DNA sequence specificity of mitoxantrone

Interaction of mitoxantrone with abasic sites - DNA strand cleavage and inhibition of apurinic/apyrimidinic endonuclease 1, APE1

Mitoxantrone (1,4-dihydroxy-5,8-bis[2-(2-hydroxyethylamino)ethylamino]-anthracene-9,10-dione) is a clinically-relevant synthetic anthracenedione that functions as a topoisomerase II poison by trapping DNA double-strand break intermediates. Mitoxantrone binds to DNA via both stacking interactions with DNA bases and hydrogen bonding with the sugar-phosphate backbone. It has been shown that mitoxantrone inhibits apurinic/apyrimidinic (AP) endonuclease 1 (APE1)-catalyzed incision of DNA containing a tetrahydrofuran (THF) moiety and more recently, that mitoxantrone forms Schiff base conjugates at AP sites in DNA. In this study, mitoxantrone-mediated inhibition of APE1 at THF sites was shown to be consistent with preferential binding to, and thermal stabilization of DNA containing a THF site as compared to non-damaged DNA. Investigations into the properties of mitoxantrone at AP and 3' α,β-unsaturated aldehyde sites demonstrated that in addition to being a potent inhibitor of APE1 at these biologically-relevant substrates (∼ 0.5 μM IC50 on AP site-containing DNA), mitoxantrone also incised AP site-containing DNA by catalyzing β- and β/δ-elimination reactions. The efficiency of these reactions to generate the 3' α,β-unsaturated aldehyde and 3' phosphate products was modulated by DNA structure. Although these cell-free reactions revealed that mitoxantrone can generate 3' phosphates, cells lacking polynucleotide kinase phosphatase did not show increased sensitivity to mitoxantrone treatment. Consistent with its ability to inhibit APE1 activity on DNAs containing either an AP site or a 3' α,β-unsaturated aldehyde, combined exposures to clinically-relevant concentrations of mitoxantrone and a small molecule APE1 inhibitor revealed additive cytotoxicity. These data suggest that in a cellular context, mitoxantrone may interfere with APE1 DNA repair functions.

Investigation of reactive properties, adsorption on fullerene, DFT, molecular dynamics simulation of an anthracene derivative targeting dihydrofolate reductase and human dUTPase

Anthracenes are aromatic compounds with flexible structure and reactivity which are of great interest to theoretical and experimental chemists. Theoretical investigations of 1,4-dihydroxy-5,8-bis[2-(2-hydroxyethylamino)ethylamino]anthracene-9,10-dione (Mitoxantrone) (DDEA) based on density functional theory, molecular dynamics and adsorption on fullerene are reported in the present research. The suitable situation for adsorption with fullerene (C60) is the cyclohex-2-ene-1,4-dione ring of DDEA. Selected quantum-molecular descriptors have been calculated to predict the most reactive sites of the DDEA molecule. Interactions of DDEA with water have been studied using MD simulations. MD simulations were also used to study solubility parameter, a significant quantity for the development of pharmaceutical formulations. The affinity of DDEA on human dihydrofolate reductase and deoxyuridine triphosphatase enzymes was investigated by MD simulation of the protein-ligand complex obtained by molecular docking study.Communicated by Ramaswamy H. Sarma.

Mitoxantrone, More than Just Another Topoisomerase II Poison

Mitoxantrone is a synthetic anthracenedione originally developed to improve the therapeutic profile of the anthracyclines and is commonly applied in the treatment of breast and prostate cancers, lymphomas, and leukemias. A comprehensive overview of the drug's molecular, biochemical, and cellular pharmacology is presented here, beginning with the cardiotoxic nature of its predecessor doxorubicin and how these properties shaped the pharmacology of mitoxantrone itself. Although mitoxantrone is firmly established as a DNA topoisomerase II poison within mammalian cells, it is now clear that the drug interacts with a much broader range of biological macromolecules both covalently and noncovalently. Here, we consider each of these interactions in the context of their wider biological relevance to cancer therapy and highlight how they may be exploited to further enhance the therapeutic value of mitoxantrone. In doing so, it is now clear that mitoxantrone is more than just another topoisomerase II poison.

