The diverse functions of the hepatitis B core/capsid protein (HBc) in the viral life cycle: Implications for the development of HBc-targeting antivirals

cccDNA epigenetic regulator as target for therapeutical vaccine development against hepatitis B

Chronic hepatitis B virus infection (CHB) remains a global health concern, with currently available antiviral therapies demonstrating limited effectiveness in preventing hepatocellular carcinoma (HCC) development. Two primary challenges in CHB treatment include the persistence of the minichromosome, covalently closed circular DNA (cccDNA) of the hepatitis B virus (HBV), and the failure of the host immune response to eliminate cccDNA. Recent findings indicate several host and HBV proteins involved in the epigenetic regulation of cccDNA, including HBV core protein (HBc) and HBV x protein (HBx). Both proteins might contribute to the stability of the cccDNA minichromosome and interact with viral and host proteins to support transcription. One potential avenue for CHB treatment involves the utilization of therapeutic vaccines. This paper explores HBV antigens suitable for epigenetic manipulation of cccDNA, elucidates their mechanisms of action, and evaluates their potential as key components of epigenetically-driven vaccines for CHB therapy. Molecular targeted agents with therapeutic vaccines offer a promising strategy for addressing CHB by targeting the virus and enhancing the host's immunological response. Despite challenges, the development of these vaccines provides new hope for CHB patients by emphasizing the need for HBV antigens that induce effective immune responses without causing T cell exhaustion.

Colchicine-mediated selective autophagic degradation of HBV core proteins inhibits HBV replication and HBV-related hepatocellular carcinoma progression

The HBV core protein (HBc) is an important viral protein of HBV that plays an indispensable role in the lifecycle of HBV, including capsid assembly and transport, reverse transcription and virus release. In recent years, evidence has shown that HBc may be involved in the malignant progression of HCC. Thus, HBc is an attractive target for antiviral agents and provides a new strategy for the treatment of HBV-related HCC. Here, we identified a novel anti-HBc compound-colchicine, an alkaloid compound-that promoted selective autophagic degradation of HBc through the AMPK/mTOR/ULK1 signalling pathway. We further confirmed that colchicine promoted the selective autophagy of HBc by enhancing the binding of HBc to the autophagy receptor p62. Finally, we evaluated the effects of colchicine on HBV replication and HBc-mediated HCC metastasis in vitro and in vivo. Our research indicated that the inhibitory effects of colchicine on HBV and HBV-related HCC depend on the selective autophagic degradation of HBc. Thus, colchicine is not only a promising therapeutic strategy for chronic hepatitis B but also a new treatment for HBV-related HCC.

Deciphering the phospho-signature induced by hepatitis B virus in primary human hepatocytes

Phosphorylation is a major post-translation modification (PTM) of proteins which is finely tuned by the activity of several hundred kinases and phosphatases. It controls most if not all cellular pathways including anti-viral responses. Accordingly, viruses often induce important changes in the phosphorylation of host factors that can either promote or counteract viral replication. Among more than 500 kinases constituting the human kinome only few have been described as important for the hepatitis B virus (HBV) infectious cycle, and most of them intervene during early or late infectious steps by phosphorylating the viral Core (HBc) protein. In addition, little is known on the consequences of HBV infection on the activity of cellular kinases. The objective of this study was to investigate the global impact of HBV infection on the cellular phosphorylation landscape early after infection. For this, primary human hepatocytes (PHHs) were challenged or not with HBV, and a mass spectrometry (MS)-based quantitative phosphoproteomic analysis was conducted 2- and 7-days post-infection. The results indicated that while, as expected, HBV infection only minimally modified the cell proteome, significant changes were observed in the phosphorylation state of several host proteins at both time points. Gene enrichment and ontology analyses of up- and down-phosphorylated proteins revealed common and distinct signatures induced by infection. In particular, HBV infection resulted in up-phosphorylation of proteins involved in DNA damage signaling and repair, RNA metabolism, in particular splicing, and cytoplasmic cell-signaling. Down-phosphorylated proteins were mostly involved in cell signaling and communication. Validation studies carried out on selected up-phosphorylated proteins, revealed that HBV infection induced a DNA damage response characterized by the appearance of 53BP1 foci, the inactivation of which by siRNA increased cccDNA levels. In addition, among up-phosphorylated RNA binding proteins (RBPs), SRRM2, a major scaffold of nuclear speckles behaved as an antiviral factor. In accordance with these findings, kinase prediction analysis indicated that HBV infection upregulates the activity of major kinases involved in DNA repair. These results strongly suggest that HBV infection triggers an intrinsic anti-viral response involving DNA repair factors and RBPs that contribute to reduce HBV replication in cell culture models.

Class A capsid assembly modulator apoptotic elimination of hepatocytes with high HBV core antigen level in vivo is dependent on de novo core protein translation

Capsid assembly is critical in the hepatitis B virus (HBV) life cycle, mediated by the viral core protein. Capsid assembly is the target for new anti-viral therapeutics known as capsid assembly modulators (CAMs) of which the CAM-aberrant (CAM-A) class induces aberrant shaped core protein structures and leads to hepatocyte cell death. This study aimed to identify the mechanism of action of CAM-A modulators leading to HBV-infected hepatocyte elimination where CAM-A-mediated hepatitis B surface antigen (HBsAg) reduction was evaluated in a stable HBV replicating cell line and in AAV-HBV-transduced C57BL/6, C57BL/6 SCID, and HBV-infected chimeric mice with humanized livers. Results showed that in vivo treatment with CAM-A modulators induced pronounced reductions in hepatitis B e antigen (HBeAg) and HBsAg, associated with a transient alanine amino transferase (ALT) increase. Both HBsAg and HBeAg reductions and ALT increase were delayed in C57BL/6 SCID and chimeric mice, suggesting that adaptive immune responses may indirectly contribute. However, CD8+ T cell depletion in transduced wild-type mice did not impact antigen reduction, indicating that CD8+ T cell responses are not essential. Transient ALT elevation in AAV-HBV-transduced mice coincided with a transient increase in endoplasmic reticulum stress and apoptosis markers, followed by detection of a proliferation marker. Microarray data revealed antigen presentation pathway (major histocompatibility complex class I molecules) upregulation, overlapping with the apoptosis. Combination treatment with HBV-specific siRNA demonstrated that CAM-A-mediated HBsAg reduction is dependent on de novo core protein translation. To conclude, CAM-A treatment eradicates HBV-infected hepatocytes with high core protein levels through the induction of apoptosis, which can be a promising approach as part of a regimen to achieve functional cure.

IMPORTANCE

Treatment with hepatitis B virus (HBV) capsid assembly modulators that induce the formation of aberrant HBV core protein structures (CAM-A) leads to programmed cell death, apoptosis, of HBV-infected hepatocytes and subsequent reduction of HBV antigens, which differentiates CAM-A from other CAMs. The effect is dependent on the de novo synthesis and high levels of core protein.

Structural basis for nuclear import of hepatitis B virus (HBV) nucleocapsid core

Nuclear import of the hepatitis B virus (HBV) nucleocapsid is essential for replication that occurs in the nucleus. The ~360-angstrom HBV capsid translocates to the nuclear pore complex (NPC) as an intact particle, hijacking human importins in a reaction stimulated by host kinases. This paper describes the mechanisms of HBV capsid recognition by importins. We found that importin α1 binds a nuclear localization signal (NLS) at the far end of the HBV coat protein Cp183 carboxyl-terminal domain (CTD). This NLS is exposed to the capsid surface through a pore at the icosahedral quasi-sixfold vertex. Phosphorylation at serine-155, serine-162, and serine-170 promotes CTD compaction but does not affect the affinity for importin α1. The binding of 30 importin α1/β1 augments HBV capsid diameter to ~620 angstroms, close to the maximum size trafficable through the NPC. We propose that phosphorylation favors CTD externalization and prompts its compaction at the capsid surface, exposing the NLS to importins.

