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Ndlovu H, Lawal IO, Mdanda S, Kgatle MM, Mokoala KMG, Al-Ibraheem A, Sathekge MM. [ 18F]F-Poly(ADP-Ribose) Polymerase Inhibitor Radiotracers for Imaging PARP Expression and Their Potential Clinical Applications in Oncology. J Clin Med 2024; 13:3426. [PMID: 38929955 PMCID: PMC11204862 DOI: 10.3390/jcm13123426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 05/30/2024] [Accepted: 06/06/2024] [Indexed: 06/28/2024] Open
Abstract
Including poly(ADP-ribose) polymerase (PARP) inhibitors in managing patients with inoperable tumors has significantly improved outcomes. The PARP inhibitors hamper single-strand deoxyribonucleic acid (DNA) repair by trapping poly(ADP-ribose)polymerase (PARP) at sites of DNA damage, forming a non-functional "PARP enzyme-inhibitor complex" leading to cell cytotoxicity. The effect is more pronounced in the presence of PARP upregulation and homologous recombination (HR) deficiencies such as breast cancer-associated gene (BRCA1/2). Hence, identifying HR-deficiencies by genomic analysis-for instance, BRCA1/2 used in triple-negative breast cancer-should be a part of the selection process for PARP inhibitor therapy. Published data suggest BRCA1/2 germline mutations do not consistently predict favorable responses to PARP inhibitors, suggesting that other factors beyond tumor mutation status may be at play. A variety of factors, including tumor heterogeneity in PARP expression and intrinsic and/or acquired resistance to PARP inhibitors, may be contributing factors. This justifies the use of an additional tool for appropriate patient selection, which is noninvasive, and capable of assessing whole-body in vivo PARP expression and evaluating PARP inhibitor pharmacokinetics as complementary to the currently available BRCA1/2 analysis. In this review, we discuss [18F]Fluorine PARP inhibitor radiotracers and their potential in the imaging of PARP expression and PARP inhibitor pharmacokinetics. To provide context we also briefly discuss possible causes of PARP inhibitor resistance or ineffectiveness. The discussion focuses on TNBC, which is a tumor type where PARP inhibitors are used as part of the standard-of-care treatment strategy.
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Affiliation(s)
- Honest Ndlovu
- Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa; (H.N.); (S.M.); (M.M.K.); (K.M.G.M.)
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
| | - Ismaheel O. Lawal
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA 30322, USA
| | - Sipho Mdanda
- Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa; (H.N.); (S.M.); (M.M.K.); (K.M.G.M.)
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
| | - Mankgopo M. Kgatle
- Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa; (H.N.); (S.M.); (M.M.K.); (K.M.G.M.)
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
| | - Kgomotso M. G. Mokoala
- Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa; (H.N.); (S.M.); (M.M.K.); (K.M.G.M.)
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
| | - Akram Al-Ibraheem
- Department of Nuclear Medicine, King Hussein Cancer Center (KHCC), Al-Jubeiha P.O. Box 1269, Amman 11941, Jordan;
| | - Mike M. Sathekge
- Nuclear Medicine Research Infrastructure (NuMeRI), Steve Biko Academic Hospital, Pretoria 0001, South Africa; (H.N.); (S.M.); (M.M.K.); (K.M.G.M.)
- Department of Nuclear Medicine, University of Pretoria & Steve Biko Academic Hospital, Private Bag X169, Pretoria 0001, South Africa;
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2
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Tago T, Toyohara J. Step-by-step optimisation of the radiosynthesis of the brain HDAC6 radioligand [ 18F]FSW-100 for clinical applications. EJNMMI Radiopharm Chem 2024; 9:45. [PMID: 38831171 PMCID: PMC11147973 DOI: 10.1186/s41181-024-00277-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Accepted: 05/27/2024] [Indexed: 06/05/2024] Open
Abstract
BACKGROUND Histone deacetylase 6 (HDAC6) is an emerging target for the treatment and diagnosis of proteinopathies. [18F]FSW-100 was recently developed as a promising brain-penetrating radioligand for HDAC6 PET imaging and the process validation of [18F]FSW-100 radiosynthesis for clinical use is complete, but no detailed synthetic strategy nor process optimisation has been reported. Here, we describe the optimisation of several processes in [18F]FSW-100 radiosynthesis, including the 18F-fluorination reaction, semipurification of the 18F-intermediate, and purification of the product by high-performance liquid chromatography (HPLC), to achieve a radiochemical yield (RCY) adequate for clinical applications of the radioligand. Our findings will aid optimisation of radiosynthesis processes in general. RESULTS In the 18F-fluorination reaction, the amount of copper reagent was reduced without reducing the nonisolated RCY of the intermediate (50%), thus reducing the risk of copper contamination in the product injection solution. Optimising the solid-phase extraction (SPE) conditions for semipurification of the intermediate improved its recovery efficiency. The addition of anti-radiolysis reagents to the mobile phase for the HPLC purification of [18F]FSW-100 increased its activity yield in radiosynthesis using a high [18F]fluoride radioactivity of approximately 50 GBq. The SPE-based formulation method and additives for the injection solution were optimised, and the resulting [18F]FSW-100 injection solution was stable for over 2 h with a radiochemical purity of greater than 95%. CONCLUSIONS Of all the reconsidered processes, we found that optimisation of the SPE-based semipurification of the intermediate and of the mobile phase for HPLC purification in particular improved the RCY of [18F]FSW-100, doubling it compared to that of the original protocol. The radioactivity of [18F]FSW-100 synthesized using the optimized protocol was sufficient for multiple doses for a clinical study.
