CNSC-32. UNDERSTANDING MECHANISMS OF CHEMORADIATION RESISTANCE UTILISING PATIENT-DERIVED 3D NEUROSPHERES

Abstract Glioblastoma (GB) is the most aggressive primary brain tumour, accounting for 60% of all brain cancers in adults with a 5-year patient survival of just 7%. Despite intensive treatment with surgery, radiation (IR) and chemotherapy with temozolomide (TMZ), GB often resists intervention, continuing to grow and invade into the surrounding tissue. Understanding the mechanisms of treatment resistance in GB patients is crucial to further develop therapies to be delivered alongside the standard of care to increase the potential of tumour cell death. This project aims to identify subgroups of patient-derived GB cell lines that exhibit resistance to therapeutic interventions and to uncover molecular drivers of IR and TMZ resistance. Neurospheres, derived from patient tumour cells, were treated with either 88µM TMZ, 12Gy IR or 88µM TMZ and 12Gy IR together over 5 days, then characterised through invasion assays, proliferative immunohistochemistry with Ki67, and mass spectrometry (n=8). Further analyses for relative stem cell abundance using flow cytometry as well as spatial transcriptomics of Ki67+ cells to identify specific drivers of resistance in retained proliferative regions following treatment are ongoing. Two treatment resistant subgroups were identified featuring either a) retained invasion (n=3), with chemoradiation failing to significantly reduce invasion compared to control neurospheres, or b) retained proliferation (n=3), with Ki67+ cells present throughout treated neurospheres. Proteomic analysis revealed significant differences in pathway regulation between treatment resistant subgroups, including mechanisms of metabolic reprogramming, immune regulation, and stemness signalling, indicating distinct mechanisms of resistant phenotypes. This research has revealed molecular mechanisms and potential predictive biomarkers of treatment response, as well as therapeutic targets to aid the prevention of chemoradiation resistance.