Activation of the anti-cancer drug ifosphamide by rat liver microsomal P450 enzymes

doi:10.1016/0006-2952(93)90310-S

Biochemical Pharmacology

Volume 45, Issue 8, 22 April 1993, Pages 1685-1694

https://doi.org/10.1016/0006-2952(93)90310-S Get rights and content

Abstract

The NADPH-dependent metabolism of ifosphamide catalyzed by rat liver microsomes was investigated in order to identify individual P450 enzymes that activate this anti-cancer drug and to ascertain their relationship to the P450 enzymes that activate the isomeric drug cyclophosphamide. Pretreatment of rats with phenobarbital or clofibrate increased by up to 8-fold the activation of both ifosphamide and cyclophosphamide catalyzed by isolated liver microsomes. Studies using P450 form-selective inhibitory antibodies demonstrated that constitutively expressed P450s belonging to subfamily 2C (forms 2C11/2C6) make significant contributions to the activation of both oxazaphosphorines in uninduced male rat liver microsomes, while the phenobarbital-inducible P450 2B1 was shown to be a major catalyst of these activations in phenobarbital-induced microsomes. Pretreatment of rats with dexamethasone increased liver microsomal activation of ifosphamide ~6-fold without a corresponding effect on cyclophosphamide activation rates. Ifosphamide activation catalyzed by dexamethasone-induced liver microsomes was minimally inhibited by anti-P450 2B or anti-P450 2C antibodies, but was selectively inhibited by anti-P450 3A antibodies. Selective inhibition of liver microsomal ifosphamide activation was also effected by the macrolide antibiotic triacetyloleandomycin, an inhibitor of several dexamethasone-inducible 3A P450s. These studies establish that a dexamethasone-inducible family 3A P450 can make an important contribution to rat liver microsomal ifosphamide activation, and suggest that dexamethasone pretreatment might provide a useful approach for modulation of ifosphamide metabolism in order to improve its therapeutic efficacy in cancer patients.

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Activation of the anti-cancer drug ifosphamide by rat liver microsomal P450 enzymes

Abstract

J Biol Chem

Pharmacol Ther

J Biol Chem

Methods Enzymol

J Biol Chem

J Immunol Methods

Arch Biochem Biophys

Biochem Pharmacol

J Biol Chem

Biochem Pharmacol

Arch Biochem Biophys

J Biol Chem

Pharmacology of cyclo-phosphamide and metabolites

Cancer Treat Rep

Identification of the mouse aldehyde dehydrogenases important in aldophosphamide detoxification

Cancer Res

Studies on the metabolism of iso-phosphamide (NSC-109724) in men

Cancer Treat Rep

Phase II trial of ifosphamide with mesna in previously treated metastatic sarcoma

Cancer Treat Rep

Ifosphamide in experimental tumor systems

Semin Oncol

Plasma concentrations of 4-hydroxycyclophosphamide and phosphoramide mustard in patients repeatedly given high doses of cyclophosphamide in preparation for bone marrow transplantation

Cancer Treat Rep

Clinical pharmacokinetics of cyclo-phosphamide

Clin Pharmacokinet