Immunoinformatics and Evaluation of Peptide Vaccines Derived from Global Hepatitis B Viral HBx and HBc Proteins Critical for Covalently Closed Circular DNA Integrity

The Hepatitis B virus (HBV) HBx and HBc proteins play a crucial role in associating with covalently closed circular DNA (cccDNA), the primary factor contributing to intrahepatic viral persistence and a major obstacle in achieving a cure for HBV. The cccDNA serves as a reservoir for viral persistence. Targeting the viral HBc and HBx proteins' interaction with cccDNA could potentially limit HBV replication. In this study, we present epitopes identified from global consensus sequences of HBx and HBc proteins that have the potential to serve as targets for the development of effective vaccine candidates. Furthermore, conserved residues identified through this analysis can be utilized in designing novel, site-specific anti-HBV agents capable of targeting all major genotypes of HBV. Our approach involved designing global consensus sequences for HBx and HBc proteins, enabling the analysis of variable regions and highly conserved motifs. These identified motifs and regions offer potent sites for the development of peptide vaccines, the design of site-specific RNA interference, and the creation of anti-HBV inhibitors. The epitopes derived from global consensus sequences of HBx and HBc proteins emerge as promising targets for the development of effective vaccine candidates. Additionally, the conserved residues identified provide valuable insights for the development of innovative, site-specific anti-HBV agents capable of targeting all major genotypes of HBV from A to J.

Anti-hepatitis B virus activities of natural products and their antiviral mechanisms

Chronic hepatitis B (CHB) infections caused by the hepatitis B virus (HBV) continue to pose a significant global public health challenge. Currently, the approved treatments for CHB are limited to interferon and nucleos(t)ide analogs, both of which have their limitations, and achieving a complete cure remains an elusive goal. Therefore, the identification of new therapeutic targets and the development of novel antiviral strategies are of utmost importance. Natural products (NPs) constitute a class of substances known for their diverse chemical structures, wide-ranging biological activities, and low toxicity profiles. They have shown promise as potential candidates for combating various diseases, with a substantial number demonstrating anti-HBV properties. This comprehensive review focuses on the current applications of NPs in the fight against HBV and provides a summary of their antiviral mechanisms, considering their impact on the viral life cycle and host hepatocytes. By offering insights into the world of anti-HBV NPs, this review aims to furnish valuable information to support the future development of antiviral drugs.

Novel non-HAP class A HBV capsid assembly modulators have distinct in vitro and in vivo profiles

IMPORTANCE

Chronic hepatitis B is the most important cause of liver cancer worldwide and affects more than 290 million people. Current treatments are mostly suppressive and rarely lead to a cure. Therefore, there is a need for novel and curative drugs that target the host or the causative agent, hepatitis B virus itself. Capsid assembly modulators are an interesting class of antiviral molecules that may one day become part of curative treatment regimens for chronic hepatitis B. Here we explore the characteristics of a particularly interesting subclass of capsid assembly modulators. These so-called non-HAP CAM-As have intriguing properties in cell culture but also clear virus-infected cells from the mouse liver in a gradual and sustained way. We believe they represent a considerable improvement over previously reported molecules and may one day be part of curative treatment combinations for chronic hepatitis B.

Discovery of 4,5,6,7-Tetrahydropyrazolo[1.5-a]pyrizine Derivatives as Core Protein Allosteric Modulators (CpAMs) for the Inhibition of Hepatitis B Virus

Hepatitis B Virus (HBV) core protein allosteric modulators (CpAMs) are an attractive class of potential anti-HBV therapeutic agents. Here we describe the efforts toward the discovery of a series of 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine (THPP) compounds as HBV CpAMs that effectively inhibit a broad range of nucleos(t)ide-resistant HBV variants. The lead compound 45 demonstrated inhibition of HBV DNA viral load in a HBV AAV mouse model by oral administration.

Binding characteristics of pyrrole-scaffold hepatitis B virus capsid inhibitors and identification of novel potent compounds

Hepatitis B virus (HBV) capsid assembly modulators (CAMs) are currently being evaluated in clinical trials as potential curative therapies for HBV. This study used in silico computational modeling to provide insights into the binding characteristics between the HBV core protein and two pyrrole-scaffold inhibitors, JNJ-6379 and GLP-26, both in the CAM-Normal (CAM-N) series. Molecular dynamics simulations showed that the pyrrole inhibitors displayed similar general binding-interaction patterns to NVR 3-778, another CAM-N, with hydrophobic interactions serving as the major driving force. However, consistent with their higher potency, the pyrrole inhibitors exhibited stronger nonpolar interactions with key residues in a solvent-accessible region as compared to NVR 3-778. This feature was facilitated by distinct hydrogen bond interactions of the pyrrole scaffold inhibitors with the residue 140 in chain B of the HBV core protein (L140B). Based on these findings, novel CAM-N compounds were designed to mimic the interaction with L140B residue while maximizing nonpolar interactions in the solvent-accessible region. Several 1H-pyrrole-2-carbonyl substituted pyrrolidine-based compounds with various hydrophobic side chains were synthesized and evaluated. Through analyses of the structure-activity and structure-druggability relations of a series of compounds, CU15 emerged as the most promising lead CAM-N compound, exhibiting sub-nanomolar potency and good pharmacokinetic profiles. Overall, the study demonstrated a practical approach to leverage computational methods for understanding key target binding features for rationale-based design, and for guiding the identification of novel compounds.

Pre- and Post-Transcriptional Control of HBV Gene Expression: The Road Traveled towards the New Paradigm of HBx, Its Isoforms, and Their Diverse Functions

Hepatitis B virus (HBV) is an enveloped DNA human virus belonging to the Hepadnaviridae family. Perhaps its main distinguishable characteristic is the replication of its genome through a reverse transcription process. The HBV circular genome encodes only four overlapping reading frames, encoding for the main canonical proteins named core, P, surface, and X (or HBx protein). However, pre- and post-transcriptional gene regulation diversifies the full HBV proteome into diverse isoform proteins. In line with this, hepatitis B virus X protein (HBx) is a viral multifunctional and regulatory protein of 16.5 kDa, whose canonical reading frame presents two phylogenetically conserved internal in-frame translational initiation codons, and which results as well in the expression of two divergent N-terminal smaller isoforms of 8.6 and 5.8 kDa, during translation. The canonical HBx, as well as the smaller isoform proteins, displays different roles during viral replication and subcellular localizations. In this article, we reviewed the different mechanisms of pre- and post-transcriptional regulation of protein expression that take place during viral replication. We also investigated all the past and recent evidence about HBV HBx gene regulation and its divergent N-terminal isoform proteins. Evidence has been collected for over 30 years. The accumulated evidence simply strengthens the concept of a new paradigm of the canonical HBx, and its smaller divergent N-terminal isoform proteins, not only during viral replication, but also throughout cell pathogenesis.

Computer-aided drug design in seeking viral capsid modulators

Approved or licensed antiviral drugs have limited applications because of their drug resistance and severe adverse effects. By contrast, by stabilizing or destroying the viral capsid, compounds known as capsid modulators prevent viral replication by acting on new targets and, therefore, overcoming the problem of clinical drug resistance. For example. computer-aided drug design (CADD) methods, using strategies based on structures of biological targets (structure-based drug design; SBDD), such as docking, molecular dynamics (MD) simulations, and virtual screening (VS), have provided opportunities for fast and effective development of viral capsid modulators. In this review, we summarize the application of CADD in the discovery, optimization, and mechanism prediction of capsid-targeting small molecules, providing new insights into antiviral drug discovery modalities. Teaser: Computer-aided drug design will accelerate the development of viral capsid regulators, which brings new hope for the treatment of refractory viral diseases.

PPIases Par14/Par17 Affect HBV Replication in Multiple Ways

Human parvulin 14 (Par14) and parvulin 17 (Par17) are peptidyl-prolyl cis/trans isomerases that upregulate hepatitis B virus (HBV) replication by binding to the conserved ¹³³Arg-Pro¹³⁴ (RP) motif of HBc and core particles, and ¹⁹RP²⁰-²⁸RP²⁹ motifs of HBx. In the absence of HBx, Par14/Par17 have no effect on HBV replication. Interaction with Par14/Par17 enhances the stability of HBx, core particles, and HBc. Par14/Par17 binds outside and inside core particles and is involved in HBc dimer-dimer interaction to facilitate core particle assembly. Although HBc RP motif is important for HBV replication, R133 residue is solely important for its interaction with Par14/Par17. Interaction of Par14 and Par17 with HBx involves two substrate-binding residues, Glu46/Asp74 (E46/D74) and E71/D99, respectively, and promotes HBx translocation to the nucleus and mitochondria. In the presence of HBx, Par14/Par17 are efficiently recruited to cccDNA and promote transcriptional activation via specific DNA-binding residues Ser19/44 (S19/44). S19 and E46/D74 of Par14, and S44 and E71/D99 of Par17, are also involved in the recruitment of HBc onto cccDNA. Par14/Par17 upregulate HBV replication via various effects that are mediated in part through the HBx-Par14/Par17-cccDNA complex and triple HBc, Par14/Par17, and cccDNA interactions in the nucleus, as well as via core particle-Par14/Par17 interactions in the cytoplasm.

