title: Evidence for negative feedback of extracellular methotrexate on blasts of acute lymphoblastic leukemia in vitro.
abstract: OBJECTIVE
  To explore the value of high-dose methotrexate (MTX).
  
  
  METHODS
  Blast cells from 15 patients with acute lymphoblastic leukemia.
  
  
  METHODS
  We compared uptake and polyglutamation of [3H]-MTX by freshly isolated leukemic blasts in vitro after 24-hour exposure to 1, 10, and 50 microM [3H]-MTX.
  
  
  RESULTS
  Mean MTX uptake (pmol/10(6) cells) was 0.78 +/- 0.19, 2.3 +/- 0.54, and 5.9 +/- 1.9, respectively, and mean polyglutamation was 82%, 66%, and 46%. Consequently, mean MTX polyglutamates were 0.68 +/- 0.18, 1.5 +/- 0.47, and 2.2 +/- 0.67 pmol/10(6) cells. Three of 15 patient samples had no detectable polyglutamation of MTX at 50 microM but MTX polyglutamates were detectable at 1 microM. Two of these three had a decrease in MTX polyglutamates at 10 versus 1 microM. In eight precursor B cell samples there was a significant difference in median MTX polyglutamates at 1 versus 10 microM but not 10 versus 50 microM.
  
  
  CONCLUSIONS
  Increasing extracellular MTX concentrations may be counterproductive for some patients with acute lymphoblastic leukemia. If MTX polyglutamates are important for efficacy, optimal delivery of MTX may have to be determined by individual metabolism rather than by targeting a specific drug concentration.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Hum
authors.forename: A K
authors.initials: AK
authors.lastname: Smith
authors.forename: R H
authors.initials: RH
authors.lastname: Lark
authors.forename: N J
authors.initials: NJ
authors.lastname: Winick
authors.forename: B A
authors.initials: BA
authors.lastname: Kamen
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism* / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D008727:Methotrexate / Q000378:metabolism* / Q000494:pharmacology*; D011099:Polyglutamic Acid / Q000378:metabolism; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000473:pathology*; D014407:Tumor Cells, Cultured
chemical_list: D000964:Antimetabolites, Antineoplastic; D011099:Polyglutamic Acid; D008727:Methotrexate