Abstract 1823: Spatial transcriptome profiling shows a decrease in heterogeneity of GBM xenografts that regrow after irradiation and suggests novel therapeutic targets

Abstract Radiation remains a primary treatment for glioblastoma, yet tumors frequently recur within two years. As a model for investigating the biology of recurrent GBMs, we used orthotopic xenografts initiated of GBM-stem like cells (GSCs) implanted into the right striatum of nude mice. Thirty-five days post-implant, mice bearing brain tumor xenografts were locally irradiated (10Gy) and brains collected 14 and 21 days later. In untreated mice, tumors were highly diffuse with tumor cells invading from the injection site in the right hemisphere (RH) to the anterior part of the brain, invading the corpus callosum, cortex, and olfactory bulb (OB). A different growth pattern was detected in tumors that regrew after irradiation. At 14 days post-10Gy, tumors were located primarily in the OB with an increased cell density and a clearly demarcated border. 21 days post-10Gy tumor cell density increased with the demarcated border extending further into the hemisphere, i.e., farther away from the OB. This growth pattern suggests that tumor regrowth after irradiation is initiated in the OB, consistent with previous results showing that GBM cells in the OB are radioresistant compared to those in the RH. To compare transcriptomes of untreated and recurrent tumors we used digital spatial profiling (DSP). Tumor cells were identified by Sox2 staining, and regions of interest (ROIs) were selected in various locations within the OB and the RH of untreated tumors, and throughout recurrent tumors (D21 post-10Gy). Cluster analysis showed that ROIs across the OB and RH of untreated tumors were more similar to each other as compared to ROIs from the tumors that regrew after irradiation. Variance in the expression of individual genes across the ROIs was reduced in the recurrent tumors compared to the untreated tumors. These results suggest a reduction in phenotypic heterogeneity among the cells of the regrown tumor. Comparative gene expression analysis identified 463 differentially expressed genes with 319 downregulated and 144 upregulated in the recurrent versus untreated tumors. GSEA revealed a significant enrichment of pathways related to cell cycle regulation in the regrown tumors as compared to non-irradiated tumors. Further examination of the cell cycle control related pathways indicated an enrichment in proteasome genes. Specifically, 22 genes encoding proteasome proteins were significantly upregulated in the recurrent tumors compared to the untreated group, suggesting that the proteasome may provide a therapeutic target unique to the recurrent GBM. Altogether, these results suggest that this xenograft model of GBM regrowth after irradiation, characterized by an altered growth pattern and a distinct molecular profile may be useful for investigations into the biology and treatment of recurrent GBM. Citation Format: Charlotte Marie Degorre. Spatial transcriptome profiling shows a decrease in heterogeneity of GBM xenografts that regrow after irradiation and suggests novel therapeutic targets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1823.