MODL-05. ELUCIDATING THE EPIGENETIC DRIVEN TRANSCRIPTIONAL PROGRAM UNDERLYING THE INVASIVE PHENOTYPE OF THE NOVEL EGFRA289VARIANT OF GBM

Abstract

Abstract Glioblastoma (GBM) is a devastating malignant brain tumor with a dismal 15-month median survival. Current treatments have not been successful at preventing recurrence, thus novel therapeutic modalities are urgently needed. EGFR is a tyrosine kinase receptor that is commonly mutated in ~60% of GBM and is an attractive target for GBM precision oncology. Aberrant EGFR signaling drives tumor proliferation and maintenance, thus further study of common EGFR alterations in GBM, including interstitial deletions (EGFRvIII) and missense mutations (EGFRA289), is needed to develop effective EGFR-targeted therapies. This is especially important in the context of a retrospective study that showed EGFRA289 driven GBM was more clinically aggressive. EGFRA289 positive GBM had a unique, invasive radiographic signature on magnetic resonance imaging (MRI) and patients had a significantly shorter median overall survival of 6-months. We hypothesize that the malignant clinical phenotypes of EGFRA289 GBM are driven by unique epigenomic and transcriptomic, collectively referred to as (epi)genomic, programs linked to EGFRA289 signaling. Prior studies using established cell lines show that EGFRvIII overexpression drives malignant (epi)genomic programs mediated by transcription factor (TF) activation. To better understand variant specific EGFR biology in GBM, we have developed novel genetically engineered mouse astrocyte (mAc) models that overexpress wtEGFR (MA-WT), vIII (MA-v3), and EGFRA289V (MA-A289V). Phospho-immunoblots show that these mAc models have differential EGFR ligand dependance, which match published studies. Despite this difference in EGFR signaling, all mAc models have similar sensitivities to EGFR tyrosine kinase inhibitor (TKI) treatment. However, MA-A289V is more proliferative and migratory compared to the other mAc variants. Preliminary RNA-Seq on our mAc models has identified similar and unique TFs differentially expressed (DE) between MA-v3 and MA-A289V when compared to parental MA-C. Integration of RNA-Seq and CUT&RUN followed by mechanistic genetic interrogation will elucidate the relationship between EGFR variant-specific (epi)genomic mechanisms and their unique malignant phenotype.