Delayed cytotoxic and genotoxic effects in a human cell line following X-irradiation

Background: In order to clarify the relationship between delayed reproducti ve death and radiation-induced genomic instability, the colony-forming effi ciency of surviving, irradiated human squamous carcinoma cells and centrome re positive as well as centromere negative micronuclei in surviving progeny were examined. Materials and methods: Colony-forming ability and micronucleus (MN) frequen cy in binucleated cells 24 h after the addition of cytochalasin B during 2 weeks of post-irradiation growth were determined in a squamous cell carcino ma cell line (SCL-II) of human origin. In addition, centromeres in micronuc lei were detected using FISH. Results: In the human epithelial cell line used for these experiments, dela yed reproductive death was pronounced and persisted for at least 2 weeks af ter irradiation. Although there is evidence for an increased rate of centro mere positive micronuclei, but not of centromere negative micronuclei, aris ing during the first week of post-irradiation proliferation, this decreases later while the rate of delayed reproductive death remains elevated. Conclusion: In the studied cell line, the observed delayed reproductive dea th is not closely related to the investigated criteria of radiation-induced genomic instability. This casts doubt on the common assumption that delaye d reproductive death is a direct manifestation of radiation-induced genomic instability.