Synthesis and Structure of Naphthoyl Thiourea‐Based Binuclear Ruthenium(II) Arene Complexes: Studies on Anticancer Activity and Apoptotic Mechanism

Herein, the synthesis, characterization, and anticancer activity of ruthenium(II) p-cymene complexes comprising naphthoyl thiourea-based ligands are described. The synthesized N^O and N^S chelating ruthenium(II) complexes (1-3) are fully characterized by elemental analysis and spectral (fourier transform-infrared, Ultraviolet-visible, nuclear magnetic resonance, mass) methods. The structure of complex 2 has been elucidated by employing single-crystal X-ray diffraction, which verifies the two bidentate N^O and N^S coordination of the thiourea ligand to two Ru(II) centers. All the complexes have been screened for their anticancer efficacy in breast (MCF-7), colon (HT-29), liver (HepG2) cancerous cells, and noncancerous kidney (Hek-293) cells. Among them, complex 2 with an IC₅₀ concentration of 3.59 ± 0.72 μm exhibits the most potent activity in HT-29 cells, surpassing the positive control, cisplatin. This may be due to the hydrophobic nature of the p-cymene moiety and electron-releasing methoxy group in the ligand scaffold. In addition, acridine orange-ethidium bromide and Hoechst labeling of all the complexes (1-3) on HT-29 cells reveal morphological alterations such as nuclear fragmentation and chromatin condensation resulting from the death of cancerous cells via apoptosis. Biochemical assays such as reactive oxygen species, mitochondrial membrane potential, and flow cytometry strongly confirm the cell death via mitochondrial dysfunction-mediated apoptosis.