Performance of PSMA-targeted radiotheranostics in an experimental model of renal cell carcinoma.

Introduction: Renal cell carcinoma (RCC) represents cancer originating from the renal epithelium and accounts for > 90% of cancers in the kidney. Prostate-specific membrane antigen (PSMA) is overexpressed in tumor-associated neovascular endothelial cells of many solid tumors, including metastatic RCC. Although studied in several small clinical studies, PSMA-based imaging and therapy have not been pursued rigorously in preclinical RCC. This study aimed to evaluate the preclinical performance of PSMA-based radiotheranostic agents in a relevant murine model. Methods: A PSMA-overexpressing murine cell line, PSMA+ RENCA, was developed by lentiviral transduction. PSMA-based theranostic agents, 68Ga-L1/177Lu-L1/225Ac-L1, were synthesized in high radiochemical yield and purity following our reported methods. Immunocompetent BALB/c mice were used for flank and orthotopic tumor inoculation. 68Ga-L1 was evaluated in small animal PET/CT imaging in flank and PET/MR imaging in orthotopic models. Cell viability studies were conducted for 177Lu-L1 and 225Ac-L1. Proof-of-concept treatment studies were performed using 225Ac-L1 (0, 37 kBq, 2 kBq × 37 kBq, 1 week apart) using PSMA+ RENCA in the flank model. Results: Cellular uptake of 68Ga-L1, 177Lu-L1, and 225Ac-L1 confirmed the specificity of the agents to PSMA+ RENCA cells rather than to RENCA (wt) cells, which are low in PSMA expression. The uptake in PSMA+ RENCA cells at 1 h for 68Ga-L1 (49.0% incubated dose [ID] ± 3.6%ID/million cells), 177Lu-L1 (22.1%ID ± 0.5%ID)/million cells), and 225Ac-L1 (4.1% ± 0.2% ID)/million cells), respectively, were higher than the RENCA (wt) cells (~ 1%ID-2%ID/million cells). PET/CT images displayed > 7-fold higher accumulation of 68Ga-L1 in PSMA+ RENCA compared to RENCA (wt) in flank implantation at 1 h. A twofold higher accumulation of 68Ga-L1 was observed in orthotopic tumors than in normal kidneys during 1-3 h postinjection. High lung uptake was observed with 68Ga-L1 PET/MR imaging 3 weeks after orthotopic implantation of PSMA+ RENCA due to spontaneous lung metastases. The imaging data were further confirmed by immunohistochemical characterization. 225Ac-L1 (0-37 kBq) displayed a dose-dependent reduction of cell proliferation in the PSMA+ RENCA cells after 48 h incubation; ~ 40% reduction in the cells with treated 37 kBq compared to vehicle (p < 0.001); however, no effect was observed with 177Lu-L1 (0-3700 kBq) up to 144 h postinoculation, suggesting lower efficacy of ß-particle-emitting radiations in cellular studies compared to α-particle-emitting 225Ac-L1. Animals treated with 225Ac-L1 at 1 week posttumor inoculation in flank models displayed significant tumor growth delay (p < 0.03) and longer median survival of 21 days and 24 days for the treatment groups 37 kBq and 2 kBq × 37 kBq, respectively, compared to the vehicle group (12 days). Conclusion: The results suggest that a theranostic strategy targeting PSMA, employing PET and α-emitting radiopharmaceuticals, enabled tumor growth control and enhanced survival in a relevant immunocompetent murine model of RCC. These studies provide the rationale for clinical studies of PSMA-targeted theranostic agents in patients with RCC.

[68Ga]Ga-DOTAGA-Glu(FAPi)2 Shows Enhanced Tumor Uptake and Theranostic Potential in Preclinical PET Imaging.

The use of fibroblast activation protein inhibitors (FAPis) for positron emission tomography (PET) imaging in cancer has garnered significant interest in recent years, yielding promising results in preclinical and clinical settings. FAP is predominantly expressed in pathological conditions such as fibrosis and cancer, making it a compelling target. An optimized approach involves using FAPi homodimers as PET tracers, which enhance tumor uptake and retention, making them more effective candidates for therapy. Here, a UAMC-1110 inhibitor-based homodimer, DOTAGA-Glu(FAPi)2, was synthesized and radiolabeled with gallium-68, and its efficacy was evaluated in vivo for PET imaging in an endogenously FAP-expressing xenografted mouse model, U87MG. Notably, 45 min post-injection, the mean uptake of [68Ga]Ga-DOTAGA-Glu(FAPi)2 was 4.7 ± 0.5% ID/g in the tumor with low off-target accumulation. The ex vivo analysis of the FAP expression in the tumors confirmed the in vivo results. These findings highlight and confirm the tracer's potential for diagnostic imaging of cancer and as a theranostic companion.

