Molecular subtypes and the (in vitro) response of glioblastoma to temozolomide

We address the therapeutic relevance of glioblastoma (GBM)'s molecular characterization, focusing on whether a proneural-vs-mesenchymal classification may describe GBM heterogeneity, correlate to stemness and CD44 (a marker often, but conflictingly, used in GBM), and have a prognostic value in terms of temozolomide (TMZ) resistance.

We molecularly profiled 4 patient-derived GBM cells (PD-GBM) and a reference cell line (U87), validating the results in public datasets (PD-GBM, TCGA-GBM), then studying the subtype-specific response to TMZ in vitro, both under normoxia and simulated hypoxia.

Firstly, the proneural subtype transcriptionally and phenotypically correlates with higher stemness. Secondly, CD44 inversely correlates to stemness, acting as a mesenchymal marker both intra-tumorally (FACS-sorted CD44^LOW cells had higher stemness than CD44^HIGH) and inter-tumorally (also in larger datasets). Further, mesenchymal PD-GBM cells are also enriched in other hyaluronic acid (HA) surface receptors, proneural in matrix HA receptors. Finally, although TMZ stimulates a general mesenchymal shift in all cells, there are proneural-specific responses: this subtype resists TMZ better under hypoxia (vs. normoxia) in a first treatment, and in a second treatment (vs. single) under normoxia.

PD-GBM show clear proneural/stemness and mesenchymal/CD44 correlations, which may bear prognostic significance, as more proneural/stem GBMs appeared more capable to develop TMZ resistance.