A new automated NaCl based robust method for routine production of gallium-68 labeled peptides

Improved purification of cyclotron [68Ga]GaCl3 for the production of 68Ga radiopharmaceuticals

INTRODUCTION

Increased demand for NetSpot and Illuccix as requirement to receive the respective Lutathera and Pluvicto radiotherapies, and monitor subsequent response to treatment, have reinforced the need to develop alternative ways of producing gallium-68 (68Ga). Building on our efforts to produce 68Ga in a liquid target on a GE PETtrace, the goal of this work is to modify the current GE Gallium Chloride cassette using the FASTLab 2 synthesis module to produce [68Ga]GaCl3 equivalent to a 1.85 GBq generator and demonstrate compatibility with FDA-approved kits for production of 68Ga-labeled radiopharmaceuticals.

METHODS

68Ga was produced in a liquid target via the 68Zn(p,n)68Ga reaction. 68Ga was loaded onto various sizes of ZR resins (ZR Load, 0.3 mL, 1 mL, or 2 mL). The loading efficiency was determined using a dose calibrator. After washing with HNO3, 1.75 M HCl was used to elute the ZR Load resin through various sizes of a second ZR resin (ZR CG, 0 mL, 2 mL, 4 mL). Using 0.5 mL fractions, the elution profile was determined. Compatibility of the [68Ga]GaCl3 with NetSpot and Illuccix kits was investigated. Radiochemical purity (RCP) and 4 h stability were determined using radioTLC and radioHPLC. Using a modified [68Ga]GaCl3 cassette and new FASTLab program, 6 validation preparations were conducted using NetSpot and Illuccix kits for which RCP, stability, sterility and suitability were determined. Dual irradiation of 2 liquid targets was also performed, which was used to simultaneously prepare 1 NetSpot and 2 Illuccix kits by diluting the required activity with 0.1 M HCl.

RESULTS

The commercially available GE Cassette gave low RCP using commercial FDA kits. To optimize this, the loading efficiency onto ZR Load and the ratio of ZR resin used to load the initial activity and subsequent elution were explored. When using a 2:4 ratio of ZR Load to ZR CG, 97.89 % RCP was observed when a 3.8 mL [68Ga]GaCl3 solution was used. For Dotatate validation, 0.55 mL of buffer was added to 4.2 mL of [68Ga]GaCl3 which gave 1.35 GBq of formulated product. For Illuccix validation, [68Ga]GaCl3 was added to 2.5 mL of buffer which gave 1.52 GBq of [68Ga]Ga-PSMA-11. Formulated products passed package insert quality control (QC) requirements. When dual target irradiations were performed, 2.84 GBq was delivered to an external vial and used to label 1 NetSpot and 2 Illuccix kits simultaneously, and each kit also met or exceeded established QC criteria.

CONCLUSION

Methods are reported for using cyclotron-produced 68Ga from a liquid target in conjunction with FDA-approved NetSpot and Illucix kits. By employing a 2 mL ZR Load resin with a 4 mL ZR CG resin, adequate resolution between residual 68Zn and desired 68Ga was achieved. By modifying the FASTLab procedure to retain the final 2.5 mL of eluate from the ZR CG resin, [68Ga]GaCl3 equivalent to a new 1.85 GBq generator was obtained. This was suitable for labeling NetSpot and Illucix kits, resulting in high incorporation of 68Ga (RCP >95 %), which has not previously been demonstrated. Delivering [68Ga]GaCl3 into an external vial and diluting with 0.1 M HCl makes it possible to prepare multiple kits simultaneously. These new procedures should facilitate use of cyclotron-produced [68Ga]GaCl3 for clinical production going.

Long-term Nephrotoxicity after PRRT: Myth or Reality

Rationale: The kidneys are commonly considered as the potential dose-limiting organ for peptide receptor radionuclide therapy (PRRT), making the risk of nephrotoxicity a primary concern. This retrospective analysis with prospective documentation and long-term follow-up aims to assess the risk of nephrotoxicity after PRRT in a large cohort of patients with neuroendocrine neoplasms (NENs) treated at our institution over the past 18 years. Methods: A total of 1361 NEN patients treated with 1-10 cycles of 177Lu-DOTA-TOC/-NOC/-TATE, 90Y-DOTA-TOC/-NOC/-TATE, DUO-PRRT (sequential administration of 90Y- and 177Lu-), or TANDEM-PRRT (combination of 90Y- and 177Lu- on the same day concomitantly) were included in this analysis. All parameters were prospectively documented in a structured database comprising over 250 items per patient and retrospectively analyzed. Kidney function, including serum creatinine, blood urea nitrogen, cGFR, and electrolytes, was evaluated before each PRRT cycle and during follow-up. Restaging was regularly performed at 6-month intervals until death. Treatment-related adverse events were graded according to the Common Terminology Criteria for Adverse Events (CTCAE v.5.0). Results: Between 2000 and 2018, a total of 5409 cycles of PRRT were administered to 1361 NEN patients. Follow-up after complete treatment was available for 1281 patients receiving 4709 cycles of PRRT, with a median follow-up time of 69.2 months (interquartile range, 32.8-110.5 months) and a maximum follow-up time of 175 months. Baseline creatinine levels were normal in 1039/1281 (81.1%) subjects, while grade 1 (G1) renal insufficiency was present in 221/1281 (17.3%) prior to PRRT. G2 was present in 19/1281 (1.5%), and G3 in 2/1281 (0.2%). After treatment, the proportion of G3/G4 grade patients only increased from 0.2% to 0.7%. Mean creatinine levels increased from a baseline of 0.90 ± 0.30 to 1.01 ± 0.57 mg/L (80.0 ± 26.7 to 89.4 ± 50.8 μmol/L) after treatment. In our main analysis cohort of 1244 patients (4576 cycles), 200 patients experienced an increase in CTCAE creatinine grade. Age, number of treatment cycles, type of radionuclides, and length of follow-up time were the main factors affecting CTCAE creatinine grading after treatment. When comparing the subgroups treated with different radionuclides, the risk of nephrotoxicity after 90Y treatment alone and the 90Y/177Lu combination group was higher than after 177Lu treatment alone. In the 90Y treatment subgroup, the two significant risk factors for an increased CTCAE creatinine grade were identified to be age (≥60) and a long follow-up time. Conclusions: This retrospective analysis with prospective documentation in a large cohort of 1281 NEN patients receiving 4709 cycles of PRRT co-administered with renal protection, treated through the individualized approach at a single institution over 18 years, did not reveal any evidence of long-term PRRT-related renal toxicity. The results of our study suggest that with the use of proper renal protection, nephrotoxicity due to PRRT is more likely a myth than a reality.

