Identification of chlamydial T3SS inhibitors through virtual screening against T3SS ATPase.

Chlamydia trachomatis is a widespread sexually transmitted pathogen that resides within a special vacuole inside host cells. Although acute infection can be treated with antibiotics, chlamydia can enter persistent state, leading to chronic infection that is difficult to cure. Thus, novel anti-chlamydial compounds active against persistent chlamydia are required. Chlamydiae rely upon type III secretion system (T3SS) to inject effector proteins into host cell cytoplasm, and T3SS inhibitors are viewed as promising compounds for treatment of chlamydial infections. C. trachomatis ATPase SctN is an important T3SS component and has not been targeted before. We thus used virtual screening against homology modeled SctN structure to search for SctN inhibitors. Selected compounds were tested for their ability to inhibit chlamydial survival and development within eukaryotic cells, and for the ability to suppress normal T3SS functioning. We identified two compounds that were able to block normal protein translocation through T3SS and inhibit chlamydial survival within eukaryotic cells in 50-100 μm concentrations. These two novel T3SS inhibitors also possessed relatively low toxicity toward eukaryotic cells. A small series of derivatives was further synthesized for the most active of two inhibitors to probe SAR properties.