Fully Automated 89Zr Labeling and Purification of Antibodies

Fully Automated Cassette-Based Synthesis of 2-Deoxy-2-[18F]Fluorocellobiose Using Trasis AllInOne Module

Due to the continuous rise in global incidence and severity of invasive fungal infections (IFIs), particularly among immunocompromised and immunodeficient patients, there is an urgent demand for swift and accurate fungal pathogen diagnosis. Therefore, the need for fungal-specific positron emission tomography (PET) imaging agents that can detect the infection in the early stages is increasing. Cellobiose, a disaccharide, is readily metabolized by fungal pathogens such as Aspergillus species. Recently, our group reported fluorine-18 labeled cellobiose, 2-deoxy-2-[18F]fluorocellobiose ([18F]FCB), for specific imaging of Aspergillus infection. The positive imaging findings with very low background signal on delayed imaging make this ligand a promising fungal-specific imaging ligand. Inspired by this result, the decision was made to automate the radiolabeling procedure for better reproducibility and to facilitate clinical translation. A Trasis AllInOne (Trasis AIO) automated module was used for this purpose. The reagent vials contain commercially available 2-deoxy-2-[18F]fluoroglucose ([18F]FDG), glucose-1-phosphate, and enzyme (cellobiose phosphorylase). A Sep-Pak cartridge was used to purify the tracer. The overall radiochemical yield was 50%-70% (n = 6, decay corrected) in 75-min synthesis time with a radiochemical purity of > 98%. This is a highly reliable protocol to produce current good manufacturing practice (cGMP)-compliant [18F]FCB for clinical PET imaging.

Good practices for 89Zr radiopharmaceutical production and quality control

BACKGROUND

During the previous two decades, PET imaging of biopharmaceuticals radiolabeled with zirconium-89 has become a consistent tool in preclinical and clinical drug development and patient selection, primarily due to its advantageous physical properties that allow straightforward radiolabeling of antibodies (89Zr-immuno-PET). The extended half-life of 78.4 h permits flexibility with respect to the logistics of tracer production, transportation, and imaging and allows imaging at later points in time. Additionally, its relatively low positron energy contributes to high-sensitivity, high-resolution PET imaging. Considering the growing interest in radiolabeling antibodies, antibody derivatives, and other compound classes with 89Zr in both clinical and pre-clinical settings, there is an urgent need to acquire valuable recommendations and guidelines towards standardization of labeling procedures.

MAIN BODY

This review provides an overview of the key aspects of 89Zr-radiochemistry and radiopharmaceuticals. Production of 89Zr, conjugation with the mostly used chelators and radiolabeling strategies, and quality control of the radiolabeled products are described in detail, together with discussions about alternative options and critical steps, as well as recommendations for troubleshooting. Moreover, some historical background on 89Zr-immuno-PET, coordination chemistry of 89Zr, and future perspectives are provided. This review aims to serve as a quick-start guide for scientists new to the field of 89Zr-immuno-PET and to suggest approaches for harmonization and standardization of current procedures.

CONCLUSION

The favorable PET imaging characteristics of 89Zr, its excellent availability due to relatively simple production and purification processes, and the development of suitable bifunctional chelators have led to the widespread use of 89Zr. The combination of antibodies and 89Zr, known as 89Zr-immuno-PET, has become a cornerstone in drug development and patient selection in recent years. Despite the advanced state of 89Zr-immuno-PET, new developments in chelator conjugation and radiolabeling procedures, application in novel compound classes, and improved PET scanner technology and quantification methods continue to reshape its landscape towards improving clinical outcomes.

