STEM-05. CREATING PATIENT-DERIVED TUMOROIDS TO INVESTIGATE RADIORESISTANCE IN PEDIATRIC BRAIN TUMORS

Brain cancers are the most frequently diagnosed tumor types in pediatric and young adult populations. Unfortunately, they often carry a poor prognosis and face common challenges such as treatment resistances due to intra- and intertumoral heterogeneity. To fully understand the intrinsic and extrinsic mechanisms which might hinder proper care, there is an emerging need to develop precise models of brain tumors to understand resistances and to predict therapeutic responses. While tumor-derived primary cell lines are relatively easy to produce, fully replicate the complexity of tumors as they grow without interactions with and from the microenvironment. Therefore, the advent of organoid cultures represents a significant advancement in modelling development. Derived from this technology, tumoroids offer a promising solution for modeling 3D tumors and their complex microenvironment.

We develop tumoroids from fresh biopsies and patient-derived tumor xenografts. These models were rigorously validated against to initial tumor using confocal microscopy, methylome analyses, metabolomics and single-cell RNAseq. To assess the intrinsic hypoxic environment and its spatial heterogeneity, characteristic of aggressive cancers, we employed fluorescent oxygen-sensitive dye loaded polymeric nanorods.

We successfully generated tumoroids using PDX of ependymomas (BT39) and it paired relapse (BT42), two H3.3 mutated high-grade gliomas (BT35 and BT69), one ganglioglioma (BT63) and directly from fresh biopsies of DIPG sample (BT140). Several passages were obtained after primary derivation, and cryopreservation demonstrating the stability of the models over time. Tumoroids displayed similar protein and omics markers as their parental tumors and harbored specific stem cell and neural progenitor markers. The methylation patterns were entirely preserved comparing 3D models and their parental tumors, and other multiomics and metabolic approaches confirmed the accurate reconstitution of tumor complexity. The study of oxygen-sensitive nanorods highlighted the heterogeneous oxygen gradient within tumoroids.

All these initial characterized tumoroids helped us to develop radioresistant paired models.