MDB-15. INHIBITING THE IRON-SULFUR CLUSTER TRANSPORTER ABCB7 CAN POTENTIATE CISPLATIN RESPONSE IN PEDIATRIC GROUP 3 MEDULLOBLASTOMAS BY TRIGGERING FERROPTOSIS

Abstract

Abstract BACKGROUND Medulloblastoma (MB) is the most common malignant pediatric brain tumor, with group 3 tumors (G3MB) being the most aggressive. Uniquely, their aggressiveness is inversely proportional to ferroptosis activation. Intracellularly, these tumors activate iron-sulfur (Fe-S) cluster export and upregulate the expression of glutathione peroxidase 4 (GPX4), the central regulator of ferroptosis. Our main objective was to investigate whether ferroptosis evasion was a targetable driver of aggressiveness in G3MBs that can be inhibited to potentiate classical chemotherapy. We hypothesized that inhibiting Fe-S cluster export would trigger ferroptosis and potentiate cisplatin cytotoxicity in G3MBs. METHODS We repressed ABCB7 expression (si-/sh-/KO) in classic G3MB cell lines (HDMB03 and D425) and studied its impact on cancer cell growth, ferroptosis activation, mitochondrial function, and cisplatin cytotoxicity. We further investigated the impact of artesunate, an FDA-approved anti-malarial agent capable of inhibiting ABCB7, on cisplatin action and tumor burden. To rescue cells from iron overload and ferroptosis, we used deferoxamine and ferrostatin-1, respectively. RESULTS Silencing ABCB7 resulted in cytoplasmic and mitochondrial iron overload, oxidative stress, and lipid ROS, culminating in ferroptosis and growth retardation. Seahorse studies revealed a switch from oxidative phosphorylation to glycolysis, and TMRM staining revealed loss of mitochondrial membrane potential in ABCB7-silenced cells. Notably, silencing ABCB7 abrogated GPX4 expression and reduced GSH levels. Moreover, ABCB7 silencing reduced the IC50 of cisplatin 2-fold, and ABCB7-silenced cells treated with cisplatin experienced a heightened index of ferroptosis. In vivo, silencing ABCB7 resulted in smaller tumors, dramatically prolonged survival, and potentiated cisplatin action. Artesunate recapitulated ABCB7 silencing by potentiating cisplatin action, reducing tumor burden, and prolonging survival in vivo. CONCLUSION The current study illustrates how targeting mitochondrial Fe-S cluster transport can trigger ferroptosis and potentiate cisplatin in G3MBs. Our study also provides evidence for using an FDA-approved drug with the same mechanism of action to treat G3MB tumors.