Emergence of a novel lamivudine-resistant hepatitis B virus variant with a substitution outside the YMDD motif

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

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

Hydroxyalkynyl uracil derivatives as NNRTIs against HIV-1: in silico predictions, synthesis, docking and molecular dynamics simulation studies

To improve rationally the efficacy of the non-nucleoside human immunodeficiency virus (HIV-1) inhibitors, it is important to have a precise and detailed understanding of the HIV-1 reverse transcriptase (RT) and inhibitor interactions. For the 1-[(2-hydroxyethoxy) methyl]-6-(phenylthio) thymine (HEPT) type of nucleoside reverse transcriptase inhibitors (NNRTIs), the H-bond between the N-3H of the inhibitor and the backbone carbonyl group of K101 represents the major hydrophilic interaction. This H-bond contributes to the NNRTI binding affinity. The descriptor analyses of different uracil derivatives proved their good cell internalization. The bioactivity score reflected higher drug likeness score and the ligands showed interesting docking results. All molecules were deeply buried and stabilized into the allosteric site of HIV-1 RT. For majority of molecules, residues Lys101, Lys103, Tyr181 and Tyr188 were identified as key protein residues responsible for generation of H-bond and major interactions were similar to all known NNRTIs while very few molecules interacted with residues Phe227 and Tyr318. The TOPKAT protocol available in Discovery Studio 3.0 was used to predict the pharmacokinetics of the designed uracil derivatives in the human body. The molecular dynamics (MD) and post-MD analyses results reflected that the complex HIVRT:5 appeared to be more stable than the complex HIVRT:HEPT, where HEPT was used as reference. Different uracil derivatives have been synthesized by using uracil as starting material and commercially available propargyl bromide. The N-1 derivative of uracil was further reacted with sodamide and different aldehydes/ketones bearing alkyl and phenyl ring to obtain hydroxyalkynyl uracil derivatives as NNRTIs.Communicated by Ramaswamy H. Sarma.

Spacer Domain in Hepatitis B Virus Polymerase: Plugging a Hole or Performing a Role?

Hepatitis B virus (HBV) polymerase is divided into terminal protein, spacer, reverse transcriptase, and RNase domains. Spacer has previously been considered dispensable, merely acting as a tether between other domains or providing plasticity to accommodate deletions and mutations. We explore evidence for the role of spacer sequence, structure, and function in HBV evolution and lineage, consider its associations with escape from drugs, vaccines, and immune responses, and review its potential impacts on disease outcomes.

Are Humanized Mouse Models Useful for Basic Research of Hepatocarcinogenesis through Chronic Hepatitis B Virus Infection?

Chronic hepatitis B virus (HBV) infection is a global health problem that can lead to liver dysfunction, including liver cirrhosis and hepatocellular carcinoma (HCC). Current antiviral therapies can control viral replication in patients with chronic HBV infection; however, there is a risk of HCC development. HBV-related proteins may be produced in hepatocytes regardless of antiviral therapies and influence intracellular metabolism and signaling pathways, resulting in liver carcinogenesis. To understand the mechanisms of liver carcinogenesis, the effect of HBV infection in human hepatocytes should be analyzed. HBV infects human hepatocytes through transfer to the sodium taurocholate co-transporting polypeptide (NTCP). Although the NTCP is expressed on the hepatocyte surface in several animals, including mice, HBV infection is limited to human primates. Due to this species-specific liver tropism, suitable animal models for analyzing HBV replication and developing antivirals have been lacking since the discovery of the virus. Recently, a humanized mouse model carrying human hepatocytes in the liver was developed based on several immunodeficient mice; this is useful for analyzing the HBV life cycle, antiviral effects of existing/novel antivirals, and intracellular signaling pathways under HBV infection. Herein, the usefulness of human hepatocyte chimeric mouse models in the analysis of HBV-associated hepatocarcinogenesis is discussed.

Hepatitis B virus resistance to tenofovir: fact or fiction? A systematic literature review and structural analysis of drug resistance mechanisms

Background: Tenofovir (TFV) is a widely used treatment for chronic hepatitis B virus (HBV) infection. There is a high genetic barrier to the selection of TFV resistance-associated mutations (RAMs), but the distribution and clinical significance of TFV RAMs are not well understood. We here present assimilated evidence for putative TFV RAMs with the aims of cataloguing and characterising mutations that have been reported, and starting to develop insights into mechanisms of resistance. Methods: We carried out a systematic literature search in PubMed and Scopus to identify clinical, in vitro and in silico evidence of TFV resistance. We included peer-reviewed studies presenting original data regarding virological TFV breakthrough, using published methods to assess the quality of each study. We generated a list of RAMs that have been reported in association with TFV resistance, developing a 'long-list' (all reported RAMs) and a 'short-list' (a refined list supported by the most robust evidence). We assessed the potential functional and structural consequences by mapping onto the crystal structure for HIV reverse transcriptase (RT), as the structure of HBV RT has not been solved. Results: We identified a 'long-list' of 37 putative TFV RAMs in HBV RT, occurring within and outside sites of enzyme activity, some of which can be mapped onto a homologous HIV RT structure. A 'short-list' of nine sites are supported by the most robust evidence. If clinically significant resistance arises, it is most likely to be in the context of suites of multiple RAMs. Other factors including adherence, viral load, HBeAg status, HIV coinfection and NA dosage may also influence viraemic suppression. Conclusion: There is emerging evidence for polymorphisms that may reduce susceptibility to TVF. However, good correlation between viral sequence and treatment outcomes is currently lacking; further studies are essential to optimise individual treatment and public health approaches.

