Radiation biological investigations with multi cellular spheroids as an in vitro tumor model 9. estimation of dna double strand break rates of spheroid cells after x ray irradiation of spheroids
Studia Biophysica 85(2): 125-129
By aggregating a large quantity of small 3H-thymidine labeled spheroids within 4 h to form a large globe, experimental conditions were developed to study O2 supply in [animal] cell biology. The rapid transfer of the oxygenated logarithmically growing cells into the hypoxic state within the cell globes reduce the colony forming ability of the trypsinized cells to 1/2 after 6 h, and to 1/3 after 24 h. Enzymatic self-degradation of DNA was not detectable by sedimentation analysis after 6 h of rolling. Under normal growth conditions and O2 supply the DSB [double strand break in DNA] in oxic monolayer cells and cells of 1000 .mu.m spheroids are induced with a yield of 7.3 .times. 10-12 Dalton-1 Gray-1 and 1.66 .times. 10-12 Dalton-1 Gray-1. The break induction in spheroids with diameters from 50 - 150 .mu.m shows that in 2 mm culture medium an important proportion of the cells may exist under hypoxic conditions. In the multicellular spheroids hypoxic and anoxic cells exist with corresponding break induction rates, which could give an explanation for the higher survival of irradiated cells from spheroids.