Hepatitis B virus mutants associated with 3TC and famciclovir administration are replication defective

Cytosine base editing inhibits hepatitis B virus replication and reduces HBsAg expression in vitro and in vivo

Chronic hepatitis B virus (HBV) infection remains a global health problem due to the lack of treatments that prevent viral rebound from HBV covalently closed circular (ccc)DNA. In addition, HBV DNA integrates in the human genome, serving as a source of hepatitis B surface antigen (HBsAg) expression, which impairs anti-HBV immune responses. Cytosine base editors (CBEs) enable precise conversion of a cytosine into a thymine within DNA. In this study, CBEs were used to introduce stop codons in HBV genes, HBs and Precore. Transfection with mRNA encoding a CBE and a combination of two guide RNAs led to robust cccDNA editing and sustained reduction of the viral markers in HBV-infected HepG2-NTCP cells and primary human hepatocytes. Furthermore, base editing efficiently reduced HBsAg expression from HBV sequences integrated within the genome of the PLC/PRF/5 and HepG2.2.15 cell lines. Finally, in the HBV minicircle mouse model, using lipid nanoparticulate delivery, we demonstrated antiviral efficacy of the base editing approach with a >3log10 reduction in serum HBV DNA and >2log10 reduction in HBsAg, and 4/5 mice showing HBsAg loss. Combined, these data indicate that base editing can introduce mutations in both cccDNA and integrated HBV DNA, abrogating HBV replication and silencing viral protein expression.

Evidence for a Hepatitis B Virus Short RNA Fragment Directly Targeting the Cellular RRM2 Gene

The hepatitis B virus (HBV) is one of the smallest but most highly infectious human pathogens. With a DNA genome of only 3.2 kb and only four genes, HBV successfully completes its life cycle by using intricate processes to hijack the host machinery. HBV infects non-dividing liver cells in which dNTPs are limited. As a DNA virus, HBV requires dNTPs for its replication. HBV induces the ATR-mediated cellular DNA damage response pathway to overcome this constraint. This pathway upregulates R2 (RRM2) expression in generating an active RNR holoenzyme catalyzing de novo dNTP synthesis. Previously we reported that ERE, a small RNA fragment within the HBx ORF, is sufficient to induce R2 upregulation. Interestingly, there is high sequence similarity between ERE and a region within the R2 5′UTR that we named R2-box. Here, we established a mutant cell line in the R2-box region of the R2 gene using CRISPR-Cas9 technology to investigate the R2 regulation by ERE. This cell line expresses a much lower R2 level than the parental cell line. Interestingly, the HBV infection and life cycle were severely impaired. These cells became permissive to HBV infection upon ectopically R2 expression. These results validate the requirement of the R2 gene expression for HBV replication. Remarkably, the R2-box mutated cells became ERE refractory, suggesting that the homology region between ERE and R2 gene is critical for ERE-mediated R2 upregulation. Thus, along with the induction of the ATR pathway of the DNA damage response, ERE might also directly target the R2 gene via the R2-box.

RNR-R2 Upregulation by a Short Non-Coding Viral Transcript

DNA viruses require dNTPs for replication and have developed different strategies to increase intracellular dNTP pools. Hepatitis B virus (HBV) infects non-dividing cells in which dNTPs are scarce and the question is how viral replication takes place. Previously we reported that the virus induces the DNA damage response (DDR) pathway culminating in RNR-R2 expression and the generation of an active RNR holoenzyme, the key regulator of dNTP levels, leading to an increase in dNTPs. How the virus induces DDR and RNR-R2 upregulation is not completely known. The viral HBx open reading frame (ORF) was believed to trigger this pathway. Unexpectedly, however, we report here that the production of HBx protein is dispensable. We found that a small conserved region of 125 bases within the HBx ORF is sufficient to upregulate RNR-R2 expression in growth-arrested HepG2 cells and primary human hepatocytes. The observed HBV mRNA embedded regulatory element is named ERE. ERE in isolation is sufficient to activate the ATR-Chk1-E2F1-RNR-R2 DDR pathway. These findings demonstrate a non-coding function of HBV transcripts to support its propagation in non-cycling cells.

Distinctive HBV Replication Capacity and Susceptibility to Tenofovir Induced by a Polymerase Point Mutation in Hepatoma Cell Lines and Primary Human Hepatocytes

Tenofovir disoproxil fumarate (TDF) has been regarded as the most potent drug for treating patients with chronic hepatitis B (CHB). However recently, viral mutations associated with tenofovir have been reported. Here, we found a CHB patient with suboptimal response after more than 4 years of TDF treatment. Clonal analysis of hepatitis B virus (HBV) isolated from sequential sera of this patient identified the seven previously reported TDF-resistant mutations (CYELMVI). Interestingly, a threonine to alanine mutation at the 301 amino acid position of the reverse-transcriptase (RT) domain, (rtT301A), was commonly accompanied with CYELMVI at a high rate (72.7%). Since the rtT301A mutation has not been reported yet, we investigated the role of this naturally occurring mutation on the viral replication and susceptibility to tenofovir in various liver cells (hepatoma cells as well as primary human hepatocytes). A cell-based phenotypic assay revealed that the rtT301A mutation dramatically impaired the replication ability with meaningful reduction in sensitivity to tenofovir in hepatoma cell lines. However, attenuated viral replication by the rtT301A mutation was significantly restored in primary human hepatocytes (PHHs). Our findings suggest that the replication capability and drug sensitivity of HBV is different between hepatoma cell lines and PHHs. Therefore, our study emphasizes that validation studies should be performed not only in the liver cancer cell lines but also in the PHHs to understand the exact viral fitness under antiviral pressure in patients.

Mutations and methods of analysis of mutations in Hepatitis B virus

Immunization programmes against hepatitis-B are being carried out since more than three decades but still HBV is a major public health problem. Hepatitis B virus (HBV) genome consists of circular and partial double stranded DNA. Due to partial double stranded DNA, it uses an RNA intermediate during replication. This replicative strategy of HBV and lack of polymerase proofreading activity give rise to error occurrences comparable to retroviruses. The low fidelity of polymerase, overlapping reading frames and high replication rate produces many non-identical variants at every cycle of replication. Therefore, HBV spreads with mutations and variations. The mutations have been reported both in non-structural as well as structural genes of HBV genome. Recent advances in molecular biology have made easier to analyse these mutations. Hepatitis B antiviral therapy and immunization are all influenced by genetic variability. The analysis and understanding of these mutations are important for therapy against hepatitis B and updating of diagnostic tools. The present review discusses about mutations occurring in whole HBV genome. The mutation occurring both in structural and non-structural genes and non-coding regions have been described in details. It is much more informative because most of literature available, covers only individual gene or DNA regions of HBV.

Impacts of HBV rtH55R polymerase substitution on viral replication and rtM204I/V resistance to nucleoside/nucleotide antiviral drugs

BACKGROUND

High genetic variability at the reverse transcriptase (RT) region of HBV could confer resistance to nucleoside/nucleotide analogues (NUCs). The aim of this study was to identify new RT amino acid (AA) substitutions related to NUC resistance.

METHODS

HBV RT sequences of genotype C from 501 chronic hepatitis B (CHB) patients were analysed to identify potential RT substitutions related to NUC resistance. In vitro studies without and with NUCs were performed in a HepG2 cell line transfected by clones with RT harbouring wild-type or substituted AA(s) of interest.

