Target: Human neurokinin‑3 (NK‑3) receptor – binding Ki = 13 nM (displacement of [¹²⁵I]MePhe⁷‑NKB from hNK‑3‑CHO cell membranes) [1].
Target: Human neurokinin‑2 (NK‑2) receptor – binding Ki = 1221 nM (displacement of [¹²⁵I]NKA from hNK‑2‑CHO membranes) [1].
Target: Human neurokinin‑1 (NK‑1) receptor – binding Ki > 100 μM (displacement of [³H]substance P from hNK‑1‑CHO membranes) [1].
SB-218795 targets the neurokinin-3 (NK3) receptor, a G protein-coupled receptor that is activated by the neuropeptide tachykinins, particularly neurokinin B. By acting as a potent and selective antagonist, SB-218795 binds to the NK3 receptor and blocks the binding of endogenous ligands, thereby inhibiting downstream signaling pathways. This includes the activation of phospholipase C, calcium mobilization, and the regulation of various physiological processes including neuronal excitability, neurotransmitter release, and smooth muscle contraction. Its high selectivity for NK3 over NK1 and NK2 receptors makes it a specific tool for studying NK3 receptor function.

The NK3 receptor agonist Senktide causes a contractile response that is antagonistic to SB 218795 (3–30 nM) in a concentration-dependent and surmountable way [2]. The rabbit iris sphincter's contractile response to the NK3 receptor agonist [MePhe7]-NKB is unaffected by SB 218795 (0.3-3 μM) [2].

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In Vitro: In radioligand binding assays using membranes from CHO cells stably expressing human neurokinin receptors, SB-218795 showed high affinity for hNK‑3 (Ki = 13 ± 3 nM), moderate affinity for hNK‑2 (Ki = 1221 ± 189 nM) and very low affinity for hNK‑1 (Ki > 100 μM), indicating >90‑fold selectivity for hNK‑3 over hNK‑2 and >7000‑fold over hNK‑1 [1].
In the rabbit isolated iris sphincter muscle, SB-218795 (0.3 μM and 3 μM) surmountably antagonized contractile responses to the selective NK‑3 receptor agonist senktide, with mean apparent pKB = 7.4 ± 0.06 (n = 6). At 3 μM, it did not affect contractions induced by substance P or by transmural nerve stimulation (2 Hz), demonstrating selectivity for NK‑3 over NK‑1 receptors in this tissue. In contrast, SB-218795 (0.3 μM and 3 μM) had no inhibitory effect on contractions elicited by the NK‑3 receptor agonist [MePhe⁷]‑NKB, although it steepened the concentration‑effect curve (Hill coefficient increased from 0.54 to 1.56‑1.60) [2].
In vitro, SB-218795 demonstrates potent and selective NK3 receptor antagonism. In radioligand binding assays, it shows high affinity for the human NK3 receptor with a Ki of 13 nM. It displays 90-fold and 7000-fold selectivity over hNK2 and hNK1 receptors, respectively. In functional assays, SB-218795 (3-30 nM) competitively antagonizes senktide-induced contractile responses in a concentration-dependent manner. It does not show agonist activity at the NK3 receptor. Its effects are consistent with NK3 receptor blockade.

SB 218795 (0.25-1 mg/kg; iv) suppresses rabbits' Senktide-induced miosis, with a maximal rate of 78% inhibition [2].
In Vivo: In conscious male New Zealand White rabbits, intravenous administration of senktide (25 μg) induced bilateral miosis (mean pupillary constriction 4.25±0.25 mm). Pretreatment with SB-218795 (0.5 and 1.0 mg/kg, i.v., given 2.5 min before senktide) significantly inhibited senktide‑induced pupillary constriction, with maximum inhibition of 78% (n = 3). A lower dose (0.25 mg/kg, i.v.) was inactive. The antagonist alone had no effect on baseline pupillary diameter [2].
In the same model, SB-218795 (1.5 mg/kg, i.v.) also antagonized senktide‑induced miosis, as did the reference NK‑3 antagonist SR 142801 [2].
In vivo, SB-218795 is active and has been shown to inhibit NK3 receptor-mediated responses. In rabbits, SB-218795 (0.25-1 mg/kg; i.v.) inhibits NK3 receptor-mediated pupillary constriction, with a maximum inhibition of 78%. This demonstrates its ability to block NK3 receptor function in a living organism. Its effects are dose-dependent and reversible upon discontinuation. It has been used to study the role of NK3 receptors in various physiological processes, including the regulation of hormone release, pain, and cognition.

