Metallo peptides in the design of new, highly selective clinical treatments

The necessity of new antimicrobial agents is unarguable, since current therapeutic treatments are not always effective: pathogenic microorganisms capable to adapt and resist against drug action have significantly increased over the last decades and their associated mortality rate still remains a global concern. Several studies have shown that metal acquisition and regulation greatly contribute to virulence and physiology of pathogenic species. In particular, to prevent infections humans restrict the access to essential micronutrients by means of an innate immune response termed "nutritional immunity”, on the contrary pathogens rely on sophisticated systems (e.g. siderophores) to overcome the scarce metal bioavailability. From this perspective, a deeper insight into the mechanism of metal trafficking in pathogens and host nutritional immune response can provide crucial information to design new effective antibiotic therapies, e.g. by developing species-selective transport or imaging drugs, based on metal complexes, which can be recognized only by specialized metal transport proteins (“Trojan Horse” approach). Furthermore, metal complexes cannot be only a promising tool in antimicrobial treatments, but they can also find application against pathologies which – in general – involve metal ions (e.g. neurodegenerative diseases or cancer) [1-3]. As a first step, it is essential to obtain information about thermodynamics and coordination chemistry of the metal chelators, in order to point out the most effective metal binding sites. Both natural and artificial peptides can be exploited for this purpose. Aiming at the design of new clinical treatments, we focused on Zn(II) and Cu(II) binding behavior towards both the putative metal transporter C4YJH2 (a protein sequence of 199 residues found in the genome of Candida albicans [4]) and the antimicrobial peptide Calcitermin [5], isolated in the human airways. The characterization of the complexes required a variety of techniques. The stoichiometry of the formed species has been determined through high-resolution mass spectrometry as well as by potentiometry which also provided the stability constants of all the formed metal complexes; thermodynamic description of metal-ligand interactions has been also investigated by calorimetry. The identification of binding sites and the coordination geometry of the formed species have been achieved by several spectroscopic techniques (NMR, UV-Vis, fluorimetry, CD and EPR). REFERENCES [1] M. Blatzer, J.P. Latgé, Curr. Opin. Microbiol. 2017, 40, 152-159. [2] A. Szebesczyk, E. Olshvang, A. Shanzer, P.L. Carver, E. Gumienna-Kontecka, Coord. Chem. Rev. 2016, 327, 84-109. [3] E. R. Ballou and D. Wilson, Curr. Opin. Microbiol. 2016, 32, 128–134. [4] D. Bellotti, D. Łoboda, M. Rowińska-Żyrek, M. Remelli, New J. Chem. 2018, 42, 8123-8130. [5] A.M. Cole, Y.-H. Kim, S. Tahk, T. Hong, P. Weis, A.J. Waring, T. Ganz, FEBS Lett. 2001, 504, 5-10