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 Ki of 1.5 μM, but it only weakly inhibits CES1A1 (IC50 = 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.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Jun 1 2005|
ASJC Scopus subject areas
- Molecular Medicine