Design, synthesis, and biological evaluation of novel sulfamoylbenzamide derivatives as HBV capsid assembly modulators

Capsid assembly modulators (CAMs) represent a novel class of antiviral agents targeting hepatitis B virus (HBV) capsid to disrupt the assembly process. NVR 3-778 is the first CAM to demonstrate antiviral activity in patients infected with HBV. However, the relatively low aqueous solubility and moderate activity in the human body halted further development of NVR 3-778. To improve the anti-HBV activity and the drug-like properties of NVR 3-778, we designed and synthesized a series of NVR 3-778 derivatives. Notably, phenylboronic acid-bearing compound 7b (EC50 = 0.83 ± 0.33 µM, CC50 = 19.4 ± 5.0 µM) displayed comparable anti-HBV activity to NVR 3-778 (EC50 = 0.73 ± 0.20 µM, CC50 = 23.4 ± 7.0 µM). Besides, 7b showed improved water solubility (328.8 µg/mL, pH 7) compared to NVR 3-778 (35.8 µg/mL, pH 7). Size exclusion chromatography (SEC) and quantification of encapsidated viral RNA were used to demonstrate that 7b behaves as a class II CAM similar to NVR 3-778. Moreover, molecular dynamics (MD) simulations were conducted to rationalize the structure-activity relationships (SARs) of these novel derivatives and to understand their key interactions with the binding pocket, which provide useful indications for guiding the further rational design of more effective anti-HBV drugs.

Generation and Utilization of a Monoclonal Antibody against Hepatitis B Virus Core Protein for a Comprehensive Interactome Analysis

Hepatitis B virus (HBV) core antigen (HBc) is a structural protein that forms the viral nucleocapsid and is involved in various steps of the viral replication cycle, but its role in the pathogenesis of HBV infection is still elusive. In this study, we generated a mouse monoclonal antibody (mAb) against HBc and used it in antibody-based in situ biotinylation analysis in order to identify host proteins that interact with HBc. HBc antigen was produced with a wheat germ cell-free protein synthesis system and used to immunize mice. Among the established hybridoma clones, a single clone (mAb #7) was selected and further characterized for its ability in the antibody-based in situ biotinylation analysis to collect host proteins that are in the vicinity of HBc. Using mass spectrometry, we identified 215 HBc-interacting host proteins, three of which bind HBc most significantly under hypoxic conditions. Our results indicate that mAb #7 can be used to systematically identify host proteins that interact with HBc under pathophysiological conditions, and thus may be useful to explore the molecular pathways involved in HBV-induced cytopathogenesis.

Safety and efficacy of vebicorvir administered with entecavir in treatment-naïve patients with chronic hepatitis B virus infection

BACKGROUND & AIMS

Nucleos(t)ide reverse transcriptase inhibitors do not completely suppress HBV DNA in chronic HBV infection (cHBV). Vebicorvir (VBR) is an investigational core inhibitor that interferes with multiple aspects of HBV replication. This phase II trial evaluated the safety and efficacy of VBR in combination with entecavir (ETV) in treatment-naïve patients with cHBV.

METHODS

HBeAg-positive, treatment-naïve patients without cirrhosis were randomised 1:1 in a double-blind manner to once-daily VBR 300 mg+ETV 0.5 mg or placebo (PBO)+ETV 0.5 mg for 24 weeks. The primary endpoint was change in mean log₁₀ HBV DNA from Baseline to Week 12 and 24.

RESULTS

All patients in both treatment groups (PBO+ETV: 12/12; VBR+ETV: 13/13) completed the study. At Week 12, VBR+ETV led to a greater mean (SD) reduction from Baseline in log₁₀ IU/ml HBV DNA (-4.45 [1.03]) vs. PBO+ETV (-3.30 [1.18]; p = 0.0077). At Week 24, VBR+ETV led to a greater reduction from Baseline in log₁₀ IU/ml HBV DNA (-5.33 [1.59]) vs. PBO+ETV (-4.20 [0.98]; p = 0.0084). Greater mean reductions in pregenomic RNA were observed at Week 12 and 24 in patients receiving VBR+ETV vs. PBO+ETV (p <0.0001 and p <0.0001). Changes in viral antigens were similar in both groups. No drug interaction between VBR and ETV was observed. Two patients experienced HBV DNA rebound during treatment, with no resistance breakthrough detected. The safety of VBR+ETV was similar to PBO+ETV. All treatment-emergent adverse events and laboratory abnormalities were Grade 1/2. There were no deaths, serious adverse events, or evidence of drug-induced liver injury.

CONCLUSIONS

In this 24-week study, VBR+ETV provided additive antiviral activity over PBO+ETV in treatment-naïve patients with cHBV, with a favourable safety and tolerability profile.

CLINICAL TRIAL NUMBER

NCT03577171 LAY SUMMARY: Hepatitis B is a long-lasting viral infection of the liver. Current treatments can suppress hepatitis B virus but do not offer the opportunity of cure, hence, new treatment approaches are required. Herein, we show that the combination of the novel core inhibitor vebicorvir with an existing antiviral (entecavir) in treatment-naïve patients chronically infected with hepatitis B virus demonstrated greater antiviral activity than entecavir alone. Additionally, vebicorvir was safe and well tolerated. Thus, further studies evaluating its potential role in the treatment of chronic hepatitis B are warranted.

Progression of Antiviral Agents Targeting Viral Polymerases

Viral DNA and RNA polymerases are two kinds of very important enzymes that synthesize the genetic materials of the virus itself, and they have become extremely favorable targets for the development of antiviral drugs because of their relatively conserved characteristics. There are many similarities in the structure and function of different viral polymerases, so inhibitors designed for a certain viral polymerase have acted as effective universal inhibitors on other types of viruses. The present review describes the development of classical antiviral drugs targeting polymerases, summarizes a variety of viral polymerase inhibitors from the perspective of chemically synthesized drugs and natural product drugs, describes novel approaches, and proposes promising development strategies for antiviral drugs.

Safety and efficacy of vebicorvir in virologically suppressed patients with chronic hepatitis B virus infection

BACKGROUND & AIMS

HBV nucleos(t)ide reverse transcriptase inhibitors (NrtIs) do not completely suppress HBV replication. Previous reports indicate persistent viremia during NrtI treatment despite HBV DNA being undetectable. HBV core inhibitors may enhance viral suppression when combined with NrtIs. This phase II trial (NCT03576066) evaluated the efficacy and safety of the investigational core inhibitor, vebicorvir (VBR), in virologically- suppressed patients on NrtIs.

METHODS

Non-cirrhotic, NrtI-suppressed patients with chronic HBV were randomised to VBR 300 mg once daily or matching placebo (PBO) for 24 weeks. Treatment was stratified by hepatitis B e antigen (HBeAg) status. The primary endpoint was change from Baseline in serum HBeAg or hepatitis B surface antigen (HBsAg) after 24 weeks.

RESULTS

Of 73 patients enrolled, 47 were HBeAg positive and 26 were HBeAg negative. In HBeAg-positive and -negative patients, there were no differences in the change from Baseline at Week 24 for HBsAg or HBeAg. Using a novel, high-sensitivity assay to detect HBV DNA, a greater proportion of patients with detectable HBV DNA at Baseline achieved undetectable HBV DNA at Week 24 in the VBR+NrtI vs. PBO+NrtI group. In HBeAg-positive patients, a greater change from Baseline in HBV pregenomic (pg)RNA was observed at Week 24 with VBR+NrtI vs. PBO+NrtI. Treatment-emergent adverse events (TEAEs) in VBR+NrtI patients included upper respiratory tract infection, nausea, and pruritus. No serious adverse events, Grade 4 TEAEs, or deaths were reported.

CONCLUSIONS

In this 24-week study, VBR+NrtI demonstrated a favourable safety and tolerability profile. While there were no significant changes in viral antigen levels, enhanced viral suppression was demonstrated by greater changes in DNA and pgRNA with the addition of VBR compared to NrtI alone.

CLINICAL TRIALS NUMBER

NCT03576066.

