Dynamics of hepatitis B virus resistance to entecavir in a nucleoside/nucleotide-naïve patient

Human Immunodeficiency Virus-1 Drug Resistance Mutations in Iranian Treatment-experienced Individuals

BACKGROUND

Human immunodeficiency virus-1 infection still remains a global health threat. While antiretroviral therapy is the primary treatment option, concerns about the emergence of drug-resistance mutations and treatment failure in HIV-infected patients persist.

OBJECTIVE

In this study, we investigated the development of drug resistance in HIV-1-infected individuals receiving antiretroviral therapy for 6-10 years.

METHODS

In this cross-sectional study, we evaluated 144 people living with HIV-1 who had received antiretroviral therapy for at least 6 years. Plasma specimens were collected, and the HIV-1 viral load and drug-resistance mutations were assessed using molecular techniques.

RESULTS

The demographic and epidemiological characteristics of the participants were also analyzed: Twelve [8.3%) of the studied patients showed a viral load over 1000 copies per/mL, which indicates the suboptimal response to antiretroviral therapy. Significant correlations were found between viral load and CD4 count, as well as epidemiological factors, such as vertical transmission, history of imprisonment, and needle stick injuries. Drug resistance mutations were detected in 10 (83.3%) of patients who failed on antiretroviral therapy, with the most common mutations observed against nucleoside reverse transcriptase inhibitors (5 (41.7%)) and non-nucleoside reverse transcriptase inhibitors (9 (75%)). Phylogenetic analysis revealed that 12 patients who failed treatment were infected with CRF35_AD.

CONCLUSION

Our study provides important insights into the characteristics and development of drug resistance in HIV-1-infected individuals receiving long-term antiretroviral therapy in Iran. The findings underline the need for regular viral load monitoring, individualized treatment selection, and targeted interventions to optimize treatment outcomes and prevent the further spread of drug-resistant strains.

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

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

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.

Partial virological response to three different nucleotide analogues in naive patients with chronic hepatitis B

BACKGROUND

The definition of partial virological response (PVR) was proposed because of its clinical relevance. PVR relates to subsequent therapeutic failure which results in the modification of the regimen. Whether this rationale can be applied to all nucleotide analogues (NA) is not clear. This study was undertaken to analyze PVR influence on therapeutic outcomes during lamivudine, entecavir or tenofovir monotherapy in NA-naive patients with chronic hepatitis B in routine clinical practice.

METHODS

We retrospectively analyzed 150 NA-naive patients with chronic hepatitis B. These subjects received lamivudine, entecavir or tenofovir monotherapy between February 2001 and July 2013.

RESULTS

Sixty-nine patients were treated with lamivudine, 35 with entecavir, and 46 with tenofovir. The median therapeutic duration was 19.5 (6-147) months. PVR rates at 24 weeks were similar among three NAs (lamivudine 33.3%, entecavir 35.0%, tenofovir 32.4%, P=0.981). For all three NAs, patients with a higher baseline viral load or HBeAg-positive status had a higher serum viral positive rate tested by polymerase chain reaction at week 24 and 48. Cumulative probability of virological breakthrough (VBR) for patients treated with lamivudine was 67% at 5 years, and PVR at 24 weeks was the independent risk factor for VBR (HR: 3.09; 95% CI: 1.09-8.74; P=0.034); also lamivudine treated patients older than 50 years seemed to have a tendency for VBR (HR: 2.80; 95% CI: 0.99-8.18; P=0.052). A majority of entecavir and tenofovir partial responders achieved and maintained virological response with prolonged monotherapy, except one entecavir treated patient who experienced VBR due to resistance mutations.

CONCLUSIONS

Management strategy for lamivudine treatment should include adaptation of regimen according to PVR as an on-treatment response parameter due to its relation with unacceptably high VBR probability. Similar conclusion should not be directly related to entecavir or tenofovir treatment.

