Thermochromatographic separation of 45 Ti and subsequent radiosynthesis of [ 45 Ti]salan
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Thermochromatographic separation of 45Ti and subsequent radiosynthesis of [45Ti]salan Kai Giesen1 · Ingo Spahn1 · Bernd Neumaier1 Received: 30 June 2020 / Published online: 10 October 2020 © The Author(s) 2020
Abstract Due to its favorable decay properties, the non-standard radionuclide 45Ti is a promising PET isotope for tumor imaging. Additionally, titanium complexes are widely used as anti-tumor agents and 45Ti could be used to study their in vivo distribution and metabolic fate. However, although 45Ti can be obtained using the 45Sc(p,n)45Ti nuclear reaction its facile production is offset by the high oxophilicity and hydrolytic instability of T i4+ ions in aqueous solutions, which complicate recovery from the irradiated Sc matrix. Most available 45Ti recovery procedures rely on ion exchange chromatography or solvent extraction techniques which are time-consuming, produce large final elution volumes, or, in case of solvent extraction, cannot easily be automated. Thus a more widespread application of 45Ti for PET imaging has been hampered. Here, we describe a novel, solvent-free approach for recovery of 45Ti that involves formation of [ 45Ti]TiCl4 by heating of an irradiated Sc target in a gas stream of chlorine, followed by thermochromatographic separation of the volatile radiometal chloride from co-produced scandium chloride and trapping of [ 45Ti]TiCl4 in a glass vial at − 78 °C. The recovery of 45Ti amounted to 76 ± 5% (n = 5) and the radionuclidic purity was determined to be > 99%. After trapping, the [ 45Ti]TiCl4 could be directly used for 45Tiradiolabeling, as demonstrated by the successful radiosynthesis of [45Ti][Ti(2,4-salan)]. Keywords 45Ti · Separation · Thermochromatography · Ti-complexes · Radiolabeling · Radio metal complexes
Introduction Discovery of the anticancer activity of cisplatin and its clinical introduction in the 1970s have spurred interest into metal based antitumor compounds with less side effects and increased effectiveness against a broad range of cancers [1, 2]. Titanium(IV) complexes like budotitane, titanocene dichloride and their derivatives are effective against various cancer cell lines but failed in in vivo clinical trials [3–6], most likely due to their rapid (within seconds) hydrolysis under physiological conditions [7]. A more promising class of titanium-based drugs with hydrolytic half-lives in the range of hours is based on tetradentate diaminobis(phenolato) ligands (salans) [8]. Their titanium complexes selectively induce apoptotic cell death [9] and display strong antitumor properties in vitro and in tumorbearing mice [10, 11]. Further studies on their distribution, * Ingo Spahn i.spahn@fz‑juelich.de 1
Institut für Neurowissenschaften und Medizin (INM-5), Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
uptake and mechanism of action rely on imaging techniques such as positron emission tomography (PET), which allows for non-invasive assessment of the biological fate of radiolabeled drugs while they distribute in vivo. The titanium isotope 45Ti has a h
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