Induction of apoptosis by bestatin (ubenimex) in human leukemic cell lines

Abstract

We investigated the growth inhibitory activity of bestatin, an inhibitor of aminopeptidase N (CD13), on six human leukemic cell lines. Proliferation of all the cell lines except KG1 was inhibited by bestatin. P39/TSU, HL60 and U937 were highly sensitive, with 50% growth inhibitory concentrations (IC₅₀) close to the maximum serum concentration when bestatin was orally administered at 30 mg in clinical application. All cell lines except for K562 highly expressed CD13, but a clear correlation between the sensitivity to bestatin and expression of CD13 was not observed. Other aminopeptidase inhibitors such as amastatin A, arphamenine B and WM15 antibody showed no growth inhibitory effects. To confirm the growth inhibitory effects of bestatin, we quantitatively examined DNA fragmentation in five bestatin-sensitive cell lines. Bestatin dose-dependently induced DNA fragmentation in those cell lines. In case of U937, bestatin induced DNA fragmentation quantitatively and DNA ladder and enhanced caspase-3 activity. Furthermore, the growth inhibition by bestatin was reduced by the caspase inhibitor Z-Asp-CH₂-DCB. These results suggested that bestatin exhibits direct antileukemic effects against human leukemic cell lines through the induction of apoptosis.