The GARDpotency assay for potency-associated subclassification of chemical skin sensitizers – Rationale, method development and ring trial results of predictive performance and reproducibility

Robin Gradin, Angelica Johansson, Andy Forreryd, Emil Aaltonen, Anders Jerre, Olivia Larne, Ulrika Mattson, Henrik Johansson

Abstract
Proactive identification and characterization of hazards attributable to chemicals are central aspects of risk assessments. Current legislations and trends in predictive toxicology advocate a transition from in vivo methods to non-animal alternatives. For skin sensitization assessment, several OECD validated alternatives exist for hazard identification, but non-animal methods capable of accurately characterizing the risks associated with sensitizing potency are still lacking.

The GARD^TM platform utilizes exposure-induced gene expression profiles of a dendritic -like cell line in combination with machine learning to provide hazard classifications for different immunotoxicity endpoints. Recently, a novel genomic biomarker signature displaying promising potency-associated discrimination between weak and strong skin sensitizers was proposed. Here, we present the adaptation of the defined biomarker signature on a gene expression analysis platform suited for routine acquisition, confirm the validity of the proposed biomarkers, and define the GARD^TMpotency assay for prediction of skin sensitizer potency. The performance of GARD^TMpotency was validated in a blinded ring-trial, in accordance with OECD-guidance documents. The cumulative accuracy was estimated to 88.0% across three laboratories and nine independent experiments. The within-laboratory reproducibility measures ranged between 62.5% and 88.9%, and the between-laboratory reproducibility was estimated to 61.1%. Currently, no direct or systematic cause for the observed inconsistencies between the laboratories have been identified. Further investigations into the sources of introduced variability will potentially allow for increased reproducibility.

In conclusion, the in vitro GARD^TMpotency assay constitute a step forward for development of non-animal alternatives for hazard characterization of skin sensitizers.

Key words: GARD, GARDpotency, in vitro, sensitization, potency, chemical sensitizers

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