Characterization of interactions between human serum albumin and tumor-inhibiting amino alcohol platinum(II) complexes using capillary electrophoresis

Platinum(II) complexes with amino alcohol ligands are of growing interest as anticancer agents capable of changing their reactivity toward biomolecules at different pH values. The binding of such compounds to the transport protein, human serum albumin (HSA), under simulated physiological conditions (pH 7.4, 100 mM chloride, 37 °C) has been studied by capillary electrophoresis (CE), with the objective to acquire and compare their binding parameters. The association constants and stoichiometric ratios of the platinum–HSA adducts were determined by measuring the concentration changes of the peak area response of the Pt complex (after a 48 h incubation of the reaction mixture to attain equilibrium), constructing the binding isotherms, and their mathematical analysis. The investigated Pt(II) compounds were found to show moderate affinity toward HSA, with association constants ranging from 1.0 × 103 to 2.4 × 104 M−1. Such binding behavior was attributed to a distinctive structural feature of bis(amino alcohol)platinum(II) complexes, that is, existence of an equilibrium between ring-opened and ring-closed forms in solution.