Separation of Cells From a Murine Fibrosarcoma on the Basis of Size. II. Differential Effects of Cell Size and Age on Lung Retention and Colony Formation in Normal and Preconditioned Mice23

Abstract

Experiments were undertaken to investigate the influence of cell size and cell age on both the intrinsic clonogenicity and the retention efficiency of tumor cells in relation to lung colony formation after female C3Hf/Bu mice were given iv injections of fibrosarcoma (FSa) cells. With the use of the method of centrifugal elutriation, FSa cells were separated into homogeneous subpopulations according to size leading to a greater or lesser degree of synchronization. For the determination of the arrest patterns of separated subpopulations, FSa cells were labeled in vitro with [¹²⁵I]ldUrd. Three different lung colony assays were used to study the influence of cell size and age in normal untreated mice and in mice in which the efficiency of the assay was increased by pretreatment with either cyclophosphamide (CY) or whole-body irradiation. In the second group of mice, 10⁸ heavily irradiated cells were also added to the viable cell inoculum. In untreated mice, cell retention and lung colony formation correlated with the largest cells, predominantly in G₂-phase, being the most efficiently retained and yielding the most lung colonies. No effect of size or relative position in the cell cycle on lung colony formation was seen, however, in preconditioned mice. The efficiency of lung colony formation was increased 10- and 30-fold by CY and whole-body irradiation, respectively. Although cell arrest patterns correlated with lung colony formation in whole-body irradiated mice (which also received heavily irradiated cells) for all cell sizes, no such correlation was found for the smallest cells (G₁-phase) in CY-pretreated mice. We conclude that the intrinsic clonogenic ability of an FSa cell is independent of the cell parameters of size and age.