Evidence for the involvement of double-strand breaks in heat-induced cell killing.

To identify critical events associated with heat-induced cell killing, we examined foci formation of gammaH2AX (histone H2AX phosphorylated at serine 139) in heat-treated cells. This assay is known to be quite sensitive and a specific indicator for the presence of double-strand breaks. We found that the number of gammaH2AX foci increased rapidly and reached a maximum 30 minutes after heat treatment, as well as after X-ray irradiation. When cells were heated at 41.5 degrees C to 45.5 degrees C, we observed a linear increase with time in the number of gammaH2AX foci. An inflection point at 42.5 degrees C and the thermal activation energies above and below the inflection point were almost the same for cell killing and foci formation according to Arrhenius plot analysis. From these results, it is suggested that the number of gammaH2AX foci is correlated with the temperature dependence of cell killing. During periods when cells were exposed to heat, the cell cycle-dependent pattern of cell killing was the same as the cell cycle pattern of gammaH2AX foci formation. We also found that thermotolerance was due to a depression in the number of gammaH2AX foci formed after heating when the cells were pre-treated by heat. These findings suggest that cell killing might be associated with double-strand break formation via protein denaturation.

High-LET radiation enhanced apoptosis but not necrosis regardless of p53 status.

PURPOSE: We analyzed the death pattern of human lung cancer cells harboring different p53 statuses after irradiation with different levels of linear energy transfer (LET). METHODS AND MATERIALS: We used three kinds of human lung cancer cell lines with identical genotypes, except for the p53 gene. These cells were exposed to X-rays or accelerated carbon-ion beams. The cellular sensitivities were determined by a colony-forming assay. The detection and quantification of cell death (apoptosis and necrosis) were evaluated and compared by acridine orange/ethidium bromide double staining for fluorescence microscopy. RESULTS: We found that (1) there was no significant difference in cellular sensitivity to LET radiation >70 KeV/microm, although wild-type p53 cell sensitivity to X-rays was higher than that of mutated p53 or p53-null cells; (2) low-LET radiation effectively induced apoptosis in wild-type p53 cells as compared with mutated p53 and p53-null cells; and (3) high-LET radiation induced p53-independent apoptosis. CONCLUSIONS: Our findings suggest that high-LET radiotherapy is expected to be a valid application for patients carrying mutated p53 cancer cells. We proposed that the elucidation of the p53-independent apoptosis-related genes might provide new insights into radiotherapy for cancer.

Glycerol enhances CDDP-induced growth inhibition of thyroid anaplastic carcinoma tumor carrying mutated p53 gene.

To increase the chemo-sensitivity of anaplastic thyroid carcinoma, we examined the effects of glycerol on the tumor growth after CDDP treatment. The cultured cells of an anaplastic thyroid carcinoma cell line (8305c) carrying a mutated p53 gene (mp53) were transplanted into the thighs of nude mice. Tumor growth was evaluated until 24 days after intraperitoneal injection of CDDP and/or pre-injection of glycerol to the tumor. We treated the mice with half the tumor volume of glycerol (1.2 M) and/or CDDP at 6 mg/kg (BW) either of which hardly inhibited tumor growth by itself. When we treated the mice with the combination of glycerol and CDDP at these concentrations, however, a clear delay of the tumor growth was observed. We also immunohistochemically analyzed the effects of glycerol on the induction of caspase-3 activity and apoptosis. Cells positive for cleavage to active caspase-3 and 85 kDa PARP, and apoptosis were hardly observed in the tumors when they were treated with glycerol or CDDP alone. In contrast, when they were treated with CDDP combined with glycerol, such positive cells were significantly increased. It has been shown that glycerol synergistically enhanced the effects of CDDP as a tumor suppressive agent through the induction of caspase-3-mediated apoptosis in 8305c tumors. Therefore, glycerol might be useful for chemotherapy in patients with mp53 cancer cells.

Apoptosis-related gene expression after hyperthermia in human tongue squamous cell carcinoma cells harboring wild-type or mutated-type p53.

Hyperthermia is useful for the treatment of human head and neck cancer, as it is relatively easy to perform thermoregulation when compared with deep organs. In this study, we focused attention on the p53 as a predictive indicator of hyperthermic cancer therapy. We used two kinds of cell lines of a human squamous cell carcinoma (SAS) with identical backgrounds of function except for the p53 protein. We assayed the heat sensitivity, frequency of apoptosis, and apoptosis-related gene expression after heat treatment using DNA array. The SAS/neo (wild-type p53; wtp53) cells were sensitive to heat, and the induction of Caspase-3 activation and apoptosis in the wtp53 cells was clearly high compared with the SAS/mp53 (mutated p53; mp53) cells. The gene expression of apoptosis suppressive-genes such as IL-12 p35 decreased in the wtp53 cells, and IL-12 R beta1 increased in the mp53 cells, though apoptosis-promotive genes of Caspase-9, CD30 and CD40 were induced p53-independently by hyperthermia. It is suggested that heat-induced apoptosis was suppressed by IL-12-related genes in the mp53 cells. These findings strongly imply that p53 status is a useful candidate for a predictive indicator of the effectiveness in hyperthermic therapy.

Analysis of apoptosis-related gene expression after X-ray irradiation in human tongue squamous cell carcinoma cells harboring wild-type or mutated p53 gene.

Mutations in the p53 tumor suppressor gene have recently been reported to have an impact on clinical trials of several human tumors, including head and neck cancers. To confirm the p53-dependence of X-ray induced apoptosis, we used two cell lines derived from a human squamous cell carcinoma (SAS) with identical genetic backgrounds, except for the p53 gene, which are SAS/mp53 cells with mp53 and SAS/neo cells with wtp53. We previously reported that the radiosensitivity, Caspase-3 activity and apoptosis frequency in SAS/neo cells were clearly high as compared with SAS/mp53 cells. In order to elucidate the expression of apoptosis-related genes after irradiation, we used cDNA array analysis. The expressions of apoptosis-inductive genes, such as DFF40, Caspase-3, Caspase-8, Caspase-9, Caspase-10 and CRADD, were increased by X-ray irradiation in SAS cells with wtp53, but not in SAS cells expressing mp53. These results suggest that the X-ray sensitivity of wtp53 cells may come from the expression of these apoptosis-related genes.

Glycerol as a chemical chaperone enhances radiation-induced apoptosis in anaplastic thyroid carcinoma cells.

INTRODUCTION: Anaplastic thyroid carcinoma, which is one of the most aggressive, malignant tumors in humans, results in an extremely poor prognosis despite chemotherapy and radiotherapy. The present study was designed to evaluate therapeutic effects of radiation by glycerol on p53-mutant anaplastic thyroid carcinoma cells (8305c cells). To examine the effectiveness of glycerol in radiation induced lethality for anaplastic thyroid carcinoma 8305c cells, we performed colony formation assay and apoptosis analysis. RESULTS: Apoptosis was analyzed with Hoechst 33342 staining and DNA ladder formation assay. 8305c cells became radiosensitive when glycerol was added to culture medium before X-ray irradiation. Apoptosis was induced by X-rays in the presence of glycerol. However, there was little apoptosis induced by X-ray irradiation or glycerol alone. The binding activity of whole cell extracts to bax promoter region was induced by X-rays in the presence of glycerol but not by X-rays alone. CONCLUSION: These findings suggest that glycerol is effective against radiotherapy of p53-mutant thyroid carcinomas.