Novel non-heteroarylpyrimidine (HAP) capsid assembly modifiers have a different mode of action from HAPs in vitro

Identification of peptide-based hepatitis B virus capsid inhibitors based on the viral core protein

In this study, we have identified two novel peptides, 19Ac (comprising residues 91-105) and 20Ac (encompassing residues 96-110), from a systematically designed peptide library based on the Hepatitis B virus (HBV) core protein, that inhibit the assembly of HBV capsid. Peptide 20Ac exhibited about twofold the inhibitory potency of 19Ac and proved effective against both standard and morphothiadin (GLS4)-resistant HBV strains. Molecular dynamics simulations revealed that despite their overlapping sequence, 19Ac and 20Ac bonded to different regions of the core protein, thereby inhibiting capsid assembly through distinct mechanisms. These peptides could serve as valuable seed compounds for the further development of HBV capsid inhibitors, including GLS4-resistant strains.

Recent advances in screening methods enabling the discovery of novel anti-hepatitis B virus drug candidates

The global population affected by Hepatitis B virus (HBV) is approximately 296 million, but few drugs have been able to completely eradicate HBV and the range of effective treatments remains limited. Recent advancements in molecular biology and artificial intelligence, as well as a comprehensive understanding of the molecular structure of HBV, have greatly aided the rational development of anti-HBV agents. Such advancements have facilitated an increasing array of candidate drugs transitioning into clinical trials, however, no novel target-based compounds have been approved for clinical application. To expedite the progression of anti-HBV drug development, establishing a reliable and robust in vitro HBV infection system is of great importance. However, owing to the host and tissue specificity of HBV, identifying a stable and dependable cell culture system for screening all anti-HBV agents poses significant challenges. In this review, we summarize recent advances in screening methods for small-molecule inhibitors that target key stages of the HBV replication cycle from a medicinal chemistry perspective.

Selective depletion of HBV-infected hepatocytes by class A capsid assembly modulators requires high levels of intrahepatic HBV core protein

Capsid assembly mediated by hepatitis B virus (HBV) core protein (HBc) is an essential part of the HBV replication cycle, which is the target for different classes of capsid assembly modulators (CAMs). While both CAM-A ("aberrant") and CAM-E ("empty") disrupt nucleocapsid assembly and reduce extracellular HBV DNA, CAM-As can also reduce extracellular HBV surface antigen (HBsAg) by triggering apoptosis of HBV-infected cells in preclinical mouse models. However, there have not been substantial HBsAg declines in chronic hepatitis B (CHB) patients treated with CAM-As to date. To investigate this disconnect, we characterized the antiviral activity of tool CAM compounds in HBV-infected primary human hepatocytes (PHHs), as well as in HBV-infected human liver chimeric mice and mice transduced with adeno-associated virus-HBV. Mechanistic studies in HBV-infected PHH revealed that CAM-A, but not CAM-E, induced a dose-dependent aggregation of HBc in the nucleus which is negatively regulated by the ubiquitin-binding protein p62. We confirmed that CAM-A, but not CAM-E, induced HBc-positive cell death in both mouse models via induction of apoptotic and inflammatory pathways and demonstrated that the degree of HBV-positive cell loss was positively correlated with intrahepatic HBc levels. Importantly, we determined that there is a significantly lower level of HBc per hepatocyte in CHB patient liver biopsies than in either of the HBV mouse models. Taken together, these data confirm that CAM-As have a unique secondary mechanism with the potential to kill HBc-positive hepatocytes. However, this secondary mechanism appears to require higher intrahepatic HBc levels than is typically observed in CHB patients, thereby limiting the therapeutic potential.

Development of benzimidazole-based compounds as novel capsid assembly modulators for the treatment of HBV infection

Hepatitis B virus (HBV) capsid assembly modulators (CAMs) represent a promising therapeutic approach for the treatment of HBV infection. In this study, the hit compound CDI (IC50 = 2.46 ± 0.33 μM) was identified by screening of an in-house compound library. And then novel potent benzimidazole derivatives were designed and synthesized as core assembly modulators, and their antiviral effects were evaluated in vitro and in vivo biological experiments. The results indicated that compound 26f displayed the most optimized modulator of HBV capsid assembly (IC50 = 0.51 ± 0.20 μM, EC50 = 2.24 ± 0.43 μM, CC50 = 84.29 μM) and high selectivity index. Moreover, treatment with compound 26f for 14 days significantly decreased serum levels of HBV DNA levels in the Hydrodynamic-Injection (HDI) mouse model. Therefore, compound 26f could be considered as a promising candidate drug for further development of novel HBV CAMs with the desired potency and safety.

