TMET-08. RADIATION-INDUCED SLC25A22 CONTRIBUTES TO GLIOBLASTOMA RADIORESISTANCE ACQUISITION THROUGH REMODELING GLUTAMATE METABOLISM

Abstract Glioblastoma Multiforme (GBM), a malignant primary brain tumor, is treated by surgical resection followed by chemo- and radiotherapy. Nevertheless, most GBM patients show dismal prognosis due to the radioresistance acquisition of GBM cells via metabolic rewiring. Therefore, it is urgently required to discover how metabolic rewiring attributes to GBM radioresistance, and its targeting strategies. To identify GBM radioresistance driver genes, we previously established radioresistance GBM cells (RGCs) via repetitive in vivo selection, followed by mRNA sequencing, and selected candidate genes that are altered in RGCs (fold change>2 or <0.5, p-value<0.05) and also related with GBM patients’ prognosis. Here, we focused on amino acid transmembrane transporter (Gene Ontology: 0003333) and found that SLC25A22 was the most increased in RGCs. SLC25A22 exhibits uni-directional properties, exporting glutamate to cytosol, resulting in cytosolic glutamate accumulation in RGCs. Using 13C glutamine isotope tracing analysis following mitochondrial fractionation, we quantified the mitochondrial metabolic flux of glutamine. Despite decreased 13C glutamate efflux from RGCs mitochondria after genetic inhibition of SLC25A22, glutamine metabolites (a-ketoglutarate, succinate, malate, fumarate) remained constant. Cytosolic glutamate, as a substrate, is incorporated into various biosynthetic pathways, especially glutathione (GSH) and proline synthesis pathways in radioresistant GBM cells. GSH protects GBM cells by scavenging radiation-induced reactive oxygen species. Whereas, proline, a rate-limiting substrate for collagen biosynthesis, leads GBM cells to show an invasiveness phenotype via extracellular matrix remodeling. Genetic inhibition of SLC25A22 using short hairpin RNA (shRNA) or microRNA-184 mimic suppresses RGCs radioresistance and aggressiveness. Additionally, intranasal administration of microRNA-184 mimic prolonged the survival (median survival: 26 days after irradiation) of GBM-bearing mice, compared with non-target control (median survival: 16 days after irradiation). Together, our study demonstrates that SLC25A22 upregulation confers GBM radioresistance by inducing cytosolic glutamate-driven biosynthesis and suggests SLC25A22 as a therapeutic target to overcome GBM radioresistance.