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Time activity curves. Biodistribution of [ 11 C]D617 in rats saline vs. tariquidar (15 mg/kg, ip) treatment. Synthesis and biological evaluation of [ 11 C]D617: A metabolite of [ 11 C]verapamil.

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  1. Time activity curves Biodistribution of [11C]D617 in rats saline vs. tariquidar (15 mg/kg, ip) treatment Synthesis and biological evaluation of [11C]D617: A metabolite of [11C]verapamil J. Verbeek1, A. D. Windhorst1, R. C. Schuit1, J. Eriksson1, S. Syvänen2, A. A. Lammertsma1 and G. Luurtsema1 Department of 1Nuclear Medicine & PET Research, 2LACDR/Pharmacology, Leiden University, VU University Medical Center PO Box 7057, 1007MB Amsterdam, the Netherlands Email:j.verbeek@vumc.nl The biodistribution of [11C]D617 was determined in male Wistar rats (n=4) at 5, 15, 30, and 60 minutes after injection. Tissues of interest were dissected, counted for radioactivity and weighed. The biodistribution was also assessed at 30 minutes following injection of [11C]D617 in a group of rats (n=4), pre-treated with 15 mg/kg tariquidar (PgP inhibitor) via ip injection2 to investigate the PgP substrate behavior of [11C]D617. PET Imaging Wistar rats (n=4) where injected with 20 MBq [11C]D617 and scanned for 60 minutes (Siemens HRRT), subsequently injected with 15mg/kg tariquidar (iv) where after a second identical PET scan was performed. Summed images (0-60 min) are shown below. The graph below shows the time activity curves of all the scans with the whole brain as region of interest. Discussion [11C]D617 was synthesized in 62-68% yield and >99% radiochemical purity within 45 minutes with a specific activity of 70-94 GBq/µmol at end of synthesis. Brain uptake of [11C]D617 was very low (<0.1% ID/g) and homogeneous. Treatment with tariquidar via ip injection did not increase uptake of [11C]D617 in rat. This result indicated that [11C]D617 was not a PgP substrate since ip administration of tariquidar in a similar dose range has been reported to induced pharmacological effect2.HoweverPET imaging showed approximately3 times increased uptake of [11C]D617 after treatment with tariquidar, i.v. compared to the results of Syvänen3 from the PET imaging study with [11C]verapamil in the same animal model, [11C]D617 is 3-fold less active as a PgP substrate than [11C]verapamil. The discrepancy between the results after ip administration of tariquidar and the iv administration was unforeseen, but is most likely caused by pharmacokinetic effects of the different type of administration. Conclusion [11C]D617 is a PgP substrate, although less active than [11C]verapamil. References [1] Lubberink M, et al J. Cereb.Blood Flow Metab. 2007; 27, 1-10. [2] Bankstahl JP, et al Epilepsy Research 2008; 82; 1, 70-85. [3] Syvänen S, et al J. Pharmaceutical Sciences 2008; 97; 12, 5386-5400. Acknowledgements This work was funded by the EU 7th framework programme EURIPIDES, grant nr HEALTH-F5-2007-201380. The authors like to acknowledge H.J.C. Buiter, P. J. Klein, R.P. Klok, I. de Greeuw, M. Schenke, and J.D.M. Herscheid for assistance during the experiments, and the BV Cyclotron VU for providing [11C]CO2. Objective Using [11C]verapamil and positron emission tomography, it is possible to measure P-glycoprotein activity in the brain in vivo in a non-invasive manner. In the optimal kinetic model, it is assumed that the main radioactive metabolite of [11C]verapamil, [11C]D617, has similar pharmacokinetics as [11C]verapamil itself1. To assess whether this assumption is correct, the pharmacokinetic properties of [11C]D617 need to be evaluated. The aim of this study is to develop the synthesis of [11C]D617 and to assess pharmacokinetics of [11C]D617 in rat. Synthesis of desmethyl D617 and [11C]D617 The precursor for labeling D617 with C-11, compound 5, was synthesized in 4 steps (scheme 1) and subsequently reacted with [11C]methyl triflate to give [11C]D617 (scheme 2). Purification was achieved using preparative HPLC. The product was reformulated via solid phase extraction, in 10% ethanol and 90% 7.09mM NaH2PO4 in 0.9% saline, and subsequently passed over a sterile filter. Scheme 1. Synthesis of D617 and desmethyl D617; a: DMF, NaH, isopropyl bromide, RT, 5h, 77%; b: THF, n-BuLi, 1,3-dibromopropane, -78°C, 2h, 83%; c: toluene, 18-Crown-6-ether, potassium phtalimide, reflux, 6h, 86%; d: THF, EtOH, hydrazine.H2O, RT, 2h, 74%; e: methylamine, toluene, H2O, RT, 4h, 56%. Scheme 2. Radiosynthesis of [11C]D617; a: LiAlH4, THF RT, 2 min, b: HI, H2O, 130°C 2 min, c: Silvertriflate 200°C, 4 min, d: CH3CN, 50°C, 3 min. Overall yield 62-68% corrected for decay. Preparative HPLC chromatogram Zorbax bonus RPAnalytical HPLC chromatogram Kromasil100 C18 MeCN/H2O/DIPA 60/40/0,2 4 ml/min. MeCN/H2O/DIPA 40/60/0,2 1 ml/min. Ex vivo biodistribution Baseline Tariquidar treated [11C]D617 [11C]D617

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