Inhibitory activity of dioxolane purine analogs on wild-type and lamivudine-resistant mutants of hepadnaviruses

Unraveling the Consequences of Oxygen Imbalance on Early Embryo Development: Exploring Mitigation Strategies

Although well-established and adopted by commercial laboratories, the in vitro embryo production system still requires refinements to achieve its highest efficiency. Early embryonic development is a dynamic event, demanding suitable conditions to provide a high number of embryos with quality and competence. The first step to obtaining an optimized in vitro environment is to know the embryonic metabolism and energy request throughout the different stages of development. Oxygen plays a crucial role in several key biological processes necessary to sustain and complete embryonic development. Nonetheless, there is still controversy regarding the optimal in vitro atmospheric concentrations during culture. Herein, we discuss the impact of oxygen tension on the viability of in vitro-produced embryos during early development. The importance of oxygen tension is addressed as its roles regarding essential embryonic traits, including embryo production rates, embryonic cell viability, gene expression profile, epigenetic regulation, and post-cryopreservation survival. Finally, we highlight the damage caused by in vitro unbalanced oxygen tensions and strategies to mitigate the harmful effects.

Complex genetic encoding of the hepatitis B virus on-drug persistence

Tenofovir disoproxil fumarate (TDF) is one of the nucleotide analogs capable of inhibiting the reverse transcriptase (RT) activity of HIV and hepatitis B virus (HBV). There is no known HBV resistance to TDF. However, detectable variation in duration of HBV persistence in patients on TDF therapy suggests the existence of genetic mechanisms of on-drug persistence that reduce TDF efficacy for some HBV strains without affording actual resistance. Here, the whole genome of intra-host HBV variants (N = 1,288) was sequenced from patients with rapid (RR, N = 5) and slow response (SR, N = 5) to TDF. Association of HBV genomic and protein polymorphic sites to RR and SR was assessed using phylogenetic analysis and Bayesian network methods. We show that, in difference to resistance to nucleotide analogs, which is mainly associated with few specific mutations in RT, the HBV on-TDF persistence is defined by genetic variations across the entire HBV genome. Analysis of the inferred 3D-structures indicates no difference in affinity of TDF binding by RT encoded by intra-host HBV variants that rapidly decline or persist in presence of TDF. This finding suggests that effectiveness of TDF recognition and binding does not contribute significantly to on-drug persistence. Differences in patterns of genetic associations to TDF response between HBV genotypes B and C and lack of a single pattern of mutations among intra-host variants sensitive to TDF indicate a complex genetic encoding of the trait. We hypothesize that there are many genetic mechanisms of on-drug persistence, which are differentially available to HBV strains. These pervasive mechanisms are insufficient to prevent viral inhibition completely but may contribute significantly to robustness of actual resistance. On-drug persistence may reduce the overall effectiveness of therapy and should be considered for development of more potent drugs.

HBV quasispecies composition in Lamivudine-failed chronic hepatitis B patients and its influence on virological response to Tenofovir-based rescue therapy

The present study sought to evaluate the structure of HBV quasispecies in Lamivudine (LMV)-failed chronic hepatitis B (CHB) patients and its impact in defining the subsequent virological responses to Tenofovir (TDF)-based rescue-therapy. By analyzing HBV clones encompassing reverse transcriptase (RT) and surface (S) region from LMV-failed and treatment-naïve CHB patients, we identified 5 classical and 12 novel substitutions in HBV/RT and 9 substitutions in immune-epitopes of HBV/S that were significantly associated with LMV failure. In silico analysis showed spatial proximity of some of the newly-identified, mutated RT residues to the RT catalytic centre while most S-substitutions caused alteration in epitope hydrophobicity. TDF administration resulted in virological response in 60% of LMV-failed patients at 24-week but non-response in 40% of patients even after 48-weeks. Significantly high frequencies of 6 S-substitutions and one novel RT-substitution, rtH124N with 6.5-fold-reduced susceptibility to TDF in vitro, were noted at baseline in TDF non-responders than responders. Follow-up studies depicted greater evolutionary drift of HBV quasispecies and significant decline in frequencies of 3 RT and 6 S-substitutions in responder-subgroup after 24-week TDF-therapy while most variants persisted in non-responders. Thus, we identified the HBV-RT/S variants that could potentially predict unfavorable response to LMV/TDF-therapy and impede immune-mediated viral clearance.

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.

Stable Human Hepatoma Cell Lines for Efficient Regulated Expression of Nucleoside/Nucleotide Analog Resistant and Vaccine Escape Hepatitis B Virus Variants and Woolly Monkey Hepatitis B Virus

Hepatitis B virus (HBV) causes acute and chronic hepatitis B (CHB). Due to its error-prone replication via reverse transcription, HBV can rapidly evolve variants that escape vaccination and/or become resistant to CHB treatment with nucleoside/nucleotide analogs (NAs). This is particularly problematic for the first generation NAs lamivudine and adefovir. Though now superseded by more potent NAs, both are still widely used. Furthermore, resistance against the older NAs can contribute to cross-resistance against more advanced NAs. For lack of feasible HBV infection systems, the biology of such variants is not well understood. From the recent discovery of Na⁺-taurocholate cotransporting polypeptide (NTCP) as an HBV receptor new in vitro infection systems are emerging, yet access to the required large amounts of virions, in particular variants, remains a limiting factor. Stably HBV producing cell lines address both issues by allowing to study intracellular viral replication and as a permanent source of defined virions. Accordingly, we generated a panel of new tetracycline regulated TetOFF HepG2 hepatoma cell lines which produce six lamivudine and adefovir resistance-associated and two vaccine escape variants of HBV as well as the model virus woolly monkey HBV (WMHBV). The cell line-borne viruses reproduced the expected NA resistance profiles and all were equally sensitive against a non-NA drug. The new cell lines should be valuable to investigate under standardized conditions HBV resistance and cross-resistance. With titers of secreted virions reaching >3x10⁷ viral genome equivalents per ml they should also facilitate exploitation of the new in vitro infection systems.

