The effect of the methionine antagonist l-2-amino-4-methoxy- trans-3-butenoic acid on the growth and metabolism of walker carcinosarcoma in vitro

Abstract

l-2-Amino-4-methoxy- trans-3-butenoic acid (Ro07–7957) is a structural analogue ot methionine with a potent tumour growth inhibitory activity in vitro. This agent is transported by the methionine carrier system in Walker carcinoma and causes an initial dose-related depression of the acid-soluble pool of methionine. The depression of the incorporation of l-[methyl- 3H]methionine into acid-insoluble material in the presence of Ro07–7957 is greater than that of l-[2- 3H]methionine and l-[4,5( n)- 3H]lysine, suggesting an inhibition of the methylation of macromolecules as well as an inhibition of protein synthesis. There is no effect of the drug on the incorporation of [ 3H]thymidine into acid-insoluble material during the first 24 hr after treatment, while the incorporation of [5- 3H]uridine is stimulated 40 per cent. The ratio of incorporation of l-[2- 3H]methionine to l-[methyl- 14C]methionine into proteins increases with increasing drug concentration, suggesting an inhibition of protein methylation. This effect is more prevalent at 24 hr than after 8 hr of treatment. The specific activity of tRNA methylase using E. coli MRE 600 tRNA as substrate is elevated more than two-fold within 24 hr after treatment, as is also the intracellular level of S-adenosyl- l-methionine (SAM). The effects of this agent on macromolecular metabolism is in some respects similar to that observed with the carcinogen ethionine, and suggests the initial formation of an inhibitor of methylation, which is followed by a later attempt by the cells to maintain homeostasis by production of increased amounts of tRNA methylating enzymes.