EJNMMI Radiopharmacy and Chemistry最新文献

Background

Strategies that focus on delivering Auger electron emitters to highly radiosensitive intracellular targets—such as the nucleus, cell membrane, or mitochondria—are gaining attention. Targeting these organelles could enhance therapeutic efficacy while minimizing off-target toxicity by allowing lower administered doses. In this context, this study explores the therapeutic potential of ¹⁶¹Tb-labeled radiocomplexes that integrate the mitochondria-targeting triphenylphosphonium (TPP) moiety with a prostate-specific membrane antigen (PSMA) targeting vector. The goal is to assess these dual-targeted radiocomplexes for their ability to deliver conversion electrons (CE) and Auger electrons (AEs) to prostate cancer (PCa) cells, specifically targeting the mitochondria to enhance therapeutic efficacy.

Results

Two novel radiocomplexes, [¹⁶¹Tb]Tb-TPP-PSMA and [¹⁶¹Tb]Tb-TPP-G₃-PSMA, were synthesized with high radiochemical yield and purity. The proposed structures were validated using HPLC and ESI-MS analysis, with their ^natTb counterparts serving as reference compounds. In vitro experiments included cellular uptake, internalization, mitochondrial uptake, and DNA damage assays in PSMA-positive PCa cell lines. Clonogenic assays were performed to evaluate cell survival post-treatment. In vivo studies were conducted using SCID/Beige mice bearing PCa xenografts and involved µSPECT/CT imaging and radiometabolite analysis to evaluate biodistribution, pharmacokinetics, tumor uptake and in vivo stability of the radiocomplexes. Both [¹⁶¹Tb]Tb-TPP-PSMA and [¹⁶¹Tb]Tb-TPP-G₃-PSMA showed high radiochemical stability and were efficiently internalized by PSMA-positive cells, while showing minimal uptake in PSMA-negative cells. These dual-targeted radiocomplexes demonstrated significantly higher mitochondrial uptake compared to the non-TPP-containing [¹⁶¹Tb]Tb-PSMA-617, leading to increased DNA damage and enhanced radiocytotoxicity. In vivo, the dual-targeted complexes demonstrated PSMA-specific tumor uptake and pharmacokinetics comparable to [¹⁶¹Tb]Tb-PSMA-617, with effective clearance from non-target tissues.

Conclusions

The TPP-modified ¹⁶¹Tb-radiocomplexes effectively targeted the mitochondria of PSMA-positive PCa cells, leading to increased DNA damage and reduced cell viability compared to single-targeted radiocomplexes. These findings suggest that dual-targeting strategies, which combine PSMA and mitochondrial targeting, can enhance the therapeutic potential of radiopharmaceuticals for prostate cancer treatment.

Background

[¹¹C]TGN-020 has been developed as a positron emission tomography (PET) tracer for imaging aquaporin-4 (AQP4) in the brain and used in clinical studies. Previously, [¹¹C]TGN-020 was synthesized through the acylation of [¹¹C]nicotinic acid, produced by the reaction of 3-bromopyridine and n-butyllithium with [¹¹C]CO₂, with 2-amino-1,3,4-thiadiazole. In this study, to enhance the automated radiosynthesis efficiency of [¹¹C]TGN-020, we optimized its radiosynthesis procedure using our in-house developed ¹¹C-labeling synthesizer.

Results

[¹¹C]TGN-020 was synthesized via direct [¹¹C]CO₂ fixation using n-butyllithium and 3-bromopyridine in tetrahydrofuran, followed by treatment of lithium [¹¹C]nicotinic acetate with isobutyl chloroformate and subsequent acylation with 2-amino-1,3,4-thiadiazole in the presence of N,N-diisopropylethylamine. The optimized process significantly improved the radiosynthesis efficiency of [¹¹C]TGN-020, achieving a high radiochemical yield based on [¹¹C]CO₂ (610‒1700 MBq, 2.8 ± 0.7%) at the end of synthesis (n = 12) and molar activity (A_m) of 160–360 GBq/μmol at the end of synthesis (n = 5). The radiosynthesis time and radiochemical purity were approximately 60 min and > 95% (n = 12), respectively. PET studies based on [¹¹C]TGN-020 with different A_m values were performed using healthy rats. The radioactive uptake of [¹¹C]TGN-020 with high A_m in the cerebral cortex was slightly higher than that with low A_m.

Conclusions

[¹¹C]TGN-020 with high A_m was obtained in reproducible radiochemical yield. Overall, the proposed optimization process for the radiosynthesis of [¹¹C]TGN-020 can facilitate its application as a PET radiopharmaceutical for clinical use.

