Inhibition of p53 protein phosphorylation by 9-hydroxyellipticine: a possible anticancer mechanism

Novel carbazole-oxadiazoles as potential Staphylococcus aureus germicides

Staphylococcus aureus resistance poses nonnegligible threats to the livestock industry. In light of this, carbazole-oxadiazoles were designed and synthesized for treating S. aureus infection. Bioassay discovered that 3,6-dibromocarbazole derivative 13a had effective inhibitory activities to several Gram-positive bacteria, in particular to S. aureus, S. aureus ATCC 29213, MRSA and S. aureus ATCC 25923 (MICs = 0.6-4.6 nmol/mL), which was more active than norfloxacin (MICs = 6-40 nmol/mL). Subsequent studies showed that 3,6-dibromocarbazole derivative 13a acted rapidly on S. aureus ATCC 29213 and possessed no obvious tendency to induce bacterial resistance. Further evaluations indicated that 3,6-dibromocarbazole derivative 13a showed strong abilities to disrupt bacterial biofilm and interfere with DNA, which might be the power sources of antibacterial performances. Moreover, 3,6-dibromocarbazole derivative 13a also exhibited slight cell lethality toward Hek 293 T and LO2 cells and low hemolytic toxicity to red blood cells. The above results implied that the active molecule 13a could be studied in the future development of agricultural available antibiotics.

Discovery of Selective RNA-Binding Small Molecules by Affinity-Selection Mass Spectrometry

Recent advances in understanding the relevance of noncoding RNA (ncRNA) to disease have increased interest in drugging ncRNA with small molecules. The recent discovery of ribocil, a structurally distinct synthetic mimic of the natural ligand of the flavin mononucleotide (FMN) riboswitch, has revealed the potential chemical diversity of small molecules that target ncRNA. Affinity-selection mass spectrometry (AS-MS) is theoretically applicable to high-throughput screening (HTS) of small molecules binding to ncRNA. Here, we report the first application of the Automated Ligand Detection System (ALIS), an indirect AS-MS technique, for the selective detection of small molecule-ncRNA interactions, high-throughput screening against large unbiased small-molecule libraries, and identification and characterization of novel compounds (structurally distinct from both FMN and ribocil) that target the FMN riboswitch. Crystal structures reveal that different compounds induce various conformations of the FMN riboswitch, leading to different activity profiles. Our findings validate the ALIS platform for HTS screening for RNA-binding small molecules and further demonstrate that ncRNA can be broadly targeted by chemically diverse yet selective small molecules as therapeutics.

Determination of binding modes and binding constants for the complexes of 6H-pyrido[4,3-b]carbazole derivatives with DNA

The binding modes and binding constants for the complexes of forty types of pyridocarbazole derivatives 1-40 with double stranded DNAs (dsDNAs) were reported. The binding modes were determined by a combination of a deflection spectroscopy and orientation of the corresponding molecule in the DNA-based film with chain alignment. All of the compounds exhibited the intercalation-binding mode. Its binding constants K_a for the complexes, determined by quartz crystal microbalance (QCM), varied from 1.7×10⁵ to 4.5×10⁷M^-1 according to the substituents on the pyridocarbazole framework and the sequences of dsDNA. The binding constants K_a of pyridocarbazole derivatives possessing the 2-(ω-amino)alkyl group and 5-(ω-amino)alkylcarbamyl group were larger than those of the corresponding ω-ureido derivatives. These ω-amino compounds exhibited strong GC base-pair preference in complexation. The K_a values decreased with the increasing NaCl concentration. It was clarified by a molecular modeling that the framework of the 2-tethered ω-amino derivative was completely overlapped with the stacking GC base-pairs leading to the formation of the stable intercalative-complex, and that the framework of the 5-tethered ureido derivative was half overlapped leading to the formation of the unstable complex. Furthermore, there were good linear relationships between lnK_a and the relative stabilities S_rel of the complexes. Contrary to our expectation, there was no linear relationship between lnK_a and IC₅₀ against Sarcoma-180, NIH3T3, and HeLa S-3 cell lines.

