Flow cytometry of isolated nuclei prepared from gL rat brain tumor

Nuclei isolated by grinding 9L rat brain tumors gave a DNA distribution consisting of a 2C DNA peak due to noncycling normal cells and a bimodal distribution beginning at about 4C DNA due to the cycling tumor cells. Autoradiographic studies of nuclei from rats that received a pulse of ³H-TdR in vitro confirmed that the majority of proliferating cells were in the bimodal part of the distribution. The fraction of cells in S-phase determined from the DNA distributions was 15.3%. This is consistent with a labeling index of 18% determined from autoradiographs from tumor tissue and an S-phase fraction of 17% determined from a fraction of labeled mitosis analysis (assuming that G(o)). of the 53% noncycling cells are in G₀). The authors also determined by audoradiographic analysis of cells sorted from the tumor's mid-S-phase region, that only 58% of these cells were labeled. They attribute this mostly to the presence of fluorescent debris from necrotic nuclei in this part of the distribution.