Development of a novel in vitro respiratory sensitization assay and its application in an integrated testing strategy (ITS)

Currently, evaluating respiratory sensitization is challenging with a lack of mechanistic understanding and appropriate testing methods. Given the similarities between skin and respiratory sensitization, using defined approach (DA) in OECD Test Guideline (TG) 497 will be helpful. However, adopting skin sensitization DA is not reliable in predicting respiratory sensitization and has not been validated. To address this limitation, we developed an in vitro respiratory sensitization assay (RS assay) to assess the inflammatory responses associated with respiratory sensitization. Additionally, we investigated the applicability of direct peptide reactivity assay (DPRA) for respiratory sensitization testing. Combined with in silico structure–activity relationship (SAR) predictions derived from the respiratory sensitization reactive domain, respiratory sensitization integrated testing strategy (ITS) was established. RS assay showed 80% sensitivity, 100% specificity, and 90% accuracy. The respiratory sensitization ITS demonstrated more higher predictive capacity for respiratory sensitization than an individual test method, with 90% sensitivity, 100% specificity, and 95% accuracy when using the 20 reference chemicals. When using respiratory sensitization ITS, hazard identification and sub-categorization of potency as strong, moderate/weak, and negative were possible. As a non-animal testing approach, the respiratory sensitization ITS represents a significant milestone for regulating respiratory sensitizers.