3-(Dipropylamino)-5-hydroxybenzofuro[2,3-f]quinazolin-1(2H)-one (DPA-HBFQ-1) plays an inhibitory role on breast cancer cell growth and progression

A series of unknown 3-(alkyl(dialkyl)amino)benzofuro[2,3-f]quinazolin-1(2H)-ones 4-17 has been synthesized as new ellipticine analogs, in which the carbazole moiety and the pyridine ring were replaced by a dibenzofuran residue and a pyrimidine ring, respectively. The synthesis of these benzofuroquinazolinones 4-17 was performed in a simple one-pot reaction using 3-aminodibenzofuran or its 2-methoxy derivative, as starting materials. From 3-(dipropylamino)-5-methoxybenzofuro[2,3-f] quinazolin-1(2H)-one (13), we prepared 3-(dipropylamino)-5-hydroxybenzofuro[2,3-f]quinazolin-1(2H)-one (18), referred to as DPA-HBFQ-1. The cytotoxic activities of all the synthesized compounds, tested in different human breast cancer cell lines, revealed that DPA-HBFQ-1 was the most active compound. In particular, the latter was able to inhibit anchorage-dependent and -independent cell growth and to induce apoptosis in estrogen receptor alpha (ERα)-positive and -negative breast cancer cells. It did not affect proliferation and apoptotic responses in MCF-10A normal breast epithelial cells. The observed effects have been ascribed to an enhanced p21(Cip1/WAF1) expression in a p53-dependent manner of tumor suppressor and to a selective inhibition of human topoisomerase II. In addition, DPA-HBFQ-1 exerted growth inhibitory effects also in other cancer cell lines, even though with a lower cytotoxic activity. Our results indicate DPA-HBFQ-1 as a good candidate to be useful as cancer therapeutic agent, particularly for breast cancer.

Chemical Library Screening and Structure-Function Relationship Studies Identify Bisacodyl as a Potent and Selective Cytotoxic Agent Towards Quiescent Human Glioblastoma Tumor Stem-Like Cells

Cancer stem-like cells reside in hypoxic and slightly acidic tumor niches. Such microenvironments favor more aggressive undifferentiated phenotypes and a slow growing "quiescent state" which preserves them from chemotherapeutic agents that essentially target proliferating cells. Our objective was to identify compounds active on glioblastoma stem-like cells, including under conditions that mimick those found in vivo within this most severe and incurable form of brain malignancy. We screened the Prestwick Library to identify cytotoxic compounds towards glioblastoma stem-like cells, either in a proliferating state or in more slow-growing "quiescent" phenotype resulting from non-renewal of the culture medium in vitro. Compound effects were assessed by ATP-level determination using a cell-based assay. Twenty active molecules belonging to different pharmacological classes have thus been identified. Among those, the stimulant laxative drug bisacodyl was the sole to inhibit in a potent and specific manner the survival of quiescent glioblastoma stem-like cells. Subsequent structure-function relationship studies led to identification of 4,4'-dihydroxydiphenyl-2-pyridyl-methane (DDPM), the deacetylated form of bisacodyl, as the pharmacophore. To our knowledge, bisacodyl is currently the only known compound targeting glioblastoma cancer stem-like cells in their quiescent, more resistant state. Due to its known non-toxicity in humans, bisacodyl appears as a new potential anti-tumor agent that may, in association with classical chemotherapeutic compounds, participate in tumor eradication.

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.

Synthesis and in vitro antitumor activity of novel 2-alkyl-5-methoxycarbonyl-11-methyl-6H-pyrido[4,3-b]carbazol-2-ium and 2-alkylellipticin-2-ium chloride derivatives

Twenty-one types of novel ellipticine derivatives and pyridocarbazoles (5-methoxycarbonyl-11-methyl-6H-pyrido[4,3-b]carbazoles) with a nitrosourea moiety, linked by an oxydiethylene unit at the 2 position, were synthesized, and their cytotoxicity against HeLa S-3 cells was evaluated. Some of these new compounds exhibited potent antitumor activity by comparison with that of ellipticine.