Discovery of carboxyl-containing heteroaryldihydropyrimidine derivatives as novel HBV capsid assembly modulators with significantly improved metabolic stability

Interfering with the assembly of hepatitis B virus (HBV) capsid is a promising approach for treating chronic hepatitis B (CHB). In order to enhance the metabolic stability and reduce the strong hERG inhibitory effect of HBV capsid assembly modulator (CAM) GLS4, we rationally designed a series of carboxyl-containing heteroaryldihydropyrimidine (HAP) derivatives based on structural biology information combined with medicinal chemistry strategies. The results from biological evaluation demonstrated that compound 6a-25 (EC50 = 0.020 μM) exhibited greater potency than the positive drug lamivudine (EC50 = 0.09 μM), and was comparable to the lead compound GLS4 (EC50 = 0.007 μM). Furthermore, it was observed that 6a-25 reduced levels of core protein (Cp) and capsid in cells. Preliminary assessment of drug-likeness revealed that 6a-25 exhibited superior water solubility (pH 2.0: 374.81 μg mL-1; pH 7.0: 6.85 μg mL-1; pH 7.4: 25.48 μg mL-1), liver microsomal metabolic stability (t1/2 = 108.2 min), and lower hERG toxicity (10 μM inhibition rate was 72.66%) compared to the lead compound GLS4. Overall, compound 6a-25 holds promise for further investigation.

Novel Drug Development in Chronic Hepatitis B Infection: Capsid Assembly Modulators and Nucleic Acid Polymers

Currently approved treatment of patients with chronic hepatitis B infection is insufficient to achieve functional cure. Numerous new compounds are identified, and among many, capsid assembly modulators (CAMs) and nucleic acid polymers (NAPs) are 2 classes of virus-directing agents in clinical development. CAMs interfere with viral pregenomic RNA encapsidation and are effective in viral load reduction but have limited effects on hepatitis B surface antigen (HBsAg). NAPs prevent HBsAg release from hepatocytes and induce intracellular degradation, leading to potent suppression of serum HBsAg when combined with nucleoside analogues and pegylated interferon demonstrated by initial data, but awaiting further confirmation studies.

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.

Structure-based Design of Novel Hepatitis B Virus Capsid Assembly Modulators

Small-molecule capsid assembly modulators (CAMs) have been recently recognized as promising antiviral agents for curing chronic hepatitis B virus (HBV) infection. A target-based in silico screening study is described, aimed towards the discovery of novel HBV CAMs. Initial optimization of four weakly active screening hits was performed via focused library synthesis. Lead compound 42 and close analogues 56 and 57 exhibited in vitro potency in the sub- and micromolar range along with good physico-chemical properties and were further evaluated in molecular docking and mechanism of action studies.

Biology of the hepatitis B virus (HBV) core and capsid assembly modulators (CAMs) for chronic hepatitis B (CHB) cure

Hepatitis B virus (HBV) is a hepadnavirus, a small DNA virus that infects liver tissue, with some unusual replication steps that share similarities to retroviruses. HBV infection can lead to chronic hepatitis B (CHB), a life-long infection associated with significant risks of liver disease, especially if untreated. HBV is a significant global health problem, with hundreds of millions currently living with CHB. Currently approved strategies to prevent or inhibit HBV are highly effective, however, a cure for CHB has remained elusive. To achieve a cure, elimination of the functionally integrated HBV covalently closed chromosomal DNA (cccDNA) genome is required. The capsid core is an essential component of HBV replication, serving roles when establishing infection and in creating new virions. Over the last two and a half decades, significant efforts have been made to find and characterize antivirals that target the capsid, specifically the HBV core protein (Cp). The antivirals that interfere with the kinetics and morphology of the capsid, termed capsid assembly modulators (CAMs), are extremely potent, and clinical investigations indicate they are well tolerated and highly effective. Several CAMs offer the potential to cure CHB by decreasing the cccDNA pools. Here, we review the biology of the HBV capsid, focused on Cp, and the development of inhibitors that target it.

