Flavonoids are well-known antioxidants and have shown the ability to prevent tumor formation and recurrence. Especially in dietary flavonoids, they have provided convenience and consistence of intake for long-term prevention of tumor formation. Previous reports suggested that S100 calcium-binding protein A7 (S100A7) might activate epithelial–mesenchymal transition (EMT) signaling and promote the metastasis of tumor cells; however, the regulatory signaling was unclear. In this study, we found that S100A7 was highly expressed in cancer cells and could be reduced by luteolin (Lu) and quercetin (Qu) through Src/Stat3 signaling. We found that the protein levels of S100A7, phosphorylated Src (p-Src), and p-Stat3 were increased in A431-III cells. Flavonoids Lu and Qu reduce protein levels of p-Src, p-Stat3 and S100A7 in A431-III cells. Treatment of A431-III cells with Src inhibitor SU6656 and Stat3 inhibitor S3I-201 also reduced the protein levels of S100A7. Transactivation activity of 5′-upstream regions of S100A7 was activated by Stat3 but was reduced by treatment with Lu, Qu, SU6656 and S3I-201. The treatment also reduced the migratory and invasive abilities of A431-III cells. In a further analysis of EMT markers, the protein level of E-cad increased and that of Twist decreased after treatment with the inhibitors and flavonoids. Overexpression of S100A7 decreased the protein level of E-cad and increased the Twist level, whereas knockdown of S100A7 had the opposite effects. Treatment with S3I-201, Lu and Qu, compared to the control, were found to decrease metastasis of tumor cells in zebrafish larvae. These results suggest that Lu and Qu may inhibit Src/Stat3/S100A7 signaling to reduce tumorigenesis of cancer cells.

High UBE2S in malignant cancers contributes to cell motility through EMT signaling and is reversed by luteolin and quercetin.

Highly invasive A431‐III cells, which are derived from parental A431‐P cells, were originally isolated by three successive passages through a Boyden chamber using a Matrigel‐coated membrane support. The greater invasion potential shown by A431‐III cells was due to their increased ability to spread/migrate, which was associated with enhanced MMP activity. The tumor progression events evoked by A431‐P cells compared to A431‐III cells may help identify useful strategies for evaluating the epithelial–mesenchymal transition (EMT) and these cell lines could be a reliable model for evaluating tumor metastasis events. Using this approach, we evaluated the effects of luteolin and quercetin using the A431‐P/A431‐III EMT model. These flavonoids reversed cadherin switching, downregulated EMT markers, and nullified the invasion ability of A431‐III cells. Overexpression of MMP‐9 resulted in induction of the EMT in A431‐P cells and this could be reversed by treating with luteolin or quercetin. Cotreatment of A431‐P and A431‐III cells with epidermal growth factor (EGF) plus luteolin or quercetin resulted in a more epithelial‐like morphology, led to reduced levels of EGF‐induced markers of EMT, and caused the restoration of cell–cell junctions. E‐cadherin was decreased by EGF, but increased by luteolin and quercetin. Our results suggest that luteolin and quercetin are potentially beneficial agents that target and prevent the occurrence of EMT in epidermal carcinoma cells. These chemicals also have the ability to attenuate tumor progression in A431‐III cells. Luteolin and quercetin show inherent potential as chemopreventive/antineoplastic agents and do this by abating tumor progression through a reversal of EMT. (Cancer Sci2011; 102: 1829–1839)