MolPharm xPharm- The Comprehensive Pharmacology Reference

Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
QUICK SEARCH:   [advanced]


     

Molecular Pharmacology Fast Forward
First published on October 27, 2004; DOI: 10.1124/mol.104.004978

0026-895X/05/6702-453-459$20.00
Mol Pharmacol 67:453-459, 2005

This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
mol.104.004978v1
67/2/453    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Damaraju, V. L.
Right arrow Articles by Sawyer, M. B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Damaraju, V. L.
Right arrow Articles by Sawyer, M. B.
ORIGINAL ARTICLE

Characterization of Binding of Folates and Antifolates to Brush-Border Membrane Vesicles Isolated from Human Kidney

Vijaya L. Damaraju, Katherine F. Hamilton, Michelle L. Seth-Smith, Carol E. Cass, and Michael B. Sawyer

Department of Oncology, University of Alberta, Edmonton, Alberta, Canada (V.L.D., K.F.H., M.L.S.-S., C.E.C., M.B.S.); and the Departments of Experimental Oncology (V.L.D., K.F.H., C.E.C.) and Medical Oncology (M.L.S.-S., C.E.C., M.B.S.), Cross Cancer Institute, Edmonton, Alberta, Canada

Abstract

Antifolates such as methotrexate, raltitrexed, and pemetrexed are among the most effective and widely used anticancer drugs. The antifolates are also among the most unpredictable of anticancer drugs with respect to pharmacokinetics and toxicity. In this study, we assessed the binding of folates and antifolates to the folate receptors (FRs) of human proximal tubules and the effects of pH on binding. Binding of [3H]folic acid was pH-dependent, with maximal binding seen at pH 6. Equilibrium binding experiments with [3H]folic acid showed that Kd values were unaffected, and Bmax values increased as the pH was decreased from 8.0 to 6.0. Increasing the osmolarity at pH 6.0 had no effect on intravesicular content, confirming that increased site-specific binding caused the observed changes in Bmax values. Enzymatic cleavage of glycosyl-phosphatidylinositol linkages abolished binding of [3H]folic acid to brush-border membrane vesicles, suggesting that [3H]folic acid was bound to FRs. In concentration-effect experiments conducted at different pH values, the antifolates raltitrexed and (2S)-2-[o-fluoro-p-[N-(2,7-dimethyl-4-oxo-3,4-dihydroquinazolin-6-yl-methyl)-N-(prop-2-ynyl)amino]benzamido]-4-(tetrazol-5-yl) butyric acid (ZD9331) bound more tightly as pH increased from 6.0 to 8.0, whereas binding of 10-propargyl-5,8-dideazafolic acid (CB3717) was unchanged. The results obtained when Ki values were converted to binding energies suggested that binding of some, but not all, antifolates and folates to FRs was pH-dependent, further indicating roles of luminal pH in renal reabsorption or secretion processes.

Received July 14, 2004; accepted October 25, 2004

Address correspondence to: Dr. Michael B. Sawyer, Department of Medical Oncology, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2 Canada. E-mail: michsawy{at}cancerboard.ab.ca






Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
All ASPET Journals Molecular Pharmacology Pharmacological Reviews
Molecular Interventions Drug Metabolism and Disposition

Copyright © 2005 by the American Society for Pharmacology and Experimental Therapeutics