DMG-56. Defining the transcriptional and signalling pathways that drive invasion in Diffuse Midline Gliomas

Abstract Diffuse midline gliomas (DMG) H3K27-altered are aggressive paediatric tumours with poor prognoses, characterised by their extensive infiltration of the central nervous system. Radiotherapy is administered to all patients to control local tumour growth and slow disease evolution. However, distant progression and intracranial metastases remain a common challenge impacting DMG patients’ survival. Using patient-derived 3D avatars to model interindividual invasion, we previously showed that 3D models mirror the invasive behaviour of the parental tumours, thus proving the ability of DMG to infiltrate as an autonomous characteristic of tumour cells. We can predict metastatic evolution by using patient cells at diagnosis and we identified the cell-autonomous BMP7-related signalling as a major regulator of DMG motility and invasion. Extended analyses reveal that BMP7 secretion regulates a phenotypic switch and turn poorly invasive, mesenchymal-like into highly invasive, amoeboid like cells. Amoeboid migration is rather independent of adhesion to the substrates and as such, is not sensitive to substrate stiffness. On the opposite, mesenchymal migration is dependent on substrate adhesion and is generally faster on stiff substrates. We therefore postulated that highly invasive cells with amoeboid phenotype would be less sensitive to stiffness, and explored how BMP7 regulate this stiffness sensitivity. Looking for transcriptional regulators of this invasive state, we further identified the OPC fate regulator NKX2-2. Targeting of NKX2-2 decreased DIPG cell invasion and altered their morphology with shorter processes pointing to impaired tumour cell connectivity. Interestingly, NKX2-2 extinction did not revert high invasive DMG to a Mesenchymal state, but reprogrammed cells in a Neuroblast fate, and also reduced proliferation notably through the decrease of NLGN3. Together, our work dissects invasion mechanisms in DMG. The complex upstream regulation of this signalling opens up perspectives for its targeting, in order to tackle the inexorable extension of this disease following focal treatment such as radiotherapy.