Evaluation of a chloride-based 89Zr isolation strategy using a tributyl phosphate (TBP)-functionalized extraction resin

89Zr-Labeled DFO@Durvalumab-HSA nanoparticles: In vitro potential for triple-negative breast cancer

This study presents the development and evaluation of a DFO@mAb-NP (DFO@Durvalumab-HSA-DTX nanoparticle) nanoplatform for imaging in triple-negative breast cancer (TNBC). The nanoplatform demonstrated significant changes postconjugation with DFO, evidenced by increased particle size from 178.1 ± 5 nm to 311 ± 26 nm and zeta potential alteration from -31.9 ± 3 mV to -40.5 ± 0.8 mV. Fourier-transform infrared spectroscopy and ultraviolet spectral analyses confirmed successful DFO conjugation, with notable shifts in peak wavelengths. High labeling efficiency was achieved with 89Zr, as indicated by thin layer radio chromatography and high-performance liquid radio chromatography results, with labeling efficiencies of 98 ± 2% for 89Zr-DFO@mAb and 96 ± 3% for 89Zr-DFO@mAb-NP. The nanoplatforms maintained stability over 24 h, showing less than 5% degradation. Lipophilicity assays revealed logP values of 0.5 ± 0.03 for 89Zr-DFO@mAb-NP and 0.98 ± 0.2 for 89Zr-DFO@mAb, indicating a higher lipophilic tendency in the radiolabeled Durvalumab. Cell uptake experiments showed an initial high uptake in MDA-MB-468 cells (45.1 ± 3.2%), which decreased over time, highlighting receptor-specific interactions. These comprehensive findings suggest the promising potential of the DFO@mAb-NP nanoplatform for targeted imaging in TNBC, with implications for improved diagnostic accuracy and treatment strategies.

[89Zr]ZrCl4 for direct radiolabeling of DOTA-based precursors

INTRODUCTION

Zirconium-89 (89Zr) is a positron emitter with several advantages over other shorter-lived positron emission tomography (PET) compatible radiometals such as gallium-68 or copper-64. These include practically unlimited availability, extremely low cost, greatly facilitated distribution logistics, positron energy fit for medical PET imaging, and sufficiently long physical half-life to enable PET imaging at later time points for patient-specific dosimetry estimations. Despite these apparent benefits, the reception of 89Zr in the nuclear medicine community has been tepid. The driving factor for the absence of broader adaptation is mostly routed in its final formulation - [89Zr]zirconium oxalate. While serving as a suitable precursor solution for the gold standard chelator deferoxamine (DFO), [89Zr]Zr-oxalate is inaccessible for the most commonly used chelators, such as the macrocyclic DOTA, due to its pre-chelated state. Consequently, pioneering work has been conducted by multiple research groups to create oxalate-free forms of [89Zr]Zr4+, either via chemical conversion of oxalate into other counterion forms or via direct radiochemical isolation of [89Zr]ZrCl4, showing that [89Zr]Zr-DOTA complexes are possible and stable. However, this success was accompanied by challenges, including complex and labor-intensive radiochemical processing and radiolabeling procedures as well as the relatively minuscule conversion rates. Here, we report on the direct production of [89Zr]ZrCl4 avoiding oxalate and metal contaminants to enable efficient radiolabeling of DOTA constructs.

METHODS

We based our direct production of [89Zr]ZrCl4 on previously reported methods and further optimized its quality by including an additional iron-removing step using the TK400 Resin. Here, we avoided using oxalic acid and effectively minimized the content of trace metal contaminants. Our two-step purification procedure was automated, and we confirmed excellent radionuclide purity, minimal trace metals content, great reactivity over time, and high specific molar activity. In addition, DOTA-based PSMA-617 and DOTAGA-based PSMA-I&T were radiolabeled to demonstrate the feasibility of direct radiolabeling and to estimate the maximum apparent specific activities. Lastly, the biodistribution of [89Zr]Zr-PSMA-617 was assessed in mice bearing PC3-PIP xenografts, and the results were compared to the previously published data.

