Functional effects of the 5-HT1D receptor antagonist GR 127,935 at human 5-HT1Dα, 5-HT1Dβ, 5-HT1A and opposum 5-HT1B receptors

Abstract

The functional activity and selectivity of the novel 5-HT_1D receptor antagonist GR 127,935 (2′-methyl-4′-(5-methyl-1,2,4 oxadiazol-3-yl)-biphenyl-4-carboxylic acid [4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-amide) was investigated at cloned human 5-HT_1A, 5-HT_1Dα HT_1Dβ and opposum kidney (OK) 5-HT_1B receptor sites. 5-HT₁ receptor-mediated activity was studied by measuring the inhibition of forskolin-induced cAMP formation in cell lines expressing these receptors (B_max (fmol/mg protein): human epitheloid carcinoma HeLa/5-HT_1A: 1285, OK/5-HT_1B: 52, Chinese hamster ovary CHO-K1/5-HT_1Dα: 181 and CHO-K1/5-HT_1Dβ: 685). GR 127,935 did not show 5-HT_1Dβ receptor-mediated agonist activity in permanently transfected CHO-K1 cells, whereas at submicromolar and higher concentrations intrinsic agonist activity was observed in HeLa/5-HT_1A,OK/5-HT_1B and CHO-K1/5-HT_1Dα cells. GR 127,935 showed potent (K_B value: 1.3 nM) and silent antagonism at CHO-K1/5-HT_1Dβ receptor sites. The antagonists activtity of 1 μM of GR 127,935 at CHO-K1/5-HT_1Dα and OK/5-HT_1B receptor sites was only partial and less pronounced. This contrasts with the silent antagonism of methiothepin at the 5-HT_1Dα (K_B value = 11.8 nM), 5-HT_1Dβ (K_B value = 6.9 nM) and 5-HT_1B (K_B value = 49.3 nM) receptor subtypes. GR 127,935, when tested at 10 μM, was found to be a weak and partial antagonist of HeLa/5-HT_1A receptors. In conclusion, GR 127,935 is a potent and effective antagonist of cloned human 5-HT_1Dβ receptor sites in transfected CHO-K1 cells but is only able to partially antagonise CHO-K1/5-HT_1Dα, OK/5-HT_1B and Hela/5-HT_1A receptor sites at micromolar concentrations.