LAY SUMMARY

Core inhibitors represent a novel approach for the treatment of chronic hepatitis B virus (HBV) infection, with mechanisms of action distinct from existing treatments. In this study, vebicorvir added to existing therapy reduced HBV replication to a greater extent than existing treatment and was generally safe and well tolerated.

Capsid Assembly Modulators as Antiviral Agents against HBV: Molecular Mechanisms and Clinical Perspectives

Despite a preventive vaccine being available, more than 250 million people suffer from chronic hepatitis B virus (HBV) infection, a major cause of liver disease and HCC. HBV infects human hepatocytes where it establishes its genome, the cccDNA with chromosomal features. Therapies controlling HBV replication exist; however, they are not sufficient to eradicate HBV cccDNA, the main cause for HBV persistence in patients. Core protein is the building block of HBV nucleocapsid. This viral protein modulates almost every step of the HBV life cycle; hence, it represents an attractive target for the development of new antiviral therapies. Capsid assembly modulators (CAM) bind to core dimers and perturb the proper nucleocapsid assembly. The potent antiviral activity of CAM has been demonstrated in cell-based and in vivo models. Moreover, several CAMs have entered clinical development. The aim of this review is to summarize the mechanism of action (MoA) and the advancements in the clinical development of CAMs and in the characterization of their mod of action.

Structure-Based Discovery of N-Sulfonylpiperidine-3-carboxamides as Novel Capsid Assembly Modulators for Potent Inhibition of HBV Replication

As a key element during HBV replication, a nucleocapsid is considered a promising target for the treatment of chronic hepatitis B. The present study aimed to identify small molecules as novel capsid assembly modulators with antiviral activity. Structure-based virtual screening of an integrated compound library led to the identification of several types of HBV inhibitors. Among these inhibitors, N-sulfonylpiperidine-3-carboxamides (SPCs) potently reduced the amount of secreted HBV DNA. Through structure–activity relationship studies, we identified an SPC derivative, namely, C-39, which exhibited the highest antiviral activity without causing cytotoxicity. Mechanism studies showed that C-39 dose-dependently inhibited the formation of HBV capsid, synthesis of cccDNA, e antigen (HBeAg), viral pregenomic RNA (pgRNA), and HBV DNA levels, thereby restraining HBV replication. In summary, SPCs represent a new class of capsid assembly modulators. Further optimization of SPCs is expected to obtain new antiviral drugs against HBV infection.

Inhibitory Activities of Ranunculus japonicus Thunb. Ethanol Extract against Hepatitis B Virus

The chronic hepatitis B virus (HBV) infection is a worldwide public health problem, which cannot be cured by current therapeutics due to the persistence of viral CCC DNA in the infected hepatocytes. Screening from medicinal herbs for anti-HBV activities showed that the ethanol extract from Ranunculus japonicus Thunb. could decrease the production of HBV e antigen (HBeAg). Further study showed that the extract had no effect on core protein expression but significantly reduced the efficiency of viral capsid assembly. The levels of viral pgRNA and total core DNA were not affected significantly. However, the ratio of RC DNA/SS DNA decreased, indicating that the conversion of RC DNA from SS DNA was delayed by the extract. More interestingly, though similar levels of RC DNA were accumulated, the CCC DNA level and its formation efficiency were reduced significantly, which was also consistent with the decreased level of HBeAg, indicating that Ranunculus japonicus Thunb. extract could inhibit the CCC DNA formation. Together, this study found that Ranunculus japonicus Thunb. extract could inhibit HBV replication at multiple steps, especially showed significant inhibitory effects on capsid assembly and CCC DNA formation. This article is protected by copyright. All rights reserved.

An automated microfluidic platform for the screening and characterization of novel hepatitis B virus capsid assembly modulators

To date, hepatitis B virus (HBV) capsid assembly modulators (CAMs), which target the viral core protein and induce the formation of non-functional viral capsids, have been identified and characterized in microtiter plate-based biochemical or cell-based in vitro assays. In this work, we developed an automated microfluidic screening assay, which uses convection-dominated Taylor-Aris dispersion to generate high-resolution dose-response curves, enabling the measurements of compound EC₅₀ values at very short incubation times. The measurement of early kinetics down to 7.7 seconds in the microfluidic format was utilized to discriminate between the two different classes of CAMs known so far. The CAM (-N), leading to the formation of morphologically normal capsids and the CAM (-A), leading to aberrant HBV capsid structures. CAM-A compounds like BAY 41-4109 and GLS4 showed rapid kinetics, with assembly rates above 80% of the core protein after only a 7 second exposure to the compound, whereas CAM-N compounds like ABI-H0731 and JNJ-56136379 showed significantly slower kinetics. Using our microfluidic system, we characterized two of our in-house screening compounds. Interestingly, one compound showed a CAM-N/A intermediate behavior, which was verified with two standard methods for CAM classification, size exclusion chromatography, and anti-HBc immunofluorescence microscopy. With this proof-of-concept study, we believe that this microfluidic system is a robust primary screening tool for HBV CAM drug discovery, especially for the hit finding and hit-to-lead optimization phases. In addition to EC₅₀ values, this system gives valuable first information about the mode of action of novel CAM screening compounds.

Toward a complete cure for chronic hepatitis B: Novel therapeutic targets for hepatitis B virus

Hepatitis B virus (HBV) affects approximately 250 million patients worldwide, resulting in the progression to cirrhosis and hepatocellular carcinoma, which are serious public health problems. Although universal vaccination programs exist, they are only prophylactic and not curative. In the HBV life cycle, HBV forms covalently closed circular DNA (cccDNA), which is the viral minichromosome, in the nuclei of human hepatocytes and makes it difficult to achieve a complete cure with the current nucleos(t)ide analogs and interferon therapies. Current antiviral therapies rarely eliminate cccDNA; therefore, lifelong antiviral treatment is necessary. Recent trials for antiviral treatment of chronic hepatitis B have been focused on establishing a functional cure, defined by either the loss of hepatitis B surface antigen, undetectable serum HBV DNA levels, and/or seroconversion to hepatitis B surface antibody. Novel therapeutic targets and molecules are in the pipeline for early clinical trials aiming to cure HBV infection. The ideal strategy for achieving a long-lasting functional or complete cure might be using combination therapies targeting different steps of the HBV life cycle and immunomodulators. This review summarizes the current knowledge about novel treatments and combination treatments for a complete HBV cure.

Pharmacomodulation of a ligand targeting the HBV capsid hydrophobic pocket

Hepatitis B virus (HBV) is a small enveloped retrotranscribing DNA virus and an important human pathogen. Its capsid-forming core protein (Cp) features a hydrophobic pocket proposed to be central notably in capsid envelopment. Indeed, mutations in and around this pocket can profoundly modulate, and even abolish, secretion of enveloped virions. We have recently shown that Triton X-100, a detergent used during Cp purification, binds to the hydrophobic pocket with micromolar affinity. We here performed pharmacomodulation of pocket binders through systematic modifications of the three distinct chemical moieties composing the Triton X-100 molecule. Using NMR and ITC, we found that the flat aromatic moiety is essential for binding, while the number of atoms of the aliphatic chain modulates binding affinity. The hydrophilic tail, in contrast, is highly tolerant to changes in both length and type. Our data provide essential information for designing a new class of HBV antivirals targeting capsid–envelope interactions.

Small-molecule binding to the Hepatitis B virus core protein hydrophobic pocket, a possible strategy for targeting viral particle assembly.

The HBV Core Protein and Core Particle Both Bind to the PPiase Par14 and Par17 to Enhance Their Stabilities and HBV Replication

We recently reported that the PPIase Par14 and Par17 encoded by PIN4 upregulate HBV replication in an HBx-dependent manner by binding to conserved arginine–proline (RP) motifs of HBx. HBV core protein (HBc) has a conserved ¹³³RP¹³⁴ motif; therefore, we investigated whether Par14/Par17 bind to HBc and/or core particles. Native agarose gel electrophoresis (NAGE) and immunoblotting and co-immunoprecipitation were used. Chromatin immunoprecipitation from HBV-infected HepG2-hNTCP-C9 cells was performed. NAGE and immunoblotting revealed that Par14/Par17 bound to core particles and co-immunoprecipitation revealed that Par14/Par17 interacted with core particle assembly-defective, and dimer-positive HBc-Y132A. Thus, core particles and HBc interact with Par14/Par17. Par14/Par17 interacted with the HBc ¹³³RP¹³⁴ motif possibly via substrate-binding E46/D74 and E71/D99 motifs. Although Par14/Par17 dissociated from core particles upon heat treatment, they were detected in 0.2 N NaOH-treated opened-up core particles, demonstrating that Par14/Par17 bind outside and inside core particles. Furthermore, these interactions enhanced the stabilities of HBc and core particles. Like HBc-Y132A, HBc-R133D and HBc-R133E were core particle assembly-defective and dimer-positive, demonstrating that a negatively charged residue at position 133 cannot be tolerated for particle assembly. Although positively charged R133 is solely important for Par14/17 interactions, the ¹³³RP¹³⁴ motif is important for efficient HBV replication. Chromatin immunoprecipitation from HBV-infected cells revealed that the S19 and E46/D74 residues of Par14 and S44 and E71/D99 residues of Par17 were involved in recruitment of ¹³³RP¹³⁴ motif-containing HBc into cccDNA. Our results demonstrate that interactions of HBc, Par14/Par17, and cccDNA in the nucleus and core particle–Par14/Par17 interactions in the cytoplasm are important for HBV replication.

