RNA and protein synthesis of irradiated Ehrlich ascites tumour cells. I. In vivo investigations related to the cell cycle.

The effects of roentgen irradiation on the incorporation of 3H-uridine and 14C-leucine into RNA and protein and the RNA and protein contents of in vivo growing Ehrlich ascites tumour cells were studied. The results were related to changes in the composition of cells in cell cycle and compared with the synthesis of RNA and protein in cell material from various parts of the cell cycle obtained by means of elutriator centrifuging. The incorporation expressed by the ratio between acid insoluble/acid soluble activity was unchanged for RNA during the observation period up to 24 hours after a dose of 5.0 Gy. The ratio for protein was markedly decreased between 4 and 24 hours. This decrease was partly due to a decrease of the pool size of leucine as studied by changing the amounts of 14C leucine used. From these studies, the existence of at least two pools, an expandable and a non-expandable fixed pool can be concluded. There were no differences in the decrease of protein-synthesis between cells from the various parts of the cell cycle. The RNA and protein contents of the irradiated cells from various parts of the cell cycle corresponded to those of non-irradiated cells except for G1/early S-phase cells at 15 and 24 hours after irradiation. Possible reasons for this discrepancy are discussed.

Energy metabolism and ATP turnover time during the cell cycle in roentgen irradiated Ehrlich ascites tumour cells.

The cell-cycle related energy metabolism after roentgen irradiation of in vivo growing Ehrlich ascites tumour cells was investigated in cell fractions obtained by elutriator centrifuging. The oxygen consumption and the lactate and pyruvate production, measured in vitro after 4.5, 5 and 9 Gy up to 24 h, were undisturbed, while the decrease in the in vivo ATP content was dose-independent in all parts of the cell cycle. On the basis of these data the ATP turnover time was found to be decreased. The decrease in the ATP content is considered to be less likely to be due to membrane leakage or increased ATP consumption than to reduced ATP production. Since in vitro incubation normalizes the ATP content, it is suggested that environmental factors in the ascites liquid after irradiation cause a decrease in the ATP production. Low ATP contents of the cells do not appear to influence the irradiation-induced changes in the cell flow through the cell cycle.

Non-effectivity of roentgen irradiation in an in vivo rapidly growing murine lymphosarcoma.

The survival time of mice bearing a rapidly growing murine lymphosarcoma (cell doubling time 9.6 h) is hardly influenced by roentgen irradiation with fractions of 2 Gy, not even if delivered according to superfractionated schedules. Growth kinetic measurements reveal an almost complete mitotic block 6 h after exposure, followed by a large overshoot in cell proliferative activity. The dose-response curve for in vivo irradiated cells has a D0 of 1.9 and lacks a shoulder. Hence, repair of sublethal damage must be of restricted significance. The extremely strong proliferative capability appears to lead to rapid repopulation of the tumour. Typically, surviving cells show a high content of RNA and protein.

Kinetics of cell proliferation in a rapidly growing murine lymphosarcoma.

The growth kinetics of a murine lymphosarcoma were investigated the spleen and liver of mice by means of quantitative flow-cytofluorometric DNA measurements in individual cells in combination with 3H-thymidine incorporation into the DNA. The amount of DNA in the S-phase cells was calculated from the resulting DNA histograms. From the 3H-thymidine incorporation, related to the amount of S-phase DNA, the relative changes in the duration of the S-phase during the growth of the lymphosarcoma were estimated. A marked prolongation of the duration of the S-phase was observed in the course of the growth of the lymphosarcoma. The disappearance of cells of higher ploidy normally found in the liver indicates the elimination of those normal cells in the course of the tumour growth.