Synthetic histatin analogues with broad-spectrum antimicrobial activity

Histatins are salivary histidine-rich cationic peptides, ranging from 7 to 38 amino acid residues in length, that exert a potent killing effect in vitro on Candida albicans. Starting from the C-terminal fungicidal domain of histatin 5 (residues 11-24, called dh-5) a number of substitution analogues were chemically synthesized to study the effect of amphipathicity of the peptide in helix conformation on candidacidal activity. Single substitutions in dh-5 at several positions did not have any effect on fungicidal activity. However, multi-site substituted analogues (dhvar1 and dhvar2) exhibited a 6-fold increased activity over dh-5. In addition, dhvar1 and dhvar2 inhibited the growth of the second most common yeast found in clinical isolates, Torulopsis glabrata, of oral- and non-oral pathogens such as Prevotella intermedia and Streptococcus mutans, and of a methicillin-resistant Staphylococcus aureus. In their broad-spectrum activity, dhvar1 and dhvar2 were comparable to magainins (PGLa and magainin 2), antimicrobial peptides of amphibian origin. Both the fungicidal and the haemolytic activities of dhvar1, dhvar2 and magainins increased at decreasing ionic strength.