Discovery and evaluation of 3-(2-isocyanobenzyl)-1H-indole derivatives as potential quorum sensing inhibitors for the control of Pseudomonas aeruginosa infections in vitro†

Quorum sensing (QS) inhibition stands out as an innovative therapeutic strategy for combating infections caused by drug-resistant pathogens. In this study, we assessed the potential of 3-(2-isocyanobenzyl)-1H-indole derivatives as novel quorum sensing inhibitors (QSIs). Initial screenings of their QS inhibitory activities were conducted against Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum CV026. Notably, six 3-(2-isocyanobenzyl)-1H-indole derivatives (4, 12, 25, 28, 32, and 33) exhibited promising QS, biofilms, and pyocyanin inhibitory activities under minimum inhibitory concentrations (MICs) against P. aeruginosa PAO1. Among them, 3-(2-isocyano-6-methylbenzyl)-1H-indole (IMBI, 32) emerged as the most promising candidate, demonstrating superior biofilm and pyocyanin inhibition. Further comprehensive studies revealed that derivative 32 at 25 μg mL⁻¹ inhibited biofilm formation by 70% against P. aeruginosa PAO1, as confirmed by scanning electron microscopy (SEM). Additionally, derivative 32 substantially increased the susceptibility of mature biofilms, leading to a 57% destruction of biofilm architecture. In terms of interfering with virulence factors in P. aeruginosa PAO1, derivative 32 (25 μg mL⁻¹) displayed remarkable inhibitory effects on pyocyanin, protease, and extracellular polysaccharides (EPS) by 73%, 51%, and 37%, respectively, exceeding the positive control resveratrol (RSV). Derivative 32 at 25 μg mL⁻¹ also exhibited effective inhibition of swimming and swarming motilities. Moreover, it downregulated the expressions of QS-related genes, including lasI, lasR, rhlI, rhlR, pqsR, sdhB, sucD, sodB, and PA5439, by 1.82- to 10.87-fold. Molecular docking, molecular dynamics simulations (MD), and energy calculations further supported the stable binding of 32 to LasR, RhlI, RhlR, EsaL, and PqsR antagonizing the expression of QS-linked traits. Evaluation of the toxicity of derivative 32 on HEK293T cells via CCK-8 assay demonstrated low cytotoxicity. Overall, this study underscores the efficacy of derivative 32 in inhibiting virulence factors in P. aeruginosa. Derivative 32 emerges as a potential QSI for controlling P. aeruginosa PAO1 infections in vitro and an anti-biofilm agent for restoring or enhancing drug sensitivity in drug-resistant pathogens.