Abstract
ObjectiveRecent studies showed that ethanol in the reaction mixture improves radiolabelling with trivalent radiometals in terms of precursor amount, reaction time, reaction temperature and radiolysis. With regard to clinical application, this effect is of practical interest in radiopharmacy. The aim of this study was to evaluate whether the positive effect of ethanol can be exploited in automated systems utilizing NaCl-post processing.MethodsGallium-68 was obtained from a 1.85 GBq 68Ge/68Ga-generator. Radiolabelling was performed on an automated 68Ga-labelling cassette module. The standard labelling protocol was used without modifications. 0–40 vol% ethanol were added to the reaction mixture. Quality control was performed using radioHPLC and radioTLC.ResultsUtilization of additional ethanol on an automated cassette module can be achieved by adding ethanol directly to the buffer solution without further modifications of the standard procedure. Radiolysis was decreased significantly as analysed by radioHPLC.ConclusionIt was possible to combine the positive effects of ethanol on radiolabelling efficacy and radiolysis with the standard labelling procedure of an automated cassette module system. The whole process guarantees safe preparation of highly pure 68Ga-peptide for clinical application.
Highlights
One of the most versatile chelators available is the macrocycle 1,4,7,10-tetraazacyclotetradecane 1,4,7,10 tetra acetic acid (DOTA)
It was possible to combine the positive effects of ethanol on radiolabelling efficacy and radiolysis with the standard labelling procedure of an automated cassette module system
To be able to determine any effect of ethanol on radiolabelling yields, it was necessary to determine an initial state without ethanol addition, were radiolabelling yields are low enough to measure any effect of ethanol
Summary
One of the most versatile chelators available is the macrocycle 1,4,7,10-tetraazacyclotetradecane 1,4,7,10 tetra acetic acid (DOTA). It is known since 1976 (Stetter and Frank 1976) and was initially used as complexing agent for lanthanides, as it forms stable complexes with most bivalent and trivalent metals (Alexander 1995). The first, and until today used, medical application of DOTA is as the contrast agent gadoteric acid were unfunctionalized DOTA is complexing Gd3+ (Caravan et al 1999). In nuclear medicine one of the first DOTA derivatives utilized was DOTA-(0)-Phe (1)-Tyr (3))octreotide (DOTA-TOC). It can be applied for both diagnosis, radiolabelled e.g. with gallium-68, or therapy, with e.g. lutetium-177 (Lamberts et al 1990). The biological active site in DOTA-TOC, TOC, is a somatostatin analogous that binds to somatostatin receptors
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