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BRET-Based Biosensors to Measure Agonist Efficacies in Histamine H 1 Receptor-Mediated G Protein Activation, Signaling and Interactions with GRKs and β-Arrestins. Int J Mol Sci 2022; 23:ijms23063184. [PMID: 35328605 PMCID: PMC8953162 DOI: 10.3390/ijms23063184] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/10/2022] [Accepted: 03/11/2022] [Indexed: 02/04/2023] Open
Abstract
The histamine H1 receptor (H1R) is a G protein-coupled receptor (GPCR) and plays a key role in allergic reactions upon activation by histamine which is locally released from mast cells and basophils. Consequently, H1R is a well-established therapeutic target for antihistamines that relieve allergy symptoms. H1R signals via heterotrimeric Gq proteins and is phosphorylated by GPCR kinase (GRK) subtypes 2, 5, and 6, consequently facilitating the subsequent recruitment of β-arrestin1 and/or 2. Stimulation of a GPCR with structurally different agonists can result in preferential engagement of one or more of these intracellular signaling molecules. To evaluate this so-called biased agonism for H1R, bioluminescence resonance energy transfer (BRET)-based biosensors were applied to measure H1R signaling through heterotrimeric Gq proteins, second messengers (inositol 1,4,5-triphosphate and Ca2+), and receptor-protein interactions (GRKs and β-arrestins) in response to histamine, 2-phenylhistamines, and histaprodifens in a similar cellular background. Although differences in efficacy were observed for these agonists between some functional readouts as compared to reference agonist histamine, subsequent data analysis using an operational model of agonism revealed only signaling bias of the agonist Br-phHA-HA in recruiting β-arrestin2 to H1R over Gq biosensor activation.
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Höring C, Seibel U, Tropmann K, Grätz L, Mönnich D, Pitzl S, Bernhardt G, Pockes S, Strasser A. A Dynamic, Split-Luciferase-Based Mini-G Protein Sensor to Functionally Characterize Ligands at All Four Histamine Receptor Subtypes. Int J Mol Sci 2020; 21:ijms21228440. [PMID: 33182741 PMCID: PMC7698210 DOI: 10.3390/ijms21228440] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Revised: 11/06/2020] [Accepted: 11/08/2020] [Indexed: 02/06/2023] Open
Abstract
In drug discovery, assays with proximal readout are of great importance to study target-specific effects of potential drug candidates. In the field of G protein-coupled receptors (GPCRs), the determination of GPCR-G protein interactions and G protein activation by means of radiolabeled GTP analogs ([35S]GTPγS, [γ-32P]GTP) has widely been used for this purpose. Since we were repeatedly faced with insufficient quality of radiolabeled nucleotides, there was a requirement to implement a novel proximal functional assay for the routine characterization of putative histamine receptor ligands. We applied the split-NanoLuc to the four histamine receptor subtypes (H1R, H2R, H3R, H4R) and recently engineered minimal G (mini-G) proteins. Using this method, the functional response upon receptor activation was monitored in real-time and the four mini-G sensors were evaluated by investigating selected standard (inverse) agonists and antagonists. All potencies and efficacies of the studied ligands were in concordance with literature data. Further, we demonstrated a significant positive correlation of the signal amplitude and the mini-G protein expression level in the case of the H2R, but not for the H1R or the H3R. The pEC50 values of histamine obtained under different mini-G expression levels were consistent. Moreover, we obtained excellent dynamic ranges (Z’ factor) and the signal spans were improved for all receptor subtypes in comparison to the previously performed [35S]GTPγS binding assay.
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Affiliation(s)
- Carina Höring
- Correspondence: (C.H.); , (A.S.); Tel.: +49-941-943-4748 (C.H.); +49-941-943-4821 (A.S.)
| | | | | | | | | | | | | | | | - Andrea Strasser
- Correspondence: (C.H.); , (A.S.); Tel.: +49-941-943-4748 (C.H.); +49-941-943-4821 (A.S.)
