Integrated skin sensitisation assessmentSummary 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:
- the direct peptide reactivity assay (DPRA) which measures covalent binding of a sensitiser to skin proteins,
- KeratinoSens™ assay for the measurement of keratinocyte activation, and
- 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.
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.
Data used in SaferSkin™
|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|
|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