In June 2021, the OECD published Guideline No. 497 on Defined Approaches for Skin Sensitisation. There are two defined approaches published, known as the 2o3 and the ITS. The 2o3 uses two concordant results from either the DPRA, KeratinoSens™, or the h-CLAT assays to predict hazard (sensitiser/non-sensitiser). The ITS applies a score to results from the DPRA, the h-CLAT and an in silico model to predict United Nations Globally Harmonized System (GHS) sub-categories (1A/1B/Not Classified). The ITS can use Derek Nexus as the in silico model (known as v1) or use OECD QSAR Toolbox (known as v2).
In this paper, co-author and Principal Scientist, Martyn Chilton discusses how to resolve inconclusive predictions from defined approaches for skin sensitisation in OECD Guideline No. 497.