Broad-spectrum inhibitor of non-structural protein 2 protease shows therapeutic efficacy against Venezuelan equine encephalitis viral infection.

The nsP2 protease offers a unique opportunity to develop both narrow- and broad-spectrum direct-acting antiviral drugs against the family of togaviruses, given its critical role in viral replication. In this work, we report the identification of potent, broad-spectrum inhibitors of the nsP2 protease that cover nearly all members of the Togaviridae family and have translational potential, as they selectively block viral replication in cell cultures. The three classes of potent inhibitors have a C5-substituted pyrrole, tetrahydroquinoline, or indole-based scaffold. The lead candidate, BFB78, is metabolically stable when exposed to mouse and human liver phase I and phase II metabolic enzymes, exhibits good exposure in mouse plasma, and can cross the blood-brain barrier. BFB78 demonstrated 100% therapeutic efficacy, as measured by survival, in lethal mice models of VEEV infection and significantly reduced viral titer by more than four logs in mouse brains at 50 mg/kg body weight, on average. Additional preclinical studies are underway on BFB78 and the indole-based inhibitors of the nsP2 protease as potential broad-spectrum candidates. In addition, the inhibitors with the tetrahydroquinoline motif appear to be good candidates with narrow-spectrum activity against BFV, ONV, CHIKV, and MAYV.