Characterization of a Novel Pyranopyridine Inhibitor of the AcrAB Efflux Pump of Escherichia coli

<jats:title>ABSTRACT</jats:title> <jats:p> Members of the resistance-nodulation-division (RND) family of efflux pumps, such as AcrAB-TolC of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Escherichia coli</jats:named-content> , play major roles in multidrug resistance (MDR) in Gram-negative bacteria. A strategy for combating MDR is to develop efflux pump inhibitors (EPIs) for use in combination with an antibacterial agent. Here, we describe MBX2319, a novel pyranopyridine EPI with potent activity against RND efflux pumps of the <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Enterobacteriaceae</jats:named-content> . MBX2319 decreased the MICs of ciprofloxacin (CIP), levofloxacin, and piperacillin versus <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">E. coli</jats:named-content> AB1157 by 2-, 4-, and 8-fold, respectively, but did not exhibit antibacterial activity alone and was not active against AcrAB-TolC-deficient strains. MBX2319 (3.13 μM) in combination with 0.016 μg/ml CIP (minimally bactericidal) decreased the viability (CFU/ml) of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">E. coli</jats:named-content> AB1157 by 10,000-fold after 4 h of exposure, in comparison with 0.016 μg/ml CIP alone. In contrast, phenyl-arginine-β-naphthylamide (PAβN), a known EPI, did not increase the bactericidal activity of 0.016 μg/ml CIP at concentrations as high as 100 μM. MBX2319 increased intracellular accumulation of the fluorescent dye Hoechst 33342 in wild-type but not AcrAB-TolC-deficient strains and did not perturb the transmembrane proton gradient. MBX2319 was broadly active against <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Enterobacteriaceae</jats:named-content> species and <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Pseudomonas aeruginosa</jats:named-content> . MBX2319 is a potent EPI with possible utility as an adjunctive therapeutic agent for the treatment of infections caused by Gram-negative pathogens. </jats:p>