Abstract
The aim of this study was to assess the cardiovascular effect of MA-2029, a selective motilin receptor antagonist highly expected for the treatment of irritable bowel syndrome (IBS). MA-2029 inhibited the human ether-a-go-go-related gene (hERG) current at 100 µg/ml, but shortened action potential duration (APD) in isolated guinea pig papillary muscles at 10 and 100 µg/ml and the corrected QT (QTc) interval after oral administration of 30 and 300 mg/kg in conscious telemetered dogs. The discrepancy was probably caused by blockade of the Ca2+ channel because MA-2029 inhibited the Ca2+ current in isolated guinea pig myocytes. MA-2029 at 100 µg/ml also decreased the maximum rising velocity and action potential amplitude in the action potential study, indicating that MA-2029 has Na+ channel blocking potential. In the cardiovascular study, MA-2029 at 30 mg/kg induced slight cardiovascular changes such as hypotension, QTc shortening, and PR prolongation possibly caused by Ca2+ channel blockade. The plasma concentration at 4 hr after 30 mg/kg administration was 2.10 µg/ml, 200-fold higher than the effective concentration of MA-2029 as a motilin receptor antagonist. These results suggest that MA-2029 has sufficient cardiovascular safety although it inhibits multiple ion channels at supra-effective concentrations. On the other hand, cisapride, an effective IBS drug, showed clear hERG inhibition and APD prolongation at 100 ng/ml. Cisapride exhibited a narrow safety margin because it caused QT prolongation potential even at the therapeutic concentration. In conclusion, MA-2029 is a novel drug highly expected for the treatment of IBS with lower cardiovascular risk than cisapride.
