Lipidated Analogs of the LL-37-Derived Peptide Fragment KR12—Structural Analysis, Surface-Active Properties and Antimicrobial Activity

Abstract

An increasing number of multidrug-resistant pathogens is a serious problem of modern medicine and new antibiotics are highly demanded. In this study, different n-alkyl acids (C₂-C₁₄) and aromatic acids (benzoic and <i>trans</i>-cinnamic) were conjugated to the <i>N</i>-terminus of KR12 amide. The effect of this modification on antimicrobial activity (ESKAPE bacteria and biofilm of <i>Staphylococcus aureus</i>) and cytotoxicity (human red blood cells and HaCaT cell line) was examined. The effect of lipophilic modifications on helicity was studied by CD spectroscopy, whereas peptide self-assembly was studied by surface tension measurements and NMR spectroscopy. As shown, conjugation of the KR12-NH₂ peptide with C₄-C₁₄ fatty acid chains enhanced the antimicrobial activity with an optimum demonstrated by C₈-KR12-NH₂ (MIC 1-4 μg/mL against ESKAPE strains; MBEC of <i>S. aureus</i> 4-16 μg/mL). Correlation between antimicrobial activity and self-assembly behavior of C₁₄-KR12-NH₂ and C₈-KR12-NH₂ has shown that the former self-assembled into larger aggregated structures, which reduced its antimicrobial activity. In conclusion, <i>N</i>-terminal modification can enhance antimicrobial activity of KR12-NH₂; however, at the same time, the cytotoxicity increases. It seems that the selectivity against pathogens over human cells can be achieved through conjugation of peptide <i>N</i>-terminus with appropriate n-alkyl fatty and aromatic acids.