Vol. 59, Issue 1, 30-37, January 2001

SCH-202676: An Allosteric Modulator of Both Agonist and Antagonist Binding to G Protein-Coupled Receptors

Ahmad B. Fawzi, Douglas Macdonald,¹ Lawrence L. Benbow, April Smith-Torhan, Hongtao Zhang, Blair C. Weig, Ginny Ho, Deen Tulshian, Maurine E. Linder, and Michael P. Graziano

Central Nervous System/Cardiovascular Research, Schering-Plough Research Institute, Kenilworth, New Jersey (A.B.F., D.M., L.L.B., A.S.-T., H.Z., B.C.W., G.H., D.T., M.P.G.); and Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri (M.E.L.)

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-, -, and -opioid, - and -adrenergic, muscarinic M₁ and M₂, and dopaminergic D₁ and D₂ receptors, 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-(-thio)triphosphate binding to purified recombinant G_o- or G-stimulated ADP-ribosylation of G_o by pertussis toxin. In addition, SCH-202676 inhibited antagonist binding to the ₂-adrenergic receptor expressed in Escherichia coli, a system devoid of classical heterotrimeric G proteins. SCH-202676 inhibited radiolabeled agonist and antagonist binding to the _2a-adrenergic receptor with an IC₅₀ value of 0.5 µM, decreased the B_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 _2a-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.