RADIATION-INDUCED APOPTOSIS IN HUMAN SARCOMA AND GLIOMA CELL-LINES

Six human soft-tissue sarcoma and 14 glioma cell lines, exhibiting con siderable differences in radioresponsiveness and histological grade of differentiation of the parental tumour, were examined with respect to apoptosis development after irradiation with Co-60 gamma-rays. After test doses of 6 and 25 Gy, significant changes characteristic of apopt osis occurring within 6 to 30 hr were exhibited by only 2 differentiat ed sarcoma cell lines, EL7 and ESS2. The characteristic internucleosom al fragmentation of DNA was detected as early as 6 hr after exposure o f subconfluent monolayer cultures to 6 Gy. It was limited to cells tha t had detached from the culture plate, whereas adherent cells showed r andom degradation of DNA namely after higher doses (25Gy) or longer in cubation times (30 hr). As assessed by fluorescence microscopy of unfi xed cultures stained with Hoechst 33342 and propidium iodide, the prop ortion of cells showing apoptotic bodies in non-irradiated controls wa s <0.1% and 0.3% for EL7 and ESS2, respectively. The dose-response rel ationship for apoptosis was determined at 9 hr post-irradiation. After 2 Gy, the percentage of apoptotic cells was elevated to 3.4% in EL7 a nd 4.5% in ESS2 cultures. Saturation was obtained above 6 Gy, with 8.4 % apoptosis in EL7 and 15% in ESS2 after 25 Gy. Taken together, rapid ionizing-radiation-induced apoptosis seems to be limited to a subgroup of sarcomas and is unlikely to occur in gliomas. (C) 1995 Wiley-liss, Inc.