PROJECT SUMMARY/ABSTRACT Glioblastomas (GBMs), neoplasms composed of glial cells and their precursors, are among the deadliest primary brain cancers, and are incurable with current therapies. There is an urgent unmet clinical need for new treatments for GBM and related high-grade malignant gliomas. GBM tumorigenicity is often driven by genetic aberrations in receptor tyrosine kinases (RTKs), such as EGFR, and the Pi-3 kinase (PI3K) signaling pathway. Through our team’s collaborative translational research efforts, we discovered that the YAP and TAZ transcription co- activators, effectors of the Hippo pathway that promote gene expression via TEAD co-factors, as key drivers of GBM tumorigenicity downstream of oncogenic EGFR signaling. In testing YAP/TAZ function, our team discovered that pharmacologic inhibition of YAP/TAZ with the FDA-approved drug verteporfin (VP) potently and specifically provokes growth arrest and cell death of EGFR-mutant/amplified GBM cells, but spares normal neural stem cells. VP inhibits YAP and TAZ by blocking their association with TEAD co-activators, which bind to DNA. We found that VP specifically suppressed expression of YAP/TAZ transcriptional targets, including EGFR, and that VP treatment conferred significant survival benefits in an orthotopic GBM xenograft model and a mouse genetic GBM model. Our results led us to perform a phase 0 clinical trial of VP in patients with recurrent GBM, which showed that VP is absorbed in GBM tumor cells and that VP induced changes consistent with inhibition of YAP/TAZ function. Based on our results, we have initiated a phase 1/2 clinical trial of VP to determine optimal dosing of VP in GBM patients. Here, we propose to investigate the therapeutic potential of YAP/TAZ inhibition and to capitalize our VP clinical trials, we propose to Aim 1) Identify YAP/TAZ target genes that underlie the epigenetic basis of YAP/TAZ dependency in GBM progression, Aim 2) Determine mechanisms of adaptation to YAP/TAZ inhibition and verteporfin resistance in pre-clinical GBM models in order to identify epigenomic adaptations specific that allow GBM stem cells to escape therapeutic targeting, and Aim 3) Evaluate the impact of verteporfin combined with anti-angiogenic therapies on GBM stem cells and the tumor microenvironment in immunocompetent mouse models and in specimens from human patients on our clinical trial of VP. The broader goals of this project are to establish a basis and strategies for therapeutic targeting YAP/TAZ activity in GBM using repurposed VP as a treatment for GBM.