Maturation of a Key Resource – The Germanium-68/Gallium-68 Generator: Development and New Insights

Performance and long-term consistency of five Galliform 68Ge/68Ga generators used for clinical Ga-68 preparations over a 4 year period

BACKGROUND

Gallium-68 is a positron emitter for PET applications that can be produced without cyclotron by a germanium (Ge-68) chloride/gallium (Ga-68) chloride generator. Short half-life (67.71 min) of Ga-68, matching pharmacokinetic properties of small biomolecules, facilitates isotope utilization in compounding radiopharmaceuticals for PET imaging. The increasing cost of good manufacturing practice-compliant generators has strengthened the need for radionuclide efficient use by planning specific radiopharmaceutical sessions during the week, careful maintenance of the generator and achievement of high labeling yield and radiochemical purity (RCP) of the radiolabeled molecules.

METHODS

The aim of this study was to evaluate the annual performance of five consecutive 68Ge/68Ga generators used for small-scale preparations of 68Ga-radiopharmaceuticals. To assess the long-term efficiency of isotope production we measured the weekly elution yield. To assess process efficiency we measured elution yield, labeling yield and RCP of four radiopharmaceutical preparations (68Ga-DOTATOC, 68Ga-PSMA-HBED-CC, 68Ga-PENTIXAFOR and 68Ga-DOTATATE).

RESULTS

The annual mean elution yield of the generators was 74.7%, higher than that indicated by the manufacturer, and it never went below 65%. The Ge-68 level in the final products was under the detection limits in all the produced batches (mean value 0.0000048%). The RCP of radiopharmaceuticals determined by high-performance liquid chromatography was 98 ± 0.22%. The mean yield of radiolabelling was 64.68, 68.71, 57 and 63.68% for 68Ga-DOTATOC, 68Ga-PSMA-HBED-CC, 68GaPENTIXAFOR and 68Ga-DOTATATE.

CONCLUSION

The ability to prepare in the hospital radiopharmacy high-purity and pharmaceutically acceptable 68Ga-radiolabeled probes on a routine basis facilitates patient access to precision imaging for clinical and research aims.

A Prospective Investigation of Tumor Hypoxia Imaging with 68Ga-Nitroimidazole PET/CT in Patients with Carcinoma of the Cervix Uteri and Comparison with 18F-FDG PET/CT: Correlation with Immunohistochemistry

Hypoxia in cervical cancer has been associated with a poor prognosis. Over the years ⁶⁸Ga labelled nitroimidazoles have been studied and have shown improved kinetics. We present our initial experience of hypoxia Positron Emission Tomography (PET) imaging in cervical cancer with ⁶⁸Ga-Nitroimidazole derivative and the correlation with ¹⁸F-FDG PET/CT and immunohistochemistry. Twenty women with cervical cancer underwent both ¹⁸F-FDG and ⁶⁸Ga-Nitroimidazole PET/CT imaging. Dual-point imaging was performed for ⁶⁸Ga-Nitroimidazole PET. Immunohistochemical analysis was performed with hypoxia inducible factor-1α (HIF-1α). We documented SUVmax, SUVmean of the primary lesions as well as tumor to muscle ratio (TMR), tumor to blood (TBR), metabolic tumor volume (MTV) and hypoxic tumor volume (HTV). There was no significant difference in the uptake of ⁶⁸Ga-Nitroimidazole between early and delayed imaging. Twelve patients had uptake on ⁶⁸Ga-Nitroimidazole PET. Ten patients demonstrated varying intensities of HIF-1α expression and six of these also had uptake on ⁶⁸Ga-Nitroimidazole PET. We found a strong negative correlation between HTV and immunohistochemical staining (r = −0.660; p = 0.019). There was no correlation between uptake on PET imaging and immunohistochemical analysis with HIF-1α. Two-thirds of the patients demonstrated hypoxia on ⁶⁸Ga-Nitroimidazole PET imaging.

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Prospects for the production of radioisotopes and radiobioconjugates for theranostics

The development of diagnostic methods in medicine as well as the progress in the synthesis of biologically active compounds allows the use of selected radioisotopes for the simultaneous diagnosis and treatment of diseases, especially cancerous ones, in patients. This approach is called theranostic. This review article includes chemical and physical characterization of chosen theranostic radioisotopes and their compounds that are or could be useful in nuclear medicine.

High-Efficiency Cationic Labeling Algorithm of Macroaggregated Albumin with 68Gallium

Purpose

The generator product radionuclide gallium-68(⁶⁸Ga) is widely used for PET/CT imaging agents and the ⁶⁸Ga-labeled MAA is an attractive alternative to ^99mTc-labeled MAA. Using a commercially available MAA labeling kit for ^99mTc, we presented a reliable synthesis protocol with a highly efficient, organic solvent-free cationic method in GMP conditions in the Scintomics automated synthesis unit.

