Abstract 5015: γ-Tocotrienol inhibition of metastatic phenotypic behavior is associated with a decrease in galectin-3 expression and distribution in the highly malignant mouse +SA mammary tumor cells

γ-Tocotrienol is a rare natural isoform of vitamin E that displays potent apoptotic and anti-metastatic activity against breast cancer. Galectin-3 is a protein that plays an important role in metastasis by binding to glycoconjugates on receptors and extracellular matrix proteins. Studies were conducted to investigate the effects of γ-tocotrienol on galectin-3 expression and activity in highly malignant mouse +SA mammary tumor cells. Computer-aided molecular modeling studies were carried out within the active site of galectin-3 based on the crystal structure (5EXO) obtained from the protein data bank with a known ligand, and anticancer agents (salirasib, γ-tocotrienol, and β-lactose) galectin-3 docking scores and amino acid interactions were determine. Treatment effects on galectin-3 expression and distribution was determined by Western blot analysis and immunocytochemical fluorescent staining, respectively. Treatment effects on +SA cellular migration and invasion was also determined. Results show that salirasib and β-lactose (known inhibitors of galectin-3) that share some pharmacophoric properties with γ- tocotrienol, with protein docking studies showing that salirasib (active binding -2.8) and γ- tocotrienol (active binding -2.87) had a similar binding score and binding moieties. Western blot analysis shows that γ-tocotrienol treatment induces a downregulation of galectin-3 expression, whereas immunocytochemistry studies shows that galectin-3 is highly expressed in +SA cells, and treatment with 5 μM γ-tocotrienol greatly reduced galectin-3 expression in these cells. Furthermore, galectin-3 was found to form globular structures on the outer membrane of +SA cells in the vehicle-treated control group, and +SA group, and a high level of fibronectin on the outside of +SA cells, and γ-tocotrienol greatly attenuated galectin-3 expression and distribution in +SA cells. Furthermore, treatment with 1.5 μM histamine significantly stimulated +SA mammary tumor cell migration, whereas combined treatment with 5 μM γ-tocotrienol completely blocked histamine-induced +SA cell migration. In summary, these results demonstrate for the first time that γ-tocotrienol treatment inhibits extracellular galectin-3 expression and disrupts galectin-3 carbohydrate binding, activation and migration of +SA mammary tumor cells. These findings also suggest that γ-tocotrienol may provide significant benefits in the prevention and/or treatment of metastatic breast cancer. This study was sup