DNA-drug recognition and effects on topoisomerase II-mediated cytotoxicity. A three-mode binding model for ellipticine derivatives

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.

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.

Anticancer and Immunomodulatory Activities of a Novel Water-Soluble Derivative of Ellipticine

Cancer still remains a major public health concern around the world and the search for new potential antitumor molecules is essential for fighting the disease. This study evaluated the anticancer and immunomodulatory potential of the newly synthetized ellipticine derivate: sodium bromo-5,11-dimethyl-6H-pyrido[4,3-b]carbazole-7-sulfonate (Br-Ell-SO₃Na). It was prepared by the chlorosulfonation of 9-bromoellipticine. The ellipticine-7-sulfonic acid itself is not soluble, but its saponification with sodium hydroxide afforded a water-soluble sodium salt. The cytotoxicity of Br-Ell-SO₃Na was tested against cancerous (K562 cell line) and non-cancerous cells (Vero cell line and human peripheral blood mononuclear cells (PBMC)) using a Methylthiazoletetrazolium (MTT) assay. Cell cycle arrest was assessed by flow cytometry and the immunomodulatory activity was analyzed through an enzyme-linked immunosorbent assay (ELISA)_. The results showed that the Br-Ell-SO₃Na molecule has specific anticancer activity (IC₅₀ = 35 µM) against the K562 cell line, once no cytotoxicity effect was verified against non-cancerous cells. Cell cycle analysis demonstrated that K562 cells treated with Br-Ell-SO₃Na were arrested in the phase S. Moreover, the production of IL-6 increased and the expression of IL-8 was inhibited in the human PBMC treated with Br-Ell-SO₃Na. The results demonstrated that Br-Ell-SO₃Na is a promising anticancer molecule attested by its noteworthy activity against the K562 tumor cell line and immunomodulatory activity in human PBMC cells.

Novel 11-Substituted Ellipticines as Potent Anticancer Agents with Divergent Activity against Cancer Cells

Ellipticines have well documented anticancer activity, in particular with substitution at the 1-, 2-, 6- and 9-positions. However, due to limitations in synthesis and coherent screening methodology the full SAR profile of this anticancer class has not yet been achieved. In order to address this shortfall, we have set out to explore the anticancer activity of this potent natural product by substitution. We currently describe the synthesis of novel 11-substituted ellipticines with two specific derivatives showing potency and diverging cellular growth effects.

Concentration-response studies of the chromosome-damaging effects of topoisomerase II inhibitors determined in vitro using human TK6 cells

Topoisomerase II (topo II) inhibitors are commonly used as chemotherapy to treat multiple types of cancer, though their use is also associated with the development of therapy related acute leukemias. While the chromosome-damaging effects of etoposide, a topo II poison, have been proposed to act through a threshold mechanism, little is known about the chromosome damaging effects and dose responses for the catalytic inhibitors of the enzyme. The current study was designed to further investigate the potencies and concentration-response relationships of several topoisomerase II inhibitors, including the topoisomerase II poison etoposide, as well as catalytic inhibitors aclarubicin, merbarone, ICRF-154 and ICRF-187 using both a traditional in vitro micronucleus assay as well as a flow-cytometry based version of the assay. Benchmark dose (BMD) analysis was used to identify models that best fit the data and estimate a BMD, in this case the concentration at which a one standard deviation increase above the control frequency would be expected. All of the agents tested were potent in inducing micronuclei in human lymphoblastoid TK6 cells, with significant increases seen at low micromolar, and in the cases of aclarubicin and etoposide, at low nanomolar concentrations. Use of the anti-kinetochore CREST antibody with the microscopy-based assay demonstrated that the vast majority of the micronuclei originated from chromosome breakage. In comparing the two versions of the micronucleus assay, significant increases in micronucleated cells were observed at similar or lower concentrations using the traditional microscopy-based assay. BMD modeling of the data exhibited several advantages and proved to be a valuable alternative for concentration-response analysis, producing points of departure comparable to those derived using traditional no-observed or lowest-observed genotoxic effect level (NOGEL or LOGEL) approaches.

