Sensitivity of Confluent and Cycling Embryonic Hamster Cells to Sulfur Mustard, 1,3-Bis(2-Chloroethyl)-1-Nitrosourea, and Actinomycin D2

Abstract

Transitions between the stationary, or confluent, state and the active, or cycling, state were examined for hamster embryo cells in vitro. Values of several cell parameters (fraction of cells synthesizing DNA, rate of DNA synthesis, amount of DNA per cell, growth rate) indicated that cells entered the stationary phase in G₁ and then slowly doubled their DNA content without further division. The sensitivity to sulfur mustard or 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) was not significantly different for active or confluent cells. Sensitivity to actinomycin D, however, was greater for confluent than for active cells. We conclude that the “stationary phase” of confluent hamster embryo cells does not correspond to the G₀ of hematopoietic stem cells, and, furthermore, that a state of “no cell cycle” is not by itself sufficient to confer resistance to the drugs studied. The post-treatment ability to repair damage caused by sulfur mustard or BCNU was not enhanced by a state of “no cell cycle.”