title: The mechanism of transport of the multitargeted antifolate (MTA) and its cross-resistance pattern in cells with markedly impaired transport of methotrexate.
abstract: MTA (LY231514) is an antifolate that targets multiple folate-dependent enzymes. In this report, MTA transport was characterized in wild-type L1210 cells and variants with impaired membrane transport or polyglutamation. MTA influx via the reduced folate carrier was somewhat faster (approximately 30%) than that for methotrexate (MTX). Unlike MTX, MTA was rapidly polyglutamated in L1210 cells; hence, a folylpoly-gamma-glutamate synthetase-deficient L1210 variant was used to assess net transport and efflux properties. The MTA transmembrane gradient for exchangeable drug was 2.5 times greater than the MTX gradient, attributable primarily to an efflux rate constant 40% that of MTX. No MTA was bound to dihydrofolate reductase. When grown with folic acid, MTX-resistant L1210 variants with mutations in the reduced folate carrier demonstrated cross-resistance to MTA, markedly reduced MTA accumulation, and only a slightly decreased intracellular folate cofactor pool as compared to L1210 cells. However, when 5-formyltetrahydrofolate was the growth substrate, these MTX-resistant cells were less resistant or negligibly resistant to MTA, accumulated more MTA, and had a lower folate pool as compared to L1210 cells. MTA activity and the intracellular folate pool in L1210 cells were inversely related. These data indicate that MTA polyglutamation in L1210 cells is favored by both the generation of high intracellular drug levels and high MTA affinity for FPGS relative to MTX. Cells resistant to MTX because of impaired transport may retain appreciable sensitivity to MTA because of a concurrent reduction in tetrahydrofolate cofactor transport resulting in cellular folate depletion, which diminishes endogenous folate suppression of MTA polyglutamation.
authors.affiliation: Department of Medicine, Albert Einstein Comprehensive Cancer Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: R
authors.initials: R
authors.lastname: Zhao
authors.forename: S
authors.initials: S
authors.lastname: Babani
authors.forename: F
authors.initials: F
authors.lastname: Gao
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: I D
authors.initials: ID
authors.lastname: Goldman
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D019008:Drug Resistance, Neoplasm; D005492:Folic Acid / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000493:pharmacokinetics*; D005971:Glutamates / Q000493:pharmacokinetics*; D006147:Guanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D002955:Leucovorin / Q000378:metabolism / Q000494:pharmacology; D007939:Leukemia L1210 / Q000201:enzymology / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008727:Methotrexate / Q000493:pharmacokinetics*; D051379:Mice; D000068437:Pemetrexed; D010453:Peptide Synthases / Q000378:metabolism; D011099:Polyglutamic Acid / Q000096:biosynthesis; D011454:Prostaglandins A / Q000494:pharmacology
chemical_list: D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D005493:Folic Acid Antagonists; D005971:Glutamates; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011454:Prostaglandins A; C492292:Slc19a2 protein, mouse; D000068437:Pemetrexed; D011099:Polyglutamic Acid; D006147:Guanine; D005492:Folic Acid; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase; D002955:Leucovorin; C100573:prostaglandin A1; D008727:Methotrexate