Effects of ellipticine on ALDH1A1-expressing breast cancer stem cells--an in vitro and in silico study

Targeting breast cancer stem cells (BCSCs) offers a promising strategy for breast cancer treatment. We examined the plant alkaloid ellipticine for its efficacy to inhibit the expression of aldehyde dehydrogenase 1 class A1 (ALDH1A1)-positive BCSCs by in vitro and in silico methods. At 3 mM concentration, ellipticine decreased the expression of ALDH1A1-positive BCSCs by 62% (p = 0.073) in the MCF7 cell line and by 53% (p = 0.024) in the SUM159 cell line compared to vehicle-treated cultures. Ellipticine significantly reduced the formation of mammospheres, whereas paclitaxel enhanced mammosphere formation in both the treated cell lines. Interestingly, when treated with a combination of ellipticine and paclitaxel, the percentage of ALDH1A1-positive BCSCs dropped by several fold in vitro. A homology model of Homo sapiens ALDH1A1 was built using the crystal structure of NAD-bound sheep liver class I aldehyde dehydrogenase [PDB ID: 1BXS] as a template. Molecular simulation and docking studies revealed that the amino acids Asn-117 and Asn-121, Glu-249, Cys-302, and Gln-350, present in the active site of human ALDH1A1, played a vital role in interacting with the drug. The present study suggests that ellipticine reduces the proliferation and self-renewal ability of ALDH1A1-positive BCSCs and can be used in combination with a cytotoxic drug like paclitaxel for potential targeting of BCSCs.

Old drug, new target: ellipticines selectively inhibit RNA polymerase I transcription

Transcription by RNA polymerase I (Pol-I) is the main driving force behind ribosome biogenesis, a fundamental cellular process that requires the coordinated transcription of all three nuclear polymerases. Increased Pol-I transcription and the concurrent increase in ribosome biogenesis has been linked to the high rates of proliferation in cancers. The ellipticine family contains a number of potent anticancer therapeutic agents, some having progressed to stage I and II clinical trials; however, the mechanism by which many of the compounds work remains unclear. It has long been thought that inhibition of Top2 is the main reason behind the drugs antiproliferative effects. Here we report that a number of the ellipticines, including 9-hydroxyellipticine, are potent and specific inhibitors of Pol-I transcription, with IC(50) in vitro and in cells in the nanomolar range. Essentially, the drugs did not affect Pol-II and Pol-III transcription, demonstrating a high selectivity. We have shown that Pol-I inhibition occurs by a p53-, ATM/ATR-, and Top2-independent mechanism. We discovered that the drug influences the assembly and stability of preinitiation complexes by targeting the interaction between promoter recognition factor SL1 and the rRNA promoter. Our findings will have an impact on the design and development of novel therapeutic agents specifically targeting ribosome biogenesis.

Mutant p53 exhibits trivial effects on mitochondrial functions which can be reactivated by ellipticine in lymphoma cells

Increasing evidence has shown that a fraction of the wild-type (wt) form of the tumor suppressor p53, can translocate to mitochondria due to genotoxic stress. The mitochondrial targets of wt p53 have also been studied. However, whether mutant p53, which exists in 50% of human cancers, translocates to mitochondria and affects mitochondrial functions is unclear. In this study, we used doxorubicin, a chemotherapeutic drug, to treat five human lymphoma cell lines with wt, mutant or deficient in p53, to induce p53 activation and mitochondrial translocation. Our results demonstrated that mutant p53, like wt p53, was induced upon doxorubicin treatment. Similarly, a fraction of mutant p53 also translocated to mitochondria. However, Complex I and II activities in the mitochondria were compromised only in wt p53-bearing cells after doxorubicin treatment, but not in mutant p53-bearing cells. Similarly, doxorubicin treatment caused greater cell death only in wt p53-bearing cells, but not in mutant p53-bearing cells. When p53 deficient Ramos cells were transfected with mutant p53 (249S), the cells showed resistance to doxorubicin-induced cell death and decreases in complex activities. To reactivate mutant p53 and reverse chemoresistance, ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) was used to treat mutant p53 cells. Ellipticine enhanced p53 mitochondrial translocation, decreased Complex I activity, and sensitized p53 mutant cells to doxorubicin-induced apoptosis. In summary, our studies suggest that mutations in p53 may not hinder p53's mitochondrial translocation, but impair its effects on mitochondrial functions. Therefore, restoring mutant p53 by ellipticine may sensitize these cells to chemotherapy.