Bay41-4109-induced aberrant polymers of hepatitis b capsid proteins are removed via STUB1-promoted p62-mediated macroautophagy

The hepatitis B virus (HBV) core protein (HBc) functions in multiple steps of the viral life cycle. Heteroaryldihydropyrimidine compounds (HAPs) such as Bay41-4109 are capsid protein allosteric modulators that accelerate HBc degradation and inhibit the virion secretion of HBV, specifically by misleading HBc assembly into aberrant non-capsid polymers. However, the subsequent cellular fates of these HAP-induced aberrant non-capsid polymers are not well understood. Here, we discovered that that the chaperone-binding E3 ubiquitin ligase protein STUB1 is required for the removal of Bay41-4109-induced aberrant non-capsid polymers from HepAD38 cells. Specifically, STUB1 recruits BAG3 to transport Bay41-4109-induced aberrant non-capsid polymers to the perinuclear region of cells, thereby initiating p62-mediated macroautophagy and lysosomal degradation. We also demonstrate that elevating the STUB1 level enhances the inhibitory effect of Bay41-4109 on the production of HBeAg and HBV virions in HepAD38 cells, in HBV-infected HepG2-NTCP cells, and in HBV transgenic mice. STUB1 overexpression also facilitates the inhibition of Bay41-4109 on the cccDNA formation in de novo infection of HBV. Understanding these molecular details paves the way for applying HAPs as a potentially curative regimen (or a component of a combination treatment) for eradicating HBV from hepatocytes of chronic infection patients.

Hepatitis B virus (HBV) infects more than 250 million people worldwide chronically. It is a major pathogen causing liver cirrhosis and hepatocellular carcinoma now. The HBV capsid protein (HBc) plays multiple roles in the viral life cycle, and many antivirals targeting HBc such as Heteroaryldihydropyrimidine compounds (HAPs) are under clinical trial recently. This study aimed to investigate how a HAP compound Bay41-4109 induces the degradation of HBc protein. Bay41-4109 induces aberrant non-capsid polymers, which form in complex with the chaperone-binding E3 ubiquitin ligase protein STUB1 and co-chaperone BAG3 and are transported to the perinuclear compartment. Subsequently, Bay41-4109-induced aberrant non-capsid polymers are removed by p62-mediated macroautophagy and lysosomal degradation. STUB1 overexpression accelerates Bay41-4109-induced degradation of HBc protein, and thus enhances the effect of Bay41-4109 on inhibiting secretion of HBeAg and HBV virions. When Bay41-4109 are enforced during HBV infection, de novo cccDNA formation were also negatively regulated by STUB1 overexpression. Altogether, this study provides novel mechanistic insights into developing more potent and safe HAP-based antiviral treatment.

A Pleiotropic Role of the Hepatitis B Virus Core Protein in Hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is one of the most common factors associated with hepatocellular carcinoma (HCC), which is the sixth most prevalent cancer among all cancers worldwide. However, the pathogenesis of HBV-mediated hepatocarcinogenesis is unclear. Evidence currently available suggests that the HBV core protein (HBc) plays a potential role in the development of HCC, such as the HBV X protein. The core protein, which is the structural component of the viral nucleocapsid, contributes to almost every stage of the HBV life cycle and occupies diverse roles in HBV replication and pathogenesis. Recent studies have shown that HBc was able to disrupt various pathways involved in liver carcinogenesis: the signaling pathways implicated in migration and proliferation of hepatoma cells, apoptosis pathways, and cell metabolic pathways inducing the development of HCC; and the immune system, through the expression and production of proinflammatory cytokines. In addition, HBc can modulate normal functions of hepatocytes through disrupting human host gene expression by binding to promoter regions. This HBV protein also promotes HCC metastasis through epigenetic alterations, such as micro-RNA. This review focuses on the molecular pathogenesis of the HBc protein in HBV-induced HCC.

ATM-Dependent Phosphorylation of Hepatitis B Core Protein in Response to Genotoxic Stress

Chronic hepatitis caused by infection with the Hepatitis B virus is a life-threatening condition. In fact, 1 million people die annually due to liver cirrhosis or hepatocellular carcinoma. Recently, several studies demonstrated a molecular connection between the host DNA damage response (DDR) pathway and HBV replication and reactivation. Here, we investigated the role of Ataxia-telangiectasia-mutated (ATM) and Ataxia telangiectasia and Rad3-related (ATR) PI3-kinases in phosphorylation of the HBV core protein (HBc). We determined that treatment of HBc-expressing hepatocytes with genotoxic agents, e.g., etoposide or hydrogen peroxide, activated the host ATM-Chk2 pathway, as determined by increased phosphorylation of ATM at Ser1981 and Chk2 at Thr68. The activation of ATM led, in turn, to increased phosphorylation of cytoplasmic HBc at serine-glutamine (SQ) motifs located in its C-terminal domain. Conversely, down-regulation of ATM using ATM-specific siRNAs or inhibitor effectively reduced etoposide-induced HBc phosphorylation. Detailed mutation analysis of S-to-A HBc mutants revealed that S170 (S168 in a 183-aa HBc variant) is the primary site targeted by ATM-regulated phosphorylation. Interestingly, mutation of two major phosphorylation sites involving serines at positions 157 and 164 (S155 and S162 in a 183-aa HBc variant) resulted in decreased etoposide-induced phosphorylation, suggesting that the priming phosphorylation at these serine-proline (SP) sites is vital for efficient phosphorylation of SQ motifs. Notably, the mutation of S172 (S170 in a 183-aa HBc variant) had the opposite effect and resulted in massively up-regulated phosphorylation of HBc, particularly at S170. Etoposide treatment of HBV infected HepG2-NTCP cells led to increased levels of secreted HBe antigen and intracellular HBc protein. Together, our studies identified HBc as a substrate for ATM-mediated phosphorylation and mapped the phosphorylation sites. The increased expression of HBc and HBe antigens in response to genotoxic stress supports the idea that the ATM pathway may provide growth advantage to the replicating virus.

Acetophenone 4-nitrophenylhydrazone inhibits Hepatitis B virus replication by modulating capsid assembly

Hepatitis B virus (HBV) is the causative agent of chronic liver disease and is correlated with the development of subsequent hepatic cirrhosis and hepatocellular carcinoma. Current antiviral therapy using nucleos(t)ide analogs is effective in suppressing viral replication and interrupting disease progression, but HBV is rarely cured completely. Thus, there remains an unmet need for the development of novel anti-HBV drugs. Here, we report the identification of N-(4-Nitrophenyl)-1-phenylethanone hydrazone (ANPH) as a novel structural class of selective inhibitors targeting the replication of the HBV genome using adenovirus vector-mediated HBV genome transduction. ANPH inhibited viral genome replication in HepG2.2.15 cells by inducing the formation of empty capsids devoid of pregenomic RNA without affecting its transcription and translation. Biochemical assays using a truncated core protein consisting of the assembly domain showed that ANPH accelerates the formation of morphologically intact capsids. Taken together, we propose that ANPH might provide a new structural scaffold to design a new anti-HBV drug in medicinal chemistry as well as chemical probes for HBV core protein functions in the future.

