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Medulloblastoma (MB), the most common malignant pediatric brain tumor and a leading cause of childhood mortality, is stratified into four primary subgroups, i.e. SHH (sonic hedgehog), WNT (wingless), and non-SHH/WNT groups 3 and 4, the latter representing high-risk MB. Haploinsufficiency of 17p13.3, which houses the tumor suppressor gene miR-1253, characterizes high-risk tumors. Despite improvements in targeted therapies, a limited proportion of these patients survive the disease. Capitalizing on the tumor suppressive properties of miRNAs as adjuncts to chemotherapy provides a promising alternative to current therapeutic strategies. In this study, we explored the potentiating effects of miR-1253 on cisplatin cytotoxicity in group 3 MB. First, in silico and in vitro analyses revealed an upregulation of ABCB7, a mitochondrial iron transporter and putative target of miR-1253, in MB cell lines and group 3 MB tumors. Overexpression of miR-1253 resulted in downregulation of ABCB7 and GPX4, a critical ferroptosis regulator, which consequently increased labile mitochondrial iron pool and, in turn, mitochondrial ROS (mtROS). Complementarily, we demonstrated, using CRISPR knockdown of ABCB7, ferroptosis induction with downregulation of GPx4 expression, liberation of free iron, mtROS generation and lipid peroxidation. Cisplatin is reported as an inducer of both apoptosis and ferroptosis-mediated cancer cell death. Therapeutically, the combination of miR-1253 and cisplatin led to an additive effect on cell viability, colony formation, apoptosis, and ROS generation. In turn, treatment with mtROS inhibitor (MnTBAP) and ferroptosis inhibitor (Ferrostatin) lead to partial recovery from the cytotoxic effects of this combination therapy. These studies identify an miR-1253-induced ferroptosis pathway targeting the ABCB7/GPX4/mtROS axis in group 3 MB. They further provide proof-of-concept in using miR-based therapeutics to augment treatment efficacy of current chemotherapeutics in the treatment of high-risk tumors.

BIOL-06. MIR-1253 POTENTIATES CISPLATIN RESPONSE IN PEDIATRIC GROUP 3 MEDULLOBLASTOMA BY REGULATING FERROPTOSIS