Biodistribution of a Radiolabeled Antibody in Mice as an Approach to Evaluating Antibody Pharmacokinetics

Abstract

(1) Background: Monoclonal antibodies are used in the treatment of multiple conditions including cancer, autoimmune disorders, and infectious diseases. One of the initial steps in the selection of an antibody candidate for further pre-clinical development is determining its pharmacokinetics in small animal models. The use of mass spectrometry and other techniques to determine the fate of these antibodies is laborious and expensive. Here we describe a straightforward and highly reproducible methodology for utilizing radiolabeled antibodies for pharmacokinetics studies. (2) Methods: Commercially available bifunctional linker CHXA" and ¹¹¹Indium radionuclide were used. A melanin-specific chimeric antibody A1 and an isotype matching irrelevant control A2 were conjugated with the CHXA", and then radiolabeled with ¹¹¹In. The biodistribution was performed at 4 and 24 h time points in melanoma tumor-bearing and healthy C57BL/6 female mice. (3) The biodistribution of the melanin-binding antibody showed the significant uptake in the tumor, which increased with time, and very low uptake in healthy melanin-containing tissues such as the retina of the eye and melanized skin. This biodistribution pattern in healthy tissues was very close to that of the isotype matching control antibody. (4) Conclusions: The biodistribution experiment allows us to assess the pharmacokinetics of both antibodies side by side and to make a conclusion regarding the suitability of specific antibodies for further development.

Keywords: antibodies; biodistribution; mouse models; pharmacokinetics; radiolabeling.

Figure 1

Biodistribution of ¹¹¹In-labeled antibodies Ab1 to melanin and isotype matching irrelevant control Ab2 in C57BL6 mice at 4 and 24 h after IV administration. (A) Ab1 antibody in B16F10 melanoma bearing mice; (B) Ab2 in healthy mice. Blue and orange bars represent 4 and 24 h time points, respectively. The error bars represent the SEM of sample groups of 4–5 mice.