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Littmann T, Buschauer A, Bernhardt G. Split luciferase-based assay for simultaneous analyses of the ligand concentration- and time-dependent recruitment of β-arrestin2. Anal Biochem 2019; 573:8-16. [PMID: 30853375 DOI: 10.1016/j.ab.2019.02.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 02/22/2019] [Accepted: 02/25/2019] [Indexed: 12/17/2022]
Abstract
Functional selectivity of agonists has gained increasing interest in G protein-coupled receptor (GPCR) research, e.g. due to expectations of drugs with reduced adverse effects. Different agonist-dependent GPCR conformations are conceived to selectively activate a balanced or imbalanced intracellular signalling response, involving e.g. different Gα subtypes, Gβγ-subunits and β-arrestins. To discriminate between the different signalling pathways (bias), sensitive techniques are needed that do not interfere with signalling. We applied split luciferase complementation to the GPCR/β-arrestin2 interaction and thoroughly analysed the influence of its implementation on intracellular signalling. This led to an assay enabling the functional characterization of ligands at the hH1R, the hM1,5R and the hNTS1R in live HEK293T cells. As demonstrated at the hM1,5R, the assay was sensitive enough to identify iperoxo as a superagonist. Time-dependent analyses of the recruitment of β-arrestin2 became possible, allowing the identification of class A and class B GPCRs, due to the differential duration of their interaction with β-arrestin2 and their recycling to the cell membrane. The developed β-arrestin2 recruitment assay, which provides concentration- and time-dependent information on the interaction between GPCRs and β-arrestin2 upon stimulation of the receptor, should be broadly applicable and of high value for the analysis of agonist bias.
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Affiliation(s)
- Timo Littmann
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany.
| | - Armin Buschauer
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Günther Bernhardt
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany.
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Littmann T, Ozawa T, Hoffmann C, Buschauer A, Bernhardt G. A split luciferase-based probe for quantitative proximal determination of Gα q signalling in live cells. Sci Rep 2018; 8:17179. [PMID: 30464299 PMCID: PMC6249299 DOI: 10.1038/s41598-018-35615-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 11/08/2018] [Indexed: 01/04/2023] Open
Abstract
The earlier an activation of a G protein-dependent signalling cascade at a G protein-coupled receptor (GPCR) is probed, the less amplificatory effects contribute to the measured signal. This is especially useful in case of a precise quantification of agonist efficacies, and is of paramount importance, when determining agonist bias in relation to the β-arrestin pathway. As most canonical assays with medium to high throughput rely on the quantification of second messengers, and assays affording more proximal readouts are often limited in throughput, we developed a technique with a proximal readout and sufficiently high throughput that can be used in live cells. Split luciferase complementation (SLC) was applied to assess the interaction of Gαq with its effector phospholipase C-β3. The resulting probe yielded an excellent Z' value of 0.7 and offers a broad and easy applicability to various Gαq-coupling GPCRs (hH1R, hM1,3,5R, hNTS1R), expressed in HEK293T cells, allowing the functional characterisation of agonists and antagonists. Furthermore, the developed sensor enabled imaging of live cells by luminescence microscopy, as demonstrated for the hM3R. The versatile SLC-based probe is broadly applicable e.g. to the screening and the pharmacological characterisation of GPCR ligands as well as to molecular imaging.
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Affiliation(s)
- Timo Littmann
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany.
| | - Takeaki Ozawa
- Department of Chemistry, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Carsten Hoffmann
- Institute of Molecular Cell Biology, University Hospital Jena, University of Jena, Hans-Knöll-Str. 2, D-07745, Jena, Germany
| | - Armin Buschauer
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Günther Bernhardt
- Institute of Pharmacy, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany.