RESULTS

Among 261 NUC-treated CHB patients, we found a high detection rate of rtM204I/V substitution (30.7% [80/261]). We identified a new substitution of rtH55R, and its detection rate had a significantly increasing trend from 3.8% (9/240) in the untreated group to 7.2% (13/181) or 33.8% (27/80) in the treated group with rtM204 or with rtM204I/V substitutions (P<0.0001). In vitro studies showed that rtH55R had a similar HBV DNA level compared to wild type. The rtH55R+rtM204I clone had a significantly better replication capacity than the rtM204I clone without NUCs (P<0.05). The replication capacity of the rtM204I clone was found to significantly decrease under lamivudine treatment, but this was not found in the rtH55R+rtM204I clone.

CONCLUSIONS

We identified a new HBV RT substitution of rtH55R in genotype-C-infected CHB patients. It is frequently found in combination with rtM204I/V substitution under NUC treatment. In vitro studies suggest that it might play some replication compensatory role in rtM204I mutants under lamivudine treatment.

The stilbene derivatives, nucleosides, and nucleosides modified by stilbene derivatives

In this short review, including 187 references, the issues of biological activity of stilbene derivatives and nucleosides and the biological and medicinal potential of fusion of these two classes are discussed. The stilbenes, especially the stilbenoids, and nucleosides are both biologically active. Hybrids formed from binding of these compounds have not yet been broadly studied. However, those that have been investigated exhibit desirable medicinal properties. The review is divided in such parts: I. Derivative of stilbene (biomedical investigations, biological activities in cells, enzymes and hazard), parts II. naturally occurred nucleoside and its derivatives: uridine, thymidine and 5-methyluridine, cytidine, adenosine, guanosine and part III. hybrid molecules- drugs and hybrid molecules- nucleoside - stilbene and its derivative.

Naturally occurring core protein mutations compensate for the reduced replication fitness of a lamivudine-resistant HBV isolate

Hepatitis B virus (HBV) replicates its DNA genome through reverse transcription of an RNA intermediate. The lack of proofreading capacity of the viral DNA polymerase results in a high mutation rate of HBV genome. Under the selective pressure created by the nucleos(t)ide analogue (NA) antiviral drugs, viruses with resistance mutations are selected. However, the replication fitness of NA-resistant mutants is markedly reduced compared to wild-type. Compensatory mutations in HBV polymerase, which restore the viral replication capacity, have been reported to arise under continuous treatment with lamivudine (LMV). We have previously identified a highly replicative LMV-resistant HBV isolate from a chronic hepatitis B patient experiencing acute disease exacerbation. Besides the common YMDD drug-resistant mutations, this isolate possesses multiple additional mutations in polymerase and core regions. The transcomplementation assay demonstrated that the enhanced viral replication is due to the mutations of core protein. Further mutagenesis study revealed that the P5T mutation of core protein plays an important role in the enhanced viral replication through increasing the levels of capsid formation and pregenomic RNA encapsidation. However, the LMV-resistant virus harboring compensatory core mutations remains sensitive to capsid assembly modulators (CpAMs). Taken together, our study suggests that the enhanced HBV nucleocapsid formation resulting from core mutations represents an important viral strategy to surmount the antiviral drug pressure and contribute to viral pathogenesis, and CpAMs hold promise for developing the combinational antiviral therapy for hepatitis B.

Durability of the virological response after lamivudine discontinuation in lamivudine-resistant patients with a complete virological response after lamivudine and adefovir combination therapy

We investigated the durability of virological response after lamivudine (LAM) discontinuation in LAM-resistant chronic hepatitis B (CHB) patients with complete virological response after LAM-adefovir (ADV) combination therapy. We enrolled 58 patients switched to ADV monotherapy with undetectable viral loads (<12 IU/ml) and normal alanine aminotransferase levels after ADV add-on combination treatment for at least 6 months in LAM-resistant CHB patients. Virologic relapse was defined as HBV DNA detection at more than 20 IU/ml by quantitative polymerase chain reaction determined on two consecutive measurements. During median 40.9 months of follow-up (range 11.5-79.0 months), seven (12.1%) patients experienced virological relapse. The cumulative rate of virological relapse at 3 and 5 years was 5.5% and 22.4%, respectively. Two patients had elevated alanine aminotransferase during virological relapse. These seven patients with virological relapse had undetectable HBV DNA after switching to tenofovir therapy. In our study, switching to ADV monotherapy resulted in sustained HBV DNA suppression in 87.9% of the patients during median 40.9 months follow-up. This adapting step-down strategy, switching from combination therapy to monotherapy in virologically suppressed CHB patients with stable liver disease, may reduce the cost burden and the risk of potentially harmful effects of combination therapy. J. Med. Virol. 89:85-90, 2017. © 2016 Wiley Periodicals, Inc.

Hepatitis B virus molecular biology and pathogenesis

As obligate intracellular parasites, viruses need a host cell to provide a milieu favorable to viral replication. Consequently, viruses often adopt mechanisms to subvert host cellular signaling processes. While beneficial for the viral replication cycle, virus-induced deregulation of host cellular signaling processes can be detrimental to host cell physiology and can lead to virus-associated pathogenesis, including, for oncogenic viruses, cell transformation and cancer progression. Included among these oncogenic viruses is the hepatitis B virus (HBV). Despite the availability of an HBV vaccine, 350-500 million people worldwide are chronically infected with HBV, and a significant number of these chronically infected individuals will develop hepatocellular carcinoma (HCC). Epidemiological studies indicate that chronic infection with HBV is the leading risk factor for the development of HCC. Globally, HCC is the second highest cause of cancer-associated deaths, underscoring the need for understanding mechanisms that regulate HBV replication and the development of HBV-associated HCC. HBV is the prototype member of the Hepadnaviridae family; members of this family of viruses have a narrow host range and predominately infect hepatocytes in their respective hosts. The extremely small and compact hepadnaviral genome, the unique arrangement of open reading frames, and a replication strategy utilizing reverse transcription of an RNA intermediate to generate the DNA genome are distinguishing features of the Hepadnaviridae. In this review, we provide a comprehensive description of HBV biology, summarize the model systems used for studying HBV infections, and highlight potential mechanisms that link a chronic HBV-infection to the development of HCC. For example, the HBV X protein (HBx), a key regulatory HBV protein that is important for HBV replication, is thought to play a cofactor role in the development of HBV-induced HCC, and we highlight the functions of HBx that may contribute to the development of HBV-associated HCC.

The efficacy of tenofovir-based therapy in patients showing suboptimal response to entecavir-adefovir combination therapy

Background/Aims:

Before tenofovir (TDF) become available in South Korea, combination therapy with entecavir (ETV) and adefovir (ADV) was the most potent regimen for chronic hepatitis B (CHB) patients who fail to respond to rescue therapy for drug resistance. We analyzed the efficacy of ETV-ADV combination therapy and investigated the clinical and clonal results of TDF-based rescue therapy in CHB patients refractory to this combination.

Methods:

We retrospectively reviewed the medical records of CHB patients treated for up to 3 years with ETV-ADV combination therapy as a rescue therapy for drug resistance. In cases refractory to this combination, clinical and clonal analyses were performed for TDF-based rescue therapy.

Results:

The analysis was performed on 48 patients. Twelve patients achieved a virological response (VR) within 3 years. A VR was subsequently achieved in nine of the ten patients without a VR who switched to TDF monotherapy. A VR was also achieved in six of the seven patients who switched to lamivudine-TDF combination therapy, and in two of the two patients who switched to ETV-TDF combination therapy. In an in vitro susceptibility test, viral replication was detected with TDF monotherapy but not with ETV-TDF combination therapy.

Conclusions:

The efficacy of ETV-ADV combination therapy was insufficient in CHB patients who were refractory to rescue therapy. A more potent regimen such as ETV-TDF combination therapy may be considered in such refractory cases.