Production of medical isotope (68)Ge based on a novel chromatography separation technique and assembling of (68)Ge/(68)Ga generator

A double-column chromatography separation technique was involved for isolation of ⁶⁸Ge from a bombarded Ga-Ni alloy target. About 185 MBq ⁶⁸Ge obtained was used for assembling SnO₂-based ⁶⁸Ge/⁶⁸Ga generator. Approximately 70% of ⁶⁸Ga in high radioactivity concentration was eluted from generator with excellent radionuclidic, radiochemical and chemical purity. ⁶⁸Ga was quite adequate for radiolabeling with DOTATATE or PSMA-617 with a high labelling efficiency of >92%. The double-column chromatography technique possessed a potential application prospect of ⁶⁸Ge/⁶⁸Ga production, aiding the development of ⁶⁸Ga in nuclear medicine.

Comparison of [18F]DOPA and [68Ga]DOTA-TOC as a PET imaging tracer before peptide receptor radionuclide therapy

Background

In treatment of neuroendocrine neoplasms (NENs), confirmation of somatostatin receptor expression with 68Ga-DOTA somatostatin analogues is mandatory to determine eligibility for peptide receptor radionuclide therapy (PRRT). [18F]DOPA can detect additional lesions compared to [68Ga]DOTA-TOC. The aim of this study was to explore differences in tumour detection of both tracers and their relevance for selecting patients for PRRT. We retrospectively studied eight patients with NENs who underwent both [68Ga]DOTA-TOC and carbidopa-enhanced [18F]DOPA PET/CT, before first-time PRRT with [177Lu]DOTA-TATE. Tracer order was influenced due to stock availability or to detect suspected metastases with a second tracer. On CT, disease control was defined as a lesion showing complete response, partial response, or stable disease, according to RECIST 1.1. criteria.

Results

Seven patients with in total 89 lesions completed four infusions of 7.4 GBq [177Lu]DOTA-TATE, one patient received only two cycles. Before treatment, [18F]DOPA PET/CT detected significantly more lesions than [68Ga]DOTA-TOC PET/CT (79 vs. 62, p < .001). After treatment, no difference in number of lesions with disease control was found for [18F]DOPA-only (5/27) and [68Ga]DOTA-TOC-only lesions (4/10, p = .25). [18F]DOPA detected more liver metastases (24/27) compared to [68Ga]DOTA-TOC (7/10, p = .006). Six patients showed inpatient heterogeneity in treatment response between [18F]DOPA-only and [68Ga]DOTA-TOC-only lesions.

Conclusions

Response to PRRT with [177Lu]DOTA-TATE was comparable for both [68Ga]DOTA-TOC- and [18F]DOPA-only NEN lesions. [18F]DOPA may be capable of predicting response to PRRT while finding more lesions compared to [68Ga]DOTA-TOC, although these additional lesions are often small of size and undetected by diagnostic CT.

New Fully Automated Preparation of High Apparent Molar Activity 68Ga-FAPI-46 on a Trasis AiO Platform

A large number of applications for fibroblast activation protein inhibitors (FAPI)-based PET agents have been evaluated in conditions ranging from cancer to non-malignant diseases such as myocardial infarction. In particular, ⁶⁸Ga-FAPI-46 was reported to have a high specificity and affinity for FAP-expressing cells, a fast and high accumulation in tumor lesions/injuries together with a fast body clearance when investigated in vivo. Due to the increasing interest in the use of the agent both preclinically and clinically, we developed an automated synthesis for the production of ⁶⁸Ga-FAPI-46 on a Trasis AiO platform. The new synthetic procedure, which included the processing of the generator eluate using a strong cation exchange resin and a final purification step through an HLB followed by a QMA cartridge, yielded ⁶⁸Ga-FAPI-46 with high radiochemical purity (>98%) and apparent molar activity (271.1 ± 105.6 MBq/nmol). Additionally, the in vitro and in vivo properties of the product were assessed on glioblastoma cells and mouse model. Although developed for the preparation of ⁶⁸Ga-FAPI-46 for preclinical use, our method can be adapted for clinical production as a reliable alternative to the manual (i.e., cold kit) or modular systems preparations already described in the literature.

Feasibility, Biodistribution and Preliminary Dosimetry in Peptide-Targeted Radionuclide Therapy (PTRT) of Diverse Adenocarcinomas using 177Lu-FAP-2286: First-in-Human Results

Fibroblast activation protein (FAP) is a promising target for diagnosis and therapy of numerous malignant tumors. FAP-2286 is the conjugate of a FAP-binding peptide, which can be labeled with radionuclides for theranostic applications. We present the first-in-human results using ¹⁷⁷Lu-FAP-2286 for peptide-targeted radionuclide therapy (PTRT). Methods: PTRT using ¹⁷⁷Lu-FAP-2286 was performed in 11 patients with advanced adenocarcinomas of pancreas, breast, rectum and ovary after prior confirmation of uptake on ⁶⁸Ga-FAP-2286/-FAPI-04- PET/CT. Results: Administration of ¹⁷⁷Lu-FAP-2286 (5.8 ± 2.0 GBq; range, 2.4-9.9 GBq) was well tolerated, with no adverse symptoms or clinically detectable pharmacologic effects being noticed or reported in any of the patients. The whole-body effective doses were 0.07 ± 0.02 Gy/GBq (range 0.04 - 0.1). The mean absorbed doses for kidneys and red marrow were 1.0 ± 0.6 Gy/GBq (range 0.4 - 2.0) and 0.05 ± 0.02 Gy/GBq (range 0.03 - 0.09), respectively. Significant uptake and long tumor retention of ¹⁷⁷Lu-FAP-2286 resulted in high absorbed tumor doses, e.g., 3.0 ± 2.7 Gy/GBq (range 0.5 - 10.6) in bone metastases. No grade (G) 4 adverse events were observed. G3 events occurred in 3 patients - 1 pancytopenia, 1 leukocytopenia and 1 pain flare-up; 3 patients reported pain-response. Conclusion: ¹⁷⁷Lu-FAP-2286 PTRT, applied in a broad spectrum of cancers, was relatively well-tolerated with acceptable side effects and demonstrated long retention of the radiopeptide. Prospective clinical studies are warranted.

Comparison of 18F-DOPA Versus 68Ga-DOTATOC as Preferred PET Imaging Tracer in Well-Differentiated Neuroendocrine Neoplasms

PURPOSE

The aim of this study was to retrospectively compare 18F-FDOPA versus 68Ga-DOTATOC PET in lesion detection rates and laboratory tumor markers in patients with neuroendocrine neoplasms (NENs).

PATIENTS AND METHODS

All patients with histologically proven NEN between May 2015 and February 2019 were included who underwent both 18F-DOPA and 68Ga-DOTATOC PET scans within 6 months from each other (mean, 75; median, 38; range, 2-168 days). All patients, except those with pancreatic NEN, received carbidopa before 18F-DOPA PET. Based on the number of lesions on both modalities, patients were divided into 3 categories: more lesions on 18F-DOPA (DOPA > DOTA), more lesions on 68Ga-DOTATOC (DOTA > DOPA), and equal number of lesions (DOPA = DOTA). Tumor markers chromogranin A, serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) within a maximum of 3 months around either scan were retrieved from the patients' charts.