Safety, tolerability, pharmacokinetics, and antiviral activity of the novel core protein allosteric modulator ZM-H1505R (Canocapavir) in chronic hepatitis B patients: a randomized multiple-dose escalation trial

BACKGROUND

Hepatitis B virus (HBV) core protein-targeting antivirals (CpTAs) are promising therapeutic agents for treating chronic hepatitis B (CHB). In this study, the antiviral activity, pharmacokinetics (PK), and tolerability of ZM-H1505R (Canocapavir), a chemically unique HBV CpTA, were evaluated in patients with CHB.

METHODS

This study was a double-blind, randomized, placebo-controlled phase 1b trial in Chinese CHB patients. Noncirrhotic and treatment-naive CHB patients were divided into three cohorts (10 patients per cohort) and randomized within each cohort in a ratio of 4:1 to receive a single dose of 50, 100, or 200 mg of Canocapavir or placebo once a day for 28 consecutive days.

RESULTS

Canocapavir was well tolerated, with the majority of adverse reactions being grade I or II in severity. There were no serious adverse events, and no patients withdrew from the study. Corresponding to 50, 100, and 200 mg doses of Canocapavir, the mean plasma trough concentrations of the drug were 2.7-, 7.0-, and 14.6-fold of its protein-binding adjusted HBV DNA EC50 (135 ng/mL), respectively, with linear PK and a low-to-mild accumulation rate (1.26-1.99). After 28 days of treatment, the mean maximum HBV DNA declines from baseline were -1.54, -2.50, -2.75, and -0.47 log10 IU/mL for the 50, 100, and 200 mg of Canocapavir or placebo groups, respectively; and the mean maximum pregenomic RNA declines from baseline were -1.53, -2.35, -2.34, and -0.17 log10 copies/mL, respectively.

CONCLUSIONS

Canocapavir treatment is tolerated with efficacious antiviral activity in CHB patients, supporting its further development in treating HBV infection.

TRIAL REGISTRATION

ClinicalTrials.gov, number NCT05470829).

Molecular elucidation of drug-induced abnormal assemblies of the hepatitis B virus capsid protein by solid-state NMR

Hepatitis B virus (HBV) capsid assembly modulators (CAMs) represent a recent class of anti-HBV antivirals. CAMs disturb proper nucleocapsid assembly, by inducing formation of either aberrant assemblies (CAM-A) or of apparently normal but genome-less empty capsids (CAM-E). Classical structural approaches have revealed the CAM binding sites on the capsid protein (Cp), but conformational information on the CAM-induced off-path aberrant assemblies is lacking. Here we show that solid-state NMR can provide such information, including for wild-type full-length Cp183, and we find that in these assemblies, the asymmetric unit comprises a single Cp molecule rather than the four quasi-equivalent conformers typical for the icosahedral T = 4 symmetry of the normal HBV capsids. Furthermore, while in contrast to truncated Cp149, full-length Cp183 assemblies appear, on the mesoscopic level, unaffected by CAM-A, NMR reveals that on the molecular level, Cp183 assemblies are equally aberrant. Finally, we use a eukaryotic cell-free system to reveal how CAMs modulate capsid-RNA interactions and capsid phosphorylation. Our results establish a structural view on assembly modulation of the HBV capsid, and they provide a rationale for recently observed differences between in-cell versus in vitro capsid assembly modulation.

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.

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.

