Synthesis and evaluation of anticancer activity in vitro and in vivo of photoactivated iridium(III) complex

In this article, using NNIP (2-(2-nitronaphthalen-1-yl)-1H-imidazo4,5-f1,10phenanthroline) as a ligand to synthesise and characterise a new iridium(III) complex, Ir(piq)2(NNIP)PF6 (Ir1, where piq = 1-phenylisoquinoline) and to explore its anticancer activity as a photosensitiser against HeLa cancer cells and the corresponding mechanisms of inducing cancer cell death. The cytotoxicity of Ir1 against HeLa, B16 and normal NIH3T3 cells was assessed using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Unexpectedly, Ir1 initially shows no cytotoxicity against those cells (half maximal inhibitory concentration, IC50 200 μM) in the dark. However, upon white light irradiation, Ir1 significantly increased cytotoxicity, especially on HeLa cancer cells with a low IC50 value of 3.1 ± 0.3 μM. The anticancer mechanism was explored through various techniques, including cellular uptake, mitochondrial co-localisation, ROS production, mitochondrial permeability transition pore opening and the change in the mitochondrial membrane potential. Subsequently, lipid peroxidation was investigated with a C11-BODIPY581/591 probe to affirm the occurrence of ferroptosis. Additionally, metabolic impacts were probed by conducting lactate dehydrogenase release and adenosine 5′-triphosphate (ATP) quantification assays. Apoptosis, pyroptosis and immunogenic cell death were also explored. The light-activated antitumour in vivo revealed that Ir1 can effectively inhibit the tumour growth with an inhibitory rate of 53.2%. These findings demonstrate that Ir1 induces cancer cell demise by a mitochondrial apoptotic pathway mediated by ROS, ferroptosis and pyroptosis.