MEDB-52. Organoids as preclinical models to improve and personalize disease outcome for sonic hedgehog medulloblastoma

Abstract

Four main medulloblastoma (MB) molecular subgroups are known, including the sonic hedgehog (SHH) subgroup, which represents ~25% of MB cases. The 5-year overall survival of SHH-MB is ~80%. However, survival between patients is highly diverse and dependent on the driver mutation(s) of the tumor. Patients with TP53 mutated tumors (often accompanied with MYCN and/or GLI2 amplifications) don’t respond well to current therapies and have a 10-year overall survival below 20%. Therefore, there is a need for new and more tailored therapies for these patients. In this study we aim to screen patient-derived organoid models of TP53-mutated SHH MB with a library of ~200 different compounds. We have optimized the cultures of two PDX-derived and one patient-derived organoid line in vitro. The lines will be screened in a high-throughput manner and the best hits and combinations will be validated in corresponding in vivo PDX models. To further assess the role of specific mutations in therapy outcome of TP53-mutated SHH MB, cerebellar organoids generated from human iPSCs were genetically modified with overexpression of dominant-negative P53 (DNP53) alone or in combination with MYCN and/or GLI2. Introduction of DNP53 and MYCN overexpression in cerebellar organoids at day 28/35 leads to the outgrowth of a Ki67-positive proliferating mass after three weeks, indicating tumor growth. Further analyses are ongoing to see how they match SHH-MB patient tumors. These genetically engineered organoid models may elucidate the role of specific mutations in therapy response and/or resistance. In addition, as tumors in these genetically engineered cerebellar organoids arise in a microenvironment of normal cerebellar cell types, initial safety of drugs on cerebellar cells can be assessed. In conclusion, different organoid models of TP53-mutated SHH MB will enable us to find more effective treatments and to better understand how to treat patients with different mutation combinations.