Preclinical Evaluation of (89)Zr-Desferrioxamine-Bexmarilimab, a Humanized Antibody Against Common Lymphatic Endothelial and Vascular Endothelial Receptor-1, in a Rabbit Model of Renal Fibrosis

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 being associated with cancer, CLEVER-1 is also associated with fibrosis. To facilitate prospective human PET studies, we preclinically evaluated (89)Zr-labeled bexmarilimab in rabbits. Methods: Bexmarilimab was conjugated with desferrioxamine (DFO) and radiolabeled with (89)Zr. Retained immunoreactivity was confirmed by flow cytometry. The distribution kinetics of intravenously administered (89)Zr-DFO-bexmarilimab (0.1 mg/kg) were determined for up to 7 d in a rabbit model of renal fibrosis mediated by unilateral ureteric obstruction. The in vivo stability of (89)Zr-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: (89)Zr-DFO-bexmarilimab cleared rapidly from the blood circulation and distributed to the liver and spleen. At 24 h after injection, PET/CT, ex vivo γ-counting, and autoradiography demonstrated that there was significantly higher (89)Zr-DFO-bexmarilimab uptake in unilateral ureteric obstruction–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 (89)Zr-DFO-bexmarilimab support future human PET studies to, for example, stratify patients for bexmarilimab treatment, evaluate the efficacy of treatment, or monitor disease progression.