Methods

The labeling process was performed by incubating for 7 min at 90 ^°C in the borax vial containing the generator product ⁶⁸GaCl₃ MAA-HEPES eluted from the PSH⁺ cartridge with 1.5 mL 5 molar NaCl. Quality control of the final product content was examined, and radiopharmaceutical production was carried out in accordance with GMP guidelines.

Results

⁶⁸Ga eluted from the generator was obtained in more than 99% radiochemical purity and efficiency. In this case, the labeling efficiency was found to be >99%. When the results of SEM-EDX analysis in the final product were examined, it was determined that most of toxic metals were no appreciable in the product content.

Conclusions

The radiochemical and chemical purity of the final product allows direct use without purification steps to remove "free ⁶⁸Ga" or other toxic compounds.

Examination of metallic impurities of 68Ge/68Ga generators used for radioactive labeling of peptides in clinical PET applications

BACKGROUND/AIM

Especially suitable for PET due to its nuclear physical and radiochemical properties, the positron emitter Gallium-68 (Ga) occurs by electron capture from Germanium-68 (Ge). In such a radionuclide generator, the germanium is bound to an insoluble, inert column matrix and forms a secular radioactive balance with 68Ga obtained in the hour. As a result of the limited radiochemical selectivity of the elution process, the eluate obtained is basically contaminated with the main nuclide traces, so that the eluate becomes a mixture of Ga and Ge radionuclides. Also, the generator eluate contains a number to metal cations that reduce specific radioactivity and can compete with 68Ga. The presence of toxic metal that can be found in the eluate carries the risks of contamination at every step from the production of generators to radiopharmaceutical production.

MATERIALS AND METHOD

In our study, by collecting the eluate of the Ge/Ga generators used with different identities in different centers in Turkey, we report comparative analysis of metal contamination in the generator eluate. The eluates of 68Ge/68Ga generators to five different identities were collected. Eluates were analyzed by inductively coupled plasma-mass spectrometry.

RESULTS AND CONCLUSION

As a result, each generator contains metallic impurities different from its certificate.

Conjugated Photosensitizers for Imaging and PDT in Cancer Research

Early cancer detection and perfect understanding of the disease are imperative toward efficient treatments. It is straightforward that, for choosing a specific cancer treatment methodology, diagnostic agents undertake a critical role. Imaging is an extremely intriguing tool since it assumes a follow up to treatments to survey the accomplishment of the treatment and to recognize any conceivable repeating injuries. It also permits analysis of the disease, as well as to pursue treatment and monitor the possible changes that happen on the tumor. Likewise, it allows screening the adequacy of treatment and visualizing the state of the tumor. Additionally, when the treatment is finished, observing the patient is imperative to evaluate the treatment methodology and adjust the treatment if necessary. The goal of this review is to present an overview of conjugated photosensitizers for imaging and therapy.

Modelling of the 177mLu/177Lu radionuclide generator

In order to determine the potential of ^177mLu/¹⁷⁷Lu radionuclide generator in ¹⁷⁷Lu production it is important to establish the technical needs that can lead to a clinically acceptable ¹⁷⁷Lu product quality. In this work, a model that includes all the processes and the parameters affecting the performance of the ^177mLu/¹⁷⁷Lu radionuclide generator has been developed. The model has been based on the use of a ligand to complex ^177mLu ions, followed by the separation of the freed ¹⁷⁷Lu ions. The dissociation kinetics of the Lu-ligand complex has been found to be the most crucial aspect governing the specific activity and ^177mLu content of the produced ¹⁷⁷Lu. The dissociation rate constants lower than 1*10^-11 s^-1 would be required to lead to onsite ¹⁷⁷Lu production with specific activity close to theoretical maximum of 4.1 TBq ¹⁷⁷Lu/mg Lu and with ^177mLu content of less than 0.01%. Lastly, the calculations suggest that more than one patient dose per week can be supplied for a period of up to 7 months on starting with the ^177mLu produced using 3 g Lu₂O₃ target with 60% ¹⁷⁶Lu enrichment. The requirements of the starting ^177mLu activity production needs to be adapted depending on the required patient doses, and the technical specifications of the involved ^177mLu-¹⁷⁷Lu separation process.

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).

