Post by Torben Osterlund

The glucocorticoid receptor transactivation assay (GRTA) has just been published as an OECD Test Guideline (https://lnkd.in/ebrz8tM9). As CSO of Pepper, I have been closely involved in this process, and I want to explain why it matters scientifically. Years of interlaboratory coordination, rigorous review, and careful scientific work culminating in a formal OECD Test Guideline adoption is not something you take for granted. Seeing this come through gave me a real sense of satisfaction 😊. The story of the project can be found here (https://lnkd.in/esVhHAmi). Within six and a half years, the assay, developed in Prof. Patrick Balaguer's INSERM laboratory in Montpellier, was taken through selection, preparation, laboratory tender, onboarding, training, transferability assessment, and blinded ring trial, ultimately producing the scientific basis for the Test Guideline. The GRTA detects activation of the glucocorticoid receptor in a human cell line, a mechanistic endpoint relevant to endocrine disruptor characterisation across immune response, metabolism, and developmental biology. The inter-laboratory ring trial was conducted with INERIS, Toxem, and Tame-Water (now Inovalys), and the validation study was published in Toxicology In Vitro in 2025. I want to acknowledge Patrick Balaguer and his team, all participating laboratories, the expert contributors across different domains, the OECD Expert Panel and WNT for their challenges and proposals that shaped the final guideline, and Anne Gourmelon and Nathalie Delrue from the OECD Test Guidelines Secretariat for their support throughout the process. What comes next is equally demanding. The RARTA validation report has completed, peer reviewed, and Test Guideline drafting is underway. Three more projects are expected to finalise ring trials this year. Each one follows the same standard of scientific rigour. If you are working on ED method development, interlaboratory studies, or OECD submissions, I am happy to connect and exchange.