DNA Interaction and Antitumor Activity of A Copper(II) Complex Containing Sparfloxacin and Triazine Derivatives

DNA is an important target for antitumor drugs, hence investigation of the interaction between drug molecules and DNA can help to design targeted DNA antitumor drugs. New ternary copper(II) complex [Cu(Sf)(PyTA)(H2O)]center dot ClO4 center dot 3.5H(2)O [Sf= sparfloxacin, 5-amino-1-cyclopropyl-7-(cis-3,5-dimethyl-1-piperazinyl)-6,8-difluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid, PyTA=2.4-diamino-6-(2'-pyridyl)-1,3,5-triazine] was synthesized and characterized by elemental analyses, molar conductivity measurement and various spectroscopic techniques such as infrared, ultraviolet-visible, and electrospray ionization mass spectra. The interaction of the complex with DNA was investigated using electronic absorption spectroscopy, KI fluorescence quench, viscosity measurement and molecular docking techniques. It was found that the complex could bind to DNA through an intercalation mode being related with the quinoline ring of ligand Sf, and the corresponding binding constant K-b is 1.23 x 10(4) L/mol. Moreover, the antitumor activity of the complex was evaluated using the MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide] method, revealing that the complex displayed favorable cytotoxic effects [IC50 =(57.0 +/- 1.6)similar to(77.6 +/- 1.4) mu mol/L] toward cancer cells (A549, Bel-7402 and Eca-109) and less toxic towards normal cells (3T3). Most importantly, the cytotoxic mechanism of the complex towards Eca-109 cells was explored by single cell gel electrophoresis assay, Hoechst 33342 staining, Annexin V-FITC/PI double dye flow cytometry, measurement of mitochondrial membrane potential change, detection of intracellular cytochrome C and Ca2+ levels, and test of cell cycle arrest. Single cell gel electrophoresis assay (comet assays) demonstrated that the complex could damage DNA and cause apoptosis. Double staining analysis showed that the complex could induce apoptosis in Eca-109 cells. Cell cycle arrest studies revealed the cell growth arrest at S and G2/M phases. The complex also could induce a reduction in the mitochondrial membrane potential and release of the cytochrome C, and increase the intracellular Ca2+ level. The results demonstrated that the complex could induce apoptosis in Eca-109 cells through DNA-binding mitochondria' dysfunctional pathways, which was accompanied by the cell growth arrest at S and G2/M phases and damage of DNA.