ACT-132577 is the major and pharmacologically active metabolite of macitentan (ACT-064992), which is dual ETA/ETB endothelin (ET) receptor antagonist designed for tissue targeting.

Ambrisentan (alternative Names: BSF 208075; GSK 1325760; GSK1325760A; Letairis) is an endothelin receptor antagonist that is selective for the endothelin type-A (ETA) receptor. The chemical name of ambrisentan is (+)-(2S)-2-[(4,6-dimethylpyrimidin-2-yl)oxy]-3-methoxy-3,3-diphenylpropanoic acid. Ambrisentan is indicated for the treatment of pulmonary arterial hypertension. It is approved in Europe, Canada and the United States for use as a single agent to improve exercise ability and delay clinical worsening. In addition, it is approved in the United States for use in combination with tadalafil to reduce the risks of disease progression, hospitalization and to improve exercise ability. As an endothelin receptor antagonist, ambrisentan prevents endogenous endothelin peptide from constricting the muscles in blood vessels, allowing them to relax and permit a reduction in blood pressure. Endothelin-1 (ET-1) is a potent autocrine and paracrine peptide. Two receptor subtypes, ETA and ETB, mediate the effects of ET-1 in the vascular smooth muscle and endothelium. The primary actions of ETA are vasoconstriction and cell proliferation, while the predominant actions of ETB are vasodilation, antiproliferation, and ET-1 clearance. In patients with PAH, plasma ET-1 concentrations are increased as much as 10-fold and correlate with increased mean right atrial pressure and disease severity. ET-1 and ET-1 mRNA concentrations are increased as much as 9-fold in the lung tissue of patients with PAH, primarily in the endothelium of pulmonary arteries. These findings suggest that ET-1 may play a critical role in the pathogenesis and progression of PAH. Ambrisentan is a high-affinity (Ki=0.011 nM) ETA receptor antagonist with a high selectivity for the ETA versus ETB receptor (>4000-fold). The clinical impact of high selectivity for ETA is not known.

Bosentan is a dual endothelin receptor antagonist important in the treatment of pulmonary artery hypertension (PAH). It is licensed in the United States, the European Union and other countries by Actelion Pharmaceuticals for the management of PAH under the trade name Tracleer®. Bosentan is used to treat pulmonary hypertension by blocking the action of endothelin molecules that would otherwise promote narrowing of the blood vessels and lead to high blood pressure. Bosentan competitively antagonizes the binding of 125I-labeled ET-1 to human vascular smooth muscle cells (predominantly ETA receptors) with an inhibition constant (Ki ) of 4.7 nM and to human placenta membranes (predominantly ETB receptors) with a Ki of 95 nM. Furthermore, bosentan is specific for endothelin receptors and does not interfere with the binding of a variety of peptides, neurotransmitters, growth factors, or eicosanoids to their receptors.

Enrasentan is an orally active mixed endothelin A/B receptor antagonist with a 100-fold greater affinity for the endothelin A receptor. In an animal model of hypertension and cardiac hypertrophy the drug has reduced blood pressure, prevented cardiac hypertrophy and preserved myocardial function. In rats with hyperinsulinemia and hypertension enrasentan normalized blood pressure and prevented cardiac and renal damage. In rats with stroke the drug reduced the ischemic area in the brain. Enrasentan had been in phase II clinical trial for the treatment of heart failure but the results suggested that enrasentan does not appear to have favorable effects on ventricular remodeling.

Darusentan is an orally active, propanoic acid-based endothelin receptor antagonist (ERA) that selectively blocks endothelin-1 (ET-1) binding to the endothelin type-A (ETA) receptor. Darusentan exhibited subnanomolar binding affinity and approximately 1000-fold selectivity for the ETA receptor in binding experiments conducted in vitro under steady-state conditions. Darusentan is orally bioavailable and, when administered to humans, maximum plasma concentrations are observed within 1–2 h post dosing. The mean elimination half-life is relatively long (>15 h), which is consistent with once-daily dosing. Darusentan is primarily glucuronidated by Phase II enzymes in the liver, and the major route of elimination of Darusentan and its metabolites is via the bile. Some glucuronidated metabolites of Darusentan are also excreted in the urine. Darusentan doses up to 300 mg/day were well tolerated and associated with a manageable safety profile in patients with resistant hypertension (RHTN). The most frequently reported adverse events in Ddarusentan-treated subjects were peripheral edema (17%) and headache (11%), which were mostly mild or moderate in severity. Other commonly reported adverse events in the Darusentan treatment group were sinusitis (8%), dizziness (7%), upper respiratory tract infection (5%) and gastroenteritis (5%). In phase III clinical trial the mean reductions in clinic systolic and diastolic blood pressures were 9/5 mm Hg with placebo, 17/10 mm Hg with Darusentan 50 mg, 18/10 mm Hg with Darusentan 100 mg, and 18/11 mm Hg with Darusentan 300 mg. Unfortunately, phase III clinical trial evaluating Darusentan did not achieve its co-primary efficacy endpoints of achieving a change in systolic and diastolic blood pressure after 14 weeks compared to a placebo. Perhaps for this reason, shortly after the top-line results of this study became known, the sponsor announced that Darusentan would not be developed further for resistant hypertension.

