Ellipticine increases the superhelical density of intracellular SV40 DNA by intercalation

Synthesis of novel carbazole hydrazine-carbothioamide scaffold as potent antioxidant, anticancer and antimicrobial agents

BACKGROUND

Carbazole-based molecules containing thiosemicarbazide functional groups are recognized for their diverse biological activities, particularly in enhancing therapeutic anticancer effects through inhibiting crucial pathways. These derivatives also exhibit noteworthy antioxidant properties.

OBJECTIVES

This study aims to synthesize, characterize, and evaluate the antioxidant and anticancer activities of 18 novel carbazole derivatives.

METHODS

The radical scavenging capabilities of the compounds were assessed using the 2,2-diphenyl-1-picrylhydrazyl assay. Antiproliferative activities were evaluated on MCF-7 cancer cell lines through viability assays. Additionally, the modulation of the PI3K/Akt/mTOR pathway, apoptosis/necrosis induction, and cell cycle analysis were conducted for the most promising anticancer agents.

RESULTS

nine compounds showed potent antioxidant activities with IC50 values lower than the positive control acarbose, with compounds 4 h and 4y exhibiting the highest potency (IC50 values of 0.73 and 0.38 µM, respectively). Furthermore, compounds 4o and 4r displayed significant anticancer effects, with IC50 values of 2.02 and 4.99 µM, respectively. Compound 4o, in particular, exhibited promising activity by targeting the PI3K/Akt/mTOR signaling pathway, inhibiting tumor survival, inducing apoptosis, and causing cell cycle arrest in MCF-7 cell lines. Furthermore, compound 4o was showed significant antimicrobial activities against S. aureus and E. coli, and antifungal effect against C. albicans. Its potential to overcome drug resistance through this pathway inhibition highlights its promise as an anticancer agent. Molecular docking simulations supported these findings, revealing favorable binding profiles and interactions within the active sites of the enzymes PI3K, AKT1, and mTOR. Moreover, assessing the druggability of the newly synthesized thiosemicarbazide derivatives demonstrated optimal physicochemical properties, further endorsing their potential as drug candidates.

Synthesis of Cytotoxic Quino[4,3-b]carbazole Frameworks through an Intramolecular Diels-Alder Reaction

An intramolecular Diels-Alder reaction of positionally isomeric indole-2/3-phenylvinyl-N-alkynylated (N-phenylsulfonyl)amines has been successfully exploited for the synthesis of quino[4,3-b]carbazole and its analogues. This reaction proceeds through a [4 + 2] cycloaddition followed by elimination and deprotection of phenylsulfonyl units to afford the quinocarbazoles in moderate to good yields. The reaction features a broad substrate scope and remarkable functional group forbearance. A preliminary in vitro cytotoxicity evaluation of representative quino[4,3-b]carbazoles was performed against NCI-H460 human cancer cell culture. Among the quino[4,3-b]carbazoles evaluated, five of the fluorine-containing quinocarbazoles displayed nano molar range (0.8-2.0 nm) GI50 values. The UV-vis and fluorescence spectral studies of representative quinocarbazoles were also performed. Like ellipticine, four of the quinocarbazoles displayed dual emissions confirming the existence of p-quinonoid like tautomeric forms in a polar protic solvent.

Advances in heterocycles as DNA intercalating cancer drugs

The insertion of a molecule between the bases of DNA is known as intercalation. A molecule is able to interact with DNA in different ways. DNA intercalators are generally aromatic, planar, and polycyclic. In chemotherapeutic treatment, to suppress DNA replication in cancer cells, intercalators are used. In this article, we discuss the anticancer activity of 10 intensively studied DNA intercalators as drugs. The list includes proflavine, ethidium bromide, doxorubicin, dactinomycin, bleomycin, epirubicin, mitoxantrone, ellipticine, elinafide, and echinomycin. Considerable structural diversities are seen in these molecules. Besides, some examples of the metallo-intercalators are presented at the end of the chapter. These molecules have other crucial properties that are also useful in the treatment of cancers. The successes and limitations of these molecules are also presented.

Bioactive Olivacine Derivatives-Potential Application in Cancer Therapy

Olivacine and its derivatives are characterized by multidirectional biological activity. Noteworthy is their antiproliferative effect related to various mechanisms, such as inhibition of growth factors, enzymes, kinases and others. The activity of these compounds was tested on cell lines of various tumors. In most publications, the most active olivacine derivatives exceeded the effects of doxorubicin (a commonly used anticancer drug), so in the future, they may become the main new anticancer drugs. In this publication, we present the groups of the most active olivacine derivatives obtained. In this work, the in vitro and in vivo activity of olivacine and its most active derivatives are presented. We describe olivacine derivatives that have been in clinical trials. We conducted a structure-activity relationship (SAR) analysis that may be used to obtain new olivacine derivatives with better properties than the available anticancer drugs.