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Wittmann HJ, Strasser A. Competitive association binding kinetic assays: a new tool to detect two different binding orientations of a ligand to its target protein under distinct conditions? Naunyn Schmiedebergs Arch Pharmacol 2017; 390:595-612. [DOI: 10.1007/s00210-017-1362-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 02/10/2017] [Indexed: 01/24/2023]
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Hattori Y, Seifert R. Pharmacological Characterization of Human Histamine Receptors and Histamine Receptor Mutants in the Sf9 Cell Expression System. Handb Exp Pharmacol 2017; 241:63-118. [PMID: 28233175 PMCID: PMC7120522 DOI: 10.1007/164_2016_124] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
A large problem of histamine receptor research is data heterogeneity. Various experimental approaches, the complex signaling pathways of mammalian cells, and the use of different species orthologues render it difficult to compare and interpret the published results. Thus, the four human histamine receptor subtypes were analyzed side-by-side in the Sf9 insect cell expression system, using radioligand binding assays as well as functional readouts proximal to the receptor activation event (steady-state GTPase assays and [35S]GTPγS assays). The human H1R was co-expressed with the regulators of G protein signaling RGS4 or GAIP, which unmasked a productive interaction between hH1R and insect cell Gαq. By contrast, functional expression of the hH2R required the generation of an hH2R-Gsα fusion protein to ensure close proximity of G protein and receptor. Fusion of hH2R to the long (GsαL) or short (GsαS) splice variant of Gαs resulted in comparable constitutive hH2R activity, although both G protein variants show different GDP affinities. Medicinal chemistry studies revealed profound species differences between hH1R/hH2R and their guinea pig orthologues gpH1R/gpH2R. The causes for these differences were analyzed by molecular modeling in combination with mutational studies. Co-expression of the hH3R with Gαi1, Gαi2, Gαi3, and Gαi/o in Sf9 cells revealed high constitutive activity and comparable interaction efficiency with all G protein isoforms. A comparison of various cations (Li+, Na+, K+) and anions (Cl-, Br-, I-) revealed that anions with large radii most efficiently stabilize the inactive hH3R state. Potential sodium binding sites in the hH3R protein were analyzed by expressing specific hH3R mutants in Sf9 cells. In contrast to the hH3R, the hH4R preferentially couples to co-expressed Gαi2 in Sf9 cells. Its high constitutive activity is resistant to NaCl or GTPγS. The hH4R shows structural instability and adopts a G protein-independent high-affinity state. A detailed characterization of affinity and activity of a series of hH4R antagonists/inverse agonists allowed first conclusions about structure/activity relationships for inverse agonists at hH4R. In summary, the Sf9 cell system permitted a successful side-by-side comparison of all four human histamine receptor subtypes. This chapter summarizes the results of pharmacological as well as medicinal chemistry/molecular modeling approaches and demonstrates that these data are not only important for a deeper understanding of HxR pharmacology, but also have significant implications for the molecular pharmacology of GPCRs in general.
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Affiliation(s)
- Yuichi Hattori
- Department of Molecular and Medical Pharmacology, Graduate School of Medical and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
| | - Roland Seifert
- Institute of Pharmacology, Medical School of Hannover, Hannover, Germany
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Strasser A, Wittmann HJ. Molecular Modelling Approaches for the Analysis of Histamine Receptors and Their Interaction with Ligands. Handb Exp Pharmacol 2017; 241:31-61. [PMID: 28110354 DOI: 10.1007/164_2016_113] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Several experimental techniques to analyse histamine receptors are available, e.g. pharmacological characterisation of known or new compounds by different types of assays or mutagenesis studies. To obtain insights into the histamine receptors on a molecular and structural level, crystal structures have to be determined and molecular modelling studies have to be performed. It is widely accepted to generate homology models of the receptor of interest based on an appropriate crystal structure as a template and to refine the resulting models by molecular dynamic simulations. A lot of modelling techniques, e.g. docking, QSAR or interaction fingerprint methods, are used to predict binding modes of ligands and pharmacological data, e.g. affinity or even efficacy. However, within the last years, molecular dynamic simulations got more and more important: First of all, molecular dynamic simulations are very helpful to refine the binding mode of a ligand to a histamine receptor, obtained by docking studies. Furthermore, with increasing computational performance it got possible to simulate complete binding pathways of ions or ligands from the aqueous extracellular phase into the allosteric or orthosteric binding pocket of histamine receptors.
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Affiliation(s)
- Andrea Strasser
- Department of Pharmaceutical/Medicinal Chemistry II, Institute of Pharmacy, University of Regensburg, Universitäts-Str. 31, Regensburg, 93040, Germany.
