PT  - JOURNAL ARTICLE
AU  - Ilaria Badagnani
AU  - Richard A. Castro
AU  - Travis R. Taylor
AU  - Claire M. Brett
AU  - Conrad C. Huang
AU  - Douglas Stryke
AU  - Michiko Kawamoto
AU  - Susan J. Johns
AU  - Thomas E. Ferrin
AU  - Elaine J. Carlson
AU  - Esteban G. Burchard
AU  - Kathleen M. Giacomini
TI  - Interaction of Methotrexate with Organic-Anion Transporting Polypeptide 1A2 and Its Genetic Variants
AID  - 10.1124/jpet.106.104364
DP  - 2006 Aug 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 521--529
VI  - 318
IP  - 2
4099  - http://jpet.aspetjournals.org/content/318/2/521.short
4100  - http://jpet.aspetjournals.org/content/318/2/521.full
SO  - J Pharmacol Exp Ther2006 Aug 01; 318
AB  - Methotrexate (MTX) is used in patients with malignant and autoimmune diseases. This drug is primarily excreted unchanged in the urine, and its net excretion occurs via active secretory and reabsorptive processes. We characterized the interaction of MTX with human organic-anion transporting polypeptide transporter (OATP) 1A2, which is expressed in tissues important for MTX disposition and toxicity, such as the intestine, kidney, liver, and endothelial cells of the blood-brain barrier. In Xenopus laevis oocytes expressing OATP1A2, the uptake of the model substrate, estrone-3-sulfate (ES), was enhanced 30-fold compared with uninjected oocytes. MTX uptake in oocytes expressing OATP1A2 was saturable (Km = 457 ± 118 μM; Vmax = 17.5 ± 4.9 pmol/oocyte/60 min) and sensitive to extracellular pH. That is, acidic pHs stimulated MTX uptake by as much as 7-fold. Seven novel protein-altering variants were identified in 270 ethnically diverse DNA samples. Four protein-altering variants in OATP1A2 exhibited altered transport of ES and/or MTX. The common variant, protein reference sequence (p.) Ile13Thr, was hyperfunctional for ES and MTX and showed a 2-fold increase in the Vmax for ES. The common variant, p. Glu172Asp, exhibited reduced maximal transport capacity for ES and MTX. p. Arg168Cys was hypofunctional, and p. Asn277DEL was nonfunctional. Because of its expression on the apical membrane of the distal tubule and in tissues relevant to MTX disposition and toxicity, these findings suggest that OATP1A2 may play a role in active tubular reabsorption of MTX and in MTX-induced toxicities. Furthermore, genetic variation in OATP1A2 may contribute to variation in MTX disposition and response. The American Society for Pharmacology and Experimental Therapeutics