Preparation of a Zirconium-89 Labeled Clickable DOTA Complex and Its Antibody Conjugate

Desferrioxamine B (DFO) is the clinical standard chelator for preparing zirconium-89 labeled antibodies. In the current study, the stabilities of a zirconium-89 labeled panitumumab (PAN; Vectibix®) with three different chelators (DFO, DFO*, and DOTA) were compared. PAN is an anti-HER1/EGFR monoclonal antibody approved by the FDA for the treatment of HER1-expressing colorectal cancers and was used as the model antibody for this study. DFO/DFO* conjugates of PAN were directly radiolabeled with zirconium-89 at room temperature to produce [89Zr]Zr-DFO/DFO*-PAN conjugates following a well-established procedure. A zirconium-89 labeled DOTA-PAN conjugate was prepared by an indirect radiolabeling method. A cyclooctyne-linked DOTA chelator (BCN-DOTA-GA) was first radiolabeled with zirconium-89 at 90 °C under a two-step basic pH adjustment method followed by conjugation with PAN-tetrazene at 37 °C to produce a labeled conjugate, BCN-[89Zr]Zr-DOTA-GA-PAN. High reproducibility of the radiolabeling was observed via this two-step basic pH adjustment. The overall radiochemical yield was 40-50% (n = 12, decay uncorrected) with a radiochemical purity of >95% in 2 h synthesis time. All three conjugates were stable in whole human serum for up to 7 days at 37 °C. The kinetic inertness of the conjugates was assessed against the EDTA challenge. BCN-[89Zr]Zr-DOTA-GA-PAN exhibited excellent inertness followed by [89Zr]Zr-DFO*-PAN. [89Zr]Zr-DFO-PAN displayed the lowest level of inertness.

Automated radiolabeling and handling of 177 Lu- and 225 Ac-PSMA-617 using a robotic pipettor

While automated modules for F-18 and C-11 radiosyntheses are standardized with features such as multiple reactors, vacuum connection and semi-preparative HPLC, labeling and processing of compounds with radiometals such as Zr-89, Lu-177 and Ac-225 often do not require complex manipulations and are frequently performed manually by a radiochemist. These procedures typically involve transferring solutions to and from vials using pipettes followed by heating of the reaction mixture, and do not require all the features found in most commercial automated synthesis units marketed as F-18 or C-11 modules. Here we present an efficient automated method for performing radiosyntheses involving radiometals by adapting a commercially available robotic pipettor originally developed for high-throughput processing of biological samples. While a robotic pipettor is less costly than a radiosynthesis module, it holds many similar advantages over manual radiosynthesis such as minimization of operator error, lower operator exposure rates, and abbreviated synthesis times, among others. To demonstrate the feasibility of using the OpenTrons OT-2 robotic pipettor to perform automated radiosyntheses, we radiolabeled and formulated 177 Lu-PSMA-617 and 225 Ac-PSMA-617 on the system. The OT-2 was then used to help streamline the quality control process for both products, further minimizing manual handling by and exposure to the radiochemist.

Intranasal administration enhances size-dependent pulmonary phagocytic uptake of poly(lactic-co-glycolic acid) nanoparticles

BACKGROUND

Nanoparticles exhibit distinct behaviours within the body, depending on their physicochemical properties and administration routes. However, in vivo behaviour of poly(lactic-co-glycolic acid) (PLGA) nanoparticles, especially when administered nasally, remains unexplored; furthermore, there is a lack of comparative analysis of uptake efficiency among different administration routes. Therefore, here, we aimed to comprehensively investigate the real-time in vivo behaviour of PLGA nanoparticles across various administration routes. PLGA-NH2 nanoparticles of three sizes were synthesised using an oil-in-water single-emulsion method. We assessed their uptake by murine macrophage RAW264.7 cells using fluorescence microscopy. To enable real-time tracking, we conjugated p-SCN-Bn-deferoxamine to PLGA-NH2 nanoparticles and further radiolabelled them with 89Zr-oxalate before administration to mice via different routes. Nanoparticle internalisation by lung immune cells was monitored using fluorescence-activated cell sorting analysis.

RESULTS

The nanoparticle sizes were 294 ± 2.1 (small), 522.5 ± 5.58 (intermediate), and 850 ± 18.52 nm (large). Fluorescent labelling did not significantly alter the nanoparticle size and charge. The level of uptake of small and large nanoparticles by RAW264.7 cells was similar, with phagocytosis inhibition primarily reducing the internalisation of large particles. Positron emission tomography revealed that intranasal delivery resulted in the highest and most targeted pulmonary uptake, whereas intravenous administration led to accumulation mainly in the liver and spleen. Nasal delivery of large nanoparticles resulted in enhanced uptake by myeloid immune cells relative to lymphoid cells, whereas dendritic cell uptake initially peaked but declined over time.

