The sensitivity of cultured mammalian cells in different stages of the division cycle to nitrogen and sulfur mustards.

Strain L mouse fibroblasts growing in vitro were exposed to varying concentrations of nitrogen and sulfur mustards, and the surviving fraction of cells was measured by their ability to form macroscopically visible colonies. Nitrogen mustard required 3 hours but sulfur mustard less than 1 hour to exert maximum killing effect. The mean lethal dose (D37) for nitrogen mustard acting for 1 hour on an exponentially growing cul ture was 0.16 /Ag/mi. The Dar for the uninterrupted action of sulfur mustard on ex ponentially growing cells was 0.192 @ag/ml.Partially synchronously growing cultures were prepared by the addition of 5-fluoro-92'-deoxyuridine, followed 16 hours later by the addition of thymidine. Cell samples were taken from the synchronized culture at various times, and their sensitivity to the mustards was ascertained. With nitrogen mustard the D@ obtained for cells in the period of DNA synthesis was 0.08 @g/ml. The Dg, for G2 cells was 0.18 @g/ml.Cells in the G1 stage were also less sensitive than those in the period of DNA synthesis, but it was not possible to obtain a quantitative value. Sulfur mustard gave similar results.