Efficient long-term amplification of hepatitis B virus isolates after infection of slow proliferating HepG2-NTCP cells

D-cycloserine, a potential candidate for reducing Hepatitis B virus cccDNA in vitro

Hepatitis B virus (HBV) is a 3.2 kb hepatotropic DNA that possesses a unique episomal DNA form known as covalently closed circular DNA (cccDNA). cccDNA is the major risk factor for persistent HBV infection and consequently causes chronic liver diseases such as hepatitis, cirrhosis, and hepatocellular carcinoma. To prevent the progression of liver disease, eradication of HBV, especially cccDNA, is essential. In this study, we established a drug screening system using artificial recombinant HBV cccDNA (rcccDNA), which is regulated by a loxP-HBV genome and CRE expression. To identify potential drugs targeting cccDNA, a total of 379 antiviral reagents were tested. Among them, several chemicals including danoprevir, L- and D-cycloserine, phenytoin sodium, amantadine, and germacrone showed a decrease in cccDNA levels. Especially, D-cycloserine diminished the secretion of HBV antigens and induced cccDNA degradation in the HBV infection system. This screening system helps to develop the therapeutic drug target to cccDNA This screening system may help develop therapeutic drugs targeting cccDNA.

HBV-induced N6 methyladenosine modification of PARP1 enhanced AFB1-related DNA damage and synergistically contribute to HCC

Hepatitis B virus (HBV) infection and Aflatoxin B1 (AFB1) exposure are major contributors to the high incidence of hepatocellular carcinoma (HCC) in Southern Africa and Southeast Asia. Investigating the synergistic mechanisms between these factors will help to elucidate the pathogenesis, identify potential therapeutic targets, and reduce disease incidence. Oxidative stress in the cell line was assessed using ROS, MDA, and 8-OHdG assays. DNA damage was evaluated through the Comet assay and γ-H2AX detection. Sanger sequencing was employed to detect TP53 R249S mutations. RIP and Me-RIP assays were performed to investigate the interaction between YTH N6-methyladenosine RNA Binding Protein 2 (YTHDF2) and Poly(ADP-ribose) polymerase 1 (PARP1). The exogenous Cytochrome P450 3A4(CYP3A4)-Sodium/Taurocholate Cotransporting Polypeptide(NTCP) expression cell model was validated for its ability to metabolize AFB1 and support HBV infection. HBV infection increased YTHDF2 expression while suppressing PARP1 both in vitro and in vivo. Additionally, HBV infection exacerbated AFB1-induced DNA damage in both experimental settings. Interference with or pharmacological inhibition of PARP1 significantly worsened HBV- and AFB1-induced DNA damage, while PARP1 overexpression partially alleviated the damage. These findings provide compelling evidence that HBV aggravates AFB1-induced DNA damage by inhibiting PARP1. Further investigation revealed that YTHDF2 interference reversed HBV's regulatory effect on PARP1, while exogenous YTHDF2 addition mimicked HBV's effect by promoting PARP1 degradation. RIP (RNA immunoprecipitation) experiments confirmed that YTHDF2 directly binds to PARP1 mRNA, and MeRIP experiments showed that YTHDF2 increases m6A methylation of PARP1 mRNA. CYP3A4-NTCP overexpression enables liver cell lines to metabolize AFB1 and support HBV infection. HBV enhances AFB1-induced DNA damage by promoting PARP1 degradation, thereby synergistically contributing to HCC development.

Establishment of a Hepatitis B Virus Reporter System Harboring an HiBiT-Tag in the PreS2 Region

BACKGROUND

Approximately 296 million people have chronic hepatitis B (CHB) caused by hepatitis B virus (HBV). Current standard treatment, nucleos(t)ide analogs, are not efficient enough to eradicate HBV from the hepatocytes. Thus, developing new drugs for CHB is needed to achieve complete cure.

METHODS

Here we established a novel HBV reporter system, HBV-HiBiT-PS2, to screen new drugs for CHB. HBV-HiBiT-PS2 was constructed by adding an HiBiT-tag at the 5' end of preS2 and introduced this into HepG2-NTCP cells. Culture supernatant containing HBV-HiBiT-PS2 virions was fractionated by sucrose density gradient ultracentrifugation to characterize their components. Replication kinetics and reporter function of HBV-HiBiT-PS2 were determined by analyzing the parameters for HBV replication in the presence or absence of HBV inhibitors.

RESULTS

HBV-HiBiT-PS2 could be used for monitoring most of the replication cycle of HBV. The effects of well-characterized HBV inhibitors could be evaluated by the HiBiT activity. HBV-HiBiT-PS2 could be specialized for screening secretion inhibitors for hepatitis B surface antigen (HBsAg) because most of the HiBiT activity was derived from subviral particles which are the multimers of HBsAg.

CONCLUSIONS

We demonstrated that HBV-HiBiT-PS2 would be a robust tool for screening novel drugs, especially HBsAg secretion inhibitors, targeted against CHB.

Neuropilin-1 is a novel host factor modulating the entry of hepatitis B virus

BACKGROUND & AIMS

Sodium taurocholate cotransporting polypeptide (NTCP) has been identified as the cellular receptor for HBV. However, hepatocytes expressing NTCP exhibit varying susceptibilities to HBV infection. This study aimed to investigate whether other host factors modulate the process of HBV infection.

METHODS

Liver biopsy samples obtained from children with hepatitis B were used for single-cell sequencing and susceptibility analysis. Primary human hepatocytes, HepG2-NTCP cells, and human liver chimeric mice were used to analyze the effect of candidate host factors on HBV infection.

RESULTS

Single-cell sequencing and susceptibility analysis revealed a positive correlation between neuropilin-1 (NRP1) expression and HBV infection. In the HBV-infected cell model, NRP1 overexpression before HBV inoculation significantly enhanced viral attachment and internalization, and promoted viral infection in the presence of NTCP. Mechanistic studies indicated that NRP1 formed a complex with LHBs (large hepatitis B surface proteins) and NTCP. The NRP1 b domain mediated its interaction with conserved arginine residues at positions 88 and 92 in the preS1 domain of LHBs. This NRP1-preS1 interaction subsequently promoted the binding of preS1 to NTCP, facilitating viral infection. Moreover, disruption of the NRP1-preS1 interaction by the NRP1 antagonist EG00229 significantly attenuated the binding affinity between NTCP and preS1, thereby inhibiting HBV infection both in vitro and in vivo.

CONCLUSIONS

Our findings indicate that NRP1 is a novel host factor for HBV infection, which interacts with preS1 and NTCP to modulate HBV entry into hepatocytes.

IMPACT AND IMPLICATIONS

HBV infection is a global public health problem, but the understanding of the early infection process of HBV remains limited. Through single-cell sequencing, we identified a novel host factor, NRP1, which modulates HBV entry by interacting with HBV preS1 and NTCP. Moreover, antagonists targeting NRP1 can inhibit HBV infection both in vitro and in vivo. This study could further advance our comprehension of the early infection process of HBV.

Exploring the tolerable region for HiBiT tag insertion in the hepatitis B virus genome

A cell culture system that allows the reproduction of the hepatitis B virus (HBV) life cycle is indispensable to exploring novel anti-HBV agents. To establish the screening system for anti-HBV agents, we exploited the high affinity and bright luminescence (HiBiT) tag and comprehensively explored the regions in the HBV genome where the HiBiT tag could be inserted. The plasmids for the HiBiT-tagged HBV molecular clones with a 1.38-fold HBV genome length were prepared. The HiBiT tag was inserted into five regions: preS1, preS2, hepatitis B e (HBe), hepatitis B X (HBx), and hepatitis B polymerase (HB pol). HiBiT-tagged HBVs were obtained by transfecting the prepared plasmids into sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells, and their infectivity was evaluated in human primary hepatocytes and HepG2/NTCP cells. Among the evaluated viruses, the infection of HiBiT-tagged HBVs in the preS1 or the HB pol regions exhibited a time-dependent increase of the hepatitis B surface antigen (HBsAg) level after infection to HepG2/NTCP cells as well as human primary hepatocytes. Immunostaining of the hepatitis B core (HBc) antigen in infected cells confirmed these viruses are infectious to those cells. However, the time-dependent increase of the HiBiT signal was only detected after infection with the HiBiT-tagged HBV in the preS1 region. The inhibition of this HiBiT-tagged HBV infection in human primary hepatocytes and HepG2/NTCP cells by the preS1 peptide could be detected by measuring the HiBiT signal. The infection system with the HiBiT-tagged HBV in HepG2/NTCP cells facilitates easy, sensitive, and high-throughput screening of anti-HBV agents and will be a useful tool for assessing the viral life cycle and exploring antiviral agents.

IMPORTANCE

Hepatitis B virus (HBV) is the principal causative agent of chronic hepatitis. Despite the availability of vaccines in many countries, HBV infection has spread worldwide and caused chronic infection. In chronic hepatitis B patients, liver inflammation leads to cirrhosis, and the accumulation of viral genome integration into host chromosomes leads to the development of hepatocellular carcinoma. The currently available treatment strategy cannot expect the eradication of HBV. To explore novel anti-HBV agents, a cell culture system that can detect HBV infection easily is indispensable. In this study, we examined the regions in the HBV genome where the high affinity and bright luminescence (HiBiT) tag could be inserted and established an HBV infection system to monitor infection by measuring the HiBiT signal by infecting the HiBiT-tagged HBV in sodium taurocholate cotransporting polypeptide-transduced HepG2 (HepG2/NTCP) cells. This system can contribute to screening for novel anti-HBV agents.