Ellipticine cytotoxicity to cancer cell lines - a comparative study

Ellipticine is a potent antineoplastic agent exhibiting multiple mechanisms of action. This anticancer agent should be considered a pro-drug, whose pharmacological efficiency and/or genotoxic side effects are dependent on its cytochrome P450 (CYP)- and/or peroxidase-mediated activation to species forming covalent DNA adducts. Ellipticine can also act as an inhibitor or inducer of biotransformation enzymes, thereby modulating its own metabolism leading to its genotoxic and pharmacological effects. Here, a comparison of the toxicity of ellipticine to human breast adenocarcinoma MCF-7 cells, leukemia HL-60 and CCRF-CEM cells, neuroblastoma IMR-32, UKF-NB-3 and UKF-NB-4 cells and U87MG glioblastoma cells and mechanisms of its action to these cells were evaluated. Treatment of all cells tested with ellipticine resulted in inhibition of cell growth and proliferation. This effect was associated with formation of two covalent ellipticine-derived DNA adducts, identical to those formed by 13-hydroxy- and 12-hydroxyellipticine, the ellipticine metabolites generated by CYP and peroxidase enzymes, in MCF-7, HL-60, CCRF-CEM, UKF-NB-3, UKF-NB-4 and U87MG cells, but not in neuroblastoma UKF-NB-3 cells. Therefore, DNA adduct formation in most cancer cell lines tested in this comparative study might be the predominant cause of their sensitivity to ellipticine treatment, whereas other mechanisms of ellipticine action also contribute to its cytotoxicity to neuroblastoma UKF-NB-3 cells.

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.

A high-content chemical screen identifies ellipticine as a modulator of p53 nuclear localization

p53 regulates apoptosis and the cell cycle through actions in the nucleus and cytoplasm. Altering the subcellular localization of p53 can alter its biological function. Therefore, small molecules that change the localization of p53 would be useful chemical probes to understand the influence of subcellular localization on the function of p53. To identify such molecules, a high-content screen for compounds that increased the localization of p53 to the nucleus or cytoplasm was developed, automated, and conducted. With this image-based assay, we identified ellipticine that increased the nuclear localization of GFP-mutant p53 protein but not GFP alone in Saos-2 osteosarcoma cells. In addition, ellipticine increased the nuclear localization of endogenous p53 in HCT116 colon cancer cells with a resultant increase in the transactivation of the p21 promoter. Increased nuclear p53 after ellipticine treatment was not associated with an increase in DNA double stranded breaks, indicating that ellipticine shifts p53 to the nucleus through a mechanism independent of DNA damage. Thus, a chemical biology approach has identified a molecule that shifts the localization of p53 and enhances its nuclear activity.

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.

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.

The mechanism of ellipticine-induced apoptosis and cell cycle arrest in human breast MCF-7 cancer cells

