P01.39.A CHARACTERIZATION OF AN IDH1-MUTANT ASTROCYTOMA CELL BIOBANK REVEALS A QUIESCENT STATE OF ASTROCYTE-LIKE CELLS WHICH DRIVES CELLULAR HETEROGENEITY UNDER THE INFLUENCE OF NOTCH PATHWAY

Abstract BACKGROUND IDH1-mutant diffuse low-grade gliomas—oligodendrogliomas and astrocytomas—are slow-growing brain tumors that can progress to higher grades and exhibit significant intratumoral cellular heterogeneity. Previous studies identified three populations in these tumors: astrocyte-like, oligodendrocyte-like, and stem-like cells. Some cells appear to be in a quiescent-like state, while others are actively dividing. However, the link between glioma cell phenotype and quiescence—and its contribution to heterogeneity—remains poorly understood, largely due to the lack of appropriate experimental models. METHODS In this study, we established a biobank of four patient-derived astrocytoma cell lines of varying grades and mutations, characterized using multi-omics. We then used CD44 and GLAST to isolate astrocyte-like and oligodendrocyte-like populations to investigate their properties and roles in tumor heterogeneity. RESULTS One specific cell line, LGG275, derived from a grade 2 astrocytoma, was identified as the relevant in vitro model for studying cellular heterogeneity. This slow-growing cell line harbors an IDH1 mutation, as well as TP53 and ATRX mutations, and CDKN2A loss, resulting in D-2-hydroxyglutarate (D2-HG) production and an alternative lengthening of telomeres (ALT) phenotype. It exhibits cellular heterogeneity, including astrocyte-like, oligodendrocyte-like, and stem-like populations. We have found that the astrocyte-like population corresponds to a quiescent state, resembling quiescent neural stem cells (qNSC). The oligodendrocyte-like population, on the other hand, reflects an active NSC state. Astrocyte-like cells are also plastic and can switch to an oligodendrocyte-like phenotype to restore cellular heterogeneity. This plasticity is regulated by the Notch pathway. In contrast, other established astrocytoma cell lines from our panel, particularly those derived from higher-grade tumors, display more complex subclonal architectures and a greater proportion of cancer stem-like cells, highlighting LGG275 as a simplified and tractable model to dissect the mechanisms underlying glioma plasticity. CONCLUSION We developed and annotated four new astrocytoma cell lines that recapitulate patient tumor features. LGG275 stands out as a simplified yet informative model to study glioma heterogeneity and plasticity, uncovering a notch-dependent transition from quiescence to activity in glioma cells.