Kathleen M. Welch

Efficacy of CI-1020, an endothelin-A receptor antagonist, in hypoxic pulmonary hypertension

We previously showed that CI-1020, an endothelin (ET)-A-selective receptor antagonist, dose-dependently blocked acute hypoxic pulmonary hypertension (PH) in rats. In this study we show that CI-1020 can reverse existing PH and prevent progression of right ventricular hypertrophy (RVH) in rats exposed to chronic hypoxia. Male Sprague-Dawley rats were exposed to 20 days of hypoxia (10% O2) with CI-1020 treatment (20 or 40 mg/kg/day) starting on day 10. On day 20 of hypoxia, the rats were instrumented under anesthesia with a pulmonary artery cannula and allowed to recover to consciousness before measurement of mean pulmonary arterial pressure (MPAP). Blood samples were then collected for plasma ET-1 measurements, the rats killed, and their hearts dissected, dried, and weighed. RV/LV + septum ratio (g/g) was used as an index of RVH (RVHi). Normoxic rats and rats exposed to hypoxia for only 10 days were also evaluated as controls. Normoxic rats had MPAPs of 13 +/- 1 mm Hg, plasma ET-1 levels of 2.1 +/- 0.1 pg/ml, and an average RVHi of 0.29 +/- 0.03. Rats exposed to 10 or 20 days of hypoxia had MPAPs of 33 +/- 2 and 44 +/- 0 mm Hg, plasma ET-1 levels of 4.2 +/- 0.8 and 4.6 +/- 0.8 pg/ml, and average RVHis of 0.47 +/- 0.05 and 0.52 +/- 0.03, respectively. In comparison, rats treated with CI-1020 had MPAPs that were 37% (20 mg/kg/day) and 44% (40 mg/kg/day) lower than untreated 20-day hypoxic rats. Furthermore, rats dosed with 40 mg/kg/day of CI-1020 had MPAPs that were significantly lower (24%) than control 10-day hypoxic rats, indicating a significant reversal of PH. Along with this reversal in PH, their average RVHi was 23% lower (p < 0.05) relative to untreated 20-day hypoxic rats.

The endothelin-A-receptor antagonist PD 180988 (CI-1034) selectively reverses the pulmonary vasoconstrictor response to hypoxia in the lamb.

Endothelin-1 (ET-1) is assigned a mediator role in the constrictor response of the pulmonary vasculature to hypoxia. Accordingly, a recently developed endothelin-A (ETA) antagonist, PD180988, was tested in the chronically instrumented newborn lamb to verify this possibility and, at the same time, to study a potential new treatment for pulmonary hypertension (PH). PD180988, given by infusion after a priming bolus, had an insignificant effect on the pulmonary circulation under normoxia, while it reversed the sustained pulmonary constriction caused by hypoxia. No appreciable change was noted under either experimental condition in the systemic circulation and cardiac contractility. We conclude that PD180988 is a selective inhibitor of hypoxic pulmonary vasoconstriction and lends itself to therapeutic use in infants.

Structure-based Drug Design of Pyrrolidine-1, 2-dicarboxamides as a Novel Series of Orally Bioavailable Factor Xa Inhibitors

A novel series of pyrrolidine‐1,2‐dicarboxamides was discovered as factor Xa inhibitors using structure‐based drug design. This series consisted of a neutral 4‐chlorophenylurea P1, a biphenylsulfonamide P4 and a d‐proline scaffold (1, IC50 = 18 nm). Optimization of the initial hit resulted in an orally bioavailable, subnanomolar inhibitor of factor Xa (13, IC50 = 0.38 nm), which was shown to be efficacious in a canine electrolytic model of thrombosis with minimal bleeding.

Endothelin B receptors on human endothelial and smooth-muscle cells show equivalent binding pharmacology.

We have described the pharmacologic profiles of endothelin B receptors in human endothelial cells and vascular and nonvascular smooth-muscle cells. First, by amplifying endothelin B receptor numbers through the use of phosphoramidon and intact cell-binding techniques, we demonstrated the presence of these receptors in human umbilical vein endothelial cells (100% endothelin B receptors), human aortic smooth-muscle cells (22% endothelin B, 78% endothelin A receptors), and human bronchial smooth-muscle cells (55% endothelin B, 45% endothelin A receptors) by using [125I]-endothelin-1 radioligand binding. The typical binding profiles of the endothelin B receptors were established through competition binding curve analysis with endothelin-1, endothelin-3, sarafotoxin 6c, and the endothelin A receptor-selective antagonist BQ-123. In the presence of BQ-123, a diverse group of antagonists, including PD 142893, BQ-788, SB 209670, and Ro 47-0203, were used to probe for binding differences indicative of multiple endothelin B-receptor subtypes. The results indicate a rank order of potency for the antagonists of BQ-788 > SB 209670 > PD 142893 > Ro 47-0203 for each cell line, and that between any of these human cell lines, measurements of [125I]-endothelin-1-binding antagonism for each of the four test compounds differed by less than twofold. Although this study cannot discount the possibility of more than one endothelin B-receptor subtype in humans, it does indicate that these tissues express receptors that show equivalent binding pharmacology.