A novel prostanoid EP1 receptor antagonist, ONO-8539, reduces acid-induced heartburn symptoms in healthy male volunteers: a randomized clinical trial

Background Patients with proton pump inhibitor (PPI)refractory gastroesophageal reflux disease (GERD) have unmet clinical needs. Recently, we reported that esophageal prostaglandin E-2 (PGE(2)) plays a crucial role in the generation of heartburn. In the present study, we focused on the PGE(2) receptor, EP1, and investigated the effects of ONO-8539, a novel EP1 receptor antagonist, on heartburn symptoms in healthy male volunteers. Methods This prospective, double-blind, placebo-controlled, two-period crossover study was performed in 20 healthy male subjects. The novel prostanoid EP1 receptor antagonist, ONO-8539 (450 mg), was administered once 4 h prior to acid perfusion test. During the test, hydrochloric acid (0.15 mol l(-1)) was perfused into the lower esophagus for 30 min. Acid perception threshold was quantified by the time to first sensation of heartburn and intensity of GI symptoms determined using a validated categorical rating scale, and the area under the curve (AUC) as the total symptom score. Results ONO-8539 significantly reduced a total heartburn symptom score, not other upper GI symptom scores, during acid perfusion compared with placebo (AUC for heartburn, 85.0 +/- 10.6 for placebo and 56.5 +/- 7.2 for ONO-8539; P < 0.01), and significantly extended the time to first sensation of heartburn compared with placebo (5.7 +/- 4.3 min for placebo and 9.7 +/- 7.2 min for ONO-8539; P < 0.05). Conclusions ONO-8539 attenuated acid-induced heartburn in healthy male subjects, suggesting that EP1 receptors play a role in generation of heartburn symptoms. ONO-8539 is a potential novel therapeutic option for controlling heartburn symptoms in GERD patients.