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Dual-parameter flow cytometry, following bromodeoxyuridine (BrdUrd) incorporation and propidium iodide (PI) uptake into DNA, was used to study the effects of oestradiol and/or insulin on cell cycle kinetics of human breast cancer cells in vitro. After a lag-period of 6-12 h, an optimum in the percentage of S-phase cells was reached between 18 and 24 h after hormone administration. A 1 h pulse of oestradiol was as effective as the continuous presence of oestradiol in pushing the cells from quiescent growing cultures into the cell cycle. A 1 h pulse of insulin was less effective than continuous administration. The addition of doxorubicin resulted in an accumulation of the cells in the late S/G2M-phases. It is concluded that dual-parameter flow cytometry allows accurate assessment of the effects of hormones and chemotherapy on the cell cycle. Therefore this method is very suitable for studying the interaction of hormones and chemotherapy on cell growth.

The polyanionic compound suramin can inhibit the proliferation of cells of various origin, including from breast cancer. We have studied the effects of suramin on cell cycle kinetics and distribution of MCF-7 human breast cancer cells in vitro. It was found that both under serum-containing and serum-free culture conditions, and in the absence or presence of oestradiol or insulin-like growth factor-1, prolonged exposure (> or = 48 h) to suramin caused an accumulation of surviving cells in the G2/M-phase of the cell cycle. At a concentration of more than 100 micrograms ml-1 suramin significantly inhibited cell proliferation. The observed effects of suramin on breast cancer cells in vitro, i.e. antiproliferative effects and accumulation of cells in the G2/M-phase of the cell cycle, may have beneficial consequences in the application of treatment strategies based on a combination of suramin with cell cycle specific drugs or radiation therapy.