Ellipticine, a cytotoxic plant alkaloid, is known to inhibit topoisomerase II. Here, we first report the molecular mechanism of ellipticine's apoptotic action in human breast MCF-7 cancer cells. Treatment of cells with ellipticine resulted in inhibition of growth, and G2/M phase arrest of the cell cycle. This effect was associated with a marked increase in the protein expression of p53 and, p21/WAF1 and KIP1/p27, but not of WAF1/p21. Ellipticine treatment increased the expression of Fas/APO-1 and its ligands, mFas ligand and sFas ligand, and subsequent activation of caspase-8. The mitochondrial apoptotic pathway amplified the Fas/Fas ligand death receptor pathway by Bid interaction. This effect was found to result in a significant increase in activation of caspase-9. Taken together, we have concluded that the molecular mechanisms during ellipticine-mediated growth inhibition and induction of apoptosis in MCF-7 cells were due to (1) cell cycle arrest and induction of apoptosis, (2) induction of p53 and KIP1/p27 expression, (3) triggering of Fas/Fas ligand pathway, (4) disruption of mitochondrial function, and (5) the apoptotic signaling was amplified by cross-talk between Fas death receptor and mitochondrial apoptotic pathway.

The therapeutic potential of targeting the cell cycle

With the advent of modern molecular genetics, molecular biology and biochemistry has come a revolution in oncology drug discovery research. We are rapidly developing an increased understanding in the mechanisms driving cellular proliferation, transformation, differentiation and metastasis. The hope is that from these advances will emerge novel therapeutics that are more specific, more efficacious and less toxic than their predecessors. Uncontrolled proliferation is a hallmark of a cancer cell. Over the past two decades it has become increasingly clear that molecules that directly control cell cycle progression accumulate defects during tumourigenesis. These defects can result in the loss of checkpoint control and/or the inappropriate activation of the 'drivers' of cell cycle progression, the cyclin-dependent kinases (cdks). This review will describe the recent advances in our understanding of cell cycle regulation and its relation to tumourigenesis, and highlight the potential for the development of novel anticancer therapeutics.

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.

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.

The cell cycle: a review of regulation, deregulation and therapeutic targets in cancer

The cell cycle is controlled by numerous mechanisms ensuring correct cell division. This review will focus on these mechanisms, i.e. regulation of cyclin-dependent kinases (CDK) by cyclins, CDK inhibitors and phosphorylating events. The quality checkpoints activated after DNA damage are also discussed. The complexity of the regulation of the cell cycle is also reflected in the different alterations leading to aberrant cell proliferation and development of cancer. Consequently, targeting the cell cycle in general and CDK in particular presents unique opportunities for drug discovery. This review provides an overview of deregulation of the cell cycle in cancer. Different families of known CDK inhibitors acting by ATP competition are also discussed. Currently, at least three compounds with CDK inhibitory activity (flavopiridol, UCN-01, roscovitine) have entered clinical trials.

Rat microsomes activating the anticancer drug ellipticine to species covalently binding to deoxyguanosine in DNA are a suitable model mimicking ellipticine bioactivation in humans

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.

1,5-dimethyl-6H-pyridazino[4,5-b]carbazole, a 3-aza bioisoster of the antitumor alkaloid olivacine

A series of b-fused carbazoles structurally related to pyrido[4,3-b]carbazole-type alkaloids was prepared, utilizing the Diels-Alder reaction of 1-methylpyrano[3,4-b]indol-3(9H)-one with electron-deficient acetylenic dienophiles as the key step. The title compound (14) thus obtained in only four steps represents a new 3-aza analog of the antitumor natural product, olivacine.

A novel high-through-put assay for screening of pro-apoptotic drugs

Screening for anti-cancer substances is commonly conducted using viability assays. An inherent problem with this approach is that all compounds that are toxic and growth inhibitory, irrespective of mechanism of action, will score positive. It would be beneficial to be able to screen for compounds that specifically induce apoptosis. We here describe an ELISA-assay based on a monoclonal antibody (M30) which recognizes a neo-epitope on cytokeratin 18 exposed after cleavage by caspases during apoptosis. We show that this assay detects apoptosis in epithelial cells and that the sensitivity is sufficient for screening in the 96-well format. We used the M30-ELISA assay to screen 500 low molecular weight compounds from a chemical library from the National Cancer Institute and identified 16 drugs with strong pro-apoptotic activity, suggesting that the assay is a useful tool for discovery of pro-apoptotic drugs.

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.