Roles of Hepatitis B Virus Mutations in the Viral Reactivation after Immunosuppression Therapies

Reactivation of hepatitis B virus (HBV) is a major problem in patients receiving chemotherapy for malignant diseases or immunosuppression therapies. It has been thought that a reduction in the immune responses might result in the reactivation of HBV replication from covalently closed circular DNA (cccDNA) residing in hepatocytes. However, not only the host’s immune status, but also viral mutations have been reported to be associated with reactivation. Especially, several case reports about amino acid mutations in hepatitis B surface antigen (HBsAg) that escape from immune reactions have been reported, and recent reports showed that the frequencies of such mutations are higher than previously expected. In this review, we summarize the characteristics of viral mutations, including immune escape mutations in HBV-reactivated patients, and discuss their significance.

CTL-associated and NK cell-associated immune responses induce different HBV DNA reduction patterns in chronic hepatitis B patients

The activation of hepatitis B virus (HBV)-related hepatitis is associated with both natural killer (NK) cells and cytotoxic T lymphocytes (CTLs). We analyzed the association between the immune response and changes in the proportion of Pre-S deletion variants. We quantified Pre-S deleted HBV (HBV-del) and wild-type HBV (HBV-wt) DNA levels in sera obtained from HBV-infected mice and chronic hepatitis B patients. In chronic hepatitis B patients, the HBV-del proportion usually increased during or after ALT elevation but did not occur during all ALT elevations. To clarify this difference in the immunological responses, we performed in vivo analyses using HBV-infected human hepatocyte chimeric mice. Although HBV-del proportions did not change in mice with NK cell-associated hepatitis or in mice treated with entecavir, the proportions sharply increased in mice with CTL-associated hepatitis. Furthermore, the number of patients in which HBV-del proportions were greater than 5% was significantly higher in chronic hepatitis B patients than in asymptomatic carriers (P = 0.023). We identified associations between virological response in chronic hepatitis B patients and two different immune responses. The proportion of HBV-del variants could be a useful biomarker for distinguishing between chronic hepatitis and asymptomatic carriers.

No Resistance to Tenofovir Alafenamide Detected through 96 Weeks of Treatment in Patients with Chronic Hepatitis B Infection

Tenofovir alafenamide (TAF) has shown equivalent efficacy and improved safety profiles for patients with chronic hepatitis B (CHB) compared to tenofovir disoproxil fumarate (TDF). However, limited data are available for its resistance profiles. In two clinical trials, 1,298 hepatitis E antigen-positive and -negative patients with CHB were randomized 2:1 and treated with TAF (n = 866) or TDF (n = 432). Baseline nucleos(t)ide analog resistance substitutions in HBV polymerase/reverse transcriptase (Pol/RT) were assessed using INNO-LiPA Multi-DR v2/v3. Resistance surveillance was conducted for patients with viremia (HBV DNA ≥ 69IU/ml) by HBV Pol/RT sequencing at week 96 or at discontinuation. In vitro phenotypic analysis was performed for patients with conserved site substitutions or virologic breakthrough while adherent to the study drug. At baseline, the majority of patients harbored virus with wild-type Pol/RT (89.2%), with 10.8% harboring resistance associated mutations. A similar percentage of patients in the TAF or TDF groups qualified for sequence analysis through week 96 (TAF, 11.1%; TDF, 10.9%). Of these, a small percentage of patients experienced virologic breakthrough (TAF, 2.8%; TDF, 3.2%) that was often associated with drug nonadherence (TAF, 30%; TDF, 50%). Across treatment groups, 132 patients qualified for sequence analysis through week 96, with nearly half having no sequence changes from baseline (43.2%). Most sequence changes occurred at polymorphic positions, and no isolates showed a reduction in susceptibility in vitro After 96 weeks, the proportion of patients achieving virus suppression (HBV DNA < 69 IU/ml) was similar across treatment groups, and no substitutions associated with resistance to TAF or TDF were detected. (These studies have been registered at ClinicalTrials.gov under identifiers NCT01940471 and NCT01940341.).

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

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

Development of a Novel Site-Specific Pegylated Interferon Beta for Antiviral Therapy of Chronic Hepatitis B Virus

Although nucleot(s)ide analogues and pegylated interferon alpha 2a (PEG-IFN-α2a) can suppress hepatitis B virus (HBV) replication, it is difficult to achieve complete HBV elimination from hepatocytes. A novel site-specific pegylated recombinant human IFN-β (TRK-560) was recently developed. In the present study, we evaluated the antiviral effects of TRK-560 on HBV replication in vitro and in vivo. In vitro and in vivo HBV replication models were treated with antivirals including TRK-560, and changes in HBV markers were evaluated. To analyze antiviral mechanisms, cDNA microarray analysis and an enzyme-linked immunoassay (ELISA) were performed. TRK-560 significantly suppressed the production of intracellular HBV replication intermediates and extracellular HBV surface antigen (HBsAg) (P < 0.001 and P < 0.001, respectively), and the antiviral effects of TRK-560 were enhanced in combination with nucleot(s)ide analogues, such as entecavir and tenofovir disoproxil fumarate. The reduction in HBV DNA levels by TRK-560 treatment was significantly higher than that by PEG-IFN-α2a treatment both in vitro and in vivo (P = 0.004 and P = 0.046, respectively), and intracellular HBV covalently closed circular DNA (cccDNA) reduction by TRK-560 treatment was also significantly higher than that by PEG-IFN-α2a treatment in vivo (P = 0.0495). cDNA microarrays and ELISA for CXCL10 production revealed significant differences between TRK-560 and PEG-IFN-α2a in the induction potency of interferon-stimulated genes. TRK-560 shows a stronger antiviral potency via higher induction of interferon-stimulated genes and stronger stimulation of immune cell chemotaxis than PEG-IFN-α2a. As HBsAg loss and HBV cccDNA eradication are important clinical goals, these results suggest a potential role for TRK-560 in the development of more effective treatment for chronic hepatitis B infection.

