STUDIES ON THE KINETICS OF INITIAL CYCLE PROGRESSION IN VITRO OF ASCITES TUMOUR CELLS SUBSEQUENT TO ISOLATION FROM ASCITES FLUID

A method is described for determining the duration of cell cycle phases traversed by cells responding to release from proliferation restraint. Experiments have been performed with arrested Yoshida ascites hepatoma cells allowed to re-enter the growing stage after transfer of cells from the late stage of ascites into an in vitro incubation system. Experimentally, this method requires information on the rate of incorporation of labelled thymidine and on the rate of increase in cell number. The rate of ¹⁴C]thymidine incorporation in vitro was shown to be directly proportional to the number of cells synthesizing DNA. This was shown by correlating data from measurements of the rate of thymidine incorporation with those from measurements of the labelling index of the cell population. Theoretically, the method is based on analysis of the region limited by two integral curves, one corresponding to the kinetics of cell entry into and the other to the kinetics of exit from the S-phase. From data on the actual rate of increase in the total number of cells and data on the S-phase duration it is possible to obtain information on the cytokinetics of growth resumption by the ascites cell population.