Chitosan-TiO2 composite: A potential 68Ge/68Ga generator column material

A durable and ready to use ⁶⁸Ge-⁶⁸Ga generator column material is required for its routine use in radiopharmaceutical procedures. The present work comprises preliminary studies for development and evaluation of chitosan-TiO₂ based microsphere (C-TOM) composite towards its competence as a column material. The batch uptake studies showed higher distribution coefficients for ⁶⁸Ge vis-à-vis ⁶⁸Ga in the complete concentration range of HCl examined (0.01-1 mol.L^-1). Furthermore, C-TOM showed enduring physical and chemical stability in 0.01 mol.L^-1 HCl with persistent ⁶⁸Ga elution profiles (>95%) and negligible ⁶⁸Ge breakthrough (2 × 10^-4%) for the preliminary evaluation period of ∼2 months. Overall, the studies indicated that, ⁶⁸Ga with high radionuclidic purity (≥99.99%) can be eluted routinely in a small volume (∼1.5 mL) of 0.01 mol.L^-1 HCl proving its potentials as a novel solid phase extractant for ⁶⁸Ge/⁶⁸Ge generator system.

Radiosynthesis and pre-clinical evaluation of [68Ga] labeled antimicrobial peptide fragment GF-17 as a potential infection imaging PET radiotracer

The antimicrobial peptide fragment GF-17 was synthesized in-house and conjugated with DOTA and measured molecular mass of DOTA-GF-17 conjugate was 2489 Da. The peptide conjugate was purified and labeled with [⁶⁸Ga]. The best radiolabeling efficiency (95.0%) of [⁶⁸Ga]DOTA-GF-17 was achieved at pH 4 with peptide conjugate amount of 20.0 nmol with 30 min of heating at 95 °C. The product remained stable for up to 3 h. The plasma protein binding and lipophilicity for [⁶⁸Ga]DOTA-GF-17 were 80.98% and -3.12 respectively. The uptake studies with [⁶⁸Ga]DOTA- GF-17 in S.aureus and P.aeruginosa bacterial strains demonstrated binding of 69.08% and 43.69% respectively. The animal bio-distribution and PET imaging studies were in agreement showing similar pattern for organs' tracer distribution and renal excretion. The tracer had rapid blood clearance and uptake in bone marrow and muscles was very low. The highest uptake of [⁶⁸Ga]DOTA-GF-17 was observed at 45 min and 120 min in S.aureus and P.aeruginosa infections respectively. [⁶⁸Ga]DOTA-GF-17 could be a promising PET tracer and holds a great scope for taking the product further to perform extensive PET studies in animal infection (using gram negative/positive strains) models to prove the diagnostic utility of this novel PET tracer for futuristic clinical applications.

Synthesis, gallium-68 radiolabelling and biological evaluation of a series of triarylphosphonium-functionalized DO3A chelators

Radiolabelled lipophilic cations that accumulate in mitochondria according to the magnitude of the mitochondrial membrane potential can be used to report non-invasively on mitochondrial dysfunction in cardiovascular disease, cardiotoxicity, and cancer. While several such cations are already commercially available for SPECT imaging, PET offers greater promise in terms of sensitivity, resolution, and capacity for dynamic imaging and pharmacokinetic modelling. We have therefore synthesised a series of three triarylphosphonium-functionalised DO3A chelators for positron emitter gallium-68, with differing alkyl-functionalisation motifs to provide opportunities for tunable lipophilicity as a means of optimising their pharmacokinetics. To assess their capacity to report on mitochondrial membrane potential, we assessed their pharmacokinetic profiles in isolated tumour cells and isolated perfused rat hearts before and after mitochondrial depolarisation with the ionophore CCCP. All three compounds radiolabelled with over 97% RCY and exhibited log D values of between -3.12 and -1.81. In vitro assessment of the uptake of the radiotracers in cultured tumour cells showed a three-fold increase in uptake compared to unchelated [⁶⁸Ga]Ga(iii). However, each complex exhibited less than 1% retention in healthy hearts, which was not significantly diminished by mitochondrial depolarisation with CCCP. This preliminary work suggests that while this approach is promising, the lipophilicity of this class of tracers must be increased in order for them to be useful as cardiac or cancer imaging agents.

Production of novel diagnostic radionuclides in small medical cyclotrons

The global network of cyclotrons has expanded rapidly over the last decade. The bulk of its industrial potential is composed of small medical cyclotrons with a proton energy below 20 MeV for radionuclides production. This review focuses on the recent developments of novel medical radionuclides produced by cyclotrons in the energy range of 3 MeV to 20 MeV. The production of the following medical radionuclides will be described based on available literature sources: Tc-99 m, I-123, I-124, Zr-89, Cu-64, Ga-67, Ga-68, In-111, Y-86 and Sc-44. Remarkable developments in the production process have been observed in only some cases. More research is needed to make novel radionuclide cyclotron production available for the medical industry.