| | - Hans-Joachim Wittmann
- Department of Pharmaceutical/Medicinal Chemistry II, Institute of Pharmacy, University of Regensburg, Universitäts-Str. 31, Regensburg, 93040, Germany
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Lieb S, Littmann T, Plank N, Felixberger J, Tanaka M, Schäfer T, Krief S, Elz S, Friedland K, Bernhardt G, Wegener J, Ozawa T, Buschauer A. Label-free versus conventional cellular assays: Functional investigations on the human histamine H 1 receptor. Pharmacol Res 2016; 114:13-26. [PMID: 27751876 DOI: 10.1016/j.phrs.2016.10.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 10/11/2016] [Accepted: 10/11/2016] [Indexed: 01/07/2023]
Abstract
A set of histamine H1 receptor (H1R) agonists and antagonists was characterized in functional assays, using dynamic mass redistribution (DMR), electric cell-substrate impedance sensing (ECIS) and various signaling pathway specific readouts (Fura-2 and aequorin calcium assays, arrestin recruitment (luciferase fragment complementation) assay, luciferase gene reporter assay). Data were gained from genetically engineered HEK293T cells and compared with reference data from GTPase assays and radioligand binding. Histamine and the other H1R agonists gave different assay-related pEC50 values, however, the order of potency was maintained. In the luciferase fragment complementation assay, the H1R preferred β-arrestin2 over β-arrestin1. The calcium and the impedimetric assay depended on Gq coupling of the H1R, as demonstrated by complete inhibition of the histamine-induced signals in the presence of the Gq inhibitor FR900359 (UBO-QIC). Whereas partial inhibition by FR900359 was observed in DMR and the gene reporter assay, pertussis toxin substantially decreased the response in DMR, but increased the luciferase signal, reflecting the contribution of both, Gq and Gi, to signaling in these assays. For antagonists, the results from DMR were essentially compatible with those from conventional readouts, whereas the impedance-based data revealed a trend towards higher pKb values. ECIS and calcium assays apparently only reflect Gq signaling, whereas DMR and gene reporter assays appear to integrate both, Gq and Gi mediated signaling. The results confirm the value of the label-free methods, DMR and ECIS, for the characterization of H1R ligands. Both noninvasive techniques are complementary to each other, but cannot fully replace reductionist signaling pathway focused assays.
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Affiliation(s)
- S Lieb
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - T Littmann
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - N Plank
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - J Felixberger
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - M Tanaka
- Department of Chemistry, School of Science, University of Tokyo, Tokyo, Japan
| | - T Schäfer
- Department of Chemistry and Pharmacy, Molecular and Clinical Pharmacy, Friedrich-Alexander Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
| | - S Krief
- Bioprojet Biotech, 35762 Saint-Grégoire, France
| | - S Elz
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - K Friedland
- Department of Chemistry and Pharmacy, Molecular and Clinical Pharmacy, Friedrich-Alexander Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
| | - G Bernhardt
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - J Wegener
- Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, D-93040 Regensburg, Germany
| | - T Ozawa
- Department of Chemistry, School of Science, University of Tokyo, Tokyo, Japan
| | - A Buschauer
- Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany.
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9
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Panula P, Chazot PL, Cowart M, Gutzmer R, Leurs R, Liu WLS, Stark H, Thurmond RL, Haas HL. International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors. Pharmacol Rev 2016; 67:601-55. [PMID: 26084539 DOI: 10.1124/pr.114.010249] [Citation(s) in RCA: 374] [Impact Index Per Article: 46.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.
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Affiliation(s)
- Pertti Panula
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Paul L Chazot
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Marlon Cowart
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Ralf Gutzmer
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Rob Leurs
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Wai L S Liu
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Holger Stark
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Robin L Thurmond
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
| | - Helmut L Haas
- Department of Anatomy, and Neuroscience Center, University of Helsinki, Finland (P.P.); School of Biological and Biomedical Sciences, University of Durham, United Kingdom (P.L.C.); AbbVie, Inc. North Chicago, Illinois (M.C.); Department of Dermatology and Allergy, Hannover Medical School, Hannover, Germany (R.G.); Department of Medicinal Chemistry, Amsterdam Institute of Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands (R.L.); Ziarco Pharma Limited, Canterbury, United Kingdom (W.L.S.L.); Institute of Pharmaceutical and Medical Chemistry and Institute of Neurophysiology, Medical Faculty, Westfalische-Wilhelms-University, Muenster, Germany (H.L.H.); Heinrich-Heine-University Duesseldorf, Germany (H.S.); and Janssen Research & Development, LLC, San Diego, California (R.L.T.)
