Evaluation of the cytotoxicity of transition metal complexes: DNA cleavage of copper complexes in cells

Abstract

Transition metal complexes, particularly copper(II) compounds have received an increasing attention for cytotoxic effect. Copper compounds coordinated to various types of ligands exhibit considerable nuclease activity that is mostly measured by using the Agarose Gel Electrophoresis (AGE) of pDNA digested by the compounds of interest. In attempt to gain more insight into the cytotoxicity of transition metal complexes, namely their binding and cleavage capacity towards DNA, copper(II) compound [Cu(L)Cl](CH3OH) was prepared using a Schiff base ligand, 2-(pyridin-2-yl)hydrazono)methyl)phenol. The latter has been synthesized by condensation reaction between 2-hydrazinopuridine and salicylaldehyde and characterized by x-ray crystallography, mass spectrometry (MS), NMR and IR spectroscopy. [Cu(L)Cl](CH3OH) DNA binding properties were examined by spectrophotometric DNA titration (UV-visible spectroscopy) and EtBr displacement assay (fluorescence spectroscopy) using ct-DNA. The nuclease activity was evaluated by conversion of the Sc DNA into Nck and Lin forms using the AGE of pBR322 and pA1 DNA. A new method for evaluating the extent of DNA cleavage within living cells has been developed. The method was studied on Mach1 E. coli bacteria cells using vanadyl acetylacetonate, VIVO(acac)2, and copper(II) complex, [Cu(L)Cl](CH3OH). This new technique consists of bacterial cells culture, exposure of bacterial cells to concerned compounds, pDNA purification, and the AGE of pDNA extracted from exposed cells. DNA binding results show that the complex interacts with ct-DNA. The calculated values of intrinsic binding (Kb) and Stern-Volmer quenching (Ksv) constants were of 5.98 x 104 M-1 and 399.9 M-1, respectively. In contrary to pRB322 DNA, [Cu(L)Cl](CH3OH cleaves pA1 pDNA cleavage in presence of mercaptopropionic acid (MPA). Furthermore, VIVO(acac)2 DNA cleavage inside living cells was observed by using the new developed procedure.