Preclinical Evaluation of89Zr-Desferrioxamine-Bexmarilimab, a Humanized Antibody Against Common Lymphatic Endothelial and Vascular Endothelial Receptor-1, in a Rabbit Model of Renal Fibrosis

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Bexmarilimab is a new humanized monoclonal antibody against common lymphatic endothelial and vascular endothelial receptor-1 (CLEVER-1), and is in clinical trials for macrophage-guided cancer immunotherapy. In addition to cancer, CLEVER-1 is also associated with fibrosis. To facilitate prospective human PET studies, we preclinically evaluated 89Zr-labeled bexmarilimab in rabbits. Methods: Bexmarilimab was conjugated with desferrioxamine (DFO) and radiolabeled with 89Zr. Retained immunoreactivity was confirmed by flow cytometry. Distribution kinetics of intravenously administered 89Zr-DFO-bexmarilimab (0.1 mg/kg) for up to 7 days in a rabbit model of renal fibrosis mediated by unilateral ureteric obstruction (UUO). The in-vivo stability of 89Zr-DFO-bexmarilimab was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with autoradiography. Additionally, we estimated the human radiation dose from data obtained in healthy rabbits. Results:89Zr-DFO-bexmarilimab cleared rapidly from the blood circulation and distributed to the liver and spleen. At 24 hours post-injection, PET/CT, ex-vivo gamma counting and autoradiography demonstrated that there was significantly higher 89Zr-DFO-bexmarilimab uptake in UUO-operated fibrotic renal cortex, characterized by abundant CLEVER-1-positive cells, than in contralateral or healthy kidneys. The estimated effective dose for a 70-kg human was 0.70 mSv/MBq. Conclusion: The characteristics of 89Zr-DFO-bexmarilimab support future human PET studies to, for example, stratify patients for bexmarilimab treatment, evaluate the efficacy of treatment, or monitor disease progression.

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