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10
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Hammer SG, Gobleder S, Naporra F, Wittmann HJ, Elz S, Heinrich MR, Strasser A. 2,4-Diaminopyrimidines as dual ligands at the histamine H1 and H4 receptor-H1/H4-receptor selectivity. Bioorg Med Chem Lett 2015; 26:292-300. [PMID: 26718844 DOI: 10.1016/j.bmcl.2015.12.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 12/10/2015] [Accepted: 12/10/2015] [Indexed: 11/20/2022]
Abstract
Distinct diaminopyrimidines, for example, 4-(4-methylpiperazin-1-yl)-5,6-dihydrobenzo[h]quinazolin-2-amine are histamine H4 receptor (H4R) antagonists and show high affinity to the H4R, but only a moderate affinity to the histamine H1 receptor (H1R). Within previous studies it was shown that an aromatic side chain with a distinct distance to the basic amine and aromatic core is necessary for affinity to the human H1R (hH1R). Thus, a rigid aminopyrimidine with a tricyclic core was used as a lead structure. There, (1) the flexible aromatic side chain was introduced, (2) the substitution pattern of the pyrimidine core was exchanged and (3) rigidity was decreased by opening the tricyclic core. Within the present study, two compounds with similar affinity in the one digit μM range to the human H1R and H4R were identified. While the affinity at the hH1R increased about 4- to 8-fold compared to the parent diaminopyrimidine, the affinity to the hH4R decreased about 5- to 8-fold. In addition to the parent diaminopyrimidine, two selected compounds were docked into the H1R and H4R and molecular dynamic studies were performed to predict the binding mode and explain the experimental results on a molecular level. The two new compounds may be good lead structures for the development of dual H1/H4 receptor ligands with affinities in the same range.
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Affiliation(s)
- Sebastian G Hammer
- Department of Chemistry and Pharmacy, Pharmaceutical Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schuhstraße 19, D-91052 Erlangen, Germany
| | - Susanne Gobleder
- Department of Pharmaceutical/Medicinal Chemistry I, Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - Franziska Naporra
- Department of Pharmaceutical/Medicinal Chemistry I, Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - Hans-Joachim Wittmann
- Department of Pharmaceutical/Medicinal Chemistry II, Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - Sigurd Elz
- Department of Pharmaceutical/Medicinal Chemistry I, Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany
| | - Markus R Heinrich
- Department of Chemistry and Pharmacy, Pharmaceutical Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schuhstraße 19, D-91052 Erlangen, Germany.
| | - Andrea Strasser
- Department of Pharmaceutical/Medicinal Chemistry II, Institute of Pharmacy, University of Regensburg, D-93040 Regensburg, Germany.
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11
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Wittmann HJ, Strasser A. Binding pathway of histamine to the hH4R, observed by unconstrained molecular dynamics. Bioorg Med Chem Lett 2015; 25:1259-68. [DOI: 10.1016/j.bmcl.2015.01.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Revised: 01/20/2015] [Accepted: 01/21/2015] [Indexed: 11/24/2022]
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12
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Kooistra AJ, Kuhne S, de Esch IJP, Leurs R, de Graaf C. A structural chemogenomics analysis of aminergic GPCRs: lessons for histamine receptor ligand design. Br J Pharmacol 2014; 170:101-26. [PMID: 23713847 DOI: 10.1111/bph.12248] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 04/26/2013] [Accepted: 05/03/2013] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND AND PURPOSE Chemogenomics focuses on the discovery of new connections between chemical and biological space leading to the discovery of new protein targets and biologically active molecules. G-protein coupled receptors (GPCRs) are a particularly interesting protein family for chemogenomics studies because there is an overwhelming amount of ligand binding affinity data available. The increasing number of aminergic GPCR crystal structures now for the first time allows the integration of chemogenomics studies with high-resolution structural analyses of GPCR-ligand complexes. EXPERIMENTAL APPROACH In this study, we have combined ligand affinity data, receptor mutagenesis studies, and amino acid sequence analyses to high-resolution structural analyses of (hist)aminergic GPCR-ligand interactions. This integrated structural chemogenomics analysis is used to more accurately describe the molecular and structural determinants of ligand affinity and selectivity in different key binding regions of the crystallized aminergic GPCRs, and histamine receptors in particular. KEY RESULTS Our investigations highlight interesting correlations and differences between ligand similarity and ligand binding site similarity of different aminergic receptors. Apparent discrepancies can be explained by combining detailed analysis of crystallized or predicted protein-ligand binding modes, receptor mutation studies, and ligand structure-selectivity relationships that identify local differences in essential pharmacophore features in the ligand binding sites of different receptors. CONCLUSIONS AND IMPLICATIONS We have performed structural chemogenomics studies that identify links between (hist)aminergic receptor ligands and their binding sites and binding modes. This knowledge can be used to identify structure-selectivity relationships that increase our understanding of ligand binding to (hist)aminergic receptors and hence can be used in future GPCR ligand discovery and design.
