The tumorigenic, invasive and metastatic potential of epithelial and round subpopulations of the SW480 human colon cancer cell line

It has been reported that the SW480 human colon cancer cell line consists of E-type and R-type cells. The long-term tumorigenic potential, invasive and metastatic properties of these subclones have not been characterized. E-type and R-type cells were subcloned using limiting dilution methods from parental SW480 cells. The cell growth rate was determined by MTT colorimetric assay, and colony forming efficiency was analyzed using Matrigel-coated plates. The activity of matrix metalloproteinase (MMP) and of urokinase plasminogen activator (uPA) was assessed by zymography. Invasive and locomotive ability was analyzed using transwell chambers. In situ apoptosis detection of these subclones was also performed. In vivo long-term tumorigenicity and nodal metastasis were evaluated using nude mice. E-type cells produced spontaneously regressive tumors in spite of invasion and lymph node metastasis. In contrast, R-type cells revealed progressively growing tumors without invasion or metastasis. E-type cells exhibited increased apoptosis and invasive and motile ability, as well as strong MMP-9 and -2 activity. Although phorbol 12-myristate 13-acetate treatment induced MMP-9 activity in E-type cells, it had no effect on R-type cells. These findings suggest that E- and R-type cells may have different biological properties in terms of colon cancer progression, regression, invasion and nodal metastasis, and might serve as a useful model for these studies.