Antimicrobial Peptides and Their Superior Fluorinated Analogues: Structure-Activity Relationships as Revealed by NMR Spectroscopy and MD Calculations

Fluorinated antimicrobial lysine-based peptidomimetics with activity against methicillin-resistant Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is the predominant opportunistic pathogen in dogs causing primarily integumentary infections such as pyoderma and otitis. The worldwide emergence of methicillin-resistant S. pseudintermedius (MRSP) constitutes a significant health problem for companion animals in veterinary medicine. Thus, discovery of novel agents for treatment of MRSP-associated infections is highly warranted. In the present work, structure-activity relationships (based on testing of 37 peptidomimetics) have been explored with the aim of determining the influence of oligomer length as well as effect of fluorination, end-group modification, and length of hydrophobic side chains. Incorporation of fluorine atoms and elongation of hydrophobic side chains both conferred overall increased potency without significantly enhancing the hemolytic properties of the compounds. Importantly, it was found that when targeting MRSP, the peptidomimetic length could be reduced from 12 to 8 residues without substantial loss of antibacterial activity. By contrast, introduction of end-group modifications did not improve the activity against MRSP (10 strains tested), but conferred increased activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, albeit the concomitantly increased hemolytic properties resulted in a slightly lowered cell selectivity.

Lysine-Based α-Peptide/β-Peptoid Peptidomimetics: Influence of Hydrophobicity, Fluorination, and Distribution of Cationic Charge on Antimicrobial Activity and Cytotoxicity

Multidrug-resistant bacteria pose a serious threat to public health worldwide. Previously, α-peptide/β-peptoid hybrid oligomers were found to display activity against Gram-negative multidrug-resistant bacteria. In the present work, the influence of hydrophobicity, fluorination, and distribution of cationic/hydrophobic residues on antimicrobial, hemolytic, and cytotoxic properties of α-peptide/β-peptoid hybrids were investigated. An array of 22 peptidomimetics was tested. Analogues with enhanced hydrophobicity were found to exhibit increased activity against Gram-positive bacteria. Incorporation of fluorinated residues into the peptidomimetics conferred increased potency against Gram-positive bacteria, while hemolytic properties and activity against Gram-negative bacteria depended on the degree and type of fluorination. Generally, shorter oligomers were less potent than the corresponding longer analogues. However, some short analogues exhibited equal or higher antimicrobial activity. The alternating hydrophobic/cationic design proved superior to other distribution patterns of cationic side chains and hydrophobic moieties.