Project description:Brain tumors are among the most malignant cancers and can arise from neural stem cells or oligodendrocyte progenitor cells (OPCs). Glioma-propagating cells (GPCs) that have stem-like properties have been derived from tumor variants such as glioblastoma multiforme (GBM) and oligodendroglial tumors, the latter being more chemosensitive with better prognosis. It has been suggested that such differences in chemosensitivity arise from the different profiles of OPCs versus neural stem cells. We thus explored if GPCs derived from these glioma variants can serve as reliable in vitro culture systems for studies. We utilized gene expression analyses, since GBM and oligodendrogliomas can be molecularly classified. Accordingly, we derived a gene signature distinguishing oligodendroglial GPCs from GBM GPCs collated from different studies, which was enriched for the Wnt, Notch and TGF-beta pathways. Using a novel method in glioma biology, the Connectivity Map, we mapped the strength of gene signature association with patient gene expression profiles in 2 independent glioma databases [GSE16011, http://caintegrator-info.nci.nih.gov/rembrandt]. Our gene signature consistently stratified survival in glioma patients. This data would suggest that in vitro low passage GPCs are similarly driven by transcriptomic changes that characterize the favorable outcome of oligodendrogliomas over GBM. Additionally, the gene signature was associated with the 1p/19q co-deletion status, the current clinical indicator of chemosensitivity. Our gene signature detects molecular heterogeneity in oligodendroglioma patients that cannot be accounted for by histology or the 1p/19q status alone, and highlights the limitation of morphology-based histological analyses in tumor classification, consequently impacting on treatment decisions. Total RNA obtained from primary neurosphere culture from brain tumor specimens of 6 patients were compared. Replicate arrays were performed for all 6 neurosphere cultures.

Project description:Oligodendrogliomas are defined by IDH-mutations and codeletions of chromosomal arms 1p and 19q. In the past, case reports and small studies described gliomas with sarcomatous features arising from oligodendrogliomas, so called oligosarcomas. Here, we report a series of 23 IDH-mutant oligosarcomas forming a distinct methylation class. The tumors were recurrences from prior oligodendrogliomas or developed de novo. Precursor tumors of 11 oligosarcomas were histologically and molecularly indistinguishable from conventional oligodendrogliomas. Oligosarcoma tumor cells were embedded in a dens network of reticulin fibers, frequently showing p53 accumulation, positivity for SMA, and gain of H3K27 trimethylation (H3K27me3) as compared to primary lesions. In 5 oligosarcomas no 1p/19q codeletion was detectable, although it was present in the primary lesions. Oligosarcomas harbored an increased chromosomal copy number variation load with frequent CDKN2A/B deletions. Proteomic profiling demonstrated oligosarcomas to be highly distinct from conventional grade 3 oligodendrogliomas with consistent evidence for a smooth muscle differentiation. Expression of several tumor suppressors was reduced with NF1 being lost frequently. In contrast, oncogenic YAP1 was aberrantly overexpressed in oligosarcomas. Panel sequencing revealed mutations in NF1 and TP53 along with IDH1/2 and TERT promoter mutations. Survival of patients was significantly poorer for oligosarcomas than for grade 3 oligodendrogliomas and comparable to that of grade 4 IDH-mutant astrocytomas. These results establish oligosarcoma as a distinct type of IDH-mutant glioma differing from conventional oligodendrogliomas on the histologic, epigenetic, proteomic, molecular and clinical level. Diagnosis can be based on the characteristic DNA methylation profile or the combined evidence of sarcomatous histology, IDH-mutation and an oligodendroglioma-typical molecular alteration as TERT promoter mutation and/or 1p/19q codeletion.

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Stem-like glioma-propagating cells contribute to molecular heterogeneity and survival outcome in oligodendroglial tumors

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