[68Ga]Ga-FAP-2286-Synthesis, Quality Control and Comparison with [18F]FDG PET/CT in a Patient with Suspected Cholangiocellular Carcinoma.

[68Ga]Ga-FAP-2286 is a new peptide-based radiopharmaceutical for positron-emission tomography (PET) that targets fibroblast activation protein (FAP). This article describes in detail the automated synthesis of [68Ga]Ga-FAP-2286 using a commercially available synthesis tool that includes quality control for routine clinical applications. The synthesis was performed using a Scintomics GRP-3V module and a GMP grade 68Ge/68Ga generator. A minor alteration for transferring the eluate to the module was established, eliminating the need for new method programming. Five batches of [68Ga]Ga-FAP-2286 were tested to validate the synthesis. A stability analysis was conducted up to 3 h after production to determine the shelf-life of the finished product. The automated synthesis on the Scintomics GRP-3V synthesis module was found to be compliant with all quality control requirements. The shelf-life of the product was set to 2 h post-production based on the stability study. A patient suffering from cholangiocellular carcinoma that could not be clearly detected by conventional imaging, including a [18F]FDG-PET/CT, highlights the potential use of [68Ga]Ga-FAP-PET/CT.

Automated Production of [68Ga]Ga-Desferrioxamine B on Two Different Synthesis Platforms.

Background/Objectives: PET imaging of bacterial infection could potentially provide added benefits for patient care through non-invasive means. [68Ga]Ga-desferrioxamine B-a radiolabelled siderophore-shows specific uptake by human-pathogenic bacteria like Staphylococcus aureus or Pseudomonas aeruginosa and sufficient serum stability for clinical application. In this report, we present data for automated production of [68Ga]Ga-desferrioxamine B on two different cassette-based synthesis modules (Modular-Lab PharmTracer and GRP 3V) utilising commercially obtainable cassettes together with a licensed 68Ge/68Ga radionuclide generator. Methods: Quality control, including the determination of radiochemical purity, as well as a system suitability test, was set up via RP-HPLC on a C18 column. The two described production processes use an acetic acid/acetate buffer system with ascorbic acid as a radical scavenger for radiolabelling, yielding ready-to-use formulations with sufficient activity yield. Results: Batch data analysis demonstrated radiochemical purity of >95% by RP-HPLC combined with ITLC and excellent stability up to 2 h after synthesis. Specifications for routine production were set up and validated with four masterbatches for each synthesis module. Conclusions: Based on this study, an academic clinical trial for imaging of bacterial infection was initiated. Both described synthesis methods enable automated production of [68Ga]Ga-desferrioxamine B in-house with high reproducibility for clinical application.

Visualisation of in vivo protein synthesis during mycobacterial infection through [68Ga]Ga-DOTA-puromycin µPET/MRI.

Radiolabelled puromycin analogues will allow the quantification of protein synthesis through nuclear medicine-based imaging. A particularly useful application could be the non-invasive longitudinal visualisation of mycobacterial activity through direct quantification of puromycin binding. This study assesses the value of [68Ga]Ga-DOTA-puromycin in the visualisation of mycobacteria through positron emission tomography combined with magnetic resonance imaging (µPET/MRI). The radiopharmaceutical was produced by previously published and validated methods. [68Ga]Ga-DOTA-Puromycin imaging was performed on severe immunodeficient mice infected with Bacille Calmette-Guérin-derived M. Bovis (BCG). Acute and chronic infection stages were examined by µPET/MRI. A follow-up group of animals acted as controls (animals bearing S. aureus-derived infection and sterile inflammation) to assess tracer selectivity. [68Ga]Ga-DOTA-puromycin-µPET/MRI images revealed the acute, widespread infection within the right upper shoulder and armpit. Also, [68Ga]Ga-DOTA-puromycin signal sensitivity measured after a 12-week period was lower than that of [18F]FDG-PET in the same animals. A suitable correlation between normalised uptake values (NUV) and gold standard histopathological analysis confirms accurate tracer accumulation in viable bacteria. The radiopharmaceutical showed infection selectivity over inflammation but accumulated in both M. Bovis and S. Aureus, lacking pathogen specificity. Overall, [68Ga]Ga-DOTA-puromycin exhibits potential as a tool for non-invasive protein synthesis visualization, albeit without pathogen selectivity.

Intra-arterial PSMA injection using hepatic arterial infusion pump in intrahepatic cholangiocarcinoma: a proof-of-concept study.