Pathogenicity and transcriptomic profiling reveals immunology molecular hallmarks after CA10 virus infection

BACKGROUND

Hand, foot and mouth disease (HFMD) is a common infectious disease caused by viral infection by a variety of enteroviruses, with coxsackievirus A 10 (CA10) having become more prevalent in recent years.

METHODS

In this study, models of CA10 infection were established in 7-day-old Institute of Cancer Research (ICR) mice by intraperitoneal injection to analyze the pathogenicity of the virus. RNA sequencing analysis was used to screen the differentially expressed genes (DEGs) after CA10 infection. Coxsackievirus A 16 (CA16) and enterovirus 71 (EV71) infections were also compared with CA10.

RESULTS

After CA10 virus infection, the mice showed paralysis of the hind limbs at 3 days post infection and weight loss at 5 days post infection. We observed viral replication in various tissues and severe inflammatory cell infiltration in skeletal muscle. The RNA-sequencing analysis showed that the DEGs in blood, muscle, thymus and spleen showed heterogeneity after CA10 infection and the most up-regulated DEGs in muscle were enriched in immune-related pathways. Compared with CA16 and EV71 infection, CA10 may have an inhibitory effect on T helper (Th) cell differentiation and cell growth. Additionally, the common DEGs in the three viruses were most enriched in the immune system response, including the Toll-like receptor pathway and the nucleotide-binding and oligomerization domain (NOD)-like pathway.

CONCLUSIONS

Our findings revealed a group of genes that coordinate in response to CA10 infection, which increases our understanding of the pathological mechanism of HFMD.

Arsenic trioxide impacts hepatitis B virus core nuclear localization and efficiently interferes with HBV infection

The key to a curative treatment of hepatitis B virus (HBV) infection is the eradication of the intranuclear episomal covalently closed circular DNA (cccDNA), the stable persistence reservoir of HBV. Currently, established therapies can only limit HBV replication but fail to tackle the cccDNA. Thus, novel therapeutic approaches toward curative treatment are urgently needed. Recent publications indicated a strong association between the HBV core protein SUMOylation and the association with promyelocytic leukemia nuclear bodies (PML-NBs) on relaxed circular DNA to cccDNA conversion. We propose that interference with the cellular SUMOylation system and PML-NB integrity using arsenic trioxide provides a useful tool in the treatment of HBV infection. Our study showed a significant reduction in HBV-infected cells, core protein levels, HBV mRNA, and total DNA. Additionally, a reduction, albeit to a limited extent, of HBV cccDNA could be observed. Furthermore, this interference was also applied for the treatment of an established HBV infection, characterized by a stably present nuclear pool of cccDNA. Arsenic trioxide (ATO) treatment not only changed the amount of expressed HBV core protein but also induced a distinct relocalization to an extranuclear phenotype during infection. Moreover, ATO treatment resulted in the redistribution of transfected HBV core protein away from PML-NBs, a phenotype similar to that previously observed with SUMOylation-deficient HBV core. Taken together, these findings revealed the inhibition of HBV replication by ATO treatment during several steps of the viral replication cycle, including viral entry into the nucleus as well as cccDNA formation and maintenance. We propose ATO as a novel prospective treatment option for further pre-clinical and clinical studies against HBV infection.

IMPORTANCE

The main challenge for the achievement of a functional cure for hepatitis B virus (HBV) is the covalently closed circular DNA (cccDNA), the highly stable persistence reservoir of HBV, which is maintained by further rounds of infection with newly generated progeny viruses or by intracellular recycling of mature nucleocapsids. Eradication of the cccDNA is considered to be the holy grail for HBV curative treatment; however, current therapeutic approaches fail to directly tackle this HBV persistence reservoir. The molecular effect of arsenic trioxide (ATO) on HBV infection, protein expression, and cccDNA formation and maintenance, however, has not been characterized and understood until now. In this study, we reveal ATO treatment as a novel and innovative therapeutic approach against HBV infections, repressing viral gene expression and replication as well as the stable cccDNA pool at low micromolar concentrations by affecting the cellular function of promyelocytic leukemia nuclear bodies.

Antiviral effect of peptoids on hepatitis B virus infection in cell culture

Although antimicrobial peptides have been shown to inactivate viruses through disruption of their viral envelopes, clinical use of such peptides has been hampered by a number of factors, especially their enzymatically unstable structures. To overcome the shortcomings of antimicrobial peptides, peptoids (sequence-specific N-substituted glycine oligomers) mimicking antimicrobial peptides have been developed. We aimed to demonstrate the antiviral effects of antimicrobial peptoids against hepatitis B virus (HBV) in cell culture. The anti-HBV activity of antimicrobial peptoids was screened and evaluated in an infection system involving the HBV reporter virus and HepG2.2.15-derived HBV. By screening with the HBV reporter virus infection system, three (TM1, TM4, and TM19) of 12 peptoids were identified as reducing the infectivity of HBV, though they did not alter the production levels of HBs antigen in cell culture. These peptoids were not cytotoxic at the evaluated concentrations. Among these peptoids, TM19 was confirmed to reduce HBV infection most potently in a HepG2.2.15-derived HBV infection system that closely demonstrates authentic HBV infection. In cell culture, the most effective administration of TM19 was virus treatment at the infection step, but the reduction in HBV infectivity by pre-treatment or post-treatment of cells with TM19 was minimal. The disrupting effect of TM19 targeting infectious viral particles was clarified in iodixanol density gradient analysis. In conclusion, the peptoid TM19 was identified as a potent inhibitor of HBV. This peptoid prevents HBV infection by disrupting viral particles and is a candidate for a new class of anti-HBV reagents.

MiR-143-3p/FNDC5 axis: a novel regulator of insulin sensitivity

PURPOSE

Insulin resistance is a key hallmark in type 2 diabetes. In recent decades, there have been numerous studies of the causes of insulin resistance. microRNAs (miRNAs) participate in the regulation of multiple aspects of energy metabolism and miR-143-3p has been shown to induce insulin resistance. We aimed to predict the downstream targets of miR-143-3p and found a miR-143-3p binding site on the 3'-untranslated region of FNDC5 (Fibronectin type III domain containing 5) mRNA.

METHODS

We first confirmed that FNDC5 mRNA is a target of miR-143-3p using a double luciferase experiment, then constructed a prokaryotic expression system for the mature form of FNDC5, irisin, and expressed and purified irisin protein. We transfected a miR-143-3p mimic into HepG2-NTCP (Na+-taurocholate cotransporting polypeptide) cells using an NTCP targeting vector, then 24 h later, the glucose concentration of the culture medium, western blot analysis was analyzed. We next co-incubated the cells transfected with the miR-143-3p mimic with irisin for 12 h following by the assay of glucose uptake and AKT phosphorylation.

RESULTS

The glucose concentration of the culture medium was higher than that associated with control miRNA-transfected cells (p < 0.01). Western blot analysis showed that the miR-143-3p mimic significantly reduced the expression of FNDC5 (p < 0.05) and the phosphorylation of AKT (Protein kinase B) (p < 0.05), implying impaired insulin signaling. which increased the glucose uptake (p < 0.0001) and AKT phosphorylation in the cells (p < 0.05).

CONCLUSION

We conclude that FNDC5 is a direct target of miR-143-3p and that miR-143-3p induces insulin resistance by reducing its expression.

Recent Advances in the Development of Sulfamoyl-Based Hepatitis B Virus Nucleocapsid Assembly Modulators

Hepatitis B virus (HBV) is the primary contributor to severe liver ailments, encompassing conditions such as cirrhosis and hepatocellular carcinoma. Globally, 257 million people are affected by HBV annually and 887,000 deaths are attributed to it, representing a substantial health burden. Regrettably, none of the existing therapies for chronic hepatitis B (CHB) have achieved satisfactory clinical cure rates. This issue stems from the existence of covalently closed circular DNA (cccDNA), which is difficult to eliminate from the nucleus of infected hepatocytes. HBV genetic material is composed of partially double-stranded DNA that forms complexes with viral polymerase inside an icosahedral capsid composed of a dimeric core protein. The HBV core protein, consisting of 183 to 185 amino acids, plays integral roles in multiple essential functions within the HBV replication process. In this review, we describe the effects of sulfamoyl-based carboxamide capsid assembly modulators (CAMs) on capsid assembly, which can suppress HBV replication and disrupt the production of new cccDNA. We present research on classical, first-generation sulfamoyl benzocarboxamide CAMs, elucidating their structural composition and antiviral efficacy. Additionally, we explore newly identified sulfamoyl-based CAMs, including sulfamoyl bicyclic carboxamides, sulfamoyl aromatic heterocyclic carboxamides, sulfamoyl aliphatic heterocyclic carboxamides, cyclic sulfonamides, and non-carboxamide sulfomoyl-based CAMs. We believe that certain molecules derived from sulfamoyl groups have the potential to be developed into essential components of a well-suited combination therapy, ultimately yielding superior clinical efficacy outcomes in the future.

