Sulfonyl Homoserine Lactones Are Tunable Probes to Inhibit the Quorum Sensing Receptor RhlR and Reduce Swarming...

We report non-native small molecules capable of inhibiting a key quorum sensing receptor─RhlR─in the opportunistic pathogen Pseudomonas aeruginosa. This protein is a member of the LuxR-type receptor family that is common to Gram-negative bacteria and recognizes N-acyl l-homoserine lactone (AHL) signals. RhlR has emerged as an increasingly important regulator of virulence pathways in P. aeruginosa, in concert with several other quorum sensing receptors, including LasR, QscR, and PqsR. Chemical inhibition of RhlR represents an approach to both study the role of RhlR in this quorum sensing signaling hierarchy and attenuate infection by P. aeruginosa. Small-molecule RhlR antagonists with high potencies and defined modes of action remain relatively scarce, however. AHL analogs with non-native acyl side chains represent a well-studied class of LuxR-type receptor modulators, but replacement of the native amide with alternate isosteres has been far less examined. In the current study, we investigated the activity of a series of sulfonamide AHL analogs as RhlR antagonists using transcriptional reporter assays. We identified meta-substituted aryl- and short-chain alkylsulfonyl lactones as potent and efficacious classes of synthetic RhlR antagonists. The activity profiles of the aryl derivatives were readily tuned via altering the position and electronics of aryl ring substituents. The most potent antagonists were active in P. aeruginosa and could significantly reduce its swarming motility, a key virulence determinant. Computational modeling revealed these compounds can be accommodated within the RhlR ligand-binding site and certain interactions may be required for high inhibitory potency.