Haloganan: A novel antimicrobial peptide for treatment of wound infections

• We demonstrate several issues that should be considered for development of new drug based on antimicrobial peptides (AMPs).
• From a structure–activity relationship study, we designed a new AMP (haloganan) with advantage over HG1 that has been known for promising candidate of new AMP-drug to cope with skin infections.
• Haloganan is resistant to digestion with proteases occurring in serum and tissue fluid.
• Haloganan maintains its antimicrobial activity under conditions containing anionic components of extracellular matrix or phospholipids occurring in human serum and/or wound fluid.

HG1 is a Leu-rich antimicrobial peptide (AMP). Previously, the peptide was shown to lose its activity in human serum although it possessed potent and broad spectrum antimicrobial activity against a wide range of pathogenic microbes. In an attempt to design an HG1 isomer that can overcome the problem of HG1, a structure–activity relationship study was conducted by substitution of each of five Leu residues with a Gln residue. Each substitute was tested for its antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) or Candida strains. In addition, the antimicrobial activity of HG1 isomers was examined in the presence of glycosaminoglycans or lipid components occurring in the extracellular matrix, human serum and wound fluid. As a result, it was determined that the third residue (Leu) in the sequence of HG1 was mainly responsible for abrogation of its antimicrobial activity in human serum or wound fluid. An HG1 isomer (L3Q) with a Gln-3 substitution exhibited a potent antibacterial activity in 50% human serum. While the anti-MRSA activity of L3Q was equivalent to that of HG1, its anti-Candida activity was found to be substantially reduced. In order to improve anti-Candida activity of L3Q, its cationicity was enhanced by replacement of the C-terminal Ala-19 with a Lys residue. Overall, an HG1 isomer with two substitutions of Gln-3 and Lys-19, named haloganan, was verified to have an advantage over HG1 in that it exerted its potent antimicrobial activity under conditions containing human serum and/or wound fluid.