EJNMMI Radiopharmacy and Chemistry最新文献

Background

Radiopharmaceutical therapy (RPT) uses radionuclides that decay via one of three therapeutically relevant decay modes (alpha, beta, and internal conversion (IC) / Auger electron (AE) emission) to deliver short range, highly damaging radiation inside of diseased cells, maintaining localized dose distribution and sparing healthy cells. Antimony-119 (¹¹⁹Sb, t_1/2 = 38.19 h, EC = 100%) is one such IC/AE emitting radionuclide, previously limited to in silico computational investigation due to barriers in production, chemical separation, and chelation. A theranostic (therapeutic/diagnostic) pair can be formed with ¹¹⁹Sb’s radioisotopic imaging analogue ¹¹⁷Sb (t_1/2 = 2.80 h, E_γ = 158.6 keV, I_γ = 85.9%, β⁺ = 262.4 keV, I_β+ = 1.81%).

Results

Within, we report techniques for sustainable and cost-effective production of pre-clinical quality and quantity, radionuclidically pure ¹¹⁹Sb and ¹¹⁷Sb, novel low energy photon measurement techniques for ¹¹⁹Sb activity determination, and physical yields for various tin target isotopic enrichments and thicknesses using (p, n) and (d, n) nuclear reactions. Additionally, we present a two-column separation providing a radioantimony yield of 73.1% ± 6.9% (N = 3) and tin separation factor of (6.8 ± 5.5) x 10⁵ (N = 3). Apparent molar activity measurements for deuteron produced ¹¹⁷Sb using the chelator TREN-CAM were measured at 42.4 ± 25 MBq ¹¹⁷Sb/µmol (1.14 ± 0.68 mCi/µmol), and we recovered enriched ¹¹⁹Sn target material at a recycling efficiency of 80.2% ± 5.5% (N = 6) with losses of 11.6 mg ± 0.8 mg (N = 6) per production.

Conclusion

We report significant steps in overcoming barriers in ¹¹⁹Sb production, chemical isolation and purification, enriched target material recycling, and chelation, helping promote accessibility and application of this promising therapeutic radionuclide. We describe a method for ¹¹⁹Sb activity measurement using its low energy gamma (23.87 keV), negating the need for attenuation correction. Finally, we report the largest yet-measured ¹¹⁹Sb production yields using proton and deuteron irradiation of natural and enriched targets and radioisotopic purity > 99.8% at end of purification.

Background

In the central nervous system, type 2 vesicular monoamine transporters (VMAT2) are responsible for the reuptake of monoamines from synaptic junction back to pre-synaptic terminal vesicles. These transporters are functionally crucial as they reflect the integrity of monoamine neurons. D6-[¹⁸F]FP-(+)-DTBZ, a novel deuterated VMAT2 radioligand, has shown promise as a potential PET tracer for the diagnosis of Parkinson’s disease (PD). This study evaluates the biodistribution and dosimetry of D6-[¹⁸F]FP-(+)-DTBZ and includes a head-to-head comparison with its non-deuterated version, [¹⁸F]FP-(+)-DTBZ (AV-133), in healthy individuals and PD patients.

Results

The automated synthesis of D6-[¹⁸F]FP-(+)-DTBZ using the SPE method was accomplished in 35 min, yielding a high radiochemical purity (> 99%) and high radiochemical yields (35 ± 5%). The biodistribution and dosimetry study indicated an effective dose of 37.1 ± 7.2 μSv/MBq, with the liver receiving the highest radiation dose (289.6 ± 42.1 μGy/MBq), followed by pancreas (185.2 ± 29.1 μGy/MBq). Brain imaging with D6-[¹⁸F]FP-(+)-DTBZ exhibited a significantly increased uptake in VMAT2-rich regions, particularly the striatum. In a head-to-head comparison between [¹⁸F]FP-(+)-DTBZ and D6-[¹⁸F]FP-(+)-DTBZ, the latter exhibited approximately 15% higher SUVR in the caudate, putamen, and nucleus accumbens. Preliminary studies in PD patients showed a substantial reduction in VMAT2 uptake in the striatum, with the most pronounced decrease observed in the putamen (a 53% decline).

Conclusions

D6-[¹⁸F]FP-(+)-DTBZ is a safe and improved VMAT2-specific imaging agent, which may be suitable for diagnosing PD by evaluating changes in VMAT2 binding of monoamine neurons in the brain.