Restrictive influence of SAMHD1 on Hepatitis B Virus life cycle

Deoxynucleotide triphosphates (dNTPs) are essential for efficient hepatitis B virus (HBV) replication. Here, we investigated the influence of the restriction factor SAMHD1, a dNTP hydrolase (dNTPase) and RNase, on HBV replication. We demonstrated that silencing of SAMHD1 in hepatic cells increased HBV replication, while overexpression had the opposite effect. SAMHD1 significantly affected the levels of extracellular viral DNA as well as intracellular reverse transcription products, without affecting HBV RNAs or cccDNA. SAMHD1 mutations that interfere with the dNTPase activity (D137N) or in the catalytic center of the histidine-aspartate (HD) domain (D311A), and a phospho-mimetic mutation (T592E), abrogated the inhibitory activity. In contrast, a mutation diminishing the potential RNase but not dNTPase activity (Q548A) and a mutation disabling phosphorylation (T592A) did not affect antiviral activity. Moreover, HBV restriction by SAMHD1 was rescued by addition of deoxynucleosides. Although HBV infection did not directly affect protein level or phosphorylation of SAMHD1, the virus upregulated intracellular dATPs. Interestingly, SAMHD1 was dephosphorylated, thus in a potentially antiviral-active state, in primary human hepatocytes. Furthermore, SAMHD1 was upregulated by type I and II interferons in hepatic cells. These results suggest that SAMHD1 is a relevant restriction factor for HBV and restricts reverse transcription through its dNTPase activity.

Genetic variation of occult hepatitis B virus infection

Occult hepatitis B virus infection (OBI), characterized as the persistence of hepatitis B virus (HBV) surface antigen (HBsAg) seronegativity and low viral load in blood or liver, is a special form of HBV infection. OBI may be related mainly to mutations in the HBV genome, although the underlying mechanism of it remains to be clarified. Mutations especially within the immunodominant “α” determinant of S protein are “hot spots” that could contribute to the occurrence of OBI via affecting antigenicity and immunogenicity of HBsAg or replication and secretion of virion. Clinical reports account for a large proportion of previous studies on OBI, while functional analyses, especially those based on full-length HBV genome, are rare.

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.

Substitution at rt269 in Hepatitis B Virus Polymerase Is a Compensatory Mutation Associated with Multi-Drug Resistance

The emergence of compensatory mutations in the polymerase gene of drug resistant hepatitis B virus (HBV) is associated with treatment failure. We previously identified a multi-drug resistant HBV mutant, which displayed resistance towards lamivudine (LMV), clevudine (CLV), and entecavir (ETV), along with a strong replication capacity. The aim of this study was to identify the previously unknown compensatory mutations, and to determine the clinical relevance of this mutation during antiviral therapy. In vitro mutagenesis, drug susceptibility assay, and molecular modeling studies were performed. The rtL269I substitution conferred 2- to 7-fold higher replication capacity in the wild-type (WT) or YMDD mutation backbone, regardless of drug treatment. The rtL269I substitution alone did not confer resistance to LMV, ETV, adefovir (ADV), or tenofovir (TDF). However, upon combination with YMDD mutation, the replication capacity under LMV or ETV treatment was enhanced by several folds. Molecular modeling studies suggested that the rtL269I substitution affects template binding, which may eventually lead to the enhanced activity of rtI269-HBV polymerase in both WT virus and YMDD mutant. The clinical relevance of the rtL269I substitution was validated by its emergence in association with YMDD mutation in chronic hepatitis B (CHB) patients with sub-optimal response or treatment failure to LMV or CLV. Our study suggests that substitution at rt269 in HBV polymerase is associated with multi-drug resistance, which may serve as a novel compensatory mutation for replication-defective multi-drug resistant HBV.

Current and future antiviral drug therapies of hepatitis B chronic infection

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

Pre-existing mutations in reverse transcriptase of hepatitis B virus in treatment-naive Chinese patients with chronic hepatitis B

High rate of viral replication and lacking of proofreading activity in hepatitis B virus (HBV) polymerase lead to the generation of mutations in HBV virus. Mutations in the reverse transcriptase (RT) region of HBV polymerase are demonstrated to be strongly associated with drug resistance during antiviral treatment. However, the presence of mutations as well as its clinical significance in treatment-naïve hepatitis patients (defined as pre-existing mutations) need to be further investigated. In the present study, a total of 168 serum samples from treatment-naive chronic hepatitis B (CHB) patients were collected, and the RT region of HBV polymerase was sequenced. The results showed that pre-existing mutations in the RT region of HBV polymerase were detected in 43 of 168 (25.6%) treatment-naive CHB patients within which there were no well-characterized primary nucleotide analogs (NAs) resistance sites. Three dominant sites at rt191, rt207 and rt226 were found mutant in 7(16.28%), 8(18.60%), and 14(32.56%) samples respectively among these 43 patients. No significant correlation was found between pre-existing mutations and gender, age, HBV genotype, ALT, HBeAg or HBV DNA loads. However, patients with pre-existing RT mutations under HBeAg sero-negative status exhibited decreased HBV DNA loads, which contributed to the decreased HBV DNA loads in the total HBeAg sero-negative patients. The above investigation indicated that there was a prevalence of pre-existing mutations in RT region of HBV polymerase which might affect the serum HBV DNA level in treatment-naive CHB patients. Its effects on the occurrence of NAs resistance and the prognosis after treatment need to be further investigated.

High incidence of lamivudine-resistance-associated vaccine-escape HBV mutants among HIV-coinfected patients on prolonged antiretroviral therapy

BACKGROUND

Worldwide, frequent emergence of lamivudine (3TC)-resistant HBV mutants has been reported in HIV-HBV-coinfected patients during long-term antiretroviral therapy (ART) that contains 3TC as the sole anti-HBV drug. Three major patterns of mutations in HBV polymerase gene, namely single (rtM204V), double (rtL180M+rtM204V) and triple (rtV173L+rtL180M+rtM204V) mutations, are associated with 3TC-resistance; additionally, the triple mutation has vaccine-escape potential due to a corresponding change in overlapping surface gene. Data from India, a major reservoir for HIV and HBV infection, is lacking. Here we investigated the effect of long-term 3TC treatment on virological response for HBV and characterized the 3TC-resistant HBV mutations in a cohort of HIV-HBV-coinfected patients from eastern India.

METHODS

A cross-sectional study was performed in HIV-infected patients (n=563) receiving 3TC-containing ART for ≥6 months from the major ART centre of eastern India during 2011-2012. The hepatitis B surface antigen-positive HIV-infected patients (n=62) were categorized into four groups with comparable sample size according to the 3TC exposure for ≥6-<12 months (group I; n=15), ≥12-<24 months (group II; n=20), ≥24-<48 months (group III; n=13) and ≥48 months (group IV; n=14). Patients' plasma samples were examined for hepatitis B e antigen (HBeAg), HBV DNA, viral load and covalently closed circular DNA (cccDNA). HBV reverse transcriptase region was sequenced.

RESULTS

With a longer period of 3TC exposure, the frequency of HIV-HBV-coinfected patients having HBV DNA suppression decreased. The prevalence of HBeAg-positivity, serum HBV DNA load >2,000 IU/ml and 3TC-resistant mutations simultaneously increased. Remarkably, the 3TC-resistant triple mutation predominated over the double mutation in this cohort (32.26% versus 19.34%) and prevailed in significantly higher frequency among HBV viraemic patients experiencing 3TC for ≥48 months (60% versus 10%; P=0.03). Patients with 3TC-resistant triple mutants had HBV genotype-D, high serum HBV DNA load and elevated alanine aminotransferase level, and presence of cccDNA in their serum.

