Poziotinib (0.6 μM) and Ko143 (0.6 μM), an ABCG2 inhibitor, significantly increased the intracellular accumulation of [3H]-mitoxantrone, a substrate for the ABCG2 transporter [47], in the S1-M1-80 colon cancer cells but did not significantly affect accumulation on the S1 parental cells. This evidence concerns the gene ABCG2 and malignant colon neoplasm.