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

Abstract

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 experiments revealed that the identified ligands bind to the same site of PqsR by adopting different binding modes. These findings will be utilized in a future fragment-growing approach aiming at novel therapeutic options for the treatment of P. aeruginosa infections.

The art of antibacterial warfare: Deception through interference with quorum sensing–mediated communication

“…Hit compounds were identified with high affinity for the PqsR ligand-binding domain that strongly inhibit PqsR activity in a heterologous E. coli-based reporter system. However, these compounds (hydroxamic acid-derivatives and 2-amino-oxadiazoles) displayed reduced PqsR-antagonistic activity when evaluated in P. aeruginosa [51,52].…”

In-depth Profiling of MvfR-Regulated Small Molecules in Pseudomonas aeruginosa after Quorum Sensing Inhibitor Treatment

“…So far, a number of MvfR antagonists and PqsBC inhibitors have been developed that efficiently reduced HHQ and PQS production in P. aeruginosa (Zender et al, 2013; Lu et al, 2014a; Starkey et al, 2014). The aim of this work was to gather detailed information about the effects of these QS Inhibitors (QSIs) on the production of MvfR-related small molecules including 2-AA, DHQ, HQNO, HHQ, and PQS.…”

Flexible Fragment Growing Boosts Potency of Quorum‐Sensing Inhibitors against Pseudomonas aeruginosa Virulence

“…During two previously reported fragment‐optimization approaches, compounds 1 and 2 (Table ) were discovered. The thermodynamic profiles of these optimized fragments were compared to the best screening hits derived from previously reported SPR screenings . Initially, compound 3 was ranked lower due to its lower affinity .…”

“…Furthermore, an HTS campaign led to benzamide‐benzimidazole compounds showing efficacy in different mouse models, which emphasizes the in vivo relevance of targeting PqsR in infectious diseases . To overcome the poor physicochemical profiles of the HHQ‐derived QSI, we initiated two fragment screenings using surface plasmon resonance (SPR) technology . These approaches led to the hydroxamic acid 1 and the 2‐amino‐oxadiazole 2 (Table ).…”