Simultaneous cytokinetic measurement of aneuploid tumors and associated diploid cells following continuous labelling with chlorodeoxyuridine

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Abstract
Cells from a murine tumor, MCa‐K, were continuously labelled with the thymidine analogue chlorodeoxyuridine (CldUrd) and analyzed by bivariate flow cytometry in order to measure the growth fraction (GF) and potential doubling time (Tpot) of both the DNA‐aneuploid tumor cells and the associated DNA‐diploid cells. MCa‐K has a DNA index of 1.7, rendering two, partially overlapping, populations observable with labelled and unlabelled cells in each population. The data from these tumors may be divided into three regions of differing DNA content, with one region containing a pure DNA‐diploid population, a second region with both cell types, and a third region including only DNA‐aneuploid cells. Equations are presented to characterize the fractions of labelled cells in each region as a function of labelling time and cell type, thereby permitting estimation of the proliferative properties of the populations. These equations include the possibility that DNA‐aneuploid cells cease cycling both in G1 and in S phase to account for the observed numbers of unlabelled cells with S phase contents. The estimated value of Tpot of the DNA‐diploid cells is 126.0 h with a GF of 42%, while that of the DNA‐aneuploid cells is 36.9 h with a GF of 69%. It is also estimated that between 2% and 6% of all DNA‐aneuploid cells starting DNA synthesis cease cycling, leading to 25% of the cells having an S‐phase DNA content being noncycling.