The anticancer drug ellipticine exerts its genotoxic effects after metabolic activation by cytochrome P450 (CYP) enzymes. The present study has examined the role of cytochrome P450 oxidoreductase (POR) and cytochrome b5 (Cyb5), electron donors to P450 enzymes, in the CYP-mediated metabolism and disposition of ellipticine in vivo. We used Hepatic Reductase Null (HRN) and Hepatic Cytochrome b5/P450 Reductase Null (HBRN) mice. HRN mice have POR deleted specifically in hepatocytes; HBRN mice also have Cyb5 deleted in the liver. Mice were treated once with 10 mg/kg body weight ellipticine (n = 4/group) for 24 h. Ellipticine-DNA adduct levels measured by 32P-postlabelling were significantly lower in HRN and HBRN livers than in wild-type (WT) livers; however no significant difference was observed between HRN and HBRN livers. Ellipticine-DNA adduct formation in WT, HRN and HBRN livers correlated with Cyp1a and Cyp3a enzyme activities measured in hepatic microsomes in the presence of NADPH confirming the importance of P450 enzymes in the bioactivation of ellipticine in vivo. Hepatic microsomal fractions were also utilised in incubations with ellipticine and DNA in the presence of NADPH, cofactor for POR, and NADH, cofactor for Cyb5 reductase (Cyb5R), to examine ellipticine-DNA adduct formation. With NADPH adduct formation decreased as electron donors were lost which correlated with the formation of the reactive metabolites 12- and 13-hydroxy-ellipticine in hepatic microsomes. No difference in adduct formation was observed in the presence of NADH. Our study demonstrates that Cyb5 contributes to the P450-mediated bioactivation of ellipticine in vitro, but not in vivo.

• Keywords
• Cytochrome P450, Cytochrome b(5), DNA Adducts, Metabolism, Mouse models,
• MeSH
• DNA Adducts metabolism   MeSH
• Aryl Hydrocarbon Hydroxylases metabolism   MeSH
• Cytochrome P-450 CYP3A MeSH
• Cytochrome-B(5) Reductase deficiency   genetics   MeSH
• Cytochromes b5 deficiency   genetics   MeSH
• Ellipticines metabolism   pharmacology   MeSH
• Phenotype MeSH
• Genotype MeSH
• Hepatocytes enzymology   MeSH
• Microsomes, Liver enzymology   MeSH
• Liver enzymology   MeSH
• Activation, Metabolic MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• NADPH-Ferrihemoprotein Reductase metabolism   MeSH
• Antineoplastic Agents metabolism   pharmacology   MeSH
• Cytochrome P-450 Enzyme System metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• Aryl Hydrocarbon Hydroxylases MeSH
• CYP3A protein, mouse MeSH Browser
• Cytochrome P-450 CYP3A MeSH
• Cytochrome-B(5) Reductase MeSH
• Cytochromes b5 MeSH
• Ellipticines MeSH
• ellipticine MeSH Browser
• NADPH-Ferrihemoprotein Reductase MeSH
• Antineoplastic Agents MeSH
• Cytochrome P-450 Enzyme System MeSH

Ellipticine is a DNA-damaging agent acting as a prodrug whose pharmacological efficiencies and genotoxic side effects are dictated by activation with cytochrome P450 (CYP). Over the last decade we have gained extensive experience in using pure enzymes and various animal models that helped to identify CYPs metabolizing ellipticine. In this review we focus on comparison between the in vitro and in vivo studies and show a necessity of both approaches to obtain valid information on CYP enzymes contributing to ellipticine metabolism. Discrepancies were found between the CYP enzymes activating ellipticine to 13-hydroxy- and 12-hydroxyellipticine generating covalent DNA adducts and those detoxifying this drug to 9-hydroxy- and 7-hydroellipticine in vitro and in vivo. In vivo, formation of ellipticine-DNA adducts is dependent not only on expression levels of CYP3A, catalyzing ellipticine activation in vitro, but also on those of CYP1A that oxidize ellipticine in vitro mainly to the detoxification products. The finding showing that cytochrome b5 alters the ratio of ellipticine metabolites generated by CYP1A1/2 and 3A4 explained this paradox. Whereas the detoxification of ellipticine by CYP1A and 3A is either decreased or not changed by cytochrome b5, activation leading to ellipticine-DNA adducts increased considerably. We show that (I) the pharmacological effects of ellipticine mediated by covalent ellipticine-derived DNA adducts are dictated by expression levels of CYP1A, 3A and cytochrome b5, and its own potency to induce these enzymes in tumor tissues, (II) animal models, where levels of CYPs are either knocked out or induced are appropriate to identify CYPs metabolizing ellipticine in vivo, and (III) extrapolation from in vitro data to the situation in vivo is not always possible, confirming the need for these animal models.

• MeSH
• Cytochrome P-450 CYP1A1 deficiency   genetics   metabolism   MeSH
• Ellipticines pharmacology   MeSH
• Hepatocytes drug effects   metabolism   MeSH
• Rats MeSH
• Mice MeSH
• DNA Damage * MeSH
• Antineoplastic Agents pharmacology   MeSH
• Uncoupling Agents pharmacology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Cytochrome P-450 CYP1A1 MeSH
• Ellipticines MeSH
• ellipticine MeSH Browser
• Antineoplastic Agents MeSH
• Uncoupling Agents MeSH