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Affiliation(s)
- Tetsuro Tago
- Research Team for Neuroimaging, Tokyo Metropolitan Institute for Geriatrics and Gerontology, 35-2 Sakae-Cho, Itabashi-Ku, Tokyo, 173-0015, Japan
| | - Jun Toyohara
- Research Team for Neuroimaging, Tokyo Metropolitan Institute for Geriatrics and Gerontology, 35-2 Sakae-Cho, Itabashi-Ku, Tokyo, 173-0015, Japan.
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3
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Webb EW, Cheng K, Winton WP, Klein BJ, Bowden GD, Horikawa M, Liu SW, Wright JS, Verhoog S, Kalyani D, Wismer M, Krska SW, Sanford MS, Scott PJ. Development of High-Throughput Experimentation Approaches for Rapid Radiochemical Exploration. J Am Chem Soc 2024; 146:10581-10590. [PMID: 38580459 PMCID: PMC11099536 DOI: 10.1021/jacs.3c14822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2024]
Abstract
Positron emission tomography is a widely used imaging platform for studying physiological processes. Despite the proliferation of modern synthetic methodologies for radiolabeling, the optimization of these reactions still primarily relies on inefficient one-factor-at-a-time approaches. High-throughput experimentation (HTE) has proven to be a powerful approach for optimizing reactions in many areas of chemical synthesis. However, to date, HTE has rarely been applied to radiochemistry. This is largely because of the short lifetime of common radioisotopes, which presents major challenges for efficient parallel reaction setup and analysis using standard equipment and workflows. Herein, we demonstrate an effective HTE workflow and apply it to the optimization of copper-mediated radiofluorination of pharmaceutically relevant boronate ester substrates. The workflow utilizes commercial equipment and allows for rapid analysis of reactions for optimizing reactions, exploring chemical space using pharmaceutically relevant aryl boronates for radiofluorinations, and constructing large radiochemistry data sets.
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Affiliation(s)
- E. William Webb
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
| | - Kevin Cheng
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
| | - Wade P. Winton
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
| | - Brandon J.C. Klein
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Gregory D. Bowden
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University Tuebingen, Tuebingen 72074, Germany
- Cluster of Excellence iFIT (EXC 2180) “Image-Guided and Functionally Instructed Tumor Therapies”, Eberhard Karls University, Tuebingen 72074, Germany
| | - Mami Horikawa
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - S. Wendy Liu
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
| | - Jay S. Wright
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
| | - Stefan Verhoog
- Translational Imaging, Merck and Co., Inc., West Point, PA 19486, United States
| | - Dipannita Kalyani
- Discovery Chemistry, Merck Research Laboratories, Merck and Co., Inc., Rahway, NJ 07065, United States
| | - Michael Wismer
- Discovery Chemistry, Merck Research Laboratories, Merck and Co., Inc., Rahway, NJ 07065, United States
| | - Shane W. Krska
- Discovery Chemistry, Merck Research Laboratories, Merck and Co., Inc., Rahway, NJ 07065, United States
| | - Melanie S. Sanford
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Peter J.H. Scott
- Department of Radiology, University of Michigan Medical School, 1301 Catherine Street, Ann Arbor, Michigan 48109, United States
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 North University Avenue, Ann Arbor, Michigan 48109, United States
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4
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Lai TH, Wenzel B, Dukić-Stefanović S, Teodoro R, Arnaud L, Maisonial-Besset A, Weber V, Moldovan RP, Meister S, Pietzsch J, Kopka K, Juratli TA, Deuther-Conrad W, Toussaint M. Radiosynthesis and biological evaluation of [ 18F]AG-120 for PET imaging of the mutant isocitrate dehydrogenase 1 in glioma. Eur J Nucl Med Mol Imaging 2024; 51:1085-1096. [PMID: 37982850 PMCID: PMC10881675 DOI: 10.1007/s00259-023-06515-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 11/06/2023] [Indexed: 11/21/2023]
