Persistent intracellular binding of mitoxantrone in a human colon carcinoma cell line

Cytoskeletal reorganization and cell death in mitoxantrone-treated lung cancer cells

The aim of this study was to investigate the cytotoxic effect of mitoxantrone on two human non-small cell lung cancer cell lines, A549 (p53+) and H1299 (p53-). To our knowledge, this is the first study to evaluate the impact of MXT on the organization of cytoskeletal proteins. Analyses were performed using fluorescence and transmission electron microscopy, spectrophotometric techniques, flow cytometry and Western blotting. It was shown that H1299 cells are significantly more sensitive to mitoxantrone than the A549 cell line, and that the growth-inhibitory effect of the drug is dose-dependent only after longer incubation. The observed presence of ring-like microtubule structures and mitochondria surrounding the nuclei of H1299 cells could be a manifestation of increased tubulin polymerization requiring large amounts of energy, whereas the loss of actin stress fibers was presumably not the cause but rather the consequence of cell death induction. Treatment with mitoxantrone also led to the appearance of structures resembling agresomes in H1299 cells and to nucleolar segregation in both cell lines. It was demonstrated that cells arrested in the S phase were most susceptible to cell death induction, and that triggered intracellular changes led mainly to apoptosis. High concentrations induced necrosis and some H1299 cells exhibited morphological features of mitotic catastrophe.

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.

Quantitative confocal spectral imaging analysis of mitoxantrone within living K562 cells: intracellular accumulation and distribution of monomers, aggregates, naphtoquinoxaline metabolite, and drug-target complexes

Confocal spectral imaging (CSI) technique was used for quantitative analysis of the uptake, subcellular localization, and characteristics of localized binding and retention of anticancer agent mitoxantrone (MITOX) within human K562 erythroleukemia cells. The CSI technique enables identification of the state and interactions of the drug within the living cells. Utilizing this unique property of the method, intracellular distributions were examined for monomeric MITOX in polar environment, MITOX bound with hydrophobic cellular structures, naphthoquinoxaline metabolite, and nucleic acid-related complexes of MITOX. The features revealed were compared for the cells treated with 2 microM or 10 microM of MITOX for 1 h and correlated to the known data on antitumor action of the drug. MITOX was found to exhibit high tendency to self-aggregation within intracellular media. The aggregates are concluded to be a determinant of long-term intracellular retention of the drug and a source of persistent intracellular binding of MITOX. Considerable penetration of MITOX in the hydrophobic cytoskeleton structures as well as growing accumulation of MITOX bound to nucleic acids within the nucleus were found to occur in the cells treated with a high concentration of the drug. These effects may be among the factors stimulating and/or accompanying high-dose mitoxantrone-induced programmed cell death or apoptosis.

Localization and molecular interactions of mitoxantrone within living K562 cells as probed by confocal spectral imaging analysis

Studying mechanisms of drug antitumor action is complicated by the lack of noninvasive methods enabling direct monitoring of the state and interactions of the drugs within intact viable cells. Here we present a confocal spectral imaging (CSI) technique as a method of overcoming this problem. We applied this method to the examination of localization and interactions of mitoxantrone (1, 4-dihydroxy-5, 8-bis-[([2-(2-hydroxyethyl)-amino]ethyl)amino]-9,10-anthracenedione dihydrochloride), a potent antitumor drug, in living K562 cells. A two-dimensional set of fluorescence spectra of mitoxantrone (MITOX) recorded with micron resolution within a drug-treated cell was analyzed to reveal formation of drug-target complexes and to create the maps of their intracellular distribution. The analysis was based on detailed in vitro modeling of drug-target (DNA, RNA, DNA topoisomerase II) interactions and environmental effects affecting drug fluorescence. MITOX exposed to aqueous intracellular environment, MITOX bound to hydrophobic cellular structures, complexes of MITOX with nucleic acids, as well as the naphtoquinoxaline metabolite of MITOX were simultaneously detected and mapped in K562 cells. These states and complexes are known to be immediately related to the antitumor action of the drug. The results obtained present a basis for the subsequent quantitative analysis of concentration and time-dependent accumulation of free and bound MITOX within different compartments of living cancer cells.