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Affiliation(s)
- A J Kooistra
- Faculty of Sciences, Amsterdam Institute for Molecules, Medicines and Systems, VU University Amsterdam, The Netherlands
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13
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Seifert R, Strasser A, Schneider EH, Neumann D, Dove S, Buschauer A. Molecular and cellular analysis of human histamine receptor subtypes. Trends Pharmacol Sci 2013; 34:33-58. [PMID: 23254267 PMCID: PMC3869951 DOI: 10.1016/j.tips.2012.11.001] [Citation(s) in RCA: 126] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 11/03/2012] [Accepted: 11/05/2012] [Indexed: 01/08/2023]
Abstract
The human histamine receptors hH(1)R and hH(2)R constitute important drug targets, and hH(3)R and hH(4)R have substantial potential in this area. Considering the species-specificity of pharmacology of H(x)R orthologs, it is important to analyze hH(x)Rs. Here, we summarize current knowledge of hH(x)Rs endogenously expressed in human cells and hH(x)Rs recombinantly expressed in mammalian and insect cells. We present the advantages and disadvantages of the various systems. We also discuss problems associated with the use of hH(x)R antibodies, an issue of general relevance for G-protein-coupled receptors (GPCRs). There is much greater overlap in activity of 'selective' ligands for other hH(x)Rs than the cognate receptor subtype than generally appreciated. Studies with native and recombinant systems support the concept of ligand-specific receptor conformations, encompassing agonists and antagonists. It is emerging that for characterization of hH(x)R ligands, one cannot rely on a single test system and a single parameter. Rather, multiple systems and parameters have to be studied. Although such studies are time-consuming and expensive, ultimately, they will increase drug safety and efficacy.
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Affiliation(s)
- Roland Seifert
- Institute of Pharmacology, Medical School of Hannover, Hannover, Germany.
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14
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Strasser A, Wittmann HJ, Buschauer A, Schneider EH, Seifert R. Species-dependent activities of G-protein-coupled receptor ligands: lessons from histamine receptor orthologs. Trends Pharmacol Sci 2012; 34:13-32. [PMID: 23228711 DOI: 10.1016/j.tips.2012.10.004] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Revised: 10/26/2012] [Accepted: 10/31/2012] [Indexed: 12/26/2022]
Abstract
Histamine is a biogenic amine that exerts its biological effects as a neurotransmitter and local mediator via four histamine receptor (HR) subtypes (H(x)Rs) - H(1)R, H(2)R, H(3)R, and H(4)R - belonging to the superfamily of G-protein-coupled receptors (GPCRs). All four H(x)Rs exhibit pronounced differences in agonist and/or antagonist pharmacology among various species orthologs. The species differences constitute a problem for animal experiments and drug development. This problem applies to GPCRs with diverse ligands. Here, we summarize our current knowledge on H(x)R orthologs as a case study for species-dependent activity of GPCR ligands. We show that species-specific pharmacology also provides unique opportunities to study important aspects of GPCR pharmacology in general, including ligand-binding sites, the roles of extracellular domains in ligand binding and receptor activation, agonist-independent (constitutive) receptor activity, thermodynamics of ligand/receptor interaction, receptor-activation mechanisms, and ligand-specific receptor conformations.
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Affiliation(s)
- Andrea Strasser
- Department of Pharmaceutical/Medicinal Chemistry II, University of Regensburg, Regensburg, Germany.
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15
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Wittmann HJ, Seifert R, Strasser A. Influence of the N-terminus and the E2-loop onto the binding kinetics of the antagonist mepyramine and the partial agonist phenoprodifen to H1R. Biochem Pharmacol 2011; 82:1910-8. [DOI: 10.1016/j.bcp.2011.09.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 09/07/2011] [Accepted: 09/07/2011] [Indexed: 10/17/2022]
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16
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Interactions of recombinant human histamine H1, H2, H3, and H4 receptors with 34 antidepressants and antipsychotics. Naunyn Schmiedebergs Arch Pharmacol 2011; 385:145-70. [DOI: 10.1007/s00210-011-0704-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Accepted: 10/12/2011] [Indexed: 11/26/2022]
