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Abstract
Positron emission tomography (PET) constitutes a functional imaging technique that is harnessed to probe biological processes in vivo. PET imaging has been used to diagnose and monitor the progression of diseases, as well as to facilitate drug development efforts at both preclinical and clinical stages. The wide applications and rapid development of PET have ultimately led to an increasing demand for new methods in radiochemistry, with the aim to expand the scope of synthons amenable for radiolabeling. In this work, we provide an overview of commonly used chemical transformations for the syntheses of PET tracers in all aspects of radiochemistry, thereby highlighting recent breakthrough discoveries and contemporary challenges in the field. We discuss the use of biologicals for PET imaging and highlight general examples of successful probe discoveries for molecular imaging with PET - with a particular focus on translational and scalable radiochemistry concepts that have been entered to clinical use.
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Affiliation(s)
- Jian Rong
- Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Rd, Atlanta, GA, 30322, USA
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Ahmed Haider
- Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Rd, Atlanta, GA, 30322, USA
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Troels E Jeppesen
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Lee Josephson
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Steven H Liang
- Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Rd, Atlanta, GA, 30322, USA.
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA.
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2
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Schlesinger M, Jentschel C, Pietzsch HJ, Kopka K, Mamat C. Copper-free click bioconjugation of technetium-99m complexes using strained cyclononyne derivatives. Dalton Trans 2023; 52:3024-3032. [PMID: 36779384 DOI: 10.1039/d2dt03965f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Click chemistry, in particular copper-free click reactions, has gained growing interest for radiolabelling purposes in the field of radiopharmaceutical sciences. [99mTc][Tc(CO)3(H2O)3]+ works as an excellent starting complex for the radiolabelling of biomolecules under mild conditions. A new chelator, investigated for the copper-free strain-promoted cycloaddition (SPAAC), was synthesised containing the 2,2'-dipicolylamine (DPA) moiety for the 99mTc-tricarbonyl core and compared with a DPA chelator based on activated esters for conventional radiolabelling. For the copper-free click labelling procedure, a DPA containing 4,8-diazacyclononyne moiety was prepared from a sulfonyl-modified diamide (four steps, 64% yield) followed by the Nicholas reaction with butyne-1,3-diol. The 99mTc-DPA-DACN-complex was prepared with a radiochemical conversion (RCC) of 89% after 30 min. The following SPAAC reaction with an azide-functionalised PSMA molecule was performed within 4-5 hours at 100 °C to obtain the PSMA (prostate-specific membrane antigen) targeting 99mTc-complex with 79% RCC and without side products. For comparison, a second DPA-chelator based on a tetrafluorophenyl (TFP) ester was prepared (three steps, 64% yield) and was successfully radiolabelled with [[99mTc]Tc(CO)3(H2O)3]+ with 89% RCC after 20 min and >99% radiochemical purity after separation using an RP18 cartridge. The subsequent conjugation of an amine-functionalised PSMA targeting molecule was performed with 23% RCC after 150 min. Two other unknown side products were observed indicating the decomposition of the TFP ester during the labelling. All nonradioactive Re(CO)3 complexes were synthesised from (Et4N)2[ReBr3(CO)3] (91% yield for the natRe-DPA-TFP ester, 76% yield for natRe-DPA-DACN) and characterised to confirm the identity of the 99mTc-complexes.
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Affiliation(s)
- Marlene Schlesinger
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. .,Universität Leipzig, Fakultät für Chemie und Mineralogie, Johannisallee 29, D-04103 Leipzig, Germany
| | - Christian Jentschel
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany.
| | - Hans-Jürgen Pietzsch
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany.
| | - Klaus Kopka
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. .,Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Constantin Mamat
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. .,Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
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3
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Abstract
The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile techniques to introduce fluorine‐18, especially for the radiolabelling of biologically or pharmacologically active molecules. Taking into consideration that the introduction of fluorine‐18 (t1/2=109.8 min) mostly proceeds under harsh conditions, radiolabelling of such molecules represents a challenge and is of enormous interest. Ideally, it should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. Special attention has been drawn to 2‐fluoroethyl and 3‐fluoropropyl groups, which are often the active sites of radiofluorinated compounds. Precursors containing an ammonium leaving group – such as a strained azetidinium or aziridinium moiety – can help to overcome these obstacles leading to a convenient and mild introduction of [18F]fluoride with high radiochemical yields.
