A genotoxicity test system based on p53R2 gene expression in human cells: assessment of its reactivity to various classes of genotoxic chemicals.

The tumor suppressor, p53, plays an important role in DNA damage repair, by regulating the expression of target genes. One p53-target gene, p53R2, which encodes a subunit of ribonucleotide reductase, is activated by DNA damage. We have previously developed a genotoxicity test system, using human cell lines and a p53R2-dependent luciferase reporter gene assay. 80 chemicals have been examined with this system and 40 of 43 Ames-positive chemicals induced luciferase activity. Eight Ames-negative genotoxic chemicals also induced luciferase activity. Although this assay system could, potentially, be applied to the rapid screening of chemicals that are potentially genotoxic to humans, the ability of the assay to detect genotoxic effects was unclear. In this study, to evaluate the performance of this assay system, several different types of DNA damaging agents were screened. 27 chemicals, whose genotoxic mechanisms are well known, were screened. All genotoxic compounds, except for anti-metabolites and histone deacetylase HDAC inhibitors, showed significant luciferase activity with the following rank order of potency: topoisomerase II inhibitors, intercalaters>bleomycin>topoisomerase I inhibitors>alkylating agents=DNA cross-linking agents=polycyclic aromatic hydrocarbons>spindle poisons. This assay showed greater response to those genotoxic agents that induce DNA double strand break damage compared to those agents that cause other forms of DNA damage. DNA double strand breakage initiates genomic instability, a feature of carcinogenicity. These results indicate that this assay system could be a helpful tool for predicting chemical genotoxicity and carcinogenicity in humans.