RESPONSE OF CULTURED 9L-CELLS TO SPIROHYDANTOIN MUSTARD AND X-RAYS

Rat brain tumor cells (9L) were treated in vitro for 1 hr with 2 μg/ml (∼30% survival) of spirohydantoin mustard (SHM) 4 and 24 hr before, during, and 4 and 24 hr after graded doses of radiation (0-20 Gy). The resulting survival curves generated from colony formation data and corrected for drug kill indicate that for all schedules SHM enhanced the radiation response, particularly for surviving fractions greater than 0.5. Analysis of the combination data using isobolograms indicates the effects of the separate agents were additive in producing either 1, 2, or 3 log cell kills. Therefore, the enhancement of the radiation response by SHM can be explained solely on the basis of the shapes of the single agent survival curves. © 1979.