Preparation of 5-[ 131 I]iodotubercidin for the detection of adenosine kinase
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Preparation of 5‑[131I]iodotubercidin for the detection of adenosine kinase Dirk Bier1 · Marcus Holschbach1 · Franziska Wedekind2 · Wiebke Sihver3 · Birte Drewes1 · Annette Schulze1 · Felix Neumaier1,4 · Bernd Neumaier1,4 · Andreas Bauer2 Received: 17 September 2020 / Accepted: 14 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract 5-Iodotubercidin is a prototype adenosine kinase (AK) inhibitor with potent anti-seizure activity in rodent epilepsy models. Using the chloramine-T method for radioiodination of tubercidin with 131I, we prepared no-carrier-added 5-[131I]iodotubercidin (5-[131I]IT) in a radiochemical yield of 61 ± 13% and with a radiochemical purity of > 99% (molar activity = 10–40 GBq/ µmol). In vitro competition and saturation experiments demonstrated specific binding of 5-[131I]IT in rodent brain slices (KD ~ 31 nM), but ex vivo autoradiography revealed its accumulation in cerebral vessels. We conclude that 5-[131I]IT could be a useful tool for the detection and quantification of AK in in vitro studies. Keywords Nucleoside adenosine kinase inhibitor (AKI) · n.c.a. radioiodination · Iodotubercidin · In vitro/ex vivo autoradiography
Introduction The purine ribonucleoside adenosine (Ado) is a short-lived neuronal signaling molecule and metabolic regulator formed by intra- and extracellular breakdown of adenine nucleotides. Cerebral ischemia, epileptic seizures and traumatic brain injury lead to a dramatic increase of extracellular Ado that mediates feedback inhibition of excitatory activity and is supposed to be one of the mechanisms by which the brain protects itself from injury [1–5]. Ado is mainly metabolized by adenosine kinase (AK), an evolutionary conserved cytosolic phosphotransferase that catalyzes its conversion into * Dirk Bier d.bier@fz‑juelich.de 1
Institute of Neuroscience and Medicine, Nuclear Chemistry (INM‑5), Forschungszentrum Jülich GmbH, Jülich, Germany
2
Molecular Organization of the Brain (INM‑2), Forschungszentrum Jülich GmbH, Wilhelm‑Johnen‑Straße, 52428 Jülich, Germany
3
Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany
4
Institute of Radiochemistry and Experimental Molecular Imaging, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany
adenosine monophosphate (AMP). Because cellular uptake of Ado is driven by a bidirectional facilitated diffusion transporter [5], inhibition of AK decreases reuptake and results in increased extracellular Ado concentrations [6–10]. AK inhibitors (AKIs) have been shown to exert a number of protective functions, making them candidate drugs for antiinflammatory [11–13], anti-nociceptive [14–16] and anticonvulsive [6, 11, 14–18] therapy. 5-Iodotubercidin (5-IT) is a tubercidin analog and prototype of the ribonucleoside AKIs that suppresses AK by competing with Ado for binding to the enzyme [17, 19–21]. Other potent members of this group with different heterocyclic cores and/or substituen
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