Trial registration Chinese Clinical Trial Registry, ChiCTR2200057218, Registered 16 August 2021, https://www.chictr.org.cn/bin/project/edit?pid=142725.

Background

Technetium-99 m-labelled macroaggregated human serum albumin ([99mTc]Tc-MAA) is commonly used for lung perfusion scintigraphy. The European Pharmacopoeia (Eu.Ph.) specifies thin-layer chromatography (TLC) as the only method to assess its radiochemical purity (RCP). Similarly, TLC is the sole method reported in the literature to evaluate the RCP of Gallium-68-labelled MAA [⁶⁸ Ga]Ga-MAA, recently introduced for lung perfusion PET/CT imaging. Since [⁶⁸ Ga]Ga-MAA is prepared from commercial kits originally designed for the preparation of [99mTc]Tc-MAA, it is essential to optimize and validate the preparation methods for [⁶⁸ Ga]Ga-MAA.

Results

We tested a novel, simplified method for the preparation of [⁶⁸ Ga]Ga-MAA that does not require organic solvents, prewash or final purification steps to remove radioactive impurities. We assessed the final product using radio-TLC, radio-UV-HPLC, and radio SDS-PAGE. Overall, our quality control (QC) method successfully detected [⁶⁸ Ga]Ga-MAA along with all potential impurities, including free Ga-68, [⁶⁸ Ga]Ga-HSA, unlabeled HSA, which may occur during labelling process and HEPES residual, a non-toxic but non-human-approved contaminant, used as buffer solution. We then applied our QC system to [⁶⁸ Ga]Ga-MAA prepared under different conditions (25°–40°–75°–95 °C), thus defining the optimal temperature for labelling. Scanning Electron Microscopy (SEM) analysis of the products obtained through our novel method confirmed that most [⁶⁸ Ga]Ga-MAA particles preserved the morphological structure and size distribution of unlabeled MAA, with a particle diameter range of 25–50 μm, assuring diagnostic efficacy.

Conclusions

We optimized a novel method to prepare [⁶⁸ Ga]Ga-MAA through a QC system capable of monitoring all impurities of the final products.

Background

²¹¹At-radiopharmaceuticals are currently the subject of growing studies for targeted alpha therapy of cancers, which leads to the widening of the scope of the targeting vectors, from small molecules to peptides and proteins. This has prompted, during the past decade, to a renewed interest in developing novel ²¹¹At-labelling approaches and novel prosthetic groups to address the diverse scenarios and to reach improved efficiency and robustness of procedures as well as an appropriate in vivo stability of the label.

Main body

Translated from the well-known (radio)iodine chemistry, the long preferred electrophilic astatodemetallation using trialkylaryltin precursors is now complemented by new approaches using electrophilic or nucleophilic At. Alternatives to the astatoaryl moiety have been proposed to improve labelling stability, and the range of prosthetic groups available to label proteins has expanded.

Conclusion

In this report, we cover the evolution of radiolabelling chemistry, from the initial strategies developed in the late 1970’s to the most recent findings.

Background

Gastroparesis (GP) is a prevalent sensorimotor disorder characterized by delayed gastric emptying without mechanical obstruction, posing significant diagnostic challenges. Gastric emptying scintigraphy (GES) is the gold standard for diagnosing GP. However, its accuracy can be compromised by many medications that affect gastric motility. This study evaluates the impact of medication reconciliation on the diagnostic accuracy of GES.

Results

A significant proportion of patients (75%) were on medications known to affect gastric motility. Recommendations for medication adjustments were communicated, with 30% non-adherence. Adjustments in GES interpretations were necessary for 20% of patients following comprehensive medication reviews. The involvement of radiopharmacists facilitated accurate diagnostic conclusions, underscoring the critical role of medication reconciliation in GES accuracy.

Conclusion

Medication reconciliation enhanced the accuracy of GES in diagnosing gastroparesis, emphasizing the need to integrate clinical pharmacy practices into nuclear medicine. This interdisciplinary approach not only improves diagnostic accuracy but also enhances patient safety, advocating for the adoption of such practices in the management of gastroparesis.

Background

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

Main body

This selection of highlights provides commentary on 19 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first-in-human application of novel radiopharmaceuticals.

Conclusion

Trends in radiochemistry and radiopharmacy are highlighted. Hot topics cover the entire scope of EJNMMI Radiopharmacy and Chemistry, demonstrating the progress in the research field in many aspects.

