Synthesis, characterization and induction of ferroptosis of iridium(III) complexes against melanoma B16 cells

Abstract

The synthesis of ligand, 2-(2-methyl-4-hydroxyl)phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (MHIP), and corresponding new iridium(III) complexes: [Ir(ppy)2(MHIP)]PF6 (ppy = 2-phenylpyridine, 9a), [Ir(bzq)2(MHIP)]PF6 (bzq = benzo[h]quinolone, 9b) and [Ir(piq)2(MHIP)]PF6 (piq = 1-phenylisoquinoline, 9c) were reported. The antiproliferative activity of compounds 9a-9c on cancer HepG2, B16, A549 cells, normal LO2 cells were tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, it was found that the three complexes showed moderate cytotoxicity on A549 and B16 cells. However, after further irradiation, the cytotoxicity was greatly enhanced, especially, 9a, 9b and 9c display significant cytotoxicity toward B16 cells with a low IC50 value of 3.1 ± 0.3 µM for 9a, 4.9 ± 0.8 µM for 9b, and 0.4 ± 0.1 µM for 9c, respectively. The effects of 9a-9c on the invasive ability of B16 cells were explored by colony formation and scratch experiments, the results demonstrate that the complexes can efficiently block the cell proliferation and migration. The co-localization assay found that 9a-9c accumulate in the mitochondria and lead to the apoptosis of B16 cells by decreasing the mitochondrial membrane potential, altering the structure of microtubule proteins, damaging the structure of the cellular DNA, and changing the expression of related proteins. The decrease of glutathione (GSH) concentration, the increase of malondialdehyde (MDA), the downregulation of GPX4, and C11-BODIPY staining results confirmed that 9a, 9b and 9c led to ferroptosis. In addition, we explored the relevant signaling pathways through RNA sequencing assay and speculated on possible anticancer mechanisms. Together, these results indicate that the synthesized new iridium(III) complexes 9a-9c can induce cell death via a ROS-mediated mitochondrial dysfunction apoptosis and ferroptosis.