Subcellular localisation of the antitumour drug mitoxantrone and the induction of DNA damage in resistant and sensitive human colon carcinoma cells

Cellular uptake and subcellular localisation of the antitumour agent mitoxantrone were studied in a human colon-carcinoma cell line and a mitoxantrone-resistant subline showing features consistent with an atypical multidrug-resistance phenotype involving altered topoisomerase II. Flow cytometry indicated a reduced uptake of mitoxantrone in the resistant line. Confocal microscopy indicated that mitoxantrone-associated fluorescence was primarily found within discrete cytoplasmic inclusions and around the periphery of the nucleus, with low levels being observed within the nucleus. The frequency of cytoplasmic inclusions was reduced in mitoxantrone-resistant cells as compared with parental cells. Fluorescence in cytoplasmic inclusions persisted throughout a 24-h post-treatment period in both cell lines. The results suggest that the persistence of mitoxantrone in cells is a determinant for the continuous induction of DNA damage, perhaps through chronic topoisomerase II trapping, and that modified sequestration may contribute to clinically relevant moderate levels of non-classic multidrug resistance.

Expression of cytokeratin confers multiple drug resistance

The cytokeratin network is an extensive filamentous structure in the cytoplasm whose biological function(s) is unknown. Based upon previous data showing the modification of cytokeratin by mitoxantrone, we investigated the ability of cytokeratin networks to influence the survival response of cells to chemotherapeutic agents. We have compared the survival of mouse L fibroblasts lacking cytokeratins with that of L cells transfected with cytokeratins 8 and 18 in the presence of chemotherapeutic drugs. The expression of cytokeratins 8 and 18 conferred a multiple drug resistance phenotype on cells exposed to mitoxantrone, doxorubicin, methotrexate, melphalan, Colcemid, and vincristine. The degree of drug resistance was 5-454 times that of parental cells, depending upon the agent used. Drug resistance could not be attributed to altered growth characteristics, altered drug accumulation, or an altered drug efflux in the transfected cells. Cytokeratin does not confer resistance to ionizing radiation, which damages DNA independently of intracellular transport mechanisms. These data suggest a role for cytokeratin networks in conferring a drug resistance phenotype.

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.

Inhibition of Growth, Morphological and Morphometrical Changes Induced by Amido-anthraquinone Derivatives in NCTC 2544 and HeLa Cells

In this work, we have studied cytotoxicity induced in NCTC 2544 and HeLa cell lines by two newly-synthesised potential anticancer drugs, the amido-anthraquinone derivatives 8-diethylaminopropionamido-1,4,5-trihydroxy-9,10-anthracenedione bromide (A888) and 5,8-bisdiethylaminopropionamido-1,4-dihydroxy-9,10-anthracenedione dibromide (A890). The results have been compared to the results obtained with mitoxantrone, a well-known anticancer agent. Using the neutral red uptake assay, A888 showed less cytotoxic action compared to mitoxantrone and A890. According to the results of morphological analysis after exposure for five hours, anthraquinone derivatives induced the formation of cytoplasmic vacuoles and changes in the arrangement of nucleus in both cell lines. On the basis of morphometrical analysis, we have observed an increase in total cellular area with a decrease in the nuclear/cytoplasmic ratio. We have found that the increase in total cellular area was higher in NCTC 2544 cells than in HeLa cells. From these data, we can conclude that NCTC cells are more sensitive to the compounds tested than HeLa cells. However, the growth inhibition assay and morphological analysis did not confirm these results.

Biochemical pharmacology of anthracenediones and anthrapyrazoles

DNA intercalating antitumor agents represent one of the more widely used classes of therapeutic agents in clinical oncology. Although a decisive mechanism to explain their ability to kill tumor cells has not been fully defined, the past decade has shown vast progress toward identifying key possibilities. The anthracenediones and anthrapyrazoles represent two latter generation classes of DNA intercalators that show great clinical promise as antitumor drugs. This article will review the currently known biochemical pharmacology for these agents and integrate these data into a broader picture touching on mechanisms of tumor cell kill.

Mitoxantrone. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in the chemotherapy of cancer

