Effects of acronycine, bleomycin and cytosine arabinoside on the cell cycle. Some aspects of their interaction with radiation determined by pulse cytophotometry.

The influence of three chemotherapeutic agents, acronycine, bleomycin and cytosine arabinoside, alone and combined with radiation, on cell cycle progression and viability of L-cells was examined. The percentages of cells in G1, S and (G2 + M)-phases as derived from pulse cytophotometric DNA distribution patterns were recorded as a function of exposure time. After 24-h treatment with 10 microgram/ml acronycine, 46.4% of cells were accumulated in (G2 + M)-phase compared to 12.1% in the controls. This accumulation was significantly enhanced by an irradiation with 150 rads of X-rays resulting in arresting 63.1% of cells in this phase. Similar findings were obtained after a 24-h treatment with 100 microgram/ml bleomycin. 54.4% of cells were arrested in (G2 + M)-phase by the chemical treatment alone, while the combined treatment, bleomycin and radiation, yielded an accumulation of 66.3% of cells in G2 + M. A 24-h exposure to 0.2 microgram/ml cytosine arabinoside (Ara-C) produced a reversible block of 72.8% of cells in S phase compared to 27.4% in the control cultures. This S block was less pronounced after the combined treatment (51.1%). Some implications of the results for combined therapy are discussed.