p53-dependent Thermal Enhancement of Cellular Sensitivity against Different LET Radiation in Human Squamous Cell Carcinomas.

PURPOSE: To investigate the dependence on p53 gene status of the thermal enhancement of cellular sensitivity against different levels of linear energy transfer (LET) from X-rays or carbon-ion (C-) beams. MATERIALS AND METHODS: Two kinds of human squamous cell carcinoma cell lines were used with an identical genotype except for the p53 gene. SAS/mp53 cells were established by transfection with mutated p53 (mp53) gene to SAS cells having functional wild-type p53 (wtp53). As the control, a neo vector was transfected to the SAS cells (SAS/neo cells). Both cells were exposed to X-rays or accelerated C-beams (30-150 KeV microm(-1)) followed by heating at 44 degrees C. Cellular sensitivity was determined by colony-forming activity. Induction of apoptosis was analysed by Hoechst 33342 staining of apoptotic bodies and agarose-gel electrophoresis for the formation of DNA ladders. RESULTS: It was found that (1) there was no significant difference in cellular sensitivity between SAS/neo and SAS/mp53 cells to LET radiation of >30 KeV microm(-1), although the radiosensitivity of SAS/neo cells to X-rays was higher (1.2-fold) than that of SAS/mp53 cells; (2) there was an interactive thermal enhancement of radiosensitivity below an LET of 70 KeV microm(-1) in SAS/neo cells, although only additive thermal enhancement was observed in SAS/mp53 cells through all LET levels examined; (3) low-LET radiation induced apoptosis only in SAS/neo cells; (4) high-LET radiation at an isosurvival dose-induced apoptosis of SAS/neo cells at a higher frequency compared with that with low-LET radiation; (5) high-LET radiation-induced p53-independent apoptosis in SAS/mp53 cells; and (6) thermal enhancement of cellular sensitivity to X-rays was due to induction of p53-dependent apoptosis. CONCLUSIONS: The findings suggest that thermal enhancement of radiosensitivity may result from p53-dependent apoptosis induced by inhibition of p53-dependent cell survival system(s) through either regulation of the cell cycle or induction of DNA repair. It is also suggested that the analysis of p53 gene status of cancer cells may predict response to combined therapies with low-LET radiation and hyperthermia

Influence of the shielding on the space radiation biological effectiveness

To investigate whether the bystander effect mediated nitric oxide (NO) radicals excreted from the tumor irradiated with accelerated carbon ion beams modulates growth of the unirradiated tumor at an opposite side in the same mouse. Also, to investigate whether NO generating agents can sensitize the tumoricidal effect by accelerated carbon ion beams. NO at the relatively low concentrations, which excreted from the irradiated donor tumors with accelerated carbon ion beams induced both inhibition and stimulation of tumor regrowth. These findings indicate the importance of an intercellular signal transduction pathway initiated by NO in cellular response to radiation. On the other hand, NO at the relatively high concentrations (0.3 mM) sensitized the tumoricidal effect of X-rays in the p53-independent manner

Nitric oxide mediated bifunctional bystander effect induced by heavy-ion radiation in HSG cells

The 2nd International Workshop on Space Radiation Researc

Radiation-induced growth inhibition in transplanted human tongue carcinomas with different p53 gene status

BACKGROUND AND PURPOSE: To test p53-dependency in radiation cancer therapy with X-rays (low-linear energy transfer (LET)) or carbon-ion (C-) beams (high-LET heavy ion), we analyzed the radiation-induced growth rate and apoptosis induction in human tongue carcinomas transplanted into nude mice. MATERIALS AND METHODS: The SAS cells transfected with mutant p53 gene (SAS/mp53) or a neo control gene (SAS/neo) were transplanted into the thigh of each nude mouse. By measuring the tumor weight (TW), tumor regrowth delay was evaluated when the relative tumor weight (RW) reached 5-fold that of the control group. Apoptosis was analyzed by immunohistochemical and ApopTag stainings. RESULTS: SAS/mp53 tumors were more resistant to X-ray irradiation than SAS/neo tumors, but not to C-beam irradiation. The relative biological effectiveness (RBE) of C-beams compared to X-rays was 2.1 in SAS/neo tumors and 2.6 in SAS/mp53 tumors. Apoptotic cells were more frequently observed in SAS/neo tumors than in SAS/mp53 tumors in X-ray irradiation but not in C-beam irradiation. CONCLUSION: The radiation-induced growth inhibition of transplanted SAS cells is suggested to be p53-dependent in X-ray irradiation but not in C-beam irradiation. C-beams are proposed as being useful for cancer radiation therapy regardless of p53 gene status

p53-dependent hyperthermic enhancement of tumour growth inhibition by X-ray or carbon-ion beam irradiation

To elucidate p53-dependency on combined treatment with radiation and hyperthermia, growth inhibition and apoptosis were analysed using transplantable human tumour. Human head and neck squamous cell carcinoma (HNSCC) cells carrying different p53 genes were transplanted into the thigh of nude mice. When the mean diameter of tumour reached 5-6 mm, the tumours were exposed to X-rays (2 Gy) or Carbon-ion (C-) beams (1 Gy) followed by heating at 42 degrees C for 20 min. Tumour growth inhibition was evaluated by measuring the diameters of tumour. The induction of apoptosis and accumulation of apoptosis-related proteins were also analysed by immunohistochemical staining. Synergistic enhancement of tumour growth inhibition by hyperthermia was observed in wild-type p53 tumours treated with X-rays or C-beams but not in mutant p53 tumours. The incidence of apoptotic cells and activated-caspase-3-positive cells after combined treatment with them were significantly high in wild-type p53 tumours compared with that in mutant p53 tumours. The hyperthermic enhancement of tumour growth inhibition by X-ray- or C-beam-irradiation was p53-dependent, suggesting that it might be highly correlated with p53-dependent apoptosis