TY - JOUR T1 - Light-induced radiosynthesis of <sup>89</sup>ZrDFO-azepin-onartuzumab for imaging the hepatocyte growth factor receptor JF - Journal of Nuclear Medicine JO - J Nucl Med DO - 10.2967/jnumed.119.237180 SP - jnumed.119.237180 AU - Simon Klingler AU - Rachael Fay AU - Jason P. Holland Y1 - 2020/01/01 UR - http://jnm.snmjournals.org/content/early/2020/01/09/jnumed.119.237180.abstract N2 - Methods that provide rapid access to radiolabeled antibodies are vital in the development of diagnostic and radiotherapeutic agents for positron emission tomography (PET) or radioimmunotherapy. The human hepatocyte growth factor receptor (c-MET) signaling pathway is dysregulated in a number of malignancies including gastric cancer, and is an important biomarker in drug discovery. Here, we used a photoradiochemical approach to produce 89Zr-radiolabeled onartuzumab (a monovalent, anti-human c-MET antibody), starting directly from the fully formulated drug (MetMAb). Methods: Simultaneous 89Zr-radiolabeling and protein conjugation was performed in one-pot reactions containing 89Zr-oxalate, the photoactive chelate DFO-aryl azide (DFO-ArN3) and MetMAb to give 89ZrDFO-azepin-onartuzumab. As a control, 89ZrDFO-Bn-NCS-onartuzumab was prepared via a conventional two-step process using pre-purified onartuzumab and DFO-Bn-NCS. Radiotracers were purified by using size-exclusion methods and evaluated by radiochromatography. Radiochemical stability was studied in human serum and immunoreactivity was determined by cellular binding assays using MKN-45 gastric carcinoma cells. PET imaging at multiple time points (0–72 h) was performed in female athymic nude mice bearing subcutaneous MKN-45 xenografts. Biodistribution experiments were performed after the final image. Tumor specificity of 89ZrDFO-azepin-onartuzumab was assessed by competitive inhibition (blocking) studies. Results: Initial photoradiosynthesis experiments produced 89ZrDFO-azepin-onartuzumab in &lt;15 min. with an isolated decay-corrected radiochemical yield (RCY) of 24.8%, a radiochemical purity (RCP) ~90% and a molar activity (Am) of ~1.5 MBq nmol-1. Reaction optimization improved the radiochemical conversion (RCC) of 89ZrDFO-azepin-onartuzumab to 56.9±4.1% (n = 3), with isolated RCYs of 41.2±10.6% (n = 3), and RCPs &gt;90%. Conventional methods produced 89ZrDFO-Bn-NCS-onartuzumab with isolated RCY &gt;97%, RCP &gt;97% and Am ~14.0 MBq nmol-1. Both radiotracers were immunoreactive and stable in human serum. PET imaging and biodistribution studies showed high tumor uptake for both radiotracers. By 72 h, tumor and liver uptake reached 15.37±5.21 %ID g-1, 6.56±4.03 %ID g-1, respectively for 89ZrDFO-azepin-onartuzumab (n = 4), and 21.38±11.57 %ID g-1 and 18.84±6.03 %ID g-1 for 89ZrDFO-Bn-NCS-onartuzumab (n = 4). Blocking experiments gave a statistically significant reduction in tumor uptake (6.34±0.47 %ID g-1) of 89ZrDFO-azepin-onartuzumab (n = 4). Conclusion: Experiments demonstrate that photoradiosynthesis is a viable alternative approach for producing 89Zr-radiolabeled antibodies direct in protein formulation buffer which reduces protein aggregation and liver uptake. ER -