Comparison of macrocyclic and acyclic chelators for gallium-68 radiolabelling
Gallium-68 ( 68 Ga) is a positron-emitting isotope used for clinical PET imaging of peptide receptor expression. 68 Ga radiopharmaceuticals used in molecular PET imaging consist of disease-targeting biomolecules tethered to chelators that complex 68 Ga 3+ . Ideally, the chelator will rapidly, quanti...
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Veröffentlicht in: | RSC advances 2017-01, Vol.7 (78), p.49586-49599 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Gallium-68 (
68
Ga) is a positron-emitting isotope used for clinical PET imaging of peptide receptor expression.
68
Ga radiopharmaceuticals used in molecular PET imaging consist of disease-targeting biomolecules tethered to chelators that complex
68
Ga
3+
. Ideally, the chelator will rapidly, quantitatively and stably coordinate
68
Ga
3+
at room temperature, near neutral pH and low chelator concentration, allowing for simple routine radiopharmaceutical formulation. Identification of chelators that fulfil these requirements will facilitate development of kit-based
68
Ga radiopharmaceuticals. Herein the reaction of a range of widely used macrocyclic and acyclic chelators with
68
Ga
3+
is reported. Radiochemical yields have been measured under conditions of varying chelator concentrations, pH (3.5 and 6.5) and temperature (25 and 90 °C). These chelators are: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), 1,4,7-triazacyclononane macrocycles substituted with phosphonic (NOTP) and phosphinic (TRAP) groups at the amine, bis(2-hydroxybenzyl)ethylenediaminediacetic acid (HBED), a tris(hydroxypyridinone) containing three 1,6-dimethyl-3-hydroxypyridin-4-one groups (THP) and the hexadentate tris(hydroxamate) siderophore desferrioxamine-B (DFO). Competition studies have also been undertaken to assess relative complexation efficiencies of each chelator for
68
Ga
3+
under different pH and temperature conditions. Performing radiolabelling reactions at pH 6.5, 25 °C and 5-50 μM chelator concentration resulted in near quantitative radiochemical yields for all chelators, except DOTA. Radiochemical yields either decreased or were not substantially improved when the reactions were undertaken at lower pH or at higher temperature, except in the case of DOTA. THP and DFO were the most effective
68
Ga
3+
chelators at near-neutral pH and 25 °C, rapidly providing near-quantitative radiochemical yields at very low chelator concentrations. NOTP and HBED were only slightly less effective under these conditions. In competition studies with all other chelators, THP demonstrated highest reactivity for
68
Ga
3+
complexation under all conditions. These data point to THP possessing ideal properties for rapid, one-step kit-based syntheses of
68
Ga-biomolecules for molecular PET imaging. LC-MS and
1
H,
13
C{
1
H} and
71
Ga NMR studies of HBED complexes of Ga
3+
showed that under the analytical conditions employed in this st |
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ISSN: | 2046-2069 2046-2069 |
DOI: | 10.1039/c7ra09076e |