Inhibition of protein synthesis and cell proliferation in cultured human breast cancer cells treated with mitoxantrone

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.

Functional ribosome biogenesis is a prerequisite for p53 destabilization: impact of chemotherapy on nucleolar functions and RNA metabolism

The production and processing of ribosomal RNA is a complex and well-coordinated nucleolar process for ribosome biogenesis. Progress in understanding nucleolar structure and function has lead to the unexpected discovery of the nucleolus as a highly sensitive sensor of cellular stress and an important regulator of the tumor suppressor p53. Inhibition of ribosomal RNA metabolism has been shown to activate a signaling pathway for p53 induction. This review elucidates the potential of classical and recently developed chemotherapeutic drugs to stabilize p53 by inhibiting nucleolar functions.

The activity of xenobiotic enzymes and the cytotoxicity of mitoxantrone in MCF 7 human breast cancer cells treated with inducing agents

This study investigated the effect of inducers on the major enzymes responsible for metabolising the quinone antitumor agent mitoxantrone, and on its cytotoxicity in MCF 7 human breast cancer cells. Four inducers were used: 1,2-benzanthracene (BA), phenobarbitone (PB); rifampicin (R) and dexamethasone (DEX). Of these, BA was the most effective, increasing cytochrome P450 dependent metabolism 64-fold and DT-diaphorase activity 1.6-fold. R did not cause an increase in any of the enzyme activities measured and, in fact inhibited glutathione peroxidase activity. PB and DEX increased NADPH cytochrome c reductase activity but had no effect on either DT-diaphorase or cytochrome P450 dependent activities. BA potentiated the cytotoxicity of mitoxantrone in terms of leakage of lactate dehydrogenase (LDH) activity and loss of reduced glutathione (GSH) and protein from cultures. PB had a smaller potentiating effect on cytotoxicity and DEX had no effect. Studies with the enzyme inhibitors, dicoumarol (inhibits DT-diaphorase) and metyrapone (inhibits cytochrome P450), indicate that at least two reactive species are involved in mitoxantrone cytotoxicity. One intermediate, formed by cytochrome P450, caused LDH leakage and GSH depletion. Formation of the second intermediate was catalysed by DT-diaphorase and this hydroquinone caused loss of intracellular protein and GSH. We propose that autooxidation of the hydroquinone resulting in generation of reactive oxygen species contributes to mitoxantrone cytotoxicity. Concomitant exposure to inducing agents may alter the cytotoxicity associated with many cytotoxic drugs, not just mitoxantrone, and this is an important consideration as many cytotoxics have a narrow therapeutic index.

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 toxicity on Ehrlich ascites tumour cells: inhibition of the transplasma membrane redox activity

This study focused on the potent cytotoxic effect that mitoxantrone produces on Ehrlich ascites tumour cells. Host mice treated with mitoxantrone showed a life span three times higher than control non-treated host mice. Mitoxantrone also showed a potent cytotoxic effect on Ehrlich cells incubated in vitro for only a few hours. Studies on the effect of mitoxantrone on a plasma membrane redox system showed that mitoxantrone inhibits this activity, which is apparently related to cell proliferation.

Biochemical lesions in DNA associated with the antiproliferative effects of mitoxantrone in the hepatoma cell

The H-35 rat hepatoma cell was markedly more sensitive to the anthracenedione mitoxantrone (IC50, 0.05 microM) than to the anthracycline antibiotics daunorubicin (IC50, 0.5 microM) and Adriamycin (IC50, 2.5 microM). In the rat hepatoma cell, mitoxantrone inhibited DNA and protein syntheses, with minimal effects on RNA synthesis. In contrast to daunorubicin, mitoxantrone induced both DNA strand breaks and DNA-protein cross links. The capacity of mitoxantrone to induce more extensive DNA cleavage than anthracycline antibiotics such as daunorubicin may be related to the sustained cellular retention of mitoxantrone (62% of accumulated drug) as compared to that for daunorubicin (32% of accumulated drug). Protein-associated DNA cleavage is likely to be one of the primary lesions contributing to the antiproliferative activity of mitoxantrone in the hepatoma cell, although marked growth inhibition was observed without corresponding alterations in DNA integrity.

