Tilman Läppchen1, Yvonne Kiefer2, Jason P Holland3, Mark D Bartholomä4. 1. Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetterstrasse 55, D-79106 Freiburg, Germany; Department of Nuclear Medicine, Inselspital, Bern University Hospital and University of Bern, Freiburgstrasse, CH-3010 Bern, Switzerland. 2. Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetterstrasse 55, D-79106 Freiburg, Germany. 3. Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetterstrasse 55, D-79106 Freiburg, Germany; Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland. 4. Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetterstrasse 55, D-79106 Freiburg, Germany. Electronic address: mark.bartholomae@uniklinik-freiburg.de.
Abstract
INTRODUCTION: We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three five-membered azaheterocyclic arms for complexation of the PET nuclides gallium-68 and copper-64. The main objective of this study was to evaluate the stability and pharmacokinetics of 68Ga- and 64Cu-complexes of the bifunctional chelator NODIA-Me 1 covalently bound to a PSMA targeting vector in vivo. METHODS: NODIA-Me 1 was conjugated to the PSMA targeting Glu-NH-CO-NH-Lys moiety to give the bioconjugate NODIA-Me-NaI-Ahx-PSMA 4. The stability of [68Ga]4 and [64Cu]4 was assessed in vitro by serum stability studies. The PSMA binding affinity was determined in competitive cell experiments in LNCaP cells using 68Ga-PSMA-HBED-CC as radioligand. The stability and pharmacokinetics of [68Ga]4 and [64Cu]4 was evaluated by PET imaging and ex vivo biodistribution studies in mice bearing subcutaneous LNCaP tumors. RESULTS: In human serum, [68Ga]4 and [64Cu]4 remained intact to 85% (3 h) and 92% (24 h), respectively. Nature of the metal chelate influenced PSMA binding affinity with IC50 of 233 ± 10 nM for uncomplexed 4, 681 ± 7 nM for Cu-4 and 176 ± 10 nM for Ga-4. In animal studies, [68Ga]4 and [64Cu]4 revealed low uptake (≤1% IA g-1) in the majority of organs. Kidney uptake at 1 h p.i. was 6.28 ± 0.92% IA g-1 and 4.96 ± 0.79% IA g-1 and specific tumor uptake was 1.33 ± 0.46% IA g-1 and 2.15 ± 0.38% IA g-1 for [68Ga]4 and [64Cu]4, respectively. CONCLUSION: The bifunctional chelator NODIA-Me 1 was successfully conjugated to a PSMA targeting moiety. In small-animal PET imaging and ex vivo biodistribution studies, 68Ga- and 64Cu-labelled conjugates specifically delineated PSMA-positive LNCaP tumors and exhibited rapid renal clearance from non-target tissues with no significant demetallation/transchelation in vivo. The results support further development of this novel chelating platform for production of 68Ga- and 64Cu-labelled radiopharmaceuticals.
INTRODUCTION: We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three five-membered azaheterocyclic arms for complexation of the PET nuclides gallium-68 and copper-64. The main objective of this study was to evaluate the stability and pharmacokinetics of 68Ga- and 64Cu-complexes of the bifunctional chelator NODIA-Me 1 covalently bound to a PSMA targeting vector in vivo. METHODS:NODIA-Me 1 was conjugated to the PSMA targeting Glu-NH-CO-NH-Lys moiety to give the bioconjugate NODIA-Me-NaI-Ahx-PSMA 4. The stability of [68Ga]4 and [64Cu]4 was assessed in vitro by serum stability studies. The PSMA binding affinity was determined in competitive cell experiments in LNCaP cells using 68Ga-PSMA-HBED-CC as radioligand. The stability and pharmacokinetics of [68Ga]4 and [64Cu]4 was evaluated by PET imaging and ex vivo biodistribution studies in mice bearing subcutaneous LNCaP tumors. RESULTS: In human serum, [68Ga]4 and [64Cu]4 remained intact to 85% (3 h) and 92% (24 h), respectively. Nature of the metal chelate influenced PSMA binding affinity with IC50 of 233 ± 10 nM for uncomplexed 4, 681 ± 7 nM for Cu-4 and 176 ± 10 nM for Ga-4. In animal studies, [68Ga]4 and [64Cu]4 revealed low uptake (≤1% IA g-1) in the majority of organs. Kidney uptake at 1 h p.i. was 6.28 ± 0.92% IA g-1 and 4.96 ± 0.79% IA g-1 and specific tumor uptake was 1.33 ± 0.46% IA g-1 and 2.15 ± 0.38% IA g-1 for [68Ga]4 and [64Cu]4, respectively. CONCLUSION: The bifunctional chelator NODIA-Me 1 was successfully conjugated to a PSMA targeting moiety. In small-animal PET imaging and ex vivo biodistribution studies, 68Ga- and 64Cu-labelled conjugates specifically delineated PSMA-positive LNCaP tumors and exhibited rapid renal clearance from non-target tissues with no significant demetallation/transchelation in vivo. The results support further development of this novel chelating platform for production of 68Ga- and 64Cu-labelled radiopharmaceuticals.
Authors: Sebastian Martin; Stephan Maus; Tobias Stemler; Florian Rosar; Fadi Khreish; Jason P Holland; Samer Ezziddin; Mark D Bartholomä Journal: Mol Imaging Biol Date: 2020-08-27 Impact factor: 3.488