title: 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.
abstract: 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.
authors.affiliation: Biotechnology Research and Training Center, Indiana University School of Medicine, 1345 W. 16th Street, Room L3-304, Indianapolis, IN 46202, USA.
authors.forename: Sonal P
authors.initials: SP
authors.lastname: Sanghani
authors.forename: Sara K
authors.initials: SK
authors.lastname: Quinney
authors.forename: Tyler B
authors.initials: TB
authors.lastname: Fredenburg
authors.forename: Wilhelmina I
authors.initials: WI
authors.lastname: Davis
authors.forename: Daryl J
authors.initials: DJ
authors.lastname: Murry
authors.forename: William F
authors.initials: WF
authors.lastname: Bosron
mesh_terms: D000595:Amino Acid Sequence; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism*; D043182:Carboxylesterase / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D003001:Cloning, Molecular; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D006868:Hydrolysis; D000077146:Irinotecan; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction
chemical_list: D007527:Isoenzymes; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; C474609:CES1 protein, human; D043182:Carboxylesterase; D002166:Camptothecin