LC-MS/MS method for the characterization of the forced degradation products of Entecavir

A rapid, specific, and reliable isocratic LC-MS/MS method has been developed and validated for the identification and characterization of the stressed degradation products of Entecavir (ETV). ETV, an antiviral drug, was subjected to hydrolysis (acidic, alkaline, and neutral), oxidation, photolysis and thermal stress, as per the international conference on harmonization specified conditions. The drug showed extensive degradation under oxidative and acid hydrolysis stress conditions. However, it was stable to thermal, acidic, neutral, and photolysis stress conditions. A total of five degradation products were observed and the chromatographic separation of the drug and its degradation products were achieved on a Waters Symmetry C18 (250 mm × 4.6 mm, id, 5 μm) column using 20 mM ammonium acetate (pH 3)/acetonitrile (50:50, v/v) as a mobile phase. The degradation products were characterized by LC-MS/MS and its fragmentation pathways were proposed. The LC-MS method was validated with respect to specificity, linearity, accuracy, and precision. No previous reports were found in the literature regarding the degradation behavior of ETV.

Quasispecies and pre-existing drug-resistant mutations of hepatitis B virus in patients with chronic hepatitis B

Background/Aims

To investigate pre-existing hepatitis B virus (HBV) quasispecies and the genotypic evolution of several variants.

Methods

From six patients with lamivudine (LAM) failure, serum samples at pretreatment, 6 months of LAM therapy, and virologic breakthrough were obtained. One hundred clones with HBV inserts in each patient were sequenced at each time point. Pretreatment serum samples were also analyzed from six patients who achieved good responses to LAM therapy.

Results

Among the six patients with LAM failure, the analysis of 100 clones from patient 1 revealed the substitutions L180M in 1% of clones and V173L in 2% of clones. Patient 2 had substitutions of L80V, W153Q, and L180M. In patient 3, mutations conferring resistance to adefovir at V84I (5%), I169L (1%), and N236H (7%) and entecavir at S202G (2%) were detected. Patient 4 had mutations at T128N (1%), I169L (1%), V173L (2%), A181V (1%), and Q215H (1%). In patient 5, M204V/I was detected in 1% and 2% of clones, respectively. L80I and V173L were also identified in patient 6. In the six patients who responded to LAM, the degree of overall quasispecies was less than those with LAM failure.

Conclusions

Various HBV quasispecies associated with drug resistance existed before treatment, and the quasispecies dynamically changed through LAM therapy.

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.

Evaluation of anti-HBV drug resistant mutations among patients with acute symptomatic hepatitis B in the United States

BACKGROUND & AIMS

Reported HBV drug resistance mutations among previously untreated patients with chronic hepatitis B are variable. Whether resistant HBV strains are transmitted in the acute setting is uncertain. We sought to document the presence of antiviral resistance (AVR) mutations in patients with acute HBV (AHB) infection.

METHODS

AHB infection was defined by HBsAg/IgM anti-HBc positivity, ALT>10X ULN and compatible clinical history. The TRUGENE HBV kit was used to perform genotyping and direct sequencing of the viral polymerase. INNO-LiPA HBV DRv2 and DRv3 were used to detect AVR mutations. Clonal sequencing was conducted on selected specimens.

RESULTS

Twenty-three patients were evaluated (mean age, 43 years; 54% male; 39% African American, 39% Caucasian, 13% Hispanic and 4% Asian). The mean peak ALT was 1554.2IU/L and mean peak total serum bilirubin was 12 mg/dl. The HBV DNA median viral load (N = 15) was 5.14 log(10)IU/ml. Nineteen patients were genotype A, and 1 each were genotype C, D, E and G. HBV drug resistance mutations were not detected by direct sequencing or INNO-LiPA. Clonal sequencing was conducted on 192 clones isolated from three patients and showed rtA181T, rtM250V and rtS202G mutations at an overall frequency of 1.54%, 1.39%, and 1.67% respectively.

CONCLUSIONS

We detected adefovir/lamivudine and entecavir relevant mutations in a minor population (<2%) of viral clones by clonal sequencing only. The clinical significance of these mutations is uncertain and may represent small populations of quasi-species vs. transmission of drug resistant strains.