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Affiliation(s)
- Falco Reissig
- Institut für Radiopharmazeutische Krebsforschung Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328, Dresden, Germany.,Fakultät Chemie und Lebensmittelchemie, Technische Universität Dresden, 01062, Dresden, Germany
| | - Constantin Mamat
- Institut für Radiopharmazeutische Krebsforschung Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328, Dresden, Germany.,Fakultät Chemie und Lebensmittelchemie, Technische Universität Dresden, 01062, Dresden, Germany
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Kwan KH, Burvenich IJG, Centenera MM, Goh YW, Rigopoulos A, Dehairs J, Swinnen JV, Raj GV, Hoy AJ, Butler LM, Scott AM, White JM, Ackermann U. Synthesis and fluorine-18 radiolabeling of a phospholipid as a PET imaging agent for prostate cancer. Nucl Med Biol 2020; 93:37-45. [PMID: 33310350 DOI: 10.1016/j.nucmedbio.2020.11.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 11/14/2020] [Accepted: 11/22/2020] [Indexed: 12/22/2022]
Abstract
INTRODUCTION Altered lipid metabolism and subsequent changes in cellular lipid composition have been observed in prostate cancer cells, are associated with poor clinical outcome, and are promising targets for metabolic therapies. This study reports for the first time on the synthesis of a phospholipid radiotracer based on the phospholipid 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine (PC44:12) to allow tracking of polyunsaturated lipid tumor uptake via PET imaging. This tracer may aid in the development of strategies to modulate response to therapies targeting lipid metabolism in prostate cancer. METHODS Lipidomics analysis of prostate tumor explants and LNCaP tumor cells were used to identify PC44:12 as a potential phospholipid candidate for radiotracer development. Synthesis of phosphocholine precursor and non-radioactive standard were optimised using click chemistry. The biodistribution of a fluorine-18 labeled analogue, N-{[4-(2-[18F]fluoroethyl)-2,3,4-triazol-1-yl]methyl}-1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine ([18F]2) was determined in LNCaP prostate tumor-bearing NOD SCID gamma mice by ex vivo biodistribution and PET imaging studies and compared to biodistribution of [18F]fluoromethylcholine. RESULTS [18F]2 was produced with a decay-corrected yield of 17.8 ± 3.7% and an average radiochemical purity of 97.00 ± 0.89% (n = 6). Molar activity was 85.1 ± 3.45 GBq/μmol (2300 ± 93 mCi/μmol) and the total synthesis time was 2 h. Ex vivo biodistribution data demonstrated high liver uptake (41.1 ± 9.2%ID/g) and high splenic uptake (10.9 ± 9.1%ID/g) 50 min post-injection. Ex vivo biodistribution showed low absolute tumor uptake of [18F]2 (0.8 ± 0.3%ID/g). However, dynamic PET imaging demonstrated an increase over time of the relative tumor-to-muscle ratio with a peak of 2.8 ± 0.5 reached 1 h post-injection. In contrast, dynamic PET of [18F]fluoromethylcholine demonstrated no increase in tumor-to-muscle ratios due to an increase in both tumor and muscle over time. Absolute uptake of [18F]fluoromethylcholine was higher and peaked at 60 min post injection (2.25 ± 0.29%ID/g) compared to [18F]2 (1.44 ± 0.06%ID/g) during the 1 h dynamic scan period. CONCLUSIONS AND ADVANCES IN KNOWLEDGE This study demonstrates the ability to radiolabel phospholipids and indicates the potential to monitor the in vivo distribution of phospholipids using fluorine-18 based PET.
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Affiliation(s)
- Kim H Kwan
- School of Chemistry, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Australia
| | - Ingrid J G Burvenich
- Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Australia.
| | - Margaret M Centenera
- Adelaide Medical School and Freemasons Foundation Centre for Men's Health, University of Adelaide, Adelaide, Australia; South Australian Health and Medical Research Institute, Adelaide, Australia
| | - Yit Wooi Goh
- Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Australia
| | - Angela Rigopoulos
- Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Australia
| | - Jonas Dehairs
- Laboratory of Lipid Metabolism and Cancer, Department of Oncology, LKI - Leuven Cancer Institute, KU Leuven - University of Leuven, Leuven, Belgium
| | - Johannes V Swinnen
- Laboratory of Lipid Metabolism and Cancer, Department of Oncology, LKI - Leuven Cancer Institute, KU Leuven - University of Leuven, Leuven, Belgium
| | - Ganesh V Raj
- Department of Urology, UT Southwestern Medical Center at Dallas, TX, USA; Department of Pharmacology, UT Southwestern Medical Center at Dallas, TX, USA
| | - Andrew J Hoy
- School of Medical Sciences, The University of Sydney, Sydney, Australia
| | - Lisa M Butler
- Adelaide Medical School and Freemasons Foundation Centre for Men's Health, University of Adelaide, Adelaide, Australia; South Australian Health and Medical Research Institute, Adelaide, Australia
| | - Andrew M Scott
- Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Australia; Department of Molecular Imaging and Therapy, Austin Health, Heidelberg, Australia; Department of Medicine, Melbourne University, Melbourne, Australia
| | - Jonathan M White
- School of Chemistry, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Australia
| | - Uwe Ackermann
- Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Australia; Department of Molecular Imaging and Therapy, Austin Health, Heidelberg, Australia; Department of Medicine, Melbourne University, Melbourne, Australia.
