In Vitro Characterization of Intestinal and Hepatic Transporters: MRP2
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The transporter field has grown extensively over the past decade. Analogous to drug metabolizing enzymes such as the cytochrome P450s, transporters play a major role in defining pharmacokinetic, safety and efficacy profiles of drugs. Multidrug resistance-associated protein 2 (MRP2, ABCC2 ) is an ATP-dependent efflux pump that belongs to the ATP binding cassette (ABC) superfamily of transporters, and is localized at the apical membrane of polarized cells from a variety of human tissues including enterocytes, hepatocytes and renal proximal tubules. It is highly expressed in liver, intestine and kidney, with lesser expression in other tissues. MRP2 primarily transports organic anions and large bulky conjugated compounds and shares some overlapping substrate specificity with other ABC family members including P-glycoprotein (P-gp) and the breast cancer resistance protein (BCRP).
Understanding whether investigational compounds are potential MRP2 substrates or inhibitors during drug discovery and development may potentially help to explain why drug candidates show poor bioavailability or are rapidly cleared by hepatic efflux. This chapter outlines various in vitro techniques that can be used to examine whether compounds are substrates and/or inhibitors of MRP2 (ATPase assays, vesicular transport assays and/or MDCKII-MRP2 overexpressing cells) and assess the role of MRP2 in attenuating intestinal absorption of drugs (wild-type and MRP2 knockdown Caco-2 cells) or in mediating their hepatobiliary excretion (wild-type and MRP2 knockdown human hepatocytes cultured in sandwich configuration). The primary aim of the chapter is to provide a range of assay options. However, the strategy around when/if/why/ or how a specific assay(s) should be used will depend on a number of factors such as physiochemical properties, drug target, overall distribution, etc, and is therefore ultimately left to the reader.