Mutations in the S gene and in the overlapping reverse transcriptase region in chronic hepatitis B Chinese patients with coexistence of HBsAg and anti-HBs

Background

The mechanism underlying the coexistence of hepatitis B surface antigen and antibodies to HBsAg in chronic hepatitis B patients remains unknown.

Aims

This research aimed to determine the clinical and virological features of the rare pattern.

Methods

A total of 32 chronic hepatitis B patients infected by HBV genotype C were included: 15 carrying both HBsAg and anti-HBs (group I) and 17 solely positive for HBsAg (group II). S gene and reverse transcriptase region sequences were amplified, sequenced and compared with the reference sequences.

Results

The amino acid variability within major hydrophilic region, especially the “a” determinant region, and within reverse transcriptase for regions overlapping the major hydrophilic region in group I is significantly higher than those in group II. Mutation sI126S/T within the “a” determinant was the most frequent change, and only patients from group I had the sQ129R, sG130N, sF134I, sG145R amino acid changes, which are known to alter immunogenicity.

Conclusions

In chronic patients, the concurrent HBsAg/anti-HBs serological profile is associated with an increased aa variability in several key areas of HBV genome. Additional research on these genetic mutants are needed to clarify their biological significance for viral persistence.

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.

Practical Considerations For Developing Nucleoside Reverse Transcriptase Inhibitors

Nucleoside reverse transcriptase inhibitors (NRTI) remain a cornerstone of current antiretroviral regimens in combinations usually with a non-nucleoside reverse transcriptase inhibitor (NNRTI), a protease inhibitor (PI), or an integrase inhibitor (INI). The antiretroviral efficacy and relative safety of current NRTI results from a tight and relatively specific binding of their phosphorylated nucleoside triphosphates (NRTI-TP) with the HIV-1 reverse transcriptase which is essential for replication. The intracellular stability of NRTI-TP produces a sustained antiviral response, which makes convenient dosing feasible. Lessons learned regarding NRTI pharmacology screening, development, and use are discussed. NRTI and prodrugs currently under clinical development are outlined.

Management of treatment failure in chronic hepatitis B

Antiviral therapy of chronic hepatitis B remains a clinical challenge. The primary goal of therapy is to prevent liver disease progression. Because of the mechanism of viral persistence in infected hepatocytes, long-term antiviral therapy is needed in the majority of patients. Incomplete viral suppression and emergence of drug resistance is a major concern. The correct choice of a first-line potent therapy to achieve sustained long-term suppression of viral replication provides the best chance of preventing treatment failure and drug resistance. Clinical studies have demonstrated that drugs with a high barrier to resistance, such as entecavir and tenofovir, have significantly lower rates of resistance when compared with those with a low barrier to resistance such as lamivudine, adefovir, or telbivudine. Management of treatment failure requires a precise clinical and accurate virologic monitoring as well as an early treatment intervention with appropriate complementary drugs with respect to their cross-resistance profile. Long-term surveillance for treatment efficacy and possible emergence of drug resistance is necessary for those patients who have been sequentially treated with multiple antivirals. Finally, the identification of novel treatment targets remains a major research challenge to improve the efficacy of current antiviral therapy.

Emerging pipeline drugs for hepatitis B infection

INTRODUCTION

Chronic hepatitis B virus (HBV) infection continues to represent a global health concern with an estimated 350 - 400 million people infected worldwide. Current treatment options are either of two IFN-based therapies or either of five oral nucleos(t)ide analogs which are used as monotherapy or in combination. Control of viral replication can be achieved basically in all patients today. However, despite the clinical efficacy of antivirals, long-term management remains a clinical challenge mainly due to the slow kinetics of HBsAg clearance. Emergence of viral resistance has been a challenge in the past with some but not all oral therapies. The development of novel therapeutic agents with different mechanisms of action might provide new opportunities to clear HBsAg and achieve HBsAg seroconversion which could be maintained off therapy. The long-term efficacy of combinations of IFN and/or nucleos(t)ide analogs might achieve antiviral synergy, preventing drug resistance and clearing viral covalently close circular DNA and infected cells.

AREAS COVERED

This article provides a review of recent data on the safety and efficacy of existing and emerging agents for the treatment of chronic hepatitis B infection.

EXPERT OPINION

Currently, entecavir and tenofovir offer a safe and effective treatment option for patients with chronic HBV with minimal to no resistance. Although entecavir and tenofovir are able to suppress replication in essentially all patients, achieving HBsAg seroconversion remains suboptimal among all antiviral therapy. There are a number of new therapies in the pipeline for the treatment of chronic HBV infection as well as revisiting IFN combined or sequential to antiviral therapy.

Selection of chronic hepatitis B therapy with high barrier to resistance

Antiviral drug resistance is a crucial factor that frequently determines the success of long-term therapy for chronic hepatitis B. The development of resistance to nucleos(t)ide analogues has been associated with exacerbations in liver disease and increased risk of emergence of multidrug resistance. The selection of a potent nucleos(t)ide analogue with a high barrier to resistance as a first-line therapy, such as entecavir or tenofovir, provides the best chance of achieving long-term treatment goals and should be used wherever possible. The barrier to resistance of a given nucleos(t)ide analogue is influenced by genetic barrier, drug potency, patient adherence, pharmacological barrier, viral fitness, mechanism of action, and cross-resistance. In countries with limited health-care resources, the selection of a therapy with a high barrier to resistance is not always possible and alternative strategies for preventing resistance might be needed, although limited data are available to support these strategies.

