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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1980 May;77(5):2919–2922. doi: 10.1073/pnas.77.5.2919

Methotrexate polyglutamate synthesis by cultured human breast cancer cells.

R L Schilsky, B D Bailey, B A Chabner
PMCID: PMC349517  PMID: 6156458

Abstract

We studied the conversion of methotrexate to poly-gamma-glutamyl derivatives by cultured human breast cancer cells. After incubation with 2 micro M [3',5',9-3H]methotrexate, MCF-7 cells were washed free of extracellular drug and were boiled to lyse cells and to release drug bound to dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3). The supernatant fraction was chromatographed on Sephadex G-15 to separate parent drug from polyglutamate forms. These cells rapidly and quantitatively converted methotrexate to polyglutamates, such that after 24 hr of incubation, 70 +/- (SEM) 3% of intracellular methotrexate existed as polyglutamates. Examination of that portion of intracellular methotrexate specifically bound to dihydrofolate reductase indicated that, with prolonged incubation, methotrexate polyglutamates become the predominant drug form bound to the enzyme. These studies demonstrate that methotrexate polyglutamates are readily formed in human tumor cells and bind to dihydrofolate reductase. Because these forms of the drug may be selectively retained within the cell, they may be important determinants of the duration of action and, ultimately, the cytotoxicity of methotrexate in human solid tumors.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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