Ex vivo resistance in childhood acute lymphoblastic leukemia: Correlations between BCRP, MRP1, MRP4 and MRP5 ABC transporter expression and intracellular methotrexate polyglutamate accumulation

Leuk Res. 2019 Apr:79:45-51. doi: 10.1016/j.leukres.2019.02.008. Epub 2019 Feb 23.


Chemoresistance is an important factor in the treatment failure of childhood acute lymphoblastic leukemia (ALL). One underlying mechanism of chemoresistance involves (over)expression of ATP-dependent drug efflux transporters such as multidrug resistance protein 1-5 (MRP1-5) and breast cancer resistance protein (BCRP), which can extrude the important antileukemia drug methotrexate (MTX). Survival of childhood ALL critically depends on the leukemic blasts' capacity for intracellular retention of MTX and MTX-polyglutamates. This pilot study assessed whether expression of MRP1, MRP4, MRP5 and BCRP (real-time PCR) in primary childhood ALL blasts (n = 23) correlated with ex vivo resistance to MTX (assayed by in situ thymidylate synthase inhibition assay (TSIA)), ex vivo accumulation of (radioactive) MTX polyglutamates, and patient survival. Results show that high MRP4 expression is correlated with ex vivo MTX resistance assayed by TSIA (P = 0.01). Moreover, elevated MRP4 and BCRP expression correlated with lower accumulation of MTX-PGs (P = 0.004 and P = 0.03, respectively). Combined high expression of BCRP and MRP4 even further impacted reduced MTX-PG accumulation (P = 0.02). Overall survival was lower (P logrank = 0.04) in children with ALL cells which featured a relatively high expression of both BCRP and MRP4 transporters. These results underscore the impact of high drug efflux transporter expression, notably MRP4 and BCRP, in diminished MTX response in childhood ALL.

Keywords: ABC transporters; BCRP; Childhood acute lymphoblastic leukemia; MRP1; MRP4; MRP5; Methotrexate; Methotrexate polyglutamates (MTX-PG); Multidrug resistance (MDR).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily G, Member 2 / genetics*
  • ATP-Binding Cassette Transporters / genetics
  • Adolescent
  • Child
  • Child, Preschool
  • Cytoplasm / drug effects
  • Cytoplasm / metabolism
  • Drug Resistance, Neoplasm / genetics*
  • Drug Screening Assays, Antitumor
  • Female
  • Gene Expression Regulation, Leukemic / drug effects
  • Humans
  • Infant
  • Infant, Newborn
  • Male
  • Methotrexate / analogs & derivatives*
  • Methotrexate / metabolism
  • Methotrexate / therapeutic use*
  • Multidrug Resistance-Associated Proteins / genetics*
  • Neoplasm Proteins / genetics*
  • Pilot Projects
  • Polyglutamic Acid / analogs & derivatives*
  • Polyglutamic Acid / metabolism
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma* / drug therapy
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma* / genetics
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma* / pathology
  • Primary Cell Culture
  • Tumor Cells, Cultured


  • ABCC4 protein, human
  • ABCC5 protein, human
  • ABCG2 protein, human
  • ATP Binding Cassette Transporter, Subfamily G, Member 2
  • ATP-Binding Cassette Transporters
  • Multidrug Resistance-Associated Proteins
  • Neoplasm Proteins
  • Polyglutamic Acid
  • methotrexate polyglutamate
  • multidrug resistance-associated protein 1
  • Methotrexate