RESULTS

A total of 18 batches, ranging from 6.9 to 20 GBq (186 to 541 mCi), were produced. The specific molar activity for [89Zr]ZrCl4 exceeded 0.96 GBq (26 mCi) per nanomole of zirconium. The radionuclidic purity was >99 %, and the trace metals content was in the <1 ppm range. The [89Zr]ZrCl4 remained in its reactive chemical form for at least five days when stored in cyclic olefin polymer (COP) vials. Batches of 11.1 GBq (300 mCi) of [89Zr]Zr-PSMA-617 and 14.4 GBq (390 mCi) of [89Zr]Zr-PSMA-I&T, corresponding to specific activities of 11.1 MBq/μg (0.3 mCi/μg), and 14.4 MBq/μg (0.39 mCi/μg), respectively, were produced. [89Zr]Zr-PSMA-617 animal PET imaging results were in agreement with the previously published data.

CONCLUSION

In this work, we report on a suitable application of TK400 Resin to remove iron during [89Zr]ZrCl4 radiochemical isolation. The breakthrough allows for direct radiolabeling of DOTA-based constructs with [89Zr]ZrCl4, leading to high apparent molar activities and excellent conversion rates.

A new targetry system for production of zirconium-89 radioisotope with Cyclone-30 cyclotron

In this study, an efficient method for targetry and production of zirconium-89 radioisotope (89Zr) with Cyclone-30 cyclotron was developed. The preparation of a highly pure compressed yttrium oxide target material and design of a target made by copper for better heat transfer was performed. Electrodeposition of target with gold was done to prevent the entry of metallic impurities (copper, zinc and other trace metal elements). Nuclear reaction cross sections for optimization of production with new target and irradiation parameters of the target were evaluated. The prepared 89Zr in the form of [89Zr] Zr-oxalate had high radionuclidic purity (>99.9%) and a low chemical impurity concentration (<0.1 ppm for copper and zinc elements). The yield of 89Zr radioisotope production via the reaction of 89Y(p,n)89Zr was measured to be 77 ± 9.5 MBq/μAh (time of irradiation = 3, the current 20–30 µA). [89Zr] Zr-oxalate specific-activity was in the range 2.319641 × 104–3.479443 × 104 MBq/mmol of Oxalate.

Anion exchange and extraction chromatography tandem column isolation of zirconium-89 (89Zr) from cyclotron bombarded targets using an automated fluidic platform

The long-lived positron emitter ⁸⁹Zr is a highly promising nuclide employed in diagnostic Positron Emission Tomography (PET) imaging. Methods of radiochemical processing to obtain ⁸⁹Zr for clinical use are traditionally performed with a single hydroxamate resin column. Herein, we present a tandem column purification method for the preparation of high-purity ⁸⁹Zr from cyclotron bombarded natural Y metal foils. The primary column is a macroporous, strongly basic anion exchange resin on styrene divinylbenzene co-polymer. The secondary microcolumn, with an internal volume of 33 μL, is packed with an extraction chromatography resin (ExCR) loaded with di-(2-ethylhexyl)phosphoric acid (HDEHP). A condition of "inverted selectivity" is presented, wherein the ⁸⁹Zr elution from the primary column is synonymous with the load condition on the secondary column. The ability to transfer ⁸⁹Zr from one column to the next allows two sequential purification steps to be performed prior to the final elution of the ⁸⁹Zr product. This approach assures delivery of high purity ⁸⁹Zr. The tandem column purification process has been implemented into a prototype automated fluidic system. Optimization of the method is presented, followed by evaluation of the process using seven cyclotron bombarded Y metal foil targets. Once optimized, we found that 93.7 ± 2.3% of the ⁸⁹Zr present in the foils was recovered in the secondary column elution fraction (0.8 M oxalic acid). Radiochromatograms of the product elution peaks enabled determination of full width at half-maximum (FWHM) and ⁸⁹Zr collection yields as a function of volume. Because of the small size of the secondary microcolumn, a ⁸⁹Zr product volume of ∼0.28 mL is reported, which provides a substantially increased nuclide concentration over traditional methods. Finally, we evaluated the transchelation of the resulting ⁸⁹Zr oxalate product to deferoxamine mesylate (DFOM) salt. We observed effective specific activities (ESA) and bindable metals concentrations ([M_B]) that exceed those reported by the traditional single hydroxamate column method.

