Cationic amphipathic peptide analogs of cathelicidin LL‐37 as a probe in the development of antimicrobial/anticancer agents

Cathelicidin LL‐37 belongs to the class of human defense peptides and is overexpressed in many cancers. Segments of LL‐37 derived through biochemical processes have a wide range of activities. In this study, novel analogs of the 13‐amino acid cathelicidin 17‐29 amide segment F17KRIV21QR23IK25DF27LR‐NH2 were prepared and examined for their antimicrobial and hemolytic activities, as well as for their cytotoxicity on cancer bronchial epithelial cells. Selected substitutions were performed on residues R23 and K25 in the hydrophilic side, V21and F27 in the hydrophobic side of the interphase, and F17 that interacts with cell membranes. Specific motifs IIKK and LLKKL with anticancer and antimicrobial activities isolated from animals were also inserted into the 17‐29 fragment to investigate how they affect activity. Substitution of the amino‐terminal positive charge by acetylation and replacement of lysine by the aliphatic leucine in the peptide analog Ac‐FKRIVQRIL25DFLR‐NH2 resulted in significant cytotoxicity against A549 cancer cells with an IC50 value 3.90 μg/mL, with no cytotoxicity to human erythrocytes. The peptide Ac‐FKRIVQI23IKK26FLR‐NH2, which incorporates the IIKK motif and the peptides FKRIVQL23L24KK26L27LR‐NH2 and Ac‐FKRIVQL23L24KK26L27LR‐NH2, which incorporate the LLKKL motif, displayed potent antimicrobial activity against gram‐negative bacteria (MIC 3–7.5 μg/mL) and substantial cytotoxicity against bronchial epithelial cancer cells, (IC50 12.9–9.8 μg/mL), with no cytotoxic activity for human erythrocytes. The helical conformation of the synthetic peptides was confirmed by circular dichroism. Our study shows that appropriate substitutions, mainly in positions of the interphase, as well as the insertion of the motifs IIKK and LLKKL in the cathelicidin 17‐29 segment, may lead to the preparation of effective biological compounds. In this study, novel analogs of the cathelicidin 17‐29 segment, F17KRIV21QR23IK25DF27LR‐NH2 were prepared and examined for their antimicrobial and hemolytic activity, as well as for their cytotoxicity on cancer bronchial epithelial cells. Our study shows that appropriate substitutions mainly in positions of the interphase, as well as the insertion of the motifs IIKK and LLKKL in the cathelicidin 17‐29 segment, may lead to the preparation of effective biological compounds.