title: Molecular insights into microbial β-glucuronidase inhibition to abrogate CPT-11 toxicity.
abstract: Bacterial β-glucuronidases expressed by the symbiotic intestinal microbiota appear to play important roles in drug-induced epithelial cell toxicity in the gastrointestinal (GI) tract. For the anticancer drug CPT-11 (irinotecan) and the nonsteroidal anti-inflammatory drug diclofenac, it has been shown that removal of the glucuronide moieties from drug metabolites by bacterial β-glucuronidases in the GI lumen can significantly damage the intestinal epithelium. Furthermore, selective disruption of bacterial β-glucuronidases by small molecule inhibitors alleviates these side effects, which, for CPT-11 {7-ethyl-10-[4-(1-piperidino)-1-piperidino]}, can be dose limiting. Here we characterize novel microbial β-glucuronidase inhibitors that inhibit Escherichia coli β-glucuronidase in vitro with Ki values between 180 nM and 2 μM, and disrupt the enzyme in E. coli cells, with EC50 values as low as 300 nM. All compounds are selective for E. coli β-glucuronidase without inhibiting purified mammalian β-glucuronidase, and they do not impact the survival of either bacterial or mammalian cells. The 2.8 Å resolution crystal structure of one inhibitor bound to E. coli β-glucuronidase demonstrates that it contacts and orders only a portion of the "bacterial loop" present in microbial, but not mammalian, β-glucuronidases. The most potent compound examined in this group was found to protect mice against CPT-11-induced diarrhea. Taken together, these data advance our understanding of the chemical and structural basis of selective microbial β-glucuronidase inhibition, which may improve human drug efficacy and toxicity.
authors.affiliation: Departments of Biochemistry, Chemistry and Microbiology, University of North Carolina at Chapel Hill, NC, USA.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Roberts
authors.forename: Bret D
authors.initials: BD
authors.lastname: Wallace
authors.forename: Madhu Kumar
authors.initials: MK
authors.lastname: Venkatesh
authors.forename: Sridhar
authors.initials: S
authors.lastname: Mani
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Redinbo
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000633:toxicity; D002417:Cattle; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology; D005260:Female; D005966:Glucuronidase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D006023:Glycoproteins / Q000494:pharmacology*; D000077146:Irinotecan; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D051379:Mice; D008807:Mice, Inbred BALB C
chemical_list: D004791:Enzyme Inhibitors; D006023:Glycoproteins; C011473:beta-glucuronidase inhibitor; D000077146:Irinotecan; D005966:Glucuronidase; D002166:Camptothecin