The Proliferative State of Clonogenic Cells In the Lewis Lung Tumour After Treatment With Cytotoxic Agents

Abstract

The proportion of clonogenic cells from the [mouse] Lewis lung carcinoma which are in S-phase of the cell cycle was measured as the fraction killed by a short exposure to hydroxyurea in vitro. Estimates of the proportions of S-phase cells before and 30 min after doses of .gamma.-radiation of 1000-2000 rad suggested no alternation in the cell cycle age distribution due to these doses of radiation. As the survivors of these high doses of radiation were predominantly hypoxic, the results imply that hypoxic cells have the same cell cycle age distribution as oxygenated cells in Lewis lung tumors. After treatment with cyclophosphamide or CCNU [1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea], the proportion of S-phase cells among the survivors exceeded the faction of S-phase cells in untreated populations. This increase was consistent with a relative resistance of S-phase cells to alkylating agents and nitrosoureas.