Mitoxantrone is a dihydroxyanthracenedione derivative which as intravenous mono- and combination therapy has demonstrated therapeutic efficacy similar to that of standard induction and salvage treatment regimens in advanced breast cancer, non-Hodgkin's lymphoma, acute nonlymphoblastic leukaemia and chronic myelogenous leukaemia in blast crisis; it appears to be an effective alternative to the anthracycline component of standard treatment regimens in these indications. Mitoxantrone is also effective as a component of predominantly palliative treatment regimens for hepatic and advanced ovarian carcinoma. Limited studies suggest useful therapeutic activity in multiple myeloma and acute lymphoblastic leukaemia. Regional therapy of malignant effusions, hepatic and ovarian carcinomas has also been very effective, with a reduction in systemic adverse effects. Mitoxantrone inhibits DNA synthesis by intercalating DNA, inducing DNA strand breaks, and causing DNA aggregation and compaction, and delays cell cycle progression, particularly in late S phase. In vitro antitumour activity is concentration- and exposure time-proportional, and synergy with other antineoplastic drugs has been demonstrated in murine tumour models. Leucopenia may be dose-limiting in patients with solid tumours, whereas stomatitis may be dose-limiting in patients with leukaemia. Other adverse effects are usually of mild or moderate severity although cardiac effects, particularly congestive heart failure, may be of concern, especially in patients with a history of anthracycline therapy, mediastinal irradiation or cardiovascular disease. Mitoxantrone displays an improved tolerability profile compared with doxorubicin and other anthracyclines, although myelosuppression may occur more frequently. Thus, mitoxantrone is an effective and better tolerated alternative to the anthracyclines in most haematological malignancies, in breast cancer and in advanced hepatic or ovarian carcinoma. Further studies may consolidate its role in the treatment of these and other malignancies.

Evidence for impaired mitoxantrone and vinblastine binding in P388 murine leukemia cells with multidrug resistance

Multidrug resistance is associated with a P170 glycoprotein efflux pump that limits net drug accumulation in resistant cell lines. Other evidence has suggested that diminished net drug uptake in multidrug resistant (MDR) cells is due to decreased drug binding as well. To assess the contribution of binding differences to net drug accumulation and retention in MDR cells, mitoxantrone and vinblastine, two agents commonly associated with the MDR phenotype but with different mechanisms of action and intracellular binding sites, were studied in P388 murine leukemia cells. For both drugs, resistance was associated with a marked reduction in tightly bound drug which can account for the diminished net drug accumulation in this cell line; even at 1 microM vinblastine when the exchangeable component was one-half that of the sensitive cells, the nonexchangeable component was only one-seventh. For mitoxantrone, the exchangeable drug component was greater in resistant cells at low drug levels (1 microM) and similar at high drug levels (10 microM). For vinblastine, the exchangeable drug component was decreased in the resistant cells at 1 microM, but the difference compared to sensitive cells became neglible at 10 microM. The data indicate that diminished net drug uptake in the P388 MDR cell line was associated with a marked decrease in tightly bound, i.e. nonexchangeable, drug fractions for both mitoxantrone and vinblastine. Therefore, alterations in intracellular binding are in important factor in the decreased cellular uptake and retention of drugs in the multidrug resistance phenomenon. The relationship between these changes and the P170 efflux pump requires further clarification.

Mitoxantrone-DNA binding and the induction of topoisomerase II associated DNA damage in multi-drug resistant small cell lung cancer cells

The cytotoxicity anti-tumour intercalating agents such as the anthraquinone mitoxantrone is thought to relate to DNA binding and the trapping of DNA topoisomerase II complexes on cellular DNA. We have studied the uptake, nuclear location, DNA binding mode and DNA damaging capacity of mitoxantrone in a small cell lung carcinoma cell line (NCI-H69) compared with an in vitro-derived variant subline (NCI-H69/LX4) that exhibits "classical" multi-drug resistance (MDR). Variant cells maintained under doxorubicin selection showed reduced RNA levels that returned to control values within 7 days of growth under non-selective conditions. Variant cells released from selection stress showed resistance to DNA cleavage by doxorubicin, mitoxantrone, 4'-epidoxorubicin, 4'-deoxy-doxorubicin but reduced resistance to aclacinomycin A and a 9-alkyl substituted anthracycline in broad agreement with the cross-resistance patterns for cytotoxicity. Mitoxantrone treated NCI-H69 cells were found to accumulate DNA-protein crosslinks during a 4 hr post-treatment incubation period whereas variant cells maintained depressed levels of crosslinking. There was no apparent abnormality in the availability or drug sensitivity of topoisomerase II assayed in crude nuclear extracts of NCI-H69/LX4 cells. Whole cell uptake of radiolabelled mitoxantrone was depressed (50%) in NCI-H69/LX4 compared with NCI-H69, whereas assessment of nuclear-bound drug in individual cells by a fluorescence quenching technique showed at least a 10-fold greater level of target protection. The quenching results provide evidence of a high affinity, saturable mode of drug binding, favoured at low drug concentrations, that correlated with DNA cleavage capacity. We propose that the cytotoxic action of mitoxantrone is dependent upon a restricted and persistent form of binding to DNA that favours the long-term or progressive trapping of topoisomerase II complexes.