Radiolabeling of PSMA-617 with 89Zr: A novel use of DMSO to improve radiochemical yield and preliminary small-animal PET results

INTRODUCTION

Novel diagnostic and therapeutic options are urgently needed for patients with metastatic castration-resistant prostate cancer (CRPC). PSMA-617 is one of the most promising ligands that bind to prostate specific membrane antigen (PSMA), the cell surface biomarker of CRPC. Of the radiolabeled PSMA ligands developed to date, [⁶⁸Ga]Ga-PSMA-617 is most commonly used for PSMA positron emission tomography (PET) prior to radioligand therapy (RLT) with [¹⁷⁷Lu]Lu-PSMA-617. However, the presence of ⁶⁸Ga radioactivity (half-life 68 m) in urine at the early PET imaging time point complicates optimization of the therapeutic dose of PSMA-617 labeled with ¹⁷⁷Lu (half-life 6.7 d). Thus, PET imaging with the long-lived positron emitter ⁸⁹Zr (half-life 3.3 d) would be better suited in order to optimize the dose of [¹⁷⁷Lu]Lu-PSMA-617 as ⁸⁹Zr PET allows scans after excretion of the radioactive urine. Until now, PSMA-617 could not be radiolabeled with ⁸⁹Zr with high radiochemical yield due to poor incorporation of ⁸⁹Zr into 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). Here we report a novel method for radiolabeling PSMA-617 with ⁸⁹Zr and the preliminary results of small-animal PET with [⁸⁹Zr]Zr-PSMA-617.

METHODS

We labeled PSMA-617 with ⁸⁹Zr in a 1:1 mixture of DMSO and HEPES buffer at 90 °C for 30 min, followed by quality control analysis by HPLC. We then determined the dissociation constant (K_d) and logD values of [⁸⁹Zr]Zr-PSMA-617. We obtained PET images of [⁸⁹Zr]Zr-PSMA-617 at 24 h in mice bearing both LNCaP (PSMA-positive) and PC-3 (PSMA-negative) tumors (N = 5). The ex vivo [⁸⁹Zr]Zr-PSMA-617 biodistribution was then examined separately using tissue samples of LNCaP-bearing mice at 2 h (N = 4) and 24 h (N = 4).

RESULTS

[⁸⁹Zr]Zr-PSMA-617 was prepared with a radiochemical yield of 70 ± 9%. The K_d value was 6.8 ± 3.5 nM. The logD value was -4.05 ± 0.20. PET images showed the highest uptake in LNCaP tumors (maximum standardized uptake value, SUV_max = 0.98 ± 0.32) and low uptake in kidneys (SUV_max = 0.18 ± 0.7) due to the absence of urine radioactivity.

CONCLUSION

[⁸⁹Zr]Zr-PSMA-617 was successfully prepared using DMSO and HEPES buffer. [⁸⁹Zr]Zr-PSMA-617 visualized PSMA-positive LNCaP tumors in the absence of radioactive urine 24 h p.i.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This method of radiolabeling PSMA-617 with ⁸⁹Zr using DMSO would be suitable for future clinical trials. Prediction of radiation dose by using [⁸⁹Zr]Zr-PSMA-617 leads to the safe and effective RLT with [¹⁷⁷Lu]Lu-PSMA-617.

Side-by-Side Comparison of Five Chelators for 89Zr-Labeling of Biomolecules: Investigation of Chemical/Radiochemical Properties and Complex Stability

