This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jackson, R. C. Articles by Harrap, K. R. Search for Related Content PubMed PubMed Citation Articles by Jackson, R. C. Articles by Harrap, K. R.

Intrinsic Resistance to Methotrexate of Cultured Mammalian Cells in Relation to the Inhibition Kinetics of Their Dihydrofolate Reductases¹

Department of Applied Biochemistry, Institute of Cancer Research, Sutton, Surrey, England

Four cultured mammalian cell lines, differing in intrinsic resistance to methotrexate over a 70-fold range, have been compared with respect to several biochemical factors that might influence response to the drug. Cellular activity of the enzymes dihydrofolate reductase and thymidylate synthetase and the total levels of folate cofactors did not vary by more than a factor of 2 among the cell lines. All the cell types were able to transport extracellular methotrexate efficiently across the cell membrane, and at comparable rates. A kinetic study of highly purified dihydrofolate reductases from the four sources revealed small differences in the K_m values for dihydrofolate and reduced nicotinamide adenine dinucleotide phosphate. A study was made of the inhibition of the four dihydrofolate reductases by methotrexate, and K_i values were obtained by fitting the Zone B equation of Goldstein (Goldstein, A., J. Gen. Physiol., 27: 529–580, 1944) to the resulting data. Values of K_i determined by this method correlated with intrinsic resistance of the cell lines and showed a 25-fold range from the most sensitive to the most resistant line. It is concluded that the response of a cell to methotrexate is significantly influenced by the dissociation constant of its dihydrofolate reductase-methotrexate complex.

¹ This work was supported by grants from the Medical Research Council, the Cancer Research Campaign, and the Ludwig Institute for Cancer Research, London Branch.

² Present address: Laboratory for Experimental Oncology, Indiana University, Indianapolis, Ind. 46202.

Received 6/11/75. Accepted 2/16/76.

This article has been cited by other articles:

				M. Maguire, P. C. Nield, T. Devling, R. E. Jenkins, B. K. Park, R. Polanski, N. Vlatkovic, and M. T. Boyd MDM2 Regulates Dihydrofolate Reductase Activity through Monoubiquitination Cancer Res., May 1, 2008; 68(9): 3232 - 3242. [Abstract] [Full Text] [PDF]

				M. J. Barnes, E. J. Estlin, G. A. Taylor, G. W. Aherne, A. Hardcastle, J. J. McGuire, J. A. Calvete, J. Lunec, A. D. J. Pearson, and D. R. Newell Impact of Polyglutamation on Sensitivity to Raltitrexed and Methotrexate in Relation to Drug-induced Inhibition of de Novo Thymidylate and Purine Biosynthesis in CCRF-CEM Cell Lines Clin. Cancer Res., September 1, 1999; 5(9): 2548 - 2558. [Abstract] [Full Text] [PDF]