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.