ADRA.
OECD TG 442C: Amino Acid Derivative Reactivity Assay
The Amino Acid Derivative Reactivity Assay (ADRA) assay is an in chemical method used to assess skin sensitization hazard of chemicals.
The assay evaluates a substance’s ability to react with synthetic model amino acid derivatives containing either lysine or cysteine, providing a binary classification that identifies test substances as either skin sensitizers or non‑sensitizers.
Targeting Key Event 1 of the skin sensitization AOP
ADRA is included in OECD Test Guideline 442C and addresses Key Event 1 (KE1) of the Adverse Outcome Pathway (AOP) for skin sensitization: Covalent binding to skin proteins.
For poorly soluble substances, replacing DPRA
ADRA offers a key practical advantage over DPRA by extending the applicability domain to poorly soluble substances.
Aside from this distinction, available data* show that ADRA has an applicability domain largely overlapping with DPRA: It performs best for neat, straightforward organic chemicals with direct protein reactivity and may also be applied to mixtures of known composition. Substances requiring metabolic activation (pro‑haptens) or containing metals fall outside the assay’s applicability domain.
*Reference: OECD TG 442C, Appendix II
Defined approaches for poorly soluble substances (OECD TG 497)
Use ADRA (OECD TG 442C) to complement GARDskin (OECD TG 442E) in defined approaches for skin sensitization (DASS), supporting regulatory testing of applicability to poorly soluble substances, including:
- 2o3 Defined Approach: Combination of ADRA and GARD®skin for hazard identification.
- Integrated testing strategy (ITS): Combination of ADRA, GARD®skin, and in silico methods to support hazard identification and GHS/CLP potency sub-categorization (1A/1B).
