Abstracts vii263 NEURO-ONCOLOGY • November 2022 therapy (RT) with temozolomide (TMZ). This study implemented machine learning (ML) algorithms to predict treatment phase: pre-surgery, post- surgery, pre-radiation, and post radiation based on untargeted metabolomics data. METHODS: Thirty-six patients with glioblastoma IDH wildtype (18 methylguanine methyltransferase [MGMT] methylated, 16 MGMT unmethylated, 2 MGMT status unknown) were enrolled into this study. Serum samples obtained from patients on the same day before surgery, 2 days after surgery, before starting their concurrent chemoradiation, and after concluding this phase of treatment. Blood samples were obtained via antecubital phlebotomy without regard for time of the day, diet, or fasting status. Untargeted metabolomics by GC-TOF mass spectrometry were obtained and compared. The proposed ML models analyzed 105 samples from 36 patients utilizing 157 structurally identifed blood metabolites. Multinomial Logistic Regression (MLR) and GradientBoostingClassifer (GB Classifer) were used to classify patient samples based on detected changes in blood metabolites. The classifcation performance of these models was evaluated using performance metrics and AUC scores. RESULTS: Post radi- ation; signifcant increase in the following metabolites: glycine, serine, threo- nine, oxoproline, 6-deoxyglucose, gluconic acid, glycerol-alpha-phosphate, ethanolamine, propyleneglycol, triethanolamine, xylitol, and fumaric acid were noted while signifcant decrease in 3-aminopiperidine 2,6-dione was noted post radiation. MLR produced 78% accuracy, 75% precision, and AUC = 0.89, and GB Classifer produced 75% accuracy, 77% precision and AUC = 0.91. Finally, we presented a pattern of metabolites changes per clinical stage based on pairwise correlations. CONCLUSIONS: This study represent the frst serum metabolic signature associated with RT in patients with glioblastoma. The results from the classifcation algorithms and pairwise correlations showed that blood metabolites have the potential to predict phase of treatment and potentially enable to evaluate response to treatment in patients with glioblastoma in a relatively small cohort. TMET-09. LOSS OF MAT2A COMPROMISES METHIONINE METABOLISM AND REPRESENTS A VULNERABILITY IN H3K27M MUTANT GLIOMAS. Matthew Halbert 1 , Brian Golbourn 2 , Katharine Halligan 3 , Srinidhi Varadharajan 4 , Brian Krug 5 , Nneka Mbah 6 , Nisha Kabir 5 , Ann-Catherine Stanton 3 , Abigail Locke 3 , Stephanie Casillo 7 , Yanhua Zhao 8 , Lauren Sanders 9 , Allison Cheney 10 , Steven Mullett 11 , Apeng Chen 7 , Michelle Wassell 3 , Anthony Andren 6 , Jennifer Perez 7 , Esther Jane 7 , Daniel Premkumar 1 , Robert Koncar 7 , Shideh Mirhadi 12 , Lauren McCarl 3 , Yue-Fang Chang 3 , Yigen Wu 11 , Taylor Gatesman 1 , Andrea Cruz 7 , Michal Zapotocky 13 , Baoli Hu 7 , Gary Kohanbash 7 , Xiuxing Wang 14 , Alenoush Vartanian 3 , Michael Moran 15 , Frank Lieberman 16 , Nduka Amankulor 17 , Stacy Wendell 1 , Olena M. Vaske 9 , Ashok Panigraphy 3 , James Felker 18 , Kelsey C. Bertrand 4 , Claudia Kleinman 5 , Jeremy N. Rich 7 , Robert M. Friedlander 7 , Alberto Broniscer 18 , Costas Lyssiotis 6 , Nada Jabado 19 , Ian F. Pollack 20 , Stephen C. Mack 4 , and Sameer Agnihotri 7 ; 1 University of Pittsburgh School of Medicine, Pittsburgh, PA, USA, 2 The Broad Institute, Boston, MA, USA, 3 UPMC, Pittsburgh, USA, 4 St. Judes, Memphis, USA, 5 McGill University, Montreal, Canada, 6 University of Michigan, Ann Arbor, USA, 7 University of Pittsburgh School of Medicine, Pittsburgh, USA, 8 Baylor College of Medicine, Houston, USA, 9 University of