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ups are a number of organ on a chip technologies that are localize within specific regions of the brain, highlighting
currently developed for assaying different disease states [69] the need for different microenvironments for modeling
and testing drug effects and metabolization. [70] tumor growth and invasiveness. To circumvent this, mouse
models have been generated for studying tumor propagation
On the opposite side of the spectrum is the need to resolve via orthotopic or subcutaneous xenografting of tumor cells.
the mechanisms underlying brain infiltration of single These experiments, however, are ethically controversial if
tumor cells, which necessitates approaches allowing the inappropriately conducted, costly, labor intensive and need
quantitative analysis of molecular events in individual lengthy time periods for animal surgery and subsequent
cells. This problem was tackled for the activation status of tumor development (especially for low grade tumors). These
the important Rho family GTPase’s - Rho, Rac and Cdc42 challenges and limitations highlight the need for developing
- in glioma cells. Hirata et al. used Rho-GTPase- a novel system wherein living brain tissue can be used as an
[53]
[53]
FRET (Förster energy resonance transfer) probes, where ideal matrix for studying tumor cell growth and invasion.
[72]
spatial activation of the GTPase’s was monitored by a One such system is the organotypic culture, where cellular
shift in fluorescence signal. Rho-family GTPase-FRET constituents of organs or parts of organs are allowed to
fusion protein-expressing glioma cells were orthotopically regrow into or persist as organ replacements.
implanted in rat brains and later analyzed inside brain
slice cultures derived of these brains using two-photo An excellent overview of 3D organotypic cultures has
microscopy. This study revealed higher Rac1 and Cdc42 and recently been provided, which describes their potentials
[73]
lower RhoA activities in glioblastoma cells penetrating the as experimental systems to visualize cellular mechanisms
brain parenchyma than those advancing in the perivascular that drive tissue development, to study the genetic
regions, and suggested that different driver mechanisms regulation of cell behaviors in tissues and to evaluate the
could exist for single cell dispersion in glioma. role of micro environmental factors in normal development
and disease. One hallmark of organotypic cultures is the
Together, these studies highlight the need for adapting the tissue environment mimicking the structural and functional
model system to the specifics of the biological context, specifics of the organ of origin. This turns them into
with the consequent inclusion of biophysical or chemical attractive models for cancer research to explore tumor host
components that best reflect the in vivo situation. Besides tissue interactions and to advance therapeutic approaches.
high-throughput screening platforms for the identification of
novel pro-metastatic key players or alternative interference Organotypic brain slice culture for visualization
strategies against metastatic dissemination, we also need and quantification of brain tumor cell
improved phenotype-based single cell analysis to decipher dissemination
clonal differences and micro environmental impact on OBSCs allow culture, maintenance and long-term survival
tumor behavior at the single cell level. of sections from any tissue of the CNS. Slices are mostly
cultured at an air/liquid interface by either continuous
Organotypic brain slice culture (OBSC) in rotation using the roller tube method or on a semi porous
primary brain tumor research membrane using the Stoppini method. Brain tissue slice
[74]
A number of causal gene(s) and associated genetic mutations, cultures maintain their normal cytoarchitecture, complex
molecular changes, probable targets and treatments for cell relationships and biochemical and electrophysiological
a variety of primary brain tumors have been identified. properties. OBSCs have been widely used in the field of
Despite of this, the process of dissemination, metastasis of neurobiology for synaptogenesis, neurogenesis, myelin
the tumor cells from the primary site, and tumor recurrence, formation, as models for studying neurodegeneration, for
which is the leading cause for brain tumor related mortality neuroprotective and neurotoxic assays, etc. [67] In the field of
in patients, remain obscure. Total removal of the primary brain tumor research, they are an ideal platform to access the
tumor is on many occasions impossible at the microscopic tumor microenvironment under intact anatomical conditions.
level due to the insidious infiltration of the tumor cells Indeed, Jung et al. [71] established a brain tumor slice model
into the surrounding brain tissue. This majorly results in wherein they used human white matter specimens in the
[71]
therapeutic failure and urges for model systems that allow upper chambers of transwell culture dishes. After 24 h,
addressing brain tumor cell invasion specifically. Standard control human astrocytoma cells stably expressing enhanced
3D in vitro invasion assays use ECM macromolecules that GFP or GFP-RHAMM (receptor for hyaluronan-mediated
mimic the basement membrane (e.g. matrigel) as barriers to motility) transfected astrocytoma cells were placed in a
tumor invasion. These assays (described above and in table small centrally punched-out hole in the slice. The infiltration
1) although quick, reliable, commercially available and easy and migratory behavior of the GFP-expressing astrocytoma
to perform, have several limitations. They do not take into cells could be easily studied using confocal laser scanning
account the unique ECM composition in the brain and thus microscopy (CF-LSM) up to 30 days post implantation. The
provide artificial environments that fail to closely mimic authors were able to demonstrate that different astrocytoma
the normal brain tissue/tumor environment. This is further cell lines display different degrees of invasion and that
emphasized by the fact that distinct types of brain tumors the migration of the human astrocytoma cells could be

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