Hydrolysis of irinotecan and its oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin, by human carboxylesterases CES1A1, CES2, and a newly expressed carboxylesterase isoenzyme, CES3

Drug Metab Dispos. 2004 May;32(5):505-11. doi: 10.1124/dmd.32.5.505.


Carboxylesterases metabolize ester, thioester, carbamate, and amide compounds to more soluble acid, alcohol, and amine products. They belong to a multigene family with about 50% sequence identity between classes. CES1A1 and CES2 are the most studied human isoenzymes from class 1 and 2, respectively. In this study, we report the cloning and expression of a new human isoenzyme, CES3, that belongs to class 3. The purified recombinant CES3 protein has carboxylesterase activity. Carboxylesterases metabolize the carbamate prodrug 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11; irinotecan) to its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), a potent topoisomerase I inhibitor. CYP3A4 oxidizes CPT-11 to two major oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin (APC) and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC). In this study, we investigate whether these oxidative metabolites, NPC and APC, can be metabolized to SN-38 by purified human carboxylesterases, CES1A1, CES2, and CES3. We find that CPT-11, APC, and NPC can all be metabolized by carboxylesterases to SN-38. CES2 has the highest catalytic activity of 0.012 min(-1) microM(-1) among the three carboxylesterases studied for hydrolysis of CPT-11. NPC was an equally good substrate of CES2 in comparison to CPT-11, with a catalytic efficiency of 0.005 min(-1) microM(-1). APC was a very poor substrate for all three isoenzymes, exhibiting a catalytic activity of 0.015 x 10(-3) min(-1) microM(-1) for CES2. Catalytic efficiency of CES3 for CPT-11 hydrolysis was 20- to 2000-fold less than that of CES1A1 and CES2. The relative activity of the three isoenzymes was CES2 > CES1A1 >> CES3, for all three substrates.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Camptothecin / analogs & derivatives*
  • Camptothecin / metabolism*
  • Carboxylesterase / biosynthesis*
  • Carboxylesterase / chemistry
  • Carboxylesterase / isolation & purification
  • Carboxylesterase / metabolism*
  • Carboxylic Ester Hydrolases / biosynthesis
  • Carboxylic Ester Hydrolases / genetics*
  • Carboxylic Ester Hydrolases / isolation & purification
  • Carboxylic Ester Hydrolases / metabolism*
  • Cloning, Molecular
  • Gene Expression Regulation, Enzymologic
  • Humans
  • Hydrolysis
  • Irinotecan
  • Isoenzymes / biosynthesis
  • Isoenzymes / genetics
  • Isoenzymes / isolation & purification
  • Isoenzymes / metabolism
  • Liver / enzymology
  • Molecular Sequence Data
  • Oxidation-Reduction


  • Isoenzymes
  • Irinotecan
  • Carboxylic Ester Hydrolases
  • CES1 protein, human
  • Carboxylesterase
  • Camptothecin