(1) Background: Monoclonal antibodies are used in the treatment of multiple conditions\nincluding cancer, autoimmune disorders, and infectious diseases. One of the initial steps in\nthe selection of an antibody candidate for further pre-clinical development is determining its\npharmacokinetics in small animal models. The use of mass spectrometry and other techniques to\ndetermine the fate of these antibodies is laborious and expensive. Here we describe a straightforward\nand highly reproducible methodology for utilizing radiolabeled antibodies for pharmacokinetics\nstudies. (2) Methods: Commercially available bifunctional linker CHXAâ? and 111Indium radionuclide\nwere used. A melanin-specific chimeric antibody A1 and an isotype matching irrelevant control\nA2 were conjugated with the CHXAâ?, and then radiolabeled with 111In. The biodistribution was\nperformed at 4 and 24 h time points in melanoma tumor-bearing and healthy C57BL/6 female mice.\n(3) The biodistribution of the melanin-binding antibody showed the significant uptake in the tumor,\nwhich increased with time, and very low uptake in healthy melanin-containing tissues such as the\nretina of the eye and melanized skin. This biodistribution pattern in healthy tissues was very close\nto that of the isotype matching control antibody. (4) Conclusions: The biodistribution experiment\nallows us to assess the pharmacokinetics of both antibodies side by side and to make a conclusion\nregarding the suitability of specific antibodies for further development.
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