ABCB1 and neoplasm: HIF-1 gene silencing improved tumor cell susceptibility in cancer cell lines to chemotherapy agents including doxorubicin [125], cisplatin [126], gemcitabine [127], and 5-fluorouracil (5-FU) [128], and it also reduced the MDR1 gene and its product, which is P-glycoprotein (P-gp).