ID #1012 Establishing Patient-Derived and iPSC–Organoid Models of High-Risk Childhood Astroblastoma

Background Astroblastoma (ABM) is a newly recognized, molecularly defined rare CNS tumor (Astroblastoma, MN1-altered, WHO CNS5, 2021) that predominantly affects children, adolescents, and young adults. Despite substantial morbidity and mortality, treatment remains largely limited to surgery and radiation. Targeted therapy development has been hampered by limited understanding of the molecular mechanisms and absence of faithful experimental models. We recently reported three clinically relevant epigenetic subgroups of ABM defined by recurrent gene fusions: MN1::BEND2 (Group A), EWSR1::BEND2 (Group B), and MN1::CXXC5 (Group C). While these oncofusions strongly associate with subgroup identity, their causal roles in tumorigenesis and therapeutic response remain unclear. Objectives To establish biologically faithful experimental models for Astroblastoma, to identify actionable therapeutic vulnerabilities. Methods Patient-derived cell lines, tumoroids, and xenografts (PDX) were generated from surgically resected tumors and characterized by immunophenotyping, signaling assays, STR profiling, and whole-genome sequencing. To develop orthogonal models for other onconfusions, human iPSCs were genetically engineered with doxycycline-inducible MN1::BEND2, EWSR1::BEND2, or MN1::CXXC5 fusions genes. The modified iPSC were differentiated into radial glial stem cells within 3D cerebral organoids and the fusion proteins were expressed by addition of doxycycline in the culture media. Results/Discussion We generated the first patient-derived ABM cell line, tumoroid, and patient-derived xenograft (PDX) from a recurrent MN1::CXXC5-positive tumor. The cell line demonstrated stable long-term growth and expressed canonical astroblastoma markers: Nestin, Vimentin, S100, PDGFRB. PDGF ligand stimulation activated MAPK and STAT3 signaling in the cell line, consistent with the reported PDGFR pathway activation in ABM. iPSC-derived organoids successfully generated radial glial cells in vitro and supported inducible expression of oncofusions genes, providing a complementary developmental platform. Together, we have established a robust, framework for ABM which will be used for drug screening to identify therapeutic vulnerabilities for ABM.