Intratumoral heterogeneity of malignant gliomas measured in vitro.

PURPOSE

To evaluate the extent of intratumoral heterogeneity of radiation sensitivity in malignant gliomas, by comparing the intrinsic radiation sensitivity of different glioma sublines derived from the same tumor.

METHODS AND MATERIALS

The study was performed on five early established malignant gliomas (passage 3-10). Each specimen was quickly cut into three equal pieces (except for one specimen, where only two pieces were obtained). Each piece was processed independently, disintegrated 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 sensitivity of sublines was calculated using the surviving fraction at 2 Gy and the mean inactivation dose as the measured parameters. The DNA content of the cell lines as well as their cell cycle analysis was determined using flow cytometry.

RESULTS

The mean calculated surviving fraction at 2 Gy of all the sublines was 0.37 +/- 0.14, the mean mean inactivation dose was 1.98 +/- 0.63. The intertumoral coefficient of variation 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 ploidy status or in the distribution of cells in the cell cycle.

CONCLUSION

There is a significant intratumoral heterogeneity of radiation sensitivity in some malignant gliomas. This heterogeneity may limit the predictive power of surviving fraction at 2 Gy or mean inactivation dose, especially when their values are based upon a single measurement/single biopsy. In the meantime, this heterogeneity may be a factor in the discrepancy between unexpectedly sensitive tumor cell lines in vitro and their high clinical radiation resistance.