RESULTS

18F-DOPA revealed significantly more lesions compared with 68Ga-DOTATOC (611 vs 385, P < 0.05). Twenty-four patients were included in the DOPA > DOTA group with 16 small intestinal (SI) NENs, 3 large intestinal, 4 pancreatic, and 1 tumor of unknown origin (TUO). For the 9 patients in the DOTA > DOPA group, 4 were SI, 2 pancreatic, 1 lung, and 2 TUOs. Twelve patients in the DOPA = DOTA group had 6 pancreatic tumors, 3 SI, 1 ovarian, and 2 TUOs. Only serotonin and 5-HIAA showed significant higher values for DOPA > DOTA compared with DOTA > DOPA (mean 24 vs 4, P < 0.05, and 320 vs 81, P < 0.05, respectively). Cutoff values of 20 nmol/109 for serotonin, 185 μg/L for chromogranin A, and 200 nmol/L for 5-HIAA were found to include almost exclusively DOPA > DOTA patients.

CONCLUSIONS

There is an advantage of carbidopa pretreated 18F-DOPA over 68Ga-DOTATOC PET, especially for large intestinal NENs with high levels of biomarkers. There seems to be a relationship between increased biomarker value and improved lesion detection rates with the 18F-DOPA PET scan, which requires further prospective analysis.

Fully-automated production of [68Ga]Ga-FAPI-46 for clinical application

BACKGROUND

[68Ga]Ga-FAPI-46 is a promising radiopharmaceutical for in vivo detection of the fibroblast activation protein by positron emission tomography. Until now, the synthesis of [68Ga]Ga-FAPI-46 has been only performed manually. Our aim was to evaluate the automated synthesis of this radiopharmaceutical on two different commercially available synthesis modules in order to make the tracer readily available for clinical application.

RESULTS

The synthesis of [68Ga]Ga-FAPI-46 with different amounts of precursor (10-50 μg) on the Modular Lab PharmTracer (MLPT) and Modular Lab eazy (ML eazy) from Eckert & Ziegler with a customized synthesis template and a customized single-use cassette yielded best results with 50 μg FAPI-46 for clinical multi-dose application. All relevant quality control parameters tested (e.g. sterility, stability and radiochemical purity) were in accordance with the European Pharmacopoeia.

CONCLUSIONS

[68Ga]Ga-FAPI-46 was successfully synthesized fully-automated on the synthesis modules Modular Lab PharmTracer and ML eazy and is, thus, available for multi-dose application in clinical settings.

Automated synthesis of 68 Ga/177 Lu-PSMA on the Trasis miniAllinOne

Prostate-specific membrane antigen (PSMA)-based radioligands for positron emission tomography (PET)/computed tomography (CT) studies represent the gold standard for detection of recurrent prostate cancer (PCa). [⁶⁸ Ga]PSMA-HBED-CC is a PET radiotracer suitable for detection of PCa, and its clinical use has become widespread over the last few years. In this contribution, we detail our GMP-compliant production of [⁶⁸ Ga]PSMA-HBED-CC using the Trasis miniAllinOne radiosynthesizer and report synthetic and clinical data for the first 100 productions of 2019. Additionally, we detail our efforts towards a GMP-compliant production of the radiotherapeutic [¹⁷⁷ Lu]PSMA-I&T using the same synthesis module. PSMA-based radioligand therapy (RLT) offers a possible future treatment in cases of metastatic castration-resistant PCa, and GMP-compliant routine production methods are therefore called for. This report highlights how PSMA-based agents for theranostic purposes can be conveniently produced at a single radiochemistry Good Manufacturing Practice (GMP) site, thereby facilitating optimized detection and treatment of PCa.

Fully-automated production of [68Ga]Ga-PentixaFor on the module Modular Lab-PharmTracer

Background

PentixaFor is a promising radiopharmaceutical for positron emission tomography in the detection of different tumor entities and other diseases. Until now, the synthesis of [⁶⁸Ga]Ga-PentixaFor was reported for the automated synthesis module from Scintomics® only. Our aim was to evaluate the automated synthesis of this radiopharmaceutical on a different module in order to make it available for a broader community.

Results

The synthesis of [⁶⁸Ga]Ga-PentixaFor with different amounts of PentixaFor (50 μg, 30 μg and 20 μg) on the Modular Lab PharmTracer (MLPT) from Eckert & Ziegler with the already established synthesis template for [⁶⁸Ga]Ga-DOTATOC yielded best results with 50 μg PentixaFor for clinical multi-dose application. All different quality control parameters tested (e.g. sterility, stability and radiochemical purity) were in accordance with the European Pharmacopoeia.

Conclusions

[⁶⁸Ga]Ga-PentixaFor was successfully synthesized fully-automated on the synthesis module Modular Lab PharmTracer and can be used for multi-dose application in clinical settings.

A Step-by-Step Guide for the Novel Radiometal Production for Medical Applications: Case Studies with 68Ga, 44Sc, 177Lu and 161Tb

The production of novel radionuclides is the first step towards the development of new effective radiopharmaceuticals, and the quality thereof directly affects the preclinical and clinical phases. In this review, novel radiometal production for medical applications is briefly elucidated. The production status of the imaging nuclide 44Sc and the therapeutic β--emitter nuclide 161Tb are compared to their more established counterparts, 68Ga and 177Lu according to their targetry, irradiation process, radiochemistry, and quality control aspects. The detailed discussion of these significant issues will help towards the future introduction of these promising radionuclides into drug manufacture for clinical application under Good Manufacturing Practice (GMP).

203/212Pb Theranostic Radiopharmaceuticals for Image-guided Radionuclide Therapy for Cancer

