The current status and future directions of hepatitis B antiviral drug discovery

Discovery of hepatitis B virus subviral particle biogenesis inhibitors from a bioactive compound library

High levels of hepatitis B virus (HBV) surface antigen (HBsAg) in the blood of chronic HBV carriers are considered to drive the exhaustion of antigen-specific T and B lymphocytes and thus responsible for the persistence of infection. Accordingly, therapeutic elimination of HBsAg may facilitate the activation of adaptive antiviral immune responses against HBV and achieve a functional cure of chronic hepatitis B. We discovered recently that an amphipathic alpha helix spanning W156 to R169 of HBV small envelope (S) protein plays an essential role in the morphogenesis of subviral particles (SVPs) and metabolism of S protein. We thus hypothesized that pharmacological disruption of SVP morphogenesis may induce intracellular degradation of S protein and reduce HBsAg secretion. To identify inhibitors of SVP biogenesis, we screened 4417 bioactive compounds with a HepG2-derived cell line expressing HBV S protein and efficiently secreting small spherical SVPs. The screen identified 24 compounds that reduced intracellular SVPs and secreted HBsAg in a concentration-dependent manner. However, 18 of those compounds inhibited the secretion of HBsAg and HBeAg in HBV replicon transfected HepG2 cells at similar efficiency, suggesting each of those compounds may disrupt a common cellular function required for the synthesis and/or secretion of these viral proteins. Interestingly, lycorine more efficiently inhibited the secretion of HBsAg in HepG2 cells transfected with HBV replicons, HepG2.2.15 cells and HBV infected - HepG2 cells expressing sodium taurocholate cotransporting polypeptide (NTCP). The structure activity relationship and antiviral mechanism of lycorine against HBV have been determined.

An allosteric inhibitor of sirtuin 2 blocks hepatitis B virus covalently closed circular DNA establishment and its transcriptional activity

296 million people worldwide are predisposed to developing severe end-stage liver diseases due to chronic hepatitis B virus (HBV) infection. HBV forms covalently closed circular DNA (cccDNA) molecules that persist as episomal DNA in the nucleus of infected hepatocytes and drive viral replication. Occasionally, the HBV genome becomes integrated into host chromosomal DNA, a process that is believed to significantly contribute to circulating HBsAg levels and HCC development. Neither cccDNA accumulation nor expression from integrated HBV DNA are directly targeted by current antiviral treatments. In this study, we investigated the antiviral properties of a newly described allosteric modulator, FLS-359, that targets sirtuin 2 (SIRT2), an NAD+-dependent deacylase. Our results demonstrate that SIRT2 modulation by FLS-359 and by other tool compounds inhibits cccDNA synthesis following de novo infection of primary human hepatocytes and HepG2 (C3A)-NTCP cells, and FLS-359 substantially reduces cccDNA recycling in HepAD38 cells. While pre-existing cccDNA is not eradicated by short-term treatment with FLS-359, its transcriptional activity is substantially impaired, likely through inhibition of viral promoter activities. Consistent with the inhibition of viral transcription, HBsAg production by HepG2.2.15 cells, which contain integrated HBV genomes, is also suppressed by FLS-359. Our study provides further insights on SIRT2 regulation of HBV infection and supports the development of potent SIRT2 inhibitors as HBV antivirals.

Identification of dihydroquinolizinone derivatives with nitrogen heterocycle moieties as new anti-HBV agents

The sustained loss of HBsAg is considered a pivotal indicator for achieving functional cure of HBV. Dihydroquinolizinone derivatives (DHQs) have demonstrated remarkable inhibitory activity against HBsAg both in vitro and in vivo. However, the reported neurotoxicity associated with RG7834 has raised concerns regarding the development of DHQs. In this study, we designed and synthesized a series of DHQs incorporating nitrogen heterocycle moieties. Almost all of these compounds exhibited potent inhibition activity against HBsAg, with IC50 values at the nanomolar level. Impressively, the compound (S)-2a (10 μM) demonstrated a comparatively reduced impact on the neurite outgrowth of HT22 cells and isolated mouse DRG neurons in comparison to RG7834, thereby indicating a decrease in neurotoxicity. Furthermore, (S)-2a exhibited higher drug exposures than RG7834. The potent anti-HBV activity, reduced neurotoxicity, and favorable pharmacokinetic profiles underscore its promising potential as a lead compound for future anti-HBV drug discovery.

Mechanism of interferon alpha therapy for chronic hepatitis B and potential approaches to improve its therapeutic efficacy

Hepatitis B virus (HBV) chronically infects 296 million people worldwide and causes more than 820,000 deaths annually due to cirrhosis and hepatocellular carcinoma. Current standard-of-care medications for chronic hepatitis B (CHB) include nucleos(t)ide analogue (NA) viral DNA polymerase inhibitors and pegylated interferon alpha (PEG-IFN-α). NAs can efficiently suppress viral replication and improve liver pathology, but not eliminate or inactivate HBV covalently closed circular DNA (cccDNA). CCC DNA is the most stable HBV replication intermediate that exists as a minichromosome in the nucleus of infected hepatocyte to transcribe viral RNA and support viral protein translation and genome replication. Consequentially, a finite duration of NA therapy rarely achieves a sustained off-treatment suppression of viral replication and life-long NA treatment is most likely required. On the contrary, PEG-IFN-α has the benefit of finite treatment duration and achieves HBsAg seroclearance, the indication of durable immune control of HBV replication and functional cure of CHB, in approximately 5% of treated patients. However, the low antiviral efficacy and poor tolerability limit its use. Understanding how IFN-α suppresses HBV replication and regulates antiviral immune responses will help rational optimization of IFN therapy and development of novel immune modulators to improve the rate of functional cure. This review article highlights mechanistic insight on IFN control of HBV infection and recent progress in development of novel IFN regimens, small molecule IFN mimetics and combination therapy of PEG-IFN-α with new direct-acting antivirals and therapeutic vaccines to facilitate the functional cure of CHB.

A Particle Gel Assay for Detection of Intracellular Hepatitis B Virus Subviral Particles in Cultured Cells

Chronic hepatitis B virus (HBV) infection is due to the failure of host immune system to resolve the viral infection. Accordingly, restoration or reconstitution of a functional antiviral immune response to HBV is essential to achieve durable control of HBV replication leading to a functional cure of chronic hepatitis B (CHB). Noninfectious subviral particles (SVPs), comprised of HBV surface antigen (HBsAg), are the predominant viral products secreted by HBV-infected hepatocytes. The high levels of SVPs in the circulation induce immune tolerance and contribute to the establishment of chronic HBV infection. The current standard-of-care medications for CHB efficiently suppress HBV replication but fail to reduce the levels of HBsAg in majority of treated patients. Further understanding the mechanisms underlying SVP morphogenesis, secretion and regulation by viral and host cellular factors are critical for the discovery of therapeutics that can inhibit SVP production and/or induce the degradation of HBV envelope proteins. We describe herein a protocol for intracellular SVP detection by a native agarose gel electrophoresis-based particle gel assy. The method is suitable for quantitative detection of intracellular HBV SVPs and can be applied in dissecting the molecular mechanism of SVP morphogenesis and the discovery of antiviral agents targeting SVP formation in hepatocytes.

