Multiple mechanisms of resistance to methotrexate and novel antifolates in human CCRF-CEM leukemia cells and their implications for folate homeostasis

Robert Mauritz, Godefridus J. Peters, David G. Priest, Yehuda G. Assaraf, Stavit Drori, Ietje Kathmann, Paul Noordhuis, Marlene A. Bunni, Andre Rosowsky, Jan H. Schornagel, Herbert M. Pinedo, Gerrit Jansen

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


We determined the mechanisms of resistance of human CCRF-CEM leukemia cells to methotrexate (MTX) vs. those to six novel antifolates: the polyglutamatable thymidylate synthase (TS) inhibitors ZD1694, multitargeted antifolate, pemetrexed, ALIMTA (MTA) and GW1843U89, the non-polyglutamatable inhibitors of TS, ZD9331, and dihydrofolate reductase, PT523, as well as DDATHF, a polyglutamatable glycinamide ribonucleotide transformylase inhibitor. CEM cells were made resistant to these drugs by clinically relevant intermittent 24 hr exposures to 5-10 μM of MTX, ZD1694, GW1843U89, MTA and DDATHF, by intermittent 72 hr exposures to 5 μM of ZD9331 and by continuous exposure to stepwise increasing concentrations of ZD9331, GW1843U89 and PT523. Development of resistance required only 3 cycles of intermittent drug exposure to ZD1694 and MTA, but 5 cycles for MTX, DDATHF and GW1843U89 and 8 cycles for ZD9331. The predominant mechanism of resistance to ZD1694, MTA, MTX and DDATHF was impaired polyglutamylation due to ∼ 10-fold decreased folylpolyglutamate synthetase activity. Resistance to intermittent exposures to GW1843U89 and ZD9331 was associated with a 2-fold decreased transport via the reduced folate carrier (RFC). The CEM cell lines resistant to intermittent exposures to MTX, ZD1694, MTA, DDATHF, GW1843U89 and ZD9331 displayed a depletion (up to 4-fold) of total intracellular reduced folate pools. Resistance to continuous exposure to ZD9331 was caused by a 14-fold increase in TS activity. CEM/GW70, selected by continuous exposure to GW1843U89 was 50-fold resistant to GW1843U89, whereas continuous exposure to PT523 generated CEM/PT523 cells that were highly resistant (1550-fold) to PT523. Both CEM/GW70 and CEM/PT523 displayed cross-resistance to several antifolates that depend on the RFC for cellular uptake, including MTX (95- and 530-fold). CEM/GW70 cells were characterized by a 12-fold decreased transport of [3H]MTX. Interestingly, however, CEM/GW70 cells displayed an enhanced transport of folic acid, consistent with the expression of a structurally altered RFC resulting in a 2.6-fold increase of intracellular folate pools. CEM/PT523 cells displayed a markedly impaired (100-fold) transport of [3H]MTX along with 12-fold decreased total folate pools. In conclusion, multifunctional mechanisms of resistance in CEM cells have a differential impact on cellular folate homeostasis: decreased polyglutamylation and transport defects lead to folate depletion, whereas a structurally altered RFC protein can provoke expanded intracellular folate pools.

Original languageEnglish (US)
Pages (from-to)105-115
Number of pages11
JournalBiochemical Pharmacology
Issue number2
StatePublished - Jan 15 2002
Externally publishedYes


  • Antifolate resistance
  • Folate homeostasis
  • Folylpolyglutamate synthetase
  • Polyglutamylation
  • Reduced folate carrier
  • Thymidylate synthase

ASJC Scopus subject areas

  • Pharmacology


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