Acyclic nucleoside thiophosphonates as potent inhibitors of HIV and HBV replication

9-[2-(Thiophosphonomethoxy)ethyl]adenine 3 and (R)-9-[2-(Thiophosphonomethoxy)propyl]adenine 4 were synthesized as the first thiophosphonate nucleosides bearing a sulfur atom at the α-position of the acyclic nucleoside phosphonates PMEA and PMPA. Thiophosphonates S-PMEA 3 and S-PMPA 4 were evaluated for in vitro activity against HIV-1 (subtypes A to G), HIV-2 and HBV-infected cells, and found to exhibit potent antiretroviral activity. We showed that their diphosphate forms S-PMEApp 5 and S-PMPApp 6 are readily incorporated by wild-type (WT) HIV-1 RT into DNA and act as DNA chain terminators. Compounds 3 and 4 were evaluated for in vitro activity against a broad panel of DNA and RNA viruses and displayed beside HIV a moderate activity against herpes simplex virus and vaccinia viruses. In order to measure enzymatic stabilities of the target derivatives 3 and 4, kinetic data and decomposition pathways were studied at 37 °C in several media.

Fitness and infectivity of drug-resistant and cross-resistant hepatitis B virus mutants: why and how is it studied?

The emergence of hepatitis B virus (HBV) drug-resistant (and multidrug-resistant) strains during long-term therapy with nucleoside/nucleotide analogues is associated with treatment failure and, therefore, represents a clinical challenge. For clinicians, the close monitoring and management of resistance has become a key issue in clinical practice. For HBV virologists, the understanding of the mechanism of emergence of specific mutant strains in the viral quasispecies during treatment is also an important issue. If a particular viral strain can emerge in the quasispecies within a particular environment, it is probably because its fitness is superior to other strains. The present review focuses on viral fitness as well as viral infectivity, and in particular on technical means that are available to study this viral fitness in vitro and in animal models.

Hepatitis B virus replication in primary macaque hepatocytes: crossing the species barrier toward a new small primate model

The development of new anti-hepatitis B virus (HBV) therapies, especially immunotherapeutic approaches, has been limited by the lack of a primate model more accessible than chimpanzees. We have previously demonstrated that sylvanus and cynomolgus macaques are susceptible to in vivo HBV infection after intrahepatic HBV DNA inoculation. In this study, we evaluated the susceptibility of primary macaque hepatocytes (PMHs) to HBV infection with a highly efficient HBV genome-mediated transfer system via a recombinant baculovirus (Bac-HBV). Freshly prepared PMHs, isolated from macaque liver tissue by collagenase perfusion, were transduced with Bac-HBV, and intermediates of replication were followed for 9 days post-transduction. Evidence of HBV replication (hepatitis B surface antigen secretion, viral DNA, RNA, and covalently closed circular DNA) was detected from day 1 to day 9 post-transduction. HBV markers were dose-dependent and still detectable at a multiplicity of infection of 10. Importantly, transduced PMHs secreted all typical forms of HBV particles, as evidenced by a cesium chloride gradient as well as transmission electron microscopy. Furthermore, the Toll-like receptor 9 (TLR9) ligand was used to stimulate freshly prepared macaque peripheral blood mononuclear cells to generate TLR9-induced cytokines. We then demonstrated the antiviral effects of both TLR9-induced cytokines and nucleoside analogue (lamivudine) on HBV replication in transduced PMHs.

CONCLUSION

Baculovirus-mediated genome transfer initiated a full HBV replication cycle in PMHs; thus highlighted both the baculovirus efficiency in crossing the species barrier and macaque susceptibility to HBV infection. Moreover, our results demonstrate the relevance of thus system for antiviral compound evaluations with either nucleoside analogues or inhibitory cytokines. Cynomolgus macaques are readily available, are immunologically closely related to humans, and may therefore represent a promising model for the development of new immunotherapeutic strategies.

Control of hepatitis B virus replication by innate response of HepaRG cells

Hepatitis B virus (HBV) is currently viewed as a stealth virus that does not elicit innate immunity in vivo. This assumption has not yet been challenged in vitro because of the lack of a relevant cell culture system. The HepaRG cell line, which is physiologically closer to differentiated hepatocytes and permissive to HBV infection, has opened new perspectives in this respect.HBV baculoviruses were used to initiate an HBV replication in both HepG2 and HepaRG cells. To monitor HBV replication, the synthesis of encapsidated DNA, and secretion of hepatitis B surface antigen (HBsAg), was respectively analyzed by southern blot and enzyme-linked immunosorbent assay. The induction of a type I interferon (IFN) response was monitored by targeted quantitative reverse transcription polymerase chain reaction (qRT-PCR), low-density arrays, and functional assays. The invalidation of type I IFN response was obtained by either antibody neutralization or RNA interference. We demonstrate that HBV elicits a strong and specific innate antiviral response that results in a noncytopathic clearance of HBV DNA in HepaRG cells. Challenge experiment showed that transduction with Bac-HBV-WT, but not with control baculoviruses, leads to this antiviral response in HepaRG cells, whereas no antiviral response is observed in HepG2 cells. Cellular gene expression analyses showed that IFN-beta and other IFN-stimulated genes were up-regulated in HepG2 and HepaRG cells, but not in cells transduced by control baculoviruses. Interestingly, a rescue of viral replication was observed when IFN-beta action was neutralized by antibodies or RNA interference of type I IFN receptor.

CONCLUSION

Our data suggest that a strong HBV replication is able to elicit a type I IFN response in HepaRG-transduced cells.

Lack of pharmacokinetic interaction between amdoxovir and reduced- and standard-dose zidovudine in HIV-1-infected individuals

Amdoxovir (AMDX) inhibits HIV-1 containing the M184V/I mutation and is rapidly absorbed and deaminated to its active metabolite, beta-D-dioxolane guanosine (DXG). DXG is synergistic with zidovudine (ZDV) in HIV-1-infected primary human lymphocytes. A recent in silico pharmacokinetic (PK)/enzyme kinetic study suggested that ZDV at 200 mg twice a day (b.i.d.) may reduce toxicity without compromising efficacy relative to the standard 300-mg b.i.d. dose. Therefore, an intense PK clinical study was conducted using AMDX/placebo, with or without ZDV, in 24 subjects randomized to receive oral AMDX at 500 mg b.i.d., AMDX at 500 mg plus ZDV at 200 or 300 mg b.i.d., or ZDV at 200 or 300 mg b.i.d. for 10 days. Full plasma PK profiles were collected on days 1 and 10, and complete urine sampling was performed on day 9. Plasma and urine concentrations of AMDX, DXG, ZDV, and ZDV-5'-O-glucuronide (GZDV) were measured using a validated liquid chromatography-tandem mass spectrometry method. Data were analyzed using noncompartmental methods, and multiple comparisons were performed on the log-transformed parameters, at steady state. Coadministration of AMDX with ZDV did not significantly change either of the plasma PK parameters or percent recovery in the urine of AMDX, DXG, or ZDV/GZDV. Larger studies with AMDX/ZDV, with a longer duration, are warranted.