Production and Purification of Cell Culture-generated Hepatitis B Virus by Transient Transfection and Density Gradient

An efficient cell culture system for hepatitis B virus (HBV) is indispensable for research on viral characteristics and antiviral agents. Currently, for HBV infection assays in cell culture, HBV genome-integrated cell line-derived viruses are commonly used. However, these viruses are not suitable for the evaluation of polymorphism-dependent viral characteristics or resistant mutations against anti-viral agents. To detect the infection of cell culture-generated HBV (HBVcc) by the transient transfection of the HBV molecular clone, a large amount of purified viruses is needed, because such viruses exhibit limited infection efficiencies in cell culture. Here, we describe how to generate and purify HBVcc by the transient transfection of HBV molecular clones. This system provides a powerful tool for studying the infection and propagation of HBV and for developing anti-viral agents against HBV.

Cell Culture Systems for Studying Hepatitis B and Hepatitis D Virus Infections

The hepatitis B virus (HBV) and hepatitis D virus (HDV) infections cause liver disease, including hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). HBV infection remains a major global health problem. In 2019, 296 million people were living with chronic hepatitis B and about 5% of them were co-infected with HDV. In vitro cell culture systems are instrumental in the development of therapeutic targets. Cell culture systems contribute to identifying molecular mechanisms for HBV and HDV propagation, finding drug targets for antiviral therapies, and testing antiviral agents. Current HBV therapeutics, such as nucleoside analogs, effectively suppress viral replication but are not curative. Additionally, no effective treatment for HDV infection is currently available. Therefore, there is an urgent need to develop therapies to treat both viral infections. A robust in vitro cell culture system supporting HBV and HDV infections (HBV/HDV) is a critical prerequisite to studying HBV/HDV pathogenesis, the complete life cycle of HBV/HDV infections, and consequently identifying new therapeutics. However, the lack of an efficient cell culture system hampers the development of novel antiviral strategies for HBV/HDV infections. In vitro cell culture models have evolved with significant improvements over several decades. Recently, the development of the HepG2-NTCP sec+ cell line, expressing the sodium taurocholate co-transporting polypeptide receptor (NTCP) and self-assembling co-cultured primary human hepatocytes (SACC-PHHs) has opened new perspectives for a better understanding of HBV and HDV lifecycles and the development of specific antiviral drug targets against HBV/HDV infections. We address various cell culture systems along with different cell lines and how these cell culture systems can be used to provide better tools for HBV and HDV studies.

Current and novel modalities for management of chronic hepatitis B infection

Over 296 million people are estimated to have chronic hepatitis B viral infection (CHB), and it poses unique challenges for elimination. CHB is the result of hepatitis B virus (HBV)-specific immune tolerance and the presence of covalently closed circular DNA as mini chromosome inside the nucleus and the integrated HBV. Serum hepatitis B core-related antigen is the best surrogate marker for intrahepatic covalently closed circular DNA. Functional HBV "cure" is the durable loss of hepatitis B surface antigen (HBsAg), with or without HBsAg seroconversion and undetectable serum HBV DNA after completing a course of treatment. The currently approved therapies are nucleos(t)ide analogues, interferon-alpha, and pegylated-interferon. With these therapies, functional cure can be achieved in < 10% of CHB patients. Any variation to HBV or the host immune system that disrupts the interaction between them can lead to reactivation of HBV. Novel therapies may allow efficient control of CHB. They include direct acting antivirals and immunomodulators. Reduction of the viral antigen load is a crucial factor for success of immune-based therapies. Immunomodulatory therapy may lead to modulation of the host immune system. It may enhance/restore innate immunity against HBV (as toll-like-receptors and cytosolic retinoic acid inducible gene I agonist). Others may induce adaptive immunity as checkpoint inhibitors, therapeutic HBV vaccines including protein (HBsAg/preS and hepatitis B core antigen), monoclonal or bispecific antibodies and genetically engineered T cells to generate chimeric antigen receptor-T or T-cell receptor-T cells and HBV-specific T cells to restore T cell function to efficiently clear HBV. Combined therapy may successfully overcome immune tolerance and lead to HBV control and cure. Immunotherapeutic approaches carry the risk of overshooting immune responses causing uncontrolled liver damage. The safety of any new curative therapies should be measured in relation to the excellent safety of currently approved nucleos(t)ide analogues. Development of novel antiviral and immune modulatory therapies should be associated with new diagnostic assays used to evaluate the effectiveness or to predict response.

Forthcoming Developments in Models to Study the Hepatitis B Virus Replication Cycle, Pathogenesis, and Pharmacological Advancements

Hepatitis, liver cirrhosis, and hepatocellular carcinoma are all manifestations of chronic hepatitis B. Its pathogenesis and molecular mechanism remain mysterious. As medical science progresses, different models are being used to study the disease from the physiological and molecular levels. Animal models have played an unprecedented role in achieving in-depth knowledge of the disease while posing no risk of harming humans throughout the study. The scarcity of acceptable animal models has slowed progress in hepatitis B virus (HBV) research and preclinical testing of antiviral medicines since HBV has a narrow species tropism and exclusively infects humans and higher primates. The development of human chimeric mice was supported by a better understanding of the obstacles to interspecies transmission, which has substantially opened the way for HBV research in vivo and the evaluation of possible chronic hepatitis B therapeutics. Animal models are cumbersome to handle, not accessible, and expensive. Hence, it is herculean to investigate the HBV replication cycle in animal models. Therefore, it becomes essential to build a splendid in vitro cell culture system to demonstrate the mechanisms attained by the HBV for its multiplication and sustenance. We also addressed the advantages and caveats associated with different models in examining HBV.

In vitro cell culture models to study hepatitis B and D virus infection

Chronic infection with the hepatitis B virus (HBV) and hepatitis D virus (HDV) can cause a major global health burden. Current medication regimens can repress viral replication and help to control disease progression, but a complete cure is hardly achieved due to the difficulties to eradicate viral templates (cccDNA and integrates). To develop novel curative antiviral therapies for HBV/HDV infection, it is vital to precisely understand the details of the molecular biology of both viruses and the virus-host interactions. One important prerequisite for gaining this aim is the availability of suitable in vitro models that support HBV/HDV infection, replicate both viruses via their authentic template and allow to adequately study host cell responses. The discovery of sodium taurocholate cotransporting polypeptide (NTCP) receptor as the most crucial host factor promoted HBV/HDV research to a new era. Recently, the structure of human NTCP was solved, gaining a deeper understanding of HBV recognition as the bona fide receptor. After decades of continuous efforts, new progress has been achieved in the development of cell culture models supporting HBV/HDV study. This review summarizes the cell culture models currently available, discusses the advantages and disadvantages of each model, and highlights their future applications in HBV and HDV research.

Identification of neutralizing epitopes in the preS2 domain of the hepatitis B virus

Hepatitis B virus (HBV) infection is a major public health problem. The sodium taurocholate cotransporting polypeptide (NTCP) has been identified as an essential HBV receptor. Human hepatocytes are infected with HBV via binding between the preS1 region of the HBV large envelope protein and the NTCP. However, the role of preS2 in HBV entry is not well understood. In this study, we induced anti-preS2 serum in mice by DNA immunization, and showed that the resulting antiserum neutralized HBV infectivity. Competition assays using overlapping peptides suggested that the neutralizing epitope is located in the N-terminal region of preS2. In addition, monoclonal antibodies targeting the N-terminal region of preS2 neutralized HBV infectivity, indicating that these domains are critical epitopes for viral neutralization. These findings provide new insights into the HBV entry machinery while suggesting a novel modality for the prevention and treatment of HBV infection.

Liver Organoid Potential Application for Hepatitis E Virus Infection

Despite the advances in hepatitis E virus (HEV) cell infection models' development, HEV infection efficacy in these cell models is still low, which hampers the further study of molecular mechanism of HEV infection and replication and even the interaction between HEV and host. Along with the advances in the technology for liver organoids generation, major efforts will be made to develop liver organoids for HEV infection. Here, we summarize the entire new and impressive cell culture system of liver organoids and discuss their potential application in HEV infection and pathogenesis. Liver organoids can be generated from tissue-resident cells isolated from biopsies of adult tissues or from iPSCs/ESCs differentiation, which can expand the large-scale experiments such as antiviral drug screening. Different types of liver cells working together can recapitulate the liver organ maintaining the physiological and biochemical microenvironments to support cell morphogenesis, migration, and response to viral infections. Efforts to optimize the protocols for liver organoids generation will speed up the research for HEV infection and pathogenesis and even the antiviral drug identification and evaluation.

Establishment and Characterization of an HBV Viral Spread and Infectious System following Long-Term Passage of an HBV Clinical Isolate in the Primary Human Hepatocyte and Fibroblast Coculture System

The existing cell culture-based methods to study hepatitis B virus (HBV) have limitations and do not allow for viral long-term passage. The aim of this study was to develop a robust in vitro long-term viral passage system with optimized cell culture conditions and a viral isolate with the ability to spread and passage. An HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized primary human hepatocyte (PHH)/human fibroblast coculture system. The passaged UV-treated virus was sequenced and further characterized. In addition, a panel of mutant viruses containing different combinations of mutations observed in this virus was investigated. The clinical isolate was passaged for 20 rounds with 21 days per round in an optimized PHH/human fibroblast coculture system while subject to UV mutagenesis. This passaged UV-mutated isolate harbored four mutations: G225A (sR24K) in the S gene, A2062T in the core gene, and two mutations G1764A and C1766T (xV131I) in the basal core promoter (BCP) region. In vitro characterization of the four mutations suggested that the two BCP mutations G1764A and C1766T contributed to the increased viral replication and viral infectivity. A robust in vitro long-term HBV viral passage system has been established by passaging a UV-treated clinical isolate in an optimized PHH/fibroblast coculture system. The two BCP mutations played a key role in the virus's ability to passage. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization. IMPORTANCE The existing cell culture-based methods to study HBV have limitations and do not allow for viral long-term passage. In this study, an HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized PHH/human fibroblast coculture system. This passaged UV-mutated isolate carried four mutations across the HBV genome, and in vitro characterization of the four mutations suggested that the two basal core promoter (BCP) mutations G1764A and C1766T played a key role in the virus's ability to passage. In summary, we have developed a robust in vitro long-term HBV viral passage system by passaging an UV-treated HBV genotype A clinical isolate in an optimized PHH/human fibroblast coculture system. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization.

