Accumulation of non-cycling cells with a G2-DNA content in ageing solid tumours. Study of the Ca 755 mammary adenocarcinoma of mice.

Mouse mammary adenocarcinoma Ca 755 was studied at two times in its growth: the exponential (8 days) and plateau phase (20 days). Cycling cells were labelled with [3H]thymidine injections at 4-hr intervals over 72-hr periods, i.e. three to five times longer than the generation times for the twentieth day and eighth day tumour cells respectively. By autoradiography, the increase of non-cycling cells in ageing tumours was confirmed. By single cell cytophotometry used after Feulgen staining it has been shown that the cells with a high DNA content (especially a G2-DNA amount) were in a higher proportion in the twentieth day tumours than in their eighth day counterparts. Combined cytophotometric and autoradiographic procedures have shown that nearly all cells with a G2-DNA content entered a non-cycling state in ageing tumours.