Current status of endothelin blockade for the treatment of cardiovascular and pulmonary vascular disease.

With recognition of the significant role of the endothelin system in cardiovascular and pulmonary vascular diseases, attention has turned to the therapeutic application of agents that antagonize this system. Three strategies can be employed: dual endothelin receptor (ETA and ETB) antagonism, selective ETA antagonism and inhibition of endothelin-converting enzymes. The first two strategies have been evaluated in late-phase clinical trials, with mixed results. The use of the dual endothelin receptor antagonist bosentan in pulmonary arterial hypertension has been successful. Available data are less compelling, but nonetheless promising, for the use of bosentan in digital ulceration secondary to systemic sclerosis, and tezosentan (another dual receptor blocker) in acute heart failure. Both types of receptor antagonists, however, have been evaluated in systemic hypertension and chronic systolic heart failure and are unlikely to be further developed in these areas. For the treatment of hypertension, their (moderate) efficacy and safety/tolerability profiles appear no more favorable than existing antihypertensive agents. In terms of treatment for chronic heart failure, these agents appear to offer no further benefit over standard therapy for the treatment of chronic heart failure, and in fact, may be associated with poorer outcomes. The complexity of the endothelin system and its diverse roles in multiple disease states will ensure its position as a target for drug development.