Preclinical characterization of AB-506, an inhibitor of HBV replication targeting the viral core protein

Identification of novel tetrahydroquinoxaline derived phenyl ureas as modulators of the hepatitis B virus nucleocapsid assembly

A key step of hepatitis B virus (HBV) replication is the selective packaging of pregenomic RNA (pgRNA) by core protein (Cp) dimers, forming a nucleocapsid where the reverse transcriptional viral DNA replication takes place. One approach in the development of new anti-HBV drugs is to disrupt the assembly of HBV nucleocapsids by misdirecting Cp dimers to assemble morphologically normal capsids devoid of pgRNA. In this study, we built upon our previous discovery of benzamide-derived HBV capsid assembly modulators by exploring fused bicyclic scaffolds with an exocyclic amide that is β, γ to the fused ring, and identified 1,2,3,4-tetrahydroquinoxaline derived phenyl ureas as a novel scaffold. Structure-activity relationship studies showed that a favorable hydrophobic substitution can be tolerated at the 2-position of the 1,2,3,4-tetrahydroquinoxaline core, and the resulting compound 88 demonstrated comparable or improved antiviral potencies in mouse and human hepatocyte-derived HBV-replicating cell lines compared to our previously reported benzamide compound, 38017 (8). In addition, a novel bis-urea series based on 1,2,3,4-tetrahydroquinoxaline was also found to inhibit HBV DNA replication with sub-micromolar EC50 values. The mode of action of these compounds is consistent with specific inhibition of pgRNA encapsidation into nucleocapsids in hepatocytes.

Design, synthesis, and structure-activity relationship of a bicyclic HBV capsid assembly modulator chemotype leading to the identification of clinical candidate AB-506

Disruption of the HBV capsid assembly process through small-molecule interaction with HBV core protein is a validated target for the suppression of hepatitis B viral replication and the development of new antivirals. Through combination of key structural features associated with two distinct series of capsid assembly modulators, a novel aminochroman-based chemotype was identified. Optimization of anti-HBV potency through generation of SAR in addition to further core modifications provided a series of related functionalized aminoindanes. Key compounds demonstrated excellent cellular potency in addition to favorable ADME and pharmacokinetic profiles and were shown to be highly efficacious in a mouse model of HBV replication. Aminoindane derivative AB-506 was subsequently advanced into clinical development.

Hepatitis B Virus Epsilon (ε) RNA Element: Dynamic Regulator of Viral Replication and Attractive Therapeutic Target

Hepatitis B virus (HBV) chronically infects millions of people worldwide, which underscores the importance of discovering and designing novel anti-HBV therapeutics to complement current treatment strategies. An underexploited but attractive therapeutic target is ε, a cis-acting regulatory stem-loop RNA situated within the HBV pregenomic RNA (pgRNA). The binding of ε to the viral polymerase protein (P) is pivotal, as it triggers the packaging of pgRNA and P, as well as the reverse transcription of the viral genome. Consequently, small molecules capable of disrupting this interaction hold the potential to inhibit the early stages of HBV replication. The rational design of such ligands necessitates high-resolution structural information for the ε-P complex or its individual components. While these data are currently unavailable for P, our recent structural elucidation of ε through solution nuclear magnetic resonance spectroscopy marks a significant advancement in this area. In this review, we provide a brief overview of HBV replication and some of the therapeutic strategies to combat chronic HBV infection. These descriptions are intended to contextualize our recent experimental efforts to characterize ε and identify ε-targeting ligands, with the ultimate goal of developing novel anti-HBV therapeutics.

Viral sequence analysis of chronic hepatitis B patients treated with the capsid assembly modulator JNJ-56136379 in the JADE phase 2a study

BACKGROUND & AIMS

In the monotherapy arms of the phase 2 JADE study (ClinicalTrials.gov Identifier: NCT03361956) evaluating the safety and efficacy of JNJ-56136379 (capsid assembly modulator-class E) with/without nucleos(t)ide analogue (NA), viral breakthroughs (VBT) were observed, leading to JNJ-56136379 monotherapy discontinuation. We present the viral sequencing analysis of JNJ-56136379±NA-treated hepatitis B virus (HBV)-infected patients.

METHODS

The HBV full genome was sequenced using next generation sequencing. Baseline amino acid (aa) polymorphisms were defined as changes versus the universal HBV reference sequence (sequence read frequency >15%). Emerging mutations were defined as aa changes versus baseline sequence (frequency <1% at baseline and ≥15% post-baseline).

RESULTS

6/28 JNJ-56136379 75 mg monotherapy arm patients experienced VBT; all 6 had emerging JNJ-56136379-resistant variants T33N (n = 5; fold change [FC] = 85) or F23Y (n = 1; FC = 5.2). 1/32 JNJ-56136379 250 mg arm patients (genotype-E) had <1 log₁₀ IU/mL decline in HBV DNA at Week 4, experienced VBT at Week 8, and carried the I105T baseline polymorphism (FC = 7.9), but had no emerging variants. Eight additional monotherapy-treated patients had shallow second phases of their HBV DNA profile and emerging T33N (n = 7) or F23Y (n = 1) variants. NA initiation (switch [75 mg arm]; add-on [250 mg arm]) in all monotherapy patients with VBT resulted in HBV DNA decline in all patients. No VBT was observed during JNJ-56136379+NA combination therapy.

CONCLUSIONS

JNJ-56136379 monotherapy resulted in VBT and was associated with the selection of JNJ-56136379-resistant variants. Efficacy of NA treatment (de novo combination or rescue therapy for VBT) was not impacted, confirming the lack of cross-resistance between these drug classes.

