Betulinic acid inhibits aminopeptidase N activity

The triterpene betulinic acid inhibits the activity of aminopeptidase N (EC 3.4.11.2) in a dose-dependent manner. An IC50 of 7.3 +/- 1.4 microM was determined for betulinic acid. This inhibitory activity is higher than that of bestatin' (IC50 = 16.9 +/- 4.1 microM), a well known inhibitor of this enzyme. The finding supports the idea that betulinic acid acts as anti-melanoma agent via inhibition of aminopeptidase N activity.