Prostate-specific membrane antigen (PSMA) targeted tracers show increased uptake in several malignancies, indicating a potential for peptide radioligand therapy. Intra-arterial injection of radiotracers can increase the therapeutic window. This study aimed to evaluate the feasibility of intra-arterial injection of [68Ga]Ga-PSMA-11 for intrahepatic cholangiocarcinoma and compare tracer uptake after intrahepatic arterial injection and intravenous injection. Three patients with intrahepatic cholangiocarcinoma received [68Ga]Ga-PSMA-11 through a hepatic arterial infusion pump, followed by positron emission tomography/computed tomography (PET/CT). Two-three days later, patients underwent PET/CT after intravenous [68Ga]Ga-PSMA-11 injection. All tumours showed higher uptake on the intra-arterial scan compared with the intravenous scan: the intra-arterial / intravenous standardised uptake value normalised by lean body mass ratios were 1.40, 1.46, and 1.54. Local intra-arterial PSMA injection is possible in patients with intrahepatic cholangiocarcinoma. Local injection increases tumour-to-normal tissue ratios, increasing the therapeutic window for theranostic applications. RELEVANCE STATEMENT: Intra-arterial Prostate specific membrane antigen (PSMA) injection increases the therapeutic window for potential theranostic application in intrahepatic cholangiocarcinoma. KEY POINTS: Three patients with intrahepatic cholangiocarcinoma underwent PET/CT after intra-arterial and intravenous injection of [68Ga]Ga-PSMA-11. Intra-arterial injection showed higher uptake than intravenous injection. PSMA-targeted imaging could be valuable for a subset of intrahepatic cholangiocarcinoma patients.

Development of Alginate-Based Biodegradable Radioactive Microspheres Labeled with Positron Emitter through Click Chemistry Reaction: Stability and PET Imaging Study.

Biodegradable radioactive microspheres labeled with positron emitters hold significant promise for diagnostic and therapeutic applications in cancers and other diseases, including arthritis. The alginate-based polymeric microspheres offer advantages such as biocompatibility, biodegradability, and improved stability, making them suitable for clinical applications. In this study, we developed novel positron emission tomography (PET) microspheres using alginate biopolymer radiolabeled with gallium-68 (68Ga) through a straightforward conjugation reaction. Polyethylenimine (PEI)-decorated calcium alginate microspheres (PEI-CAMSs) were fabricated and further modified using azadibenzocyclooctyne-N-hydroxysuccinimide ester (ADIBO-NHS). Subsequently, azide-functionalized NOTA chelator (N3-NOTA) was labeled with [68Ga]Ga to obtain [68Ga]Ga-NOTA-N3, which was then reacted with the surface-modified PEI-CAMSs using strain-promoted alkyne-azide cycloaddition (SPAAC) reaction to develop [68Ga]Ga-NOTA-PEI-CAMSs, a novel PET microsphere. The radiolabeling efficiency and radiochemical stability of [68Ga]Ga-NOTA-PEI-CAMSs were determined using the radio-instant thin-layer chromatography-silica gel (radio-ITLC-SG) method. The in vivo PET images were also acquired to study the in vivo stability of the radiolabeled microspheres in normal mice. The radiolabeling efficiency of [68Ga]Ga-NOTA-PEI-CAMSs was over 99%, and the microspheres exhibited high stability (92%) in human blood serum. PET images demonstrated the stability and biodistribution of the microspheres in mice for up to 2 h post injection. This study highlights the potential of biodegradable PET microspheres for preoperative imaging and targeted radionuclide therapy. Overall, the straightforward synthesis method and efficient radiolabeling technique provide a promising platform for the development of theranostic microspheres using other radionuclides such as 90Y, 177Lu, 188Re, and 64Cu.

[68Ga]Ga-Schizokinen, a Potential Radiotracer for Selective Bacterial Infection Imaging.

Gallium-68-labeled siderophores as radiotracers have gained interest for the development of in situ infection-specific imaging diagnostics. Here, we report radiolabeling, in vitro screening, and in vivo pharmacokinetics (PK) of gallium-68-labeled schizokinen ([68Ga]Ga-SKN) as a new potential radiotracer for imaging bacterial infections. We radiolabeled SKN with ≥95% radiochemical purity. Our in vitro studies demonstrated its hydrophilic characteristics, neutral pH stability, and short-term stability in human serum and toward transchelation. In vitro uptake of [68Ga]Ga-SKN by Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and S. epidermidis, but no uptake by Candida glabrata, C. albicans, or Aspergillus fumigatus, demonstrated its specificity to bacterial species. Whole-body [68Ga]Ga-SKN positron emission tomography (PET) combined with computerized tomography (CT) in healthy mice showed rapid renal excretion with no or minimal organ uptake. The subsequent ex vivo biodistribution resembled this fast PK with rapid renal excretion with minimal blood retention and no major organ uptake and showed some dissociation of the tracer in the urine after 60 min postinjection. These findings warrant further evaluation of [68Ga]Ga-SKN as a bacteria-specific radiotracer for infection imaging.

Comparison of 68Ga-FAP-2286 and 18F-FDG PET/CT in the diagnosis of advanced lung cancer.

