Synthesis and mitochondria-localized iridium (III) complexes induce cell death through pyroptosis and ferroptosis pathways

This paper introduces a new ligand, 4,6-dichloro-5-(1H-imidazo [4,5-f]phenanthroline-2-yl)pyrimidin-2-amine (DPPA), and its corresponding new iridium(III) complexes: [Ir(ppy)2(DPPA)](PF6) (2a) (where ppy represents deprotonated 2-phenylpyridine), [Ir(bzq)2(DPPA)](PF6) (2b) (with bzq indicating deprotonated benzo[h]quinoline), and [Ir(piq)2(DPPA)](PF6) (2c) (piq denoting deprotonated 1-phenylisoquinoline). The cytotoxic effects of both DPPA and 2a, 2b, and 2c were evaluated against human lung carcinoma A549, melanoma B16, colorectal cancer HCT116, human hepatocellular carcinoma HepG2 cancer cell lines, as well as the non-cancerous LO2 cell line using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. While DPPA exhibited moderate anticancer activity toward A549, B16, HCT116 and HepG2 cells, complexes 2a, 2b, and 2c displayed remarkable efficacy against A549, B16, and HCT116 cells. The cell colonies and wound healing were investigated. Moreover, various aspects of the anticancer mechanisms were explored. The cell cycle analyses revealed that the complexes block cell proliferation of A549 cells during the S phase. Complex 2c induce an early apoptosis, while 2a and 2b cause a late apoptosis. The interaction of 2a, 2b and 2c with endoplasmic reticulum and mitochondria was identified, leading to elevated ROS and Ca2+ amounts. This resulted in a reduced mitochondrial membrane potential, mitochondrial permeability transition pore opening, and an increase of cytochrome c. Also, ferroptosis was investigated through measurements of intracellular glutathione (GSH), malondialdehyde (MDA), and recombinant glutathione peroxidase (GPX4) protein expression. The pyroptosis was explored via cell morphology, release of lactate dehydrogenase (LDH) and expression of pyroptosis-related proteins. RNA sequencing was applied to examine the signaling pathways. Western blot analyses illuminated that the complexes regulate the expression of Bcl-2 family proteins. Additionally, an in vivo antitumor study demonstrated that complex 2c exhibited a remarkable inhibitory rate of 58.58% in restraining tumor growth. In summary, the findings collectively suggest that the iridium(III) complexes induce cell death via ferroptosis, apoptosis by a ROS-mediated mitochondrial dysfunction pathway and GSDMD-mediated pyroptosis.