Abstract
Glioma are clinically challenging tumors due to their location and invasiveness nature, which often hinder complete surgical resection. The evaluation of the isocitrate dehydrogenase mutation status has become crucial for effective patient stratification. Through a transdisciplinary approach, we have developed an 18F-labeled ligand for non-invasive assessment of the IDH1R132H variant by using positron emission tomography (PET) imaging. In this study, we have successfully prepared diastereomerically pure [18F]AG-120 by copper-mediated radiofluorination of the stannyl precursor 6 on a TRACERlab FX2 N radiosynthesis module. In vitro internalization studies demonstrated significantly higher uptake of [18F]AG-120 in U251 human high-grade glioma cells with stable overexpression of mutant IDH1 (IDH1R132H) compared to their wild-type IDH1 counterpart (0.4 vs. 0.013% applied dose/µg protein at 120 min). In vivo studies conducted in mice, exhibited the excellent metabolic stability of [18F]AG-120, with parent fractions of 85% and 91% in plasma and brain at 30 min p.i., respectively. Dynamic PET studies with [18F]AG-120 in naïve mice and orthotopic glioma rat model reveal limited blood-brain barrier permeation along with a low uptake in the brain tumor. Interestingly, there was no significant difference in uptake between mutant IDH1R132H and wild-type IDH1 tumors (tumor-to-blood ratio[40-60 min]: ~1.7 vs. ~1.3). In conclusion, our preclinical evaluation demonstrated a target-specific internalization of [18F]AG-120 in vitro, a high metabolic stability in vivo in mice, and a slightly higher accumulation of activity in IDH1R132H-glioma compared to IDH1-glioma. Overall, our findings contribute to advancing the field of molecular imaging and encourage the evaluation of [18F]AG-120 to improve diagnosis and management of glioma and other IDH1R132H-related tumors.
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Affiliation(s)
- Thu Hang Lai
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
- Department of Research and Development, ROTOP Pharmaka GmbH, Dresden, Germany
| | - Barbara Wenzel
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
| | - Sladjana Dukić-Stefanović
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
| | - Rodrigo Teodoro
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
| | - Lucie Arnaud
- Université Clermont Auvergne, Imagerie Moléculaire et Stratégies Théranostiques, UMR 1240, Inserm, Clermont- Ferrand, France
| | - Aurélie Maisonial-Besset
- Université Clermont Auvergne, Imagerie Moléculaire et Stratégies Théranostiques, UMR 1240, Inserm, Clermont- Ferrand, France
| | - Valérie Weber
- Université Clermont Auvergne, Imagerie Moléculaire et Stratégies Théranostiques, UMR 1240, Inserm, Clermont- Ferrand, France
| | - Rareş-Petru Moldovan
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
| | - Sebastian Meister
- Institute of Radiopharmaceutical Cancer Research, Department of Radiopharmaceutical and Chemical Biology, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
| | - Jens Pietzsch
- Institute of Radiopharmaceutical Cancer Research, Department of Radiopharmaceutical and Chemical Biology, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
- School of Science, Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Dresden, Germany
| | - Klaus Kopka
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
- School of Science, Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Dresden, Germany
- German Cancer Consortium (DKTK), Partner Site Dresden, Dresden, Germany
- National Center for Tumor Diseases (NCT) Dresden, University Hospital Carl Gustav Carus, Dresden, Germany
| | - Tareq A Juratli
- National Center for Tumor Diseases (NCT) Dresden, University Hospital Carl Gustav Carus, Dresden, Germany
- Department of Neurosurgery, Faculty of Medicine, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Winnie Deuther-Conrad
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany
| | - Magali Toussaint
- Institute of Radiopharmaceutical Cancer Research, Department of Neuroradiopharmaceuticals, Helmholtz-Zentrum Dresden-Rossendorf, Research site Leipzig, Leipzig, Germany.
