Structure-based discovery of two antiviral inhibitors targeting the NS3 helicase of Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a flavivirus that threatens more than half of the world's population. Vaccination can prevent the disease, but no specific antiviral drug is yet available for clinical therapy, and the death rate caused by JEV can reach as high as 60%. The C-terminus of non-structural protein 3 (NS3) of flavivirus encodes helicase and has been identified as a potential drug target. In this study, high throughput molecular docking was employed to identify candidate JEV NS3 helicase inhibitors in a commercial library containing 250,000 compounds. Forty-one compounds were then tested for their ability to inhibit NS3 activity. Two compounds inhibited unwinding activity strongly but had no effect on the ATPase activity of the protein. Western blots, IFA, and plaque reduction assays demonstrated that both compounds inhibited the virus in cell culture. The EC50s of the two compounds were 25.67 and 23.50 μM, respectively. Using simulated docking, the two compounds were shown to bind and block the NS3 RNA unwinding channel, consistent with the results of the enzyme inhibition tests. The atoms participating in intramolecular interaction were identified to facilitate future compound optimization.