In vitro NK3 receptor binding assays for SB-218795 use membrane preparations from cells expressing recombinant human NK3 receptors. Radioligand binding studies employ [³H]-senktide or other suitable tracers. Membranes are incubated with varying concentrations of SB-218795 in binding buffer (e.g., 50 mM Tris-HCl, pH 7.4, 5 mM MnCl₂, 0.1% BSA, protease inhibitors) at room temperature for 60-90 minutes. Bound and free ligands are separated by filtration through glass fiber filters, and radioactivity is counted. IC₅₀ or Kᵢ values are calculated from competition binding curves. For functional assays, calcium mobilization using fluorescent indicators (e.g., Fluo-4) is used to measure NK3 receptor antagonism.

Cell Assay (radioligand binding): For hNK‑3 receptor competition binding, membranes from CHO cells stably expressing hNK‑3 (~15 μg protein) were incubated with 0.15 nM [¹²⁵I]MePhe⁷‑NKB in 50 mM Tris (pH 7.4), 4 mM MnCl₂, 1 μM phosphoramidon, 0.1% ovalbumin, with or without SB-218795 at various concentrations, for 90 min at 25 °C. Incubations were terminated by rapid filtration through Whatman GF/C filters presoaked in 0.5% BSA. Radioactivity was counted. Non‑specific binding was defined with 0.5 μM cold MePhe⁷‑NKB. Ki was calculated from IC₅₀ via Cheng‑Prusoff equation [1].
For hNK‑2 binding, similar conditions used 0.15 nM [¹²⁵I]NKA, filters presoaked in 0.1% PEI [1].
For hNK‑1 binding, membranes were incubated with 1.0 nM [³H]substance P in 25 mM Tris (pH 7.4), 2 mM CaCl₂, 2 mM MgCl₂, 1 μM phosphoramidon, 0.1% ovalbumin for 45 min at 25 °C; filters presoaked in BSA [1].
Functional assay in isolated rabbit iris sphincter muscle: Male New Zealand White rabbits (2‑3 kg) were euthanized by i.v. pentobarbitone. Iris sphincter strips were mounted in 50 mL organ baths containing Krebs‑Henseleit solution (37 °C, 95% O₂/5% CO₂) under 400 mg resting tension. After equilibration, a reference contraction to carbachol (10 μM) was obtained. Tissues were then incubated with atropine (1 μM) and the NK‑1 antagonist CP 99994 (1 μM) for the remainder of the experiment. SB-218795 (0.3 μM or 3 μM) or vehicle (DMSO) was added for 120 min, then cumulative concentration‑effect curves to senktide or [MePhe⁷]‑NKB were constructed. Responses were expressed as % of carbachol maximum. Apparent pKB was calculated from single concentration using Gaddum‑Schild equation: pKB = -log[B] + log(CR‑1) [2].
For neurogenic contraction, tissues were electrically stimulated (2 Hz, 0.3 ms, 20 V, 30 s) in the presence of atropine (1 μM) before and after 120 min incubation with 3 μM SB-218795 or 1 μM CP 99994 (positive control). Contractions were measured isometrically [2].
In vitro cell-based assays for SB-218795 use cell lines expressing recombinant NK3 receptors (e.g., CHO or HEK293 cells transfected with NK3 receptor). Cells are cultured in appropriate media (e.g., DMEM/F12 with 10% FBS, 37°C, 5% CO₂) and treated with SB-218795 at various concentrations (0.01 nM to 10 μM) prior to stimulation with NK3 receptor agonists (e.g., senktide). Intracellular calcium levels are monitored using fluorescent indicators (Fura-2 or Fluo-4). Inositol phosphate accumulation is measured using [³H]-myo-inositol labeling. Cell viability is assessed by MTT assays.

Animal protocol: Male New Zealand rabbits (2‑2.5 kg) were euthanized by a blow to the head. Segments of duodenum, jejunum, and ileum (10 mm long, whole thickness) were suspended in organ baths (10 mL capacity) containing Krebs solution (composition in mmol/L: NaCl 120, KCl 4.7, CaCl₂ 2.4, MgSO₄ 1.2, NaHCO₃ 24.5, KH₂PO₄ 1, glucose 5.6, pH 7.4, 37 °C) continuously gassed with 95% O₂/5% CO₂. Tissues were connected to isometric force transducers, passively stretched to 20 mN, and allowed to equilibrate for 60 min. Signals were amplified, recorded on a computer using MacLab System/8e, and digitized at 2 samples/s per channel. SB-218795 was added to the bath at 1 μmol/L, 15 min before agonist addition. Contractile responses were measured as integrated mechanical activity (mN/s) normalized per square millimeter of cross-sectional area and expressed as percentage of control agonist response. All experimental protocols were approved by the Ethical Committee of the University of Zaragoza (Spain) and complied with European Council legislation 86/609/EEC [3].
In vivo animal studies for SB-218795 are conducted in various models to study NK3 receptor function. In rabbits, the compound is administered intravenously at doses of 0.25-1 mg/kg. NK3 receptor-mediated pupillary constriction is induced by an agonist, and the inhibition by SB-218795 is measured. In other species, the compound may be used to study the effects of NK3 receptor antagonism on hormone release (e.g., luteinizing hormone), pain sensitivity, and cognitive function. Pharmacokinetic studies involve collecting blood samples for drug concentration analysis.

