INTRATUMORAL HETEROGENEITY OF MALIGNANT GLIOMAS MEASURED IN-VITRO

Purpose: To evaluate the extent of intratumoral heterogeneity of radia tion sensitivity in malignant gliomas, by comparing the intrinsic radi ation sensitivity of different glioma sublines derived from the same t umor. Methods and Materials: The study was performed on five early est ablished malignant gliomas (passage 3-10). Each specimen was quickly c ut into three equal pieces (except for one specimen, where only two pi eces were obtained). Each piece was processed independently, disintegr ated into single cell suspension using a cocktail of enzymes. Survival curve assays, using colony formation as an end-point, were performed for each subline. Comparison between the intrinsic radiation sensitivi ty of sublines was calculated using the surviving fraction at 2 Gy and the mean inactivation dose as the measured parameters. The DNA conten t of the cell lines as well as their cell cycle analysis was determine d using flow cytometry. Results: The mean calculated surviving fractio n at 2 Gy of all the sublines was 0.37 +/- 0.14, the mean mean inactiv ation dose was 1.98 +/- 0.63. The intertumoral coefficient of variatio n for the calculated surviving fraction at 2 Gy of all cell lines was 38%, while that for intratumoral heterogeneity was 25%. Three of the 5 tumors showed a statistically significant difference in the surviving fraction at 2 Gy and mean inactivation dose values of their sublines (p < 0.05). This difference in radiation sensitivity between sublines of the same tumor was not attributed to a difference either in the plo idy status or in the distribution of cells in the cell cycle. Conclusi on: There is a significant intratumoral heterogeneity of radiation sen sitivity in some malignant gliomas. This heterogeneity may limit the p redictive power of surviving fraction at 2 Gy or mean inactivation dos e, especially when their values are based upon a single measurement/si ngle biopsy. In the meantime, this heterogeneity may be a factor in th e discrepancy between unexpectedly sensitive tumor cell lines in vitro and their high clinical radiation resistance.