Abstract LB175: Identification of therapeutic targets in high-risk SHH medulloblastoma

Abstract Background: Medulloblastoma (MB) is the most common malignant pediatric intracranial solid tumor derived from transformed neuroepithelial stem (NES) cells, and is comprised of four main subgroups: WNT, SHH, Group 3, and Group 4. A subgroup of SHH MB patients with amplification of MYCN and GLI2, and mutation of TP53 (MGT) exhibit extremely poor prognosis, and resistance to chemotherapy. Chemical and genetic screens are needed to unravel potential therapeutic targets. However, there are no reliable SHH MB cell lines, patient derived xenografts (PDX) are difficult to grow at scale for genetic screens, and tumor lines lack an isogenic control to identify targets that would be toxic to healthy cells. To circumvent these issues, we utilize a human induced pluripotent stem cell (iPSC) model of MB to generate MGT tumors in vivo which can subsequently be cultured in vitro to perform therapeutic screens along with an isogenic NES cell control line. Method: iPSCs from a healthy adult were differentiated towards NES cells, transduced with MYCN, GLI2, and TP53R248Q and implanted orthotopically into immunocompromised (NSG) mice. Resulting MGT tumors were cultured in vitro and, along with control (empty vector) NES cells, were subjected to a drug screen (360 unique compounds from the SBP Oncology Dose Library (ODL3), and CTD2 Informer Set) and a whole genome CRISPR interference (CRISPRi) screen. MB MGT PDX tumors were maintained in NSG mice and analyzed for cell viability in response to in vitro drug treatments in 384 well plates with CellTiter-Glo cell viability assay. Results: MGT NES cells were fully penetrant within 35 days post injection. MGT tumor lines were resistant to in vitro treatment with chemotherapy drugs etoposide and cyclophosphamide. The drug screen showed MGT tumors were more sensitive than control NES cells to inhibitors targeting NEDD8 Activating Enzyme E1 subunit 1 (NAE), translation elongation, and BCL2 family of proteins. Similarly, the CRISPRi screen showed MGT tumors were more dependent than NES cells on genes involved in pathways for Neddylation, tRNA amino-acylation, and members of the BCL2 family. In support of these findings, the translation elongation inhibitor was more toxic to MB MGT PDX than control cells (analysis of Neddylation and BCL2 inhibitors on MB MGT PDX is ongoing). Conclusion: Here, we show that the human stem cell model of MB can be used to identify therapeutic targets that are effective against PDX tumor cells in vitro. Specifically, targeting translation elongation is a potential therapeutic target to treat MGT MB tumors. Citation Format: Bo Cheng, Jamie Vu, Darren Finlay, Theophilos Tzaridis, Maria Poblete, Luke A. Gilbert, Till Milde, Qianqian Li, Martine F. Roussel, Kristiina Vuori, Robert J. Wechsler-Reya, Miller Huang. Identification of therapeutic targets in high-risk SHH medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB175.