Fully Automated ⁸⁹Zr Labeling and Purification of Antibodies

Dozens of monoclonal antibodies (mAbs) have been approved for clinical use, and hundreds more are under development. To support these developments and facilitate a personalized medicine approach, PET imaging and quantification of mAbs, after chelation with desferrioxamine B (DFO) and radiolabeling with ⁸⁹Zr, has become attractive. Also, the use of ⁸⁹Zr-mAbs in preclinical and clinical studies is expanding rapidly. Despite these rapid developments, ⁸⁹Zr radiolabeling is still performed manually. Therefore, we aimed to develop a simple, fully automated, good-manufacturing-practice (GMP)-compliant production procedure for the ⁸⁹Zr labeling of mAbs. Such procedures should increase the robustness and capacity of ⁸⁹Zr-mAb production while minimizing the radiation dose to the operator. Here, the procedures for fully automated ⁸⁹Zr-mAb production are described and applied to produce batches of ⁸⁹Zr-DFO-N-suc-cetuximab and ⁸⁹Zr-DFO-N-suc-rituximab suitable for clinical use. Both products had to meet the GMP-compliant quality standards with respect to yield, radiochemical purity, protein integrity, antigen binding, sterility, and endotoxin levels. Methods: Automated ⁸⁹Zr labeling of mAbs was developed on a Scintomics GRP 2V module and comprised the following steps: reagent transfer to the ⁸⁹Zr-containing reaction vial, mixing of the reagents followed by a 60-min reaction at room temperature to obtain optimal radiolabeling yields, and product purification using a PD-10 desalting column. Results: Radiochemical yields of ⁸⁹Zr-DFO-N-suc-cetuximab and ⁸⁹Zr-DFO-N-suc-rituximab were all more than 90% according to instant thin-layer chromatography. Isolated yields were 74.6% ± 2.0% and 62.6% ± 3.0% for ⁸⁹Zr-DFO-N-suc-cetuximab and ⁸⁹Zr-DFO-N-suc-rituximab, respectively, which are similar to isolated yields obtained using GMP protocols for manual ⁸⁹Zr labeling of mAbs. To meet the GMP-compliant quality standards, only the radiochemically pure fractions were collected from PD-10, resulting in a lower isolated yield than the radiochemical yield according to instant thin-layer chromatography. The radiochemical purity and protein integrity were more than 95% for both products, and the antigen binding was 95.6% ± 0.6% and 87.1% ± 2.2% for ⁸⁹Zr-DFO-N-suc-cetuximab and ⁸⁹Zr-DFO-N-suc-rituximab, respectively. The products were sterile, and the endotoxin levels were within acceptable limits, allowing future clinical production using this procedure. Conclusion: Procedures for fully automated GMP-compliant production of ⁸⁹Zr-mAbs were developed on a commercially available synthesis module, which also allows the GMP production of other radiolabeled mAbs.