Cytotoxicity of spergualin and amine oxidase activity in medium

The cytotoxicity of spergualin on cultured L5178Y cells is dependent on the kind of serum contained in culture media. Spergualin has stronger cytotoxicity to L5178Y cells in calf serum (IC50 = 2 micrograms/ml) than in horse serum (IC50 = 60 micrograms/ml). This was thought to be caused by amine oxidase in sera. Because calf serum was rich in amine oxidase and horse serum was very poor. Spergualin was found to be oxidized by either calf serum or amine oxidase purified from beef plasma. Aminoguanidine, an amine oxidase inhibitor suppressed the spergualin effect to inhibit the growth of L5178Y cells in calf serum to the level in horse serum. On the other hand, in horse serum the spergualin cytotoxicity was enhanced by addition of amine oxidase. These results suggested to us that spergualin might be inactive in itself and that the amine oxidase-oxidized product might play an essential role in inhibiting the growth of cells.