Delineating the Cellular Hierarchy of Glioblastoma and Gliosarcoma for Identification of Therapeutic Targets

Abstract

Glioblastoma (GBM) and its more aggressive variant gliosarcoma (GSM) are the most lethal primary brain tumours, containing glioma stem cells (GSCs) which are resistant to current treatments. We compared the cellular hierarchy and molecular heterogeneity of GBM and GSM to identify genetic drivers of tumour growth and potential therapeutic targets. Fresh frozen human GBM and GSM specimens and 6 cell lines were interrogated using qRT‐PCR for expression of genes controlling self‐renewal and multilineage differentiation. SOX2 was overexpressed, whereas its core partners OCT4 and NANOG showed 90‐180 fold lower expression. Downstream targets ESRRB, PROX1, NESTIN and PAX6 had variable expression. GSC‐associated marker CD133 was highly expressed in both frozen GBM and GSM, but less so in the cell lines. Neural genes MAP2 and GAP43 and glial genes GFAP and S100B showed variable expression. Epithelial signatures (cytokeratin 18) were detected in GSM and to a lesser extent in GBM. Expression of E‐cadherin was significantly higher in GBM than in GSM (P<0.05), suggesting greater cell motility in GSM. Endodermal signatures (GATA4) were more highly expressed in GBM. Overall, GSM showed greater variation in gene expression than GBM. The presence of neural, epithelial and endodermal signatures suggests multipotential of GSCs. The stronger presence of different lineages in GSM reflects its greater heterogeneity, providing further evidence that GSM is a different disease to GBM and highlighting the need for patient‐tailored treatments.