Novel Inhibitors of LuxO to Control Quorum Sensing in Vibrio species

Abstract

Quorum sensing is a cell-to-cell communication process used by bacteria to coordinate behaviors in response to cell population density. In Vibrio cholerae, the pathogen responsible for the diarrheal disease cholera, the activation of quorum sensing represses virulence factor production and biofilm formation. As such, molecules that activate quorum sensing in this system possess the potential to attenuate pathogenicity in this important disease. Recently, a High-Throughput Screen (HTS) identified a set of structurally distinct molecules that target LuxO, the central response regulator conserved in Vibrio species, which has remained relatively unexplored to date. In this work, one of the hits was optimized using a Structure-Activity Relationship (SAR) analysis. Three locations in the HTS hit were targeted for modification; the library of analogues with these modifications was constructed using an efficient three-step synthesis pathway. Biological evaluation of the analogues in V. cholerae revealed that their affinity for the binding pocket is improved with a simple methyl group substituted at the 3-nitrogen, a furan group acyl side chain, and a methoxy-substituted quinoline core. Of the three positions, the quinoline core was particularly important for general potency, while the presence of the furan group appeared to have implications for inducing activation. Among the molecules identified, the most promising were compound 2, with an EC\(_{50}\) of 3.3 μM and an 81 % maximal response, and compound 14 with an EC\(_{50}\) of 2.7 μM and a 104% maximal response. These two compounds were subsequently tested in Vibrio parahaemolyticus and Vibrio harveyi to assess their broad-spectrum capabilities; both compounds showed significant activity. This study has revealed a structurally distinct, novel inhibitor of quorum sensing in a biologically important organism that can serve as a valuable tool in the exploration of the downstream control of quorum sensing in Vibrio species, and more broadly in the development of novel therapeutic approaches to control these pathogens.