In a xenograft tumor mouse model, we discovered that the mixture of C2 and L-OHP reversed the resistance of HCT116/L-OHP cells to L-OHP and inhibited tumor growth; furthermore, C2 down-regulated the gene expression levels of <i>P-gp</i> and <i>BCRP</i> and decreased <i>P-gp's</i> drug efflux activity. This evidence concerns the gene ABCG2 and neoplasm.