The effects of diphenylhydantoin on murine astrocytoma radiosensitivity.

Diphenylhydantoin is a well known anticonvulsant used primarily in the treatment of epilepsy. The prophylactic use of diphenylhydantoin has been suggested for certain cerebral metastases, and it is routinely administered to prevent seizures induced by intracranial neoplasms and/or surgery. Patients with malignant gliomas treated with diphenylhydantoin frequently receive radiation therapy. The effects of a clinical concentration of diphenylhydantoin in combination with gamma radiation was investigated using the C6 astrocytoma cell line in both monolayer and three dimensional multicellular spheroid cultures. Diphenylhydantoin at 7.2 X 10(-5) M (20 micrograms/ml) significantly increased the doubling time (23%) of the C6 astrocytoma cells in monolayer, but did not affect their survival as measured by plating efficiency. No changes were seen in spheroid growth or plating efficiency of the cells dissociated from spheroids at this concentration. Diphenylhydantoin at the clinical concentration tested was not associated with an alteration in radiation sensitivity of C6 astrocytoma cells in monolayer or three dimensional multicellular spheroid cultures.