Purpose: The 68Ga/177Lu-FAP-2286 is a newly developed tumor imaging agent that shows potential for visualizing and treating tumor stroma. The objective of this research was to evaluate the effectiveness of 68Ga-FAP-2286 PET/CT and 18F-FDG PET/CT in diagnosing advanced lung cancer. Methods: In this prospective study, patients with lung cancer who underwent 68Ga-FAP-2286 and 18F-FDG PET/CT examinations between September 2022 and June 2023 were analyzed. Lesion uptake was converted to SUVmax. A paired T-test was used to compare the SUVmax, and the number of positive lesions detected by the two methods was recorded. Results: In total, 31 participants (median age: 56 years) were assessed. The uptake of 68Ga-FAP-2286 was significantly higher than that of 18F-FDG in primary lesions (9.90 ± 5.61 vs. 6.09 ± 2.84, respectively, P < 0.001), lymph nodes (7.95 ± 2.75 vs. 5.55 ± 1.59, respectively, P=0.01), and bone metastases (7.74 ± 3.72 vs. 5.66 ± 3.55, respectively, P=0.04). Furthermore, the detection sensitivity of lymph nodes using 68Ga-FAP-2286 PET/CT was superior to that with 18F-FDG PET/CT [100% (137/137) vs. 78.8% (108/137), respectively], as well as for bone metastases [100% (384/384) vs. 68.5% (263/384), respectively]. However, the detection sensitivity for primary tumors using both modalities was comparable [100% (13/13) for both]. Conclusion: Compared to 18F-FDG PET/CT, 68Ga-FAP-2286 PET/CT demonstrated better lesion detection capabilities for lung cancer, particularly in lymph nodes and bone metastases, providing compelling imaging evidence for the efficacy of 177Lu-FAP-2286 treatment.

Training and assessing convolutional neural network performance in automatic vascular segmentation using Ga-68 DOTATATE PET/CT.

To evaluate a convolutional neural network's performance (nnU-Net) in the assessment of vascular contours, calcification and PET tracer activity using Ga-68 DOTATATE PET/CT. Patients who underwent Ga-68 DOTATATE PET/CT imaging over a 12-month period for neuroendocrine investigation were included. Manual cardiac and aortic segmentations were performed by an experienced observer. Scans were randomly allocated in ratio 64:16:20 for training, validation and testing of the nnU-Net model. PET tracer uptake and calcium scoring were compared between segmentation methods and different observers. 116 patients (53.5% female) with a median age of 64.5 years (range 23-79) were included. There were strong, positive correlations between all segmentations (mostly r > 0.98). There were no significant differences between manual and AI segmentation of SUVmean for global cardiac (mean ± SD 0.71 ± 0.22 vs. 0.71 ± 0.22; mean diff 0.001 ± 0.008, p > 0.05), ascending aorta (mean ± SD 0.44 ± 0.14 vs. 0.44 ± 0.14; mean diff 0.002 ± 0.01, p > 0.05), aortic arch (mean ± SD 0.44 ± 0.10 vs. 0.43 ± 0.10; mean diff 0.008 ± 0.16, p > 0.05) and descending aorta (mean ± SD < 0.001; 0.58 ± 0.12 vs. 0.57 ± 0.12; mean diff 0.01 ± 0.03, p > 0.05) contours. There was excellent agreement between the majority of manual and AI segmentation measures (r ≥ 0.80) and in all vascular contour calcium scores. Compared with the manual segmentation approach, the CNN required a significantly lower workflow time. AI segmentation of vascular contours using nnU-Net resulted in very similar measures of PET tracer uptake and vascular calcification when compared to an experienced observer and significantly reduced workflow time.

Synthesis, Radiolabeling, and Biodistribution Study of a Novel DOTA-Peptide for Targeting Vascular Endothelial Growth Factor Receptors in the Molecular Imaging of Breast Cancer.

As angiogenesis plays a pivotal role in tumor progression and metastasis, leading to more cancer-related deaths, the angiogenic process can be considered as a target for diagnostic and therapeutic applications. The vascular endothelial growth factor receptor-1 (VEGR-1) and VEGFR-2 have high expression on breast cancer cells and contribute to angiogenesis and tumor development. Thus, early diagnosis through VEGFR-1/2 detection is an excellent strategy that can significantly increase a patient's chance of survival. In this study, the VEGFR1/2-targeting peptide VGB3 was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), using 6-aminohexanoic acid (Ahx) as a spacer to prevent steric hindrance in binding. DOTA-Ahx-VGB3 was radiolabeled with Gallium-68 (68Ga) efficiently. An in vitro cell binding assay was assessed in the 4T1 cell line. The tumor-targeting potential of [68Ga]Ga-DOTA-Ahx-VGB3 was conducted for 4T1 tumor-bearing mice. Consequently, high radiochemical purity [68Ga]Ga-DOTA-Ahx-VGB3 (RCP = 98%) was prepared and stabilized in different buffer systems. Approximately 17% of the radiopeptide was internalized after 2 h incubation and receptor binding as characterized by the IC50 value being about 867 nM. The biodistribution and PET/CT studies revealed that [68Ga]Ga-DOTA-Ahx-VGB3 reached the tumor site and was excreted rapidly by the renal system. These features convey [68Ga]Ga-DOTA-Ahx-VGB3 as a suitable agent for the noninvasive visualization of VEGFR-1/2 expression.