Enhancement of the antiviral activity of poly r(A-U) by ametantrone and mitoxantrone

The role of ametantrone (HAQ) and mitoxantrone (DHAQ) in modulating the antiviral and interferon-inducing activities of poly r(A-U) was examined using the human foreskin fibroblast-vesicular stomatitis virus (HSF-VSV) bioassay system in which the concentration of poly r(A-U) was fixed at 0.05 mM or 0.2 mM while the HAQ or DHAQ concentration was varied to produce variable HAQ (or DHAQ)/ribonucleotide ratios ranging from 1:16 to 2:1. HAQ, DHAQ and poly r(A-U) tested individually were not efficacious antiviral agents. When poly r(A-U) was combined with the ametantrone or mitoxantrone the antiviral activity was potentiated 10-fold at HAQ (or DHAQ)/ribonucleotide ratios in the region of 1/4 to 1/6. The interferon-inducing activity of the HAQ (or DHAQ)/poly r(A-U) combinations were equal to the sum of the interferon-inducing activity of the poly r(A-U) and the HAQ (or DHAQ). These results indicate that the HAQ and DHAQ potentiate the antiviral activity of the poly r(A-U) without the superinduction of interferon. The direct viral inactivation study demonstrated that HAQ, DHAQ, poly r(A-U) and the HAQ (or DHAQ)/poly r(A-U) combinations did not inactivate the VSV at concentrations near the viral 50% inhibitory dose.

Influence of mitoxantrone on nucleolar function in MDA-MB-231 human breast tumor cell line

The effect of mitoxantrone (DHAQ) on [3H]thymidine and [3H]uridine incorporation by exponentially growing MDA-MB-231, a human breast tumor cell line has been studied. The results have indicated that DHAQ was more effective in inhibiting [3H]thymidine than [3H]uridine incorporation in a concentration dependent manner. Following drug treatment at 20 ng/ml concentration, 50% inhibition of growth and [3H]thymidine incorporation were noted, whereas [3H]uridine incorporation was only inhibited by about 12%. At 2000 ng/ml of DHAQ the inhibition of cell growth, [3H]thymidine and [3H]uridine incorporations were 78%, 95% and 62%, respectively. Nuclear-associated radioactivity detected at light and electron microscope autoradiographic levels after [3H]thymidine and [3H]uridine incorporations, into DHAQ treated cells indicated that DHAQ prevented the accumulation of radioactivity into the nuclei in a concentration dependent manner. These results gave further indication that mitoxantrone induced a definitive alteration of nuclear template activities, correlated with nuclear functional-structural relation and suggested that the nucleoli were the primary site of DHAQ action.

Relationship between the pharmacological activity of antitumor drugs Ametantrone and mitoxantrone (Novatrone) and their ability to condense nucleic acids

Ametantrone (HAQ) and mitoxantrone (DHAQ) are structurally similar antitumor drugs of the anthracenedione class. The cytostatic, cytotoxic, and antitumor activities of these drugs are different, with DHAQ being 10-100 times more potent, per molar basis. Both drugs are strong intercalators and intercalative modes of binding are suspected as relevant to their pharmacological activity. No significant differences, however, that could explain the differences in pharmacological activity are observed in their intercalative properties with respect to base specificity and binding affinity. A correlation, however, is evident between their potency and ability to condense nucleic acids inasmuch as DHAQ condenses nucleic acids at concentrations that are lower by a factor of 5-40 than those of HAQ and these effects can be observed at their pharmacological concentrations. The condensation is base- and sugar-specific and the long purine sequences of single-stranded RNA are the most sensitive. Electron microscopy of L1210 cells exposed a short time (90 min) to 0.21-21 microM DHAQ reveals segregation of nucleoli; the segregated granular portion shows increased electron opacity. In some preparations patchy areas of nuclear chromatin characterized by increased electron opacity can be seen. The results are compatible with the possibility that pharmacological effects of these antitumor drugs could involve condensation of nucleic acids, primarily of RNA in nucleoli.