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.

Chromium(VI) but not chromium(III) species decrease mitoxantrone affinity to DNA

Binding of mitoxantrone (MXT) to double-stranded DNA has been investigated as a model drug-DNA binding system to evaluate the effects of various forms of chromium on the binding properties. We have found that Cr(III), which binds strongly to DNA, does not affect the MXT affinity to DNA. In contrast, Cr(VI), in the form of chromate ions CrO(4)(2-), decreases the MXT affinity to DNA despite electrostatic repulsions with phosphate-deoxyribose chains of DNA. The MXT-DNA binding constant was found to decrease from (1.96 ± 0.005) × 10(5) to (0.77 ± 0.018) × 10(5) M(-1) for Cr(VI) concentration changing from 0 to 30 μM. The influence of Cr(VI) on MXT-DNA binding has been attributed to the oxidation of guanine residue, thus interrupting the intercalation of MXT into the DNA double helix at the preferential CpG intercalation site. This supposition is corroborated by the observed increase in the MXT binding site size from 2 bp (base pairs) to 4-6 bp in the presence of Cr(VI). The measurements of the MXT-DNA binding constant and the MXT binding site size on a DNA molecule have been carried out using spectroscopic, voltammetric, and nanogravimetric techniques, providing useful information on the mechanism of the interactions.

Spectroscopic studies of the effects of anticancer drug mitoxantrone interaction with calf-thymus DNA

Mitoxantrone (MTX) (1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9,10-anthracenedione) is a synthetic antineoplastic drug, widely used as a potent chemotherapeutic agent in the treatment of various types of cancer. It is structurally similar to classical anthracyclines. Widespread interest in the anticancer agent mitoxantrone has arisen because of its apparent lower risk of cardio-toxic effects compared to the naturally occurring anthracyclines. In the present work, we investigated the interaction of mitoxantrone with DNA in the buffer solution at physiological pH using Fourier transform infrared (FTIR), UV-Visible absorption and circular dichroism spectroscopic techniques. FTIR analysis revealed the intercalation of mitoxantrone between the DNA base pairs along with its external binding with phosphate-sugar backbone. The binding constant calculated for mitoxantrone-DNA association was found to be 3.88×10(5)M(-1) indicating high affinity of drug with DNA double helix. Circular dichroism spectroscopic results suggest that there are no major conformational changes in DNA upon interaction with drug except some perturbations in native B-DNA at local level. The present work shows the capability of spectroscopic analysis to characterize the nature of drug-biomolecule complex and the effects of such interaction on the structure of biomolecule.

Disordering of human telomeric G-quadruplex with novel antiproliferative anthrathiophenedione

Linear heteroareneanthracenediones have been shown to interfere with DNA functions, thereby causing death of human tumor cells and their drug resistant counterparts. Here we report the interaction of our novel antiproliferative agent 4,11-bis[(2-{[acetimido]amino}ethyl)amino]anthra[2,3-b]thiophene-5,10-dione with telomeric DNA structures studied by isothermal titration calorimetry, circular dichroism and UV absorption spectroscopy. New compound demonstrated a high affinity (K(ass)∼10⁶ M⁻¹) for human telomeric antiparallel quadruplex d(TTAGGG)₄ and duplex d(TTAGGG)₄∶d(CCCTAA)₄. Importantly, a ∼100-fold higher affinity was determined for the ligand binding to an unordered oligonucleotide d(TTAGGG TTAGAG TTAGGG TTAGGG unable to form quadruplex structures. Moreover, in the presence of Na+ the compound caused dramatic conformational perturbation of the telomeric G-quadruplex, namely, almost complete disordering of G-quartets. Disorganization of a portion of G-quartets in the presence of K+ was also detected. Molecular dynamics simulations were performed to illustrate how the binding of one molecule of the ligand might disrupt the G-quartet adjacent to the diagonal loop of telomeric G-quadruplex. Our results provide evidence for a non-trivial mode of alteration of G-quadruplex structure by tentative antiproliferative drugs.

