Hit Identification of New Potent PqsR Antagonists as Inhibitors of Quorum Sensing in Planktonic and Biofilm Grown .

Current treatments for infections are becoming less effective because of the increasing rates of multi-antibiotic resistance. Pharmacological targeting of virulence through inhibition of quorum sensing (QS) dependent virulence gene regulation has considerable therapeutic potential. In , the QS system regulates the production of multiple virulence factors as well as biofilm maturation and is a promising approach for developing antimicrobial adjuvants for combatting drug resistance. In this work, we report the hit optimisation for a series of potent novel inhibitors of PqsR, a key regulator of the system, bearing a 2-((5-methyl-5-[1,2,4]triazino[5,6-]indol-3-yl)thio) acetamide scaffold. The initial hit compound (PAO1-L IC 0.98 ± 0.02 μM, PA14 inactive at 10 μM) was obtained through a virtual screening campaign performed on the PqsR ligand binding domain using the University of Nottingham Managed Chemical Compound Collection. Hit optimisation gave compounds with enhanced potency against strains PAO1-L and PA14, evaluated using -based QS bioreporter assays. Compound (PAO1-L IC 0.25 ± 0.12 μM, PA14 IC 0.34 ± 0.03 μM) is one of the most potent PqsR antagonists reported showing significant inhibition of pyocyanin production and system signaling in both planktonic cultures and biofilms. The co-crystal structure of with the PqsR ligand binding domain revealed the specific binding interactions occurring between inhibitor and this key regulatory protein.