Catechol-phytochemical conjugates potentiate quorum quenching and antivirulence response against Pseudomonas...

Development of drug hybrids with anti-quorum sensing (QS) and antivirulence properties has been widely regarded as a viable alternative for combating drug resistance in Pseudomonas aeruginosa. In this study, conjugates (1-3) were synthesized using three naturally-occurring phytochemicals: guaiacol, vanillin, and eugenol via pharmacophoric hybridization with catechol moiety. Among the synthesized conjugates that showed broad-spectrum antibacterial activity and iron-chelating potential, catechol-vanillin conjugate (2) demonstrated relatively higher degree of QS inhibition and significantly reduced AHL production (49.5 %) in P. aeruginosa. Although catechol-guaiacol (1) & catechol-eugenol (3) conjugates drastically attenuated pseudomonal virulence, catechol-vanillin conjugate (2) showed maximum curtailment over hemolysin (42.8 %), pyocyanin (56.5 %), alginate (49.9 %), rhamnolipid (32.7 %) production and protease/elastase (39.1 %/68.8 %) activity alongside impeding motility phenotypes at sub-MIC levels. These findings were correlated with molecular docking studies that predicted strong interactions between catechol-vanillin conjugate (2) and PqsR receptor (-11.87 kcal mol^-1) of P. aeruginosa. Analytical TLC further confirmed a notable reduction in PQS production, thereby confirming that conjugate 2 extends antivirulence response via curtailment of Pqs pathway. Additionally, all the synthesized conjugates (1-3) exhibited a non-cytotoxic (biocompatible) nature towards sheep erythrocytes and HEK 293 cells in vitro, thereby paving way for pre-clinical validation of their antivirulence potential in animal models in vivo.