title: Enhanced clearance of topoisomerase I inhibitors from human colon cancer cells by glucuronidation.
abstract: As part of a program to identify novel mechanisms of resistance to topoisomerase I (topo I) inhibitors, the cellular pharmacology of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of clinically used irinotecan (CPT-11) and NU/ICRF 505, an anthraquinone-tyrosine conjugate, has been investigated in two human colorectal cancer (CRC) cell lines. Two novel metabolites of NU/ICRF 505 (M1 and M2) and a single metabolite of SN-38 (M1) were detected by high performance liquid chromatography in the culture medium of HT29 cells but were absent in HCT116 cells. Identities of all three metabolites were established by a combination of biochemical and physicochemical techniques. M1 of SN-38 was the C10-(beta)-glucuronide of the parent lactone while M1 of NU/ICRF 505 was the C4-O-glucuronide and M2 the tyrosine-O-glucuronide, both of the parent compound. Drug transport studies revealed that by 24hr HT29 cells had effectively cleared 82.5% of NU/ICRF 505 (10 microM) into the culture medium as the two glucuronides. In contrast, intracellular concentrations of NU/ICRF 505 were maintained in HCT116 cells in the absence of glucuronidation at a level 550 times greater than in HT29 cells. HT29 cells cleared 40.9% of SN-38 (1 microM) as the glucuronide to the culture medium, while the parent drug was maintained at a level 2-fold greater in HCT116 cells. Enhanced drug clearance due to glucuronidation may contribute to intrinsic drug resistance of human CRC.
authors: Imperial Cancer Research Fund, Medical Oncology Unit, Western General Hospital, EH4 2XU, Edinburgh, UK. j.cummings@icrf.icnet.uk
authors: Jeffrey
authors: J
authors: Cummings
authors: Gary
authors: G
authors: Boyd
authors: Brian T
authors: BT
authors: Ethell
authors: Janet S
authors: JS
authors: Macpherson
authors: Brian
authors: B
authors: Burchell
authors: John F
authors: JF
authors: Smyth
authors: Duncan I
authors: DI
authors: Jodrell
mesh_terms: D000880:Anthraquinones / Q000378:metabolism / Q000493:pharmacokinetics*; D002166:Camptothecin / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D005965:Glucuronates / Q000378:metabolism; D020719:Glucuronides / Q000493:pharmacokinetics*; D019073:HT29 Cells; D006801:Humans; D000077146:Irinotecan; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008657:Metabolic Clearance Rate; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: C441475:7-ethyl-10-hydroxycamptothecin glucuronide; D000880:Anthraquinones; D004791:Enzyme Inhibitors; D005965:Glucuronates; D020719:Glucuronides; C100645:NU-ICRF 505; D059004:Topoisomerase I Inhibitors; D014443:Tyrosine; D000077146:Irinotecan; D002166:Camptothecin