DNA strand breakage by peroxidase-activated mitoxantrone

Emerging small-molecule treatments for multiple sclerosis: focus on B cells

Multiple sclerosis (MS) is a major cause of disability in young adults. Following an unknown trigger (or triggers), the immune system attacks the myelin sheath surrounding axons, leading to progressive nerve cell death. Antibodies and small-molecule drugs directed against B cells have demonstrated good efficacy in slowing progression of the disease. This review focusses on small-molecule drugs that can affect B-cell biology and may have utility in disease management. The risk genes for MS are examined from the drug target perspective. Existing small-molecule therapies for MS with B-cell actions together with new drugs in development are described. The potential for experimental molecules with B-cell effects is also considered. Small molecules can have diverse actions on B cells and be cytotoxic, anti-inflammatory and anti-viral. The current B cell-directed therapies often kill B-cell subsets, which can be effective but lead to side effects and toxicity. A deeper understanding of B-cell biology and the effect on MS disease should lead to new drugs with better selectivity, efficacy, and an improved safety profile. Small-molecule drugs, once the patent term has expired, provide a uniquely sustainable form of healthcare.

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.

Multidimensional protein identification technology analysis highlights mitoxantrone-induced expression modulations in the primary prostate cancer cell proteome

Chemotherapeutic agents as they are used today have limited effectiveness against prostate cancer, but may potentially be used in new combinations with more efficacious results. Mitoxantrone, used for palliation of prostate cancer, has recently been found by our group to improve the susceptibility of primary prostate cancer cells to killing through the Fas-mediated death pathway. Here we used a shotgun proteomics approach to first profile the entire prostate cancer proteome and then identify specific factors involved in this mitoxantrone response. Peptides derived from primary prostate cancer cells treated with or without 100 nM mitoxantrone were analyzed by multidimensional protein identification technology (MudPIT). Strict limits and data filtering hierarchies were applied to identify proteins with high confidence. We identified 1498 proteins belonging to the prostate cancer proteome, 83 of which were significantly upregulated and 27 of which were markedly downregulated following mitoxantrone treatment. These proteins perform diverse functions, including ceramide production, tumour suppression, and oxidative reduction. Detailed proteomic analyses of prostate cancer cells and their response to mitoxantrone will further our understanding of its mechanisms of action. Identification of proteins influenced by treatment with mitoxantrone or other compounds may lead to the development of more effective drug combinations against prostate cancer.

Synthesis and Human Telomerase Inhibition of a Series of Regioisomeric Disubstituted Amidoanthraquinones

Telomerase is the enzymatic activity that maintains the ends of eukaryotic chromosomes. Telomerase activity is detected in most tumor cells whereas it is low or undetectable in most normal somatic cells. Expression of the telomerase catalytic component, the human telomerase reverse transcriptase (hTERT), is believed to be controlled primarily at the level of transcription. Because of this selective expression property of telomerase, it has been touted as a specific target for antitumor chemotherapeutics. However, a concern for the applicability of telomerase inhibitors is that they require a long lag time for telomeres to be shortened to critical length before cancer cells stop proliferating. Here we investigate telomerase inhibitory, cytotoxicity and the hTERT repressing effects on a number of synthesized 2,6-diamidoanthraquinones and 1,5-diamidoanthraquinones as compared to their disubstituted homologues. We found that several of the 1,5-diamidoanthraquinones and 2,6-diamidoanthraquinones inhibited telomerase activity effectively with IC50 at the sub-micro to micro molar range and caused acute cytotoxicity to cancer cells with EC50 similar or better than that of mitoxantrone. Particularly, 2,6-diamidoanthraquinone with 2-ethylaminoacetamido side chains 33, even though not affecting cell proliferation, showed to be endowed with a strong telomerase effect, probably related to a marked stabilization of the G-quadruplex-binding structure. The results suggested that these compounds caused multiple effects to cancer cells. More significantly, they overcome the long lag period problem of classical telomerase inhibitors that they are also potent cytotoxic agents. These results greatly expand the potential of tricyclic anthraquinone pharmacophore in preventive and/or curative therapy.

