Rat liver microsomes were irradiated with gamma-rays at a dose rate of 1.31 Gys-1. The extent of lipid peroxidation, measured in terms of malondialdehyde (MDA) formed, increased with radiation dose. The presence of calmodulin antagonists during irradiation decreased lipid peroxidation. The order of their protective efficiency was: chlorpromazine (CPZ) greater than promethazine (PMZ) greater than trimeprazine (TMZ). Their protective effect was diminished in the presence of ferrous (Fe2+) ions and was restored on addition of EDTA. However, calmodulin antagonists considerably inhibited radiation-induced lipid peroxidation in the presence of ferric (Fe3+) ions. Calmodulin antagonists also decreased the cytochrome P-450 content of microsomes. These results are discussed with respect to their applicability to radiotherapy. A possible mechanism for the inhibition of radiation-induced lipid peroxidation is suggested.

Effects of calmodulin antagonists on radiation-induced lipid peroxidation in microsomes.

Glucose deprivation has been hypothesized to cause cytotoxicity by inducing metabolic oxidative stress in human cancer cells. The current work tests the hypothesis that 2-deoxy-d-glucose (2DG) combined with cisplatin [cis-diamminedichloroplatinum(II)] can enhance cytotoxicity in human head and neck cancer cells (FaDu) by mechanisms involving oxidative stress. Exposure of FaDu cells to the combination of 2DG and cisplatin resulted in a significant decrease in cell survival when compared with 2DG or cisplatin alone. Treatment with 2DG and cisplatin also caused perturbations in parameters indicative of oxidative stress, including decreased intracellular total glutathione and increased percentage of glutathione disulfide. Simultaneous treatment with the thiol antioxidant N-acetylcysteine (NAC) inhibited parameters indicative of oxidative stress, as well as protected FaDu cells from the cytotoxic effects of cisplatin alone and the combination of 2DG and cisplatin. In addition, polyethylene glycol-conjugated antioxidant enzymes (PEG-superoxide dismutase and PEG-catalase) also protected FaDu cells from 2DG toxicity. An inhibitor of glutathione synthesis, l-buthionine-[S,R]-sulfoximine (BSO), sensitized FaDu cells to the cytotoxic effects of 2DG and cisplatin, and these effects were inhibited by NAC. Furthermore, the combination of 2DG, cisplatin, and BSO significantly increased the percentage of glutathione disulfide, which was also inhibited by NAC. These results support the hypothesis that exposure of human head and neck cancer cells to 2DG combined with cisplatin enhances cytotoxicity via metabolic oxidative stress. These findings provide a strong biochemical rationale for evaluating inhibitors of glucose and hydroperoxide metabolism in combination with cisplatin for the treatment of head and neck cancer.

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2-Deoxy-D-glucose combined with cisplatin enhances cytotoxicity via metabolic oxidative stress in human head and neck cancer cells.

Results of numerous studies demonstrate that membranes are important sites of cell damage by both ionizing radiation and hyperthermia. Modification of membrane properties (mainly lipid fluidity) af...

Membrane effects of ionizing radiation and hyperthermia.

Exposure to ionizing radiation is believed to cause cell injury via the production of free radicals that are thought to induce oxidative damage. It has been proposed that exposure to agents that enhance oxidative stress-induced injury by disrupting thiol metabolism may sensitize cells to the cytotoxic effects of ionizing radiation. Recently, it has been shown that glucose deprivation selectively induces cell injury in transformed human cells via metabolic oxidative stress (J. Biol. Chem., 273: 5294–5299; Ann. N.Y. Acad. Sci., 899: 349–362), resulting in profound disruptions in thiol metabolism. Because 2-deoxy-d-glucose (2DG) is a potent inhibitor of glucose metabolism thought to mimic glucose deprivation in vivo, the hypothesis that exposure to 2DG might be capable of inducing radiosensitization in transformed cells via perturbations in thiol metabolism was tested. When HeLa cells were exposed to 2DG (4–10 mm) for 4–72 h, cell survival decreased (20–90%) in a dose- and time-dependent fashion. When HeLa cells were treated with 6 mm 2DG for 16 h before ionizing radiation exposure, radiosensitization was observed with a sensitizer enhancement ratio of 1.4 at 10% isosurvival. Treatment with 2DG was also found to cause decreases in intracellular total glutathione content (50%). Simultaneous treatment with the thiol antioxidant N-acetylcysteine (NAC; 30 mm) protected HeLa cells against the cytotoxicity and radiosensitizing effects of 2DG, without altering radiosensitivity in the absence of 2DG. Furthermore, treatment with NAC partially reversed the 2DG-induced decreases in total glutathione content, as well as augmented intracellular cysteine content. Finally, the cytotoxicity and radiosensitizing effects of 2DG were more pronounced in v-Fos-transformed versus nontransformed immortalized rat cells, and this radiosensitization was also inhibited by treatment with NAC. These results support the hypothesis that exposure to 2DG causes cytotoxicity and radiosensitization via a mechanism involving perturbations in thiol metabolism and allows for the speculation that these effects may be more pronounced in transformed versus normal cells.