Current Progress in the Development of Hepatitis B Virus Capsid Assembly Modulators: Chemical Structure, Mode-of-Action and Efficacy

Hepatitis B virus (HBV) is a major causative agent of human hepatitis. Its viral genome comprises partially double-stranded DNA, which is complexed with viral polymerase within an icosahedral capsid consisting of a dimeric core protein. Here, we describe the effects of capsid assembly modulators (CAMs) on the geometric or kinetic disruption of capsid construction and the virus life cycle. We highlight classical, early-generation CAMs such as heteroaryldihydropyrimidines, phenylpropenamides or sulfamoylbenzamides, and focus on the chemical structure and antiviral efficacy of recently identified non-classical CAMs, which consist of carboxamides, aryl ureas, bithiazoles, hydrazones, benzylpyridazinones, pyrimidines, quinolines, dyes, and antimicrobial compounds. We summarize the therapeutic efficacy of four representative classical compounds with data from clinical phase 1 studies in chronic HBV patients. Most of these compounds are in phase 2 trials, either as monotherapy or in combination with approved nucleos(t)ides drugs or other immunostimulatory molecules. As followers of the early CAMs, the therapeutic efficacy of several non-classical CAMs has been evaluated in humanized mouse models of HBV infection. It is expected that these next-generation HBV CAMs will be promising candidates for a series of extended human clinical trials.

Hepatitis B Core-Related Antigen and New Therapies for Hepatitis B

The hepatitis B core-related antigen (HBcrAg) is an unprecedented novel HBV biomarker that plays an essential role in reflecting covalently closed circular DNA (cccDNA) in chronic hepatitis B (CHB) because its levels correlate with intrahepatic cccDNA and serum HBV DNA. In this review, we describe the clinical application of serum HBcrAg in CHB patients, with a particular focus on new therapies targeting intrahepatic HBV replication. (1) HBcrAg can be detected in clinical cases where serum HBV DNA is undetectable during anti-HBV therapy. (2) A highly sensitive HBcrAg assay (iTACT-HBcrAg) may be useful for monitoring HBV reactivation, as an alternative to HBV DNA. (3) Decreased HBcrAg levels have been significantly associated with promising outcomes in CHB patients, reducing the risk of progression or recurrence of hepatocellular carcinoma. Additionally, we focus on and discuss several drugs in development that target HBV replication, and monitoring HBcrAg may be useful for determining the therapeutic efficacies of such novel drugs. In conclusion, HBcrAg, especially when measured by the recently developed iTACT-HBcrAg assay, may be the most appropriate surrogate marker, over other HBV biomarkers, to predict disease progression and treatment response in CHB patients.

Clinical efficacy of a novel, high-sensitivity HBcrAg assay in the management of chronic hepatitis B and HBV reactivation

BACKGROUND & AIMS

A fully automated, novel high-sensitivity hepatitis B core-related antigen assay (iTACT-HBcrAg) has been developed. We demonstrate the clinical utility of iTACT-HBcrAg for monitoring chronic hepatitis B (CHB) and for the early detection of HBV reactivation.

METHODS

After fundamental assessments, the clinical performance of iTACT-HBcrAg was compared with other HBV markers. i) Serial sera, available from 161 HBeAg-negative patients with CHB and persistently undetectable HBV DNA, were measured by iTACT-HBcrAg and a conventional HBcrAg assay (G-HBcrAg). ii) Serial sera from 13 HBV-reactivated patients were measured by iTACT-HBcrAg and an ultra-high-sensitivity HBsAg immune complex transfer-chemiluminescent enzyme immunoassay (lower limit of detection; 0.0005 IU/ml, ICT-CLEIA) to compare HBV DNA detection. iii) To elucidate the various HBcrAg components detected by iTACT-HBcrAg, OptiPrep density gradient centrifugation analysis was performed on sera obtained before and after HBV reactivation.

RESULTS

The analytical performance of iTACT-HBcrAg was satisfactory. The sensitivity of iTACT-HBcrAg (2.1 Log U/ml) was approximately 10-fold greater than that of G-HBcrAg (2.8 Log U/ml). i) HBcrAg was detectable in the sera of 97.5% (157/161) of patients with CHB by iTACT-HBcrAg, of whom 75.2% (121/161) had ≥2.8 Log U/ml HBcrAg and 22.4% (36/161) had 2.1-2.8 Log U/ml HBcrAg, which was undetectable by G-HBcrAg. ii) 9 and 2 of 13 HBV-reactivated patients were HBcrAg-positive by iTACT-HBcrAg before and at HBV DNA positivity, respectively; 7 and 4 were HBcrAg-positive by iTACT-HBcrAg before and at HBsAg-positivity by ICT-CLEIA, respectively. iii) The HBcrAg detected by iTACT-HBcrAg before HBV reactivation was contained in empty particles (22 KDa precore protein).

