Advancing Skin Sensitization Potency Categorization Using U-SENS™ in OECD TG 497

OECD Guideline 497 includes defined approaches (DAs) that combine new approach methodologies (NAMs) to predict skin sensitization hazard and categorize potency according to the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS). To increase flexibility, the OECD allows the substitution in the DAs of NAMs addressing the same key events (KEs) in the adverse outcome pathway (AOP). This study evaluated the implementation of the U-SENS™ assay for dendritic cell activation (KE3) within two integrated testing strategy (ITS) DAs. First, EC150 threshold values were determined via computational modeling to convert CD86 stimulation index data into ITS DA scores. The performance of the modified ITS DAs was then evaluated against available Local Lymph Node Assay (LLNA) and human reference data. For hazard identification, the ITS DAs achieved 79% balanced accuracy compared with LLNA data, and 73-74% compared with human data. For potency categorization, correct classification rates were 67-68% against LLNA and 65-67% against human data. In comparison, the LLNA showed lower performance, with 58% balanced accuracy for hazard identification and 60% for potency categorization against human data. Selected case studies illustrate the practical application of these DAs following the Guideline 497 decision flowchart. Overall, findings underscore that incorporating U-SENS™ into ITS DAs enhances flexibility without compromising predictive capacity and outperforms traditional animal testing in providing reliable skin sensitization classification outcomes.