“2 out of 3” weight of evidenceSummary of defined approach

This method uses a weight of evidence approach by taking a majority of two congruent results of the first 3 key events (represented by the results of the DPRA, KeratinoSens™, and h-CLAT assays). This method returns a simple prediction of the compound being a sensitiser or non-sensitiser. Our implementation of this model performs an overall assessment using a 2 out of 3 majority voting approach, where if 2 out of the 3 assays are positive for a tested compound, then the substance is rated to be a skin sensitiser, and a substance is rated as a non-sensitiser if 2 out of the 3 tests are negative. The details of how each test is deemed positive or negative are described in the corresponding OECD guidelines for each of the 3 in vitro tests [1-3]. The accuracy of this model (based on the dataset of 213 compounds from the Bausch et al [4]) is 79% when compared to LLNA and 90% when compared to human data (see Table 1 below).

Table 1. Cooper statistics for the “2 out of 3” majority voting method compared to the LLNA or human reference data, respectively.
Compared to LLNA dataCompared to human data
Accuracy79%90%
Sensitivity82%90%
Specificity72%90%
Positive predictive value89%96%
Negative predictive value59%79%

Advantages of the “2 out of 3” weight of evidence approach include:

  • This approach could be customised for users as it is flexible enough to allow for the inclusion of new assays as the need arises.
  • Prediction can be made on any compound as long as the results of three in vitro assays are provided and the compound is within the applicability domain of the 3 assays.
  • It offers quick prioritisation as it returns a simple sensitiser/non-sensitiser prediction.
  • Prediction for a given compound is independent of the others (i.e. there is no training/fitting)

Experimental values used in SaferSkin™

Input parametersProvided by userCalculated by application
Experimental values
DPRA assay: DPRACys, DPRALys
KeratinoSens™ assay: KEC1.5
h-CLAT: CD54 and CD86 (positive/negative)
References
  • (1) OECD,
    Test No. 442C: In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA) 2015
  • (2) OECD,
    Test No. 442D: In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method 2018
  • (3) OECD,
    Test. No. 442E: In Vitro Skin Sensitisation: In Vitro Skin Sensitisation assays addressing the Key Event on activation of dendritic cells on the Adverse Outcome Pathway for Skin Sensitisation 2018
  • (4) C. Bausch, S. N. Kolle, T. Ramirez, T. Eltze, E. Fabian, A. Mehling, W. Teubner, B. van Ravenzwaay and R. Landsiedel;Regul. Toxicol. Pharmacol. 2012