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Schüß C, Behr V, Beck-Sickinger AG. Illuminating the neuropeptide Y 4 receptor and its ligand pancreatic polypeptide from a structural, functional, and therapeutic perspective. Neuropeptides 2024; 105:102416. [PMID: 38430725 DOI: 10.1016/j.npep.2024.102416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/12/2024] [Accepted: 02/20/2024] [Indexed: 03/05/2024]
Abstract
The neuropeptide Y4 receptor (Y4R), a rhodopsin-like G protein-coupled receptor (GPCR) and the hormone pancreatic polypeptide (PP) are members of the neuropeptide Y family consisting of four receptors (Y1R, Y2R, Y4R, Y5R) and three highly homologous peptide ligands (neuropeptide Y, peptide YY, PP). In this family, the Y4R is of particular interest as it is the only subtype with high affinity to PP over NPY. The Y4R, as a mediator of PP signaling, has a pivotal role in appetite regulation and energy homeostasis, offering potential avenues for the treatment of metabolic disorders such as obesity. PP as anorexigenic peptide is released postprandial from the pancreas in response to food intake, induces satiety signals and contributes to hamper excessive food intake. Moreover, this system was also described to be associated with different types of cancer: overexpression of Y4R have been found in human adenocarcinoma cells, while elevated levels of PP are related to the development of pancreatic endocrine tumors. The pharmacological relevance of the Y4R advanced the search for potent and selective ligands for this receptor subtype, which will be significantly progressed through the elucidation of the active state PP-Y4R cryo-EM structure. This review summarizes the development of novel PP-derived ligands, like Obinepitide as dual Y2R/Y4R agonist in clinical trials or UR-AK86c as small hexapeptide agonist with picomolar affinity, as well as the first allosteric modulators that selectively target the Y4R, e.g. VU0506013 as potent Y4R positive allosteric modulator or (S)-VU0637120 as allosteric antagonist. Here, we provide valuable insights into the complex physiological functions of the Y4R and PP and the pharmacological relevance of the system in appetite regulation to open up new avenues for the development of tool compounds for targeted therapies with potential applications in metabolic disorders.
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Affiliation(s)
- Corinna Schüß
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Germany.
| | - Victoria Behr
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Germany
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2
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Gleixner J, Kopanchuk S, Grätz L, Tahk MJ, Laasfeld T, Veikšina S, Höring C, Gattor AO, Humphrys LJ, Müller C, Archipowa N, Köckenberger J, Heinrich MR, Kutta RJ, Rinken A, Keller M. Illuminating Neuropeptide Y Y 4 Receptor Binding: Fluorescent Cyclic Peptides with Subnanomolar Binding Affinity as Novel Molecular Tools. ACS Pharmacol Transl Sci 2024; 7:1142-1168. [PMID: 38633582 PMCID: PMC11019746 DOI: 10.1021/acsptsci.4c00013] [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: 01/12/2024] [Revised: 02/20/2024] [Accepted: 02/29/2024] [Indexed: 04/19/2024]
Abstract
The neuropeptide Y (NPY) Y4 receptor (Y4R), a member of the family of NPY receptors, is physiologically activated by the linear 36-amino acid peptide pancreatic polypeptide (PP). The Y4R is involved in the regulation of various biological processes, most importantly pancreatic secretion, gastrointestinal motility, and regulation of food intake. So far, Y4R binding affinities have been mostly studied in radiochemical binding assays. Except for a few fluorescently labeled PP derivatives, fluorescence-tagged Y4R ligands with high affinity have not been reported. Here, we introduce differently fluorescence-labeled (Sulfo-Cy5, Cy3B, Py-1, Py-5) Y4R ligands derived from recently reported cyclic hexapeptides showing picomolar Y4R binding affinity. With pKi values of 9.22-9.71 (radioligand competition binding assay), all fluorescent ligands (16-19) showed excellent Y4R affinity. Y4R saturation binding, binding kinetics, and competition binding with reference ligands were studied using different fluorescence-based methods: flow cytometry (Sulfo-Cy5, Cy3B, and Py-1 label), fluorescence anisotropy (Cy3B label), and NanoBRET (Cy3B label) binding assays. These experiments confirmed the high binding affinity to Y4R (equilibrium pKd: 9.02-9.9) and proved the applicability of the probes for fluorescence-based Y4R competition binding studies and imaging techniques such as single-receptor molecule tracking.
