Anticancer effect evaluation of iridium(III) complexes targeting mitochondria and endoplasmic reticulum

Ligand HMSPIP (2-(4-(methylsulfonyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its iridium(III) complexes [Ir(ppy)2(HMSPIP)]PF6 (ppy = 2-phenylpyridine, Ir1) and [Ir(bzq)2(HMSPIP)]PF6 (bzq = benzo[h]quinoline, Ir2) were synthesized. The complexes were characterized by 1H NMR, 13C NMR, and UV/Vis spectra. The cytotoxicity of the complexes toward cancer cells were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method, the scratch wound healing and colony-forming were also investigated. MTT assay certificated that the complexes show high toxic effect on the HeLa cells. The cell cycle assay illustrated that the complexes blocked cell growth at G0/G1 phase in HeLa cells. A series of subsequent experiments showed that the complexes first enter the endoplasmic reticulum (ER) and then enter the mitochondria, leading to an increase in intracellular Ca2+ and reactive oxygen species (ROS) content, depolarizing mitochondrial membrane potential (MMP), and ultimately resulting in apoptosis. In addition, the experimental results revealed that the complexes not only increase the level of ROS but also inhibit the production of GSH and eventually produce large amounts of MDA and further leading to cell death. Taken together, we consider that the complexes can be used as potential candidate drugs for HeLa cancer treatment.