance and active management of suboptimal responses.

METHODS

A systematic review of the literature, with a focus on recent guidelines, was undertaken.

RESULTS

Among the six drugs licensed for the treatment of chronic hepatitis B in the US, the preferred agents in 2008 will include entecavir, peginterferon alfa-2a, possibly telbivudine, and tenofovir following licensure. When using an oral agent, a major focus of management is on the selection of a drug with high potency and low rate of resistance, and active on-treatment management to optimize therapy. Preventing the sequelae of antiviral drug resistance and appropriate management when resistance is initially detected are also the major focus of current management. The addition of an antiviral agent that is not cross-resistant is critical to restore suppression of viral replication.

CONCLUSIONS

Newer agents and modified treatment strategies, especially using combination therapy, hold promise to optimize the management of patients with chronic hepatitis B by achieving the high potency and the lowest rate of resistance.

The antiviral drug selected hepatitis B virus rtA181T/sW172* mutant has a dominant negative secretion defect and alters the typical profile of viral rebound

The hepatitis B virus (HBV) mutation that encodes rtA181T is selected in the viral polymerase during antiviral drug therapy and can also encode a stop codon in the overlapping surface gene at amino acid 172 (sW172*) resulting in truncation of the last 55 amino acids of the C-terminal hydrophobic region of the surface proteins. This mutation is usually detected as a mixed population with wild-type HBV. In vitro analysis revealed that the rtA181T/sW172* variant is not only defective in secretion of viral particles causing intracellular retention of surface proteins, it also has a dominant negative effect on virion but not subviral particle secretion when coexpressed with the wild type. This dominant negative effect was attributed to the truncated S protein alone. Furthermore, these truncated surface proteins were less glycosylated, and the truncated L protein was able to support virion secretion. Examination of sequential HBV DNA levels in patients failing lamivudine or adefovir therapy where only the rtA181T change was detected via polymerase chain reaction sequencing revealed that viral load rebound did not occur or was not as large as usually observed with drug-resistant HBV.

CONCLUSION

The rtA181T/sW172* variant has a secretory defect and exerts a dominant negative effect on wild-type HBV virion secretion. The selection of rtA181T/sW172* reduced the typical extent of virological breakthrough, resulting in a missed diagnosis of drug resistance if viral load was used as the only criterion for drug failure, necessitating HBV polymerase chain reaction sequencing or other genotypic methods to diagnose antiviral drug resistance in these cases.

Hepatitis B: reflections on the current approach to antiviral therapy

This article summarizes the current state of antiviral therapy of hepatitis B with special attention given to areas that remain controversial or poorly defined. Strict adherence to liver association practice guidelines may result in missed opportunities to treat patients with significant underlying liver disease. In particular, recommended ALT thresholds may not appropriately reflect disease activity or degree of fibrosis. There is growing evidence that an alternative treatment paradigm for preventing late-stage disease complications may be indicated in highly viremic patients with early life exposure to hepatitis B. Pegylated interferon therapy is often a better choice for young to middle-aged patients with genotype A and B because of the higher rate of HBeAg seroconversion and a greater chance for HBsAg seroconversion in both HBeAg-positive and -negative patients as compared to nucleoside analogs. Nucleoside analog monotherapy is the current standard of care for many patients. However, long-term monotherapy results in resistance to a variable degree and sequential monotherapy may result in multi-drug resistant virus. Which patients would specifically benefit from early combination therapy also remains poorly defined. The rapidity and robustness of the suppression of HBV DNA while on a nucleoside analog should be monitored relatively early during treatment because it affects treatment outcome and the rate of resistance. While great progress has been made in treating hepatitis B, many important issues require further study.

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

BACKGROUND/AIMS

The efficacy of anti-viral therapy for chronic hepatitis B virus (HBV) is lost upon the emergence of resistant virus. Using >500 patient HBV isolates from several entecavir clinical trials, we show that phenotypic susceptibility correlates with genotypic resistance and patient virologic responses.

METHODS

The full-length HBV or reverse transcriptase gene was amplified from patient sera, sequenced, and cloned into an HBV expression vector. Entecavir susceptibilities of individual virus clones and patient quasispecies populations were analyzed in conjunction with the sequenced resistance genotype and the patient's virologic response.

RESULTS

Entecavir susceptibility decreased approximately 8-fold for isolates with various constellations of lamivudine resistance substitutions. The spectrum of additional substitutions that emerged during therapy at residues rtT184, rtS202, or rtM250 displayed varying levels of entecavir susceptibility according to the specific resistance substitutions and the proportion of resistant variants in the quasispecies. Phenotypic analyses of samples associated with virologic breakthrough confirmed the role of these residue changes in entecavir resistance. Additional longitudinal phenotypic analyses showed that decreased susceptibility correlated with both genotypic resistance and increased circulating HBV DNA.

