The contribution of deficient DNA repair to chromosomal radiosensitivity of CHO cells after G2 irradiation.

We compared cytogenetic responses of the parental Chinese hamster ovary (CHO) cell line and its DNA repair-deficient strains to irradiation during the G2 phase. Chromatid breaks were quantified in cells entering metaphase in the presence or absence of cytosine arabinoside (ara-C) 0.5-1.5 hours after exposure to x-rays or UV-C. Addition of ara-C, an inhibitor of DNA repair replication, significantly increased chromatid break frequency (CBF) in the parental line, but not in the strains deficient in nucleotide excision repair (NER). This increase (ara-C effect) was comparable to that in repair-proficient normal human lymphocytes. We conclude that CBF in cells entering metaphase in the presence of ara-C 0.5-1.5 hours after DNA damage represents a functional in vitro assay for evaluating the DNA repair capacity of mammalian cells in culture.