RESUMEN
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 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 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 b(5), 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-hydroxyellipticine 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-12-ylium, determined by quantum chemical calculations, explains this phenomenon. The amounts of the 13-hydroxyellipticine-derived 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.
Asunto(s)
Antineoplásicos Fitogénicos/metabolismo , Citocromo P-450 CYP3A/metabolismo , Citocromos b5/metabolismo , Elipticinas/metabolismo , Profármacos/metabolismo , Animales , Antineoplásicos Fitogénicos/farmacología , Arilamina N-Acetiltransferasa/metabolismo , ADN/metabolismo , Elipticinas/farmacología , Humanos , Profármacos/farmacología , Conejos , Sulfotransferasas/metabolismoRESUMEN
OBJECTIVES: Ellipticine is a potent antineoplastic agent exhibiting multiple mechanisms of its action. Recently, we have found that 13-hydroxyellipticine, formed from ellipticine as the predominant metabolite in human livers, is bound to deoxyguanosine in DNA, generating the major DNA adduct in vivo and in vitro. The development of the methods suitable for the preparation of this adduct in the amounts sufficient for identification of its structure and those for its isolation and partial characterization is the aim of this study. METHODS: High performance liquid chromatography (HPLC) was employed for separation of 13-hydroxyellipticine-mediated deoxyguanosine adduct. The 32P-postlabeling technique was utilized to detect this adduct in DNA. RESULTS: The formation of the 13-hydroxyellipticine-derived deoxyguanosine adduct in DNA in vitro was increased under the alkaline pH of the incubations and by the formation of the sulfate and acetate conjugates of 13-hydroxyellipticine generated by reactions with 3'-phosphoadenosine-5'-phosphosulfate (PAPS) or acetyl-coenzyme A (acetyl-CoA) catalyzed by human sulfotransferases (SULTs) 1A1 and 1A2 and N,O-acetyltransferases (NATs) 1 and 2. The HPLC method suitable for separation the 13-hydroxyellipticine-derived deoxyguanosine adduct from other reactants, deoxyguanosine and 13-hydroxyellipticine, was developed. The structure of this adduct is proposed to correspond to the product formed from ellipticine-13-ylium with the exocyclic 2-NH2 group of guanine in DNA. CONCLUSIONS: The data are the first report on HPLC isolation of the deoxyguanosine adduct formed by 13-hydroxyellipticine in DNA and its partial characterization.
Asunto(s)
Aductos de ADN/química , ADN/química , Desoxiguanosina/química , Elipticinas/química , Acetilcoenzima A/metabolismo , Arilamina N-Acetiltransferasa/metabolismo , Arilsulfotransferasa/metabolismo , Autorradiografía , Catálisis , Aductos de ADN/aislamiento & purificación , Concentración de Iones de Hidrógeno , Indicadores y Reactivos , Isoenzimas/metabolismo , Fosfoadenosina Fosfosulfato/químicaRESUMEN
Ellipticine is an antineoplastic agent, whose mode of antitumor and/or toxic side effects is based on DNA intercalation, inhibition of topoisomerase II and formation of DNA adducts mediated by cytochromes P450 and peroxidases. We investigated the formation and persistence of DNA adducts generated in rat, the animal model mimicking the bioactivation of ellipticine in human. Using (32)P-postlabeling, ellipticine-DNA adducts were found in liver, kidney, lung, spleen, heart and brain of female and male rats exposed to ellipticine (4, 40 and 80 mg/kg body weight, i.p.). The two major adducts were identical to the deoxyguanosine adducts generated in DNA by 13-hydroxy- and 12-hydroxyellipticine in vitro as confirmed by HPLC of the isolated adducts. At four post-treatment times (2 days, 2, 10 and 32 weeks) DNA adducts in rats treated with 80 mg/kg of ellipticine were analyzed in each tissue to study their long-term persistence. In all organs maximal adduct levels were found 2 days after administration. At all time points highest total adduct levels were in liver (402 adducts/10(8) nucleotides after 2 days and 3.6 adducts/10(8) nucleotides after 32 weeks), kidney and lung followed by spleen, heart and brain. Total adduct levels decreased over time to 0.8-8.3% of the initial levels till the latest time point and showed a biphasic profile, a rapid loss during the first 2 weeks was followed by a much slower decline till 32 weeks. These results, the first characterization of persistence of ellipticine-DNA adducts in vivo, are necessary to evaluate genotoxic side effects of ellipticine.
