title: Side population in human glioblastoma is non-tumorigenic and characterizes brain endothelial cells.
abstract: The identification and significance of cancer stem-like cells in malignant gliomas remains controversial. It has been proposed that cancer stem-like cells display increased drug resistance, through the expression of ATP-binding cassette transporters that detoxify cells by effluxing exogenous compounds. Here, we investigated the 'side population' phenotype based on efflux properties of ATP-binding cassette transporters in freshly isolated human glioblastoma samples and intracranial xenografts derived thereof. Using fluorescence in situ hybridization analysis on sorted cells obtained from glioblastoma biopsies, as well as human tumour xenografts developed in immunodeficient enhanced green fluorescence protein-expressing mice that allow an unequivocal tumour-stroma discrimination, we show that side population cells in human glioblastoma are non-neoplastic and exclusively stroma-derived. Tumour cells were consistently devoid of efflux properties regardless of their genetic background, tumour ploidy or stem cell associated marker expression. Using multi-parameter flow cytometry we identified the stromal side population in human glioblastoma to be brain-derived endothelial cells with a minor contribution of astrocytes. In contrast with their foetal counterpart, neural stem/progenitor cells in the adult brain did not display the side population phenotype. Of note, we show that CD133-positive cells often associated with cancer stem-like cells in glioblastoma biopsies, do not represent a homogenous cell population and include CD31-positive endothelial cells. Interestingly, treatment of brain tumours with the anti-angiogenic agent bevacizumab reduced total vessel density, but did not affect the efflux properties of endothelial cells. In conclusion our findings contribute to an unbiased identification of cancer stem-like cells and stromal cells in brain neoplasms, and provide novel insight into the complex issue of drug delivery to the brain. Since efflux properties of endothelial cells are likely to compromise drug availability, transiently targeting ATP-binding cassette transporters may be a valuable therapeutic strategy to improve treatment effects in brain tumours.
authors: NorLux Neuro-Oncology Laboratory, Centre de Recherche Public de la Santé (CRP-Santé), Department of Oncology NorLux Neuro-Oncology Laboratory 84, Val Fleuri, L- 1526 Luxembourg.
authors: Anna
authors: A
authors: Golebiewska
authors: Sébastien
authors: S
authors: Bougnaud
authors: Daniel
authors: D
authors: Stieber
authors: Nicolaas H C
authors: NH
authors: Brons
authors: Laurent
authors: L
authors: Vallar
authors: Frank
authors: F
authors: Hertel
authors: Barbara
authors: B
authors: Klink
authors: Evelin
authors: E
authors: Schröck
authors: Rolf
authors: R
authors: Bjerkvig
authors: Simone P
authors: SP
authors: Niclou
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001932:Brain Neoplasms / Q000737:chemistry / Q000473:pathology*; D045744:Cell Line, Tumor; D042783:Endothelial Cells / Q000737:chemistry / Q000473:pathology*; D005260:Female; D005909:Glioblastoma / Q000737:chemistry / Q000473:pathology*; D006801:Humans; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008875:Middle Aged; D014411:Neoplastic Stem Cells / Q000737:chemistry / Q000473:pathology*; D010641:Phenotype; D023041:Xenograft Model Antitumor Assays / Q000379:methods