Cultivation and identification of human colon cancer stem cell-like cells and antiproliferative effects of n-3 polyunsaturated fatty acids

AIM: To cultivate stem-like spheres from SW620 cell line in the specific serum-free medium and evaluate the features of the cancer stem cells, and to investigate the effects of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on the growth of SW620 stem cell-like cells. METHODS: Human colon cancer stem cell-like cells (CSCLC) were obtained from SW620 spheres cultured in serum-free medium. These cells were tested for the expression of SSEA-1 and TRA-1-81 by immunofluorescence staining. The mRNA expression of Sox-2 and Oct-4 was detected by real-time PCR. The efficiency of colony formation on a soft agar gel and tumor formation in the nude mice was compared between SW620 adherent cells and CSCLC. The inhibitory effects of 5-fluorouracil (5-FU) and mitomycin C on both types of cells were measured by MTS assay. MTS assay, Annexin V/PI staining and trypan blue staining were used to determine the effects of DHA and EPA on both types of cells. MTS assay was also used to analyze the combined effect of DHA or EPA with chemotherapeutic drugs on SW620 CSCLC. RESULTS: SW620 cells formed spheres in serum-free culture. The cells from spheres highly expressed SSEA-1 and TRA-1-81, transiently expressed Sox-2 and Oct-4genes and were more resistant to 5-FU and mitomycin C treatments. These cells exhibited a greater ability in clone formation and tumorigenicity, indicating that these cells carried stem cell-like features, hence were considered SW620-derived CSCLC. DHA and/or EPA suppressed SW620 CSCLC by inhibiting cell growth, inducing cell apoptosis and sensitizing them to chemotherapeutic drugs. CONCLUSION: The cells with stem cell-like features, such as high efficiency in clonogenicity, tumorigenicity and resistance to chemotherapeutic drugs, can be obtained from SW620 spheres cultured in serum-free condition. DHA and EPA induce apoptosis in SW620-derived CSCLC and sensitize them to chemotherapeutic drugs.