Intracellular inhibition of carboxylesterases by benzil: modulation of CPT-11 cytotoxicity.
Carboxylesterases are ubiquitous proteins responsible for the detoxification of xenobiotics. However, these enzymes also activate prodrugs, such as the anticancer agents capecitabine and CPT-11. As a consequence, overexpression of carboxylesterases within tumor cells sensitizes these cells to CPT-11. We have recently identified two classes of carboxylesterase inhibitors based on either a benzil (diphenylethane-1,2-dione) or a benzene sulfonamide scaffold and showed that these compounds inhibit carboxylesterases with Kis in the low nanomolar range. Because both classes of inhibitors show reversible enzyme inhibition, conventional in vitro biochemical assays would not accurately reflect the in situ levels of carboxylesterase activity or inhibition. Therefore, we have developed a novel assay for the determination of intracellular carboxylesterase activity using 4-methylumbelliferone as a substrate. These studies show that benzil and a dimethylbenzil analogue efficiently enter cells and inhibit human intestinal carboxylesterase and rabbit liver carboxylesterase intracellularly. This inhibition results in reduced cytotoxicity to CPT-11 due to the lack of carboxylesterase-mediated conversion of the prodrug to SN-38. These results suggest that intracellular modulation of carboxylesterase activity with benzil or its analogues may be applied to minimize the toxicity of normal cells to CPT-11.
Hyatt
Janice L
JL
Department of Molecular Pharmacology, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105-2794, USA.
Tsurkan
Lyudmila
L
Wierdl
Monika
M
Edwards
Carol C
CC
Danks
Mary K
MK
Potter
Philip M
PM
D000818:Animals; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors*; D045744:Cell Line, Tumor; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007422:Intestines / Q000201:enzymology; D000077146:Irinotecan; D008099:Liver / Q000201:enzymology; D010658:Phenylglyoxal / Q000031:analogs & derivatives* / Q000494:pharmacology; D011355:Prodrugs / Q000493:pharmacokinetics / Q000494:pharmacology; D011817:Rabbits
D011355:Prodrugs; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; D010658:Phenylglyoxal; C006697:benzil; D002166:Camptothecin