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5
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Pretze M, Neuber C, Kinski E, Belter B, Köckerling M, Caflisch A, Steinbach J, Pietzsch J, Mamat C. Synthesis, radiolabelling and initial biological characterisation of 18F-labelled xanthine derivatives for PET imaging of Eph receptors. Org Biomol Chem 2020; 18:3104-3116. [PMID: 32253415 DOI: 10.1039/d0ob00391c] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Eph receptor tyrosine kinases, particularly EphA2 and EphB4, represent promising candidates for molecular imaging due to their essential role in cancer progression and therapy resistance. Xanthine derivatives were identified to be potent Eph receptor inhibitors with IC50 values in the low nanomolar range (1-40 nm). These compounds occupy the hydrophobic pocket of the ATP-binding site in the kinase domain. Based on lead compound 1, we designed two fluorine-18-labelled receptor tyrosine kinase inhibitors ([18F]2/3) as potential tracers for positron emission tomography (PET). Docking into the ATP-binding site allowed us to find the best position for radiolabelling. The replacement of the methyl group at the uracil residue ([18F]3) rather than the methyl group of the phenoxy moiety ([18F]2) by a fluoropropyl group was predicted to preserve the affinity of the lead compound 1. Herein, we point out a synthesis route to [18F]2 and [18F]3 and the respective tosylate precursors as well as a labelling procedure to insert fluorine-18. After radiolabelling, both radiotracers were obtained in approximately 5% radiochemical yield with high radiochemical purity (>98%) and a molar activity of >10 GBq μmol-1. In line with the docking studies, first cell experiments revealed specific, time-dependent binding and uptake of [18F]3 to EphA2 and EphB4-overexpressing A375 human melanoma cells, whereas [18F]2 did not accumulate at these cells. Since both tracers [18F]3 and [18F]2 are stable in rat blood, the novel radiotracers might be suitable for in vivo molecular imaging of Eph receptors with PET.
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Affiliation(s)
- Marc Pretze
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. and Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Christin Neuber
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany.
| | - Elisa Kinski
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany.
| | - Birgit Belter
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany.
| | - Martin Köckerling
- Universität Rostock, Institut für Chemie - Anorganische Festkörperchemie, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany
| | - Amedeo Caflisch
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Jörg Steinbach
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. and Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Jens Pietzsch
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. and Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Constantin Mamat
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany. and Technische Universität Dresden, Fakultät Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
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6
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Geri S, Krunclova T, Janouskova O, Panek J, Hruby M, Hernández‐Valdés D, Probst B, Alberto RA, Mamat C, Kubeil M, Stephan H. Light-Activated Carbon Monoxide Prodrugs Based on Bipyridyl Dicarbonyl Ruthenium(II) Complexes. Chemistry 2020; 26:10992-11006. [PMID: 32700815 PMCID: PMC7496190 DOI: 10.1002/chem.202002139] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Indexed: 12/13/2022]
Abstract
Two photoactivatable dicarbonyl ruthenium(II) complexes based on an amide-functionalised bipyridine scaffold (4-position) equipped with an alkyne functionality or a green-fluorescent BODIPY (boron-dipyrromethene) dye have been prepared and used to investigate their light-induced decarbonylation. UV/Vis, FTIR and 13 C NMR spectroscopies as well as gas chromatography and multivariate curve resolution alternating least-squares analysis (MCR-ALS) were used to elucidate the mechanism of the decarbonylation process. Release of the first CO molecule occurs very quickly, while release of the second CO molecule proceeds more slowly. In vitro studies using two cell lines A431 (human squamous carcinoma) and HEK293 (human embryonic kidney cells) have been carried out in order to characterise the anti-proliferative and anti-apoptotic activities. The BODIPY-labelled compound allows for monitoring the cellular uptake, showing fast internalisation kinetics and accumulation at the endoplasmic reticulum and mitochondria.
