The effect of ploidy on the modification of the shoulder region of hypoxic cell-survival curves by the biradical, Ro.03-6061.

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 Do 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 Do value. In a second system, the biradical selectivity 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 Do 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 Do 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.