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Tutov A, Chen X, Werner RA, Mühlig S, Zimmermann T, Nose N, Koshino K, Lapa C, Decker M, Higuchi T. Rationalizing the Binding Modes of PET Radiotracers Targeting the Norepinephrine Transporter. Pharmaceutics 2023; 15:pharmaceutics15020690. [PMID: 36840011 PMCID: PMC9963373 DOI: 10.3390/pharmaceutics15020690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/09/2023] [Accepted: 02/15/2023] [Indexed: 02/22/2023] Open
Abstract
PURPOSE A new PET radiotracer 18F-AF78 showing great potential for clinical application has been reported recently. It belongs to a new generation of phenethylguanidine-based norepinephrine transporter (NET)-targeting radiotracers. Although many efforts have been made to develop NET inhibitors as antidepressants, systemic investigations of the structure-activity relationships (SARs) of NET-targeting radiotracers have rarely been performed. METHODS Without changing the phenethylguanidine pharmacophore and 3-fluoropropyl moiety that is crucial for easy labeling, six new analogs of 18F-AF78 with different meta-substituents on the benzene-ring were synthesized and evaluated in a competitive cellular uptake assay and in in vivo animal experiments in rats. Computational modeling of these tracers was established to quantitatively rationalize the interaction between the radiotracers and NET. RESULTS Using non-radiolabeled reference compounds, a competitive cellular uptake assay showed a decrease in NET-transporting affinity from meta-fluorine to iodine (0.42 and 6.51 µM, respectively), with meta-OH being the least active (22.67 µM). Furthermore, in vivo animal studies with radioisotopes showed that heart-to-blood ratios agreed with the cellular experiments, with AF78(F) exhibiting the highest cardiac uptake. This result correlates positively with the electronegativity rather than the atomic radius of the meta-substituent. Computational modeling studies revealed a crucial influence of halogen substituents on the radiotracer-NET interaction, whereby a T-shaped π-π stacking interaction between the benzene-ring of the tracer and the amino acid residues surrounding the NET binding site made major contributions to the different affinities, in accordance with the pharmacological data. CONCLUSION The SARs were characterized by in vitro and in vivo evaluation, and computational modeling quantitatively rationalized the interaction between radiotracers and the NET binding site. These findings pave the way for further evaluation in different species and underline the potential of AF78(F) for clinical application, e.g., cardiac innervation imaging or molecular imaging of neuroendocrine tumors.
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Affiliation(s)
- Anna Tutov
- Pharmaceutical and Medicinal Chemistry, Institute of Pharmacy and Food Chemistry, University of Würzburg, D-97074 Würzburg, Germany
| | - Xinyu Chen
- Nuclear Medicine, Faculty of Medicine, University of Augsburg, D-86156 Augsburg, Germany
- Department of Nuclear Medicine and Comprehensive Heart Failure Center, University Hospital Würzburg, D-97080 Würzburg, Germany
| | - Rudolf A. Werner
- Department of Nuclear Medicine and Comprehensive Heart Failure Center, University Hospital Würzburg, D-97080 Würzburg, Germany
- Division of Nuclear Medicine, The Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Saskia Mühlig
- Department of Nuclear Medicine and Comprehensive Heart Failure Center, University Hospital Würzburg, D-97080 Würzburg, Germany
| | - Thomas Zimmermann
- Pharmaceutical and Medicinal Chemistry, Institute of Pharmacy and Food Chemistry, University of Würzburg, D-97074 Würzburg, Germany
| | - Naoko Nose
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-0082, Japan
| | - Kazuhiro Koshino
- Department of Systems and Informatics, Hokkaido Information University, Ebetsu 069-0832, Japan
| | - Constantin Lapa
- Nuclear Medicine, Faculty of Medicine, University of Augsburg, D-86156 Augsburg, Germany
| | - Michael Decker
- Pharmaceutical and Medicinal Chemistry, Institute of Pharmacy and Food Chemistry, University of Würzburg, D-97074 Würzburg, Germany
- Correspondence: (M.D.); (T.H.); Tel.: +49-(931)-201-35455 (T.H.)
| | - Takahiro Higuchi
- Department of Nuclear Medicine and Comprehensive Heart Failure Center, University Hospital Würzburg, D-97080 Würzburg, Germany
- Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-0082, Japan
- Correspondence: (M.D.); (T.H.); Tel.: +49-(931)-201-35455 (T.H.)
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Sijben HJ, van Oostveen WM, Hartog PBR, Stucchi L, Rossignoli A, Maresca G, Scarabottolo L, IJzerman AP, Heitman LH. Label-free high-throughput screening assay for the identification of norepinephrine transporter (NET/SLC6A2) inhibitors. Sci Rep 2021; 11:12290. [PMID: 34112854 PMCID: PMC8192900 DOI: 10.1038/s41598-021-91700-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 05/17/2021] [Indexed: 12/23/2022] Open
Abstract
The human norepinephrine transporter (NET) is an established drug target for a wide range of psychiatric disorders. Conventional methods that are used to functionally characterize NET inhibitors are based on the use of radiolabeled or fluorescent substrates. These methods are highly informative, but pose limitations to either high-throughput screening (HTS) adaptation or physiologically accurate representation of the endogenous uptake events. Recently, we developed a label-free functional assay based on the activation of G protein-coupled receptors by a transported substrate, termed the TRACT assay. In this study, the TRACT assay technology was applied to NET expressed in a doxycycline-inducible HEK 293 JumpIn cell line. Three endogenous substrates of NET-norepinephrine (NE), dopamine (DA) and epinephrine (EP)-were compared in the characterization of the reference NET inhibitor nisoxetine. The resulting assay, using NE as a substrate, was validated in a manual HTS set-up with a Z' = 0.55. The inhibitory potencies of several reported NET inhibitors from the TRACT assay showed positive correlation with those from an established fluorescent substrate uptake assay. These findings demonstrate the suitability of the TRACT assay for HTS characterization and screening of NET inhibitors and provide a basis for investigation of other solute carrier transporters with label-free biosensors.
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Affiliation(s)
- Hubert J Sijben
- Division of Drug Discovery and Safety, LACDR, Leiden University, P.O. Box 9502, 2300RA, Leiden, The Netherlands
| | - Wieke M van Oostveen
- Division of Drug Discovery and Safety, LACDR, Leiden University, P.O. Box 9502, 2300RA, Leiden, The Netherlands
| | - Peter B R Hartog
- Division of Drug Discovery and Safety, LACDR, Leiden University, P.O. Box 9502, 2300RA, Leiden, The Netherlands
| | - Laura Stucchi
- Axxam S.p.A, Openzone Science Park, Bresso, Milan, Italy
| | | | | | | | - Adriaan P IJzerman
- Division of Drug Discovery and Safety, LACDR, Leiden University, P.O. Box 9502, 2300RA, Leiden, The Netherlands
| | - Laura H Heitman
- Division of Drug Discovery and Safety, LACDR, Leiden University, P.O. Box 9502, 2300RA, Leiden, The Netherlands.
- Oncode Institute, Leiden, The Netherlands.
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