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Affiliation(s)
- Stepan Geri
- Institute of Radiopharmaceutical Cancer ResearchHelmholtz-Zentrum Dresden-RossendorfBautzner Landstrasse 40001328DresdenGermany
| | - Tereza Krunclova
- Department of Biological ModelsInstitute of Macromolecular ChemistryHeyrovsky Square 216206PragueCzech Republic
| | - Olga Janouskova
- Department of Biological ModelsInstitute of Macromolecular ChemistryHeyrovsky Square 216206PragueCzech Republic
| | - Jiri Panek
- Supramolecular Polymer SystemsInstitute of Macromolecular ChemistryHeyrovsky Square 216206PragueCzech Republic
| | - Martin Hruby
- Supramolecular Polymer SystemsInstitute of Macromolecular ChemistryHeyrovsky Square 216206PragueCzech Republic
| | | | - Benjamin Probst
- Department of ChemistryUniversity of ZurichWinterthurerstr. 1908057ZurichSwitzerland
| | - Roger A. Alberto
- Department of ChemistryUniversity of ZurichWinterthurerstr. 1908057ZurichSwitzerland
| | - Constantin Mamat
- Institute of Radiopharmaceutical Cancer ResearchHelmholtz-Zentrum Dresden-RossendorfBautzner Landstrasse 40001328DresdenGermany
| | - Manja Kubeil
- Institute of Radiopharmaceutical Cancer ResearchHelmholtz-Zentrum Dresden-RossendorfBautzner Landstrasse 40001328DresdenGermany
| | - Holger Stephan
- Institute of Radiopharmaceutical Cancer ResearchHelmholtz-Zentrum Dresden-RossendorfBautzner Landstrasse 40001328DresdenGermany
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7
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Neuber C, Belter B, Mamat C, Pietzsch J. Radiopharmacologist's and Radiochemist's View on Targeting the Eph/Ephrin Receptor Tyrosine Kinase System. ACS Omega 2020; 5:16318-16331. [PMID: 32685795 PMCID: PMC7364440 DOI: 10.1021/acsomega.0c01058] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 05/25/2020] [Indexed: 05/06/2023]
Abstract
In the past decade, there have been extensive efforts to open up the Eph/ephrin subfamily of the receptor tyrosine kinase family for diagnostic and therapeutic applications. Besides classical pharmaceutical developments, which focus either on drugs targeting the extracellular ligand binding domains or on the intracellular tyrosine kinase domains of these receptors, there also have been first radiopharmaceutical approaches. Here the focus is on the development of specific and selective probes for molecular imaging, particularly by means of positron emission tomography, and the functional characterization of the Eph/ephrin subfamily in certain target tissues. The aim of this mini-review is to summarize the different approaches toward Eph-targeting radiotracers by using antibodies, peptides, and small molecules and to discuss their radiopharmacological characterization. With regard to the small molecules, further considerations will focus on the design and synthesis of nonradioactive reference compounds and precursors as well as on radiolabeling strategies.
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Affiliation(s)
- Christin Neuber
- Helmholtz-Zentrum
Dresden-Rossendorf (HZDR), Institute of Radiopharmaceutical Cancer
Research, Department of Radiopharmaceutical
and Chemical Biology, 01328 Dresden, Germany
| | - Birgit Belter
- Helmholtz-Zentrum
Dresden-Rossendorf (HZDR), Institute of Radiopharmaceutical Cancer
Research, Department of Radiopharmaceutical
and Chemical Biology, 01328 Dresden, Germany
| | - Constantin Mamat
- Helmholtz-Zentrum
Dresden-Rossendorf (HZDR), Institute of Radiopharmaceutical Cancer
Research, Department of Radionuclide Theragnostics, 01328 Dresden, Germany
- Technische
Universität Dresden, School of Science,
Faculty of Chemistry and Food Chemistry, 01062 Dresden, Germany
| | - Jens Pietzsch
- Helmholtz-Zentrum
Dresden-Rossendorf (HZDR), Institute of Radiopharmaceutical Cancer
Research, Department of Radiopharmaceutical
and Chemical Biology, 01328 Dresden, Germany
- Technische
Universität Dresden, School of Science,
Faculty of Chemistry and Food Chemistry, 01062 Dresden, Germany
- E-mail:
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Wagener K, Renisch D, Schinnerer M, Worm M, Jakob Y, Eberhardt K, Rösch F. Copper-catalyzed click reactions: quantification of retained copper using 64Cu-spiked Cu(I), exemplified for CuAAC reactions on liposomes. RADIOCHIM ACTA 2018. [DOI: 10.1515/ract-2018-3000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Abstract
The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is a powerful, highly reliable and selective reaction which allows for a rapid synthesis in high yields and under mild conditions (pH, temperature). However, the cytotoxicity of copper requires its complete removal prior to an application in vivo. This is an issue especially when it comes to CuAAC reactions on macromolecular structures or drug delivery systems, as copper might be retained by these systems. Thus, a quantification of the final copper content of these systems is inevitable, which we exemplified for a CuAAC reaction on liposomes using 64Cu-spiked Cu(I). In this respect, a Cu(II) nitrate solution was irradiated at the TRIGA Mark II research reactor Mainz to obtain c.a. [64Cu]Cu(II). The irradiated solution was directly used for a CuAAC on liposomes. After purification, their copper content was calculated utilizing γ-ray spectrometry. Only 0.018% of the added 64Cu-activity was still present in the liposome containing fractions after purification. This refers to a total amount of copper of 0.17 ng. The amount of retained copper is so low, that an in vivo application of the liposomes is absolutely reasonable. Besides this particular study, the experimental methodology may be applied to study many other CuAAC reactions, used for the synthesis of radiolabeled or non-radioactive species, which are intended for human applications.
