Wnt/β-catenin Signaling Inhibitors Suppress the Tumor-initiating Properties of a CD44CD133 Subpopulation of Caco-2 Cells

Tumor-initiating cells or cancer stem cells are a subset of cancer cells that have tumorigenic potential in human cancer. Although several markers have been proposed to distinguish tumor-initiating cells from colorectal cancer cells, little is known about how this subpopulation contributes to tumorigenesis. Here, we characterized a tumor-initiating cell subpopulation from Caco-2 colorectal cancer cells. Based on the findings that Caco-2 cell subpopulations express different cell surface markers, we were able to discriminate three main fractions, CD44CD133, CD44CD133, and CD44CD133 subsets, and characterized their biochemical and tumorigenic properties. Our results show that CD44CD133 cells possessed an unusual capacity to proliferate and could form tumors when transplanted into NSG mice. Additionally, primary tumors grown from CD44CD133 Caco-2 cells contained mixed populations of CD44CD133 and non-CD44CD133 Caco-2 cells, indicating that the full phenotypic heterogeneity of the parental Caco-2 cells was re-created. Notably, only the CD44CD133 subset of Caco-2-derived primary tumors had tumorigenic potential in NSG mice, and the tumor growth of CD44CD133 cells was faster in secondary xenografts than in primary transplants. Gene expression analysis revealed that the Wnt/β-catenin pathway was over-activated in CD44CD133 cells, and the growth and tumorigenic potential of this subpopulation were significantly suppressed by small-molecule Wnt/β-catenin signaling inhibitors. Our findings suggest that the CD44CD133 subpopulation from Caco-2 cells was highly enriched in tumorigenic cells and will be useful for investigating the mechanisms leading to human colorectal cancer development.