A Tobramycin Vector Enhances Synergy and Efficacy of Efflux Pump Inhibitors against Multidrug-Resistant Gram-Negative Bacteria

Drug efflux mechanisms interact synergistically with the outer membrane permeability barrier of Gram-negative bacteria, leading to intrinsic resistance that presents a major challenge for antibiotic drug development. Efflux pump inhibitors (EPIs) which block the efflux of antibiotics synergize antibiotics, but the clinical development of EPI/antibiotic combination therapy to treat multidrug-resistant (MDR) Gram-negative infections has been challenging. This is in part caused by the inefficiency of current EPIs to penetrate the outer membrane and resist efflux. We demonstrate that conjugation of a tobramycin (TOB) vector to EPIs like NMP, paroxetine, or DBP enhances synergy and efficacy of EPIs in combination with tetracycline antibiotics against MDR Gram-negative bacteria including Pseudomonas aeruginosa. Besides potentiating tetracycline antibiotics, TOB–EPI conjugates can also suppress resistance development to the tetracycline antibiotic minocycline, thereby providing a strategy to develop more effective adjuvants to rescue tetracycline antibiotics from resistance in MDR Gram-negative bacteria.