Simultaneous quantification of 9-(beta-D-1,3-dioxolan-4-yl)guanine, Amdoxovir and Zidovudine in human plasma by liquid chromatography-tandem mass spectrometric assay

A sensitive method was developed and validated for simultaneous measurement of an investigational antiviral nucleoside, Amdoxovir (DAPD), its deaminated metabolite 9-(beta-D-1,3-dioxolan-4-yl)guanine (DXG), and Zidovudine (ZDV) in human plasma. This method employed high-performance liquid chromatography-tandem mass spectrometry with electrospray ionization. DXG and DAPD separation with sufficient resolution was necessary since they differ in only one mass to charge ratio, which increases the risk of overlapping MS/MS signals. However, the new method was observed to have functional sensitivity and specificity without interference. Samples were purified by ultrafiltration after protein precipitation with methanol. The total run time was 29 min. A linear calibration range from 2 to 3000 ng mL(-1) and 2 to 5000 ng mL(-1) was achieved for DAPD and DXG, and ZDV, respectively. Precisions and accuracies were both +/-15% (+/-20% for the lower limit of quantification) and recoveries were higher than 90%. Matrix effects/ion suppressions were also investigated. The analytes were chemically stable under all relevant conditions and the method was successfully applied for the analysis of plasma samples from HIV-infected persons treated with combinations of DAPD and ZDV.

Hepatitis B virus variants

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

Benefits and risks of combination therapy for hepatitis B

In successful antiviral therapy of hepatitis B, drug combinations, particularly combinations without cross-resistance, can delay or prevent the emergence of drug-resistant mutants. Because drug-resistant mutants are archived and may limit future therapeutic options, prevention is important for long-term therapeutic efficacy. Additionally, combining drugs may achieve synergistic or additive antiviral effects compared with single drug therapy. Undesirable aspects of combination therapy include higher treatment costs and possibly lower adherence rates (due to pill number or complexity of regimen). Potentially harmful effects of combination therapy include higher rates of side effects, reduced efficacy due to drug competition, and the risk of multidrug-resistant hepatitis B virus (HBV) if combination therapy is insufficient to prevent resistance. Combination therapy has been shown to reduce the rate of drug resistance in chronic hepatitis B, but only when drugs with a low barrier to resistance are used (lamivudine, adefovir). Combination therapies may achieve greater degrees of HBV DNA suppression, but this has not been associated with higher rates of seroconversion (hepatitis B e antigen or hepatitis B surface antigen) compared to single drug therapy. The benefit of combination therapy has yet to be demonstrated with agents that are associated with a high barrier to resistance (tenofovir, entecavir). The use of combination therapy is recommended in specific patient groups: those with decompensated cirrhosis, those coinfected with human immunodeficiency virus and HBV who are on antiretroviral therapy, those who have undergone liver transplantation, and those with drug-resistant HBV infection. There is insufficient evidence to recommend combination therapy as first-line therapy for all patients with chronic hepatitis B.

The rtA194T polymerase mutation impacts viral replication and susceptibility to tenofovir in hepatitis B e antigen-positive and hepatitis B e antigen-negative hepatitis B virus strains

Tenofovir is a new effective treatment option for patients with chronic hepatitis B, but could be potentially hampered by mutations in the hepatitis B virus (HBV) polymerase conferring drug resistance. Drug resistance may occur preferentially if long-term administration is required, for example, in patients with hepatitis B e antigen (HBeAg)-negative HBV infection bearing precore (PC) and basal core promoter (BCP) mutations. The rtA194T polymerase mutation has been found in HBV/HIV coinfected patients during tenofovir treatment and may be associated with tenofovir resistance. We generated replication-competent HBV constructs harboring rtA194T alone or in addition to lamivudine (LAM) resistance (rt180M + rtM204V), PC mutations, and BCP mutations and assessed their replicative capacity after transient transfection in human hepatoma cells. The rtA194T polymerase mutation alone or in conjunction with LAM resistance reduced the replication efficiency as compared with wild-type (WT) HBV. In contrast, combination of rtA194T (+/- LAM resistance) with HBeAg-negative PC or BCP mutants increased the replication capacity of the drug-resistant polymerase mutants, thereby restoring the viral replication to similar levels as WT clones. Clones harboring rtA194T showed partial resistance to tenofovir in vitro and also to LAM but remained susceptible to telbivudine and entecavir.

CONCLUSION

The rtA194T polymerase mutation is associated with partial tenofovir drug resistance and negatively impacts replication competence of HBV constructs. Viral replication, however, can be restored to WT levels, if these polymerase mutations occur together with precore or basic core promoter substitutions as found in HBeAg-negative hepatitis B. Patients with HBeAg-negative chronic HBV infection may therefore be at particular risk when developing drug resistance to tenofovir. Telbivudine or entecavir should be considered as effective alternative treatment options for these patients.

