Feline mammary carcinoma stem cells are tumorigenic, radioresistant, chemoresistant and defective in activation of the ATM/p53 DNA damage pathway.

Cancer stem cells were identified in a feline mammary carcinoma cell line by demonstrating expression of CD133 and utilising the tumour sphere assay. A population of cells was identified that had an invasive, mesenchymal phenotype, expressed markers of pluripotency and enhanced tumour formation in the NOD-SCID mouse and chick embryo models. This population of feline mammary carcinoma stem cells was resistant to chemotherapy and radiation, possibly due to aberrant activation of the ATM/p53 DNA damage pathway. Epithelial-mesenchymal transition was a feature of the invasive phenotype. These data demonstrate that cancer stem cells are a feature of mammary cancer in cats.

Flow cytometric techniques for detection of candidate cancer stem cell subpopulations in canine tumour models.

The cancer stem cell (CSC) hypothesis proposes that tumour growth is maintained by a distinct subpopulation of 'CSC'. This study applied flow cytometric methods, reported to detect CSC in both primary and cultured cancer cells of other species, to identify candidate canine subpopulations. Cell lines representing diverse canine malignancies, and cells derived from spontaneous canine tumours, were evaluated for expression of stem cell-associated surface markers (CD34, CD44, CD117 and CD133) and functional properties [Hoecsht 33342 efflux, aldehyde dehydrogenase (ALDH) activity]. No discrete marker-defined subsets were identified within established cell lines; cells derived directly from spontaneous tumours demonstrated more heterogeneity, although this diminished upon in vitro culture. Functional assays produced variable results, suggesting context-dependency. Flow cytometric methods may be adopted to identify putative canine CSC. Whilst cell lines are valuable in assay development, primary cells may provide a more rewarding model for studying tumour heterogeneity in the context of CSC. However, it will be essential to fully characterize any candidate subpopulations to ensure that they meet CSC criteria.

CD44 is associated with proliferation, rather than a specific cancer stem cell population, in cultured canine cancer cells.

BACKGROUND: The cancer stem cell hypothesis proposes that tumours are maintained by a population of cancer stem cells (CSC), which must be eradicated to prevent disease relapse after treatment. Cells expressing high levels of CD44 have been identified as candidate CSC in a variety of human tumours. This study sought to investigate CD44 expression and its potential as a CSC marker in canine cancer. METHODS: CD44 expression in several canine cancer cell lines was determined by flow cytometry. Cells with low and high levels of CD44 expression were examined for differences in growth characteristics, colony forming ability, drug sensitivity and cell cycle profile. RESULTS: CD44(High) cells demonstrated enhanced growth and colony forming capacity, under both adherent and low-density serum free ("tumoursphere") conditions. However, no difference in sensitivity to doxorubicin was seen between the two populations. Moreover, whilst most CD44(Low) cells were in resting or G1 growth phase, an increased proportion of CD44(High) cells were in G2M phase of the cell cycle. Upon proliferation in culture, both populations gave rise to progeny with a full spectrum of CD44 expression. CONCLUSION: CD44 expression is associated with proliferation in cultured canine cancer cells, but transient and fluctuating expression may limit its utility as a CSC marker.