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-imidazo[4,5-f][1,10]phenanthroline) 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.