ETB/endothelin receptor type B (IC50 = 1.2 nM)
BQ-788 selectively targets the endothelin B (ETB) receptor, with high affinity. It shows selectivity for ETB over ETA receptors. It binds to the ETB receptor and blocks the binding of endothelin-1, endothelin-2, and endothelin-3, thereby inhibiting ETB-mediated signaling pathways.

At an IC50 of 1.2 nM, BQ-788 competitively and potently blocks the binding of 125I-labeled ET-1 to the ETB receptor in human Gilardi heart cells (hGH). However, it only faintly inhibits binding to the human neuroblastoma cell line. The IC50 of 1300 nM is observed for the binding of ETA receptors in SK-N-MC cells. At doses as high as 10 μM, BQ-788 exhibits no agonistic action and suppresses ETB-selective agonist-induced vasoconstriction in a competitive manner (pA2, 8.4). Additionally, bronchoconstriction, cell proliferation, and clearance of injected ET-1 are among the biological functions of ET-1 that BQ-788 suppresses [1].
In vitro, BQ-788 inhibits ETB receptor-mediated responses, such as vasodilation, nitric oxide production, and cell proliferation. It shows IC50 values in the nanomolar range for ETB receptor binding. It is used to study the role of ETB receptors in various cell types, including endothelial cells, smooth muscle cells, and cancer cells.

In awake rats, boosting response is not inhibited by BQ-788 (3 mg/kg/h, iv), but it is completely inhibited by ETB receptor-mediated antihypertensive drugs induced by pharmacological doses of ET-1- or sarafotoxin6c (0.5 nmol/kg, iv). Moreover, BQ-788 markedly raised ET-1 plasma concentrations, which is thought to be a sign of possible in vivo ETB receptor blockade. BQ-788 (3 mg/kg/h, intravenously) raised blood pressure in Dahl salt-sensitive hypertensive (DS) rats by about 20 mm Hg. According to reports, BQ-788 can also prevent tumor growth, bronchoconstriction caused by ET-1, and organ failure caused by lipopolysaccharide [1]. The ET-1 dose-response curve shifted eight times to the left when BQ 788 (3 mg/kg) was administered, suggesting a major role for the ETB dilator receptor [2]. Mice's mechanical hyperalgesia (47% and 42%), thermal hyperalgesia (68% and 76%), edema (50% and 30%), myeloperoxidase activity (64% and 32%), and notable pain-like behavior were all decreased when 30 nmol BQ-788 was injected into the foot. Moreover, the production of superoxide anion in the spinal cord (45% and 41%), peripheral (47% and 47%), and spinal cord (47% and 47%) was decreased by intraplantar administration of clazosentan or BQ-788. 33% and 54% of superoxide anions are produced. ) are lipid peroxidation, in turn [3].

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The overall effects of endothelin-1 (ET-1) on blood pressure are caused by a composite activation of constrictor ETA and ETB receptors and dilator ETB receptors. Therefore, it is difficult to accurately compare the ETA activity of selective ETA receptor antagonists (BQ 123 and BMS 182874) with mixed ETA/ETB antagonists (SB 209670 and bosentan) on the cumulative dose-response curve to ET-1. The development of a selective ETB antagonist (BQ 788), which inhibits both the dilator and constrictor ETB receptors, offered the opportunity to investigate the role of ETB receptors in the response to exogenous ET-1 in the pithed rat. BQ 788 (3 mg/kg) resulted in an eightfold leftward shift in the ET-1 dose-response curve, suggesting a significant involvement of ETB dilator receptors. In the absence or presence of BQ 788, each ET antagonist evoked a rightward shift from vehicle. With the exception of BMS 182874, BQ 788 increased the magnitude of the shifts. Furthermore, the profile of the shifts changed from nonparallel to parallel in the presence of BQ 788. The inclusion of BQ 788 also altered the rank order of the ET antagonists tested. The results presented describe an in vivo system that accurately characterizes the ETA activity of ET antagonists. [2]
In vivo, BQ-788 is used to block ETB receptor function in animal models. It has been shown to reverse ETB-mediated vasodilation, increase blood pressure, and modulate renal function. It is used to study the role of ETB receptors in cardiovascular, renal, and pulmonary diseases.

