Surface expression marker profile in colon cancer cell lines and sphere-derived cells suggests complexity in CD26(+) cancer stem cells subsets

Taking advantage of eight established cell lines from colorectal cancer patients at different stages of the disease and the fact that all of them could form spheres, cell surface biomarkers of cancer stem cells and epithelial-mesenchymal transition were tested. The aim was to investigate cancer stem cells and metastatic stem cells in order to provide functional characterization of circulating tumor cells and promote the development of new anti-metastatic therapies. Our model showed an important heterogeneity in EpCAM, CD133, CD44, LGR5, CD26 and E-cadherin expression. We showed the presence of a subset of E-cadherin(+) (some cells being E-cadherin(high)) expressing CD26(+) (or CD26(high)) together with the well-known CSC markers LGR5 and EpCAM(high), sometimes in the absence of CD44 or CD133. The already described CD26(+)/E-cadherin(low) or (negative) and CD26(+)/EpCAM(−)/CD133(−) subsets were also present. Cell division drastically affected the expression of all markers, in particular E-cadherin, so new-born cells resembled mesenchymal cells in surface staining. CD26 and/or dipeptidyl peptidase 4 inhibitors have already shown anti-metastatic effects in pre-clinical models, and the existence of these CD26(+) subsets may help further research against cancer metastasis.