G(sα)-selective G protein antagonists

Suramin acts as a G protein inhibitor because it inhibits the rate-limiting step in activation of the G(α) subunit, i.e., the exchange of GDP for GTP. Here, we have searched for analogues that are selective for G(sα). Two compounds have been identified: NF449 (4,4′,4",4′"-[carbonyl-bis[imino-5,1,3-benzenetriyl bis-(carbonylimino)]]tetrakis-(benzene-1,3-disulfonate) and NF503 (4,4′-[carbonylbis[imino-3,1-phenylene-(2,5-benzimidazolylene)carbonylimino]]bis-benzenesulfonate). These compounds (i) suppress the association rate of guanosine 5′-[γ-thio]triphosphate ([(35)S]GTP[γS]) binding to G(sα-s) but not to G(iα-1), (ii) inhibit stimulation of adenylyl cyclase activity in S49 cyc(−) membranes (deficient in endogenous G(sα)) by exogenously added G(sα-s), and (iii) block the coupling of β-adrenergic receptors to G(s) with half-maximum effects in the low micromolar range. In contrast to suramin, which is not selective, NF503 and NF449 disrupt the interaction of the A(1)-adenosine receptor with its cognate G proteins (G(i)/G(o)) at concentrations that are >30-fold higher than those required for uncoupling of β-adrenergic receptor/G(s) tandems; similarly, the angiotensin II type-1 receptor (a prototypical G(q)-coupled receptor) is barely affected by the compounds. Thus, NF503 and NF449 fulfill essential criteria for G(sα)-selective antagonists. The observations demonstrate the feasibility of subtype-selective G protein inhibition.