DISCOVERING DRUG SENSITIVITIES IN MEDULLOBLASTOMA USING PATIENT- AND PDX-DERIVED TUMOROIDS

BACKGROUND Medulloblastoma (MB) is one of the most common malignant pediatric brain tumor types and is subdivided into four major types: WNT, SHH, Group 3 and Group 4. Treatment, including resection, cranio-spinal radiotherapy, and chemotherapy, often leads to undesirable long-term side effects. MB prognosis depends on type, subtype, and genetic alterations, reflecting the high level of heterogeneity observed in these tumors and indicating that specific patient populations with particularly poor prognosis require alternative treatment approaches. Therefore, preclinical models are essential for recapitulating MB heterogeneity and developing subtype-specific treatments. METHODS Long-term in vitro MB tumoroid models were developed from patient and PDX tumors and molecularly characterized using DNA methylation and transcriptomic analyses. High-throughput single drug screening (225 compounds) and combination screening were performed to identify (subtype-specific) drug sensitivities. RESULTS Fifteen tumoroid lines were established from TP53-mutated SHH (n=6), Group 3 (G3) MYC-amplified (n=4) and non-amplified (n=5) patient (n=6) and PDX (n=9) tumors. DNA methylation analyses confirmed the maintenance of molecular identity in these tumoroids after long-term culture (>5 passages). Transcriptome analyses reveal a more proliferative, progenitor-like phenotype in these tumoroids compared to patient/PDX tumors. Hight-throughput drug screens identified both common and type-specific drug sensitivities within MB. Notably, drugs targeting CDK7, CDK12, CHECK1, BCL2L, and HDAC demonstrated efficacy in both G3 and TP53-mutated SHH-MB, while TOP1/2 and MDM2 inhibitors were specific for G3-MB. Currently, these drugs are being further investigated to select the most effective synergistic drug combinations for in vivo validation in PDX models. CONCLUSIONS Thus far, we have established already fifteen MB tumoroid models representing SHH-MB and G3-MB and identified several drug targets, including cell cycle kinases and HDACs. Tumoroids closely resemble patient tumors, based on methylome and transcriptome, enhancing their relevance for drug discovery applications in a high-throughput fashion and for prioritizing new treatment strategies for MB patients in clinical trials.