Receptor-targeted image-guided Radionuclide Therapy (TRT) is increasingly recognized as a promising approach to cancer treatment. In particular, the potential for clinical translation of receptor-targeted alpha-particle therapy is receiving considerable attention as an approach that can improve outcomes for cancer patients. Higher Linear-energy Transfer (LET) of alpha-particles (compared to beta particles) for this purpose results in an increased incidence of double-strand DNA breaks and improved-localized cancer-cell damage. Recent clinical studies provide compelling evidence that alpha-TRT has the potential to deliver a significantly more potent anti-cancer effect compared with beta-TRT. Generator-produced 212Pb (which decays to alpha emitters 212Bi and 212Po) is a particularly promising radionuclide for receptor-targeted alpha-particle therapy. A second attractive feature that distinguishes 212Pb alpha-TRT from other available radionuclides is the possibility to employ elementallymatched isotope 203Pb as an imaging surrogate in place of the therapeutic radionuclide. As direct non-invasive measurement of alpha-particle emissions cannot be conducted using current medical scanner technology, the imaging surrogate allows for a pharmacologically-inactive determination of the pharmacokinetics and biodistribution of TRT candidate ligands in advance of treatment. Thus, elementally-matched 203Pb labeled radiopharmaceuticals can be used to identify patients who may benefit from 212Pb alpha-TRT and apply appropriate dosimetry and treatment planning in advance of the therapy. In this review, we provide a brief history on the use of these isotopes for cancer therapy; describe the decay and chemical characteristics of 203/212Pb for their use in cancer theranostics and methodologies applied for production and purification of these isotopes for radiopharmaceutical production. In addition, a medical physics and dosimetry perspective is provided that highlights the potential of 212Pb for alpha-TRT and the expected safety for 203Pb surrogate imaging. Recent and current preclinical and clinical studies are presented. The sum of the findings herein and observations presented provide evidence that the 203Pb/212Pb theranostic pair has a promising future for use in radiopharmaceutical theranostic therapies for cancer.

Quantitative Test-Retest Measurement of 68Ga-PSMA-HBED-CC in Tumor and Normal Tissue

The PET radiotracer ⁶⁸Ga-PSMA (prostate-specific membrane antigen)-HBED-CC (N,N'-bis [2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid) shows potential as an imaging biomarker for recurrent and metastatic prostate cancer. The purpose of this study was to determine the repeatability of ⁶⁸Ga-PSMA-HBED-CC in a test-retest trial in subjects with metastatic prostate adenocarcinoma. Methods: Subjects with metastatic prostate cancer underwent 2 PET/CT scans with ⁶⁸Ga-PSMA-HBED-CC within 14 d (mean, 6 ± 4 d). Lesions in bone, nodes, prostate/bed, and visceral organs, as well as representative normal tissues (salivary glands and spleen), were segmented separately by 2 readers. Absolute and percentage differences in SUV_max and SUV_mean were calculated for all test-retest regions. Repeatability was assessed using percentage difference, within-subject coefficient of variation (wCV), repeatability coefficient (RC), and Bland-Altman analysis. Results: Eighteen subjects were evaluated, 16 of whom demonstrated local or metastatic disease on ⁶⁸Ga-PSMA-HBED-CC PET/CT. In total, 136 lesions were segmented in bone (n = 99), nodes (n = 27), prostate/bed (n = 7), and viscera (n = 3). The wCV for SUV_max was 11.7% for bone lesions and 13.7% for nodes. The RC was ±32.5% SUV_max for bone lesions and ±37.9% SUV_max for nodal lesions, meaning 95% of the normal variability between 2 measurements will be within these numbers, so larger differences are likely attributable to true biologic changes in tumor rather than normal physiologic or measurement variability. wCV in the salivary glands and spleen was 8.9% and 10.7% SUV_mean, respectively. Conclusion: Repeatability measurements for PET/CT test-retests with ⁶⁸Ga-PSMA-HBED-CC showed a wCV of 12%-14% SUV_max and an RC of ±33%-38% SUV_max in bone and nodal lesions. These estimates are an important aspect of ⁶⁸Ga-PSMA-HBED-CC as a quantitative imaging biomarker. These estimates are similar to those reported for ¹⁸F-FDG, suggesting that ⁶⁸Ga-PSMA-HBED-CC PET/CT may be useful in monitoring response to therapy.

From Bench to Bedside-The Bad Berka Experience With First-in-Human Studies

Precision oncology is being driven by rapid advances in novel diagnostics and therapeutic interventions, with treatments targeted to the needs of individual patients on the basis of genetic, biomarker, phenotypic, or psychosocial characteristics that distinguish a given patient from other patients with similar clinical presentations. Inherent in the theranostics paradigm is the assumption that diagnostic test results can precisely determine whether an individual is likely to benefit from a specific treatment. As part and integral in the current era of precision oncology, theranostics in the context of nuclear medicine aims to identify the appropriate molecular targets in neoplasms (diagnostic tool), so that the optimal ligands and radionuclides (therapeutic tool) with favorable labeling chemistry can be selected for personalized management of a specific disease, taking into consideration the specific patient, and subsequently monitor treatment response. Over the past two decades, the use of gallium-68 labeled peptides for somatostatin receptor (SSTR)-targeted PET/CT (or PET/MRI) imaging followed by lutetium-177 and yttrium-90 labeled SSTR-agonist for peptide receptor radionuclide therapy has demonstrated remarkable success in the management of neuroendocrine neoplasms, and paved the way to other indications of theranostics. Rapid advances are being made in the development of other peptide-based radiopharmaceuticals, small molecular-weight ligands and with newer radioisotopes with more favorable kinetics, potentially useful for theranostics strategies for the clinical application. The present review features the Bad Berka experience with first-in-human studies of new radiopharmaceuticals, for example, prostate-specific membrane antigen ligand, gastrin-releasing peptide receptor, neurotensin receptor 1 ligand, novel SSTR-targeting peptides and nonpeptide, and bone-seeking radiopharmaceuticals. Also new radioisotopes, for example, actinium (²²⁵Ac), copper (⁶⁴Cu), scandium (⁴⁴Sc), and terbium (¹⁵²Tb/¹⁶¹Tb) will be discussed briefly demonstrating the development from basic science to precision oncology in the clinical setting.

Development of 68Ga-labelled ultrasound microbubbles for whole-body PET imaging

Microbubble (MB) contrast agents have revolutionalised the way ultrasound (US) imaging can be used clinically and pre-clinically. Contrast-enhanced US offers improvements in soft-tissue contrast, as well as the ability to visualise disease processes at the molecular level. However, its inability to provide in vivo whole-body imaging can hamper the development of new MB formulations. Herein, we describe a fast and efficient method for achieving 68Ga-labelling of MBs after a direct comparison of two different strategies. The optimised approach produces 68Ga-labelled MBs in good yields through the bioorthogonal inverse-electron-demand Diel-Alder reaction between a trans-cyclooctene-modified phospholipid and a new tetrazine-bearing HBED-CC chelator. The ability to noninvasively study the whole-body distribution of 68Ga-labelled MBs was demonstrated in vivo using positron emission tomography (PET). This method could be broadly applicable to other phospholipid-based formulations, providing accessible solutions for in vivo tracking of MBs.

