Effect of lactose derivatives on metastatic potential of B16 melanoma cells

The effects of various sugars and sugar derivatives on lung colonization (i.e., metastatic deposition) of the highly metastatic BL6 clone of B16 mouse melanoma cells in syngeneic mice were studied, based on the assumption that carbohydrate structures, particularly those with a Gal terminus, play a crucial role in defining the metastatic potential of B16 cells. After incubation with sugar compounds (usually at 0.1 M concentration), tumor cells were injected via the tail vein into 8-week old female mice. Mice were sacrificed after 18-21 days, and tumor cell colonies in lung were counted under a dissecting microscope. Only methyl beta-D-lactoside and lacto-N-tetraose caused significant reduction (35-45% and 36%, respectively) of metastatic deposition compared to controls. Methyl beta-D-lactoside did not exhibit a growth inhibitory effect on BL6 tumor cells, as determined by several methods: in vitro [3H]thymidine incorporation assay, in vitro plating in RPMI-1640 medium culture under physiological conditions followed by cell counting, and in vivo subcutaneous inoculation of age-matched C57/BL mice followed by tumor measurement. These results indicate that the inhibitory effect of methyl beta-D-lactoside on tumor deposition was not related to its effect on tumor cell growth.