TMOD-12. COMPARING TUMOR CELL INVASION AND MYELOID CELL COMPOSITION IN GENETICALLY IDENTICAL PRIMARY AND RELAPSING GLIOBLASTOMA

Abstract

Abstract Glioblastoma (GBM) recurrence after treatment is almost inevitable, but addressing this issue with adequate preclinical models has remained challenging. Here, we introduce a GBM mouse model allowing non-invasive and scalable de-bulking of a tumor mass located deeply in the brain, which can be combined with conventional therapeutic approaches. Towards this aim we genetically engineered mouse GBM cells to stably express the herpes simplex virus thymidine kinase. Strong reduction of the GBM volume is achieved after pharmacologically inducing a tumor-specific cell death mechanism by the prodrug ganciclovir. This is followed by GBM re-growth over a predictable timeframe. Pharmacological de-bulking followed by tumor relapse was accomplished with an orthotopic mouse glioma model. Relapsing experimental tumors recapitulated pathological features often observed in recurrent human GBM, like increased invasiveness or altered immune cell composition. Orthotopic implantation of GBM cells originating from biopsies of one patient at initial or follow-up treatment reproduced these findings. Interestingly, relapsing GBM of both models contained a much higher ratio of monocyte-derived macrophages (MDMs) versus microglia than primary GBM. This was not altered when combining pharmacological de-bulking with invasive surgery. We interpret that factors released from viable primary GBM cells preferentially attract microglia whereas relapsing tumors preponderantly release chemoattractants for MDMs. All in all, this relapse model has the capacity to provide novel insights into clinically highly relevant aspects of GBM treatment.