New anthracenedione derivatives with improved biological activity by virtue of stable drug-DNA adduct formation

Mitoxantrone is an anticancer agent that acts as a topoisomerase II poison, however, it can also be activated by formaldehyde to form DNA adducts. Pixantrone, a 2-aza-anthracenedione with terminal primary amino groups in its side chains, forms formaldehyde-mediated adducts with DNA more efficiently than mitoxantrone. Molecular modeling studies indicated that extension of the "linker" region of anthracenedione side arms would allow the terminal primary amino greater flexibility and thus access to the guanine residues on the opposite DNA strand. New derivatives based on the pixantrone and mitoxantrone backbones were synthesized, and these incorporated primary amino groups as well as extended side chains. The stability of DNA adducts increased with increasing side chain length of the derivatives. A mitoxantrone derivative bearing extended side chains (7) formed the most stable adducts with ∼100-fold enhanced stability compared to mitoxantrone. This finding is of great interest because long-lived drug-DNA adducts are expected to perturb DNA-dependent functions at all stages of the cell cycle.

DNA binding by pixantrone

The binding of the anticancer drug pixantrone (6,9-bis[(2-aminoethyl)amino]benzo[g]isoquinoline-5,10-dione dimaleate) to the octanucleotide duplexes d(ACGATCGT)(2) and the corresponding C-5 methylated cytosine ((5Me)C) analogue d(A(5Me)CGAT(5Me)CGT)(2) has been studied by NMR spectroscopy and molecular modelling. The large upfield shifts observed for the resonances from the aromatic protons of pixantrone upon addition to either d(ACGATCGT)(2) or the corresponding (5Me)C analogue is consistent with the drug binding the octanucleotides by intercalation. The selective reduction in the sequential NOEs between the C(2)-G(3) and C(6)-G(7) nucleotides in NOESY spectra of either octanucleotide with added pixantrone confirms the intercalative binding mechanism. Strong NOEs from the side-chain ethylene protons of pixantrone to the H5 protons and the 5-CH(3) protons of the C(2) and C(6) residues of d(ACGATCGT)(2) and d(A(5Me)CGAT(5Me)CGT)(2), respectively, indicate that pixantrone predominantly intercalates from the DNA major groove at the 5'-CG and 5'-(5Me)CG sites. Simple molecular models based on the conclusions from the NMR experiments indicated that the (5Me)C groups do not represent a steric barrier to intercalation from the major groove. However, the observation of weak NOEs from the ethylene protons of pixantrone to a variety of minor groove protons from either octanucleotide suggests that the drug can also associate in the minor groove.

In vitro transcription assay for resolution of drug-DNA interactions at defined DNA sequences

A major class of anticancer agents in current clinical use exerts its anticancer effects by binding covalently or non-covalently to DNA. A detailed understanding of the nature of these drug-DNA complexes would be expected to lead to better uses of these drugs, and also assist with the design of improved drug derivatives. Here, we present a transcriptional footprinting assay that can be implemented to define the DNA sequence specificity and kinetics associated with drug-DNA complexes. The basic steps involve the formation of drug-DNA complexes, the formation of synchronised initiated transcripts, and finally transcriptional elongation to reveal drug blockage sites that impede the progression of RNA polymerase. We have used the "in vitro transcription assay" to investigate many covalent drug-DNA interactions; most notably those obtained using anthracycline anticancer agents such as doxorubicin and anthracenedione-based anticancer agents, including mitoxantrone and pixantrone.

