Collect. Czech. Chem. Commun. 2006, 71, 1169-1185

The Effect of pH on Peroxidase-Mediated Oxidation of and DNA Adduct Formation by Ellipticine

Jitka Poljakováa, Martin Dračínskýa, Eva Freib, Jiří Hudečeka and Marie Stiborováa,*

a Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic
b Division of Molecular Toxicology, German Cancer Research Center, In Neuenheimer Feld 280, 69120 Heidelberg, Germany


In order to understand the mechanism of enzymatic activation of an antineoplastic agent ellipticine, we investigated the effect of pH on the efficiency of three model peroxidases (bovine lactoperoxidase, human myeloperoxidase and horseradish peroxidase) in oxidation of ellipticine and in formation ellipticine-DNA adducts. The formation of the major ellipticine metabolite, ellipticine dimer, in which two ellipticine residues are connected through nitrogen N6 in the pyrrole ring of one of the ellipticine moieties and carbon C9 of the other ellipticine, and formation of four ellipticine-DNA adducts were analyzed. All three peroxidases oxidize ellipticine to dimer and form ellipticine-DNA adducts, but lactoperoxidase and myeloperoxidase were less efficient in these processes than horseradish peroxidase. More than one order of magnitude higher rates of formation of dimer and amounts of the DNA adducts were found upon horseradish peroxidase than in reactions with lactoperoxidase or myeloperoxidase. An acid pH optimum was found for the formation of ellipticine dimer (pH 6.4), while the highest binding of ellipticine activated by peroxidases to DNA was detectable at pH 8.4. Likewise, the highest binding of 5-(hydroxymethyl)ellipticine, a metabolite of ellipticine generated by cytochrome P450, to DNA was found at pH 8.4. The results presented here are a contribution to the explanation of the reaction mechanism of formation of the major deoxyguanosine adduct in DNA generated from ellipticine in vivo and in vitro by its activation with cytochromes P450 and peroxidases.

Keywords: Ellipticine; Anticancer drugs; Peroxidases; Cytochrome P450; Oxidations; DNA adducts; 32P-Postlabeling; Mechanism of activation; Metabolism; DNA intercalation.

References: 35 live references.