Dual-Nuclide Radiopharmaceuticals for Positron Emission Tomography Based Dosimetry in Radiotherapy

Improvement of the accuracy of dosimetry in radionuclide therapy has the potential to increase patient safety and therapeutic outcomes. Although positron emission tomography (PET) is ideally suited for acquisition of dosimetric data because PET is inherently quantitative and offers high sensitivity and spatial resolution, it is not directly applicable for this purpose because common therapeutic radionuclides lack the necessary positron emission. This work reports on the synthesis of dual-nuclide labeled radiopharmaceuticals with therapeutic and PET functionality, which are based on common and widely available metal radionuclides. Dual-chelator conjugates, featuring interlinked cyclen- and triazacyclononane-based polyphosphinates DOTPI and TRAP, allow for strictly regioselective complexation of therapeutic (e.g., 177 Lu, 90 Y, or 213 Bi) and PET (e.g., 68 Ga) radiometals in the same molecular framework by exploiting the orthogonal metal ion selectivity of these chelators (DOTPI: large cations, such as lanthanide(III) ions; TRAP: small trivalent ions, such as GaIII ). Such DOTPI-TRAP conjugates were decorated with 3 Gly-urea-Lys (KuE) motifs for targeting prostate-specific membrane antigen (PSMA), employing Cu-catalyzed (CuAAC) as well as strain-promoted (SPAAC) click chemistry. These were labeled with 177 Lu or 213 Bi and 68 Ga and used for in vivo imaging of LNCaP (human prostate carcinoma) tumor xenografts in SCID mice by PET, thus proving practical applicability of the concept.

Re-thinking the role of radiometal isotopes: Towards a future concept for theranostic radiopharmaceuticals

The potential and future role of certain metal radionuclides, for example, ⁴⁴ Sc, ⁸⁹ Zr, ⁸⁶ Y, ⁶⁴ Cu, ⁶⁸ Ga, ¹⁷⁷ Lu, ²²⁵ Ac, and ²¹³ Bi, and several terbium isotopes has been controversially discussed in the past decades. Furthermore, the possible benefits of "matched pairs" of isotopes for tandem applications of diagnostics and therapeutics (theranostics) have been emphasized, while such approaches still have not made their way into routine clinical practice. Analysis of bibliographical data illustrates how popularity of certain nuclides has been promoted by cycles of availability and applications. We furthermore discuss the different practical requirements for diagnostic and therapeutic radiopharmaceuticals and the resulting consequences for efficient development of clinically useful pairs of radionuclide theranostics, with particular emphasis on the underlying economical factors. Based on an exemplary assessment of overall production costs for ⁶⁸ Ga and ¹⁸ F radiopharmaceuticals, we venture a look into the future of theranostics and predict that high-throughput PET applications, that is, diagnosis of frequent conditions, will ultimately rely on ¹⁸ F tracers. PET radiometals will occupy a niche in the clinical low-throughput sector (diagnosis of rare diseases), but above all, dominate preclinical research and clinical translation. Matched isotope pairs will be of lesser relevance for theranostics but may become important for future PET-based therapeutic dosimetry.

Gallium-68 EDTA PET/CT for Renal Imaging

Nuclear medicine renal imaging provides important functional data to assist in the diagnosis and management of patients with a variety of renal disorders. Physiologically stable metal chelates like ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine penta-acetate (DTPA) are excreted by glomerular filtration and have been radiolabelled with a variety of isotopes for imaging glomerular filtration and quantitative assessment of glomerular filtration rate. Gallium-68 ((68)Ga) EDTA PET usage predates Technetium-99m ((99m)Tc) renal imaging, but virtually disappeared with the widespread adoption of gamma camera technology that was not optimal for imaging positron decay. There is now a reemergence of interest in (68)Ga owing to the greater availability of PET technology and use of (68)Ga to label other radiotracers. (68)Ga EDTA can be used a substitute for (99m)Tc DTPA for wide variety of clinical indications. A key advantage of PET for renal imaging over conventional scintigraphy is 3-dimensional dynamic imaging, which is particularly helpful in patients with complex anatomy in whom planar imaging may be nondiagnostic or difficult to interpret owing to overlying structures containing radioactive urine that cannot be differentiated. Other advantages include accurate and absolute (rather than relative) camera-based quantification, superior spatial and temporal resolution and integrated multislice CT providing anatomical correlation. Furthermore, the (68)Ga generator enables on-demand production at low cost, with no additional patient radiation exposure compared with conventional scintigraphy. Over the past decade, we have employed (68)Ga EDTA PET/CT primarily to answer difficult clinical questions in patients in whom other modalities have failed, particularly when it was envisaged that dynamic 3D imaging would be of assistance. We have also used it as a substitute for (99m)Tc DTPA if unavailable owing to supply issues, and have additionally examined the role of (68)Ga EDTA PET/CT for measuring glomerular filtration rate and split renal function.

