Effects of endothelin-1 on airway and parenchymal mechanics in guinea-pigs

Endothelin B receptor, a new target in cancer immune therapy

The endothelins and their G protein-coupled receptors A and B have been implicated in numerous diseases and have recently emerged as pivotal players in a variety of malignancies. Tumors overexpress the endothelin 1 (ET-1) ligand and the endothelin-A-receptor (ET(A)R). Their interaction induces tumor growth and metastasis by promoting tumor cell survival and proliferation, angiogenesis, and tissue remodeling. On the basis of results from xenograft models, drug development efforts have focused on antagonizing the autocrine-paracrine effects mediated by ET-1/ET(A)R. In this review, we discuss a novel role of the endothelin-B-receptor (ET(B)R) in tumorigenesis and the effect of its blockade during cancer immune therapy. We highlight key characteristics of the B receptor such as its specific overexpression in the tumor compartment; and specifically, in the tumor endothelium, where its activation by ET-1 suppresses T-cell adhesion and homing to tumors. We also review our recent findings on the effects of ET(B)R-specific blockade in increasing T-cell homing to tumors and enhancing the efficacy of otherwise ineffective immunotherapy.

The role of endothelin-1 in hyperoxia-induced lung injury in mice

Background

As prolonged hyperoxia induces extensive lung tissue damage, we set out to investigate the involvement of endothelin-1 (ET-1) receptors in these adverse changes.

Methods

Experiments were performed on four groups of mice: control animals kept in room air and a group of mice exposed to hyperoxia for 60 h were not subjected to ET-1 receptor blockade, whereas the dual ETA/ETB-receptor blocker tezosantan (TEZ) was administered via an intraperitoneal pump (10 mg/kg/day for 6 days) to other groups of normal and hyperoxic mice. The respiratory system impedance (Zrs) was measured by means of forced oscillations in the anesthetized, paralyzed and mechanically ventilated mice before and after the iv injection of ET-1 (2 μg). Changes in the airway resistance (Raw) and in the tissue damping (G) and elastance (H) of a constant-phase tissue compartment were identified from Zrs by model fitting.

Results

The plasma ET-1 level increased in the mice exposed to hyperoxia (3.3 ± 1.6 pg/ml) relative to those exposed to room air (1.6 ± 0.3 pg/ml, p < 0.05). TEZ administration prevented the hyperoxia-induced increases in G (13.1 ± 1.7 vs. 9.6 ± 0.3 cmH₂O/l, p < 0.05) and H (59 ± 9 vs. 41 ± 5 cmH₂O/l, p < 0.05) and inhibited the lung responses to ET-1. Hyperoxia decreased the reactivity of the airways to ET-1, whereas it elevated the reactivity of the tissues.

Conclusion

These findings substantiate the involvement of the ET-1 receptors in the physiopathogenesis of hyperoxia-induced lung damage. Dual ET-1 receptor antagonism may well be of value in the prevention of hyperoxia-induced parenchymal damage.

Endothelin system: the double-edged sword in health and disease

The endothelin system consists of two G-protein-coupled receptors, three peptide ligands, and two activating peptidases. Its pharmacological complexity is reflected by the diverse expression pattern of endothelin system components, which have a variety of physiological and pathophysiological roles. In the vessels, the endothelin system has a basal vasoconstricting role and participates in the development of diseases such as hypertension, atherosclerosis, and vasospasm after subarachnoid hemorrhage. In the heart, the endothelin system affects inotropy and chronotropy, and it mediates cardiac hypertrophy and remodeling in congestive heart failure. In the lungs, the endothelin system regulates the tone of airways and blood vessels, and it is involved in the development of pulmonary hypertension. In the kidney, it controls water and sodium excretion and acid-base balance, and it participates in acute and chronic renal failure. In the brain, the endothelin system modulates cardiorespiratory centers and the release of hormones. More advanced functional analysis of the endothelin system awaits not only additional pharmacological studies using highly specific endothelin antagonists but also the generation of genetically altered rodent models with conditional loss-of-function and gain-of-function manipulations.