Dietary supplementation with secoisolariciresinol diglycoside (SDG) reduces experimental metastasis of melanoma cells in mice

We investigated the effect of dietary supplementation with secoisolariciresinol diglycoside (SDG), a lignan precursor isolated from flaxseed, on experimental metastasis of B16BL6 murine melanoma cells in C57BL/6 mice. Four diets were compared: a basal diet (control group) and the basal diet supplemented with SDG at 73, 147 or 293 μmol/kg (equivalent to SDG provided in the 2.5, 5 or 10% flaxseed diet). Mice were fed the diet for 2 weeks before and after an intravenous injection of 0.6×105 tumor cells. At necropsy, the number and size of tumors that formed in the lungs were determined. The median number of tumors in the control group was 62, and those in the SDG-supplemented groups were 38, 36 and 29, respectively. The last was significantly different from the control (P<0.01). Dietary supplementation with SDG at 73, 147 and 293 μmol/kg also decreased tumor size (tumor cross-sectional area and volume) in a dose-dependent manner compared with the control values. These results show that SDG reduced pulmonary metastasis of melanoma cells and inhibited the growth of metastatic tumors that formed in the lungs. It is concluded that dietary supplementation with SDG reduces experimental metastasis of melanoma cells in mice.