title: Dynamics of antifolate transport via the reduced folate carrier and the membrane folate receptor in murine leukaemia cells in vitro and in vivo.
abstract: Murine L1210 leukaemia cells expressing either the reduced folate carrier (RFC) or the membrane folate receptor (MFR) were studied in vitro and in vivo to assess the dynamics of membrane transport of two categories antifolates; folate-based inhibitors of dihydrofolate reductase (methotrexate, edatrexate, aminopterin, PT523, and PT644) and thymidylate synthase (TS) [CB3717, raltitrexed, plevitrexed (BGC9331), pemetrexed and GW1843]. The potency of in situ inhibition of TS was used as an endpoint to analyze the in vitro dynamics of RFC/MFR-membrane transport of these antifolates. Both for L1210-RFC and L1210-MFR cells, the potency of in situ TS inhibition was closely correlated with increasing affinities of these transporters for the antifolates (r = 0.64, P < 0.05 and r = -0.65, P < 0.05, respectively). Within the group of antifolates for which MFR had a low binding affinity, those that had the ability to become polyglutamylated, were more potent inhibitors of TS in situ activity than non-polyglutamatable antifolates. In vivo activity of methotrexate, edatrexate, raltitrexed and pemetrexed was assessed in L1210-RFC and L1210-MFR bearing mice that were fed either a standard or a folate-deficient chow. Dietary folate depletion significantly reduced the MTD for methotrexate (sevenfold), edatrexate (sevenfold), raltitrexed (50-fold) and pemetrexed (150-fold). Based on increased life spans, antitumor effects of methotrexate and edatrexate were markedly better in L1210-RFC bearing mice on the folate-deficient chow (ILS: 455 and 544%, respectively) than on standard chow (ILS: 213 and 263%, respectively). No therapeutic effects of methotrexate and edatrexate were observed for L1210-MFR bearing mice on either chow condition, which may be consistent with the low binding affinity for MFR. Irrespective of the folate diet status, pemetrexed and raltitrexed were inactive against both L1210-RFC and L1210-MFR bearing mice, which may be due to high circulating plasma thymidine levels. Collectively, this study underscores that modulation of dietary folate status can provide a basis within which the therapeutic effect of antifolates may be further improved.
authors.affiliation: Department of Medical Oncology, VU University Medical Center, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Mauritz
authors.forename: Godefridus J
authors.initials: GJ
authors.lastname: Peters
authors.forename: Ietje
authors.initials: I
authors.lastname: Kathmann
authors.forename: Habte
authors.initials: H
authors.lastname: Teshale
authors.forename: Paul
authors.initials: P
authors.lastname: Noordhuis
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Comijn
authors.forename: Herbert M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
mesh_terms: D000818:Animals; D001202:Ascitic Fluid / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000187:drug effects; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D005493:Folic Acid Antagonists / Q000493:pharmacokinetics* / Q000627:therapeutic use; D005494:Folic Acid Deficiency / Q000378:metabolism; D066298:In Vitro Techniques; D007939:Leukemia L1210 / Q000175:diagnosis* / Q000473:pathology; D020714:Maximum Tolerated Dose; D026901:Membrane Transport Proteins / Q000378:metabolism*; D051379:Mice; D008811:Mice, Inbred DBA; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011099:Polyglutamic Acid / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D058978:Reduced Folate Carrier Protein; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors
chemical_list: D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D005493:Folic Acid Antagonists; D026901:Membrane Transport Proteins; D009363:Neoplasm Proteins; D011956:Receptors, Cell Surface; D058978:Reduced Folate Carrier Protein; C548700:Slc19a1 protein, mouse; D011099:Polyglutamic Acid; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase