title: Hydrolysis of capecitabine to 5'-deoxy-5-fluorocytidine by human carboxylesterases and inhibition by loperamide.
abstract: Capecitabine is an oral prodrug of 5-fluorouracil that is indicated for the treatment of breast and colorectal cancers. A three-step in vivo-targeted activation process requiring carboxylesterases, cytidine deaminase, and thymidine phosphorylase converts capecitabine to 5-fluorouracil. Carboxylesterases hydrolyze capecitabine's carbamate side chain to form 5'-deoxy-5-fluorocytidine (5'-DFCR). This study examines the steady-state kinetics of recombinant human carboxylesterase isozymes carboxylesterase (CES) 1A1, CES2, and CES3 for hydrolysis of capecitabine with a liquid chromatography/mass spectroscopy assay. Additionally, a spectrophotometric screening assay was utilized to identify drugs that may inhibit carboxylesterase activation of capecitabine. CES1A1 and CES2 hydrolyze capecitabine to a similar extent, with catalytic efficiencies of 14.7 and 12.9 min(-1) mM(-1), respectively. Little catalytic activity is detected for CES3 with capecitabine. Northern blot analysis indicates that relative expression in intestinal tissue is CES2 > CES1A1 > CES3. Hence, intestinal activation of capecitabine may contribute to its efficacy in colon cancer and toxic diarrhea associated with the agent. Loperamide is a strong inhibitor of CES2, with a K(i) of 1.5 muM, but it only weakly inhibits CES1A1 (IC(50) = 0.44 mM). Inhibition of CES2 in the gastrointestinal tract by loperamide may reduce local formation of 5'-DFCR. Both CES1A1 and CES2 are responsible for the activation of capecitabine, whereas CES3 plays little role in 5'-DFCR formation.
authors.affiliation: Department of Pharmacy Practice, Purdue University, Indianapolis, IN 46202, USA. wbosron@iupui.edu
authors.forename: S K
authors.initials: SK
authors.lastname: Quinney
authors.forename: S P
authors.initials: SP
authors.lastname: Sanghani
authors.forename: W I
authors.initials: WI
authors.lastname: Davis
authors.forename: T D
authors.initials: TD
authors.lastname: Hurley
authors.forename: Z
authors.initials: Z
authors.lastname: Sun
authors.forename: D J
authors.initials: DJ
authors.lastname: Murry
authors.forename: W F
authors.initials: WF
authors.lastname: Bosron
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism*; D000069287:Capecitabine; D043182:Carboxylesterase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism*; D005472:Fluorouracil / Q000031:analogs & derivatives; D041981:Gastrointestinal Tract / Q000201:enzymology; D006801:Humans; D006868:Hydrolysis; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008139:Loperamide / Q000494:pharmacology*; D011355:Prodrugs / Q000378:metabolism*
chemical_list: D000964:Antimetabolites, Antineoplastic; D007527:Isoenzymes; D011355:Prodrugs; D003841:Deoxycytidine; D000069287:Capecitabine; D008139:Loperamide; C418208:5'-deoxy-5-fluorocytidine; D043182:Carboxylesterase; D005472:Fluorouracil