Genotype-specific mutations in the polymerase gene of hepatitis B virus potentially associated with resistance to oral antiviral therapy

The evolution of hepatitis B virus (HBV) and the role of different variants during antiviral therapy may be influenced by HBV genotype. We have therefore analysed substitutions potentially related to nucleos(t)ide analogues (NAs) resistance at 42 positions within RT-region in a cohort of patients with chronic hepatitis B in relation to HBV-genotype. RT mutations analysis was performed by direct sequencing in 200 NAs-naïve patients and in 64 LAM or LAM+ADV experienced patients with NAs resistance, infected mainly by HBV-genotypes D and A. 27 polymorphic-sites were identified among the 42 positions analysed and 64 novel mutations were detected in 23 positions. Genotype-D displayed the highest mutation frequency (6.4%) among all HBV-genotypes analysed. Single or multiple mutations were detected in 80% of naïve patients. Overall, the most frequent single mutations were at residues rt54, rt53 and rt91 which may associate with significantly lower HBV-DNA levels (p=0.001). Comparison with sequencing data of patients failing LMV or LAM+ADV therapy revealed an higher frequency of novel genotype-specific mutations if compared with naïve patients: 3 mutations under LAM monotherapy in HBV-D (rtS85F; rtL91I; rtC256G) and 3 mutations under ADV therapy in HBV-A (rtI53V; rtW153R; rtF221Y). In HBV-D treated patients the dominant resistance mutation was rtL80V (31.4%) and rtM204I (60%) in LAM+ADV group while LAM-treated patients showed a preference of rtM204V (51.9%). Interestingly, none of HBV-A patients had mutation rtM204I under ADV add-on treatment but all of them had the "V" AA substitution. These results suggested that in patients with CHB, HBV-genotype might be relevant in the evolution and development of drug resistance showing also different mutation patterns in the YMDD motif between HBV genotype D and A.

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.

Laboratory evaluation of three regimens of treatment of chronic hepatitis B: tenofovir, entecavir and combination of lamivudine and adefovir

BACKGROUND

Chronic hepatitis B is a disease of concern due to its life-threatening complications like cirrhosis, and hepatocellular carcinoma (HCC) in 20-40% of patients. There are about 400 million people affected worldwide with HBV, and over 300,000 die every year from HBV-related diseases. Oral antivirals like lamivudine, adefovir, entecavir, and tenofovir are commonly used to treat chronic hepatitis B. In this study, we tried to evaluate the comparative efficacy of these drugs alone and in combination.

MATERIALS AND METHODS

Chronic hepatitis B patients with HBV-DNA more than 10⁴Copies/mL irrespective of their HBeAg status (n=60) were enrolled in a prospective study. 21, 20, and 19 patients were treated with lamivudine (100 mg/day) plus adefovir (10 mg/day) combination entecavir monotherapy (0.5 mg/day) and tenofovir monotherapy (300 mg/day), respectively and were followed up for 24 weeks with their virological, serological, and biochemical markers measured at 12 and 24 weeks.

RESULTS

After 24 weeks of treatment, there was no significant difference between the 3 groups in suppressing HBV-DNA to undetectable levels. The median decrease in HBV-DNA levels from baseline was better with tenofovir and entecavir monotherapies than lamivudine and adefovir combination, which was statistically significant. There was no significant difference between the 3 groups in HBsAg and HBeAg seroconversion and normalization of biochemical parameters.

CONCLUSION

Entecavir and tenofovir monotherapy were found to be more effective than lamivudine plus adefovir combination in reducing the HBV-DNA levels. However, lamivudine plus adefovir combination was not too inferior, especially when cost of treatment was taken into consideration.

Role of hepatitis B virus genetic barrier in drug-resistance and immune-escape development

BACKGROUND

Impact of hepatitis B virus genetic barrier, defined as the number and type of nucleotide substitutions required to overcome drug/immune selective pressure, on drug-resistance/immune-escape development is unknown.

METHODS

Genetic barrier was calculated according to Van de Vijver (2006) in 3482 hepatitis B virus-reverse transcriptase/HBV surface antigen sequences from 555 drug-naïve patients and 2927 antiviral-treated patients infected with hepatitis B virus genotypes A-G.

RESULTS

Despite high natural variability, genetic barrier for drug-resistance development is identical amongst hepatitis B virus genotypes, but varies according to drug-resistance mutation type. Highest genetic barrier is found for secondary/compensatory mutations (e.g. rtL80I/V-rtL180M-rtV173L), whilst most primary mutations (including rtM204V-rtA181T/V-rtI169T-rtA194T) are associated with low genetic barrier. An exception is rtM204I, which can derive from a transition or a transversion. Genotypes A and G are more prone to develop immune/diagnostic-escape mutations sT114R and sG130N. Vaccine-escape associated sT131N-mutation is a natural polymorphism in both A and G genotypes.