Antitumor Activity of New Olivacine Derivatives

Olivacine is an alkaloid-containing pyridocarbazole structure. It is isolated from the bark of the evergreen timber tree, Aspidosperma olivaceum. Its well-documented anticancer activity led to the synthesis of new derivatives, which are semisynthetic and fully synthetic pyridocarbazoles. This study aimed to evaluate the potential antineoplastic activity of four newly synthesized olivacine derivatives. Multidrug resistance is a common phenomenon causing failure in the chemotherapy of many tumors. It is mainly related to increased function of P-glycoprotein, an efflux pump removing cytostatic out of the cells. The cell lines used in the study were colorectal carcinoma cell lines: LoVo (doxorubicin-sensitive) and LoVo/DX (doxorubicin-resistant). The NHDF cell line was used to assess cell viability. First, the cells were incubated with olivacine derivatives. In the next step, the following assays were performed: DCF-DA assay, MTT assay, rhodamine 123 assay, detection of apoptosis, proliferation inhibition-mitotic index. The tested compounds showed higher antineoplastic potential and lower toxicity than the reference compound ellipticine. The results indicate that the new olivacine derivatives are good candidates for future anticancer drugs.

The anticancer drug ellipticine activated with cytochrome P450 mediates DNA damage determining its pharmacological efficiencies: studies with rats, Hepatic Cytochrome P450 Reductase Null (HRN™) mice and pure enzymes

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.

Ellipticine oxidation and DNA adduct formation in human hepatocytes is catalyzed by human cytochromes P450 and enhanced by cytochrome b5

Ellipticine is an antineoplastic agent considered a pro-drug, the pharmacological and genotoxic effects of which are dependent on cytochrome P450 (CYP)- and/or peroxidase-mediated activation to covalent DNA adducts. We investigated whether ellipticine-DNA adducts are formed in human hepatic microsomes and human hepatocytes. We then identified which human CYPs oxidize ellipticine to metabolites forming DNA adducts and the effect of cytochrome b(5) on this oxidation. 13-Hydroxyellipticine, the metabolite forming the major ellipticine-DNA adduct, was generated mainly by CYP3A4 and 1A1, followed by CYP2D6>2C19>1B1>1A2>2E1 and >2C9. Cytochrome b(5) increased formation of this metabolite by human CYPs, predominantly by CYP1A1, 3A4, 1A2 and 2C19. Formation of 12-hydroxyellipticine is generated mainly by CYP2C19, followed by CYP2C9>3A4>2D6>2E1 and >2A6. Other CYPs were less active (CYP2C8 and 2B6) or did not oxidize ellipticine to this metabolite (CYP1A1, 1A2 and 1B1). CYP2D6 was the most efficient enzyme generating ellipticine N(2)-oxide. CYP3A4 and 1A1 in the presence of cytochrome b(5) are mainly responsible for bioactivation of ellipticine to DNA adduct 1 (formed by ellipticine-13-ylium from 13-hydroxyellipticine), while 12-hydroxyellipticine generated during the CYP2C19-mediated ellipticine oxidation is the predominant metabolite forming ellipticine-12-ylium that generates ellipticine-DNA adduct 2. These ellipticine-DNA adducts were also generated by human hepatic microsomes and in primary human hepatocytes exposed to ellipticine. Ellipticine is toxic to these hepatocytes, decreasing their viability; the IC(50) value of ellipticine in these cells was 0.7 μM. In liver CYP3A4 is the predominant ellipticine activating CYP species, which is expected to result in efficient metabolism after oral ingestion of ellipticine in humans.

The mechanism of cytotoxicity and DNA adduct formation by the anticancer drug ellipticine in human neuroblastoma cells

Ellipticine is an antineoplastic agent, whose mode of action is based mainly on DNA intercalation, inhibition of topoisomerase II and formation of covalent DNA adducts mediated by cytochromes P450 and peroxidases. Here, the molecular mechanism of DNA-mediated ellipticine action in human neuroblastoma IMR-32, UKF-NB-3 and UKF-NB-4 cancer cell lines was investigated. Treatment of neuroblastoma cells with ellipticine resulted in apoptosis induction, which was verified by the appearance of DNA fragmentation, and in inhibition of cell growth. These effects were associated with formation of two covalent ellipticine-derived DNA adducts, identical to those formed by the cytochrome P450- and peroxidase-mediated ellipticine metabolites, 13-hydroxy- and 12-hydroxyellipticine. The expression of these enzymes at mRNA and protein levels and their ability to generate ellipticine-DNA adducts in neuroblastoma cells were proven, using the real-time polymerase chain reaction, Western blotting analyses and by analyzing ellipticine-DNA adducts in incubations of this drug with neuroblastoma S9 fractions, enzyme cofactors and DNA. The levels of DNA adducts correlated with toxicity of ellipticine to IMR-32 and UKF-NB-4 cells, but not with that to UKF-NB-3 cells. In addition, hypoxic cell culture conditions resulted in a decrease in ellipticine toxicity to IMR-32 and UKF-NB-4 cells and this correlated with lower levels of DNA adducts. Both these cell lines accumulated in S phase, suggesting that ellipticine-DNA adducts interfere with DNA replication. The results demonstrate that among the multiple modes of ellipticine antitumor action, formation of covalent DNA adducts by ellipticine is the predominant mechanism of cytotoxicity to IMR-32 and UKF-NB-4 neuroblastoma cells.

