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Kerpa S, Schulze VR, Holzapfel M, Cvancar L, Fischer M, Maison W. Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T 1 relaxivity of Gd-complexes. ChemistryOpen 2024; 13:e202300298. [PMID: 38224205 PMCID: PMC11230940 DOI: 10.1002/open.202300298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2023] [Revised: 12/15/2023] [Indexed: 01/16/2024] Open
Abstract
High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1=7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.
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Affiliation(s)
- Svenja Kerpa
- Department of Chemistry, Institute of Pharmacy, Universität Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
| | - Verena R Schulze
- Fraunhofer Institute for Applied Polymer Research IAP, Center for Applied Nanotechnology CAN, Universität Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
| | - Malte Holzapfel
- Fraunhofer Institute for Applied Polymer Research IAP, Center for Applied Nanotechnology CAN, Universität Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
| | - Lina Cvancar
- Hamburg School of Food Science, Institute of Food Chemistry, University of Hamburg, Grindelallee 117, 20146, Hamburg, Germany
| | - Markus Fischer
- Hamburg School of Food Science, Institute of Food Chemistry, University of Hamburg, Grindelallee 117, 20146, Hamburg, Germany
| | - Wolfgang Maison
- Department of Chemistry, Institute of Pharmacy, Universität Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
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Maier KB, Rust LN, Kupara CI, Woods M. Diastereoselective Synthesis of α-Aryl-Substituted LnDOTA Chelates from Achiral Starting Materials by Deracemization Under Mild Conditions. Chemistry 2023; 29:e202301887. [PMID: 37519104 DOI: 10.1002/chem.202301887] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 07/26/2023] [Accepted: 07/26/2023] [Indexed: 08/01/2023]
Abstract
Substituted derivatives of the DOTA framework are of general interest to alter chelate properties and facilitate the conjugation of chelates to other molecular structures. However, the scope of substituents that can be introduced into the α-position has traditionally been limited by the availability of a suitable enantiopure starting materials to facilitate a stereoselective synthesis. Tetra-substituted DOTA derivatives with phenyl and benzoate substituents in the α-position have been prepared. Initial syntheses used enantiopure starting materials but did not afford enantiopure products. This indicates that the integrity of the stereocenters was not preserved during synthesis, despite the homo-chiral diastereoisomer being the major reaction product. The homochiral diastereoisomer could be produced as the major or sole reaction product when starting from racemic or even achiral materials. Deracemization was found to occur during chelation through the formation of an enolate stabilized by the aryl substituent. This general ability of aryl groups to enable deracemization greatly increases the range of substituents that can be introduced into DOTA-type ligands with diastereochemical selectivity.
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Affiliation(s)
- Karley B Maier
- Department of Chemistry, Portland State University 1719, SW 10th Ave, Portland, OR 97201, USA
| | - Lauren N Rust
- Department of Chemistry, Portland State University 1719, SW 10th Ave, Portland, OR 97201, USA
| | - Charlene I Kupara
- Department of Chemistry, Portland State University 1719, SW 10th Ave, Portland, OR 97201, USA
| | - Mark Woods
- Department of Chemistry, Portland State University 1719, SW 10th Ave, Portland, OR 97201, USA
- Advanced Imaging Research Center, Oregon Health and Science University, 1381 SW Sam Jackson Park Road, Portland, OR 97239, USA
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3
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Outzen L, Münzmay M, Frangioni JV, Maison W. Synthesis of Modular Desferrioxamine Analogues and Evaluation of Zwitterionic Derivatives for Zirconium Complexation. ChemMedChem 2023; 18:e202300112. [PMID: 37057615 DOI: 10.1002/cmdc.202300112] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 04/12/2023] [Accepted: 04/13/2023] [Indexed: 04/15/2023]
Abstract
The natural siderophore desferrioxamine B (DFOB) has been used for targeted PET imaging with 89 Zr before. However, Zr-DFOB has a limited stability and a number of derivatives have been developed with improved chelation properties for zirconium. We describe the synthesis of pseudopeptidic analogues of DFOB with azido side chains. These are termed AZA-DFO (hexadentate) and AZA-DFO* (octadentate) and are assembled via a modular synthesis from Orn-β-Ala and Lys-β-Ala. Nine different chelators have been conjugated to zwitterionic moieties by copper-catalyzed azide-alkyne cycloaddition (CuAAC). The resulting water-soluble chelators form Zr complexes under mild conditions (room temperature for 90 min). Transchelation assays with 1000-fold excess of EDTA and 300-fold excess of DFOB revealed that a short spacing of hydroxamates in (Orn-β-Ala)3-4 leads to improved complex stability compared to a longer spacing in (Lys-β-Ala)3-4 . We found that the alignment of amide groups in the pseudopeptide backbone and the presence of zwitterionic sidechains did not compromise the stability of the Zr-complexes with our chelators. We believe that the octadentate derivative AZA-DFO* is particularly valuable for the preparation of new Zr-chelators for targeted imaging which combine tunable pharmacokinetic properties with high complex stability and fast Zr-complexation kinetics.
