Synthesis, structural characterization, and investigation of anti-glioblastoma activity of copper complexes supported by bis(pyrazol-1-yl)acetate ligands functionalized with memantine

Abstract

The new ligand bis(1H-pyrazol-1-yl)acetyl-3,5-dimethyladamantane-1-amide (L^Mem) was synthesized by conjugating the drug memantine with the bifunctional species bis(pyrazol-1-yl)acetic acid and used as supporting ligand of copper(II) and copper(I) complexes 1-7. In the synthesis of the Cu^I complexes, the lipophilic triphenylphosphine (PPh₃) and hydrophilic 1,3,5-triaza-7-phosphaadamantane (PTA) were selected as co-ligands, in order to stabilize copper in +1 oxidation state and to confer different solubility properties to the corresponding metal complexes. The electronic and molecular structures of Cu^I and Cu^II coordination compounds were investigated by high resolution Synchrotron Radiation-induced X-ray Photoelectron Spectroscopy (SR-XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The local structure around the copper ion sites was studied combining Density Functional Theory (DFT) modelling and X-ray Absorption Fine Structure (XAFS) spectroscopy, in both X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structures (EXAFS) regions. X-ray diffraction (XRD) studies were carried out on suitable crystals to describe the molecular structure and the intermolecular contacts of the L^Mem ligand. Among all Cu complexes tested, compounds 4 and 5 exhibited potent antiproliferative and cytotoxic effects in U87, T98, and U251 glioma cell lines. These effects were associated with increased reactive oxygen species (ROS) production and mitochondrial dysfunction, as evidenced by mitochondrial depolarization and altered intracellular distribution. Furthermore, the cytotoxic activity of these compounds was shown to be Cu-dependent, as it was effectively inhibited by the Cu chelator tetrathiomolybdate, confirming the essential role of copper in their mechanism of action.

Keywords: Copper; Cytotoxicity; Glioblastoma; Memantine-conjugated ligands; SR-XPS and XAS; Single-crystal XRD.