Vol. 296, Issue 3, 768-775, March 2001

Pharmacology of SB-273779, a Nonpeptide Calcitonin Gene-Related Peptide 1 Receptor Antagonist

Nambi Aiyar, Robert A. Daines, Jyoti Disa, Pamela A. Chambers, Charles F. Sauermelch, Marie-J. Quiniou, Nassirah Khandoudi, Bernard Gout, Stephen A. Douglas and Robert N. Willette

Departments of Cardiovascular Pharmacology (N.A., J.D., C.F.S., S.A.D., R.N.W.) and Medicinal Chemistry (R.A.D., P.A.C.), SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania; and SmithKline Beecham Pharmaceuticals, Unité de Recherche, Saint-Grégoire, France (M.-J.Q., N.K., B.G.)

Calcitonin gene-related peptide (CGRP), a potent vasodilatory and cardiotonic peptide, has a potential role for CGRP in diverse physiologic and pathophysiologic situations such as congestive heart failure, diabetes, migraine, and neurogenic inflammation. Although a peptide CGRP receptor antagonist, CGRP_8-37, is available, its utility presents significant limitations for these indications. Here, we describe the properties of SB-(+)-273779 [N-methyl-N-(2-methylphenyl)-3-nitro-4-(2-thiazolylsulfinyl)nitrobenzanilide], a selective nonpeptide antagonist of CGRP₁ receptor. SB-(+)-273779 inhibited ¹²⁵I-labeled CGRP binding to SK-N-MC (human neuroblastoma cells) and human cloned CGRP₁ receptor with K_i values of 310 ± 40 and 250 ±15 nM, respectively. SB-(+)-273779 also inhibited CGRP (3 nM)-activated adenylyl cyclase in these systems with IC₅₀ values of 390 ±10 nM (in SK-N-MC) and 210 ±16 nM (recombinant human CGRP receptors). Prolonged treatment (>30 min) of SK-N-MC cells with SB-(+)-273779 followed by extensive washing resulted in reduction in maximum CGRP-mediated adenylyl cyclase activity, suggesting that this compound has irreversible binding characteristics. In addition, SB-(+)-273779 antagonized CGRP-mediated 1) stimulation of intracellular Ca²⁺ in recombinant CGRP receptors in HEK-293 cells, 2) inhibition of insulin-stimulated [¹⁴C]deoxyglucose uptake in L6 cells, 3) vasodilation in rat pulmonary artery, and 4) decrease in blood pressure in anesthetized rats. SB-(+)-273779 tested at 3 µM had no significant affinity for calcitonin, endothelin, angiotensin II, and -adrenergic receptors under standard ligand binding assays. SB-(+)-273779 also did not inhibit forskolin and pituitary adenylate cyclase-activating polypeptide. These results suggest that SB-(+)-273779 is a valuable tool for studying CGRP-mediated functional responses in complex biological systems.