Asunto(s)
Antineoplásicos/toxicidad , Aductos de ADN , Elipticinas/toxicidad , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Relación Dosis-Respuesta a Droga , Femenino , Riñón/efectos de los fármacos , Riñón/metabolismo , Hígado/efectos de los fármacos , Hígado/metabolismo , Pulmón/efectos de los fármacos , Pulmón/metabolismo , Masculino , Miocardio/metabolismo , Ratas , Ratas Wistar , Bazo/efectos de los fármacos , Bazo/metabolismoRESUMEN
Ellipticine is a potent antineoplastic agent exhibiting the multimodal mechanism of its action. This article reviews the mechanisms of predominant pharmacological and cytotoxic effects of ellipticine and shows the results of our laboratories indicating a novel mechanism of its action. The prevalent mechanisms of ellipticine antitumor, mutagenic and cytotoxic activities were suggested to be intercalation into DNA and inhibition of DNA topoisomerase II activity. We demonstrated a new mode of ellipticine action, formation of covalent DNA adducts mediated by its oxidation with cytochromes P450 (CYP) and peroxidases. The article reports the molecular mechanism of ellipticine oxidation by CYPs and identifies human and rat CYPs responsible for ellipticine metabolic activation and detoxication. It also presents a role of peroxidases (i.e. myeloperoxidase, cyclooxygenases, lactoperoxidase) in ellipticine oxidation leading to ellipticine-DNA adducts. The 9-hydroxy- and 7-hydroxyellipticine metabolites formed by CYPs and the major product of ellipticine oxidation by peroxidases, the dimer, in which the two ellipticine skeletons are connected via N(6) of the pyrrole ring of one ellipticine molecule and C9 in the second one, are the detoxication metabolites. On the contrary, 13-hydroxy- and 12-hydroxyellipticine, produced by ellipticine oxidation with CYPs, the latter one formed also spontaneously from another CYP- and peroxidase-mediated metabolite, ellipticine N(2)-oxide, are metabolites responsible for formation of two ellipticine-derived deoxyguanosine adducts in DNA. The results reviewed here allow us to propose species, two carbenium ions, ellipticine-13-ylium and ellipticine-12-ylium, as reactive species generating two major DNA adducts seen in vivo in rats treated with ellipticine. The study forms the basis to further predict the susceptibility of human cancers to ellipticine.
Asunto(s)
Antineoplásicos/farmacología , Elipticinas/farmacología , Animales , Antineoplásicos/química , Sistema Enzimático del Citocromo P-450/metabolismo , Aductos de ADN/efectos de los fármacos , Elipticinas/química , Humanos , Oxidación-ReducciónRESUMEN
Ellipticine is an antineoplastic agent, the mode of action of which is considered to be based on DNA intercalation and inhibition of topoisomerase II. We found that ellipticine also forms the cytochrome P450 (CYP)-mediated covalent DNA adducts. We now identified the ellipticine metabolites formed by human CYPs and elucidated the metabolites responsible for DNA binding. The 7-hydroxyellipticine, 9-hydroxyellipticine, 12-hydroxyellipticine, 13-hydroxyellipticine, and ellipticine N(2)-oxide are generated by hepatic microsomes from eight human donors. The role of specific CYPs in the oxidation of ellipticine and the role of the ellipticine metabolites in the formation of DNA adducts were investigated by correlating the levels of metabolites formed in each microsomal sample with CYP activities and with the levels of the ellipticine-derived deoxyguanosine adducts in DNA. On the basis of this analysis, formation of 9-hydroxyellipticine and 7-hydroxyellipticine was attributable to CYP1A1/2, whereas production of 13-hydroxyellipticine and ellipticine N(2)-oxide, the metabolites responsible for formation of two major DNA adducts, was attributable to CYP3A4. Using recombinant human enzymes, oxidation of ellipticine to 9-hydroxyellipticine and 7-hydroxyellipticine by CYP1A1/2 and to 13-hydroxyellipticine and N(2)-oxide by CYP3A4 was corroborated. Homologue modeling and docking of ellipticine to the CYP3A4 active center was used to explain the predominance of ellipticine oxidation by CYP3A4 to 13-hydroxyellipticine and N(2)-oxide.
