Transferability and Reproducibility of the HepaRG CometChip Assay

This interlaboratory evaluation of HepaRG CometChip was conducted to assess transferability and reproducibility of this new approach methodology (NAM) across four laboratories. Concentrations inducing up to ~70% relative cytotoxicity were determined by the organizing laboratory, and frozen chemical formulation blocks were sent to each participant. When noncytotoxic, 10 mM was the maximum dose. Cultures were exposed once daily for three consecutive days, and both cytotoxicity assessment, via ATP quantification, and comet analysis, commenced 3-4 h after initiation of the final exposure. Positive response was statistical pairwise significance (p < 0.05) with concentration-related increases in %Tail DNA across ≥ 2 consecutive exposures. For 8 of 11 compounds, all four labs generated unanimous test results, with four negative compounds (2-acetylaminofluorene [2-AAF], 2,4-dichlorophenol, eugenol and hydroquinone) and four positive compounds (azidothymidine, benzo(a)pyrene [BP], cyclophosphamide [CP], ethyl methanesulfonate).For the remaining chemicals, three of four labs generated negative calls for amitrole, cadmium chloride, and DMBA. In cases where bulky lesions were anticipated, the magnitude of %Tail DNA was low, due to the inherent insensitivity of the alkaline comet assay (not the CometChip per se) to detect bulky adducts repaired by nucleotide excision repair. This is supported by the small magnitude in %Tail DNA induced by BP and CP. Taken together, for all compounds there was majority agreement in CometChip results across participating laboratories supporting that the endpoint is readily transferable to new labs. Overall, this platform is a promising human-relevant NAM, with a physiologically relevant detoxification process that could be incorporated into rodent replacement strategies.