Trial of thromboxane receptor inhibition with ifetroban: TP receptors regulate eicosanoid homeostasis in aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is the triad of asthma, nasal polyposis, and respiratory reactions to COX-1 inhibitors. Overproduction of cysteinyl leukotrienes and underproduction of prostaglandin E2 (PGE2) are hallmarks of AERD. A mouse model predicted a key role for the thromboxane-prostanoid (TP) receptor in AERD.

OBJECTIVE

Our aim was to determine whether ifetroban, a TP receptor antagonist, attenuates aspirin-induced respiratory symptoms in patients with AERD.

METHODS

A total of 35 patients with AERD completed a 4-week double-blinded, placebo-controlled trial of ifetroban and underwent an oral aspirin challenge. The primary outcome was change in the provocative dose of aspirin that caused a 2-point increase in Total Nasal Symptom Score. Changes in lung function, eicosanoid levels, and platelet and mast cell activation were assessed. Cultured human nasal fibroblasts were stimulated with or without the TP agonist U46619 and assayed for prostanoid production.

RESULTS

Ifetroban was well tolerated in AERD and did not change the mean 2-point increase in Total Nasal Symptom Score (P = .763). Participants taking ifetroban had greater aspirin-induced nasal symptoms and a greater decline in FEV1 value than did participants receiving placebo (-18.8% ± 3.6% with ifetroban vs -8.4% ± 2.1% with placebo [P = .017]). Four weeks of ifetroban significantly increased urinary leukotriene E4 levels and decreased nasal PGE2 levels compared with placebo. Peak aspirin-induced urinary thromboxane levels correlated with peak urinary leukotriene E4 and prostaglandin D2 metabolite levels in participants taking ifetroban. U46119 significantly potentiated the production of PGE2 by cultured nasal fibroblasts from subjects with AERD but not by cultured nasal fibroblasts from controls without polypoid sinusitis.

CONCLUSION

Contrary to our hypothesis, TP receptor blockade worsened aspirin-induced reactions in AERD, possibly by exacerbating dysregulation of the eicosanoid system. TP signaling on stromal cells may be critical to maintaining PGE2 production when COX-2 function is low.

Perspectives on the advances in the pharmacotherapeutic management of Duchenne muscular dystrophy

INTRODUCTION

: Duchenne muscular dystrophy (DMD) is a progressive genetic disease characterized by muscular weakness with a global prevalence of 7.1 cases per 100,000 males. DMD is caused by mutations of the dystrophin gene on the X chromosome which is responsible for dystrophin protein production. Dystrophin is a cytoskeletal protein that contributes to structural support in muscle cells. DMD mutations result in dystrophin protein deficiency which leads to muscle damage and the associated clinical presentation.

AREAS COVERED

: Corticosteroids such as prednisone and deflazacort are routinely given to patients to treat inflammation, but their use is limited by the occurrence of side effects and a lack of standardized prescribing. Exon-skipping medications are emerging as treatment options for a small portion of DMD patients even though efficacy is uncertain. Many new therapeutics are under development that target inflammation, fibrosis, and dystrophin replacement.

EXPERT OPINION

: Because of side effects associated with corticosteroid use, there is need for better alternatives to the standard of care. Excessive cost is a barrier to patients receiving medications that have yet to have established efficacy. Additional therapies have the potential to help patients with DMD, although most are several years away from approval for patient use.

Ifetroban reduces coronary artery dysfunction in a mouse model of Duchenne muscular dystrophy

Dilated cardiomyopathy contributes to morbidity and mortality in Duchenne muscular dystrophy (DMD), an inheritable muscle-wasting disease caused by a mutation in the dystrophin gene. Preclinical studies in mouse models of muscular dystrophy have demonstrated reduced cardiomyopathy and improved cardiac function following oral treatment with the potent and selective thromboxane A₂/prostanoid receptor (TPr) antagonist ifetroban. Furthermore, a phase 2 clinical trial (NCT03340675, Cumberland Pharmaceuticals) is currently recruiting subjects to determine whether ifetroban can improve cardiac function in patients with DMD. Although TPr is a promising therapeutic target for the treatment of dilated cardiomyopathy in DMD, little is known about TPr function in coronary arteries that perfuse blood through the cardiac tissue. In the current study, isolated coronary arteries from young (∼3-5 mo) and aged (∼9-12 mo) mdx mice, a widely used mouse model of DMD, and age-matched controls were examined using wire myography. Vasoconstriction to increasing concentrations of TPr agonist U-46619 (U4) was enhanced in young mdx mice versus controls. In addition, young mdx mice displayed a significant attenuation in endothelial cell-mediated vasodilation to increasing concentrations of the muscarinic agonist acetylcholine (ACh). Since TPr activation was enhanced in young mdx mice, U4-mediated vasoconstriction was measured in the absence and the presence of ifetroban. Ifetroban reduced U4-mediated vasoconstriction in young mdx mice and both aged mdx and control mice. Overall, our data demonstrate enhanced coronary arterial vasoconstriction to TPr activation in young mdx mice, a phenotype that could be reversed with ifetroban. These data could have important therapeutic implications for improving cardiovascular function in DMD.NEW & NOTEWORTHY This investigation revealed 1) impaired acetylcholine-mediated vasodilation, 2) increased U-46619-mediated vasoconstriction, and 3) reversal of the increase in U-46619-mediated vasoconstriction by the thromboxane A₂/prostanoid receptor (TPr) antagonist ifetroban in left anterior descending coronary arteries isolated from young mdx mice, a model of Duchenne muscular dystrophy (DMD). Ifetroban has been used in preclinical studies to demonstrate improved cardiac function in mouse models of muscular dystrophy and is currently being investigated in a phase 2 clinical trial in patients with DMD. The current study supports the role of ifetroban in improving coronary artery function in preclinical DMD models, which may contribute to improved cardiovascular health.