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Baker JG, Summers RJ. Adrenoceptors: Receptors, Ligands and Their Clinical Uses, Molecular Pharmacology and Assays. Handb Exp Pharmacol 2024. [PMID: 38926158 DOI: 10.1007/164_2024_713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
The nine G protein-coupled adrenoceptor subtypes are where the endogenous catecholamines adrenaline and noradrenaline interact with cells. Since they are important therapeutic targets, over a century of effort has been put into developing drugs that modify their activity. This chapter provides an outline of how we have arrived at current knowledge of the receptors, their physiological roles and the methods used to develop ligands. Initial studies in vivo and in vitro with isolated organs and tissues progressed to cell-based techniques and the use of cloned adrenoceptor subtypes together with high-throughput assays that allow close examination of receptors and their signalling pathways. The crystal structures of many of the adrenoceptor subtypes have now been determined opening up new possibilities for drug development.
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Affiliation(s)
- Jillian G Baker
- Cell Signalling, Medical School, Queen's Medical Centre, University of Nottingham, Nottingham, UK.
- Department of Respiratory Medicine, Nottingham University Hospitals NHS Trust, Nottingham, UK.
| | - Roger J Summers
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia.
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Braga Emidio N, Small BM, Keller AR, Cheloha RW, Wingler LM. Nanobody-Mediated Dualsteric Engagement of the Angiotensin Receptor Broadens Biased Ligand Pharmacology. Mol Pharmacol 2024; 105:260-271. [PMID: 38164609 PMCID: PMC10877709 DOI: 10.1124/molpharm.123.000797] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/15/2023] [Accepted: 12/04/2023] [Indexed: 01/03/2024] Open
Abstract
Dualsteric G protein-coupled receptor (GPCR) ligands are a class of bitopic ligands that consist of an orthosteric pharmacophore, which binds to the pocket occupied by the receptor's endogenous agonist, and an allosteric pharmacophore, which binds to a distinct site. These ligands have the potential to display characteristics of both orthosteric and allosteric ligands. To explore the signaling profiles that dualsteric ligands of the angiotensin II type 1 receptor (AT1R) can access, we ligated a 6e epitope tag-specific nanobody (single-domain antibody fragment) to angiotensin II (AngII) and analogs that show preferential allosteric coupling to Gq (TRV055, TRV056) or β-arrestin (TRV027). While the nanobody itself acts as a probe-specific neutral or negative allosteric ligand of N-terminally 6e-tagged AT1R, nanobody conjugation to orthosteric ligands had varying effects on Gq dissociation and β-arrestin plasma membrane recruitment. The potency of certain AngII analogs was enhanced up to 100-fold, and some conjugates behaved as partial agonists, with up to a 5-fold decrease in maximal efficacy. Nanobody conjugation also biased the signaling of TRV055 and TRV056 toward Gq, suggesting that Gq bias at AT1R can be modulated through molecular mechanisms distinct from those previously elucidated. Both competition radioligand binding experiments and functional assays demonstrated that orthosteric antagonists (angiotensin receptor blockers) act as non-competitive inhibitors of all these nanobody-peptide conjugates. This proof-of-principle study illustrates the array of pharmacological patterns that can be achieved by incorporating neutral or negative allosteric pharmacophores into dualsteric ligands. Nanobodies directed toward linear epitopes could provide a rich source of allosteric reagents for this purpose. SIGNIFICANCE STATEMENT: Here we engineer bitopic (dualsteric) ligands for epitope-tagged angiotensin II type 1 receptor by conjugating angiotensin II or its biased analogs to an epitope-specific nanobody (antibody fragment). Our data demonstrate that nanobody-mediated interactions with the receptor N-terminus endow angiotensin analogs with properties of allosteric modulators and provide a novel mechanism to increase the potency, modulate the maximal effect, or alter the bias of ligands.
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Affiliation(s)
- Nayara Braga Emidio
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (N.B.E., R.W.C.) and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina (B.M.S., A.R.K., L.M.W.)
| | - Brandi M Small
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (N.B.E., R.W.C.) and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina (B.M.S., A.R.K., L.M.W.)
| | - Amanda R Keller
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (N.B.E., R.W.C.) and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina (B.M.S., A.R.K., L.M.W.)
| | - Ross W Cheloha
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (N.B.E., R.W.C.) and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina (B.M.S., A.R.K., L.M.W.)
| | - Laura M Wingler
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (N.B.E., R.W.C.) and Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina (B.M.S., A.R.K., L.M.W.)