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Affiliation(s)
- Jakob Gleixner
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Sergei Kopanchuk
- Institute
of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Lukas Grätz
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Maris-Johanna Tahk
- Institute
of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Tõnis Laasfeld
- Institute
of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Santa Veikšina
- Institute
of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Carina Höring
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Albert O. Gattor
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Laura J. Humphrys
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Christoph Müller
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Nataliya Archipowa
- Institute
of Biophysics and Physical Biochemistry, Faculty of Biology and Preclinical
Medicine, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
| | - Johannes Köckenberger
- Department
of Chemistry and Pharmacy, Molecular and Clinical Pharmacy, Friedrich-Alexander-University Erlangen-Nürnberg, Nikolaus-Fiebiger-Straße 10, D-91058 Erlangen, Germany
| | - Markus R. Heinrich
- Department
of Chemistry and Pharmacy, Molecular and Clinical Pharmacy, Friedrich-Alexander-University Erlangen-Nürnberg, Nikolaus-Fiebiger-Straße 10, D-91058 Erlangen, Germany
| | - Roger Jan Kutta
- Institute
of Physical and Theoretical Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Ago Rinken
- Institute
of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Max Keller
- Institute
of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
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3
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Geers DWT, Gavriel K, Neumann K. Rapid, traceless and facile peptide cyclization enabled by tetrazine-thiol exchange. J Pept Sci 2024; 30:e3548. [PMID: 37779097 DOI: 10.1002/psc.3548] [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: 06/02/2023] [Revised: 08/25/2023] [Accepted: 09/14/2023] [Indexed: 10/03/2023]
Abstract
Cyclic peptides offer many advantages compared to their linear counterparts, including prolonged stability within the biological environment and enhanced binding affinity. Typically, peptides are cyclized by forming an amide bond, either on-resin or in solution, through extensive use of orthogonal protecting groups or chemoselective ligation strategies, respectively. Here, we show that the chemoselective tetrazine-thiol exchange is a powerful tool for rapid in situ cyclization of peptides without the need for additional activation reagents or extensive protecting group reshuffling. The reaction between N-terminal sulfide-bearing unsymmetric tetrazines and internal cysteines occurs spontaneously within a mildly acidic environment (pH 6.5) and is of traceless nature. The rapidly available unsymmetric sulfide tetrazine building blocks can be incorporated on resin using standard solid-phase peptide synthesis protocols and are orthogonal to trifluoroacetic acid cleavage conditions. The cyclized peptides display high stability, even when incubated with a large excess of free thiols. Due to its traceless and mild nature, we expect that the tetrazine-thiol exchange will be of high value for the in situ formation of cyclic peptide libraries, thus being applicable in drug discovery and development.
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Affiliation(s)
- Daniëlle W T Geers
- Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - Katerina Gavriel
- Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - Kevin Neumann
- Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
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4
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Calderón JC, Plut E, Keller M, Cabrele C, Reiser O, Gervasio FL, Clark T. Extended Metadynamics Protocol for Binding/Unbinding Free Energies of Peptide Ligands to Class A G-Protein-Coupled Receptors. J Chem Inf Model 2024; 64:205-218. [PMID: 38150388 DOI: 10.1021/acs.jcim.3c01574] [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: 12/29/2023]
Abstract
A metadynamics protocol is presented to characterize the binding and unbinding of peptide ligands to class A G-protein-coupled receptors (GPCRs). The protocol expands on the one previously presented for binding and unbinding small-molecule ligands to class A GPCRs and accounts for the more demanding nature of the peptide binding-unbinding process. It applies to almost all class A GPCRs. Exemplary simulations are described for subtypes Y1R, Y2R, and Y4R of the neuropeptide Y receptor family, vasopressin binding to the vasopressin V2 receptor (V2R), and oxytocin binding to the oxytocin receptor (OTR). Binding free energies and the positions of alternative binding sites are presented and, where possible, compared with the experiment.
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Affiliation(s)
- Jacqueline C Calderón
- Computer-Chemistry-Center, Department of Chemistry and Pharmacy, Friedrich-Alexander-University Erlangen-Nuernberg, Naegelsbachstr. 25, Erlangen 91052, Germany
| | - Eva Plut
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg 93040, Germany
| | - Max Keller
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg D-93040, Germany
| | - Chiara Cabrele
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg 93040, Germany
| | - Oliver Reiser
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg 93040, Germany
| | | | - Timothy Clark
- Computer-Chemistry-Center, Department of Chemistry and Pharmacy, Friedrich-Alexander-University Erlangen-Nuernberg, Naegelsbachstr. 25, Erlangen 91052, Germany
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5
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Gleixner J, Gattor AO, Humphrys LJ, Brunner T, Keller M. [ 3H]UR-JG102-A Radiolabeled Cyclic Peptide with High Affinity and Excellent Selectivity for the Neuropeptide Y Y 4 Receptor. J Med Chem 2023; 66:13788-13808. [PMID: 37773891 DOI: 10.1021/acs.jmedchem.3c01224] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/01/2023]
Abstract
The family of human neuropeptide Y receptors (YRs) comprises four subtypes (Y1R, Y2R, Y4R, and Y5R) that are involved in the regulation of numerous physiological processes. Until now, Y4R binding studies have been predominantly performed in hypotonic sodium-free buffers using 125I-labeled derivatives of the endogenous YR agonists pancreatic polypeptide or peptide YY. A few tritium-labeled Y4R ligands have been reported; however, when used in buffers containing sodium at a physiological concentration, their Y4R affinities are insufficient. Based on the cyclic hexapeptide UR-AK86C, we developed a new tritium-labeled Y4R radioligand ([3H]UR-JG102, [3H]20). In sodium-free buffer, [3H]20 exhibits a very low Y4R dissociation constant (Kd 0.012 nM). In sodium-containing buffer (137 mM Na+), the Y4R affinity is lower (Kd 0.11 nM) but still considerably higher compared to previously reported tritiated Y4R ligands. Therefore, [3H]20 represents a useful tool compound for the determination of Y4R binding affinities under physiological-like conditions.
