THE INTERACTION OF ETOPOSIDE WITH RADIATION - VARIATION IN CYTOTOXICITY WITH THE SEQUENCE OF TREATMENT

Etoposide is commonly used ir combination with radiation but the best method of integrating these two treatment modalities is not known. In this study, the interaction of etoposide and radiation was investigate d using V79 hamster lung fibroblast cells. It was discovered that etop oside (0.25 mug/ml) was a dramatic radiosensitizer if it was given for a 24 hour exposure after radiation. If the cells were exposed to the same concentration of etoposide for 24 hours prior to radiation, minim al or no radiosensitization occurred. Radiosensitization correlated wi th a prolongation of the radiation-induced G2 cell cycle arrest. These initial studies indicate that the sequence of radiation and etoposide treatments is important in order to maximize cytotoxicity in V79 cell s. Further work using human cell lines will be required to determine t he clinical applications of this discovery.