Conditionally tumorigenic clone of C6 cells is induced by gamma-irradiation.
BACKGROUND: Established cell lines are often heterogeneous in their response to ionizing radiation. The tumorigenicity of some cells can be rapidly induced by gamma-radiation. MATERIALS AND METHODS: The tumorigenicity of individual clones of C6 rat glioblastoma cells and the effect of gamma-radiation on their growth in vivo was studied by intracranial implantation into Wistar rats. RESULTS: A clone was found, C6#11, that was conditionally tumorigenic. It either did not form a tumor, or grew into a small encapsulated tumor, and did not cause death or neurological deficits in the animals. Gamma-irradiation of the animals (head only) with implanted C6#11 induced a fully developed invasive tumor that killed them within 25 days. Three grays of radiation of C6#11 cells two hours prior to implantation induced their tumorigenicity as well. The in vitro characteristics of the C6#11 cells as compared to a highly tumorigenic clone did not correlate with their behavior in vivo. CONCLUSION: The C6#11 clone is the first model of an experimental tumor that acquires tumorigenicity in an immuno-competent host immediately after low dose irradiation of the cells.