Multidrug resistance associated proteins as determining factors of pharmacokinetics and pharmacodynamics of drugs.

The multidrug resistance associated proteins (MRP1, MRP2, MRP3, MRP4, MRP5, MRP6, MRP7, MRP8 and MRP9) belong to the ATP-binding cassette superfamily (ABCC family) of transporters. They are expressed differentially in the liver, kidney, intestine, brain and other tissues. These transporters are localized to the apical and/or basolateral membrane of the hepatocytes, enterocytes, renal proximal tubule cells and endothelial cells of the blood-brain barrier. Several MRPs (mainly MRP1-3) are associated with tumor resistance which is often caused by an increased efflux and decreased intracellular accumulation of natural product anticancer drugs and other anticancer agents. MRPs transport a structurally diverse array of important endogenous substances and xenobiotics and their metabolites (in particular conjugates) with different substrate specificity and transport kinetics. Most MRPs are subject to induction and inhibition by a variety of compounds. Several nuclear receptors, including pregnane X receptor (PXR), liver X receptor (LXR), and farnesoid receptor (FXR) participate in the regulation of MRPs. MRPs play an important role in the absorption, distribution and elimination of various drugs in the body and thus may affect their efficacy and toxicity and cause drug-drug interactions. MRPs located in the blood-brain barrier can restrict the penetration of compounds into the central nervous system. Mutation of MRP2 causes Dubin-Johnson syndrome, while mutations in MRP6 are responsible for pseudoxanthoma elasticum. More recently, mutations in mouse Mrp6/Abcc6 gene is associated with dystrophic cardiac calcification (DCC), a disease characterized by hydroxyapatite deposition in necrotic myocytes. A single nucleotide polymorphism, 538G>A in the MRP8/ABCC11 gene, is responsible for determination of earwax type. A better understanding of the function and regulating mechanism of MRPs can help minimize and avoid drug toxicity, unfavourable drug-drug interactions, and to overcome drug resistance.