Restoring and Enhancing the Potency of Existing Antibiotics against Drug-Resistant Gram-Negative Bacteria through the Development of Potent Small-Molecule Adjuvants

Abstract

The rapid and persistent emergence of drug-resistant bacteria poses a looming public health crisis. The possible task of developing new sets of antibiotics to replenish the existing ones is daunting to say the least. Searching for adjuvants that restore or even enhance the potency of existing antibiotics against drug-resistant strains of bacteria represents a practical and cost-effective approach. Herein, we describe the discovery of potent adjuvants that extend the antimicrobial spectrum of existing antibiotics and restore their effectiveness toward drug-resistant strains including mcr-1-expressing strains. From a library of cationic compounds, MD-100, which has a diamidine core structure, was identified as a potent antibiotic adjuvant against Gram-negative bacteria. Further optimization efforts including the synthesis of ∼20 compounds through medicinal chemistry work led to the discovery of a much more potent compound MD-124. MD-124 was shown to sensitize various Gram-negative bacterial species and strains, including multidrug resistant pathogens, toward existing antibiotics with diverse mechanisms of action. We further demonstrated the efficacy of MD-124 in an ex vivo skin infection model and in an in vivo murine systemic infection model using both wild-type and drug-resistant Escherichia coli strains. MD-124 functions through selective permeabilization of the outer membrane of Gram-negative bacteria. Importantly, bacteria exhibited low-resistance frequency toward MD-124. In-depth computational investigations of MD-124 binding to the bacterial outer membrane using equilibrium and steered molecular dynamics simulations revealed key structural features for favorable interactions. The very potent nature of such adjuvants distinguishes them as very useful leads for future drug development in combating bacterial drug resistance.

Small Molecule IITR00693 (2-Aminoperimidine) Synergizes Polymyxin B Activity against Staphylococcus aureus and Pseudomonas aeruginosa

“…Additionally, we also noted that the PB-FL shows differences in degree of binding to polymyxin B-resistant versus susceptible strains (Figure S3C). Our results show that IITR00693 can potentiate the attachment of polymyxin B on the cell envelope of S. aureus (Figure B) and that the nature of the interaction of polymyxin B on the S. aureus cell envelope is quite strong, as we observed fluorescence signal after three washing steps.…”

Bisbenzamidine and Bisbenzguanidine Ureas Act as Antibacterial Agents against Pseudomonas aeruginosa

“…Poly‐nitrogenous compounds, [5] cationic diamidine compounds, [16] and diimidazole compounds [14,15] that are not antibiotics on their own have been found to act as adjuvants that can sensitize Gram‐negative bacteria to a variety of antibiotics, which increases antibiotic activity. Specifically, we recently developed a series of pentamidine derived poly‐nitrogenous compounds that can readily accumulate in and weakly potentiate erythromycin against biofilm‐forming PA stain PA 9027 [5] .…”

“…Specifically, we recently developed a series of pentamidine derived poly‐nitrogenous compounds that can readily accumulate in and weakly potentiate erythromycin against biofilm‐forming PA stain PA 9027 [5] . Wang and co‐workers found that polyaromatic diamidine compounds can interact with the negatively charged outer membrane of Gram‐negative bacteria such as EC, AB, and KP, which increases antibiotic activity of novobiocin, rifampicin, and clarithromycin against these strains [16] . Recently, Melander and co‐workers found that 2‐aminoimidazole dimers can potentiate clarithromycin and related macrolide antibiotics against AB with low cytotoxicity against human cells through a mechanism unrelated to outer membrane perturbation.…”

H2S Scavenger as A Universal Strategy to Deplete Bacteria-derived H2S for Antibacterial Sensitization

“…Over the past decades, a series of such adjuvants have been elegantly developed for antibacterial sensitization and/or drug resistance reversion. [11][12][13][14][15][16][17][18][19][20] In addition to the genotypic resistance, the bacteria can become refractory to antibiotics without genetic mutations by transiently entering dormancy, which is known as phenotypic resistance or tolerance. 21 The subpopulation of bacteria with such a phenotypic resistance is termed as persisters, which reside mainly inside the biofilm, making them inaccessible to antibiotics and thus hard to be eradicated.…”