Complex dynamics of hepatitis B virus resistance to adefovir

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

CONCLUSION

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

Management and prevention of drug resistance in chronic hepatitis B

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

[Combination therapy in chronic hepatitis B]

The HBV genome variability is responsible for the complexitiy of the viral quasi-species and its evolution during the course of the infection. During antiviral therapy, the persistence of infected cells is another important determinant involved in the selection of drug resistant strains. The development of nucleoside analogs with complementary resistance profiles has provided the rationale for add-on strategies in case of virologic breakthrough. The current trend is to add antivirals earlier, before the rebound of viral load, especially in case of partial virologic response. Clinical trials are required to determine if a de novo combination of nucleoside analogs provides an added benefit compared to an early add-on strategy. However, de novo combination is recommended in patients whose liver functions cannot tolerate treatment failure, and in patients with a high risk of developing viral resistance because of a complex viral quasi-species prior to therapy.

Initiation of hepatitis B virus genome replication and production of infectious virus following delivery in HepG2 cells by novel recombinant baculovirus vector

One of the major problems in gaining further insight into hepatitis B virus (HBV)/host-cell interactions is to improve the existing cellular models for the study of HBV replication. The first objective of this study was to improve the system based on transduction of HepG2 cells with a recombinant baculovirus to study HBV replication. A new HBV recombinant baculovirus, Bac-HBV-1.1, in which the synthesis of pre-genomic RNA is driven by a strong mammalian promoter, was generated. Transduction with this new recombinant baculovirus led to higher levels of HBV replication in HepG2 cells compared with levels obtained with previously described baculovirus vectors. The initiation of a complete HBV DNA replication cycle in Bac-HBV-1.1-transduced HepG2 cells was shown by the presence of HBV replicative intermediates, including covalently closed circular DNA (cccDNA). Only low levels of cccDNA were detected in the nucleus of infected cells. Data showed that cccDNA resulted from the recycling of newly synthesized nucleocapsids and was bound to acetylated histones in a chromatin-like structure. HBV particles released into the supernatant of transduced HepG2 cells were infectious in differentiated HepaRG cells. Several Bac-HBV-1.1 baculoviruses containing HBV strains carrying mutations conferring resistance to lamivudine and/or adefovir were constructed. Phenotypic analysis of these mutants confirmed the results obtained with the transfection procedures. In conclusion, an improved cell-culture system was established for the transduction of replication-competent HBV genomes. This will be useful for future studies of the fitness of HBV mutants.

Selection of an entecavir-resistant mutant despite prolonged hepatitis B virus DNA suppression, in a chronic hepatitis B patient with preexistent lamivudine resistance: successful rescue therapy with tenofovir

BACKGROUND AND OBJECTIVE

Entecavir has potent activity against hepatitis B virus. Drug resistance has not been reported in nucleoside-naïve patients and is low in lamivudine-refractory patients.

METHODS AND RESULTS

A 43-year-old man was treated with lamivudine for hepatitis B e antigen-positive chronic hepatitis B. A viral breakthrough owing to a drug-resistant mutant was observed and entecavir 1 mg daily was added. After the viral load had been near the lower detection range of the PCR assay for 30 weeks, lamivudine was discontinued. The serum hepatitis B virus DNA remained low until a second viral breakthrough was observed after 45 weeks of entecavir monotherapy. Treatment was switched from entecavir to tenofovir disoproxil 245 mg daily, which resulted in a decline below 1000 copies/ml. Sequence analysis revealed the presence of rtL180M and rtM204V lamivudine-resistant-associated mutations at the start of entecavir treatment. During entecavir treatment, the rtS202G mutation was selected. Retrospective analysis revealed that during lamivudine treatment three other mutations had been selected as well, namely rtE1D, rtV207L, and rtI220L.

CONCLUSION

We describe the first case of entecavir resistance in a lamivudine-resistant patient with good initial suppression of viral replication for 70 weeks. On the basis of the data from cross-resistance and sensitivity testing in vitro and treatment outcomes, tenofovir proves to be a good treatment option for entecavir-resistant patients.

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.

Hepatitis B: reflections on the current approach to antiviral therapy

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

Short communication cellular pharmacology of 9-(beta-D-1,3-dioxolan-4-yl) guanine and its lack of drug interactions with zidovudine in primary human lymphocytes

Amdoxovir, currently in Phase II clinical trials, is rapidly converted to 9-(beta-D-1,3-dioxolan-4-yl)guanine (DXG) by adenosine deaminase in vitro and in humans. The cellular pharmacology of DXG in primary human lymphocytes, including dose-response relationships, intracellular half-life of DXG triphosphate (DXG-TP), and combination studies were determined. DXG produced high levels of DXG-TP with a long half-life (16 h) in activated human peripheral blood mononuclear cells. Since zidovudine (ZDV) and DXG select for different resistance mutations, co-formulation of the these two drugs is an attractive proposition. A combination study between DXG and ZDV showed no reduction of DXG-TP or ZDV-TP. Taken together, these results suggest that an appropriately designed DXG prodrug could be given once a day and that co-formulation with ZDV might be a possibility.

Direct detection of lamivudine-resistant hepatitis B virus mutants by a multiplex PCR using dual-priming oligonucleotide primers

Mutations in the YMDD motif of the hepatitis B virus (HBV) polymerase gene increase lamivudine resistance of HBV, highlighting the clinical importance of accurate and sensitive detection of HBV mutants. Using dual-priming oligonucleotide primer technology, an assay that can detect mutations at codons 180 (L528M) and 204 (YVDD, YIDD, and YSDD) by a single-step multiplex PCR was developed. This Seeplex Lami-DR assay was sufficiently sensitive to detect 10(3)HBV/ml and was able to detect minor mutants comprising as little as 2% of the viral population. Mutants were detected in 57 of 65 serum samples (88%) from patients with chronic hepatitis B who had been treated with lamivudine (median, 32 months; range, 1-83 months). The agreement with direct sequencing was only 38.5% (25/65). Discrepancies between these methods resulted from detection of additional mutants by the Seeplex Lami-DR assay, as confirmed by a novel verification analysis. This assay is not only highly accurate and sensitive, but is also simple and cost-effective, requiring no expensive probes, laborious sequencing procedures, or digestion with restriction enzymes. Accordingly, the Seeplex HBV Lami-DR assay should be considered as a first-line, cost-effective tool for detecting viral mutations in patients with chronic hepatitis B receiving lamivudine therapy.

