Liver

Drug disposition is the net result of the different processes involved in drug uptake, metabolism and excretion. Members of the uptake transporter family, as well as certain efflux transporters and drug metabolizing enzymes are key players in drug disposition.

The screening of the interaction of test drugs, nutrients and other molecules with hepatic efflux and uptake transporters is an excellent way to study their hepatobiliary DMPK and to lower the risk of hepatotoxicity caused by bile acid retention. Several of the basolateral and apical transporters for bile acids are thought to be targets of drugs that induce cholestasis.

To gain information on biliary clearance, BSEP, MRP2, BCRP and P-gp transporter interactions need to be investigated. For the detection of possible interactions on the basolateral membrane, MRP3, MRP4 and MRP5 efflux transporters should be considered.

The involvement of human uptake transporters in the hepatic transport processes is just as crucial as the role of the efflux transporters. When investigating hepatobiliary disposition, it is highly recommended to perform screens for NTCP, OATP-C (OATP2 / OATP1B1), OATP8 (OATP1B3), OATP-B (OATP2B1), OAT2 and OCT1. In case of rat pharmacokinetic studies, Rat Ntcp, rat Oatp1 (Oatp1a1), rat Oatp2 (Oatp1a4), rat Oatp4 (Oatp1b2), rat Oat2 and ratOct1 should be considered.

Localization of efflux and uptake transporters in hepatocytes

Available assays within the liver package

• MDR1 PREDEASY ATPase
• MDR1 PREDIVEZ vesicular transport
• ratMdr1b PREDEASY ATPase
• MRP2 PREDEASY ATPase, ratMrp2 ATPase
• MRP2 PREDIVEZ vesicular transport
• BCRP-HAM PREDEASY ATPase
• BCRP-M PREDIVEZ vesicular transport
• mouseBsep ATPase
• BSEP vesicular transport, mouseBsep vesicular transport
• MRP3 PREDEASY ATPase
• MRP3 PREDIVEZ vesicular transport
• MRP5 PREDIVEZ vesicular transport

• MDR1 Calcein Assay
• Hoechst Assay (BCRP)
• OATP1B1, OATP1B3, OATP2B1 and ratOatp1a1 uptake transporter assay
• NTCP, ratNtcp uptake transporter assay
• OCT1 uptake transporter assay

• Double transfected cells (OATP-B - BCRP)
• MDCKII BCRP AB/BA transport
• MDCKII mouseBcrp1 AB/BA transport

• Rat experiments for Mrp2, Bsep and Bcrp

Screening strategy

1. Transporter interaction and penetration package: Conduct membrane based assays for the major transporters in the liver: ATPase first, then vesicular transport (MRP2, BCRP, BSEP-VT, P-gp). Uptake transporters (OATPs, NTCP) can be tested in inhibitory cellular assays. For positive hits detailed transport characterization can be done in direct vesicular or cellular assays. Follow with studying transport in double transfectant cell monolayer assays.
2. Drug-drug interaction and toxicity assessment: Start with inhibitory, membrane based assays for BSEP, MRP2 (BCRP), inhibitory cellular uptake transporter assays for OATPs and NTCP.