TMIC-66. A NEW MOUSE MODEL THAT COMBINES DRIVER MUTATIONS TO ACCURATELY RECAPITULATE THE DIVERSE PHENOTYPES OF HUMAN GLIOBLASTOMA

Abstract To effectively beat glioblastoma, new pre-clinical models are needed: to dissect the biology of processes like migration and therapy resistance; to understand immune suppression and immunotherapy; and to use as a model for testing in therapeutic development. We have developed a new panel of glioblastoma mouse models, which engineer well-characterised glioblastoma driver mutations into an immortalised eGFP murine astrocyte-like cell. These “GEM-CLeM” are Genetically Engineered Mouse Cell Line Models. When transplanted intra-cranially into immunocompetent mice, these lines formed tumors with the key characteristics of glioblastoma – migratory and invasive, with rapid proliferation and infiltration of suppressive immune cells. The eGFP expression allowed detection of glioblastoma cells in situ and ex vivo, and the ability to readily distinguish tumor and stromal components of the tumors. Importantly, different combinations of driver mutations led to diverse tumor phenotypes. Loss of Pten with over-expression of mutant RAS generated tumors with 100% efficiency and the same time to tumor onset as the commonly used GL261 cell line. However, unlike GL261 tumors the Pten-RASV12 tumors had a highly invasive edge and extensive migration, and were full of pro-tumorigenic macrophages and monocytes, with very few T-cells or dendritic cells. Together, this recapitulated the phenotype of human wildtype IDH1 glioblastoma. In contrast, the very common EGFRvIII mutant did not drive tumor formation in combination with Pten loss. We also modelled mutant IDH glioblastoma by combining loss of p53 with overexpression of IDH1R132H. These were slow growing, densely packed tumors with extensive microglial involvement in addition to pro-tumorigenic macrophages. This GEM-CLeM system combines the benefits of the traditional genetically engineered mouse models with accessible, rapid, reproducible tumor formation. The GEM-CLeM lines are amenable to further genetic manipulation, so cells can be customised with other mutations to ask important biological questions in the presence of an intact tumor immune microenvironment.