title: Functional loss of the reduced folate carrier enhances the antitumor activities of novel antifolates with selective uptake by the proton-coupled folate transporter.
abstract: Uptake of 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolates with four or three bridge carbons [compound 1 (C1) and compound 2 (C2), respectively] into solid tumors by the proton-coupled folate transporter (PCFT) represents a novel therapeutic strategy that harnesses the acidic tumor microenvironment. Although these compounds are not substrates for the reduced folate carrier (RFC), the major facilitative folate transporter, RFC expression may alter drug efficacies by affecting cellular tetrahydrofolate (THF) cofactor pools that can compete for polyglutamylation and/or binding to intracellular enzyme targets. Human tumor cells including wild-type (WT) and R5 (RFC-null) HeLa cells express high levels of PCFT protein. C1 and C2 inhibited proliferation of R5 cells 3 to 4 times more potently than WT cells or R5 cells transfected with RFC. Transport of C1 and C2 was virtually identical between WT and R5 cells, establishing that differences in drug sensitivities between sublines were independent of PCFT transport. Steady-state intracellular [³H]THF cofactors derived from [³H]5-formyl-THF were depleted in R5 cells compared with those in WT cells, an effect exacerbated by C1 and C2. Whereas C1 and C2 polyglutamates accumulated to similar levels in WT and R5 cells, there were differences in polyglutamyl distributions in favor of the longest chain length forms. In severe combined immunodeficient mice, the antitumor efficacies of C1 and C2 were greater toward subcutaneous R5 tumors than toward WT tumors, confirming the collateral drug sensitivities observed in vitro. Thus, solid tumor-targeted antifolates with PCFT-selective cellular uptake should have enhanced activities toward tumors lacking RFC function, reflecting contraction of THF cofactor pools.
authors: Graduate Program in Cancer Biology and Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan, USA.
authors: Sita Kugel
authors: SK
authors: Desmoulin
authors: Lei
authors: L
authors: Wang
authors: Lisa
authors: L
authors: Polin
authors: Kathryn
authors: K
authors: White
authors: Juiwanna
authors: J
authors: Kushner
authors: Mark
authors: M
authors: Stout
authors: Zhanjun
authors: Z
authors: Hou
authors: Christina
authors: C
authors: Cherian
authors: Aleem
authors: A
authors: Gangjee
authors: Larry H
authors: LH
authors: Matherly
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D005493:Folic Acid Antagonists / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D058979:Proton-Coupled Folate Transporter / Q000378:metabolism*; D011624:Pteroylpolyglutamic Acids / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism / Q000494:pharmacology*; D011758:Pyrroles / Q000378:metabolism / Q000494:pharmacology*; D058978:Reduced Folate Carrier Protein / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013763:Tetrahydrofolates / Q000378:metabolism; D013876:Thiophenes / Q000378:metabolism / Q000494:pharmacology*; D059016:Tumor Microenvironment
chemical_list: D000970:Antineoplastic Agents; D005493:Folic Acid Antagonists; D058979:Proton-Coupled Folate Transporter; D011624:Pteroylpolyglutamic Acids; D011743:Pyrimidines; D011758:Pyrroles; D058978:Reduced Folate Carrier Protein; D013763:Tetrahydrofolates; D013876:Thiophenes