Abstract The rampant growth of Diffuse Midline Gliomas make them very difficult to cure. However, we hypothesize DMGs may arise long before children present with devastating symptoms and fast-growing tumors, and that they may be associated with a pre-malignant or ‘pre-transformation’ phase, like other gliomas such as those that harbor IDH mutations. Our hypothesis is supported by observations of children diagnosed incidentally with DMGs while asymptomatic1,2, in addition to the finding that histone mutations are insufficient to induce glioma formation as single driver events3-5. To study cellular evolution after H3K27M acquisition, we developed new isogenic human neural stem cell models expressing H3K27M or wild-type H3 (H3WT), and performed transcriptional, epigenetic, and functional profiling of the models at multiple timepoints after introduction of the H3 cassette. Interestingly, H3K27M expression initially induced growth defects, caused by cell cycle dysregulation, but cellular growth rates quickly normalized due to adaptive processes. Introduction of loss-of-function alterations in cell-cycle regulators abrogated H3K27M-mediated growth defects, indicating that H3K27M imposes a selective pressure favoring loss of cell cycle control. Time analysis of clonal evolution of whole-genome sequences of more than 100 diffuse midline gliomas reveal early aneuploidy events that may allow pre-malignant glioma cells to tolerate expression of H3K27M. These observations raise the intriguing possibility that expression of H3.3K27M is initially toxic across multiple cell types, creating a bottleneck that shapes subsequent glioma evolution. They also raise the possibility that screening strategies for early detection of asymptomatic histone mutant DMGs may one day present therapeutic opportunity for children prior transformation, increasing the opportunity for cure. 1. Yeo, K. K. et al. Incidental Diffuse Midline Glioma, H3 K27-Altered of the Pons Without Significant Coalterations. JCO Precis. Oncol. e2400944 (2025) doi:10.1200/PO-24-00944 2. Damodharan, S., Helgager, J. & Puccetti, D. Indolent presentation of a diffuse midline glioma, H3 K27-altered. Childs Nerv. Syst. ChNS Off. J. Int. Soc. Pediatr. Neurosurg. 39, 833–835 (2023) 3. Larson, J. D. et al. Histone H3.3 K27M Accelerates Spontaneous Brainstem Glioma and Drives Restricted Changes in Bivalent Gene Expression. Cancer Cell 35, 140-155.e7 (2019). 4. Khadka, P. et al. PPM1D mutations are oncogenic drivers of de novo diffuse midline glioma formation. Nat. Commun. 13, 604 (2022) 5. McNicholas, M. et al. A Compendium of Syngeneic, Transplantable Pediatric High-Grade Glioma Models Reveals Subtype-Specific Therapeutic Vulnerabilities. Cancer Discov. 13, 1592–1615 (2023)
Poux et al. (Tue,) studied this question.