Optimizing the radiosynthesis of [68Ga]DOTA-MLN6907 peptide containing three disulfide cyclization bonds - a GCC specific chelate for clinical radiopharmaceuticals

In the present study, the effect of radiolabeling conditions on radiolabeling efficiency and achievable specific activity of a DOTA-conjugated highly-lipophilic peptide containing three disulfide cyclization bonds was examined. The peptide is designed to bind specifically (with high affinity) to cell-surface receptor guanylyl cyclase C (GCC), which is universally expressed by colorectal cancer cells. The effect of systematic variation of chemical parameters pH, mass of peptide, acetate buffer concentration (ionic strength), and inclusion of ethanol in the radiolabeling reaction vessel on achievable specific activity and labeling efficiency was examined. In addition, a unique approach to acetone-based elution of ⁶⁸Ga from an initial cation-exchange pre-concentration column is introduced, which improved radiochemical yield and radiochemical purity. For the evaluation of the acetone-based method, two different post-radiolabeling reverse-phase (C18) approaches to purify the final radiolabeled peptide were tested. These results revealed the potential for peptide degradation via the cleavage of disulfide cyclization bonds to form free thiols when using one of these C18 cartridges. The final optimized procedure enabled radiolabeling efficiency of greater than 99% and specific activity greater than 35 MBq/nmole in less than 30 min. The optimized parameters were amenable to the use of an automated ⁶⁸Ge/⁶⁸Ga generator and fluid-handling system for clinical production of the GCC receptor-specific [⁶⁸Ga]DOTA-MLN6907 peptide. The chemical characteristics of individual peptides govern the most appropriate radiolabeling conditions for the preparation of radiopharmaceuticals.

Peptide Receptor Radionuclide Therapy in Grade 3 Neuroendocrine Neoplasms: Safety and Survival Analysis in 69 Patients

To date, limited data are available concerning peptide receptor radionuclide therapy (PRRT) of grade 3 (G3) neuroendocrine neoplasms (NENs) with a Ki-67 proliferation index of greater than 20%. The purpose of this study was to analyze the long-term outcome, efficacy, and safety of PRRT in patients with somatostatin receptor (SSTR)-expressing G3 NENs. Methods: A total of 69 patients (41 men; age, 28-81 y) received PRRT with ¹⁷⁷Lu- or ⁹⁰Y-labeled somatostatin analogs (DOTATATE or DOTATOC). Twenty-two patients had radiosensitizing chemotherapy. Kaplan-Meier analysis was performed to calculate progression-free survival (PFS) and overall survival (OS), defined from the start of PRRT, including a subgroup analysis for patients with a Ki-67 index of less than or equal to 55% and a Ki-67 index of greater than 55%. Treatment response was evaluated according to RECIST 1.1 as well as molecular imaging criteria (European Organization for Research and Treatment of Cancer). Short- and long-term toxicity was documented (Common Terminology Criteria for Adverse Events, v 5.0) using a structured database (comprising >250 items per patient) and retrospectively analyzed. Results: Forty-six patients had pancreatic NENs, 11 had unknown primary cancer, 6 had midgut NENs, 3 had gastric NENs, and 3 had rectal NENs. The median follow-up was 94.3 mo. The median PFS was 9.6 mo, and the median OS was 19.9 mo. For G3 NENs with a Ki-67 index of less than or equal to 55% (n = 53), the median PFS was 11 mo and the median OS was 22 mo. Patients with a Ki-67 index of greater than 55% (n = 11) had a median PFS of 4 mo and a median OS of 7 mo. For patients with positive SSTR imaging but no ¹⁸F-FDG uptake, the median PFS was 24 mo and the median OS was 42 mo. A significant difference was found for both PFS and OS, with median PFS of 16 mo and 5 mo and median OS of 27 mo and 9 mo for an SUV_max of greater than 15.0 and an SUV_max of less than or equal to 15.0, respectively, on SSTR PET. In the group with ¹⁸F-FDG uptake scored as 3 or 4, the median PFS was 7.1 mo and the median OS was 17.2 mo. In the group with ¹⁸F-FDG uptake scored as 0-2, the median PFS was 24.3 mo and the median OS was 41.6 mo. PRRT was well tolerated by all patients; no grade 3 or grade 4 hematotoxicity occurred, and no clinically significant decline in renal function was observed. There was no hepatotoxicity. Conclusion: PRRT was tolerated well, without significant adverse effects, and was efficacious in G3 NENs; the clinical outcome was promising, especially in patients with a Ki-67 index of less than or equal to 55% and even in patients for whom chemotherapy had failed. Baseline ¹⁸F-FDG along with SSTR molecular imaging was useful for stratifying G3 NEN patients with high uptake on SSTR PET/CT and no or minor ¹⁸F-FDG avidity-a mismatch pattern that was associated with a better long-term prognosis.

Semi-automated system for concentrating 68Ga-eluate to obtain high molar and volume concentration of 68Ga-Radiopharmaca for preclinical applications

INTRODUCTION

⁶⁸Ga-radiopharmaceuticals are common in the field of Nuclear Medicine to visualize receptor-mediated processes. In contrast to straightforward labeling procedures for clinical applications, preclinical in vitro and in vivo applications are hampered for reasons like e.g. volume restriction, activity concentration, molar activity and osmolality. Therefore, we developed a semi-automatic system specifically to overcome these problems. A difficulty appeared unexpectedly, as intrinsic trace metals derived from eluate (Zn, Fe and Cu) are concentrated as well in amounts that influence radiochemical yield and thus lower molar activity.

METHODS

To purify Gallium-68 and to reduce the high elution volume of a ⁶⁸Ga-generator, a NaCl-based method using a column containing PS-H⁺ was implemented in a low volume PEEK system. Influence on reducing osmolality, acidity and the amount of PS-H⁺ resin (15-50 mg) was investigated. [⁶⁸Ga]Ga was desorbed from the PS-H⁺ resin with acidified 2-5 M NaCl (containing 0.05 M of HCl) and ⁶⁸Ga-activity was collected. DOTA-TATE was used as a peptide model. All buffers and additives used for labeling were mixed with Chelex 100 (~1 g/50 mL) for >144 h and eventually filtered using a 0.22 μm filter (Millipore). Quantification of metals was performed after labeling by HPLC (UV).

RESULTS

Gallium-68 activity could be desorbed from PS-H⁺ cation column with 3 M NaCl, and >60% (120-180 MBq) of [⁶⁸Ga]Ga was collected in <0.3 mL. Taking into account the used amount of ⁶⁸Ga-eluate, buffer and other excipients, the overall amount of trace metal per labeling was <1.5 nmol. DOTA-TATE could be labeled with [⁶⁸Ga]Ga with high radiochemical yield, >99% (ITLC), and a radiochemical purity of >95% (HPLC).

CONCLUSION

With the here described concentration system and metal purification technique, a low activity containing ⁶⁸Ga-generator can be used to label DOTA-peptide in preclinical applicable amounts >60 MBq/nmol (40-60 MBq/0.1 mL) and within 20 min.

