MMRi62 induces iron depletion-driven apoptosis through a ferritin-independent mechanism

Abstract

The modulation of iron metabolism is increasingly explored as a therapeutic strategy in cancer, particularly through the induction of ferroptosis. Given the central role of ferritin as a major intracellular iron buffer, targeting ferritin represents an attractive strategy to disrupt iron homeostasis; however, the lack of pharmacological approaches capable of selectively targeting ferritin currently limits the therapeutic exploitation of this vulnerability. MMRi62, initially developed to target the MDM2-MDM4 axis, has been proposed to induce ferroptosis via ferritin degradation. Here, we revisited this hypothesis in the context of medulloblastoma (MB). Contrary to this proposed mechanism, we found that MMRi62 does not trigger ferroptosis but instead induces robust apoptotic cell death. This effect is observed in both p53-mutant DAOY and p53 wild-type HD-MB03 cells, as well as in c-Myc/OTX2-driven medulloblastoma-like tumours genetically induced in brain organoids. Although ferritin degradation occurs upon treatment, genetic dissection demonstrates that neither ferritin itself nor ferritinophagy are required for MMRi62-induced cytotoxicity. Together, these findings rule out ferritin-dependent mechanisms as primary drivers of cytotoxicity. Instead, we uncovered that MMi62 induces a profound rewiring of iron metabolism consistent with a canonical iron starvation response, accompanied by a marked reduction in intracellular iron levels. Consistently, the UV-visible spectroscopic data were in agreement with the proposed iron-chelating properties of MMRi62. Taken together, our findings identify iron depletion-driven apoptosis, rather than ferroptosis, independently of ferritin degradation, as the primary mechanism of MMRi62 cytotoxicity in MB, refining its mode of action and highlighting iron homeostasis as a therapeutic vulnerability.