IRBM-Z-1 is a non-competitive allosteric inhibitor of the Zika virus (ZIKV) NS2B-NS3 protease, identified through phenotypic screening for ZIKV replication inhibitors. In vitro, IRBM-Z-1 inhibits recombinant ZIKV NS2B-NS3 protease with an IC50 of 1.8 ± 0.8 μM and binds the protease with a KD of 1.52 ± 0.75 μM. In ZIKV replicon assays, IRBM-Z-1 suppresses viral RNA replication with an EC50 of 6.0 ± 1.9 μM and inhibits ZIKV-induced cytopathic effects in cell culture with an EC50 of approximately 6.25 μM, while showing no significant cytotoxicity at concentrations up to 32 μM. Activity is strongly dependent on NS3 residue I156, with the I156T mutation markedly reducing potency.