In this work, five different chelating agents, namely DFO, CTH-36, DFO*, 3,4,3-(LI-1,2-HOPO) and DOTA-GA, were compared with regard to the relative kinetic inertness of their corresponding ⁸⁹Zr complexes to evaluate their potential for in vivo application and stable ⁸⁹Zr complexation. The chelators were identically functionalized with tetrazines, enabling a fully comparable, efficient, chemoselective and biorthogonal conjugation chemistry for the modification of any complementarily derivatized biomolecules of interest. A small model peptide of clinical relevance (TCO-c(RGDfK)) was derivatized via iEDDA click reaction with the developed chelating agents (TCO = trans-cyclooctene and iEDDA = inverse electron demand Diels-Alder). The bioconjugates were labeled with ⁸⁹Zr⁴⁺, and their radiochemical properties (labeling conditions and efficiency), logD_(7.4), as well as the relative kinetic inertness of the formed complexes, were compared. Furthermore, density functional theory (DFT) calculations were conducted to identify potential influences of chelator modification on complex formation and geometry. The results of the DFT studies showed-apart from the DOTA-GA derivative-no significant influence of chelator backbone functionalization or the conjugation of the chelator tetrazines by iEDDA. All tetrazines could be efficiently introduced into c(RGDfK), demonstrating the high suitability of the agents for efficient and chemoselective bioconjugation. The DFO-, CTH-36- and DFO*-modified c(RGDfK) peptides showed a high radiolabeling efficiency under mild reaction conditions and complete ⁸⁹Zr incorporation within 1 h, yielding the ⁸⁹Zr-labeled analogs as homogenous products. In contrast, 3,4,3-(LI-1,2-HOPO)-c(RGDfK) required considerably prolonged reaction times of 5 h for complete radiometal incorporation and yielded several different ⁸⁹Zr-labeled species. The labeling of the DOTA-GA-modified peptide was not successful at all. Compared to [⁸⁹Zr]Zr-DFO-, [⁸⁹Zr]Zr-CTH-36- and [⁸⁹Zr]Zr-DFO*-c(RGDfK), the corresponding [⁸⁹Zr]Zr-3,4,3-(LI-1,2-HOPO) peptide showed a strongly increased lipophilicity. Finally, the relative stability of the ⁸⁹Zr complexes against the EDTA challenge was investigated. The [⁸⁹Zr]Zr-DFO complex showed-as expected-a low kinetic inertness. Unexpectedly, also, the [⁸⁹Zr]Zr-CTH-36 complex demonstrated a high susceptibility against the challenge, limiting the usefulness of CTH-36 for stable ⁸⁹Zr complexation. Only the [⁸⁹Zr]Zr-DFO* and the [⁸⁹Zr]Zr-3,4,3-(LI-1,2-HOPO) complexes demonstrated a high inertness, qualifying them for further comparative in vivo investigation to determine the most appropriate alternative to DFO for clinical application.

Cyclotron Production of PET Radiometals in Liquid Targets: Aspects and Prospects

The present review describes the methodological aspects and prospects of the production of Positron Emission Tomography (PET) radiometals in a liquid target using low-medium energy medical cyclotrons. The main objective of this review is to delineate and discuss the critical factors involved in the liquid target production of radiometals, including type of salt solution, solution composition, beam energy, beam current, the effect of irradiation duration (length of irradiation) and challenges posed by in-target chemistry in relation with irradiation parameters. We also summarize the optimal parameters for the production of various radiometals in liquid targets. Additionally, we discuss the future prospects of PET radiometals production in the liquid targets for academic research and clinical applications. Significant emphasis has been given to the production of ⁶⁸Ga using liquid targets due to the growing demand for ⁶⁸Ga labeled PSMA vectors, [⁶⁸Ga]- Ga-DOTATATE, [⁶⁸Ga]Ga-DOTANOC and some upcoming ⁶⁸Ga labeled radiopharmaceuticals. Other PET radiometals included in the discussion are ⁸⁶Y, ⁶³Zn and ⁸⁹Zr.

Preclinical Molecular PET-CT Imaging Targeting CDCP1 in Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignancy in the world, with 22% of patients presenting with metastatic disease and a further 50% destined to develop metastasis. Molecular imaging uses antigen-specific ligands conjugated to radionuclides to detect and characterise primary cancer and metastases. Expression of the cell surface protein CDCP1 is increased in CRC, and here we sought to assess whether it is a suitable molecular imaging target for the detection of this cancer. CDCP1 expression was assessed in CRC cell lines and a patient-derived xenograft to identify models suitable for evaluation of radio-labelled 10D7, a CDCP1-targeted, high-affinity monoclonal antibody, for preclinical molecular imaging. Positron emission tomography-computed tomography was used to compare zirconium-89 (⁸⁹Zr)-10D7 avidity to a nonspecific, isotype control ⁸⁹Zr-labelled IgGκ1 antibody. The specificity of CDCP1-avidity was further confirmed using CDCP1 silencing and blocking models. Our data indicate high avidity and specificity for of ⁸⁹Zr-10D7 in CDCP1 expressing tumors at. Significantly higher levels than normal organs and blood, with greatest tumor avidity observed at late imaging time points. Furthermore, relatively high avidity is detected in high CDCP1 expressing tumors, with reduced avidity where CDCP1 expression was knocked down or blocked. The study supports CDCP1 as a molecular imaging target for CRC in preclinical PET-CT models using the radioligand ⁸⁹Zr-10D7.

