Biomedical Engineering Reference
In-Depth Information
this point. To elucidate the issues that remain, technically challenging mouse
models need to be developed that allow for the specific killing or impairment of
the proposed colon-cancer stem cells in a given tumor.
5 In Vitro Expansion of Colon-Cancer Stem Cells
To facilitate research on stem cells and recently on cancer stem cells, special cell
culture methods have been developed. For colon-cancer stem cells, cells with an
immature phenotype from a dissociated CRC are commonly cultured in spe-
cialized medium containing high amounts of growth factors such as endothelial
growth factor (EGF) and basic fibroblast growth factor (bFGF) in the absence
of serum. Moreover the cells are cultured in special treated plastics that do not
allow for adhesion of the cells. In the resulting cultures the cells grow as spheres
in suspension (Fig 2). The cells in these cultures express high amounts of the
colon-cancer stem cell markers (including CD133 and CD44) and do not
express differentiation-associated proteins (CK-20 and CDX2). As previously
found in glioblastomas (Singh et al., 2004), it has been established that these
culture techniques enrich for the cancer stem cells present in the primary
malignancy (Vermeulen et al., submitted).
Fig. 2 (a) A typical spheroid in a colon-cancer stem cell culture. Spheroids are cultured in
specially prepared cell culture flasks that do not allow the cells to adhere. High levels of bFGF
and EGF are present in the culture medium. (b) Differentiated colon-cancer spheroid culture.
Here cancer stem cell medium is removed and replaced by serum-containing medium. More-
over the cells are transferred to culture-treated plastics that do allow the cells to adhere. Cells
lose the expression of stem cell marker CD133 and gain expression of cytokeratin-20. (c)
Depicted is a spheroid that was transferred into matrigel and overlaid with serum-containing
medium. The colon-cancer stem cells differentiate and start forming tubular structures
Interestingly these cancer stem cell cultures can be differentiated in vitro
when subjected to differentiation-inducing conditions. For colon-cancer stem
cells this is achieved by allowing them to adhere to tissue culture-treated plastics
and providing them with fetal calf serum-containing medium. Moreover
