Relapse and metastasis are frequent in colon cancer and may be linked to stem cell characteristics.This study isolated side population(SP) cells from a colon cancer cell line(Colo-320) and examined ...their self-renewal and differentiation abilities.Compared to non-SP(NSP) cells,SP colon cancer cells were more tumorigenic in vivo and exhibited more invasive characteristics and a greater ability to form colonies.Additionally,more cells were in G0/G1 phase and more highly expressed the multidrug resistance protein BCRP/ABCG2.We achieved enhanced chemotherapy sensitivity by transfecting SP cells with a hairpin-like,small interfering RNA(si RNA) eukaryotic expression plasmid targeting BCRP/ABCG2.