Off to a good start? Review of the predictivity of reactivity methods modelling the molecular initiating event of skin sensitization

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Nathalie Alépée
Fleur Tourneix
Akanksha Singh
Nadège Ade
Sébastien Grégoire


The assessment of skin sensitising properties of chemicals has moved away from the traditional animal methods to new approach methodologies (NAM), guided by qualitative mechanistic understanding operationalised in an adverse outcome pathway (AOP). As with any AOP, the molecular initiating event (MIE) of covalent binding of a chemical to skin proteins is particularly important. This MIE has been modelled by several test methods by measuring the reaction of a test chemical with model peptides in chemico. To better understand the similarities and differences, a data repository with publicly available data for the Direct Peptide Reactivity Assay (DPRA), Amino acid Derivative Reactivity Assay (ADRA) and kinetic DPRA (kDPRA), as well as the Peroxidase Peptide Reactivity Assay (PPRA) was assembled. The repository comprises 260 chemicals with animal and human reference data, data on four relevant physico-chemical properties, and between 161 to 242 test chemical results per test method. First, an overview of the experimental conditions of the four test methods was compiled allowing to readily compare them. Second, data analyses demonstrated that the test methods’ predictivity was consistently reduced for poorly water-soluble chemicals and that the DPRA and ADRA can be used interchangeably. It also revealed new categorisation thresholds for the DPRA and ADRA potentially relevant for strategic uses. In summary, a detailed assessment of reactivity test methods is provided, highlighting their potential and limitations. The results presented are intended to stimulate scientific discussion around test methods modelling the MIE of the skin sensitisation AOP.

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Alépée, N., Tourneix, F., Singh, A., Ade, N. and Grégoire, S. (2023) “Off to a good start? Review of the predictivity of reactivity methods modelling the molecular initiating event of skin sensitization”, ALTEX - Alternatives to animal experimentation. doi: 10.14573/altex.2212201.

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