Amphiphilic Tobramycin–Lysine Conjugates Sensitize Multidrug Resistant Gram-Negative Bacteria to Rifampicin and Minocycline

Abstract

Chromosomally encoded low membrane permeability and highly efficient efflux systems are major mechanisms by which Pseudomonas aeruginosa evades antibiotic actions. Our previous reports have shown that amphiphilic tobramycin-fluoroquinolone hybrids can enhance efficacy of fluoroquinolone antibiotics against multidrug-resistant (MDR) P. aeruginosa isolates. Herein, we report on a novel class of tobramycin-lysine conjugates containing an optimized amphiphilic tobramycin-C12 tether that sensitize Gram-negative bacteria to legacy antibiotics. Combination studies indicate the ability of these conjugates to synergize rifampicin and minocycline against MDR and extensively drug resistant (XDR) P. aeruginosa isolates and enhance efficacy of both antibiotics in the Galleria mellonella larvae in vivo infection model. Mode of action studies indicate that the amphiphilic tobramycin-lysine adjuvants enhance outer membrane cell penetration and affect the proton motive force, which energizes efflux pumps. Overall, this study provides a strategy for generating effective antibiotic adjuvants that overcome resistance of rifampicin and minocycline in MDR and XDR Gram-negative bacteria including P. aeruginosa.

Amphiphilic lysine conjugated to tobramycin synergizes legacy antibiotics against wild‐type and multidrug‐resistant Pseudomonas aeruginosa

“…In agreement with our previous findings, conjugates ( 1 and 2 ) and amphiphilic lysine reference 4 displayed limited activity while conjugate 3 exhibited moderate activity against P. aeruginosa . MIC values of >256, 128, 32, and 256 µg/mL were found for 1 , 2 , 3 and reference 4 , respectively, against wild‐type P. aeruginosa PAO1 strain (Table and Supporting Information Tables S1‐S3).…”

“…The observed antibiotic potentiation of amphiphilic lysine‐tobramycin conjugate 3 may be explained by our previous findings. In preliminary mode‐of‐action studies, conjugate 3 displayed an enhanced membrane permeabilization and depolarization of P. aeruginosa relative to amphiphilic lysine reference 4 . This may lead to a substantial increase of intracellular antibiotic concentration as the conjugate facilitate the efficient entry of otherwise membrane‐hindered antibiotics.…”

“…An amphiphilic lysine ( 4 ) (Figure ), devoid of tobramycin, was also synthesized as a reference. Scheme briefly describes their synthesis as we had previously reported . Reductive amination of 10‐chloro‐9‐anthraldehyde ( 5 ) and corresponding aliphatic primary amine ( 6a ‐ d ) afforded a secondary amine ( 7a ‐ d ).…”

“… Synthesis of amphiphilic lysine‐tobramycin conjugates 1 ‐ 3 and amphiphilic lysine reference 4 , as previously published . Conjugates 1 ‐ 3 were obtained as HCl salts while amphiphilic lysine 4 was obtained as TFA salt…”

“…Moreover, we recently reported that some amphiphilic aminoglycosides may possess beneficial immunomodulatory properties . In preliminary work, we recently demonstrated that amphiphilic lysines conjugated to tobramycin strongly synergized minocycline and rifampicin against antibiotic‐resistant P. aeruginosa . Herein, we further expand the adjuvant profile of amphiphilic lysine‐tobramycin conjugates in combinations with other classes of clinically used legacy antibiotics to eradicate MDR/XDR P. aeruginosa .…”