RS-127445 5-HT Receptor antagonist

RS-127445 is a novel high affinity, selective 5-HT2B receptor antagonist devoid of detectable intrinsic activity. This compound is found to have nM affinity and 1000 fold selectivity for the 5-HT2B receptor. It is thus among the highest affinity, most selective 5-HT2B receptor ligands. This chemical 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. [1]

Radioligand binding

The selectivity of RS-127445 for 5-HT2B receptors is examined by testing this compound for affinity at over 100 additional ion channel or receptor binding sites. CHO-K1 cells expressing human 5-HT2A, 5-HT2B or 5-HT2C receptors are harvested using 2 mM EDTA in phosphate buffered saline. Cell membranes are prepared by four cycles of homogenization and centrifugation (48,000×g for 15 min). Each assay is established so as to achieve steady state conditions and to optimize specific binding. For the 5-HT2A receptor, membranes from 1×10⁶ cells are incubated with 0.2 nM [³H]-ketanserin at 32 °C for 60 min. Nonspecific binding is determined using 10 μM methysergide. For the 5-HT2B receptor, membranes from 1.5×10⁶ cells are incubated with 0.2 nM [³H]-5-HT at 48 °C for 120 min. Nonspecific binding is determined using 10 μM 5-HT. For the 5-HT2C receptor, membranes from 3×10⁵ cells are incubated with 0.5 nM [³H]-mesulergine at 32 °C for 60 min. Nonspecific binding is determined using 10 μM methysergide. Assays are terminated by vacuum filtration through glass fibre filters (GF/B) which has been pretreated with 0.1% polyethyleneimine. Total and bound radioactivity is determined by liquid scintillation counting. Greater than 90% specific binding is achieved in each of these assays.

RS-127445 is readily absorbed with no obvious dose or route-dependent limitations and rapidly absorbed following both oral and intraperitoneal administration with peak plasma concentrations being achieved within 15 min of dosing. This compound's concentration in the plasma are proportional to the administered dose. When administered at a dose of 5 mg/kg with approximately 60% of an intraperitoneal dose and 14% of the oral dose is bioavailable. Its concentration in the plasma is predicted to fully saturate accessible 5-HT2B receptors can be readily achieved and maintained in the rat. This chemical administered at 1 to 10 mg/kg with oral significantly inhibits visceral hypersensitivity up to 35 to 74% provoked by restraint stress. Oral administration produces a significant suppression of TNBS-induced visceral hypersensitivity (15 to 62% inhibition at 3 to 30 mg/kg), although it has no significant effect on the visceral nociceptive threshold of native rats. It administrated orally with 1 to 30 mg/kg also dose-dependently reduce the restraint stress-induced defecation in native and TNBS-treated rats. [2]. This compound inhibits colonic motility and defecation. [3]