Abstract
Eleven triterpene acids, 1-11, isolated from the leaves of Eriobotrya japonica, were evaluated for inhibition of DNA topoisomerase (Topo) I and cytotoxicity against human leukemia (HL60) and melanoma cell lines (CRL1579). Among the compounds tested, four compounds, δ-oleanolic acid (4), ursolic acid (5), 3-O-(E)-p-coumaroyl tormentic acid (8), and betulinic acid (10), exhibited potent Topo I inhibitory activity (IC(50) 20.3-36.5 µM) and cytotoxicity against HL60 (EC(50) 5.0-8.1 µM). Upon assessing the apoptosis-inducing activity in HL60 cells, compound 8 exhibited induction of apoptosis detected by the observation of DNA fragmentation and membrane phospholipid exposure in flow cytometry. Western blot analysis showed that compound 8 markedly reduced the levels of procaspases-3 and 9, while being increased the levels of cleaved caspases-3 and 9. On the other hand, compound 8 exerted almost no influence on the expression of caspase-8. In addition, compound 8 increased significantly Bax/Bcl-2 ratio and activated caspase-2. These results suggested that compound 8 induced apoptotic cell death in HL60 via mainly mitochondrial pathway by, at least in part, Topo I inhibition. Therefore, compound 8 may be promising lead compound for developing an effective drug for treatment of leukemia.
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