Diverse effects of 9-hydroxyellipticine on the chemosensitivity of human pancreatic cancer cells harboring p53 mutations

Recently, it has been shown that 9-hydroxyellipticine (9-HE), an antitumor alkaloid has a unique property of restoring functional wild-type (wt) p53 activity via inhibition of mutant (mt) p53 protein phosphorylation. In the present study, we investigated the effect of 9-HE on the drug sensitivity of human pancreatic cancer cells. Exposure of cells to 9-HE at a relatively low concentration of 1 microM induced almost no cell death but was sufficient to restore wt p53 activity, as evidenced by an induction of endogenous p21WAF1/CIP1 concomitant with G1 and G2/M arrests in cell-cycle progression. Pretreatment with 1 microM 9-HE markedly enhanced cell killing when combined with cisplatin or mitomycin C. In contrast, 9-HE pretreatment protected cells from killing by 5-fluorouracil, VP-16, or vincristine. These effects of 9-HE were specific for several cell lines containing mt p53 and were not observed in p53-negative or wt p53 expressing cells. Taken together, these findings suggest that 9-HE may exert different effects on the drug sensitivity of pancreatic cancer cells displaying p53 mutations possibly through restoration of wt p53.

Protection against 12-O-tetradecanoylphorbol-13-acetate induced skin-hyperplasia and tumor promotion, in a two-stage carcinogenesis mouse model, by the 2,3-dimethyl-6(2-dimethylaminoethyl)-6H-indolo-[2,3-b]quinoxaline analogue of ellipticine

The effects of topical applications of 2,3-dimethyl-6(2-dimethylaminoethyl)-6H-indolo-[2,3-b]quinoxaline (B-220), on 12-O-tetradecanoylphorbol-13-acetate (TPA) or benzoylperoxide (BPO) induced promotion of skin tumors and hyperplasia were studied in female SENCAR mice. Papillomas were induced by initiation with 7,12-dimethylbenz[a]anthracene (DMBA), followed by promotion biweekly with TPA or BPO. Administration of B-220 1 h before TPA promotion resulted in a prolonged latency period of tumor appearance and a significantly reduced (up to 15% of positive controls) papilloma yield at 20 weeks. Moreover, if B-220 treatment was terminated after 20 weeks and TPA treatment continued, papilloma development resumed indicating that initiated tumor cells were still present but were unable to grow with B-220 present. If B-220 pretreatment was not given during the first 10 weeks of TPA promotion, incidence at 20 weeks was not reduced but tumor multiplicity was still decreased. In addition a marked reduction of the TPA induced sustained epidermal hyperplasia was observed in the long term experiment. Neither the inflammatory response nor the increase in the number of apoptotic cells seen in short term experiment after a single TPA treatment were inhibited by B-220. B-220 administration before BPO promotion had no effect on the appearance of BPO induced papillomas or epidermal hyperplasia, suggesting that TPA and BPO promote tumor formation via at least partially different mechanisms. In experiments where B-220 was applied topically 1 h before DMBA initiation, little or no effect was seen. No morphological changes in mouse skin due to long term exposure (two times/week, 39 weeks) to B-220 were found. In conclusion, we present evidence that B-220 is a potent inhibitor of mouse skin tumor promotion by TPA, but has little effect on the initiation step or the survival of initiated cells.

[The relationship between p53 protein and c-erb B-2 expression and apoptosis in colorectal cancer]

In order to elucidate the relationship between tumor growth and various kinds of gene expression and the occurrence of apoptosis in the front portion of neoplastic invasion, 57 advanced colorectal cancers were studied by immunohistochemical staining of p53, c-erb B-2, the TUNEL method and electron microscopy. Light microscopically, the columnar epithelial cells of adenocarcinoma frequently showed a decrease in high and a fall off into the lumen in tumor invasive forefront. Immunohistochemically the positive rate of p53 and c-erb B-2 in tumors with high vascular invasion were higher (p < 0.05) than in those with low vascular invasion. There was a close correlation between the vascular or lymphatic invasion and positive immunoreactivity of p53 and c-erb B-2. The apoptosis index was demonstrated to be related to vessel invasion, over expression of p53 and inflammatory cell infiltration around the front portion of the tumor invasion. These results suggested that p53. c-erb B-2 and the apoptosis index should be evaluated in conjunction with the prognostic factors in colorectal cancer. The infiltrative inflammatory cells may induce apoptosis of the tumor cells.

