C7-substituted Quinolines as Potent Inhibitors of AdeG Efflux Pumps in Acinetobacter baumannii

Efflux, mediated by a series of multidrug efflux pumps, is a major contributor to antibiotic resistance in Gram-negative bacteria. Efflux pump inhibitors (EPIs), which can block efflux, have the potential to be used as adjuvant therapies to re-sensitize bacteria to existing antibiotics. In this study, 36 quinoline-based compounds were synthesized as potential EPIs targeting Resistance Nodulation Division (RND) family pumps in the multidrug-resistant pathogen Acinetobacter baumannii . In A. baumannii strains with overexpressed AdeFGH (chloramphenicol-adapted) and AdeABC (AYE, Ab5075-UW), these compounds enhanced Hoechst dye accumulation, indicating general efflux inhibition, and potentiated chloramphenicol which is an AdeG substrate. The research focused on two generations of quinoline compounds, with modifications at the C-7 position of first-generation compounds to improve hydrophobic interactions with the Phe loop in the AdeG efflux pump, to generate second-generation compounds. The modified quinolines showed strong pump inhibition and significant chloramphenicol potentiation, with MIC reductions of 4- to 64-fold. Notably, compounds 1.8 and 3.8 exhibited the highest inhibitory activity, while compounds 1.3 and 3.3 showed up to 64-fold potentiation, highlighting the importance of specific structural features at the C-7 position for efflux pump inhibition. The study also revealed selective inhibition of AdeFGH over AdeABC, with no potentiation observed for gentamicin, showing the specificity of these quinoline- based inhibitors. Importantly, the compounds showed no toxicity in a Galleria mellonella model at a 50 mg/kg dose level, highlighting their suitability as potential antibiotic adjuvants for combating bacterial resistance.