[68Ga]PSMA-11 for positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer.

INTRODUCTION: Theranostics targeting prostate-specific membrane antigen (PSMA) represent a new targeted approach for prostate cancer care that combines diagnostic and therapeutic radiopharmaceuticals to diagnose and treat the disease. Positron emission tomography (PET) is the imaging method of choice and several diagnostic radiopharmaceuticals for quantifying PSMA have received FDA approval and are in clinical use. [68Ga]Ga-PSMA-11 is one such imaging agent and the focus of this article. One beta-emitting radioligand therapy ([177Lu]Lu-PSMA-617) has also received FDA approval for prostate cancer treatment, and several other alpha- and beta-emitting radioligand therapies are in clinical trials. AREAS COVERED: Theranostics targeting PSMA in men with prostate cancer are discussed with a focus on use of [68Ga]Ga-PSMA-11 for imaging PSMA-positive lesions in men with prostate cancer. The review covers [68Ga]Ga-PSMA-11 manufacture, current regulatory status, comparison of [68Ga]Ga-PSMA-11 to other imaging techniques, clinical updates, and emerging applications of artificial intelligence for [68Ga]Ga-PSMA-11 PET. EXPERT OPINION: [68Ga]Ga-PSMA-11 is used in conjunction with a PET/CT scan to image PSMA positive lesions in men with prostate cancer. It is manufactured by chelating precursor with68Ga, either from a generator or cyclotron, and has regulatory approval around the world. It is widely used clinically in conjunction with radioligand therapies like [177Lu]Lu-PSMA-617.

Synthesis and Evaluation of the First 68Ga-Labeled C-Terminal Hydroxamate-Derived Gastrin-Releasing Peptide Receptor-Targeted Tracers for Cancer Imaging with Positron Emission Tomography.

Gastrin-releasing peptide receptor (GRPR), overexpressed in many solid tumors, is a promising imaging marker and therapeutic target. Most reported GRPR-targeted radioligands contain a C-terminal amide. Based on the reported potent antagonist D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH, we synthesized C-terminal hydroxamate-derived [68Ga]Ga-LW02075 ([68Ga]Ga-DOTA-pABzA-DIG-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH) and [68Ga]Ga-LW02050 ([68Ga]Ga-DOTA-Pip-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH), and compared them with the closely related and clinically validated [68Ga]Ga-SB3 ([68Ga]Ga-DOTA-pABzA-DIG-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt). Binding affinities (Ki) of Ga-SB3, Ga-LW02075, and Ga-LW02050 were 1.20 ± 0.31, 1.39 ± 0.54, and 8.53 ± 1.52 nM, respectively. Both Ga-LW02075 and Ga-LW02050 were confirmed to be GRPR antagonists by calcium release assay. Imaging studies showed that PC-3 prostate cancer tumor xenografts were clearly visualized at 1 h post injection by [68Ga]Ga-SB3 and [68Ga]Ga-LW02050 in PET images, but not by [68Ga]Ga-LW02075. Ex vivo biodistribution studies conducted at 1 h post injection showed that the tumor uptake of [68Ga]Ga-LW02050 was comparable to that of [68Ga]Ga-SB3 (5.38 ± 1.00 vs. 6.98 ± 1.36 %ID/g), followed by [68Ga]Ga-LW02075 (3.97 ± 1.71 %ID/g). [68Ga]Ga-SB3 had the highest pancreas uptake (37.3 ± 6.90 %ID/g) followed by [68Ga]Ga-LW02075 (17.8 ± 5.24 %ID/g), while the pancreas uptake of [68Ga]Ga-LW02050 was only 0.53 ± 0.11 %ID/g. Our data suggest that [68Ga]Ga-LW02050 is a promising PET tracer for detecting GRPR-expressing cancer lesions.

Development of a versatile [68Ga]Ga-FAPI-46 automated synthesis suitable to multi-elutions of germanium-68/gallium-68 generators.

