Survival in subpopulations of cells derived from solid KHT sarcomas by centrifugal elutriation following treatment with CCNU and MISO.

Misonidazole (MISO) has been shown to enhance the cytotoxicity of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in a number of different animal tumor systems. We have investigated the response to therapy of the various subpopulations of cells comprising the KHT sarcoma, to determine whether chemopotentiation occurred as a preferential enhancement of killing in one subpopulation of cells. Twenty-four hr after drug treatment, cells dissociated from solid tumors were separated into homogeneous populations based on cell size by the technique of centrifugal elutriation. By this method the majority of the non-neoplastic cells could be removed and the tumor cells separated into fractions containing 90 to 95% G1 cells, 70 to 75% S cells and 70 to 80% G2M cells. Clonogenic cell survival was measured for each elutriated fraction. In vivo treatment with 0.5 mg/g MISO produced no measurable cell-kill across the cell cycle. Those cells in late G1 and S phase 24 hr after treatment were most sensitive to CCNU alone. The enhancement of CCNU cytotoxicity by MISO occurred primarily in the early G1 and S fractions. These data suggest that chemopotentiation does not occur equally in all tumor cell subpopulations and that some specificity of enhanced cell killing exists.