CONCLUSIONS

Our study provides valuable insights into advancing nanomedicine and drug delivery, with the potential for expanding the clinical applications of nanoparticles.

Automated radiosynthesis of [89Zr]Zr-DFOSq-Durvalumab for imaging of PD-L1 expressing tumours in vivo

OBJECTIVES

⁸⁹Zr-labelled proteins are gaining importance in clinical research in a variety of diseases. To date, no clinical study has been reported that utilizes an automated approach for radiosynthesis of ⁸⁹Zr-labelled radiopharmaceuticals. We aim to develop an automated method for the clinical production of ⁸⁹Zr-labelled proteins and apply this method to Durvalumab, a monoclonal antibody targeting PD-L1 immune-checkpoint protein. PD-L1 expression is poorly understood and can be up-regulated over the course of chemo- and radiotherapy treatment. The ImmunoPET multicentre study aims to examine the dynamics of PD-L1 expression via ⁸⁹Zr-Durvalumab PET imaging before, during, and after chemoradiotherapy. The developed automated technique will enable reproducible clinical production of [⁸⁹Zr]Zr-DFOSq-Durvalumab for this study at three different sites.

METHODS

Conjugation of Durvalumab to H₃DFOSqOEt was optimized for optimal chelator-to-antibody ratio. Automated radiolabelling of H₃DFOSq-Durvalumab with zirconium-89 was optimized on the disposable cassette based iPHASE technologies MultiSyn radiosynthesizer using a modified cassette. Activity losses were tracked using a dose calibrator and minimized by optimizing fluid transfers, reaction buffer, antibody formulation additives and pH. The biological profile of the radiolabelled antibody was confirmed in vivo in PD-L1+ (HCC827) and PD-L1- (A549) murine xenografts. Clinical process validation and quality control were performed at three separate study sites to satisfy clinical release criteria.

RESULTS

H₃DFOSq-Durvalumab with an average CAR of 3.02 was obtained. Radiolabelling kinetics in succinate (20 mM, pH 6) were significantly faster when compared to HEPES (0.5 M, pH 7.2) with >90 % conversion observed after 15 min. Residual radioactivity in the ⁸⁹Zr isotope vial was reduced from 24 % to 0.44 % ± 0.18 % (n = 7) and losses in the reactor vial were reduced from 36 % ± 6 % (n = 4) to 0.82 % ± 0.75 % (n = 4) by including a surfactant in the reaction and formulation buffers. Overall process yield was 75 % ± 6 % (n = 5) and process time was 40 min. Typically, 165 MBq of [⁸⁹Zr]Zr-DFOSq-Durvalumab with an apparent specific activity of 315 MBq/mg ± 34 MBq/mg (EOS) was obtained in a volume of 3.0 mL. At end-of-synthesis (EOS), radiochemical purity and protein integrity were always >99 % and >96 %, respectively, and dropped to 98 % and 65 % after incubation in human serum for 7 days at 37 °C. Immunoreactive fraction in HEK293/PD-L1 cells was 83.3 ± 9.0 (EOS). Preclinical in vivo data at 144 h p.i. showed excellent SUV_max in PD-L1+ tumour (8.32 ± 0.59) with a tumour-background ratio of 17.17 ± 3.96. [⁸⁹Zr]Zr-DFOSq-Durvalumab passed all clinical release criteria at each study site and was deemed suitable for administration in a multicentre imaging trial.

CONCLUSION

Fully automated production of [⁸⁹Zr]Zr-DFOSq-Durvalumab for clinical use was achieved with minimal exposure to the operator. The cassette-based approach allows for consecutive productions on the same day and offers an alternative to currently used manual protocols. The method should be broadly applicable to other proteins and has the potential for clinical impact considering the growing number of clinical trials investigating ⁸⁹Zr-labelled antibodies.

