ABCB1 and colon adenocarcinoma: , Caco-2 cell (human colon adenocarcinoma cell line) and Madin-Darby canine kidney epithelial cells transfected with the human MDR1 gene (MDCK-MDR1), have been well developed for permeability and absorption screening, of which Caco-2 cell monolayer model has been widely adopted as a preferable tool [43].