Molecular mechanism of capsid disassembly in hepatitis B virus

The disassembly of a viral capsid leading to the release of its genetic material into the host cell is a fundamental step in viral infection. In hepatitis B virus (HBV), the capsid consists of identical protein monomers that dimerize and then arrange themselves into pentamers or hexamers on the capsid surface. By applying atomistic molecular dynamics simulation to an entire solvated HBV capsid subjected to a uniform mechanical stress protocol, we monitor the capsid-disassembly process and analyze the process down to the level of individual amino acids in 20 independent simulation replicas. The strain of an isotropic external force, combined with structural fluctuations, causes structurally heterogeneous cracks to appear in the HBV capsid. Analysis of the monomer-monomer interfaces reveals that, in contrast to the expectation from purely mechanical considerations, the cracks mainly occur within hexameric sites, whereas pentameric sites remain largely intact. Only a small subset of the capsid protein monomers, different in each simulation, are engaged in each instance of disassembly. We identify specific residues whose interactions are most readily lost during disassembly; R127, I139, Y132, N136, A137, and V149 are among the hot spots at the interfaces between dimers that lie within hexamers, leading to disassembly. The majority of these hot-spot residues are conserved by evolution, hinting to their importance for disassembly by avoiding overstabilization of capsids.

Treatments for HBV: A Glimpse into the Future

The hepatitis B virus is responsible for most of the chronic liver disease and liver cancer worldwide. As actual therapeutic strategies have had little success in eradicating the virus from hepatocytes, and as lifelong treatment is often required, new drugs targeting the various phases of the hepatitis B virus (HBV) lifecycle are currently under investigation. In this review, we provide an overview of potential future treatments for HBV.

The Functions of Hepatitis B Virus Encoding Proteins: Viral Persistence and Liver Pathogenesis

About 250 million people worldwide are chronically infected with Hepatitis B virus (HBV), contributing to a large burden on public health. Despite the existence of vaccines and antiviral drugs to prevent infection and suppress viral replication respectively, chronic hepatitis B (CHB) cure remains a remote treatment goal. The viral persistence caused by HBV is account for the chronic infection which increases the risk for developing liver cirrhosis and hepatocellular carcinoma (HCC). HBV virion utilizes various strategies to escape surveillance of host immune system therefore enhancing its replication, while the precise mechanisms involved remain elusive. Accumulating evidence suggests that the proteins encoded by HBV (hepatitis B surface antigen, hepatitis B core antigen, hepatitis B envelope antigen, HBx and polymerase) play an important role in viral persistence and liver pathogenesis. This review summarizes the major findings in functions of HBV encoding proteins, illustrating how these proteins affect hepatocytes and the immune system, which may open new venues for CHB therapies.

Hepatitis B virus-host interactions and novel targets for viral cure

Chronic infection with HBV is a major cause of advanced liver disease and hepatocellular carcinoma. Nucleos(t)ide analogues effectively control HBV replication but viral cure is rare. Hence treatment has often to be administered for an indefinite duration, increasing the risk for selection of drug resistant virus variants. PEG-interferon-α-based therapies can sometimes cure infection but suffer from a low response rate and severe side-effects. CHB is characterized by the persistence of a nuclear covalently closed circular DNA (cccDNA), which is not targeted by approved drugs. Targeting host factors which contribute to the viral life cycle provides new opportunities for the development of innovative therapeutic strategies aiming at HBV cure. An improved understanding of the host immune system has resulted in new potentially curative candidate approaches. Here, we review the recent advances in understanding HBV-host interactions and highlight how this knowledge contributes to exploiting host-targeting strategies for a viral cure.

Viral hepatitis: Milestones, unresolved issues, and future goals

In this review the current overall knowledge on hepatitis A, B, C, D, and E will be discussed. These diseases are all characterized by liver inflammation but have significant differences in distribution, transmission routes, and outcomes. Hepatitis B virus and hepatitis C virus are transmitted by exposure to infected blood, and in addition to acute infection, they can cause chronic hepatitis, which in turn can evolve into cirrhosis. It is estimated that more than 300 million people suffer from chronic hepatitis B or C worldwide. Hepatitis D virus, which is also transmitted by blood, only affects hepatitis B virus infected people, and this dual infection results in worse liver-related outcomes. Hepatitis A and E spread via the fecal-oral route, which corresponds mainly to the ingestion of food or water contaminated with infected stools. However, in developed countries hepatitis E is predominantly a zoonosis. Although hepatitis A virus and hepatitis E virus are usually responsible for a self-limiting hepatitis, a serious, rarely fatal illness is also possible, and in immunosuppressed patients, such as organ transplant recipients, hepatitis E virus infection can become chronic. The description of goals achieved, unresolved issues, and the latest research on this topic may make it possible to speculate on future scenarios in the world of viral hepatitis.

Silencing hepatitis B virus covalently closed circular DNA: The potential of an epigenetic therapy approach

Global prophylactic vaccination programmes have helped to curb new hepatitis B virus (HBV) infections. However, it is estimated that nearly 300 million people are chronically infected and have a high risk of developing hepatocellular carcinoma. As such, HBV remains a serious health priority and the development of novel curative therapeutics is urgently needed. Chronic HBV infection has been attributed to the persistence of the covalently closed circular DNA (cccDNA) which establishes itself as a minichromosome in the nucleus of hepatocytes. As the viral transcription intermediate, the cccDNA is responsible for producing new virions and perpetuating infection. HBV is dependent on various host factors for cccDNA formation and the minichromosome is amenable to epigenetic modifications. Two HBV proteins, X (HBx) and core (HBc) promote viral replication by modulating the cccDNA epigenome and regulating host cell responses. This includes viral and host gene expression, chromatin remodeling, DNA methylation, the antiviral immune response, apoptosis, and ubiquitination. Elimination of the cccDNA minichromosome would result in a sterilizing cure; however, this may be difficult to achieve. Epigenetic therapies could permanently silence the cccDNA minichromosome and promote a functional cure. This review explores the cccDNA epigenome, how host and viral factors influence transcription, and the recent epigenetic therapies and epigenome engineering approaches that have been described.

Hepatitis B Virus-Encoded MicroRNA (HBV-miR-3) Regulates Host Gene PPM1A Related to Hepatocellular Carcinoma

BACKGROUND

Hepatitis B is a liver infection disease caused by the Hepatitis B Virus (HBV) that can become chronic and develop into hepatocellular carcinoma. HBV was classified as a double-stranded DNA virus. Currently, there is a report showing that HBV virus-encoded miRNA called HBV-miR-3 controls the replication of HBV. However, the regulation of HBV-miR-3 in host cells remains unclear.

OBJECTIVE

This study aimed to investigate the regulation of HBV-miR-3 in host gene target which is related to chronic HBV infection and HCC process.

METHODS

In this study, we analyzed the read count of HBV-miR-3 from next-generation sequencing of chronic hepatitis patients in Pegylated interferon alpha-2a (PEG-IFN-α-2a) treatment. To understand the regulation of HBV-miR-3 in host cells, the HBV-miR-3 recognition sites were predicted in host target genes using miRDB. The effect of HBV-miR-3 in host cells was examined using qPCR and 3' UTR dual luciferase assay.

RESULTS

The read count of HBV-miR-3 was found in chronic hepatitis patients before treatment. Moreover, the decrease of HBV-miR-3 was correlated with response group of chronic hepatitis patients after treatment. On the other hand, the abundance of HBV-miR-3 showed no difference in nonresponse group of chronic patients after PEG-IFN-α-2a treatment. To study the role of HBV-miR-3 in patients, four HBV-miR-3 target regions from Protein phosphatase 1A (PPM1A) and DIX domain containing 1 (DIXDC1) were identified in the human genome using miRDB. Interestingly, we found that HBV-miR-3 hybridized with PPM1A mRNA. The mRNA expression from RT-qPCR showed no difference between HepG2 transfected with pSilencer_scramble or pSilencer_HBV-miR-3. However, the reporter assay showed that PPM1A mRNA was suppressed by HBV-miR-3. The protein expression of PPM1A showed a decrease in cells overexpressing HBV-miR-3. Finally, the HBV-miR-3 can promote cell proliferation in cells overexpressing HBV-miR-3.

CONCLUSION

This study is the first report showed the HBV encoded miRNA can regulate host gene expression. HBV-miR-3 silenced PPM1A by inhibiting the translation process of PPM1A. The downregulation of PPM1A promotes cell proliferation related to HCC development.

