Abstract
A novel thiadiazole compound, SCH-202676 (N-(2,3-diphenyl-1,2,4-thiadiazol-5-(2H)-ylidene)methanamine), has been identified as an inhibitor of both agonist and antagonist binding to G protein-coupled receptors (GPCRs). SCH-202676 inhibited radioligand binding to a number of structurally distinct, heterologously expressed GPCRs, including the human μ-, δ-, and κ-opioid, α- and β-adrenergic, muscarinic M1 and M2, and dopaminergic D1 and D2receptors, but not to the tyrosine kinase epidermal growth factor receptor. SCH-202676 had no direct effect on G protein activity as assessed by [35S]guanosine-5′-O-(γ-thio)triphosphate binding to purified recombinant Goα- or Gβ γ-stimulated ADP-ribosylation of Goα by pertussis toxin. In addition, SCH-202676 inhibited antagonist binding to the β2-adrenergic receptor expressed in Escherichia coli, a system devoid of classical heterotrimeric G proteins. SCH-202676 inhibited radiolabeled agonist and antagonist binding to the α2a-adrenergic receptor with an IC50 value of 0.5 μM, decreased theB max value of the binding sites with a slight increase in the K D value, and inhibited agonist-induced activation of the receptor. The effects of SCH-202676 were reversible. Incubation of plasma membranes with 10 μM SCH-202676 did not alter subsequent radioligand binding to the α2a-adrenergic receptor and the dopaminergic D1 receptor. Taken together, our data suggest that SCH-202676 has the unique ability to allosterically regulate agonist and antagonist binding to GPCRs in a manner that is both selective and reversible. The scope of the data presented suggests this occurs by direct interaction with a structural motif common to a large number of GPCRs or by activation/inhibition of an unidentified accessory protein that regulates GPCR function.
Footnotes
- Received June 14, 2000.
- Accepted September 22, 2000.
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Send reprint requests to: Ahmad B. Fawzi, Ph.D., Schering-Plough Research Institute, 2015 Galloping Hill Rd., K15-C405 (4600), Kenilworth, NJ 07033-0539. E-mail:ahmad.fawzi{at}spcorp.com
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↵1 Present address: CNS Biochemical Pharmacology, Aventis Pharmaceuticals, Bridgewater, New Jersey.
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This work was supported by United States Public Health Services Grant GM51466 (M.E.L.).
- The American Society for Pharmacology and Experimental Therapeutics
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