Endothelin receptor antagonists: novel agents for the treatment of hypertension?

Practical synthesis of potential endothelin receptor antagonists of 1,4-benzodiazepine-2,5-dione derivatives bearing substituents at the C3-, N1- and N4-positions

The expedient synthesis of various 1,4-benzodiazepine-2,5-dione compounds, particularly those having substituents at the C3-, N1- and N4-positions is achieved. The important features in these synthetic strategies include: (i) using the coupling reaction of isatoic anhydride with alpha-amino ester for direct construction of the core structure of 1,4-benzodiazepine-2,5-dione; (ii) using potassium carbonate as the base of choice for selective alkylation at the N1-site, while using lithiated 2-ethylacetanilide as the required base to furnish the N4-alkylation; and (iii) using 2-nitrobenzoyl chloride as a synthetic equivalent of anthranilic acid to facilitate the polyethylene resin-bound liquid-phase combinatorial synthesis. The prepared 1,4-benzodiazepine-2,5-dione compounds are evaluated for endothelin receptor antagonism by a functional assay that measures the inhibitory activity against the change of intramolecular calcium ion concentration induced by endothelin-1. The preliminary results indicate that 1,4-benzodiazepine-2,5-diones bearing two flanked aryl substituents at the N1- and N4-sites show better inhibitory activity than the corresponding unalkylated and N-monoalkylated compounds. A promising candidate, 1-benzyl-7-chloro-3-isopropyl-4-(3-methoxybenzyl)-1,4-benzodiazepine-2,5-dione (17b), exhibits an IC50 value in low nM range.

The future of endothelin-receptor antagonism as treatment for systemic hypertension

Endothelin (ET) is an endogenous peptide secreted predominantly by endothelial cells that mediates its effects via vasoconstriction and hypertrophy of vascular smooth muscle. Because the role of ET has been described in multiple pathologic processes in cardiovascular disease, including hypertension, there has been a strong interest in the development of therapeutic agents that inhibit ET receptors. ET receptor antagonists have shown much promise in disease states such as pulmonary arterial hypertension, essential hypertension, and various forms of secondary hypertension. This review serves to summarize the current role of ET and ET receptor antagonists in both the pathophysiology and the treatment of hypertension.

Role of endothelins in animal models of hypertension: focus on cardiovascular protection

Investigation of the regulation of vascular function by endothelium-derived factors has been a prominent topic of research in the field of hypertension during the last decade. Of the different endothelial factors, endothelins, which play an important role in vasodilatation-vasoconstriction balance, have been the subject of great interest and an impressive number of publications. This peptide, a very potent vasoconstrictor, triggers as well events involved in growth, proliferation, matrix production and local inflammation. In parallel, its role in hypertension has evolved from a simple vasoconstrictor to a central local regulator of vascular homeostasis contributing not only to the elevation of blood pressure, but also to the complications of hypertension. This review summarizes research on endothelins and its receptor antagonists in experimental hypertension, with special emphasis on vascular remodeling and target-organ protection.

An update on the status of endothelin receptor antagonists for hypertension

Endothelin receptor antagonists (ETRA) are actively developed by the pharmaceutical industry for several cardiovascular indications. In the context of hypertension, preclinical studies are increasingly focused on prevention or regression of end-organ damage and drug combination than on control of arterial pressure in monotherapy, as most experimental models have already been studied. In general, the antihypertensive effect of ETRA is limited but the overwhelming efficacy of this class of drugs to prevent several end-organ damages warrants judicious combination. However, the few studies looking at regression of hypertension-induced cardiovascular alterations proved less successful, suggesting that ETRA should be used early in the treatment of hypertension to obtain full benefit. Judging from the progression of ongoing trials and the development of new trials patients suffering from pulmonary hypertension and heart failure may be the first to benefit from this new class of drugs. However, it is expected that once on the market, responsive subsets of hypertensive patients will be identified and will benefit from end-organ protection.

Norepinephrine-induced aortic hyperplasia and extracellular matrix deposition are endothelin-dependent

BACKGROUND

Sympathetic hyperactivity is observed in several disease states and may contribute to cardiovascular hypertrophic remodeling. Endothelin has been suggested to be a mediator of hypertrophy.

OBJECTIVE

To examine the involvement of endothelin in maintaining the growth response induced by exogenous norepinephrine.

DESIGN AND METHODS

Rats were treated with norepinephrine (2.5 microg/Kg per min subcutaneously) for 2 and 4 weeks, alone or in association with the selective endothelin-A (ETA) receptor antagonist, darusentan (LU135252, 30 mg/Kg per day orally) for weeks 3 and 4.

RESULTS

Increases in medial cell number and accumulation of collagen and elastin characterized norepinephrine-induced aortic remodeling. These effects occurred without marked changes of mean arterial pressure, but may be related to enhanced pressure variability in addition to direct effects of norepinephrine. Inhibition of ETA receptors by darusentan reversed aortic alterations produced by infusion of norepinephrine. Evaluation of medial apoptosis did not reveal any significant change in any group at 4 weeks.

CONCLUSIONS

Antagonism of ETA receptors effectively and rapidly reversed norepinephrine-induced aortic structural and compositional changes, suggesting a central role of endothelin in mediating this response. Thus, ETA receptor antagonists may help to regress large artery remodeling in conditions of increased circulating catecholamine concentrations.

Potent nonpeptide endothelin antagonists: synthesis and structure-activity relationships of pyrazole-5-carboxylic acids

We have previously reported the identification of pyrazole-5-carboxylic acids as a new class of endothelin antagonists from low affinity pyrazol-5-ol ligands, which were obtained by random screening assays. We describe herein the synthesis and the structure activity relationships (SARs) of these pyrazole-5-carboxylic acids with potent ET(A) selective, mixed ET(A)/ET(B) or moderately ET(B) selective antagonist activities.

1,3-Disubstituted-2-carboxy quinolones: highly potent and selective endothelin A receptor antagonists

The design, synthesis, and in vitro biological activity of a series of 2-carboxy quinolone antagonists selective for the endothelin A receptor are presented. Introduction of a second acid group in position 3 of the quinolone ring increases dramatically the selectivity for ET(A).

Nonpeptide endothelin antagonists: from lower affinity pyrazol-5-ols to higher affinity pyrazole-5-carboxylic acids

Random screening of compounds in endothelin receptor (ET(A) and ET(B)) binding assays led to the discovery of a new class of pyrazol-5-ol ligands. Characterization of structural features crucial for binding activities of these pyrazol-5-ols, by structure activity-relationship (SAR) studies, allowed us to design a novel class of pyrazole-5-carboxylic acids as more potent ET antagonists.