Interactions of mitoxantrone with duplex and triplex DNA studied by electrospray ionization mass spectrometry

We have examined interactions between mitoxantrone (MXT) and DNA duplexes or triplexes with different base compositions by using electrospray ionization mass spectrometry (ESI-MS), respectively. MXT interacts preferentially with DNA duplexes compared to the triplexes. In the mass spectrum of the duplex-MXT mixture, the complex peaks dominated in the ratios of duplex/MXT of 1:1, 1:2 and 1:3, and the 1:2 duplex/MXT peak was the most abundant. In contrast, only 1:1 triplex-MXT complexes were observed in the mass spectrum of the triplex-MXT mixture, and the most intensive peak was a free triplex ion without MXT. Moreover, no sequence selectivity of MXT to different DNA duplexes was found while MXT showed greater affinity to the triplexes that have adjacent TAT or C(+)GC sequences. In the course of sustained off-resonance irradiation collision-induced dissociation (SORI-CID), the MXT-duplex complexes generated two separated strands, and the MXT remained on the purine strand side. UV/Vis spectra showed that MXT interacted with DNA by intercalation. Compared with emodin (a duplex intercalator) and napthylquinoline (a triplex binder), we found that the side chain of MXT might play a role in the binding of MXT to the duplexes and the triplexes. ESI-MS shows an advantage in speed and straightforwardness for the study of drug interactions with nucleic acids.

Formaldehyde-activated Pixantrone is a monofunctional DNA alkylator that binds selectively to CpG and CpA doublets

The topoisomerase II poison mitoxantrone is important in the clinical management of human malignancies. Pixantrone, a novel aza-anthracenedione developed to improve the therapeutic profile of mitoxantrone, can efficiently alkylate DNA after formaldehyde activation. In vitro transcriptional analysis has now established that formaldehyde-activated pixantrone generates covalent adducts selectively at discrete CpG or CpA dinucleotides, suggesting that the activated complex binds to guanine or cytosine (or both) bases. The stability of pixantrone adduct-induced transcriptional blockages varied considerably, reflecting a mixture of distinct pixantrone adduct types that may include relatively labile monoadducts and more stable interstrand cross-links. 6,9-Bis-[[2-(dimethylamino)ethyl]amino]benzo[g]isoquinoline-5,10-dione (BBR 2378), the dimethyl N-substituted analog of pixantrone, could not form adducts, suggesting that pixantrone alkylates DNA through the primary amino functions located in each side chain of the drug. Pixantrone generated DNA adducts only when guanine was present in substrates and exhibited a lack of adduct formation with inosine-containing polynucleotides, confirming that the N2 amino group of guanine is the site for covalent attachment of the drug. Mass spectrometric analysis of oligonucleotide-drug complexes confirmed that formation of covalent pixantrone-DNA adducts is mediated by a single methylene linkage provided by formaldehyde and that this occurs only with guanine-containing double stranded oligonucleotide substrates. CpG methylation, an epigenetic modification of the mammalian genome, significantly enhanced the generation of pixantrone-DNA adducts within a methylated DNA substrate, indicating that the methylated dinucleotide may be a favored target in a cellular environment.

A theoretical study on interactions between mitoxantrone as an anticancer drug and DNA: application in drug design

This research is an effort to further understand the physicochemical interaction between the novel drug, mitoxantrone (MTX) and its biologic receptor, DNA. The ultimate goal is to design drugs that interact more with DNA. Understanding the physicochemical properties of the drug as well as the mechanism by which it interacts with DNA, it should ultimately allow the rational design of novel anti-cancer or anti-viral drugs. Molecular modelling on the complex formed between MTX and DNA presented that this complex was indeed fully capable of participating in the formation of a stable intercalation site. Furthermore, the molecular geometries of MTX and the DNA bases (adenine, guanine, cytosine and thymine) were optimized with the aid of the B3LYP/6-31G* method. The properties of the isolated intercalator and its stacking interactions with the adenine...thymine (AT) and guanine...cytosine (GC) nucleic acid base pairs were studied with the DFTB method (density functional tight-binding), an approximate version of the DFT method, that was extended to cover the London dispersion energy. The B3LYP/6-31G* stabilization energies of the intercalator...base pair complexes were found 10.06 kcal/mol and 21.64 kcal/mol for AT...MTX and GC...MTX, respectively. It was concluded that the dispersion energy and the electrostatic interaction contributed to the stability of the intercalator.DNA base pair complexes. The results concluded from the comparison of the DFTB method and the Hartree-fock method point out that these methods show close results and support each other.

