Murine Mammary Tumour Cells In Vitro. I. the Development of A Quiescent State

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Abstract
Three mouse mammary tumor lines (66, 67 and 68H) derived from a single mouse mammary tumor were investigated for their growth kinetics and development of quiescent cells in unfed monolayer cultures. All 3 lines develop pure quiescent populations when grown in unfed plateau cultures. A dramatic cell-cycle redistribution accompanied the proliferating (P) to quiescent (Q) transition, with the percentage of cells having a G1 DNA content increasing from 50% in the P state to > 97% in the Q state. As the cultures progressed from exponential to plateau growth, a decrease of .gtoreq. 50% in cellular RNA was observed in all 3 lines. This property enables the clear identification of P vs. Q cells by flow cytometry using the 2 step acridine organe assay. Autoradiographic data verified that these plateau cells were quiescent since < 2.5% of the cells incorporated [3H]TdR when labeled for .apprx. 2 doubling times. Further comparison of the P and Q cells showed that; the Coulter volume of Q cells was .apprx. 1/2 that of P cells in all 3 lines; viability, as measured by dye exclusion was > 95% in all cultures regardless of their proliferative state; and colony-forming ability decreased as the cells entered the quiescent state. In each of these cell lines the development of Q-cell populations was marked by similar changes in all measured parameters. These quiescent tumor cells provide a relatively simple model to evaluate what, if any, important differences exist between the response of P vs. Q cells to various therapeutic agents.