Ternary Dinuclear Copper(II) Complexes of a Hydroxybenzamide Ligand with Diimine Coligands: the 5,6-dmp Ligand Enhances DNA Binding and Cleavage and Induces Apoptosis

Abstract

The dinuclear copper(II) complexes [Cu(2)(LH)(2)(diimine)(2)(ClO(4))(2)](ClO(4))(2) (1-4), where LH = 2-hydroxy-N-[2-(methylamino)ethyl]benzamide and diimine = 2,2'-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp; 3), and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq; 4), have been isolated and characterized. The X-ray crystal structure of complex 1 contains two copper(II) centers bridged by the phenolate moiety of the amide ligand. All of the complexes display a ligand-field band (630-655 nm) and the PhO(-)-to-Cu(II) ligand-to-metal charge-transfer band (405-420 nm) in solution. Absorption and emission spectral studies and viscosity measurements indicate that complex 4 interacts with calf thymus DNA more strongly than all of the other complexes through strong partial intercalation of the extended planar ring (dpq) with a DNA base stack. Interestingly, 3 exhibits a DNA binding affinity higher than 2, suggesting the involvement in hydrophobic interaction of coordinated 5,6-dmp with the DNA surface. In contrast to the increase in relative viscosities of DNA bound to 2-4, a decrease in viscosity of DNA bound to 1 is observed, indicating a shortening of the DNA chain length through formation of kinks or bends. All of the complexes exhibit an ability to cleave DNA (pUC19 DNA) in a 5% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an oxidant at 100 μM complex concentration, which varies as 4 > 2 > 1 > 3. The order of DNA the cleavage ability at 30 μM concentration in the presence ascorbic acid is 4 > 2 > 1 > 3, and, interestingly, 4 alone shows an ability to convert supercoiled DNA into nicked-coiled DNA even at 6 μM concentration, beyond which complete degradation is observed and the pathway of oxidative DNA cleavage involves hydroxyl radicals. In the presence of distamycin, all of the complexes, except 3, show decreased DNA cleavage activity, suggesting that the complexes prefer to bind in the DNA minor groove. All of the complexes exhibit prominent DNA cleavage even at very low concentrations (nM) in the presence of H(2)O(2) as an activator, with the order of cleavage efficiency being 3 > 2 > 4 > 1. Studies on the anticancer activity toward HEp-2 human larynx cell lines reveal that the ability of the complexes to kill the cancer cell lines varies as 3 > 4 > 2 > 1. Also, interestingly, the IC(50) value of 3 is lower than that of cisplatin, suggesting that the hydrophobicity of methyl groups on the 5 and 6 positions of the complex enhances the anticancer activity. The mode of cell death effected by the complex has been explored by using various biochemical techniques like comet assay, mitochondrial membrane potency, and Western blotting. The complex has been found to induce nuclear condensation and fragmentation in cell lines. Also, it triggers activation of caspases by releasing cytochrome c from mitochondria to cytosol, suggesting that it induces apoptosis in cells via the mitochondrial pathway.

Synthesis and the characterization of Schiff-base copper complexes: Reactivity with DNA, 4-NPP and BNPP

“…Several copper complexes have been found to exhibit these modes of interaction. Furthermore, a number of the copper complexes have been found to exhibit cytotoxicity levels that are comparable to or greater than that of cisplatin [26][27][28][29][30][31][32][33][34][35][36][37][38][39].…”

Synthesis, Molecular Structure, DNA/Protein Binding, Cytotoxicity, Apoptosis, Reactive Oxygen Species, and Mitochondrial Membrane Potential of Dibenzoxanthenes Derivatives

“…The hypochromism is 45.83 % with red shift of 3 nm and 26.32 % with red shift of 2 nm for compounds 3 and 4, respectively. Hypochromism is caused by the strong interaction between compounds and CT DNA base pairs (Ramakrishnan et al 2011). These characteristics indicate that two compounds interact with DNA most likely through a mode that involves a stacking interaction between the aromatic chromophore and the base pairs of DNA.…”

A novel Schiff base derived from the gabapentin drug and copper (II) complex: Synthesis, characterization, interaction with DNA/protein and cytotoxic activity

“…[22,23]. Many copper (II) complexes with biological activities such as antibacterial, anti-cancer and cancer inhibiting properties have already been dealt with in the literature [24,25]. Palaniandavar and co-workers have reported that copper (II) complexes are the best alternatives to cisplatin because copper plays many significant parts in biological systems and is a biocompatible metal [26], considering the strong interactions of copper complexes with DNA through surface associations or intercalation [27].…”