A simple method for preparation of pure 68 Ga-acetate precursor for formulation of radiopharmaceuticals: Physicochemical characteristics of the 68 Ga eluate of the SnO2 based-68 Ge/68 Ga column generator

Gallium-68 radioisotope is an excellent source in clinical positron emission tomography application due to its ease of availability from germanium-68 (⁶⁸ Ge)/gallium-68 (⁶⁸ Ga) generator having a shelf life of 1 year. In this paper, a modified method for purification of the primary eluate of ⁶⁸ Ge-⁶⁸ Ga generator by using a small cation exchange resin (Dowex-50) column has been described. The breakthrough of ⁶⁸ Ge before and after purification of ⁶⁸ Ga eluate was 0.014% and 0.00027%, respectively. The average recovery yield of ⁶⁸ Ga after purification was 84% ± 8.6% (SD, n = 335). The results of the physiochemical studies confirmed that the ⁶⁸ Ga-acetate obtained is suitable for labeling of radiopharmaceuticals.

PSA-Stratified Performance of 18F- and 68Ga-PSMA PET in Patients with Biochemical Recurrence of Prostate Cancer

Several studies outlined the sensitivity of ⁶⁸Ga-labeled PET tracers against the prostate-specific membrane antigen (PSMA) for localization of relapsed prostate cancer in patients with renewed increase in the prostate-specific antigen (PSA), commonly referred to as biochemical recurrence. Labeling of PSMA tracers with ¹⁸F offers numerous advantages, including improved image resolution, longer half-life, and increased production yields. The aim of this study was to assess the PSA-stratified performance of the ¹⁸F-labeled PSMA tracer ¹⁸F-DCFPyL and the ⁶⁸Ga-labeled reference ⁶⁸Ga-PSMA-HBED-CC. Methods: We examined 191 consecutive patients with biochemical recurrence according to standard acquisition protocols using ¹⁸F-DCFPyL (n = 62, 269.8 MBq, PET scan at 120 min after injection) or ⁶⁸Ga-PSMA-HBED-CC (n = 129, 158.9 MBq, 60 min after injection). We determined PSA-stratified sensitivity rates for both tracers and corrected our calculations for Gleason scores using iterative matched-pair analyses. As an orthogonal validation, we directly compared tracer distribution patterns in a separate cohort of 25 patients, sequentially examined with both tracers. Results: After prostatectomy (n = 106), the sensitivity of both tracers was significantly associated with absolute PSA levels (P = 4.3 × 10^-3). Sensitivity increased abruptly, when PSA values exceeded 0.5 μg/L (P = 2.4 × 10^-5). For a PSA less than 3.5 μg/L, most relapses were diagnosed at a still limited stage (P = 3.4 × 10^-6). For a PSA of 0.5-3.5 μg/L, PSA-stratified sensitivity was 88% (15/17) for ¹⁸F-DCFPyL and 66% (23/35) for ⁶⁸Ga-PSMA-HBED-CC. This significant difference was preserved in the Gleason-matched-pair analysis. Outside of this range, sensitivity was comparably low (PSA < 0.5 μg/L) or high (PSA > 3.5 μg/L). After radiotherapy (n = 85), tracer sensitivity was largely PSA-independent. In the 25 patients examined with both tracers, distribution patterns of ¹⁸F-DCFPyL and ⁶⁸Ga-PSMA-HBED-CC were strongly comparable (P = 2.71 × 10^-8). However, in 36% of the PSMA-positive patients we detected additional lesions on the ¹⁸F-DCFPyL scan (P = 3.7 × 10^-2). Conclusion: Our data suggest that ¹⁸F-DCFPyL is noninferior to ⁶⁸Ga-PSMA-HBED-CC, while offering the advantages of ¹⁸F labeling. Our results indicate that imaging with ¹⁸F-DCFPyL may even exhibit improved sensitivity in localizing relapsed tumors after prostatectomy for moderately increased PSA levels. Although the standard acquisition protocols, used for ¹⁸F-DCFPyL and ⁶⁸Ga-PSMA-HBED-CC in this study, stipulate different activity doses and tracer uptake times after injection, our findings provide a promising rationale for validation of ¹⁸F-DCFPyL in future prospective trials.

Estimation of radiation dosimetry for 68Ga-HBED-CC (PSMA-11) in patients with suspected recurrence of prostate cancer

INTRODUCTION

This study was performed to estimate the human radiation dosimetry for [⁶⁸Ga]Ga-HBED-CC (PSMA-11) (⁶⁸Ga PSMA-11).

