Effects of ACNU, a water-soluble nitrosourea derivative, on survival and cell kinetics of cultured HeLa S3 cells

Abstract

Effects of a water-soluble nitrosourea, 1(4-aminomethylpyrimidine-5yl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) was investigated on cultured HeLa S3 cells with regard to their lethality and cell progression through the cell cycle. The survival curve of exponentially growing cells exposed to increasing concentrations of the drug for 1 hr was characterized by a threshold type of response ( D o = 7.0 μg/ml·l hr, D q 3.5 μg/ml·1 hr ). Throughout the cell cycle, ACNU exerted its main killing effect on cells in the G 1 and G 2 + M phases, whereas cells in S were resistant to the drug. The change in their age-response was due to the D o value of the dose-survival curve rather than the D q . Effects of cell progression were also examined at a low concentration of ACNU (5.0 μg/ml), which allowed 80% of treated cells to survive. Delayed transit was observed in the S phase, and more markedly in the G 2 + M phase. The magnitude of these perturbations depended on the position of the cell cycle at which the drug was administered. Cells treated in the G 1 and early S phases showed a much longer duration of S and G 2 + M phases than cells treated in mid-S phase. Cells treated in the late S and G 2 phases could normally pass through mitosis, but were subsequently blocked in the G 2 phase following a prolonged S phase in the next cell cycle. These studies revealed that there seems to be some positive relationship of the effect of ACNU on cell progression and cell killing throughout the cell cycle.