Background

Overexpression of human epidermal growth factor receptor type 2 (HER2) occurs in multiple carcinomas. For example, up to 20% of breast cancer cases are classified as HER2 positive (HER2+). Treatment of this condition typically involves immunotherapy using monoclonal antibodies, such as trastuzumab or pertuzumab. The precise targeting of monoclonal antibodies to HER2+ tumour lesions can be used as well in radioimmunotherapy to deliver medical radionuclides exactly to the afflicted area and therefore minimize radiation exposure of healthy tissues. In this study, DOTA conjugates of monoclonal antibodies trastuzumab and pertuzumab were prepared and tested in vitro. One of these, ²²⁵Ac-DOTA-pertuzumab, was also the subject of an ex vivo biodistribution study with normal as well as HER2+ and HER2- tumour-xenografted mice. This radioconjugate has not been previously described.

Results

Three DOTA-conjugates of HER2 targeting monoclonal antibodies, one of trastuzumab and two of pertuzumab, were prepared and radiolabelled with ²²⁵Ac in different molar ratios. This procedure led to an optimisation of the preparation and radiolabelling process. The radioconjugates were shown to be highly stable in vitro in both fetal bovine serum and phosphate buffered saline under room temperature and decreased temperature for 10 days. In vitro cell studies with HER2-overexpressing cell-line (SKOV-3) and low HER2-expressing cell line (MDA-MB-231) proved that radioconjugates of both antibodies have high binding specificity and affinity towards HER2 receptors. These findings were confirmed for a novel radioconjugate ²²⁵Ac-DOTA-pertuzumab in an ex vivo biodistribution study, where uptake in HER2+ tumour was 50 ± 14% ID/g and HER2- tumour showed uptake comparable with healthy tissues (max. 5.0 ± 1.7% ID/g). The high uptake observed in the spleen can be attributed to the elimination of the antibody, as well as the use of an immunedeficient mouse strain (SCID).

Conclusions

During this study, the optimization of preparation and radiolabelling of HER2 targeting antibodies with ²²⁵Ac was accomplished. Furthermore, the radioconjugate ²²⁵Ac-DOTA-pertuzumab was prepared and evaluated for the first time. The radioconjugates of both tested antibodies demonstrated excellent qualities in terms of stability and HER2 receptor affinity. Initial ex vivo studies indicated that especially the radioconjugate ²²⁵Ac-DOTA-pertuzumab is a very promising candidate for further more detailed in vivo studies.

Background

Non-steroidal anti-inflammatory drugs (NSAIDs), such as diclofenac, are globally recognized as the primary choice for alleviating kidney pain and ureteric colic. This study examines the effects of long-term diclofenac administration on renography using two radiopharmaceuticals: 99mTc-mercaptoacetyltriglycine (99mTc-MAG3), which is excreted almost exclusively by the renal tubules, and 99mTc-diethylenetriamine pentaacetic acid (99mTc-DTPA), which is predominantly excreted by glomerular filtration.

Results

Diclofenac administration caused a rightward shift in renograms, indicating delayed renal uptake and clearance for both tracers. For 99mTc-MAG3, the average time to peak activity (Tmax) increased from 2.88 ± 0.3 min (control) to 4.2 ± 0.3 min (treated), while time from peak to 50% activity (T½) rose from 4.16 ± 0.1 min to 5.48 ± 0.5 min. For 99mTc-DTPA, Tmax increased from 4.3 ± 0.4 min to 12.9 ± 2.0 min, and T½ extended from 13.35 ± 1.5 min to 29.75 ± 2.0 min (n = 12; *p < 0.05 for all comparisons). Delayed tracer arrival in the bladder was particularly pronounced with 99mTc-DTPA.

Conclusions

Chronic diclofenac exposure significantly delays Tmax and T½ for both tracers, with a greater impact observed using 99mTc-DTPA. These findings highlight 99mTc-MAG3 as the preferred radiopharmaceutical for renography in settings involving long-term NSAID administration, ensuring accurate and reliable interpretation and minimizing variability associated with radiopharmaceutical selection.

Background

The gastrin-releasing peptide receptor (GRPR) is overexpressed in the majority of primary prostate cancer lesions, with persistent expression in lymph nodes and bone metastases, making it a legitimate molecular target for diagnostic imaging and staging. This study presents the synthesis and preclinical evaluation of [¹⁸F]MeTz-PEG₂-RM26, a GRPR antagonist which utilises the Inverse Electron Demand Diels-Alder (IEDDA) reaction for ¹⁸F-labelling. This click-chemistry approach allows for site-specific incorporation of fluorine-18 under mild conditions, preserving the peptide’s structural integrity and biological activity. Receptor specificity and affinity of [¹⁸F]MeTz-PEG₂-RM26 were evaluated in vitro using GRPR-expressing PC-3 cells. Furthermore, the biodistribution profile of [¹⁸F]MeTz-PEG₂-RM26 was assessed in NMRI mice and its tumour-targeting capability was investigated in mice bearing PC-3 xenografts.