BQ-788, a selective endothelin (ET) B-receptor antagonist, was developed by Banyu. This compound is widely used to demonstrate the role of ET-1 and ET(B) receptor subtypes in physiological and/or pathophysiological conditions. BQ-788 was studied against hypertension. However, this study was discontinued. Besides, was shown that BQ788 could protect against brain edema by inhibiting vascular endothelial growth factor-A-mediated decrease in claudin-5. The intralesional applications of BQ788 were well tolerated and showed signs of directly and indirectly reducing the viability of melanoma cells.

Ambrisentan (alternative Names: BSF 208075; GSK 1325760; GSK1325760A; Letairis) is an endothelin receptor antagonist that is selective for the endothelin type-A (ETA) receptor. The chemical name of ambrisentan is (+)-(2S)-2-[(4,6-dimethylpyrimidin-2-yl)oxy]-3-methoxy-3,3-diphenylpropanoic acid. Ambrisentan is indicated for the treatment of pulmonary arterial hypertension. It is approved in Europe, Canada and the United States for use as a single agent to improve exercise ability and delay clinical worsening. In addition, it is approved in the United States for use in combination with tadalafil to reduce the risks of disease progression, hospitalization and to improve exercise ability. As an endothelin receptor antagonist, ambrisentan prevents endogenous endothelin peptide from constricting the muscles in blood vessels, allowing them to relax and permit a reduction in blood pressure. Endothelin-1 (ET-1) is a potent autocrine and paracrine peptide. Two receptor subtypes, ETA and ETB, mediate the effects of ET-1 in the vascular smooth muscle and endothelium. The primary actions of ETA are vasoconstriction and cell proliferation, while the predominant actions of ETB are vasodilation, antiproliferation, and ET-1 clearance. In patients with PAH, plasma ET-1 concentrations are increased as much as 10-fold and correlate with increased mean right atrial pressure and disease severity. ET-1 and ET-1 mRNA concentrations are increased as much as 9-fold in the lung tissue of patients with PAH, primarily in the endothelium of pulmonary arteries. These findings suggest that ET-1 may play a critical role in the pathogenesis and progression of PAH. Ambrisentan is a high-affinity (Ki=0.011 nM) ETA receptor antagonist with a high selectivity for the ETA versus ETB receptor (>4000-fold). The clinical impact of high selectivity for ETA is not known.

Bosentan is a dual endothelin receptor antagonist important in the treatment of pulmonary artery hypertension (PAH). It is licensed in the United States, the European Union and other countries by Actelion Pharmaceuticals for the management of PAH under the trade name Tracleer®. Bosentan is used to treat pulmonary hypertension by blocking the action of endothelin molecules that would otherwise promote narrowing of the blood vessels and lead to high blood pressure. Bosentan competitively antagonizes the binding of 125I-labeled ET-1 to human vascular smooth muscle cells (predominantly ETA receptors) with an inhibition constant (Ki ) of 4.7 nM and to human placenta membranes (predominantly ETB receptors) with a Ki of 95 nM. Furthermore, bosentan is specific for endothelin receptors and does not interfere with the binding of a variety of peptides, neurotransmitters, growth factors, or eicosanoids to their receptors.

Bosentan is a dual endothelin receptor antagonist important in the treatment of pulmonary artery hypertension (PAH). It is licensed in the United States, the European Union and other countries by Actelion Pharmaceuticals for the management of PAH under the trade name Tracleer®. Bosentan is used to treat pulmonary hypertension by blocking the action of endothelin molecules that would otherwise promote narrowing of the blood vessels and lead to high blood pressure. Bosentan competitively antagonizes the binding of 125I-labeled ET-1 to human vascular smooth muscle cells (predominantly ETA receptors) with an inhibition constant (Ki ) of 4.7 nM and to human placenta membranes (predominantly ETB receptors) with a Ki of 95 nM. Furthermore, bosentan is specific for endothelin receptors and does not interfere with the binding of a variety of peptides, neurotransmitters, growth factors, or eicosanoids to their receptors.

Enrasentan is an orally active mixed endothelin A/B receptor antagonist with a 100-fold greater affinity for the endothelin A receptor. In an animal model of hypertension and cardiac hypertrophy the drug has reduced blood pressure, prevented cardiac hypertrophy and preserved myocardial function. In rats with hyperinsulinemia and hypertension enrasentan normalized blood pressure and prevented cardiac and renal damage. In rats with stroke the drug reduced the ischemic area in the brain. Enrasentan had been in phase II clinical trial for the treatment of heart failure but the results suggested that enrasentan does not appear to have favorable effects on ventricular remodeling.