Abstract 5841: A genome wide CRISPR-Cas9 screen identifies mediators of resistance to dual PI3K/mTOR inhibition in glioblastoma multiforme

Abstract Glioblastoma multiforme (GBM) is a highly aggressive primary brain tumor with a devastating 5-year survival rate of 6. 8%. The current standard of care, consisting of surgery, radiation, and temozolomide (TMZ), has remained unchanged for over the past 15 years despite its limited efficacy and the serious therapy-related adverse events associated to this regimen. Although some frequent genetic alterations have been identified in GBM, no targeted therapies have shown efficacy in these patients to date. Among these, the phosphoinositide 3-kinase (PI3K) pathway is a signaling network that regulates cell growth, proliferation, migration, and invasion. Extensive molecular characterization of GBM has identified alterations in the components of the PI3K pathway in 80% of primary GBMs, including amplification of receptor tyrosine kinases (RTKs), activating mutations in the PI3K catalytic subunit (PIK3CA), loss-of-function mutations in the PI3K regulatory subunit (PIK3R1), and loss of the major tumor suppressor of the pathway, phosphatase and tensin homologue (PTEN). Despite the universal upregulation of PI3K pathway signaling associated with these genetic alterations, clinical trials investigating PI3K inhibitors in GBM have failed due to insufficient antitumor activity and dose-limiting toxicities. To elucidate mechanisms of resistance to PI3K inhibition in GBM, we used a genome-wide functional CRISPR-Cas9 knockout screen to identify genes that mediate resistance to the dual PI3K/mTOR inhibitor XL765 in PTEN-null SF295 GBM cells. We identified reactivation of the PI3K pathway and inhibition of autophagy as potential resistance mechanisms to dual PI3K/mTOR inhibition. Using orthogonal approaches, we will functionally validate our candidate hits through mechanistic studies, with patient-derived models, and with in vivo orthotopic xenografts. Our findings will elucidate novel mechanisms of resistance to PI3K/mTOR inhibition in GBM and will streamline rational drug combinations aimed to overcome resistance, thus eventually maximizing therapeutic responses to PI3K inhibitors in GBM. Citation Format: Annalisa V. Ferrotta, Arianna Izawa-Ishiguro, Meaghan Grogan, Ingo K. Mellinghoff. A genome wide CRISPR-Cas9 screen identifies mediators of resistance to dual PI3K/mTOR inhibition in glioblastoma multiforme abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5841.