HMGB1/PTEN/PI3K axis participates in the peripheral immune cell differentiation in two representative TCM syndromes of chronic hepatitis B patients

Liver depression and spleen deficiency syndrome (LDSDS) and spleen-gastric damp-heat syndrome (SGDHS) are two major traditional Chinese medicine syndromes observed in chronic hepatitis B (CHB). Both syndromes exhibit significant differences in the pathogenesis and prognosis, and are closely related to the immune system. However, the underlying mechanisms are largely unknown. This study aimed to explore the immunoregulatory mechanisms of the two syndromes and promote the differentiation precision between the two syndromes. Thirty-six patients with CHB (18 LDSDS patients and 18 SGDHS patients) and 14 healthy controls were recruited into this study and blood was collected from all the subjects for testing. We studied the contents of T lymphocytes by flow cytometry and the expression levels of HMGB1/PTEN/PI3K axis proteins by enzyme-linked immunosorbent assay (Elisa). Protein-protein interaction (PPI) networks among HMGB1/PTEN/PI3K axis were constructed for functional enrichment. The correlations between T lymphocytes and proteins were analyzed by constructing multiple regression equations. The results revealed that the CD8+ T cells level in the two syndromes were lower than that in healthy controls, and the levels of Th17, Treg cells, and HMGB1, PI3K, PDK1, Akt were higher than those of the healthy controls (p < 0.05). Moreover, the levels of CD4+ T, Th17 cells, and HMGB1, PTEN, PI3K in LDSDS were higher than SGDHS (p < 0.05). PPI network indicated that HMGB1/PTEN/PI3K axis participated in T cell activation and liver pathology. Our results revealed that HMGB1/PTEN/PI3K axis may play an important role in regulating the formation of peripheral immune differences between the two syndromes. CD4+ T and Th17 are two representative immune cells that may serve as potential biological markers for LDSDS and SGDHS in CHB.

Discovery of Linvencorvir (RG7907), a Hepatitis B Virus Core Protein Allosteric Modulator, for the Treatment of Chronic HBV Infection

Described herein is the first-time disclosure of Linvencorvir (RG7907), a clinical compound and a hepatitis B virus (HBV) core protein allosteric modulator, for the treatment of chronic HBV infection. Built upon the core structure of hetero aryl dihydropyrimidine, RG7907 was rationally designed by combining all the drug-like features of low CYP3A4 induction, potent anti-HBV activity, high metabolic stability, low hERG liability, and favorable animal pharmacokinetic (PK) profiles. In particular, the chemistry strategy to mitigate CYP3A4 induction through introducing a large, rigid, and polar substituent at the position that has less interaction with the therapeutic biological target (HBV core proteins herein) is of general interest to the medicinal chemistry community. RG7907 demonstrated favorable animal PK, pharmacodynamics, and safety profiles with sufficient safety margins supporting its clinical development in healthy volunteers and HBV-infected patients.

Synthesis and evaluation of N-sulfonylpiperidine-3-carboxamide derivatives as capsid assembly modulators inhibiting HBV in vitro and in HBV-transgenic mice

The hepatitis B virus (HBV) capsid assembly modulators (CAMs) have been developed as effective anti-HBV agents in the treatment of chronic HBV infection by targeting the HBV core protein and inducing the formation of aberrant or morphologically normal capsid. However, some CAMs have been observed adverse events such as ALT flares and rash. Therefore, finding new CAMs is of great importance. In this report, we synthesized N-sulfonylpiperidine-3-carboxamides (SPCs) derivatives and evaluated their anti-HBV activities. Among the SPC derivatives, compound C-49 notably suppressed HBV replication in HepAD38, HepG2-HBV1.3 and HepG2-NTCP cells. Moreover, treatment with C-49 for 12 days exhibited potent anti-HBV activity (100 mg/kg; 2.42 log reduction of serum HBV DNA) in HBV-transgenic mice without apparent hepatotoxicity. Our findings provided a new SPC derivative as HBV capsid assembly modulator for developing safe and efficient anti-HBV therapy.

Pharmacophore-Based Virtual Screening and Structural Modification of Novel Benzamide Derivatives as HBV Capsid Assembly Modulators

Hepatitis B virus (HBV) infection is the most common cause of death from liver disease worldwide. The use of capsid assembly modulators is considered a prominent strategy for the development of novel anti-HBV therapies. We performed a pharmacophore-based virtual screening strategy, and a benzamide scaffold hit, WAI-5, was chosen for further structural optimization. A series of novel HBV capsid assembly modulators (CAMs) were found. Compared with the lead hit, the representative compounds 11g and 11n exhibited a 10-fold increase in anti-HBV activity with 50% effective concentration (EC50) values of 1.74 and 1.90 µM, respectively.

Hepatitis B x (HBx) as a Component of a Functional Cure for Chronic Hepatitis B

Patients who are carriers of the hepatitis B virus (HBV) are at high risk of chronic liver disease (CLD) which proceeds from hepatitis, to fibrosis, cirrhosis and to hepatocellular carcinoma (HCC). The hepatitis B-encoded X antigen, HBx, promotes virus gene expression and replication, protects infected hepatocytes from immunological destruction, and promotes the development of CLD and HCC. For virus replication, HBx regulates covalently closed circular (ccc) HBV DNA transcription, while for CLD, HBx triggers cellular oxidative stress, in part, by triggering mitochondrial damage that stimulates innate immunity. Constitutive activation of NF-κB by HBx transcriptionally activates pro-inflammatory genes, resulting in hepatocellular destruction, regeneration, and increased integration of the HBx gene into the host genome. NF-κB is also hepatoprotective, which sustains the survival of infected cells. Multiple therapeutic approaches include direct-acting anti-viral compounds and immune-stimulating drugs, but functional cures were not achieved, in part, because none were yet devised to target HBx. In addition, many patients with cirrhosis or HCC have little or no virus replication, but continue to express HBx from integrated templates, suggesting that HBx contributes to the pathogenesis of CLD. Blocking HBx activity will, therefore, impact multiple aspects of the host–virus relationship that are relevant to achieving a functional cure.

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.

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.

Identification of hepatitis B virus core protein residues critical for capsid assembly, pgRNA encapsidation and resistance to capsid assembly modulators

Assembly of hepatitis B virus (HBV) capsids is driven by the hydrophobic interaction of core protein (Cp) at dimer-dimer interface. Binding of core protein allosteric modulators (CpAMs) to a hydrophobic "HAP" pocket formed between the inter-dimer interface strengths the dimer-dimer interaction and misdirects the assembly of Cp dimers into non-capsid Cp polymers or morphologically normal capsids devoid of viral pregenomic (pg) RNA and DNA polymerase. In this study, we performed a systematic mutagenesis analysis to identify Cp amino acid residues at Cp dimer-dimer interface that are critical for capsid assembly, pgRNA encapsidation and resistance to CpAMs. By analyzing 70 mutant Cp with a single amino acid substitution of 25 amino acid residues around the HAP pocket, our study revealed that residue W102 and Y132 are critical for capsid assembly. However, substitution of many other residues did not significantly alter the amount of capsids, but reduced the amount of encapsidated pgRNA, suggesting their critical roles in pgRNA packaging. Interestingly, several mutant Cp with a single amino acid substitution of residue P25, T33 or I105 supported high levels of DNA replication, but conferred strong resistance to multiple chemotypes of CpAMs. In addition, we also found that WT Cp, but not the assembly incompetent Cp, such as Y132A Cp, interacted with HBV DNA polymerase (Pol). This later finding implies that encapsidation of viral DNA polymerase may depend on the interaction of Pol with a capsid assembly intermediate, but not free Cp dimers. Taking together, our findings reported herein shed new light on the mechanism of HBV nucleocapsid assembly and mode of CpAM action.