Biological characteristics comparison of HBV rtA181T mutants with truncated or substituted HBsAg expression in vitro and in vivo model systems

The hepatitis B virus(HBV) polymerase rtA181T mutation is selected during long-term antiviral therapy. As the polymerase gene completely overlaps with the envelope (S) gene, HBV rtA181T mutation also carries sW172 mutations. In this study, we investigated whether there were biological differences between rtA181T/sW172* (coding truncated HBsAg) and rtA181T/sW172L (coding substituted HBsAg) mutants. In cell experiments, a slight decline of viral replication was observed in both two mutants as compared to wild-type strains, but the levels of supernatant HBsAg and HBV DNA in rtA181T/sW172* were significantly lower than those in rtA181T/sW172L transfected cells. In animal experiments, we were amazed to find that viral replication in rtA181T/sW172* mutant increased and maintained significantly longer than that in rtA181T/sW172L mutant, while no significant difference was observed between rtA181T/sW172L and wild-type strains. Compared with wild-type strains, there were intracellular accumulations of HBsAg and HBcAg in rtA181/sW172* but none in rtA181/sW172L mutant strains. Importantly, we also found that truncated HBsAg could increase the activity of HBV core promoter, but substituted HBsAg could not. In summary, the characteristics of above two rtA181T mutants mentioned above were significantly different, and it is necessary and important for us to distinguish sW172* truncated mutation from sW172L substituted mutation.

Nucleos(t)ide analogues causes HBV S gene mutations and carcinogenesis

BACKGROUND

The long-term use of nucleos(t)ide analogues causes drug resistance and mutations in the HBV reverse transcriptase (RT) region of the polymerase gene. The RT region overlaps the HBV surface gene (S gene) and therefore, the mutations in the RT region simultaneously modify S gene sequence. Certain mutations in the RT region bring about truncated S proteins because the corresponding changed S gene encodes a stop codon which results in the loss of a large portion of the C-terminal hydrophobic region of HBV surface protein. The rtA181T/sW172*, rtM204I/sW196* and rtV191I/sW182* are the most frequently reported drug-resistant mutations with C-terminal truncation, these mutations have oncogenic potential.

DATA SOURCES

PubMed and Web of Science were searched using terms: "hepatitis B virus", "HBV drug resistance mutation", "HBV surface protein", "HBV truncation", "hepatocellular carcinoma", "rtA181T/sW172*", "rtM204I/sW196*", "rtV191I/sW182*", and relevant articles published in English in the past decades were reviewed.

RESULTS

The rtA181T/sW172* and rtV191I/sW182* mutants occurred more frequently than the rtM204I/sW196* mutant both in chronic hepatitis B patients and the HBV-related hepatocellular carcinoma tissues. Although these mutations occur naturally, nucleos(t)ide analogues therapy is the main driving force. These mutations may exist alone or coexist with other HBV mutations. All these three mutants impair the virion secretion and result in HBV surface protein retention and serum HBV DNA level reduction. These mutations possess potential carcinogenic properties. The three mutations are resistant to more than one nucleos(t)ide analogue and therefore, it is difficult to treat the patients with the truncated mutations.

CONCLUSIONS

Nucleos(t)ide analogues induce drug resistance and HBV S gene truncated mutations. These mutations have potential carcinogenesis.

Genetic variation of hepatitis B virus and its significance for pathogenesis

Hepatitis B virus (HBV) has a worldwide distribution and is endemic in many populations. Due to its unique life cycle which requires an error-prone reverse transcriptase for replication, it constantly evolves, resulting in tremendous genetic variation in the form of genotypes, sub-genotypes, and mutations. In recent years, there has been considerable research on the relationship between HBV genetic variation and HBV-related pathogenesis, which has profound implications in the natural history of HBV infection, viral detection, immune prevention, drug treatment and prognosis. In this review, we attempted to provide a brief account of the influence of HBV genotype on the pathogenesis of HBV infection and summarize our current knowledge on the effects of HBV mutations in different regions on HBV-associated pathogenesis, with an emphasis on mutations in the preS/S proteins in immune evasion, occult HBV infection and hepatocellular carcinoma (HCC), mutations in polymerase in relation to drug resistance, mutations in HBV core and e antigen in immune evasion, chronicalization of infection and hepatitis B-related acute-on-chronic liver failure, and finally mutations in HBV x proteins in HCC.

Effect of tenofovir disoproxil fumarate on drug-resistant HBV clones

BACKGROUND & AIMS

Tenofovir disoproxil fumarate (TDF) has been approved for chronic hepatitis B treatment, and favorable susceptibility of hepatitis B virus (HBV) has been indicated. However, differences in TDF susceptibility among HBV genotypes and drug-resistant strains are unclear. In this study, TDF susceptibilities between genotypes A and C were evaluated in vitro and in vivo using several drug-resistant HBV clones.

METHODS

HBV expression plasmids were constructed from sera of HBV carriers, and drug-resistant substitutions were introduced by site-directed mutagenesis. TDF susceptibility was evaluated by changes of core-associated HBV replication intermediates in vitro or by change of serum HBV DNA in human hepatocyte chimeric mice carrying each HBV clone in vivo.

RESULTS

TDF susceptibilities of lamivudine-resistant clones (rtL180M/M204V) and lamivudine plus entecavir-resistant clones (rtL180M/S202G/M204V) were similar to wild type clones in vitro. However, lamivudine plus adefovir-resistant clones (rtA181T/N236T) acquired tolerance to TDF, and the rtN236T mutation was considered to be a causal substitution for TDF resistance. Furthermore, genotypic differences in TDF susceptibility were also observed between genotypes A and C in vitro, and the differences could be confirmed in vivo (p = 0.023).

CONCLUSIONS

The present study indicates that TDF susceptibility varies among HBV genotypes and drug-resistant HBV clones.

Mutation analysis of hepatitis B virus reverse transcriptase region among untreated chronically infected patients in Ahvaz city (South-West of Iran)

BACKGROUND

It has been revealed that mutations can occur spontaneously and naturally in HBV reverse transcriptase (RT) region among untreated patients. These HBV mutants pre-exist as minor viral population in naive patients and can emerge as major viral population, conferring drug resistance and treatment failure.

OBJECTIVES

The aim of this study was to investigate and identify prevalent mutations of RT region of hepatitis B virus genome in patients with chronic hepatitis B (CHB) untreated with antiviral drugs in South-West of Iran.

