Umbelliferone Inhibits Zika Virus (ZIKV) NS5 Activity and Replication In Vitro

This study focused on the inhibitory effects of umbelliferone on Zika virus (ZIKV) NS5 activity and viral replication in vitro. Umbelliferone exhibited no detectable cytotoxicity and inhibited ZIKV replication while showing no activity against Japanese encephalitis virus (JEV), another member of the Flaviviridae family. Structure-activity relationship studies on structurally related derivatives of umbelliferone revealed that the hydroxyl group at the C7 position is critical for suppression of ZIKV replication. To identify the stage of the ZIKV life cycle targeted by umbelliferone, we performed a time-of-drug-addition assay, which showed that umbelliferone exerted antiviral activity at a postentry stage of infection. Because umbelliferone did not inhibit NS3-mediated proteolytic processing of the viral polyprotein into mature proteins, it likely acted at a stage of the viral life cycle after polyprotein processing. Further in silico molecular docking analyses with ZIKV proteins predicted that umbelliferone targets ZIKV NS5. Consistent with this result, umbelliferone disrupted the ZIKV NS5 activity in vitro. These overall findings establish umbelliferone as a potent inhibitor of ZIKV NS5, supporting its potential as a lead compound for anti-ZIKV therapeutic drug development.