Modl-28. living ex vivo organotypic brain slice cultures as a comprehensive substrate for tumor engraftment and analysis

Abstract Heterogeneity, drug resistance, tumor infiltration, and invasiveness significantly contribute to the poor prognosis often associated with brain cancers. To enhance drug development, it is crucial to have models that accurately replicate human responses. Standard in vitro methods to culture, treat and analyze brain tumors often lack resemblance to the original tumor and provide limited insight. To address these challenges, we developed an organotypic brain slice culture (OBSC) model that recapitulates in vivo tumor characteristics within a functional tumor microenvironment (TME) and provides rapid results. OBSCs effectively measure engrafted tumor growth, morphology, and invasion rates. Furthermore, engrafted tumors can undergo relevant therapeutic treatments and be analyzed for drug outcomes. In a 4-day assay, we successfully engrafted a diverse range of brain cancer cell lines, including low-passage lines that struggle to establish in vivo. These cell lines maintain tumor-specific invasion patterns, interact with the OBSC microenvironment, and display killing patterns consistent with in vivo tumor responses. Notably, invasive, metastatic, and diffuse tumor cell lines migrate outward on OBSCs, while densely growing lines contract inward. To further validate OBSCs as a model for the TME, we treated MB231BR, LN229, and U373 tumor lines with TR107, an experimental ClpP inhibitor derived from ONC201. This therapeutic family maximizes tumor elimination by targeting normal cells within the TME. In vitro experiments showed TR107 achieving incomplete tumor kill on cell lines grown in vitro, whereas treatment on OBSCs led to complete tumor kill, suggesting OBSCs' contribution to TME-based tumor elimination. Conclusively, OBSCs provide a valuable platform for studying brain cancers and accurately replicating tumor behavior and responses to therapies within the TME. This model has the potential to advance drug development and deepen our understanding of brain cancer biology, ultimately improving prognoses and treatment outcomes for patients.