Characterization of Ro 04-6790 and Ro 63-0563: potent and selective antagonists at human and rat 5-HT₆ receptors

Abstract

1. This study describes the in vitro characterization of two potent and selective 5-HT₆ receptor antagonists at the rat and human recombinant 5-HT₆ receptor.

2. In binding assays with [³H]-LSD, 4-amino-N-(2,6 bis-methylamino-pyrimidin-4-yl)-benzene sulphonamide (Ro 04-6790) and 4-amino-N-(2,6 bis-methylamino-pyridin-4-yl)-benzene sulphonamide (Ro 63-0563) had mean pK_i values ±s.e.mean at the rat 5-HT₆ receptor of 7.35±0.04 and 7.83±0.01, respectively and pK_i values at the human 5-HT₆ receptor of 7.26±0.06 and 7.91±0.02, respectively.

3. Both compounds were found to be over 100 fold selective for the 5-HT₆ receptor compared to 23 (Ro 04-6790) and 69 (Ro 63-0563) other receptor binding sites.

4. In functional studies, neither compound had any significant effect on basal levels of cyclicAMP accumulation in Hela cells stably expressing the human 5-HT₆ receptor, suggesting that the compounds are neither agonists nor inverse agonists at the 5-HT₆ receptor. However, both Ro 04-6790 and Ro 63-0563 behaved as competitive antagonists with mean ±s.e.mean pA₂ values of 6.75±0.07 and 7.10±0.09, respectively.

5. In rats habituated to observation cages, Ro 04-6790 produced a behavioural syndrome similar to that seen following treatment with antisense oligonucleotides designed to reduce the expression of 5-HT₆ receptors. This behavioural syndrome consisted of stretching, yawning and chewing.

6. Ro 04-6790 and Ro 63-0563 represent valuable pharmacological tools for the identification of 5-HT₆ receptors in natural tissues and the study of their physiological function.

Full Text

The Full Text of this article is available as a PDF (354.4 KB).