Manual vs automated 68 Ga-radiolabelling-A comparison of optimized processes

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

BACKGROUND

Steps have been taken by pharmaceutical companies to obtain marketing authorisation of PSMA ligands in the European Union. Since December 2022, Locametz® (PSMA-11, gozetotide) is licensed as kit for manual radiolabelling with gallium-68 and commercially available since mid-2023. The Summary of Product Characteristic (SmPC) describes manual radiolabelling with a maximum activity after radiolabelling of 1369 MBq. We aimed for radiolabelling with a higher activity to increase production efficiency, and thus, automated radiolabelling is strongly preferred over manual radiolabelling to reduce radiation exposure to personnel. The aim of this study was to develop and validate a method for automated radiolabelling of the Locametz® kit using ~ 2000 MBq of gallium-68 eluate for radiolabelling.

RESULTS

Automated radiolabelling of [68Ga]Ga-PSMA-11 using the Locametz® kit provided a product which complies to the Ph. Eur., had a shelf-life of 6 h at room temperature, and theoretically reduced radiation exposure 5.7 times. Radiolabelling with one and two generator(s) resulted in a radiochemical yield of 91-102% and 96-101% after preparation, respectively. The radiochemical purity ranged from 98.0 to 99.6% for radiolabelling with one generator and ranged from 98.4 to 99.3% for radiolabelling with two generators with similar stability. The activity of the final product was much higher when using two generators, 1961-2035 MBq compared to 740-1260 MBq, which leads to ~ 1.5 times more patient syringes available per preparation.

CONCLUSION

Automated radiolabelling of [68Ga]Ga-PSMA-11 using the Locametz® kit with higher gallium-68 activity than specified in the SmPC results in a product that is in compliance with the Ph. Eur. monograph and has a shelf-life of 6 h at room temperature. Radiolabelling with two generators proved possible and resulted in a product with similar quality but with much higher efficiency.

[68Ga]Ga-FAPI-46 synthesis on a GAIA® module system: Thorough study of the automated radiolabeling reaction conditions

The influence of several parameters involved in the 68Ga radiolabeling of FAPI-46 was studied at the scale of the automated reaction. Among the buffers tested, HEPES 0.3 M pH 4 allowed both high radiochemical purity (RCP) and radiochemical yield (RCY), without prepurification of 68Ga but after final purification of [68Ga]Ga-FAPI-46 on a C18 cartridge. A longer reaction time did not show significant benefit on the RCP, while higher loads of FAPI-46 and gentisic acid as anti-radiolysis compound allowed better RCY.

"One Method to Label Them All": A Single Fully Automated Protocol for GMP-Compliant 68Ga Radiolabeling of PSMA-11, Transposable to PSMA-I&T and PSMA-617

BACKGROUND

Prostate-specific membrane antigen (PSMA) is an ideal target for molecular imaging and targeted radionuclide therapy in prostate cancer. Consequently, various PSMA ligands were developed. Some of these molecules are functionalized with a chelator that can host radiometals, such as 68Ga for PET imaging. The 68Ga radiolabeling step benefits from process automation, making it more robust and reducing radiation exposure.

OBJECTIVE

To design a single automated radiolabeling protocol for the GMP-compliant preparation of [68Ga]Ga-PSMA-11, transposable to the production of [68Ga]Ga-PSMA-617 and [68Ga]Ga-PSMA-I&T.

METHODS

A GAIA® synthesis module and a GALLIAD® generator were used. Radio-TLC and radio-HPLC methods were validated for radiochemical purity (RCP) determination. Three [68Ga]Ga-PSMA-11 validation batches were produced and thoroughly tested for appearance and pH, radionuclide identity and purity, RCP, stability, residual solvent and sterility. Minimal modifications were made to the reagents and disposables for optimal application to other PSMA ligands.

RESULTS

[68Ga]Ga-PSMA-11 for clinical application was produced in 27 min. The 3 validation batches met the quality criteria expected by the European Pharmacopoeia to allow routine production. For optimal transposition to PSMA-617, the solid phase extraction cartridge was changed to improve purification of the radiolabeled product. For application to PSMA-I&T, the buffer solution initially used was replaced by HEPES 2.7 M to achieve good radiochemical yields. Residual HEPES content was checked in the final product and was below the Ph. Eur. threshold.

CONCLUSION

A single automated radiolabeling method on the GAIA® module was developed and implemented for 68Ga radiolabeling of 3 PSMA ligands, with slight adjustments for each molecule.

