Overview of the development of HBV small molecule inhibitors

Structural optimization of phthalazine derivatives for anti-HBV activities to improve oral bioavailability

The hepatitis B virus (HBV) capsid protein forms a protective nucleocapsid essential for viral replication, establishing capsid assembly modulation as a promising therapeutic strategy. Based on previous mechanistic studies, we identified phthalazine derivatives as potent HBV capsid assembly modulators (CAMs), with Yhhu6517 exhibiting submicromolar antiviral activity in vitro. However, its clinical translation was hindered by poor oral pharmacokinetics (PK), due to rapid first-pass metabolism of oxidation-prone primary alcohol groups. Through metabolic stability-guided structure-activity relationship (SAR) studies involving systematic replacement of primary alcohols with non-primary alcohol-derived hydrophilic groups, we optimized the fragments to yield compound 2p. This optimized candidate 2p maintained a potent anti-HBV activity (IC50 = 0.016 μM in HepG2.2.15 cells) while demonstrating improved an oral bioavailability (F = 80.6 % in mice) and enhanced plasma exposure (AUC0-24h = 10.3 μg·h/mL). These findings confirm phthalazine-based anti-HBV agents, with compound 2p emerging as a candidate for the further development.

Salicylamide derivatives as potent HBV inhibitors: insights into structure-activity relationships

Current HBV treatment with nucleos(t)ide analogs requires lifelong administration and is associated with the risk of drug resistance, underscoring the urgent need for novel antivirals with alternative targets. Herein, we reported the design, synthesis, and biological evaluation of a series of salicylamide derivatives as potent anti-HBV agents. The nine selected compounds exhibited dose-dependent inhibitory effects on HBV replication, as evidenced by significant reductions in both virion DNA and the secretion levels of HBsAg and HBeAg. Among them, compounds 50 and 56 exhibited the highest anti-HBV activity (IC50 = 0.52 and 0.47 μM, respectively) and selectivity (SI = 20.1 and 17.6, respectively). Mechanistic studies revealed that compounds 27, 31, and 47 impaired HBV core protein (HBc) expression, while compound 50 disrupted capsid formation without significantly affecting HBc expression. These findings highlight the therapeutic potential of salicylamide derivatives as promising anti-HBV agents and provide a foundation for further structural optimization and mechanistic exploration.

Design, Synthesis, and Bioevaluation of Matrine Derivatives as Potential Anti-Hepatitis B Virus Agents

Hepatitis B virus (HBV) is a causative reagent that frequently causes progressive liver diseases, leading to the development of acute hepatitis, chronic hepatitis, cirrhosis, and eventually hepatocellular carcinoma. Despite several antiviral drugs, including interferon-α and nucleotide derivatives, being approved for clinical treatment of HBV, critical issues remain unresolved, e.g., their low-to-moderate efficacy and adverse side effects, as well as resistant strains. In this study, twenty-three matrine derivatives were synthesized, and their antiviral effects against HBV were evaluated. Of these, eleven compounds inhibited HBeAg secretion significantly more than the positive control, lamivudine (3TC). Among the compounds synthesized in this study, compounds 4a and 4d had the most potent inhibitory activity, with IC50 value of 41.78 and 33.68 μM, respectively. Compounds 1h, 4a, and 4d were also subjected to molecular docking studies. These compounds inhibited viral gene expression and viral propagation in a cell culture model. Thus, we believe our compounds could serve as resource for antiviral drug development.

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.

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

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

Development of anti-HBV agents targeting HBV capsid proteins

Hepatitis B is a viral hepatitis, which is caused by infection of hepatitis B virus (HBV). This disease progresses to chronic hepatitis, cirrhosis and liver cancer. To treat hepatitis B, exclusion of virus and covalently closed circular DNA (cccDNA) that is formed in hepatocyte nucleus is necessary. A hepatitis B capsid protein (HBc) is an indispensable protein, which forms the capsid that encapsulates viral DNA. Since HBc is correlated to the transcriptional regulation of cccDNA, this protein would be an attractive target for complete cure of hepatitis B. By in silico screening of a library of compounds, a small compound, Cpd4 (1), which binds to a hydrophobic cavity located in the inner pocket on the tetramer interface of HBc proteins, was identified. In anti-HBV assays, this synthetic compound, Cpd4 (1) decreased the amount of HBV core related antigen (HBcrAg), which has been correlated with the proliferation of HBV, and decreased the amount of HBV surface antigen (HBsAg), which is correlated with the amount of cccDNA. Based on Cpd4 (1) as a lead compound, 20 derivatives of 1 were designed and synthesized and their structure-activity relationships were examined. As a result, specific interactions between each compound and amino acid residues of the target protein appeared to be unimportant but the shape/size of compounds which can bind to the hydrophobic cavity might be important in the expression of high anti-HBV activity, and a more potent derivative, TKB-HBV-CA-001 (3b), was discovered. These results will be useful in the development of novel anti-HBV agents for a complete cure of hepatitis B.