Multidrug resistance protein 1 (MDR1) is a member of the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, and White). MDR1 is a member of the MDR/TAP subfamily. Members of the MDR/TAP subfamily are involved in multidrug resistance. MDR1 is an ATP-dependent drug efflux pump for xenobiotic compounds with broad substrate specificity. It is responsible for decreased drug accumulation in multidrug-resistant cells and often mediates the development of resistance to anticancer drugs. MDR1 also functions as a transporter in the blood-brain barrier [taken from NCBI Entrez Gene (Gene ID: 5243)].