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Varakumar P, Rajagopal K, Aparna B, Raman K, Byran G, Gonçalves Lima CM, Rashid S, Nafady MH, Emran TB, Wybraniec S. Acridine as an Anti-Tumour Agent: A Critical Review. Molecules 2022; 28:molecules28010193. [PMID: 36615391 PMCID: PMC9822522 DOI: 10.3390/molecules28010193] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 12/14/2022] [Accepted: 12/21/2022] [Indexed: 12/28/2022] Open
Abstract
This review summarized the current breakthroughs in the chemistry of acridines as anti-cancer agents, including new structural and biologically active acridine attributes. Acridine derivatives are a class of compounds that are being extensively researched as potential anti-cancer drugs. Acridines are well-known for their high cytotoxic activity; however, their clinical application is restricted or even excluded as a result of side effects. The photocytotoxicity of propyl acridine acts against leukaemia cell lines, with C1748 being a promising anti-tumour drug against UDP-UGT's. CK0403 is reported in breast cancer treatment and is more potent than CK0402 against estrogen receptor-negative HER2. Acridine platinum (Pt) complexes have shown specificity on the evaluated DNA sequences; 9-anilinoacridine core, which intercalates DNA, and a methyl triazene DNA-methylating moiety were also studied. Acridine thiourea gold and acridinone derivatives act against cell lines such as MDA-MB-231, SK-BR-3, and MCF-7. Benzimidazole acridine compounds demonstrated cytotoxic activity against Dual Topo and PARP-1. Quinacrine, thiazacridine, and azacridine are reported as anti-cancer agents, which have been reported in the previous decade and were addressed in this review article.
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Affiliation(s)
- Potlapati Varakumar
- Department of Pharmaceutical Chemistry, JSS College of Pharmacy (JSS Academy of Higher Education & Research), Ooty 643001, India
| | - Kalirajan Rajagopal
- Department of Pharmaceutical Chemistry, JSS College of Pharmacy (JSS Academy of Higher Education & Research), Ooty 643001, India
- Correspondence: (K.R.); (T.B.E.); (S.W.)
| | - Baliwada Aparna
- Department of Pharmaceutical Chemistry, JSS College of Pharmacy (JSS Academy of Higher Education & Research), Ooty 643001, India
| | - Kannan Raman
- Department of Pharmaceutical Chemistry, JSS College of Pharmacy (JSS Academy of Higher Education & Research), Ooty 643001, India
| | - Gowramma Byran
- Department of Pharmaceutical Chemistry, JSS College of Pharmacy (JSS Academy of Higher Education & Research), Ooty 643001, India
| | | | - Salma Rashid
- Department of Pharmacy, Faculty of Allied Health Sciences, Daffodil International University, Dhaka 1207, Bangladesh
| | - Mohammed H. Nafady
- Faculty of Applied Health Science Technology, Misr University for Science and Technology, Giza 12568, Egypt
| | - Talha Bin Emran
- Department of Pharmacy, Faculty of Allied Health Sciences, Daffodil International University, Dhaka 1207, Bangladesh
- Department of Pharmacy, BGC Trust University Bangladesh, Chittagong 4381, Bangladesh
- Correspondence: (K.R.); (T.B.E.); (S.W.)
| | - Sławomir Wybraniec
- Department of Chemical Technology and Environmental Analysis, Faculty of Chemical Engineering and Technology, Cracow University of Technology, Warszawska 24, 31-155 Krakow, Poland
- Correspondence: (K.R.); (T.B.E.); (S.W.)