Exploring the radiosynthesis and in vitro characteristics of [68 Ga]Ga-DOTA-Siglec-9

Vascular adhesion protein 1 is a leukocyte homing-associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283-297 of sialic acid-binding IgG-like lectin 9 (Siglec-9) "CARLSLSWRGLTLCPSK" bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([⁶⁸ Ga]Ga-DOTA-Siglec-9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [⁶⁸ Ga]Ga-DOTA-Siglec-9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [⁶⁸ Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non decay-corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [⁶⁸ Ga]Ga-DOTA-Siglec-9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [⁶⁸ Ga]Ga-DOTA-Siglec-9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [⁶⁸ Ga]Ga-DOTA-Siglec-9 are suitable as a positron emission tomography tracer.

Localization of Unknown Primary Site with 68Ga-DOTATOC PET/CT in Patients with Metastatic Neuroendocrine Tumor

Localization of the site of the unknown primary tumor is critical for surgical treatment of patients presenting with neuroendocrine tumor (NET) with metastases. Methods: Forty patients with metastatic NET and unknown primary site underwent ⁶⁸Ga-DOTATOC PET/CT in a single-site prospective study. The ⁶⁸Ga-DOTATOC PET/CT was considered true-positive if the positive primary site was confirmed by histology or follow-up imaging. The scan was considered false-positive if no primary lesion was found corresponding to the ⁶⁸Ga-DOTATOC-positive site. All negative scans for primary tumor were considered false-negative. A scan was classified unconfirmed if ⁶⁸Ga-DOTATOC PET/CT suggested a primary, however, no histology was obtained and imaging follow-up was not confirmatory. Results: The true-positive, false-positive, false-negative, and unconfirmed rates for unknown primary tumor were 38%, 7%, 50%, and 5%, respectively. Conclusion:⁶⁸Ga-DOTATOC PET/CT is an effective modality in the localization of unknown primary in patients with metastatic NET.

Rapid Synthesis of 68Ga-labeled macroaggregated human serum albumin (MAA) for routine application in perfusion imaging using PET/CT

^99mTc-labeled MAA is commonly used for single photon emission computed tomography SPECT. In contrast, positron emission tomography/CT (PET/CT) delivers images with significantly higher resolution. The generator produced radionuclide ⁶⁸Ga is widely used for PET/CT imaging agents and ⁶⁸Ga-labeled MAA represents an attractive alternative to ^99mTc-labeled MAA. We report a simple and rapid NaCl based labeling procedure for the labeling of MAA with ⁶⁸Ga using a commercially available MAA labeling kit for ^99mTc. The procedure delivers ⁶⁸Ga-labeled MAA with a high specific activity and a high labeling efficiency (>99%). The synthesis does not require a final step of separation or the use of organic solvents.

The effect of purification of Ga-68-labeled exendin on in vivo distribution

BACKGROUND

Ga-labeled radiotracers are increasingly used for PET imaging. During the labeling procedure, formation of (68)Ga-colloid may occur. Upon i.v. injection, (68)Ga-colloid will accumulate rapidly in the liver, spleen, and bone marrow, resulting in reduced target-to-background ratios. In this study, we applied a thin layer chromatography (TLC) method to measure colloid content and we studied the effect of the purification method on the in vivo characteristics of (68)Ga-labeled DOTA-exendin-3. DOTA-exendin-3 was labeled with (68)Ga, and the colloid content was measured by TLC on silica gel ITLC with two mobile phases. The labeling mixture was purified by gel filtration on a 5-ml G25M column, by reversed-phase high-performance liquid chromatography (RP-HPLC) using a C8 column or by solid phase extraction (SPE) on an HLB cartridge. The in vivo characteristics of the preparations were determined in BALB/c nude mice, and PET images were acquired 1 h p.i. using a microPET scanner. In these studies, unpurified (68)Ga-DOTA-exendin-3 and (111)In-DOTA-exendin-3 were used as a reference.

RESULTS

The colloid content of (111)In-DOTA-exendin-3 and unpurified, gel filtration, RP-HPLC- and SPE-purified (68)Ga-DOTA exendin-3 was <3, 7, 9, <3, and <3 %, respectively. Unpurified (68)Ga-DOTA exendin-3 showed high liver and spleen uptake. Gel filtration partly removed (68)Ga-colloid from the preparation, resulting in moderate liver and spleen SPE-purified (68)Ga-DOTA exendin-3 showed very low liver and spleen uptake, that was similar to that of RP-HPLC purified (68)Ga-DOTA exendin-3.

CONCLUSIONS

We showed that the colloid content can be measured by TLC and that solid phase extraction and HPLC completely remove (68)Ga-colloid from (68)Ga-labeled tracer preparations, resulting in very low liver and spleen uptake. This study clearly shows the importance of removal of (68)Ga-colloid from preparations.

Experience in production of (68)Ga-DOTA-NOC for clinical use under an Expanded Access IND

[(68)Ga]Ga-DOTA-NOC was produced under an Expanded Access IND for 174 clinical PET/CT studies to evaluate patients with neuroendocrine tumors. Production employed either the TiO2-based Eckert & Ziegler (EZAG) (68)Ge/(68)Ga-generator (with fractionated elution), or the SiO2-based ITG (68)Ge/(68)Ga-generator. In both cases, [(68)Ga]Ga-DOTA-NOC was reliably produced, without pre-synthesis purification of the(68)Ga generator eluate, using readily-implemented manual synthesis procedures. [(68)Ga]Ga-DOTA-NOC radiochemical purity averaged 99.2±0.4%. Administered (68)Ga dose averaged 181±22 MBq, and administered peptide mass averaged 43.2±5.2µg (n=47) and 23.9±5.7µg (n=127), respectively, using the EZAG and ITG generators. At dose expiration, (68)Ge breakthrough in the final product averaged 2.7×10(-7)% and 5.4×10(-5%) using the EZAG and ITG generators, respectively.

Radiolabeling of DOTA-like conjugated peptides with generator-produced (68)Ga and using NaCl-based cationic elution method

Gallium-68 (⁶⁸Ga) is a generator-produced radionuclide with a short half-life (t_½ = 68 min) that is particularly well suited for molecular imaging by positron emission tomography (PET). Methods have been developed to synthesize ⁶⁸Ga-labeled imaging agents possessing certain drawbacks, such as longer synthesis time because of a required final purification step, the use of organic solvents or concentrated hydrochloric acid (HCl). In our manuscript, we provide a detailed protocol for the use of an advantageous sodium chloride (NaCl)-based method for radiolabeling of chelator-modified peptides for molecular imaging. By working in a lead-shielded hot-cell system, ⁶⁸Ga³⁺ of the generator eluate is trapped on a cation exchanger cartridge (100 mg, ∼8 mm long and 5 mm diameter) and then eluted with acidified 5 M NaCl solution directly into a sodium acetate-buffered solution containing a DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) or DOTA-like chelator-modified peptide. The main advantages of this procedure are the high efficiency and the absence of organic solvents. It can be applied to a variety of peptides, which are stable in 1 M NaCl solution at a pH value of 3–4 during reaction. After labeling, neutralization, sterile filtration and quality control (instant thin-layer chromatography (iTLC), HPLC and pH), the radiopharmaceutical can be directly administered to patients, without determination of organic solvents, which reduces the overall synthesis-to-release time. This procedure has been adapted easily to automated synthesis modules, which leads to a rapid preparation of ⁶⁸Ga radiopharmaceuticals (12–16 min).

