RS 127445

RS-127445(MT 500) is a selective 5-HT2B receptor antagonist with pKi of 9.5 and pIC50 of 10.4 [1].

5-HT2B receptor belongs to the 5-HT2 receptor family which binds the neurotransmitter serotonin. It plays important role relevant to serotonin, including neuronal sensitization to tactile stimuli.

RS 127445 is a selective serotonin 5-HT2B receptor inhibitor. RS-127445 is found to have nM affinity and 1000 fold selectivity for the 5-HT2B receptor [2]. RS-127445 potently blocks the 5-HT evoked increase in inositol phosphate formation and blocks the 5-HT evoked increases in intracellular calcium concentrations with a potency 1000 times greater than that of yohimbine.

In rat model, oral administration of RS-127445 at 1 to 10 mg/kg resulted in significant inhibition of visceral hypersensitivity up to 35 to 74% triggered by restraint stress [3]. Moreover, 3 to 30 mg/ kg of RS-127445 resulted in a significant inhibition of TNBS-induced visceral hypersensitivity varied from 15 to 62% [3].

References:
[1].  O'Mahony, S M et al. 5-HT2B receptors modulate visceral hypersensitivity in a stress-sensitive animal model of brain-gut axis dysfunction. Neurogastroenterology & Motility, 2012, 22(5): 573-578.
[2].  Ohashi-Doi K et al. A selective, high affinity 5-HT2B receptor antagonist inhibits visceral hypersensitivity in rats. Neurogastroenterology & Motility, 2010, 22(2): 69-76.
[3].  Bassil A K et al. Inhibition of colonic motility and defecation by RS-127445 suggests an involvement of the 5-HT2B receptor in rodent large bowel physiology. British Journal of Pharmacology, 2009, 158(1): 252-258.

Inhibition of colonic motility and defecation by RS-127445 suggests an involvement of the 5-HT2B receptor in rodent large bowel physiology.[Pubmed:19371340]

Br J Pharmacol. 2009 Sep;158(1):252-8.

BACKGROUND: 5-HT(2B) receptors are localized within the myenteric nervous system, but their functions on motor/sensory neurons are unclear. To explore the role of these receptors, we further characterized the 5-HT(2B) receptor antagonist RS-127445 and studied its effects on peristalsis and defecation. EXPERIMENTAL APPROACH: Although reported as a selective 5-HT(2B) receptor antagonist, any interactions of RS-127445 with 5-HT(4) receptors are unknown; this was examined using the recombinant receptor and Biomolecular Interaction Detection technology. Mouse isolated colon was mounted in tissue baths for isometric recording of neuronal contractions evoked by electrical field stimulation (EFS), or under an intraluminal pressure gradient to induce peristalsis; the effects of RS-127445 on EFS-induced and on peristaltic contractions were measured. Faecal output of rats in grid-bottom cages was measured over 3 h following i.p. RS-127445 and separately, validation of the effective doses was achieved by determining the free, unbound fraction of RS-127445 in blood and brain. KEY RESULTS: RS-127445 (up to 1 micromol x L(-1)) did not interact with the 5-HT(4) receptor. RS-127445 (0.001-1 micromol x L(-1)) did not affect EFS-induced contractions of the colon, although at 10 micromol x L(-1) the contractions were reduced (to 36 +/- 8% of control, n= 4). RS-127445 (0.1-10 micromol x L(-1)) concentration-dependently reduced peristaltic frequency (n= 4). RS-127445 (1-30 mg x kg(-1)), dose-dependently reduced faecal output, reaching significance at 10 and 30 mg x kg(-1) (n= 6-11). In blood and brain, >98% of RS-127445 was protein-bound. CONCLUSIONS AND IMPLICATIONS: High-protein binding of RS-127445 indicates that relatively high doses are required for efficacy. The results suggest that 5-HT(2B) receptors tonically regulate colonic motility.

RS-127445: a selective, high affinity, orally bioavailable 5-HT2B receptor antagonist.[Pubmed:10455251]

Br J Pharmacol. 1999 Jul;127(5):1075-82.

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.

RS-127445 is a selective 5-HT2B receptor antagonist with pKi of 9.5 and pIC50 of 10.4, exhibits >1000-fold selectivity against other 5-HT receptors.

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