The Effect of Ploidy on the Modification of the Shoulder Region of Hypoxic Cell-survival Curves by the Biradical, Ro.03-6061

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Abstract
The biradical nitroxyl, Ro. 03-6061, sensitizes two lines of mouse L cell to ionizing radiation when the cells are rendered hypoxic. Although the biradical reduces the D0 value of the hypoxic cell-survival curve in each instance, it has no significant effect on the shoulder region. A hybrid line produced from these two strains is more radioresistant than either parent. In this instance, the biradical suppresses the shoulder region of the hypoxic cell-survival curve, but has no effect on the D0 value. In a second system, the biradical selectively sensitizes hypoxic cells of a diploid and a tetraploid clone of Syrian hamster cells (BHK21/C15). The survival-curve characteristics of both clones are similar. The biradical reduces the D0 value but does not significantly change the shoulder region of the hypoxic cell-survival curve. An aneuploid line sub-cultured from the tetraploid clone is much more resistant to radiation. In this instance, there is a decrease in the D0 value of hypoxic cells in the presence of the biradical, but the extrapolation number is increased to a value similar to that for cells irradiated in air.