PGP and colon carcinoma: For large-scale Pgp screening of new chemical entities (NCEs), often BBB surrogate models such as MDR1-transfected MDCKII (Madin-Darby canine kidney strain II) and LLC-PK1 (Lilly Laboratories cells—porcine kidney 1) cells or a human colon carcinoma cell line (Caco-2) are used as general barrier models, because these polarized epithelial cells form tight monolayers resulting in high transepithelial/-endothelial electrical resistance (TEER) and low paracellular permeability, thus enabling to study transcellular Pgp-mediated vectorial drug transport [14–20].