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Affiliation(s)
- Jakob Gleixner
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Albert O Gattor
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Laura J Humphrys
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Thomas Brunner
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Max Keller
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
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6
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Plut E, Calderón JC, Stanojlović V, Gattor AO, Höring C, Humphrys LJ, Konieczny A, Kerres S, Schubert M, Keller M, Cabrele C, Clark T, Reiser O. Stereochemistry-Driven Interactions of α,γ-Peptide Ligands with the Neuropeptide Y Y 4-Receptor. J Med Chem 2023. [PMID: 37440703 DOI: 10.1021/acs.jmedchem.3c00363] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/15/2023]
Abstract
The G-protein-coupled Y4-receptor (Y4R) and its endogenous ligand, pancreatic polypeptide (PP), suppress appetite in response to food intake and, thus, are attractive drug targets for body-weight control. The C-terminus of human PP (hPP), T32-R33-P34-R35-Y36-NH2, penetrates deep into the binding pocket with its tyrosine-amide and di-arginine motif. Here, we present two C-terminally amidated α,γ-hexapeptides (1a/b) with sequence Ac-R31-γ-CBAA32-R33-L34-R35-Y36-NH2, where γ-CBAA is the (1R,2S,3R)-configured 2-(aminomethyl)-3-phenylcyclobutanecarboxyl moiety (1a) or its mirror image (1b). Both peptides bind the Y4R (Ki of 1a/b: 0.66/12 nM) and act as partial agonists (intrinsic activity of 1a/b: 50/39%). Their induced-fit binding poses in the Y4R pocket are unique and build ligand-receptor contacts distinct from those of the C-terminus of the endogenous ligand hPP. We conclude that energetically favorable interactions, although they do not match those of the native ligand hPP, still guarantee high binding affinity (with 1a rivaling hPP) but not the maximum receptor activation.
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Affiliation(s)
- Eva Plut
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Jacqueline C Calderón
- Department of Chemistry and Pharmacy, Computer-Chemistry-Center, Friedrich-Alexander-University Erlangen-Nürnberg, 91052 Erlangen, Germany
| | - Vesna Stanojlović
- Department of Biosciences and Medical Biology, University of Salzburg, 5020 Salzburg, Austria
| | - Albert O Gattor
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Carina Höring
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Laura J Humphrys
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Adam Konieczny
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Sabine Kerres
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Mario Schubert
- Department of Biosciences and Medical Biology, University of Salzburg, 5020 Salzburg, Austria
| | - Max Keller
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
| | - Chiara Cabrele
- Department of Biosciences and Medical Biology, University of Salzburg, 5020 Salzburg, Austria
| | - Timothy Clark
- Department of Chemistry and Pharmacy, Computer-Chemistry-Center, Friedrich-Alexander-University Erlangen-Nürnberg, 91052 Erlangen, Germany
| | - Oliver Reiser
- Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, 93053 Regensburg, Germany
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7
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Sánchez ML, Rodríguez FD, Coveñas R. Neuropeptide Y Peptide Family and Cancer: Antitumor Therapeutic Strategies. Int J Mol Sci 2023; 24:9962. [PMID: 37373115 DOI: 10.3390/ijms24129962] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Revised: 05/30/2023] [Accepted: 06/07/2023] [Indexed: 06/29/2023] Open
Abstract
Currently available data on the involvement of neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) and their receptors (YRs) in cancer are updated. The structure and dynamics of YRs and their intracellular signaling pathways are also studied. The roles played by these peptides in 22 different cancer types are reviewed (e.g., breast cancer, colorectal cancer, Ewing sarcoma, liver cancer, melanoma, neuroblastoma, pancreatic cancer, pheochromocytoma, and prostate cancer). YRs could be used as cancer diagnostic markers and therapeutic targets. A high Y1R expression has been correlated with lymph node metastasis, advanced stages, and perineural invasion; an increased Y5R expression with survival and tumor growth; and a high serum NPY level with relapse, metastasis, and poor survival. YRs mediate tumor cell proliferation, migration, invasion, metastasis, and angiogenesis; YR antagonists block the previous actions and promote the death of cancer cells. NPY favors tumor cell growth, migration, and metastasis and promotes angiogenesis in some tumors (e.g., breast cancer, colorectal cancer, neuroblastoma, pancreatic cancer), whereas in others it exerts an antitumor effect (e.g., cholangiocarcinoma, Ewing sarcoma, liver cancer). PYY or its fragments block tumor cell growth, migration, and invasion in breast, colorectal, esophageal, liver, pancreatic, and prostate cancer. Current data show the peptidergic system's high potential for cancer diagnosis, treatment, and support using Y2R/Y5R antagonists and NPY or PYY agonists as promising antitumor therapeutic strategies. Some important research lines to be developed in the future will also be suggested.
