title: In vitro characterization of hepatic flavopiridol metabolism using human liver microsomes and recombinant UGT enzymes.
abstract: OBJECTIVE
  To assess the contribution of drug metabolism to the variability on flavopiridol glucuronidation observed in cancer patients, and to determine the ability of all known human UDP-glucuronosyltransferase (UGT) isoforms to glucuronidate flavopiridol.
  
  
  METHODS
  Inter-individual variation in flavopiridol glucuronidation was determined by HPLC using hepatic microsomes from 62 normal liver donors. Identification of enzymes capable of glucuronidating flavopiridol was determined by LC/MS using human embryonic kidney 293 (HEK293) cells stably expressing all sixteen known human UGTs.
  
  
  RESULTS
  The major product of the flavopiridol glucuronidation reaction in human liver microsomes was FLAVO-7-G. High variability (coefficient of variation = 49%) was observed in the glucuronidation of flavopiridol by human liver microsomes. In vitro formation of FLAVO-7-G and FLAVO-5-G was mainly catalyzed by UGT1A9 and UGT1A4, respectively. Similar catalytic efficiencies (Vmax/Km) were observed for human liver microsomes (1.6 microl/min/mg) and UGT1A9 (1.5 microl/min/mg).
  
  
  CONCLUSIONS
  UGT1A9 is the major UGT involved in the hepatic glucuronidation of flavopiridol in humans. The data suggests that hepatic glucuronidation may be a major determinant of the variable systemic glucuronidation of flavopiridol in cancer patients. The large variability in flavopiridol glucuronidation may be due to differences in liver metabolism among individuals, as a result of genetic differences in UGT1A9.
authors.affiliation: Department of Medicine, University of Chicago, Illinois 60637, USA.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Ramírez
authors.forename: Lalitha
authors.initials: L
authors.lastname: Iyer
authors.forename: Kim
authors.initials: K
authors.lastname: Journault
authors.forename: Patrick
authors.initials: P
authors.lastname: Bélanger
authors.forename: Federico
authors.initials: F
authors.lastname: Innocenti
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Ratain
authors.forename: Chantal
authors.initials: C
authors.lastname: Guillemette
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism*; D005419:Flavonoids / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D005965:Glucuronates / Q000378:metabolism; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010880:Piperidines / Q000378:metabolism*; D015742:Propofol / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: C471033:5-O-glucopyranuronosylflavopiridol; C471032:7-O-glucopyranuronosylflavopiridol; D000970:Antineoplastic Agents; D005419:Flavonoids; D005965:Glucuronates; D020719:Glucuronides; D007527:Isoenzymes; D010880:Piperidines; D011994:Recombinant Proteins; C077990:alvocidib; D014453:Glucuronosyltransferase; D015742:Propofol