Inhibition of the replication of hepatitis B virus in vitro by a novel 2,6-diaminopurine analog, beta-LPA

Antiviral therapy of chronic hepatitis B remains a major clinical problem worldwide. Like lamivudine, nucleoside analogs have become the focus of investigation of anti-hepatitis B virus (anti-HBV) drugs. Here, beta-LPA is a novel 2,6-diaminopurine analog found to possess potent anti-HBV activity. In HepG2.2.15 cell line, beta-LPA had a 50% effective concentration (EC(50)) of 0.01 microM against HBV, as determined by analysis of secreted and intracellular episomal HBV DNA. Levels of HBV surface antigen (HBsAg) and e antigen (HBeAg) in drug-treated cultures revealed that beta-LPA had no significant inhibitory effects on HBsAg and HBeAg. beta-LPA didn't show any cytotoxicity up to 0.4 microM with a 50% cytotoxic concentration (CC(50)) of 50 microM. Furthermore, treatment with beta-LPA resulted in no apparent inhibitory effects on mitochondrial DNA content. Considering the potent inhibition of HBV DNA synthesis and no obvious toxicity of beta-LPA, this compound should be further explored for development as an anti-HBV drug.

Clevudine is Efficiently Phosphorylated to the Active Triphosphate form in Primary Human Hepatocytes

Background

Clevudine (CLV) is a nucleoside analogue of the unnatural l-configuration that has demonstrated potent activity against hepatitis B virus (HBV) in vitro and in Phase III clinical studies. Human hepatoma cell lines are the only liver-derived cells in which CLV metabolism has been investigated. Here, we examine CLV metabolism in primary human hepatocytes, which better represent CLV metabolism in the liver.

Methods

HPLC analysis of primary human hepatocyte extracts incubated with radiolabelled CLV was used to determine the time course of CLV phosphorylation. Effects of the exogenous cell concentration of CLV on phosphorylation were assessed and the half-life of the CLV phosphorylated forms was determined.

Results

The major CLV metabolite formed in human primary hepatocytes was 5‘-monophosphate, whereas in the hepatoma cell lines the major metabolite was 5’-triphosphate. The level of CLV 5’-triphosphate was similar in both cell types. In primary hepatocytes the conversion of CLV 5’-monophosphate to the corresponding 5’-diphosphate was the rate-limiting step in CLV phosphorylation; the level of CLV phosphorylation was dependent upon exogenous drug concentration and exposure time. CLV 5’-triphosphate accumulated rapidly with peak levels observed after ∼8 h. When cells were incubated with 1 μM CLV, the approximate maximal plasma concentration achieved in individuals receiving the 30 mg dose, the average intracellular concentration of CLV 5’-triphosphate was 41.3 ±8.4 pmols/106 cells (∼10 μM). The initial half-life of CLV triphosphate was ∼11 h.

Conclusions

These results are consistent with once daily CLV dosing currently being used in Phase III clinical studies.

Antiviral therapy of chronic hepatitis B: prevention of drug resistance

The emergence of viral resistance during treatment is becoming an important clinical issue for hepatitis B virus (HBV) antiviral therapy. Considerable progress has been achieved in the efficacy of treatment, with the development of new drugs that allow a sustained suppression of HBV replication, or at least maintain the viral load below a clinically relevant threshold. Although most drugs currently registered for the treatment of chronic hepatitis B are effective in suppressing viral load, long-term therapy is required to avoid viral reactivation and progression of liver disease. Because of the variability of the HBV genome, such long-term treatments are associated with the emergence of resistant viral strains, which may compromise the initial clinical benefit of the treatment.

Emerging drugs for hepatitis B

Chronic hepatitis B remains a treatment challenge despite the availability of new nucleoside analogs. This is due to the persistence of viral infection during therapy, which exposes the patient to the risk of developing antiviral drug resistance. Therefore, new polymerase inhibitors are needed to manage resistance to existing drugs and new trials of combination therapy are required to delay drug resistance. In the future, antiviral agents targeting other steps of the viral life cycle will be needed to achieve antiviral synergy and prevent antiviral drug resistance. Immune modulators are also expected to enhance antiviral response and to achieve sustained response. Discovery of new antiviral drugs and design of new treatment strategies are, therefore, needed to manage this disease, which is still the main cause of cirrhosis and hepatocellular carcinoma worldwide.

Antiviral effect of orally administered (-)-beta-D-2-aminopurine dioxolane in woodchucks with chronic woodchuck hepatitis virus infection

(-)-beta-D-2-Aminopurine dioxolane (APD) is a nucleoside prodrug that is efficiently converted to 9-(beta-D-1,3-dioxolan-4-yl)guanine (DXG). DXG has antiviral activity in vitro against hepatitis B virus (HBV) but limited aqueous solubility, making it difficult to administer orally to HBV-infected individuals. APD is more water soluble than DXG and represents a promising prodrug for the delivery of DXG. A placebo-controlled, dose-ranging efficacy and pharmacokinetic study was conducted with woodchucks that were chronically infected with woodchuck hepatitis virus (WHV). APD was efficiently converted to DXG after oral and intravenous administrations of APD, with serum concentrations of DXG being higher following oral administration than following intravenous administration, suggestive of a considerable first-pass intestinal and/or hepatic metabolism. APD administered orally at 1, 3, 10, and 30 mg/kg of body weight per day for 4 weeks produced a dose-dependent antiviral response. Doses of 3 and 10 mg/kg/day reduced serum WHV viremia by 0.4 and 0.7 log(10) copies/ml, respectively. The 30-mg/kg/day dose resulted in a more pronounced, statistically significant decline in serum WHV viremia of 1.9 log(10) copies/ml and was associated with a 1.5-fold reduction in hepatic WHV DNA. Individual woodchucks within the highest APD dose group that had declines in serum WHV surface antigen levels, WHV viremia, and hepatic WHV DNA also had reductions in hepatic WHV RNA. There was a prompt recrudescence of WHV viremia following drug withdrawal. Therefore, oral administration of APD for 4 weeks was safe in the woodchuck model of chronic HBV infection, and the effect on serum WHV viremia was dose dependent.