DNA adduct formation by the anticancer drug ellipticine in human leukemia HL-60 and CCRF-CEM cells

Ellipticine induces formation of two DNA adducts in leukemia HL-60 and CCRF-CEM cells, identical with deoxyguanosine adducts generated by ellipticine metabolites 13-hydroxyellipticine and 12-hydroxyellipticine in vitro and in vivo. The ellipticine cytotoxicity to HL-60 (IC(50)=0.64microM) and CCRF-CEM cells (IC(50)=4.7microM) correlates with levels of DNA adducts. The different expressions of enzymes activating ellipticine in cells explain this finding. While cytochrome P450 1A1 and cyclooxygenase-1 are expressed in both cells, HL-60 cells express also high levels of another activator, myeloperoxidase. The results suggest the adduct formation as a new mode of antitumor action of ellipticine for leukemia.

Formation and persistence of DNA adducts of anticancer drug ellipticine in rats

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.

Synthesis and Biological Evaluation of Indoloquinolines and Pyridocarbazoles: A New Example of Unexpected Photoreduction Accompanying Photocyclization

Indoloquinoline alkaloid cryptolepine and pyridocarbazole alkaloid ellipticine are of great interest because in vitro and in vivo studies revealed their good cytotoxic properties. In order to obtain some biologically active analogs of these compounds, we developed a synthesis based on the photocyclization of tertiary N-substituted enaminones derived from 1,3-cyclohexandione and 3 or 6-aminoquinoline. The angular cyclized compounds thus obtained were tested in vitro on K 562 cells and A 2780 doxorubicin sensitive and resistant cells. All compounds were less effective than doxorubicin in sensitive cells but their activity wasn't decreased by MDR resistance.

Molecular mechanisms of antineoplastic action of an anticancer drug ellipticine

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.

Mammalian peroxidases activate anticancer drug ellipticine to intermediates forming deoxyguanosine adducts in DNA identical to those foundin vivo and generated from 12-hydroxyellipticine and 13-hydroxyellipticine

Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation, inhibition of topoisomerase II and cytochrome P450-mediated formation of covalent DNA adducts. This is the first report on the molecular mechanism of ellipticine oxidation by peroxidases (human myeloperoxidase, human and ovine cyclooxygenases, bovine lactoperoxidase, horseradish peroxidase) to species forming ellipticine-DNA adducts. Using NMR spectroscopy, the structures of 2 ellipticine metabolites were identified; the major product is the ellipticine dimer, in which the 2 ellipticine skeletons are connected via N(6) of the pyrrole ring of one ellipticine molecule and C9 in the second one. The minor metabolite is ellipticine N(2)-oxide. Using (32)P-postlabeling and [(3)H]-labeled ellipticine, we showed that ellipticine binds covalently to DNA after its activation by peroxidases. The DNA adduct pattern induced by ellipticine consisted of a cluster of up to 4 adducts. The 2 adducts are indistinguishable from the 2 major adducts generated between deoxyguanosine in DNA and either 13-hydroxy- or 12-hydroxyellipticine or in rats treated with ellipticine, or if ellipticine was activated with human hepatic and renal microsomes. The results presented here are the first characterization of the peroxidase-mediated oxidative metabolites of ellipticine and we have proposed species, 2 carbenium ions, ellipticine-13-ylium and ellipticine-12-ylium, as reactive species generating 2 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.

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

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 nitrogenN6in 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 ellipticinein vivoandin vitroby its activation with cytochromes P450 and peroxidases.

DNA adduct formation by the anticancer drug ellipticine in rats determined by 32P postlabeling

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.

