Experimental induction of apoptosis by a combination of etoposide and radiation treatment.

The present study was undertaken to investigate cell death (particularly apoptosis) induced by etoposide, radiation, and both, and to examine p53 protein expression in relation to cell death. Nude mice transplanted with a human tumor (ependymoblastoma) were treated with etoposide (5-40 mg/kg) or 1-2 Gy X-ray irradiation or both. The tumor was excised at different points after treatment, and tumor tissue specimens were used to check for apoptosis and p53 protein expression by TUNEL, p53 protein staining, etc. Induction of p53-dependent apoptosis was observed in the etoposide treatment group, the X-ray irradiation group, and the combined (etoposide + X-ray irradiation) group. Etoposide 10 mg/kg was found to be approximately equivalent to 1 Gy X-ray irradiation in ability to induce apoptosis. When etoposide treatment was combined with X-ray irradiation at intervals of 3-6 hours, an approximately additive effect was observed.