The effect of adriamycin and radiation on G2 progression

The effect of the DNA-intercalating antibiotic adriamycin on the progression of Chinese hamster ovary cells into mitosis, and on the delay induced by ionizing radiation, was studied using the mitotic cell selection procedure to monitor the rate of cell division. Following the addition of adriamycin, the mitotic rate remained unaltered for a refractory period and then decreased to zero. This effect was concentration dependent with transition points between the S-G2 boundary for 0.1 mug/ml and late G2 for 250 mug/ml. Cells treated with either a 10- or 30-min pulse of 1.0 mug adriamycin per ml exhibited a refractory period identical to that observed for continuous treatment. However, after a delay of congruent to 3.5 or congruent to 5 hr, respectively, cell division resumed. The mitotic rate of cells that received 150 rads of X-ray at the oneset of an adriamycin pulse declined coincident with that of radiation only, but resumed coincident with those receiving adriamycin only. This implies that radiation-induced division delay (congruent to 3 hr) was repaired before cells recovered from adriamycin-induced division delay and that the two agents were not additive. This lack of synergism is in contrast to that observed for cell lethality.