A cell-based assay to discover inhibitors of Zika virus RNA-dependent RNA polymerase.

Zika virus (ZIKV) belongs to Flaviviridae, the Flavivirus genus. Its infection causes congenital brain abnormalities and Guillain-Barré syndrome. However, there are no effective vaccines, no FDA-approved drugs to manage ZIKV infection. The non-structural protein NS5 of ZIKV has been recognized as a valuable target of antivirals because of its RNA-dependent RNA polymerase (RdRp) and methyltransferase (MTase) activities essential for viral RNA synthesis. Here, we report a cell-based assay for discovering inhibitors of ZIKV NS5 and found that 5-Azacytidine potently inhibits ZIKV NS5, with EC50 of 4.9 μM. Furthermore, 5-Azacytidine suppresses ZIKV replication by inhibiting NS5-mediated viral RNA transcription. Therefore, we have developed a cell-based ZIKV NS5 assay which can be deployed to discover ZIKV NS5 inhibitors and demonstrated the potential of 5-Azacytidine for further development as a ZIKV NS5 inhibitor.