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stimulated or, using antisense targeting strategies, specifically death or changes in protein expression were successfully
blocked. In an analogous study it was demonstrated that analyzed. Thus, Chadwick et al. used the OBSC system
[79]
[71]
(1) the invasive behavior of the astrocytoma cells in the brain as a qualitative and quantitative assay to calculate the fold
slice co-culture is not always identical to the results obtained change in the number of cells during the period of slice
from 2D migration studies, (2) the tumor cells spread out culture. Furthermore, they investigated either the whole brain
multidirectionally, (3) frozen human normal brain tissue or specific regions within the brain, to assess environmental
can be used for the organotypic culture, (4) there were no impact on primary brain tumor cell growth.
obvious signs of necrosis, and (5) the brain cytoarchitecture
and viability was preserved for at least 14 days. [72] Organotypic brain slice culture to study the
microenvironmental impact
Although the human origin of the biopsies used as the host Malignant astrocytoma/GBM cause mortality by local tumor
tissue in these studies excludes species-specific effects in growth and brain invasion rather than systemic metastasis.
the co-culture, slices from newborn rat or mouse brains are GBM tumor cells diffusely infiltrate the brain parenchyma
excellent alternatives. They offer several advantages: brain within and along the white matter tracts or around cerebral
regions corresponding to the in vivo tumor localization can be blood vessels, and rarely penetrate basal lamina structures
[53]
chosen, developmental stage of the brain slice can be adjusted, at the glial limitans externa. Analogously, malignant
multiple replicas from same brain region can be generated, medulloblastoma must also infiltrate cerebellar tissue for
and the use of transgenic animals allows modification of distal dissemination. Moreover, resection of MB tumors is
the cellular microenvironment. Ohnishi et al. established inevitably followed by relapse if the patients are not treated
[75]
OBSCs from 2-day-old neonatal rat brains, which were with cranio-spinal radiotherapy and chemotherapy, suggesting
transferred on double-layered membranes consisting of two the occurrence of local dissemination of tumor cells from the
different membrane types and maintained at an interface primary medulloblastoma. In vitro studies aiming at better
between the air and the culture medium. The slices were understanding the local invasion process have been hampered
then co-cultured with C6 glioma cells labeled with PKH2 by the lack of identification of the brain ECM macromolecules
fluorescent dye. After 2 days of co-culture, the exogenous involved and the only poorly understood implication of the
application of the chemotactic stimulator neural cell adhesion cellular microenvironment. In vivo approaches on the other
molecule L1 triggered tumor cell migration from the upper to hand, offer too little spatial and temporal resolution to
the bottom membrane through the brain slice. Since this monitor tumor-microenvironment interactions appropriately.
[75]
study lacked CF-LSM analysis, OBSCs were subsequently Thus, OBSCs could provide an important platform to study
performed by the slightly modified Stoppini method, which the cross-talk between the tumor cells and normal cells in
allowed quantifying glioma cell invasion using confocal a physiologically relevant environment. OBSCs can be
microscopy. This study revealed that the migrating cells used for investigating the microenvironment and its impact
[76]
showed a strong increase in immunoreactivity for matrix on the growth and spread of primary brain tumors, and for
metalloproteinase 2 and 9. Analogous OBSC technology testing the measures that could be taken to prevent or treat it
[76]
was later used for mouse brain slices to quantify the effectively. Although, there is a lack of vascular supply to
[79]
invasiveness of glioma [77] and to correlate it with histological the tissue in the slices, capillaries do survive in these sections
type. Both studies used human, DiI-stained glioma biopsy without any circulation. Despite of the fact that there is
[78]
[80]
tumor fragments and GFP-expressing spheroids directly no blood flow and that the capillaries are not functional, it is
implanted in the cortex of brain slices derived from 7 day likely that they are still capable of expressing and secreting
old mice. This intraslice implantation system could be various molecules, [81] which could affect other cell types in
maintained in culture for 2 to 4 weeks. Quantification of the slice culture including the tumor cells. In addition, the
the distance and density of the tumor cell invasion revealed intriguing exchange between tumor cells and astrocytes and
that GBMs were 2-4 times more invasive than the lower the suspected tumor promoting functions of astrocytes [41-43]
grade glioma cells (LGGs). Within the different groups urges for novel studies addressing the therapeutic potential of
and grades of GBMs and LGGs, heterogeneity in terms of the astrocyte-tumor interaction, for which organotypic slice
invasion was seen. It was also observed that the spheroids culture would be an ideal system.
were less invasive in comparison to the directly grafted
fragments. Overall using this system, Palfi et al. [77,78] and de Along with their use for monitoring tumor dissemination,
Bouard et al. could successfully recapitulate, monitor and OBSCs have also been used for high resolution imaging
[77]
quantify the invasion of single cells and the dissemination of cytoskeletal structures in living glioblastoma cells. For
of glioma ex vivo. Recently, Chadwick et al. [79] developed this, glioblastoma cells were transfected with GFP-actin and
OBSCs from postnatal day 6 mice and cultured the whole placed onto murine brain slices and spinal cord explants.
brain slices on membrane inserts coated with laminin. Tumor Using live-cell imaging to visualize the cytoskeleton of the
cells (astrocytoma and medulloblastoma) were stained with tumor cells, a major change in the gross morphology from a
Cm-DiI for monitoring, and dispensed on the center of the solid, two dimensional state to a three dimensional substrate
slice. This co-culture system remained viable for one week was noted. This morphological change was characterized
and effects of drug therapies on tumor cell proliferation, cell by long, dendritic-like processes that displayed regions

Journal of Cancer Metastasis and Treatment ¦ Volume 2 ¦ May 18, 2016 ¦ 159