CHANGES OCCURRING DURING GROWTH OF EHRLICH ASCITES CELLS IN-VIVO

Kinetic studies of Ehrlich ascites tumour cells 2 and 13 days after transplantation showed that at 13 days mean cell cycle time was increased and there was an extremely long DNA synthetic period (S). Examination of the distribution of label over chromatids at various times after injection of tritiated thymidine (3H-TdR) showed that in the 2 day population there was little variation in cell cycle time but in the 13-day tumour there was a minor fraction of fast cycling cells which had different chromosome number. Distribution of chromosome number in the two populations was the same and so the kinetic changes were not the result of selection of cells of particular ploidy. Microdensitometric measurements of Feulgen stained cells followed by autoradiography to identify cells in S, showed that in the later tumour the decrease in cells in S was accompanied by an increase in cells with G1 DNA values. Repeated injections of 3H-TdR to mice with 2-day old tumours labelled all the tumour cells but, when given to mice with 13-day old tumours did not label 20-51% of the tumour cells. Most of the cells which were unlabelled after multiple injections of 3H-TdR had G1 DNA contents and their ability to divide quickly once the tumour mass was reduced by transplantation or aspiration was demonstrated. Analysis of the distribution of cell size, using the Coulter counter, showed that as the tumour aged there was an increase in modal cell size and there were more larger cells. This was correlated with an increase in the mean protein content of cells as the tumour aged, as determined by microdensitometric measurements of cells stained with naphthol yellow S. The correlation of individual cell DNA and protein contents suggested a wide range of protein contents for all cells and the possibility of a threshold content which must be reached before DNA synthesis begins is discussed. © 1969.