This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend 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 Goldenberg, G. J. Articles by Cormack, D. V. Search for Related Content PubMed PubMed Citation Articles by Goldenberg, G. J. Articles by Cormack, D. V.

Mechanism of Cyclophosphamide Transport by L5178Y Lymphoblasts in Vitro¹

Department of Medicine, University of Manitoba, and The Manitoba Institute of Cell Biology [G. J. G., H. B. L.] and Department of Physics, The Manitoba Cancer Treatment and Research Foundation and the Department of Medical Microbiology, University of Manitoba [D. V. C.], Winnipeg, Manitoba, R3E 0V9, Manitoba, Canada

Mechanism of transport of the alkylating agent cyclophosphamide-¹⁴C was investigated in L5178Y lymphoblasts in vitro. A time course of cyclophosphamide uptake showed a rapid, initial phase, probably due to binding of drug to the cell surface. Subsequent uptake into the cells was carrier mediated and consisted of two components. Analysis of cyclophosphamide uptake over a 40-fold range of drug concentration showed biphasic kinetics with evidence of saturation only at low drug concentrations whereas, at high drug levels, uptake occurred by a second transport system that was technically nonsaturable. After correction for binding and the interaction of two-component transport, kinetic parameters for low-dose transport consisted of a Michaelis constant K_m (mean ± S.E.) of 0.39 ± 0.03 mM and a transport capacity V_max of 0.49 ± 0.07 x 10^-17 moles/min/cell. At high-dose cyclophosphamide transport, the apparent K_m was 75 ± 29 mM, and the V_max was 49 ± 14 x 10^-17 moles/min/cell. Both low- and high-dose cyclophosphamide transport were temperature sensitive and partially dependent on sodium. In addition, low-dose transport was inhibited by oligomycin and cyanide. Other alkylating agents and several naturally occurring substrates did not inhibit cyclophosphamide transport; thus, a native substrate was not identified for the cyclophosphamide carrier, and transport was by a mechanism separate from that of other alkylating agents.

Evidence that low-dose cyclophosphamide transport was mediated by a facilitated diffusion process was that uptake obeyed saturation kinetics, was temperature and sodium dependent, was partially dependent on metabolic energy, and cell/medium concentration gradients did not exceed unity. Although high-dose drug uptake failed to show saturation kinetics, the demonstration of temperature and sodium dependence also suggested that high-dose uptake may be carrier mediated.

Cyclophosphamide uptake by chick embryo liver cells was examined also; uptake was temperature sensitive and exhibited biphasic kinetics similar to that observed in L5178Y cells, suggesting a similar mechanism of drug transport in normal liver and leukemic cells.

¹ This work was supported by a grant from the National Cancer Institute of Canada.

² Clinical Research Associate of the National Cancer Institute of Canada.

Received 6/ 3/74. Accepted 8/27/74.

This article has been cited by other articles:

				L. Panasci, J.-P. Paiement, G. Christodoulopoulos, A. Belenkov, A. Malapetsa, and R. Aloyz Chlorambucil Drug Resistance in Chronic Lymphocytic Leukemia: The Emerging Role of DNA Repair Clin. Cancer Res., March 1, 2001; 7(3): 454 - 461. [Abstract] [Full Text]

				C. V. Uglea, I. N. Albu, A. Vatajanu, M. Croitoru, D. Iurea, M. Isac, and R. M. Ottenbrite Polyanionic Polymers. I. Synthesis, Characterization, and Potential Medical Applications of Benzocaine Modified Carboxymethylcellulose Journal of Bioactive and Compatible Polymers, January 1, 1994; 9(4): 448 - 461. [Abstract] [PDF]