CONCLUSION

Genetic barrier and reverse transcriptase/HBV surface antigen overlapping can synergistically influence hepatitis B virus drug-resistance/immune-escape development. The different immune-escape potential of specific hepatitis B virus genotypes could have important clinical consequences in terms of disease progression, vaccine strategies and correct HBV surface antigen detection.

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.

Partial virological response to entecavir in treatment-naive patients with chronic hepatitis B

BACKGROUND

The proposed definition of a partial virological response (PVR) to nucleos(t)ide analogue therapy in the 2009 European Association for the Study of the Liver (EASL) guidelines is based on limited evidence, especially in terms of the cutoff HBV DNA level and the time point at which to judge it. This study assessed optimal PVR criteria for predicting virological response (VR) at week 96 in treatment-naive patients with chronic hepatitis B (CHB) receiving entecavir (ETV).

METHODS

A total of 175 patients (126 men, 49 women) who completed 96 weeks of first-line ETV therapy were prospectively recruited. For predicting VR at week 96, the area under the receiver operating characteristic curve (AUC) was used to find the optimal time point and the Youden index was used to calculate the optimal cutoff HBV DNA level.

RESULTS

After 96 weeks of ETV therapy, 139 (79.4%) patients achieved VR. The AUC at week 48 was significantly better than that at week 24 for predicting VR at week 96 (P=0.023). The optimal cutoff HBV DNA level at week 48 was 35 IU/ml. Forty-one (23.4%) patients met this PVR criteria of ETV (HBV DNA level >35 IU/ml at week 48).

CONCLUSIONS

An HBV DNA level >35 IU/ml at week 48 is the optimal PVR criteria for predicting non-VR at week 96 in treatment-naive patients with CHB who are receiving ETV. This study supports the proposed EASL PVR for ETV based on scientific evidence.

The efficacy of entecavir therapy in chronic hepatitis B patients with suboptimal response to adevofir

BACKGROUND

An increasing number of patients with chronic hepatitis B (CHB) have experienced treatment failure to adefovir (ADV) and their management poses a growing challenge. Very limited data are available on the efficacy of entecavir (ETV) in patients previously treated with ADV.

AIM

To examine the effect of ETV monotherapy on HBV DNA and ALT levels in CHB patients previously treated with ADV, but switched to ETV due to suboptimal response.

METHODS

Study candidates were enrolled from five community gastroenterology clinics in the U.S. Each completed at least 12 months of ETV treatment after being previously treated with ADV and experiencing suboptimal response. Primary and secondary outcome measurements were complete viral suppression (CVS, HBV DNA <100 IU/mL) and biochemical response (BR, ALT < 40 U/L), respectively.

RESULTS

A total of 60 patients were included in this analysis. Twelve were lamivudine (LAM)-experienced and none were LAM-resistant. At time of switch to ETV, no patients had experienced CVS. The CVS rate was 68% after 12 months of ETV therapy. The BR rate was 67% at switch to ETV and 80% after 12 months. There was no significant difference in response rates between LAM-experienced and naïve patients. Among the eight patients with ADV resistance, each achieved CVS after 12 months of ETV therapy and seven achieved BR.

CONCLUSIONS

In patients with suboptimal response to adefovir, complete viral suppression and biochemical response can be achieved in the majority by 12 months after switching to entecavir, including patients with prior exposure to lamivudine and those with adefovir resistance.

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

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

Evolutionary pattern of full hepatitis B virus genome during sequential nucleos(t)ide analog therapy

The evolutionary and mutational pattern of full hepatitis B virus (HBV) quasispecies during sequential nucleos(t)ide analog (NUC) therapy remains unclear. In this study, full-length HBV clones were generated from serial serum samples of five chronic hepatitis B patients who received sequential NUC therapies (treated patients) and two untreated patients with acute flares. The evolutionary and mutational patterns of full HBV quasispecies were studied. In the three treated patients who received lamivudine as initial antiviral therapy, nucleotide polymorphism and nonsynonymous divergence all decreased at lamivudine breakthrough but increased after rescue therapies. Conversely, two other treated patients showed a distinct change in divergence during adefovir-telbivudine sequential therapies. Untreated subjects exhibited increased polymorphism and divergence in the preC/C region at ALT flare. Four of the treated patients presented amino acid changes in the "a" determinant during NUC therapy. All of the treated subjects showed amino acid changes within the known T-cell or B-cell epitopes in the surface or core antigen, most of which were accompanied by mutations in reverse transcriptase (RT) region. Co-variations in the core promoter, the preC region and in the known epitopes of the preS gene accompanied by RT mutations, were common. In untreated patients, most of these co-variations located in the preC/C gene. In conclusion, the distribution of genetic variability of HBV shows remarkably different patterns between the treated and untreated subjects and the quasispecies divergence of different regions of HBV may vary remarkably even within a single host.