CONCLUSIONS

Considering this alarmingly high incidence of 3TC-resistant triple mutation and its possible clinical/public health implications, proper management of 3TC-resistance among HIV-HBV-coinfected patients is an urgent necessity in India.

Update on hepatitis B virus infection

Chronic infection with hepatitis B virus (HBV) leads to the development of hepatocellular carcinoma and/or chronic liver failure. Despite extensive research, the immunopathogenesis is not completely understood. Viral persistence and clinical outcomes following HBV infection depend on viral factors and host factors; including genetic factors that determine a host’s immune mechanisms. The primary goal of chronic hepatitis B (CHB) treatment is to eradicate HBV or to at least maintain suppression of HBV replication. Despite recent advances in anti-viral agents for chronic HBV infection, complete eradication of the virus has been difficult to achieve. Agents for the treatment of CHB are divided mainly into two groups: immunomodulating agents and antiviral nucleos(t)ide analogues (NAs). Although NAs are safe, effective and easily administered orally, their long-term use poses the risk of drug resistance. Currently, international evidence-based guidelines have been developed to support physicians in managing CHB patients. However, treatment of patients with drug resistance is still challenging, as only a few classes of anti-HBV drugs are available and cross-resistance between drugs can occur. In addition, as the currently available genotypic test for detection of drug resistance still has limitations in identifying the different substitutions present in the same viral genome, the development of a new virologic test to overcome this limitation is necessary. Among the predictive factors associated with response to pegylated interferon (PEG-IFN) therapy, hepatitis B surface antigen quantification is considered to be a surrogate marker for monitoring response to PEG-IFN. Current practice guidelines stress the importance of profound and durable HBV viral suppression in the treatment of CHB patients. To this end, it is essential to choose a potent antiviral drug with a low risk of resistance for initial treatment of CHB to achieve sustained virological response. This review highlights recent advances in the understanding of the immunopathogenesis of HBV and currently available and developing treatment strategies against HBV infection.

Impact of the rtI187V polymerase substitution of hepatitis B virus on viral replication and antiviral drug susceptibility

A high prevalence of the rtI187V polymerase substitution of hepatitis B virus (HBV) was detected in nucleoside/nucleotide-analogue-naive and -treated chronic hepatitis B (CHB) patients. We aimed at assessing the replicative capacity and susceptibility to lamivudine (LAM) and adefovir (ADV) in vitro of HBV harbouring rtI187V alone or in conjunction with LAM- or ADV-resistant mutations. The reverse transcriptase region of HBV isolates was directly sequenced from a cohort of 300 CHB patients from China. Replication-competent HBV constructs containing rtI187V and combined with LAM-resistant (rtM204I, rtL180M/rtM204V) mutations were generated, and compared with WT, LAM-resistant single (rtM204I) or double (rtL180M/rtM204V) and ADV-resistant (rtN236T) clones. In a Chinese cohort of 300 CHB patients, 8.7 % (26/300) showed substitution of rtI187 with V. Of note, the rtI187V prevalence in HBV genotype B was significantly higher than that in HBV genotype C (95.2 vs 4.8 %). In vitro phenotypic assays showed that the viruses bearing the rtI187V substitution had impaired replication efficacy when compared with the WT and the virus carrying rtI187V combined with LAM-resistant single or double mutations showed even more significantly impaired replicative capacities. Furthermore, rtI187V HBV remained susceptible towards treatment with LAM or ADV in vitro whereas the combination of the rtI187V substitution with LAM-resistant mutations rendered HBV resistant to LAM but still sensitive to ADV. Our study revealed that the rtI187V substitution in the HBV polymerase frequently occurred in CHB patients, particularly those with HBV genotype B. However, the emergence of the rtI187V substitution significantly impaired viral replication but without affecting drug sensitivity in vitro.

Mechanisms of hepatitis B virus resistance development

Hepatitis B virus (HBV) resistance to nucleos(t)ide analogue (NA) therapy is essentially structure specific, with each NA falling within three main structural groups. Resistance to each of these is characterized by specific mutations in the reverse transcriptase domains of the HBV polymerase, and may be associated with compensatory mutations which can increase replication. HBV polymerase is considered to have a traditional 'right-handed' structural conformation, and each of the resistance mutations is predicted to cause a specific structural change of the polymerase, thereby preventing incorporation of NA into replicating DNA. The selection of resistance occurs at different rates for each NA, and is affected by the high mutational rate of HBV and the ability of the drug to suppress viral replication. Some mutations or combinations of mutations may be associated with multidrug resistance, limiting treatment options. In contrast to most other viruses, resistance in HBV is confounded by the overlapping surface gene, the major NA-resistant mutations also altering the surface proteins in most cases, potentially altering virus secretion and neutralization, which may pose a public health threat in the future.

Options for the management of antiviral resistance during hepatitis B therapy: reflections on battles over a decade

Although much advancement has been achieved in the treatment of chronic hepatitis B, antiviral resistance is still a challenging issue. Previous generation antiviral agents have already developed resistance in a number of patients, and it is still being used especially in resource limited countries. Once antiviral resistance occurs, it predisposes to subsequent resistance, resulting in multidrug resistance. Therefore, prevention of initial antiviral resistance is the most important strategy, and appropriate choice and modification of therapy would be the cornerstone in avoiding treatment failures. Until now, management of antiviral resistance has been evolving from sequential therapy to combination therapy. In the era of tenofovir, the paradigm shifts again, and we have to decide when to switch and when to combine on the basis of newly emerging clinical data. We expect future eradication of chronic hepatitis B virus infection by proper prevention and optimal management of antiviral resistance.

Randomized trial of lamivudine, adefovir, and the combination in HBeAg-positive chronic hepatitis B

The aim of this study was to compare the efficacy of lamivudine or adefovir alone for 96 weeks versus initial treatment with the combination of lamivudine and adefovir for 12 to 24 weeks followed by adefovir alone. One hundred and fifty patients with HBeAg-positive chronic hepatitis B were randomized equally to lamivudine and adefovir diprivoxil combination therapy (LA), lamivudine alone (L), or adefovir dipivoxil alone (A) in a multicenter randomized clinical trial. In the LA group, the earliest time for lamivudine discontinuation was 12 weeks and adefovir monotherapy was continued until 96 weeks. Groups L and A received monotherapies for 96 weeks. At 12 weeks, the decrease in HBV DNA, percentage of patients with negative HBV DNA, and ALT normalization rate for the LA group were comparable to those of group L, but superior to those of group A. At 24 weeks, the rates of negative HBV DNA and HBeAg seroconversion of group LA were significantly higher than the monotherapy groups. This superiority was subsequently preserved during the maintenance phase with adefovir monotherapy. Starting at 48 weeks, the mean HBV DNA level of group L increased over the 24-week level. In contrast, the A group's rates of virological response, biochemical response, and HBeAg seroconversion continued to improve. At week 96, the percentage of patients with undetectable DNA and HBe seroconversion of LA group (100%, 51%) was higher than that of L (66%, 21%) and A group (49%, 33%), while no significant difference was observed between the L and A groups. During the course of therapy, no lamivudine- or adefovir-resistance mutations were discovered in the LA group. Rates of adverse reactions were comparable between the three groups. Combination therapy with lamivudine and adefovir for 12 to 24 weeks followed by adefovir monotherapy significantly improved antiviral efficacy and reduced drug resistance without compromising safety and tolerability compared to either drug alone in HBeAg-positive chronic hepatitis B.