MATERIALS AND METHODS

A total of 45 cases with CHB who did not receive the treatment of lamivudine and any other antivirus drugs within the last one year were randomly chosen. After sample collection and HBV DNA extraction, RT region was amplified by polymerase chain reaction (PCR). Then PCR products were sequenced and HBV RT region mutations and amino acid changes were analyzed either manually or using web-based programs, on the basis of comparison of the obtained sequences with a set of HBV reference sequences.

RESULTS

A total of 23 (51.1%) mutations and amino acid changes were detected in studied 45 untreated patients. Of these, 3 (6.6%) patients had primary resistance mutation (rtM204I, rtA181T and rtA181S) and 20 (44.4%) patients had secondary resistance mutations.

CONCLUSION

High prevalence of mutations was found in HBV RT region of untreated patients. Most of these mutations were associated with resistance to adefovir and one patient had primary resistance mutation to lamivudine. Awareness of these resistance patterns might help in the antiviral therapy and for predicting clinical outcomes.

Different mechanism of selection of adefovir-resistant mutant viruses during adefovir monotherapy in patients with lamivudine-resistant chronic hepatitis B

BACKGROUND

Adefovir (ADV) resistance is more frequent in lamivudine (LMV)-resistant chronic hepatitis B (CHB) patients than in nucleos(t)ide analogue-naïve patients. The majority of LMV-resistant mutants harbor the rtM204V/I mutation, while a minor fraction harbor the rtA181V/T mutation. We aimed to elucidate the mechanism of the high rate of ADV resistance in LMV-resistant patients during ADV therapy.

METHODS

We performed a clonal analysis of HBV reverse transcriptase in treatment-naïve (n = 3) and LMV-resistant patients before ADV therapy (n = 14). Dynamic changes in the viral population (n = 9) during ADV therapy were also analyzed.

RESULTS

Before ADV therapy, rtA181V/T was observed in 30 of 680 clones (4.4%) from 7 patients with LMV resistance under dominant rt204V/I mutation and in one of 150 clones in treatment-naïve patients. The rtA181V/T mutation was more frequently found in clones from LMV-resistant patients than in treatment-naïve patients (p = 0.029). The rtN236T mutation was not observed in any clone. During ADV therapy, most rtM204V/I mutants were replaced by wild type in all 3 patients without the rtA181V/T mutation and in one patient with the rtA181V/T mutation. Subsequently, wild type was replaced by the rtN236T and/or rtA181V/T mutant. In patients with the rtA181V/T mutation (n = 6), the rtA181V/T mutant overtook the rtM204V/I mutant in 3 of 4 patients with ADV resistance. In 2 patients without ADV resistance, most of the viral population was replaced by wild type by the last follow-up.

CONCLUSION

The high rate of ADV resistance in patients with LMV-resistance might be attributable to preexisting rtA181V/T mutant virus.

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

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

Mouse models of hepatitis B virus infection comprising host-virus immunologic interactions

Hepatitis B virus (HBV) infection is one of the most prevalent infectious diseases associated with various human liver diseases, including acute, fulminant and chronic hepatitis; liver cirrhosis; and hepatocellular carcinoma. Despite the availability of an HBV vaccine and the development of antiviral therapies, there are still more than 350 million chronically infected people worldwide, approximately 5% of the world population. To understand the virus biology and pathogenesis in HBV-infected patients, several animal models have been developed to mimic hepatic HBV infection and the immune response against HBV, but the narrow host range of HBV infection and lack of a full immune response spectrum in animal models remain significant limitations. Accumulating evidence obtained from studies using a variety of mouse models that recapitulate hepatic HBV infection provides several clues for understanding host-virus immunologic interactions during HBV infection, whereas the determinants of the immune response required for HBV clearance are poorly defined. Therefore, adequate mouse models are urgently needed to elucidate the mechanism of HBV elimination and identify novel targets for antiviral therapies.

rtM204Q may serve as a novel lamivudine-resistance-associated mutation of hepatitis B virus

Background and Aims

Lamivudine (LAM) is still widely used for anti-HBV therapy in China. The study aimed to clarify whether a newly-found rtM204Q mutation from patients was associated with the drug resistance.

Methods

HBV complete reverse-transcriptase region was screened by direct sequencing and verified by clonal sequencing. Replication-competent plasmids containing patient-derived 1.1mer mutant or wild-type viral genome were constructed and transfected into HepG2 cells. After cultured with or without serially-diluted antiviral drugs, intracellular HBV replicative intermediates were quantitated for calculating the 50% effective concentration of drug (EC₅₀).

Results

A total of 12,000 serum samples of 9,830 patients with chronic HBV infection were screened. rtM204Q mutation was detected in seven LAM-refractory patients. By contrast, rtM204I/rtM204V mutations were detected in 2,502 patients' samples. The rtM204Q emerged either alone or in concomitance with rtM204I/rtM204V, and all were accompanied with virologic breakthrough in clinical course. Clonal sequencing verified that rtM204Q mutant was predominant in viral quasispecies of these samples. Phenotypic analysis showed that rtM204Q mutant had 89.9% of replication capacity and 76-fold increased LAM EC₅₀ of the concomitant wild-type strain. By contrast, rtM204I mutant in the sample had lower replication capacity and higher LAM resistance (46.3% and 1396-fold increased LAM EC₅₀ of the wild-type strain) compared to rtM204Q mutant. rtM204Q mutant was susceptible to adefovir dipivoxil (ADV) in vitro and ADV/ADV+LAM rescue therapy in clinic.

Conclusion

rtM204Q is suggested to be a novel LAM-resistance-associated mutation. It conferred a moderate resistance with higher competent natural replication capacity compared to rtM204I mutation.