METHODS

Under an RDRC-approved research protocol, we evaluated the biodistribution and pharmacokinetics of ⁶⁸Ga PSMA-11 with serial PET imaging following intravenous administration to nine prostate cancer patients in whom clinical [¹¹C]acetate PET/CT exams had been independently performed under Expanded Access IND 118,204. List-mode imaging was performed over the initial 0-10min post-injection with the pelvis in the field-of-view. Whole-body images were acquired, pelvis-to-head, at 15, 60, and 90-min post-injection. Additional images of the pelvis were acquired at 40-min and 115-min, and voided urine collected from each subject at 48-min and 120-min post-injection. Radiation dosimetry estimates were calculated from these data using the OLINDA software package.

RESULTS

Renal uptake was high and relatively invariant, ranging from 11% to 14% of the injected dose between 15 and 90-min post-injection. Radioactivity collected in the voided urine accounted for 14% of the injected dose over a period of 120-min. Lymph nodes and skeletal metastases suspicious for prostate cancer recurrence were detected in a greater number of patients using ⁶⁸Ga PSMA-11 than using ¹¹C-acetate.

CONCLUSION

Kidneys are the critical organ following ⁶⁸Ga PSMA-11 administration, receiving an estimated dose of 0.413mGy/MBq.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This study confirms that the kidneys will be the critical organ following intravenous administration of ⁶⁸Ga PSMA-11, and provided data consistent with the expectation that ⁶⁸Ga PSMA-11 will be superior to [¹¹C]acetate for defining sites of recurrence in prostate cancer patients presenting with biochemical relapse.

Radiolabeled enzyme inhibitors and binding agents targeting PSMA: Effective theranostic tools for imaging and therapy of prostate cancer

Because of the broad incidence, morbidity and mortality associated with prostate-derived cancer, the development of more effective new technologies continues to be an important goal for the accurate detection and treatment of localized prostate cancer, lymphatic involvement and metastases. Prostate-specific membrane antigen (PSMA; Glycoprotein II) is expressed in high levels on prostate-derived cells and is an important target for visualization and treatment of prostate cancer. Radiolabeled peptide targeting technologies have rapidly evolved over the last decade and have focused on the successful development of radiolabeled small molecules that act as inhibitors to the binding of the N-acetyl-l-aspartyl-l-glutamate (NAAG) substrate to the PSMA molecule. A number of radiolabeled PSMA inhibitors have been described in the literature and labeled with SPECT, PET and therapeutic radionuclides. Clinical studies with these agents have demonstrated the improved potential of PSMA-targeted PET imaging agents to detect metastatic prostate cancer in comparison with conventional imaging technologies. Although many of these agents have been evaluated in humans, by far the most extensive clinical literature has described use of the ⁶⁸Ga and ¹⁷⁷Lu agents. This review describes the design and development of these agents, with a focus on the broad clinical introduction of PSMA targeting motifs labeled with ⁶⁸Ga for PET-CT imaging and ¹⁷⁷Lu for therapy. In particular, because of availability from the long-lived ⁶⁸Ge (T_1/2=270days)/⁶⁸Ga (T_1/2=68min) generator system and increasing availability of PET-CT, the ⁶⁸Ga-labeled PSMA targeted agent is receiving widespread interest and is one of the fastest growing radiopharmaceuticals for PET-CT imaging.

Mechanochemical synthesis of mesoporous tin oxide: a new generation nanosorbent for (68)Ge/(68)Ga generator technology

The present article reports the synthesis and characterization of mesoporous tin oxide (MTO) nanoparticles by a solid-state mechanochemical route. The synthesized material was used as an advanced sorbent material for (68)Ge/(68)Ga radionuclide generator technology. Gallium-68 (t½ = 68 min) obtained from the (68)Ge/(68)Ga generator is an important diagnostic radioisotope which holds tremendous potential in the non-invasive monitoring of various diseases, including cancer, using positron emission tomography (PET). The crystallite size of the MTO nanoparticles was in the range of 6-12 nm with a large surface area of 265 ± 16 m(2) g(-1), while the mean pore radius was found to be 2.1 ± 0.6 nm. Determination of the zeta-potential of the MTO nanoparticles dispersed in solutions at different pH values aided in understanding the sorption and separation mechanisms, which were based on the surface charge developed on the nanosorbent. The sorption capacity observed under column-flow conditions was 85 ± 5 mg Ge per g of nanosorbent. A clinical-scale (68)Ge/(68)Ga generator (740 MBq) was developed using this nanosorbent. Gallium-68 could be regularly eluted from this generator over a prolonged period of 1 year with >70% elution yield and met all the requirements for clinical use. The suitability of (68)Ga obtained from it was evaluated in preclinical settings by the preparation of a (68)Ga-labeled peptide containing the arginine-glycine-aspartic acid (RGD) motif. To the best of our knowledge, this is the first report on the synthesis of MTO nanoparticles by a mechanochemical route which could be effectively utilized for the routine preparation of clinical-scale (68)Ge/(68)Ga generators. The promising results obtained in this study would facilitate greater implementation of mechanochemistry for the synthesis of nanosorbents for radionuclide generator technology since this method is simple, economical and convenient.