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Papay RS, Macdonald JD, Stauffer SR, Perez DM. Characterization of a novel positive allosteric modulator of the α 1A-Adrenergic receptor. CURRENT RESEARCH IN PHARMACOLOGY AND DRUG DISCOVERY 2022; 4:100142. [PMID: 36544813 PMCID: PMC9762201 DOI: 10.1016/j.crphar.2022.100142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 10/27/2022] [Accepted: 11/15/2022] [Indexed: 12/05/2022] Open
Abstract
α1-Adrenergic Receptors (ARs) are G-protein Coupled Receptors (GPCRs) that regulate the sympathetic nervous system via the binding and activation of norepinephrine (NE) and epinephrine (Epi). α1-ARs control various aspects of neurotransmission, cognition, cardiovascular functions as well as other organ systems. However, therapeutic drug development for these receptors, particularly agonists, has been stagnant due to unwanted effects on blood pressure regulation. We report the synthesis and characterization of the first positive allosteric modulator (PAM) for the α1-AR based upon the derivation of the α1A-AR selective imidazoline agonist, cirazoline. Compound 3 (Cmpd-3) binds the α1A-AR with high and low affinity sites (0.13pM; 54 nM) typical of GPCR agonists, and reverts to a single low affinity site of 100 nM upon the addition of GTP. Comparison of Cmpd-3 versus other orthosteric α1A-AR-selective imidazoline ligands reveal unique properties that are consistent with a type I PAM. Cmpd-3 is both conformationally and ligand-selective for the α1A-AR subtype. In competition binding studies, Cmpd-3 potentiates NE-binding at the α1A-AR only on the high affinity state of NE with no effect on the Epi-bound α1A-AR. Moreover, Cmpd-3 demonstrates signaling-bias and potentiates the NE-mediated cAMP response of the α1A-AR at nM concentrations with no effects on the NE-mediated inositol phosphate response. There are no effects of Cmpd-3 on the signaling at the α1B- or α1D-AR subtypes. Cmpd-3 displays characteristics of a pure PAM with no intrinsic agonist properties. Specific derivation of Cmpd-3 at the R1 ortho-position recapitulated PAM characteristics. Our results characterize the first PAM for the α1-AR and holds promise for a first-in-class therapeutic to treat various diseases without the side effect of increasing blood pressure intrinsic to classical orthosteric agonists.
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Affiliation(s)
- Robert S. Papay
- The Department of Cardiovascular & Metabolic Sciences, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH, 44195, USA
| | - Jonathan D. Macdonald
- Center for Therapeutics Discovery, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH, 44195, USA
| | - Shaun R. Stauffer
- Center for Therapeutics Discovery, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH, 44195, USA
| | - Dianne M. Perez
- The Department of Cardiovascular & Metabolic Sciences, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH, 44195, USA
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Root-Bernstein R. Biased, Bitopic, Opioid–Adrenergic Tethered Compounds May Improve Specificity, Lower Dosage and Enhance Agonist or Antagonist Function with Reduced Risk of Tolerance and Addiction. Pharmaceuticals (Basel) 2022; 15:ph15020214. [PMID: 35215326 PMCID: PMC8876737 DOI: 10.3390/ph15020214] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 02/02/2022] [Accepted: 02/07/2022] [Indexed: 01/03/2023] Open
Abstract
This paper proposes the design of combination opioid–adrenergic tethered compounds to enhance efficacy and specificity, lower dosage, increase duration of activity, decrease side effects, and reduce risk of developing tolerance and/or addiction. Combinations of adrenergic and opioid drugs are sometimes used to improve analgesia, decrease opioid doses required to achieve analgesia, and to prolong the duration of analgesia. Recent mechanistic research suggests that these enhanced functions result from an allosteric adrenergic binding site on opioid receptors and, conversely, an allosteric opioid binding site on adrenergic receptors. Dual occupancy of the receptors maintains the receptors in their high affinity, most active states; drops the concentration of ligand required for full activity; and prevents downregulation and internalization of the receptors, thus inhibiting tolerance to the drugs. Activation of both opioid and adrenergic receptors also enhances heterodimerization of the receptors, additionally improving each drug’s efficacy. Tethering adrenergic drugs to opioids could produce new drug candidates with highly desirable features. Constraints—such as the locations of the opioid binding sites on adrenergic receptors and adrenergic binding sites on opioid receptors, length of tethers that must govern the design of such novel compounds, and types of tethers—are described and examples of possible structures provided.
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Chen J, Campbell AP, Wakelin LPG, Finch AM. Characterisation of bis(4-aminoquinoline)s as α 1A adrenoceptor allosteric modulators. Eur J Pharmacol 2021; 916:174659. [PMID: 34871559 DOI: 10.1016/j.ejphar.2021.174659] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 11/19/2021] [Accepted: 11/29/2021] [Indexed: 11/30/2022]
Abstract
The development of sub-type selective α1 adrenoceptor ligands has been hampered by the high sequence similarity of the amino acids forming the orthosteric binding pocket of the three α1 adrenoceptor subtypes, along with other biogenic amine receptors. One possible approach to overcome this issue is to target allosteric sites on the α1 adrenoceptors. Previous docking studies suggested that one of the quinoline moieties of a bis(4-aminoquinoline), comprising a 9-carbon methylene linker attached via the amine groups, could interact with residues outside of the orthosteric binding site while, simultaneously, the other quinoline moiety bound within the orthosteric site. We therefore hypothesized that this compound could act in a bitopic manner, displaying both orthosteric and allosteric binding properties. To test this proposition, we investigated the allosteric activity of a series of bis(4-aminoquinoline)s with linker lengths ranging from 2 to 12 methylene units (designated C2-C12). A linear trend of increasing [3H]prazosin dissociation rate with increasing linker length between C7 and C11 was observed, confirming their action as allosteric modulators. These data suggest that the optimal linker length for the bis(4-aminoquinoline)s to occupy the allosteric site of the α1A adrenoceptor is between 7 and 11 methylene units. In addition, the ability of C9 bis(4-aminoquinoline) to modulate the activation of the α1A adrenoceptor by norepinephrine was subsequently examined, showing that C9 acted as a non-competitive antagonist. Our findings indicate that the bis(4-aminoquinolines) are acting as allosteric modulators of orthosteric ligand binding, but not efficacy, in a bitopic manner.
