**Background**
The neurokinin-3 (NK3) receptor is a G protein-coupled receptor that plays a critical role in modulating various physiological and behavioral processes, particularly within the central nervous system. Dysregulation of the neurokinin system has been implicated in several neuropsychiatric disorders, including schizophrenia, where the modulation of dopamine and norepinephrine levels in the prefrontal cortex is essential for cognitive and emotional stability. Consequently, the development of selective NK3 receptor antagonists has emerged as a promising therapeutic strategy for treating schizophrenia and related cognitive impairments. In this context, we will introduce a selective, brain-permeable NK3 receptor antagonist – Talnetant.
**Definition**
Talnetant (also known as SB 223412) is a selective, competitive, brain-permeable NK3 receptor antagonist with a $K_i$ of 1.4 nM in hNK-3-CHO cells.
**In Vitro and In Vivo Studies**
According to the Talnetant description, this compound exhibits high selectivity, being 100-fold more selective for the human NK3 receptor (hNK-3) relative to the hNK-2 receptor, with no affinity for hNK-1. Regarding Talnetant in vitro activity, concentrations of 0.1-1 $\mu$M can reduce the accumulation of NKB-induced IP in U-2OS cells expressing the human NK3 receptor. Furthermore, in CHO cells, Talnetant demonstrated an $IC_{50}$ of 2.4 nM for the displacement of $[^{125}I]$neurokinin B from cloned human NK3 receptors. In HEK293 cells, it showed antagonist activity against the human NK3 receptor with $IC_{50}$ values ranging from 6.1 to 16.6 nM, as assessed by the inhibition of NKB-induced intracellular calcium levels.
The Talnetant biological activity has also been extensively validated in animal models. Talnetant In Vivo studies in conscious rabbits showed that doses of 0.5-2 mg/kg (i.v., 2 min pretreatment) inhibited senktide-induced miosis in a dose-dependent manner, with an $ED_{50}$ of 0.44 mg/kg. In male Dunkin-Hartley guinea pigs, intraperitoneal administration of Talnetant (1-100 mg/kg, 1 h) significantly attenuated senktide-induced “wet dog wagging” (WDS) behavior; specifically, at 30 mg/kg, WDS behavior was reduced from 31.1 to 16.7. Additionally, the compound significantly increased extracellular dopamine (to 238%) and norepinephrine (to 227.1%) levels in the medial prefrontal cortex and reduced haloperidol-induced dopamine increases in the vomeronasal nucleus. In conclusion, Talnetant is a potent and selective NK3 receptor antagonist with significant potential for schizophrenia-related research.
Keywords
Talnetant, 174636-32-9, SB 223412, SB223412, SB-223412, Neurokinin Receptor, NK receptor, Tachykinin receptor, NK3 receptor, hNK-3-CHO, hNK-2, schizophrenia, Inhibitor, inhibitor, inhibit
References
[1] Giardina GA, et al. Discovery of a novel class of selective non-peptide antagonists for the human neurokinin-3 receptor. 2. Identification of (S)-N-(1-phenylpropyl)-3-hydroxy-2-phenylquinoline-4-carboxamide (SB 223412). J Med Chem. 1999 Mar 25;42(6):1053-65.
[2] Houghton LA, et al. Effect of the NK(3) receptor antagonist, talnetant, on rectal sensory function and compliance in healthy humans. Neurogastroenterol Motil. 2007 Sep;19(9):732-43.
[3] Dawson LA, et al. In vitro and in vivo characterization of the non-peptide NK3 receptor antagonist SB-223412 (talnetant): potential therapeutic utility in the treatment of schizophrenia. Neuropsychopharmacology. 2008 Jun;33(7):1642-52.