Equilibrium, kinetic and HPLC study of the reactions between platinum(ii) complexes and DNA constituents in the presence and absence of glutathione

Abstract

The complex formation equilibria of [Pt(SMC)(H₂O)₂]⁺ and [Pt(terpy)H₂O]²⁺, where SMC = S-methyl-L-cysteine and terpy = 2,2′:6′,2″-terpyridine, with some biologically relevant ligands such as inosine (INO), inosine-5′-monophosphate (5′-IMP), guanosine-5′-monophosphate (5′-GMP) and glutathione (GSH) were studied. The stoichiometry and stability constants of the complexes formed are reported, and the concentration distribution of the various complex species have been evaluated as a function of pH. Also the kinetics and mechanism of the complex formation reactions were studied as a function of nucleophile concentration and temperature. For the complex [Pt(SMC)(H₂O)₂]⁺, two consecutive reaction steps, which both depend on the nucleophile concentration, were observed under all conditions. The negative entropies of activation support an associative complex formation mechanism. Reaction of guanosine-5′-monophosphate (5′-GMP) with Pt(II) complexes was carried out in the presence and absence of glutathione (GSH) at neutral pH. The rate constants clearly showed a kinetic preference toward GSH at neutral pH. The reactions were also monitored by HPLC. However, only a small amount of coordinated 5′-GMP was detected in the HPLC trace. The products were isolated and characterized by MALDI-TOF mass spectrometry.