CONCLUSIONS

iTACT-HBcrAg could be used to better monitor responses to anti-HBV treatments in HBeAg-negative patients and for the early detection of HBV reactivation.

LAY SUMMARY

A fully automated, novel high-sensitivity hepatitis B core-related antigen assay (iTACT-HBcrAg) has been developed. iTACT-HBcrAg can be used to monitor HBeAg-negative patients with chronic hepatitis B, as well as for the early detection of HBV reactivation. iTACT-HBcrAg could be used as a general marker of disease progression and treatment response.

Novel Cost-Efficient Graphene-Based Impedance Biosensor for the Analysis of Viral Cytopathogenicity and the Effect of Antiviral Drugs

Biosensors become increasingly relevant for medical diagnostics, pharmaceutical industry, and environmental technology, for example, to test new drugs easily and reliably or to detect cell growth in changing environmental conditions. Novel materials like graphene are promising candidates to produce biosensors on an industrial scale by means of printing processes. To reach this aim, methods for the reliable and automated production of electrode structures and their coating are required. We present an impedance biosensor in the format of a microtiter plate, fabricated by highly efficient roll-to-roll printing of graphene-based microstructures on large-area polymer foils. Proof-of-principle experiments show the evidence of the suitability of the printed graphene biosensors for impedance-based monitoring of viral cytopathogenicity and its inhibition in the presence of antiviral drugs. The developed system is a promising approach toward cost-efficient impedimetric biosensors for high-throughput screening in vaccine research and antiviral drug development.

Safety, pharmacokinetics, and antiviral activity of RO7049389, a core protein allosteric modulator, in patients with chronic hepatitis B virus infection: a multicentre, randomised, placebo-controlled, phase 1 trial

BACKGROUND

RO7049389, a hepatitis B virus (HBV) core protein allosteric modulator being developed for the treatment of chronic HBV infection, was found to be safe and well tolerated in healthy participants (part 1 of this study). The objective of this proof-of-mechanism study (part 2) was to evaluate the safety, pharmacokinetics, and antiviral activity of RO7049389 in patients with chronic HBV infection.

METHODS

This was a multicentre, randomised, placebo-controlled, phase 1 study. Patients with chronic HBV infection who were not currently on anti-HBV therapy were enrolled at 11 liver disease centres in Hong Kong, New Zealand, Singapore, Taiwan, and Thailand. Seven patients per dose cohort were randomly assigned (6:1) to receive oral administration of RO7049389 at 200 mg or 400 mg twice a day, or 200 mg, 600 mg, or 1000 mg once a day, for 4 weeks, or matching placebo. Randomisation was via interactive voice web response system-generated numbers, with study participants, investigators, and site personnel masked to treatment allocation. The primary endpoint of the study was safety of RO7049389 and its antiviral effect on HBV DNA concentration at the end of treatment, assessed in all patients who received at least one dose of study drug. This study is registered with ClinicalTrials.gov, number NCT02952924.

FINDINGS

Between May 21, 2017, and April 3, 2019, 62 patients were screened for eligibility, and 37 eligible patients were enrolled in five dose cohorts sequentially. All adverse events were of mild or moderate intensity. Among the 31 patients who received RO7049389, the most common adverse events were headache (in five [16%] of 31 patients), increased alanine aminotransferase (ALT; five [16%]), increased aspartate aminotransferase (AST; four [13%]), upper respiratory tract infection (four [13%]), and diarrhoea (three [10%]). The most common moderate adverse events were ALT increase (three [10%]) and AST increase (two [6%]), and there were no serious adverse events. At the end of 4 weeks treatment, mean HBV DNA declines from baseline in RO7049389-treated patients were 2·44 log₁₀ IU/mL (SD 0·98) in the 200 mg twice a day group, 3·33 log₁₀ IU/mL (1·14) in the 400 mg twice a day group, 3·00 log₁₀ IU/mL (0·54) in the 200 mg once a day group, 2·86 log₁₀ IU/mL (0·79) in the 600 mg once a day group, and 3·19 log₁₀ IU/mL (0·33) in the 1000 mg once a day group versus 0·34 log₁₀ IU/mL (0·54) in the pooled placebo patients.