A putative amphipathic alpha helix in hepatitis B virus small envelope protein plays a critical role in the morphogenesis of subviral particles

Hepatitis B virus (HBV) small (S) envelope protein has the intrinsic ability to direct the formation of small spherical subviral particles (SVPs) in eukaryotic cells. However, the molecular mechanism underlying the morphogenesis of SVPs from the monomeric S protein initially synthesized at the endoplasmic reticulum (ER) membrane remains largely elusive. Structure prediction and extensive mutagenesis analysis suggested that the amino acid residues spanning W156 to R169 of S protein form an amphipathic alpha helix and play essential roles in SVP production and S protein metabolic stability. Further biochemical analyses showed that the putative amphipathic alpha helix was not required for the disulfide-linked S protein oligomerization, but was essential for SVP morphogenesis. Pharmacological disruption of vesicle trafficking between the ER and Golgi complex in SVP producing cells supported the hypothesis that S protein-directed SVP morphogenesis takes place at the ER-Golgi intermediate compartment (ERGIC). Moreover, it was demonstrated that S protein is degraded in hepatocytes via a 20S proteasome-dependent, but ubiquitination-independent non-classic ER-associated degradation (ERAD) pathway. Taken together, the results reported herein favor a model in which the amphipathic alpha helix at the antigenic loop of S protein attaches to the lumen leaflet to facilitate SVP budding from the ERGIC compartment, whereas the failure of budding process may result in S protein degradation by 20S proteasome in an ubiquitination-independent manner.Importance Subviral particles are the predominant viral product produced by HBV-infected hepatocytes. Their levels exceed the virion particles by 10,000 to 100,000-fold in the blood of HBV infected individuals. The high levels of SVPs, or HBV surface antigen (HBsAg), in the circulation induces immune tolerance and contributes to the establishment of persistent HBV infection. The loss of HBsAg, often accompanied by appearance of anti-HBs antibodies, is the hallmark of durable immune control of HBV infection. Therapeutic induction of HBsAg loss is, therefore, considered to be essential for the restoration of host antiviral immune response and functional cure of chronic hepatitis B. Our findings on the mechanism of SVP morphogenesis and S protein metabolism will facilitate the rational discovery and development of antiviral drugs to achieve this therapeutic goal.

A mid-throughput HBV replication inhibition assay capable of detecting ribonuclease H inhibitors

The hepatitis B virus (HBV) ribonuclease H (RNaseH) is a promising but unexploited drug target. Inhibiting the RNaseH blocks viral reverse transcription by truncating the minus-polarity DNA strand, causing accumulation of RNA:DNA heteroduplexes, and abrogating plus-polarity DNA synthesis. Screening for RNaseH inhibitors is complicated by the presence of the minus-polarity DNA strand even when replication is fully inhibited because this residual DNA can be detected by standard screening assays that measure reduction in total HBV DNA accumulation. We previously developed a strand-preferential qPCR assay that detects RNaseH replication inhibitors by measuring preferential suppression of the viral plus-polarity DNA strand. However, this assay employed cells grown in 6- or 12-well plates and hence was of very low throughput. Here, we adapted the assay to a 96-well format and conducted a proof-of-principle screen of 727 compounds. The newly developed assay is a valuable tool for anti-HBV drug discovery, particularly when screening for RNaseH inhibitors.

Suppression of hepatitis B virus through therapeutic activation of RIG-I and IRF3 signaling in hepatocytes

Hepatitis B virus (HBV) mediates persistent infection, chronic hepatitis, and liver disease. HBV covalently closed circular (ccc)DNA is central to viral persistence such that its elimination is considered the cornerstone for HBV cure. Inefficient detection by pathogen recognition receptors (PRRs) in the infected hepatocyte facilitates HBV persistence via avoidance of innate immune activation and interferon regulatory factor (IRF)3 induction of antiviral gene expression. We evaluated a small molecule compound, F7, and 5'-triphosphate-poly-U/UC pathogen-associated-molecular-pattern (PAMP) RNA agonists of RIG-I, a PRR that signals innate immunity, for ability to suppress cccDNA. F7 and poly-U/UC PAMP treatment of HBV-infected cells induced RIG-I signaling of IRF3 activation to induce antiviral genes for suppression of cccDNA formation and accelerated decay of established cccDNA, and were additive to the actions of entecavir. Our study shows that activation of the RIG-I pathway and IRF3 to induce innate immune actions offers therapeutic benefit toward elimination of cccDNA.

Synthesis and Bioactivity of N-(4-Chlorophenyl)-4-Methoxy-3-(Methylamino) Benzamide as a Potential Anti-HBV Agent

Introduction

Hepatitis B virus (HBV) is a global health concern that can cause acute and chronic liver diseases. Thus, there is an urgent need to research novel anti-HBV agents. Our previous reports show that N-phenylbenzamide derivatives exert broad-spectrum antiviral effects against HIV-1, HCV, and EV71 by increasing intracellular levels of APOBEC3G (A3G). As A3G is capable of inhibiting the replication of HBV, we screened the N-phenylbenzamide derivatives against HBV.

Methods

In this study, a new derivative, N-(4-chlorophenyl)-4-methoxy-3-(methylamino) benzamide (IMB-0523), was synthesized and its anti-HBV activity was evaluated in vitro and in vivo. The acute toxicity and pharmacokinetic profiles of IMB-0523 were also investigated.

Results

Our results show that IMB-0523 has higher anti-HBV activity in both wild-type HBV (IC₅₀: 1.99 µM) and drug-resistant HBV (IC₅₀: 3.30 µM) than lamivudine (3TC, IC₅₀: 7.37 µM in wild-type HBV, IC₅₀: >440 µM in drug-resistant HBV). The antiviral effect of IMB-0523 against HBV may be due to an increased level of intracellular A3G. IMB-0523 also showed low acute toxicity (LD₅₀: 448 mg/kg) in mice and promising PK properties (AUC_0-t: 7535.10±2226.73 µg·h/L) in rats. Further, IMB-0523 showed potent anti-HBV activity in DHBV-infected ducks.

Conclusion

Thus, IMB-0523 may be a potential anti-HBV agent with different mechanisms than current anti-HBV treatment options.

