ABCB1 and malignant colon neoplasm: In our previous reports, a direct connection between ER stress and inhibition of ABCB1 activity has already been demonstrated [30], therefore, we hypothesized that androstano-arylpyrimidine 17-acetates might induce endoplasmic reticulum stress in multidrug-resistant Colo 320 colon cancer cells as well, ultimately leading to a decreased efflux function.