Some Reactions of 3-Chloroisoindolium Salts with Nucleophiles: Access to Isoindole Derivatives and Ellipticine Analogues as Potential Antiviral Agents

3-Chloro-2-substituted-1-oxoisoindolium hexachloroantimonate (1) reacted with water, ethanol and dimethyl-cyanamide to give the corresponding phthalimide derivatives 2, 3 and 4 respectively. Reaction of 1a with nitriles afforded the intermediate 2-azoniaallene salts 5 which underwent cyclisation reaction upon heating to furnish the ellipticine analogues 6. The biological activities of 6a–e against HIV-1 and HBV viruses were determined.

N-thioalkylcarbazoles derivatives as new anti-proliferative agents: synthesis, characterisation and molecular mechanism evaluation

Synthetic or natural carbazole derivatives constitute an interesting class of heterocycles, which showed several pharmaceutical properties and occupied a promising place as antitumour tools in preclinical studies. They target several cellular key-points, e.g. DNA and Topoisomerases I and II. The most studied representative, i.e. Ellipticine, was introduced in the treatment of metastatic breast cancer. However, because of the onset of dramatic side effects, its use was almost dismissed. Many efforts were made in order to design and synthesise new carbazole derivatives with good activity and reduced side effects. The major goal of the present study was to synthesise a series of new N-thioalkylcarbazole derivatives with anti-proliferative effects. Two compounds, 5a and 5c, possess an interesting anti-proliferative activity against breast and uterine cancer cell lines without affecting non-tumoural cell lines viability. The most active compound (5c) induces cancer cells death triggering the intrinsic apoptotic pathway by inhibition of Topoisomerase II.

Inhibition of Human Topoisomerase II by N,N,N-Trimethylethanammonium Iodide Alkylcarbazole Derivatives

Chemotherapy is used for the treatment of all stages of breast cancer, including the metastatic stage of the disease. Treatment regimens are generally tailored for each patient's particular situation. However, chemotherapeutic agents are the leading cause of serious drug-related adverse effects; moreover, drug resistance often occurs. In this study, we designed and synthesized a new series of N-alkylcarbazoles derived from ellipticine, an alkaloid with a carbazole skeleton initially used in the treatment of metastatic breast cancer and later dismissed because of poor aqueous solubility and severe side effects. After evaluating the binding modes of our class of newly synthesized compounds with human topoisomerase II (hTopo II), we performed hTopo II decatenation assays, identifying compound 4 f (2-(4-((3-chloro-9H-carbazol-9-yl)pentyl)piperazin-1-yl)-N,N,N-trimethylethanammonium iodide) as a good inhibitor. Moreover, 4 f and 4 g (2-(4-((3-chloro-9H-carbazol-9-yl)hexyl)piperazin-1-yl)-N,N,N-trimethylethanammonium iodide) showed a good anti-proliferative activity toward breast cancer cells, causing apoptosis by activation of the caspase pathway. Interestingly, the activity of these two compounds on triple-negative MDA-MB-231 cells, which tend to be highly metastatic and aggressive, is strictly connected to the observed inhibition of hTopo II.

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.

Inhibition of human DNA topoisomerase IIα by two novel ellipticine derivatives

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) is an antineoplastic agent that intercalates into DNA and alters topoisomerase II activity. Unfortunately, this compound displays a number of adverse properties. Therefore, to investigate new ellipticine-based compounds for their potential as topoisomerase II-targeted drugs, we synthesized two novel derivatives, N-methyl-5-demethyl ellipticine (ET-1) and 2-methyl-N-methyl-5-demethyl ellipticinium iodide (ET-2). As determined by DNA decatenation and cleavage assays, ET-1 and ET-2 act as catalytic inhibitors of human topoisomerase IIα and are both more potent than the parent compound. Neither compound impairs the ability of the type II enzyme to bind its DNA substrate. Finally, the potency of ET-1 and ET-2 as catalytic inhibitors of topoisomerase IIα appears to be related to their ability to intercalate into the double helix.

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.

