The murine embryonic limb at day 14 of gestation suppresses tumor formation by melanoma cells. Conditioned media of embryonic limbs have been found cytotoxic for B16 melanoma cells. The cytotoxicity is due to the catabolism of polyamines in the limb bud extracts by an amine oxidase in the serum supplement of the culture medium. However, a polyamine oxidase activity, similar to that in adult rat liver, is also detectable in homogenates of embryonic limbs. Thus, the embryonic limb contains the necessary components to produce polyamine-derived cytotoxic metabolites, which are present at the time programmed cell death occurs. This leads to the hypothesis that injected melanoma cells are killed incidentally by the mechanism that mediates programmed cell death.

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This work was supported in part by a gift from RJR Nabisco, Inc., and grants from the NIH, Ca 35367 and Ca-47369, and an American Cancer Society Institutional grant.

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