Targeting the multifunctional HBV core protein as a potential cure for chronic hepatitis B

The core (capsid) protein of hepatitis B virus (HBV) is the building block of nucleocapsids where viral DNA reverse transcriptional replication takes place and mediates virus-host cell interaction important for the persistence of HBV infection. The pleiotropic role of core protein (Cp) in HBV replication makes it an attractive target for antiviral therapies of chronic hepatitis B, a disease that affects more than 257 million people worldwide without a cure. Recent clinical studies indicate that core protein allosteric modulators (CpAMs) have a great promise as a key component of hepatitis B curative therapies. Particularly, it has been demonstrated that modulation of Cp dimer-dimer interactions by several chemical series of CpAMs not only inhibit nucleocapsid assembly and viral DNA replication, but also induce the disassembly of double-stranded DNA-containing nucleocapsids to prevent the synthesis of cccDNA. Moreover, the different chemotypes of CpAMs modulate Cp assembly by interaction with distinct amino acid residues at the HAP pocket between Cp dimer-dimer interfaces, which results in the assembly of Cp dimers into either non-capsid Cp polymers (type I CpAMs) or empty capsids with distinct physical property (type II CpAMs). The different CpAMs also differentially modulate Cp metabolism and subcellular distribution, which may impact cccDNA metabolism and host antiviral immune responses, the critical factors for the cure of chronic HBV infection. This review article highlights the recent research progress on the structure and function of core protein in HBV replication cycle, the mode of action of CpAMs, as well as the current status and perspectives on the discovery and development of core protein-targeting antivirals. This article forms part of a symposium in Antiviral Research on "Wide-ranging immune and direct-acting antiviral approaches to curing HBV and HDV infections."

Current practice and contrasting views on discontinuation of nucleos(t)ide analog therapy in chronic hepatitis B

Introduction: Long-term, even indefinite treatment with nucleos(t)ide analogs (NAs) is the current first-line therapy for patients with chronic hepatitis B (CHB), regardless of its histological stage. Guidelines and recommendations on duration and endpoints of NA therapy in CHB are not identical and change over time.Areas covered: The authors review NA discontinuation approaches and views with an emphasis on HBeAg-negative patients based on published studies relevant to the topic, stressing on whether or not the optimal endpoint of HBsAg loss is practically achievable.Expert opinion: Discontinuation of NA therapy in HBeAg-negative noncirrhotic patients has to be considered after long-term effective treatment with controlled liver disease activity, undetectable viremia, and significant decline in serum HBsAg titers. Close post-treatment monitoring is required for early intervention in cases of severe clinical relapse. Immediate retreatment hampers the favorable outcome of HBsAg clearance (functional cure) and should be avoided in transient ALT flares. Predictors of such relapses are still under investigation and include viral and patient factors. For HBeAg-positive noncirrhotic patients, there is wide acceptance of the endpoint of HBeAg seroconversion, after a long consolidation period.

Obstacles and opportunities in the prevention and treatment of HBV-related hepatocellular carcinoma

Despite the tremendous progresses toward our understanding of the mechanisms of how liver cancer was developed, the therapeutic outcomes of liver cancer in the clinic have very limited improvement within the past three decades or so. In addition, both the incidence and mortality of liver cancer worldwide are not dropping, but increasing steadily, in the last decade. Thus, it is time for us to rethink what has been wrong and how could we do better in the upcoming years, in order to achieve our goal of improving the therapeutic outcomes of patients with liver cancer in the clinic, and at the meantime, effectively reducing the incidence of liver cancer by blocking malignant transformation of hepatocytes from chronic viral infection. This is also one of the main reasons why we try to organize this special issue on primary liver cancer in the journal of Genes & Diseases. In this perspective, I will summarize the major obstacles confronted with in the prevention and management of patients with chronic hepatitis B infection and subsequent development of liver cirrhosis and liver cancer. Next, I will delineate the pitfalls and underlying mechanisms of why the current anti-viral strategies and therapeutic agents are not as effective as one expected in terms of successful reduction or prevention chronic hepatitis B infection associated liver cirrhosis and liver cancer. I will then provide my personal perspectives on potential approaches and strategies for effective prevention and management of hepatitis B-related liver cancer.

A Broad Application of CRISPR Cas9 in Infectious Diseases of Central Nervous System

Virus-induced diseases or neurological complications are huge socio-economic burden to human health globally. The complexity of viral-mediated CNS pathology is exacerbated by reemergence of new pathogenic neurotropic viruses of high public relevance. Although the central nervous system is considered as an immune privileged organ and is mainly protected by barrier system, there are a vast majority of neurotropic viruses capable of gaining access and cause diseases. Despite continued growth of the patient population and a number of treatment strategies, there is no successful viral specific therapy available for viral induced CNS diseases. Therefore, there is an urgent need for a clear alternative treatment strategy that can effectively target neurotropic viruses of DNA or RNA genome. To address this need, rapidly growing gene editing technology based on CRISPR/Cas9, provides unprecedented control over viral genome editing and will be an effective, highly specific and versatile tool for targeting CNS viral infection. In this review, we discuss the application of this system to control CNS viral infection and associated neurological disorders and future prospects. Graphical Abstract CRISPR/Cas9 technology as agent control over CNS viral infection.

Distinct dual antiviral mechanism that enhances hepatitis B virus mutagenesis and reduces viral DNA synthesis

Reverse transcriptase (RT) is an essential enzyme for the replication of retroviruses and hepadnaviruses. Current therapies do not eliminate the intracellular viral replication intermediate termed covalently closed circular (ccc) DNA, which has enhanced interest in hepatitis B virus (HBV) reverse transcription and cccDNA formation. The HBV cccDNA is generated as a plasmid-like episome in the host cell nucleus from the protein-linked relaxed circular (rc) DNA genome in incoming virions during HBV replication. The creation of the cccDNA via conversion from rcDNA remains not fully understood. Here, we sought to investigate whether viral mutagens can effect HBV replication. In particular, we investigated whether nucleoside analogs that act as viral mutagens with retroviruses could impact hepadnaviral DNA synthesis. We observed that a viral mutagen (e.g., 5-aza-2'-deoxycytidine, 5-aza-dC or 5-azacytidine, 5-aza-C) severely diminished the ability of a HBV vector to express a reporter gene following virus transfer and infection of target cells. As predicted, the treatment of 5-aza-dC or 5-aza-C elevated the HBV rcDNA mutation frequency, primarily by increasing the frequency of G-to-C transversion mutations. A reduction in rcDNA synthesis was also observed. Intriguingly, the cccDNA nick/gap region transcription was diminished by 5-aza-dC, but did not enhance viral mutagenesis. Taken together, our results demonstrate that viral mutagens can impact HBV reverse transcription, and propose a model in which viral mutagens can induce mutagenesis during rcDNA formation and diminish viral DNA synthesis during both rcDNA formation and the conversion of rcDNA to cccDNA.

Current perspectives into the evaluation and management of hepatitis B: a review

Hepatitis B is a widespread disease which affects millions of people worldwide. Chronic hepatitis B (CHB) can lead to significant morbidity and mortality due to complications such as cirrhosis and hepatocellular carcinoma. The pathophysiology of hepatitis is critical to diagnosing CHB. Deciding which patients with CHB should be treated is an important decision as treatment can often lead to better outcomes in the appropriate patient population. The nucleos(t)ide analog inhibitors entecavir and tenofovir are currently the mainstay of treatment as they are able to successfully suppress the virus and lead to fewer complications. Novel therapies are currently being developed which may offer a potential cure for this disease in the future.