Results

The labelling of TCO-PEG₂-RM26 precursor involved three steps: (1) synthesis of an ¹⁸F-labelled activated ester on a quaternary methyl ammonium (QMA) cartridge, (2) conjugation of the labelled ester to a tetrazine amine, and (3) attachment to TCO-PEG₂-RM26 via an IEDDA click reaction. This production method of [¹⁸F]MeTz-PEG₂-RM26 afforded a high apparent molar activity of 3.5–4.3 GBq/µmol and radiochemical purity exceeding 98%, with 43–70 MBq activity incorporation, while the entire synthesis was completed within 75 min. Both in vitro and in vivo studies confirmed the specific binding of [¹⁸F]MeTz-PEG₂-RM26 to GRPR, with a significant reduction in activity uptake observed upon receptor saturation. The radioligand exhibited rapid blood clearance and minimal bone uptake, confirming the stability of the fluorine-carbon bond. However, high hepatic uptake (12–13% IA/g at 1 h post-injection) indicated predominant hepatobiliary excretion. Receptor-mediated uptake was observed in the tumours and pancreatic tissue, although the overall activity uptake in tumours was low, likely due to the rapid hepatobiliary clearance of [¹⁸F]MeTz-PEG₂-RM26.

Conclusions

These findings demonstrate the effectiveness of the IEDDA click reaction for fluorine-18 labelling of GRPR-targeting PET tracers. Future studies should focus on increasing the hydrophilicity of the imaging probe to improve the targeting properties and biodistribution profile of the radioligand.

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 and application of radiopharmaceuticals.

Main body

This selection of highlights provides commentary on 24 different topics selected by each co-authoring 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

Prostate cancer (PC) has a 34% 5-year survival rate after progressing to metastatic castration-resistant prostate cancer (mCRPC), which occurs in 20–30% of cases. Treatments like chemotherapy, immunotherapy, and PSMA-targeted radioligand therapy (RLT) show promise, but challenges remain with tumor resistance, side effects, and dose-limiting toxicity in kidneys and bone marrow. This study investigated the hematotoxicity, treatment efficacy, and recovery after [¹⁷⁷Lu]Lu-PSMA-617 and [²²⁵Ac]Ac-PSMA-617 treatment in a syngeneic PC mouse model.

Method

Twenty-five male C57BL/6 mice were inoculated with RM1-PGLS cells and monitored using [⁶⁸Ga]Ga-PSMA-11 PET/CT. The mice were divided into five groups as follows: (1) [²²⁵Ac]Ac-PSMA-617 treatment with tumors, (2) [¹⁷⁷Lu]Lu-PSMA-617 treatment with tumors, (3) control group with tumors, (4) [²²⁵Ac]Ac-PSMA-617 treatment without tumors, and (5) [¹⁷⁷Lu]Lu-PSMA-617 treatment without tumors. Tumor volume was measured weekly, and animals were sacrificed when tumors reached 1.5 cm³. Endpoint criteria included tumor size, survival, and body mass. Blood samples were collected at different time points to assess blood cell counts and liver and kidney function.

Results

Both treatments significantly slowed tumor progression and extended survival. [²²⁵Ac]Ac-PSMA-617-treated mice had a median survival of 70 days, compared to 58 days for [¹⁷⁷Lu]Lu-PSMA-617-treated mice and 30 days for the control group. Tumor volumes were significantly reduced in both treatment groups (P < 0.05). Hematological analysis showed that both treatments reduced WBCs, RBCs, and platelets, but values normalized within 35–42 days. Liver and kidney functions remained unaffected, and no significant renal or hepatic toxicity was observed.

Conclusion

Both [²²⁵Ac]Ac-PSMA-617 and [¹⁷⁷Lu]Lu-PSMA-617 caused transient hematotoxicity without prolonged effects. The data do not explicitly support the necessity of immunocompetent models for studying therapeutic outcomes in this context. Future studies incorporating immune profiling are warranted to investigate immune system interactions in radioligand therapy further.

Background

The use of radiopharmaceuticals labelled with fluorine-18 in non-invasive imaging, particularly in Positron Emission Tomography (PET), increased significantly during the last decade. However, traditional nucleophilic fluorination synthesis methods in most cases require azeotropic drying steps, leading to loss of activity and increased synthesis time. Microfluidic devices offer improvements with shorter reaction times, higher elution efficiency, and reduced reagent quantities.