Antiviral drug-resistant HBV: standardization of nomenclature and assays and recommendations for management

Substantial advances have been made in the treatment of chronic hepatitis B in the past decade. Approved treatments for chronic hepatitis B include 2 formulations of interferon and 4 nucleos(t)ide analogues (NAs). Sustained viral suppression is rarely achieved after withdrawal of a 48-week course of NA therapy, necessitating long, and in many cases, indefinite treatment with increasing risk of development of drug resistance. Antiviral resistance and poor adherence are the most important factors in treatment failure of hepatitis B. Thus, there is a need to standardize nomenclature relating to hepatitis B antiviral resistance, and to define genotypic, phenotypic, and clinical resistance to NA therapy.

A Novel Mutation Pattern Emerging during Lamivudine Treatment Shows Cross-Resistance to Adefovir Dipivoxil Treatment

Aims

This study was conducted to clarify the resistance profile of a novel mutation pattern emerging during lamivudine (3TC) therapy and showing cross-resistance to adefovir dipivoxil (ADV) in a patient with chronic hepatitis B.

Methods and results

Successful suppression of hepatitis B virus (HBV) replication by sequential therapy of 9 MU thrice weekly interferon (IFN) and 3TC was followed by genotypical resistance detected at month 28 of therapy (month 19 of lamivudine treatment). ADV was added to 3TC therapy on month 44 of antiviral treatment. Neither alanine aminotransferase normalization nor a stable decrease in HBV viral load was observed, although ADV was used for more than 40 months. The HBV pol region was amplified from serum samples obtained before and after ADV treatment. The complete genome was cloned into a TA vector. PCR products and 7–10 clones from each cloned vector were sequenced. A novel mutation, A181S, in the reverse transcriptase gene leading to a conversion of W172C in the overlapping surface antigen gene was detected along with a M204I mutation. The complete genome comprising the A181S+M204I pattern was cloned into an expression vector and its in vitro susceptibility to 3TC, ADV, tenofovir (PMPA), clevudine (l-FMAU) and emtricitabine (FTC) were determined in transiently transfected Huh7 cells. This mutation pattern displayed more than 1,000-fold resistance to the nucleoside analogues 3TC and FTC and approximately sixfold resistance to l-FMAU, while it confers 28.23- and 5.57-fold resistance for the nucleotide analogues ADV and PMPA, respectively.

Conclusion

A new mutation pattern, A181S+M204I, arising under lamivudine treatment confers cross-resistance to ADV both in vivo and in vitro.

In vitro activity of 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy]-pyrimidine against multidrug-resistant hepatitis B virus mutants

The susceptibilities of drug-resistant hepatitis B virus (HBV) mutants to lamivudine, adefovir, tenofovir, entecavir, and 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy]-pyrimidine (PMEO-DAPym), a novel acyclic pyrimidine analogue, were assessed in vitro. Most drug-resistant mutants, including multidrug-resistant strains, remained sensitive to tenofovir and PMEO-DAPym. Therefore, the latter molecule deserves further evaluation for the treatment of HBV infection.

Clevudine: a potent inhibitor of hepatitis B virus in vitro and in vivo

Clevudine (CLV) is a nucleoside analog of the unnatural L-configuration that has potent anti-hepatitis B virus (HBV) activity in vitro and in vivo with a favorable toxicity profile in all species tested. In cell culture, CLV is readily phosphorylated to the corresponding 5'-triphosphate form of the compound. The mechanism of action of CLV involves the inhibition of the HBV polymerase by CLV 5'-triphosphate. In vivo efficacy studies performed in the duck and woodchuck models showed marked, rapid inhibition of virus replication and no significant toxicity. In the woodchuck model, there was a dose-dependent delay in viral recrudescence and a reduction or loss of covalently closed circular DNA. In Phase II clinical studies, CLV was well tolerated and exhibited potent antiviral activity at all doses investigated. In Phase III studies in both hepatitis B e antigen (HBeAg)-positive and -negative patients, CLV 30 mg administered once daily demonstrated potent antiviral efficacy and significant biochemical improvement after only 24 weeks of therapy. These effects were sustained in a significant portion of the patients when therapy was stopped after 6 months with no viral rebound occurring in approximately 3 and 16% in HBeAg-positive and -negative patients, respectively. There have been no significant safety or tolerance issues associated with the drug in these studies. Future studies will investigate the safety and tolerance of CLV 30 mg given once daily over 48 weeks and longer.

[Hepatitis B and C virus antiviral resistance]

Infection by the hepatitis B (HBV) and C (HCV) viruses is a major cause of morbidity and mortality world-wide. The clinical outcomes of infection by these viruses (e.g., chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma) depend on several factors related to the host and the viral agent. Among the latter, factors associated with the response to current antiviral therapies, such as the emergence of resistance mutants and the genotype responsible for the infection, are gaining increasing importance. As has been established for human immunodeficiency virus (HIV), the presence of resistance mutations in the viral polymerase constitutes the main problem for treating HBV infection with approved drugs and those recently applied. Methods have been developed to detect these mutations, as well as algorithms to predict the response to treatment. The outcome of treatment for HCV infection is highly influenced by the viral genotype, however, and our understanding of the molecular basis for the response to interferon in these patients has grown considerably in recent years.

Stable HepG2- and Huh7-based human hepatoma cell lines for efficient regulated expression of infectious hepatitis B virus

BACKGROUND/AIMS

Hepatitis B virus (HBV) cannot be propagated in cultured cells but two human hepatoma cell lines, HepG2 and Huh7, support virus replication when transfected with HBV DNA. If standardization is required stably transfected cell lines provide distinct advantages. One such line, HepG2.2.15, is widely used in antiviral research but HBV production is limited and difficult to control. Our aim was to establish stable, inducibly HBV producing HepG2 and Huh7 cell lines that overcome these limitations.

