Severibuxine, Isolated from Severinia buxifolia, Induces Apoptosis in HL-60 Leukemia Cells

In an ongoing search for cancer-preventing compounds derived from plant sources, we isolated the quinolin-2,4-dione alkaloid severibuxine from the root bark of Severinia buxifolia collected in Taiwan and then examined the apoptotic effect of this compound. Severibuxine showed cytotoxicity to leukemia HL-60 cells (IC50 = 12.3±0.6 μM). Fluorescence microscopic analysis of cells stained with Hoechst 33342 indicated that the percentage of apoptotic cells showing nuclear condensation and fragmentation increased in a time-dependent manner. In addition, the activities of caspase-9 and caspase-3 were also enhanced in a time-dependent manner upon treatment with severibuxine. The addition of caspase-9 and caspase-3 inhibitors blocked severibuxine-mediated apoptosis. Upon treatment with severibuxine, the mitochondrial membrane potential decreased in a time-dependent manner. Severibuxine induced apoptosis in HL-60 cells through activation of the caspase-9/caspase-3 pathway, which is triggered by mitochondrial dysfunction.