Discovery and Characterization of Pure RhlR Antagonists against Pseudomonas aeruginosa Infections

Abstract

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic human pathogen that forms biofilms and produces virulence factors via quorum sensing (QS). Blocking the QS system in P. aeruginosa is an excellent strategy to reduce biofilm formation and the production of virulence factors. RhlR plays an essential role in the QS system of P. aeruginosa. We synthesized 55 analogues based on the chemical structure of 4-gingerol and evaluated their RhlR inhibitory activities using the cell-based reporter strain assay. Comprehensive structure–activity relationship studies identified the alkynyl ketone 30 as the most potent RhlR antagonist. This compound displayed selective RhlR antagonism over LasR and PqsR, strong inhibition of biofilm formation, and reduced production of virulence factors in P. aeruginosa. Furthermore, the survival rate of Tenebrio molitor larvae treated with 30 in vivo greatly improved. Therefore, compound 30, a pure RhlR antagonist, can be utilized for developing QS-modulating molecules in the control of P. aeruginosa infections.

Combined Treatment of 6-Gingerol Analog and Tobramycin for Inhibiting Pseudomonas aeruginosa Infections

“…Figure 5A shows the binding activities of the chemicals toward representative QS receptors (LasR, RhlR, and PqsR). Compound 30 displayed selective RhlR antagonism over LasR and PqsR in P. aeruginosa , which is consistent with the results of our previous study ( 24 ). Following combined treatment with compound 30 and tobramycin, antagonistic binding activities were observed in LasR, RhlR, and PqsR.…”

“…2C and D ) with similar inhibition patterns, suggesting that tobramycin inhibited biofilm formation through antibacterial activity. Compound 30 significantly reduced P. aeruginosa biofilm formation under static and flow conditions through the disruption of QS processes ( 24 ). However, QS inhibitors generally have lower biofilm inhibitory activity than antibiotics ( 20 ).…”

“…Compound 30, an RhlR antagonist of P. aeruginosa , inhibits biofilm formation and virulence factor production via the disruption of the QS system ( 24 ). Based on the biofilm inhibition mechanism of compound 30, it can be hypothesized that adjuvant effects are related to QS systems.…”

“…Furthermore, RhlR plays an important role in regulating the cytotoxicity of lung epithelial cells ( 46 ). Compound 30, a strong RhlR antagonist, effectively reduced biofilm formation and production of virulence factors in P. aeruginosa ( 24 ), indicating that compound 30 may be used as a possible target for therapeutic development in chronic infections. Furthermore, when compound 30 was treated with tobramycin, biofilm formation and production of virulence factors greatly decreased compared to those in single treatments, through improved RhlR antagonism activity ( Fig.…”

“…Compound 30 is a 6-gingerol analog with a difluorine head group, alkynyl ketone, and a short alkyl chain length ( Fig. 1 ) ( 24 ). This compound displayed improved binding affinity for RhlR over other QS receptors (LasR and PqsR) with a structure similar to that of BHL (i.e., signal molecule binding to RhlR).…”