Characterization of CPT-11 hydrolysis by human liver carboxylesterase isoforms hCE-1 and hCE-2.
7-Ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxy-camptothecin (irinotecan; CPT-11) is a prodrug activated by carboxylesterase enzymes. We characterized the hydrolysis of CPT-11 by two recently identified human carboxylesterase (hCE) enzymes, hCE-1 and hCE-2. Km and Vmax for hCE-1 and hCE-2 are 43 microM and 0.53 nmol/min/mg protein and 3.4 microM and 2.5 nmol/min/mg protein, respectively. hCE-2 has a 12.5-fold higher affinity for CPT-11 and a 5-fold higher maximal rate of CPT-11 hydrolysis when compared with hCE-1. In cytotoxicity assays, incubation of 1 microM CPT-11 with hCE-2 (3.6 microg/ml) resulted in a 60% reduction in survival of SQ20b cells. No significant reduction in cell survival was observed after incubation of CPT-11 with hCE-1. These data indicate that hCE-2 is a high-affinity, high-velocity enzyme with respect to CPT-11. hCE-2 likely plays a substantial role in CPT-11 activation in human liver at relevant pharmacological concentrations.
Humerickhouse
R
R
Department of Medicine, University of Chicago, Illinois 60637-1470, USA.
Lohrbach
K
K
Li
L
L
Bosron
W F
WF
Dolan
M E
ME
D000595:Amino Acid Sequence; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism* / Q000494:pharmacology; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D000077146:Irinotecan; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D016415:Sequence Alignment
D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D002166:Camptothecin