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Poster presented at ACT 2020: Applicability of GARD™skin for Accurate Assessment of Challenging Substances in the Context of Skin Sensitization Testing

J. Schmidt, A. Forreryd, H. Johansson, J. Li, A. Johansson
SenzaGen, Inc., Raleigh, NC, USA, SenzaGen AB, Lund, Sweden

 

Link to the poster

 

Conclusion

  • GARDskin demonstrated an overall high applicability for the evaluated challenging substances with 80% predictive accuracy compared to existing human data.
  • GARDskin demonstrated excellent applicability for pre/pro-haptens and low water solubility substances, correctly classifying all such compounds in the herein investigated dataset.
  • GARDskin also showed high applicability for assessment of surfactants with 89% predictive accuracy compared to existing human data, correctly classifying 8 out of 9 internally tested surfactants, including well known challenging ones such as Sodium Dodecyl Sulphate (SDS) and Benzalkonium chloride.

Abstract

Current legislations and trends in predictive toxicology advocate a transition from in vivo methods for hazard and risk assessments to non-animal alternatives. However, certain groups of chemicals, including substances with severe membrane-damaging properties, pre- and pro-haptens, and those with high log P ratios, have been shown to be challenging to assess using cell-based assays in the context of skin sensitization testing. The aim of this study was to evaluate the applicability of GARDskin for such challenging substances, using an overlapping subset of chemicals previously tested in an integrated tested strategy (ITS) based on validated, aqueous in vitro assays, as well as in a series of Reconstructed Human Epidermis (RHE)-based assays.

The GARDskin assay (Genomic Allergen Rapid Detection) is a robust in vitro assay for identification of potential chemical skin sensitizers with over 90% prediction accuracy and broad applicability. The assay is included in the OECD Test Guideline Program (OECD TGP 4.106) and has gone through a formal validation study. The assay evaluates the gene expression of endpoint-specific genomic biomarkers in a human dendritic-like cell line following exposure to the test substance. Exposure-induced gene expression patterns are analysed using pattern recognition and machine-learning technology, providing classifications of each test item as a skin sensitizer or a non-sensitizer.

The applicability of GARDskin for a total of twelve challenging substances, including pre- and pro-haptens, low water-soluble substances, two surfactants and three additional substances known to have conflictive results when comparing in vitro and in vivo data were evaluated in this study. All twelve substances were selected from the Mehling et al. 2019 publication which reported results from three OECD validated in vitro methods, the “2 out of 3” Integrated Testing Strategy, three RHE-based models and the murine local lymph node assay (LLNA). Human potency classification was available for ten out of the twelve substances.

The GARDskin prediction results were reported from previously published studies, or from in house validation studies. Predictive accuracies were calculated by comparing skin sensitization classifications from different test methods to the available human data of each substance respectively. (N=10). To further explore and substantiate the GARDskin applicability for surfactants, additional GARDskin data for a total of nine surfactants are presented in order to complement the Mehling dataset with respect to the availability of human data.

The GARDskin assay demonstrated overall high applicability for the evaluated challenging substances, with 80% predictive accuracy compared to existing human data. GARDskin correctly classified all pre-and pro-haptens and low water-soluble substances in the data set. Furthermore, high applicability of GARDskin for severe membrane disruptive substances such as surfactants was demonstrated, with 89% predictive accuracy compared to existing human data.

 

Poster presented at ACT 2020: Dose-Response Analysis in GARD™ for Assessment of Skin Sensitizer Potency

J. Schmidt, A. Forreryd, R. Gradin2, H. Johansson.
SenzaGen Inc., Raleigh, NC., SenzaGen AB, Lund, Sweden.

 

Link to the poster

 

Conclusion

  • As an adaptation from the GARDskin assay, GARDskin Dose-Response is suitable for quantitative skin sensitizing potency assessment of chemicals.
  • The experimental readout, referred to as cDV0, corresponds to the lowest dose required to elicit a positive response in GARDskin. As such, experimental protocols are analogous to the LLNA, in which the cDV0 corresponds to the EC3-value.
  • The cDV0 may be used to directly monitor sensitizing potency, or further used to extrapolate LLNA EC3-values, estimation of Human Potency categories, or CLP 1A/1B classifications.

