TMIC-30. FOREBRAIN TO HINDBRAIN INVASION IN GLIOBLASTOMA IS DIRECTED BY ANATOMICALLY DISTINCT REACTIVE ASTROCYTES

Abstract Initial detection of glioblastoma (GBM) often reveals a large mass in the forebrain; however, the hazard for many patients lies in extensive invasion that can extend far from the primary tumor. New evidence suggests that end-stage GBM coincides with malignant infiltration of the pons and brainstem. Mechanisms that direct tumor cells from initial positions within the forebrain to terminal positions in the brainstem are largely unknown. Our analysis indicates that spatially defined, reactive astrocytes instruct GBM cells to either proliferate or invade. During development, astrocytes help establish directional gradients and boundaries that mediate proper routing of migrating neural cells and extending axons. We posit that onco-reactive astrocytes re-engage these guidance programs to direct tumor cells to the brainstem. To test this hypothesis, we exposed a series of human GBM models to media conditioned by cortical, midbrain, or brainstem reactive astrocytes. When treated with cortical conditioned media, tumor cells were driven into a state of hyper-proliferation, which mirrored early-stage forebrain tumor generation. In contrast, midbrain and brainstem conditioned medias suppressed proliferation and enhanced the rate of tumor cell migration. RNA sequencing corroborated these functional data, identifying cell division programs augmented in GBM cells exposed to cortical astrocyte conditioned media. This contrasted with axon development and guidance programs enriched in GBM cells exposed to midbrain and especially brainstem conditioned medias. Finally, mRNA and protein analysis identified region-specific engagement with the Eph-ephrin guidance system patterned along a forebrain to hindbrain trajectory. These data support a new hypothesis that GBM tumors recapitulate a form of neurodevelopment, invading specific anatomic regions based on cues generated by resident reactive astrocytes.