Apoptosis Induction in Human Leukemic Promyelocytic HL-60 and Monocytic U937 Cell Lines by Goniothalamin

Goniothalamin is an active compound extracted from Goniothalamus griffithii, a local plant found innorthern Thailand. Goniothalamin inhibits cancer cell growth but is also toxic to normal cells. The aims ofthis study were to identify the cytotoxic effect of goniothalamin and the mechanism of cell death in humanHL-60 and U937 cells. Cytotoxicity was determined by MTT assay and cell cycle profiles were demonstratedby staining with propidium iodide (PI) and flow cytometry. Apoptosis was confirmed by staining withannexin V-FITC/propidium iodide (PI) and flow cytometry. Reduction of mitochondrial transmembranepotential was determined by staining with dihexyloxacarbocyanine iodide and flow cytometry and expressionof Smac, caspase-8 and -9 was demonstrated by Western blotting. Goniothalamin inhibited growth ofHL-60 and U937 cell lines. An increase of SubG1 phase was found in their cell cycle profiles, indicatingapoptosis as the mode of cell death. Apoptosis was confirmed by the flip-flop of phosphatidylserine usingannexin V-FITC/PI assay in HL60 and U937 cells in a dose response manner. Furthermore, reduction ofmitochondrial transmembrane potential was found in both cell types while expression of caspase-8, -9 andSmac/Diablo was increased in HL-60 cells. Taken together, our results indicate that goniothalamin-treatedhuman leukemic cells undergo apoptosis via intrinsic and extrinsic pathways.