Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

3.3 Glioma Culture Systems Introduction
showed higher levels of EGFR than any other cell line, perhaps explaining its
resistance to differentiation upon EGF withdrawal or BMP treatment [404].
The CD133 and CD15 cell surface markers are expressed on fetal and adult
neural progenitors and brain tumour-initiating cells (see Section 3.2). For
G144 and G179, heterogeneity for both markers was observed, similarly to
fetal NS cells [480], whereas G166 was found to be negative consistently with
the microarray expression data. The fact that CD133 was not present on
all GNS cell lines confirmed that this marker does not universally identify tu-
mourigenic cells in malignant glioma. Unlike CD133 and CD15, the hyaluronic
acid-binding protein CD44, characterised as an astrocyte precursor marker and
recently demonstrated to also mark NS cells in vitro [401], was uniformly ex-
pressed in all GNS cell lines [404].
To demonstrate the proof of principle of the utility of GNS cells with respect to
the shortcomings of the neurosphere assay (see Section 2.2), a small-scale chem-
ical screen of known pharmaceutical drugs was carried out. Importantly, the
results of this screen extended to human brain cancer stem cells the observa-
tion that mouse neurospheres are sensitive to modulation of neurotransmitter
pathways, and future more in depth studies will have to determine whether the
drugs found in the screen that modulate the serotonin pathway of the adherent
GNS cell lines, can limit growth of xenograft tumours in vivo [404].
In their paper, Pollard et al [404] have tackled two critical issues of the brain
cancer stem cell hypothesis:
1. How to maintain and expand pure populations of cancer stem cells in
vitro by expanding them as cell lines using the adherent culture methods
previously established for fetal and human NS cells [107,481]. Specifi-
cally, Pollard et al have demonstrated that suspension culture is not a
requirement for successful long-term propagation of tumour-derived stem
cells, and that expansion in adherent conditions overcomes the limita-
tions of the neurosphere culture paradigm, such as increased levels of
differentiation and apoptosis.
2. Elucidation of the phenotypic similarities between GNS cells and the en-
dogenous progenitors within the developing and adult nervous system,
e.g. NEP cells, radial glia, glial progenitors, oligodendrocyte progeni-
tor cells, and SVZ astrocytes. For example, G144 cells strongly express
markers of the oligodendrocyte precursor cell lineage and are biased to-
ward oligodendrocyte differentiation, while G179 cells appear to be more
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