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Affiliation(s)
- Junli Chen
- Department of Pharmacology, School of Medical Sciences, UNSW Australia, Sydney, NSW, 2052, Australia
| | - Adrian P Campbell
- Department of Pharmacology, School of Medical Sciences, UNSW Australia, Sydney, NSW, 2052, Australia
| | - Laurence P G Wakelin
- Department of Pharmacology, School of Medical Sciences, UNSW Australia, Sydney, NSW, 2052, Australia
| | - Angela M Finch
- Department of Pharmacology, School of Medical Sciences, UNSW Australia, Sydney, NSW, 2052, Australia.
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Perez DM. Current Developments on the Role of α 1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism. Front Cell Dev Biol 2021; 9:652152. [PMID: 34113612 PMCID: PMC8185284 DOI: 10.3389/fcell.2021.652152] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 04/29/2021] [Indexed: 12/13/2022] Open
Abstract
The α1-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α2-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α1-AR subtypes (α1A, α1B, α1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.
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Affiliation(s)
- Dianne M Perez
- The Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH, United States
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Perez DM. α 1-Adrenergic Receptors in Neurotransmission, Synaptic Plasticity, and Cognition. Front Pharmacol 2020; 11:581098. [PMID: 33117176 PMCID: PMC7553051 DOI: 10.3389/fphar.2020.581098] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 09/11/2020] [Indexed: 12/14/2022] Open
Abstract
α1-adrenergic receptors are G-Protein Coupled Receptors that are involved in neurotransmission and regulate the sympathetic nervous system through binding and activating the neurotransmitter, norepinephrine, and the neurohormone, epinephrine. There are three α1-adrenergic receptor subtypes (α1A, α1B, α1D) that are known to play various roles in neurotransmission and cognition. They are related to two other adrenergic receptor families that also bind norepinephrine and epinephrine, the β- and α2-, each with three subtypes (β1, β2, β3, α2A, α2B, α2C). Previous studies assessing the roles of α1-adrenergic receptors in neurotransmission and cognition have been inconsistent. This was due to the use of poorly-selective ligands and many of these studies were published before the characterization of the cloned receptor subtypes and the subsequent development of animal models. With the availability of more-selective ligands and the development of animal models, a clearer picture of their role in cognition and neurotransmission can be assessed. In this review, we highlight the significant role that the α1-adrenergic receptor plays in regulating synaptic efficacy, both short and long-term synaptic plasticity, and its regulation of different types of memory. We will also present evidence that the α1-adrenergic receptors, and particularly the α1A-adrenergic receptor subtype, are a potentially good target to treat a wide variety of neurological conditions with diminished cognition.
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Affiliation(s)
- Dianne M Perez
- The Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH, United States
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Gao ZG, Toti KS, Campbell R, Suresh RR, Yang H, Jacobson KA. Allosteric Antagonism of the A 2A Adenosine Receptor by a Series of Bitopic Ligands. Cells 2020; 9:cells9051200. [PMID: 32408534 PMCID: PMC7290864 DOI: 10.3390/cells9051200] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 05/03/2020] [Accepted: 05/10/2020] [Indexed: 12/11/2022] Open
Abstract
Allosteric antagonism by bitopic ligands, as reported for many receptors, is a distinct modulatory mechanism. Although several bitopic A2A adenosine receptor (A2AAR) ligand classes were reported as pharmacological tools, their receptor binding and functional antagonism patterns, i.e., allosteric or competitive, were not well characterized. Therefore, here we systematically characterized A2AAR binding and functional antagonism of two distinct antagonist chemical classes. i.e., fluorescent conjugates of xanthine amine congener (XAC) and SCH442416. Bitopic ligands were potent, weak, competitive or allosteric, based on the combination of pharmacophore, linker and fluorophore. Among antagonists tested, XAC, XAC245, XAC488, SCH442416, MRS7352 showed Ki binding values consistent with KB values from functional antagonism. Interestingly, MRS7396, XAC-X-BY630 (XAC630) and 5-(N,N-hexamethylene)amiloride (HMA) were 9–100 times weaker in displacing fluorescent MRS7416 binding than radioligand binding. XAC245, XAC630, MRS7396, MRS7416 and MRS7322 behaved as allosteric A2AAR antagonists, whereas XAC488 and MRS7395 antagonized competitively. Schild analysis showed antagonism slopes of 0.42 and 0.47 for MRS7396 and XAC630, respectively. Allosteric antagonists HMA and MRS7396 were more potent in displacing [3H]ZM241385 binding than MRS7416 binding. Sodium site D52N mutation increased and decreased affinity of HMA and MRS7396, respectively, suggesting possible preference for different A2AAR conformations. The allosteric binding properties of some bitopic ligands were rationalized and analyzed using the Hall two-state allosteric model. Thus, fluorophore tethering to an orthosteric ligand is not neutral pharmacologically and may confer unexpected properties to the conjugate.
