Doxorubicin-induced oxygen free radical formation in sensitive and doxorubicin-resistant variants of rat glioblastoma cell lines

ROS signalling in the biology of cancer

Increased reactive oxygen species (ROS) production has been detected in various cancers and has been shown to have several roles, for example, they can activate pro-tumourigenic signalling, enhance cell survival and proliferation, and drive DNA damage and genetic instability. Counterintuitively ROS can also promote anti-tumourigenic signalling, initiating oxidative stress-induced tumour cell death. Tumour cells express elevated levels of antioxidant proteins to detoxify elevated ROS levels, establish a redox balance, while maintaining pro-tumourigenic signalling and resistance to apoptosis. Tumour cells have an altered redox balance to that of their normal counterparts and this identifies ROS manipulation as a potential target for cancer therapies. This review discusses the generation and sources of ROS within tumour cells, the regulation of ROS by antioxidant defence systems, as well as the effect of elevated ROS production on their signalling targets in cancer. It also provides an insight into how pro- and anti-tumourigenic ROS signalling pathways could be manipulated in the treatment of cancer.

Antimutagenic and antirecombinagenic activities of noni fruit juice in somatic cells of Drosophila melanogaster

Noni, a Hawaiian name for the fruit of Morinda citrifolia L., is a traditional medicinal plant from Polynesia widely used for the treatment of many diseases including arthritis, diabetes, asthma, hypertension and cancer. Here, a commercial noni juice (TNJ) was evaluated for its protective activities against the lesions induced by mitomycin C (MMC) and doxorrubicin (DXR) using the Somatic Mutation and Recombination Test (SMART) in Drosophila melanogaster. Three-day-old larvae, trans-heterozygous for two genetic markers (mwh and flr3 ), were co-treated with TNJ plus MMC or DXR. We have observed a reduction in genotoxic effects of MMC and DXR caused by the juice. TNJ provoked a marked decrease in all kinds of MMC- and DXR-induced mutant spots, mainly due to its antirecombinagenic activity. The TNJ protective effects were concentration-dependent, indicating a dose-response correlation, that can be attributed to a powerful antioxidant and/or free radical scavenger ability of TNJ.

A possible role for oxidation stress in lymphoid leukaemias and therapeutic failure

The aim of this study was to evaluate the role of oxidative stress in the pathobiology of lymphoid leukaemias and its involvement in leukaemic relapse. For this purpose the generation of peroxides by mononuclear cells, the erythrocyte activity of superoxide-dismutase (SOD) and glutathione peroxidase (GL-PX), and the plasma levels of reduced glutathione (GSH) and vitamin E (VIT E) were determined in 52 patients with two different types of lymphoid leukaemias, chronic lymphocytic leukaemia (CLL) and acute lymphoblastic leukaemia (ALL), 36 prior to chemotherapy and 16 treated patients. A decrease in SOD and GL-PX activities was observed in ALL patients prior to therapy, while a decrease in GSH and VIT E plasma levels was observed in untreated CLL, as compared to age-matched controls. An increase in peroxides formation occurred in both types of leukaemia, as compared to age-matched controls. There are significant differences for GSH, VIT E and peroxides generation between the different types of leukaemias. In relapsed ALL patients a decrease in peroxides generation was observed which may be due to the increase of the non-enzymatic defences GSH and VIT E. These data suggest the involvement of oxidative stress in acute and chronic lymphoid leukaemias and leukaemic relapse.

A critical evaluation of the mechanisms of action proposed for the antitumor effects of the anthracycline antibiotics adriamycin and daunorubicin

The mechanisms responsible for the antiproliferative and cytotoxic effects of the anthracycline antibiotics doxorubicin (Adriamycin) and daunorubicin (daunomycin) have been the subject of considerable controversy. This commentary addresses the potential role of DNA synthesis inhibition, free radical formation and lipid peroxidation, DNA binding and alkylation, DNA cross-linking, interference with DNA strand separation and helicase activity, direct membrane effects, and the initiation of DNA damage via the inhibition of topoisomerase II in the interaction of these drugs with the tumor cell. One premise underlying this analysis is that only studies utilizing drug concentrations that reflect the plasma levels in the patient after either bolus administration or continuous infusion are considered to reflect the basis for drug action in the clinic. The role of free radicals in anthracycline cardiotoxicity is also discussed.

Effects of high doses of vitamins C and E against doxorubicin-induced chromosomal damage in Wistar rat bone marrow cells

Doxorubicin (DXR) is one of the major antitumoral agents available for clinical use. In addition to intercalating into the DNA molecule, this drug generates free radicals. Vitamins C (VC) and E (VE) can protect normal cells from the damage caused by radicals without interfering with the cytotoxicity of DXR against tumors. The objective of the present study was to investigate the possible protective effect of VC and/or VE on mammalian cells treated with DXR in vivo. Animals treated with the lowest doses of VC and/or VE, alone or in combination, plus a single dose of DXR presented a statistically significant reduction in total number of chromosome aberrations and in number of abnormal metaphases. The highest vitamin doses tested caused no changes in the parameters analyzed when compared with control. Under the present experimental conditions, the efficiency of VC and/or VE in protecting against chromosome damage was dependent on the dose used.