Epidemiological, virological and clinical characteristics of HBV infection in 223 HIV co-infected patients: a French multi-centre collaborative study

Background

Chronic hepatitis B (CHB) is a clinical concern in human immunodeficiency virus (HIV)-infected individuals due to substantial prevalence, difficulties to treat, and severe liver disease outcome. A large nationwide cross-sectional multicentre analysis of HIV-HBV co-infected patients was designed to describe and identify parameters associated with virological and clinical outcome of CHB in HIV-infected individuals with detectable HBV viremia.

Methods

A multicenter collaborative cross-sectional study was launched in 19 French University hospitals distributed through the country. From January to December 2007, HBV load, genotype, clinical and epidemiological characteristics of 223 HBV-HIV co-infected patients with an HBV replication over 1000 IU/mL were investigated.

Results

Patients were mostly male (82%, mean age 42 years). Genotype distribution (A 52%; E 23.3%; D 16.1%) was linked to risk factors, geographic origin, and co-infection with other hepatitis viruses. This genotypic pattern highlights divergent contamination event timelines by HIV and HBV viruses. Most patients (74.7%) under antiretroviral treatment were receiving a drug with anti-HBV activity, including 47% receiving TDF. Genotypic lamivudine-resistance detected in 26% of the patients was linked to duration of lamivudine exposure, age, CD4 count and HIV load. Resistance to adefovir (rtA181T/V) was detected in 2.7% of patients. Advanced liver lesions were observed in 54% of cases and were associated with an older age and lower CD4 counts but not with viral load or genotype. Immune escape HBsAg variants were seldom detected.

Conclusions

Despite the detection of advanced liver lesions in most patients, few were not receiving anti-HBV drugs and for those treated with the most potent anti-HBV drugs, persistent replication suggested non-optimal adherence. Heterogeneity in HBV strains reflects epidemiological differences that may impact liver disease progression. These findings are strong arguments to further optimize clinical management and to promote vaccination in HIV-infected patients.

Clonal evolution of hepatitis B virus polymerase gene mutations during lamivudine-adefovir combination treatment

AIM: To identify hepatitis B virus polymerase gene mutations during antiviral therapy using lamivudine-adefovir sequential monotherapy followed by lamivudine-adefovir combination therapy.

METHODS: The patient cohort included four adult chronic hepatitis B patients who had undergone sequential monotherapy, first with lamivudine (LMV) and then, after developing viral breakthrough, with adefovir (ADV) therapy. All of the patients had non-response or viral breakthrough after LMV-ADV sequential monotherapy, which resulted in the switching of their antiviral regimen to LMV-ADV combination therapy. Eleven serum samples from the four patients who showed non-response to rescue LMV-ADV combination therapy were collected sequentially at a time before the antiviral treatment and then during the LMV monotherapy, ADV monotherapy, and LMV-ADV combination therapy. For the genotypic analysis, the whole 1310-bp polymerase gene region was amplified, cloned and sequenced.

RESULTS: All patients had been previously treated with 100 mg of LMV once daily for a 15- to 26-mo period. The emergence of resistance mutations to LMV, such as rtM204V/I and/or rtL180M, were found in all patients. Their antiviral regimens were switched to ADV monotherapy as the second line treatment. All patients had viral breakthrough or non-response after the LMV-ADV sequential monotherapy. ADV-resistant mutations were detected after 13 to 19 mo of LMV-ADV sequential monotherapy. The rtA181V/T mutations were predominantly identified during the ADV treatment in the LMV-resistant patients. Twenty-seven of 38 clones were combined with an amino acid change at rt181; three clones had mutations in rt236 and one clone had a combined mutation. The rtA181V/T mutations were not suppressed by the LMV-ADV combination therapy. Thirty-nine of 64 clones showed an rtA181V/T mutation and six clones showed combined mutations in rt181 and rt236. Mutations in rt204 re-emerged during the combination treatment. The rt181 and rt204 mutations did not co-exist in one clone.

CONCLUSION: Add-on lamivudine therapy with adefovir for adefovir resistance may not suppress the pre-existing adefovir-resistant mutation that develops during lamivudine-adefovir sequential monotherapy.

Biological characteristics of the rtA181T/sW172* mutant strain of Hepatitis B virus in animal model

Background

The effects of Hepatitis B virus (HBV) rtA181T/sW172* mutation on viral replication and pathogenicity was concerned recently. This study aimed to investigate the biological characteristics of rtA181T/sW172* mutant strain of HBV in animal model.

Methods

The rtA181T/sW172* mutant plasmid was constructed using the pHBV4.1 (wild type HBV) as a template. The wild and mutant HBV replication mouse models were established utilizing a hydrodynamic technique. The titers of hepatitis B surface antigen (HBsAg), hepatitis B e antigen, and HBV DNA in serum, and the levels of HBsAg, hepatitis B core antigen(HBcAg), HBV DNA replication intermediates (HBV DNA RI) and HBV RNA in liver were measured after 1, 3, 5, 7, 10, 12 and 15 days of plasmid injection.

Results

In wild-type HBV replication mouse model, serum HBsAg was high on day 1, 3, and 5, but became lower since day 7; while in mutant HBV mouse model, serum HBsAg was always at very low level. In liver tissues, HBV DNA RI of wild type HBV was detected on day 1 after transfection. The level subsequently peaked on day 3, gradually declined after day 5, and was almost undetectable on day 10. However, the HBV DNA RI levels of the mutant strain were always higher and lasted longer until day 15. Consistently, the expression levels of HBsAg and HBcAg in liver of the mutant group were significantly increased.

Conclusions

In the case of the HBV rtA181T/sW172* mutation, the secretion of serum HBsAg was impaired, whereas HBV DNA replication and HBsAg/HBcAg expression were increased in liver. These results suggest that the mutation can impair HBsAg secretion, and may cause the accumulation of viral core particles in liver.

