Considerations for the Development of an Integrated Testing Strategy for Skin Sensitization

Non-animal test methods for skin sensitization have to consider the complex interactions of chemicals with the different parts of the skin immune system (Cumberbatch et al., 1992). A few chemicals act as prohaptens and can be converted to a hapten by oxidation, skin metabolism, or ultraviolet radiation (Karschuk et al., 2010). the hapten (parent or converted chemical) may penetrate the skin and interact with skin proteins and immature dendritic cells (DCs). these immature DCs internalize and process haptenated carrier-proteins and, once activated, migrate from the skin to the draining lymph node, terminate maturation, and present fragments of the haptenated carrier-proteins to tcells, leading to an antigen-specific immune response (Aeby et al., 2010). A large international research, development, and evaluation effort by various companies and organizations (e.g., COlIPA) has already lead to the proposal or publication of different approaches that may be included in toolboxes of non-animal test methods for characterizing skin sensitizer potency. A careful combination of some of these methods should allow risk assessment decisions to be made without the need for new animal test data in the near future (Aeby et al., 2010). the Beiersdorf toolbox described here consists of in silico and in vitro methods supported by physico-chemical and toxicological tools and reviews of historical data: 1. Indications based on physico-chemical properties: determination of chemical domains, presence or absence of structural alerts (structure activity relationships = SAR), prediction of chemical reactivity 2. In silico tools: DeReK, tOPCAt, MultiCase 3. Read-across based on similar chemicals with available experimental historical data: animal data, human data, in vitro data 4. Exposure: depending on product applications; determination of bioavailability, adsorption, penetration, transformation of chemical (metabolism, oxidation, ultraviolet radiation) 5. In chemico or in vitro methods: a. Biophysical properties, protein binding: Direct Peptide Reactivity Assay (DPRA; Gerberick et al., 2007) b. Cellular stress: KeratinoSens (Natsch et al., 2011) c. Dendritic cell activation: Peripheral Blood Monocytederived Dendritic Cell (PBMDC) assay (Reuter et al., 2011). the approach being evaluated at Beiersdorf for the determination of a predicted eC3 (peC3) and of a “No expected Sensitization Induction Level” (NESIL) includes, as a first step, an evaluation of the hapten or prohapten properties of the chemical (probable modifications by oxidation, metabolism, or ultraviolet radiation). the expected exposure is calculated with a combination of bioavailability, chemical domain, and reactivity data, as well as physico-chemical information (e.g., logP). An initial hazard prediction and the definition of an expected potency (peC3 and NeSIl) range are then attempted. Historical data, in silico tools, and read across can be used as additional support. the second step is expected to lead to the narrowing and confirmation of the calculated pEC3/NESIL range. Suitable in vitro assays selected according to the results of the first step include bioavailability (adsorption, penetration, transformaConsiderations for the Development of an Integrated Testing Strategy for Skin Sensitization