Highly enriched CD133⁺CD44⁺ stem-like cells with CD133⁺CD44^high metastatic subset in HCT116 colon cancer cells

Stem-like cancer cells (SLCCs) are distinct cellular subpopulation in colon cancer that is essential for tumor maintenance. Previous studies indicated that SLCCs accounted for only a minor subset in a given cancer model. However, we found that SLCCs frequency varied among a panel of colon cancer cell lines, with HCT116 cells composed mainly of SLCCs, as demonstrated by colonosphere forming capability and CD133 expression. Indeed, flow cytometric analysis revealed more than 60% HCT116 cells co-expressed the putative SLCCs markers CD133 and CD44. Compared with non-CD133⁺CD44⁺ cells, FACS sorted CD133⁺CD44⁺ cells were undifferentiated, endowed with extensive self-renewal and epithelial lineage differentiation capacity in vitro. CD133⁺CD44⁺ exhibited enhanced tumorigeneicity in NOD/SCID mice. One thousand CD133⁺CD44⁺ cells initiated xenograft tumors efficiently (3/6) while 1 × 10⁵ non-CD133⁺CD44⁺ cells could only form palpable nodule with much slower growth rate (1/6). More interestingly, long-term cultured self-renewing CD133⁺CD44⁺ cells enriched CD133⁺CD44^high subset, which expressed epithelial to mesenchymal transition marker, were more invasive in vitro and responsible solely for liver metastasis in vivo. In conclusion, these data demonstrated for the first time that CD133⁺CD44⁺ SLCCs were highly enriched in HCT116 cells and that metastatic SLCCs resided exclusively in a CD133⁺CD44^high subpopulation.