Automated light-induced synthesis of 89Zr-radiolabeled antibodies for immuno-positron emission tomography

Clinical production of 89Zr-radiolabeled antibodies (89Zr-mAbs) for positron emission tomography imaging relies on the pre-conjugation of desferrioxamine B (DFO) to the purified protein, followed by isolation and characterization of the functionalized intermediate, and then manual radiosynthesis. Although highly successful, this route exposes radiochemists to a potentially large radiation dose and entails several technological and economic hurdles that limit access of 89Zr-mAbs to just a specialist few Nuclear Medicine facilities worldwide. Here, we introduce a fully automated synthesis box that can produce individual doses of 89Zr-mAbs formulated in sterile solution in < 25 min starting from [89Zr(C2O4)4]4- (89Zr-oxalate), our good laboratory practice-compliant photoactivatable desferrioxamine-based chelate (DFO-PEG3-ArN3), and clinical-grade antibodies without the need for pre-purification of protein. The automated steps include neutralization of the 89Zr-oxalate stock, chelate radiolabeling, and light-induced protein conjugation, followed by 89Zr-mAb purification, formulation, and sterile filtration. As proof-of-principle, 89ZrDFO-PEG3-azepin-trastuzumab was synthesized directly from Herceptin in < 25 min with an overall decay-corrected radiochemical yield of 20.1 ± 2.4% (n = 3), a radiochemical purity > 99%, and chemical purity > 99%. The synthesis unit can also produce 89Zr-mAbs via the conventional radiolabeling routes from pre-functionalized DFO-mAbs that are currently used in the clinic. This automated method will improve access to state-of-the-art 89Zr-mAbs at the many Nuclear Medicine and research institutions that require automated devices for radiotracer production.

Comparison of analytical methods for antibody conjugates with application in nuclear imaging - Report from the trenches

INTRODUCTION

Monoclonal antibodies (mAbs) are widely used in nuclear imaging. Radiolabelling with positron emitting radionuclides, typically radiometals, requires the incorporation of a bifunctional chelator for the formation of the radiometal-mAb complex. Additionally, mAbs can be conjugated with small molecules capable to undergo bioorthogonal click reactions in vivo, enabling pre-targeting strategies. The determination of the number of functionalities attached to the mAb is critically important to ensure a good labelling yield or to guarantee pre-targeting efficacy. In this work, we compare three different analytical methods for the assessment of average functionalisation and heterogeneity of the conjugated mAbs.

METHODS

Two selected mAbs (Trastuzumab and Bevacizumab) were randomly conjugated through lysine residues with 3-10 equivalents p-isothiocyanatobenzyl-desferrioxamine (p-NCS-Bz-DFO) or 20-200 equivalents trans-cyclooctene-N-hydroxysuccinimide ester (TCO-NHS). The DFO- or TCO-to-mAb ratio were determined using three different methods: direct titration (radiometric for DFO-conjugated mAbs, photometric for TCO-conjugated mAbs), MALDI/TOF MS mass analysis (Matrix-Assisted Laser Desorption-Ionization/Time of Flight Mass Spectrometry), and UPLC/ESI-TOF MS mass analysis (Ultra High Performance Liquid Chromatography/Electrospray Ionization-Time of Flight Mass Spectrometry).

RESULTS

Radiometric and photometric titrations provided information on the average number of DFO and TCO functionalities per mAb respectively. MALDI/TOF MS provided equivalent results to those obtained by titration, although investigation of the heterogeneity of the resulting mixture was challenging and inaccurate. UPLC/ESI-TOF MS resulted in good peak resolution in the case of DFO-conjugated mAbs, where an accurate discrimination of the contribution of mono-, di- and tri-substituted mAbs could be achieved by mathematical fitting of the spectra. However, UPLC/ESI-TOF MS was unable to discriminate between different conjugates when the smaller TCO moiety was attached to the mAbs.

