Multidrug resistance protein 1 (MDR) is a membrane-associated protein belonging to the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across e, Xenopus/Amphibian,tra- and intra-cellular membranes. MDR is a member of the MDR/TAP subfamily. Members of the MDR/TAP subfamily are involved in multidrug resistance. MDR is responsible for decreased drug accumulation in multidrug-resistant cells and often mediates the development of resistance to anticancer drugs. MDR also functions as a transporter in the blood-brain barrier.