MODL-16. SOMATICALLY ENGINEERED MOUSE MODELS RECAPITULATING CELLULAR AND MOLECULAR FEATURES OF HUMAN GBM

Abstract

Abstract INTRODUCTION Mouse models are instrumental in advancing our understanding of glioblastoma (GBM), however many commonly used models have features that limit their practicality or applicability. These limitations can include an incomplete immune context, a requirement for complex breeding strategies, high cost of specialized lines, and unpredictability in where tumors arise. We sought to develop and validate a mouse modeling system for some of the major human GBM subtypes that overcame these practical challenges. METHODS In vivo electroporation was used to introduce genetic alterations into periventricular cells of early postnatal C57Bl6/j mice. PiggyBac transposon/transposase and CRISPR-Cas9 systems were used to overexpress (OE) or knock out (KO) genes associated with mesenchymal (Nf1-KO/Pten-KO/p53-KO), classical (EGFRvIII-OE/Cdkn2a-KO/Pten-KO), and proneural (Pdgfra-OE/Cdk4-OE/p53-KO) IDH-WT GBM subtypes. KO or OE was confirmed by Indel Detection by Amplicon Analysis and immunofluorescent staining (IF). Tumours were analyzed for histologic, immunohistochemical, and transcriptional (RNAseq) features. RESULTS Tumors arose with near complete penetrance and median survivals of 36 to 116 days amongst models. All tumors were GFAP-expressing high-grade gliomas, with distinct phenotypes associated with different genetic combinations. Nf1-KO/Pten-KO/p53-KO tumors were composed of spindle cells. EGFRvIII-OE/Cdkn2a-KO/Pten-KO and Pdgfra-OE/Cdk4-OE/p53-KO tumors showed prevalence of small, round cells. Molecularly, Nf1-KO/Pten-KO/p53-KO tumors were enriched for human mesenchymal signature and displayed more differentiated phenotype. The Nf1-KO/Pten-KO/p53-KO model also showed increased stromal cells and macrophages. The other models had mixed proneural and classical profiles and were enriched for OPC- and NPC-like gene signatures found in human GBM. Once tumors formed, cells from each model were transplantable into C57Bl6/j mice to generate subsequent tumors. CONCLUSION We developed and validated a rapid, versatile, and reproducible system to model GBMs. These models allow for controlled study of GBM pathogenesis, progression, and treatment response, and allow for robust generation of syngeneic implantable mouse models that can serve as valuable tools for preclinical testing.