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

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

Comparison of rescue strategies in lamivudine-resistant patients with chronic hepatitis B

Lamivudine (LAM) resistance now poses a major problem in the management of patients with chronic hepatitis B virus (HBV) infection. We retrospectively collected clinical data on chronic HBV-infected patients who had developed LAM resistance under de novo LAM monotherapy and subsequently took nucleos(t)ide analogs as rescue strategy in our hospital. From initiation of rescue therapies to January 2012, incidence of antiviral drug resistance was 23.67%, 18%, 6.94% and 0% (P=0.007) in the group of switching to adefovir dipivoxil (ADV) monotherapy, switching to entecavir (ETV) monotherapy, adding on ADV and switching to combination of ADV and ETV. At month 12, the median levels of serum HBV DNA were respectively 9300IU/mL, 4648IU/mL, 2054IU/mL and 100IU/mL (P<0.001), and the cumulative rates of serum ALT normalization were respectively 75%, 84%, 93% and 100% (P=0.003). Additionally, the strategy of switching to ADV monotherapy induced more single rtA181T mutations. In conclusion, switching to ADV monotherapy has been widely used in real-world clinical practice in China, however, due to the high incidence of drug resistance, switching to neither ADV nor ETV monotherapy is optimal when LAM resistance occurs; combination of ADV and ETV is most effective, whereas the strategy of adding on ADV is rational for most of LAM-resistant Chinese patients with chronic hepatitis B.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

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

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

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

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

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

Treatment response and evolution of HBV resistance during lamivudine plus adefovir or entecavir therapy in patients with adefovir-resistant mutants

BACKGROUND

Here, we investigated the treatment response and evolution of HBV resistance during lamivudine (LAM) plus adefovir (ADV) and entecavir (ETV) monotherapy in patients with ADV-resistant mutants.

METHODS

Of the 53 patients with ADV-resistant mutants, 25 received combined LAM plus ADV therapy (LAM+ADV group) and 28 received ETV monotherapy (ETV group) for at least 12 months (median 24 months and range 12-67 months).

RESULTS

During 24 months therapy, no significant difference was noted in HBV DNA reduction from baseline, HBV DNA<200 copies/ml, hepatitis B e antigen loss and ALT normalization between the two groups. In the LAM+ADV group, patients with single rtN236T resistant mutation had higher rates of undetectable HBV DNA than those with the double mutant rtA181T/V+rtN236T at months 3-18 of therapy. No virological breakthrough occurred except for one patient with rtN236T resistant mutation who experienced virological and biochemical breakthrough after the emergence of an additional rtA181T mutant under LAM+ADV therapy. Of the 28 patients receiving ETV monotherapy, ETV-resistant mutants developed in 8. The cumulative rates of ETV-resistant mutations and virological breakthrough at months 12, 24 and 36 were 3.6%, 25.7% and 46.8%, respectively. ADV-resistant mutations were rapidly replaced by LAM-resistant mutations (median 12 months) followed by ETV-resistant mutations.

CONCLUSIONS

There was no significant difference in virological response between the LAM+ADV and ETV groups in patients with ADV-resistant mutants. LAM+ADV were less effective in patients with the double mutant rtA181T/V+rtN236T than the single rtN236T mutation. The incidence of ETV-resistant mutation was high in patients with LAM/ADV-resistant mutants treated with ETV monotherapy.

Molecular epidemical characteristics of Lamivudine resistance mutations of HBV in southern China

BACKGROUND

Lamivudine (LMV), as the preferred oral drug for use in treatment of HBV, always results in development of resistance mutations after long-term treatment. In this study we investigated chronic hepatitis B (CHB) patients in southern China to determine whether different HBV genotypes affect the incidence of LMV resistance mutations.

MATERIAL/METHODS

The study recruited 185 CHB patients living in southern China. Enzyme-linked immunosorbent assay was used to test for HBV serological markers, and HBV DNA was quantified by real-time PCR. Sequencing was performed to detect HBV genotypes and mutations.

RESULTS

There were 49.19% (91/185) CHB patients with HBV resistant to LMV. Only 2 genotypes were found: B and C; 62.16% (115/185) of patients were infected with genotype B HBV and 37.84% (70/185) of patients were infected with genotype C HBV. The incidence rate of LMV resistance was not significantly different between genotype B and C (49.57% vs. 48.57%, P>0.05). For the mean age and sex ratio, no significant difference was found. The pattern of rtM204I alone was predominantly observed (36.26%, 33/91), followed by rtM204V+rtL180M (23.08%, 21/91). The overall incidence rate of rtM204I mutation in genotype B (45.61%, 26/57) was more frequent than that in genotype C (20.59%, 7/34) (45.61% vs. 20.59%, P<0.05), but the incidence rate of other mutation patterns was not significantly different between genotypes B and C.

CONCLUSIONS

Our results emphasize that a LMV resistance test before treatment is of great importance in rational and optimal CHB therapy.

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.

Telbivudine in combination with adefovir versus adefovir monotherapy in HBeAg-positive, lamivudine-resistant chronic hepatitis B

PURPOSE

Lamivudine (LAM) resistance is common on lamivudine monotherapy for chronic hepatitis B. This study examined the safety and efficacy of telbivudine (LDT) given with adefovir (ADV) versus ADV monotherapy in patients with chronic, lamivudine-resistant HBV infection.

METHODS

An open-label, 96 week study with planned recruitment of 150 HBeAg-positive, lamivudine-experienced Asian patients with a confirmed YMDD resistance mutation, randomized 1:1 to receive ADV alone or with LDT. The study was terminated early due to difficulty in enrolling monotherapy patients. At termination, 42 patients had received study medication for 8-61 weeks. Due to incomplete enrolment, summary statistics only were prepared, without significance testing.

RESULTS

A total of 42 patients underwent rescue therapy (switch to ADV or LDT + ADV; n = 21 per group). Median treatment duration was 48 weeks in both groups. HBV DNA changes from baseline were greater in the LDT + ADV arm at all time points (Week 48: -7.4 log10 vs. -4.9 log10 copies/ml), and serum DNA was undetectable (<300 copies/mL) at week 48 in 38.5% (5/13) on LDT + ADV versus 0% (0/9) on ADV monotherapy Two patients (9.6%) on ADV monotherapy experienced virologic breakthrough without evidence of ADV resistance, but none on LDT + ADV; and no confirmed ADV resistance was observed in any on-treatment sample. HBeAg loss occurred in three patients on LDT + ADV and one patient on ADV monotherapy through week 48. Safety profiles were similar between the arms.