Neutralization of hepatitis B virus with vaccine-escape mutations by hepatitis B vaccine with large-HBs antigen

Although the current hepatitis B (HB) vaccine comprising small-HBs antigen (Ag) is potent and safe, attenuated prophylaxis against hepatitis B virus (HBV) with vaccine-escape mutations (VEMs) has been reported. We investigate an HB vaccine consisting of large-HBsAg that overcomes the shortcomings of the current HB vaccine. Yeast-derived large-HBsAg is immunized into rhesus macaques, and the neutralizing activities of the induced antibodies are compared with those of the current HB vaccine. Although the antibodies induced by the current HB vaccine cannot prevent HBV infection with VEMs, the large-HBsAg vaccine-induced antibodies neutralize those infections. The HBV genotypes that exhibited attenuated neutralization via these vaccines are different. Here, we show that the HB vaccine consisting of large-HBsAg is useful to compensate for the shortcomings of the current HB vaccine. The combined use of these HB vaccines may induce antibodies that can neutralize HBV strains with VEMs or multiple HBV genotypes.

Advances in multi-omics research on viral hepatitis

Viral hepatitis is a major global public health problem that affects hundreds of millions of people and is associated with significant morbidity and mortality. Five biologically unrelated hepatotropic viruses account for the majority of the global burden of viral hepatitis, including hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV). Omics is defined as the comprehensive study of the functions, relationships and roles of various types of molecules in biological cells. The multi-omics analysis has been proposed and considered key to advancing clinical precision medicine, mainly including genomics, transcriptomics and proteomics, metabolomics. Overall, the applications of multi-omics can show the origin of hepatitis viruses, explore the diagnostic and prognostics biomarkers and screen out the therapeutic targets for viral hepatitis and related diseases. To better understand the pathogenesis of viral hepatitis and related diseases, comprehensive multi-omics analysis has been widely carried out. This review mainly summarizes the applications of multi-omics in different types of viral hepatitis and related diseases, aiming to provide new insight into these diseases.

HepG2-NTCP Subclones Exhibiting High Susceptibility to Hepatitis B Virus Infection

HepG2 cells reconstituted with Hepatitis B virus (HBV) entry receptor sodium taurocholate co-transporting polypeptide (NTCP) are widely used as a convenient in vitro cell culture infection model for HBV replication studies. As such, it is pertinent that HBV infectivity is maintained at steady-state levels for an accurate interpretation of in vitro data. However, variations in the HBV infection efficiency due to imbalanced NTCP expression levels in the HepG2 cell line may affect experimental results. In this study, we performed single cell-cloning of HepG2-NTCP-A3 parental cells via limiting dilution and obtained multiple subclones with increased permissiveness to HBV. Specifically, one subclone (HepG2-NTCP-A3/C2) yielded more than four-fold higher HBV infection compared to the HepG2-NTCP-A3 parental clone. In addition, though HBV infectivity was universally reduced in the absence of polyethylene glycol (PEG), subclone C2 maintained relatively greater permissiveness under PEG-free conditions, suggesting the functional heterogeneity within parental HepG2-NTCP-A3 may be exploitable in developing a PEG-free HBV infection model. The increased viral production correlated with increased intracellular viral antigen expression as evidenced through HBcAg immunofluorescence staining. Further, these subclones were found to express different levels of NTCP, albeit with no remarkable morphology or cell growth differences. In conclusion, we isolated the subclones of HepG2-NTCP-A3 which support efficient HBV production and thus provide an improved in vitro HBV infection model.

Selected ginsenosides interfere efficiently with hepatitis B virus mRNA expression levels and suppress viral surface antigen secretion

Ginsenosides are a class of natural steroid glycosides and triterpene saponins found in Panax ginseng. After screening of a commercial ginsenoside compound library for low cellular cytotoxicity and the ability to mediate efficient reductions in hepatitis B virus (HBV) mRNA expression levels in HepG2.2.15 cells, three ginsenosides (Rg6, Rh4, and Rb3) are selected. Thereafter, using the same cellular model, all three ginsenosides are shown to mediate efficient, selective inhibition of HBV mRNA expression levels, and also interfere with the secretion of both HBV particles and hepatitis B surface antigen (HBsAg). Drug combination studies are performed in both HepG2.2.15 and HBV-infected HepG2-NTCPsec+ cell models with the selected ginsenosides and lamivudine (LMV), a nucleoside analogue used to treat chronic hepatitis B (CHB) infections. These studies, involving RT-qPCR and ELISA, suggest that Rh4/LMV combinations in particular act synergistically to inhibit the secretion of HBV particles and HBsAg. Therefore, on the assumption that appropriate in vivo data are in future agreement, Rh4, in particular, might be used in combination with nucleoside/nucleotide analogues (NUCs) to devise an effective, cost-efficient combination therapy for the treatment of patients with CHB infections.

Susceptibility of Drug Resistant Hepatitis B Virus Mutants to Besifovir

Currently, interferon alpha and nucleos(t)ide analogues (NAs) are clinically available to treat hepatitis B virus (HBV) infection. Several NAs, including lamivudine (LMV), adefovir (ADV), entecavir (ETV) and tenofovir (TDF or TAF) have been approved and administered to chronic hepatitis B (CHB) patients. NAs inhibit HBV DNA synthesis by targeting the reverse transcriptase (RT) domain of HBV polymerase. Several mutations in the RT domain which lead to drug resistance against NAs have been reported, even for TDF and TAF which are highly potent with very low resistance rate. Besifovir (BFV) is a new antiviral dGMP analogue able to be used as a new NA drug for the control of CHB infection. Drug resistance to BFV is not well known due to its shorter duration of clinical use. Recently, we reported that rtL180M (M) and rtM204V (V) mutations, already resistant to LMV, are associated with BFV resistance. However, the susceptibility to BFV of previously known HBV mutants resistant to various drugs has not been studied. To investigate this, we performed in vitro drug susceptibility assays using natural and artificial mutants that are associated with resistance to LMV, ADV, ETV or TDF. As a result, LMV-resistant mutants were not susceptible to BFV and ETV-resistant clones showed partial resistance against BFV as well. However, ADV-resistant mutants were highly sensitive to BFV. In case of tenofovir-resistant mutations, the HBV mutants harboring primary mutations to tenofovir resistance were susceptible to BFV. Therefore, our study revealed that BSV may serve as an alternative drug for patients with ADV-, ETV-, TDF- or TAF-resistance.

A single hepatitis B virus genome with a reporter allows the entire viral life cycle to be monitored in primary human hepatocytes

For the development of antiviral agents to eliminate hepatitis B virus (HBV), it is essential to establish an HBV cell culture system that can easily monitor HBV infection. Here, we created a novel HBV infection monitoring system using a luminescent 11-amino acid reporter, the high-affinity subunit of nano-luciferase binary technology (HiBiT). The HiBiT-coding sequence was inserted at the N-terminus of preS1 in a 1.2-fold plasmid encoding a genotype C HBV genome. After transfection of HepG2 cells with this HiBiT-containing plasmid, the supernatant was used to prepare a recombinant cell culture-derived virus (HiBiT-HBVcc). Primary human hepatocytes (PXB) were inoculated with HiBiT-HBVcc. Following inoculation, intracellular and extracellular HiBiT activity and the levels of various HBV markers were determined. Reinfection of naive PXB cells with HiBiT-HBVcc prepared from HiBiT-HBVcc-infected PXB cells was analyzed. When PXB cells were infected with HiBiT-HBVcc at several titers, extracellular HiBiT activity was detected in a viral titer-dependent manner and was correlated with intracellular HiBiT activity. Inhibitors of HBV entry or replication suppressed extracellular HiBiT activity. Viral DNA, RNA, and proteins were detectable, including covalently closed circular DNA, by Southern blot analysis. The synthesis of relaxed-circular DNA from single-stranded DNA in HiBiT-HBV decreased to one third of that of wild-type HBV, and the infectivity of HiBiT-HBVcc decreased to one tenth of that of wild-type HBVcc. HiBiT-HBVcc prepared from PXB cells harboring HiBiT-HBV was able to infect naive PXB cells. Conclusions: Recombinant HiBiT-HBV can undergo the entire viral life cycle, thus facilitating high-throughput screening for HBV infection in vitro using supernatants. This system will be a powerful tool for developing antiviral agents.

