The Radiation Response of Hypoxic Cells in EMT6 Spheroids in Suspension Culture Does Model Data from EMT6 Tumors

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Abstract
Radiation survival curves of EMT6/Ed [mouse mammary sarcoma] spheroids were obtained under conditions which eliminate changes in O2 concentration between group and irradiation. These curves show a high-dose, resistant component which is nearly parallel to the curves obtained when spheroids were irradiated under N. Thus, EMT6 [mouse mammary sarcoma] spheroids appear to model accurately the radiation responses of EMT6 tumors [to anticancer radiotherapy]. In contrast, when spheroids were grown to relatively high density (300-400 spheroids/250 ml spinner flask), then separated into several flasks for irradiation, an increase in O2 concentration in the medium occurred which fully oxygenated the previously hypoxic cells. The 2 causes for the O2 depletion in sealed growth flasks were quantitated. Depletion of total O2 in the flask occurred, and O2 consumption kept the growth medium well below equilibrium with O2 in the gas phase. Smaller but similar effects on O2 concentration were found in flasks containing V79 [Chinese hamster lung] spheroids.