Transporter studies with the 3-O-sulfate conjugate of 17alpha-ethinylestradiol: assessment of human liver drug transporters.

17alpha-Ethinylestradiol (EE2), a component of oral contraceptives, is known to undergo considerable first-pass 3-O-sulfation in the intestine and liver. Once formed, the 3-O-sulfate conjugate (EE2-Sul) is detected in circulation at appreciable levels (versus parent EE2) and is present in bile. Therefore, hepatic uptake of EE2-Sul was assessed with suspensions of cryopreserved human primary hepatocytes. In this instance, there was evidence for active (temperature-dependent) uptake, which was described by a two-K(m) (Michaelis constant) model (K(m1) = 220 nM; K(m2) = 15.5 microM). Uptake was inhibited (approximately 90%) by bromosulfophthalein but not by tetraethylammonium or p-aminohippurate. In agreement, EE2-Sul was shown to be a substrate of recombinant organic anion transporter peptides (OATP1B1 and OATP2B1), and Na(+)/taurocholate-cotransporting polypeptide (NTCP), expressed individually in human embryonic kidney (HEK) 293 cells. Transport by OATP1B1 was described by two K(m) values (87 nM and 141 microM), whereas OATP2B1- and NTCP-mediated uptake into HEK-293 cells conformed to single K(m) kinetics (10.7 and 2.6 microM, respectively). EE2-Sul was also assessed as an efflux transporter substrate using membrane vesicles expressing bile salt export pump, breast cancer resistance protein (BCRP), and individual forms of multidrug resistance-associated protein (MRP1, MRP2, and MRP3). Transport studies were also conducted with a cell line expression P-glycoprotein. Only vesicles that contained BCRP exhibited ATP-dependent uptake of EE2-Sul (K(m1) = 2.9 and K(m2) = 307 microM). Collectively, the data show that hepatic uptake of EE2-Sul can be mediated by three transporters (OATP1B1, OATP2B1, and NTCP), whereas biliary excretion of EE2-Sul into bile likely involves BCRP.

Transporter studies with the 3-O-sulfate conjugate of 17alpha-ethinylestradiol: assessment of human kidney drug transporters.

17alpha-Ethinylestradiol (EE2), a synthetic and potent estrogen receptor agonist, is extensively metabolized in both intestine and liver and is largely excreted in bile and urine as the 3-O-sulfate (EE2-Sul) and 3-O-glucuronide. In the present study, EE2-Sul was evaluated as a substrate of various transporters known to be expressed in the kidney. Uptake studies were performed with human epithelial cells [human embryonic kidney (HEK)-293] that contained individually expressed organic cation transporter 2 (OCT2), organic anion transporter (OAT) forms 3 and 4, and multidrug and toxin extrusion 1 (MATE1). The transporter phenotyping studies were extended to include insect cell (Sf9) membrane vesicles that expressed multidrug resistance-associated protein 4 (MRP4) and Madin-Darby canine kidney cells that expressed OAT1. Based on the results obtained, we concluded that EE2-Sul serves as a substrate of OAT3 and OAT4, but not OCT2, OAT1, MATE1, and MRP4. First, EE2-Sul uptake was highly increased in OAT3/HEK-293 cells (versus mock/HEK-293 cells) and was inhibited by OAT3 inhibitors such as bromosulfophthalein (BSP), cimetidine, and probenecid. OAT3-mediated uptake also conformed to single-K(m) (Michaelis constant) kinetics (K(m) = 21.1 microM). Second, EE2-Sul uptake was also significantly higher in OAT4/HEK-293 cells and was inhibited by BSP, methotrexate, and probenecid. In contrast to OAT3, OAT4-dependent uptake was characterized by a two-K(m) model (K(m1) = 1.6 microM; K(m2) = 195 microM). Based on the results of this study, we hypothesize that EE2-Sul is taken up into renal proximal tubule cells by OAT3, and OAT4 plays a role in its secretion into the renal brush border lumen.

Assessment of P-gp and MRP1 activities using MultiDrugQuant Assay Kit: a preliminary study of correlation between protein expressions and its functional activities in newly diagnosed acute leukaemia patients.

Multidrug resistance (MDR) is believed to be responsible for poor response of patients towards chemotherapy particularly patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). The best-characterized resistance mechanism is the one mediated by permeability-glycoprotein (P-gp) encoded by MDR1 gene, which is responsible for drug efflux. We studied P-gp and multidrug resistance-associated protein 1 (MRP1) expression and functional activities in 43 newly diagnosed acute leukemia cases (19 paediatric ALL cases and 24 adult AML cases). The expression and functional activities were examined using flow cytometry and MultiDrugQuant assay kit (involving calcein AM uptake and efflux). P-gp and MRP1 expression and its functional activities were observed in 68.4% of paediatric ALL. In adult AML cases, all cases expressed MRP1 and its functional activities but only 58.3% were positive for P-gp and its functional activities. We were able to show a significant correlation between the expression of the multidrug resistant protein (P-gp and MRP1) and their functional activity in adult AML and paediatric ALL samples.