Biomedical Engineering Reference
In-Depth Information
example, in neural cells it was found that a population of undifferentiated cells
was maintained by culturing the cells in a non-adherent condition. These
neurospheres are enriched for stem and progenitor cells and contain cells that
are multipotent (Reynolds and Weiss 1996). Using the results obtained with
neural cells, Dontu et al. established that breast CSCs can be enriched by
plating cells in serum-replacement media on ultralow attachment plates
(Dontu et al. 2003a). The enrichment of breast CSCs by culture conditions
favoring SC survival and self-renewal has been used to further characterize
these cells (Dontu et al. 2003b, 2004; Liu et al. 2006). In prostate cancer, it was
demonstrated that purified prostate CSCs also grow as prostataspheres when
maintained in culture (Patrawala et al. 2006; Hurt et al. 2008), however, until
recently this approach was not used as a means to enrich prostate cancer stem
cells for further study.
Recently, this approach was utilized by Li et al. where they were showed that
holoclones generated from the PC3 prostate cancer cell line were enriched for
tumor-initiating cells that could be serially transplanted in NOD/SCIDmice (Li
et al. 2008). The term holoclone has been used in the keratinocyte literature,
where single cell suspensions of keratinocytes give rise to three types of colonies:
the holoclone which is highly enriched for cells that do not differentiate (abort),
the paraclone which can only be maintained for a short number of passages
before it differentiates, and the meroclone which is a mixture of the other two
types of clones (Barrandon and Green 1987). Morphologically the PC3-derived
holoclones are similar to the prostataspheres that were grown from purified
CSCs. The PC3-derived holoclones also expressed high levels of CD44 and
integrin-a2b1, markers that also identify prostatic CSCs. Since this research was
done with a single cell line, further studies need to be conducted to determine if
enrichment of prostatic CSCs can be achieved through this culture system.
3.3 Identification of Prostatic Cancer Stem Cells Through Surface
Markers
One method for the identification of CSCs utilizes cell surface markers as a
means for identification and isolation. Most surface markers used to date have
been selected based on an understanding of where the SCs may be located (basal
cell markers) or from an understanding of the important markers in both
hematopoetic and embryonic SCs.
3.3.1 Normal Prostate Stem Cell Markers
Collins et al. (2001), taking advantage of the known association of SCs with
basement membranes, identified integrin-a2b1 cells in normal prostate that
showed increased colony-forming ability when compared to the total basal
cell population. Further characterization of these cells determined that they