Direct acting antivirals for the treatment of chronic viral hepatitis

The development and evaluation of antiviral agents through carefully designed clinical trials over the last 25 years have heralded a new dawn in the treatment of patients chronically infected with the hepatitis B and C viruses, but not so for the D virus (HBV, HCV, and HDV). The introduction of direct acting antivirals (DDAs) for the treatment of HBV carriers has permitted the long-term use of these compounds for the continuous suppression of viral replication, whilst in the case of HCV in combination with the standard of care [SOC, pegylated interferon (PegIFN), and ribavirin] sustained virological responses (SVRs) have been achieved with increasing frequency. Progress in the case of HDV has been slow and lacking in significant breakthroughs.This paper aims to summarise the current state of play in treatment approaches for chonic viral hepatitis patients and future perspectives.

Pre-existing YMDD mutants in treatment-naïve patients with chronic hepatitis B are not selected during lamivudine therapy

Although the rate at which mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) motif of hepatitis B virus polymerase form is high during prolonged lamivudine (LAM) therapy, these mutations sometimes occur naturally in treatment-naïve patients with chronic hepatitis B. The prevalence of natural YMDD mutants differs geographically, and its clinical significance during LAM therapy is unknown. This study aimed to investigate whether pre-existing YMDD mutants were selected during LAM therapy. It included 14 treatment-naïve patients who were treated with LAM for at least 9 months. LAM resistance was evaluated before and at 3-month intervals during treatment. Mutations were analyzed by direct sequencing, restriction fragment mass polymorphism (RFMP) assays, and a single-step multiplex polymerase chain reaction (PCR) test using dual-priming oligonucleotide (DPO) primers. DPO-based multiplex PCR showed two YMDD mutations in two patients before LAM therapy; rtM204V and rtL180M + rtM204V/I. Further, two patients had an rtL180M mutation without an accompanying rtM204V/I mutation. No mutant was detected in any patient by direct sequencing or the RFMP assay before LAM therapy. A virological response was observed at 3 months in all patients with pre-existing YMDD mutants. All mutations disappeared after 3 months of LAM therapy, and during the follow-up period, no re-emergence was detected by any of the three methods. Further, the viral load was suppressed optimally. In conclusion, pre-existing YMDD mutants were cleared early during the course of LAM therapy, which produced a consistent virological response, and the mutants were not selected by LAM therapy.

KASL Clinical Practice Guidelines: Management of chronic hepatitis B

The guideline on the management of chronic hepatitis B (CHB) was first developed in 2004 and revised in 2007 by the Korean Association for the Study of the Liver (KASL). Since then there have been many developments, including the introduction of new antiviral agents and the publications of many novel research results from both Korea and other countries. In particular, a large amount of knowledge on antiviral resistance--which is a serious issue in Korea--has accumulated, which has led to new strategies being suggested. This prompted the new guideline discussed herein to be developed based on recent evidence and expert opinion.

TARGET POPULATION

The main targets of this guideline comprise patients who are newly diagnosed with CHB and those who are followed or treated for known CHB. This guideline is also intended to provide guidance for the management of patients under the following special circumstances: malignancy, transplantation, dialysis, coinfection with other viruses, pregnancy, and children.

rtL180M mutation of hepatitis B virus is closely associated with frequent virological resistance to adefovir dipivoxil therapy

BACKGROUND AND AIM

We intended to investigate the effects of pre-existing mutations at reverse transcriptase region of hepatitis B virus (HBV) on the occurrence of virological breakthrough (VB) to adefovir dipivoxil (ADV) in patients with lamivudine (LAM)-resistant chronic hepatitis B (CHB).

METHODS

Ninety-seven patients with LAM-resistant CHB were treated with ADV at a dose of 10 mg daily, and were followed for a median period of 13 months. Just before the initiation of ADV therapy, the whole length of reverse transcriptase region of serum HBV-DNA was sequenced using direct sequencing.

RESULTS

All patients had genotype C HBV and mutations in the YMDD motif, specifically, YIDD (65%), YVDD (28%), or both (7%). The rtL180M and rtL80V/I mutations were identified in 68% and 69%, respectively. The cumulative probability of VB was 19% and 27% at 1 and 2 years, respectively. There was no difference in the occurrence of VB with regard to types of YMDD mutation or rtL80V/I. However, interestingly, patients carrying rtL180M experienced VB during ADV monotherapy more frequently than those not carrying rtL180M (2-year cumulative probability of VB: 37% vs 3% at 2 years, P < 0.01). On multivariate Cox proportional hazards analysis, rtL180M (hazard ratio [HR]: 8.62, 95% confidence interval: 1.08-69.09, P = 0.042) and decrease in HBV-DNA for 1 year of treatment (HR: 0.69, 95% CI: 0.51-0.95, P = 0.024) are independently associated with VB.

CONCLUSIONS

The rtL180M mutation of HBV, as well as a small decrease in HBV-DNA after 1 year of treatment might be closely associated with frequent occurrence of virological resistance to ADV in patients with LAM-resistant CHB.

Emergence of HBV resistance to lamivudine (3TC) in HIV/HBV co-infected patients in The Gambia, West Africa

BACKGROUND

Lamivudine (3TC) is a potent inhibitor of both Hepatitis B virus (HBV) and Human Immunodeficiency Virus (HIV) replication and is part of first-line highly active antiretroviral therapy (HAART) in the Gambia. Unfortunately, the effectiveness of 3TC against HBV is limited by the emergence of resistant strains.

AIM

The aim of this retrospective study was to characterise 3TC-resistant mutations in HBV from co-infected patients receiving HAART, by generating HBV polymerase sequence data and viral loads from HBV genotype E infected patients, both at initiation and during a course of 3TC therapy.

METHOD

Samples from 21 HBV chronic carriers co-infected with HIV-1 (n = 18), HIV-2 (n = 2) and HIV-dual (n = 1) receiving HAART for a period of 6-52 months were analysed for the emergence of 3TC-resistance mutations.

FINDINGS

Sixteen out of 21 HBV/HIV co-infected patients responded well to HAART treatment maintaining suppression of HBV viraemia to low (≤ 104 copies/mL) (n = 5) or undetectable levels (< 260 copies/ml) (n = 11). Out of the 5 non-responders, 3 had developed 3TC-resistant HBV strains showing mutations in the YMDD motif at position 204 of the RT domain of the HBV polymerase. One patient showed the M204V+ L180M+ V173L+ triple mutation associated with a vaccine escape phenotype, which could be of public health concern in a country with a national HBV vaccination programme. All except one patient was infected with HBV genotype E.

CONCLUSIONS

Our findings confirm the risk of 3TC mutations in HAART patients following monotherapy. This is a novel study on 3TC resistance in HBV genotype E patients and encourage the use of tenofovir (in association with 3TC), which has not shown unequivocally documented HBV resistance to date, as part of first-line therapy in HIV/HBV co-infected patients in West Africa.HBV- hepatitis B infection; HIV- human immunodeficiency virus; HAART- antiretroviral therapy.

Molecular characterization of a novel entecavir mutation pattern isolated from a multi-drug refractory patient with chronic hepatitis B infection

BACKGROUND

Prolonged antiviral treatment results in selection and accumulation of resistant strains in quasispecies pool in hepatitis B virus (HBV) infection.

OBJECTIVES

The aim of this study was to characterise a novel HBV pattern which shows resistance to lamivudine, adefovir dipivoxil and entecavir using in vitro phenoyping assay.

