Biophysical Characterization of Cationic Antibacterial Oligothioetheramides

Membrane-Active Nonivamide Derivatives as Effective Broad-Spectrum Antimicrobials: Rational Design, Synthesis, and Biological Evaluation

Antibiotic resistance is emerging as a "global public health concern". To address the growing epidemic of multidrug-resistant pathogens, the development of novel antimicrobials is urgently needed. In this study, by biomimicking cationic antibacterial peptides, we designed and synthesized a series of new membrane-active nonivamide and capsaicin derivatives as peptidomimetic antimicrobials. Through modulating charge/hydrophobicity balance and rationalizing structure-activity relationships of these peptidomimetics, compound 51 was identified as the lead compound. Compound 51 exhibited potent antibacterial activity against both Gram-positive bacteria (MICs = 0.39-0.78 μg/mL) and Gram-negative bacteria (MICs = 1.56-6.25 μg/mL), with low hemolytic activity and low cytotoxicity. Compound 51 displayed a faster bactericidal action through a membrane-disruptive mechanism and avoided bacterial resistance development. Furthermore, compound 51 significantly reduced the microbial burden in a murine model of keratitis infected by Staphylococcus aureus or Pseudomonas aeruginosa. Hence, this design strategy can provide a promising and effective solution to overcome antibiotic resistance.

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

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.

PEGylated Oligothioetheramide Prodrugs Activated by Host Serum Proteases

Due to the increasing prominence of antibiotic resistance, novel drug discovery and delivery approaches targeting bacteria are essential. In this work we evaluate a prodrug design to improve the cytotoxic profile of polycationic oligothioetheramides (oligoTEAs), which are promising antimicrobials. Herein we chemically modify the oligoTEA, PDT-4G, with a polyethylene glycol (PEG) and show that 1, 2, and 5 kDa PEGs mitigate cytotoxicity. As PEGylation reduces antibacterial activity, we evaluate two peptide linkers which, unlike oligoTEAs, are susceptible to proteolytic cleavage in serum. To gain insight into the prodrug reactivation, two linkers were tested, the 5-residue peptide sequence LMPTG, and the dipeptide sequence VC-PABC. In the presence of 20 % serum, prodrugs made with the VC-PABC linker successfully inhibited bacterial growth. Overall, we observed reactivation of oligoTEAs facilitated by serum protease cleavage of the peptide linkers. This work opens the door to the future design of antimicrobial prodrugs with tunable release profiles.

Applications of Discrete Synthetic Macromolecules in Life and Materials Science: Recent and Future Trends

In the last decade, the field of sequence-defined polymers and related ultraprecise, monodisperse synthetic macromolecules has grown exponentially. In the early stage, mainly articles or reviews dedicated to the development of synthetic routes toward their preparation have been published. Nowadays, those synthetic methodologies, combined with the elucidation of the structure-property relationships, allow envisioning many promising applications. Consequently, in the past 3 years, application-oriented papers based on discrete synthetic macromolecules emerged. Hence, material science applications such as macromolecular data storage and encryption, self-assembly of discrete structures and foldamers have been the object of many fascinating studies. Moreover, in the area of life sciences, such structures have also been the focus of numerous research studies. Here, it is aimed to highlight these recent applications and to give the reader a critical overview of the future trends in this area of research.

Design of a PEGylated Antimicrobial Prodrug with Species-Specific Activation

The rise of multidrug-resistant (MDR) "superbugs" has created an urgent need to develop new classes of antimicrobial agents to target these organisms. Oligothioetheramides (oligoTEAs) are a unique class of antimicrobial peptide (AMP) mimetics with one promising compound, BDT-4G, displaying potent activity against MDR Pseudomonas aeruginosa clinical isolates. Despite widely demonstrated potency, BDT-4G and other AMP mimetics have yet to enjoy broad preclinical success against systemic infections, primarily due to their cytotoxicity. In this work, we explore a prodrug strategy to render BDT-4G inactive until it is exposed to an enzyme secreted by the targeted bacteria. The prodrug consists of polyethylene glycol (PEG) conjugated to BDT-4G by a peptide substrate. PEG serves to inactivate and reduce the toxicity of BDT-4G by masking its cationic charge and antimicrobial activity is recovered following site-specific cleavage of the short peptide linker by LasA, a virulence factor secreted by P. aeruginosa. This approach concurrently reduces cytotoxicity by greater than 1 order of magnitude in vitro and provides species specificity through the identity of the cleavable linker.

Organic Polymer Nanoparticles with Primary Ammonium Salt as Potent Antibacterial Nanomaterials

Bacterial infections induced by drug-resistant strains have become a global crisis. A membrane-disrupted mechanism is considered as an effective way to kill bacteria with little chance to trigger drug resistance. It is necessary to explore and develop new materials based on the membrane-disrupted mechanism to combat bacterial resistance. Here we report the design of organic nanoparticles based on a polymer (PDCP) as highly effective inhibition and bactericidal reagents. The PDCP is devised to have a hydrophobic skeleton and hydrophilic side chain modified with protonated primary amines, which could self-assemble to form organic nanoparticles (PDCP-NPs). By taking advantage of the large surface to volume ratio of nanoparticles, the synthesized PDCP-NPs have enriched positive charges and multiple membrane-binding sites. Research results display that PDCP-NPs have highly potent antibacterial activity in vitro and vivo, especially for Gram-negative bacteria with low toxicity against mammalian cells. This work design will inspire researchers to develop more membrane-disrupted bactericide and advance the applications of organic nanoparticles in the antibacterial area.

An on-demand nanoplatform for enhanced elimination of drug-resistant bacteria

We establish an “on-demand” nanoplatform based on acid-degradable scaffolds by conjugating glycomimetic-based galactose ligands to target a key lectin on P. aeruginosa and guanidine moieties.