Evaluation of a PACAP Peptide Analogue Labeled with (68)Ga Using Two Different Chelating Agents

OBJECTIVE

The authors have conjugated chelating agents (DOTA and NODAGA) with a peptide (pituitary adenylate cyclase-activating peptide [PACAP] analogue) that has a high affinity for VPAC1 receptors expressed on cancer cells. To determine a suitable chelating agent for labeling with (68)Ga, they have compared the labeling kinetics and stability of these peptide conjugates.

METHODS

For labeling, (68)GaCl3 was eluted in 0.1 M HCl from a [(68)Ge-(68)Ga] generator. The influences of peptide concentration, pH, and temperature on the radiolabeling efficiency were studied. The stability was evaluated in saline, human serum, DTPA, transferrin, and metallic ions (FeCl3, CaCl2, and ZnCl2). Cell binding assay was performed using human breast cancer cells (T47D). Tissue biodistribution was studied in normal athymic nude mice.

RESULTS

Optimal radiolabeling (>95.0%) of the DOTA-peptide conjugates required a higher (50°C-90°C) temperature and 10 minutes of incubation at pH 2-5. The NODAGA-peptide conjugate needed incubation only at 25°C for 10 minutes. Both radiocomplexes were stable in saline, serum, as well as against transchelation and transmetallation. Cell binding at 37°C for 15 minutes of incubation with (68)Ga-NODAGA-peptide was 34.0% compared to 24.5% for (68)Ga-DOTA-peptide. Tissue biodistribution at 1 hour postinjection of both (68)Ga-labeled peptide conjugates showed clearance through the kidneys.

CONCLUSIONS

NODAGA-peptide showed more convenient radiolabeling features than that of DOTA-peptide.

First-In-Human Study Demonstrating Tumor-Angiogenesis by PET/CT Imaging with (68)Ga-NODAGA-THERANOST, a High-Affinity Peptidomimetic for αvβ3 Integrin Receptor Targeting

(68)Ga-NODAGA-THERANOST™ is an αvβ3 integrin antagonist and the first radiolabeled peptidomimetic to reach clinical development for targeting integrin receptors. In this first-in-human study, the feasibility of integrin receptor peptidomimetic positron emission tomography/computed tomography (PET/CT) imaging was confirmed in patients with non-small-cell lung cancer and breast cancer.

METHODS

Patients underwent PET/CT imaging with (68)Ga NODAGA-THERANOST. PET images were analyzed qualitatively and quantitatively and compared to 2-deoxy-2-((18)F) fluoro-d-glucose ((18)F-FDG) findings. Images were obtained 60 minutes postinjection of 300-500 MBq of (68)Ga-NODAGA-THERANOST.

RESULTS

(68)Ga-NODAGA-THERANOST revealed high tumor-to-background ratios (SUVmax=4.8) and uptake at neoangiogenesis sites. Reconstructed fused images distinguished cancers with high malignancy potential and enabled enhanced bone metastasis detection. (18)F-FDG-positive lung and lymph node metastases did not show uptake, indicating the absence of neovascularization.

CONCLUSIONS

(68)Ga-NODAGA-THERANOST was found to be safe and effective, exhibiting in this study rapid blood clearance, stability, rapid renal excretion, favorable biodistribution and PK/PD, low irradiation burden (μSv/MBq/μg), and convenient radiolabeling. This radioligand might enable theranostics, that is, a combination of diagnostics followed by the appropriate therapeutics, namely antiangiogenic therapy, image-guided presurgical assessment, treatment response evaluation, prediction of pathologic response, neoadjuvant-peptidomimetic-radiochemotherapy, and personalized medicine strategies. Further clinical trials evaluating (68)Ga-NODAGA-THERANOST are warranted.

Preparation of ⁶⁸Ga-labelled DOTA-peptides using a manual labelling approach for small-animal PET imaging

(68)Ga-DOTA-peptides are a promising PET radiotracers used in the detection of different tumours types due to their ability for binding specifically receptors overexpressed in these. Furthermore, (68)Ga can be produced by a (68)Ge/(68)Ga generator on site which is a very good alternative to cyclotron-based PET isotopes. Here, we describe a manual labelling approach for the synthesis of (68)Ga-labelled DOTA-peptides based on concentration and purification of the commercial (68)Ga/(68)Ga generator eluate using an anion exchange-cartridge. (68)Ga-DOTA-TATE was used to image a pheochromocytoma xenograft mouse model by a microPET/CT scanner. The method described provides satisfactory results, allowing the subsequent (68)Ga use to label DOTA-peptides. The simplicity of the method along with its implementation reduced cost, makes it useful in preclinical PET studies.

Radiosynthesis of clinical doses of ⁶⁸Ga-DOTATATE (GalioMedix™) and validation of organic-matrix-based ⁶⁸Ge/⁶⁸Ga generators

INTRODUCTION

68Ga-DOTATATE is a radiolabeled peptide-based agonist that targets somatostatin receptors overexpressed in neuroendocrine tumors. Here, we present our results on validation of organic matrix 68Ge/68Ga generators (ITG GmbH) applied for radiosynthesis of the clinical doses of 68Ga-DOTATATE (GalioMedixTM).

METHODS

The clinical grade of DOTATATE (25 μg±5 μg) compounded in 1 M NaOAc at pH=5.5 was labeled manually with 514±218 MBq (13.89±5.9 mCi) of 68Ga eluate in 0.05 N HCl at 95°C for 10 min. The radiochemical purity of the final dose was validated using radio-TLC. The quality control of clinical doses included tests of their osmolarity, endotoxin level, radionuclide identity, filter integrity, pH, sterility and 68Ge breakthrough.

RESULTS

The final dose of 272±126 MBq (7.35±3.4 mCi) of 68Ga-DOTATATE was produced with a radiochemical yield (RCY) of 99%±1%. The total time required for completion of radiolabeling and quality control averaged approximately 35 min. This resulted in delivery of 50%±7% of 68Ga-DOTATATE at the time of calibration (not decay corrected).

