The human multidrug resistance protein MRP5 transports folates and can mediate cellular resistance against antifolates

Peter Wielinga, Jan Hendrik Hooijberg, Sjofn Gunnarsdottir, Ietje Kathmann, Glen Reid, Noam Zelcer, Kasper van der Born, Marcel de Haas, Ingrid van der Heijden, Gertjan Kaspers, Jan Wijnholds, Gerrit Jansen, Godefridus Peters, Piet Borst

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108 Citations (Scopus)


Members of the multidrug resistance protein family, notably MRP1-4/ABCC1-4, and the breast cancer resistance protein BCRP/ABCG2 have been recognized as cellular exporters for the folate antagonist methotrexate (MTX). Here we show that MRP5/ABCC5 is also an antifolate and folate exporter based on the following evidence: (a) Using membrane vesicles from HEK293 cells, we show that MRP5 transports both MTX (KM = 1.3 mmol/L and VMAX = 780 pmol per mg protein per minute) and folic acid (KM = 1.0 mmol/L and VMAX = 875 pmol per mg protein per minute). MRP5 also transports MTX-glu2 (KM = 0.7 mmol/L and VMAX = 450 pmol per mg protein per minute) but not MTX-glu3. (b) Both accumulation of total [3H]MTX and of MTX polyglutamates were significantly reduced in MRP5 overexpressing cells. (c) Cell growth inhibition studies with MRP5 transfected HEK293 cells showed that MRP5 conferred high-level resistance (>160-fold) against the antifolates MTX, GW1843, and ZD1694 (raltitrexed) in short-term (4 hours) incubations with high drug concentrations; this resistance was proportional to the MRP5 level. (d) MRP5-mediated resistance (8.5- and 2.1-fold) was also found in standard long-term incubations (72 hours) at low concentrations of ZD1694 and GW1843. These results show the potential of MRP5 to mediate transport of (anti)folates and contribute to resistance against antifolate drugs.

Original languageEnglish
Pages (from-to)4425-4430
Number of pages6
JournalCancer research
Issue number10
Publication statusPublished - 15 May 2005


  • Biological Transport
  • Cell Line
  • Folic Acid Antagonists/pharmacokinetics
  • Folic Acid/pharmacokinetics
  • Humans
  • Methotrexate/analogs & derivatives
  • Multidrug Resistance-Associated Proteins/metabolism
  • Polyglutamic Acid/analogs & derivatives
  • Substrate Specificity

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