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Affiliation(s)
- Lasse Outzen
- Department of Chemistry, University of Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
| | - Moritz Münzmay
- Department of Chemistry, University of Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
| | | | - Wolfgang Maison
- Department of Chemistry, University of Hamburg, Bundesstrasse 45, 20146, Hamburg, Germany
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Holzapfel M, Baldau T, Kerpa S, Guadalupi G, Qi B, Liu Y, Parak WJ, Maison W. Solution Structure and Relaxivity of Ln‐DOTXAZA Derivatives. Eur J Inorg Chem 2022. [DOI: 10.1002/ejic.202200432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Malte Holzapfel
- Fraunhofer Institute for Applied Polymer Research: Fraunhofer-Institut fur Angewandte Polymerforschung IAP Center for Applied Nanoscience GERMANY
| | - Torben Baldau
- Universität Hamburg: Universitat Hamburg Department of Chemistry GERMANY
| | - Svenja Kerpa
- Universität Hamburg: Universitat Hamburg Department of Chemistry GERMANY
| | | | - Bing Qi
- Universität Hamburg: Universitat Hamburg Center for Hybrid Nanostructure GERMANY
| | - Yang Liu
- Universität Hamburg: Universitat Hamburg Center for Hybrid Nanostructure GERMANY
| | - Wolfgang J. Parak
- Universität Hamburg: Universitat Hamburg Center for Hybrid Nanostructure GERMANY
| | - Wolfgang Maison
- University of Hamburg Chemistry Bundesstr. 45 20146 Hamburg GERMANY
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Kaeopookum P, Petrik M, Summer D, Klinger M, Zhai C, Rangger C, Haubner R, Haas H, Hajduch M, Decristoforo C. Comparison of 68Ga-labeled RGD mono- and multimers based on a clickable siderophore-based scaffold. Nucl Med Biol 2019; 78-79:1-10. [PMID: 31678781 DOI: 10.1016/j.nucmedbio.2019.09.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 09/23/2019] [Accepted: 09/30/2019] [Indexed: 02/06/2023]
Abstract
Cyclic pentapeptides containing the amino acid sequence arginine-glycine-aspartic (RGD) have been widely applied to target αvβ3 integrin, which is upregulated in various tumors during tumor-induced angiogenesis. Multimeric cyclic RGD peptides have been reported to be advantageous over monomeric counterparts for angiogenesis imaging. Here, we prepared mono-, di-, and trimeric cyclic arginine-glycine-aspartic-D-phenylalanine-lysine (c (RGDfK)) derivatives by conjugation with the natural chelator fusarinine C (FSC) using click chemistry based on copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC). The αvβ3 binding properties of 68Ga-labeled mono-, di-, and trimeric c(RGDfK) peptides were evaluated in vitro as well as in vivo and compared with the references monomeric [68Ga]GaNODAGA-c(RGDfK) and trimeric [68Ga]GaFSC(suc-c(RGDfK))3. All 68Ga-labeled c(RGDfK) peptides displayed hydrophilicity (logD = -2.96 to -3.80), low protein binding and were stable in phosphate buffered-saline (PBS) and serum up to 2 h. In vitro internalization assays with human melanoma M21 (αvβ3-positive) and M21-L (αvβ3-negative) cell lines showed specific uptake of all derivatives and increased in the series: mono- < di- < trimeric peptide. The highest tumor uptake, tumor-to-background ratios, and image contrast were found for the dimeric [68Ga]GaMAFC(c(RGDfK)aza)2. In conclusion, we developed a novel strategy for direct, straight forward preparation of mono-, di-, and trimeric c(RGDfK) conjugates based on the FSC scaffold. Interestingly, the best αvβ3 imaging properties were found for the dimeric [68Ga]GaMAFC(c(RGDfK)aza)2.