California, Santa Cruz, Santa Cruz, CA, USA, 10 University of California, Santa Cruz, Santa Cruz, USA, 11 University of Pittsburgh, Pittsburgh, USA, 12 University of Toronto, Toronto, USA, 13 Hospital for Sick Children, Toronto, Canada, 14 Nanjing Medical University, Nanjing, China (People's Republic), 15 Hospital for Sick Children, Toronto, USA, 16 University of Pittsburgh, Pittsburgh, PA, USA, 17 U Penn, Phildelphia, USA, 18 UPMC Children's Hospital, Pittsburgh, USA, 19 The Research Institute of the McGill University Health Center, Montréal, Canada, 20 Children's Hospital of Pittsburgh, Pittsburgh, USA H3K27-mutant diffuse midline gliomas (DMGs) are defned as grade IV tumors by the World Health Organization. DMGs are inoperable and re- sistant to chemo/radio therapies. Median survival ranges from 8-11 months, with 2% of patients surviving beyond 5 years. H3K27M mutations lead to global epigenetic and transcriptional reprogramming driven by global loss of negative transcriptional regulator H3K27 trimethylation (H3K27me3). Loss of H3K27me3 is an initiating event in gliomagenesis. This disease lacks appropriate models to predict disease biology and response to treatment. Therefore, we developed a novel syngeneic H3K27M mouse model. An un- biased integrated systems biology approach identifed that H3K27M but not isogenic controls relied on the amino acid methionine and the enzyme Me- thionine Adenosyltransferase 2A (MAT2A). MAT2A is a central regulator of one-carbon metabolism by converting methionine to S-adenosylmethionine (SAM), the universal methyl-donor for protein and nucleotide methyla- tion reactions. In complementary genetic approaches, we applied these fndings to patient-derived cell lines with the H3K27M mutation. We hy- pothesize that MAT2A abrogation, genetic/pharmacological, would alter DMG viability by disrupting the methylome. The current MAT2A sensi- tivity paradigm is based on Methylthioadenosine Phosphorylase (MTAP) deletion through a synthetic lethal mechanism. We provide a novel mech- anism whereby H3K27M cells are sensitive to MAT2A loss, independent of MTAP and through Adenosylmethionine Decarboxylase 1 (AMD1) overexpression disrupting MAT2A regulation. This results in H3K27M cells having lower MAT2A protein levels, conferring a sensitivity by inhibiting residual MAT2A. Genetic/pharmacological aberrations to MAT2A resulted in reduced proliferation. Parallel H3K36me3 ChIP and RNA-sequencing identifed loss of oncogenic and developmental transcriptional programs as- sociated with MAT2A loss. In vivo syngeneic and patient-derived xenograft models with both inducible MAT2A knockdown or methionine restricted diets showed extended survival. These results suggest novel interactions be- tween methionine metabolism and the epigenome of H3K27M gliomas and provide evidence that MAT2A, presents exploitable therapeutic vulnerabil- ities in histone mutant gliomas. TMET-10. FATTY ACID METABOLISM REGULATES IMMUNE REACTIVITY OF IRRADIATED GLIOBLASTOMA Mara De Martino 1 , Camille Daviaud 1 , Evagelia Laiakis 2 , and Claire Vanpouille-Box 3 ; 1 Department of Radiation Oncology, Weill Cornell Medicine, New York, USA, 2 Department of Oncology, Georgetown University, Washington, USA, 3 Department of Radiation Oncology, Weill Cornell Medicine, Sandra and Edward Meyer Cancer Center, New York, USA Radiation therapy (RT) is the standard-of-care for glioblastoma (GBM) and is the only treatment for inoperable brain tumors. In multiple cancer, RT stimulates anti-tumor immunity by at least activating cancer cell-intrinsic type I interferon (IFN-I) responses. However, GBM inevitably