Re-Evaluations of Zr-DFO Complex Coordination Chemistry for the Estimation of Radiochemical Yields and Chelator-to-Antibody Ratios of 89Zr Immune-PET Tracers

(1) Background: Deferoxamine B (DFO) is the most widely used chelator for labeling of zirconium-89 (89Zr) to monoclonal antibody (mAb). Despite the remarkable developments of the clinical 89Zr-immuno-PET, chemical species and stability constants of the Zr-DFO complexes remain controversial. The aim of this study was to re-evaluate their stability constants by identifying species of Zr-DFO complexes and demonstrate that the stability constants can estimate radiochemical yield (RCY) and chelator-to-antibody ratio (CAR). (2) Methods: Zr-DFO species were determined by UV and ESI-MS spectroscopy. Stability constants and speciation of the Zr-DFO complex were redetermined by potentiometric titration. Complexation inhibition of Zr-DFO by residual impurities was investigated by competition titration. (3) Results: Unknown species, ZrHqDFO2, were successfully detected by nano-ESI-Q-MS analysis. We revealed that a dominant specie under radiolabeling condition (pH 7) was ZrHDFO, and its stability constant (logβ111) was 49.1 ± 0.3. Competition titration revealed that residual oxalate inhibits Zr-DFO complex formation. RCYs in different oxalate concentration (0.1 and 0.04 mol/L) were estimated to be 86% and >99%, which was in good agreement with reported results (87%, 97%). (4) Conclusion: This study succeeded in obtaining accurate stability constants of Zr-DFO complexes and estimating RCY and CAR from accurate stability constants established in this study.

Production of a broad palette of positron emitting radioisotopes using a low-energy cyclotron: Towards a new success story in cancer imaging?

Over the last several years, positron emission tomography (PET) has matured as an indispensable component of cancer diagnostics. Owing to the large variability observed among the cancer patients and the need to personalize individual patient's diagnosis and treatment, the need for new positron emitting radioisotopes has continued to grow. This mini review opens with a brief introduction to the criteria for radioisotope selection for PET imaging. Subsequently, positron emitting radioisotopes are categorized as: established, emerging and futuristic, based on the stages of their advancement. The production methodologies and the radiochemical separation procedures for obtaining the important radioisotopes in a form suitable for preparation of radiopharmaceuticals for PET imaging are briefly discussed.

Expanding PET-applications in life sciences with positron-emitters beyond fluorine-18

Positron-emission-tomography (PET) has become an indispensable diagnostic tool in modern nuclear medicine. Its outstanding molecular imaging features allow repetitive studies on one individual and with high sensitivity, though no interference. Rather few positron-emitters with near favourable physical properties, i.e. carbon-11 and fluorine-18, furnished most studies in the beginning, preferably if covalently bound as isotopic label of small molecules. With the advancement of PET-devices the scope of in vivo research in life sciences and especially that of medical applications expanded, and other than "standard" PET-nuclides received increasing significance, like the radiometals copper-64 and gallium-68. Especially during the last decades, positron-emitters of other chemical elements have gotten into the focus of interest, concomitant with the technical advancements in imaging and radionuclide production. With known nuclear imaging properties and main production methods of emerging positron-emitters their usefulness for medical application is promising and even proven for several ones already. Unfortunate decay properties could be corrected for, and β+-emitters, especially with a longer half-life, provided new possibilities for application where slower processes are of importance. Further on, (bio)chemical features of positron-emitters of other elements, among there many metals, not only expanded the field of classical clinical investigations, but also opened up new fields of application. Appropriately labelled peptides, proteins and nanoparticles lend itself as newer probes for PET-imaging, e.g. in theragnostic or PET/MR hybrid imaging. Furthermore, the potential of non-destructive in-vivo imaging with positron-emission-tomography directs the view on further areas of life sciences. Thus, exploiting the excellent methodology for basic research on molecular biochemical functions and processes is increasingly encouraged as well in areas outside of health, such as plant and environmental sciences.

