In Q3 2023, the OECD has conducted the peer-review of the interlaboratory validation of the ToxTracker assay by a panel of experts, nominated by their National Coordinators. A report on the successful ToxTracker validation results was recently published on the OECD website.

Significance of the validation

The battery of in vitro assays that are currently accepted for regulatory genotoxicity testing includes the bacterial Ames, mouse lymphoma, and mammalian cell gene mutation tests. Chromosome damage is assessed by the in vitro micronucleus and chromosome aberration assays.

This battery of in vitro genotoxicity assays generally has a sufficient sensitivity for genotoxicant identification but occasionally suffers from:

• A relative high frequency of misleading positive test results (i.e., low specificity)
• The lack of mechanistic insight into these positive test results, which can be a serious challenge in the hazard assessment of chemicals and pharmaceuticals.
• The inability to provide information about the MoA of genotoxic substances.

In summary, improvement of the battery in vitro genotoxicity assays could improve the prediction of in vivo genotoxicity.

The ToxTracker assay is a reporter gene assay that reliably predicts the genotoxicity of compounds. By integrating the different reporter genes, ToxTracker is able to provide insight into the MoA of genotoxic compounds by predicting the induction of mutagenic DNA lesions, clastogenic effects, induction of aneugenicity and indirect genotoxicity caused by oxidative stress and protein damage in a single assay.

An interlaboratory validation of this assay is a significant step towards its integration into widely accepted regulatory frameworks.

Ring trial framework and outcomes

In the ToxTracker interlaboratory validation project, the assay was installed in the seven participating expert laboratories. An overview of these laboratories and scientist involved is given below.

The interlaboratory validation confirmed the accuracy of ToxTracker to correctly predict in vivo genotoxicity with a sensitivity of 87% and a specificity of 90%. The information on the MoA of chemicals was used to discriminate between direct DNA reactive compounds and secondary genotoxicity due to oxidative stress and protein damage. ToxTracker was considered as a valuable addition to the battery of genotoxicity assays that is applied for regulatory applications.

View the full report at https://www.oecd.org/chemicalsafety/testing/peerreviewsongoing.htm

Next steps

After this peer-review of the validation by OECD, Toxys is currently looking at the next steps toward an OECD test guideline for ToxTracker.

The manuscript about the results from the interlaboratory validation of ToxTracker was recently published in EMM.

Start your own study using ToxTracker

If you are considering implementing ToxTracker in your study, we are happy to help you in setting up your project at Toxys. Feel free to learn more about our assay and reach out to us below.