Implantation of glioblastoma spheroids into organotypic brain slice cultures as a model for investigating effects of irradiation: A proof of concept

Glioblastoma is the most frequent malignant brain tumor with an overall survival of only 14.6 months. Novel in vitro models preserving both tumor tissue and the interface between tumor and brain tissue are highly needed in order to develop novel efficient therapeutic strategies. Additionally, models for studying the effects of radiotherapy in combination with novel strategies are lacking but important since radiotherapy is the most successful non-surgical treatment of brain tumors. The aim of this study was to establish a glioblastoma spheroid-organotypic rat brain slice culture model comprising both tumors, tumor-brain interface and brain tissue to provide a proof of concept that this model is useful for studying effects of radiotherapy. Organotypic brain slice cultures cultured for 1-2 days or 11-16 days corresponding to immature brain and mature brain respectively were irradiated with doses between 10 and 50 Gy. There was a high uptake of the cell death marker propidium iodide in the immature cultures. In addition, MAP2 expression decreased whereas GFAP expression increased in these cultures suggesting neuronal death and astrogliosis. We therefore proceeded with the mature cultures. Using confocal time-lapse microscopy and detection of tumor cells by immunohistochemistry, tumor cell migration from the spheroids into the slice cultures was revealed, and found to be unaffected by irradiation. However, the expression of the proliferation marker MIB-1 decreased. In conclusion the results showed - as an initial proof of concept - that the established model has potential value in glioblastoma research for developing novel therapeutic strategies comprising irradiation.