Apigenin inhibits HeLa sphere-forming cells through inactivation of casein kinase 2α.

The protein kinase casein kinase 2 (CK2) has been implicated in stem cell maintenance and its aberrant activation has been demonstrated in several types of cancer, including cervical cancer. In the present study, it was demonstrated that the sphere-forming cells (SFCs) of HeLa cell lines exhibited self-renewal capacity, indicating that they possessed the properties of cervical cancer stem-like cells. HeLa-derived SFCs exhibited a higher level of CK2α protein, compared with the parental cells. Apigenin, a dietary flavonoid, led to a dose-dependent inhibition of the self-renewal capacity and the protein expression of CK2α in HeLa-derived SFCs. Furthermore, forced overexpression of CK2α resulted in a decrease in the inhibition of CK2α expression and the self-renewal capacity induced by apigenin in HeLa-derived SFCs. These results suggested that apigenin inhibits the self-renewal capacity of HeLa-derived SFCs through downregulation of CK2α expression.

Apigenin inhibits the self-renewal capacity of human ovarian cancer SKOV3­derived sphere-forming cells.

Casein kinase 2 (CK2) is a protein kinase which is frequently activated in cancer. The Hedgehog (Hh) signaling pathway is involved in the stimulation of cancer stem cell growth. Its aberrant activation has been validated in several types of cancer, including ovarian cancer. In the present study, the sphere­forming cells (SFCs) of the human ovarian cancer SKOV3 cell line were observed to have self­renewal capacity, indicating the possession of ovarian cancer stem­like cell properties. SKOV3­derived SFCs had higher levels of CK2α and glioma­associated oncogene 1 (Gli1) proteins compared with those of parental cells. Apigenin, a common flavonoid, significantly inhibited the self­renewal capacity and the protein expression of CK2α and Gli1 proteins in the SKOV3­derived SFCs, which occurred in a concentration­dependent manner. In addition, CK2α small interfering RNA downregulated the protein expression of CK2α and Gli1 and synergistically inhibited the self­renewal capacity of the SKOV3­derived SFCs with apigenin. However, forced overexpression of CK2α resulted in an increase in the expression of CK2α and Gli1 and attenuated the apigenin­inhibited self­renewal effect in the SKOV3­derived SFCs. These results suggested that apigenin inhibited the self­renewal capacity of SKOV3­derived SFCs and was involved in downregulating the expression of Gli1 by the inhibition of CK2α.

Activation of the apoptosis signal-regulating kinase 1/c-Jun N-terminal kinase pathway is involved in the casticin-induced apoptosis of colon cancer cells.

Casticin is one of the main components of the fruits of Vitex rotundifolia L. Studies have shown that casticin inhibits the growth of various cancer cells, including colon cancer. In the present study, the anti-carcinogenic effects of casticin on human colon cancer and the underlying mechanisms were investigated. The results revealed that casticin significantly induced apoptosis of HT-29, HCT-116, SW480 and Caco-2 cells, induced the accumulation of reactive oxygen species (ROS) and increased the protein levels of apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase (JNK) and B-cell lymphoma 2-interacting mediator of cell death (Bim) in HT-29 cells. Pretreatment with N-acetylcysteine, an antioxidant chemical compound, inhibited the activation of ASK1, JNK and Bim, as well as the apoptosis induced by casticin. Small interfering RNA targeting ASK1 significantly attenuated the induction of JNK and Bim activation and apoptotic cell death by casticin treatment. SP600125, a specific JNK inhibitor, attenuated Bim activation and apoptosis, but did not alter ASK1 phosphorylation levels. In addition, casticin treatment resulted in apoptosis by the same mechanism in HCT-116, SW480 and Caco-2 cells. These results suggest that casticin significantly induced apoptosis by the activation of the ASK1-JNK-Bim signaling cascade and the accumulation of ROS in colon cancer cells.

Casticin inhibits epithelial-mesenchymal transition of liver cancer stem cells of the SMMC-7721 cell line through downregulating Twist.

