Considering the need to explore the new inhibitors and due to the insufficient data regarding the potential of ISO to prevent or reverse cancer cell resistance, this study aims to investigate the effects of ISO on membrane transporters (P-gp, BCRP, MRP 1, 2, and 5), the expression on a transcriptional level, and the protein expression of P-gp in DLD1 and HCT-116 colorectal cancer cells. The gene discussed is ABCG2; the disease is cancer.