Thrombin-Derived Peptides Potentiate the Activity of Gram-Positive-Specific Antibiotics against Gram-Negative Bacteria

Abstract

The continued rise of antibiotic resistance threatens to undermine the utility of the world’s current antibiotic arsenal. This problem is particularly troubling when it comes to Gram-negative pathogens for which there are inherently fewer antibiotics available. To address this challenge, recent attention has been focused on finding compounds capable of disrupting the Gram-negative outer membrane as a means of potentiating otherwise Gram-positive-specific antibiotics. In this regard, agents capable of binding to the lipopolysaccharide (LPS) present in the Gram-negative outer membrane are of particular interest as synergists. Recently, thrombin-derived C-terminal peptides (TCPs) were reported to exhibit unique LPS-binding properties. We here describe investigations establishing the capacity of TCPs to act as synergists with the antibiotics erythromycin, rifampicin, novobiocin, and vancomycin against multiple Gram-negative strains including polymyxin-resistant clinical isolates. We further assessed the structural features most important for the observed synergy and characterized the outer membrane permeabilizing activity of the most potent synergists. Our investigations highlight the potential for such peptides in expanding the therapeutic range of antibiotics typically only used to treat Gram-positive infections.

Structure–Activity Studies with Bis-Amidines That Potentiate Gram-Positive Specific Antibiotics against Gram-Negative Pathogens

“…In agreement with previous studies, novobiocin and vancomycin showed no antimicrobial activity against the indicator E. coli BW25113 strain at the highest concentration tested of 200 μg/mL. 7 , 56 Checkerboard assays with compounds 21 , 22 , and 23b in combination with novobiocin revealed the compounds to be superior synergists compared to pentamidine ( Table 2 , Figure 6 ), a finding in line with the results obtained when the same bis-amidines were evaluated with erythromycin and rifampicin. In general, PMBN was found to be a more potent synergist than the bis-amidines with the exception of compound 22 in combination with erythromycin which resulted in very effective growth prevention of the E. coli indicator strain.…”

Synergy by Perturbing the Gram-Negative Outer Membrane: Opening the Door for Gram-Positive Specific Antibiotics

“…To this end, we prepared a series of 12-mer thrombin-derived peptides and showed that a number of them are, indeed, potent synergists. 148 The most active synergist thus identified (peptide 6 , Table 3 ) was further investigated by means of an alanine scan, leading to the discovery of more potent variants (peptides 14 and 19 , Table 3 ). Notably, these peptides were found to be non-hemolytic, and their synergistic activity was shown to extend to rifampicin, erythromycin, and novobiocin against multiple Gram-negative strains, including those with mcr -mediated resistance.…”

“…Notably, these peptides were found to be non-hemolytic, and their synergistic activity was shown to extend to rifampicin, erythromycin, and novobiocin against multiple Gram-negative strains, including those with mcr -mediated resistance. 148 …”

“…Given the capacity of PMB to also bind and neutralize LPS, our group was interested in assessing whether these thrombin-derived peptides might also exhibit the synergistic behavior of PMBN. To this end, we prepared a series of 12-mer thrombin-derived peptides and showed that a number of them are, indeed, potent synergists . The most active synergist thus identified (peptide 6 , Table ) was further investigated by means of an alanine scan, leading to the discovery of more potent variants (peptides 14 and 19 , Table ).…”

CycA-Dependent Glycine Assimilation Is Connected to Novobiocin Susceptibility in Escherichia coli

“…Low permeability across the outer membrane has been considered the major reason why NOV was ineffective against Gram-negative bacteria. However, recent studies have shown that some peptides can be used to repurpose NOV as an effective antibacterial agent against Gram-negative bacteria ( 4 , 5 ).…”