An analog of the host-defense peptide hymenochirin-1B with potent broad-spectrum activity against multidrug-resistant bacteria and immunomodulatory properties

Hymenochirin-1B (IKLSPETKDN(10)LKKVLKGAIK(20)GAIAVAKMV.NH2) is a cationic, amphipathic, alpha-helical, host-defense peptide, first isolated from skin secretions of the Congo clawed frog Hymenochirus boettgeri (Pipidae). Structure-activity relationships were investigated by synthesizing analogs in which the Pro(5), Glu(6) and Asp(9) on the hydrophilic face of the alpha-helix are substituted by one or more L-lysine or D-lysine residues. Although replacement with L-lysine generates analogs with increased antimicrobial potency against a range of Gram-positive and Gram-negative bacteria (up to 8-fold), the peptides are more hemolytic. Increasing the cationicity of hymenochirin-1B while reducing the helicity by substitutions with D-lysine generates analogs that are between 2 and 8 fold more potent than the native peptide and are equally or less hemolytic. [E6k,D9k]hymenochirin-1B represents a candidate for drug development as it shows high potency against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and a range of Gram-negative bacteria, including multidrug-resistant strains of Acinetobacter baumannii and Stenotrophomonas maltophilia (MIC in the range 0.8-3.1 mu M) and NDM-1 carbapenemase-producing clinical isolates of Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae and Citrobacter freundii(MIC in the range 3.1-6.25 mu M), and low hemolytic activity (LC50=302 mu M). [E6k,D9k]hymenochirin-1B, at a concentration of 2.5 mu M, significantly (P < 0.05) stimulates the production of the anti-inflammatory cytokines IL-4 and IL-10 by human peripheral blood mononuclear cells but is without significant effect on production of the pro-inflammatory cytokines TNF-alpha and IL-17. (C) 2013 Elsevier Inc. All rights reserved.