Synthesis, characterization, anticancer efficacy evaluation of ruthenium(II) and iridium(III) polypyridyl complexes toward A549 cells

A new ligand DFIP (2-(dibenzo[b,d]furan-3-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its two complexes iridium(III) [Ir(ppy)₂(DFIP)](PF₆) (ppy = 2-phenylpyridine, Ir1) and ruthenium(II) [Ru(bpy)₂(DFIP)](PF₆)₂ (bpy = 2,2′-bipyridine, Ru1) were synthesized and characterized. The anticancer effects of the two complexes on A549, BEL-7402, HepG2, SGC-7901, HCT116 and normal LO2 cells were tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Complex Ir1 shows high cytotoxic activity on A549, BEL-7402, SGC-7901 and HepG2, Ru1 exhibits moderate anticancer activity toward A549, BEL-7402 and SGC-7901 cells. The IC₅₀ values of Ir1 and Ru1 toward A549 are 7.2 ± 0.1 and 22.6 ± 1.4 μM, respectively. The localization of complexes Ir1 and Ru1 in the mitochondrial, intracellular accumulation of reactive oxygen species (ROS) levels, and the changes of mitochondrial membrane potential (MMP) and cytochrome c (cyto-c) were investigated. Apoptosis and cell cycle were detected by flow cytometry. Immunogenic cell death (ICD) was used to detect the effects of Ir1 and Ru1 on the A549 using a confocal laser scanning microscope. The expression of apoptosis-related proteins was detected by western blotting. Ir1 and Ru1 can increase the intracellular ROS levels and release cyto-c, reduce the MMP, leading to the apoptosis of A549 cells and blocking the A549 cells at the G0/G1 phase. Additionally, the complexes caused a decrease of the expression of polyADP-ribose polymerase (PARP), caspase 3, Bcl-2 (B-cell lymphoma-2), PI3K (phosphoinositide-3 kinase) and upregulated the expression of Bax. All these findings indicated that the complexes exert anticancer efficacy to induce cell death through immunogenic cell death, apoptosis, and autophagy.

Graphical abstract