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

ABSTRACT

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.