Discovery of Novel Pyrimidine-Based Capsid Assembly Modulators as Potent Anti-HBV Agents

Core assembly modulators of viral capsid proteins have been developed as an effective treatment of chronic hepatitis B virus (HBV) infection. In this study, we synthesized novel potent pyrimidine derivatives as core assembly modulators, and their antiviral effects were evaluated in in vitro and in vivo biological experiments. One of the synthesized derivatives, compound 23h (R¹ = MeSO₂, R² = 1-piperidin-4-amine, R³ = 3-Cl-4-F-aniline) displayed potent inhibitory effects in the in vitro assays (52% inhibition in the protein-based assay at 100 nM and an IC₅₀ value of 181 nM in the serum HBV DNA quantification assay). Moreover, treatment with compound 23h for 5 weeks significantly decreased serum levels of HBV DNA levels (3.35 log reduction) in a human liver-chimeric uPA/SCID mouse model, and these effects were significantly increased when 23h was combined with tenofovir, a nucleotide analogue inhibitor of reverse transcriptase used for the treatment of HBV infection.

Host Epigenetic Alterations and Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most frequent primary malignancy of the liver and a leading cause of cancer-related deaths worldwide. Although much progress has been made in HCC drug development in recent years, treatment options remain limited. The major cause of HCC is chronic hepatitis B virus (HBV) infection. Despite the existence of a vaccine, more than 250 million individuals are chronically infected by HBV. Current antiviral therapies can repress viral replication but to date there is no cure for chronic hepatitis B. Of note, inhibition of viral replication reduces but does not eliminate the risk of HCC development. HBV contributes to liver carcinogenesis by direct and indirect effects. This review summarizes the current knowledge of HBV-induced host epigenetic alterations and their association with HCC, with an emphasis on the interactions between HBV proteins and the host cell epigenetic machinery leading to modulation of gene expression.

Development of a cellular high-content, immunofluorescent HBV core assay to identify novel capsid assembly modulators that induce the formation of aberrant HBV core structures

Hepatitis B Virus (HBV) core protein has multiple functions in the viral life cycle and is an attractive target for new anti-viral therapies. Capsid assembly modulators (CAMs) target the core protein and induce the formation of either morphologically normal (CAM-N) or aberrant structures (CAM-A), both devoid of genomic material. To date a diverse family of CAM-N chemotypes has been identified, but in contrast, described CAM-As are based on the heteroaryldihydropyrimidine (HAP) scaffold. We used the HBV-inducible HepG2.117 cell line with immunofluorescent labeling of HBV core to develop and validate a cellular high-content image-based assay where aggregated core structures are identified using image analysis spot texture features. Treatment with HAPs led to a dose- and time-dependent formation of aggregated core appearing as dot-like structures in the cytoplasm and nucleus. By combining a biochemical and cellular screening approach, a compound was identified as a novel non-HAP scaffold able to induce dose-dependent formation of aberrant core structures, which was confirmed by electron microscopy and native gel electrophoresis. This compound displayed anti-HBV activity in HepG2.117 cells, providing proof-of-concept for our screening approach. We believe our combined biochemical and cellular high-content screening method will aid in expanding the range of CAM-A chemotypes.

Next-generation sequencing for the diagnosis of hepatitis B: current status and future prospects

INTRODUCTION

Hepatitis B virus (HBV) causes a complex and persistent infection with a major impact on patients health. Viral-genome sequencing can provide valuable information for characterizing virus genotype, infection dynamics and drug and vaccine resistance.

AREAS COVERED

This article reviews the current literature to describe the next-generation sequencing progress that facilitated a more comprehensive study of HBV quasispecies in diagnosis and clinical monitoring.

EXPERT OPINION

HBV variability plays a key role in liver disease progression and treatment efficacy. Second-generation sequencing improved the sensitivity for detecting and quantifying mutations, mixed genotypes and viral recombination. Third-generation sequencing enables the analysis of the entire HBV genome, although the high error rate limits its use in clinical practice.

Sulfamoylbenzamide-based Capsid Assembly Modulators for Selective Inhibition of Hepatitis B Viral Replication

As the spread of infections caused by hepatitis B virus (HBV) threatens public health worldwide, investigations from multiple perspectives and of various mechanisms of action are urgently required to increase the HBV cure rate. Targeting the encapsidation of the nuclear capsid protein (core protein, HBc) has emerged as an attractive strategy for inhibiting the viral assembly process; however, a drug targeting this mechanism has not yet been approved. We synthesized novel sulfamoylbenzamides (SBAs) as capsid assembly modulators of HBV and found that the effects and safety profiles of compounds 3 and 8 have potential therapeutic applicability against HBV. The formation of tubular particles was time-dependent in the presence of 3, indicating a new mode of protein assembly by SBA compounds. Our findings provide a new entity for developing safe and efficient treatments for HBV infection.

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.

Hepatitis B virus RNA decline without concomitant viral antigen decrease is associated with a low probability of sustained response and hepatitis B surface antigen loss

BACKGROUND

Serum hepatitis B virus (HBV) RNA may reflect intrahepatic HBV replication. Novel anti-viral drugs have shown potent HBV RNA decline without concomitant hepatitis B surface antigen (HBsAg) decrease. How this relates to off-treatment response is yet unclear.

AIM

To study the degree of on-treatment viral antigen decline among patients with pronounced HBV RNA decrease in relation to off-treatment sustained response and HBsAg loss.

METHODS

HBV RNA, HBsAg and hepatitis B core-related antigen (HBcrAg) were quantified in patients with chronic hepatitis B who participated in two randomised controlled trials of peginterferon-based therapy. Sustained response (HBV DNA <2000 IU/mL) and/or HBsAg loss were assessed in patients with and without on-treatment HBV RNA response (either >2 log HBV RNA decline or >1 log decline resulting in an undetectable value at on-treatment week 24), stratified by concomitant HBsAg decline (<0.5/0.5-1/>1 log).

RESULTS

We enrolled 279 patients; 176 were hepatitis B e antigen (HBeAg)-positive, and 103 were HBeAg-negative. Sustained response was achieved in 20.4% of patients. At on-treatment week 24, HBV RNA response was associated with higher sustained response rates (27.4% vs 13.0% in non-responders, P =  0.004). However, among patients with an HBV RNA response (n = 135), 56.4% did not experience >0.5 log HBsAg decline. Among HBV RNA responders, sustained response was achieved in 47.6% of those with >1 log HBsAg decline (n = 20/42), vs 16.0% with <0.5 log decline (n = 12/75, P = 0.001). Similar results were obtained with HBcrAg and when response was defined as HBsAg loss.

CONCLUSIONS

In this cohort, many patients with HBV RNA response during peginterferon-based treatment did not experience HBsAg and/or HBcrAg decline. The absence of concomitant decline in these viral antigens was associated with low rates of treatment response and HBsAg loss. Future trials should therefore consider kinetics of combined biomarkers to assess anti-viral efficacy. Trial registration, ClinicalTrials.gov: NCT00114361, NCT00146705.

Hepatitis B virus core protein promotes the expression of neuraminidase 1 to facilitate hepatocarcinogenesis

Neuraminidase 1 (NEU1) has been reported to be associated with hepatocellular carcinoma (HCC). However, the function and associated molecular mechanisms of NEU1 in hepatitis B virus (HBV)-related HCC have not been well investigated. In the present study, the expression of NEU1 mediated by HBV and HBV core protein (HBc) was measured in hepatoma cells. The expression of NEU1 protein was detected via immunohistochemical analysis in HBV-associated HCC tissues. The role of NEU1 in the activation of signaling pathways and epithelial-mesenchymal transition (EMT) and the proliferation and migration of hepatoma cells mediated by HBc was assessed. We found that NEU1 was upregulated in HBV-positive hepatoma cells and HBV-related HCC tissues. HBV promoted NEU1 expression at the mRNA and protein level via HBc in hepatoma cells. Mechanistically, HBc was able to enhance the activity of the NEU1 promoter through NF-κB binding sites. In addition, through the increase in NEU1 expression, HBc contributed to activation of downstream signaling pathways and EMT in hepatoma cells. Moreover, NEU1 facilitated the proliferation and migration of hepatoma cells mediated by HBc. Taken together, our findings provide novel insight into the molecular mechanism underlying the oncogenesis mediated by HBc and demonstrate that NEU1 plays a vital role in HBc-mediated functional abnormality in HCC. Thus, NEU1 may serve as a potential therapeutic target in HBV-associated HCC.