Researchers describe characteristics of a selective endothelin (ET) ET(B) receptor antagonist, BQ-788 [N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine], which is widely used to demonstrate the role of endogenous or exogenous ETs in vitro and in vivo. In vitro, BQ-788 potently and competitively inhibited (125)I-labeled ET-1 binding to ET(B) receptors in human Girrardi heart cells (hGH) with an IC(50) of 1.2 nM, but only poorly inhibited the binding to ET A receptors in human neuroblastoma cell line SK-N-MC cells (IC(50), 1300 nM). In isolated rabbit pulmonary arteries, BQ-788 showed no agonistic activity up to 10 microM and competitively inhibited the vasoconstriction induced by an ET(B)-selective agonist (pA(2), 8.4). BQ-788 also inhibited several bioactivities of ET-1, such as bronchoconstriction, cell proliferation, and clearance of perfused ET-1. Thus, it is confirmed that BQ-788 is a potent, selective ET(B) receptor antagonist. In vivo, in conscious rats, BQ-788, 3 mg/kg/h, i.v., completely inhibited a pharmacological dose of ET-1- or sarafotoxin6c (S6c) (0.5 nmol/kg, i.v.)-induced ET(B) receptor-mediated depressor, but not pressor responses. Furthermore, BQ-788 markedly increased the plasma concentration of ET-1, which is considered an index of potential ET(B) receptor blockade in vivo. In Dahl salt-sensitive hypertensive (DS) rats, BQ-788, 3 mg/kg/h, i.v., increased blood pressure by about 20 mm Hg. It is reported that BQ-788 also inhibited ET-1-induced bronchoconstriction, tumor growth and lipopolysaccharide-induced organ failure. These data suggest that BQ-788 is a good tool for demonstrating the role of ET-1 and ET(B) receptor subtypes in physiological and/or pathophysiological conditions.[1]
ETB receptor binding assays are performed using membranes from cells expressing recombinant ETB receptors or native tissues. Radiolabeled endothelin-1 is used as a tracer. Various concentrations of BQ-788 are added, and bound radioactivity is measured. IC50 or Ki values are calculated from competition binding curves.

Myeloperoxidase (MPO) assay[3]
Neutrophil migration to the hind paw skin tissue of mice was evaluated using a MPO kinetic-colourimetric assay, as described previously. Samples of paw skin tissue were collected 7 h after the stimulus in ice-cold 50 mM K2HPO4 buffer (pH 6.0) containing 0.5% hexadecyltrimethylammonium bromide (HTAB) and kept at −80 °C until use. Samples were homogenised, centrifuged (16 100×g × 4 min), with the resulting supernatant being assayed for MPO activity spectrophotometrically at 450 nm, with three readings in 1 min. The MPO activity of samples was compared to a standard curve of neutrophils. Briefly, 10 µL of sample was mixed with 200 µL of 50 mM phosphate buffer, pH 6.0, containing 0.167 mg/mL o-dianisidine dihydrochloride and 0.015% hydrogen peroxide. The results are presented as MPO activity (number of neutrophils ×104/mg of skin paw).

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Leukocyte recruitment in the peritoneal cavity[3]
Leukocyte recruitment in the peritoneal cavity was evaluated 6 h after i.p. KO2 injection (30 µg/cavity). Total leukocyte counts were performed in a Neubauer chamber after dilution in Turk’s solution (2% acetic acid). Differential cell counts were performed using the Fast Panotic Kit for histological analysis, and the values are expressed as the number of cells (×106) per cavity. Total and differential cell counts were performed under a light microscope.
Cells expressing ETB receptors (e.g., CHO cells transfected with ETB) are cultured. Cells are treated with BQ-788 and then stimulated with endothelin-1. ETB-mediated signaling is assessed by measuring intracellular calcium levels, cAMP production, or ERK phosphorylation. Cell proliferation is assessed by MTT assay.

All measures were taken following the injection of KO2 in the paw, with the exception of the writhing response and leukocyte recruitment, which were performed following the injection of KO2 into the peritoneal cavity. The following groups were used: saline (no stimulus); KO2+saline (stimulus + treatment vehicle); KO2+clazosentan (stimulus + ETA antagonist); and KO2 + BQ-788 (stimulus + ETB antagonist). Therefore, in all tests mice received intraplantar (i.pl.) pre-treatment with vehicle (saline), or clazosentan (ETA antagonist; 3, 10 or 30 nmol) or BQ-788 (ETB antagonist; 3, 10 or 30 nmol); except in the tests that evaluated writhing response and leukocyte recruitment in which mice were pre-treated by intraperitoneal (i.p.) route with vehicle (saline), or clazosentan (ETA antagonist; 30 nmol), or BQ-788 (ETB antagonist, 30 nmol), 30 min before stimulus. Based on the mechanical hyperalgesia, thermal hyperalgesia and oedema results (Figure 2), the dose of 30 nmol of the ETA or ETB antagonists was chosen and used for the subsequent experiments. At the indicated time points, the following parameters were determined: mechanical and thermal hyperalgesia; as well as oedema (Figure 2), overt pain-like behaviours (Figure 3), myeloperoxidase (MPO) activity and leukocyte recruitment (Figure 4). Furthermore, paw skin and spinal cord superoxide anion production, as well as lipid peroxidation (Figure 5) and cytokine production (Figure 6), were also evaluated. The doses of KO2 and time points for sample analysis were determined as described previously. KO2 was diluted in sterile saline immediately before application. [3]
Animal studies use rodent models. BQ-788 is administered via intravenous injection, intraperitoneal injection, or osmotic minipump infusion. Blood pressure is measured by telemetry or tail-cuff plethysmography. Renal function is assessed by measuring urine output and electrolyte excretion. Tissues are collected for histological analysis.

BQ-788 (MW 671.87) is a peptide-like compound. It is typically administered by injection due to poor oral bioavailability. It has a relatively short half-life in vivo. Detailed pharmacokinetic parameters are not extensively documented.