Gallium-68-labeled FAPI-46 has recently been proposed as a novel positron emission tomography imaging probe to diagnose and monitor a wide variety of cancers. Promising results from several ongoing clinical trials have led to a soaring demand for this radiotracer. Typical [68Ga]Ga-FAPI-46 labeling protocols do not cope with multiple generator elutions, leaving radiopharmacies unable to scale-up the production and meet the demand. Here, we propose a robust and efficient automated radiosynthesis of [68Ga]Ga-FAPI-46 on the Trasis miniAllinOne synthesizer, featuring a prepurification step which allows multiple generator elutions and ensures compatibility with a wide range of gallium-68 generators. Our approach was to optimize the prepurification step by first testing five different cationic cartridge chemistries. Only the strong cationic exchange (SCX) cartridges tested had sufficient affinities for quantitative trapping of >99.9%, while the weak cationics did not exceed 50%. Packaging, rinsing, or flowing of the selected SCX cartridges was not noticeable, but improvements in fluidics managed to save time. Based on our previous development experience of [68Ga]Ga-FAPI-46, radiolabeling optimization was also carried out at different temperatures during 10 min. At temperatures above 100°C, radiochemical yield (RCY) > 80% was achieved without significantly increasing the chemical impurities (<5.5 µg mL-1). The optimized sequence was reproducibly conducted with three different brands of widely used generators (RCY >88%). A comparison with radiosyntheses carried out without prepurification steps was also conclusive in terms of RCY, radiochemical yield, and chemical purity. Finally, high-activity tests using elutions from three generators were also successful for these parameters. [68Ga]Ga-FAPI-46 was consistently obtained in good radiochemical yields (>89%, n = 3), and the final product quality was compliant with internal specifications based on European Pharmacopoeia. This process is suitable for GMP production and allows scaling-up of routine productions, higher throughput, and, ultimately, better patient care.

Tailoring Fibroblast-Activation Protein Targeting for Theranostics: A Comparative Preclinical Evaluation of the 68Ga- and 177Lu-Labeled Monomeric and Dimeric Fibroblast-Activation Protein Inhibitors DOTA.SA.FAPi and DOTAGA.(SA.FAPi)2.

BACKGROUND: FAP radiopharmaceuticals show promise for cancer diagnosis; however, their limited tumor residency hinders treatment. This study compared two FAPi derivatives, DOTA.SA.FAPi and DOTAGA.(SA.FAPi)2, labeled with gallium-68 and lutetium-177, aiming to determine an optimum combination for creating theranostic pairs. METHODS: The radiotracers were studied for lipophilicity, binding to human serum proteins, and binding to human cancer-associated fibroblasts (CAFs) in vitro, including saturation and internalization/externalization studies. PET/SPECT/CT and biodistribution studies were conducted in PC3 and U87MG xenografts for [68Ga]Ga-DOTA.SA.FAPi and [68Ga]Ga-DOTAGA.(SA.FAPi)2. [177Lu]Lu-DOTA.SA.FAPi and [177Lu]Lu-DOTAGA.(SA.FAPi)2, were evaluated in PC3 xenografts. Biodistribution studies of [68Ga]Ga-DOTA.SA.FAPi were performed in healthy male and female mice. RESULTS: All radiotracers exhibited strong binding to FAP. Their internalization rate was fast while only [177Lu]Lu-DOTAGA.(SA.FAPi)2 was retained longer in CAFs. [68Ga]Ga-DOTAGA.(SA.FAPi)2 and [177Lu]Lu-DOTAGA.(SA.FAPi)2 displayed elevated lipophilicity and affinity for human serum proteins compared to [68Ga]Ga-DOTA.SA.FAPi and [177Lu]Lu-DOTA.SA.FAPi. In vivo studies revealed slower washout of [68Ga]Ga-DOTAGA.(SA.FAPi)2 within 3 h compared to [68Ga]Ga-DOTA.SA.FAPi. The tumor-to-tissue ratios of [68Ga]Ga-DOTAGA.(SA.FAPi)2 versus [68Ga]Ga-DOTA.SA.FAPi did not exhibit any significant differences. [177Lu]Lu-DOTAGA.(SA.FAPi)2 maintained a significant tumor uptake even after 96 h p.i. compared to [177Lu]Lu-DOTA.SA.FAPi. CONCLUSIONS: Dimeric compounds hold promise for therapy, while monomers are better suited for diagnostics. Finding the right combination is essential for effective disease management.

Performance evaluation of iterative PET reconstruction with resolution recovery incorporating Gallium-68 positron range correction.

