Study of the interaction of the [Ru3O(CH3COO)6(THIQ)2(CH3OH)]PF6 complex with human serum albumin: the influence of lability and hydrophobicity on the development of ruthenium metallopharmaceuticals

Abstract

In this project, the objective is the synthesis and characterization of a novel trinuclear ruthenium acetate [Ru3O(CH3COO)6(THIQ)2(CH3OH)]PF6 (where THIQ = 5,6,7,8-tetrahydroisoquinoline) in order to study its interaction with human serum albumin (HSA), with the aim of obtaining a complex:HSA adduct in the future, which would function as a drug candidate carrier. For the characterization of the complex it will be used the techniques of electronic absorption spectroscopy, vibrational spectroscopy in the infrared region, nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR), cyclic voltammetry, spectroelectrochemistry, mass spectrometry and elemental analysis. The evaluation of the interaction with HSA will be done through a kinetic and thermodynamic approach. From the kinetic point of view, the reaction of the complex (which contains the methanol ligand as a labile site) with histidine, an amino acid present in HSA, will be studied by spectrophotometric monitoring. Histidine was chosen as the protein binding site model due to literature precedents and because it contains good binding groups (imidazole and carboxylate function) for Ru(III) ions. The reaction will be studied under conditions of pseudo-first order in relation to histidine, where the dependence of kobs with the variation of concentration of this ligand and with temperature will also be investigated, in order to characterize the reaction and verify if this amino acid is a viable site for complex binding to HSA. For the study of thermodynamic parameters, HSA solutions will be titrated with the complex in order to verify the quenching of protein fluorescence as an index of interaction. The data will be treated through the Stern-Volmer equations, for determination of interaction constants. The dependence of the value of these constants on temperature variations will be analyzed by the van't Hoff plot, and the parameters of DH, DS and DG that characterize the interaction will be determined. It is expected that the N-heterocyclic THIQ ligand, which contains a non-aromatic ring in its structure and provides hydrophobicity to the complex, assists weak interactions with albumin and that the labile site (coordinated methanol) allows the eventual chemical binding of the complex with the HSA, potentially to histidine residues.