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Affiliation(s)
- Piriya Kaeopookum
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria; Research and Development Division, Thailand Institute of Nuclear Technology, Nakhon Nayok, Thailand
| | - Milos Petrik
- Institute of Molecular and Translational Medicine, Faculty of Medicine and Dentistry, Palacky University, Olomouc, Czech Republic
| | - Dominik Summer
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Maximilian Klinger
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Chuangyan Zhai
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria; School of Forensic Medicine, Southern Medical University, Guangzhou, China
| | - Christine Rangger
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Roland Haubner
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Hubertus Haas
- Division of Molecular Biology, Biocenter, Medical University Innsbruck, Innsbruck, Austria
| | - Marian Hajduch
- Institute of Molecular and Translational Medicine, Faculty of Medicine and Dentistry, Palacky University, Olomouc, Czech Republic
| | - Clemens Decristoforo
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria.
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Aoki T, Yoshizawa H, Yamawaki K, Yokoo K, Sato J, Hisakawa S, Hasegawa Y, Kusano H, Sano M, Sugimoto H, Nishitani Y, Sato T, Tsuji M, Nakamura R, Nishikawa T, Yamano Y. Cefiderocol (S-649266), A new siderophore cephalosporin exhibiting potent activities against Pseudomonas aeruginosa and other gram-negative pathogens including multi-drug resistant bacteria: Structure activity relationship. Eur J Med Chem 2018; 155:847-868. [PMID: 29960205 DOI: 10.1016/j.ejmech.2018.06.014] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 05/21/2018] [Accepted: 06/04/2018] [Indexed: 12/21/2022]
Abstract
The structure-activity relationship (SAR) for a novel series of catechol conjugated siderophore cephalosporins is described with their in vitro activities against multi-drug resistant Gram-negative pathogens including Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia and Enterobacteriaceae. Cefiderocol (3) was one of the best molecules which displayed well-balanced and potent activities against multi-drug resistant Gram-negative pathogens including carbapenem resistant bacteria among the prepared compounds with the modified C-7 side chain and the modified C-3 side chain. Cefiderocol (3) is a highly promising parenteral cephalosporin for the treatment of multi-drug resistant Gram-negative infection.
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Affiliation(s)
- Toshiaki Aoki
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan.
| | - Hidenori Yoshizawa
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Kenji Yamawaki
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Katsuki Yokoo
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Jun Sato
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Shinya Hisakawa
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Yasushi Hasegawa
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Hiroki Kusano
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Masayuki Sano
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Hideki Sugimoto
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Yasuhiro Nishitani
- Medicinal Chemistry Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Takafumi Sato
- Drug Discovery & Disease Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Masakatsu Tsuji
- Drug Discovery & Disease Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Rio Nakamura
- Drug Discovery & Disease Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Toru Nishikawa
- Drug Discovery & Disease Research Laboratory, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
| | - Yoshinori Yamano
- Pharmaceutical Research Division, Shionogi & Co., Ltd., 1-1, Futabacho, 3-chome, Toyonaka, 561-0825, Osaka, Japan
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Binuclear gadolinium(III) complex based on DTPA and 1,3-bis(4-aminophenyl)adamantane as a high-relaxivity MRI contrast agent. Polyhedron 2018. [DOI: 10.1016/j.poly.2018.01.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Whittenberg JJ, Li H, Zhou H, Koziol J, Desai AV, Reichert DE, Kenis PJA. “Click Chip” Conjugation of Bifunctional Chelators to Biomolecules. Bioconjug Chem 2017; 28:986-994. [DOI: 10.1021/acs.bioconjchem.6b00703] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Joseph J. Whittenberg
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Hairong Li
- Radiological
Sciences Division, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, Campus Box 8225, St. Louis, Missouri 63110, United States
| | - Haiying Zhou
- Radiological
Sciences Division, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, Campus Box 8225, St. Louis, Missouri 63110, United States
| | - Jan Koziol
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Amit V. Desai
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - David E. Reichert
- Radiological
Sciences Division, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, Campus Box 8225, St. Louis, Missouri 63110, United States
| | - Paul J. A. Kenis
- Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
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Notni J, Wester HJ. A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry. Chemistry 2016; 22:11500-8. [PMID: 27333118 DOI: 10.1002/chem.201600928] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Indexed: 12/23/2022]
Abstract
The copper-catalyzed cycloaddition of organic azides and alkynes (CuAAC) is one of the most popular reactions for rapid assembly of multifunctional molecular frameworks from commercially available building blocks. It is also attractive for synthesis of conjugates of multidentate chelate ligands (chelators) with molecular targeting vectors, such as peptides or proteins, which serve as precursors for labeling with metal radionuclides or are useful as MRI contrast agents after Gd(III) complexation. However, applicability of CuAAC for such purposes is complicated by formation of unwanted copper chelates. The alternative use of copper-free click chemistry, for example, the strain-promoted alkyne-azide cycloaddition (SPAAC) or the Diels-Alder reaction of tetrazines and strained alkenes, entails other specific challenges: Introduction of large, isomerically non-homogeneous and hydrophobic linker groups affects product homogeneity and can severely change pharmacokinetic profiles. Against this background, this review elucidates scope and applicability of both Cu-catalyzed and Cu-free alkyne-azide cycloadditions pertinent to the elaboration of radiometal chelates and MRI contrast agents, with an emphasis on strategies to tackle the problem of copper complexation during CuAAC.
