Cys^2,7EtαCGRP is a potent agonist for CGRP₁ receptors in SK-N-MC cells

Abstract

The present study reveals that cystein^2,7 ethyl-amideαCGRP (Cys^2,7EtαCGRP), an advertised calcitonin gene-related peptide 2 (CGRP₂) receptor subtype-selective agonist, is also a potent agonist for the calcitonin gene-related peptide 1 (CGRP₁) receptors natively expressed in the SK-N-MC human neuroblastoma cell line. Cys^2,7EtαCGRP and α calcitonin gene-related peptide (αCGRP) promote cyclic AMP accumulation in intact SK-N-MC cells to the same extent with EC₅₀ of 1.6 ± 0.2 and 0.4 ± 0.08 nM, respectively. The antagonist α calcitonin gene-related peptide-8-37 (αCGRP-(8-37)) produces a concentration-dependent rightward shift of the αCGRP- and Cys^2,7EtαCGRP concentration–response curves with K_B-values (71 ± 33 and 47 ± 21 nM, respectively). The competitive antagonism by αCGRP-(8-37) and the similar K_B-values suggests that αCGRP and Cys^2,7EtαCGRP stimulate the same receptor. In competition binding studies with [¹²⁵I]-αCGRP on SK-N-MC cell membranes, Cys^2,7EtαCGRP and αCGRP-(8-37) display high affinity for the majority of the binding sites with K_i-values of 0.030 ± 0.013 and 0.60 ± 0.013 nM, respectively. The present findings are at odds with the proclaimed utilization of Cys^2,7EtαCGRP as a CGRP₂ receptor-selective pharmacological tool. Differences between the agonistic profile of this ligand in this and other experimental systems might be species – or even cell type – dependent.