Interaction of copper(ii) (3 + 2) N-chelating complexes with DNA and BSA: hydrolytic DNA cleavage and ROS-mediated apoptosis

Abstract

Mixed-ligand copper(II) complexes of the form [Cu(L)(phen)](ClO₄)₂, where L is (6-methylpyridin-2-ylmethylene)-(pyridin-2-ylmethyl)amine (L1) and (6-methylpyridin-2-ylmethylene)-(pyridin-2-ylethyl)amine (L2), are obtained and characterized using analytical, spectral, and electrochemical methods. A distorted square pyramidal coordination geometry is observed in the single-crystal X-ray structure of [Cu(L2)(phen)](ClO₄)₂. DFT calculations of copper(II) complexes in solution offered insights into the molecular geometry, electronic properties, and quantum chemical descriptors. Complexes interact hydrophobically with calf thymus (CT) DNA through partial intercalation, as demonstrated by absorption spectral titration, EthBr displacement assay, and circular dichroic spectral and electrochemical investigations. They undergo a static process of quenching when exposed to bovine serum albumin (BSA) protein. Both complexes cleave pUC19 supercoiled (SC) DNA in the absence of an activator at concentrations of 130–140 μM, degrading SC DNA into nicked circular (NC) DNA and thereby indicating that they are effective hydrolytic chemical nucleases. They are notable for exhibiting cytotoxicity against human cervical carcinoma (HeLa) and human lung epithelial adenocarcinoma (A549) cell lines with potency greater than cisplatin, demonstrating that they have the potential to be effective anticancer drugs. They preferentially target cancer cells because they are non-toxic to human lung epithelial (L132) cells and normal mouse embryonic fibroblasts (NIH 3T3). AO/EB and DAPI staining, annexin-V-FITC staining assay, propidium iodide assay, and metal-assisted reactive oxygen species generation indicated an apoptotic mode of cell death, possibly by causing membrane instability and initiating apoptosis. These complexes can also stop the proliferation of A549 cancer cells by causing cell cycle arrest at the S-phase. Their efficiency as promising drugs for targeted cancer treatment is highlighted in this study.