Multispectroscopic methods reveal different modes of interaction of anti cancer drug mitoxantrone with Poly(dG-dC).Poly(dG-dC) and Poly(dA-dT).Poly(dA-dT)

The interaction of mitoxantrone with alternating Poly(dG-dC).Poly(dG-dC) and Poly(dA-dT).Poly(dA-dT) duplex has been studied by absorption, fluorescence and Circular Dichroism (CD) spectroscopy at Drug to Phosphate base pair ratios D/P=20.0-0.04. Binding to GC polymer occurs in two distinct modes: partial stacking characterized by red shifts of 18-23nm at D/P=0.2-0.8 and external binding at D/P=1.0-20.0 whereas that to AT polymer occurs externally in the entire range of D/P. The binding constant and number of binding sites is 3.7×10(5)M(-1), 0.3 and 1.3× 10(4)M(-1), 1.5 in GC and AT polymers, respectively at low D/P ratios. CD binding isotherms show breakpoints at D/P=0.1, 0.5 and 0.25, 0.5 in GC and AT polymers, respectively. The intrinsic CD bands indicate that the distortions in GC polymer are significantly higher than that in AT polymer. Docking studies show partial insertion of mitoxantrone rings between to GC base pairs in alternating GC polymer. Side chains of mitoxantrone interact specifically with base pairs and DNA backbone. The studies are relevant to the understanding of suppression or inhibition of DNA cleavage on formation of ternary complex with topoisomerase-II enzyme and hence the anti cancer action.

Interaction of anticancer drug mitoxantrone with DNA hexamer sequence d-(CTCGAG)2 by absorption, fluorescence and circular dichroism spectroscopy

The interaction of mitoxantrone with d-(CTCGAG)2 has been studied by absorption, fluorescence and circular dichroism (CD) spectroscopy. The hypochromism and quenching of fluorescence showed that about four mitoxantrone molecules may be binding externally to DNA hexamer sequence at high drug to nucleic (D/N) acid duplex ratios (28.0-1.1). At lower D/N ratios (1.0-0.2), a red shift in absorption maxima at 610 and 660 nm by 15 and 20 nm, respectively and a red shift in emission maxima by 11 nm accompanied by increase in absorbance and emission has been observed. The equilibrium constant for binding at low (1.0-0.2) and high (28.0-1.1) D/N ratios is 1.8×10(5) M(-1) and 1.38×10(6) M(-1), respectively. The CD spectra show change in intensity of bands accompanied by appearance of induced bands at 325 nm and 650-700 nm. The 251 nm band shows blue shift at D/N ratio of 0.25 and 0.5. The binding isotherms show stoichiometry of 0.25 and 0.5 mitoxantrone molecules binding per duplex. The results suggest stacking of aromatic chromophore of mitoxantrone with terminal base pair of DNA strand forming a sandwiched structure of mitoxantrone between four and two duplex molecules. These investigations are relevant to the formation of ternary complex with topoisomerase enzyme and hence an understanding of anti tumor action of mitoxantrone.

Analysis of covalent ellipticine- and doxorubicin-derived adducts in DNA of neuroblastoma cells by the ³²P-postlabeling technique

BACKGROUND

Ellipticine and doxorubicin are antineoplastic agents, whose action is based mainly on DNA damage such as intercalation, inhibition of topoisomerase II and formation of covalent DNA adducts. The key target to resolve which of these mechanisms are responsible for ellipticine and doxorubicin anticancer effects is the development of suitable methods for identifying their individual DNA-damaging effects. Here, the (32)P-postlabeling method was tested to detect covalent DNA adducts formed by ellipticine and doxorubicin.

METHODS

The standard procedure of (32)P-postlabeling assay, this procedure under ATP-deficient conditions, the version using extraction of adducts with n-butanol and the nuclease P1 enrichment version were used to analyze ellipticineand/ or doxorubicin-derived DNA adducts.