BACKGROUND: The distance traveled by the positron before annihilation with an electron, the so-called positron range, negatively effects the positron emission tomography (PET) image quality for radionuclides emitting high-energy positrons such as Gallium-68 (68Ga). PURPOSE: In this study, the effect of a tissue-independent positron range correction for Gallium-68 (68Ga-PRC) was investigated based on phantom measurements. The effect of the 68Ga-PRC was also explored in four patients. METHODS: The positron range distribution profile of 68Ga in water was generated via Monte Carlo simulation. That profile was mapped to a spatially invariant 3D convolution kernel which was incorporated in the OSEM and Q.Clear reconstruction algorithms to perform the 68Ga-PRC. In addition, each reconstruction method included point spread function (PSF) modeling and time-of-flight information. For both Fluorine-18 (18F) and 68Ga, the NEMA IQ phantom was filled with a sphere-to-background ratio of 10:1 and scanned with the GE Discovery MI 5R PET/CT system. Standard non-positron range correction (PRC) reconstructions were performed for both radionuclides, while also PRC reconstructions were performed for 68Ga. Reconstructions parameters (OSEM: number of updates, Q.Clear: beta value) were adapted to achieve similar noise levels between the corresponding reconstructions. The effect of 68Ga-PRC was assessed for both OSEM and Q.Clear reconstructions and compared to non-PRC reconstructions for 68Ga and 18F in terms of image contrast, noise, recovery coefficient (RC), and spatial resolution. For the clinical validation, 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) and 68Ga-DOTATOC PET scans were included of two patients each. For each PET scan, patients were injected with 1.5 MBq/kg of 68Ga-PSMA or 68Ga-DOTATOC and the contrast-to-noise ratio (CNR) was calculated and compared to the non-PRC reconstructions. RESULTS: For OSEM reconstructions, including the 68Ga-PRC improved the RC by 9.4% (3.7%-19.3%) and spatial resolution by 21.7% (4.6 mm vs. 3.6 mm) for similar noise levels. For Q.Clear reconstructions, 68Ga-PRC modeling improved the RC by 6.7% (2.8%-10.5%) and spatial resolution by 15.3% (5.9 mm vs. 5.0 mm) while obtaining similar noise levels. In the patient data, the use of 68Ga-PRC enhanced the CNR by 13.2%. CONCLUSIONS: Including 68Ga-PRC in the PET reconstruction enhanced the image quality of 68Ga PET data compared to the standard non-PRC reconstructions for similar noise levels. Limited patient results also supported this improvement.

Synthesis and Evaluation of Novel 68Ga-Labeled [D-Phe6,Leu13ψThz14]bombesin(6-14) Analogs for Cancer Imaging with Positron Emission Tomography.

Gastrin-releasing peptide receptor (GRPR) is overexpressed in various cancers and is a promising target for cancer diagnosis and therapy. However, the high pancreas uptake and/or metabolic instability observed for most reported GRPR-targeted radioligands might limit their clinical applications. Our group recently reported a GRPR-targeted antagonist tracer, [68Ga]Ga-TacsBOMB2 ([68Ga]Ga-DOTA-Pip-D-Phe6-Gln7-Trp8-Ala9-Val10-Gly11-His12-Leu13ψThz14-NH2), which showed a minimal pancreas uptake in a preclinical mouse model. In this study, we synthesized four derivatives with unnatural amino acid substitutions (Tle10-derived Ga-LW01158, NMe-His12-derived Ga-LW01160, α-Me-Trp8- and Tle10-derived Ga-LW01186, and Tle10- and N-Me-Gly11-derived Ga-LW02002) and evaluated their potential for detecting GRPR-expressing tumors with positron emission tomography (PET). The binding affinities (Ki(GRPR)) of Ga-LW01158, Ga-LW01160, Ga-LW01186, and Ga-LW02002 were 5.11 ± 0.47, 187 ± 17.8, 6.94 ± 0.95, and 11.0 ± 0.39 nM, respectively. [68Ga]Ga-LW01158, [68Ga]Ga-LW01186, and [68Ga]Ga-LW02002 enabled clear visualization of subcutaneously implanted human prostate cancer PC-3 tumor xenografts in mice in PET images. Ex vivo biodistribution studies showed that [68Ga]Ga-LW01158 had the highest tumor uptake (11.2 ± 0.65 %ID/g) and good tumor-to-background uptake ratios at 1 h post-injection. Comparable in vivo stabilities were observed for [68Ga]Ga-LW01158, [68Ga]Ga-LW01186, and [68Ga]Ga-LW02002 (76.5-80.7% remaining intact in mouse plasma at 15 min post-injection). In summary, the Tle10 substitution, either alone or combined with α-Me-Trp8 or NMe-Gly11 substitution, in Ga-TacsBOMB2 generates derivatives that retained good GRPR binding affinity and in vivo stability. With good tumor uptake and tumor-to-background imaging contrast, [68Ga]Ga-LW01158 is promising for detecting GRPR-expressing lesions with PET.

Synthesis and evaluation of a 68Ga-labeled spermine derivative for tumor PET imaging.