https://cancerres.aacrjournals.org/content/canres/63/12/3413.full.pdf

2-Deoxy-d-Glucose-induced Cytotoxicity and Radiosensitization in Tumor Cells Is Mediated via Disruptions in Thiol Metabolism

Calmodulin is a ubiquitous, calcium-binding protein that is responsible for many of the intracellular actions of calcium. Recent evidence suggests that calmodulin may regulate cellular proliferation and that its function may be altered in malignancy. The discovery that drugs such as phenothiazines antagonize the action of calmodulin led to the study of these antagonists against tumor cells. It is now appreciated that calmodulin antagonists are cytotoxic, can restore the sensitivity of resistant cells to drugs such as doxorubicin and vincristine, and can augment the cytotoxicity of bleomycin. This report addresses the possibility of developing new forms of chemotherapeutic agents that work by disrupting the function of this intriguing molecule.

Calmodulin: a potential target for cancer chemotherapeutic agents.

SummaryChlorpromazine sensitized E. coli B/r, thymocytes and Yoshida ascites-tumour cells to 60Co gamma-rays, preferentially, under hypoxic conditions. Residual sensitization was observed in E. coli B/r. The radiosensitization by chlorpromazine was found to be due to the reaction of radiolytically-induced hydroxyl radicals with the sensitizer. When both procaine HCl and chlorpromazine were present during anoxic irradiation of E. coli B/r, there was no additive effect. But the addition of procaine HCl after irradiation to cells sensitized by chlorpromazine had an effect that was significantly greater than that produced even by oxygen. A similar effect was observed when lignocaine or tetracaine was used in place of procaine. The possible mechanisms involved in radiosensitization by chlorpromazine and in the post-irradiation effect of local anaesthetics in cells sensitized to 60Co gamma-rays by chlorpromazine are discussed.

Modification of Radiation Effects in Single-cell Systems by Membrane-binding Agents

SummaryA review of the literature on radiosensitization reveals that at least some of the non-nitro compounds, such as metabolic inhibitors and membrane-active drugs, could be considered as potentially valuable radiosensitizers for possible use in future cancer radiotherapy.

Non-nitro radiation sensitizers.

MANY carbonyl compounds by virtue of the electron affinitive property1 of their C=O groups are good radiosensitisers in bacterial as well as mammalian cells2–4. The electronic charge distribution at the carbonyl bond of some local anaesthetics belonging to the class of esters represented by the general formula (I) given below is also known to play an important role in their anaesthetic action5–6. If these esters are found to be radiosensitisers they may prove very valuable in radiation therapy. Here we present data on one such compound, procaine hydrochloride (II) which is commonly used as a local anaesthetic and has been found to enhance radiation lethality of Escherichia coli B/r under anoxia.

B.B. Singh

Papers

Modification of Radiation Effects in Single-cell Systems by Membrane-binding Agents

Non-nitro radiation sensitizers.

Enhancement of radiation lethality of E. coli B/r by procaine hydrochloride

Role of bacterial membranes in radiosensitization.

Cytotoxic effect of chlorpromazine and its interaction with radiation on a mouse fibrosarcoma.