The TK6 host cells are p53 competent and familiar to most genetic toxicology laboratories. A patented GFP reporter system exploits the proper regulation of the GADD45a gene. The assay delivers both high specificity and high sensitivity and detects all common mechanistic classes of genotoxin. The 96-well microplate format takes about 20 minutes to prepare and delivers results after a 48 hour incubation. A single microplate is sufficient for the simultaneous testing of 4 compounds over 9 serial dilutions. The protocol is also readily automated using standard laboratory liquid-handling equipment.
GADD45a mediates the adaptive response to genotoxic stress. The patented GFP fluorescence reporter includes complex regulatory elements. The assay gives positive results for direct acting agents, as well as aneugens, and topoisomerase and polymerase inhibitors. Importantly the assay gives correct negative results for non-carcinogens, including many which give misleading positive results in other in vitro tests.
The Assay Protocol
Nine, 2-fold dilutions of each compound together with positive controls are set out in the microplate and growing cells are added to each well. After incubation and measurement in a microplate reader, simple software gives automated decisions and a clear graphical output.
A unique combination of both high-specificity and high-sensitivity genotoxicity assessment in a human cell line has been demonstrated. See:
High-specificity and high-sensitivity genotoxicity assessment in a human cell line: Validation of the GreenScreen HC GADD45a-GFP genotoxicity assay. Hastwell P.W. et al (2006) Mutation Research 607: 160-175.