Effect of coordination mode of thiosemicarbazone on the biological activities of its Ru(II)-benzene complexes: Biomolecular interactions and anticancer activity via ROS-mediated mitochondrial apoptosis

Abstract

Ru(II)-benzene complexes (P1 and P2) were synthesized using a thiosemicarbazone ligand (L1) in two different coordination modes, monodentate S and bidentate N,S, through carefully adjusted reaction conditions. Comprehensive characterization of the complexes was achieved through single crystal X-ray diffraction, revealing a piano-stool geometry around the Ru(II) ion. To evaluate the binding capabilities of the complexes towards CT DNA and BSA, UV–Vis and/or hydrodynamic methods were utilized. Docking studies further validated the intercalative binding mode with DNA, in agreement with the experimental findings, and identified specific BSA amino acids involved in the binding interactions. Based on the results of binding studies, cytotoxicity of the ligand and complexes was appraised in various cancer and normal cell lines alongside the commercial pharmaceutics. Complexes P1 and P2 displayed a promising activity against MDA-MB-231 [IC50 = 5.11 (P1) and 3.48 μM (P2)] and PANC-1 [IC50 = 7.20 (P1) and 4.85 μM (P2)] cancer cells; with the bidentate system (P2) exhibiting a higher activity than its monodentate congener P1, although both of them showed superior activity than the reference drugs. Various bioassays including Western blot analysis revealed the mode of cell death to be apoptosis, which was further concluded to be via the ROS-mediated mitochondrial signaling pathway.