Murine Mammary Tumour Cells In Vitro. Ii. Recruitment of Quiescent Cells

Abstract The development of a pure quiescent (Q) tumour cell population can be induced in three mouse mammary tumour lines (66, 67 and 68H) by nutrient deprivation. When these Q cells were removed from nutrient‐deprived cultures and replated in fresh medium at a lower cell concentration within 72 hr of entering quiescence virtually all of the Q cells could re‐enter the proliferating (P) state. This recruitment was characterized by an increase in cell volume, an increase in total cellular RNA, and a resumption of cell division. the length of the Q to P transition varied among the three cell lines and the depth of the quiescent state depended on the amount of time the cells had been quiescent. Once re‐entry into the P compartment was completed, cell‐cycle times, as estimated by the culture doubling time, were the same as the cells that had not entered the Q state. however, after 72 hr in quiescence, not all of the 66 cells could reattach after trypsinization and of those that could reattach 50% were incapable of either increasing their RNA levels to that of proliferating G1 cells or entering S. Clonogenicity of the nutrient‐deprived Q cells in these lines decreases exponentially from time the cells enter quiescence with approximate half‐times of 32, 34, and 96 hr for the 66, 68H and 67 cells, respectively. Slnce clonogenicity was already declining at a time when all the Q cells could re‐enter the P compartment, the ability of a Q cell to form a colony is not determined solely by its capacity to re‐enter the proliferating compartment.