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[18F]fluorocholine is the fluorinated analog of [11C]choline and is used in positron emission tomography to monitor tumor metabolic activity. Although important to optimize its use and expand the clinical indications, the molecular determinants of fluorocholine cellular uptake are poorly characterized. In this work, we described the influx kinetics of fluorocholine mediated by the organic cation transporter 2 (OCT2, SLC22A2) and compared with that of choline. Then we characterized the expression pattern of OCT2 in renal cell carcinoma (RCC). In HEK293 cells stably transfected with OCT2 fluorocholine influx, kinetics was biphasic, suggesting two independent binding sites: a high-affinity (Km = 14 ± 8 µM, Vmax = 1.3 ± 0.5 nmol mg-1 min-1) and a low-affinity component (Km = 1.8 ± 0.3 mM, Vmax = 104 ± 4.5 nmol mg-1 min-1). Notably, choline was found to be transported with sigmoidal kinetics typical of homotropic positive cooperativity (h = 1.2, 95% confidence interval 1.1-1.3). OCT2 mRNA expression level was found significantly decreased in primary but not in metastatic RCC. Tissue microarray immunostaining of 216 RCC biopsies confirmed that the OCT2 protein level was consistent with that of the mRNA. The kinetic properties described in this work suggest that OCT2 is likely to play a dominant role in [18F]fluorocholine uptake in vivo. OCT2-altered expression in primary and metastatic cancer cells, as compared with the surrounding tissues, could be exploited in RCC imaging, especially to increase the detection sensitivity for small metastatic lesions, a major clinical challenge during the initial staging of RCC.

This report is the summary of presentations at the symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics, April 26-30, at Experimental Biology 2014 in San Diego, CA. The presentations focused on the role of transporters in imaging in health and disease and on assessing transporter function in vivo. Imaging is an important diagnostic tool in clinics and is a novel tool for in vivo visualization of transporter function. Many imaging substrates and endogenous markers for organ function are organic anions. In this symposium, the bile salt transporter sodium taurocholate cotransporting polypeptide and the liver organic anion transporting polypeptides (OATPs) as well as the renal organic anion transporters (OATs) were addressed in detail; e.g., OATPs mediate transport of contrast agents used for magnetic resonance imaging of the liver or transport agents used for hepatobiliary scintigraphy, and OATs transport substances used in renography. In addition, the symposium also focused on the multidrug-resistance transporter 1 (MDR1 or P-gp), which is the most important gatekeeper in epithelial or endothelial barriers for preventing entry of potentially harmful substances into organs. Novel substrates suitable for positron emission tomography (PET) allow the study of such transporters at the blood-brain barrier or while they are mediating uptake of drugs into hepatocytes, and, importantly, PET tracers also now allow renography. Finally, quantitative data on transporter expression in human organs allow the development of improved physiologically based pharmacokinetic (PBPK) models for drug disposition. Hence, the combined efforts using novel substrates for in vivo visualization of transporters and quantification of transporters will lead to a deeper understanding of transporter function in disease and allow development of novel PBPK models for disease states.

CYP2C9 is an important drug-metabolizing enzyme that metabolizes, e. g., warfarin, antidiabetics, and antiphlogistics. However, the endogenous regulation of this enzyme is largely unknown. In this study, we examined the role of GATA transcription factors in the gene expression of CYP2C9. We investigated four putative GATA binding sites within the first 200 base pairs of CYP2C9 promoter at the positions I: -173/-170, II: -167/-164, III: -118/ -115, and IV: -106/-103. Luciferase activity driven by a wildtype CYP2C9 promoter construct was strongly up-regulated in Huh-7 cells upon cotransfection with expression plasmids for GATA-2 and GATA-4, whereas mutations introduced into GATA binding site III or I and II reduced this induction to a significant extent. Electrophoretic mobility shift assays revealed specific binding of GATA-4 and GATA-6 to the oligonucleotides containing GATA binding sites I and II. Furthermore, the association of GATA-4 with CYP2C9 promoter was confirmed by chromatin immunoprecipitation assays in HepG2 cells. Taken together, these data strongly suggest an involvement of liver-specific transcription factor GATA-4 in the transcriptional regulation of CYP2C9. Swedish Research Council; Stockholm County Council; Danish Agency of Science, Technology and Innovation; Lundbeck Foundation; Portuguese Foundation for Science and Technology [SFRH/BPD/34152/2006 IBB/CBME]

International audience; Interleukin (IL) 1beta is a proinflammatory cytokine known to markedly alter expression of major organic anion transporters in rodent hepatocytes. However, its effects toward human hepatic transporters remain poorly characterized. Therefore, the present study was aimed at determining IL-1beta effects on expression of organic anion transporters in primary human hepatocytes and highly differentiated human hepatoma HepaRG cells. Exposure to 1 ng/ml IL-1beta was first shown to markedly repress mRNA expression of sodium-taurocholate cotransporting polypeptide (NTCP), a major sinusoidal transporter handling bile acids, in both human hepatocytes and HepaRG cells. It concomitantly reduced NTCP protein levels and NTCP-mediated cellular uptake of taurocholate in HepaRG cells. Other transporters such as the influx transporters organic anion transporting polypeptide (OATP)-B, OATP-C, and OATP8 and the efflux pumps multidrug resistance-associated protein (MRP) 2, MRP3, MRP4, and breast cancer resistance protein were also down-regulated at mRNA levels in human hepatocytes treated by IL-1beta for 24 h, and most of these transporters were similarly repressed in IL-1beta-exposed HepaRG cells; the cytokine also reduced bile salt export pump (BSEP) and OATP-C protein expression in human hepatocytes. IL-1beta was further shown to activate the extracellular signal-regulated protein kinase (ERK) in human hepatocytes and HepaRG cells; however, chemical inhibition of this kinase failed to counteract repressing effects of IL-1beta toward NTCP, BSEP, OATP-B, and OATP-C. Taken together, these data indicate that IL-1beta treatment reduced expression of major organic anion transporters in human hepatic cells in an ERK-independent manner. Such IL-1beta effects may likely participate in both cholestasis and alterations of hepatic detoxification pathways caused by inflammation in humans.