Discovery and Biophysical Characterization of 2-Amino-oxadiazoles as Novel Antagonists of PqsR, an Important Regulator of Pseudomonas aeruginosa Virulence

The human pathogen Pseudomonas aeruginosa employs alkyl quinolones for cell-to-cell communication. The Pseudomonas quinolone signal (PQS) regulates various virulence factors via interaction with the transcriptional regulator PqsR. Therefore, we consider the development of PqsR antagonists a novel strategy to limit the pathogenicity of P. aeruginosa. A fragment identification approach using surface plasmon resonance screening led to the discovery of chemically diverse PqsR ligands. The optimization of the most promising hit (5) resulted in the oxadiazole-2-amine 37 showing pure antagonistic activity in Escherichia coli (EC50 = 7.5 μM) and P. aeruginosa (EC50 = 38.5 μM) reporter gene assays. 37 was able to diminish the production of the PQS precursor HHQ in a PqsH-deficient P. aeruginosa mutant. The level of the major virulence factor pyocyanin was significantly reduced in wild-type P. aeruginosa. In addition, site-directed mutagenesis in combination with isothermal titration calorimetry and NMR INPHARMA ex...