Pimobendan Inhibits HBV Transcription and Replication by Suppressing HBV Promoters Activity

Current anti-HBV therapeutic strategy relies on interferon and nucleos(t)ide-type drugs with the limitation of functional cure, inducing hepatitis B surface antigen (HBsAg) loss in very few patients. Notably, the level of HBsAg has been established as an accurate indicator to evaluate the drug efficacy and predict the disease prognosis, thus exploring a novel drug targeting HBsAg will be of great significance. Herein, by screening 978 compounds from an FDA-approved drug library and determining the inhibitory function of each drug on HBsAg level in HepG2.2.15 cells supernatant, we identified that pimobendan (Pim) has a powerful antiviral activity with relatively low cytotoxicity. The inhibitory effect of Pim on HBsAg as well as other HBV markers was validated in HBV-infected cell models and HBV-transgenic mice. Mechanistically, real-time PCR and dual-luciferase reporter assay were applied to identify the partial correlation of transcription factor CAAT enhancer-binding protein α (C/EBPα) with the cccDNA transcription regulated by Pim. This indicates Pim is an inhibitor of HBV transcription through suppressing HBV promoters to reduce HBV RNAs levels and HBsAg production. In conclusion, Pim was identified to be a transcription inhibitor of cccDNA, thereby inhibiting HBsAg and other HBV replicative intermediates both in vitro and in vivo. This report may provide a promising lead for the development of new anti-HBV agent.

Host cell-dependent late entry step as determinant of hepatitis B virus infection

Hepatitis B virus (HBV) has a highly restricted host range and cell tropism. Other than the human sodium taurocholate cotransporting polypeptide (huNTCP), the HBV entry receptor, host determinants of HBV susceptibility are poorly understood. Woodchucks are naturally infected with woodchuck hepatitis virus (WHV), closely related to HBV, but not with HBV. Here, we investigated the capabilities of woodchuck hepatic and human non-hepatic cell lines to support HBV infection. DNA transfection assays indicated that all cells tested supported both HBV and WHV replication steps post entry, including the viral covalently closed circular DNA (cccDNA) formation, which is essential for establishing and sustaining infection. Ectopic expression of huNTCP rendered one, but not the other, woodchuck hepatic cell line and the non-hepatic human cell line competent to support productive HBV entry, defined here by cccDNA formation during de novo infection. All huNTCP-expressing cell lines tested became susceptible to infection with hepatitis D virus (HDV) that shares the same entry receptor and initial steps of entry with HBV, suggesting that a late entry/trafficking step(s) of HBV infection was defective in one of the two woodchuck cell lines. In addition, the non-susceptible woodchuck hepatic cell line became susceptible to HBV after fusion with human hepatic cells, suggesting the lack of a host cell-dependent factor(s) in these cells. Comparative transcriptomic analysis of the two woodchuck cell lines revealed widespread differences in gene expression in multiple biological processes that may contribute to HBV infection. In conclusion, other than huNTCP, neither human- nor hepatocyte-specific factors are essential for productive HBV entry. Furthermore, a late trafficking step(s) during HBV infection, following the shared entry steps with HDV and before cccDNA formation, is subject to host cell regulation and thus, a host determinant of HBV infection.

Fundamental studies on, and development of therapies against, chronic hepatitis B virus (HBV) infection, which inflicts hundreds of millions worldwide, are impeded by deficiencies in HBV-susceptible animal models. HBV displays a strict species and cell tropism that are not clearly understood. Here, by studying replication of HBV, and the related woodchuck hepatitis virus, in human and woodchuck hepatic or non-hepatic cells, we found that non-hepatic human cells and some woodchuck hepatic cells could support productive HBV entry after expression of the human cell receptor for HBV. Moreover, by studying the infection of hepatitis D virus, which shares the same entry receptor and initial steps of entry with HBV, we could narrow down a host determinant of HBV infection operating at a late entry/trafficking step(s). Our study thus provides new insights into determinants of HBV host tropism and facilitates the development of HBV-susceptible animal models.

Establishment and Characterization of a New Cell Culture System for Hepatitis B Virus Replication and Infection

Hepatitis B virus (HBV) is a primary cause of chronic liver diseases in humans. HBV infection exhibits strict host and tissue tropism. HBV core promoter (Cp) drives transcription of pregenomic RNA (pgRNA) and plays a key role in the viral life cycle. Hepatocyte nuclear factor 4α (HNF4α) acts as a major transcriptional factor that stimulates Cp. In this work, we reported that BEL7404 ​cell line displayed a high efficiency of DNA transfection and high levels of HBV antigen expression after transfection of HBV replicons without prominent viral replication. The introduction of exogenous HNF4α and human sodium taurocholate cotransporting polypeptide (hNTCP) expression into BEL7404 made it permissive for HBV replication and susceptible to HBV infection. BEL7404-derived cell lines with induced HBV permissiveness and susceptibility were constructed by stable co-transfection of hNTCP and Tet-inducible HNF4α followed by limiting dilution cloning. HBV replication in such cells was sensitive to inhibition by nucleotide analog tenofovir, while the infection was inhibited by HBV entry inhibitors. This cell culture system provides a new and additional tool for the study of HBV replication and infection as well as the characterization of antiviral agents.

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BEL7404 ​cells are characterized by a high transfection efficiency, but do not support canonical HBV replication.

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BEL7404 ​cells lack endogenous HNF4α expression, and exogenous HNF4α rescues canonical HBV replication.

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BEL7404 ​cells with stable hNTCP and inducible HNF4α expression support HBV infection and inducible replication.

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BEL7404-derived cell lines supporting HBV infection retain high transfection efficiencies and allow testing of antivirals.

Translational Strategies to Eliminate Chronic Hepatitis B in Children: Prophylaxis and Management in East Asian Countries

Translational medical research on hepatitis B virus (HBV) infection and chronic hepatitis B (CHB) pathogenesis provides guidance on strengthening the treatment and prevention strategies of CHB. Preventing vertical transmission is the key to eliminating HBV infection in children. The understanding of HBV replication, hepatocyte turnover, and the fate of covalently closed circular DNA (cccDNA) would help establish a personalized application of the guidelines, especially concerning the discontinuation of nucleos(t)ide analog (NA) treatment in children. Transplacental leakage of HBV-infected maternal blood is suggested as the leading cause of vertical transmission. Prenatal maternal prophylaxis could diminish maternal HBV viremia at delivery, to reduce the risk of neonatal HBV infection. The meaning of the expression "no additional risk of breast milk feeding" is thereby explained. Understanding the untreated natural course of CHB in children and the course changeable by treatment is important to apply individualistic strategies and avoid the immoral selection of treatment indications. NAs with potent efficacy and a high barrier to drug resistance should be used as first-line treatment to reduce the likelihood of NA-resistant HBV development because the rate of mutant HBV emergence might count on the infected hepatocyte turnover rate in chronic HBV infection. Although elimination of intranuclear cccDNA is difficult by NAs alone, a cure is possible by human immunity and hepatocyte turnover. The reduction of intranuclear cccDNA occurs after the destruction of HBV-infected hepatocytes, non-cytolytic immune response, apoptosis of hepatocytes, and compensatory cell proliferation. Therefore, consolidation therapy after NA-induced hepatitis B e-antigen seroconversion must be necessary for a sufficient period. This review also summarizes the treatment strategies of CHB in children based on the practical application of translational research.

Identification and Characterization of Besifovir-Resistant Hepatitis B Virus Isolated from a Chronic Hepatitis B Patient

Hepatitis B virus (HBV) is known to cause severe liver diseases such as acute or chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Chronic hepatitis B (CHB) infection is a major health problem with nearly 300 million individuals infected worldwide. Currently, nucleos(t)ide analogs (NAs) and interferon alpha are clinically approved treatments for HBV infection. NAs are potent antiviral agents that bind to HBV polymerase and block viral reverse transcription and replication. Besifovir dipivoxil maleate (BSV) is a newly developed NA against HBV in the form of acyclic nucleotide phosphonate that is available for oral administration similar to adefovir and tenofovir. Until now, resistance to BSV treatment has not been reported. In this study, we found a CHB patient who showed viral breakthrough after long-term treatment with BSV. The isolated HBV DNA from patient’s serum were cloned into the replication-competent HBV 1.2 mer and the sequence of reverse transcriptase (RT) domain of HBV polymerase were analyzed. We also examined the drug susceptibility of generated clones in vitro. Several mutations were identified in HBV RT domain. A particular mutant harboring ten RT mutations showed resistance to BSV treatment in vitro. The ten mutations include rtV23I (I), rtH55R (R), rtY124H (H), rtD134E (E), rtN139K (K), rtL180M (M), rtM204V (V), rtQ267L (L), rtL269I (I) and rtL336M (M). To further identify the responsible mutations for BSV resistance, we performed in vitro drug susceptibility assay on several artificial clones. As a result, our study revealed that rtL180M (M) and rtM204V (V) mutations, already known as lamivudine-resistant mutations, confer resistance to BSV in the CHB patient.

The enhancement role of Matrigel on HBV infection in HepG2-NTCP cells

The hepatoma cell lines stably expressing sodium taurocholate cotransporting polypeptide (NTCP), the receptor of hepatitis B virus (HBV) infection, serve as important infection models for studying viral biology and drug discovery. However, the efficiency of infection greatly varies. In this study, we studied the effects and potential mechanisms of Matrigel® hESC-qualified (M-hq), a biological basement membrane matrix commonly used in cell culture, on promotion HBV in vitro infection in HepG2-NTCP cells. For the first time, our findings demonstrate that M-hq could enhance the infection efficiency of cell culture-derived HBV with no impact on the cell viability, the HBV transcription and response to antiviral treatments. The infection enhancement is reproducible and is suggested to occur at HBV attachment step. Our study suggests that this novel system is applicable for studying HBV biology and new drugs.