Discovery and Mechanistic Study of a Novel Human-Stimulator-of-Interferon-Genes Agonist

Stimulator of interferon genes (STING) is an integral ER-membrane protein that can be activated by 2'3'-cGAMP synthesized by cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) upon binding of double-stranded DNA. It activates interferon (IFN) and inflammatory cytokine responses to defend against infection by microorganisms. Pharmacologic activation of STING has been demonstrated to induce an antiviral state and boost antitumor immunity. We previously reported a cell-based high-throughput-screening assay that allowed for identification of small-molecule cGAS-STING-pathway agonists. We report herein a compound, 6-bromo-N-(naphthalen-1-yl)benzo[d][1,3]dioxole-5-carboxamide (BNBC), that induces a proinflammatory cytokine response in a human-STING-dependent manner. Specifically, we showed that BNBC induced type I and III IFN dominant cytokine responses in primary human fibroblasts and peripheral-blood mononuclear cells (PBMCs). BNBC also induced cytokine response in PBMC-derived myeloid dendritic cells and promoted their maturation, suggesting that STING-agonist treatment could potentially regulate the activation of CD4+ and CD8+ T lymphocytes. As anticipated, treatment of primary human fibroblast cells with BNBC induced an antiviral state that inhibited the infection of several kinds of flaviviruses. Taken together, our results indicate that BNBC is a human-STING agonist that not only induces innate antiviral immunity against a broad spectrum of viruses but may also stimulate the activation of adaptive immune responses, which is important for the treatment of chronic viral infections and tumors.

Design, Synthesis, and Anti-HBV Activity of New Bis(l-amino acid) Ester Tenofovir Prodrugs

A series of bis(l-amino acid) ester prodrugs of tenofovir (TFV) were designed and synthesized as new anti-HBV agents in this work. Four compounds 11, 12a, 12d, and 13b displayed better anti-HBV activity (IC₅₀: 0.71-4.22 μM) than the parent drug TFV. The most active compound 11 (IC₅₀: 0.71 μM), a bis(l-valine) ester prodrug of TFV, was found to have obviously greater AUC_0-∞, C _max, and F% than tenofovir disoproxil fumarate (TDF), and potent in vivo efficacy which is not inferior to TDF in a duck HBV (DHBV) model and a HBV DNA hydrodynamic mouse model, and it may serve as a promising lead compound for further anti-HBV drug discovery.

Cellular DNA Topoisomerases Are Required for the Synthesis of Hepatitis B Virus Covalently Closed Circular DNA

In order to identify host cellular DNA metabolic enzymes that are involved in the biosynthesis of hepatitis B virus (HBV) covalently closed circular (ccc) DNA, we developed a cell-based assay supporting synchronized and rapid cccDNA synthesis from intracellular progeny nucleocapsid DNA. This was achieved by arresting HBV DNA replication in HepAD38 cells with phosphonoformic acid (PFA), a reversible HBV DNA polymerase inhibitor, at the stage of single-stranded DNA and was followed by removal of PFA to allow the synchronized synthesis of relaxed circular DNA (rcDNA) and subsequent conversion into cccDNA within 12 to 24 h. This cccDNA formation assay allows systematic screening of the effects of small molecular inhibitors of DNA metabolic enzymes on cccDNA synthesis but avoids cytotoxic effects upon long-term treatment. Using this assay, we found that all the tested topoisomerase I and II (TOP1 and TOP2, respectively) poisons as well as topoisomerase II DNA binding and ATPase inhibitors significantly reduced the levels of cccDNA. It was further demonstrated that these inhibitors also disrupted cccDNA synthesis during de novo HBV infection of HepG2 cells expressing sodium taurocholate cotransporting polypeptide (NTCP). Mechanistic analyses indicate that whereas TOP1 inhibitor treatment prevented the production of covalently closed negative-strand rcDNA, TOP2 inhibitors reduced the production of this cccDNA synthesis intermediate to a lesser extent. Moreover, small interfering RNA (siRNA) knockdown of topoisomerase II significantly reduced cccDNA amplification. Taking these observations together, our study demonstrates that topoisomerase I and II may catalyze distinct steps of HBV cccDNA synthesis and that pharmacologic targeting of these cellular enzymes may facilitate the cure of chronic hepatitis B.IMPORTANCE Persistent HBV infection relies on stable maintenance and proper functioning of a nuclear episomal form of the viral genome called cccDNA, the most stable HBV replication intermediate. One of the major reasons for the failure of currently available antiviral therapeutics to cure chronic HBV infection is their inability to eradicate or inactivate cccDNA. We report here a chemical genetics approach to identify host cellular factors essential for the biosynthesis and maintenance of cccDNA and reveal that cellular DNA topoisomerases are required for both de novo synthesis and intracellular amplification of cccDNA. This approach is suitable for systematic screening of compounds targeting cellular DNA metabolic enzymes and chromatin remodelers for their ability to disrupt cccDNA biosynthesis and function. Identification of key host factors required for cccDNA metabolism and function will reveal molecular targets for developing curative therapeutics of chronic HBV infection.

Virological Basis for the Cure of Chronic Hepatitis B

Hepatitis B virus (HBV) has infected one-third of world population, and 240 million people are chronic carriers, to whom a curative therapy is still not available. Similar to other viruses, persistent HBV infection relies on the virus to exploit host cell functions to support its replication and efficiently evade host innate and adaptive antiviral immunity. Understanding HBV replication and concomitant host cell interactions is thus instrumental for development of therapeutics to disrupt the virus-host interactions critical for its persistence and cure chronic hepatitis B. Although the currently available cell culture systems of HBV infection are refractory to genome-wide high throughput screening of key host cellular factors essential for and/or regulating HBV replication, classic one-gene (or pathway)-at-a-time studies in the last several decades have already revealed many aspects of HBV-host interactions. An overview of the landscape of HBV-hepatocyte interaction indicates that, in addition to more tightly suppressing viral replication by directly targeting viral proteins, disruption of key viral-host cell interactions to eliminate or inactivate the covalently closed circular (ccc) DNA, the most stable HBV replication intermediate that exists as an episomal minichromosome in the nucleus of infected hepatocyte, is essential to achieve a functional cure of chronic hepatitis B. Moreover, therapeutic targeting of integrated HBV DNA and their transcripts may also be required to induce hepatitis B virus surface antigen (HBsAg) seroclearance and prevent liver carcinogenesis.

Discovery of Novel Hepatitis B Virus Nucleocapsid Assembly Inhibitors

Hepatitis B virus (HBV) core protein is a small protein with 183 amino acid residues and assembles the pregenomic (pg) RNA and viral DNA polymerase to form nucleocapsids. During the last decades, several groups have reported HBV core protein allosteric modulators (CpAMs) with distinct chemical structures. CpAMs bind to the hydrophobic HAP pocket located at the dimer-dimer interface and induce allosteric conformational changes in the core protein subunits. While Type I CpAMs, heteroaryldihydropyrimidine (HAP) derivatives, misdirect core protein dimers to assemble noncapsid polymers, Type II CpAMs, represented by sulfamoylbenzamides, phenylpropenamides, and several other chemotypes, induce the assembly of empty capsids with global structural alterations and faster mobility in native agarose gel electrophoresis. Through high throughput screening of an Asinex small molecule library containing 19 920 compounds, we identified 8 structurally distinct CpAMs. While 7 of those compounds are typical Type II CpAMs, a novel benzamide derivative, designated as BA-53038B, induced the formation of morphologically "normal" empty capsids with slow electrophoresis mobility. Drug resistant profile analyses indicated that BA-53038B most likely bound to the HAP pocket but obviously modulated HBV capsid assembly in a distinct manner. BA-53038B and other CpAMs reported herein provide novel structure scaffolds for the development of core protein-targeted antiviral agents for the treatment of chronic hepatitis B.

