High Throughput Screening for Small-Molecule Inhibitors of Type III Secretion in Yersinia pestis

Yersinia pestis, Yersinia pseudotuberculosis and Yersinia enterocolitica, utilize a plasmid encoded type III secretion system (T3SS) to promote infection by delivering Yersinia outer proteins (Yops) into the cytosol of mammalian cells. This T3SS is absolutely required for Yersinia virulence, which makes T3SS an attractive target in the development of novel therapeutics for treatment of plague and other Yersinia infections. In this study, a new method for high throughput screening (HTS) of small molecules for the ability to inhibit type III secretion (T3S) in Y. pestis has been developed. In comparison with screening assays employed by others, this method is very simple and rapid, and thus well suited for examining very large compound sets. Using this method, we screened a diverse collection of libraries at the US National Screening Laboratory. The initial examination of 70,966 compounds and mixtures from 13 libraries resulted in 431 primary hits. Strong positive indications of inhibition were observed at a rate of 0.01%, while moderate and weak but potentially meaningful signals were observed at rates of 0.056% and 0.54% respectively. Further characterizations were conducted on selected primary hits in Y. pestis. Of the eight compounds examined in secondary assays, four show good promise as leads for structure activity relationship studies. They are a diverse group, each having chemical scaffolds not only distinct from one another, but also distinct from previously described candidate T3S inhibitors.