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sensors ) and it should have a high-throughput potential. of the matrix should be adjusted to those in the location of
[54]
growth and metastatic dissemination of the tumor under
To understand the causes and consequences during investigation. In this context, Fernandez-Fuente et al.
[60]
pathophysiological progression from a primary neoplastic investigated the impact of different environmental conditions
lesion in the brain towards a metastatic cancer and to pre- on glioblastoma stem cells (GSCs). They found that GSCs
clinically test potential intervention strategies, we thus
require model systems that mimic not only the proteomic grown in collagen-based 3D conditions were markedly less
heterogeneity of the tumor cell itself but also the reciprocal susceptible to receptor tyrosine kinase inhibition by currently
interactions between the tumor and the receiving brain available inhibitors, suggesting that oncogene addiction of
tissue [Figure 2]. The following paragraph provides an tumor cells could also be bypassed by adhesion signaling. [61]
overview over some recent approaches in primary brain Interestingly, matrix stiffness or the addition of hyaluronic
tumor research. It highlights the difficulty to design an acid (HA) did not affect the sensitivity of the GSCs in this
optimal, tumor-adapted system and emphasizes the need to study. Primary cells from glioma patient tumor material
further improve currently used systems. exposed to increasing concentrations of HA responded with
rounded morphology and reduced migration, suggesting
2D and 3D model systems in primary brain that HA concentrations may affect glioma cell behavior.
[62]
tumor research Consistently, addition of HA to porous chitosan scaffolds [63] or
A number of articles have been published in the last few years to artificial hydrogels increased the expression of stem cell
[64]
that used in vitro model systems to evaluate effects of novel markers and VEGF and HIF-1, respectively. However, the
potential treatment strategies on growth, viability or motile finding that increasing matrix stiffness - by adding agarose to
behavior of primary brain tumors [Table 1]. A general consensus a collagen I matrix - blocks glioma invasiveness, suggested
[19]
has been reached in that 3D cell culture model systems reflect that stiffness alone and independent of ligand binding acted
the specifics of the in vivo situation better compared to 2D as a critical determinant for primary brain tumor cell function.
model systems. On the down side of this was the lack of An improved in vitro environment for brain tumor research
high-throughput capability of 3D methods that hampered would consist of neuronal and brain-resident interstitial
until a few years ago their broader use in combination with cells that secrete the brain-specific ECM components into
in screening approaches. A milestone in this context was the which the brain tumor cells can then be implanted. Such
generation of spheroid cultures in 96 or even 384 well format an environment was established from brain tissue extracts
from primary brain tumors that allowed the parallel testing or on micro filters (Hi-spots) on which GBM cell sensitivity
large sample sizes. [54-56] In these studies, diagnostic dyes and to anti-proliferative compounds was tested. [65] Despite its
fluorescent proteins were used individually or in combination high-throughput potential, a setback of this method is the
for probing cellular functions on the one hand and for lack of control over the cellular composition in the Hi-spots
discriminating specific cell populations on the other hand. A and the absence of brain-specific architectural organization.
general protocol describing the reproducible establishment A while ago, a simple but intriguing co-culture model of
and microscopy-based analysis of spheroid cultures using medulloblastoma and leptomeningeal cells was published,
fluorescent protein quantification in high throughput was and it indicated paracrine, growth-promoting effects of
described recently. As an alternative to fluorometric read- latter that might be instrumental for studying the notoriously
[57]
outs, electrochemical impedance spectroscopy was used to difficult to grow primary tumor cells in vitro. The ideal
[66]
quantify different susceptibilities of 2D versus 3D spheroid “organotypic environment” for primary brain tumor research
culture of glioblastoma and neuroblastoma cell lines to was already in development in the early seventies of the last
cytotoxic compounds and to determine the therapeutic century, when the organotypic brain slice culture (OBSC)
[58]
window of these compounds. Using different combination of technology was established. The advantages of OBSCs are
[67]
dyes to separate subpopulation of cells grown in co-culture that micro environmental parameters and a relatively correct
combined with diagnostic flow cytometry and two-photon architectural organization are maintained that mimic the in
microscopy allowed to further refine the selective output of vivo situation (see below).
3D methods. However, high-throughput capabilities and
[54]
accuracy of a selected read-out has to be carefully balanced Increasing complexity: system impact and single
and discriminating phenotypic differences at single cell cell behavior
level in 3D cultures in high throughput remains a formidable Neither are tumor functions disconnected from other tissues
challenge. and the organs nor can the impact of tissues or organs on drug
efficacy in the targeted tumor be predicted. An interesting
The impact of the embedding matrix on the approach to evaluate the effect of metabolic activity on
behavior of the tumor cell cytotoxicity of compounds and chemotherapeutics in vitro
The choice of the embedding matrix is of outmost was tested by Ma and colleagues using a 3D micro-tissue
importance for 3D cultures, in particularly for primary brain perfusion system. TMZ and IFO were perfused through
[68]
tumors that encounter in vivo mostly brain parenchyma and hepatocytes before exposure to GBM cells and a clear
collagen-rich surfaces and structures in the subarachnoid impact of hepatocyte-provided cytochrome P450 on IFO
space. [23,24,59] Hence, the biophysical and chemical properties activation could be shown. Analogous experimental follow-

Journal of Cancer Metastasis and Treatment ¦ Volume 2 ¦ May 18, 2016 ¦ 157