To further investigate if PZ-34 and PZ-38 can reverse ABCG2-mediated MDR in a drug resistant cancer cell line, we used the drug-selected breast cancer cell line MCF7/AdVp3000 which over-expresses ABCG2 and tested an additional anticancer drug substrate of ABCG2, Adriamycin. This evidence concerns the gene ABCG2 and breast cancer.