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Affiliation(s)
- Johannes Notni
- Lehrstuhl für Pharmazeutische Radiochemie, Technische Universität München, Walther-Meißner Strasse 3, 85748, Garching, Germany.
| | - Hans-Jürgen Wester
- Lehrstuhl für Pharmazeutische Radiochemie, Technische Universität München, Walther-Meißner Strasse 3, 85748, Garching, Germany
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Kriemen E, Holzapfel M, Ruf E, Rehbein J, Maison W. Synthesis and Structural Analysis of 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraazidoethylacetic Acid (DOTAZA) Complexes. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201500789] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Baranyai Z, Reich D, Vágner A, Weineisen M, Tóth I, Wester HJ, Notni J. A shortcut to high-affinity Ga-68 and Cu-64 radiopharmaceuticals: one-pot click chemistry trimerisation on the TRAP platform. Dalton Trans 2015; 44:11137-46. [PMID: 25999035 DOI: 10.1039/c5dt00576k] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Due to its 3 carbonic acid groups being available for bioconjugation, the TRAP chelator (1,4,7-triazacyclononane-1,4,7-tris(methylene(2-carboxyethylphosphinic acid))) is chosen for the synthesis of trimeric bioconjugates for radiolabelling. We optimized a protocol for bio-orthogonal TRAP conjugation via Cu(I)-catalyzed Huisgen-cycloaddition of terminal azides and alkynes (CuAAC), including a detailed investigation of kinetic properties of Cu(II)-TRAP complexes. TRAP building blocks for CuAAC, TRAP(alkyne)3 and TRAP(azide)3 were obtained by amide coupling of propargylamine/3-azidopropyl-1-amine, respectively. For Cu(II) complexes of neat and triply amide-functionalized TRAP, the equilibrium properties as well as pseudo-first-order Cu(II)-transchelation, using 10 to 30 eq. of NOTA and EDTA, were studied by UV-spectrophotometry. Dissociation of any Cu(II)-TRAP species was found to be independent on the nature or excess of a competing chelator, confirming a proton-driven two-step mechanism. The respective thermodynamic stability constants (log K(ML): 19.1 and 17.6) and dissociation rates (k: 38 × 10(-6) and 7 × 10(-6) s(-1), 298 K, pH 4) show that the Cu(II) complex of the TRAP-conjugate possesses lower thermodynamic stability but higher kinetic inertness. At pH 2-3, its demetallation with NOTA was complete within several hours/days at room temperature, respectively, enabling facile Cu(II) removal after click coupling by direct addition of NOTA trihydrochloride to the CuAAC reaction mixture. Notwithstanding this, an extrapolated dissociation half life of >100 h at 37 °C and pH 7 confirms the suitability of TRAP-bioconjugates for application in Cu-64 PET (cf. t(1/2)(Cu-64) = 12.7 h). To showcase advantages of the method, TRAP(DUPA-Pep)3, a trimer of the PSMA inhibitor DUPA-Pep, was synthesized using 1 eq. TRAP(alkyne)3, 3.3 eq. DUPA-Pep-azide, 10 eq. Na ascorbate, and 1.2 eq. Cu(II)-acetate. Its PSMA affinity (IC50), determined by the competition assay on LNCaP cells, was 18-times higher than that of the corresponding DOTAGA monomer (IC50: 2 ± 0.1 vs. 36 ± 4 nM), resulting in markedly improved contrast in Ga-68-PET imaging. In conclusion, the kinetic inertness profile of Cu(II)-TRAP conjugates allows for simple Cu(II) removal after click functionalisation by means of transchelation, but also confirms their suitability for Cu-64-PET as demonstrated previously (Dalton Trans., 2012, 41, 13803).
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Affiliation(s)
- Zsolt Baranyai
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4032, Hungary
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