Interplay of conjugating enzymes with OATP uptake transporters and ABCC/MRP efflux pumps in the elimination of drugs

Abstract

Background: Biliary excretion is a major elimination route of many drugs and their metabolites. Hepatobiliary elimination is a vectorial process involving uptake transporters in the basolateral hepatocyte membrane, possibly Phase I and Phase II metabolizing enzymes, and ATP-dependent efflux pumps in the apical hepatocyte membrane. Objectives: Because many drugs and their metabolites are anions, this review focuses on transporters involved in their hepatocellular uptake (members of the organic anion transporting polypeptide (OATP) family) and biliary elimination (apical conjugate efflux pump ABCC2/MRP2). Methods: The molecular and functional characteristics of the human OATP and ABCC/MRP transporters are presented, including a detailed overview of endogenous and drug substrates. Examples illustrate the interplay of transporters with Phase II conjugating enzymes. Model systems to study the vectorial transport of organic anions are also discussed. Results/conclusions: OATP uptake transporters, conjugating enzymes, and ABCC2/MRP2 work in concert to enable the hepatobiliary elimination of anionic drugs and their metabolites. It is increasingly important to understand how genetic variants of these transporters and enzymes influence the interindividual variability of drug elimination.

Keywords::

• ABC transporters
• ABCC2/MRP2
• ABCC3/MRP3
• ABCC4/MRP4
• ABCC6/MRP6
• conjugating enzymes
• drug-metabolizing enzymes
• drug transporters
• hepatobiliary elimination
• OATP uptake transporters
• OATP1B1
• OATP1B3
• OATP2B1
• Phase I metabolism
• Phase II metabolism
• SLCO genes

Acknowledgements

The authors' work on the function of drug transporters is supported in parts by the German Cancer Research Center, Heidelberg, the Robert-Bosch Foundation, Stuttgart, and by a grant from the Deutsche Krebshilfe, Bonn (grant number 107150).