CONCLUSION

LDT + ADV combination treatment showed better outcomes against lamivudine resistant HBV than ADV alone, with a similar safety profile.

Human microRNA hsa-miR-125a-5p interferes with expression of hepatitis B virus surface antigen

MicroRNAs are small non-coding RNAs that modulate gene expression at post-transcriptional level, playing a crucial role in cell differentiation and development. Recently, some reports have shown that a limited number of mammalian microRNAs are also involved in anti-viral defense. In this study, the analysis of the hepatitis B virus (HBV) genome by the computer program MiRanda led to the identification of seven sites that are potential targets for human liver microRNAs. These sites were found to be clustered in a 995-bp segment within the viral polymerase ORF and the overlapping surface antigen ORF, and conserved among the most common HBV subtypes. The HBV genomic targets were then subjected to a validation test based on cultured hepatic cells (HepG2, HuH-7 and PLC/PRF/5) and luciferase reporter genes. In this test, one of the selected microRNAs, hsa-miR-125a-5p, was found to interact with the viral sequence and to suppress the reporter activity markedly. The microRNA was then shown to interfere with the viral translation, down-regulating the expression of the surface antigen. Overall, these results support the emerging concept that some mammalian microRNAs play a role in virus-host interaction. Furthermore, they provide the basis for the development of new strategies for anti-HBV intervention.

Management of hepatitis B: Consensus of the Japan Society of Hepatology 2009

Recently, much progress has been made in the field of hepatitis B, such as natural history of the disease in relation to the amount of hepatitis B virus (HBV) DNA, genotypes of HBV influencing the natural course and treatment effects, mutations of HBV influencing the severity of the disease and development of hepatocellular carcinoma, and antiviral treatment such as nucleos(t)ide analogues and pegylated interferon. To make the consensus for the diagnosis, management and treatment of hepatitis B, a meeting was held during 45th annual meeting of Japan Society of Hepatology (JSH) in June 2009. In the meeting, recommendations and informative statements were discussed on the following subjects: (i) natural history of HBV infection; (ii) clinical implication of HBV genotypes; (iii) HBV mutations and their potential impact on pathogenesis of HBV infection; (iv) indications for antiviral treatment of chronic hepatitis B; (v) nucleos(t)ide analogues for chronic hepatitis B; and (vi) interferon therapy for chronic hepatitis B. The presenters reviewed the data on these subjects and proposed the consensus statements and recommendations. These statements were discussed among the organizers and presenters, and were approved by the participants of the meeting. In the current report, the relevant data were reviewed and the 12 consensus statements and nine recommendations on chronic hepatitis B were described.

Animal model for study of human hepatitis viruses

Human hepatitis B virus (HBV) and hepatitis C virus (HCV) infect only chimpanzees and humans. Analysis of both viruses has long been hampered by the absence of a small animal model. The recent development of human hepatocyte chimeric mice has enabled us to carry out studies on viral replication and cellular changes induced by replication of human hepatitis viruses. Various therapeutic agents have also been tested using this model. In the present review, we summarize published studies using chimeric mice and discuss the merits and shortcomings of this model.

Lamivudine-resistance mutations can be selected even at very low levels of hepatitis B viraemia

OBJECTIVE

To investigate lamivudine (LAM)-resistance profiles of hepatitis B virus (HBV) at the early stages of virological breakthrough (serum HBV-DNA 12-345IU/ml) or when HBV-DNA is undetectable.

METHODS

Sixty-four HBV-mono-infected patients were enrolled: 25 had virological breakthrough with serum HBV-DNA ranging from 12 to 345IU/ml during first-line LAM-monotherapy; 24 were on LAM-monotherapy, and 15 were on LAM+adefovir dipivoxil (ADV) with undetectable serum HBV-DNA (<12IU/ml).

RESULTS

HBV-reverse transcriptase was successfully sequenced in 22 (88.0%) LAM-treated patients with HBV-DNA between 12 and 345IU/ml, and in 12 (30.8%) patients receiving LAM (±ADV) with HBV-DNA<12IU/ml. Drug-resistance mutations were observed in 17 (77.2%) LAM-treated patients with virological breakthrough: 8 M204V, 7 M204I, 1 M204I/V, and 1 A181T. One or ≥2 compensatory mutations were found in 10 (58.8%) and in 4 (23.5%) patients. Drug-resistance mutations were present also in patients with undetectable serum HBV-DNA: M204I was detected in 2 patients receiving LAM-monotherapy, and V84M in 1 patient receiving LAM+ADV.

CONCLUSION

Overall findings support the existence of drug-resistance mutations even at very low levels of viral replication. The persistence of low-level HBV replication and consequent drug-resistance emergence should be considered when choosing therapeutic strategies.

New pharmacologic therapies in chronic hepatitis B

Approximately 350 million persons worldwide are chronically infected with hepatitis B, which can result in cirrhosis, liver failure, and hepatocellular carcinoma. Currently, 2 interferons and 5 nucleos(t)ide analogues have been approved for the treatment of chronic hepatitis B (CHB). This article discusses the mechanisms of action, pharmacokinetics, optimal dose, clinical efficacy, and side effects of medications used for the treatment of CHB.

Predicting resistance mutations using protein design algorithms

Drug resistance resulting from mutations to the target is an unfortunate common phenomenon that limits the lifetime of many of the most successful drugs. In contrast to the investigation of mutations after clinical exposure, it would be powerful to be able to incorporate strategies early in the development process to predict and overcome the effects of possible resistance mutations. Here we present a unique prospective application of an ensemble-based protein design algorithm, K*, to predict potential resistance mutations in dihydrofolate reductase from Staphylococcus aureus using positive design to maintain catalytic function and negative design to interfere with binding of a lead inhibitor. Enzyme inhibition assays show that three of the four highly-ranked predicted mutants are active yet display lower affinity (18-, 9-, and 13-fold) for the inhibitor. A crystal structure of the top-ranked mutant enzyme validates the predicted conformations of the mutated residues and the structural basis of the loss of potency. The use of protein design algorithms to predict resistance mutations could be incorporated in a lead design strategy against any target that is susceptible to mutational resistance.