The existence of cancer stem cells (CSCs) is central to the pathogenesis and therapeutic target of human hepatocellular carcinoma. The aim of this study was to investigate the effects of casticin on epithelial-mesenchymal transition (EMT) of liver cancer stem cells (LCSCs) derived from the SMMC-7721 cell line. Our results demonstrated that CD133+ sphere-forming cells (SFCs) sorted from the SMMC-7721 cell line not only possessed a higher capacity to form tumor spheroids in vitro, but also had a greater potential to form tumors when implanted in Balb/c-nu mice, indicating that CD133+ SFCs possessed similar traits to LCSCs. Casticin increased the expression levels of E-cadherin and decreased those of N-cadherin in LCSCs. Treatment of LCSCs with casticin for 48 h also decreased the levels of the EMT-associated transcription factor, Twist. Overexpression of Twist attenuated the casticin-induced regulation of E-cadherin and N-cadherin protein expression, as well as the EMT capacity of LCSCs. In conclusion, CD133+ SFCs of the SMMC-7721 cell line may represent a subpopulation of LCSCs with the characteristics of EMT. Furthermore, casticin targeted LCSCs through the inhibition of EMT by downregulating Twist.

Casticin induces breast cancer cell apoptosis by inhibiting the expression of forkhead box protein M1.

Casticin is an active ingredient derived from Fructus Viticis, a traditional Chinese medicine. This study aimed to investigate the role of forkhead box O3 (FOXO3a) in breast cancer cells and examine the regulatory mechanisms of FOXO3a in response to casticin treatment of the cells by ELISA, flow cytometry, small interfering RNA (siRNA) transfection and western blot analysis. Casticin treatment induced apoptosis and reduced the expression of the transcription factor forkhead box protein M1 (FOXM1). In addition, FOXM1 repression induced by casticin treatment was associated with the activation of FOXO3a via increased dephosphorylation. Notably, silencing FOXO3a expression by siRNA-mediated gene knockdown attenuated casticin-mediated apoptosis. Collectively, these findings suggest that FOXO3a is a critical mediator of the inhibitory effects of casticin on apoptosis in breast cancer cells.

Regulation of the FOXO3a/Bim signaling pathway by 5,7-dihydroxy-8-nitrochrysin in MDA-MB-453 breast cancer cells.

We previously demonstrated that 5,7-dihydroxy-8-nitrochrysin (NOC), a novel synthetic chrysin analog, preferentially inhibits HER-2/neu-overexpressing MDA-MB-453 breast cancer cell growth by inducing apoptosis; however, the precise molecular mechanism was unclear. In this study, we demonstrated that NOC significantly induces apoptosis of MDA-MB-453 cells and that this is primarily mediated through a mitochondrial death cascade. This was presented as a loss of mitochondrial membrane potential, release of cytochrome c and activation of caspase-9. NOC induces a significant increase in levels of the BH3-only protein Bim. Small interfering RNA-mediated knockdown of Bim markedly attenuated NOC-induced apoptosis. An upstream transcriptional regulator of Bim, forkhead box O3a transcription factor (FOXO3a), experienced a decrease in phosphorylation and nuclear translocation. Silencing of FOXO3a resulted in a marked attenuation in the expression of Bim, as well as protection against NOC-mediated apoptosis. Furthermore, NOC-induced activation and nuclear localization of FOXO3a was associated with reduced levels of Akt phosphorylation. These results suggest that NOC induces apoptosis in MDA-MB-453 human breast cancer cells via caspase activation and modulation of the Akt/FOXO3a pathway.

Casticin induces ovarian cancer cell apoptosis by repressing FoxM1 through the activation of FOXO3a.

Casticin, a polymethoxyflavone, is reported to have anticancer activities. The aim of the present study was to examine the molecular mechanisms by which casticin induces apoptosis in ovarian cancer cells. The human ovarian cancer cell lines SKOV3 and A2780 were cultured in vitro. Various molecular techniques, including histone/DNA enzyme-linked immunosorbent assay (ELISA), reverse transcription polymerase chain reaction (RT-PCR), western blot analysis and gene transfection, were used to assess the expression of FOXO3a and forkhead box protein M1 (FoxM1) in casticin-treated ovarian cancer cell lines. Casticin-induced apoptotic cell death was accompanied by the activation of transcription factor FOXO3a, with a concomitant decrease in the expression levels of FoxM1 and its downstream target factors, namely survivin and polo-like kinase 1 (PLK1), and an increase in p27KIP1. A small inhibitory RNA (siRNA) knockout of FoxM1 potentiated casticin-induced apoptosis in ovarian cancer cells. Silencing FOXO3a expression using siRNA increased FoxM1 expression levels and clearly attenuated the induction of apoptosis by casticin treatment. These results show that casticin-induced apoptosis in ovarian cancer may be caused by the activation of FOXO3a, leading to FoxM1 inhibition.