Interaction of apo-transferrin with anticancer ruthenium complexes NAMI-A and its reduced form

NAMI-A i.e. (ImH)[trans-RuCl(4)(DMSO)(Im)] (where Im is imidazole) is a ruthenium(III) complex with promising antimetastatic activity, which has been classified for II phase clinical trial. In this study, its binding properties toward apo-transferrin (apo-Tf) with regard to its hydrolytic and redox behavior are systematically investigated by the use of fluorescence spectroscopy. The reaction of NAMI-A and its reduced form with apo-Tf is proceeded by formation of aqua derivatives and the presence of at least one labile aqua ligand is sufficient to form adducts. It is found that presence of bicarbonate is not necessary for interaction of studied ruthenium complexes with apo-Tf. The calculated association constants for both NAMI-A and its reduced form are very similar with the values of 1.28 × 10(4)M(-1) and 1.36 × 10(4)M(-1) at 37 °C, respectively however, the reduced derivatives reach the equilibrium ca. 8-10 times slower. The percentage of ruthenium content in protein fractions separated from protein-unbounded ruthenium by using FPLC (fast protein liquid chromatography) method is rather high and depends on redox state of the complex, for most samples is found higher for reduced species.