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Affiliation(s)
- Karolin Wagener
- Institute of Nuclear Chemistry, Johannes Gutenberg University , Fritz-Strassmann-Weg 2 , 55128 Mainz , Germany
| | - Dennis Renisch
- Institute of Nuclear Chemistry, Johannes Gutenberg University , Fritz-Strassmann-Weg 2 , 55128 Mainz , Germany
| | - Meike Schinnerer
- Institute of Physical Chemistry, Johannes Gutenberg University , Jakob-Welder-Weg 11 , 55128 Mainz , Germany
| | - Matthias Worm
- Institute of Organic Chemistry, Johannes Gutenberg University , Duesbergweg 10-14 , 55128 Mainz , Germany
| | - Yvonne Jakob
- Institute of Nuclear Chemistry, Johannes Gutenberg University , Fritz-Strassmann-Weg 2 , 55128 Mainz , Germany
| | - Klaus Eberhardt
- Institute of Nuclear Chemistry, Johannes Gutenberg University , Fritz-Strassmann-Weg 2 , 55128 Mainz , Germany
| | - Frank Rösch
- Institute of Nuclear Chemistry, Johannes Gutenberg University , Fritz-Strassmann-Weg 2 , 55128 Mainz , Germany
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9
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Morris O, Fairclough M, Grigg J, Prenant C, McMahon A. A review of approaches to 18
F radiolabelling affinity peptides and proteins. J Labelled Comp Radiopharm 2018; 62:4-23. [DOI: 10.1002/jlcr.3634] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 04/23/2018] [Accepted: 04/23/2018] [Indexed: 12/15/2022]
Affiliation(s)
- O. Morris
- Wolfson Molecular Imaging Centre; The University of Manchester; UK
- CRUK/EPSRC Imaging Centre in Cambridge & Manchester; The University of Manchester; UK
| | - M. Fairclough
- Wolfson Molecular Imaging Centre; The University of Manchester; UK
- CRUK/EPSRC Imaging Centre in Cambridge & Manchester; The University of Manchester; UK
| | | | - C. Prenant
- Wolfson Molecular Imaging Centre; The University of Manchester; UK
- CRUK/EPSRC Imaging Centre in Cambridge & Manchester; The University of Manchester; UK
| | - A. McMahon
- Wolfson Molecular Imaging Centre; The University of Manchester; UK
- CRUK/EPSRC Imaging Centre in Cambridge & Manchester; The University of Manchester; UK
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10
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Abstract
Positron emission tomography (PET) imaging study of fluorine-18 labeled biomolecules is an emerging and rapidly growing area for preclinical and clinical research. The present review focuses on recent advances in radiochemical methods for incorporating fluorine-18 into biomolecules via "direct" or "indirect" bioconjugation. Recently developed prosthetic groups and pre-targeting strategies, as well as representative examples in 18 F-labeling of biomolecules in PET imaging research studies are highlighted.
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Affiliation(s)
- Hema S. Krishnan
- Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Longle Ma
- Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Neil Vasdev
- Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
| | - Steven H. Liang
- Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA, 02114, USA
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11
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Abstract
The advent of click chemistry has had a profound influence on almost all branches of chemical science. This is particularly true of radiochemistry and the synthesis of agents for positron emission tomography (PET), single photon emission computed tomography (SPECT), and targeted radiotherapy. The selectivity, ease, rapidity, and modularity of click ligations make them nearly ideally suited for the construction of radiotracers, a process that often involves working with biomolecules in aqueous conditions with inexorably decaying radioisotopes. In the following pages, our goal is to provide a broad overview of the first 10 years of research at the intersection of click chemistry and radiochemistry. The discussion will focus on four areas that we believe underscore the critical advantages provided by click chemistry: (i) the use of prosthetic groups for radiolabeling reactions, (ii) the creation of coordination scaffolds for radiometals, (iii) the site-specific radiolabeling of proteins and peptides, and (iv) the development of strategies for in vivo pretargeting. Particular emphasis will be placed on the four most prevalent click reactions-the Cu-catalyzed azide-alkyne cycloaddition (CuAAC), the strain-promoted azide-alkyne cycloaddition (SPAAC), the inverse electron demand Diels-Alder reaction (IEDDA), and the Staudinger ligation-although less well-known click ligations will be discussed as well. Ultimately, it is our hope that this review will not only serve to educate readers but will also act as a springboard, inspiring synthetic chemists and radiochemists alike to harness click chemistry in even more innovative and ambitious ways as we embark upon the second decade of this fruitful collaboration.
