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

Abstract

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 CGRP₁receptor 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 IC₅₀values 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 α-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.