Mutant cells defective in DNA repair pathways provide a sensitive high-throughput assay for genotoxicity.

Chemicals used industrially and commercially are required by law to be assessed for their genotoxic potential. However, all currently used assays have major limitations and despite intense effort, there is no universal agreement on which tests should be employed, or how to interpret results. We have developed a new assay system using the chicken DT40 B cell line that offers a number of significant advantages over current methodologies. Our assay could provide enhanced sensitivity using genetically defined and phenotypically characterized mutants defective in DNA repair pathways. Furthermore, analysis of the mutants, using DNA repair proficient wild-type cells as a negative control, minimizes false negative outcomes. Assessing the different responses of a panel of mutants representative of all repair pathways, mechanistic detail of genotoxicity can be determined. This unique feature, as well as reducing the false positive rate, strengthens positive identifications and is useful when extrapolating results to the human context. Our panel of mutants is likely to be useful in screening large compound libraries for an emerging class of chemotherapeutic drugs, which includes inhibitors of DNA repair enzymes such as PARP and DNA polymerases.