TMIC-62. INVESTIGATING THE ROLE OF OSTEOPONTIN IN RADIORESISTANCE OF H3.3-G34R PEDIATRIC HIGH-GRADE GLIOMA

Abstract Pediatric high-grade gliomas (pHGGs) are currently the leading cause of cancer-related deaths in children. Around 15% of pHGGs harbor a glycine to arginine (G34R) mutation in histone H3.3. Gliomas in general, including H3.3-G34R gliomas, contain cell populations that are resistant to chemotherapy and radiation therapy. These resistant cell populations are responsible for tumor recurrence seen in over 90% of patients within two years after treatment. Uncovering molecular mechanisms responsible for radiation resistance is essential for the development of new targeted therapies against glioma. In our lab’s H3.3-G34R mouse model, we have observed mice that are both radioresistant and radiosensitive. In order to investigate potential mechanisms of resistance leading to this phenotype, we performed single-cell RNA sequencing (scRNA-seq) on 3 non-treated (NT) glioma-bearing mice, 3 mice resistant to treatment (R), and 3 mice susceptible to treatment (S). The scRNA-seq data was processed and filtered using FastQC, Cellranger, CellBender, and DoubletFinder before downstream analysis. Ligand-receptor interaction analysis using CellChat in conjunction with differential expression analysis demonstrated differential expression and secretion of a cytokine known as Secreted Phosphoprotein 1 (SPP1)/Osteopontin (OPN) from tumor-associated microglia and macrophages. Current literature on SPP1 has suggested that its expression may play a role in tumor aggressiveness. However, there is conflicting evidence regarding its mechanism of action when secreted from tumor-associated microglia and macrophages. Additionally, its role in radioresistance has yet to be fully explored. We will present data utilizing in vitro and in vivo experimentation to elucidate the role that differential expression of SPP1 may play in the radioresistance of our H3.3-G34R mouse model. Supported by grants from NIH-NINDS, the Pediatric Brain Tumor Foundation, and Ian’s Friends Foundation