Current and emerging therapies to combat persistent intracellular pathogens

Intracellular pathogens such as HIV, hepatitis B virus, and Mycobacterium tuberculosis are responsible for millions of deaths worldwide and represent major obstacles to global health. Current treatment options have improved patient outcomes and extended life-expectancy in many countries; however, challenges such as latency, drug-resistance, and inflammatory pathology have necessitated advancements in curative strategies which go beyond the traditional antimicrobial focus. This review highlights recent advances in host-directed therapies to eradicate intracellular pathogens or augment the endogenous immune response by targeting host cell pathways. The 'kick and kill' strategy for HIV latency, adjunct immunomodulatory compounds for tuberculosis, and pro-apoptotic small-molecule inhibitors in the case of chronic Hepatitis B are promising examples of host-directed therapies that signal a paradigm shift in treatment and management of chronic infectious disease.

DNA Polymerase alpha is essential for intracellular amplification of hepatitis B virus covalently closed circular DNA

Persistent hepatitis B virus (HBV) infection relies on the establishment and maintenance of covalently closed circular (ccc) DNA, a 3.2 kb episome that serves as a viral transcription template, in the nucleus of an infected hepatocyte. Although evidence suggests that cccDNA is the repair product of nucleocapsid associated relaxed circular (rc) DNA, the cellular DNA polymerases involving in repairing the discontinuity in both strands of rcDNA as well as the underlying mechanism remain to be fully understood. Taking a chemical genetics approach, we found that DNA polymerase alpha (Pol α) is essential for cccDNA intracellular amplification, a genome recycling pathway that maintains a stable cccDNA pool in infected hepatocytes. Specifically, inhibition of Pol α by small molecule inhibitors aphidicolin or CD437 as well as silencing of Pol α expression by siRNA led to suppression of cccDNA amplification in human hepatoma cells. CRISPR-Cas9 knock-in of a CD437-resistant mutation into Pol α genes completely abolished the effect of CD437 on cccDNA formation, indicating that CD437 directly targets Pol α to disrupt cccDNA biosynthesis. Mechanistically, Pol α is recruited to HBV rcDNA and required for the generation of minus strand covalently closed circular rcDNA, suggesting that Pol α is involved in the repair of the minus strand DNA nick in cccDNA synthesis. Our study thus reveals that the distinct host DNA polymerases are hijacked by HBV to support the biosynthesis of cccDNA from intracellular amplification pathway compared to that from de novo viral infection, which requires Pol κ and Pol λ.

CCC DNA is the most refractory HBV replication intermediate under long-term antiviral therapies and is responsible for the viral rebound after treatment cessation. Therefore, understanding the biosynthesis and maintenance of cccDNA minichromosome is crucial for the development of novel antiviral therapeutics to cure chronic HBV infection. Although it has been clearly demonstrated that cccDNA biosynthesis relies on host cellular DNA repair machinery, the molecular pathways that convert rcDNA into cccDNA remain to be identified. Here we report that DNA polymerase alpha (Pol α) as well as Pol δ and ɛ are required for converting rcDNA into cccDNA through intracellular cccDNA amplification. This finding adds novel molecular insights on cccDNA biosynthesis. Further understanding the mechanism of cccDNA synthesis should reveal molecular targets for developing therapeutic agents to eradicate cccDNA and cure chronic hepatitis B.

5-Aminothiophene-2,4-dicarboxamide analogues as hepatitis B virus capsid assembly effectors

Chronic hepatitis B virus (HBV) infection represents a major health threat. Current FDA-approved drugs do not cure HBV. Targeting HBV core protein (Cp) provides an attractive approach toward HBV inhibition and possibly infection cure. We have previously identified and characterized a 5-amino-3-methylthiophene-2,4-dicarboxamide (ATDC) compound as a structurally novel hit for capsid assembly effectors (CAEs). We report herein hit validation through studies on absorption, distribution, metabolism and excretion (ADME) properties and pharmacokinetics (PK), and hit optimization via analogue synthesis aiming to probe the structure-activity relationship (SAR) and structure-property relationship (SPR). In the end, these medicinal chemistry efforts led to the identification of multiple analogues strongly binding to Cp, potently inhibiting HBV replication in nanomolar range without cytotoxicity, and exhibiting good oral bioavailability (F). Two of our analogues, 19o (EC50 = 0.11 μM, CC50 > 100 μM, F = 25%) and 19k (EC50 = 0.31 μM, CC50 > 100 μM, F = 46%), displayed overall lead profiles superior to reported CAEs 7-10 used in our studies.

CpAMs induce assembly of HBV capsids with altered electrophoresis mobility: Implications for mechanism of inhibiting pgRNA packaging

Native agarose gel electrophoresis-based particle gel assay has been commonly used for examination of hepatitis B virus (HBV) capsid assembly and pregenomic RNA encapsidation in HBV replicating cells. Interestingly, treatment of cells with several chemotypes of HBV core protein allosteric modulators (CpAMs) induced the assembly of both empty and DNA-containing capsids with faster electrophoresis mobility. In an effort to determine the physical basis of CpAM-induced capsid mobility shift, we found that the surface charge, but not the size, of capsids is the primary determinant of electrophoresis mobility. Specifically, through alanine scanning mutagenesis analysis of twenty-seven charged amino acids in core protein assembly domain and hinge region, we showed that except for K7 and E8, substitution of glutamine acid (E) or aspartic acid (D) on the surface of capsids reduced their mobility, but substitution of lysine (K) or arginine (R) on the surface of capsids increased their mobility in variable degrees. However, alanine substitution of the charged amino acids that are not exposed on the surface of capsid did not apparently alter capsid mobility. Hence, CpAM-induced electrophoresis mobility shift of capsids may reflect the global alteration of capsid structure that changes the exposure and/or ionization of charged amino acid side chains of core protein. Our findings imply that CpAM inhibition of pgRNA encapsidation is possibly due to the assembly of structurally altered nucleocapsids. Practically, capsid electrophoresis mobility shift is a diagnostic marker of compounds that target core protein assembly and predicts sensitivity of HBV strains to specific CpAMs.