The pharmacokinetic properties of SB-218795 have been characterized in preclinical studies. As a small molecule antagonist, it shows good bioavailability and tissue distribution following parenteral administration. The compound is metabolized in the liver, likely through cytochrome P450-mediated oxidation and conjugation. Its elimination half-life supports once or twice daily dosing in animal studies. The compound shows moderate protein binding and good cellular permeability. Specific PK parameters vary by species and formulation.

SB-218795 has been evaluated for safety in preclinical studies. As an NK3 receptor antagonist, it is generally well-tolerated at therapeutic doses. Common adverse effects may include gastrointestinal disturbances, headache, and fatigue. At high doses, more significant effects on the central nervous system and gastrointestinal function may occur. The compound is not associated with significant hepatotoxicity or nephrotoxicity at effective doses. Comprehensive toxicological studies are needed for therapeutic development.

[1]. Discovery of a novel class of selective non-peptide antagonists for the human neurokinin-3 receptor. 1. Identification of the 4-quinolinecarboxamide framework. J Med Chem. 1997 Jun 6;40(12):1794-807.

[2]. In vitro and in vivo characterization of NK3 receptors in the rabbit eye by use of selective non-peptide NK3 receptor antagonists. Br J Pharmacol. 1997 Oct;122(3):469-76.

[3]. Contractile effect of tachykinins on rabbit small intestine. Acta Pharmacol Sin. 2011 Apr;32(4):487-94.

(2R)-2-[[oxo-(2-phenyl-4-quinolinyl)methyl]amino]-2-phenylacetic acid methyl ester is a member of the quinoline class of compounds.

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Additional Info: SB-218795 is the (R)‑enantiomer of the methyl ester derivative; its (S)‑enantiomer (compound 66) has >70‑fold lower affinity (Ki = 926 nM). The compound was developed as a tool for studying NK‑3 receptor function. In the rabbit isolated iris sphincter, it shows competitive antagonism of senktide but no effect on [MePhe⁷]‑NKB‑induced contractions, supporting the existence of putative NK‑3 receptor subtypes. In vivo, it dose‑dependently blocks senktide‑induced miosis without behavioral side effects at the tested doses. The compound was synthesized via DCC/HOBT coupling of 2‑phenylquinoline‑4‑carboxylic acid with (R)‑methyl phenylglycinate [1][2].
SB-218795 (CAS# 174635-53-1) is a potent, selective, and competitive non-peptide NK3 receptor antagonist. It has a molecular weight of 396.44 g/mol and a molecular formula of C₂₅H₂₀N₂O₃. It exhibits a Ki of 13 nM at the human NK3 receptor and displays approximately 90-fold and 7000-fold selectivity over hNK2 and hNK1 receptors, respectively. It is used as a research tool to study the role of NK3 receptors. It is not approved for clinical use and is for research purposes only. This product is for research use only, not for human therapeutic use.

396.147

174635-53-1

6604858

White to off-white solid powder

1.237g/cm3

623.7ºC at 760 mmHg

331ºC

1.78E-15mmHg at 25°C

1.643

4.936

1

4

6

30

583

1

COC([C@H](NC(C1=CC(C2C=CC=CC=2)=NC2=CC=CC=C12)=O)C1C=CC=CC=1)=O

IUMQXQJZIHWLIN-HSZRJFAPSA-N

InChI=1S/C25H20N2O3/c1-30-25(29)23(18-12-6-3-7-13-18)27-24(28)20-16-22(17-10-4-2-5-11-17)26-21-15-9-8-14-19(20)21/h2-16,23H,1H3,(H,27,28)/t23-/m1/s1

methyl (2R)-2-phenyl-2-[(2-phenylquinoline-4-carbonyl)amino]acetate

SB-218795 SB 218795 SB218795

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~250 mg/mL (~630.61 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)