Comparative studies of total cross-linking, cell survival and cell cycle perturbations in chinese hamster cells treated with alkylating agents in vitro

Abstract

The toxicities of 4-hydroperoxycyclophosphamide (4-OOH CY), phosphoramide mustard (PM), melphalan (MEL) and busulphan (BU) have been compared in Chinese hamster cells, V-79-753B. The initial total amount of cross-linking was a determining factor for the clonogenic survival of cells treated with MEL or PM. Although 4-OOH CY generated cross-links in this cell line, this damage did not account for the toxicity of the compound. There was no evidence for cross-link formation in cells treated with BU, even at a dose of the drug (1000 μg/ml) that was too toxic to measure clonogenic survival. Comparison for the four compounds at equitoxic doses showed that both PM and MEL caused the arrest of the cell cycle at G 2 which persisted after drug removal. This was accompanied by a decline in the population growth rate and a decrease in total cell count. In contrast, both BU and 4-OOH CY caused a temporary arrest of the cell cycle G 2, 24 hr after drug removal. However, the cell cycle distribution returned the control values within 3–4 days after treatment. Both BU and 4-OOH CY showed little effect on the initial growth rate of the cells. It is concluded that the initial amount of cross-links contributes to the toxicity of PM and MEL. However, it is unlikely that the generation of cross-links is of major importance for the toxicity of either 4-OOH CY or BU.