Determination of infectious hepatitis B virus particles by an end-point dilution assay identifies a novel class of inhibitors

The quantification of infectious virus particles is fundamental to perform in vitro virology studies. To determine the number of hepatitis B virus (HBV) genome-containing particles in vitro, the genome equivalents (GEq) are measured using quantitative PCR (qPCR). However, in addition to infectious virions, HBV DNA-containing, non-infectious HBV particles are also produced in vitro, which can lead to an over-estimation of the number of infectious HBV particles when analyzed by qPCR. Here, we establish an end-point dilution assay that can precisely determine the number of infectious HBV particles. The cell-based HBV infection assay uses a 384-well plate format and enables the calculation of the 50% tissue culture infective dose (TCID₅₀) in a semi-automated manner. Cell culture-derived HBV (HBVcc), produced by either stable HBV-replicating cells (HepAD38) or HBV-infected HepG2-NTCP cells, as well as patient-derived HBV sera were serially diluted and used to infect naïve target cells. Applying the end-point dilution assay, we infected HepG2-NTCP cells with PEG precipitated HBV derived from HepAD38-and HepG2-NTCPsec+ cell supernatants, calculated the TCID₅₀/mL, converted to plaque-forming units (PFUs), and generated the specific infectivity (ratio of PFU/GEq). As a result, a TCID₅₀/mL of 7.22 × 10⁶ and 2.16 × 10⁶, and the specific infectivity of 1/13,816 and 1/8798 were calculated for HepAD38 and HepG2-NTCPsec+ cell supernatants, respectively. The specific infectivity further increased by approximately 2-fold after removal of non-infectious "naked" particles by immunoprecipitation. Purification of HepAD38 cell supernatants by heparin columns increased the TCID₅₀/mL and specific infectivity by 18- and 15-fold, respectively. Interestingly, non-purified patient-derived HBV sera from two individuals had a specific infectivity of 1/88 and 1/3609. After converting TCID₅₀ to multiplicity of infection (MOI) values, we inoculated HepG2-NTCP cells with HBVcc based on GEq or MOI values and demonstrated that MOI-based infection leads to more reproducible infection rates. Furthermore, the assay was validated using serially diluted lamivudine, an HBV replication inhibitor, inhibiting HBV DNA secretion and infectious viral progeny by approx. 56- and 470-fold, respectively. Interestingly, we identified dexmedetomidine (DMM), an alpha-2 adrenergic agonist, inhibiting the secretion of infectious viral progeny by approx. 6-fold, without interfering in the secretion of HBV DNA. Taken together, we developed an assay that is suitable for the standard quantification of infectious HBV particles. We identified DMM as a novel inhibitor that exclusively interferes with the secretion of infectious HBV particles without affecting the secretion of HBV genomes. This end-point dilution assay enables the precise determination of the number of infectious HBV particles, assessment of the specific infectivity and stability of HBV particles, and identification of novel classes of HBV inhibitors.

NLRX1 can counteract innate immune response induced by an external stimulus favoring HBV infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells

INTRODUCTION

This study is aimed at the determination of the effect of the immune-regulatory factor NLRX1 on the antiviral activity of hepatocytes against an external stimuli favoring hepatitis B virus infection, and to explore its mechanism of action.

METHODS

A HepG2-NTCP model was established using the LV003 lentivirus. Cells were transfected using an overexpression vector and NLRX1 siRNA to achieve overexpression and interference of NLRX1 expression (OV-NLRX1, si-NLRX1). Levels of HBsAg and HBcAg were determined using Western blotting analysis and immunohistochemical analysis. The levels of hepatitis B virus DNA and hepatitis B virus cccDNA were determined by real-time quantitative polymerase chain reaction. The expression and transcriptional activity of IFN-α, IFN-β, and IL-6 were measured using real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and promoter-luciferase reporter plasmids. Co-immunoprecipitation was used to determine the effect of NLRX1 on the interaction between MAVS and RIG-1. Western blotting was used to obtain the phosphorylation of essential proteins in the MAVS-RLRs signaling pathways.

RESULTS

NLRX1 promoted HepG2-NTCP cell hepatitis B virus infection. Compared to the control group, the levels of HBsAg, HBcAg, hepatitis B virus cccDNA, and hepatitis B virus DNA increased in the OV-NLRX1 group and decreased in the si-NLRX1. Co-immunoprecipitation results showed that NLRX1 competitively inhibited the interaction between MAVS and RIG-1, and inhibited the phosphorylation of p65, IRF3, and IRF7. Additionally, NLRX1 reduced the transcription activity and expression levels of the final products: IFN-α, IFN-β, and IL-6.

CONCLUSIONS

NLRX1 can counteract innate immune response induced by an external stimuli favoring hepatitis B virus infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells. Inhibition of the MAVS-RLR-mediated signaling pathways leads to a decline in the expression levels of I-IFN and IL-6.

Curcumin inhibited hepatitis B viral entry through NTCP binding

Hepatitis B virus (HBV) has been implicated in hepatitis and hepatocellular carcinoma. Current agents (nucleos(t)ide analogs and interferons) could only attenuate HBV infection. A combination of agents targeting different stages of viral life cycle (e.g., entry, replication, and cccDNA stability) was expected to eradicate the infection. Curcumin (CCM) was investigated for inhibitory action toward HBV attachment and internalization. Immortalized hepatocyte-like cells (imHCs), HepaRG and non-hepatic cells served as host cells for binding study with CCM. CCM decreased viral load, HBeAg, HBcAg (infectivity), intracellular HBV DNA, and cccDNA levels. The CCM-induced suppression of HBV entry was directly correlated with the density of sodium-taurocholate co-transporting polypeptide (NTCP), a known host receptor for HBV entry. The site of action of CCM was confirmed using TCA uptake assay. The affinity between CCM and NTCP was measured using isothermal titration calorimetry (ITC). These results demonstrated that CCM interrupted HBV entry and would therefore suppress HBV re-infection.

In-vitro and in-vivo models for hepatitis B cure research

PURPOSE OF REVIEW

Antiviral therapy for chronic hepatitis B infection is rarely curative, thus research in HBV cure strategies is a priority. Drug development and testing has been hampered by the lack of robust cell culture systems and small animal models. This review summarizes existing models for HBV cure research and focuses on recent developments since 2017 until today.

RECENT FINDINGS

The field has progressed in the development of cell culture and animal models to study HBV. Although early cell culture systems relied on transfection of HBV genomes in hepatoma cell lines, novel models expressing the entry receptor for HBV are susceptible to infection. Improved culture conditions for primary human hepatocytes, the primary target of HBV, have enabled the screening and validation of novel antivirals. Mouse models grafted with partially humanized livers are suitable for testing viral entry inhibitors or direct acting antivirals, and can be reconstituted with human immune cells to analyze immunotherapies. Other immunocompetent models include mice transduced with HBV genomes or woodchucks infected with their native hepatitis virus.

SUMMARY

Model systems for HBV research have helped lay the groundwork for the development and optimization of antiviral and immune-based therapeutic approaches that are now moving to clinical trials.

Amino Acid Polymorphism in Hepatitis B Virus Associated With Functional Cure

BACKGROUND & AIMS

To provide an adequate treatment strategy for chronic hepatitis B, it is essential to know which patients are expected to have a good prognosis and which patients do not require therapeutic intervention. Previously, we identified the substitution of isoleucine to leucine at amino acid 97 (I97L) in the hepatitis B core region as a key predictor among patients with stable hepatitis. In this study, we attempted to identify the point at which I97L affects the hepatitis B virus (HBV) life cycle and to elucidate the underlying mechanisms governing the stabilization of hepatitis.

METHODS

To confirm the clinical features of I97L, we used a cohort of hepatitis B e antigen-negative patients with chronic hepatitis B infected with HBV-I97 wild-type (wt) or HBV-I97L. The effects of I97L on viral characteristics were evaluated by in vitro HBV production and infection systems with the HBV reporter virus and cell culture-generated HBV.

RESULTS

The ratios of reduction in hepatitis B surface antigen and HBV DNA were higher in patients with HBV-I97L than in those with HBV-I97wt. HBV-I97L exhibited lower infectivity than HBV-I97wt in both infection systems with reporter HBV and cell culture-generated HBV. HBV-I97L virions exhibiting low infectivity primarily contained a single-stranded HBV genome. The lower efficiency of cccDNA synthesis was demonstrated after infection of HBV-I97L or transfection of the molecular clone of HBV-I97L.

CONCLUSIONS

The I97L substitution reduces the level of cccDNA through the generation of immature virions with single-stranded genomes. This I97L-associated low efficiency of cccDNA synthesis may be involved in the stabilization of hepatitis.

