The role of methionine in methotrexate-sensitive and methotrexate-resistant mouse leukemia L1210 cells.

A mouse L1210 leukemia cell line was made 25-fold resistant to methotrexate (MTX) and had altered methionine transport and metabolism. L1210 cells resistant to methotrexate also had a 50-fold decrease in the exogenous methionine requirement for optimal cell growth compared to the parent cells. This change in methionine requirement was associated with differences in methionine metabolism between MTX-sensitive and MTX-resistant cell lines. Analysis of amino acid transport systems revealed different Kt and Vmax properties of methionine and nonmetbolizable amino acid analogues. There was a greater than twofold decrease in the initial sodium-dependent uptake of methionine in the resistant cells. Amino acid competition experiments revealed altered substrate specificities in the resistant cells. The cellular alterations occurring upon resistance may result from methotrexate-membrane interactions, and have been previously observed in cisplatinum-resistant cells. Thus modulation of methionine metabolism may provide the biochemical basis for MTX and cisplatinum collateral resistance.