P-gp

P-glycoprotein (P-gp) inhibitors block a drug efflux pump that contributes to multidrug resistance in cells. P-gp, also called multidrug resistance protein 1 (MDR1) or ATP-binding cassette subfamily B member 1 (ABCB1), uses energy from adenosine triphosphate (ATP) hydrolysis. It was first described in 1976 as a surface glycoprotein of drug-resistant Chinese hamster ovary cells. A crystal structure later showed a large drug-binding pocket that accounts for its broad substrate range. Verapamil and its metabolite norverapamil hydrochloride are early inhibitors, and verapamil is also listed under Calcium Channels. Later inhibitors include valspodar, tariquidar, LY335979 and elacridar, which also blocks breast cancer resistance protein (BCRP).