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Defective transport is a common mechanism of acquired methotrexate resistance in acute lymphocytic leukemia and is associated with decreased reduced folate carrier expression. 1997

R Gorlick, and E Goker, and T Trippett, and P Steinherz, and Y Elisseyeff, and M Mazumdar, and W F Flintoff, and J R Bertino
Program of Molecular Pharmacology and Therapeutics, Memorial Sloan-Kettering Cancer Center, New York 10021, USA.

Methotrexate (MTX) transport was examined in 27 patients with untreated acute lymphocytic leukemia (ALL) and 31 patients with relapsed ALL using a previously described fluorescent MTX analog (PT430) displacement assay (Blood 80:1158, 1992). Only 13% of untreated patients were considered to have impaired MTX transport, whereas more than 70% of relapsed patients had evidence of impaired MTX transport. To further characterize the basis for this defect, Northern analyses for the reduced folate carrier (RFC) were performed on the RNA available from the leukemic blasts of 24 patients in whom MTX transport had been measured. Six of nine samples with impaired MTX transport had decreased RFC expression (one had no detectable RFC expression), while three had no decrease in RFC expression. None of 15 samples with normal MTX transport had decreased RFC expression. A reverse-transcriptase polymerase chain reaction (RT-PCR) assay was developed to quantitate RFC mRNA expression more accurately. Decreased RFC expression was demonstrated in six of the nine samples with impaired MTX transport, confirming the results obtained by Northern blot. These data indicate decreased RFC expression associated with impaired MTX transport is observed in relapsed ALL following treatment with MTX-containing therapy.

UI MeSH Term Description Entries
D008565 Membrane Proteins Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors. Cell Membrane Protein,Cell Membrane Proteins,Cell Surface Protein,Cell Surface Proteins,Integral Membrane Proteins,Membrane-Associated Protein,Surface Protein,Surface Proteins,Integral Membrane Protein,Membrane Protein,Membrane-Associated Proteins,Membrane Associated Protein,Membrane Associated Proteins,Membrane Protein, Cell,Membrane Protein, Integral,Membrane Proteins, Integral,Protein, Cell Membrane,Protein, Cell Surface,Protein, Integral Membrane,Protein, Membrane,Protein, Membrane-Associated,Protein, Surface,Proteins, Cell Membrane,Proteins, Cell Surface,Proteins, Integral Membrane,Proteins, Membrane,Proteins, Membrane-Associated,Proteins, Surface,Surface Protein, Cell
D008727 Methotrexate An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of TETRAHYDROFOLATE DEHYDROGENASE and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA. Amethopterin,Methotrexate Hydrate,Methotrexate Sodium,Methotrexate, (D)-Isomer,Methotrexate, (DL)-Isomer,Methotrexate, Dicesium Salt,Methotrexate, Disodium Salt,Methotrexate, Sodium Salt,Mexate,Dicesium Salt Methotrexate,Hydrate, Methotrexate,Sodium, Methotrexate
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D001752 Blast Crisis An advanced phase of chronic myelogenous leukemia, characterized by a rapid increase in the proportion of immature white blood cells (blasts) in the blood and bone marrow to greater than 30%. Blast Phase,Blast Crises,Blast Phases,Crises, Blast,Crisis, Blast,Phase, Blast,Phases, Blast
D002352 Carrier Proteins Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes. Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier
D002648 Child A person 6 to 12 years of age. An individual 2 to 5 years old is CHILD, PRESCHOOL. Children
D002675 Child, Preschool A child between the ages of 2 and 5. Children, Preschool,Preschool Child,Preschool Children
D004351 Drug Resistance Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration. Resistance, Drug
D005452 Fluoresceins A family of spiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3-one derivatives. These are used as dyes, as indicators for various metals, and as fluorescent labels in immunoassays. Tetraiodofluorescein
D005492 Folic Acid A member of the vitamin B family that stimulates the hematopoietic system. It is present in the liver and kidney and is found in mushrooms, spinach, yeast, green leaves, and grasses (POACEAE). Folic acid is used in the treatment and prevention of folate deficiencies and megaloblastic anemia. Pteroylglutamic Acid,Vitamin M,Folacin,Folate,Folic Acid, (D)-Isomer,Folic Acid, (DL)-Isomer,Folic Acid, Calcium Salt (1:1),Folic Acid, Monopotassium Salt,Folic Acid, Monosodium Salt,Folic Acid, Potassium Salt,Folic Acid, Sodium Salt,Folvite,Vitamin B9,B9, Vitamin

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