METHODS

Based on the tetracycline (Tet)-regulated TetOFF system, a Tet-responsive promoter-controlled HBV genome was introduced into separately established, well-regulatable HepG2 and Huh7 lines expressing Tet-responsive trans-activators (tTAs). Stable clones were analyzed for regulatability and levels of HBV expression, quality of the virus produced, and responsiveness towards antivirals.

RESULTS

HepG2- and Huh7-based cell lines were established which, Tet-controllably, produce more HBV than HepG2.2.15 cells. The secreted virions were infectious for primary tupaia hepatocytes, and the cell lines responded as well as HepG2.215 cells to different antivirals.

CONCLUSIONS

The new HBV cell lines should be valuable tools for academic and pharmaceutical HBV research. The parental tTA-cells will facilitate the generation of additional lines, producing HBV variants, or other genes, in an identical host cell background.

Mutations affecting the replication capacity of the hepatitis B virus

The genetic variability of the hepatitis B virus (HBV) encounters two compounding forces: a high viral copy number produced during active replication and the lack of proofreading activity in the HBV polymerase, resulting in a high mutational rate. A large pool of quasispecies is generated in which the fittest virus, i.e. the virus that replicates best, becomes the dominant species. Immune and antiviral selection pressures result in vaccine/immunoglobulin escape mutants and antiviral resistant variants. Viruses encoding changes associated with antiviral resistance often have reduced replication in vitro, but the accumulation of additional mutations helps restore viral fitness. These compensatory mutations may occur not only in the polymerase gene but also in other genes such as the overlapping envelope gene, the precore gene, or in regulatory regions such as the basal core promoter. In this report we aim to review the new findings that have appeared in recent months.

Randomized, double-blind study of emtricitabine (FTC) plus clevudine versus FTC alone in treatment of chronic hepatitis B

Emtricitabine (FTC) is approved for the treatment of human immunodeficiency virus. FTC and clevudine (CLV) have activity against hepatitis B virus (HBV). This report summarizes the results of a double-blind, multicenter study of patients with chronic hepatitis B who had completed a phase 3 study of FTC and were randomized 1:1 to 200 mg FTC once daily (QD) plus 10 mg CLV QD or 200 mg FTC QD plus placebo for 24 weeks with 24 weeks of follow-up. One hundred sixty-three patients were treated (82 with FTC plus CLV [FTC+CLV] and 81 with FTC); 72% were men, 53% were Asian, 47% were Caucasian, and 52% were hepatitis B e antigen positive, and the median baseline HBV DNA level was 6 log(10) copies/ml. After 24 weeks of treatment, 74% (FTC+CLV) versus 65% (FTC alone) had serum HBV DNA levels of <4,700 copies/ml (P = 0.114) (Digene HBV Hybrid Capture II assay). Twenty-four weeks posttreatment, the mean change in serum HBV DNA levels from baseline was -1.25 log(10) copies/ml (FTC+CLV), 40% had undetectable viremia (versus 23% for FTC alone), and 63% had normal alanine aminotransferase levels (versus 42% for FTC alone) (P < or = 0.025 for all endpoints). The safety profile was similar between arms during treatment, with less posttreatment exacerbation of hepatitis B in the combination arm. In summary, after 24 weeks of treatment, no significant difference between arms was observed, but there was a significantly greater virologic and biochemical response 24 weeks posttreatment in the FTC+CLV arm.

Treatment options in HBV

The available evidence on interferon-alpha (IFN) treatment for chronic hepatitis B is sufficient to conclude that in patients with HBeAg positive chronic hepatitis, standard IFN therapy significantly improves clearance of HBeAg (number needed to treat [NNT] = 4), loss of HBV-DNA (NNT = 4) and clearance of HBsAg (NNT = 18). HBeAg positive patients with normal or slightly raised ALT should be treated only if there is histological evidence of progressive disease. In patients with HBeAg negative chronic hepatitis, less than 20% of subjects who have achieved an end-of-treatment virological response after a course of standard IFN maintain a sustained virological response in the long-term. IFN treatment could help to delay or prevent disease decompensation and liver-related deaths but further large studies are needed. Lamivudine is effective at reducing, and sometimes clearing, HBV replication in heavily immunosuppressed patients and can be safely administered to patients with advanced liver disease. Lamivudine should be continued over an undefined extended period of time, with a switch from lamivudine to adefovir if there is an HBV-DNA breakthrough under therapy. Adefovir, excluding cost, is preferable to lamivudine as a first-choice because there is less chance of inducing resistance. The long-term benefit of lamivudine and adefovir and the role of combinations is under investigation.

HBV virological assessment

Management of hepatitis B virus (HBV) infected patients involves serological diagnosis, quantitation of HBV-DNA and measurement of HBV drug resistance. Different serological markers such as HBsAg, anti-HBs, anti-HBc (total and IgM), HBeAg and anti-HBe are assessed by immunoassays in order to define the infection status. The emergence of surface mutants however is a continuous challenge to design more effective immunoassays. Commercially available quantitative HBV-DNA assays with increased sensitivity and wider linear range give a more accurate estimate of viral replication and contribute decisively in the initiation and the monitoring of the response to HBV therapy. Genotypic drug resistance assays are important diagnostic tools, since the administration of nucleoside/nucleotide analogues to HBV infected patients leads to the development of drug resistance patterns very much dependent on the treatment regimen. Special issues have to be taken into consideration regarding HBV/HIV-1 co-infected patients, since concominant HIV and HBV replication results in higher rates of HBV replication. Current efforts are focused on the standardization of HBV-DNA assays (qualitative and quantitative), of HBV drug resistance assays as well as in the development of new assays and markers that will help in the prognosis and management of HBV infection (quantitative detection of pre-core mutants and HBV ccc-DNA assays).