Small molecule screen yields inhibitors of pseudomonas homoserine lactone‐induced host responses

Summary Pseudomonas aeruginosa infections are commonly associated with cystic fibrosis, pneumonias, neutropenia and burns. The P. aeruginosa quorum sensing molecule N‐(3‐oxo‐dodecanoyl) homoserine lactone (C12) cause multiple deleterious host responses, including repression of NF‐κB transcriptional activity and apoptosis. Inhibition of C12‐mediated host responses is predicted to reduce P. aeruginosa virulence. We report here a novel, host‐targeted approach for potential adjunctive anti‐Pseudomonal therapy based on inhibition of C12‐mediated host responses. A high‐throughput screen was developed to identify C12 inhibitors that restore NF‐κB activity in C12‐treated, lipopolysaccharide (LPS)‐stimulated cells. Triazolo[4,3‐a]quinolines with nanomolar potency were identified as C12‐inhibitors that restore NF‐κB‐dependent luciferase expression in LPS‐ and TNF‐stimulated cell lines. In primary macrophages and fibroblasts, triazolo[4,3‐a]quinolines inhibited C12 action to restore cytokine secretion in LPS‐stimulated cells. Serendipitously, in the absence of an inflammatory stimulus, triazolo[4,3‐a]quinolines prevented C12‐mediated responses, including cytotoxicity, elevation of cytoplasmic calcium, and p38 MAPK phosphorylation. In vivo efficacy was demonstrated in a murine model of dermal inflammation involving intradermalC12 administration. The discovery of triazolo[4,3‐a]quinolines provides a pharmacological tool to investigate C12‐mediated host responses, and a potential host‐targeted anti‐Pseudomonal therapy. Pseudomonas aeruginosa infections result in high mortality rates and constitute a significant health care burden. Antimicrobials are the mainstay of anti‐Pseudomonal therapy; however, increasing antibiotic resistance mandates development of new approaches to combat infections. The homoserine lactone C12, a Pseudomonal quorum‐sensing molecule, initiates deleterious host effects including apoptosis and repression of NF‐?B transcription. Nanomolar potency inhibitors of C12‐mediated host responses discovered by high throughput screening are described that are predicted to attenuate bacterial virulence.