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5
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Bowden GD, Stotz S, Dunkel G, Haas S, Kimmerle E, Schaller M, Weigelin B, Herfert K, Pichler BJ, Maurer A. [ 18F] pFBC, a Covalent CLIP-Tag Radiotracer for Detection of Viral Reporter Gene Transfer in the Murine Brain. Bioconjug Chem 2024; 35:254-264. [PMID: 38308817 DOI: 10.1021/acs.bioconjchem.3c00551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2024]
Abstract
Preclinical models of neurological diseases and gene therapy are essential for neurobiological research. However, the evaluation of such models lacks reliable reporter systems for use with noninvasive imaging methods. Here, we report the development of a reporter system based on the CLIP-tag enzyme and [18F]pFBC, an 18F-labeled covalent CLIP-tag-ligand synthesized via a DoE-optimized and fully automated process. We demonstrated its specificity using a subcutaneous xenograft model and a model of viral vector-mediated brain gene transfer by engineering HEK293 cells and striatal neurons to express membrane-tethered CLIP-tag protein. After in vitro characterization of the reporter, mice carrying either CLIP-tag expressing or control subcutaneous xenografts underwent dynamic [18F]pFBC PET imaging. The CLIP-tag expressing xenografts showed a significantly higher uptake than control xenografts (tumor-to-muscle ratio 5.0 vs 1.7, p = 0.0379). In vivo, metabolite analysis by radio-HPLC from plasma and brain homogenates showed only one radio-metabolite in plasma and none in the brain. In addition, [18F]pFBC showed fast uptake and rapid clearance from the brain in animals injected with adeno-associated virus (AAV)-CLIP in the right striatum but no right-to-left (R-L) uptake difference in the striata in the acquired PET data. In contrast, autoradiography showed a clear accumulation of radioactivity in the AAV-CLIP-injected right striatum compared to the sham-injected left striatum control. CLIP-tag expression and brain integrity were verified by immunofluorescence and light sheet microscopy. In conclusion, we established a novel reporter gene system for PET imaging of gene expression in the brain and periphery and demonstrated its potential for a wide range of applications, particularly for neurobiological research and gene therapy with viral vectors.
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Affiliation(s)
- Gregory D Bowden
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
| | - Sophie Stotz
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
| | - Gina Dunkel
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
| | - Sabrina Haas
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
| | - Elena Kimmerle
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
| | - Martin Schaller
- Department of Dermatology, University Hospital Tuebingen, 72076 Tuebingen, Germany
| | - Bettina Weigelin
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
| | - Kristina Herfert
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
| | - Bernd J Pichler
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
| | - Andreas Maurer
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, 72076 Tuebingen, Germany
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6
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Zhou D, Chu W, Chen H, Xu J. Exploration of Directing-Group-Assisted, Copper-Mediated Radiofluorination and Radiosynthesis of [ 18F]Olaparib. ACS Med Chem Lett 2024; 15:116-122. [PMID: 38229754 PMCID: PMC10788942 DOI: 10.1021/acsmedchemlett.3c00465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 12/08/2023] [Accepted: 12/13/2023] [Indexed: 01/18/2024] Open
Abstract
Copper-mediated radiofluorination (CMRF) of organoboronic precursors is the method of choice for late-stage radiofluorination of aromatic compounds as positron emission tomography (PET) radiotracers. However, CMRF generally requires harsh reaction conditions, a large amount of substrates, and harsh solvents (e.g., DMA) to proceed, affording variable radiochemical yields (RCYs). Using [18F]tosyl fluoride as the source of [18F]fluoride, we have found a highly efficient CMRF of organoboronic precursors, assisted by a directing group (DG) at the ortho position. The reaction can be carried out under mild conditions (even at room temperature) in acetonitrile and results in high RCYs, providing a novel strategy for the radiofluorination of aromatic compounds. The exploration of this strategy also provided more information about side reactions in CMRF. Using this strategy, [18F]olaparib has been radiosynthesized in high RCYs, with high molar activity and high chemical and radiochemical purities, demonstrating the great potential of DG-assisted CMRF in the preparation of 18F-labeled PET radiotracers.
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Affiliation(s)
- Dong Zhou
- Department of Radiology, School of
Medicine, Washington University in Saint
Louis, Saint Louis, Missouri 63110, United States
| | - Wenhua Chu
- Department of Radiology, School of
Medicine, Washington University in Saint
Louis, Saint Louis, Missouri 63110, United States
| | - Huaping Chen
- Department of Radiology, School of
Medicine, Washington University in Saint
Louis, Saint Louis, Missouri 63110, United States
| | - Jinbin Xu
- Department of Radiology, School of
Medicine, Washington University in Saint
Louis, Saint Louis, Missouri 63110, United States
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7
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Craig A, Kogler J, Laube M, Ullrich M, Donat CK, Wodtke R, Kopka K, Stadlbauer S. Preparation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein via Sulfur [ 18F]Fluoride Exchange Reaction. Pharmaceutics 2023; 15:2749. [PMID: 38140090 PMCID: PMC10747913 DOI: 10.3390/pharmaceutics15122749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 11/14/2023] [Accepted: 12/02/2023] [Indexed: 12/24/2023] Open
Abstract
Early detection and treatment of cancers can significantly increase patient prognosis and enhance the quality of life of affected patients. The emerging significance of the tumor microenvironment (TME) as a new frontier for cancer diagnosis and therapy may be exploited by radiolabeled tracers for diagnostic imaging techniques such as positron emission tomography (PET). Cancer-associated fibroblasts (CAFs) within the TME are identified by biomarkers such as fibroblast activation protein alpha (FAPα), which are expressed on their surfaces. Targeting FAPα using small-molecule 18F-labeled inhibitors (FAPIs) has recently garnered significant attention for non-invasive tumor visualization using PET. Herein, two potent aryl-fluorosulfate-based FAPIs, 12 and 13, were synthetically prepared, and their inhibition potency was determined using a fluorimetric FAP assay to be IC50 9.63 and 4.17 nM, respectively. Radiofluorination was performed via the sulfur [18F]fluoride exchange ([18F]SuFEx) reaction to furnish [18F]12 and [18F]13 in high activity yields (AY) of 39-56% and molar activities (Am) between 20-55 GBq/µmol. In vitro experiments focused on the stability of the radiolabeled FAPIs after incubation with human serum, liver microsomes and liver cytosol. Preliminary PET studies of the radioligands were performed in healthy mice to investigate the in vivo biodistribution and 18F defluorination rate. Fast pharmacokinetics for the FAP-targeting tracers were retained and considerable bone uptake, caused by either 18F defluorination or radioligand accumulation, was observed. In summary, our findings demonstrate the efficiency of [18F]SuFEx as a radiolabeling method as well as its advantages and limitations with respect to PET tracer development.