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Affiliation(s)
| | - Pierre Adumeau
- Department of Chemistry, Hunter College of the City University of New York , 413 East 69th Street, New York, New York 10028, United States
| | - Jason S Lewis
- Department of Radiology, Weill Cornell Medical College , 520 East 70th Street, New York, New York 10065, United States
| | - Brian M Zeglis
- Department of Chemistry, Hunter College of the City University of New York , 413 East 69th Street, New York, New York 10028, United States.,Department of Radiology, Weill Cornell Medical College , 520 East 70th Street, New York, New York 10065, United States.,Ph.D. Program in Chemistry, The Graduate Center of the City University of New York , 365 5th Avenue, New York, New York 10016, United States
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12
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Mamat C, Pretze M, Gott M, Köckerling M. Synthesis, dynamic NMR characterization and XRD studies of novel N, N'-substituted piperazines for bioorthogonal labeling. Beilstein J Org Chem 2016; 12:2478-2489. [PMID: 28144316 PMCID: PMC5238536 DOI: 10.3762/bjoc.12.242] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Accepted: 10/31/2016] [Indexed: 12/12/2022] Open
Abstract
Novel, functionalized piperazine derivatives were successfully synthesized and fully characterized by 1H/13C/19F NMR, MS, elemental analysis and lipophilicity. All piperazine compounds occur as conformers resulting from the partial amide double bond. Furthermore, a second conformational shape was observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a, monoclinic, space group C2/c, a = 24.587(2), b = 7.0726(6), c = 14.171(1) Å, β = 119.257(8)°, V = 2149.9(4) Å3, Z = 4, Dobs = 1.454 g/cm3) and the alkyne derivative 4-(but-3-yn-1-yl)-1-(4-fluorobenzoyl)piperazine (4b, monoclinic, space group P21/n, a = 10.5982(2), b = 8.4705(1), c = 14.8929(3) Å, β = 97.430(1)°, V = 1325.74(4) Å3, Z = 4, Dobs = 1.304 g/cm3) were obtained from a saturated ethyl acetate solution. The rotational conformation of these compounds was also verified by XRD. As proof of concept for future labeling purposes, both nitropiperazines were reacted with [18F]F–. To test the applicability of these compounds as possible 18F-building blocks, two biomolecules were modified and chosen for conjugation either using the Huisgen-click reaction or the traceless Staudinger ligation.
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Affiliation(s)
- Constantin Mamat
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany; Technische Universität Dresden, Fachrichtung Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Marc Pretze
- Medizinische Fakultät Mannheim der Universität Heidelberg, Institut für Klinische Radiologie und Nuklearmedizin, Theodor-Kutzner-Ufer 1-3, D-68167 Mannheim, Germany
| | - Matthew Gott
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany
| | - Martin Köckerling
- Universität Rostock, Institut für Chemie - Festkörperchemie, Albert-Einstein-Straße 3a, D-18059 Rostock, Germany
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13
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Affiliation(s)
- Sudheendran Mavila
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva-84105, Israel
| | - Or Eivgi
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva-84105, Israel
| | - Inbal Berkovich
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva-84105, Israel
| | - N. Gabriel Lemcoff
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva-84105, Israel
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14
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Ebert K, Wiemer J, Caballero J, Köckerling M, Steinbach J, Pietzsch J, Mamat C. Development of indazolylpyrimidine derivatives as high-affine EphB4 receptor ligands and potential PET radiotracers. Bioorg Med Chem 2015; 23:6025-35. [PMID: 26189032 DOI: 10.1016/j.bmc.2015.06.040] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Revised: 06/05/2015] [Accepted: 06/11/2015] [Indexed: 01/06/2023]
Abstract
Due to their essential role in the pathogenesis of cancer, members of the Eph (erythropoietin-producing hepatoma cell line-A2) receptor tyrosine kinase family represent promising candidates for molecular imaging. Thus, the development and preparation of novel radiotracers for the noninvasive imaging of the EphB4 receptor via positron emission tomography (PET) is described. First in silico investigations with the indazolylpyrimidine lead compound which is known to be highly affine to EphB4 were executed to identify favorable labeling positions for an introduction of fluorine-18 to retain the affinity. Based on this, reference compounds as well as precursors were developed and labeled with carbon-11 and fluorine-18, respectively. For this purpose, a protecting group strategy essentially had to be generated to prevent unwanted methylation and to enable the introduction of fluorine-18. Further, a convenient radiolabeling strategy using [(11)C]methyl iodide was established which afforded the isotopically labeled radiotracer in 30-35% RCY (d.c.) which is identical with the original inhibitor molecule. A spiro ammonium precursor was prepared for radiolabeling with fluorine-18. Unfortunately, the labeling did not lead to the desired (18)F-radiotracer under the chosen conditions.
