Anticancer evaluation of a manganese complex on HeLa and MCF-7 cancer cells: design, deterministic solvothermal synthesis approach, Hirshfeld analysis, DNA binding, intracellular reactive oxygen species production, electrochemical characterization and density functional theory

Herein, a deterministic solvothermal strategy was employed to synthesize an efficient anticancer agent ‘cis-dichlorobis(1,10-phenanthroline)manganese(II)’ (Mn(phen)₂Cl₂). A single-crystal X-ray diffraction analysis revealed that Mn(phen)₂Cl₂ crystallizes in a triclinic system with the space group P-1. Cyclic voltammetric studies of Mn(phen)₂Cl₂ indicated that the electrode process occurs only due to complex formation and has a diffusion-controlled mechanism. Density functional theory estimations showed that the Mn(phen)₂Cl₂ is quite stable and exists in sextet spin state (five unpaired electrons) as the most stable form and hence, Mn(phen)₂Cl₂ is a high spin complex. Mn(phen)₂Cl₂ demonstrated significant anticancer potential against HeLa and MCF-7 cancer cells and less toxic behaviour towards normal BHK-21 cells. Fluorescence imaging confirmed that the production of reactive oxygen species (ROS) in HeLa cells by Mn(phen)₂Cl₂ induces oxidized fluorescence of dichlorofluorescein which emitted fluorescence at 530 nm after excitation at 488 nm. The microscopic investigation of apoptotic effect of Mn(phen)₂Cl₂ using propidium iodide and 4′,6-diamidino-2-phenylindole staining indicated that nuclear condensation, cell detachment and shrinkage occur after treatment with IC₅₀ values of Mn(phen)₂Cl₂. Furthermore, an assessment of caspase-9 and caspase-3 activity after exposure to Mn(phen)₂Cl₂ in HeLa cells indicated that at IC₅₀ values of Mn(phen)₂Cl₂, 1.5 fold and 4.8 fold increase in caspase-9 and caspase-3 activity, respectively, occurs. The measurement of mitochondrial membrane potential of a cationic dye (JC-1) showed a decrease in mitochondrial membrane potential in both HeLa and MCF-7 cells depicting that compound might have adopted intrinsic pathway of apoptosis. Ability of Mn(phen)₂Cl₂ to interact with HS-DNA demonstrates hyperchromicity with slight blue shift from 269 nm to 265 nm showing a non-covalent interaction with Gibbs free energy of ΔG = −14.62 kJ/mol.

Communicated by Ramaswamy H. Sarma