In vitro characterization of hepatic flavopiridol metabolism using human liver microsomes and recombinant UGT enzymes

Pharm Res. 2002 May;19(5):588-94. doi: 10.1023/a:1015341726183.


Purpose: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents / metabolism*
  • Flavonoids / metabolism*
  • Gas Chromatography-Mass Spectrometry
  • Glucuronates / metabolism
  • Glucuronides / metabolism
  • Glucuronosyltransferase / genetics
  • Glucuronosyltransferase / metabolism*
  • Humans
  • In Vitro Techniques
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Microsomes, Liver / enzymology
  • Microsomes, Liver / metabolism*
  • Piperidines / metabolism*
  • Propofol / metabolism
  • Recombinant Proteins / metabolism
  • Tumor Cells, Cultured


  • 5-O-glucopyranuronosylflavopiridol
  • 7-O-glucopyranuronosylflavopiridol
  • Antineoplastic Agents
  • Flavonoids
  • Glucuronates
  • Glucuronides
  • Isoenzymes
  • Piperidines
  • Recombinant Proteins
  • alvocidib
  • Glucuronosyltransferase
  • Propofol