Quantitative Studies of Relationships between Tumor Cell Ploidy and Dose Response to Ionizing Radiation in Vivo: Modification of Radiation Response in a Previously Irradiated Tumor

Abstract

ggradiation was demonstrated in vivo between two closely related murine lymphocytic leukemias, one diploid and the other tetraploid. Dose-response curves were determined under oxygenated and anoxic conditions; in either condition the slopes of the dose-response curves were similar, but the extrapolation number for the tetraploid tumor exceeded that for the diploid tumor by a factor of approximately 2. A tumor line of diploid origin was subjected to 1000 rads of x irradiation at each of fifty sequential passages in vivo with 10/ sup 6/ tumor cells transplanted at each passage to minimize the chance of selection from small numbers of surviving celis. During the fifty irradiated passages, this tumor line was noted to have altered radiation response with a greater proportion of tumor cells surviving any given radiation dose, increased nucleic acid content per cell was seen, and tetraploid and aneuploid cells appeared in the population. The application of these findings to the acquired radioresistance reported by radiotherapists in the treatment of human cancer is discussed. (auth)