Evaluating N-difluoromethyltriazolium triflate as a precursor for the synthesis of high molar activity [18F]fluoroform

The trifluoromethyl group is a prominent motif in biologically active compounds and therefore of great interest for the labeling with the positron emitter fluorine-18 for positron emission tomography (PET) imaging. Multiple labeling strategies have been explored in the past; however, most of them suffer from low molar activity due to precursor degradation. In this study, the potential of 1-(difluoromethyl)-3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium triflate as precursor for the synthesis of the [18F]trifluoromethylation building block [18F]fluoroform with high molar activity was investigated. The triazolium precursor was reacted under various conditions with [18F]fluoride, providing [18F]fluoroform with radiochemical yields (RCY) and molar activities (Am) comparable and even superior with already existing methods. Highest molar activities (Am = 153 ± 14 GBq/μmol, dc, EOS) were observed for the automated procedure on the Neptis® perform module. Due to its easy handling and good RCY and Am in the [18F]fluoroform synthesis, the triazolium precursor is a valuable alternative to already known precursors

Fully Automated 89 Zr 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

Synthesis and evaluation of [18F]cinacalcet for the imaging of parathyroid hyperplasia

Introduction: Parathyroid hyperplasia is a disease characterized by overactive parathyroid glands secreting increased levels of parathyroid hormone. Surgical removal of the parathyroid glands is the standard treatment but requires precise pre-operative localization of the glands. However, currently available imaging modalities show limited sensitivity. Since positron emission tomography (PET) is a molecular imaging technique with high accuracy and sensitivity, our aim was to develop a new PET tracer for overactive parathyroid glands imaging by radiolabelling cinacalcet, a drug binding to the calcium-sensing receptor of the parathyroid glands. Methods: [18F]Cinacalcet was synthesized by copper-catalysed [18F]trifluoromethylation of a boronic acid precursor using high molar activity [18F]fluoroform. Ex vivo biodistribution and metabolism were evaluated in 12 healthy male Wistar rats at 5, 15, 45 and 90 min. PET scans were performed at baseline and after blocking with NPS R-568. Results: [18F]Cinacalcet was obtained in an overall radiosynthesis time of 1 h with a radiochemical purity of 98 ± 1%, a radiochemical yield of 8 ± 4% (overall, n = 7, corrected for decay) and a molar activity of 40 ± 11 GBq/μmol (n = 7, at EOS). The ex vivo biodistribution showed uptake in the thyroid and parathyroid glands as well as in other glands such as adrenals, salivary glands and pancreas. The tracer was rapidly cleared from the blood via liver and kidneys and showed fast metabolism. PET images confirmed uptake in the target organ. However, in a blocking study with NPS R-568 specific binding of [18F]cinacalcet to the CaSR could not be confirmed. Conclusions: [18F]Cinacalcet was successfully synthesized. First in vivo experiments in healthy rats showed uptake of the tracer in the target organ and fast metabolism, encouraging further in vivo evaluation of this tracer

Preparation and evaluation of 89Zr-Zevalin for monitoring of 90Y-Zevalin biodistribution with positron emission tomography

Purpose: To evaluate whether 89Zr can be used as a PET surrogate label for quantification of 90Y-ibritumomab tiuxetan ( 90Y-Zevalin) biodistribution and dosimetry before myeloablative radioimmunotherapy. Methods: Zevalin was labelled with 89Zr by introducing N-succinyldesferal (N-sucDf) as a second chelate. For comparison of the in vitro stability of 89Zr-Zevalin and 88Y-Zevalin (as a substitute for 90Y), samples were incubated in human serum at 37°C up to 6 days. Biodistribution of 89Zr-Zevalin and 88Y-Zevalin was assessed at 24, 48, 72 and 144 h p.i. by co-injection in nude mice bearing the non-Hodgkin's lymphoma (NHL) xenograft line Ramos. The clinical performance of 89Zr-Zevalin-PET was evaluated via a pilot imaging study in a patient with NHL, who had undergone [18F]FDG-PET 2 weeks previously. Results: Modification of Zevalin with N-sucDf resulted in an N-sucDf-to-antibody molar ratio of 0.83±0.04. After radiolabelling and purification, the radiochemical purity and immunoreactivity of 89Zr-Zevalin always exceeded 95% and 80%, respectively. 89Zr-Zevalin showed the same stability in serum as 88Y-Zevalin, with a radiochemical purity >95% during a period of 6 days. The co-injected 89Zr-Zevalin and 88Y-Zevalin conjugates showed a very similar biodistribution, except for liver and bone accumulation at 72 and 144 h p.i., which was significantly higher for 89Zr than for 88Y. PET images obtained after injection of 89Zr-Zevalin showed clear targeting of all known tumour lesions. Conclusion: 89Zr-Zevalin and 88Y-Zevalin showed a very similar biodistribution in mice, implying that 89Zr-Zevalin-PET might be well suited for prediction of 90Y-Zevalin biodistribution in a myeloablative setting