Colorectal cancer stem cells: Characterization and functional analysis.

4124 Background: Cancer stem cells are defined as cells within a tumour that are able to self-renew and differentiate into all cell lineages within that tumour. With our extensive panel of colorectal cell lines, our aims are: 1) To characterise and isolate cancer stem cells based on stem cell markers, morphological appearances and the ability to form multiple lineages; 2) To understand how cancer stem cells drive tumour growth and progression. METHODS: 1) Fluorescent Activated Cell Sorting (FACS); 2) In vitro soft agar clonogenic and Matrigel differentiation assays; 3) In vivo tumourigenic NOD/SCID mice assay; 4) Confocal immunofluorescence imaging. RESULTS: 1) A subpopulation of cells can differentiate into crypt-like megacolonies, retaining the ability to self-renew and differentiate. SW1222 cell line forms heterogeneous colonies when single cells are plated in Matrigel. Megacolonies can both self-renew and form terminally differentiated small colonies, whereas small colonies cannot form megacolonies. Megacolonies develop crypt-like structures and increase their expression of differentiation markers (CDX-1, CK-20) over time. Experiments are currently under way to confirm that cells from megacolonies are able to initiate tumours in NOD/SCID mice. Some cell lines retain the ability to differentiate into both neuroendocrine and epithelial lineages. 2) CD44+CD24+ enriches for the cancer stem cell population. Colorectal cancer cell lines HCT116, HT29, LS180, LS174T and SW1222 express both CD44 and CD24. The CD44+CD24+ subpopulation is the most clonogenic. In SW1222, CD44+CD24+ cells enrich for megacolonies and can reform all four CD44/CD24 subpopulations. 3) Hypoxia reduces differentiation, increases stem-like phenotype and enhances clonogenicity. Hypoxia increases the proportion of undifferentiated colorectal cancer cells when plated on Matrigel and increases clonogenicity. CONCLUSIONS: 1) Colorectal cancer cell lines contain subpopulations of cells that have the ability to self-renew, differentiate and drive tumour growth, and may be characterised by their cell surface markers and colony morphology. 2) CD44+CD24+ can be used as markers for colorectal cancer stem cells. 3) Hypoxia increases the stem-like phenotype of cancer cells, reduces differentiation and increases clonogenicity. No significant financial relationships to disclose.