Aldehyde dehydrogenase 1 positive glioblastoma cells show brain tumor stem cell capacity
Michael Rasper
0
1
2
3
4
Andrea Scha fer
0
1
2
3
4
Guido Piontek
0
1
2
3
4
Julian Teufel
0
1
2
3
4
Gero Brockhoff
0
1
2
3
4
Florian Ringel
0
1
2
3
4
Stefan Heindl
0
1
2
3
4
Claus Zimmer
0
1
2
3
4
Ju rgen Schlegel
()
0
1
2
3
4
0
Obstetrics, Caritas Hospital St Josef, University of Regensburg
, Regensburg,
Germany
(G.B.);
Department
1
Center for Environmental Health (GmbH)
, Neuherberg,
Germany
(J.S.);
Department of Gynaecology
2
Division of Neuropathology, Institute of Pathology, Technische Universita t Mu nchen
, Mu nchen,
Germany
3
Department of Neuroradiology
, Klinikum rechts der Isar,
Technische Universita t Mu nchen
, Mu nchen
4
of Neurosurgery
, Klinikum rechts der Isar,
Technische Universita t Mu nchen
, Mu nchen,
Germany
(F.R.)
-
Glioblastoma (GBM) is the most aggressive primary
brain tumor and is resistant to all therapeutic regimens.
Relapse occurs regularly and might be caused by a
poorly characterized tumor stem cell (TSC)
subpopulation escaping therapy. We suggest aldehyde
dehydrogenase 1 (ALDH1) as a novel stem cell marker in
human GBM. Using the neurosphere formation assay
as a functional method to identify brain TSCs, we
show that high protein levels of ALDH1 facilitate
neurosphere formation in established GBM cell lines. Even
single ALDH1 positive cells give rise to colonies and
neurospheres. Consequently, the inhibition of ALDH1
in vitro decreases both the number of neurospheres
and their size. Cell lines without expression of ALDH1
do not form tumor spheroids under the same culturing
conditions. High levels of ALDH1 seem to keep tumor
cells in an undifferentiated, stem cell-like state indicated
by the low expression of beta-III-tubulin. In contrast,
ALDH1 inhibition induces premature cellular
differentiation and reduces clonogenic capacity. Primary cell
cultures obtained from fresh tumor samples approve
the established GBM cell line results.
Glioblastoma (GBM) is the most common primary
brain tumor in adults with a medium survival of
approximately 15 months.1 Despite various efforts to improve the
postoperative therapeutic regimen within the last years,
the prognosis of this highly aggressive tumor has remained
poor. Relapse occurs regularly after resection, irradiation,
and chemotherapy. This could in part be due to the
existence of so-called tumor stem cells (TSCs), a cellular
subfraction within GBM contributing to recurrent tumor
growth and resistance to drugs and irradiation. Within
the last decade, TSCs have been identified and isolated in
a variety of hematologic and solid neoplasms. The
characterization of these cells seems to be crucial for a better
understanding of tumor biology and for the development
of more efficient antitumor therapies.
Owing to the TSC paradigm, hematologic and solid
tumors consist of hierarchically ordered cellular
subdivisions. TSCs are believed to harbor the ability to keep a
tumor alive and growing: pluripotency, self-renewal,
and resistance to chemo- and irradiation therapy. This
concept arose from the notion that a subpopulation of
cancer cells shows similarity to normal stem cells.2
Leukemias were the first malignancies from which cells
could be isolated that showed the potential to self-renew
and to drive tumor formation and growth.3
A stem cell subfraction has been described in brain
tumors and especially in high-grade astrocytomas.
Singh et al.4 were the first to identify and purify, a
population with stem cell properties in pediatric solid brain
tumors. Those cells were identified by their ability to
form spheroids (neurospheres) when grown under
serum-free cell culture conditions and by the expression
of CD133 and nestin. CD133 (also known as
prominin-1), a 120-kDa pentaspan transmembrane
glycoprotein, has been found to be a marker of stemness in
hematopoietic5 and neural cells.6 Together with nestin,
an intermediate filament protein expressed by
undifferentiated neuroepithelial cells7 and tumors of the CNS,8
CD133 has long remained the most important TSC
marker in malignant glioma.
Aldehyde dehydrogenase 1 (ALDH1) is a
cytoplasmatic stem cell marker in a variety of malignant tumors.
As a member of the ALDH enzyme family, ALDH1
catalyzes the oxidation of intracellular aldehydes including the
transformation of retinol to retinoic acid (RA). RA is a
modulator of cell proliferation and differentiation that
possibly contributes to the maintenance of an
undifferentiated stem cell phenotype. Jones et al.9 presented a
method to isolate human cells via flow cytometry
depending on the amount of cytosolic ALDH. They were able to
enrich human hematopoietic precursor cells capable
of reconstituting bone marrow in irradiated animals.
Recently, Ginestier et al.10 found ALDH1 to be a stem
cell marker in breast carcinoma associated with poor
clinical outcome. Since then ALDH1 has been described
as a marker of stemness in other solid malignancies
including lung cancer11 and colorectal cancer.12
Here, we show that ALDH1 overexpression
correlates with stem c (...truncated)