How to de-risk a false positive in vitro genotoxicity test?

Vera Rogiers and Gamze Ates

In vitro Toxicology and Dermato-Cosmetology (IVTD), Vrije Universiteit Brussel, BE
As a possible solution to de-risk false positive in vitro genotoxicity results obtained through the currently used 2-test battery (Ames test, in vitro micronucleus test), other in vitro tests  such as a reconstructed skin micronucleus test or a 3D-based comet assay, could be applied. Also, in silico methods, biokinetic data and mechanistic information could be used in a Weight of Evidence (WoE) approach. Here, a testing strategy was developed which integrates the currently used 2-test in vitro battery either with computational tools, reporter-based assays or genomic fingerprinting. The results can be summarized as follows: (i) by integrating a variety of in silico tools a sensitivity of 53-87% and a specificity of 52-71% was obtained; (ii) by integrating 2 reporter-based assays (ToxTracker and Vitotox) a sensitivity of 93% and specificity of 73% was found; (iii) the best results were obtained by integrating genomic fingerprinting, which was realized by developing a qPCR-array, based on an 84-gene fingerprint. The latter could be retrieved from gene expression analyses on whole genome microarrays, using the human HepaRG cell line as an in vitro model. Testing the qPCR array with 12 known genotoxic and non-genotoxic compounds showed a sensitivity and specificity of 83%. This methodology is proposed as a pragmatic approach, which together with expert advice, seems to be the way forward for cosmetic ingredients in case of misleading positive results when no in vivo testing is possible. It adds weight to the evidence.