A radiopharmaceutical [89Zr]Zr-DFO-nimotuzumab for immunoPET with epidermal growth factor receptor expression in vivo

Abstract Introduction The potential of the positron-emitting zirconium-89 ( 89 Zr) ( t 1/2  = 78.4 h) has been recently reported for immune positron emission tomography (immunoPET) radioimmunoconjugates design. In our work, we explored the optimized preparation of [ 89 Zr]Zr-DFO-nimotuzumab, and evaluated 89 Zr-labeled monoclonal antibody (mAb) construct for targeted imaging of epidermal growth factor receptor (EGFR) overexpressed in glioma. Methods To optimize the radiolabeling efficiency of 89 Zr with DFO-nimotuzumab, multiple immunoconjugates and radiolabeling were performed. Radiolabeling yield, radiochemical purity, stability, and activity assay were investigated to characterize [ 89 Zr]Zr-DFO-nimotuzumab for chemical and biological integrity. The in vivo behavior of this tracer was studied in mice bearing subcutaneous U87MG (EGFR-positive) tumors received a 3.5 ± 0.2 MBq/dose using PET/CT imaging. One group mice bearing subcutaneous U87MG (EGFR-positive) tumors received [ 89 Zr]Zr-DFO-nimotuzumab (3.5 ± 0.2 MBq, ~3 μg) (nonblocking) for immunoPET; the other group had 30 μg predose (blocking) of cold nimotuzumab 24 h prior to [ 89 Zr]Zr-DFO-nimotuzumab. Results [ 89 Zr]Zr-DFO-nimotuzumab was prepared with high radiochemical yield (>90%), radiochemical purity (>99%), and specific activity (115 ± 0.8 MBq/mg). In vitro validation showed that [ 89 Zr]Zr-DFO-nimotuzumab had an initial immunoreactive fraction of 0.99 ± 0.05 and remained active for up to 5 days. A biodistribution study revealed excellent stability of [ 89 Zr]Zr-DFO-nimotuzumab in vivo compared with 89 Zr as a bone seeker. High uptake in the liver and heart and modest penetration in the brain were observed, with no significant accumulation of activity in other organs. ImmunoPET studies also indicated prominent image contrast that remarkably high uptake up to ~20%ID/g for nonblocking and ~2%ID/g for blocking in tumor between 12 and 120 h after administration. Conclusion These studies developed a radiopharmaceutical [ 89 Zr]Zr-DFO-nimotuzumab with optimized synthesis. The potential utility of [ 89 Zr]Zr-DFO-nimotuzumab in assessing EGFR status in glioma was demonstrated in this study.