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TAMI-47. EVALUATION OF THE EFFECT OF MICROENVIRONMENTAL STRESSES ON GLIOMA STEMNESS IN VITRO AND EX VIVO


 Glioblastoma is the highest-grade glioma and most aggressive brain tumor, affecting both adults and children. Treatment includes surgery followed by chemotherapy, most frequently in the form of temozolomide treatment, radiation and in some cases by application of tumor-treating fields. Tumor recurrence is very common and is driven by cells exhibiting a treatment-resistant cancer stem cell phenotype, located in specific niches, namely the hypoxic and perivascular niche. While previous studies have delved into the role of the microenvironment in supporting glioma stemness and therapy resistance, little is known about how the stromal cells themselves respond to microenvironmental stresses. Here, we show that one cell type of the tumor microenvironment, the astrocyte, becomes activated after treatment with radiation, temozolomide or hypoxia in vitro, showing an increase in GFAP and Vimentin expression as well as morphological changes. Activated astrocytes also change their secretome, secreting cytokines such as IL6, IL7, CCL2 and CCL8, all associated with worse prognosis in several patient cohorts. Importantly, conditioned medium or extracellular matrix from activated astrocytes induce stemness features in glioma cells, measured by increased side population or radiation resistant fractions. To evaluate our findings in a more relevant model, we use an ex vivo organotypic culture system for brain sections from our experimental mouse model of glioma. Cultures are maintained for up to 21 days in 21%, 5% or 1% O2 with a high proportion of surviving tumor and stromal cells. We intend to use the ex vivo system to evaluate the effect of microenvironmental stresses on glioma stemness. Our study suggests that the tumor microenvironment that has been exposed to stressors such as radiation, chemotherapy or hypoxia is important in maintaining stemness and therefore treatment resistance in glioblastoma. Further research is required to address these stress-induced changes and provide better treatment options for glioblastoma patients.