Mechanism of Action and Resistance Evasion of an Antimicrobial Oligomer against Multidrug-Resistant Gram-Negative Bacteria

Abstract

The last resort for treating multidrug-resistant (MDR) Pseudomonas aeruginosa and other MDR Gram-negative bacteria is a class of antibiotics called the polymyxins; however, polymyxin-resistant isolates have emerged. In response, antimicrobial peptides (AMPs) and their synthetic mimetics have been investigated as alternative therapeutic options. Oligothioetheramides (oligoTEAs) are a class of synthetic, sequence-defined oligomers composed of N-allylacrylamide monomers and an abiotic dithiol backbone that is resistant to serum degradation. Characteristic of other AMP mimetics, the precise balance between charge and hydrophobicity has afforded cationic oligoTEAs potent antimicrobial activity, particularly for the compound BDT-4G, which consists of a 1,4-butanedithiol backbone and guanidine pendant groups, the latter of which provides a cationic charge at physiological pH. However, the activity and mechanism of cationic oligoTEAs against MDR Gram-negative isolates have yet to be fully investigated. Herein, we demonstrated the potent antimicrobial activity of BDT-4G against clinical isolates of P. aeruginosa with a range of susceptibility profiles, assessed the kinetics of bactericidal activity, and further elucidated its mechanism of action. Activity was also evaluated against a panel of polymyxin-resistant isolates, including intrinsically-resistant species. We demonstrate that BDT-4G can evade some of the mechanisms conferring resistance to polymyxin B and thus may have therapeutic potential.

Development of Host-Cleavable Antibody–Bactericide Conjugates against Extracellular Pathogens

“…BDT-4G was synthesized as previously described. 15 The drug conjugate was synthesized by coupling the C-terminus of the LVPRG linker to the free primary amine on BDT-4G (Scheme S1 and Figure S3) and then conjugating a maleimide group (Mal) to the Nterminus of the peptide via a short PEG 4 linker (Scheme S2 and Figure S4). To determine the location of linker cleavage, the conjugate was incubated in 40 units/mL thrombin or 50% serum for 4 h at 37 °C and the cleavage fragments were analyzed via MALDI-TOF MS.…”

“…BDT-4G was synthesized as previously described . The drug conjugate was synthesized by coupling the C-terminus of the LVPRG linker to the free primary amine on BDT-4G (Scheme S1 and Figure S3) and then conjugating a maleimide group (Mal) to the N-terminus of the peptide via a short PEG 4 linker (Scheme S2 and Figure S4).…”

“…The oligoTEA BDT-4G is a potent bactericidal agent against P. aeruginosa that exerts its mechanism of action via permeabilization and destabilization of the bacterial cell membrane . However, the cationic charge of this oligoTEA, which allows BDT-4G to interact electrostatically with the negatively charged bacterial cell membrane, also imparts toxicity against mammalian cells, which contain some anionic lipids but generally have a neutral surface charge .…”

“…The MIC assays were performed as previously described with several modifications . For the ABC MIC assay (Figures b and S12a), P.…”

“…BDT-4G has displayed potent activity against a range of P. aeruginosa clinical isolates, including meropenem- and polymyxin-resistant isolates . However, BDT-4G is currently dose-limited in vivo due to its inherent toxicity conferred by its cationic charge.…”