The pharmacological activity of DSP-6952, a novel compound was investigated, compared to that of clinically efficacious gastrointestinal (GI) prokinetic 5-hydroxytryptamine(4) (5-HT4) receptor agonists. DSP-6952 had a strong affinity of Ki = 51.9 nM for 5-HT4(b) receptor, and produced contraction in the isolated guinea pig colon with EC50 of 271.6 nM and low intrinsic activity of 57%, similar to tegaserod and mosapride. In the development of the 5-HT4 receptor agonists, cardiovascular risk was deliberately evaluated, because some related prokinetics were reported to cause with cardiovascular adverse events, such as ventricular arrhythmias or ischemia. DSP-6952 showed minimal effects up to 100 mu M in human ether-a-go-go-related gene (hERG) channels or guinea pig cardiomyocytes. In telemetered conscious monkeys, DSP-6952 did not affect blood pressure or any electrocardiogram (ECG) up to 180 mg/kg, p.o.; however, DSP-6952 transiently increased heart rate, as well as in anesthetized dogs. The positive chronotropic effects of DSP-6952 were completely antagonized by a 5-HT4 receptor antagonist, and another 5-HT4 receptor agonist, TD-5108 also increased heart rate. These effects are considered a class effect seen in clinically developing and marketed 5-HT4 receptor agonists, and have not been regarded as a critical issue in clinical use. DSP-6952 did not induce contraction in the rabbit coronary artery up to 100 mu M, which differed from tegaserod or sumatriptan. These results show that DSP-6952 does not have cardiac ischemic risk via coronary vasoconstriction. In conclusion, DSP-6952 is a promising GI prokinetic compound with partial 5-HT4 receptor agonistic activity as well as a favorable cardiovascular safety profile.