Synthesis and antitumor activity of 1,8-diaminoanthraquinone derivatives

Continuing our ongoing studies on cytotoxic substances, a series of regioisomeric disubstituted aminoanthraquinone (DAAQ) derivatives have been synthesized as cytotoxic activity based on a proposed bioactive amino conformation. To assess the biological activity of amino-substitution in the side-chains of anthraquinone located at positions 1 and 8 of the anthraquinone ring system. The aim of the study was to determine if members of the anthraquinone family could be used as adjuncts to increase the growth inhibiting effect of anticancer agents in rat glioma C6 cells, human hepatoma G2 cells and 2.2.15 cells. In vitro cytotoxicity data is reported for the compounds and some indications of structure--activity relationships have been discerned. A number of compounds were found to have good cytotoxicity against proliferation in these three cell lines. This has led to the discovery some of the DAAQ as a conformationally constrained structure possessing anticancer properties that displays cytotoxicity for these above cell lines and is being investigated further.

Mitoxantrone and ametantrone induce interstrand cross-links in DNA of tumour cells

We show here that mitoxantrone and ametantrone induce interstrand DNA cross-links in HeLa S3 cells. These cross-links were observed only in cellular system suggesting that metabolism of the drugs is a necessary step leading to DNA cross-linking. Biologically inactive analogue of mitoxantrone, compound NSC 321458, did not induce cross-links in DNA of tumour cells which suggests that DNA cross-linking is associated with the cytotoxic and anti-tumour activity of these compounds.

Mitoxantrone-induced DNA strand breaks in cell-cultures of malignant human astrocytoma and glioblastoma tumors

In this study mitoxantrone (Mtx) induced DNA strand breaks were measured with the alkaline elution technique in short term cell cultures derived from human gliomas. Glioblastomas or astrocytomas from 5 patients who underwent intracranial surgery were cultured and incubated i h with different concentrations of Mtx (0, 0.01, 0.1 and 1.0 microgram/ml). The alkaline elution method was modified to measure DNA lesions in human gliomas. Mtx induced DNA strand breaks in a dose dependent manner in all cell cultures tested. There was a linear increase of DNA strand break frequency induced by Mtx between 0.01-1.0 microgram/ml. concerning these in vitro data, Mtx might be potentially useful for the treatment of patients with malignant brain tumors.

In vitro DNA crosslinking by Ledakrin, an antitumor derivative of 1-nitro-9-aminoacridine

Using agarose gel electrophoresis we confirmed that Ledakrin is capable of incurring covalent crosslinking in pBR322 plasmid DNA and also in poly(dGdC) in the presence of a simple activating system containing DTT. The identification of adducts resulting from DNA crosslinking was carried out by 32P-post-labelling assay. We assumed that such adduct(s) should be brought about more readily with double-stranded than with single-stranded polynucleotides or nucleotides. Since our earlier experiments had shown that guanine is a major site of covalent binding of 1-nitroacridines, we compared DNA adduct formation by Ledakrin for ctDNA, dG-containing synthetic homopolymers and 3'-pdG. 32P-Post-labelling assay revealed two adduct spots that were enhanced in samples containing double-stranded substrates in which interstrand crosslinking between guanines was possible, namely ctDNA and poly(dGdC).

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.

The interaction of antitumor-active anthraquinones with biologically important redox couples: I. Spectrophotometric investigation of the interaction of carminic acid and mitoxantrone with the iron (II, III) and copper (I, II) redox couples

Studying the interaction of antitumor-active anthraquinones with biologically important redox couples is important in understanding the possible reductive or oxidative mode of metabolism of these antineoplastic agents coupled with the formation of free radicals. The interactions of such anthraquinones, i.e., carminic acid (CA) and mitoxantrone (Mx) with iron(II, III) and copper(I, II) redox couples in oxygenated and deaerated solutions, were investigated by UV-Visible and IR-spectroscopy. The superoxide radical reagent, nitroblue tetrazolium (NBT), was added to the metal and anthraquinone solutions and their binary mixtures at varying pH. Formazan, the reduction product of NBT, was produced mainly as a result of Fe(II)-NBT and Fe(II)-Mx-NBT interactions. The ternary mixtures of the lower valencies of iron and copper with CA and NBT exhibited intensive charge-transfer bands in the visible region, while metal-Mx-NBT combinations did not produce such bands, possibly due to the blockage of the redox-active aminoethanolamine side-chains of Mx through coordination with the metals. Copper-Mx combinations showed an oxygen sensitivity as spectral evidence was obtained for the oxidative transformation of Mx to the cyclic primary metabolite. The results were evaluated in regard to the possible oxidative activation of the studied anthracenediones with iron and copper systems.

