γ-Tocotrienol Reversal of Epithelial-to-Mesenchymal Transition in Human Breast Cancer Cells is Mediated through a Suppression of Canonical Wnt and Hedgehog Signaling

Abstract

γ-Tocotrienol, a natural isoform within the vitamin E family of compounds, displays potent antiproliferative, apoptotic and reversal of epithelial-to-mesenchymal transition (EMT) activity against breast cancer using treatment doses that have little or no effect on normal cell viability. EMT is a route by which epithelial cells undergo various biochemical alterations leading to the acquisition of mesenchymal traits. Several aberrant signaling pathways are involved in EMT-dependent cancer metastasis. Specifically, dysregulation of the canonical Wnt and Hedgehog pathways are intimately involved in promoting breast cancer EMT and metastasis. Therefore, studies were conducted to examine effects of γ-tocotrienol on Wnt and Hedgehog signaling. Results from these studies demonstrate that γ-tocotrienol significantly inhibits canonical Wnt and Hedgehog signaling by inhibiting receptors, co-receptors and ligand expression, as well as inhibiting expression of cytosolic and nuclear signaling proteins within these pathways. Additional studies showed that γ-tocotrienol treatment increased the expression of negative regulators of both the Wnt and Hedgehog pathways. These findings demonstrate that γ-tocotrienol reversal of EMT is mediated, at least in part, through the inhibition of canonical Wnt and Hedgehog signaling, and strongly suggest that this form of vitamin E may provide significant benefit in the prevention and treatment of metastatic breast cancer.