Interaction of anticancer drug mitoxantrone with DNA analyzed by electrochemical and spectroscopic methods

Cyclic voltammetry coupled with different spectroscopic (UV/Vis, fluorescence and Raman) techniques were used to study the interaction of mitoxantrone (MTX), an antitumor drug, with calf thymus DNA in acetate buffer solutions (pH 4.5). The interaction of MTX with DNA could result a considerable decrease in the MTX peak currents and a hypochromic and bathochromic shift in the maximum adsorption bands of MTX as well as the emission quenching in the MTX fluorescence spectra. The variations in the electrochemical and spectral characteristics of MTX indicated MTX bind to DNA by an intercalative mode. This conclusion was reinforced by Raman data. The merely particular vibrations were affected in Raman, suggesting that only a portion of the chromophore of MTX was involved in the intercalation into DNA duplex. These studies are valuable for a better understanding the detailed mode of MTX-DNA interaction, which should be important in deeper insight into the therapeutic efficacy of MTX and design of new DNA targeted drug.

Electrochemical determination of interaction parameters for DNA and mitoxantrone in an irreversible redox process

Mitoxantrone (MXT), an anti-tumor antibiotic, shows irreversible electrochemical behavior at a waxed graphite electrode in a 0.05 M Tris-HCl buffer (pH 7.4) solution. The interaction between MXT and calf thymus DNA (ctDNA) in solution has been studied using cyclic voltammetry. An electrochemical equation suitable for examining the binding of irreversibly electroactive molecules to DNA is established. Determination of diffusion coefficients of both free and binding MXT (D(f), D(b)), the binding constant (K) and binding site size (s base pairs per molecule, bp) of MXT with DNA was performed on the basis of the equation. A nonlinear fit analysis of the experimental data yielded: D(f)=3.76 x 10(-5) cm(2)s(-1), D(b)=2.73 x 10(-7) cm(2)s(-1), K=8.7 x 10(9) cm(3)mol(-1), s=2.8 bp. The results demonstrate that MXT binds tightly to ctDNA and covers three base pairs. The anthraquinone of MXT, which is a planar heterocyclic ring, intercalates between the DNA's base pairs. The two aminoethylamino side-chains of the drug fit to the major groove reinforce the combination of MXT and DNA. The results show that MXT is a DNA intercalator with a high binding constant compared to those of other anthraquinones.

Formaldehyde activation of mitoxantrone yields CpG and CpA specific DNA adducts

Recently we have found that mitoxantrone, like Adria-mycin, can be activated by formaldehyde and subsequently form adducts which stabilise double-stranded DNA in vitro. This activation by formaldehyde may be biologically relevant since formaldehyde levels are elevated in those tumours in which mitoxan-trone is most cytotoxic. In vitro transcription analysis revealed that these adducts block the progression of RNA polymerase during transcription and cause truncated RNA transcripts. There was an absolute requirement for both mitoxantrone and formaldehyde in transcriptional blockage formation and the activated complex was found to exhibit site specificity, with blockage occurring prior to CpG and CpA sites in the DNA (non-template strand). The stability of the adduct at 37 degrees C was site dependent. The half-lives ranged from 45 min to approximately 5 h and this was dependent on both the central 2 bp blockage site as well as flanking sequences. The CpG specificity of mitoxantrone adduct sites was also confirmed independently by a lambda exonuclease digestion assay.