INTERPRETATION

RO7049389 was safe and well tolerated and demonstrated antiviral activity over 4 weeks of treatment in patients with chronic HBV infection. These findings support further clinical development of RO7049389 as a component of novel combination treatment regimens for patients with chronic HBV infection.

FUNDING

F Hoffmann-La Roche.

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.

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.

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."

Discovery of (1H-Pyrazolo[3,4-c]pyridin-5-yl)sulfonamide Analogues as Hepatitis B Virus Capsid Assembly Modulators by Conformation Constraint

Hepatitis B virus (HBV) capsid assembly modulators (CAMs) have been suggested to be effective anti-HBV agents in both preclinical and clinical studies. In addition to blocking HBV replication, CAMs could reduce the formation of covalently closed circular DNA (cccDNA), which accounts for the persistence of HBV infection. Here, we describe the discovery of (1H-indazole-5-yl)sulfonamides and (1H-pyrazolo[3,4-c]pyridin-5-yl)sulfonamides as new CAM chemotypes by constraining the conformation of the sulfamoylbenzamide derivatives. Lead optimization resulted in compound 56 with an EC₅₀ value of 0.034 μM and good metabolic stability in mouse liver microsomes. To increase the solubility, the amino acid prodrug (65) and its citric acid salt (67) were prepared. Compound 67 dose dependently inhibited HBV replication in a hydrodynamic injection-based mouse model of HBV infection, while 56 did not show in vivo anti-HBV activity, likely owing to its suboptimal solubility. This class of compounds may serve as a starting point to develop novel anti-HBV drugs.

Bioassay-guided isolation of anti-hepatitis B virus flavonoid myricetin-3-O-rhamnoside along with quercetin from Guiera senegalensis leaves

Recently, we have shown in vitro anti-hepatitis B virus (HBV) activity of G. senegalensis J.F. Gmel leaves, and Identified quercetin and other flavonoids by HPTLC. Here we report bioassay-directed fractionation of G. senegalensis leaves using column chromatography and isolation of two flavonoinds from the n-butanol fraction, their structure determination (1H NMR, 13C NMR and 2D-NMR) and assessment of antiviral activities (HBsAg and HBeAg assay) in HBV-reporter HepG2.2.2.15 cells. Further molecular docking was performed against HBV polymerase (Pol/RT) and capsid (Core) proteins as well as host-receptor sodium taurocholate co-transporting polypeptide (NTCP). The two isolated bioactive compounds were identified as quercetin and myricetin-3-O-rhamnoside. Quercetin significantly inhibited synthesis of HBsAg and HBeAg by about 60% and 62%, respectively as compared to myricetin-3-O-rhamnoside by 44% and 35%, respectively. Molecular docking of the two anti-HBV flavonoids revealed their higher binding affinities towards Pol/RT than Core and NTCP. In conclusion, this is the first report on anti-HBV active myricetin-3-O-rhamnoside along with quercetin isolated from G. senegalensis leaves. Their possible mode of anti-HBV activities are suggested through binding with viral Pol/RT and Core as well as host NTCP proteins.

Novel Hepatitis B Virus Capsid Assembly Modulator Induces Potent Antiviral Responses In Vitro and in Humanized Mice

Hepatitis B virus (HBV) affects an estimated 250 million chronic carriers worldwide. Though several vaccines exist, they are ineffective for those already infected. HBV persists due to the formation of covalently closed circular DNA (cccDNA)-the viral minichromosome-in the nucleus of hepatocytes. Current nucleoside analogs and interferon therapies rarely clear cccDNA, requiring lifelong treatment. Our group identified GLP-26, a novel glyoxamide derivative that alters HBV nucleocapsid assembly and prevents viral DNA replication. GLP-26 exhibited single-digit nanomolar anti-HBV activity, inhibition of HBV e antigen (HBeAg) secretion, and reduced cccDNA amplification, in addition to showing a promising preclinical profile. Strikingly, long term combination treatment with entecavir in a humanized mouse model induced a decrease in viral loads and viral antigens that was sustained for up to 12 weeks after treatment cessation.

