Reconstructed human epidermis‐based testing strategy of skin sensitization potential and potency classification using epidermal sensitization assay and in silico data

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Abstract
The hazards and potency of skin sensitizers are traditionally determined using animal tests such as the local lymph node assay (LLNA); however, significant progress has been made in the development of non‐animal test methods addressing the first three mechanistic key events of adverse outcome pathway in skin sensitization. We developed the epidermal sensitization assay (EpiSensA), which is a reconstructed human epidermis‐based assay, by measuring four genes related to critical keratinocyte responses during skin sensitization. Four in vitro skin sensitization test methods (EpiSensA, direct peptide reactivity assay [DPRA], KeratinoSens™, and human cell line activation test [h‐CLAT]) were systematically evaluated using 136 chemicals including lipophilic chemicals and pre/pro‐haptens, which may be related to assay‐specific limitations. The constructed database included existing and newly generated data. The EpiSensA showed a broader applicability domain and predicted the hazards with 82.4% and 78.8% accuracy than LLNA and human data. The EpiSensA could detect 76 out of 88 sensitizers at lower concentrations than the LLNA, indicating that the EpiSensA has higher sensitivity for the detection of minor sensitizing constituents. These results confirmed the potential use of the EpiSensA in evaluating a mixture of unknown compositions that can be evaluated by animal tests. To combine different information sources, the reconstructed human epidermis‐based testing strategy (RTS) was developed based on weighted multiple information from the EpiSensA and TImes MEtabolism Simulator platform for predicting Skin Sensitization (TIMES‐SS; RTSv1) or Organization for Economic Cooperation and Development (OECD) QSAR Toolbox automated workflow (RTSv2). The predictivities of the hazards and Globally Harmonized System (GHS) subcategories were equal to or better than the defined approaches (2 out of 3, integrated testing strategy [ITS]v1, and ITSv2) adopted as OECD Guideline 497.

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