Dynamics of hepatitis B virus resistance to adefovir in lamivudine-resistant patients

AIM: To investigate the dynamic changes of hepatitis B virus (HBV) mutants in lamivudine-resistant chronic hepatitis B (LAM-R CHB) patients who received sequential monotherapy with adefovir dipivoxil (ADV).

METHODS: Twenty-eight consecutive LAM-R CHB patients with viral breakthrough or inadequate virologic response during ADV monotherapy were studied. The dynamics of HBV mutants were analyzed over time by detecting the quantity of HBV DNA using real-time fluorescent quantitative PCR and by sequencing PCR products. Additionally, PCR-TA cloning was performed to study the dynamics of HBV quasispecies in 2 patients.

RESULTS: HBV DNA load fluctuated with the evolution of HBV mutants. Of all patients, 24 developed LAM resistance-associated substitutions during LAM therapy, and 4 had no resistance-associated mutations; 13 had LAM resistance-associated mutations, 11 had ADV resistance-associated mutations, and 7 had no resistance-associated mutations. Of 11 patients with ADV resistance-associated mutations, 6 had A181V mutation, 3 had A181T mutation, 1 had N236T mutation, and 1 had A181T/V+N236T mutation. PCR-TA cloning analysis showed that LAM-resistant viral population was gradually replaced by ADV-resistant viruses during ADV sequential monotherapy. We also detected rtI233M and rtA194T mutations that are associated with resistance to ADV and tenofovir, respectively.

CONCLUSION: Viral quasispecies dynamics in LAM-R CHB patients during ADV sequential monotherapy may manifest as various forms, such as LAM resistance-associated mutations with/without ADV resistance-associated mutations, or absence of resistance-associated mutations. Potential resistance quasispecies could be detected by PCR-TA cloning.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

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

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.

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.

A new strategy for constructing in vitro replication-competent 1.3 copies of hepatitis B virus genome

In the absence of a robust infectable cell culture system, assays related to replication of clinical HBV isolates are based on the transfection of replication-competent HBV DNA into hepatoma cell lines that are able to replicate and secrete HBV virions. Current methods for constructing HBV 1.1 genomes work well for drug susceptibility assays, but are not very suitable for research on HBV replication capacity or regulation since a heterogeneous promoter is required to drive pgRNA transcription. A new strategy for constructing HBV 1.3 genomes that contain HBV intrinsic promoter necessary for pgRNA transcription is reported in this paper. Using this strategy, three HBV 1.3 genomes from isolates of three patients were constructed. When the three HBV 1.3 genomes were transfected into the HepG2 cell line, replicative intermediates were detectable by Southern blotting with digoxigenin-labeled DNA probe in two of the three constructs. Using overlap extension PCR and avoiding as much as possible the digestion-and-ligation process, this strategy could be applied to constructing longer-than-genome units for most genotypes of HBV strains.

Long-term monitoring shows hepatitis B virus resistance to entecavir in nucleoside-naïve patients is rare through 5 years of therapy

Patients with chronic hepatitis B virus (HBV) infection who develop antiviral resistance lose benefits of therapy and may be predisposed to further resistance. Entecavir (ETV) resistance (ETVr) results from HBV reverse transcriptase substitutions at positions T184, S202, or M250, which emerge in the presence of lamivudine (LVD) resistance substitutions M204I/V +/- L180M. Here, we summarize results from comprehensive resistance monitoring of patients with HBV who were continuously treated with ETV for up to 5 years. Monitoring included genotypic analysis of isolates from all patients at baseline and when HBV DNA was detectable by polymerase chain reaction (> or = 300 copies/mL) from Years 1 through 5. In addition, genotyping was performed on isolates from patients experiencing virologic breakthrough (> or = 1 log(10) rise in HBV DNA). In vitro phenotypic ETV susceptibility was determined for virologic breakthrough isolates, and for HBV containing novel substitutions emerging during treatment. The results over 5 years of therapy showed that in nucleoside-naïve patients, the cumulative probability of genotypic ETVr and genotypic ETVr associated with virologic breakthrough was 1.2% and 0.8%, respectively. In contrast, a reduced barrier to resistance was observed in LVD-refractory patients, as the LVD resistance substitutions, a partial requirement for ETVr, preexist, resulting in a 5-year cumulative probability of genotypic ETVr and genotypic ETVr associated with breakthrough of 51% and 43%, respectively. Importantly, only four patients who achieved < 300 copies/mL HBV DNA subsequently developed ETVr.

CONCLUSION

Long-term monitoring showed low rates of resistance in nucleoside-naïve patients during 5 years of ETV therapy, corresponding with potent viral suppression and a high genetic barrier to resistance. These findings support ETV as a primary therapy that enables prolonged treatment with potent viral suppression and minimal resistance.

Antiviral resistance and hepatitis B therapy

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

Pharmacology, clinical efficacy and safety of lamivudine in hepatitis B virus infection

Lamivudine was the first nucleoside analog for the treatment of chronic hepatitis B (CHB). It is well-tolerated and induces a decrease in serum HBV DNA levels associated with normalization of serum alanine aminotransferase levels. However, a sustained response with hepatitis B 'e' antigen to anti-hepatitis B e seroconversion is obtained in a smaller proportion of patients and hepatitis B surface antigen loss is exceptional. The response is maintained during therapy, and needs to be continued indefinitely in the majority of patients since withdrawal of treatment is generally followed by a rapid reappearance of the virus. However, mutations can be induced in long-term treatment.

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

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

CONCLUSION

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