Differential stabilization of topoisomerase-II-DNA cleavable complexes by doxorubicin and etoposide in doxorubicin-resistant rat glioblastoma cells

Using the technique of alkaline filter elution, we have evaluated the DNA damage induced by doxorubicin and etoposide in a rat glioblastoma cell line, C6, and its doxorubicin-selected resistant variant, C6 0.5. DNA damage paralleled drug-induced cytotoxicity, but it appeared that the same DNA damage generated much less cytotoxicity in resistant cells than in sensitive ones, resistant cells being able to tolerate more DNA damage than sensitive cells. We have then quantified the doxorubicin- and etoposide-induced complexes between topoisomerase II (topoII) DNA with the technique of SDS/KCl precipitation. Etoposide produced a concentration-dependent increase in topoII-DNA complexes, which was higher in resistant cells at equitoxicity, just as was DNA damage. In contrast, doxorubicin-induced topoII-DNA complexes, which were much less abundant than those induced by etoposide, were not differently produced in sensitive and resistant cells. This indicates that the DNA damage occurring in resistant cells at high doxorubicin concentrations might originate from source other than topoII-DNA complex formation. When verapamil was added during drug exposure, it restored doxorubicin intracellular accumulation to the level reached in sensitive cells, partially reversed both doxorubicin and etoposide resistance, increased the formation of etoposide-induced topoII-DNA complexes, but not those induced by doxorubicin. Immunoblot analysis of topoII as well as the measure of its catalytic activity in nuclear extracts revealed a quantitative defect of this enzyme in the resistant line. When inhibiting this activity by doxorubicin and etoposide, we observed that the concentrations of etoposide required for a given inhibition of kinetoplast DNA decatenation are much higher that those of doxorubicin. The topoII extracted from both cell lines is, therefore, much more sensitive to doxorubicin than to etoposide, but no difference in drug sensitivity was evident between sensitive and resistant cells, indicating that no qualitative alteration in topoII catalytic activity was likely to occur.

Effects of doxorubicin on cardiomyocytes with reduced level of superoxide dismutase

Our previous studies have shown that isolated adult rat cardiomyocytes with normal and reduced Cu/Zn SOD activities are equally susceptible to extracellularly generated oxidants (hydrogen peroxide, glucose oxidase/glucose and xanthine oxidase/xanthine systems). In the present study we exposed myocytes with reduced SOD activity to doxorubicin (adriamycin). Cardiotoxicity of doxorubicin has been attributed to the production of superoxide anion inside the cell. Cardiomyocytes with reduced SOD activity, but normal ATP content and viability, were obtained by the treatment of isolated cells with diethyldithiocarbamate (DDC). DDC-treated myocytes were significantly less resistant to doxorubicin than controls. Doxorubicin-stimulated superoxide anion formation, measured by the rate of SOD-inhibitable acetylated cytochrome C reduction, was significantly higher in the cytosolic fraction of DDC-treated cells compared to controls. These results indicate that for isolated cardiac myocytes an essential part of cytotoxicity of doxorubicin can be explained by the formation of superoxide anion and that the level of intracellular SOD activity should be considered as a significant factor for cell protection.

Free radical formation by ansamycin benzoquinone in human breast tumor cells: implications for cytotoxicity and resistance

The benzoquinonoid ansamycin antibiotics, geldanamycin and herbimycin A, are potent cytotoxins against tumor cells in vitro. We have examined the mechanism of their in vitro cytotoxicity against human breast adenocarcinoma (MCF-7) cells and we have found that multidrug-resistant MCF-7/ADRR cells that exhibit the MDR phenotype and the overexpression of P-170-glycoprotein, were cross-resistant to geldanamycin and herbimycin A. Verapamil, which binds competitively with P-170-glycoprotein, enhanced geldanamycin cytotoxicity 12-fold only in resistant cells, suggesting that geldanamycin may interact with the drug efflux protein. Geldanamycin and herbimycin A, like adriamycin, were reductively activated by the NADPH-cytochrome P450-reductase and formed reactive .OH. The formation of .OH was significantly lower in resistant cells. In contrast to adriamycin, the formation of .OH was unaffected by the addition of DNA, indicating that a DNA-complexed drug was redoxactive and may, therefore, may be more effective in killing tumor cells at the DNA level. These observations indicate that both the decreased free radical formation and interactions with P170 glycoprotein may be important in geldanamycin and herbimycin A resistance in multidrug resistant human breast tumor cells.