Chinese hamster V79 cells can be grown as monolayers or in suspension as multicell spheroids. When irradiated, cells from spheroids can accumulate more sublethal damage than cells from monolayers as evidenced by a wider shoulder on the survival curve. We have attempted to determine whether this increased resistance of spheroids to damage by ionizing radiation is reflected by DNA damage. The production and repair of single-strand breaks was quantified using alkaline sucrose gradient sedimentation and hydroxylapatite chromatography. Both methods indicated that equal amounts of radiation damage per rad were produced in cells grown as single cells or as spheroids, and that postirradiation rejoining of DNA single-strand breaks also occurred with similar efficiency. Thus, these results suggest that the enhanced survival of cells irradiated as spheroids is dependent on processes other than (or in addition to) initial radiation damage to DNA.

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