Hepatitis B Virus Core Protein Mediates the Upregulation of C5α Receptor 1 via NF-κB Pathway to Facilitate the Growth and Migration of Hepatoma Cells

Purpose

C5α receptor 1 (C5AR1) is associated with the development of various human cancers. However, whether it is involved in the development of hepatitis B virus (HBV)–related hepatocellular carcinoma (HCC) is poorly understood. We explored the expression, biological role, and associated mechanisms of C5AR1 in HBV-related hepatoma cells.

Materials and Methods

The expression of C5AR1 mediated by HBV and HBV core protein (HBc) was detected in hepatoma cells. The function of nuclear factor κB (NF-κB) pathway in HBc-induced C5AR1 expression was assessed. The roles of C5AR1 in the activation of intracellular signal pathways, the upregulation of inflammatory cytokines, and the growth and migration of hepatoma cells mediated by HBc, were investigated. The effect of C5α in the development of HCC mediated by C5AR1 was also measured.

Results

C5AR1 expression was increased in HBV-positive hepatoma cells. Dependent on HBc, HBV enhanced the expression of C5AR1 at the mRNA and protein levels. Besides, HBc could promote C5AR1 expression via the NF-κB pathway. Based on the C5AR1, HBc facilitated the activation of JNK and ERK pathways and the expression and secretion of interleukin-6 in hepatoma cells. Furthermore, C5AR1 was responsible for enhancing the growth and migration of hepatoma cells mediated by HBc. Except these, C5α could promote the malignant development of HBc-positive HCC via C5AR1.

Conclusion

We provide new insight into the mechanisms of hepatocarcinogenesis mediated by HBc. C5AR1 has a significant role in the functional abnormality of hepatoma cells mediated by HBc, and might be utilized as a potential therapeutic target for HBV-related HCC.

Hepatitis B virus Core protein nuclear interactome identifies SRSF10 as a host RNA-binding protein restricting HBV RNA production

Despite the existence of a preventive vaccine, chronic infection with Hepatitis B virus (HBV) affects more than 250 million people and represents a major global cause of hepatocellular carcinoma (HCC) worldwide. Current clinical treatments, in most of cases, do not eliminate viral genome that persists as a DNA episome in the nucleus of hepatocytes and constitutes a stable template for the continuous expression of viral genes. Several studies suggest that, among viral factors, the HBV core protein (HBc), well-known for its structural role in the cytoplasm, could have critical regulatory functions in the nucleus of infected hepatocytes. To elucidate these functions, we performed a proteomic analysis of HBc-interacting host-factors in the nucleus of differentiated HepaRG, a surrogate model of human hepatocytes. The HBc interactome was found to consist primarily of RNA-binding proteins (RBPs), which are involved in various aspects of mRNA metabolism. Among them, we focused our studies on SRSF10, a RBP that was previously shown to regulate alternative splicing (AS) in a phosphorylation-dependent manner and to control stress and DNA damage responses, as well as viral replication. Functional studies combining SRSF10 knockdown and a pharmacological inhibitor of SRSF10 phosphorylation (1C8) showed that SRSF10 behaves as a restriction factor that regulates HBV RNAs levels and that its dephosphorylated form is likely responsible for the anti-viral effect. Surprisingly, neither SRSF10 knock-down nor 1C8 treatment modified the splicing of HBV RNAs but rather modulated the level of nascent HBV RNA. Altogether, our work suggests that in the nucleus of infected cells HBc interacts with multiple RBPs that regulate viral RNA metabolism. Our identification of SRSF10 as a new anti-HBV restriction factor offers new perspectives for the development of new host-targeted antiviral strategies.

Chronic infection with Hepatitis B virus (HBV) affects more than 250 million of people world-wide and is a major global cause of liver cancer. Current treatments lead to a significant reduction of viremia in patients. However, viral clearance is rarely obtained and the persistence of the HBV genome in the hepatocyte’s nucleus generates a stable source of viral RNAs and subsequently proteins which play important roles in immune escape mechanisms and liver disease progression. Therapies aiming at efficiently and durably eliminating viral gene expression are still required. In this study, we identified the nuclear partners of the HBV Core protein (HBc) to understand how this structural protein, responsible for capsid assembly in the cytoplasm, could also regulate viral gene expression. The HBc interactome was found to consist primarily of RNA-binding proteins (RBPs). One of these RBPs, SRSF10, was demonstrated to restrict HBV RNA levels and a drug, able to alter its phosphorylation, behaved as an antiviral compound capable of reducing viral gene expression. Altogether, this study sheds new light on novel regulatory functions of HBc and provides information relevant for the development of antiviral strategies aiming at preventing viral gene expression.

Slowly folding surface extension in the prototypic avian hepatitis B virus capsid governs stability

Hepatitis B virus (HBV) is an important but difficult to study human pathogen. Most basics of the hepadnaviral life-cycle were unraveled using duck HBV (DHBV) as a model although DHBV has a capsid protein (CP) comprising ~260 rather than ~180 amino acids. Here we present high-resolution structures of several DHBV capsid-like particles (CLPs) determined by electron cryo-microscopy. As for HBV, DHBV CLPs consist of a dimeric α-helical frame-work with protruding spikes at the dimer interface. A fundamental new feature is a ~ 45 amino acid proline-rich extension in each monomer replacing the tip of the spikes in HBV CP. In vitro, folding of the extension takes months, implying a catalyzed process in vivo. DHBc variants lacking a folding-proficient extension produced regular CLPs in bacteria but failed to form stable nucleocapsids in hepatoma cells. We propose that the extension domain acts as a conformational switch with differential response options during viral infection.

Hepatitis B: Current Status of Therapy and Future Therapies

Despite the availability of a protective vaccine for over 3 decades, the number of persons with chronic hepatitis B virus (HBV) infection remains high. These persons are at risk for cirrhosis and hepatocellular carcinoma. Current treatment is effective at inhibiting viral replication and reducing complications of chronic HBV infection, but is not curative. There is a need for novel, finite therapy that can cure chronic HBV infection. Several agents are in early-phase development and can be broadly viewed as agents that target the virus directly or indirectly or the host immune response. This article highlights key developments in antiviral/immunomodulatory therapy, the rationale for these approaches, and possible therapeutic regimens.

Conservation and variability of hepatitis B core at different chronic hepatitis stages

BACKGROUND

Since it is currently not possible to eradicate hepatitis B virus (HBV) infection with existing treatments, research continues to uncover new therapeutic strategies. HBV core protein, encoded by the HBV core gene (HBC), intervenes in both structural and functional processes, and is a key protein in the HBV life cycle. For this reason, both the protein and the gene could be valuable targets for new therapeutic and diagnostic strategies. Moreover, alterations in the protein sequence could serve as potential markers of disease progression.

AIM

To detect, by next-generation sequencing, HBC hyper-conserved regions that could potentially be prognostic factors and targets for new therapies.

METHODS

Thirty-eight of 45 patients with chronic HBV initially selected were included and grouped according to liver disease stage [chronic hepatitis B infection without liver damage (CHB, n = 16), liver cirrhosis (LC, n = 5), and hepatocellular carcinoma (HCC, n = 17)]. HBV DNA was extracted from patients’ plasma. A region between nucleotide (nt) 1863 and 2483, which includes HBC, was amplified and analyzed by next-generation sequencing (Illumina MiSeq platform). Sequences were genotyped by distance-based discriminant analysis. General and intergroup nt and amino acid (aa) conservation was determined by sliding window analysis. The presence of nt insertion and deletions and/or aa substitutions in the different groups was determined by aligning the sequences with genotype-specific consensus sequences.

RESULTS

Three nt (nt 1900-1929, 2249-2284, 2364-2398) and 2 aa (aa 117-120, 159-167) hyper-conserved regions were shared by all the clinical groups. All groups showed a similar pattern of conservation, except for five nt regions (nt 1946-1992, 2060-2095, 2145-2175, 2230-2250, 2270-2293) and one aa region (aa 140-160), where CHB and LC, respectively, were less conserved (P < 0.05). Some group-specific conserved regions were also observed at both nt (2306-2334 in CHB and 1935-1976 and 2402-2435 in LC) and aa (between aa 98-103 in CHB and 28-30 and 51-54 in LC) levels. No differences in insertion and deletions frequencies were observed. An aa substitution (P79Q) was observed in the HCC group with a median (interquartile range) frequency of 15.82 (0-78.88) vs 0 (0-0) in the other groups (P < 0.05 vs CHB group).

CONCLUSION

The differentially conserved HBC and HBV core protein regions and the P79Q substitution could be involved in disease progression. The hyper-conserved regions detected could be targets for future therapeutic and diagnostic strategies.