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Williams LM, He X, Vaid TM, Abdul‐Ridha A, Whitehead AR, Gooley PR, Bathgate RA, Williams SJ, Scott DJ. Diazepam is not a direct allosteric modulator of α 1-adrenoceptors, but modulates receptor signaling by inhibiting phosphodiesterase-4. Pharmacol Res Perspect 2019; 7:e00455. [PMID: 30619611 PMCID: PMC6306559 DOI: 10.1002/prp2.455] [Citation(s) in RCA: 3] [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] [Received: 10/10/2018] [Revised: 11/30/2018] [Accepted: 12/04/2018] [Indexed: 12/19/2022] Open
Abstract
α1A- and α1B-adrenoceptors (ARs) are G protein-coupled receptors (GPCRs) that are activated by adrenaline and noradrenaline to modulate smooth muscle contraction in the periphery, and neuronal outputs in the central nervous system (CNS). α1A- and α1B-AR are clinically targeted with antagonists for hypertension and benign prostatic hyperplasia and are emerging CNS targets for treating neurodegenerative diseases. The benzodiazepines midazolam, diazepam, and lorazepam are proposed to be positive allosteric modulators (PAMs) of α1-ARs. Here, using thermostabilized, purified, α1A- and α1B-ARs, we sought to identify the benzodiazepine binding site and modulatory mechanism to inform the design of selective PAMs. However, using a combination of biophysical approaches no evidence was found for direct binding of several benzodiazepines to purified, stabilized α1A- and α1B-ARs. Similarly, in cell-based assays expressing unmodified α1A- and α1B-ARs, benzodiazepine treatment had no effect on fluorescent ligand binding, agonist-stimulated Ca2+ release, or G protein activation. In contrast, several benzodiazepines positively modulated phenylephrine stimulation of a cAMP response element pathway by α1A- and α1B-ARs; however, this was shown to be caused by off-target inhibition of phosphodiesterases, known targets of diazepam. This study highlights how purified, stabilized GPCRs are useful for validating allosteric ligand binding and that care needs to be taken before assigning new targets to benzodiazepines.
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Affiliation(s)
- Lisa M. Williams
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
| | - Xiaoji He
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
- School of Chemistry and Bio21 Molecular Science and Biotechnology InstituteUniversity of MelbourneParkvilleVicAustralia
| | - Tasneem M. Vaid
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
- Department of Biochemistry and Molecular BiologyUniversity of MelbourneParkvilleVicAustralia
- The Bio21 Molecular Science and Biotechnology InstituteUniversity of MelbourneParkvilleVicAustralia
| | - Alaa Abdul‐Ridha
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
| | - Alice R. Whitehead
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
| | - Paul R. Gooley
- Department of Biochemistry and Molecular BiologyUniversity of MelbourneParkvilleVicAustralia
- The Bio21 Molecular Science and Biotechnology InstituteUniversity of MelbourneParkvilleVicAustralia
| | - Ross A.D. Bathgate
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
- Department of Biochemistry and Molecular BiologyUniversity of MelbourneParkvilleVicAustralia
| | - Spencer J. Williams
- School of Chemistry and Bio21 Molecular Science and Biotechnology InstituteUniversity of MelbourneParkvilleVicAustralia
- The Bio21 Molecular Science and Biotechnology InstituteUniversity of MelbourneParkvilleVicAustralia
| | - Daniel J. Scott
- The Florey Institute of Neuroscience and Mental HealthUniversity of MelbourneParkvilleVicAustralia
- Department of Biochemistry and Molecular BiologyUniversity of MelbourneParkvilleVicAustralia
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