CDK inhibition and cancer therapy

The cell-division cycle is a tightly controlled process that is regulated by the cyclin/CDK family of protein kinase complexes. Stringent control of this process is essential to ensure that DNA synthesis and subsequent mitotic division are accurately and coordinately executed. There is now strong evidence that CDKs, their regulators, and substrates are the targets of genetic alteration in many human cancers. As a result of this, the CDKs have been targeted for drug discovery and a number of small molecule inhibitors of CDKs have been identified.

9-Hydroxyellipticine inhibits telomerase activity in human pancreatic cancer cells

There is increasing interest in identifying potent inhibitors of telomerase because the enzyme plays a crucial role in the development of cellular immortality and carcinogenesis. We hypothesized that 9-hydroxyellipticine (9-HE), an antitumor alkaloid, would inhibit telomerase activity because the drug has a unique mechanism of inhibiting phosphorylation of mutant p53 protein via inhibition of protein kinases, thereby restoring wild-type p53 function. This study was conducted to examine the effect of 9-HE on telomerase activity in human pancreatic cancer cells with differing p53 gene status. 9-HE treatment at relatively high concentrations resulted in rapid, complete inhibition of telomerase activity, irrespective of the p53 status. We conclude that 9-HE may exert a strong inhibitory effect on telomerase activity possibly through inhibition of protein kinases rather than through restoration of functional wild-type p53.

Inhibitory effects of ginsenoside Rh2 on tumor growth in nude mice bearing human ovarian cancer cells

Ginsenoside Rh2 (Rh2), isolated from an ethanol extract of the processed root of Panax ginseng CA Meyer, inhibits the growth of B16 melanoma cells. This study was designed to evaluate the ability of Rh2 to inhibit growth of human ovarian cancer cells (HRA) in vitro and in nude mouse. Rh2 inhibited proliferations of various established human ovarian cancer cell lines in a dose-dependent manner between 10 and 60 microM in vitro and induced apoptosis at around the IC50 dose. When HRA cells were inoculated s.c. into the right flank of nude mice, all mice formed a palpable tumor within 14 days. Although i.p. administration of Rh2 alone hardly inhibited the tumor growth, when Rh2 was combined with cis-diamminedichloroplatinum(II) (CDDP) the tumor growth was significantly inhibited, compared to treatment with CDDP alone. When mice were treated p.o. with Rh2 daily (but not weekly), the tumor growth was significantly (P<0.01) inhibited, compared to CDDP treatment alone. When Rh2 was combined with CDDP, the degree of tumor growth retardation was not potentiated. The survival time was significantly (P<0.05) longer than that of medium alone-treated controls or the group treated with CDDP alone. Then, we examined whether p.o. administration of Rh2 has a dose-dependent inhibitory effect on the tumor growth. I.p. and weekly administration of CDDP had more potent antitumor activity in the order of 1 mg/kg, 2 mg/kg and 4 mg/kg, whereas p.o. and daily administration of Rh, (0.4 to 1.6 mg/kg) not only had antitumor activity comparable to that of 4 mg/kg CDDP, but also resulted in a significant increase of the survival. Doses of Rh2 used in this study did not result in any adverse side-effects as confirmed by monitoring hematocrit values and body weight, unlike 4 mg/kg CDDP, which had severe side-effects. It is noteworthy that p.o. but not i.p. treatment with Rh2 resulted in induction of apoptotic cells in the tumor in addition to augmentation of the natural killer activity in spleen cells from tumor-hearing nude mice. Thus, particularly in view of the toxicity of CDDP, Rh2 alone would seem to warrant further evaluation for treatment of recurrent or refractory ovarian tumor.