CONCLUSIONS

HBV phenotypic analysis provides additional insight as part of a resistance monitoring program that includes genotypic analysis and quantification of circulating virus.

Primary resistance, multidrug resistance, and cross-resistance pathways in HBV as a consequence of treatment failure

Antiviral resistance is now the single most important factor in treatment failure using nucleos(t)ide analogues (NA). Primary drug resistance mutations refer to amino acid change(s) that result in reduced susceptibility to an antiviral agent. Secondary compensatory mutations restore replication defects associated with primary drug resistance and may be associated with low level reduced susceptibility. Several evolutionary pathways of drug resistant HBV have been observed in patients treated with NAs. It is possible that the drug resistance mutations selected with one agent may affect the efficacy of other NAs. Several major HBV-evolutionary NA-resistance pathways (rtM204I/V, rtN236T and rtA181T/V) have now been characterised. The rtM204V/I pathway is responsible for resistance to the L: -nucleosides, such as lamivudine (LMV), telbivudine (LdT) and clevudine (CLD), and also entecavir (ETV), whilst the rtN236T pathway is responsible for adefovir (ADV) and tenofovir (TFV) resistance. Both pathways are associated with clusters of secondary mutations that can affect subsequent treatment with NAs (rtT184G, rtS202I) such as ETV. The third pathway, rtA181T/V, is associated with resistance to LMV and ADV and is a potential multi-drug resistance pathway and will probably have an impact on TFV sensitivity, either alone or with the rtN236T. In naïve patients treated with ETV, atleast three mutations arising at the same time are required: rtL180M + rtM204V plus either one of rtT184, rtS202 or rtM250 codon changes. Finally, in highly drug-experienced patients, clusters of mutations such as rtA181T/I233V/N236T/M250L, all on the one dominant HBV genome, are being detected which are associated with multi-drug resistance. Sequential treatment with nucleos(t)ide analogue reverse transcriptase inhibitors (NRTI) promotes multidrug resistance. It is likely, therefore, that development of multi-drug resistance could be reduced by combination therapy optimised to individual viral phenotypes.

The case for combination antiviral therapy for chronic hepatitis B virus infection

The treatment of hepatitis B virus (HBV) infection has been revolutionised in the past decade by the increased availability of effective antiviral agents. Many studies have shown the benefits of single agent therapy, but there is an alarming and rising rate of viral resistance, and clear evidence that viruses that harbour resistant mutations can cause liver disease and death. Current national guidelines for the treatment of HBV recommend a programme that starts with monotherapy, followed by sequential monotherapy or add-on therapy for those infections in which mutations have arisen. Very few studies starting with combination therapy have been undertaken, so there is little evidence of the clinical benefit of this approach to treatment. The studies that have been done have been short term and have concentrated on clinical parameters rather than virological resistance, which is likely to be the key determinant in the longer term. We argue that we should not wait for the evidence to use combination therapy for the treatment of HBV, since such trials may never be done and it would take several years for a benefit to become apparent. In the meantime, multidrug-resistant strains continue to hinder HBV control.

Impact of hepatitis B virus rtA181V/T mutants on hepatitis B treatment failure

BACKGROUND/AIMS

Recent clinical observations reported the occurrence of amino acid substitutions at position 181 of the HBV polymerase, associated with a viral breakthrough under lamivudine or adefovir therapy. In this study, we characterized the main variants harboring the rtA181T/V mutation isolated from 10 consecutive patients who developed lamivudine and/or adefovir resistance.

METHODS

We performed a clonal analysis of the HBV polymerase gene amplified by PCR from serum samples during viral breakthrough. The main mutants were then tested after transfection of Huh7 cells for their resistance profile to nucleoside analogs.

RESULTS

Clonal analysis revealed the co-localization on the same HBV genome of rtA181T/V with rtN236T, but not with rtM204V/I mutations following lamivudine, adefovir or lamivudine+adefovir breakthrough. In cell culture, the rtA181T/V mutation induced a decreased susceptibility to lamivudine (<10-fold), adefovir (2- to 8-fold) and tenofovir (2- to 3-fold). Interestingly, the association of rtA181T with rtN236T on one clinical isolate genome increased the resistance to these three drugs. All the tested mutants remained sensitive to entecavir.

CONCLUSIONS

Our observations suggest that a single amino acid change at position rt181 may induce cross-resistance to lamivudine and adefovir. These data emphasize the clinical relevance of genotypic and phenotypic analysis in the management of antiviral drug resistance.