RESULTS

Two covalent ellipticine-derived DNA adducts, which are associated with cytotoxicity of ellipticine to human UKF-NB-3 and UKF-NB-4 neuroblastoma cell lines, were detected by the (32)P-postlabeling method. These adducts are identical to those formed by the ellipticine metabolites, 13-hydroxy- and 12-hydroxyellipticine. In contrast, no covalent adducts formed by doxorubicin in DNA of these neuroblastoma cells and in DNA incubated with this drug and formaldehyde in vitro were detectable by the (32)P-postlabeling assay.

CONCLUSIONS

The results presented in this paper are the first to demonstrate that in contrast to covalent DNA adducts formed by ellipticine, the adducts generated by formaldehyde-mediated covalent binding of doxorubicin to DNA are not detectable by the (32)P-postlabeling assay. No DNA adducts were, detectable either in vitro, in incubations of DNA with doxorubicin or in DNA of neuroblastoma cells treated with this drug. The results also suggest that covalent binding of ellipticine to DNA of UKF-NB-3 and UKF-NB-4 neuroblastoma cell lines is the predominant mechanism responsible for the cytotoxicity of this drug. To understand the mechanisms of doxorubicin anticancer effects on neuroblastoma cells, development of novel methods for identifying covalent doxorubicin-derived DNA adducts is the major challenge for further research.

A chemical screen identifies the chemotherapeutic drug topotecan as a specific inhibitor of the B-MYB/MYCN axis in neuroblastoma

The transcription factor MycN is the prototypical neuroblastoma oncogene and a potential therapeutic target. However, its strong expression caused by gene amplification in about 30% of neuroblastoma patients is a considerable obstacle to the development of therapeutic approaches aiming at eliminating its tumourigenic activity. We have previously reported that B-Myb is essentially required for transcription of the MYCN amplicon and have also shown that B-MYB and MYCN are engaged in a feed forward loop promoting the survival/proliferation of neuroblastoma cells. We postulated that pharmacological strategies breaking the B-MYB/MYCN axis should result in clinically desirable effects. Thus, we implemented a high throughput chemical screen, using a curated library of ~1500 compounds from the National Cancer Institute, whose endpoint was the identification of small molecules that inhibited B-Myb. At the end of the screening, we found that the compounds pinafide, ellipticine and camptothecin inhibited B-Myb transcriptional activity in luciferase assays. One of the compounds, the topoisomerase-1 inhibitor camptothecin, is of considerable clinical interest since its derivatives topotecan and irinotecan are currently used as first and second line treatment agents for various types of cancer, including neuroblastoma. We found that neuroblastoma cells with amplification of MYCN are more sensitive than MYCN negative cells to camptothecin and topotecan killing. Campothecin and topotecan caused selective down-regulation of B-Myb and MycN expression in neuroblastoma cells. Notably, forced overexpression of B-Myb could antagonize the killing effect of topotecan and camptothecin, demonstrating that the transcription factor is a key target of the drugs. These results suggest that camptothecin and its analogues should be more effective in patients whose tumours feature amplification of MYCN and/or overexpression of B-MYB.

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.

Unprocessed viral DNA could be the primary target of the HIV-1 integrase inhibitor raltegravir

Integration of HIV DNA into host chromosome requires a 3'-processing (3'-P) and a strand transfer (ST) reactions catalyzed by virus integrase (IN). Raltegravir (RAL), commonly used in AIDS therapy, belongs to the family of IN ST inhibitors (INSTIs) acting on IN-viral DNA complexes (intasomes). However, studies show that RAL fails to bind IN alone, but nothing has been reported on the behaviour of RAL toward free viral DNA. Here, we assessed whether free viral DNA could be a primary target for RAL, assuming that the DNA molecule is a receptor for a huge number of pharmacological agents. Optical spectroscopy, molecular dynamics and free energy calculations, showed that RAL is a tight binder of both processed and unprocessed LTR (long terminal repeat) ends. Complex formation involved mainly van der Waals forces and was enthalpy driven. Dissociation constants (Kds) revealed that RAL affinity for unbound LTRs was stronger than for bound LTRs. Moreover, Kd value for binding of RAL to LTRs and IC50 value (half concentration for inhibition) were in same range, suggesting that RAL binding to DNA and ST inhibition are correlated events. Accommodation of RAL into terminal base-pairs of unprocessed LTR is facilitated by an extensive end fraying that lowers the RAL binding energy barrier. The RAL binding entails a weak damping of fraying and correlatively of 3'-P inhibition. Noteworthy, present calculated RAL structures bound to free viral DNA resemble those found in RAL-intasome crystals, especially concerning the contacts between the fluorobenzyl group and the conserved 5'C(4)pA(3)3' step. We propose that RAL inhibits IN, in binding first unprocessed DNA. Similarly to anticancer drug poisons acting on topoisomerases, its interaction with DNA does not alter the cut, but blocks the subsequent joining reaction. We also speculate that INSTIs having viral DNA rather IN as main target could induce less resistance.

