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Porcu A, Melis M, Turecek R, Ullrich C, Mocci I, Bettler B, Gessa GL, Castelli MP. Rimonabant, a potent CB1 cannabinoid receptor antagonist, is a Gα i/o protein inhibitor. Neuropharmacology 2018; 133:107-120. [PMID: 29407764 DOI: 10.1016/j.neuropharm.2018.01.024] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 01/10/2018] [Accepted: 01/18/2018] [Indexed: 12/25/2022]
Abstract
Rimonabant is a potent and selective cannabinoid CB1 receptor antagonist widely used in animal and clinical studies. Besides its antagonistic properties, numerous studies have shown that, at micromolar concentrations rimonabant behaves as an inverse agonist at CB1 receptors. The mechanism underpinning this activity is unclear. Here we show that micromolar concentrations of rimonabant inhibited Gαi/o-type G proteins, resulting in a receptor-independent block of G protein signaling. Accordingly, rimonabant decreased basal and agonist stimulated [35S]GTPγS binding to cortical membranes of CB1- and GABAB-receptor KO mice and Chinese Hamster Ovary (CHO) cell membranes stably transfected with GABAB or D2 dopamine receptors. The structural analog of rimonabant, AM251, decreased basal and baclofen-stimulated GTPγS binding to rat cortical and CHO cell membranes expressing GABAB receptors. Rimonabant prevented G protein-mediated GABAB and D2 dopamine receptor signaling to adenylyl cyclase in Human Embryonic Kidney 293 cells and to G protein-coupled inwardly rectifying K+ channels (GIRK) in midbrain dopamine neurons of CB1 KO mice. Rimonabant suppressed GIRK gating induced by GTPγS in CHO cells transfected with GIRK, consistent with a receptor-independent action. Bioluminescent resonance energy transfer (BRET) measurements in living CHO cells showed that, in presence or absence of co-expressed GABAB receptors, rimonabant stabilized the heterotrimeric Gαi/o-protein complex and prevented conformational rearrangements induced by GABAB receptor activation. Rimonabant failed to inhibit Gαs-mediated signaling, supporting its specificity for Gαi/o-type G proteins. The inhibition of Gαi/o protein provides a new site of rimonabant action that may help to understand its pharmacological and toxicological effects occurring at high concentrations.
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Affiliation(s)
- Alessandra Porcu
- Department of Biomedical Sciences, University of Cagliari, 09042, Monserrato, Italy; Department of Biomedicine, University of Basel, Klingelbergstrasse 50-70, CH-4056, Basel, Switzerland
| | - Miriam Melis
- Department of Biomedical Sciences, University of Cagliari, 09042, Monserrato, Italy
| | - Rostislav Turecek
- Department of Biomedicine, University of Basel, Klingelbergstrasse 50-70, CH-4056, Basel, Switzerland
| | - Celine Ullrich
- Department of Biomedicine, University of Basel, Klingelbergstrasse 50-70, CH-4056, Basel, Switzerland
| | - Ignazia Mocci
- Institute of Translational Pharmacology, National Research Council of Italy (CNR) U.O.S. of Cagliari, 09010, Pula, Italy
| | - Bernhard Bettler
- Department of Biomedicine, University of Basel, Klingelbergstrasse 50-70, CH-4056, Basel, Switzerland
| | - Gian Luigi Gessa
- Department of Biomedical Sciences, University of Cagliari, 09042, Monserrato, Italy; Guy Everett Laboratory, University of Cagliari, 09042, Monserrato, Italy; Neuroscience Institute, National Research Council of Italy (CNR), Cagliari, Italy; Center of Excellence "Neurobiology of Addiction", University of Cagliari, 09042, Monserrato, Italy
| | - M Paola Castelli
- Department of Biomedical Sciences, University of Cagliari, 09042, Monserrato, Italy; Center of Excellence "Neurobiology of Addiction", University of Cagliari, 09042, Monserrato, Italy.
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Bodle CR, Mackie DI, Roman DL. RGS17: an emerging therapeutic target for lung and prostate cancers. Future Med Chem 2013; 5:995-1007. [PMID: 23734683 PMCID: PMC3865709 DOI: 10.4155/fmc.13.91] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Ligands for G-protein-coupled receptors (GPCRs) represent approximately 50% of currently marketed drugs. RGS proteins modulate heterotrimeric G proteins and, thus, GPCR signaling, by accelerating the intrinsic GTPase activity of the Gα subunit. Given the prevalence of GPCR targeted therapeutics and the role RGS proteins play in G protein signaling, some RGS proteins are emerging as targets in their own right. One such RGS protein is RGS17. Increased RGS17 expression in some prostate and lung cancers has been demonstrated to support cancer progression, while reduced expression of RGS17 can lead to development of chemotherapeutic resistance in ovarian cancer. High-throughput screening is a powerful tool for lead compound identification, and utilization of high-throughput technologies has led to the discovery of several RGS inhibitors, thus far. As screening technologies advance, the identification of novel lead compounds the subsequent development of targeted therapeutics appears promising.
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Affiliation(s)
- Christopher R Bodle
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
| | - Duncan I Mackie
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Cancer Signaling and Experimental Therapeutics Program, The Holden Comprehensive Cancer Center, University of Iowa Hospitals & Clinics, Iowa City, IA, USA
| | - David L Roman
- The Department of Pharmaceutical Sciences & Experimental Therapeutics, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Division of Medicinal & Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City, IA, USA
- Cancer Signaling and Experimental Therapeutics Program, The Holden Comprehensive Cancer Center, University of Iowa Hospitals & Clinics, Iowa City, IA, USA
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Mackie DI, Roman DL. Development of a novel high-throughput screen and identification of small-molecule inhibitors of the Gα-RGS17 protein-protein interaction using AlphaScreen. ACTA ACUST UNITED AC 2011; 16:869-77. [PMID: 21680864 DOI: 10.1177/1087057111410427] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In this study, the authors used AlphaScreen technology to develop a high-throughput screening method for interrogating small-molecule libraries for inhibitors of the Gα(o)-RGS17 interaction. RGS17 is implicated in the growth, proliferation, metastasis, and the migration of prostate and lung cancers. RGS17 is upregulated in lung and prostate tumors up to a 13-fold increase over patient-matched normal tissues. Studies show RGS17 knockdown inhibits colony formation and decreases tumorigenesis in nude mice. The screen in this study uses a measurement of the Gα(o)-RGS17 protein-protein interaction, with an excellent Z score exceeding 0.73, a signal-to-noise ratio >70, and a screening time of 1100 compounds per hour. The authors screened the NCI Diversity Set II and determined 35 initial hits, of which 16 were confirmed after screening against controls. The 16 compounds exhibited IC(50) <10 µM in dose-response experiments. Four exhibited IC(50) values <6 µM while inhibiting the Gα(o)-RGS17 interaction >50% when compared to a biotinylated glutathione-S-transferase control. This report describes the first high-throughput screen for RGS17 inhibitors, as well as a novel paradigm adaptable to many other RGS proteins, which are emerging as attractive drug targets for modulating G-protein-coupled receptor signaling.
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Affiliation(s)
- Duncan I Mackie
- Division of Medicinal and Natural Products Chemistry, College of Pharmacy, University of Iowa, 115 South Grand Avenue, Iowa City, IA 52242, USA
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