CONCLUSIONS

68Ga eluted from the generator was directly applied for labeling of DOTA-peptide with no additional pre-concentration or pre-purification of isotope. The low acidity of 68Ga eluate allows for facile synthesis of clinical doses with radiochemical and radionuclide purity higher than 98% and average activity of 272±126 MBq (7.3±3 mCi). There is no need for post-labeling C18 Sep-Pak purification of final doses of radiotracer. Advances in knowledge and implications for patient care. The clinical interest in validation of 68Galabeled agents has increased in the past years due to availability of generators from different vendors (Eckert-Ziegler, ITG, iThemba), favorable approach of U.S. FDA agency to initiate clinical trials, and collaboration of U.S. centers with leading EU clinical sites. The list of 68Ga-labeled tracers evaluated in clinical studies should growth because of the sensitivity of PET technique, the simplicity of the shakebake approach for the dose preparation and reliability of 68Ge/68Ga generators. Our studies have confirmed the reproducible elution profile, and high reliability of ITG GmbH generators required for routine doses preparation according to FDA recommendations.

Radiolabeling optimization and characterization of (68)Ga labeled DOTA-polyamido-amine dendrimer conjugate - Animal biodistribution and PET imaging results

The present study describes the optimization of (68)Ga radiolabeling with PAMAM dendrimer-DOTA conjugate. A conjugate (PAMAM-DOTA) concentration of 11.69µM, provided best radiolabeling efficiency of more than 93.0% at pH 4.0, incubation time of 30.0min and reaction temperature ranging between 90 and 100°C. The decay corrected radiochemical yield was found to be 79.4±0.01%. The radiolabeled preparation ([(68)Ga]-DOTA-PAMAM-D) remained stable (radiolabeling efficiency of 96.0%) at room temperature and in serum for up to 4-h. The plasma protein binding was observed to be 21.0%. After intravenous administration, 50.0% of the tracer cleared from the blood circulation by 30-min and less than 1.0% of the injected activity remained in blood by 1.0h. The animal biodistribution studies demonstrated that the tracer excretes through the kidneys and about 0.33% of the %ID/g accumulated in the tumor at 1h post injection. The animal organ's biodistribution data was supported by animal PET imaging showing good 'non-specific' tracer uptake in tumor and excretion is primarily through kidneys. Additionally, DOTA-PAMAM-D conjugation with αVβ3 receptors targeting peptides and drug loading on the dendrimers may improve the specificity of the (68)Ga labeled product for imaging and treating angiogenesis respectively.

68Ga-Based radiopharmaceuticals: production and application relationship

The contribution of ⁶⁸Ga to the promotion and expansion of clinical research and routine positron emission tomography (PET) for earlier better diagnostics and individualized medicine is considerable. The potential applications of ⁶⁸Ga-comprising imaging agents include targeted, pre-targeted and non-targeted imaging. This review discusses the key aspects of the production of ⁶⁸Ga and ⁶⁸Ga-based radiopharmaceuticals in the light of the impact of regulatory requirements and endpoint pre-clinical and clinical applications.

Novel Preclinical and Radiopharmaceutical Aspects of [68Ga]Ga-PSMA-HBED-CC: A New PET Tracer for Imaging of Prostate Cancer

The detection of prostate cancer lesions by PET imaging of the prostate-specific membrane antigen (PSMA) has gained highest clinical impact during the last years. ⁶⁸Ga-labelled Glu-urea-Lys(Ahx)-HBED-CC ([⁶⁸Ga]Ga-PSMA-HBED-CC) represents a successful novel PSMA inhibitor radiotracer which has recently demonstrated its suitability in individual first-in-man studies. The radiometal chelator HBED-CC used in this molecule represents a rather rarely used acyclic complexing agent with chemical characteristics favourably influencing the biological functionality of the PSMA inhibitor. The simple replacement of HBED-CC by the prominent radiometal chelator DOTA was shown to dramatically reduce the in vivo imaging quality of the respective ⁶⁸Ga-labelled PSMA-targeted tracer proving that HBED-CC contributes intrinsically to the PSMA binding of the Glu-urea-Lys(Ahx) pharmacophore. Owing to the obvious growing clinical impact, this work aims to reflect the properties of HBED-CC as acyclic radiometal chelator and presents novel preclinical data and relevant aspects of the radiopharmaceutical production process of [⁶⁸Ga]Ga-PSMA-HBED-CC.

68Ga-DOTA and analogs: Current status and future perspectives

The construction of the ⁶⁸Ge/⁶⁸Ga generator has increased application of radiopharmaceuticals labeled with this isotope in medicine. ⁶⁸Ga-PET is widely employed in the management of neuroendocrine tumors but favorable chemistry with tri- and tetraaza-ring molecules has opened wide range of ⁶⁸Ga application in other fields of PET imaging. This review covers the radiopharmaceuticals labeled with gallium in molecular imaging and shows perspectives on the use of gallium-68 as a substitute for technetium-99, fluorine-18 and carbon-11 in some applications.

Fast and simple one-step preparation of ⁶⁸Ga citrate for routine clinical PET

The imaging of infectious and inflammatory diseases using gallium-67 (⁶⁷Ga) citrate scintigraphy has been a well-established diagnostic tool for decades. In recent times, interest has focused on PET using the short-lived positron emitting radioisotope ⁶⁸Ga. ⁶⁸Ga is not only more readily available, it also provides better quality images whose high resolution permits quantitative analyses, thus improving the management of patients suffering from infections or inflammation. The purpose of our study was to develop a fast and reliable synthesis protocol for the preparation of ⁶⁸Ga citrate under good manufacturing practice aspects without the use of organic solvents. A commercially available synthesis module was used to perform 10 syntheses with an average yield of 768 ± 31 MBq (mean ± SD) within 10 min; 92.04 ± 1.23% of the radioactivity was located in the product vial, and the rest on the cation exchange cartridge (7.48 ± 1.23%) and in the waste vial (0.47 ± 0.28%). The radiochemical purity of the product determined by instant thin-layer chromatography was greater than 99%. The products have been proven to be sterile and pyrogen-free. Variations were made in several critical synthesis parameters, and the results are presented herein. By eliminating the use of organic solvents, the previously required quality control testing of the final product by gas chromatography can be abandoned. This novel, high-yielding method allows for a more efficient synthesis of ⁶⁸Ga citrate with both shorter production time and high radiochemical purity.

Prospective of ⁶⁸Ga-radiopharmaceutical development

Positron Emission Tomography (PET) experienced accelerated development and has become an established method for medical research and clinical routine diagnostics on patient individualized basis. Development and availability of new radiopharmaceuticals specific for particular diseases is one of the driving forces of the expansion of clinical PET. The future development of the ⁶⁸Ga-radiopharmaceuticals must be put in the context of several aspects such as role of PET in nuclear medicine, unmet medical needs, identification of new biomarkers, targets and corresponding ligands, production and availability of ⁶⁸Ga, automation of the radiopharmaceutical production, progress of positron emission tomography technologies and image analysis methodologies for improved quantitation accuracy, PET radiopharmaceutical regulations as well as advances in radiopharmaceutical chemistry. The review presents the prospects of the ⁶⁸Ga-based radiopharmaceutical development on the basis of the current status of these aspects as well as wide range and variety of imaging agents.