Pyrimidotriazine derivatives as selective inhibitors of HBV capsid assembly

Chronic hepatitis B virus (HBV) infection is currently treated with nucleoside/nucleotides analogs. They are potent inhibitors of HBV DNA polymerase, which also functions as reverse transcriptase. Although nucleoside/nucleotide analogs efficiently suppress HBV replication in liver cells, they cannot eradicate HBV DNA from liver cells and cure the disease. Therefore, it is still mandatory to identify and develop effective inhibitors that target a step other than reverse transcription in the viral replication cycle. HBV capsid assembly is a critical step for viral replication and an attractive target for inhibition of HBV replication. We conducted in silico screening of compounds expected to bind to the HBV capsid dimer-dimer interaction site. The selected compounds were further examined for their anti-HBV activity in vitro. Among the test compounds, novel pyrimidotriazine derivatives were found to be selective inhibitors of HBV replication in HepG2.2.15.7 cells. Among the compounds, 2-[(2,3-dichlorophenyl)amino]-4-(4-tert-butylphenyl)-8-methyl-4H,9H-pyrimido[1,2-a][1,3,5]triazin-6-one was the most active against HBV replication. Studies on its mechanism of action revealed that the compound interfered with HBV capsid assembly determined by a cell-free capsid assembly system. Thus, the pyrimidotriazine derivatives are considered to be potential leads for novel HBV capsid assembly inhibitors.

BAY 41-4109-mediated aggregation of assembled and misassembled HBV capsids in cells revealed by electron microscopy

HBc is a small protein essential for the formation of the icosahedral HBV capsid. Its multiple roles in the replication cycle make this protein a promising target for the development of antiviral molecules. Based on the structure of HBc, a series of HBV assembly inhibitors, also known as capsid assembly modulators, were identified. We investigated the effect of BAY 41-4109, a heteroaryldihydropyrimidine derivative that promotes the assembly of a non-capsid polymer. We showed, by confocal microscopy, that BAY 41-4109 mediated HBc aggregation, mostly in the cytoplasm of Huh7 cells. Image analysis revealed that aggregate size depended on BAY 41-4109 concentration and treatment duration. Large aggregates in the vicinity of the nucleus were enclosed by invaginations of the nuclear envelope. This deformation of the nuclear envelope was confirmed by transmission electron microscopy (TEM) and immuno-TEM. These two techniques also revealed that the HBc aggregates were accumulations of capsid-like shells with an electron-dense material consisting of HBV core fragments. These findings, shedding light on the ultrastructural organization of HBc aggregates, provide insight into the mechanisms of action of BAY 41-4109 against HBV and will serve as a basis for comparison with other HBV capsid assembly inhibitors.

Evolution of Intermediates during Capsid Assembly of Hepatitis B Virus with Phenylpropenamide-Based Antivirals

Self-assembly of virus capsids is a potential target for antivirals due to its importance in the virus lifecycle. Here, we investigate the effect of phenylpropenamide derivatives B-21 and AT-130 on the assembly of hepatitis B virus (HBV) core protein. Phenylpropenamides are widely believed to yield assembly of spherical particles resembling native, empty HBV capsids. Because the details of assembly can be overlooked with ensemble measurements, we performed resistive-pulse sensing on nanofluidic devices with four pores in series to characterize the size distributions of the products in real time. With its single particle sensitivity and compatibility with typical assembly buffers, resistive-pulse sensing is well-suited for analyzing virus assembly in vitro. We observed that assembly with B-21 and AT-130 produced a large fraction of partially complete virus particles that may be on-path, off-path, or trapped. For both B-21 and AT-130, capsid assembly was more sensitive to disruption under conditions where the interprotein association energy was low at lower salt concentrations. Dilution of the reaction solutions led to the rearrangement of the incomplete particles and demonstrated that these large intermediates may be on-path, but are labile, and exist in a frustrated dynamic equilibrium. During capsid assembly, phenylpropenamide molecules modestly increase the association energy of dimers, prevent intermediates from dissociating, and lead to kinetic trapping where the formation of too many capsids has been initiated, which results in both empty and incomplete particles.