Fully automated radiolabeling of [68Ga]Ga-EMP100 targeting c-MET for PET-CT clinical imaging

BACKGROUND

c-MET is a transmembrane receptor involved in many biological processes and contributes to cell proliferation and migration during cancer invasion process. Its expression is measured by immunehistochemistry on tissue biopsy in clinic, although this technique has its limitations. PET-CT could allow in vivo mapping of lesions expressing c-MET, providing whole-body detection. A number of radiopharmaceuticals are under development for this purpose but are not yet in routine clinical use. EMP100 is a cyclic oligopeptide bound to a DOTA chelator, with nanomolar affinity for c-MET. The aim of this project was to develop an automated method for radiolabelling the radiopharmaceutical [68Ga]Ga-EMP100.

RESULTS

The main results showed an optimal pH range between 3.25 and 3.75 for the complexation reaction and a stabilisation of the temperature at 90 °C, resulting in an almost complete incorporation of gallium-68 after 10 min of heating. In these experiments, 90 µg of EMP-100 peptide were initially used and then lower amounts (30, 50, 75 µg) were explored to determine the minimum required for sufficient synthesis yield. Radiolysis impurities were identified by radio-HPLC and ascorbic acid and ethanol were used to improve the purity of the compound. Three batches of [68Ga]Ga-EMP100 were then prepared according to the optimised parameters and all met the established specifications. Finally, the stability of [68Ga]Ga-EMP100 was assessed at room temperature over 3 h with satisfactory results in terms of appearance, pH, radiochemical purity and sterility.

CONCLUSIONS

For the automated synthesis of [68Ga]Ga-EMP100, the parameters of pH, temperature, precursor peptide content and the use of adjuvants for impurity management were efficiently optimised, resulting in the production of three compliant and stable batches according to the principles of good manufacturing practice. [68Ga]Ga-EMP100 was successfully synthesised and is now available for clinical development in PET-CT imaging.

Personal dose equivalent Hp(0.07) during 68Ga-DOTA-TATE production procedures

This work presents the exposure of hands of the personnel of a nuclear medicine department who prepare and administer 68Ga-DOTA-TATE. Dosimetry measurements were performed during three 1-week sessions, for nine production procedures. A total of 360 measurements were made by using high-sensitivity MCP-N thermoluminescent detectors. Annealed detectors were and vacuum-packed in foil and then placed on each fingertip of both hands of five radiochemists and four nurses (one detector for one fingertip). The greatest exposure to ionizing radiation was found on the non-dominant left hand of radiochemists and nurses. A maximum Hp(0.07)/A value of 49.36 ± 4.95 mSv/GBq was registered for radiochemists during the 68 Ga-DOTA-DATE activity dispensing procedure. For nurses performing the radiopharmaceutical injection procedure, a corresponding maximum value of 1.28 ± 0.13 mSv/GBq was measured, while the mean value for all the nurses was 0.38 mSv/GBq. The dispensing procedure accounted for approximately 60% of the total exposure of radiochemists' fingertips. Based on the results obtained it is recommended that a ring dosimeter should be routinely placed on the middle finger of the non-dominant hand of radiochemists and nurses. Furthermore, it is proposed to systematically train workers in handling open sources of ionizing radiation, with the aim of reducing the required handling time.

Production of GMP-Compliant Clinical Amounts of Copper-61 Radiopharmaceuticals from Liquid Targets

PET imaging has gained significant momentum in the last few years, especially in the area of oncology, with an increasing focus on metal radioisotopes owing to their versatile chemistry and favourable physical properties. Copper-61 (t_1/2 = 3.33 h, 61% β⁺, E_max = 1.216 MeV) provides unique advantages versus the current clinical standard (i.e., gallium-68) even though, until now, no clinical amounts of ⁶¹Cu-based radiopharmaceuticals, other than thiosemicarbazone-based molecules, have been produced. This study aimed to establish a routine production, using a standard medical cyclotron, for a series of widely used somatostatin analogues, currently labelled with gallium-68, that could benefit from the improved characteristics of copper-61. We describe two possible routes to produce the radiopharmaceutical precursor, either from natural zinc or enriched zinc-64 liquid targets and further synthesis of [⁶¹Cu]Cu-DOTA-NOC, [⁶¹Cu]Cu-DOTA-TOC and [⁶¹Cu]Cu-DOTA-TATE with a fully automated GMP-compliant process. The production from enriched targets leads to twice the amount of activity (3.28 ± 0.41 GBq vs. 1.84 ± 0.24 GBq at EOB) and higher radionuclidic purity (99.97% vs. 98.49% at EOB). Our results demonstrate, for the first time, that clinical doses of ⁶¹Cu-based radiopharmaceuticals can easily be obtained in centres with a typical biomedical cyclotron optimised to produce ¹⁸F-based radiopharmaceuticals.

