Investigation of the major human hepatic cytochrome P450 involved in 4-hydroxylation and N-dechloroethylation of trofosfamide.
Trofosfamide and its congeners ifosfamide and cyclophosphamide are cell-cycle-nonspecific alkylating agents that undergo bioactivation catalyzed by liver cytochrome P450 (CYP) enzymes. Two NADPH-dependent metabolic routes for the anticancer drug trofosfamide, i.e., 4-hydroxylation and N-dechloroethylation, were studied in human liver microsomes and in seven recombinant human CYP isoforms (i.e., CYP1A1, 1A2, 2A6, 2B6, 2D6, 2E1, and 3A4-OR) to identify the CYP enzymes involved. Recombinant human CYP3A4 and CYP2B6 exhibited catalytic activity with respect to both pathways of trofosfamide. Enzyme kinetic analyses revealed the dominant role of human CYP3A4 in 4-hydroxylation and N-dechloroethylation of trofosfamide. This was confirmed by the observation that only the CYP3A4 contents of five samples of human liver microsomes correlated with both pathways of trofosfamide. Furthermore, ketoconazole, a selective inhibitor of CYP3A4, substantially inhibited microsomal trofosfamide 4-hydroxylation and N-dechloroethylation (50% inhibitory concentration < 1 microM for both reactions). The present study indicates that human liver microsomal CYP3A4 preferentially catalyzes the two NADPH- dependent metabolic routes of trofosfamide, which emphasizes the necessity for awareness of potential interactions with any coadministered drugs that are CYP3A4 substrates.
May-Manke
A
A
Universitäts-Kinderklinik, Abteilung Hämatologie/Onkologie, Albert-Schweitzer-Strasse 33, D-48129 Münster, Germany.
Kroemer
H
H
Hempel
G
G
Bohnenstengel
F
F
Hohenlöchter
B
B
Blaschke
G
G
Boos
J
J
D000478:Alkylation; D000935:Antifungal Agents / Q000494:pharmacology; D018906:Antineoplastic Agents, Alkylating / Q000378:metabolism* / Q000493:pharmacokinetics; D001189:Aryl Hydrocarbon Hydroxylases; D001402:B-Lymphocytes / Q000201:enzymology; D001711:Biotransformation; D002461:Cell Line, Transformed; D003520:Cyclophosphamide / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D006900:Hydroxylation; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*
D000935:Antifungal Agents; D018906:Antineoplastic Agents, Alkylating; D065607:Cytochrome P-450 Enzyme Inhibitors; D018076:DNA, Complementary; D003520:Cyclophosphamide; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C104464:CYP3A protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; C003726:trofosfamide; D007654:Ketoconazole