recur, sug- gesting that RT promotes immune evasion mechanisms. Altered fatty acid (FA) metabolism is an emerging mechanism that can account for treatment resistance and immune escape of GBM. Therefore, we hypothesize that RT induces a metabolic shift toward the production of FAs to foster im- munosuppression of GBM. Supporting this hypothesis, our data show that RT upregulates the expression of the fatty acid synthase (FASN) and the activity of the fatty acid desaturase 2 (FADS2) to generate FAs in murine GBM models, GL261 and CT2A. To determine whether FA metabolism was preventing RT-induced IFN-I, we impaired FA synthesis by inhibiting either FASN or FADS2 using genetic (CRISPR-Cas9) or pharmacological inhibitors (FASNi or FADS2i). As expected, protein quantifcation (ELISA) as well as gene expression (RT-qPCR) revealed that irradiated GBM cells released greater levels of IFN-beta 24hrs post RT; an effect that was more pronounced when FASN or FADS2 were blocked. Reinforcing the role of FA metabolism in regulating immune activation, in situ immunofuorescence of irradiated intracranial GL261 tumors showed that mice treated with FASNi improved the recruitment of CD8+ T cells into GBM. Along similar lines, fow cytometry of digested GL261 tumors revealed an increase infltration of CD11c+ CD103+ dendritic cells as well as activated CD86+ CD11b+ cells when FAs synthesis was blocked with FADS2i. Altogether, our data sug- gest that RT-induced FA synthesis represents a mechanism of resistance by preventing IFN-I and promoting immunological evasion of GBM. Targeting FA metabolism is a promising strategy to promote anti-tumor immunity and sensitize irradiated GBM to immunotherapies. TMET-11. QUINOLINATE PROMOTES ALTERNATIVELY ACTIVATED MACROPHAGE-INDUCED IMMUNE TOLERANCE IN GLIOBLASTOMA THROUGH THE NMDA/PPARG SIGNALING AXIS Pravin Kesarwani 1 , Shiva Kant 2 , Yi Zhao 1 , Antony Prabhu 1 , Katie Buelow 1 , C. Ryan Miller 3 , and Prakash Chinnaiyan 1 ; 1 Beaumont Health, Royal Oak, MI, USA, 2 Beaumont Health, Royal Oak, USA, 3 The University of Alabama at Birmingham, Birmingham, AL, USA There has been considerable interest in understanding the biological consequence and therapeutic implications of aberrant tryptophan metab- olism in brain tumors and neurodegenerative diseases. An overwhelming majority of this work has focused on the frst-step of tryptophan metab- olism (kynurenine); however, this has yet to result in clinical application. Using global metabolomic profling on >100 patient-derived brain tumors, we identifed a 64-fold accumulation of quinolinate (QA), a downstream metabolic intermediate of the tryptophan pathway, in glioblastoma when compared to low-grade glioma. As several metabolites in the tryptophan pathway have been implicated in immune modulation, we sought to deter- mine the impact of QA on the immune microenvironment. We identifed the capacity of QA to strongly skew macrophage polarization towards the “pro-tumorigenic” M2-phenotype with suppressive properties, which recent studies suggest play a dominant role in the immune microenvir- onment in glioblastoma. Intriguingly, QA conferred an “M2-like” pheno- type to M1 macrophages and microglia, attenuating their phagocytosis effciency. We went on to systematically delineate a novel mechanism of macrophage polarization through QA-induced NMDA receptor activation and Foxo1/PPARg signaling. We then determined that tumor cells and host macrophages/microglia work in concert to complete both upstream and Downloaded from https://academic.oup.com/neuro-oncology/article/24/Supplement_7/vii263/6826940 by guest on 03 March 2023