STUDY DESIGN

A male 36 years old patient diagnosed with anti HBe-positive chronic hepatitis B (CHB) had received lamivudine treatment for 7 years following an initial unsuccessfull interferon treatment. The therapy had been switched to adefovir and then to entecavir when breakthrough occcured during each treatment. This led only to a temporary HBV DNA decline which soon was followed by viral breakthrough despite the lack of known entecavir resistance mutations. Patient died after 9 months of entecavir treatment from liver failure. A total of 434 clones from 6 different serum samples were analysed retrospectively. HBV genomes bearing mutation patterns suggestive of antiviral resistance were analysed by in vitro phenotyping assay.

RESULTS

Dominance of a clone carrying L80LV, L91I, M204I, S219A, N238D, Y245H changes was detected in the last serum sample of the patient just before his death. This pattern displayed 30.4 fold resistance to entecavir when compared with the wild type HBV by in vitro phenotyping assay.

CONCLUSION

A novel mutation pattern showing a high degree of resistance to entecavir was documented. In this pattern, the S219A and Y245H mutations mainly seem to contribute to the emergence of ETV resistance.

Hepatitis B virus drug resistance to current nucleos(t)ide analogs: Mechanisms and mutation sites

Nucleos(t)ide analogs (NAs) have become the mainstream drugs for the treatment of chronic hepatitis B virus infection. Drug resistance to NAs, however, has posed a major obstacle in obtaining sustained viral suppression. Standardized definitions of terms and nomenclature in discussing NAs resistance have been proposed. Drug resistance to NAs is produced by a combination of viral, host and antiviral drug factors. A detailed understanding of the mechanisms and effects of mutation sites that cause resistance to NAs is important for the design of rational treatment and management of patients with existing drug resistance.

Identification of hepatitis B virus rtS117F substitution as a compensatory mutation for rtM204I during lamivudine therapy

OBJECTIVES

The replication defect of hepatitis B virus (HBV) lamivudine-resistant mutants can be restored by the development of compensatory mutations. Such mutations have long been recognized for the rtM204V mutant, while little is known about any compensatory mutation specific to the rtM204I mutant. The aim of this study was to search for previously unrecognized compensatory mutations following development of lamivudine-resistant mutants.

METHODS

Of 83 lamivudine-resistant patients, 49 and 34 patients harboured the rtM204I and rtM204V mutations, respectively. Serial serum samples obtained during the therapeutic course were submitted to sequence analysis. Site-directed mutagenesis experiments were performed to examine the functions of the identified associated mutations.

RESULTS

Of the 49 patients carrying the rtM204I mutation, 5 subsequently developed an rtS117F substitution during the follow-up, whereas 4 harboured an rtN124D substitution prior to the development of the rtM204I mutation. Emergence of the rtS117F mutation was associated with an increase in hepatitis activity, whereas prior existence of the rtN124D mutation was associated with decompensated liver function upon development of the rtM204I mutation. Site-directed mutagenesis experiments showed that the rtS117F mutation by itself did not confer lamivudine resistance but it compensated for replication deficiency of the rtM204I mutant in HepG2 and Mahlavu cells. Additionally, virion and hepatitis B surface antigen secretion of the rtS117F mutant was significantly impaired.

CONCLUSIONS

The rtS117F substitution served as a compensatory mutation for rtM204I. Emergence of the rtS117F mutation in lamivudine-resistant patients carrying rtM204I was associated with increased hepatitis activities. Prior existence of the rtN124D substitution was associated with liver decompensation upon development of the rtM204I mutation.

The YMDD and rtA194T mutations result in decreased replication capacity in wild-type HBV as well as in HBV with precore and basal core promoter mutations

BACKGROUND

A recent study indicated that addition of the hepatitis B e antigen (HBeAg) precore (PC) or basal core promoter (BCP) mutations to wild-type HBV offset the reduced replication of the HBV polymerase rtA194T±rtL180M+rtM204V mutations. rtA194T was reportedly associated with tenofovir resistance. We investigated these findings in genotype D HBV, where both PC and BCP naturally occur in vivo.

METHODS

A plasmid containing a wild-type 1.3 genome length genotype D HBV laboratory strain was used as a parent for PC, BCP, rtA194T±rtL180M+rtM204V, rtL180M+rtM204V and rtM204I mutants. Viral replication was evaluated by Southern blot analysis of intracellular HBV core DNA following transient transfection of HepG2 cells. Drug susceptibility was evaluated by quantitative PCR of intracellular HBV DNA.

RESULTS

PC and BCP mutations each increased HBV DNA replication by approximately 200% over wild-type. rtA194T reduced replication by <40%, whereas rtL180M+rtM204V, rtL180M+rtA194T+rtM204V or rtM204I each reduced by >75% from their respective wild-type, PC or BCP genome backbone (P<0.05). The enhanced replication by PC or BCP offset the reduction by rtA194T; however, the other reverse transcriptase (RT) mutations in PC or BCP backbones remained significantly lower than wild-type (P<0.05). Regardless of the backbone, rtA194T±rtL180M+rtM204V remained susceptible to tenofovir in vitro. rtA194T alone remained susceptible to lamivudine, while rtL180M+rtM204V and rtL180M+rtA194T+rtM204V were resistant.

CONCLUSIONS

PC or BCP mutations increased HBV DNA replication, offset the decreased replication by rtA194T alone, but they did not fully rescue the impaired replication conferred by other RT mutations as compared with wild-type. rtA194T±rtL180M+rtM204V did not confer tenofovir resistance.

Treatment of Hepatitis B e Antigen-negative Patients

Hepatitis B e antigen (HBeAg)-negative chronic hepatitis B (CHB) occurs at the late phase in hepatitis B virus (HBV) infection's natural history. The disease is characterized by progressive liver damage due to variants with mutations in the precore/core promoter region that reduce or abolish HBeAg expression. Chronic HBeAg-negative disease's prognosis is poor, with only rare incidences of spontaneous remission. Recent studies in Europe, Asia, and the United States all have reported an increased prevalence of HBeAg-negative and a decreased prevalence of HBeAg-positive chronic hepatitis; this may be related to increased awareness, decrease in new HBV infections, and aging of existing carriers. The end point of therapy for HBeAg-negative CHB patients is difficult to assess. In most studies, HBV DNA suppression and normalization of serum alanine aminotransaminase levels have been used to indicate therapeutic response. Six drugs currently are licensed for the treatment of CHB infection. These are the immunomodulatory agents (conventional interferon-alpha-2b and pegylated interferon-alpha-2a) and the nucleoside/nucleotide analogues (lamivudine, adefovir dipivoxil, entecavir, and telbivudine). Sustained treatment response rates generally are poor due to the high probability of relapse, particularly following nucleoside/nucleotide analogue therapy. As not all patients can tolerate or will respond to interferon-based therapy, maintenance therapy with nucleoside/nucleotide therapy is the alternative. However, this latter approach can lead to development of viral resistance and long-term safety concerns.

Treatment of hepatitis B in decompensated liver cirrhosis

Chronic hepatitis B infection progresses from an asymptomatic persistently infected state to chronic hepatitis, cirrhosis, decompensated liver disease, and/or hepatocellular carcinoma. About 3% of patients with chronic hepatitis develop cirrhosis yearly, and about 5% of individuals with hepatitis B cirrhosis become decompensated annually. The outcome for patients with decompensated cirrhosis is bleak. Lamivudine, the first oral antiviral agent available for hepatitis B treatment is safe and effective and can improve or stabilize liver disease in patients with advanced cirrhosis and viraemia. Viral resistance restricts its prolonged use. Entecavir and tenofovir are newer agents with excellent resistance profile to date. These and some other antiviral agents are being investigated for optimal use in this rather challenging patient group.

