FISETIN INHIBITS HUMAN MELANOMA CELL INVASION THROUGH PROMOTION OF MESENCHYMAL TO EPITHELIAL TRANSITION AND BY TARGETING MAPK AND NFкB SIGNALING PATHWAY.

Malignant melanoma is a serious form of cancer responsible for approximately 80% of skin cancer-related deaths. Activating mutations in the serine/threonine kinase BRAF occur in 60-70% of malignant melanomas. Preclinical studies have demonstrated that BRAF plays an important role in regulating the MAPK signaling cascade in melanoma. The RAF-MEK-ERK (MAPK) pathway is the key regulator of melanoma cell invasion. In addition, activation of NFкB via the MAPK pathway is regulated through MEK-induced activation of IKK. These pathways are receiving attention as potential targets for prevention/treatment of melanoma. In this study, we investigated the effect of fisetin on melanoma cell invasion and epithelial- mesenchymal transition, and delineated the molecular mechanism(s) underlying these effects. Using a Boyden chamber cell invasion assay with matrigel-coated membranes, we observed that treatment of malignant melanoma cells (A375, SK- Mel-28 and RPMI-7951) with fisetin (5-20 µM) inhibited their invasion, which was associated with a decrease in the phosphorylation of MEK and ERK1/2. In addition, fisetin inhibited the activation of IKK leading to reduction in the activation of the NFкB signaling pathway. Treatment of cells with an inhibitor of MEK (PD98059) or of NFкB (CAPE) also inhibited melanoma cell invasion. Furthermore, fisetin treatment promoted mesenchymal to epithelial transition which was associated with a decrease in mesenchymal markers (N-cadherin, vimentin, snail and fibronectin) and an increase in epithelial markers (E-cadherin and desmoglein). Employing three dimensional skin equivalents consisting of A375 cells admixed with normal human keratinocytes embedded onto a collagen- constricted fibroblast matrix, we found that fisetin treatment reduced the invasive potential of melanoma cells. Based on these observations, we suggest that fisetin alone or in combination with anti-metastatic drugs could be useful for the management of melanoma invasion or metastasis.

BRAF, cell invasion, Desmoglein, E-cadherin, epithelial-mesenchymal, transition, fibronectin, Flavonoid, malignant melanoma, MAPK signaling, melanoma, Metastasis, N-cadherin, NFκB signaling, serine/threonine kinase BRAF, snail, vimentin

Caffeic acid phenethyl ester (CAPE), Fisetin, inhibitor of MEK (PD98059)