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Cytochrome P-450-mediated O-demethylation: a route in the metabolic activation of etoposide (VP-16-213)

The antitumor agent VP-16-213 is oxidatively O-demethylated by rat liver microsomes and purified rat liver microsomal cytochrome P-450. 3-Methylcholanthrene can quantitatively induce O-demethylation of VP-16-213. The Km and Vmax values for O-demethylation by noninduced, phenobarbital-, and 3-methylc...

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Bibliographic Details
Published in:Cancer research (Chicago, Ill.) Ill.), 1987-09, Vol.47 (17), p.4658-4662
Main Authors: VAN MAANEN, J. M. S, DE VRIES, J, PAPPIE, D, VAN DEN AKKER, E, LAFLEUR, M. V. M, RETEL, J, VAN DER GREEF, J, PINEDO, H. M
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Language:English
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Summary:The antitumor agent VP-16-213 is oxidatively O-demethylated by rat liver microsomes and purified rat liver microsomal cytochrome P-450. 3-Methylcholanthrene can quantitatively induce O-demethylation of VP-16-213. The Km and Vmax values for O-demethylation by noninduced, phenobarbital-, and 3-methylcholanthrene-induced rat liver microsomes were found to be 130, 600, and 160 microM and 8.5, 11.8, and 15.6 nmol H2CO/min X mg protein, respectively. Mass spectrometric comparison of the product of O-demethylation of VP-16-213 with the synthetic metabolite resulted in identification of the orthodihydroxy derivative. In studies on the biological activity of the orthodihydroxy derivative, it was found to inactivate single- and double-stranded phiX174 DNA, to bind to calf thymus DNA and to be highly toxic against chinese hamster ovary cells.
ISSN:0008-5472
1538-7445