BQ-788 is generally well-tolerated in animal studies at pharmacologically active doses. No significant toxicity has been reported. Comprehensive toxicological profiles are not extensively documented. It is a research compound and not intended for human use.

[1]. BQ-788, a selective endothelin ET(B) receptor antagonist. Cardiovasc Drug Rev. 2002 Winter;20(1):53-66.

[2]. Effect of endothelin antagonists with or without BQ 788 on ET-1 responses in pithed rats. J Cardiovasc Pharmacol. 1995;26 Suppl 3:S216-8.

[3]. Differential regulation of oxidative stress and cytokine production by endothelin ETA and ETB receptors in superoxide anion-induced inflammation and pain in mice. J Drug Target. 2016 Oct 5:1-27.

Antihypertensive drugs: Medications used to treat acute or chronic vascular hypertension, regardless of their pharmacological mechanism. Antihypertensive drugs include diuretics (especially thiazide diuretics); β-adrenergic receptor antagonists; α-adrenergic receptor antagonists; angiotensin-converting enzyme inhibitors; calcium channel blockers; ganglion blockers; and vasodilators. Endothelin B receptor antagonists: Compounds and drugs that can bind to and inhibit or block the activation of endothelin B receptors. This study investigated whether endothelin-1 mediates superoxide anion-induced pain and inflammation via ETA or ETB receptors. Mice were pretreated with clarozide (an ETA receptor antagonist) or BQ-788 (an ETB receptor antagonist) before stimulation with the superoxide anion donor KO2. Plantar injection of 30 nmol clarozide or BQ-788 reduced mechanical hyperalgesia (47% and 42%, respectively), thermal hyperalgesia (68% and 76%, respectively), edema (50% and 30%, respectively), myeloperoxidase activity (64% and 32%, respectively), and marked pain-like behaviors, such as paw twitching (42% and 42%, respectively) and paw licking (38% and 62%, respectively). Similarly, intraperitoneal injection of 30 nmol clarozide or BQ-788 reduced intraperitoneal leukocyte recruitment (58% and 32%, respectively) and abdominal writhing (81% and 77%, respectively). Furthermore, plantar injection of clarozide or BQ-788 reduced superoxide anion production in the spinal cord (45% and 41%) and peripheral cord (47% and 47%), and lipid peroxidation levels in the spinal cord (47% and 47%) and peripheral cord (33% and 54%), respectively. Plantar injection of clarozide (but not BQ-788) reduced interleukin-1β production in the spinal cord (71%) and peripheral cord (51%), and tumor necrosis factor-α production in the spinal cord (59%) and peripheral cord (50%). Therefore, this study reveals different mechanisms by which ET-1 modulates superoxide anion-induced inflammation and pain by acting on ETA or ETB receptors. [3]
BQ-788 is a research tool used to study endothelin receptor biology. It is not an approved drug and is not in clinical trials. It is widely used in pharmacological studies to characterize the role of ETB receptors in health and disease. It is also known as BQ 788.

C34H51N5O7

641.79804

641.379

173326-37-9

BQ-788 sodium salt;156161-89-6

5311032

White to off-white solid powder

5.93

4

7

14

46

1070

5

CCCC[C@H](C(=O)O)NC(=O)[C@@H](CC1=CN(C2=CC=CC=C21)C(=O)OC)NC(=O)[C@H](CC(C)(C)C)NC(=O)N3[C@@H](CCC[C@@H]3C)C

LPAHKJMGDSJDRG-DJYQTOCQSA-N

InChI=1S/C34H51N5O7/c1-8-9-16-25(31(42)43)35-29(40)26(18-23-20-38(33(45)46-7)28-17-11-10-15-24(23)28)36-30(41)27(19-34(4,5)6)37-32(44)39-21(2)13-12-14-22(39)3/h10-11,15,17,20-22,25-27H,8-9,12-14,16,18-19H2,1-7H3,(H,35,40)(H,36,41)(H,37,44)(H,42,43)/t21-,22+,25-,26-,27+/m1/s1

(2R)-2-[[(2R)-2-[[(2S)-2-[[(2R,6S)-2,6-dimethylpiperidine-1-carbonyl]amino]-4,4-dimethylpentanoyl]amino]-3-(1-methoxycarbonylindol-3-yl)propanoyl]amino]hexanoic acid

173326-37-9; BQ-788; BQ-788 free acid; UNII-6MB0YNA8DJ; 6MB0YNA8DJ; N-cis-2,6-Dimethylpiperidinocarbonyl-beta-tBu-Ala-D-Trp(1-methoxycarbonyl)-D-Nle-OH; (2R)-2-[[(2R)-2-[[(2S)-2-[[(2S,6R)-2,6-dimethylpiperidine-1-carbonyl]amino]-4,4-dimethylpentanoyl]amino]-3-(1-methoxycarbonylindol-3-yl)propanoyl]amino]hexanoic acid; D-Norleucine, N-((cis-2,6-dimethyl-1-piperidinyl)carbonyl)-4-methyl-L-leucyl-1-(methoxycarbonyl)-D-tryptophyl-;

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 : ~170 mg/mL (~264.88 mM)

Solubility in Formulation 1: ≥ 5 mg/mL (7.79 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 50.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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