Stem Cell Markers in Epithelial Cancers

Most of the literature, and the better experiments and models derived therefrom, comes from liquid neoplasms, i.e. haematological cancers (Nguyen et al. 2012; Antoniou et al. 2013). Much effort has gone into defining the wider characteristics of, and defining markers for, stem cells in solid cancers in recent years, and panels are available from several commercial companies. As can be seen from Table 1.2, the functions ascribed are diverse and non-specific. Such markers are widely used in

Table 1.2 Solid “tumour’ cancer stem cell markers

• ABCG5: ATP binding cassette family member; transport of sterol and other lipids. Confers doxorubicin resistance

• CD90 (Thy1): Signal transduction, possible role in stem cell differentiation

• ALDH1: Aldehyde dehydrogenase (ALDH) family. Role in the conversion of retinol to retinoic acid, an important pathway for proliferation, differentiation and survival

• CD133 (Promininl): Transmembrane protein. Expressed on developing epithelia

• CD24 (HSA): Co-stimulatory role in B and T cells. Only known ligand for P-selectin. Low levels can characterize breast tumour-initiating cells. Potential cancer stem cells reported to be CD24+/CD44+

• EpCAM (epithelial cell adhesion molecule, ESA, TROP1):

Homophilic Calcium ion-independent cell adhesion molecule

• CD44 (PGP1): Multiple isoform adhesion molecule, roles in signaling, migration, and homing. CD44H, high affinity for hyaluronate; CD44V confers metastatic potential

• Hoechst SP (side population): Hoechst 33342 efflux pump present on the plasma membrane of many cell types. Activity conferred by the ABC transporter ABCG2. Inhibited by verapamil

Adapted from http://www.promab.com/services/cancer-stem-cell/ identification-platform

The stochastic model of cancer stem cells compared with the “traditional” model

Fig. 1.6 The stochastic model of cancer stem cells compared with the “traditional” model. From Antoniou et al. (2013). Reprinted by permission of Taylor & Francis, LLC research using cell lines, including HNSCC described earlier by us and others (Qiao et al. 2011; Shah et al. 2014), so we must remind ourselves how artificial such systems are and not over-interpret such studies. Several of these markers e.g. CD 40, CD 93, CD 140 and aldehyde dehydrogenase (ADH) have also been used in immunohistological staining to demonstrate “cancer stem cells” in hepatocellular carcinomas (Lingala et al. 2010).

 
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