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Affiliation(s)
- Kristin Ebert
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany
| | - Jens Wiemer
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany
| | - Julio Caballero
- Universidad de Talca, Centro de Bioinformática y Simulación Molecular, 2 Norte 685, Casilla 721, Talca, Chile
| | - Martin Köckerling
- Universität Rostock, Institut für Chemie, Anorganische Festkörperchemie, Albert-Einstein-Straße 3a, D-18057 Rostock, Germany
| | - Jörg Steinbach
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany; TU Dresden, Fachbereich Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Jens Pietzsch
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany; TU Dresden, Fachbereich Chemie und Lebensmittelchemie, D-01062 Dresden, Germany
| | - Constantin Mamat
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Radiopharmazeutische Krebsforschung, Bautzner Landstraße 400, D-01328 Dresden, Germany; TU Dresden, Fachbereich Chemie und Lebensmittelchemie, D-01062 Dresden, Germany.
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15
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Abstract
Eph receptor tyrosine kinases and ephrin ligands constitute an important cell communication system that controls development, tissue homeostasis and many pathological processes. Various Eph receptors/ephrins are present in essentially all cell types and their expression is often dysregulated by injury and disease. Thus, the 14 Eph receptors are attracting increasing attention as a major class of potential drug targets. In particular, agents that bind to the extracellular ephrin-binding pocket of these receptors show promise for medical applications. This pocket comprises a broad and shallow groove surrounded by several flexible loops, which makes peptides particularly suitable to target it with high affinity and selectivity. Accordingly, a number of peptides that bind to Eph receptors with micromolar affinity have been identified using phage display and other approaches. These peptides are generally antagonists that inhibit ephrin binding and Eph receptor/ ephrin signaling, but some are agonists mimicking ephrin-induced Eph receptor activation. Importantly, some of the peptides are exquisitely selective for single Eph receptors. Most identified peptides are linear, but recently the considerable advantages of cyclic scaffolds have been recognized, particularly in light of potential optimization towards drug leads. To date, peptide improvements have yielded derivatives with low nanomolar Eph receptor binding affinity, high resistance to plasma proteases and/or long in vivo half-life, exemplifying the merits of peptides for Eph receptor targeting. Besides their modulation of Eph receptor/ephrin function, peptides can also serve to deliver conjugated imaging and therapeutic agents or various types of nanoparticles to tumors and other diseased tissues presenting target Eph receptors.
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Affiliation(s)
| | - Elena B Pasquale
- Sanford Burnham Prebys Medical Discovery Institute, 10901 N. Torrey Pines Rd., La Jolla, CA 92037, USA.
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16
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Abstract
EphB2 interacts with cell surface-bound ephrin ligands to relay bidirectional signals. Overexpression of the EphB2 receptor protein has been linked to different types of cancer. The SNEW (SNEWIQPRLPQH) peptide binds with high selectivity and moderate affinity to EphB2, inhibiting Eph-ephrin interactions by competing with ephrin ligands for the EphB2 high-affinity pocket. We used rigorous free energy perturbation (FEP) calculations to re-evaluate the binding interactions of SNEW peptide with the EphB2 receptor, followed by experimental testing of the computational results. Our results provide insight into dynamic interactions of EphB2 with SNEW peptide. While the first four residues of the SNEW peptide are already highly optimized, change of the C-terminal end of the peptide has the potential to improve SNEW-binding affinity. We identified a PXSPY motif that can be similarly aligned with several other EphB2-binding peptides.
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Affiliation(s)
- Buyong Ma
- Basic Science Program, Leidos Biomedical Research, Inc. Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA
- Author to whom correspondence should be addressed; Buyong Ma. Tel.: +1-301-846-6540; ; Ruth Nussinov. Tel.: +1-301-846-5579;
| | - Stephanie Kolb
- Basic Science Program, Leidos Biomedical Research, Inc. Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA
| | - Michael Diprima
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - Molleshree Karna
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - Giovanna Tosato
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - Qiqi Yang
- State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai 200433, China
| | - Qiang Huang
- State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai 200433, China
| | - Ruth Nussinov
- Basic Science Program, Leidos Biomedical Research, Inc. Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA
- Sackler Inst. of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
- Author to whom correspondence should be addressed; Buyong Ma. Tel.: +1-301-846-6540; ; Ruth Nussinov. Tel.: +1-301-846-5579;
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17
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Pretze M, Mosch B, Bergmann R, Steinbach J, Pietzsch J, Mamat C. Radiofluorination and first radiopharmacological characterization of a SWLAY peptide-based ligand targeting EphA2. J Labelled Comp Radiopharm 2014; 57:660-5. [DOI: 10.1002/jlcr.3237] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 07/24/2014] [Accepted: 08/24/2014] [Indexed: 12/11/2022]
Affiliation(s)
- Marc Pretze
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
- Fachbereich Chemie und Lebensmittelchemie; Technische Universität Dresden; D-01062 Dresden Germany
