Anti-Quorum-Sensing Activity of Tryptophan-Containing Cyclic Dipeptides

Quorum sensing (QS) can regulate the pathogenicity of bacteria and the production of some virulence factors. It is a promising target for screening to find anti-virulence agents in the coming post-antibiotics era. Cyclo (L-Trp-L-Ser), one variety of cyclic dipeptides (CDPs), isolated from a marine bacteriumRheinheimera aquimaris, exhibited anti-QS activity againstChromobacterium violaceumCV026 andPseudomonas aeruginosaPAO1. Unlike the CDPs composed of phenylalanine or tyrosine, the anti-QS activity has been widely studied; however, cyclo (L-Trp-L-Ser) and derivatives, containing one tryptophan unit and one non-aromatic amino acid, have not been systematically explored. Herein, the cyclo (L-Trp-L-Ser) and seven derivatives were synthesized and evaluated. All tryptophane-contained CDPs were able to decrease the production of violacein inC.violaceumCV026 and predicted as binding within the same pocket of receptor protein CviR, but in lower binding energy compared with the natural ligand C6HSL. As forP. aeruginosaPAO1, owning more complicated QS systems, these CDPs also exhibited inhibitory effects on pyocyanin production, swimming motility, biofilm formation, and adhesion. These investigations suggested a promising way to keep the tryptophan untouched and make modifications on the non-aromatic unit to increase the anti-QS activity and decrease the cytotoxicity, thus developing a novel CDP-based anti-virulence agent.Keywords:anti-quorum sensing;cyclic dipeptides;tryptophane;Pseudomonas aeruginosa;biofilm;bacterial adhesion