Safe-in-Man Broad Spectrum Antiviral Agents

Emerging and re-emerging viral diseases occur with regularity within the human population. The conventional 'one drug, one virus' paradigm for antivirals does not adequately allow for proper preparedness in the face of unknown future epidemics. In addition, drug developers lack the financial incentives to work on antiviral drug discovery, with most pharmaceutical companies choosing to focus on more profitable disease areas. Safe-in-man broad spectrum antiviral agents (BSAAs) can help meet the need for antiviral development by already having passed phase I clinical trials, requiring less time and money to develop, and having the capacity to work against many viruses, allowing for a speedy response when unforeseen epidemics arise. In this chapter, we discuss the benefits of repurposing existing drugs as BSAAs, describe the major steps in safe-in-man BSAA drug development from discovery through clinical trials, and list several database resources that are useful tools for antiviral drug repositioning.

Modeling Hepatotropic Viral Infections: Cells vs. Animals

The lack of an appropriate platform for a better understanding of the molecular basis of hepatitis viruses and the absence of reliable models to identify novel therapeutic agents for a targeted treatment are the two major obstacles for launching efficient clinical protocols in different types of viral hepatitis. Viruses are obligate intracellular parasites, and the development of model systems for efficient viral replication is necessary for basic and applied studies. Viral hepatitis is a major health issue and a leading cause of morbidity and mortality. Despite the extensive efforts that have been made on fundamental and translational research, traditional models are not effective in representing this viral infection in a laboratory. In this review, we discuss in vitro cell-based models and in vivo animal models, with their strengths and weaknesses. In addition, the most important findings that have been retrieved from each model are described.

Advances in HBV infection and replication systems in vitro

Background

Hepatitis B virus (HBV) is a DNA virus belonging to the Hepadnaviridae family that has limited tissue and species specificity. Due to the persistence of HBV covalently closed circular DNA (cccDNA) in host cells after HBV infection, current antiviral drugs cannot eradicate HBV. Therefore, the development of an active cell culture system supporting HBV infection has become the key to studying HBV and developing effective therapeutic drugs.

Main body

This review summarizes the significant research achievements in HBV cell culture systems in vitro, including embryonic hepatocytes and primary hepatocytes, which support the virus infection process most similar to that in the body and various liver tumor cells. The discovery of the bile-acid pump sodium-taurocholate co-transporting polypeptide (NTCP) as the receptor of HBV has advanced our understanding of HBV biology. Subsequently, various liver cancer cells overexpressing NTCP that support HBV infection have been established, opening a new door for studying HBV infection. The fact that induced pluripotent stem cells that differentiate into hepatocyte-like cells support HBV infection provides a novel idea for the establishment of an HBV cell culture system.

Conclusion

Because of the host and tissue specificity of HBV, a suitable in vitro HBV infection system is critical for the study of HBV pathogenesis. Nevertheless, recent advances regarding HBV infection in vitro offer hope for better studying the biological characteristics of HBV, the pathogenesis of hepatitis B, the screening of anti-HBV drugs and the mechanism of carcinogenesis.

A new high-content screening assay of the entire hepatitis B virus life cycle identifies novel antivirals

Background & Aims

Chronic hepatitis B is an incurable disease. Addressing the unmet medical need for therapies has been hampered by a lack of suitable cell culture models to investigate the HBV life cycle in a single experimental setup. We sought to develop a platform suitable to investigate all aspects of the entire HBV life cycle.

Methods

HepG2-NTCPsec+ cells were inoculated with HBV. Supernatants of infected cells were transferred to naïve cells. Inhibition of infection was determined in primary and secondary infected cells by high-content imaging of viral and cellular factors. Novel antivirals were triaged in cells infected with cell culture- or patient-derived HBV and in stably virus replicating cells. HBV internalisation and target-based receptor binding assays were conducted.

Results

We developed an HBV platform, screened 2,102 drugs and bioactives, and identified 3 early and 38 late novel HBV life cycle inhibitors using infectious HBV genotype D. Two early inhibitors, pranlukast (EC₅₀ 4.3 μM; 50% cytotoxic concentration [CC₅₀] >50 μM) and cytochalasin D (EC₅₀ 0.07 μM; CC₅₀ >50 μM), and 2 late inhibitors, fludarabine (EC₅₀ 0.1 μM; CC₅₀ 13.4 μM) and dexmedetomidine (EC₅₀ 6.2 μM; CC₅₀ >50 μM), were further investigated. Pranlukast inhibited HBV preS1 binding, whereas cytochalasin D prevented the internalisation of HBV. Fludarabine inhibited the secretion of HBV progeny DNA, whereas dexmedetomidine interfered with the infectivity of HBV progeny. Patient-derived HBV genotype C was efficiently inhibited by fludarabine (EC₅₀ 0.08 μM) and dexmedetomidine (EC₅₀ 8.7 μM).

Conclusions

The newly developed high-content assay is suitable to screen large-scale drug libraries, enables monitoring of the entire HBV life cycle, and discriminates between inhibition of early and late viral life cycle events.

Lay summary

HBV infection is an incurable, chronic disease with few available treatments. Addressing this unmet medical need has been hampered by a lack of suitable cell culture models to study the entire viral life cycle in a single experimental setup. We developed an image-based approach suitable to screen large numbers of drugs, using a cell line that can be infected by HBV and produces large amounts of virus particles. By transferring viral supernatants from these infected cells to uninfected target cells, we could monitor the entire viral life cycle. We used this system to screen drug libraries and identified novel anti-HBV inhibitors that potently inhibit HBV in various phases of its life cycle. This assay will be an important new tool to study the HBV life cycle and accelerate the development of novel therapeutic strategies.

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We developed a high-content screening assay suitable to monitor the entire HBV life cycle and eligible to discriminate between early and late viral life cycle inhibition.

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We screened FDA-approved drugs and bioactives.

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We confirmed antiviral activity in primary and secondary assays, using stably virus replicating cells and cell culture- and patient-derived HBV.

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Novel HBV inhibitors prevent receptor binding, virus internalisation, replication, or egress of viral progeny.

Bioengineered Liver Cell Models of Hepatotropic Infections

Hepatitis viruses and liver-stage malaria are within the liver infections causing higher morbidity and mortality rates worldwide. The highly restricted tropism of the major human hepatotropic pathogens-namely, the human hepatitis B and C viruses and the Plasmodium falciparum and Plasmodium vivax parasites-has hampered the development of disease models. These models are crucial for uncovering the molecular mechanisms underlying the biology of infection and governing host-pathogen interaction, as well as for fostering drug development. Bioengineered cell models better recapitulate the human liver microenvironment and extend hepatocyte viability and phenotype in vitro, when compared with conventional two-dimensional cell models. In this article, we review the bioengineering tools employed in the development of hepatic cell models for studying infection, with an emphasis on 3D cell culture strategies, and discuss how those tools contributed to the level of recapitulation attained in the different model layouts. Examples of host-pathogen interactions uncovered by engineered liver models and their usefulness in drug development are also presented. Finally, we address the current bottlenecks, trends, and prospect toward cell models' reliability, robustness, and reproducibility.

Profibrotic Signaling and HCC Risk during Chronic Viral Hepatitis: Biomarker Development

Despite breakthroughs in antiviral therapies, chronic viral hepatitis B and C are still the major causes of liver fibrosis and hepatocellular carcinoma (HCC). Importantly, even in patients with controlled infection or viral cure, the cancer risk cannot be fully eliminated, highlighting a persisting oncogenic pressure imposed by epigenetic imprinting and advanced liver disease. Reliable and minimally invasive biomarkers for early fibrosis and for residual HCC risk in HCV-cured patients are urgently needed. Chronic infection with HBV and/or HCV dysregulates oncogenic and profibrogenic signaling within the host, also displayed in the secretion of soluble factors to the blood. The study of virus-dysregulated signaling pathways may, therefore, contribute to the identification of reliable minimally invasive biomarkers for the detection of patients at early-stage liver disease potentially complementing existing noninvasive methods in clinics. With a focus on virus-induced signaling events, this review provides an overview of candidate blood biomarkers for liver disease and HCC risk associated with chronic viral hepatitis and epigenetic viral footprints.

Identification of Two Critical Neutralizing Epitopes in the Receptor Binding Domain of Hepatitis B Virus preS1

Hepatitis B virus (HBV) infection is a major public health problem. Human hepatocytes are infected with HBV via binding between the preS1 region in the large envelope protein of HBV and sodium taurocholate cotransporting polypeptide. Although several monoclonal antibodies (MAbs) that recognize the receptor binding domain in preS1 and neutralize HBV infection have been isolated, details of neutralizing epitopes are not understood. In this study, we generated 13 MAbs targeting the preS1 receptor binding domain from preS1-specific memory B cells derived from DNA immunized mice. The MAbs were classified into three groups according to the epitope regions, designated epitopes I-III. A virus neutralization assay revealed that MAbs recognizing epitopes I and III neutralized HBV infection, suggesting that these domains are critical epitopes for viral neutralization. In addition, a neutralization assay against multiple genotypes of HBV revealed that epitope I is a semi-pangenotypic neutralizing epitope, whereas epitope III is a genotype-specific epitope. We also showed that neutralizing MAbs against preS1 could neutralize HBV bearing vaccine-induced escape mutation. These findings provide insight into novel immunoprophylaxis for the prevention and treatment of HBV infection.IMPORTANCE The HBV preS1 2-47 aa region (preS1/2-47) is essential for virus binding with sodium taurocholate cotransporting polypeptide. Several MAbs targeting preS1/2-47 have been reported to neutralize HBV infection; however, which region in preS1/2-47 contains the critical neutralizing epitope for HBV infection is unclear. Here, we generated several MAbs targeting preS1/2-47 and found that MAbs recognizing the N- or C-terminus of preS1/2-47 remarkably neutralized HBV infection. We further confirmed the neutralizing activity of anti-preS1 MAbs against HBV with vaccine escape mutation. These data clarified the relationship between the antibody epitope and the virus neutralizing activity and also suggested the potential ability of a vaccine antigen containing the preS1 region to overcome the weakness of current HB vaccines comprising the small S protein.