Background

A novel positron emission tomography (PET) imaging tracer, [¹⁸F] SynVesT-1, targeting synaptic vesicle glycoprotein 2 (SV2A), has been developed to meet clinical demand. Utilizing the Trasis AllinOne-36 (AIO) module, we’ve automated synthesis to Good Manufacturing Practice (GMP) standards, ensuring sterile, pyrogen-free production. The fully GMP-compliant robust synthesis of [¹⁸F] SynVesT-1 boosting reliability and introducing a significant degree of simplicity and its comprehensive validation for routine human use.

Results

[¹⁸F] SynVesT-1 was synthesized by small modifications to the original [¹⁸F] SynVesT-1 synthesis protocol to better fit AIO module using an in-house designed cassette and sequence. With a relatively small precursor load of 5 mg, [¹⁸F] SynVesT-1 was obtained with consistently high radiochemical yields (RCY) of 20.6 ± 1.2% (the decay-corrected RCY, n = 3) at end of synthesis. Each of the final formulated batches demonstrated radiochemical purity (RCP) and enantiomeric purity surpassing 99%. The entire synthesis process was completed within a timeframe of 80 min (75 ± 3.1 min, n = 3), saves 11 min compared to reported GMP automated synthesis procedures. The in-human PET imaging of total body PET/CT and time-of-flight (TOF) PET/MR showed that [¹⁸F] SynVesT-1 is an excellent tracer for SV2A. It is advantageous for decentralized promotion and application in multi-center studies.

Conclusion

The use of AIO synthesizer maintains high production yields and increases reliability, reduces production time and allows rapid training of production staff. Besides, the as-prepared [¹⁸F] SynVesT-1 displays excellent in vivo binding properties in humans and holds great potential for the imaging and quantification of synaptic density in vivo.

Background

Radiopharmaceuticals have been considered a special group of medicines in Europe since 1989. The use of radiopharmaceuticals that have marketing authorization should always be the first option in clinical use, however due to their special properties the availability of approved radiopharmaceuticals is limited. For this reason, they can be produced on a small scale outside the marketing authorization process.

Main body

The in-house radiopharmaceutical preparations represent an important source of these special medicines for routine nuclear medicine practice. However, a lack of harmonization in Member States’ regulations leads to extreme differences in the use and availability of radiopharmaceuticals across Europe. The aim of this work is to provide an overview of the different national regulatory frameworks in which Directive 2001/83/UE is adopted on the preparation of radiopharmaceuticals outside the marketing authorization track in Europe. Nine different national regulations have been studied to describe how unlicensed radiopharmaceuticals are prepared. Special attention is paid to reflect the minimum standards that these preparations should meet as well as the educational requirements to be a radiopharmacist in charge of them.

Conclusion

The rapid development of new radiopharmaceuticals used in radiometabolic therapy requires a common regulation that allows balance between the use and preparation of licensed and unlicensed radiopharmaceuticals. The absence of a harmonized regulation for the radiopharmaceutical small-scale preparation and the implementation of Good Manufacture Practices, leads to extreme differences in the use, quality assurance and availability of radiopharmaceuticals in Europe.

Background

Selection of the most promising radiotracer candidates for radiolabeling is a difficult step in the development of radiotracer pharmaceuticals, especially for the brain. Mass spectrometry (MS) is an alternative to study ex vivo the characteristics of candidates, but most MS studies are complicated by the pharmacologic doses injected and the dissection of regions to study candidate biodistribution. In this study, we tested the ability of a triple quadrupole analyzer (TQ LC–MS/MS) to quantify low concentrations of a validated precursor of a radiotracer targeting the DAT (LBT-999) in dissected regions. We also investigated its biodistribution on brain slices using MS imaging with desorption electrospray ionization (DESI) coupled to time-of-flight (TOF) vs. TQ mass analyzers.

Results

TQ LC–MS/MS enabled quantification of LBT-999 injected at sub-tracer doses in dissected striata. DESI-MS imaging (DESI-MSI) with both analyzers provided images of LBT-999 biodistribution on sagittal slices that were consistent with positron emission tomography (PET). However, the TOF analyzer only obtained biodistribution images at a high injected dose of LBT-999, while the TQ analyzer provided biodistribution images at lower injected doses of LBT-999 with a better signal-to-noise ratio. It also allowed simultaneous visualization of endogenous metabolites such as dopamine.

Conclusions

Our results show that LC-TQ MS/MS in combination with DESI-MSI can provide important information (biodistribution, specific and selective binding) that can facilitate the selection of the most promising candidates for radiolabeling and support the development of radiotracers.