[Disposal of radioactive contaminated waste from Ga-68-PET - calculation of a clearance level for Ge-68]

Ga-68-labeled radiotracers, particularly used for the detection of neuroendocrine tumors by means of Ga-68-DOTA-TATE or -DOTA-TOC or for the diagnosis of prostate cancer by means of Ga-68-labeled antigens (Ga 68-PSMA), become increasingly important. In addition to the high sensitivity and specificity of these radiopharmaceuticals, the short-lived radionuclide Ga-68 offers almost ideal nuclear characteristics for use in PET. Ga-68 is obtained from a germanium-gallium-generator system, so that the availability of Ga-68-labeled radiotracers is independent of an on-site-cyclotron regardless of the short half-life of Ga-68 of about 68minutes. Regarding the disposal of the radioactively contaminated waste from the preparation of the radiopharmaceutical, the eluted Ga-68 has to be considered to be additionally contaminated with its parent nuclide Ge-68. Due to this production-related impurity in combination with the short half-life of Ga-68, the radioactive waste has to be considered to be contaminated with Ge-68 and Ga-68 in radioactive equilibrium (hereafter referred to as Ge-68+). As there are no clearance levels for Ge-68+ given in the German Radiation Protection Ordinance, this work presents a method to calculate the missing value basing on a recommendation of the German Radiation Protection Commission in combination with simple geometric models of practical radiation protection. Regarding the relevant exposure scenarios, a limit value for the unrestricted clearance of Ge-68+ of 0.4 Bq/g was determined.

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.

Dual PET and Near-Infrared Fluorescence Imaging Probes as Tools for Imaging in Oncology

OBJECTIVE

The purpose of this article is to summarize advances in PET fluorescence resolution, agent design, and preclinical imaging that make a growing case for clinical PET fluorescence imaging.

CONCLUSION

Existing SPECT, PET, fluorescence, and MRI contrast imaging techniques are already deeply integrated into the management of cancer, from initial diagnosis to the observation and management of metastases. Combined positron-emitting fluorescent contrast agents can convey new or substantial benefits that improve on these proven clinical contrast agents.

Preparation of [(68)Ga]PSMA-11 for PET-CT imaging using a manual synthesis module and organic matrix based (68)Ge/(68)Ga generator

INTRODUCTION

[(68)Ga]PSMA-11 is a relatively recently introduced radiopharmaceutical for PET-CT imaging of prostate cancer patients. The availability of (68)Ge/(68)Ga generator and PSMA-11 ligand from commercial sources is facilitating the production of the radiopharmaceutical in-house. This paper describes our experience on the preparation of ~200 batches of [(68)Ga]PSMA-11 for conducting PET-CT imaging in patients suspected/suffering from prostate cancer.

METHODS

The radiosynthesis of [(68)Ga]PSMA-11 was done in a hospital based nuclear medicine department using (68)Ge/(68)Ga generator and a manual synthesis module, both supplied by Isotope Technologies Garching (ITG), Germany. The production involved the reaction of 5μg (5.3nmol) of PSMA-11 ligand in 1 ml of 0.25M sodium acetate buffer with 4ml of (68)GaCl3 in 0.05M HCl for 5min at 105°C; followed by purification in a C18 cartridge and collection through a 0.22μm pore size filter.

RESULTS

The radiochemical yields obtained were consistently high, 93.19%±3.76%, and there was hardly any batch failure. The radiochemical purity of the product was >99% and the product was stable for over 2h; however it was used in patients immediately after preparation. About 200 batches of [(68)Ga]PSMA-11 were prepared during the period and more than 300 patients received the tracer during the 14months of study. No adverse reaction was observed in any of the patients and the image qualities were consistent with literature reports.

CONCLUSION

[(68)Ga]PSMA-11 with high radiochemical and radionuclidic purity is conveniently prepared by using a (68)Ge/(68)Ga generator and manual synthesis module. The radiochemical yields are very high; and activity sufficient for 3-4 patients can be prepared in a single batch; multiple batches can be done on the same day and when needed after a gap of 1.5-2h.

Toward realization of 'mix-and-use' approach in ⁶⁸Ga radiopharmacy: preparation, evaluation and preliminary clinical utilization of ⁶⁸Ga-labeled NODAGA-coupled RGD peptide derivative

INTRODUCTION

The present article demonstrates a 'mix-and-use' approach for radiolabeling RGD peptide derivative with (68)Ga, which is easily adaptable in hospital radiopharmacy practice. The radiotracer thus formulated was successfully used for positron emission tomography (PET) imaging of breast cancer in human patients.