A Photochemical Approach to Pyridopyrroloquinoline Derivatives as New Potential Anticancer Agents

Indoloquinoline alkaloid cryptolepine and pyridocarbazole alkaloid ellipticine are of great interest because in vitro and in vivo studies revealed their good cytotoxic properties. In order to obtain some biologically active analogs of these compounds, we developped a synthesis based on the photocyclisation of tertiary N-methylated enaminones derived from cyclopentane-1,3-dione and 3 or 6-aminoquinoline. The angular cyclised compounds thus obtained were submitted to Beckmann rearrangement, preceded by the formation of a Z oxime. Finally, the delta-lactame ring was oxidized using 10% palladium/carbon in diphenylether and pyridopyrroloquinolines were obtained. These compounds and the intermediate lactams and cyclopentanopyrroloquinolines were tested in vitro on K 562 cells and A 2780 doxorubicine sensitive and resistant cells. All compounds were less effective than doxorubicine in sensitive cells but their activity wasn't decreased by MDR resistance.

DNA Adduct Formation by the Anticancer Drug Ellipticine and Its Hydroxy Derivatives in Human Breast Adenocarcinoma MCF-7 Cells

The cytotoxicity of the antineoplastic agent ellipticine and its 9- and 7-hydroxylated metabolites to human breast adenocarcinoma MCF-7 cells and their ability to generate DNA adducts in these cancer cells were investigated. Ellipticine and its 9-hydroxylated metabolite were found to be toxic to MCF-7 cells with IC50values of 1.25 and 3.25 μmol l-1for ellipticine and 9-hydroxyellipticine, respectively. In contrast, no toxicity to these cancer cells was detectable for 7-hydroxyellipticine. The nuclease P1 version of the32P-postlabeling assay yielded a pattern of ellipticine-DNA adducts with two major and one minor adducts in MCF-7 cells, similar to the pattern of adducts detected in DNA reacted with ellipticine and the reconstituted cytochrome P450 enzyme systemin vitroand in DNAin vivo. The identity of two major adducts formed in DNA of MCF-7 cells with those formed by cytochrome P450-mediated ellipticine activationin vitrowas confirmed by HPLC of the isolated adducts. 9-Hydroxyellipticine was also capable of inducing DNA adducts in MCF-7 cells, but to a lesser extent. In addition, the adducts generated by 9-hydroxyellipticine were different from those generated by ellipticine. Negligible levels of DNA adducts were detectable in DNA of MCF-7 cells exposed to 7-hydroxyellipticine. The results presented here are the first report showing the formation of covalent DNA adducts with ellipticine in human breast cancer cells in culture, and suggest the formation of covalent DNA adducts as a new mode of antitumor action of ellipticine in breast cancer.

Covalent binding of the anticancer drug ellipticine to DNA in V79 cells transfected with human cytochrome P450 enzymes

Ellipticine is a potent antineoplastic agent whose mechanism 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 (CYP). We examined a panel of genetically engineered V79 cell lines including the parental line V79MZ and recombinant cells expressing the human CYP enzymes CYP1A1, CYP1A2 or CYP3A4 for their ability to activate ellipticine. The extent of activation was determined by analysing DNA adducts by 32P-postlabelling. Ellipticine was found to be toxic to all V79 cell lines with IC(50) values ranging from 0.25 to 0.40 microM. The nuclease P1 version of the 32P-postlabelling assay yielded a similar pattern of ellipticine-DNA adducts with two major adducts in all cells, the formation of only one of which was dependent on CYP activity. This pattern is identical to that detected in DNA reacted with ellipticine and the reconstituted CYP enzyme system in vitro as confirmed by HPLC of the isolated adducts. Total adduct levels ranged from 2 to 337 adducts per 10(8) nucleotides, in the parental line and in V79 expressing CYP3A4, respectively. As in vitro, human CYP1A2 and CYP1A1 were less active. The results presented here are the first report showing the formation of CYP-mediated covalent DNA adducts by ellipticine in cells in culture, and confirm the formation of covalent DNA adducts as a new mechanism of ellipticine action.

The anticancer agent ellipticine on activation by cytochrome P450 forms covalent DNA adducts

Ellipticine is a potent antitumor agent whose mechanism of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Using [3H]-labeled ellipticine, we observed substantial microsome (cytochrome P450)-dependent binding of ellipticine to DNA. In rat, rabbit, minipig, and human microsomes, in reconstituted systems with isolated cytochromes P450 and in Supersomes containing recombinantly expressed human cytochromes P450, we could show that ellipticine forms a covalent DNA adduct detected by [32P]-postlabeling. The most potent human enzyme is CYP3A4, followed by CYP1A1, CYP1A2, CYP1B1, and CYP2C9. Another minor adduct is formed independent of enzymatic activation. The [32P]-postlabeling analysis of DNA modified by activated ellipticine confirms the covalent binding to DNA as an important type of DNA modification. The DNA adduct formation we describe is a novel mechanism for the ellipticine action and might in part explain its tumor specificity.