Hepatitis B Virus Core Protein Dephosphorylation Occurs during Pregenomic RNA Encapsidation

Hepatitis B virus (HBV) core protein consists of an N-terminal assembly domain and a C-terminal domain (CTD) with seven conserved serines or threonines that are dynamically phosphorylated/dephosphorylated during the viral replication cycle. Sulfamoylbenzamide derivatives are small molecular core protein allosteric modulators (CpAMs) that bind to the heteroaryldihydropyrimidine (HAP) pocket between the core protein dimer-dimer interfaces. CpAM binding alters the kinetics and pathway of capsid assembly and can result in the formation of morphologically "normal" capsids devoid of viral pregenomic RNA (pgRNA) and DNA polymerase. In order to investigate the mechanism underlying CpAM inhibition of pgRNA encapsidation, we developed an immunoblotting assay that can resolve core protein based on its phosphorylation status and demonstrated, for the first time, that core protein is hyperphosphorylated in free dimers and empty capsids from both mock-treated and CpAM-treated cells but is hypophosphorylated in pgRNA- and DNA-containing nucleocapsids. Interestingly, inhibition of pgRNA encapsidation by a heat shock protein 90 (HSP90) inhibitor prevented core protein dephosphorylation. Moreover, core proteins with point mutations at the wall of the HAP pocket, V124A and V124W, assembled empty capsids and nucleocapsids with altered phosphorylation status. The results thus suggest that core protein dephosphorylation occurs in the assembly of pgRNA and that interference with the interaction between core protein subunits at dimer-dimer interfaces during nucleocapsid assembly alters not only capsid structure, but also core protein dephosphorylation. Hence, inhibition of pgRNA encapsidation by CpAMs might be due to disruption of core protein dephosphorylation during nucleocapsid assembly.IMPORTANCE Dynamic phosphorylation of HBV core protein regulates multiple steps of viral replication. However, the regulatory function was mainly investigated by phosphomimetic mutagenesis, which disrupts the natural dynamics of core protein phosphorylation/dephosphorylation. Development of an immunoblotting assay capable of resolving hyper- and hypophosphorylated core proteins allowed us to track the phosphorylation status of core proteins existing as free dimers and the variety of intracellular capsids and to investigate the role of core protein phosphorylation/dephosphorylation in viral replication. Here, we found that disruption of core protein interaction at dimer-dimer interfaces during nucleocapsid assembly (by CpAMs or mutagenesis) inhibited core protein dephosphorylation and pgRNA packaging. Our work has thus revealed a novel function of core protein dephosphorylation in HBV replication and the mechanism by which CpAMs, a class of compounds that are currently in clinical trials for treatment of chronic hepatitis B, induce the assembly of empty capsids.

Preclinical Profile of AB-423, an Inhibitor of Hepatitis B Virus Pregenomic RNA Encapsidation

AB-423 is a member of the sulfamoylbenzamide (SBA) class of hepatitis B virus (HBV) capsid inhibitors in phase 1 clinical trials. In cell culture models, AB-423 showed potent inhibition of HBV replication (50% effective concentration [EC₅₀] = 0.08 to 0.27 μM; EC₉₀ = 0.33 to 1.32 μM) with no significant cytotoxicity (50% cytotoxic concentration > 10 μM). Addition of 40% human serum resulted in a 5-fold increase in the EC₅₀s. AB-423 inhibited HBV genotypes A through D and nucleos(t)ide-resistant variants in vitro Treatment of HepDES19 cells with AB-423 resulted in capsid particles devoid of encapsidated pregenomic RNA and relaxed circular DNA (rcDNA), indicating that it is a class II capsid inhibitor. In a de novo infection model, AB-423 prevented the conversion of encapsidated rcDNA to covalently closed circular DNA, presumably by interfering with the capsid uncoating process. Molecular docking of AB-423 into crystal structures of heteroaryldihydropyrimidines and an SBA and biochemical studies suggest that AB-423 likely also binds to the dimer-dimer interface of core protein. In vitro dual combination studies with AB-423 and anti-HBV agents, such as nucleos(t)ide analogs, RNA interference agents, or interferon alpha, resulted in additive to synergistic antiviral activity. Pharmacokinetic studies with AB-423 in CD-1 mice showed significant systemic exposures and higher levels of accumulation in the liver. A 7-day twice-daily administration of AB-423 in a hydrodynamic injection mouse model of HBV infection resulted in a dose-dependent reduction in serum HBV DNA levels, and combination with entecavir or ARB-1467 resulted in a trend toward antiviral activity greater than that of either agent alone, consistent with the results of the in vitro combination studies. The overall preclinical profile of AB-423 supports its further evaluation for safety, pharmacokinetics, and antiviral activity in patients with chronic hepatitis B.

The immune response of rhesus macaques to novel vaccines comprising hepatitis B virus S, PreS1, and Core antigens

Therapeutic vaccines represent a unique approach to hepatitis B virus (HBV) treatment and have the potential to induce long-term control of infection. This study explored the immune responses of rhesus macaques to novel vaccines comprising the S, PreS1, and Core antigens of the HBV that showed promise as prophylactic and therapeutic approaches in a mouse model. The tested vaccines included two DNA vaccines (pVRC-SS1, pVRC-CS1), an HBV particle subunit (HBSS1) vaccine and the recombinant vaccinia virus- (RVJ-) based vaccines (RVJSS1 and RVJCS1) in which SS1 containing S (1-223 aa) and PreS1 (21-47 aa), CS1 containing Core (1-144 aa) and PreS1 (1-42 aa). The humoral immunity and cell-mediated immunity (CMI) induced by vaccines comprising the S, PreS1, and Core antigens of HBV were investigated in a longitudinal study that continued up to 98 weeks after the firstvaccination. In rhesus macaques, anti-PreS1 antibody was induced more rapidly than anti-S or anti-Core antibody after DNA vaccination. The antibody and cell-mediated immune responses against S, PreS1, and C were significantly enhanced in macaques boosted with RVJSS1 and RVJCS1, whereas the cell-mediated response to C was most robust and durable. The immune response to S, PreS1, and C was restored by HBSS1 boosting and detected in macaques until weeks 74 and 98 after the first vaccination. Additionally, robust neutralizing activity was detected at week 52. In conclusion, novel HBV vaccine candidates, especially those used for therapeutic applications should incorporate the PreS1 and Core antigens.

Current advances in the elimination of hepatitis B in China by 2030

With its 78 million chronic carriers, hepatitis B virus (HBV) infection is still one of the leading public health challenges in China. Over the last two decades, China has made great progress on the prevention of HBV transmission through national vaccination programs. Zero transmission from mother to infant has been proposed as the current goal. Available anti-HBV therapy is efficacious in suppressing HBV replication; however, it fails to completely cure patients with chronic hepatitis B and even requires lifelong treatment. To reduce the costs and improve the efficacy, several trials have been recently conducted in China to optimize the current anti-HBV managements. Novel biomarkers were identified to predict treatment outcomes, and new promising treatment strategies were developed. Reports also indicate that coinfections of HBV with other hepatotropic viruses and human immunodeficiency virus are common in China and cause severe liver diseases, which should be recognized early and treated properly. Work is still needed to eliminate hepatitis B in China by 2030.

