Cytochrome <i>b</i><sub>5</sub> Increases Cytochrome P450 3A4-Mediated Activation of Anticancer Drug Ellipticine to 13-Hydroxyellipticine Whose Covalent Binding to DNA Is Elevated by Sulfotransferases and <i>N</i>,<i>O</i>-Acetyltransferases
作者:Marie Stiborová、Radek Indra、Michaela Moserová、Věra Černá、Martina Rupertová、Václav Martínek、Tomáš Eckschlager、René Kizek、Eva Frei
DOI:10.1021/tx3000335
日期:2012.5.21
The antineoplastic alkaloid ellipticine is a prodrug, whose pharmacological efficiency is dependent on its cytochrome P450 (P450)- and/or peroxidase-mediated activation in target tissues. The P450 3A4 enzyme oxidizes ellipticine to five 3 metabolites, mainly to 13-hydroxy- and 12-hydroxyellipticine, the metabolites responsible for the formation of ellipticine-13-ylium and ellipticine-12-ylium ions that generate covalent DNA adducts. Cytochrome b(5) alters the ratio of ellipticine p metabolites formed by P450 3A4. While the amounts of the detoxication metabolites (7-hydroxy- and 9-hydroxyellipticine) were not changed with added cytochrome b(5), 12-hydroxy- and 13-hydroxyellipticine, and ellipticine N-2-oxide increased considerably. The P450 3A4-mediated oxidation of ellipticine was significantly changed only by holo-cytochrome 65, while apo-cytochrome b(5) without heme or Mn-cytochrome b(5) had no such effect. The change in amounts of metabolites resulted in an increased formation of covalent ellipticine-DNA adducts, one of the DNA-damaging mechanisms of ellipticine antitumor action. The amounts of 13-hydroxy- and 12-hydroxyellipticine formed by P450 3A4 were similar, but more than 7-fold higher levels of the adduct. were formed by 13-hydrox-yellipticine than by 12-hydroxyellipticine. The higher susceptibility of 13-hydroxyellipticine toward heterolytic dissociation to ellipticine-13-ylium in comparison to dissociation of 12-hydroxyellipticine to ellipticine-12ylium, determined by quantum chemical calculations, explains this phenomenon. The amounts of the 13-hydroxyellipticinederived DNA adduct significantly increased upon reaction of 13-hydroxyellipticine with either 3'-phosphoadenosine-5'phosphosulfate or acetyl-CoA catalyzed by human sulfotransferases 1A1, 1A2, 1A3, and 2A1, or N,O-acetyltransferases 1 and 2. The calculated reaction free energies of heterolysis of the sulfate and acetate esters are by 10-17 kcal/mol more favorable than the energy of hydrolysis of 13-hydroxyellipticine, which could explain the experimental data.