Abstract 1825: Pharmacological evaluation of bioconjugated trastuzumab using the AbYlinkTM regio-selective conjugation technology in gastric cancer expressing HER2+

Abstract Purpose/introduction: Bioconjugation is a critical step in the development of Antibody Drug Conjugates with two main strategies dominating the field. One approach employs covalent chemistry to randomly bind a drug to the accessible Lysines or Cysteines on an antibody. The other strategy is site-specific, using covalent chemistry to bind a drug ligand at defined amino acid positions within the antibody. AbYlinkTM is a novel regio-selective labeling method for antibodies, enabling a single-step covalent conjugation of payloads such as radionuclide chelators to the Fc domain of an antibody. Given the selectivity of this reaction for the Fc region of the immunoglobulin, the affinity of the antibody to the antigen isn’t compromised, unlike randomly labelled antibodies. The chelators that are covalently attached to the antibody enable radiolabeling with radioisotopes such as Gallium-68, Lutetium-177 and Indium-111 for molecular radiotherapy or molecular imaging purposes. Experimental design: The commercially available trastuzumab was labeled via regio-selective conjugation with a DOTA-GA chelating agent using the AbYlinkTM technology, then radiolabeled with Indium-111. The in vivo biodistribution of the HER2 radiolabeled bioconjugate was evaluated in mice bearing NCI-N87 gastric cancer tumors. Results: Trastuzumab conjugation resulted in a homogeneous labeling of antibodies with a Degree of Conjugation (DoC) close to 2, conducted in a regio-selective manner. The biodistribution and imaging experiments demonstrated successful accumulation of the antibody within the NCI-N87 tumour implanted in mice. The radiolabeled conjugate remained stable in vitro and in vivo, demonstrating the AbYlink™ as a valuable tool for biologics conjugation. Conclusion: We have successfully validated in vivo the use of AbYlink™ technology in the context of Antibody Radio Conjugates. This regio-selective bioconjugation strategy holds potential for wider application across molecular radiotherapies or pharmacodynamic assessment of antibodies. Citation Format: Céline Mothes, Peggy Provent, Marie Ruch, Mathieu Moreau, Michael Claron, Alex Helbling, Viktoriia Postupalenko, Léo Marx, Patrick Garrouste, Eftychia Koumarianou. Pharmacological evaluation of bioconjugated trastuzumab using the AbYlinkTM regio-selective conjugation technology in gastric cancer expressing HER2+ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1825.