Four-year study of lamivudine and adefovir combination therapy in lamivudine-resistant hepatitis B patients: influence of hepatitis B virus genotype and resistance mutation pattern

To investigate the efficacy of long-term lamivudine (3TC) and adefovir dipivoxil (ADV) combination therapy in 3TC-resistant chronic hepatitis B virus (HBV) infected patients, we analysed 28 3TC-resistant patients treated with the combination therapy during 47 months (range, 9-75). At 12, 24, 36, and 48 months, the rates of virological response with undetectable HBV DNA (≤ 2.6 log copies/mL) were 56, 80, 86, and 92%, respectively. Among 17 hepatitis B e antigen (HBeAg)-positive patients, HBeAg disappeared in 24% at 12 months, 25% at 24 months, 62% at 36 months, and 88% at 48 months. When HBV genotypes were compared, patients with genotype B achieved virological response significantly more rapidly than those with genotype C (P=0.0496). One patient developed virological breakthrough after 54 months, and sequence analysis of HBV obtained from the patient was performed. An rtA200V mutation was present in the majority of HBV clones, in addition to the 3TC-resistant mutations of rtL180M+M204V. The rtN236T ADV-resistant mutation was observed in only 25% clones. In vitro analysis showed that the rtA200V mutation recovered the impaired replication capacity of the clone with the rtL180M+M204V mutations and induced resistance to ADV. Moreover, rtT184S and rtS202C, which are known entecavir-resistant mutations, emerged in some rtL180M+M204V clones without rtA200V or rtN236T. In conclusion, 3TC+ADV combination therapy was effective for most 3TC-resistant patients, especially with genotype B HBV, but the risk of emergence of multiple drug-resistant strains with long-term therapy should be considered. The mutation rtA200V with rtL180M+M204V may be sufficient for failure of 3TC+ADV therapy.

Hepatitis B virus genotyping among chronic hepatitis B patients with resistance to treatment with lamivudine in the City of Ribeirão Preto, State of São Paulo

INTRODUCTION

Lamivudine is a nucleoside analogue that is used clinically for treating chronic hepatitis B infection. However, the main problem with prolonged use of lamivudine is the development of viral resistance to the treatment. Mutations in the YMDD motif of the hepatitis B virus DNA polymerase gene have been associated with resistance to drug therapy. So far, there have not been many studies in Brazil reporting on genotype-dependent development of resistance to lamivudine. Thus, the aim of the present study was to determine the possible correlation between a certain genotype and increased development of resistance to lamivudine among chronic hepatitis B patients.

METHODS

HBV DNA in samples from 50 patients under lamivudine treatment was amplified by means of conventional PCR. Samples were collected at Hospital das Clínicas, FMRP-USP. The products were then sequenced and phylogenetic analysis was performed.

RESULTS

Phylogenetic analysis revealed that 29 (58%) patients were infected with genotype D, 20 (40%) with genotype A and one (2%) with genotype F. Mutations in the YMDD motif occurred in 20% of the patients with genotype A and 27.6% of the patients with genotype D.

CONCLUSIONS

Despite the small number of samples, our results indicated that mutations in the YMDD motif were 1.38 times more frequent in genotype D than in genotype A.

Hepatic Failure Caused by Reactivation of YMDD Mutants Occurring during Preemptive Lamivudine Therapy

Reactivation of hepatitis B virus (HBV) replication is a frequent phenomenon in patients receiving immunosuppressants or chemotherapy. It was recently reported that regional therapy, such as transarterial chemotherapy (TAC) or radiotherapy, can also induce HBV reactivation in patients with hepatocellular carcinoma (HCC), and this can be prevented by preemptive lamivudine treatment. We report an unusual case of fatal hepatitis caused by reactivation of the tyrosine-methionine-aspartate-aspartate (YMDD) lamivudine-resistant strain in a 51-year-old male patient with HCC who was receiving preemptive lamivudine therapy. This patient received combined helical tomotherapy and TAC for the treatment of HCC with pulmonary metastasis. HBV reactivation and hepatitis exacerbation occurred after 2 months of therapy, but preemptive antiviral therapy was continued. Laboratory tests showed that the serum HBV DNA level had increased by more than 10,000-fold and a severe elevation of the aminotransferase level to 1,060 U/L. Although adefovir was added to lamivudine immediately after detecting the YMDD mutants, the patient eventually died of hepatic failure. Our experience suggests that for preemptive therapy, the use of potent antiviral drugs with a low risk of drug resistance as well as close viral monitoring are important for chronic HBV carriers undergoing intensive anticancer therapy.

Importance of serum concentration of adefovir for Lamivudine-adefovir combination therapy in patients with lamivudine-resistant chronic hepatitis B

Lamivudine (LMV)-adefovir pivoxil (ADV) combination therapy suppresses the replication of LMV-resistant hepatitis B virus (HBV), although its efficacy in suppressing HBV varies among patients. This study analyzed the clinical, virological, and pharmaceutical factors that influence the effect of the combination therapy. Patients negative for hepatitis B virus e antigen (HBeAg) and with low HBV DNA titers immediately prior to the combination therapy effectively cleared serum HBV DNA (P=0.0348 and P=0.0310, respectively). The maximum concentration of ADV in serum (ADV Cmax) was higher in patients who showed HBV DNA clearance (P=0.0392), and the cumulative clearance rates of HBV DNA were significantly higher in patients with ADV Cmax equal to or greater than 24 ng/ml (P=0.0284). HBeAg negativity and lower HBV DNA at the start of the combination therapy and higher ADV Cmax were found to be independent factors for serum HBV DNA clearance. Serum creatinine increased significantly during the combination therapy, and the ADV Cmax was higher in patients with low creatinine clearance rates. In conclusion, higher serum concentrations of ADV are associated with a good response to therapy based on clearance of HBV DNA in serum. However, care should be taken to prevent worsening of renal function due to high ADV serum concentrations.

Low efficacy of entecavir therapy in adefovir-refractory hepatitis B patients with prior lamivudine resistance

We determined the virologic response, incidence of entecavir resistance, and evolution of lamivudine and adefovir-resistant mutants during entecavir (ETV) therapy in adefovir-refractory patients with prior lamivudine resistance. Forty adefovir-refractory chronic hepatitis B patients with prior lamivudine resistance who had received entecavir for > or = 6 months were included and monitored for virologic response and entecavir resistance. Ten per cent of patients achieved HBV DNA < 50 copies/mL by PCR after 24 weeks of ETV therapy, and an initial virologic response was observed in 12 of 40 patients (30%). Higher pretreatment ALT (P = 0.039) and the presence of the rtL180M mutation (P = 0.038) were associated with an initial virologic response. During a mean follow-up of 11.4 months, four patients (10%) experienced virologic breakthrough, while ETV-resistant mutants were detected in six patients (15%). YMDD and adefovir-resistant mutants were detected in 57 and 35% of patients at baseline, respectively. At 48 weeks of therapy, 96 and 4% of patients had YMDD and adefovir-resistant mutants, respectively. These data suggest an early development of ETV resistance and low antiviral response during ETV therapy in adefovir-refractory patients with prior lamivudine resistance.