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Wittmann HJ, Elz S, Seifert R, Straßer A. N α-Methylated phenylhistamines exhibit affinity to the hH4R—a pharmacological and molecular modelling study. Naunyn Schmiedebergs Arch Pharmacol 2011; 384:287-99. [DOI: 10.1007/s00210-011-0671-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Accepted: 07/08/2011] [Indexed: 01/08/2023]
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Sf9 cells: a versatile model system to investigate the pharmacological properties of G protein-coupled receptors. Pharmacol Ther 2010; 128:387-418. [PMID: 20705094 DOI: 10.1016/j.pharmthera.2010.07.005] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 07/12/2010] [Indexed: 11/23/2022]
Abstract
The Sf9 cell/baculovirus expression system is widely used for high-level protein expression, often with the purpose of purification. However, proteins may also be functionally expressed in the defined Sf9 cell environment. According to the literature, the pharmacology of G-protein-coupled receptors (GPCRs) functionally reconstituted in Sf9 cells is similar to the receptor properties in mammalian cells. Sf9 cells express both recombinant GPCRs and G-proteins at much higher levels than mammalian cells. Sf9 cells can be grown in suspension culture, providing an inexpensive way of obtaining large protein amounts. Co-infection with various baculoviruses allows free combination of GPCRs with different G-proteins. The absence of constitutively active receptors in Sf9 cells provides an excellent signal-to background ratio in functional assays, allowing the detection of agonist-independent receptor activity and of small ligand-induced signals including partial agonistic and inverse agonistic effects. Insect cell Gα(i)-like proteins mostly do not couple productively to mammalian GPCRs. Thus, unlike in mammalian cells, Sf9 cells do not require pertussis toxin treatment to obtain a Gα(i)-free environment. Co-expression of GPCRs with Gα(i1), Gα(i2), Gα(i3) or Gα(o) in Sf9 cells allows the generation of a selectivity profile for these Gα(i/o)-isoforms. Additionally, GPCR-G-protein combinations can be compared with defined 1:1 stoichiometry by expressing GPCR-Gα fusion proteins. Sf9 cells can also be employed for ligand screening in medicinal chemistry programs, using radioligand binding assays or functional assays, like the steady-state GTPase- or [(35)S]GTPγS binding assay. This review shows that Sf9 cells are a versatile model system to investigate the pharmacological properties of GPCRs.
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Comparison of the pharmacological properties of human and rat histamine H(3)-receptors. Biochem Pharmacol 2010; 80:1437-49. [PMID: 20688049 DOI: 10.1016/j.bcp.2010.07.027] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/20/2010] [Accepted: 07/23/2010] [Indexed: 11/20/2022]
Abstract
Ligand pharmacology of histamine H(3)-receptors is species-dependent. In previous studies, two amino acids in transmembrane domain 3 (TM III) were shown to play a significant role. In this study, we characterized human and rat histamine H(3)-receptors (hH(3)R and rH(3)R, respectively), co-expressed with mammalian G proteins in Sf9 insect cell membranes. We compared a series of imidazole-containing H(3)R ligands in radioligand binding and steady-state GTPase assays. H(3)Rs similarly coupled to Gα(i/o)-proteins. Affinities and potencies of the agonists histamine, N(α)-methylhistamine and R-(α)-methylhistamine were in the same range. Imetit was only a partial agonist. The pharmacology of imetit and proxifan was similar at both species. However, impentamine was more potent and efficacious at rH(3)R. The inverse agonists ciproxifan and thioperamide showed higher potency but lower efficacy at rH(3)R. Clobenpropit was not species-selective. Strikingly, imoproxifan was almost full agonist at hH(3)R, but an inverse agonist at rH(3)R. Imoproxifan was docked into the binding pocket of inactive and active hH(3)R- and rH(3)R-models and molecular dynamic simulations were performed. Imoproxifan bound to hH(3)R and rH(3)R in E-configuration, which represents the trans-isomer of the oxime-moiety as determined in crystallization studies, and stabilized active hH(3)R-, but inactive rH(3)R-conformations. Large differences in electrostatic surfaces between TM III and TM V cause differential orientation of the oxime-moiety of imoproxifan, which then differently interacts with the rotamer toggle switch Trp(6.48) in TM VI. Collectively, the substantial species differences at H(3)Rs are explained at a molecular level by the use of novel H(3)R active-state models.
