Small molecules inhibit hepatitis B and D virus infection by binding the small surface antigen

Current therapies for chronic hepatitis B virus (HBV) infection effectively suppress viral replication but do not achieve a functional cure. Targeting viral entry represents a promising strategy to complement existing treatments.

Small-molecule compounds were identified through structure-based virtual screening targeting SHBs (small hepatitis B surface antigen). HBV infection models using HepG2-NTCP cells and primary human hepatocytes were established to investigate the antiviral activities and underlying mechanisms of these compounds in vitro. Molecular docking analyses were performed to predict the potential binding regions of the small molecules with SHBs. In addition, we performed mutagenesis based on the predicted interaction residues, followed by functional assays to validate the docking predictions.

Assays in the HBV infection model showed that isotretinoin, ciprofibrate, and caffeic acid significantly reduced HBsAg, HBeAg, and HBV pregenomic RNA levels when administered concurrently with HBV infection. Biophysical and biochemical assays demonstrated that these compounds interacted with SHBs. In addition, molecular docking and site-directed mutagenesis-based functional assays suggested that the interaction sites may involve the AGL region. Mechanistically, the compounds mainly acted during the early stage of infection and reduced HBV attachment and internalization-associated signals. In addition, these compounds inhibited HDV infection, supporting their activity against HBV envelope-mediated viral entry.

Our findings suggest that these small molecules are promising candidates for developing novel entry inhibitors targeting SHBs, which may enhance therapeutic options against HBV and HDV.