title: Stereoselective recognition of amethopterin enantiomers by the rat proton-coupled folate transporter.
abstract: The stereoselective transport of methotrexate (L-amethopterin, L-MTX) and its enantiomer (D-amethopterin, D-MTX) by the rat proton-coupled folate transporter (rPCFT) were examined using rPCFT-expressing HEK293 cells. The initial rate of uptake of [3H]-L-MTX by the rPCFT followed Michaelis-Menten kinetics, with a Km value of 2.1 µM. Dixon plots revealed that the uptake of L-MTX by the rPCFT was inhibited in a competitive manner by unlabeled L-MTX and D-MTX, with Ki values of approximately 1.3 and 150 µM, respectively. The initial rate of uptake of D-MTX by the rPCFT also followed Michaelis-Menten kinetics, with a Km value of 190 µM. The results of the current study demonstrate that the different enantiomers of MTX are transported in a highly stereoselective manner by the rPCFT, with the uptake clearance of L-MTX being approximately 46-fold greater than that of D-MTX. The observed stereoselectivity of the rPCFT was found to be comparable with that of the human PCFT.
authors.affiliation: School of Pharmacy, Kitasato University.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Narawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Yano
authors.forename: Tomoo
authors.initials: T
authors.lastname: Itoh
mesh_terms: D000818:Animals; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008727:Methotrexate / Q000737:chemistry* / Q000378:metabolism*; D058979:Proton-Coupled Folate Transporter / Q000235:genetics / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism
chemical_list: D058979:Proton-Coupled Folate Transporter; C525126:Slc46a1 protein, rat; D008727:Methotrexate