Protein–Hapten Binding: Challenges and Limitations for In Vitro Skin Sensitization Assays

Abstract

In the search for practical alternatives to the use of animals in the predictive identification of chemicals which possess the intrinsic potential to cause sensitization of the skin, for 2 decades attention has been paid to structure -activity relationships. The work has delivered many valuable insights and has even led to the development of useful computer-based systems (e.g., DEREK). However, these efforts have been predicated very largely on an interrogation of how the chemical itself may be reactive (or may become so after metabolic intervention). Scant attention has been paid to the "substrate" with which the chemical must interact, i.e., skin protein. In this review, we consider in detail those actual protein substructures, examining what is known chemically, what may be predicted to occur, and how they can be investigated. Ultimately, understanding of the protein-hapten binding mechanisms in vitro will increase the confidence in sensitization hazard predictions using in silico tools. It could also permit development of a simple in vitro sensitization screen.

Hapten–protein binding: from theory to practical application in the in vitro prediction of skin sensitization

“…The ultimate goals within the skin sensitization field are to develop better in vitro / in silico tools for higher throughput screening of chemicals for skin sensitization hazard in early product development and to devise novel, alternative approaches to replace existing in vivo assays for predicting sensitization hazard and potency in humans (61). Better understanding of the skin sensitization process at both the cellular and molecular levels will help to support this goal.…”

Protein Binding and Metabolism Influence the Relative Skin Sensitization Potential of Cinnamic Compounds

“…Although many proteins appear to be modified in all regions of the skin, we can still expect that there are certain amino acid residues where binding is more favored than others. Determining the exact nature of the amino acids modified is the topic of further work using mass spectometry analyses (29).…”

“…In vitro cell-based systems that incorporate the key mechanistic events for sensitization, including relevant intrinsic protein-binding chemistries and activating metabolism, could be powerful alternative indicators of sensitization hazard for the future. Identification of the major protein targets in skin at the molecular level will be important knowledge to gain in this respect (29). It remains to be determined whether relative sensitization potency could also be estimated in vitro, but it is likely that knowledge of chemical reactivity alone will not be sufficient for this purpose.…”