Screening method toward ClbP-specific inhibitors

Background Colibactin is a genotoxin produced by Escherichia coli and other Enterobacteriaceae that is believed to increase the risk of colorectal cancer (CRC) of their symbiosis hosts, including human. A peptidase ClbP is the key enzyme for activation of colibactin. Inhibition of ClbP is considered to impede maturation of precolibactin into genotoxic colibactin. Therefore, ClbP-specific inhibitors could potentially prevent the onset of CRC, one of the leading causes of cancer-related deaths in the world. This study intends to establish an efficient screening system for identifying inhibitors that are specific to ClbP. Methods Two types of assays were applied in the screening procedure: a probe assay and an LC–MS assay. For the probe assay, we employed the synthesized probe which we described in our previous report. This probe can be hydrolyzed efficiently by ClbP to release a fluorophore. Hence it was applied here for detection of inhibition of ClbP. For the LC–MS assay, formation of the byproduct of precolibactin maturation process, N -myristoyl-D-asparagine, was quantified using a liquid chromatography–mass spectrometry (LC–MS) technique. The probe assay can be performed much faster, while the LC–MS assay is more accurate. Therefore, our method employed the two assays in sequence to screen a large number of compounds for inhibition of ClbP. Results A library of 67,965 standard compounds was evaluated by the screening method established in the current study, and one compound was found to show a moderate inhibitory activity against ClbP. Conclusion A simple screening method for ClbP-specific inhibitors was established. It was proven to be reliable and is believed to be useful in developing potential prophylactic agents for CRC.