Synthesis of tetra(trimethylammonio)phthalocyanato zinc tetraiodide, [ZnPc(NMe3)4]I4, and a spectrometric investigation of its interaction with calf thymus DNA

The phthalocyanine salt [ ZnPc(NMe3)4]I4was synthesized from 4-nitrophthalonitrile using a three-step procedure. The interaction of [ ZnPc(NMe3)4]4+with calf thymus DNA (CT DNA) has been investigated by UV-vis and fluorescence spectrometric methods. [ ZnPc(NMe3)4]4+exists in a non-monomeric form, proposed to be a dimer, in phosphate buffer solution (pH 6.82). Spectral changes show that in the presence of high concentrations of CT DNA added to the solution, [ ZnPc(NMe3)4]4+is bound in a monomeric state with evidence suggesting it is located in a DNA groove. At lower concentrations of DNA there is evidence of stacking of non-monomeric [ ZnPc(NMe3)4]4+onto the DNA. Two intrinsic binding constants for the interaction of [ ZnPc(NMe3)4]4+with CT DNA, 1.33 × 105and 2.56 × 104M-1have been obtained. Electrostatic binding is shown to play an important role in the interaction of [ ZnPc(NMe3)4]4+with nucleic acids.

Cytotoxic activities and DNA binding properties of 1-methyl-7H-indeno[1,2-b]quinolinium-7-(4-dimethylamino) benzylidene triflate

The interaction of calf thymus DNA (ct-DNA) with a novel synthesized pyrazolo[1,5-a]indole compound 1-methyl-7H-indeno[1,2-b]quinolinium-7-(4-dimethylamino) benzylidene triflate (MIDBT) was extensively studied by various spectroscopic techniques, viscosity measurements, and gel electrophoresis. The UV-visible observation implied that the compound interacted with ct-DNA by two binding modes, intercalating into the DNA base pairs and attaching to the helix exterior of DNA. The results of the fluorescent quenching and viscosity measurements showed that MIDBT could intercalate into DNA base pairs deeply in a classical intercalative mode. Circular dichroism results showed that the binding of MIDBT shifted ct-DNA conformation from B to A at low concentrations. In the gel electrophoresis, the compound was found to promote the cleavage of plasmid pBR 322 DNA effectively. Furthermore, cytotoxic studies of this compound against eleven selected tumor cell lines have been done. The values of 50% cytotoxic concentration (IC(50)) were in the range of 1.09-18.84 μM, exhibiting the potent cytotoxic properties.

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.

DNA and histone deacetylases as targets for neuroblastoma treatment

Neuroblastoma, a tumor of the peripheral sympathetic nervous system, is the most frequent solid extra cranial tumor in children and is a major cause of death from neoplasia in infancy. Still little improvement in therapeutic options has been made, requiring a need for the development of new therapies. In our laboratory, we address still unsettled questions, which of mechanisms of action of DNA-damaging drugs both currently use for treatment of human neuroblastomas (doxorubicin, cis-platin, cyclophosphamide and etoposide) and another anticancer agent decreasing growth of neuroblastomas in vitro, ellipticine, are predominant mechanism(s) responsible for their antitumor action in neuroblastoma cell lines in vitro. Because hypoxia frequently occurs in tumors and strongly correlates with advanced disease and poor outcome caused by chemoresistance, the effects of hypoxia on efficiencies and mechanisms of actions of these drugs in neuroblastomas are also investigated. Since the epigenetic structure of DNA and its lesions play a role in the origin of human neuroblastomas, pharmaceutical manipulation of the epigenome may offer other treatment options also for neuroblastomas. Therefore, the effects of histone deacetylase inhibitors on growth of neuroblastoma and combination of these compounds with doxorubicin, cis-platin, etoposide and ellipticine as well as mechanisms of such effects in human neuroblastona cell lines in vitro are also investigated. Such a study will increase our knowledge to explain the proper function of these drugs on the molecular level, which should be utilized for the development of new therapies for neuroblastomas.