| | - Birgit Mosch
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
| | - Ralf Bergmann
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
| | - Jörg Steinbach
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
- Fachbereich Chemie und Lebensmittelchemie; Technische Universität Dresden; D-01062 Dresden Germany
| | - Jens Pietzsch
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
- Fachbereich Chemie und Lebensmittelchemie; Technische Universität Dresden; D-01062 Dresden Germany
| | - Constantin Mamat
- Institut für Radiopharmazeutische Krebsforschung; Helmholtz-Zentrum Dresden-Rossendorf; Bautzner Landstraße 400 D-01328 Dresden Germany
- Fachbereich Chemie und Lebensmittelchemie; Technische Universität Dresden; D-01062 Dresden Germany
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18
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Brust P, van den Hoff J, Steinbach J. Development of (18)F-labeled radiotracers for neuroreceptor imaging with positron emission tomography. Neurosci Bull 2014; 30:777-811. [PMID: 25172118 DOI: 10.1007/s12264-014-1460-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2014] [Accepted: 06/02/2014] [Indexed: 12/14/2022] Open
Abstract
Positron emission tomography (PET) is an in vivo molecular imaging tool which is widely used in nuclear medicine for early diagnosis and treatment follow-up of many brain diseases. PET uses biomolecules as probes which are labeled with radionuclides of short half-lives, synthesized prior to the imaging studies. These probes are called radiotracers. Fluorine-18 is a radionuclide routinely used in the radiolabeling of neuroreceptor ligands for PET because of its favorable half-life of 109.8 min. The delivery of such radiotracers into the brain provides images of transport, metabolic, and neurotransmission processes on the molecular level. After a short introduction into the principles of PET, this review mainly focuses on the strategy of radiotracer development bridging from basic science to biomedical application. Successful radiotracer design as described here provides molecular probes which not only are useful for imaging of human brain diseases, but also allow molecular neuroreceptor imaging studies in various small-animal models of disease, including genetically-engineered animals. Furthermore, they provide a powerful tool for in vivo pharmacology during the process of pre-clinical drug development to identify new drug targets, to investigate pathophysiology, to discover potential drug candidates, and to evaluate the pharmacokinetics and pharmacodynamics of drugs in vivo.
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19
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Qin XY, Liu YN, Yu QQ, Yang LC, Liu Y, Zhou YH, Liu J. Mixed-ligand mononuclear copper(II) complex: crystal structure and anticancer activity. ChemMedChem 2014; 9:1665-71. [PMID: 24839939 DOI: 10.1002/cmdc.201402060] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Indexed: 12/12/2022]
Abstract
A novel copper(II) complex with mixed ligands including β-[(3-formyl-5-methyl-2-hydroxy-benzylidene)amino]propionic acid anion and 1,10'-phenanthroline was synthesized, and its crystal structure was thoroughly characterized. It exerted excellent inducing apoptosis, anti-angiogenesis and antiproliferative properties in vitro. The complex can bind human serum albumin (HSA) at physiological pH conditions. Remarkably, it can induce formation of the mixed parallel/antiparallel G-quadruplex structures in the G-rich sequence of the proximal vascular endothelial growth factor (VEGF) promoter, and stabilize these G-quadruplex structures, which provide an opportunity for anti-angiogenesis chemotherapeutics. Furthermore, the complex showed a strong uptake, and exhibited multiple anticancer functions by inhibiting the expression of p-Akt and p-Erk1/2 proteins and by upregulating the levels of reactive oxygen species (ROS). Because of the reported results, this new copper(II) complex qualifies itself as a potential anticancer drug candidate.
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Affiliation(s)
- Xiu-Ying Qin
- Department of Chemistry, Jinan University, Guangzhou 510632, China; College of Pharmacy, Guilin Medical University, Guilin 541004 (China)
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20
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Pretze M, Pietzsch D, Mamat C. Recent trends in bioorthogonal click-radiolabeling reactions using fluorine-18. Molecules 2013; 18:8618-65. [PMID: 23881051 DOI: 10.3390/molecules18078618] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 07/11/2013] [Accepted: 07/15/2013] [Indexed: 12/18/2022] Open
Abstract
The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile bioorthogonal conjugation techniques especially for the radiolabeling of biologically active high molecular weight compounds like peptides, proteins or antibodies. Taking into consideration that the introduction of fluorine-18 (t(1/2) = 109.8 min) proceeds under harsh conditions, radiolabeling of these biologically active molecules represents an outstanding challenge and is of enormous interest. Special attention has to be paid to the method of 18F-introduction. It should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. For these reasons and due to the high number of functional groups found in these compounds, a specific labeling procedure has to be developed for every bioactive macromolecule. Bioorthogonal strategies including the Cu-assisted Huisgen cycloaddition and its copper-free click variant, both Staudinger Ligations or the tetrazine-click reaction have been successfully applied and represent valuable alternatives for the selective introduction of fluorine-18 to overcome the afore mentioned obstacles. This comprehensive review deals with the progress and illustrates the latest developments in the field of bioorthogonal labeling with the focus on the preparation of radiofluorinated building blocks and tracers for molecular imaging.
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