Identification and characterization of clevudine-resistant mutants of hepatitis B virus isolated from chronic hepatitis B patients

Clevudine (CLV) is a nucleoside analog with potent antiviral activity against chronic hepatitis B virus (HBV) infection. Viral resistance to CLV in patients receiving CLV therapy has not been reported. The aim of this study was to characterize CLV-resistant HBV in patients with viral breakthrough (BT) during long-term CLV therapy. The gene encoding HBV reverse transcriptase (RT) was analyzed from chronic hepatitis B patients with viral BT during CLV therapy. Sera collected from the patients at baseline and at the time of viral BT were studied. To characterize the mutations of HBV isolated from the patients, we subjected the HBV mutants to in vitro drug susceptibility assays. Several conserved mutations were identified in the RT domain during viral BT, with M204I being the most common. In vitro phenotypic analysis showed that the mutation M204I was predominantly associated with CLV resistance, whereas L229V was a compensatory mutation for the impaired replication of the M204I mutant. A quadruple mutant (L129M, V173L, M204I, and H337N) was identified that conferred greater replicative ability and strong resistance to both CLV and lamivudine. All of the CLV-resistant clones were lamivudine resistant. They were susceptible to adefovir, entecavir, and tenofovir, except for one mutant clone. In conclusion, the mutation M204I in HBV RT plays a major role in CLV resistance and leads to viral BT during long-term CLV treatment. Several conserved mutations may have a compensatory role in replication. Drug susceptibility assays reveal that adefovir and tenofovir are the most effective compounds against CLV-resistant mutants. These data may provide additional therapeutic options for CLV-resistant patients.

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

Background

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

Methods/Principal Findings

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

Conclusions

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

Naturally occurring amino-acid substitutions to nucleos(t)ide analogues in treatment naive Turkish patients with chronic hepatitis B

Naturally occurring amino-acid substitutions in the hepatitis B virus (HBV) polymerase gene may be responsible for resistance to nucleoside/nucleotide (NUCs) analogues. To date, only pre-existing lamivudine resistance has been extensively studied. The aim of the present study was to determine the naturally occurring or pre-existing amino-acid substitutions related to NUCs in treatment naive Turkish patients with chronic hepatitis B (CHB). The investigation involved a total of 88 patients (65 males and 23 females; mean age, 34 years; range, 15-61 years) who were diagnosed with CHB between April 2008 and January 2009. According to HBeAg status, 66 patients were HBeAg-negative and 22 patients were HBeAg positive. Naturally occurring substitutions in the HBV polymerase region were detected by DNA sequencing in 17 (19%) and 30 (34%) patients, based on manual and geno2pheno tool database interpretation, respectively. Each amino-acid substitution appeared alone and included rtA194T, rtV214A, rtQ215S, rtI233V and rtN236T. The median values for viral load, ALT and AST were 3.3 log(10) (2.0-6.0) IU/mL, 36 (12-515) U/L and 27 (13-284) U/L, respectively, but these did not correlate with the observed amino-acid substitutions in the polymerase region. By direct sequencing, genotype D of HBV was found to still be dominant among Turkish patients. In conclusion, every patient who is diagnosed with CHB should be monitored before the start of treatment for more effective management of patient treatment options.

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

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

Evaluating the risk of hepatitis B reactivation in patients with haematological malignancies: is the serum hepatitis B virus profile reliable?

BACKGROUND/AIM

Patients with an occult hepatitis B virus (HBV) infection undergoing deep immunosuppression are potentially at risk of HBV reactivation. In order to assess whether a polymerase chain reaction (PCR) assay for HBV DNA in serum could be used to predict the reactivation of an occult HBV infection, we performed a retrospective study in a cohort of Sicilian patients with oncohaematological diseases.

METHODS

We studied by a highly sensitive ad hoc nested PCR for serum HBV DNA 75 HBsAg-negative oncohaematological patients requiring chemotherapy.

RESULTS

Thirty-three patients (44%) were HBV seronegative (anti-HBc and anti-HBs negative) and 42 patients (56%) were HBV seropositive (anti-HBc and/or anti-HBs positive). Baseline serum HBV DNA was positive in nine out of 33 HBV-seronegative patients and in nine out of 42 HBV-seropositive patients (27.3 vs. 21.4%; P=NS). HBsAg seroconversion was observed in five out of 33 seronegative vs. six out of 42 seropositive patients (15 vs. 14%, P=0.9), and in five out of 18 HBV DNA-positive vs. six out of 57 HBV DNA-negative patients (27.7 vs. 10.6%P=0.11). Hepatitis C virus infection was found in 18 patients (24.3%), although with no correlation to HBV serological status, presence of serum HBV DNA or frequency of HBsAg seroconversion.

CONCLUSIONS

In oncohaematological patients undergoing chemotherapy, highly sensitive serum HBV DNA testing at baseline has a 28% predictive ability to forecast HBsAg seroconversion in HBV DNA-positive patients, and a 90% ability to forecast persistent HBsAg negativity in HBV DNA-negative patients, a better performance than serological tests.

Lamivudine and adefovir resistance in children and young adults with chronic hepatitis B

OBJECTIVE

Long-term lamivudine (LAM) and adefovir (ADV) treatment has been found to induce the emergence of drug-resistant hepatitis B virus (HBV) in a significant number of patients with chronic hepatitis B (CHB) infection. The aim of our study was to evaluate the LAM and ADV mutations detected in our patient group.

MATERIALS AND METHODS

Twenty-four patients diagnosed with CHB were enrolled in this study. The patient group consisted of those who had received 6 months of treatment with interferon-alpha and who did not response to this therapy. Patients were evaluated based on virologic and serologic response to therapy, and were classified as responders or non-responders. The treatment of non-responders continued with LAM (3mg/kg/d, maximum 100mg/d). Due to a lack of response to treatment, ADV (10mg/g) was added to the treatment regimen of eight young adult patients. The mutations associated with HBV drug resistance were investigated using reverse hybridization methods and PCR.

RESULTS

The mutation studies indicated that 14 (58.4%) of the patients had resistance. Three patients developed ADV-associated mutations (A181T), one after 18 months of ADV; the other two had undergone 18 and 36 months of LAM therapy without ADV exposure. Although the average LAM treatment period of the patients with LAM resistance was longer than for those in whom no resistance was detected, no statistically significant difference was found.

CONCLUSIONS

HBV treatment with nucleoside analogues results in the development of mutant strains, leading to drug resistance. Therefore genotypic resistance testing is important in planning and monitoring HBV treatment.

Frequent detection of hepatitis B virus variants associated with lamivudine resistance in treated South African patients infected chronically with different HBV genotypes

This retrospective study investigated and characterized the YMDD motif of the hepatitis B virus (HBV) reverse transcriptase (RT) gene, in sequential samples of 17 South African patients with chronic hepatitis B infection on lamivudine treatment. The profile of HBV genotypes as well as the genetic variability of pre-core (pre-C) and basal core promoter regions (BCP) were also determined in these patients. Mutations within the RT gene were determined by direct sequencing using SpectruMedix SCE 2410 genetic analyzer and INNO-LiPA HBV DR (Innogenetics), while the genetic variability of the pre-C/BCP and surface gene were determined by direct sequencing only. HBV genotypes were determined by analysis of the surface, core and RT genes using a web-based genotyping tool (NCBI). HBV DNA was quantified using Cobas Amplicor HBV Monitor assay (Roche Diagnostics). Of the 17 patients, 13 (76.5%) carried YMDD mutations: 7 with rtM204I (2 HBeAg-positive and 5 HBeAg-negative) and 6 with rtM204V (4 HBeAg-positive and 2 HBeAg-negative). Of the 13 patients with resistant HBV strains, 8 (61.5%) carried genotype A, 3 (23%) genotype B, and 2 (15.3%) genotype C. Overall, only 5 of 13 (38%) patients with YMDD mutations experienced genotypic viral drug resistance and treatment failure. Of the 17 patients, 3 carried both pre-C (G1896A) and BCP (A1762T/G1764A) mutants, 1 pre-C only and 1 BCP only. This study demonstrated frequent detection of mutations associated with lamivudine-resistance in therapy-experienced South African patients infected chronically with different HBV genotypes, and confirmed that these mutations are not always accompanied by clinical relapse.