Print Email Facebook Twitter Comparison of in vitro assays in selecting radiotracers for in vivo P-glycoprotein PET imaging Title Comparison of in vitro assays in selecting radiotracers for in vivo P-glycoprotein PET imaging Author Raaphorst, R.M. Savolainen, H. Cantore, M. van de Steeg, E. van Waarde, A. Colabufo, N.A. Elsinga, P.H. Lammertsma, A.A. Windhorst, A.D. Luurtsema, G. Publication year 2017 Abstract Positron emission tomography (PET) imaging of P-glycoprotein (P-gp) in the blood-brain barrier can be important in neurological diseases where P-gp is affected, such as Alzheimer’s disease. Radiotracers used in the imaging studies are present at very small, nanomolar, concentration, whereas in vitro assays where these tracers are characterized, are usually performed at micromolar concentration, causing often discrepant in vivo and in vitro data. We had in vivo rodent PET data of [11C]verapamil, (R)-N-[18F]fluoroethylverapamil, (R)-O-[18F]fluoroethyl-norverapamil, [18F]MC225 and [18F]MC224 and we included also two new molecules [18F]MC198 and [18F]KE64 in this study. To improve the predictive value of in vitro assays, we labeled all the tracers with tritium and performed bidirectional substrate transport assay in MDCKII-MDR1 cells at three different concentrations (0.01, 1 and 50 µM) and also inhibition assay with P-gp inhibitors. As a comparison, we used non-radioactive molecules in transport assay in Caco-2 cells at a concentration of 10 µM and in calcein-AM inhibition assay in MDCKII-MDR1 cells. All the P-gp substrates were transported dose-dependently. At the highest concentration (50 µM), P-gp was saturated in a similar way as after treatment with P-gp inhibitors. Best in vivo correlation was obtained with the bidirectional transport assay at a concentration of 0.01 µM. One micromolar concentration in a transport assay or calcein-AM assay alone is not sufficient for correct in vivo prediction of substrate P-gp PET ligands. © 2017 by the authors. Licensee MDPI, Basel, Switzerland. Chemicals/CAS: calcein, 1461-15-0; multidrug resistance protein, 149200-37-3, 208997-77-7 Subject LifeMSB - Microbiology and Systems BiologyELSS - Earth, Life and Social SciencesBiomedical InnovationBiologyHealthy LivingApical and basolateral membraneBidirectional transportBlood-brain barrierCalcein-AMTritium labelingCalceinMc 224 f 18Mc 225 f 18Multidrug resistance proteinN fluoroethylverapamil f 18O fluoroethyl norverapamil f 18Radiopharmaceutical agentUnclassified drugVerapamil c 11Animal experimentAnimal tissueChemical analysisControlled studyDrug accumulationDrug blood levelDrug brain levelDrug half lifeEnzyme inhibitionFluoroethylationIn vitro studyIn vivo studyIsotope labelingMaleMouseNonhumanPositron emission tomographyPredictive valueProtein functionRadioactivityRatSynthesisTransport assay To reference this document use: http://resolver.tudelft.nl/uuid:4dee5254-232e-4a69-9ae0-eb1757d461d3 DOI https://doi.org/10.3390/ph10030076 TNO identifier 781905 ISSN 1424-8247 Source Pharmaceuticals, 10 (3) Article number 76 Document type article Files To receive the publication files, please send an e-mail request to TNO Library.