CONCLUSIONS

The three techniques offered comparable results in terms of determining the average number of conjugates per mAb. Additionally, UPLC/ESI-TOF MS was able to shed a light on the heterogeneity of the resulting functionalised mAbs, especially in the case of DFO-conjugated mAbs. Finally, while using a single analytical method might not be a reliable way to determine the average functionalisation and assess the heterogeneity of the sample, a combination of these methods could substantially improve the characterization of mAb conjugates.

State of the Art in Radiolabeling of Antibodies with Common and Uncommon Radiometals for Preclinical and Clinical Immuno-PET

Inert and stable radiolabeling of monoclonal antibodies (mAb), antibody fragments, or antibody mimetics with radiometals is a prerequisite for immuno-PET. While radiolabeling is preferably fast, mild, efficient, and reproducible, especially when applied for human use in a current Good Manufacturing Practice compliant way, it is crucial that the obtained radioimmunoconjugate is stable and shows preserved immunoreactivity and in vivo behavior. Radiometals and chelators have extensively been evaluated to come to the most ideal radiometal–chelator pair for each type of antibody derivative. Although PET imaging of antibodies is a relatively recent tool, applications with ⁸⁹Zr, ⁶⁴Cu, and ⁶⁸Ga have greatly increased in recent years, especially in the clinical setting, while other less common radionuclides such as ⁵²Mn, ⁸⁶Y, ⁶⁶Ga, and ⁴⁴Sc, but also ¹⁸F as in [¹⁸F]AlF are emerging promising candidates for the radiolabeling of antibodies. This review presents a state of the art overview of the practical aspects of radiolabeling of antibodies, ranging from fast kinetic affibodies and nanobodies to slow kinetic intact mAbs. Herein, we focus on the most common approach which consists of first modification of the antibody with a chelator, and after eventual storage of the premodified molecule, radiolabeling as a second step. Other approaches are possible but have been excluded from this review. The review includes recent and representative examples from the literature highlighting which radiometal–chelator–antibody combinations are the most successful for in vivo application.

Microfluidic Preparation of 89Zr-Radiolabelled Proteins by Flow Photochemistry

⁸⁹Zr-radiolabelled proteins functionalised with desferrioxamine B are a cornerstone of diagnostic positron emission tomography. In the clinical setting, ⁸⁹Zr-labelled proteins are produced manually. Here, we explore the potential of using a microfluidic photochemical flow reactor to prepare ⁸⁹Zr-radiolabelled proteins. The light-induced functionalisation and ⁸⁹Zr-radiolabelling of human serum albumin ([⁸⁹Zr]ZrDFO-PEG₃-Et-azepin-HSA) was achieved by flow photochemistry with a decay-corrected radiochemical yield (RCY) of 31.2 ± 1.3% (n = 3) and radiochemical purity >90%. In comparison, a manual batch photoreactor synthesis produced the same radiotracer in a decay-corrected RCY of 59.6 ± 3.6% (n = 3) with an equivalent RCP > 90%. The results indicate that photoradiolabelling in flow is a feasible platform for the automated production of protein-based ⁸⁹Zr-radiotracers, but further refinement of the apparatus and optimisation of the method are required before the flow process is competitive with manual reactions.

The emerging role of radionuclide molecular imaging of HER2 expression in breast cancer

Targeting of human epidermal growth factor type 2 (HER2) using monoclonal antibodies, antibody-drug conjugates and tyrosine kinase inhibitors extends survival of patients with HER2-expressing metastatic breast cancer. High expression of HER2 is a predictive biomarker for such specific treatment. Accurate determination of HER2 expression level is necessary for stratification of patients to targeted therapy. Non-invasive in vivo radionuclide molecular imaging of HER2 has a potential of repetitive measurements, addressing issues of heterogeneous expression and conversion of HER2 status during disease progression or in response to therapy. Imaging probes based of several classes of targeting proteins are currently in preclinical and early clinical development. Both preclinical and clinical data suggest that the most promising are imaging agents based on small proteins, such as single domain antibodies or engineered scaffold proteins. These agents permit a very specific high-contrast imaging at the day of injection.

