Novel analogues of Temporin L and their potential therapeutic application

Antimicrobial peptides (AMPs) are produced from almost all living species and are characterized by a fast-acting and efficient defence against microbial pathogens. The large interest aroused by these peptides is due to their target, that is the bacterial membrane, in which they can accumulate, increasing its permeability and causing the death of the microbes.[1] Though this way of action, the formation of resistant strains is much less likely to be induced, that happens using traditional antibiotics. The amphibian Temporins are the largest family of AMPs, consisting of more than 100 peptides. As most of the antimicrobial peptides, Temporins adopt an amphipathic a-helical secondary structure in a hydrophobic environment. Usually this condition is responsible for their antimicrobial activity, but for the most potent Temporin L (TL) this property seems to be better correlated to the hemolytic/cytolytic activity. For this reason, and with the aim to improve its therapeutic index, several SAR studies have been made on the sequence of TL. Recently, we have obtained a TL derivatives, TL-34, practically devoid of cytolytic effects in vitro and which preserves the antimicrobial activity mainly toward Gram + bacteria.[2] In this work, to further study the importance of the C-terminal region of Temporin L, we have synthesized a novel series of TL-34 analogues, in which we replaced the Gly10 residue with several amino acids characterized by a different hydrophilic/lipophilic balance and by their ability to modify the secondary structure of the sequence. These peptides were evaluated on a panel of bacterial strains, both Gram + and Gram - and on some bacterial strains isolated from human skin, resistant toward conventional antibiotics. Furthermore, the cytotoxicity on human keratinocytes was evaluated to establish their potential therapeutic application.