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

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 mu-, delta-, and kappa-opioid, alpha- and beta-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-(gamma-thio)triphosphate binding to purified recombinant G(oalpha)- or G(betagamma)-stimulated ADP-ribosylation of G(oalpha) by pertussis toxin. In addition, SCH-202676 inhibited antagonist binding to the beta2-adrenergic receptor expressed in Escherichia coli, a system devoid of classical heterotrimeric G proteins. SCH-202676 inhibited radiolabeled agonist and antagonist binding to the alpha2a-adrenergic receptor with an IC50 value of 0.5 microM, decreased the Bmax value of the binding sites with a slight increase in the KD value, and inhibited agonist-induced activation of the receptor. The effects of SCH-202676 were reversible. Incubation of plasma membranes with 10 microM SCH-202676 did not alter subsequent radioligand binding to the alpha2a-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.

Allosteric Modulation of the Adenosine Family of Receptors

“…Both amiloride analogues [21,34] and SCH-202676 [20,47] increased the dissociation rate of the antagonist [ 3 H]ZM241385 from the A 2A AR, while they did not show any effect on the dissociation rate of the agonist [ 3 H]CGS21680. The effects of these compound classes on dissociation kinetics were more pronounced at the A 2A AR than at other AR subtypes.…”

“…Other allosteric modulators (Fig. (5)) for A 1 ARs include amiloride derivatives [21], the nonselective modulator of GPCRs SCH-202676 (35, N-(2,3-diphenyl-1,2,4-thiadiazol-5(2H)-ylidene)methanamine) [20,47], and sodium ions [22]. These are nonselective allosteric modulators, as they also modulate other adenosine receptor subtypes and other GPCRs [3].…”

“…(5)) increased the dissociation rates of the antagonist radioligands, Curiously, the nonselective GPCR allosteric modulator SCH-202676 35 [20,47] increased the dissociation rate of the agonist [ 125 I]I-AB-MECA from the human A 3 AR, while it did not show any effect on the dissociation rate of a selective A 3 AR antagonist.…”

2,2′-Pyridylisatogen tosylate antagonizes P2Y1 receptor signaling without affecting nucleotide binding

“…These modulators include SCH-202676 [21][22][23], amiloride analogues [24][25][26], agmatine [27]. The results suggested that for the P2Y 1 receptor, modes of interaction of orthosteric and allosteric binding sites might be different from that of other GPCRs.…”

Investigation of the Interaction of a Putative Allosteric Modulator,N-(2,3-Diphenyl-1,2,4-thiadiazole-5-(2H)-ylidene) Methanamine Hydrobromide (SCH-202676), with M1Muscarinic Acetylcholine Receptors

“…2), was identified as an allosteric modulator of a variety of GPCRs, including mAChRs (Fawzi et al, 2001). This finding was based on radioligand binding assays performed on membrane preparations derived from cells transfected to individually express different types of GPCRs.…”