Targeting YBX1 to enhance radiation sensitivity in very high risk medulloblastoma

Pediatric central nervous system tumors, particularly medulloblastoma (MB), remain a significant challenge, with high-risk subgroups like MYC-amplified Group 3 (G3-II) and TP53-mutated Sonic Hedgehog (SHHα) exhibiting poor prognoses and frequent relapse. Current standard treatment involves maximal surgical resection, chemotherapy (CT), and radiation therapy (RT). While RT is crucial in high-risk patients to prolong survival and reduce relapse, it frequently leads to debilitating long-term neurocognitive impairment and endocrinopathies. Therefore, there is a critical need to identify agents that enhance tumor-specific RT efficacy, improving tumor radiosensitivity and reducing treatment burden. We and others have identified the RNA/DNA binding protein YBX1 as a promising therapeutic target in high-risk MB. High expression of YBX1 is seen in both primary and relapsed MB patient tumors, correlating with poor patient survival and resistance to DNA damaging agents. Recent work demonstrated that YBX1 knockdown sensitizes MB cells to radiation by altering DNA repair mechanisms. While promising, this was limited by the lack of a specific YBX1 inhibitor. We have tested SU056, the first direct YBX1 inhibitor, demonstrating its single-agent efficacy, blood-brain barrier penetration, and synergistic activity with radiotherapy in vitro in both G3-II and SHH MB cell lines, regardless of TP53 status. We hypothesize that YBX1 inhibition will synergistically enhance the anti-tumor effects of RT, potentially enabling RT dose reduction and minimizing long-term toxicities. The use of vertebrate animal models is essential for this project to accurately evaluate the blood-brain barrier penetrance of SU056 and to model the complex physiological interactions between pharmacological YBX1 inhibition and craniospinal irradiation within the native cerebellar microenvironment. This proposal leverages our pilot data to evaluate the in vivo synthetic lethality of YBX1 inhibition combined with CSI. Aim 1 will examine the in vivo efficacy of YBX1 inhibition in combination with RT in pre-clinical orthotopic models of G3-II MB, utilizing clinically relevant CSI doses and schedules. We will assess tumor response and evaluate potential toxicity to determine if YBX1 inhibition can augment current CSI in G3 MB patients without increasing long-term side effects. Aim 2 will assess YBX1 inhibition in TP53-mutant SHHα subgroup tumors, which exhibit intrinsic radioresistance. Using isogenic mouse models and patientderived xenografts in vitro and in vivo, we will test if SU056 overcomes TP53-driven radioresistance in SHHα MB. Our studies will comprehensively evaluate YBX1 inhibition as a synthetic combination with radiotherapy, aiming to improve therapeutic responses in very high-risk MB subgroups and offer new avenues for treatment to enhance quality of life. Project Number: 1R21CA313161-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Myron Evans | Institution: SEATTLE CHILDREN'S HOSPITAL, SEATTLE, WA | Award Amount: $482,624 | Activity Code: R21 | Study Section: Special Emphasis Panel[ZRG1 CTH-N (81)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11355846