Experimental and Computational Insights into the Apoptotic Potential of New Phenanthroline-Based Copper(II) Complexes: From Spectroscopic Characterization and In Vitro Cytotoxicity to In Silico Target Identification

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Abstract
Background: Two novel copper(II) coordination complexes, PH-Cu [(1,10-phenanthroline)(malonato)copper(II)] and PC-Cu [(1,10-phenanthroline)(cyclobutane-1,1-dicarboxylato)copper(II)], were synthesized and evaluated as potential anticancer agents, aiming to characterize structural properties, explore antiproliferative activity and generate mechanistic hypotheses through experimental and computational approaches. Methods: Complexes were characterized by EPR, FTIR-ATR, and ESI-MS, with preliminary SC-XRD data for PH-Cu. Antiproliferative activity was evaluated against six human cancer cell lines using the MTT assay (24 h). Subcellular effects were assessed by fluorescence microscopy and RT-qPCR. Computational studies included DFT geometry optimization, target prediction, molecular docking, and ADMET profiling. Results: Based on spectroscopic and spectrometric data and comparison with analogous Cu(II) complexes, a distorted square-pyramidal coordination geometry was proposed; this assignment was not confirmed by SC-XRD. Both complexes exhibited potent antiproliferative activity, with PH-Cu showing the highest potency in HeLa cells (IC50 = 4.22 µM). Under the same conditions, cisplatin showed substantially lower activity (HepG2: 191.1 µM; Caco-2: 129.6 µM; NCI-H69: >333.3 µM; HeLa: 21.9 µM). Fluorescence microscopy at 18 h revealed pyknosis, karyorrhexis, and microtubule disorganization, consistent with regulated cell death. RT-qPCR of PH-Cu indicated intrinsic apoptotic pathway engagement (BAX +3.20-fold; BCL2 to 0.39-fold of control). DFT-optimized bond lengths were consistent with crystallographic data for analogous complexes. Molecular docking suggested PRKCG, RELA (p65), Caspase-3, and α/β-tubulin as interaction candidates, while ADMET profiling predicted favorable intestinal absorption (>92.8%) and low BBB permeability. Conclusions: These results suggest that the [Cu(phen)] unit constitutes the primary pharmacophore, with the dicarboxylate co-ligand as a modulator of the antiproliferative profile, suggesting promising anticancer pharmacological potential.

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