METHODS

The conditions for radiolabeling NODAGA-coupled dimeric cyclic RGD peptide derivative [NODAGA-(RGD)2] with (68)Ga were optimized using (68)Ga obtained from a (68)Ge/(68)Ga generator developed in-house with CeO2-PAN composite sorbent as well as from a commercial (68)Ge/(68)Ga generator obtained from ITG, Germany. Preclinical studies were carried out in C57BL/6 mice bearing melanoma tumors. The radiotracer was prepared in a hospital radiopharmacy using (68)Ga obtained from ITG generator and used for monitoring breast cancer patients by positron emission tomography (PET) imaging.

RESULTS

(68)Ga-NODAGA-(RGD)2 could be prepared with high radiolabeling yield (>98%) and specific activity (~50 GBq/μmol) within 10 min at room temperature by mixing (68)Ga with the solution of the peptide conjugate. In vivo biodistribution studies showed significant uptake (5.24±0.39% ID/g) in melanoma tumor at 30 min post-injection, with high tumor-to-background contrast. The integrin αvβ3 specificity of the tracer was corroborated by blocking study. Preliminary clinical studies in locally advanced breast cancer (LABC) patients indicated specifically high tumor uptake (SUVmax 10-15) with good contrast.

CONCLUSIONS

This is one of the very few reports which presents preliminary clinical data on use of (68)Ga-NODAGA-(RGD)2 and the developed 'mix-and-use' holds tremendous prospect in clinical PET imaging using (68)Ga.

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.

Smoothened titania particles to improve radionuclide separation and their application to the development of a novel [68Ge]/[68Ga] generator

Smoothened titania particles for a long-lived radiopharmaceutical grade ⁶⁸Ge/⁶⁸Ga generator.

Radiolabeling of Nanoparticles and Polymers for PET Imaging

Nanomedicine has become an emerging field in imaging and therapy of malignancies. Nanodimensional drug delivery systems have already been used in the clinic, as carriers for sensitive chemotherapeutics or highly toxic substances. In addition, those nanodimensional structures are further able to carry and deliver radionuclides. In the development process, non-invasive imaging by means of positron emission tomography (PET) represents an ideal tool for investigations of pharmacological profiles and to find the optimal nanodimensional architecture of the aimed-at drug delivery system. Furthermore, in a personalized therapy approach, molecular imaging modalities are essential for patient screening/selection and monitoring. Hence, labeling methods for potential drug delivery systems are an indispensable need to provide the radiolabeled analog. In this review, we describe and discuss various approaches and methods for the labeling of potential drug delivery systems using positron emitters.

An Increasing Role for 68Ga PET Imaging: A Perspective on the Availability of Parent 68Ge Material for Generator Manufacturing in an Expanding Market

The use of gallium-68 for molecular imaging is gaining momentum world-wide. While our understanding of 68Ga chemistry, generators, and associated synthesis modules appear to have advanced to a clinically-reliable stage, uncertainty in the supply of radiopharmaceutically-suitable parent is of significant concern. In this work, we examine the current supply of 68Ge in an effort to better understand the potential for expansion of manufacturing to meet an increasing demand for 68Ga. Although specific information on sales and demand of 68Ge is highly business sensitive and thus guarded, our examination finds no shortage in the current supply of 68Ge. On the other hand, increases in the use of 68Ge generators for clinical applications in the United States point to the need for continued support for production at DOE laboratories in the United States to ensure a reliable supply and suggests that new commercial facilities may be needed to meet the increasing demand.

How to cite this article

Schultz MK, Donahue P, Musgrave NI, Zhernosekov K, Naidoo C, Razbash A, Tworovska I, Dick DW, Watkins GL, Graham MM, Runde W, Clanton JA, Sunderland JJ. An Increasing Role for 68Ga PET Imaging: A Perspective on the Availability of Parent 68Ge Material for Generator Manufacturing in an Expanding Market. J Postgrad Med Edu Res 2013;47(1):26-30.

Is there still a role for SPECT-CT in oncology in the PET-CT era?

For the evaluation of biological processes using radioisotopes, there are two competing technologies: single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Both are tomographic techniques that enable 3D localization and can be combined with CT for hybrid imaging. PET-CT has clear technical superiority including superior resolution, speed and quantitative capability. SPECT-CT currently has greater accessibility, lower cost and availability of a wider range of approved radiotracers. However, the past decade has seen dramatic growth in PET-CT with decreasing costs and development of an increasing array of PET tracers that can substitute existing SPECT applications. PET-CT is also changing the paradigm of imaging from lesion measurement to lesion characterization and target quantification, supporting a new era of personalized cancer therapy. The efficiency and cost savings associated with improved diagnosis and clinical decision-making provided by PET-CT make a cogent argument for it becoming the dominant molecular technique in oncology.