G(S-ALPHA)-SELECTIVE G-PROTEIN ANTAGONISTS

Suramin acts as a G protein inhibitor because it inhibits the rate-lim iting step in activation of the G(alpha) subunit, i.e., the exchange o f GDP for GTP, Here, we have searched for analogues that are selective for G(s alpha). Two compounds have been identified: NF449 (4,4',4 '', 4'''-[carbonyl-bis [imino-5,1,3-benzenetriyl carbonylimino)]]tetrakis- (benzene-1,3-disulfonate) and NF503 nylbis[imino-3,1-phenylene-(2,5-be nzimidazolylene) carbonylimino]] bis-benzenesulfonate). These compound s (i) suppress the association rate of guanosine 5'-[gamma-thio] triph osphate ([S-35] GTP [gamma S]) binding to G(s alpha-s) but not to G(i alpha-1), (ii) inhibit stimulation of adenylyl cyclase activity in S49 cyc(-) membranes (deficient in endogenous G(s alpha)) by exogenously added G(s alpha-s), and (iii) block the coupling of beta-adrenergic re ceptors to G(s) with half-maximum effects in the low micromolar range. In contrast to suramin, which is not selective, NF503 and NF449 disru pt the interaction of the A(1)-adenosine receptor with its cognate G p roteins (G(i)/G(o)) at concentrations that are >30-fold higher than th ose required for uncoupling of beta-adrenergic receptor/G(s) tandems; similarly, the angiotensin II type-1 receptor (a prototypical G(q)-cou pled receptor) is barely affected by the compounds. Thus, NF503 and NF 449 fulfill essential criteria for G(s alpha)-selective antagonists. T he observations demonstrate the feasibility of subtype-selective G pro tein inhibition.