Optimization and Synthesis of Pyridazinone Derivatives as Novel Inhibitors of Hepatitis B Virus by Inducing Genome-free Capsid Formation

A novel phthalazinone derivative as a capsid assembly modulator inhibits hepatitis B virus expression

Development of new anti-hepatitis B virus (HBV) drugs that target viral capsid assembly is a very active research field. We identify a novel phthalazinone derivative, compound 5832, as a potent HBV inhibitor. In this study, we intend to elaborate the antiviral effect and mechanism of 5832 against HBV in vitro and in vivo. Compound 5832 treatment induces the formation of genome-free empty capsid by interfering with the core protein assembly domain, which significantly decreases the extracellular and intracellular HBV DNA. In the AAV-HBV transduced mouse model, 5832 suppresses serum HBV DNA after 4-week treatment, and decreases HBsAg and HBeAg levels. 5832 treatment also reduces intrahepatic HBV RNA, DNA and HBcAg levels. During the follow-up period after treatment withdrawal, serum antigen levels demonstrated no increase. We demonstrate 5832 treatment could active apoptotic signaling by elevating the expression of death receptor 5 (DR5), which participated in corresponding HBcAg-positive hepatocyte eradication. Phthalazinone derivative 5832 may serve as a promising anti-HBV drug candidate to improve the treatment options for chronic HBV infection.

Discovery of (S)-N-(2-Amino-4-fluorophenyl)-4-(1-(3-(4-((dimethylamino)methyl)phenyl)-6-oxopyridazin-1(6H)-yl)ethyl)benzamide as Potent Class I Selective HDAC Inhibitor for Oral Anticancer Drug Candidate

A novel series of benzamide derivatives were successively designed and synthesized prepared from the pyridazinone scaffold. Among them, (S)-17b, demonstrated potent inhibitory activity in vitro toward human class I HDAC isoforms and human myelodysplastic syndrome (SKM-1) cell line. Also, (S)-17b strongly increased the intracellular level of acetyl-histone H3 and P21 simultaneously and effectively induced G1 cell cycle arrest and apoptosis. Through oral dosing in SKM-1 xenograft models, (S)-17b exhibited excellent in vivo antitumor activity. In addition, compound (S)-17b showed better antitumor efficacy on mouse models with intact immune system than those with thymus deficiencies. Furthermore, this compound displayed a favorable pharmacokinetic profile in ICR mice and SD rat, respectively, minimal metabolic property differences among hepatocytes from five species, and a low inhibition upon the human ether-a-go-go (hERG) channel with an IC₅₀ value of 34.6 μΜ. This novel compound (S)-17b may serve as a new drug candidate for further investigation.

A prodrug of the capsid assembly modulator improved druggability and lowing HBsAg and HBeAg for the treatment of chronic hepatitis B

CAMs were disclosed to alter cccDNA levels with sustained hepatitis B surface antigen (HBsAg) loss or seroconversion in preclinical investigation. Here, we report the discovery of a prodrug Yhhu6669 as CAMs based on the intestinal peptide transporter. This compound exhibited the promising anti-HBV activity with sustained suppression of HBV DNA, as well as HBsAg and HBeAg in the AAV HBV mouse model by oral treatment for 7 weeks and maintained for a further 8 weeks following drug withdraw. Our results show an alternative possibility for a functional cure by specific CAMs and provide the basis for the further mechanism study.

A molecular simulation study of hepatitis B virus core protein and the nuclear protein allosteric modulators of phthalazinone derivatives

Hepatitis B virus, causing hepatitis, cirrhosis, liver failure, and liver cancer, poses a serious threat to human health, and the currently approved drugs still cannot eliminate the virus completely. HBV core protein allosteric modulators (CpAMs) with a phthalazinone structure which targets the HBV core (HBc) protein have been seen as a new kind of drug because of their excellent antiviral effects. This study explores the structure-activity relationship and binding mechanism of phthalazinone molecules through three-dimensional quantitative structure-activity relationship (3D-QSAR), molecular docking, molecular dynamics, and binding free energy calculation and decomposition studies. In addition, CoMFA and CoMSIA models revealed that the steric field, the hydrophobic field, and the hydrogen bond acceptor field may play important roles in the binding process. The molecular docking and dynamics disclosed the most likely binding pose of phthalazinone derivatives with the HBc protein. The binding free energy calculation and decomposition analysis indicated that the van der Waals force was the driving force and that ValE124, ThrD109, ThrE128, LeuD140, IleD105, PheD110, ThrD33, and TrpD102 were the key residues. This study provides an important theoretical basis for the design and optimization of phthalazinone compounds.

Discovery of novel HBV capsid assembly modulators by structure-based virtual screening and bioassays

HBV capsid assembly has been regarded as an attractive potential target for anti-HBV therapy. In this study, we discovery the Novel HBV capsid assembly modulators (CAMs) through structure-based virtual screening and bioassays. A total of 16 structurally diverse compounds were purchased and assayed, including three compounds with inhibition rate > 50% at 20 μM. Further lead optimization based on the most potent compound II-1-7 (EC₅₀ = 5.6 ± 0.1 µM) were performed by using substructure searching strategy, resulting in compound II-2-9 with an EC₅₀ value of 1.8 ± 0.6 μM. In bimolecular fluorescence complementation (BiFC) assay, compound II-2-9 inhibited the HBV by disrupting the HBV capsid interactions. In summary, this study provides a highly efficient way to discover novel CAMs, and 2-aryl-4-quinolyl amide derivatives could serve as the starting point for development of novel anti-HBV drugs.