[Analogs combination therapy in chronic hepatitis B: when and how?]

Hepatitis B virus (HBV) genomic variability is responsible for the complexity of the viral quasi-species and its evolution during the course of infection. The persistence of infected cells promotes the selection of drug-resistant strains. The development of nucleoside analogs without cross-resistance has provided a rationale for combination therapy. De novo combination, with low genetic barrier drugs, prevents the emergence of resistance in the short-term for drugs with a low genetic barrier and improves the control of infection. Long-term studies are needed to determine whether de novo combination is beneficial for analogs with a high genetic barrier as well. The add-on strategy is a standard in case of emergence of resistant mutants. This strategy needs to be implemented as early as possible before the virological breakthrough, especially if the viral suppression is sub-optimal. Clinical trials are mandatory in order to assess whether a) de novo combination is better than an early add-on strategy; and b) whether in case of sub-optimal viral suppression, an early add-on strategy is better in the long-term than a switch to a more potent drug with a high genetic barrier.

Characterization of hepatitis virus B isolated from a multi-drug refractory patient

Prolonged treatment of chronic hepatitis B (CHB) with nucleoside analogues (NAs) almost invariably engenders viral resistance, and sequential NAs monotherapy can promote multi-drug resistance. This study aimed to investigate the molecular characteristics and the mutation profile of multi-drug resistant hepatitis B virus (HBV). The complete genome of HBV isolated from a multi-drug refractory patient was amplified and cloned, and 22 clones were selected for sequencing. The homology of the full-length genome between clones ranged from 98.7% to 99.9%. A precore stop codon mutation of G1896A and basic core promoter (BCP) mutations A1762T/G1764A were detected in a majority of clones. A phylogenetic analysis showed that all clones were classified as subgenotype B2. Three mutations in the surface (S) antigen region, sC76Y, sP120T and sI195M, were detected in 100%, 100% and 77.3% of the clones, respectively. In the core (C) antigen region, a mutation at codon 135 (cP135Q) was detected in 100% of clones. Lamivudine (LAM)-resistant mutations, rtL180M and rtM204V/I were detected in 86.4% of clones. Adefovir (ADV) or entecavir (ETV)-resistant mutations were not detected. Several novel mutations, such as rtT128N, rtA222T, rtS256G, rtL271M, rtS332R, and rtN/T337D, were present in a majority of clones. Furthermore, six pairs of mutations in the overlapping reverse transcriptase (RT) gene and S gene were detected. In conclusion, the complex HBV mutation profile detected in the multi-drug refractory patient highlights the problems associated with the ongoing selection of mutations, including further compensatory mutations as well as potential cross-resistance mutations.

Monotherapy versus combination therapy for the treatment of chronic hepatitis B

BACKGROUND

Nucleos(t)ide analogues, active against hepatitis B polymerase, suppress viral replication and improve clinical outcome. However, the emergence of drug-resistant mutants can result in treatment failure.

OBJECTIVES

We describe how the choice of first-line therapy is critical to long-term treatment success.

METHODS

A review of current drug therapies is provided.

RESULTS/CONCLUSIONS

Monotherapy with early-generation drugs (lamivudine or adefovir) was associated with a high rate of viral drug resistance and combination therapy with these agents was shown to reduce the incidence of resistance. The latest-generation drugs (entecavir and tenofovir) are potent inhibitors of viral replication and, in treatment-naive subjects, viral resistance to entecavir is uncommon and is not yet reported to tenofovir. Therefore, monotherapy with either entecavir or tenofovir is the current preferred option in treatment-naive patients. Combination therapy is appropriate in those with drug-resistant HBV infection, where drug choice is guided by the viral drug-resistance genotype/phenotype. Although combination therapy has been advocated in other patient groups (e.g., those with decompensated cirrhosis and following liver transplantation), there are, as yet, no data to mandate the use of combination therapy in such patients and any perceived benefit must be weighed against increased cost and risk for toxicity.

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.