RS-127445: a Selective, High Affinity, Orally Bioavailable 5-HT2B Receptor Antagonist

Overview

Journal Br J Pharmacol

Publisher Wiley

Specialty Pharmacology

Date 1999 Aug 24

PMID 10455251

Citations 26

Authors

D W Bonhaus

L A Flippin

R J Greenhouse

S Jaime

C Rocha

M Dawson

K Van Natta

L K Chang

T Pulido-Rios

A Webber

E Leung

R M Eglen

G R Martin

Affiliations

Soon will be listed here.

Abstract

Efforts to define precisely the role of 5-HT2B receptors in normal and disease processes have been hindered by the absence of selective antagonists. To address this deficiency, we developed a series of naphthylpyrimidines as potentially useful 5-HT2B receptor antagonists. RS-127445 (2-amino-4-(4-fluoronaphth-1-yl)-6-isopropylpyrimidine) was found to have nanomolar affinity for the 5-HT2B receptor (pKi = 9.5+/-0.1) and 1,000 fold selectivity for this receptor as compared to numerous other receptor and ion channel binding sites. In cells expressing human recombinant 5-HT2B receptors, RS-127445 potently antagonized 5-HT-evoked formation of inositol phosphates (pK(B) = 9.5+/-0.1) and 5-HT-evoked increases in intracellular calcium (pIC50 = 10.4+/-0.1). RS-127445 also blocked 5-HT-evoked contraction of rat isolated stomach fundus (pA2 = 9.5+/-1.1) and (+/-)alpha-methyl-5-HT-mediated relaxation of the rat jugular vein (pA2 = 9.9+/-0.3). RS-127445 had no detectable intrinsic activity in these assays. In rats, the fraction of RS-127445 that was bioavailable via the oral or intraperitoneal routes was 14 and 60% respectively. Intraperitoneal administration of RS-127445 (5 mg kg(-1)) produced plasma concentrations predicted to fully saturate accessible 5-HT2B receptors for at least 4 h. In conclusion, RS-127445 is a selective, high affinity 5-HT2B receptor antagonist suitable for use is vivo. The therapeutic potential of this molecule is being further evaluated.

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