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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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Published in: | Cancer research (Chicago, Ill.) Ill.), 1987-09, Vol.47 (17), p.4658-4662 |
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Main Authors: | , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Online Access: | Get full text |
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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. |
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ISSN: | 0008-5472 1538-7445 |