Pseudomonas aeruginosa quorum-sensing (QS) is
a sophisticated network of genome-wide regulation triggered in response
to population density. A major component is the self-inducing pseudomonas
quinolone signal (PQS) QS system that regulates the production of
several nonvital virulence- and biofilm-related determinants. Hence,
QS circuitry is an attractive target for antivirulence agents with
lowered resistance development potential and a good model to study
the concept of polypharmacology in autoloop-regulated systems per se. Based on the finding that a combination of PqsR
antagonist and PqsD inhibitor synergistically lowers pyocyanin, we
have developed a dual-inhibitor compound of low molecular weight and
high solubility that targets PQS transcriptional regulator (PqsR)
and PqsD, a key enzyme in the biosynthesis of PQS-QS signal molecules
(HHQ and PQS). In vitro, this compound markedly reduced
virulence factor production and biofilm formation accompanied by a
diminished content of extracellular DNA (eDNA). Additionally, coadministration
with ciprofloxacin increased susceptibility of PA14 to antibiotic
treatment under biofilm conditions. Finally, disruption of pathogenicity
mechanisms was also assessed in vivo, with significantly
increased survival of challenged larvae in a Galleria mellonella infection model. Favorable physicochemical properties and effects
on virulence/biofilm establish a promising starting point for further
optimization. In particular, the ability to address two targets of
the PQS autoinduction cycle at the same time with a single compound
holds great promise in achieving enhanced synergistic cellular effects
while potentially lowering rates of resistance development.