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Peptides containing the sequences 20 RRWQWR 25 and 20 RRWQWRMKKLG 30 derived from Bovine lactoferricin (LfcinB) were synthesized and their antibacterial effect against reference strains and sensitive and resistant clinical isolates of E. coli was evaluated. Tetra-branched multiple antigen peptide (MAP) ((RRWQWR) 2 -K-Ahx-C) 2 exhibited significant antibacterial activity against sensitive, resistant, and multidrug-resistant clinical isolates of E. coli. Peptide 3: RRWQWR-Nal-KKLG; MIC=16 μM, 26 [F]: (RRWQWRFKKLG) 2 -K-Ahx; MIC=15 μM, 17: (RRWQWRFK) 2 -K-Ahx; MIC=9 μM, and LfcinB (20-25) 2 : (RRWQWR) 2 -K-Ahx; MIC=11 μM exhibited the highest antibacterial activity against E. coli strains, with bactericidal effect and haemolytic effect at MIC less than 5 % and a therapeutic index >1. A synergistic effect of peptides 26 [F] and 17 with ciprofloxacin (CIP) or ceftriaxone (CEF) was observed. Prolonged treatment of E. coli ATCC 25922 with sublethal concentrations of CIP induced resistance in this strain, whereas some peptides did not induce resistance. These peptides can be considered to be promising candidates for treating infections caused by resistant strains of E. coli., (© 2024 Wiley-VHCA AG, Zurich, Switzerland.)

The cytotoxic effect against the breast cancer cell line MDA-MB-468 of the palindromic peptide LfcinB (21-25) Pal : 1 RWQWRWQWR 9 and its analogous peptides, obtained via alanine scanning, was evaluated. The results indicate that the palindromic peptide exhibited a concentration-dependent cytotoxic effect against this cell line. The cytotoxic effect of the palindromic peptide was fast and selective and was sustained for up to 48 h of treatment. MDA-MB-468 cells treated with the palindromic peptide exhibited severe cellular damage, acquiring rounded forms and shrinkage, a behavior typical of apoptotic events. The analogous peptides exhibited fewer cytotoxic effects than the original palindromic peptide, suggesting that the substitution of any amino acid with alanine diminishes the cytotoxic effect. The Arg and Trp residues proved to be the most relevant for the cytotoxic effect; the analogous peptides with substitutions of Trp with Ala did not induce a change in cellular morphology, while analogous peptides with substitutions of Arg or Gln with Ala induced cellular damage. Also, neither the palindromic peptide nor its analogues exerted a significant cytotoxic effect on normal fibroblasts, indicating that the peptides had a selective cytotoxic effect on cancerous cells. The peptide LfcinB (21-25) Pal , and its analogues exhibited antibacterial activity against E. coli and S. aureus strains and a selective cytotoxic effect against the breast cancer cell line MDA-MB-468., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)