Kinetics and regulation of cytochrome P450-mediated etoposide metabolism.
Etoposide is a DNA topoisomerase II inhibitor widely used in the treatment of a variety of malignancies that is also associated with therapy-related leukemia. The cytochrome P450 (P450)-derived catechol and quinone metabolites of etoposide may be important in the damage to the MLL (mixed lineage leukemia) gene and other genes resulting in leukemia-associated chromosomal translocations. Kinetic analysis of catechol formation by recombinant P450s was determined using liquid chromatography/selected reaction monitoring/mass spectrometry. CYP3A4 was found to play a major role in etoposide metabolism (K(m) = 77.7 +/- 27.8 microM; V(max) = 314 +/- 84 pmol of catechol/min/nmol of P450). However, CYP3A5 (K(m) = 13. 9 +/- 3.1 microM; V(max) = 19.4 +/- 0.4 pmol of catechol/min/nmol of P450) may be involved in etoposide metabolism at therapeutic concentrations of free drug. Other P450s do not appear to be involved in etoposide catechol formation. Real-time polymerase chain reaction and Western blot analysis revealed significantly increased CYP3A4 mRNA and protein levels in hepatocytes treated with 10 microM rifampicin compared with untreated cells, but only modest effects of rifampicin on CYP3A5 induction. Etoposide (40, 5, 1, and 0.25 microM) caused a slight increase in CYP3A4 mRNA in three of five batches of hepatocytes but did not result in proportionately increased CYP3A4 protein levels. At high concentrations, etoposide induced only a modest increase in CYP3A5 mRNA and protein levels in four of five batches of hepatocytes. Alternatively, coadministration of other drugs with etoposide may account for the increase in etoposide catechol formation during therapy with etoposide.
Center for Cancer Pharmacology, Department of Pharmacology, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104-6160, USA.
Xiaoliang
X
Zhuo
Naiyu
N
Zheng
Carolyn A
CA
Felix
Ian A
IA
Blair
D000328:Adult; D015153:Blotting, Western / Q000379:methods; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism / Q000494:pharmacology; D005047:Etoposide / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000378:metabolism*; D005260:Female; D022781:Hepatocytes / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000187:drug effects / Q000379:methods; D012333:RNA, Messenger; D012293:Rifampin / Q000494:pharmacology; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013347:Subcellular Fractions; D013713:Teniposide / Q000378:metabolism; D059005:Topoisomerase II Inhibitors
D012333:RNA, Messenger; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D003577:Cytochrome P-450 Enzyme System; D013713:Teniposide; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D004250:DNA Topoisomerases, Type II; D012293:Rifampin