Kinetic analysis of a split cell population following reinoculation of an Ehrlich ascites tumor.

When Ehrlich ascites cells from old tumors are inoculated into fresh hosts, their cell cycle parameters show several unusual features when studied by means of four independent techniques. These experiments measure: Labeling Index (LI); Mitotic Index (MI); Percent Labeled Mitosis (PLM); Percent of population mitotic and initially G0, (Mu/P). The minimum modifications of the standard cell-cycle model that allow simultaneous simulation of the four sets of data were then determined. These modifications are: (1) sudden shortening of transit time for the S state immediately following reinoculation; (2) a more gradual change in the transit time for M; (3) an orderly reentry of G0 cells into the beginning of the cycle; (4) a shorter first cycle for the reentering G0 cells along with a smaller coefficient of variation for the first cycle of the G0 cells. These changes allow a simultaneous simulation of the four experiments with a single parameter set. This was not achievable without the modifications. Hence, resolution of a cell population into two components allows one to account for additional kinetic features.