Characterization of [Ru(bpy)2(diamine)]2+ complexes and their DNA binding and cleavage, BSA interaction, cytotoxic, and anticancer mechanistic properties

Abstract

The ruthenium(II) complexes of the type [Ru(bpy)2(diamine)](PF6)21–3, where diamine is ethylenediamine (en, 1) or N,N-dimethylethylenediamine (dmen, 2) and N,N-diethyl-ethylenediamine (deen, 3) and bpy is 2,2′-bipyridine has been isolated and characterized. The X-ray crystal structures of 1 and 2 reveal that the compounds possess a distorted octahedral geometry composed of two amine nitrogen atoms of the diamine ligand (1, en; 2, dmen) and four nitrogen atoms of the two bpy ligands, which selectively forms a “cis-α” (2) or “cis-β” (1) isomer. The 1H and 13C NMR spectral data of the complexes disclose the nature of metal-ligand bonding, conformations of the chelate rings, and absolute configurations, which indicate that the two bpy ligands maintain their tendency to form geometrical isomers even in solution. They exhibit dπ → π* MLCT transitions, show a ligand-based radical anion (3MLCT) luminescence, and display one quasi-reversible and one non-reversible metal-based oxidative process corresponding to RuII/RuIII and RuIII/RIV redox couples respectively. They interacted with calf thymus (CT) DNA and the mode of interaction was found to be groove binding, as determined by various spectral and redox techniques. Upon interaction with CT DNA 1–3 show a decrease in current and less positive shift in the formal potential in the differential pulse voltammograms suggesting that they are involved in electrocatalytic guanine oxidation. Interestingly, 1–3 alters the DNA superhelicity upon binding with supercoiled pUC19 plasmid DNA with a reductant. Further, the quenching of the tryptophan emission of BSA in the presence of 1–3 is static. The binding is mainly entropy-driven and hydrophobic forces played a major role. The DNA and protein binding affinity and the DNA cleavage activity is in the order 2 > 3 > 1, and the higher DNA and protein binding affinity and DNA cleavage activity of 2 and 3 illustrates the strong involvement of the methyl (dmen) and ethyl (deen) groups in the hydrophobic interaction with the DNA and protein. Furthermore, the ruthenium(II) complexes, 2 and 3 exhibit moderate cytotoxicity against human breast adenocarcinoma MCF-7 and human cervical carcinoma HeLa (IC50: 48 h, 28–45 μM) cells, whereas 2 displays the best activity (IC50: 48 h, 28 μM) for MCF-7 cancer cells, which is better than that of cisplatin. Both the complexes displayed excellent selectivity by being relatively inactive against the Madin-Darby bovine kidney (MDBK) normal cells with selectivity index (SI) values ranging from 5.6 to 8.9. They block the cell cycle progression of MCF-7 cells in the G1 (2) and S (3) phases. FACSVerse analyses are suggestive of reactive oxygen species (ROS) generation and apoptotic cell death induced by 2 and 3. The induction of apoptosis in MCF-7 cells was shown by Annexin V with propidium iodide (PI) and 4’,6-diamidino-2-phenylindole (DAPI) staining methods.