Intercalative pyrimido[4',5':4,5]thieno(2,3-b)quinolines induce apoptosis in leukemic cells: a comparative study of methoxy and morpholino substitution

DNA intercalating molecules are promising anticancer agents. Polycyclic aromatic molecules such as ellipticine intercalate into double-stranded DNA and affect major physiological functions. In the present study, we have characterized two molecules with the same chemical backbone but different side chains, namely 8-methoxy pyrimido[4',5':4,5]thieno (2,3-b)quinoline-4(3H)-one (MPTQ) and 4-morpholino pyrimido[4',5':4,5]thieno(2,3-b)quinoline (morpho-PTQ) at the 8th and 4th position, respectively. Although both MPTQ and morpho-PTQ show similar biophysical properties with high DNA affinity, here we show that they differ in their biological activities. We find that MPTQ is many fold more potent than morpho-PTQ and is cytotoxic against different leukemic cell lines. IC(50) value of methoxy PTQ was estimated between 2-15 µM among the leukemic cells studied, while it was more than 200 µM when morpho-PTQ was used. Cell cycle analysis shows an increase in sub-G1 phase, without any particular cell cycle arrest. Annexin V staining in conjunction with comet assay and DNA fragmentation suggest that MPTQ induces cytotoxicity by activating apoptosis. Thus the observed low IC(50) value of MPTQ makes it a promising cancer chemotherapeutic agent.

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.

Synthesis and biological activity of 5-aza-ellipticine derivatives

Novel 5-aza-ellipticine derivatives were synthesized and tested as antitumor agents. The new compounds were prepared more readily than the analogous ellipticine derivatives, which are known to be potent anti-tumor agents Although the novel 5-aza-ellipticine derivatives are not as biologically active as their corresponding ellipticine analogues, the new compounds represent a new, readily accessible class of heteroaromatic catalytic inhibitors of topoisomerase II and possible anti-tumor agents.

Spectrometric and voltammetric investigation of interaction of neutral red with calf thymus DNA: pH effect

The interaction of neutral red (NR) with calf thymus DNA (CT DNA) was investigated by spectrometric (UV-vis, circular dichroism and fluorescence) and voltammetric techniques. It was shown that the interaction of NR with DNA depended on the values of R (R is defined as the ratio of the concentration of NR to that of CT DNA) and pH of the solution. NR intercalated into CT DNA base pairs at lower R value (R < 2.4) and following by NR aggregating along the helical surface of DNA at higher R value (R > 2.4) in pH 6.0 solution. Interestingly, we found that at lower R value, NR intercalated into CT DNA with its long axis perpendicular or parallel to the dyad axis of DNA in the solution of pH 6.0. While in pH 7.0 solution, NR bound with CT DNA through intercalation and electrostatic interactions. The electrochemical inactive complexes, NR-2CT DNA, 3NR-CT DNA, and NR-CT DNA were formed when NR interacted with nucleic acids in pH 6.0 and 7.2 solutions, respectively. The corresponding intrinsic binding constants for these complexes were obtained by UV-vis and fluorescence spectrometric methods, respectively. The CD spectra showed that the conformation of CT DNA was converted from right-handed B-DNA to left-handed Z-DNA due to the aggregating of NR along the surface of DNA in pH 6.0 solution, whereas a conversion from B-DNA to C-DNA was induced due to the interaction of DNA with NR in pH 7.2 solution. Finally, two binding modes of NR with CT DNA in aqueous with different values of pH were shown in the scheme.

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.