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Affiliation(s)
- Austin Craig
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
| | - Jürgen Kogler
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
- Faculty of Chemistry and Food Chemistry, School of Science, Technische Universität Dresden, D-01062 Dresden, Germany
| | - Markus Laube
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
| | - Martin Ullrich
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
| | - Cornelius K. Donat
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
| | - Robert Wodtke
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
| | - Klaus Kopka
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
- Faculty of Chemistry and Food Chemistry, School of Science, Technische Universität Dresden, D-01062 Dresden, Germany
| | - Sven Stadlbauer
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, D-01328 Dresden, Germany; (A.C.)
- Faculty of Chemistry and Food Chemistry, School of Science, Technische Universität Dresden, D-01062 Dresden, Germany
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8
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Hoffmann C, Kolks N, Smets D, Haseloer A, Gröner B, Urusova EA, Endepols H, Neumaier F, Ruschewitz U, Klein A, Neumaier B, Zlatopolskiy BD. Next Generation Copper Mediators for the Efficient Production of 18 F-Labeled Aromatics. Chemistry 2023; 29:e202202965. [PMID: 36214204 PMCID: PMC10100267 DOI: 10.1002/chem.202202965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Indexed: 11/07/2022]
Abstract
Cu-mediated radiofluorination is a versatile tool for the preparation of 18 F-labeled (hetero)aromatics. In this work, we systematically evaluated a series of complexes and identified several generally applicable mediators for highly efficient radiofluorination of aryl boronic and stannyl substrates. Utilization of these mediators in nBuOH/DMI or DMI significantly improved 18 F-labeling yields despite use of lower precursor amounts. Impressively, application of 2.5 μmol aryl boronic acids was sufficient to achieve 18 F-labeling yields of up to 75 %. The practicality of the novel mediators was demonstrated by efficient production of five PET-tracers and transfer of the method to an automated radiosynthesis module. In addition, (S)-3-[18 F]FPhe and 6-[18 F]FDOPA were prepared in activity yields of 23±1 % and 30±3 % using only 2.5 μmol of the corresponding boronic acid or trimethylstannyl precursor.
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Affiliation(s)
- Chris Hoffmann
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Niklas Kolks
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Daniel Smets
- Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939, Cologne, Germany
| | - Alexander Haseloer
- Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939, Cologne, Germany
| | - Benedikt Gröner
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Elizaveta A Urusova
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Heike Endepols
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany.,Faculty of Medicine and University Hospital Cologne, Department of Nuclear Medicine, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany
| | - Felix Neumaier
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Uwe Ruschewitz
- Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939, Cologne, Germany
| | - Axel Klein
- Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939, Cologne, Germany
| | - Bernd Neumaier
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
| | - Boris D Zlatopolskiy
- Faculty of Medicine and University Hospital Cologne, Institute of Radiochemistry and Experimental Molecular Imaging, University of Cologne, Kerpener Straße 62, 50937, Cologne, Germany.,Institute of Neuroscience and Medicine, Nuclear Chemistry (INM-5), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany
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9
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Wang Q, Zhang J. Current status and progress in using radiolabelled PARP-1 inhibitors for imaging PARP-1 expression in tumours. Eur J Med Chem 2022; 242:114690. [PMID: 36041258 DOI: 10.1016/j.ejmech.2022.114690] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 08/02/2022] [Accepted: 08/12/2022] [Indexed: 02/08/2023]
Abstract
Poly(ADP-ribose) polymerase-1 (PARP-1) is a key enzyme in the DNA repair process, and the overexpression of PARP-1 in several tumours makes this enzyme a promising molecular target. Recently, several PARP-1 inhibitors, such as olaparib, rucaparib, niraparib and talazoparib, have been clinically approved as anticancer drugs. Several of these inhibitors have been radiolabelled for noninvasive imaging of PARP-1 expression in several types of tumours. In this review, the background and progress for using various radiolabelled PARP-1 inhibitors for cancer diagnosis are discussed and future development directions are proposed.