Rationale for the use of aliphatic N-oxides of cytotoxic anthraquinones as prodrug DNA binding agents: a new class of bioreductive agent

NAD(P)H dependent cytochrome P450's and other haemoproteins under hypoxia, mediate two-electron reduction of a wide range of structurally dissimilar N-oxides to their respective tertiary amines. Metabolic reduction can be utilised, in acute and chronic hypoxia, to convert N-oxides of DNA affinic agents to potent and persistent cytotoxins. In this respect a knowledge of N-oxide bioreduction and the importance of the cationic nature of agents that bind to DNA by intercalation can be combined to rationalise N-oxides as prodrugs of DNA binding agents. The concept is illustrated using the alkylaminoanthraquinones which are a group of cytotoxic agents with DNA binding affinity that is dependent on the cationic nature of these compounds. The actions of the alkylaminoanthraquinones involve drug intercalation into DNA (and double stranded RNA) and inhibition of both DNA and RNA polymerases and topoisomerase Type I and II. A di-N-oxide analogue of mitoxantrone, 1,4-bis([2-(dimethylamino-N-oxide)ethyl]amino)5,8-dihydroxyanthracene -9,10- dione (AQ4N) has been shown to possess no intrinsic binding affinity for DNA and has low toxicity. Yet in the absence of air AQ4N can be reduced in vitro to a DNA affinic agent with up to 1000-fold increase in cytotoxic potency. Importantly the reduction product, AQ4, is stable under oxic conditions. Studies in vivo indicate that antitumour activity of AQ4N is manifest under conditions that promote transient hypoxia and/or diminish the oxic tumour fraction. The advantage of utilising the reductive environment of hypoxic tumours to reduce N-oxides is that, unlike conventional bioreductive agents, the resulting products will remain active even if the hypoxia that led to bioactivation is transient or the active compounds, once formed, diffuse away from the hypoxic tumour regions. Furthermore, the DNA affinic nature of the active compounds should ensure their localisation in tumour tissue.

Lack of involvement of reactive oxygen in the cytotoxicity of mitoxantrone, CI941 and ametantrone in MCF-7 cells: comparison with doxorubicin

The MCF-7 cell S9 fraction and whole MCF-7 cells can mediate one-electron-redox cycling of doxorubicin, giving rise to concomitant oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH), formation of a drug semiquinone free radical, consumption of molecular oxygen and formation of superoxide anions and hydroxyl radicals. Doxorubicin redox cycling was consistent with DNA strand breakage and cell kill in MCF-7 cells. In contrast, no evidence for redox cycling was found for mitoxantrone (MIT), CI941 or ametantrone (AMET) in MCF-7 cells. Despite the absence of redox cycling, the CI941, MIT, and AMET concentrations resulting in 50% mortality (LC50; 1.5 x 10(-10), 5.2 x 10(-9) and 1.2 x 10(-6) M, respectively) of MCF-7 cells were lower than that of DOX (3.0 x 10(-6) M). Furthermore, the higher cytotoxicity of MIT and CI941 as compared with AMET or DOX was associated with greater efficiency in inducing DNA strand breakage in MCF-7 cells as determined by alkaline elution. Since MIT and CI941 proved to be the most potent DNA-damaging and cytotoxic agents in this study, the ability of DOX to undergo redox cycling does not appear to confer increased cytotoxic potential on this agent. The present study revealed several important aspects with regards to the structural modification of anthraquinone antitumour agents. Firstly, the C1 and C4 positioning of the hydroxyethylamino side chains on MIT, CI941 and AMET is associated with a lack of flavin reductase-mediated activation of these agents. Secondly, the possession of a C5 or C8 aromatic hydroxyl group appears to be intimately involved in the enhanced DNA strand breakage and cytotoxic potency of MIT and CI941, since AMET does not possess these groups. These findings indicate that future development of quinone antitumour agents should concentrate on compounds that do not undergo redox cycling but do possess aromatic hydroxyl groups, since the latter appear to be responsible for the enhanced cytotoxicity of MIT and CI941.