A survey of the sequence-specific interaction of damaging agents with DNA: emphasis on antitumor agents

This article reviews the literature concerning the sequence specificity of DNA-damaging agents. DNA-damaging agents are widely used in cancer chemotherapy. It is important to understand fully the determinants of DNA sequence specificity so that more effective DNA-damaging agents can be developed as antitumor drugs. There are five main methods of DNA sequence specificity analysis: cleavage of end-labeled fragments, linear amplification with Taq DNA polymerase, ligation-mediated polymerase chain reaction (PCR), single-strand ligation PCR, and footprinting. The DNA sequence specificity in purified DNA and in intact mammalian cells is reviewed for several classes of DNA-damaging agent. These include agents that form covalent adducts with DNA, free radical generators, topoisomerase inhibitors, intercalators and minor groove binders, enzymes, and electromagnetic radiation. The main sites of adduct formation are at the N-7 of guanine in the major groove of DNA and the N-3 of adenine in the minor groove, whereas free radical generators abstract hydrogen from the deoxyribose sugar and topoisomerase inhibitors cause enzyme-DNA cross-links to form. Several issues involved in the determination of the DNA sequence specificity are discussed. The future directions of the field, with respect to cancer chemotherapy, are also examined.

Molecular analysis of yeast and human type II topoisomerases. Enzyme-DNA and drug interactions

The DNA sequence selectivity of topoisomerase II (top2)-DNA cleavage complexes was examined for the human (top2alpha), yeast, and Escherichia coli (i.e. gyrase) enzymes in the absence or presence of anticancer or antibacterial drugs. Species-specific differences were observed for calcium-promoted DNA cleavage. Similarities and differences in DNA cleavage patterns and nucleic acid sequence preferences were also observed between the human, yeast, and E. coli top2 enzymes in the presence of the non-intercalators fluoroquinolone CP-115,953, etoposide, and azatoxin and the intercalators amsacrine and mitoxantrone. Additional base preferences were generally observed for the yeast when compared with the human top2alpha enzyme. Preferences in the immediate flanks of the top2-mediated DNA cleavage sites are, however, consistent with the drug stacking model for both enzymes. We also analyzed and compared homologous mutations in yeast and human top2, i.e. Ser(740) --> Trp and Ser(763) --> Trp, respectively. Both mutations decreased the reversibility of the etoposide-stabilized cleavage sites and produced consistent base sequence preference changes. These data demonstrate similarities and differences between human and yeast top2 enzymes. They also indicate that the structure of the enzyme/DNA interface plays a key role in determining the specificity of top2 poisons and cleavage sites for both the intercalating and non-intercalating drugs.

DNA sequence selectivity of topoisomerases and topoisomerase poisons

Chemical agents able to interfere with DNA topoisomerases are widespread in nature, and some of them have clinical efficacy as antitumor or antibacterial drugs. Drugs which have as a target DNA topoisomerases could be divided into two categories: poisons and catalytic inhibitors. Classical topoisomerase poisons stimulate cleavage in a sequence-selective manner, yielding drug-specific cleavage intensity pattern. The mechanisms of drug interaction with DNA topoisomerases, the DNA sequence selectivity of the action of topoisomerase II poisons and the identification of structural determinants of their activity have suggested that topoisomerase II poisons may fit into a specific pharmacophore, constituted by a planar ring system with DNA intercalation or intercalation-like properties, and protruding side chains interfering with the protein side of the covalent enzyme-DNA complex. The complete definition of the diverse pharmacophores of topoisomerase II poisons will certainly be of value for the design of new agents directed to specific genomic sites, and more effective in the treatment of human cancer.

