Radiobiological investigations with multicellular spheroids as an in vitro tumor model. 9

By aggregating a large quantity of small 3H-thymidine labelled spheroids within 4 hours to form a large one, we developed experimental conditions to study oxygen supply in 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 six hours, and to 1/3 after 24 hours. Enzymatic self-degradation of DNA was not detectable by sedimentation analysis after six hours of rolling. Under normal growth conditions and oxygen supply the double strand breaks in oxic monolayer cells and cells of 1000 μm spheroids are induced with a yield of 7.3x10-12 Dalton-1Gray-1 and 1.66x10-12 Dalton-1Gray-1. The break induction in spheroids with diameters from 50 - 150 μm shows that in 2 mm culture medium an important proportion of the cells may exist under hypoxic conditions. These experiments prove that 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. (author)