The 5-HT4 receptor agonist, tegaserod, is a potent 5-HT2B receptor antagonist in vitro and in vivo.
1 Tegaserod (Zelnorm) is a potent 5-hydroxytryptamine4 (5-HT4) receptor agonist with clinical efficacy in disorders associated with reduced gastrointestinal motility and transit. The present study investigated the interaction of tegaserod with 5-HT2 receptors, and compared its potency in this respect to its 5-HT4 receptor agonist activity. 2 Tegaserod had significant binding affinity for human recombinant 5-HT2A, 5-HT2B and 5-HT2C receptors (pKi=7.5, 8.4 and 7.0, respectively). The 5-HT2B receptor-binding affinity of tegaserod was identical to that at human recombinant 5-HT4(c) receptors (mean pKi=8.4) in human embryonic kidney-293 (HEK-293) cells stably transfected with the human 5-HT4(c) receptor. 3 Tegaserod (0.1-3 microm) inhibited 5-HT-mediated contraction of the rat isolated stomach fundus potently (pA2=8.3), consistent with 5-HT(2B) receptor antagonist activity. Tegaserod produced, with similar potency, an elevation of adenosine 3',5' cyclic monophosphate in HEK-293 cells stably transfected with the human 5-HT4(c) receptor (mean pEC50=8.6), as well as 5-HT4) receptor-mediated relaxation of the rat isolated oesophagus (mean pEC50=8.2) and contraction of the guinea-pig isolated colon (mean pEC50=8.3). 4 Following subcutaneous administration, tegaserod (0.3 or 1 mg kg(-1)) inhibited contractions of the stomach fundus in anaesthetized rats in response to intravenous dosing of alpha-methyl 5-HT (0.03 mg kg(-1)) and BW 723C86 (0.3 mg kg(-1)), selective 5-HT2B receptor agonists. At similar doses, tegaserod (1 and 3 mg kg(-1) subcutaneously) evoked a 5-HT4 receptor-mediated increase in colonic transit in conscious guinea-pigs. 5 The data from this study indicate that tegaserod antagonizes 5-HT2B receptors at concentrations similar to those that activate 5-HT4 receptors. It remains to be determined whether this 5-HT2B receptor antagonist activity of tegaserod contributes to its clinical profile.
Beattie
D T
DT
Theravance, Inc., 901 Gateway Boulevard, South San Francisco, CA 94080, USA. dbeattie@theravance.com
Smith
J A M
JA
Marquess
D
D
Vickery
R G
RG
Armstrong
S R
SR
Pulido-Rios
T
T
McCullough
J L
JL
Sandlund
C
C
Richardson
C
C
Mai
N
N
Humphrey
P P A
PP
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003106:Colon / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D004947:Esophagus / Q000187:drug effects; D005748:Gastric Fundus / Q000187:drug effects; D005772:Gastrointestinal Transit / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D011312:Pressure; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D044403:Receptor, Serotonin, 5-HT2B / Q000187:drug effects*; D044422:Receptors, Serotonin, 5-HT4 / Q000187:drug effects*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*
D007211:Indoles; D044403:Receptor, Serotonin, 5-HT2B; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D044422:Receptors, Serotonin, 5-HT4; C105050:tegaserod; D000242:Cyclic AMP