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Affiliation(s)
- Qianna Wang
- Key Laboratory of Radiopharmaceuticals of Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Radiopharmaceuticals (National Medical Products Administration), College of Chemistry, Beijing Normal University, Beijing, 100875, PR China
| | - Junbo Zhang
- Key Laboratory of Radiopharmaceuticals of Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Radiopharmaceuticals (National Medical Products Administration), College of Chemistry, Beijing Normal University, Beijing, 100875, PR China.
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10
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Copper-Mediated Aromatic Fluorination Using N-Heterocycle-Carbene Ligand: Free Energy Profile of the Cu(I)/Cu(III) and Cu(II) radical Mechanisms. J Organomet Chem 2022. [DOI: 10.1016/j.jorganchem.2022.122397] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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11
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Nguyen NT, Pacelli A, Nader M, Kossatz S. DNA Repair Enzyme Poly(ADP-Ribose) Polymerase 1/2 (PARP1/2)-Targeted Nuclear Imaging and Radiotherapy. Cancers (Basel) 2022; 14:cancers14051129. [PMID: 35267438 PMCID: PMC8909184 DOI: 10.3390/cancers14051129] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/15/2022] [Accepted: 02/17/2022] [Indexed: 02/07/2023] Open
Abstract
Simple Summary In parallel to the successful clinical implementation of PARP1/2 inhibitors as anti-cancer drugs, which interfere with the DNA repair machinery, these small molecule agents have also gained attention as vehicles for molecular imaging and radiotherapy. In this review article, we summarize the development and preclinical evaluation of radioactively-labelled PARP inhibitors for positron emission tomography (PET) for many applications, such as selecting patients for PARP inhibitor treatment, response prediction or monitoring, and diagnosis of tumors. We report on early clinical studies that show safety and feasibility of PARP-imaging in humans. In addition, we summarize the latest developments in the field of PARP-targeted radiotherapy, where PARP inhibitors are studied as vehicles to deposit highly cytotoxic radioisotopes in close proximity to the DNA of tumor cells. Lastly, we look at synthetic strategies for PARP-targeted imaging and therapy agents that are compatible with large scale production and clinical translation. Abstract Since it was discovered that many tumor types are vulnerable to inhibition of the DNA repair machinery, research towards efficient and selective inhibitors has accelerated. Amongst other enzymes, poly(ADP-ribose)-polymerase 1 (PARP1) was identified as a key player in this process, which resulted in the development of selective PARP inhibitors (PARPi) as anti-cancer drugs. Most small molecule PARPi’s exhibit high affinity for both PARP1 and PARP2. PARPi are under clinical investigation for mono- and combination therapy in several cancer types and five PARPi are now clinically approved. In parallel, radiolabeled PARPi have emerged for non-invasive imaging of PARP1 expression. PARP imaging agents have been suggested as companion diagnostics, patient selection, and treatment monitoring tools to improve the outcome of PARPi therapy, but also as stand-alone diagnostics. We give a comprehensive overview over the preclinical development of PARP imaging agents, which are mostly based on the PARPi olaparib, rucaparib, and recently also talazoparib. We also report on the current status of clinical translation, which involves a growing number of early phase trials. Additionally, this work provides an insight into promising approaches of PARP-targeted radiotherapy based on Auger and α-emitting isotopes. Furthermore, the review covers synthetic strategies for PARP-targeted imaging and therapy agents that are compatible with large scale production and clinical translation.
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Affiliation(s)
- Nghia T. Nguyen
- Department of Nuclear Medicine, University Hospital Klinikum Rechts der Isar and Central Institute for Translational Cancer Research (TranslaTUM), School of Medicine, Technical University Munich, 81675 Munich, Germany;
| | - Anna Pacelli
- Department of Nuclear Medicine, University Hospital Essen, University of Duisburg–Essen, 45147 Essen, Germany; (A.P.); (M.N.)
| | - Michael Nader
- Department of Nuclear Medicine, University Hospital Essen, University of Duisburg–Essen, 45147 Essen, Germany; (A.P.); (M.N.)
