Wogonin, one of flavonoid compounds isolated from Chinese herbal plants Scutellaria baicalensis Georgi, has been recognized as a potent anti-cancer agent acting through control of growth, differentiation and apoptosis. However, the underlying molecular mechanism of its anti-cancer activity remains to be further elucidated. In this study, we investigated the potential role of wogonin in the induced-apoptosis of human breast cancer cells MCF-7. Wogonin was found to inhibit the proliferation of MCF-7 in a concentration and time-dependent manner, notably wogonin could induce G1 phase arrest of MCF-7 cells. Wogonin-induced apoptosis was accompanied by a significant decrease of the Bcl-2 and survivin and increase of Bax and p53. Wogonin also increased active apoptosis forms of caspases-3, -8, -9 significantly. Z-DEVD-fmk, a specific caspase-3 inhibitor, significantly inhibited wogonin-induced cell apoptosis. Wogonin also suppressed the phosphorylation of PI3K/Akt and induced phosphorylation of ERK. PD98059, a specific ERK inhibitor, significantly blocked wogonin-induced apoptosis. On the other hand, LY294002, a specific PI3K inhibitor, significantly increased wogonin-induced cell apoptosis. Further study indicated that LY294002 not only down-regulated the expression of survivin alone, but also enhanced the inhibition of survivin expression combined with wogonin. In conclusion, the pro-apoptotic effect of wogonin is mediated through the activation of ERK and the activation of caspases, and is correlated with the block of the PI3K/Akt/survivin signal pathways in MCF-7 cells.
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The wogonin-containing herb Scutellaria baicalensis has successfully been used for curing various diseases in traditional Chinese medicine. Wogonin has been shown to induce apoptosis in different cancer cells and to suppress growth of human cancer xenografts in vivo. However, its direct targets remain unknown. In this study, we demonstrate for the first time that wogonin and structurally related natural flavones, for example, apigenin, chrysin and luteolin, are inhibitors of cyclin-dependent kinase 9 (CDK9) and block phosphorylation of the carboxy-terminal domain of RNA polymerase II at Ser(2). This effect leads to reduced RNA synthesis and subsequently rapid downregulation of the short-lived anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1) resulting in apoptosis induction in cancer cells. We show that genetic inhibition of Mcl-1 or CDK9 expression by siRNA is sufficient to mimic flavone-induced apoptosis. Pull-down and in silico docking studies demonstrate that wogonin directly binds to CDK9, presumably to the ATP-binding pocket. In contrast, wogonin does not inhibit CDK2, CDK4 and CDK6 at doses that inhibit CDK9 activity. Furthermore, we show that wogonin preferentially inhibits CDK9 in malignant compared with normal lymphocytes. Thus, our study reveals a new mechanism of anti-cancer action of natural flavones and supports CDK9 as a therapeutic target in oncology.

Wogonin is a one of the bioactive compounds of Scutellaria baicalensi Georgi which has been shown to have antiinflammatory, anticancer, antiviral and neuroprotective effects. However, the underlying mechanisms by which wogonin induces apoptosis in cancer cells still remain speculative. Here we investigated the potential activation of MAPKs and generation of reactive oxygen species (ROS) by wogonin on MCF-7 human breast cancer cells. These results showed that wogonin induced mitochondria and death-receptor-mediated apoptotic cell death, which was characterized by activation of several caspases, induction of PARP cleavage, change of antiapoptotic/proapoptotic Bcl-2 family member ratios and cleavage of Bid. We also found that generation of ROS was an important mediator in wogonin-induced apoptosis. Further investigation revealed that wogonin activated ERK and p38 MAPKs, which was inhibited by N-acetyl cysteine (NAC), a ROS scavenger, indicating that wogonin-induced ROS are associated with MAPKs activation. These data demonstrate that wogonin may be a novel anticancer agent for treatment of breast cancer.

Wogonin, a natural monoflavonoid, has been shown to have tumor therapeutic potential in vitro and in vivo. Recently many studies have focused on the induction of apoptosis of tumor cells by wogonin. In this study, we found that wogonin could induce differentiation and G1 phase arrest of human U-937 leukemia cells. The growth of U-937 cells incubated with wogonin was inhibited in a time- and concentration-dependent manner. After treatment with wogonin, U-937 cells exhibited the characteristics of mature granulocytes, such as increased cytoplasmic-to-nuclear ratio, enhanced prominence of cytoplasmic granules, membrane ruffling, a higher NBT-reducing ability, and an increased expression of CD11b. Moreover, wogonin could induce G1 phase arrest and influenced the expression of associated proteins. For example, the expression of phorsphorylated protein kinase C (PKC) delta, p21 increased, while that of cyclin D1/cyclin-dependent kinase (CDK) 4, p-Rb decreased. The upregulation of p21 could be reversed by rottlerin, an inhibitor of PKCdelta. Taken together, wogonin induced U-937 cells to undergo granulocytic differentiation and G1 phase arrest via PKCdelta phosphorylation-induced upregulation of p21 proteins.

Previous studies revealed that wogonin, a naturally occurring monoflavonoid extracted from Scutellariae radix, possessed anticancer activity both in vitro and in vivo. However, the molecular mechanism of its potent anticancer activity remains poorly understood and warrants further investigations. In this study, we found for the first time that wogonin inhibited the growth and tumor angiogenesis of human gastric carcinoma in nude mice. We explored the inhibitory effect of wogonin on angiogenesis stimulated by vascular endothelial growth factor (VEGF) in vitro. Wogonin suppressed the VEGF-stimulated migration and tube formation of human umbilical vein endothelial cells (HUVECs). It also restrained VEGF-induced tyrosine phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2). This inhibition of receptor phosphorylation was correlated with a significant decrease in VEGF-triggered phosphorylated forms of ERK, AKT and p38. Taken together, these findings strongly suggest that wogonin might be a promising antitumor drug.