ATP-binding cassette (ABC) transporters are a family of transmembrane proteins that utilize ATP hydrolysis for translocation of substrates across membranes. Importantly, ABC transporters are known to play a crucial role in the development of multidrug resistance. Evaluation of membrane transporter pharmacology in drug absorption, disposition, and drug-drug interactions (DDI) is critical to the pharmaceutical industry's safety evaluation of new drug entities. With this goal in mind, the ABC transporters MDR1 and BCRP were selected for study. Selection was based on the considerable body of evidence supporting their crucial role in the development of multidrug resistance. BCRP and MDR1 were independently evaluated in C2BBe1 intestinal cells, a subclone of the extensively studied Caco-2 cell line. Both transporters are expressed in the luminal membrane and are ATP-dependent efflux pumps. The objective is to generate human knockout cell lines in relevant cell types that will clearly address the contribution of membrane transporters to the efficacy and safety of potential new drug candidates. Toward this end, Sigma Life Science is exploiting the zinc finger nuclease (ZFN) technology to selectively knockout the expression of BCRP and MDR1 individually as well as in combination in C2BBe1 cells for the generation of ADME toxicology cell lines. These transporter knockout cell lines are clinically significant, as they will be employed to identify the specific transporters involved in the clearance or exposure of new compounds. The development of these lines will help overcome the challenges of overlapping substrate and inhibitor specificities across transporters. All three of these cell lines were validated in A-B/B-A drug transporter studies.