CLINICAL TRIAL NUMBER

NCT03361956.

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.

Safety, pharmacokinetics and antiviral activity of ABI-H2158, a hepatitis B virus core inhibitor: A randomized, placebo-controlled phase 1 study

Treatment for chronic hepatitis B virus infection (cHBV) is mostly indefinite, with new finite-duration therapies needed. We report safety, pharmacokinetics and antiviral activity of the investigational HBV core inhibitor ABI-H2158. This Phase 1a/b study (NCT03714152) had three parts: Part A, participants received a single ascending oral dose of ABI-H2158 (5-500 mg) or placebo; Part B, participants received multiple doses of ABI-H2158 300 mg once (QD) or twice (BID) daily or placebo, for 10 days; Part C, cHBV patients received ABI-H2158 (100, 300, or 500 mg QD or 300 mg BID) or placebo, for 14 days. Ninety-three participants enrolled. In Parts A/B, there were no serious adverse events (SAEs) or deaths, and all treatment-emergent AEs (TEAEs) were Grade 1. In Part C, two patients had Grade 3 TEAEs unrelated to ABI-H2158; there were no deaths, SAEs or Grade 4 TEAEs. In Part A, median time to maximum ABI-H2158 plasma concentration (T_max ) and mean terminal elimination half-life (t_½ ) were 1-4 and 9.8-20.7 h, and area under the plasma concentration-time curve increased dose proportionally. In Part B, Day 10 T_max was 2 h, mean t_½ was 15.5-18.4 h, and exposure accumulated 1.7- to 3.1-fold. In Part C, Day 14 T_max was 1 h, exposure accumulated 1.4- to 1.8-fold, and ABI-H2158 was associated with >2 log₁₀ declines in HBV nucleic acids. In conclusion, ABI-H2158 in cHBV patients following 14 days of dosing was well tolerated and demonstrated potent antiviral activity. Safety and pharmacokinetics supported future QD dosing.

Pregenomic RNA Launch Hepatitis B Virus Replication System Facilitates the Mechanistic Study of Antiviral Agents and Drug-Resistant Variants on Covalently Closed Circular DNA Synthesis

Hepatitis B virus (HBV) replicates its genomic DNA by reverse transcription of an RNA intermediate, termed pregenomic RNA (pgRNA), within nucleocapsid. It had been shown that transfection of in vitro-transcribed pgRNA initiated viral replication in human hepatoma cells. We demonstrated here that viral capsids, single-stranded DNA, relaxed circular DNA (rcDNA) and covalently closed circular DNA (cccDNA) became detectable sequentially at 3, 6, 12, and 24 h post-pgRNA transfection into Huh7.5 cells. The levels of viral DNA replication intermediates and cccDNA peaked at 24 and 48 h post-pgRNA transfection, respectively. HBV surface antigen (HBsAg) became detectable in culture medium at day 4 posttransfection. Interestingly, the early robust viral DNA replication and cccDNA synthesis did not depend on the expression of HBV X protein (HBx), whereas HBsAg production was strictly dependent on viral DNA replication and expression of HBx, consistent with the essential role of HBx in the transcriptional activation of cccDNA minichromosomes. While the robust and synchronized HBV replication within 48 h post-pgRNA transfection is particularly suitable for the precise mapping of the HBV replication steps, from capsid assembly to cccDNA formation, targeted by distinct antiviral agents, the treatment of cells starting at 48 h post-pgRNA transfection allows the assessment of antiviral agents on mature nucleocapsid uncoating, cccDNA synthesis, and transcription, as well as viral RNA stability. Moreover, the pgRNA launch system could be used to readily assess the impacts of drug-resistant variants on cccDNA formation and other replication steps in the viral life cycle. IMPORTANCE Hepadnaviral pgRNA not only serves as a template for reverse transcriptional replication of viral DNA but also expresses core protein and DNA polymerase to support viral genome replication and cccDNA synthesis. Not surprisingly, cytoplasmic expression of duck hepatitis B virus pgRNA initiated viral replication leading to infectious virion secretion. However, HBV replication and antiviral mechanism were studied primarily in human hepatoma cells transiently or stably transfected with plasmid-based HBV replicons. The presence of large amounts of transfected HBV DNA or transgenes in cellular chromosomes hampered the robust analyses of HBV replication and cccDNA function. As demonstrated here, the pgRNA launch HBV replication system permits the accurate mapping of antiviral target and investigation of cccDNA biosynthesis and transcription using secreted HBsAg as a convenient quantitative marker. The effect of drug-resistant variants on viral capsid assembly, genome replication, and cccDNA biosynthesis and function can also be assessed using this system.

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

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

The identification of highly efficacious functionalised tetrahydrocyclopenta[c]pyrroles as inhibitors of HBV viral replication through modulation of HBV capsid assembly

Disruption of the HBV viral life cycle with small molecules that prevent the encapsidation of pregenomic RNA and viral polymerase through binding to HBV core protein is a clinically validated approach to inhibiting HBV viral replication. Herein we report the further optimisation of clinical candidate AB-506 through core modification with a focus on increasing oral exposure and oral half-life. Maintenance of high levels of anti-HBV cellular potency in conjunction with improvements in pharmacokinetic properties led to multi-log₁₀ reductions in serum HBV DNA following low, once-daily oral dosing for key analogues in a preclinical animal model of HBV replication.