Integrated skin sensitisation assessment Summary of three defined approaches

Integrated testing strategies (ITS) for regulatory safety assessments serve as a replacement for stand-alone tests and typically combine information from different sources (in vitro, in silico) to arrive at a prediction for a specified endpoint. Skin sensitisation is one such endpoint that has been prioritized by the OECD and other public agencies. It is also one of the few adverse outcomes for which an OECD-approved adverse outcome pathway (AOP) exists and validated assays assessing the key events have been developed. These assays include:

  1. the direct peptide reactivity assay (DPRA) which measures covalent binding of a sensitiser to skin proteins,
  2. KeratinoSens™ assay for the measurement of keratinocyte activation, and
  3. the human cell line activation test (h-CLAT) for measuring dendritic cell activation.

These assays have also been used in several defined approaches using in silico and in vitro methods for skin sensitisation potency prediction for humans.

Skin sensitisation AOP
AOP: Covalent Protein binding leading to Skin Sensitisation

SaferSkin™ implements three defined approaches for making predictions on the skin sensitisation potential of a compound. All of the methods use a range of data which includes the substance’s physico-chemical properties, in silico data, and in vitro data from validated and OECD-approved skin sensitisation assays.

Approaches currently implemented in SaferSkin™

Data used in SaferSkin™

Experimental values

DPRACYS, DPRALYS, Kmax Experimental value from key event 1: % of cysteine/lysine peptide depletion in the DPRA assay; peptide reactivity Cor1-C420 assay (Kmax)
KEC1.5, KEC3, IC50 Experimental values from Key Event 2: Concentration yielding 1.5/3-fold induction in Nrf2-dependent luciferase activity in the KeratinoSens™ assay; Concentration yielding 50 % reduction in cellular viability in the KeratinoSens™ assay
EC150, EC200, CV75 Experimental values from Key Event 3: Concentration yielding 150 % induction of the cell surface activation marker CD86 in the h-CLAT; Concentration yielding 200 % induction of the cell surface activation marker CD54 in the h-CLAT; Concentration yielding 25 % reduction in cell viability in the h-CLAT assay

Molecular descriptors

TIMES The highest skin sensitisation class [1-3] for the compound and its potential metabolites as predicted by TIMES* in silico model. This value is provided by the user.
Water solubility @ pH7 Predicted using ChemAxon calculator**.
LogKow Octanol/Water partition coefficient, calculated using ChemAxon calculator.
Protein binding % of compound bound to the plasma proteins as predicted by the Edelweiss Connect protein binding model.
logD @ pH7 Octanol/water partition coefficient at pH 7 as predicted by the ChemAxon calculator.
Michael acceptor If a compound is a Michael acceptor, a post-prediction correction is performed to accomodate for the anti-inflammatory effect of such chemicals.
Vapour pressure Vapour pressure of the compound measured in Pa.

(1) J. S. Jaworska, A. Natsch, C. Ryan, J. Strickland, T. Ashikaga and M. Miyazawa; Archives Toxicol.2015

(2) 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

(3) A. Natsch, R. Emter, H. Gfeller, T. Haupt and G. Ellis,Toxicol. Sci. 2015

(4) OECD,Test No. 442C: In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA) 2015

(5) OECD,Test No. 442D: In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method 2018

(6) 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