Molecular basis of the interaction of the human tyrosine phosphatase PTPN3 with the hepatitis B virus core protein

Interactions between the hepatitis B virus core protein (HBc) and host cell proteins are poorly understood, although they may be essential for the propagation of the virus and its pathogenicity. HBc has a C-terminal PDZ (PSD-95, Dlg1, ZO-1)-binding motif (PBM) that is responsible for interactions with host PDZ domain-containing proteins. In this work, we focused on the human protein tyrosine phosphatase non-receptor type 3 (PTPN3) and its interaction with HBc. We solved the crystal structure of the PDZ domain of PTPN3 in complex with the PBM of HBc, revealing a network of interactions specific to class I PDZ domains despite the presence of a C-terminal cysteine in this atypical PBM. We further showed that PTPN3 binds the HBc protein within capsids or as a homodimer. We demonstrate that overexpression of PTPN3 significantly affects HBV infection in HepG2 NTCP cells. Finally, we performed proteomics studies on both sides by pull-down assays and screening of a human PDZ domain library. We identified a pool of human PBM-containing proteins that might interact with PTPN3 in cells and that could be in competition with the HBc PBM during infection, and we also identified potential cellular partners of HBc through PDZ-PBM interactions. This study opens up many avenues of future investigations into the pathophysiology of HBV.

Establishment of a novel hepatitis B virus culture system using immortalized human hepatocytes

Recent development of hepatitis B virus (HBV) culture systems has made it possible to analyze the almost all steps of the viral life cycle. However, the reproducibility of interaction between HBV and host cells seemed inaccurate in those systems because of utilization of cancer cell lines with a difference from hepatocytes in the majority of cases. In this study, in order to resolve this point, a novel HBV culture system using non-cancer-derived immortalized human hepatocytes derived cell lines, producing exogenous human sodium taurocholate cotransporting polypeptide, was developed. One of the cell clones, E/NtG8 cells, was permissive to both blood-borne HBV (HBVbb) and culture-derived recombinant HBV when cultured in the three-dimensional condition. Furthermore, the production of infectious HBV particles, which showed the similar physicochemical properties to HBVbb, was observed for about a month after HBVbb infection in this system, suggesting that it may reproduce whole steps of the HBV lifecycle under the condition analogous to human liver cells infected with HBV. This system seemed to contribute not only to find novel interactions between HBV and host cells but also to understand mechanism of HBV pathogenesis.

A Simple and Cost-Effective DNA Preparation Method Suitable for High-Throughput PCR Quantification of Hepatitis B Virus Genomes

Hepatitis B virus (HBV) is a para-retrovirus that reverse transcribes its pregenomic RNA into relaxed circular DNA inside viral nucleocapsids. The number of HBV genomes produced in vitro is typically quantified using commercial silica-membrane-based nucleic acid purification kits to isolate total DNA followed by HBV-specific quantitative PCR (qPCR). However, despite the convenience of commercial kits, this procedure is costly and time-consuming due to multiple centrifugation steps, which produce unnecessary waste. Here, we report a rapid, cost-effective, and environmentally friendly total DNA preparation method. The assay is based on the simple incubation of detergent and proteinase K with cells or cell-free supernatants to permeabilize cells and disrupt viral particles. After heat inactivation and subsequent centrifugation to clear the lysates, DNA samples are directly subjected to qPCR to quantify HBV genomes. As a proof of concept, the assay was developed in 12-well plates to assess intra- and extracellular HBV genome equivalents (GEqs) of stably viral-replicating cell lines (e.g., HepAD38) and HBV-infected HepG2-NTCP cells, both treated with lamivudine (LMV), an HBV replication inhibitor. Viral DNA was also prepared from the serum of patients chronically infected with HBV. To validate the assay, a representative commercial DNA isolation kit was used side-by-side to isolate intra- and extracellular HBV DNA. Both methods yielded comparable amounts of HBV GEqs with comparable LMV 50% efficient concentration (EC₅₀) values. The assay was subsequently adapted to 96- and 384-well microtiter plates using HepAD38 cells. The EC₅₀ values were comparable to those obtained in 12-well plates. In addition, the calculated coefficient of variation, Z’ values, and assay window demonstrated high reproducibility and quality. We devised a novel, robust, reproducible, high-throughput microtiter plate DNA preparation method suitable for quantifying HBV GEqs by qPCR analysis. This strategy enables rapid and convenient quantitative analysis of multiple viral DNA samples in parallel to investigate intracellular HBV replication and the secretion of DNA-containing viral particles.

A genome-wide gain-of-function screen identifies CDKN2C as a HBV host factor

Chronic HBV infection is a major cause of liver disease and cancer worldwide. Approaches for cure are lacking, and the knowledge of virus-host interactions is still limited. Here, we perform a genome-wide gain-of-function screen using a poorly permissive hepatoma cell line to uncover host factors enhancing HBV infection. Validation studies in primary human hepatocytes identified CDKN2C as an important host factor for HBV replication. CDKN2C is overexpressed in highly permissive cells and HBV-infected patients. Mechanistic studies show a role for CDKN2C in inducing cell cycle G1 arrest through inhibition of CDK4/6 associated with the upregulation of HBV transcription enhancers. A correlation between CDKN2C expression and disease progression in HBV-infected patients suggests a role in HBV-induced liver disease. Taken together, we identify a previously undiscovered clinically relevant HBV host factor, allowing the development of improved infectious model systems for drug discovery and the study of the HBV life cycle.

Discovery and development of safe-in-man broad-spectrum antiviral agents

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We reviewed the discovery and development process of broad-spectrum antiviral agents.

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We summarized the information on 120 safe-in-man agents in a freely accessible database.

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Further studies will increase the number of broad-spectrum antivirals, expand the spectrum of their indications, and identify drug combinations for treatment of emerging and re-emerging viral infections.

Viral diseases are one of the leading causes of morbidity and mortality in the world. Virus-specific vaccines and antiviral drugs are the most powerful tools to combat viral diseases. However, broad-spectrum antiviral agents (BSAAs, i.e. compounds targeting viruses belonging to two or more viral families) could provide additional protection of the general population from emerging and re-emerging viral diseases, reinforcing the arsenal of available antiviral options. Here, we review discovery and development of BSAAs and summarize the information on 120 safe-in-man agents in a freely accessible database (https://drugvirus.info/). Future and ongoing pre-clinical and clinical studies will increase the number of BSAAs, expand the spectrum of their indications, and identify drug combinations for treatment of emerging and re-emerging viral infections as well as co-infections.

Identification and characterization of a novel hepatitis B virus pregenomic RNA encapsidation inhibitor

Currently, therapies to treat chronic hepatitis B (CHB) infection are based on the use of interferon-α or nucleos(t)ide analogs (NAs) to prevent viral DNA synthesis by inhibiting the reverse transcriptase activity of the hepatitis B virus (HBV) polymerase (Pol). However, these therapies are not curative; thus, the development of novel anti-HBV agents is needed. In accordance with this unmet medical need, we devised a new target- and cell-based, high-throughput screening assay to identify novel small molecules that block the initial interaction of the HBV Pol with its replication template the viral pregenomic RNA (pgRNA). We screened approximately 110,000 small molecules for the ability to prevent HBV Pol recognition of the pgRNA 5' epsilon (ε) stem-loop structure, identifying (Z)-2-(allylamino)-4-amino-N'-cyanothiazole-5-carboximidamide (AACC). Viral nucleocapsid-captured quantitative RT-PCR and Western blot results revealed that AACC significantly decreased encapsidated pgRNA levels and blocked capsid assembly without affecting core protein expression in stable HBV-replicating cells. As a result, both intra- and extracellular accumulation of viral DNA was strongly reduced. AACC treatment of HepG2-sodium taurocholate transporting polypeptide (NTCP) cells and primary human hepatocytes infected with cell culture- or patient-derived HBV isolates showed both time- and dose-dependent inhibition of infectious viral progeny and rcDNA production. Furthermore, AACC showed cross-genotypic activity against genotypes B, C, and D. Of note, AACC inhibited the viral replication of lamivudine and a capsid inhibitor-resistant HBV, and showed synergistic effects with NAs and a capsid inhibitor. In conclusion, we identified a novel class of compounds specifically targeting the ε-Pol interaction and thereby preventing the encapsidation of pgRNAs into viral capsids. This promising new HBV inhibitor class potently inhibits HBV amplification with distinct characteristics from existing NAs and other drugs currently under development, promising to add value to existing therapies for CHB.

[Development of hepatitis B virus culture systems]

Recent development of hepatitis B virus (HBV) culture systems has proceeded the molecular virological studies of the life cycle of HBV including infection step. However, the reproduction of HBV life cycle under the more physiological condition may be required to know the nature of HBV more precisely. The HBV culture system, we recently developed using immortalized human hepatocytes cultured in the three dimensional condition, seemed to be one of good tools for that purpose.