Endoplasmic Reticulum-Targeting Iridium(III) Complexes Induce Pyroptosis and Enhance Immunogenic Cell Death in MDA-MB-231 Cells

Cancer immunotherapy has revolutionized oncology by leveraging host immunity to eliminate malignant cells. In this study, five iridium­(III) complexes (Ir1–Ir5) were synthesized and evaluated for their in vitro antitumor activity against various tumor cell lines. Among these, Ir4 and Ir5 exhibited the highest cytotoxicity and the most rapid cellular uptake in MDA-MB-231 cells. Colocalization experiments confirmed their accumulation in the endoplasmic reticulum (ER) and their ability to induce pyroptosis. Additionally, both complexes triggered ER stress, leading to increased calreticulin exposure on the cell surface, high-mobility group box 1 secretion, and ATP release, which collectively promoted immunogenic cell death. In vivo, a triple-dose Ir4 vaccine regimen significantly suppressed tumor growth compared to other treatment groups. These findings highlight the potential of Ir4-based novel triple-dose vaccination as a promising cancer immunotherapy strategy.