The Defined Approaches (DAs) to Skin Sensitization Test Guideline cites 2 strategies which can be used to evaluate hazard potential of compounds and 1 strategy to evaluate GHS potency. The hazard DAs involve in vitro approaches to the evaluation of sensitization using multiple assays which evaluate different steps in the Adverse Outcome Pathway. Both the "2 out of 3" (Fig 1) and "Key Event 3/1" approaches (Fig 2) have been included in the OECD Test Guideline. The potency assessment is an extension of the Kao Integrated Testing Strategy and, in addition to the performance of the DPRA and h-CLAT assays, includes the additional step of QSAR analysis of the compound of interest. (Fig 3). This approach permits classification of sensitizers as strong (GHS1A), weak (GHS 1B) or non-classified.
The RhE Phototoxicity assay takes advantage of benefits of a reconstructed human epidermis model in evaluating phototoxic responses after exposure to test materials that are challenging or otherwise incompatible with the 3T3 NRU assay. In addition to the newly published OECD test guideline, this assay is also cited in the International Conference on Harmonization (ICH) S10 guidance document; the results of the assay are suitable for Investigative New Drug submission applications to regulatory agencies party to this consortium.
The kinetic Direct Peptide Reactivity Assay (kDPRA), under the revised OECD 442C Test Guideline, permits resolution of category 1A (Strong) sensitizers from 1B (Weak) and non-classified substances. As an in chemico test, the kDPRA can be performed efficiently and cost-effectively. This assay has the advantage of evaluating the test material over multiple time-points and concentrations of test material in order to provide a peptide conjugation (a Key Event in the Skin Sensitization AOP) rate constant. This value has been shown to be one of the most robust determinants in the evaluation of sensitization hazard1.
1 Natsch, A., Haupt, T., Wareing, B., Landsiedel, R., and Kolle, S.N., (2020) Predictivity of the kinetic direct peptide reactivity assay (kDPRA) for sensitizer potency assessment and subclassification. ALTEX, 37(4), 652-664
A Big Thank You to All Involved!
IIVS has a great deal of experience with these assays and approaches and is proud to have been a part of the validation effort of these test guidelines as part of our mission to increase the use and acceptance of New Alternative Methods in Toxicology. Congratulations to all of our colleagues who made these test guidelines possible, including BASF SE, Givaudan, NICEATM, and Helena Kandarova, and to ICAPOwho supports IIVS’ participation in the OECD expert work groups.