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

•[E6k,D9k]hymenochirin-1B is active against MRSA and multidrug-resistant Acinetobacter baumannii and Stenotrophomonas maltophilia.•The peptide is active against NDM-1 carbapenemase-producing Enterobacteriaceae.•The peptide stimulates production of IL-4 and IL-10 by human peripheral blood mononuclear cells.

Hymenochirin-1B (IKLSPETKDN10LKKVLKGAIK20GAIAVAKMV.NH2) is a cationic, amphipathic, α-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 Pro5, Glu6 and Asp9 on the hydrophilic face of the α-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 μM) 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 μM), and low hemolytic activity (LC50 = 302 μM). [E6k,D9k]hymenochirin-1B, at a concentration of 2.5 μM, 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-α and IL-17.