Cyclometalated iridium(III) complex based on isoquinoline alkaloid synergistically elicits the ICD response and IDO inhibition via autophagy-dependent ferroptosis

The development of anticancer drugs to treat triple-negative breast cancer (TNBC) is an ongoing challenge. Immunogenic cell death (ICD) has garnered considerable interest worldwide as a promising synergistic modality for cancer chemoimmunotherapy. However, only few drugs or treatment modalities can trigger an ICD response and none of them exert a considerable clinical effect against TNBC. Therefore, new agents with potentially effective chemoimmunotherapeutic response are required. In this study, five new cyclometalated Ir(III) complexes containing isoquinoline alkaloid C^N ligands were designed and synthesized. Among them, Ir-1 exhibited the highest in vitro cytotoxicity. Mechanistically, Ir-1 could trigger autophagy-dependent ferroptosis and a subsequent ferroptosis-dependent ICD response as well as indoleamine 2,3-dioxygenase (IDO) inhibition via reactive oxygen species (ROS)-mediated endoplasmic reticulum (ER) stress in MDA-MB-231 cells. When immunocompetent BALB/c mice were vaccinated with Ir-1-treated dying TNBC cells, antitumor CD8⁺ T-cell response and Foxp3⁺ T-cell depletion were induced, resulting in long-lasting antitumor immunity in TNBC cells. Moreover, combination therapy with Ir-1 and anti-PD1 could substantially augment in vivo therapeutic effects. Based on these results, Ir-1 is a promising candidate for chemoimmunotherapy against TNBC and its effects are mediated synergistically via ICD induction and IDO blockage.