Abstract

Several non-animal methods for identifying skin sensitizers have been developed with acceptable prediction performance. However, advancement of alternative methods for skin sensitizing potency assessment is still missing although a highly sought-after endpoint. The GARDskin assay is a genomics-based in vitro assay for hazard assessment of skin sensitizers, currently progressing towards regulatory acceptance. Here, we introduce GARDskin Dose-Response (DR), in which test chemicals are evaluated by the GARDskin assay in an extended range of concentrations, in order to investigate the dose-response relationship between GARDskin classifications and test chemical concentration.

For this work, 29 chemicals of various sensitizing potencies were used to evaluate the efficacy of applying the assay in this manner. Each chemical was analyzed at several concentrations using a slightly modified GARDskin protocol. At each concentration, a decision-value was produced and a classification prediction (sensitizing or non-sensitizing) was made by the GARDskin algorithm. Afterwards, the lowest concentration where a test item would provide a positive GARDskin prediction was found using linear interpolation. This concentration (cDV0) was then hypothesized to reflect the test items skin sensitizing potency. Furthermore, when comparing cDV0 to LLNA EC3 values, a statistically significant correlation was realized between the values (correlation coefficient =0.74, p-value=4.1*10-4).

These results suggest that modifying the GARDskin protocol to accommodate dose-response measurements can provide sensitizing potency information analogous to the gold-standard in vivo methods. This presentation will further explain the testing process, expand on results, and demonstrate how this method can be used for decision-making throughout all stages of product development, without having to use animal experimentation.

Testing Human Skin and Respiratory Sensitizers—What Is Good Enough?

Int. J. Mol. Sci. 2017, 18(2), 241; doi:10.3390/ijms18020241

Malmborg A., Borrebaeck C. A.K.

Abstract

Alternative methods for accurate in vitro assessment of skin and respiratory sensitizers are urgently needed. Sensitization is a complex biological process that cannot be evaluated accurately using single events or biomarkers, since the information content is too restricted in these measurements. On the contrary, if the tremendous information content harbored in DNA/mRNA could be mined, most complex biological processes could be elucidated. Genomic technologies available today, including transcriptional profiling and next generation sequencing, have the power to decipher sensitization, when used in the right context. Thus, a genomic test platform has been developed, denoted the Genomic Allergen Rapid Detection (GARD) assay. Due to the high informational content of the GARD test, accurate predictions of both the skin and respiratory sensitizing capacity of chemicals, have been demonstrated. Based on a matured dendritic cell line, acting as a human-like reporter system, information about potency has also been acquired. Consequently, multiparametric diagnostic technologies are disruptive test principles that can change the way in which the next generation of alternative methods are designed.
Keywords:

genomics; skin sensitization; adverse outcome pathways; next generation in vitro tests

From genome-wide arrays to tailor-made biomarker readout – Progress towards routine analysis of skin sensitizing chemicals with GARD.

Toxicol In Vitro. 2016 Dec;37:178-188. doi: 10.1016/j.tiv.2016.09.013. Epub 2016 Sep 13.

Forreryd A., Zeller K., Lindberg T., Johansson H., Lindstedt M

Abstract

Allergic contact dermatitis (ACD) initiated by chemical sensitizers is an important public health concern. To prevent ACD, it is important to identify chemical allergens to limit the use of such compounds in various products. EU legislations, as well as increased mechanistic knowledge of skin sensitization have promoted development of non-animal based approaches for hazard classification of chemicals. GARD is an in vitro testing strategy based on measurements of a genomic biomarker signature. However, current GARD protocols are optimized for identification of predictive biomarker signatures, and not suitable for standardized screening. This study describes improvements to GARD to progress from biomarker discovery into a reliable and cost-effective assay for routine testing. Gene expression measurements were transferred to NanoString nCounter platform, normalization strategy was adjusted to fit serial arrival of testing substances, and a novel strategy to correct batch variations was presented. When challenging GARD with 29 compounds, sensitivity, specificity and accuracy could be estimated to 94%, 83% and 90%, respectively. In conclusion, we present a GARD workflow with improved sample capacity, retained predictive performance, and in a format adapted to standardized screening. We propose that GARD is ready to be considered as part of an integrated testing strategy for skin sensitization.

KEYWORDS:

GARD; In vitro assay; Predictive genomic biomarker signature; Skin sensitization

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