Optimization of Precursor Preparation in PSMA-11 Radiolabeling to Obtain a Highly Reproducible Radiochemical Yield

[⁶⁸Ga]Ga-PSMA-11 PET/CT plays a pivotal role in the diagnosis and staging of prostate cancer because of its higher sensitivity and detection rate compared with traditional choline PET/CT. A highly reproducible radiochemical yield of the radiopharmaceutical to be used in the clinical routine is an important parameter for planning and optimization of clinical activity. During radiometallation of PSMA-11, the presence of metal ion contaminants in the peptide precursor may cause a decrease in the [⁶⁸Ga]Ga-PSMA-11 radiochemical yield because of metal ion contaminants competition with gallium-68. To optimize the radiochemical yield of [⁶⁸Ga]Ga-PSMA-11 radiosynthesis, data obtained by preparing the solution of the PSMA-11 precursor with three different methods (A, B, and C) were compared. Methods A and B consisted of the reconstitution of different quantities of precursor (1000 µg and 30 µg, respectively) to obtain a 1 µg/mL solution. In Method A, the precursor solution was aliquoted and stored frozen, while the precursor solution obtained with Method B was entirely used. Method C consisted of the reconstitution of 1000 µg of precursor taking into account net peptide content as described in European Pharmacopoeia. Radiosynthesis data demonstrated that reconstitution methods B and C gave a consistently higher and reproducible radiochemical yield, highlighting the role of metals and precursor storage conditions on the synthesis performance.

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.

Recent Breakthrough in 68Ga-Radiopharmaceuticals Cold Kits for Convenient PET Radiopharmacy

⁶⁸Ga-PET has emerged as an important diagnostic tool for precise detection and monitoring of oncological situations. Availability, cost, and radiosynthesis procedure are determining steps for success of a radioisotope/radiopharmaceutical in nuclear medicine. Availability of ⁶⁸Ga from a ⁶⁸Ge/⁶⁸Ga generator containing a long-lived parent radioisotope (⁶⁸Ge: t_1/2 = 271 days) and an inexpensive, simplified production of ⁶⁸Ga-radiopharmaceuticals through kit methodology has allowed smooth accommodation of ⁶⁸Ga-PET in clinics. The uncomplicated formulation of ⁶⁸Ga-radiopharmaceuticals from a lyophilized, cold kit is an impending breakthrough in clinical PET. The huge success of ⁶⁸Ga in neuroendocrine tumor and prostate cancer imaging along with the regulatory approval of respective cold kits has opened a pathway for development of kits for other evolving radiotracers. There is a definite scope for increased participation of commercial manufacturers and distributors of cold kits to spread the potential of ⁶⁸Ga worldwide across all the geographical locations and satellite centers.

Production of [68 Ga]Ga-PSMA: Comparing a manual kit-based method with a module-based automated synthesis approach

The labeling of peptides with gallium-68 is often initially performed by manual labeling, but with high clinical demand, other alternatives are needed. Cold-kits or automated synthesis are viable options for standardized methods and deemed pharmaceutically more acceptable. This study compares these [68 Ga]Ga-PSMA-11 production methods. Data from 40 kit-based and 40 automated syntheses of [68 Ga]Ga-PSMA-11 were analyzed. Pre-set criteria were evaluated including radiochemical purity, radionuclidic purity, chemical purity, physiological acceptability and sterility. The operator time and radiation dose received were measured. The robustness and repeatability of each method were assessed and a comparison of the running costs of each method is also provided. For both the methods all the analyzed products met the release criteria. No differences were found in radiochemical purity, radiochemical identity, radionuclidic purity, and sterility. However, radiochemical yield and apparent molar activity showed significant differences. For both methods, whole body radiation exposure to operators was lower than with manual labeling (25 - 40 μSv). The exposure during kit-based labeling (14.5 ± μSv) was seven times higher than that of automated synthesis (2.05 ± 0.99 μSv). The automated synthesis was the more expensive method. Both methods are sound alternatives to manual synthesis and offer higher quality, better radiation protection and a more reliable manufacturing of radiopharmaceuticals.