Identification and molecular characterization of distinct glioblastoma cancer stem cell populations

Malignant glioblastoma (GBM) is a highly aggressive brain tumor with a dismal prognosis and limited therapeutic options. Genomic profiling of GBM samples in the TCGA database has identified four molecular subtypes (Proneural, Neural, Classical and Mesenchymal), which may arise from different glioblastoma stem-like cell (GSC) populations. In the present study, we identify two GSC populations that produce GBM tumors by subcutaneous and intracranial injection with identical histological features. Gene expression analysis revealed that xenografts of GSCs grown as spheroid cultures had a Classical molecular subtype similar to that of bulk tumor cells. In contrast xenografts of GSCs grown as adherent cultures on laminin-coated plates expressed a Mesenchymal gene signature. Adherent GSC-derived xenografts had high STAT3 and ANGPTL4 expression as well as enrichment for stem cell markers, transcriptional networks and pro-angiogenic markers characteristic of the Mesenchymal subtype. Examination of clinical samples from GBM patients showed that STAT3 expression was directly correlated with ANGPTL4 expression, and that increased expression of these genes correlated with poor patient survival and performance. A pharmacological STAT3 inhibitor abrogated STAT3 binding to the ANGPTL4 promoter and exhibited anticancer activity in vivo. Taken together, we identified two distinct GSC populations that produce histologically identical tumors but with very different gene expression patterns, and a STAT3/ ANGPTL4 pathway in glioblastoma that may serve as a target for therapeutic intervention. 2 samples of each variable were analyzed. Cells were cultured under normal adherent conditon (Bulk tumor cells), non-adherent plates with stem cell medium (Sp-GSC) or laminin-coated plates with stem cell medium (Ad-GSC). Xenografts were generated in NSG mice by subcutaneous inoculation.