Drug Metabolism and Pharmacokinetics
Online ISSN : 1880-0920
Print ISSN : 1347-4367
ISSN-L : 1347-4367
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Chiral Recognition of Amethopterin Enantiomers by the Reduced Folate Carrier in Caco-2 Cells
Tomoya NARAWAYasuyuki TSUDATomoo ITOH
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2007 Volume 22 Issue 1 Pages 33-40

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Abstract

  Stereoselectivity of the human reduced folate carrier (RFC1) in Caco-2 cells was examined using methotrexate (L-amethopterin, L-MTX) and its antipode (D-amethopterin, D-MTX) as model substrates. The initial uptake rate of L-MTX into Caco-2 cells followed Michaelis-Menten kinetics with a Km value of approximately 1 μM. The Eadie-Hofstee plot of the RFC1-mediated L-MTX uptake showed that it was mediated by a single transport system, RFC1. Dixon plots revealed that L-MTX uptake was inhibited competitively by folic acid (FA), L-MTX and D-MTX, with Ki values of approximately 0.8, 1.5 and 180 μM, respectively. The results showed that the affinities of FA and L-MTX to RFC1 were approximately 120-fold greater than that of D-MTX. The uptake of L- and D-MTX into Caco-2 cells was also measured using LC-MS/MS analysis, which revealed that the L-MTX uptake was at least 7-fold greater than that of D-MTX. The present study revealed significant stereoselectivity of RFC1 toward amethopterin enantiomers with the L-isomer being much more favored.

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© 2007 by The Japanese Society for the Study of Xenobiotics
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