5-amino-4-imidazolecarboxamide riboside potentiates both transport of reduced folates and antifolates by the human reduced folate carrier and their subsequent metabolism.
Transport is required before reduced folates and anticancer antifolates [e.g., methotrexate (MTX)] exert their physiologic functions or cytotoxic effects. The folate/antifolate transporter with the widest tissue distribution and greatest activity is the reduced folate carrier (RFC). There is little evidence that RFC-mediated influx is posttranscriptionally regulated. We show that [(3)H]MTX influx in CCRF-CEM human childhood T-leukemia cells is potentiated up to 6-fold by exogenous 5-amino-4-imidazolecarboxamide riboside (AICAr) in a AICAr and MTX concentration-dependent manner. Metabolism to more biologically active polyglutamate forms is also potentiated for MTX and other antifolates. That potentiation of influx by AICAr is mediated by effects on the RFC is supported by analyses +/-AICAr showing (a) similarity and magnitude of kinetic constants for [(3)H]MTX influx; (b) similarity of inhibitory potency of known RFC substrates; (c) lack of potentiation in a CCRF-CEM subline that does not express the RFC; and (d) similarity of time and temperature dependence. Potentiation occurs rapidly and does not require new protein synthesis. Effects of specific inhibitors of folate metabolism and the time and sequence of AICAr incubation with cells suggest that both dihydrofolate reductase inhibition and metabolism of AICAr are essential for potentiation. Acute folate deficiency or incubation of CCRF-CEM with AICAr-related metabolites (e.g., adenosine) does not initiate potentiation. AICAr increases growth inhibitory potency of MTX and aminopterin against CCRF-CEM cells when both AICAr and antifolate are present for the first 24 hours of a 120-hour growth period. AICAr is the first small molecule that regulates RFC activity.
Grace Cancer Drug Center, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, USA. John.McGuire@RoswellPark.edu
John J
JJ
McGuire
William H
WH
Haile
Chen-Chen
CC
Yeh
D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D045744:Cell Line, Tumor; D002648:Child; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005493:Folic Acid Antagonists / Q000378:metabolism / Q000493:pharmacokinetics; D006801:Humans; D007700:Kinetics; D015458:Leukemia, T-Cell / Q000188:drug therapy / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008727:Methotrexate / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics; D051026:Phosphoribosylglycinamide Formyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D011099:Polyglutamic Acid / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000493:pharmacokinetics; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000378:metabolism*; D058978:Reduced Folate Carrier Protein; D012265:Ribonucleotides / Q000494:pharmacology*; D013347:Subcellular Fractions; D013696:Temperature; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014316:Tritium
D005493:Folic Acid Antagonists; D026901:Membrane Transport Proteins; D058978:Reduced Folate Carrier Protein; D012265:Ribonucleotides; C548699:SLC19A1 protein, human; D014316:Tritium; D011099:Polyglutamic Acid; D000620:Aminoimidazole Carboxamide; C014085:methotrexate polyglutamate; D013940:Thymidylate Synthase; D051026:Phosphoribosylglycinamide Formyltransferase; C031143:AICA ribonucleotide; D008727:Methotrexate