EXTH-64. ESTABLISHING A CLINICALLY RELEVANT MOUSE MODEL OF MESENCHYMAL GLIOBLASTOMA FOR STUDYING TME TARGETING TREATMENTS

Abstract Historically, pre-clinical GBM models have largely failed to predict response in the clinical setting. Here, we establish a more clinically faithful model using the syngeneic NFpp10a-Luc2 mesenchymal-GBM cell line to study response to resection and temozolomide (TMZ), adjuvant/neo-adjuvant anti-PD1 and Regorafenib (REGO) therapy. Cells were orthotopically implanted in C57BL/6-mice. Response to surgical and therapeutic interventions was assessed using bioluminescence imaging (BLI). Murine Microenvironment cell-population (mMCP)-counter, GSEA and multiple iteractive labelling by antibody neodeposition (MILAN, high-dimensional single-cell multiplex analysis) were employed to characterise treatment-related TME effects. We observed survival advantage in aged mice undergoing resection (resection:33.5 days vs non-resection:18 days; p = 0.0166). TMZ/anti-PD1 had no impact on tumour growth (TMZ: p = 0.9001, anti-PD1: p = 0.7933) or survival (TMZ:p = 0.3035, anti-PD1-:p = 0.6328). Neo-adjuvant anti-PD1 also conferred no survival advantage in young mice (33 vs 35 days; p = 0.9429). REGO/REGO+TMZ treatment conferred no survival benefit in young mice (REGO:p = 0.0735 and REGO+TMZ:p = 0.3945). mMCP-counter (which estimates the abundance of TME-cell populations from gene-expression data) showed resection upregulated B-cells and mast-cells, whereas TMZ caused a decreased abundance of vessels. Anti-PD1 treatment caused an enrichment of B-cells, mast-cells, and CXCR3 expression (p = 0.0045). REGO/TMZ+REGO treatment upregulated cytotoxic-lymphocyte populations. MILAN analysis showed resection increased cytotoxic-T-cells (20.3% vs pre-resection:7%). In contrast, TMZ/REGO monotherapy increased tumour-cells and decreased cytotoxic-T-cells. Anti-PD1 decreased macrophage abundance (39.8% vs control:14.5%). Likewise, TMZ+REGO decreased macrophages (11.3% vs control:35.3%) but upregulated B-cells and vessels. Overall, we have characterised response of the NFpp10a mouse model to resection, TMZ, anti-PD1 and REGO. We have shown that the model is insensitive to chemotherapy and TME-targeting therapies, mirroring patient-response patterns. Nevertheless, we observe transcriptomic and proteomic changes following TME-targeting treatments. Further analyses of these TME-associated resistance properties may help guide novel combinatorial treatment regimens. Overall, the NFpp10a model of mesenchymal GBM may be employed in future pre-clinical studies to accurately guide future clinica