Monday, 23 May 2005 - 11:00 AM

This presentation is part of: Transporters

Functional Characterization of a Hepatic Organic Anion Transport Model; OATP1B1 and MRP2 Double Transfected MDCKII cells

Kelly Bleasby, Richard Edom, and Raymond Evers. Merck and Co., Rahway, NJ

Elimination of compounds from blood into bile is a two-step process; after being taken into the hepatocyte across the sinusoidal membrane, they are effluxed across the canalicular membrane, into the bile. For lipophilic compounds this process may be achieved by passive diffusion, however for amphipathic compounds, with low diffusion rates, transporters are thought to be involved.

Previous studies suggest that recombinant cell lines differentially expressing transporters in apical and basolateral membranes are useful for the study of hepatic vectorial transport. In the present study, one such model was developed. MDCKII cells were stably transfected with OATP1B1 (SLCO1B1, OATP2, OATP-C) and MRP2 (ABCC2) and grown on semi-permeable supports, to form polarized cell monolayers expressing OATP1B1 in the basolateral membrane and MRP2 in the apical membrane.

Bidirectional transport studies demonstrated that compounds with very low passive permeabilities, e.g. E217βG, were efficiently transported by MDCKII-OATP1B1+MRP2 monolayers, but not by cells transfected with OATP1B1 or MRP2 alone. In contrast, rifampicin and cyclosporine A, which have moderate passive permeabilities, were transported across MDCKII-MRP2 and MDCKII-OATP1B1+MRP2 monolayers at similar rates, despite being previously identified as substrates and inhibitors of OATP1B1 respectively.

In conclusion, this doubly transfected MDCKII-OATP1B1+MRP2 cell line will serve as a useful tool in the identification of substrates and inhibitors and in assessing the role these transporters play in the hepatic elimination of drug candidates. Furthermore, based on a number of compounds tested, our data suggest that uptake transporters are likely to be rate determining only for compounds with a relatively low passive permeabilities.

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