Effect of paclitaxel pretreatment on radiation-induced p53-dependent apoptosis

The nim of this study was to investigate the effect of paclitaxel on radiat ion-induced p53-dependent apoptosis. A human ependymoblastoma transplanted to nude mice was used. They were treated with paclitaxel (40mg/kg), in irra diation (2Gy), or a combination of both. Apoptosis was markedly increased i n the irradiation group. p53 protein expression was well correlated with th e frequency of radiation-induced apoptosis. There was only a slight increas e in apoptosis in the paclitaxel group, with little p53 protein expression. In the combination group, the frequency of apoptosis varied with the time intervals, and the group irradiated 12 h after paclitaxel administration sh owed much less apoptosis than the irradiation group. The Ki-67 labeling ind ex in the paclitaxel group was always higher than before administration, Th e present study indicates that p53-dependent apoptosis was freguently induc ed in the human tumor in vivo by irradiation, brit nor by paclitaxel alone. When combined with irradiation, the timing affected the frequency of apopt osis and the degree of p53 protein expression.