A Novel Approach Using DNA-Repair–Deficient Chicken DT40 Cell Lines for Screening and Characterizing the Genotoxicity of Environmental Contaminants

BACKGROUND Many bacterial or mammalian cell-based test systems, such as the Ames test, chromosomal aberration assays, or gene mutation assays, are commonly used in developed countries to detect the genotoxicity of industrial chemicals. However, the specificity is generally limited and the sensitivity is not sufficiently high. In addition, most assays cannot provide information on mechanisms of genotoxicity of a given chemical. OBJECTIVES We aimed to establish a sensitive and fast screening method that is also capable of characterizing mechanisms of genotoxicity. METHODS We developed a novel bioassay employing gene-disrupted clones of the chicken DT40 B-lymphocyte line, which are designed to be deficient in several specific DNA repair pathways. Genotoxic chemicals can delay cellular proliferation in DNA-repair-deficient clones more significantly than in wild-type cells by interfering with DNA replication, thereby inducing DNA damage. In addition, we verified the validity of this assay by analyzing the genotoxicity of gamma-rays, ultraviolet (UV) light, and sodium metaarsenite (NaAsO(2)). We also characterized DNA lesions induced by NaAsO(2). RESULTS Genotoxicity of given stressors was successfully screened based on a comparison of proliferation kinetics between wild-type and DNA-repair-deficient mutants in 48 hr. We also found that NaAsO(2) apparently induces at least two types of damage: chromosomal breaks and UV photoproduct-like DNA lesions. CONCLUSION This bioassay is a reliable and sensitive screening tool for environmental mutagens as well as for further characterizing the nature of detected genotoxicity.