Discovery and preliminary characterization of a novel inhibitor of the SOS response in Pseudomonas aeruginosa

Bacterial antibiotic resistance (AR) is becoming one of the biggest threats to human health, progressively disarming the current arsenal of antimicrobial drugs. Besides efforts to develop new antimicrobial agents, strategies to avoid the onset of novel resistance mechanisms are strongly needed. The bacterial SOS response to DNA damage (a common outcome of antibiotic treatment), mainly orchestrated by LexA and RecA proteins, is one of the crucial pathways involved in AR acquisition. In previous studies, the SOS response suppression has proved to be an efficient strategy to delay the appearance of drug resistance, but currently known inhibitors of the RecA-LexA axis are limited to few compounds. From a Fluorescence Polarization (FP)-based high-throughput screening of a small molecule library, a novel hit compound (hereafter “A12”) acting as inhibitor of the Pseudomonas aeruginosa SOS system was discovered. In-vitro dose-response characterization of A12 revealed an inhibitory potency in the high micromolar range, while biophysical assays including differential scanning fluorimetry (DSF) and isothermal titration calorimetry (ITC) assessed RecA as the main target. We are currently producing and screening a sub-library based on the structure of compound A12 in order to select more potent derivatives to be tested on P. aeruginosa cultures and determine their effectiveness as antibiotic adjuvants to synergize with bactericidal treatment and delay the onset of resistance.