Evaluation of four human cell lines with distinct biotransformation properties for genotoxic screening

In a previous study, we validated an in vitro genotoxicity assay based on γH2AX quantification using the In-Cell Western (ICW) method in HepG2 cells. The assay demonstrated high sensitivity and specificity but failed to detect genotoxicity for few compounds that require specific metabolic bioactivation not sufficiently covered by HepG2 cells. The aim of the present study was to assess γH2AX ICW sensitivity using a broader range of genotoxic molecules with HepG2 cells and three additional human cell lines with distinct biotransformation properties: two cell lines expressing some phase I and II bioactivation capabilities (LS-174T and Hep3B), and one with poor general bioactivation properties (ACHN). We evaluated the four cell lines by testing 24 compounds recommended by European Centre for the Validation of Alternative Methods and a set of 24 additional chemicals with different mode of genotoxic action (MOA) (aneugenicity, DNA adducts formation, induction of oxidative stress), including some known to require specific cytochrome P450 metabolic bioactivation. Results for the 48 compounds tested showed that the γH2AX ICW assay was more sensitive with LS-174T and HepG2 cells than with Hep3B or ACHN cell lines. Among the 38 compounds tested with positive or equivocal carcinogenicity data, 36 (95%) showed a positive genotoxic response with the γH2AX ICW assay compared to only 27 (71%) using the Ames assay. We confirm that the γH2AX ICW assay on HepG2 cells, without an exogenous metabolic activation system, may be a suitable test to predict the in vivo genotoxicity of chemicals with different genotoxic MOA. Moreover, the use of the ACHN cell line in combination with LS-174T and HepG2 cells may permit in many cases to discriminate direct from bioactivated genotoxins. Overall, our results confirm the high sensitivity of the γH2AX ICW assay which, in turn, should reduce the number of animals used for genotoxicity assessment.