Experimental antitumor activity of the Ce(IV)-mitoxantrone complex and its interaction with deoxyribonucleic acid

The Ce(IV)-mitoxantrone complex exhibits a higher lethality to Ehrlich ascites tumor cells than that of the free drug and shows stronger inhibition ability on the DNA synthesis of the tumor cells. Thus the Ce(IV)-mitoxantrone complex may become a more potent antitumor drug than mitoxantrone. The different interaction model of mitoxantrone and its Ce(IV) complex with DNA were studied by the methods of spectroscopy, electrochemistry, and electrophoresis. Ce(IV) ions chelate with oxygens of the hydroxyl groups at the 1,4 position and the carbonyl function on C-9 and C-10, then intercalate into the base pairs of DNA together. The complexation of Ce(IV) gives rise to more compact binding of mitoxantrone with DNA, and leads to an additional change on the normal conformation and the double-helical structure of DNA; this may be related to the more stronger action of the complex on DNA synthesis and survival of cultured tumor cells.

A protein-mediated mechanism for the DNA sequence-specific action of topoisomerase II poisons

Chemical agents able to interfere with DNA topoisomerases are widespread in nature, and some of them have outstanding therapeutic efficacy in human cancer and infectious diseases. DNA topoisomerases are essential enzymes that govern DNA topology during fundamental nuclear metabolic processes. Topoisomerase-interfering compounds can be divided into two general categories based on the mechanism of drug action: poisons and catalytic inhibitors. In past years, investigations of the DNA sequence selectivity of topoisomerase II poisons have identified structural and molecular determinants of drug activity, and indicated that the drug receptor is likely to be at the protein-DNA interface. Moreover, the available results indicate that the biologically relevant DNA-binding activity of topoisomerase poisons is basically protein-mediated and this is discussed in this issue by Giovanni Capranico and colleagues. This suggests that topoisomerase poisons may represent a useful paradigm for small compounds able to bind to protein-DNA interfaces in a site-selective manner, thus increasing the affinity of DNA-binding proteins for specific genomic sites.

Salen-anthraquinone conjugates. Synthesis, DNA-binding and cleaving properties, effects on topoisomerases and cytotoxicity

A series of amidoethylamino-anthraquinone derivatives bearing either one or two salen (bis(salicylidene)ethylenediamine) moieties complexed with CuII or NiII have been synthesized, and their DNA-binding and cleaving properties examined. The effects of the mono- and di-substituted anthracenedione-salen conjugates on DNA cleavage mediated by topoisomerases I and II have also been determined, as well as their cytotoxicity toward human KB cells. The anthraquinone-salen. NiII conjugates bind to GC-rich sequences in DNA, but do not cleave the macromolecule. By contrast, the anthraquinone-salen. CuII hybrids do not recognize particular nucleotide sequences but efficiently induce single-strand breaks in DNA after activation. The 5,8-dihydroxy-anthraquinone conjugates are more cytotoxic and more potent toward topoisomerase II than the non-hydroxylated analogues, but they are less cytotoxic than the salen-free anthraquinones. The attachment of a salen. CuII complex to the anthraquinone chromophore can confer DNA cleaving properties in vitro, but this is at the expense of cytotoxic activity. Anthraquinone-salen. CuII complexes may find useful employ as footprinting probes for investigating ligand-DNA interactions.

DNA recognition by two mitoxantrone analogues: influence of the hydroxyl groups

The clinically useful anticancer drug mitoxantrone intercalates preferentially into 5'-(A/T)CG and 5'-(A/T)CA sites on DNA. The 5,8 hydroxyl substituents on its anthracenedione chromophore are available to interact with the double helix. Footprinting experiments with two anthraquinone derivatives structurally related to mitoxantrone and ametantrone have been undertaken to assess the influence of the hydroxyl groups on the DNA recognition process. The results confirm that they do play a role in the recognition of preferred nucleotide sequences and suggest that the binding of anthraquinones to a 5'-(A/T)CG site is dependent on the presence of the 5,8 hydroxyl substitutes whereas binding to 5'-(A/T)CA sites appears to proceed just as well without them.