Identification and characterization of colon cancer stem cells in HT-29 adenocarcinoma cell line

Cancer stem cells are subpopulation of cancer cells that show self-renewal potential and the capacity to differentiate into diverse populations comprising a tumor. One of the characteristics of CSCs is their ability to form floating spheroids under anchorage-independent conditions in a serum-free media. The aim of this study was isolation of colon cancer stem cells by sphere formation assay and characterization of them in human colonic adenocarcinoma HT-29. In this experimental study, colon CSCs markers including CD44 and EPCAM in spheroid and HT-29 cells were analyzed by flow cytometry. The expression levels of stemness genes in both spheroid and HT-29 cells were investigated using real-time PCR. Tumorigenic potential of spheroid cells was evaluated using in vivo xenografts assay. Our data showed over 92% of spheroids were CD44+/EpCAM+, while HT-29 cells only have expressed 37% of CD44/EpCAM markers. In compared with the HT-29 cells, expression levels of ‘‘stemness’’ genes, like Sox2, Oct4, Nanog, C-myc, and Klf4 were significantly increased in spheroid cells (p< 0.05). Further, As little as 2500 spheroid cells were sufficient to obtain tumor growth in nude mice, while 1x106 of HT-29 cells was needed to form tumor. Our data suggest that spheroid formed by colon cancer cell lines highly enriched in CSCs and showed increasing expression of stemness genes and tumorigenic in nude mice.