Asunto(s)
Antineoplásicos Fitogénicos/farmacología , Sistema Enzimático del Citocromo P-450/metabolismo , Aductos de ADN , Elipticinas/farmacología , Cromatografía Líquida de Alta Presión , Elipticinas/química , Humanos , Espectroscopía de Resonancia Magnética , Microsomas Hepáticos/metabolismo , Modelos Moleculares , Proteínas Recombinantes/metabolismoRESUMEN
Ellipticine is a potent antineoplastic agent whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts in vitro and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). Here, we investigated the capacity of ellipticine to form DNA adducts in vivo. Male Wistar rats were treated with ellipticine, and DNA from various organs was analyzed by (32)P postlabeling. Ellipticine-specific DNA adduct patterns, similar to those found in vitro, were detected in most test organs. Only DNA of testes was free of the ellipticine-DNA adducts. The highest level of DNA adducts was found in liver (19.7 adducts per 10(7) nucleotides), followed by spleen, lung, kidney, heart and brain. One major and one minor ellipticine-DNA adducts were found in DNA of all these organs of rats exposed to ellipticine. Besides these, 2 or 3 additional adducts were detected in DNA of liver, kidney, lung and heart. The predominant adduct formed in rat tissues in vivo was identical to the deoxyguanosine adduct generated in DNA by ellipticine in vitro as shown by cochromatography in 2 independent systems. Correlation studies showed that the formation of this major DNA adduct in vivo is mediated by CYP3A1- and CYP1A-dependent reactions. The results presented here are the first report showing the formation of CYP-mediated covalent DNA adducts by ellipticine in vivo and confirm the formation of covalent DNA adducts as a new mode of ellipticine action.
Asunto(s)
Antineoplásicos/farmacocinética , Aductos de ADN/metabolismo , Elipticinas/farmacocinética , Microsomas/metabolismo , Animales , Biotransformación , Citocromo P-450 CYP1A1/metabolismo , Citocromo P-450 CYP1A2/metabolismo , Marcaje Isotópico/métodos , Masculino , Microsomas Hepáticos/metabolismo , Especificidad de Órganos , Radioisótopos de Fósforo , Ratas , Ratas Wistar , Distribución TisularRESUMEN
Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (P450). We examined rat, rabbit, and human hepatic microsomal samples for their ability to activate ellipticine. The extent of activation was determined by binding of 3H-labeled ellipticine to DNA and by analyzing DNA adducts by 32P-postlabeling. We demonstrate that cytochrome P450 of human hepatic microsomes activating ellipticine to species binding to DNA is analogous to that of rats, but not of rabbits. Most of the ellipticine activation in rat and human hepatic microsomes is attributed to P450 enzymes of the same subfamily, P450 3A1/2 and P450 3A4, respectively, while the orthologous enzyme in rabbit hepatic microsomes, P450 3A6, is much less efficient. With purified enzymes, the major role of P450 3A1 and 3A4 in ellipticine-DNA adduct formation was confirmed. We identified deoxyguanosine as the target for P450-mediated ellipticine binding to DNA using polydeoxyribonucleotides and deoxyguanosine 3'-monophosphate. The results strongly suggest that rats are more suitable models than rabbits mimicking the metabolic activation of ellipticine in humans.