Synthesis, Structure, and Stability of Copper(II) Complexes Containing Imidazoline-Phthalazine Ligands with Potential Anticancer Activity

<b>Background/Objectives</b>: Recently, there has been great interest in metallopharmaceuticals as potential anticancer agents. In this context, presented studies aim to synthesize and evaluate of two copper(II) complexes derived from phthalazine- and imidazoline-based ligands against on three human cancer cell lines: cervix epithelial cell line (HeLa), breast epithelial-like adenocarcinoma (MCF-7), and triple-negative breast epithelial cancer cell line (MDA-MB-231), as well as non-tumorigenic cell line (HDFa). Moreover their antimicrobial, and antioxidant properties were assessed. <b>Methods</b>: The synthetized compounds-both free ligands <b>L1</b>, <b>L2</b>, <b>L3</b> and copper(II) complexes <b>C1</b> and <b>C2</b>-were characterized by elemental analysis, infrared spectroscopy. Additionally, a single-crystal X-ray diffraction studies we performed for free ligand <b>L3</b> and its copper(II) complex <b>C2</b>. The stability of Cu(II)-complexes <b>C1</b> and <b>C2</b> was evaluated by UV-Vis spectroscopy. The cytotoxic potency of free ligands and their copper(II) complexes was estimated on HeLa, MCF-7, MDA-MB-231, as well as non-cancerous HDFa by use of an MTT assay after 48 h of incubation. Moreover, the antimicrobial activity of ligands <b>L1</b> and <b>L3</b> and their copper(II) complexes <b>C1</b> and <b>C2</b> was evaluated using reference strains of the following bacteria and yeasts: <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Candida albicans</i>. The free radical scavenging properties of free ligands <b>L1</b>, <b>L3</b> and the corresponding copper(II) complexes <b>C1</b>, <b>C2</b> was tested with two colorimetric methods-ABTS, DPPH, and reduction ability assay (FRAP). Additionally, the ADME webtool was used to assess the drug-likeness of the synthesized compounds, as well as their physicochemical and pharmacokinetic properties. <b>Results</b>: Copper(II) complex <b>C2</b> exhibited antitumor properties towards MDA-MB-231 compared with Cisplatin (cancer cell viability rate of 23.6% vs. 22.5%). At a concentration of 200 μg/mL, complexes <b>C1</b> and <b>C2</b> were less cytotoxic than the reference Cisplatin against a normal, non-cancerous skin fibroblast cell line (HDFa). According to in vitro tests, <b>C2</b> reduced the viability of HeLa, MCF-7, and MDA-MB-231 cells by about 57.5-81.2%. It was evident that all compounds were devoid of antibacterial or antifungal activity. In vitro assays revealed that a moderate antiradical effect was observed for free ligand <b>L1</b> containing phthalazin-1(2<i>H</i>)-imine in the ABTS radical scavenging assay (IC₅₀ = 23.63 µg/mL). <b>Conclusions</b>: The anticancer studies revealed that the most potent compound was copper(II) complex <b>C2</b> bearing a phthalazin-1(2<i>H</i>)-one scaffold. None of the tested compounds showed antimicrobial or antifungal activity. This feature seems to be beneficial in terms of their potential uses as anticancer agents in the future. In vitro antiradical assays revealed that a moderate antioxidant effect was observed only for free ligand <b>L1</b> containing phthalazin-1(2<i>H</i>)-imine.