BACKGROUND: The polyamine transporter system (PTS), which renders it a promising target for tumor therapy and imaging applications, facilitates the transmembrane transport of polyamines. We reported a novel derivative of spermine labeled with gallium-68 ([68Ga]Ga-NOTA-Spermine) for the imaging of the PTS in mouse models of tumor. RESULTS: The radiochemical yield of [68Ga]Ga-NOTA-Spermine was determined to be 64-69 %, demonstrating exceptional stability and radiochemical purity (>98 %). Cellular uptake experiments revealed that A549 cells exhibited peak uptake of [68Ga]Ga-NOTA-Spermine at 90 min (15.4 % ± 0.68 %). Biodistribution analysis demonstrated significant accumulation of [68Ga]Ga-NOTA-Spermine in kidneys and liver, while exhibiting low uptake levels in muscle, brain, and bones. Furthermore, Micro-PET/CT scans conducted on A549 tumor-bearing mouse models indicated substantial uptake of [68Ga]Ga-NOTA-Spermine, with maximum tumor/muscle (T/M) ratios reaching 3.71. CONCLUSION: These results suggest that [68Ga]Ga-NOTA-Spermine holds potential as a PET imaging agent for tumors with high levels of PTS.

68Ga-DOTA-D-Alanine-BoroPro Radiotracer for Imaging of the Fibroblast Activation Protein in Malignant and Non-Malignant Diseases.

Recently, we reported a new fibroblast activation protein (FAP) inhibitor radiopharmaceutical based on the 99mTc-((R)-1-((6-hydrazinylnicotinoyl)-D-alanyl) pyrrolidin-2-yl) boronic acid (99mTc-HYNIC-D-Alanine-BoroPro)(99mTc-HYNIC-iFAP) structure for tumor microenvironment SPECT imaging. This research aimed to synthesize 68Ga-[2,2',2″,2‴-(2-(4-(2-(5-(((S)-1-((S)-2-boronopyrrolidin-1-yl)-1-oxopropan-2-yl)carbamoyl)pyridin-2-yl)hydrazine-1-carbothioamido)benzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid] (68Ga-DOTA-D-Alanine-BoroPro)(68Ga-iFAP) as a novel radiotracer for PET imaging and evaluate its usefulness for FAP expression in malignant and non-malignant tissues. The coupling of p-SCN-benzene DOTA with HYNIC-iFAP was used for the chemical synthesis and further labeling with 68Ga. Radiochemical purity was verified by radio-HPLC. The specificity of 68Ga-iFAP was evaluated in HCT116 cells, in which FAP expression was verified by immunofluorescence and Western blot. Biodistribution and biokinetic studies were performed in murine models. 68Ga-iFAP uptake at the myocardial level was assessed in mice with induced infarction. First-in-human images of 68Ga-iFAP in healthy subjects and patients with myocardial infarction, glioblastoma, prostate cancer, and breast cancer were also obtained. DOTA-D-Alanine BoroPro was prepared with a chemical purity of 98% and was characterized by UPLC mass spectroscopy, FT-IR, and UV-vis. The 68Ga-iFAP was obtained with a radiochemical purity of >95%. In vitro and in vivo studies demonstrated 68Ga-iFAP-specific recognition for FAP, rapid renal elimination, and adequate visualization of the glioblastoma, breast tumor, prostate cancer, and myocardial infarction sites. The results of this research justify further dosimetry and clinical trials to establish the specificity and sensitivity of 68Ga-iFAP PET for FAP expression imaging.

Automated radiolabelling of [68Ga]Ga-PSMA-11 (gallium (68Ga)-gozetotide) using the Locametz® kit and two generators.

BACKGROUND: Steps have been taken by pharmaceutical companies to obtain marketing authorisation of PSMA ligands in the European Union. Since December 2022, Locametz® (PSMA-11, gozetotide) is licensed as kit for manual radiolabelling with gallium-68 and commercially available since mid-2023. The Summary of Product Characteristic (SmPC) describes manual radiolabelling with a maximum activity after radiolabelling of 1369 MBq. We aimed for radiolabelling with a higher activity to increase production efficiency, and thus, automated radiolabelling is strongly preferred over manual radiolabelling to reduce radiation exposure to personnel. The aim of this study was to develop and validate a method for automated radiolabelling of the Locametz® kit using ~ 2000 MBq of gallium-68 eluate for radiolabelling. RESULTS: Automated radiolabelling of [68Ga]Ga-PSMA-11 using the Locametz® kit provided a product which complies to the Ph. Eur., had a shelf-life of 6 h at room temperature, and theoretically reduced radiation exposure 5.7 times. Radiolabelling with one and two generator(s) resulted in a radiochemical yield of 91-102% and 96-101% after preparation, respectively. The radiochemical purity ranged from 98.0 to 99.6% for radiolabelling with one generator and ranged from 98.4 to 99.3% for radiolabelling with two generators with similar stability. The activity of the final product was much higher when using two generators, 1961-2035 MBq compared to 740-1260 MBq, which leads to ~ 1.5 times more patient syringes available per preparation. CONCLUSION: Automated radiolabelling of [68Ga]Ga-PSMA-11 using the Locametz® kit with higher gallium-68 activity than specified in the SmPC results in a product that is in compliance with the Ph. Eur. monograph and has a shelf-life of 6 h at room temperature. Radiolabelling with two generators proved possible and resulted in a product with similar quality but with much higher efficiency.