Highly infiltrative brain tumours show reduced chemosensitivity associated with a stem cell-like phenotype

Cancer stem-like cells might have important functions in chemoresistance. We have developed a model where highly infiltrative brain tumours with a stem-like phenotype were established by orthotopic transplantation of human glioblastomas to immunodeficient rats. Serial passaging gradually transformed the tumours into a less invasive and more angiogenic phenotype (high-generation tumours). The invasive phenotype (low-generation tumours) was characterized by an increase in stem cell markers and increased phosphorylation of kinases in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. These markers were reduced in the serially passaged vascular tumours. The present study was aimed at investigating how the two phenotypes responded in vitro to doxorubicin, a clinically potent cytotoxic drug for solid tumours.

Biopsy spheroids were implanted and passaged intracranially in nude rats. Gene expression and protein analyses were performed, and drug sensitivity was assessed.

Microarray analysis revealed gene ontology categories connected to developmental aspects and negative regulators of differentiation, especially in the infiltrative stem cell-like tumours. The highly invasive stem-like phenotype was chemoresistant compared with the angiogenic phenotype. By interfering with the PI3K it was possible to sensitize tumour spheroids to chemotherapy. Real-time quantitative polymerase chain reaction showed downregulation of the stem cell markers Nestin and Musashi-1 in low-generation biopsy spheroids following PI3K inhibition.

Highly invasive tumours with a stem-like phenotype are more chemoresistant than angiogenic tumours derived from the same patients. We suggest that treatment resistance in glioblastomas can be related to PI3K/AKT activity in stem-like tumour cells, and that targeted interference with the PI3K/AKT pathway might differentiate and sensitize this subpopulation to chemotherapy.