TMIC-33. MICROENVIRONMENT-DRIVEN CHANGES IN GLIOBLASTOMA CELL STATE SIGNATURES EXAMINED USING REGION-SPECIFIC HUMAN BRAIN ORGANOIDS

Abstract Cell state plasticity is retained by all stem-like and differentiated cells within glioblastoma (GBM) tumors. GBM cells can exploit these state-shifting capacities to evade and resist therapeutics. Thus, there is a need to identify and target the regulators of GBM cell state transitions. To address this question, we use a fully human platform where hiSPC-derived organoids serve as a recipient environment to host cells engrafted directly from surgically resected GBMs. This allows us to precisely examine how microenvironmental variables impact the molecular signatures of GBM cells. We acutely isolate GBM cells from surgical resections, label cells with a GFP-lentivirus for 4 hours, and then engraft these tumor cells into parallelly patterned region-specific organoids that mimic dorsal forebrain, ventral forebrain, midbrain, and hindbrain identities. These regions were chosen as they capture derivatives of the three primary brain vesicles and because these regions contain unique cell types and signaling molecules. We performed paired single-cell RNA sequencing on tumor cells pre-engraftment and 14 days post-engraftment. Universal to all regional organoids, we find that GBM cells shift towards a neural progenitor-like and neuron-like signature within organoids, regardless of the cell state of the parent tumor prior to engraftment. To support our findings, we also observed that patient-derived glioma cell lines converge on a neural progenitor-like state within organoids. Thus, the dominance of this shared GBM cell state within organoids implies the existence of shared extrinsic factors in these immature (neurogenic) organoids that favor a progenitor-like or neuron-like identity across all four regions. We are now asking whether this bias towards neuronal and/or neural progenitor identity is a result of engrafting into young neurogenic organoids, or if the same phenomenon could be true in late-stage (post-gliogenic) mature organoids. We are also using this valuable platform and data to identify the extrinsic signals that GBM cells rely on to fulfill their plastic potential, adapt to the microenvironment, and resist therapeutics.