Novel Hepatitis B Virus Capsid-Targeting Antiviral That Aggregates Core Particles and Inhibits Nuclear Entry of Viral Cores

An estimated 240 million are chronically infected with hepatitis B virus (HBV), which can lead to liver disease, cirrhosis, and hepatocellular carcinoma. Currently, HBV treatment options include only nucleoside reverse transcriptase inhibitors and the immunomodulatory agent interferon alpha, and these treatments are generally not curative. New treatments with novel mechanisms of action, therefore, are highly desired for HBV therapy. The viral core protein (Cp) has gained attention as a possible therapeutic target because of its vital roles in the HBV life cycle. Several classes of capsid assembly effectors (CAEs) have been described in detail, and these compounds all increase capsid assembly rate but inhibit HBV replication by different mechanisms. In this study, we have developed a thermal shift-based screening method for CAE discovery and characterization, filling a much-needed gap in high-throughput screening methods for capsid-targeting molecules. Using this approach followed by cell-based screening, we identified the compound HF9C6 as a CAE with low micromolar potency against HBV replication. HF9C6 caused large multicapsid aggregates when capsids were assembled in vitro and analyzed by transmission electron microscopy. Interestingly, when HBV-expressing cells were treated with HF9C6, Cp was excluded from cell nuclei, suggesting that this compound may inhibit nuclear entry of Cp and capsids. Furthermore, mutational scanning of Cp suggested that HF9C6 binds the known CAE binding pocket, indicating that key Cp-compound interactions within this pocket have a role in determining the CAE mechanism of action.

The Role of Hepatitis B Core-Related Antigen

Hepatitis B virus (HBV) cannot be completely eliminated from infected hepatocytes due to the existence of intrahepatic covalently closed circular DNA (cccDNA). Serological biomarkers reflect intrahepatic viral replicative activity as non-invasive alternatives to liver biopsy. Hepatitis B core-related antigen (HBcrAg) is a novel biomarker that has an important role in chronic hepatitis B (CHB), because it correlates with serum HBV DNA and intrahepatic cccDNA. In clinical cases with undetectable serum HBV DNA or loss of HBsAg, HBcrAg still can be detected and the decrease in HBcrAg levels is significantly associated with promising outcomes for CHB patients. HBcrAg can predict spontaneous or treatment-induced hepatitis B envelope antigen (HBeAg) seroconversion, persistent responses before and after cessation of nucleos(t)ide analogues, potential HBV reactivation, HBV reinfection after liver transplantation, and risk of hepatocellular carcinoma progression or recurrence. In this review, the clinical applications of HBcrAg in CHB patients based on its virological features are described. Furthermore, new potential therapeutic anti-HBV agents that affect intrahepatic cccDNA are under development, and the monitoring of HBcrAg might be useful to judge therapeutic effects. In conclusion, HBcrAg might be a suitable surrogate marker beyond other HBV markers to predict the disease progression and treatment responses of CHB patients.

Naturally occurring core protein mutations compensate for the reduced replication fitness of a lamivudine-resistant HBV isolate

Hepatitis B virus (HBV) replicates its DNA genome through reverse transcription of an RNA intermediate. The lack of proofreading capacity of the viral DNA polymerase results in a high mutation rate of HBV genome. Under the selective pressure created by the nucleos(t)ide analogue (NA) antiviral drugs, viruses with resistance mutations are selected. However, the replication fitness of NA-resistant mutants is markedly reduced compared to wild-type. Compensatory mutations in HBV polymerase, which restore the viral replication capacity, have been reported to arise under continuous treatment with lamivudine (LMV). We have previously identified a highly replicative LMV-resistant HBV isolate from a chronic hepatitis B patient experiencing acute disease exacerbation. Besides the common YMDD drug-resistant mutations, this isolate possesses multiple additional mutations in polymerase and core regions. The transcomplementation assay demonstrated that the enhanced viral replication is due to the mutations of core protein. Further mutagenesis study revealed that the P5T mutation of core protein plays an important role in the enhanced viral replication through increasing the levels of capsid formation and pregenomic RNA encapsidation. However, the LMV-resistant virus harboring compensatory core mutations remains sensitive to capsid assembly modulators (CpAMs). Taken together, our study suggests that the enhanced HBV nucleocapsid formation resulting from core mutations represents an important viral strategy to surmount the antiviral drug pressure and contribute to viral pathogenesis, and CpAMs hold promise for developing the combinational antiviral therapy for hepatitis B.