title: Irinotecan activation by human carboxylesterases in colorectal adenocarcinoma cells.
abstract: Carboxylesterases play a critical role in the bioactivation of the anticancer prodrug irinotecan [7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin; CPT-11] into its active metabolite SN-38 (ethyl-10-hydroxy-camptothecin). We reported recently that human carboxylesterase-2 (hCE-2) is a higher-affinity, higher-velocity enzyme for irinotecan hydrolysis when compared with hCE-1. To further investigate the role of these isoforms, we cloned both cDNAs into the human colorectal adenocarcinoma cell line HT29. Extracts of HT29 cells transfected with hCE-2 exhibited significantly higher irinotecan hydrolysis (5.2 pmol/mg protein/hr) than hCE-1 (1.0 pmol/mg protein/hr). HT29 cells over-expressing hCE-2 were more sensitive to the toxic effects of irinotecan than cells expressing hCE-1 (EC50 = 0.3 micro M and 6.8 micro M, respectively). Our data further support the notion that hCE-2 plays a substantial role in irinotecan activation in human tissue at relevant pharmacologic concentrations.
authors.affiliation: Section of Hematology-Oncology, Department of Medicine and Cancer Research Center, University of Chicago, Chicago, Illinois 60637-1470, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Wu
authors.forename: Bingfang
authors.initials: B
authors.lastname: Yan
authors.forename: Rod
authors.initials: R
authors.lastname: Humerickhouse
authors.forename: M Eileen
authors.initials: ME
authors.lastname: Dolan
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D015153:Blotting, Western; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015723:Gene Library; D006801:Humans; D006868:Hydrolysis; D000077146:Irinotecan; D007525:Isoelectric Focusing; D007700:Kinetics; D020033:Protein Isoforms; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; D002166:Camptothecin