ABCG2 and malignant colon neoplasm: This decrease in Pgp and BCRP expression may play a role in the observed increase in doxorubicin accumulation, especially in the parental cells.243 The results suggest that, when blockade of Ref-1/APE1’s redox function blockades HIF signaling, colon cancer cells’ response to doxorubicin may be enhanced.