CNSC-64. BEYOND THE LOCAL TUMOR MICROENVIRONMENT: CHARACTERIZING CHANGES TO NEURONAL ACTIVITY INDUCED BY PEDIATRIC HIGH-GRADE GLIOMA

Abstract Bidirectional electrochemical signaling between neurons and tumor cells is emerging as a critical regulator of pediatric high-grade glioma (HGG) pathology. Neuron-tumor interactions are known to induce local neuronal hyperactivity. However, recent work tracing the projections of these neuron-tumor networks revealed that HGG neuronal recruitment extends beyond the local tumor microenvironment (TME). These findings suggest that tumor-induced hyperexcitability may spread beyond the local TME and drive brain-wide circuit-level changes. To elucidate how non-tumor innervated brain regions are affected by TME hyperactivity we first characterized neuronal hyperactivity induced by a cortical patient-derived pediatric high-grade cell line in vitro on human iPSC-derived neurons. In vitro calcium imaging experiments demonstrated an increase in the number of calcium fluctuations in glioma co-cultured neurons. In parallel, multi-electrode recordings revealed increased population spiking activity and amplitude in neurons co-cultured with glioma cells. We then xenografted these HGG cells into the prefrontal cortex of mice and performed whole brain-clearing and cFos staining on tumor-bearing vs saline-injected control samples. As cFos is an immediate early gene activated by neuronal activity, we utilized the density of cFos expression as a readout-out of neuronal activation in our atlas-aligned segmented brain section analyses. We expectedly observed increased cFos expression within the ipsilateral primary and secondary motor region, which collectively comprise the local TME. Interestingly, we additionally observed elevated cFos in non-tumor bearing brain regions on both the ipsilateral and contralateral hemispheres, largely in layer 2/3 cortical neurons. These neurons form extensive cortico-cortical projections, and we coincidingly observed increased cFos expression in known cortical projection targets of the prefrontal xenograft location, such as somatosensory, visual, and retrosplenial cortices. Our findings suggest that tumor-induced neuronal hyperactivity extends beyond the local TME in a brain-wide manner and potentially follows established neuronal circuits, rendering these connected regions vulnerable to alterations in neuronal activity.