Assessing Experimental Uncertainty in Defined Approaches: Borderline Ranges for In Chemico and In Vitro Skin Sensitization Methods Determined from Ring Trial Data

Abstract

Introduction: Prediction models of most toxicological assays translate continuous data to binary classifications (“positive” or “negative”) using cutoff values. Mostly these cutoffs do not consider data variability. Some OECD test guidelines, however, provide a range close to the cutoff. If a test result is in this range, a repetition of the test is proposed. Yet, these ranges were based on few data and not systematically derived. Materials and Methods: In the present study, we determined the borderline ranges from multilaboratory ring trial studies for five nonanimal methods addressing skin sensitization: Direct Peptide Reactivity Assay (OECD TG 442C), KeratinoSens® and LuSens (OECD TG 442D), and human cell line activation test (OECD TG 442E) as well as the kinetic direct peptide reactivity assay (update of OECD TG 442C). Results: We used a uniform statistical approach based on the log median absolute deviation. Implementing the proposed borderline ranges helps to assess certainty of both individual test results and of combinations of multiple data sources in a defined approach (DA) or an integrated approach. Conclusion: The OECD guideline on DAs for skin sensitization provides the first regulatory application of borderline ranges to the “2 out of 3” DA.