Synthesis of 4-oxotetrahydropyrimidine-1(2H)-carboxamides derivatives as capsid assembly modulators of hepatitis B virus

We report herein the synthesis and evaluation of phenyl ureas derived from 4-oxotetrahydropyrimidine as novel capsid assembly modulators of hepatitis B virus (HBV). Among the derivatives, compound 27 (58031) and several analogs showed an activity of submicromolar EC₅₀ against HBV and low cytotoxicities (>50 μM). Structure–activity relationship studies revealed a tolerance for an additional group at position 5 of 4-oxotetrahydropyrimidine. The mechanism study indicates that compound 27 (58031) is a type II core protein allosteric modulator (CpAMs), which induces core protein dimers to assemble empty capsids with fast electrophoresis mobility in native agarose gel. These compounds may thus serve as leads for future developments of novel antivirals against HBV.

Discovery of Phthalazinone Derivatives as Novel Hepatitis B Virus Capsid Inhibitors

HBV capsid assembly has been viewed as an attractive target for new antiviral therapies against HBV. On the basis of a lead compound 4r, we further investigated this target to identify novel active compounds with appropriate anti-HBV potencies and improved pharmacokinetic (PK) properties. Structure-activity relationship studies based on metabolic pathways of 4r led to the identification of a phthalazinone derivative 19f with appropriate anti-HBV potencies (IC₅₀ = 0.014 ± 0.004 μM in vitro), which demonstrated high oral bioavailability and liver exposure. In the AAV-HBV/mouse model, administration of 19f resulted in a 2.67 log reduction of the HBV DNA viral load during a 4-week treatment with 150 mg/kg dosing twice daily.

Treatment of Chronic Hepatitis B Virus Infection Using Small Molecule Modulators of Nucleocapsid Assembly: Recent Advances and Perspectives

On the basis of the recent advance of basic research on molecular biology of hepatitis B virus (HBV) infection, novel antiviral drugs targeting various steps of the HBV life cycle have been developed in recent years. HBV nucleocapsid assembly is now recognized as a hot target for anti-HBV drug development. Structural and functional analysis of HBV nucleocapsid allowed rational design and improvement of small molecules with the ability to interact with the components of HBV nucleocapsid and modulate the viral nucleocapsid assembly process. Prototypes of small molecule modulators targeting HBV nucleocapsid assembly are being preclinically tested or have moved forward in clinical trials, with promising results. This Review summarizes the recent advances in the approach to develop antiviral drugs based on the modulation of HBV nucleocapsid assembly. The antiviral mechanisms of small molecule modulators beyond the capsid formation and the potential implications will be discussed.

Identification of Compounds Targeting Hepatitis B Virus Core Protein Dimerization through a Split Luciferase Complementation Assay

The capsid of the hepatitis B virus is an attractive antiviral target for developing therapies against chronic hepatitis B infection. Currently available core protein allosteric modulators (CpAMs) mainly affect one of the two major types of protein-protein interactions involved in the process of capsid assembly, namely, the interaction between the core dimers. Compounds targeting the interaction between two core monomers have not been rigorously screened due to the lack of screening models. We report here a cell-based assay in which the formation of core dimers is indicated by split luciferase complementation (SLC). Making use of this model, 2 compounds, Arbidol (umifenovir) and 20-deoxyingenol, were identified from a library containing 672 compounds as core dimerization regulators. Arbidol and 20-deoxyingenol inhibit the hepatitis B virus (HBV) DNA replication in vitro by decreasing and increasing the formation of core dimer and capsid, respectively. Our results provided a proof of concept for the cell model to be used to screen new agents targeting the step of core dimer and capsid formation.

The Heteroaryldihydropyrimidine Bay 38-7690 Induces Hepatitis B Virus Core Protein Aggregates Associated with Promyelocytic Leukemia Nuclear Bodies in Infected Cells

Heteroaryldihydropyrimidines (HAPs) are compounds that inhibit hepatitis B virus (HBV) replication by modulating viral capsid assembly. While their biophysical effects on capsid assembly in vitro have been previously studied, the effect of HAP treatment on capsid protein (Cp) in individual HBV-infected cells remains unknown. We report here that the HAP Bay 38-7690 promotes aggregation of recombinant Cp in vitro and causes a time- and dose-dependent decrease of Cp in infected cells, consistent with previously studied HAPs. Interestingly, immunofluorescence analysis showed Cp aggregating in nuclear foci of Bay 38-7690-treated infected cells in a time- and dose-dependent manner. We found these foci to be associated with promyelocytic leukemia (PML) nuclear bodies (NBs), which are structures that affect many cellular functions, including DNA damage response, transcription, apoptosis, and antiviral responses. Cp aggregation is not an artifact of the cell system used, as it is observed in HBV-expressing HepAD38 cells, in HepG2 cells transfected with an HBV-expressing plasmid, and in HepG2-NTCP cells infected with HBV. Use of a Cp overexpression vector without HBV sequences shows that aggregation is independent of viral replication, and use of an HBV-expressing plasmid harboring a HAP resistance mutation in Cp abrogated the aggregation, demonstrating that the effect is due to direct compound-Cp interactions. These studies provide novel insight into the effects of HAP-based treatment at a single-cell level.IMPORTANCE Despite the availability of effective vaccines and treatments, HBV remains a significant global health concern, with more than 240 million individuals chronically infected. Current treatments are highly effective at controlling viral replication and disease progression but rarely cure infections. Therefore, much emphasis is being placed on finding therapeutics with new drug targets, such as viral gene expression, covalently closed circular DNA formation and stability, capsid formation, and host immune modulators, with the ultimate goal of an HBV cure. Understanding the mechanisms by which novel antiviral agents act will be imperative for the development of curative HBV therapies.