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Straßer A, Wittmann HJ. In silico analysis of the histaprodifen induced activation pathway of the guinea-pig histamine H1-receptor. J Comput Aided Mol Des 2010; 24:759-69. [DOI: 10.1007/s10822-010-9372-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Accepted: 06/28/2010] [Indexed: 10/19/2022]
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Straßer A, Wittmann HJ. 3D-QSAR CoMFA Study to Predict Orientation of Suprahistaprodifens and Phenoprodifens in the Binding-Pocket of Four Histamine H1-Receptor Species. Mol Inform 2010; 29:333-41. [DOI: 10.1002/minf.200900036] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Accepted: 02/22/2010] [Indexed: 11/08/2022]
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Strasser A. Molecular modeling and QSAR-based design of histamine receptor ligands. Expert Opin Drug Discov 2009; 4:1061-75. [DOI: 10.1517/17460440903264972] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Deml KF, Beermann S, Neumann D, Strasser A, Seifert R. Interactions of histamine H1-receptor agonists and antagonists with the human histamine H4-receptor. Mol Pharmacol 2009; 76:1019-30. [PMID: 19720730 DOI: 10.1124/mol.109.058651] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The human histamine H(4)-receptor (hH(4)R) possesses high constitutive activity and, like the human H(1)-receptor (hH(1)R), is involved in the pathogenesis of type-I allergic reactions. The study aims were to explore the value of dual H(1)/H(4)R antagonists as antiallergy drugs and to address the question of whether H(1)R ligands bind to hH(4)R. In an acute murine asthma model, the H(1)R antagonist mepyramine and the H(4)R antagonist 1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methyl-piperazine (JNJ 7777120) exhibited synergistic inhibitory effects on eosinophil accumulation in the bronchoalveolar lavage fluid. At the hH(4)R expressed in Sf9 insect cells, 18 H(1)R antagonists and 22 H(1)R agonists showed lower affinity to hH(4)R than to hH(1)R as assessed in competition binding experiments. For a small number of H(1)R antagonists, hH(4)R partial agonism was observed in the steady-state GTPase assay. Most compounds were neutral antagonists or inverse agonists. Twelve phenylhistamine-type hH(1)R partial agonists were also hH(4)R partial agonists. Four histaprodifen-type hH(1)R partial agonists were hH(4)R inverse agonists. Dimeric histaprodifen was a more efficacious hH(4)R inverse agonist than the reference compound thioperamide. Suprahistaprodifen was the only histaprodifen acting as hH(4)R partial agonist. Suprahistaprodifen was docked into the binding pocket of inactive and active hH(4)R models in two different orientations, predominantly stabilizing the active state of hH(4)R. Collectively, the synergistic effects of H(1)R and H(4)R antagonists in an acute asthma model and the overlapping interaction of structurally diverse H(1)R ligands with hH(1)R and hH(4)R indicate that the development of dual H(1)R/H(4)R antagonists is a worthwhile and technically feasible goal for the treatment of type-I allergic reactions.
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Affiliation(s)
- Karl-Friedrich Deml
- Department of Pharmacology, School of Pharmacy, University of Regensburg, Regensburg, Germany
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Wittmann HJ, Seifert R, Strasser A. Contribution of binding enthalpy and entropy to affinity of antagonist and agonist binding at human and guinea pig histamine H(1)-receptor. Mol Pharmacol 2009; 76:25-37. [PMID: 19346300 DOI: 10.1124/mol.109.055384] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
For several GPCRs, discrimination between agonism and antagonism is possible on the basis of thermodynamics parameters, such as binding enthalpy and entropy. In this study, we analyze whether agonists and antagonists can also be discriminated thermodynamically at the histamine H(1) receptor (H(1)R). Because previous studies revealed species differences in pharmacology between human H(1)R (hH(1)R) and guinea pig H(1)R (gpH(1)R), we analyzed a broad spectrum of H(1)R antagonists and agonists at hH(1)R and gpH(1)R. [(3)H]Mepyramine competition binding assay were performed at five different temperatures in a range from 283.15 to 303.15 K. In addition, we performed a temperature-dependent three-dimensional quantitative structure activity relationship study to predict binding enthalpy and entropy for histaprodifen derivatives, which can bind to H(1)R in two different orientations. Our studies revealed significant species differences in binding enthalpy and entropy between hH(1)R and gpH(1)R for some antagonists and agonists. Furthermore, in some cases, we found changes in heat capacity of the binding process that were different from zero. Differences in flexibility of the ligands may be responsible for this observation. For most ligands, the binding process to hH(1)R and gpH(1)R is clearly entropy-driven. In contrast, for the endogenous ligand histamine, the binding process is significantly enthalpy-driven at both species isoforms. Thus, a definite discrimination between antagonism and agonism based on thermodynamic parameters is possible for neither hH(1)R nor gpH(1)R, but thermodynamic analysis of ligand-binding may be a novel approach to dissect agonist- and antagonist-specific receptor conformations.
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Affiliation(s)
- Hans-Joachim Wittmann
- Faculty of Chemistry and Pharmacy, School of Pharmacy, University of Regensburg, Regensburg, Germany
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