Abstract 1304: AbYlinkTM: A site-selective labeling method for preclinical imaging of therapeutic antibodies

Clinical development of therapeutic antibodies relies on robust and thorough preclinical evaluation of multiple pharmacodynamic and pharmacokinetic parameters of antibody candidates. While current methods are available for in vitro characterization of antibodies, in vivo determination of tissue distribution, tumor accumulation and retention and potential off-target effects cannot be performed non-invasively in vivo over a prolonged period of time. Here, we used AbYlinkTM, a novel site-selective labeling method of native antibodies, enabling the single-step covalent conjugation of a radionuclide chelator to the Fc domain of any IgG antibody isotype. Given the selectivity of this reaction for the Fc region of the immunoglobulin, labeling of the antibody at this location should not compromise binding to the antigen. Chelators that are covalently attached to the antibody allows for the labeling with radioisotopes such as 68Ga, 177Lu, 111In and 89Zr, and for the sensitive and quantitative molecular in vivo measurement by Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT). AbYlinkTM also permits the conjugation of fluorescent dyes to antibodies with the aim to measure antibody pharmacodynamic parameters by intravital microscopy. In this work, we have validated the technology by labeling several antibodies and ADCs with different payloads. Importantly, antibodies conjugated with AbYlinkTM retained the same affinity to the antigen as the original, unconjugated antibodies, contrary to the randomly labelled antibodies. We will also present data on the specific radiolabeling of commercially available trastuzumab with 111Indium and the SPECT images obtained after injection of mice bearing HER2-positive tumors with 111In-trastuzumab. The present data suggest that AbYlinkTM can be used to support preclinical drug discovery tools to assist in the selection of therapeutic antibody candidates and/or for pharmacodynamic assessment of commercial antibodies. Furthermore, the specificity of the chemical conjugation suggests that AbYlinkTM can help to control the chelator distribution on the antibody drug conjugates. Citation Format: Viktoriia Postupalenko, Leo Marx, David Viertl, Natalia Gasilova, Mathilde Plantin, Nadege Gsponer, Alexandre Johanssen, Thibaut Denoel, Gerrit Hagens, Jean-Manuel Segura, Frederic Levy, Patrick Garrouste, John Prior, Margret Schottelius, Niklaus Schaefer, Origene Nyanguile. AbYlinkTM: A site-selective labeling method for preclinical imaging of therapeutic antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1304.