| Title
| - 5-Hydroxy-3,6,7,8,3‘,4‘-hexamethoxyflavone Induces Apoptosisthrough Reactive Oxygen Species Production, Growth Arrestand DNA Damage-Inducible Gene 153 Expression, and CaspaseActivation in Human Leukemia Cells
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| Abstract
| - This study examined the growth inhibitory effects of structurally related polymethoxylated flavones inhuman cancer cells. Here, we report that 5-hydroxy-3,6,7,8,3‘,4‘-hexamethoxyflavone (5-OH-HxMF)induces growth inhibition of human cancer cells and induction of apoptosis in HL-60 cells throughmodulation of mitochondrial functions regulated by reactive oxygen species (ROS). ROS generationoccurs in the early stages of 5-OH-HxMF-induced apoptosis, preceding cytochrome c release, caspaseactivation, and DNA fragmentation. The changes occurred after single breaks in DNA were detected,suggesting that 5-OH-HxMF induced irreparable DNA damage, which in turn triggered the processof apoptosis. Up-regulation of Bax was found in 5-OH-HxMF-treated HL-60 cells. In addition, acaspase-independent pathway indicated by endonuclease G also contributed to apoptosis causedby 5-OH-HxMF. Antioxidants suppress 5-OH-HxMF-induced apoptosis. 5-OH-HxMF markedlyenhanced growth arrest DNA damage-inducible gene 153 (GADD153) protein in a time-dependentmanner. N-acetylcysteine (NAC) and catalase prevented up-regulation of GADD153 expression causedby 5-OH-HxMF. These findings suggest that 5-OH-HxMF creates an oxidative cellular environmentthat induces DNA damage and GADD153 gene activation, which in turn helps trigger apoptosis inHL-60 cells. Meanwhile, ROS were proven an important inducer in this apoptotic process. The C-5hydroxyl on the ring of 5-OH-HxMF was found to be essential for the antiproliferative and apoptosis-inducing activity. Our study identified the novel mechanisms of 5-OH-HxMF-induced apoptosis andindicated that these results have significant applications as potential chemopreventive and chemotherapeutic agents. Keywords: Polymethoxylated flavones; apoptosis; cytochrome c; caspase-9; caspase-3; poly-(ADP-ribose) polymerase; antioxidant; GADD153; reactive oxygen species
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