Novel non-nucleoside inhibitors of Zika virus polymerase identified through the screening of an open library of anti-kynetoplastid compounds.

Zika virus (ZIKV) is a mosquito-borne pathogen responsible for neurological disorders (Guillain-Barré syndrome) and congenital malformations (microcephaly). Its ability to cause explosive epidemics, such as that of 2015-16, urges the identification for effective antiviral drugs. Viral polymerase inhibitors constitute one of the most successful fields in antiviral research. Accordingly, the RNA-dependent RNA polymerase activity of flavivirus NS5 protein provides a unique target for the development of direct antivirals with high specificity and low toxicity. Here we describe the discovery and characterization of two novel non-nucleoside inhibitors of ZIKV polymerase. These inhibitors, TCMDC-143406 (6) and TCMDC-143215 (15), were identified through the screening of an open resource library of anti-kinetoplastid compounds using a fluorescence-based polymerization assay based on ZIKV NS5. The two compounds inhibited ZIKV NS5 polymerase activity in vitro and ZIKV multiplication in cell culture (EC50 values of 0.5 and 2.6 μM for 6 and 15, respectively). Both compounds also inhibited the replication of other pathogenic flaviviruses, namely West Nile virus (WNV; EC50 values of 4.3 and 4.6 μM for 6 and 15, respectively) and dengue virus 2 (DENV-2; EC50 values of 3.4 and 9.6 μM for 6 and 15, respectively). Enzymatic assays confirmed that the polymerase inhibition was produced by a non-competitive mechanism. Combinatorial assays revealed an antagonistic effect between both compounds, suggesting that they would bind to the same region of ZIKV polymerase. The non-nucleoside inhibitors of ZIKV polymerase here described could constitute promising lead compounds for the development of anti-ZIKV therapies and eventually broad-spectrum anti-flavivirus drugs.