The Role of 89Zr-Immuno-PET in Navigating and Derisking the Development of Biopharmaceuticals

The identification of molecular drivers of disease and the compelling rise of biotherapeutics have impacted clinical care but have also come with challenges. Such therapeutics include peptides, monoclonal antibodies, antibody fragments and nontraditional binding scaffolds, activatable antibodies, bispecific antibodies, immunocytokines, antibody-drug conjugates, enzymes, polynucleotides, and therapeutic cells, as well as alternative drug carriers such as nanoparticles. Drug development is expensive, attrition rates are high, and efficacy rates are lower than desired. Almost all these drugs, which in general have a long residence time in the body, can stably be labeled with ⁸⁹Zr for whole-body PET imaging and quantification. Although not restricted to monoclonal antibodies, this approach is called ⁸⁹Zr-immuno-PET. This review summarizes the state of the art of the technical aspects of ⁸⁹Zr-immuno-PET and illustrates why it has potential for steering the design, development, and application of biologic drugs. Appealing showcases are discussed to illustrate what can be learned with this emerging technology during preclinical and especially clinical studies about biologic drug formats and disease targets. In addition, an overview of ongoing and completed clinical trials is provided. Although ⁸⁹Zr-immuno-PET is a young tool in drug development, its application is rapidly expanding, with first clinical experiences giving insight on why certain drug-target combinations might have better perspectives than others.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

Light-Induced Radiosynthesis of 89Zr-DFO-Azepin-Onartuzumab for Imaging the Hepatocyte Growth Factor Receptor

Methods that provide rapid access to radiolabeled antibodies are vital in the development of diagnostic and radiotherapeutic agents for PET or radioimmunotherapy. The human hepatocyte growth factor receptor (c-MET) signaling pathway is dysregulated in several 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, antihuman 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 desferrioxamine B (DFO)-aryl azide (DFO-ArN₃), and MetMAb to give ⁸⁹Zr-DFO-azepin-onartuzumab. As a control, ⁸⁹Zr-DFO-benzyl Bn-isothiocyanate Bn-NCS-onartuzumab was prepared via a conventional two-step process using prepurified 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 on female athymic nude mice bearing subcutaneous MKN-45 xenografts. Biodistribution experiments were performed after the final image was obtained. The tumor specificity of ⁸⁹Zr-DFO-azepin-onartuzumab was assessed in vivo by competitive inhibition (blocking) studies. Results: Initial photoradiosynthesis experiments produced ⁸⁹Zr-DFO-azepin-onartuzumab in less than 15 min, with an isolated decay-corrected radiochemical yield (RCY) of 24.8%, a radiochemical purity of approximately 90%, and a molar activity of approximately 1.5 MBq nmol^-1 Reaction optimization improved the radiochemical conversion of ⁸⁹Zr-DFO-azepin-onartuzumab to 56.9% ± 4.1% (n = 3), with isolated RCYs of 41.2% ± 10.6% (n = 3) and radiochemical purity of more than 90%. Conventional methods produced ⁸⁹Zr-DFO-Bn-NCS-onartuzumab with an isolated RCY of more than 97%, radiochemical purity of more than 97% and molar activity of approximately 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 (percentage injected dose [%ID]) reached 15.37 ± 5.21 %ID g^-1 and 6.56 ± 4.03 %ID g^-1, respectively, for ⁸⁹Zr-DFO-azepin-onartuzumab (n = 4) and 21.38 ± 11.57 %ID g^-1 and 18.84 ± 6.03 %ID g^-1, respectively, for ⁸⁹Zr-DFO-Bn-NCS-onartuzumab (n = 4). Blocking experiments gave a statistically significant reduction in tumor uptake (6.34 ± 0.47 %ID g^-1) of ⁸⁹Zr-DFO-azepin-onartuzumab (n = 4). Conclusion: The experiments demonstrated that photoradiosynthesis is a viable alternative approach for producing ⁸⁹Zr-radiolabeled antibodies directly in protein formulation buffer, reducing protein aggregation and liver uptake.