Results

We developed a novel micro-cartridge for [¹⁸F]fluoride trapping and elution, etched in borosilicate optical glass (BK7) using ultrashort laser pulse machining. The micro-cartridge has a bead volume of 17 µL and a maximum capacity of 8.5 mg for anion exchange resin. The micro-cartridge, without the need for QMA preconditioning, exhibited an overall trapping efficiency and recovery efficiency (RE) of (94.09 ± 0.12)% using an activity exceeding 123 GBq of [¹⁸F]fluoride. This RE was obtained using 100 µL of a standard solution of anhydrous acetonitrile with Kryptofix 2.2.2, containing only 5 µL of water and 5.4 µmol of K₂CO₃ for [¹⁸F]fluoride elution. This solution was employed directly in the radiosynthesis of [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO), resulting in a 100% radiochemical conversion (RCC) to THP-protected [¹⁸F]FMISO within 10 min at 110 °C.

Conclusions

The developed micro-cartridge provides a novel tool for integrating microfluidic chips into conventional cassettes, facilitating more efficient radiopharmaceutical preparation.

Background

The extracellular localisation of the Heat shock protein 90 (Hsp90) is associated with the diseased state and wound healing and presents a promising opportunity for cancer targeting using Positron Emission Tomography (PET) imaging and molecularly targeted radiotherapy. The aim of this work is to develop a radiotracer with low nanomolar binding affinity to target the extracellular and particularly membrane pool of Hsp90, evaluate it in vitro, and conduct preliminary PET studies in vivo in mouse tumour models. Variable Heavy domain of Heavy chain antibodies, often referred to as Nanobodies, are suitable targeting vectors for the extracellular targets due to their favourable pharmacokinetic properties and low nanomolar target affinities. The main objective of the study is to target tumours expressing extracellular and membrane Hsp90 phenotype with minimal tracer accumulation in the non-target organs, which limited the translation of previously studied small molecule cytosolic Hsp90 tracers suffering from high non-Hsp90 specific background in the abdominal area.

Results

Six nanobodies were obtained after llama immunization with recombinant Hsp90α and ELISA biopanning, produced in E. coli and screened for stability and affinity. We selected one nanobody, 4DAM26, with good thermal stability, no aggregation at elevated temperatures, and low nanomolar affinity towards Hsp90α and Hsp90β isoforms for translation as a PET radiotracer. The nanobody was bioconjugated to p-NCS-NODAGA and radiolabeled with gallium-68 with 75 ± 11% radiochemical yield and > 99% radiochemical purity and remained stable up to 3 h in phosphate buffered saline and mouse serum. Pilot in vivo evaluation using µPET/CT and ex vivo biodistribution demonstrated a favourable pharmacokinetic profile, but the tumour uptake was non-distinguishable from the background tissue.

Conclusion

Compared to the small molecule Hsp90 tracers, the studied Nb-based tracer has improved pharmacokinetics properties including renal clearance and almost no accumulation in the non-target organs. Tumour uptake, on the other hand, was minimal and could not be differentiated from the background in µPET/CT. Our experiments indicate that in the studied models, membrane and extracellular expression of Hsp90 is majorly an artifact of cellular death, as only dead/dying cells had accessible pools of Hsp90 by flow cytometry, a consequence of a leaky membrane. More fundamental research is required to reassess the role of extracellular Hsp90 in cancer, and our future efforts will be focused on improving our inventory of cytosolic Hsp90 tracers with proven Hsp90-specific tumour accumulation.

Background

Targeted alpha therapy with Ac-225 showed to be effective in treating metastatic cancers. However, the complex decay chain requires optimized radiolabeling and quality control. This study aims to determine critical parameters and establish optimal labeling and accurate measuring techniques for radiochemical yield and purity with DOTA-TATE as a model molecule. Ac-225 sources were analyzed for metals (ΣFe, Zn, Cu) and quantified by UPLC. Optimization of radiolabeling kinetics for clinical conditions was performed in regards to temperature (20–90 °C), heating time (5–60 min), pH (2.5–10, with/without excess of metal ions), buffers, quenchers, volume (0.1–10 mL) and molar activity (90–540 kBq/nmol). The quality control was investigated using radio-TLC/HPLC by changing gradient to evaluate peak separation, radiolysed peptide and impurity separation.

Results

Metal ingrowth was observed in Ac-225 stocks (n = 3), (time of arrival: 17.9, 36.8 and 101.4 nmol per 10 MBq). Optimal radiochemical yields were achieved with > 80 °C (20 min) at pH 8.5 (15 mM TRIS) up to 270 kBq. Labeling at a high pH showed a higher RCY, even in presence of an excess of metals. High stability (RCP > 90%) was achieved after addition of quenchers (cysteine, methionine, ascorbate, histidine, or gentisic acid (35 mM)) up to 24 h. For optimal determination of the radiochemical purity (indirect HPLC) fifty fractions are required.

Conclusion

The quality of Ac-225 labeled DOTA-radiopharmaceuticals is highly dependent on the pH and stabilization (buffer/quencher). Within this research it is demonstrated that optimized quality control methods and accurate measurement of the radiolabeling kinetics are crucial to ensure safe implementation for patient treatment.