Chimeric Tobramycin-Based Adjuvant TOB-TOB-CIP Potentiates Fluoroquinolone and β-Lactam Antibiotics against Multidrug-Resistant Pseudomonas aeruginosa

According to the World Health Organization, antibiotic resistance is a global health threat. Of particular importance are infections caused by multidrug-resistant Gram-negative bacteria including Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa for which limited treatment options exist. Multiple and simultaneously occurring resistance mechanisms including outer membrane impermeability, overexpression of efflux pumps, antibiotic-modifying enzymes, and modification of genes and antibiotic targets have made antibiotic drug development more difficult against these pathogens. One strategy to cope with these challenges is the use of outer membrane permeabilizers that increase the intracellular concentration of antibiotics when used in combination. In some circumstances, this approach can rescue antibiotics from resistance or repurpose currently marketed antibiotics. Tobramycin-based hybrid antibiotic adjuvants that combine two outer membrane-active components have been previously shown to potentiate antibiotics by facilitating transit through the outer membrane, resulting in increased antibiotic accumulation within the cell. Herein, we extended the concept of tobramycin-based hybrid antibiotic adjuvants to tobramycin-based chimeras by engineering up to three different membrane-active antibiotic warheads such as tobramycin, 1-(1-naphthylmethyl)-piperazine, ciprofloxacin, and cyclam into a central 1,3,5-triazine scaffold. Chimera 4 (TOB-TOB-CIP) consistently synergized with ciprofloxacin, levofloxacin, and moxifloxacin against wild-type and fluoroquinolone-resistant P. aeruginosa. Moreover, the susceptibility breakpoints of ceftazidime, aztreonam, and imipenem were reached using the triple combination of chimera 4 with ceftazidime/avibactam, aztreonam/avibactam, and imipenem/relebactam, respectively, against β-lactamase-harboring P. aeruginosa. Our findings demonstrate that tobramycin-based chimeras form a novel class of antibiotic potentiators capable of restoring the activity of antibiotics against P. aeruginosa.