| | - Susanne Kossatz
- Department of Nuclear Medicine, University Hospital Klinikum Rechts der Isar and Central Institute for Translational Cancer Research (TranslaTUM), School of Medicine, Technical University Munich, 81675 Munich, Germany;
- Correspondence:
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12
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Zhou D, Chu W, Katzenellenbogen JA. Exploration of alcohol-enhanced Cu-mediated radiofluorination toward practical labeling. J Labelled Comp Radiopharm 2022; 65:13-20. [PMID: 34617619 PMCID: PMC8727449 DOI: 10.1002/jlcr.3955] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 09/21/2021] [Accepted: 09/30/2021] [Indexed: 01/03/2023]
Abstract
Copper-mediated nucleophilic radiofluorination using boronic precursors is a promising, general method to label aromatic compounds with [18 F]fluoride. However, in various reports, large amounts of precursor (60 μmol) were needed to achieve high radiochemical conversions (RCCs), which is neither ideal nor practical for the preparation of 18 F radiopharmaceuticals. To investigate this matter, we studied alcohol-enhanced Cu-mediated nucleophilic radiofluorination using a variety of model reactions in which we varied the concentration of [18 F]fluoride (no carrier added or isotope diluted) and the amount of precursor, base, and Cu(OTF)2 (Py)4 . We found that lower amounts of precursors (e.g., 15 μmol) could be used and that the amount of base (e.g., K2 CO3 or KHCO3 ) played a critical and limiting role in the labeling reactions. Greater than one-equivalent of base and sufficient amounts of precursors and Cu(OTf)2 (Py)4 were required to achieve good to high RCCs. The RCCs were also dependent on the overall concentration of the labeling reactions, with low reaction volumes and high concentrations of reagents being preferred. Our findings will help to improve the design of radiolabeling protocols using alcohol-enhanced copper-mediated radiofluorination of boronic precursors for the preparation of 18 F labeled radiopharmaceuticals and other radiohalogen-labeled compounds.
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Affiliation(s)
- Dong Zhou
- Department of Radiology, School of Medicine, Washington University in Saint Louis, Saint Louis, MO 63110, United States
| | - Wenhua Chu
- Department of Radiology, School of Medicine, Washington University in Saint Louis, Saint Louis, MO 63110, United States
| | - John A. Katzenellenbogen
- Department of Chemistry and Cancer Center at Illinois, University of Illinois at Urbana-Champaign, IL 61801s
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13
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Bowden GD, Stotz S, Kinzler J, Geibel C, Lämmerhofer M, Pichler BJ, Maurer A. DoE Optimization Empowers the Automated Preparation of Enantiomerically Pure [ 18F]Talazoparib and its In Vivo Evaluation as a PARP Radiotracer. J Med Chem 2021; 64:15690-15701. [PMID: 34672571 DOI: 10.1021/acs.jmedchem.1c00903] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Given the clinical potential of poly(ADP-ribose) polymerases (PARP) imaging for the detection and stratification of various cancers, the development of novel PARP imaging probes with improved pharmacological profiles over established PARP imaging agents is warranted. Here, we present a novel 18F-labeled PARP radiotracer based on the clinically superior PARP inhibitor talazoparib. An automated radiosynthesis of [18F]talazoparib (RCY: 13 ± 3.4%; n = 4) was achieved using a "design of experiments" (DoE) optimized copper-mediated radiofluorination reaction. The chiral product was isolated from the reaction mixture using 2D reversed-phase/chiral radio-HPLC (>99% ee). (8S,9R)-[18F]Talazoparib demonstrated PARP binding in HCC1937 cells in vitro and showed an excellent tumor-to-blood ratio in xenograft-bearing mice (10.2 ± 1.5). Additionally, a favorable pharmacological profile in terms of excretion, metabolism, and target engagement was observed. This synthesis of [18F]talazoparib exemplifies how DoE can enable the radiosyntheses of synthetically challenging radiolabeled compounds of high interest to the imaging community.
