Development of a nebramine-cyclam conjugate as an antibacterial adjuvant to potentiate β-lactam antibiotics against multidrug-resistant P. aeruginosa


The β-lactams are the most widely used class of antibiotics due to their safety, effectiveness, and spectrum of activity. As a result of their ubiquitous usage, there has been a steady rise in β-lactam resistant Gram-negative bacteria, especially Pseudomonas aeruginosa, resulting in limited treatment options. P. aeruginosa can develop multidrug-resistant phenotypes using a multifaceted approach of β-lactamase expression, decreased porin production and increased efflux. Current β-lactamase inhibitors address drug hydrolyzing enzymes but may not be as effective in phenotypes with reduced permeability and/or overexpressed efflux pumps. Herein, we present the synthesis and biological evaluation of a nebramine-cyclam conjugate molecule that is able to potentiate β-lactam antibiotics, as well as other legacy antibiotics, against P. aeruginosa in vitro. Combination studies show that this adjuvant is able to synergize with β-lactams such as aztreonam and ceftazidime against multidrug-resistant and extremely drug-resistant clinical isolates through a hypothesized mechanism of outer membrane permeabilization. Importantly, the addition of low concentrations (8 µM) of the nontoxic nebramine-cyclam conjugate is able to further potentiate existing β-lactam/β-lactamase inhibitor combinations in β-lactamase-harboring P. aeruginosa strains. These data support a potential application of the nebramine-cyclam conjugate as an adjuvant for treating infections caused by P. aeruginosa strains that utilize multiple mechanisms of resistance.

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The authors would like to thank the University of Manitoba and the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support in the form of a discovery grant (2018-06047). We would also like to thank Prof. Ayush Kumar (University of Manitoba) for providing us with the efflux deficient strains.

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Correspondence to Frank Schweizer.

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