This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jlcr.3793 This article is protected by copyright. All rights reserved. Edelmann Martin R. (Orcid ID: 0000-0002-6116-1516) Title Radiolabeled IgG Antibodies – Impact of Various Labels on Neonatal Fc Receptor Binding Authors Martin R. Edelmann #* , Hubert Kettenberger + , Alexander Knaupp + , Tilman Schlothauer + , Michael B. Otteneder # Roche Pharma Research and Early Development, Roche Innovation Center Basel # , Munich + , F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, 4070 Basel, Switzerland. * Email: martin.edelmann@roche.com Keywords IgG pharmacokinetics, antibody, radioiodination, chelating agents, [ 3 H]NSP, FcRn, affinity chromatography Abstract The number of therapeutic antibodies in research and development as well as their complexity increases from year to year. Novel therapeutic protein formats, such as Fc-fusions, bispecific or multivalent antibodies are currently in pre-clinical and clinical development. Therefore, the need for biodistribution and imaging studies, e.g. with radiolabeled proteins are very high. However, the labeling process or the label itself can have an impact on binding to cellular receptors, e.g. to neonatal Fc receptor (FcRn), which can lead to altered PK properties compared to the unlabeled antibody. FcRn affinity chromatography allows the assessment of IgG samples with respect to their pH-dependent FcRn interaction. We analyzed IgGs with different types of labels, namely direct iodination with 125 I, chelating agents, such as DOTA and DOTAM, and [ 3 H]propionate. Direct radio-iodination leads to shifts in FcRn column retention time which might indicate a potentially faster clearance. Furthermore, high conjugation ratios of chelator lower the affinity to FcRn successively, and thus may influence the lysosomal degradation of the antibody in endothelial cells. In contrast, IgGs labeled with [ 3 H]propionate did not show any timeshifts in FcRn affinity chromatography. This article is based on the oral presentation at the IIS 2018 Prague and highlights the importance of an affinity chromatography for characterization of potential changes in affinity to FcRn itself or charge and hydrophobicity.