Vol. 61, Issue 4, 853-860, April 2002

Carriers Involved in Targeting the Cytostatic Bile Acid-Cisplatin Derivatives cis-Diammine-chloro-cholylglycinate-platinum(II) and cis-Diammine-bisursodeoxycholate-platinum(II) toward Liver Cells

Oscar Briz, Maria Angeles Serrano, Noemi Rebollo, Bruno Hagenbuch, Peter J. Meier, Hermann Koepsell, and Jose J.G. Marin

Departments of Physiology and Pharmacology (O.B., N.R., J.J.G.M.) and Biochemistry and Molecular Biology (M.A.S.), University of Salamanca, Salamanca, Spain; Division of Clinical Pharmacology and Toxicology, Department of Medicine, University Hospital, Zurich, Switzerland (B.H., P.J.M.); and Department of Anatomy, University of Würzburg, Würzburg, Germany (H.K.)

Molecular bases for targeting bile acid-cisplatin derivatives Bamet-R2 [cis-diammine-chloro-cholylglycinate-platinum(II)] and Bamet-UD2 [cis-diammine-bisursodeoxycholate-platinum(II)] toward liver cells were investigated. Carriers for bile acids [human Na⁺-taurocholate cotransporting polypeptide (NTCP)], organic anions [organic anion transporting polypeptide (OATP)], and organic cations [organic cation transporter (OCT)] were expressed in Xenopus laevis oocytes (XO) and Chinese hamster ovary (CHO) cells. Drug uptake was measured by flameless atomic absorption of platinum. Rat Oatp1- or rat Ntcp-transfected CHO cells were able to take up Bamets, but not cisplatin, severalfold more efficiently than wild-type cells. This uptake was enhanced by butyrate-induced expression of both carriers. Uptake of both Bamets by Ntcp-transfected CHO cells was stimulated by extracellular sodium. The amount of Bamets, but not cisplatin, taken up by XO was enhanced when expressing OATP-A, OATP-C, NTCP, OCT1, or OCT2, a nonhepatic OCT isoform used for comparative purposes. Bamet uptake by XO was inhibited by known substrates of these carriers (glycocholate for NTCP and OATP-C, ouabain for OATP-A, and quinine for OCT1 and OCT2). Drug uptake versus substrate concentration revealed saturation kinetics (K_m was in the 8-58 µM range), with the following order of efficiency of transport (V_max/K_m) for Bamet-R2: OATP-C > OCT2 > OATP-A > NTCP > OCT1; and the following order of efficiency of transport for Bamet-UD2: OATP-C > OCT2 > OATP-A > OCT1 > NTCP. Increasing the generation of cationic forms of Bamets by incubation in the absence of chloride increased drug uptake by OATP-A, OCT1, and OCT2 but reduced that achieved by NTCP and OATP-C. These results suggest a role for carriers of organic anions and cations in Bamet-R2 and Bamet-UD2 uptake, which may determine their ability to accumulate in liver tumor cells and/or be taken up and efficiently excreted by hepatocytes.