title: The effects of N-methyl-N'-nitro-N-nitrosoguanidine on KB cells. II. Cell sensitivity to the lethal effect of the drug as a function of the cell age and of the nature of the culture medium.
abstract: We have tested the sensitivity of KB cells to the lethal effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), measured as cell loss within the 20-h period following a 1-h drug treatment, as a function of culture age and of the medium in which treated cells were incubated after elimination of MNNG. We showed that KB cell sensitivity to the lethal effect of the drug decreased with time after seeding when the treated cells were post-incubated in drug-free medium conditioned by untreated cells of the same age as treated ones but not when they were post-incubated in fresh drug-free medium. This difference was due in part to the fact that the conditioned medium had acquired with time a protective activity for treated cells and in part to an increased competence of aging cells to be protected by this medium. By post-incubating treated stationary cells sequentially in both media, we showed that a brief (15 min) post-incubation of the cells in fresh medium was sufficient to trigger cell death even if the cells were afterwards transferred to conditioned medium. In contrast, long post-incubation in fresh medium did not cause cell death if the cells were first post-incubated in conditioned medium for about 3 h. We conclude that: the medium acted on cell sensitivity to the lethal effect of MNNG through its growth regulatory ability; quiescent cells were less sensitive to the drug than growing cells; the sensitive phase of the cell was located before S; cell hypersensitivity might be due to deficient repair of cellular lesions rather than to increased lesion formation.
mesh_terms: D002470:Cell Survival / Q000187:drug effects; D003470:Culture Media; D004261:DNA Replication / Q000187:drug effects; D006801:Humans; D007624:KB Cells / Q000166:cytology* / Q000187:drug effects; D007700:Kinetics; D008769:Methylnitronitrosoguanidine / Q000633:toxicity*; D013997:Time Factors
chemical_list: D003470:Culture Media; D008769:Methylnitronitrosoguanidine