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Affiliation(s)
- Gregory D Bowden
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Roentgenweg 15, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, Roentgenweg 13, 72076 Tuebingen, Germany
| | - Sophie Stotz
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Roentgenweg 15, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, Roentgenweg 13, 72076 Tuebingen, Germany
| | - Johannes Kinzler
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Roentgenweg 15, 72076 Tuebingen, Germany
| | - Christian Geibel
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical (Bio-)Analysis, Eberhard Karls University, Auf der Morgenstelle 8, 72076 Tuebingen, Germany
| | - Michael Lämmerhofer
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical (Bio-)Analysis, Eberhard Karls University, Auf der Morgenstelle 8, 72076 Tuebingen, Germany
| | - Bernd J Pichler
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Roentgenweg 15, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, Roentgenweg 13, 72076 Tuebingen, Germany
- German Cancer Research Center, German Cancer Consortium DKTK, Partner Site Tuebingen, Roentgenweg 13, 72076 Tuebingen, Germany
| | - Andreas Maurer
- Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, Roentgenweg 15, 72076 Tuebingen, Germany
- Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University, Roentgenweg 13, 72076 Tuebingen, Germany
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14
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Ajenjo J, Destro G, Cornelissen B, Gouverneur V. Closing the gap between 19F and 18F chemistry. EJNMMI Radiopharm Chem 2021; 6:33. [PMID: 34564781 PMCID: PMC8464544 DOI: 10.1186/s41181-021-00143-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 08/03/2021] [Indexed: 11/10/2022] Open
Abstract
Positron emission tomography (PET) has become an invaluable tool for drug discovery and diagnosis. The positron-emitting radionuclide fluorine-18 is frequently used in PET radiopharmaceuticals due to its advantageous characteristics; hence, methods streamlining access to 18F-labelled radiotracers can make a direct impact in medicine. For many years, access to 18F-labelled radiotracers was limited by the paucity of methodologies available, and the poor diversity of precursors amenable to 18F-incorporation. During the last two decades, 18F-radiochemistry has progressed at a fast pace with the appearance of numerous methodologies for late-stage 18F-incorporation onto complex molecules from a range of readily available precursors including those that do not require pre-functionalisation. Key to these advances is the inclusion of new activation modes to facilitate 18F-incorporation. Specifically, new advances in late-stage 19F-fluorination under transition metal catalysis, photoredox catalysis, and organocatalysis combined with the availability of novel 18F-labelled fluorination reagents have enabled the invention of novel processes for 18F-incorporation onto complex (bio)molecules. This review describes these major breakthroughs with a focus on methodologies for C-18F bond formation. This reinvigorated interest in 18F-radiochemistry that we have witnessed in recent years has made a direct impact on 19F-chemistry with many laboratories refocusing their efforts on the development of methods using nucleophilic fluoride instead of fluorination reagents derived from molecular fluorine gas.
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Affiliation(s)
- Javier Ajenjo
- Medical Research Council Oxford Institute for Radiation Oncology, University of Oxford, Oxford, OX3 7DQ, UK
| | - Gianluca Destro
- Medical Research Council Oxford Institute for Radiation Oncology, University of Oxford, Oxford, OX3 7DQ, UK
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3TA, UK
| | - Bart Cornelissen
- Medical Research Council Oxford Institute for Radiation Oncology, University of Oxford, Oxford, OX3 7DQ, UK
| | - Véronique Gouverneur
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3TA, UK.
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Covalent 18F-Radiotracers for SNAPTag: A New Toolbox for Reporter Gene Imaging. Pharmaceuticals (Basel) 2021; 14:ph14090897. [PMID: 34577597 PMCID: PMC8466261 DOI: 10.3390/ph14090897] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 08/30/2021] [Accepted: 09/01/2021] [Indexed: 11/26/2022] Open
Abstract
There is a need for versatile in vivo nuclear imaging reporter systems to foster preclinical and clinical research. We explore the applicability of the SNAPTag and novel radiolabeled small-molecule ligands as a versatile reporter gene system for in vivo nuclear imaging. SNAPTag is a high-affinity protein tag used in a variety of biochemical research areas and based on the suicide DNA repair enzyme O6-methylguanine methyl transferase (MGMT). Its ligands are well suited for reporter gene imaging as the benzyl guanine core scaffold can be derivatized with fluorescent or radiolabeled moieties for various applications. Three guanine-based SNAPTag ligands ([18F]FBBG, [18F]pFBG and [18F]mFBG) were synthesized in high yields and were (radio)chemically characterized. HEK293 cells were engineered to express the SNAPTag on the cell surface and served as cell model to assess target affinity by radiotracer uptake assays, Western blotting and SDS-PAGE autoradiography. A subcutaneous HEK293-SNAPTag xenograft model in immunodeficient mice was used for in vivo evaluation of [18F]FBBG and [18F]pFBG while the biodistribution of [18F]mFBG was characterized in naïve animals. The results were validated by ex vivo biodistribution studies and immunofluorescence staining of the xenografts. All three radiotracers were produced in high radiochemical purity, molar activity and good yields. Western blot analysis revealed successful SNAPTag expression by the transfected HEK293 cells. In vitro testing revealed high target affinity of all three tracers with an up to 191-fold higher signal in the HEK293-SNAPTag cells compared to untransfected cells. This was further supported by a prominent radioactive protein band at the expected size in the SDS-PAGE autoradiograph of cells incubated with [18F]FBBG or [18F]pFBG. The in vivo studies demonstrated high uptake in HEK293-SNAP xenografts compared to HEK293 xenografts with excellent tumor-to-muscle ratios (7.5 ± 4.2 for [18F]FBBG and 10.6 ± 6.2 for [18F]pFBG). In contrast to [18F]pFBG and its chemical analogue [18F]mFBG, [18F]FBBG showed no signs of unspecific bone uptake and defluorination in vivo. Radiolabeled SNAPTag ligands bear great potential for clinical applications such as in vivo tracking of cell populations, antibody fragments and targeted radiotherapy. With excellent target affinity, good stability, and low non-specific binding, [18F]FBBG is a highly promising candidate for further preclinical evaluation.
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