Induction of p53-dependent apoptosis in vivo by nedaplatin and ionizing radiation

p53 protein expression, apoptosis and growth delay induced by nedaplatin, a novel platinum compound, were investigated in vivo, and compared with thos e induced by ionizing radiation. A human ependymoblastoma with wild-type p5 3 was transplanted subcutaneously to the thighs of nude mice. The incidence s of p53 protein-positive cells and apoptosis in tumors increased following exposure to ionizing radiation. In tumors treated with nedaplatin, they al so increased, but the incidences of p53 protein-positive cells and apoptosi s induced by 32 mg/kg nedaplatin, 1/2 LD,,, were lower than those induced b y 1 Gy irradiation. However, growth-delay assay showed no significant diffe rence between the efficacy of 32 mg/kg nedaplatin and that of 1 Gy irradiat ion. These results suggest that the main antineoplastic activity caused by nedaplatin may be mediated through different mechanisms than those of the p 53-dependent early apoptosis.