The Brain Parenchymal Response to Invasive Tumor in an Ex-vivo Long-term Brain Slice Assay

Introduction: The glioma-neuronal interactions has profoundly challenged our understanding of tumor invasion, however, current models have significant shortcoming, since a dynamic assessment of the brain-tumor interface is nearly impossible, aside from utilization of murine brain slices, xenograft, and transgenic models. Our novel long-term human brain slice model allows for further assessment of the brain parenchymal and neuronal response to invasive tumors.

Methods: Specimens were obtained from patients undergoing epileptogenic disconnection surgery. Slices were acutely oxygenated in artificial CSF(aCSF) enriched with sucrose, pyruvate, vibratome sectioned (250microns), and cultured with neuroprotective media. They were transduced with GFP-fluorescent EF1-A. Patient-derived RFP-Glioblastoma organoids (GBOs) were implanted on these slices. Spatial transcriptomics was conducted by comparing GBO core, brain slice edge, and FACS sorting the brain-tumor interface for RFP+(Invasive GBO) vs GFP(invaded parenchyma) cells. Immunofluorescent staining(I.F.) was conducted on whole slices.

Results: When compared to the brain slice edge, the invaded parenchymal cells demonstrated diminished synaptic stability shown by a significant 2-fold decrease in the expression of Cell-Adhesion Molecule 3 (CADM3) as well as a 17-fold reduction in integrin alpha subunits (1, 5, 6, and 8) (P <.005). Furthermore, Myelin maintenance of Schwann cells was also impacted as demonstrated by a 6.6-fold reduction in EGR2/4 transcription (P < 0.005). These cells also had a 3-fold reduction in BDNF expression, a key player in neuronal survival and growth.

Conclusion : Understanding the brain-tumor interface is a critical frontier for elucidating the mechanism by which the brain parenchyma tolerates invasive tumor cells. The neuronal changes described above may serve as targets for potentiation to further battle glioblastoma invasion.