Evaluation of initial virological response to adefovir and development of adefovir-resistant mutations in patients with chronic hepatitis B

The aims of the present study were to assess initial virological response (IVR) to adefovir (ADV) treatment for chronic hepatitis B, to identify patients with suboptimal response and to determine the incidence of ADV-resistant mutants. All patients treated with ADV for at least 12 months were evaluated for virological response and ADV resistance. IVR was defined as a reduction > or = 4 log10 IU/mL in hepatitis B virus (HBV)-DNA at month 6. Forty-two patients were analysed. Mean treatment duration was 23 +/- 7 months; 50% had prior lamivudine (LAM) therapy (LAM resistance 62%); 88% were hepatitis B e antigen (HBeAg)-negative; and 76% carried genotype D. IVR was seen in 40.5% of patients. Higher baseline ALT level was the only factor associated with IVR (P = 0.043). Patients with IVR achieved undetectable HBV-DNA at month 12 in 77% of cases compared with only 5% of those without IVR (P < 0.001). Five (12%) patients developed ADV-resistant mutations: rtN236T in four cases and one case with an rtV207L change, which has not been previously reported. This mutation was accompanied by viral rebound and alanine aminotransferase (ALT) flare. The cumulative probability of ADV-resistant mutations at 12 and 24 months was 5% and 17% respectively. IVR defined as a reduction > or = 4 log10 IU/mL in HBV-DNA at month 6 is a useful tool to predict virological response at month 12 and to identify patients with suboptimal response to ADV. Cumulative probability of ADV resistance is higher than previously reported for nucleos(t)ide-naïve patients.

Sustained virological and biochemical responses to lamivudine and adefovir dipivoxil combination in a chronic hepatitis B infection despite mutations conferring resistance to both drugs

Background

Sequential monotherapies of nucleotide analogs used in chronic hepatitis B treatment can lead to the selection of a resistance mutation to each antiviral drug.

Case presentation

A patient with chronic hepatitis B was successively treated with lamivudine monotherapy, lamivudine-adefovir dual therapy, adefovir monotherapy and again with an adefovir-lamivudine dual therapy. Lamivudine-associated mutations (rtL180M and rtM204V/I) followed by adefovir-associated mutations (rtN236T and rtA181V) emerged during the two monotherapy regimens. Despite the presence of rtM204V/I, rtA181V, and rtN236T mutations at the beginning of the second dual therapy, sustained biochemical and virological responses have been observed thus far after 23 months.

Conclusion

This case illustrates that rtM204V/I, rtA181V, and rtN236T resistance mutations can coexist in a patient but do not preclude the recycling of lamivudine and adefovir in combination therapy, when no other therapeutic choices are available.

Tenofovir monotherapy is effective in hepatitis B patients with antiviral treatment failure to adefovir in the absence of adefovir-resistant mutations

BACKGROUND/AIMS

We sought to identify mutations associated with treatment failure to adefovir (ADV) and to determine virologic response to tenofovir (TDF) alone and in combination with emtricitabine (FTC) in these patients.

METHODS

Serum samples prior to and after the change in treatment to TDF/TDF+FTC from 13 patients were analyzed by direct sequencing and clonal analysis.

RESULTS

ADV-resistant mutations, rtA181V and rtN236T, were detected on direct sequencing in 3 of 8 patients who had virologic breakthrough. Among patients with suboptimal virologic response, rtA181T, rtI233V, and rtN236T were present on clonal analysis in 3 patients. Ten patients received TDF, 8 achieved virologic response. One had ADV-resistance at baseline and persistence of ADV-resistant mutations during TDF treatment, addition of FTC resulted in a further decrease in HBV DNA. Another patient had no ADV-resistance at baseline, and selection of ADV-resistant mutations during TDF treatment. All 3 patients who received TDF+FTC had undetectable HBV DNA within 3-12 months including 2 who had ADV-resistance at baseline.

CONCLUSIONS

TDF monotherapy is effective for patients with virologic breakthrough or suboptimal response to ADV, but combination therapy with a nucleoside analogue should be considered in patients with ADV-resistance. No novel mutations were detected.

Viral hepatitis and HIV coinfection

Persons at high risk for human immunodeficiency virus (HIV) infection are also likely to be at risk for other infectious pathogens, including hepatitis B virus (HBV) or hepatitis C virus (HCV). These are bloodborne pathogens transmitted through similar routes; for example, via injection drug use (IDU), sexual contact, or from mother to child during pregnancy or birth. In some settings, the prevalence of coinfection with HBV and/or HCV is high. In the context of effective antiretroviral therapy (ART), liver disease has emerged as a major cause of morbidity and mortality in HIV-infected persons. Further, coinfection with viral hepatitis may complicate the delivery of ART by increasing the risk of drug-related hepatoxicity and impacting the selection of specific agents (e.g., those dually active against HIV and HBV). Expert guidelines developed in the United States and Europe recommend screening of all HIV-infected persons for infection with HCV and HBV and appropriate management of those found to be chronically infected. Treatment strategies for HBV infection include the use of nucleos(t)ide analogues with or without anti-HIV activity and/or peginterferon alfa (PegIFN) whereas HCV treatment is limited to the combination of PegIFN and ribavirin (RBV). Current approaches to management of HIV-infected persons coinfected with HBV or HCV are discussed in this review.