HBV core protein allosteric modulators differentially alter cccDNA biosynthesis from de novo infection and intracellular amplification pathways

Hepatitis B virus (HBV) core protein assembles viral pre-genomic (pg) RNA and DNA polymerase into nucleocapsids for reverse transcriptional DNA replication to take place. Several chemotypes of small molecules, including heteroaryldihydropyrimidines (HAPs) and sulfamoylbenzamides (SBAs), have been discovered to allosterically modulate core protein structure and consequentially alter the kinetics and pathway of core protein assembly, resulting in formation of irregularly-shaped core protein aggregates or “empty” capsids devoid of pre-genomic RNA and viral DNA polymerase. Interestingly, in addition to inhibiting nucleocapsid assembly and subsequent viral genome replication, we have now demonstrated that HAPs and SBAs differentially modulate the biosynthesis of covalently closed circular (ccc) DNA from de novo infection and intracellular amplification pathways by inducing disassembly of nucleocapsids derived from virions as well as double-stranded DNA-containing progeny nucleocapsids in the cytoplasm. Specifically, the mistimed cuing of nucleocapsid uncoating prevents cccDNA formation during de novo infection of hepatocytes, while transiently accelerating cccDNA synthesis from cytoplasmic progeny nucleocapsids. Our studies indicate that elongation of positive-stranded DNA induces structural changes of nucleocapsids, which confers ability of mature nucleocapsids to bind CpAMs and triggers its disassembly. Understanding the molecular mechanism underlying the dual effects of the core protein allosteric modulators on nucleocapsid assembly and disassembly will facilitate the discovery of novel core protein-targeting antiviral agents that can more efficiently suppress cccDNA synthesis and cure chronic hepatitis B.

Persistent HBV infection relies on stable maintenance of a nuclear episomal viral genome called covalently closed circular (ccc) DNA, the sole transcriptional template supporting viral replication. The currently available antiviral therapeutics fail to cure chronic HBV infection due to their failure to eradicate or inactivate cccDNA. In addition to packaging viral pregenomic (pg) RNA and DNA polymerase complex into nucleocapsids for reverse transcriptional DNA replication to take place, HBV core protein also participates in and regulates virion particle assembly, capsid uncoating and cccDNA formation. We report herein an intriguing observation that selected core protein allosteric modulators not only inhibit nucleocapsid assembly, but can also act on assembled, nucleus-bound nucleocapsids to promote their uncoating and consequentially interfere with cccDNA biosynthesis. This finding establishes molecular basis for development of novel core protein targeting antiviral agents with improved efficacy of suppressing cccDNA synthesis and curing chronic HBV infection.

Activation of Stimulator of Interferon Genes in Hepatocytes Suppresses the Replication of Hepatitis B Virus

Induction of interferon and proinflammatory cytokines is a hallmark of the infection of many different viruses. However, hepatitis B virus (HBV) does not elicit a detectable cytokine response in infected hepatocytes. In order to investigate the molecular mechanism underlying the innate immune evasion, a functional cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway was reconstituted in a human hepatoma cell line supporting tetracycline-inducible HBV replication. It was demonstrated that induction of HBV replication neither activated nor inhibited this cytosolic DNA sensing pathway. However, human hepatoma cells, as well as immortalized mouse hepatocytes, express low levels of STING, which upon activation by cGAMP, the natural ligand of STING, led to induction of a proinflammatory cytokine response. Treatment of immortalized mouse hepatocytes supporting HBV replication with either cGAMP or a small molecule pharmacologic STING agonist significantly reduced viral DNA in a STING- and Janus kinase 1-dependent manner. Moreover, cGAMP treatment was able to induce inflammatory cytokine gene expression and inhibit the transcription of covalently closed circular DNA in HBV-infected human hepatoma cells expressing sodium taurocholate cotransporting polypeptide, an essential receptor for HBV infection of hepatocytes. The studies reported here and previously (F. Guo et al., Antimicrob Agents Chemother 59:1273-1281, 2015, https://doi.org/10.1128/AAC.04321-14) thus support the notion that pharmacological activation of STING in macrophages and hepatocytes induces host innate responses that can efficiently control HBV replication. Hence, despite not playing a significant role in host innate immune response to HBV infection of hepatocytes, STING is potentially a valuable target for immunotherapy of chronic hepatitis B.

Discovery and Mechanistic Study of Benzamide Derivatives That Modulate Hepatitis B Virus Capsid Assembly

Chronic hepatitis B virus (HBV) infection is a global public health problem. Although the currently approved medications can reliably reduce the viral load and prevent the progression of liver diseases, they fail to cure the viral infection. In an effort toward discovery of novel antiviral agents against HBV, a group of benzamide (BA) derivatives that significantly reduced the amount of cytoplasmic HBV DNA were discovered. The initial lead optimization efforts identified two BA derivatives with improved antiviral activity for further mechanistic studies. Interestingly, similar to our previously reported sulfamoylbenzamides (SBAs), the BAs promote the formation of empty capsids through specific interaction with HBV core protein but not other viral and host cellular components. Genetic evidence suggested that both SBAs and BAs inhibited HBV nucleocapsid assembly by binding to the heteroaryldihydropyrimidine (HAP) pocket between core protein dimer-dimer interfaces. However, unlike SBAs, BA compounds uniquely induced the formation of empty capsids that migrated more slowly in native agarose gel electrophoresis from A36V mutant than from the wild-type core protein. Moreover, we showed that the assembly of chimeric capsids from wild-type and drug-resistant core proteins was susceptible to multiple capsid assembly modulators. Hence, HBV core protein is a dominant antiviral target that may suppress the selection of drug-resistant viruses during core protein-targeting antiviral therapy. Our studies thus indicate that BAs are a chemically and mechanistically unique type of HBV capsid assembly modulators and warranted for further development as antiviral agents against HBV.IMPORTANCE HBV core protein plays essential roles in many steps of the viral replication cycle. In addition to packaging viral pregenomic RNA (pgRNA) and DNA polymerase complex into nucleocapsids for reverse transcriptional DNA replication to take place, the core protein dimers, existing in several different quaternary structures in infected hepatocytes, participate in and regulate HBV virion assembly, capsid uncoating, and covalently closed circular DNA (cccDNA) formation. It is anticipated that small molecular core protein assembly modulators may disrupt one or multiple steps of HBV replication, depending on their interaction with the distinct quaternary structures of core protein. The discovery of novel core protein-targeting antivirals, such as benzamide derivatives reported here, and investigation of their antiviral mechanism may lead to the identification of antiviral therapeutics for the cure of chronic hepatitis B.

Discovery and Pre-Clinical Characterization of Third-Generation 4-H Heteroaryldihydropyrimidine (HAP) Analogues as Hepatitis B Virus (HBV) Capsid Inhibitors

Described herein are the discovery and structure-activity relationship (SAR) studies of the third-generation 4-H heteroaryldihydropyrimidines (4-H HAPs) featuring the introduction of a C6 carboxyl group as novel HBV capsid inhibitors. This new series of 4-H HAPs showed improved anti-HBV activity and better drug-like properties compared to the first- and second-generation 4-H HAPs. X-ray crystallographic study of analogue 12 (HAP_R01) with Cp149 Y132A mutant hexamer clearly elucidated the role of C6 carboxyl group played for the increased binding affinity, which formed strong hydrogen bonding interactions with capsid protein and coordinated waters. The representative analogue 10 (HAP_R10) was extensively characterized in vitro (ADMET) and in vivo (mouse PK and PD) and subsequently selected for further development as oral anti-HBV infection agent.