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Affiliation(s)
- Manuel Lisardo Sánchez
- Laboratory of Neuroanatomy of the Peptidergic Systems, Institute of Neurosciences of Castilla and León (INCYL), University of Salamanca, 37008 Salamanca, Spain
| | - Francisco D Rodríguez
- Department of Biochemistry and Molecular Biology, Faculty of Chemical Sciences, University of Salamanca, 37008 Salamanca, Spain
- Group GIR-USAL: BMD (Bases Moleculares del Desarrollo), University of Salamanca, 37008 Salamanca, Spain
| | - Rafael Coveñas
- Laboratory of Neuroanatomy of the Peptidergic Systems, Institute of Neurosciences of Castilla and León (INCYL), University of Salamanca, 37008 Salamanca, Spain
- Group GIR-USAL: BMD (Bases Moleculares del Desarrollo), University of Salamanca, 37008 Salamanca, Spain
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8
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Qu B, Han Y, Liang T, Zhang C, Hou G, Gao F. Evaluation of a novel EphA2 targeting peptide for triple negative breast cancer based on radionuclide molecular imaging. ARAB J CHEM 2022. [DOI: 10.1016/j.arabjc.2022.104211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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9
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Müller C, Gleixner J, Tahk MJ, Kopanchuk S, Laasfeld T, Weinhart M, Schollmeyer D, Betschart MU, Lüdeke S, Koch P, Rinken A, Keller M. Structure-Based Design of High-Affinity Fluorescent Probes for the Neuropeptide Y Y 1 Receptor. J Med Chem 2022; 65:4832-4853. [PMID: 35263541 DOI: 10.1021/acs.jmedchem.1c02033] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The recent crystallization of the neuropeptide Y Y1 receptor (Y1R) in complex with the argininamide-type Y1R selective antagonist UR-MK299 (2) opened up a new approach toward structure-based design of nonpeptidic Y1R ligands. We designed novel fluorescent probes showing excellent Y1R selectivity and, in contrast to previously described fluorescent Y1R ligands, considerably higher (∼100-fold) binding affinity. This was achieved through the attachment of different fluorescent dyes to the diphenylacetyl moiety in 2 via an amine-functionalized linker. The fluorescent ligands exhibited picomolar Y1R binding affinities (pKi values of 9.36-9.95) and proved to be Y1R antagonists, as validated in a Fura-2 calcium assay. The versatile applicability of the probes as tool compounds was demonstrated by flow cytometry- and fluorescence anisotropy-based Y1R binding studies (saturation and competition binding and association and dissociation kinetics) as well as by widefield and total internal reflection fluorescence (TIRF) microscopy of live tumor cells, revealing that fluorescence was mainly localized at the plasma membrane.
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Affiliation(s)
- Christoph Müller
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Jakob Gleixner
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Maris-Johanna Tahk
- Institute of Chemistry, Faculty of Bioorganic Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Sergei Kopanchuk
- Institute of Chemistry, Faculty of Bioorganic Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Tõnis Laasfeld
- Institute of Chemistry, Faculty of Bioorganic Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Michael Weinhart
- Institute of Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Dieter Schollmeyer
- Department of Chemistry, Johannes-Gutenberg-University Mainz, Düsbergweg 10-14, 55099 Mainz, Germany
| | - Martin U Betschart
- Institute of Pharmaceutical Sciences, University of Freiburg, Albertstrasse 25, 79104 Freiburg, Germany
| | - Steffen Lüdeke
- Institute of Pharmaceutical Sciences, University of Freiburg, Albertstrasse 25, 79104 Freiburg, Germany
| | - Pierre Koch
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Ago Rinken
- Institute of Chemistry, Faculty of Bioorganic Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
| | - Max Keller
- Institute of Pharmacy, Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
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