Ruthenium(II)/(III) complexes of 4-hydroxy-pyridine-2,6-dicarboxylic acid with PPh ₃/AsPh ₃ as co-ligand: Impact of oxidation state and co-ligands on anticancer activity in vitro

With the aim to develop more efficient, less toxic, target specific metal drugs and evaluate their anticancer properties in terms of oxidation state and co-ligand sphere, a sequence of Ru ^II, Ru ^III complexes bearing 4-hydroxy-pyridine-2,6-dicarboxylic acid and PPh ₃/AsPh ₃ were synthesized and structurally characterized. Biological studies such as DNA binding, antioxidant assays and cytotoxic activity were carried out and their anticancer activities were evaluated. Interactions of the complexes with calf thymus DNA revealed that the triphenylphosphine complexes could bind more strongly than the triphenylarsine complexes. The free radical scavenging ability, assessed by a series of in vitro antioxidant assays involving DPPH radical, hydroxyl radical, nitric oxide radical, superoxide anion radical, hydrogen peroxide and metal chelating assay, showed that the Ru ^III complexes possess excellent radical scavenging properties compared to those of Ru ^II. Cytotoxicity studies using three cancer lines viz HeLa, HepG2, HEp-2 and a normal cell line NIH 3T3 showed that Ru ^II complexes exhibited substantial cytotoxic specificity towards cancer cells. Furthermore, the Ru ^II complexes were found to be superior to Ru ^III complexes in inhibiting the growth of cancer cells.