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.

Preparation of Zirconium-89 Solutions for Radiopharmaceutical Purposes: Interrelation Between Formulation, Radiochemical Purity, Stability and Biodistribution

Zirconium-89 is a promising radionuclide for nuclear medicine. The aim of the present work was to find a suitable method for obtaining zirconium-89 solutions for radiopharmaceutical purposes. For this purpose, the ion exchange behavior of zirconium-89 solutions was studied. Radio-TLC (thin layer chromatography) and biodistribution studies were carried out to understand speciation of zirconium-89 complexes and their role in the development of new radiopharmaceuticals. Three methods of zirconium-89 isolation were studied using ZR (hydroxamate) and Chelex-100 resins. It was found that ZR-resin alone is not enough to obtain stable zirconium-89 formulations. An easy and effective method of reconstitution of [⁸⁹Zr]Zr-oxalate to [⁸⁹Zr]Zr-citrate using Chelex-100 resin was developed. Developed procedures allow obtaining [⁸⁹Zr]Zr-oxalate (in 0.1 M sodium oxalate solution) and [⁸⁹Zr]Zr-citrate (in 0.1–1.0 M sodium citrate solution). These solutions are perfectly suitable and convenient for radiopharmaceutical purposes. Our results prove [⁸⁹Zr]Zr-citrate to be advantageous over [⁸⁹Zr]Zr-oxalate. During evaluation of speciation of zirconium-89 complexes, a new TLC method was developed, since it was proved that there is no comprehensive method for analysis or zirconium-89 preparations. The new method provides valuable insights about the content of “active” ionic form of zirconium-89. The interrelation of the chromatographic behavior of zirconium-89 preparations and their biodistribution was studied.

89Zr-Chloride Can Be Used for Immuno-PET Radiochemistry Without Loss of Antigen Reactivity In Vivo

⁸⁹Zr immuno-PET continues to be assessed in numerous clinical trials. This report evaluates the use of ⁸⁹Zr-chloride in the radiolabeling of monoclonal antibodies conjugated with desferrioxamine B (DFO), describes its effects on radiopharmaceutical reactivity toward antigen, and offers guidance on how to ensure long-term stability and purity. Methods: ⁸⁹Zr-DFO-trastuzumab and ⁸⁹Zr-DFO-cetuximab were prepared using ⁸⁹ZrCl₄ The stability of each was evaluated for 7 d in 20 mM histidine/240 mM sucrose buffer, 0.25 M sodium acetate (NaOAc) buffer containing 5 mg·mL^-1 n-acetyl-l-cysteine (NAC), or 0.25 M NaOAc containing 5 mg·mL^-1 l-methionine (L-MET). To assess antigen reactivity, ⁸⁹Zr-DFO-trastuzumab was evaluated using the Lindmo method and tested in PET/CT imaging of mouse models of human epidermal growth factor receptor 2-positive or -negative lung cancer. Results: Using ⁸⁹ZrCl₄, ⁸⁹Zr-DFO-trastuzumab and ⁸⁹Zr-DFO-cetuximab were prepared with increased specific activity and retained purities of 95% after 3 d when formulated in NaOAc buffer containing L-MET. Based on Lindmo analysis and small-animal PET/CT imaging, ⁸⁹Zr-DFO-trastuzumab remained reactive toward antigen after being prepared with ⁸⁹ZrCl₄ Conclusion: ⁸⁹ZrCl₄ facilitated the radiosynthesis of ⁸⁹Zr immuno-PET agents with increased specific activity. L-MET enhanced long-term solution stability better than all other formulations examined, and ⁸⁹Zr-DFO-trastuzumab remained reactive toward antigen. Although further evaluation is necessary, these initial results suggest that ⁸⁹ZrCl₄ may be useful in immuno-PET radiochemistry as radiolabeled monoclonal antibodies are increasingly integrated into precision medicine strategies.