Zibotentan in microvascular angina: a randomized, placebo-controlled, crossover trial

Abstract Background/Introduction Microvascular angina is a chronic condition characterized by abnormal myocardial blood flow leading to ischemic symptoms. Endothelin-1, a peptide secreted by endothelial cells, is a highly potent constrictor of the human coronary arterioles. Microvascular angina is associated with elevated circulating concentrations of endothelin-1, and prolonged exposure to ‘excess’ endothelin causes vasoconstriction and vascular remodelling. The chronic elevation of circulating endothelin-1 in microvascular angina may be influenced by genetic factors. Purpose Zibotentan, the most selective antagonist of the endothelin A receptor with no off-target binding to the endothelin B receptor, was evaluated in oncology trials and did not improve survival. We identified zibotentan as a potential disease-modifying therapy for patients suffering from microvascular angina. We hypothesized that zibotentan 10 mg daily for 12 weeks in addition to background medical therapy could be an efficacious and safe treatment for patients with microvascular angina. We further hypothesized that the SNP regulator of EDN1 gene expression, rs9349379 (G allele), could be a novel theragnostic biomarker. Methods The trial involved a prospective, multicentre, randomized, double-blind, placebo-controlled, sequential crossover design to assess the effects of zibotentan 10 mg or matched placebo, once daily for 12 weeks. The primary outcome was treadmill exercise duration (seconds) using the Bruce protocol. The secondary outcomes included exercise test parameters, health status questionnaires, safety (frequency and severity of severe adverse events (SAEs) and adverse events), feasibility (withdrawal rate), and biomarkers of efficacy (pharmacokinetics, pharmacodynamics). Results The study found no significant difference in exercise duration with zibotentan (-4.26 seconds; 95% CI: -19.60 to 11.06; P=0.5871). There was no effect on the secondary outcomes. However, for exploratory (mechanistic) outcomes, zibotentan increased plasma big endothelin-1, endothelin-1, and global myocardial blood flow, while reducing hemoglobin, diastolic, and systolic blood pressure (all p<0.001). Adverse events were more common during the zibotentan period (60.2%) compared to placebo (14.4%, p<0.001). Conclusion(s) In conclusion, daily administration of 10 mg zibotentan for 12 weeks did not enhance exercise duration and was commonly associated with adverse effects related to fluid retention. Further trials exploring lower zibotentan doses in combination with agents to mitigate fluid retention, and longer treatment durations, are warranted.