ABCB1 and breast cancer: Previously, we tested acetylated (10) and deacetylated pairs (11) of androstano-arylpyrimidines and showed that androstano-arylpyrimidine 17-acetates exhibited a remarkable potential to inhibit ABCB1 activity and sensitize multidrug-resistant MCF-7/KCR breast cancer cells to Doxorubicin-induced cell death [25].