Evaluation of peptoid mimics of short, lipophilic peptide antimicrobials.

Introduction: Antimicrobial peptides are proving to be promising lead compounds for therapeutics. The major disadvantage of antimicrobial peptides is their proteolytic instability in the body, with half-lives averaging less than an hour. Peptoids, or N-substituted glycines, have emerged as a promising field of peptidomimetics by retaining the beneficial properties of antimicrobial peptides while improving their stability.

Methods: This study evaluated peptoid derivatives of ultra-short lipophilic antimicrobial peptides, comparing their potency side-by-side with the most prevalent multidrug-resistant bacteria (ESKAPE) and yeast pathogens (Candida albicans and Cryptococcus neoformans).

Results: Both peptide and peptoid counterparts were most effective against Gram-positive bacteria with minimum inhibitory concentration (MIC) values as low as 1.6 and 6.3 µg/mL, respectively. In general, peptides retained better antimicrobial activity than their peptoid counterparts; however, certain peptoids proved to be more effective than peptides against Gram-negative bacteria. For example, peptoid MG10 displayed an MIC of 6.3 µg/mL against Pseudomonas aeruginosa compared with the peptide counterpart with an MIC of 100 µg/mL. All tested compounds were more potent against Cryptococcus neoformans compared with Candida albicans. Cytotoxicity analysis indicated that peptoids were generally slightly less toxic than their peptide counterparts. Additionally, trypsin rapidly degraded one of the evaluated peptides, while having no effect on comparable peptoids, demonstrating the proteolytic stability of peptoids.

Conclusion: These results indicate that direct conversion of lipopeptides to lipopeptoids can result in compounds with comparable antimicrobial activity, favorable mammalian cell toxicity, and excellent proteolytic stability.