A comparative assessment of radiochemical purity and yield of [¹⁸F]PSMA-1007 production using two different automated synthesis platforms: a head-to-head comparison

Abstract

Background

Glutamate carboxypeptidase II (GCPII), also known as prostate-specific membrane antigen (PSMA) is overexpressed in 90–100% of prostate cancer cells. The radiopharmaceutical [¹⁸F]PSMA-1007, recognised as a PET tracer for prostate cancer imaging, is based on PSMA inhibitor [Glu-CO-Lys(2Nal-Amb-Glu-Glu-PyTMA)] bound to the radioisotope Fluorine-18. [¹⁸F]Fluoride was obtained via the ¹⁸O(p,n)¹⁸F reaction using a cyclotron for medical use, while synthesis of [¹⁸F]PSMA-1007 was performed with two different platforms: FASTlab2 and NEPTIS^® Perform. Both modules enabled synthesis through nucleophilic substitution reaction and subsequent purification in solid phase extraction (SPE). Quality control process was validated according to the current specific monograph (3116) of the European Pharmacopoeia (Ph. Eur.) before clinical use.

Results

Twenty syntheses of [¹⁸F]PSMA-1007 for each module were performed in order to evaluate and compare radiochemical purity (96.58% ± 1.25 with FASTlab2 vs 95.86% ± 0.79 with NEPTIS^® Perform) and decay-corrected radiochemical yield (43.7% ± 3 with FASTlab2 vs 28.5% ± 3.1 with NEPTIS^® Perform).

Conclusion

Both platforms produced [¹⁸F]PSMA-1007 that consistently met all pharmacopoeial quality control standards. However, the FASTlab2 system demonstrated a statistically significant higher decay-corrected radiochemical yield (43.7% ± 3% vs. 28.5% ± 3.1%, p-value < 0.001 after statistical testing). While this yield difference does not impact radiochemical purity or product safety, it may represent a relevant advantage in terms of production efficiency and available activity for clinical use, which may influence the choice of synthesizer.

Background

It is estimated that prostate cancer (PCa) is the leading cause of death among men in Europe, where in 2024 it was considered to be responsible for 18% of new cancer diagnoses (Crocetti et al. 2025). Prostate-specific antigen (PSA) is an enzyme belonging to the hydrolase class, which is produced exclusively by the prostate gland; it is present in serum in small quantities (< 4 ng/ml) (Pezaro et al. 2014; Poppel et al. 2022), thus becoming a biochemical marker of prostate cancer but does not provide information on the location of the tumour (Hugosson et al. 2010). An early and accurate diagnosis is important and it is possible using conventional imaging techniques: magnetic resonance imaging (MRI) and computed tomography (CT) focus on morphological changes and contribute to a primary staging. In recent years, the biological complexity of PCa has been studied using nuclear medicine imaging techniques, in particular positron emission tomography/computed tomography (PET/CT), which allows in vivo images of pathophysiological processes through the administration of radiopharmaceuticals. Molecular imaging has a significant role in staging, prognosis and post-treatment monitoring (Berenguer et al. 2023): glutamate carboxypeptidase II (GCPII), also known as prostate-specific membrane antigen (PSMA), is a transmembrane glycoprotein (a zinc metallopeptidase) (Israeli et al. 1993; Silver et al. 1997) recognised as a marker for prostate nuclear imaging and therapy; it is normally expressed in prostate cells and overexpressed in 90–100% of PCa cells (on the cell surface) (Lapidus et al. 2000). GCPII has a N-terminal cytoplasmic domain, a transmembrane region and a C-terminal region, in which there is a catalytic domain (Lapidus et al. 2000; Bařinka et al. 2012): high levels of GCPII in advanced prostate cancer make it an outstanding target for PCa imaging/therapy, although its physiological function in this tissue is not known (Bařinka et al. 2012).

Radiopharmaceutical PSMA inhibitor [Glu-CO-Lys(2Nal-Amb-Glu-Glu-PyTMA)], an artificial peptide ligand used in nuclear medicine imaging (PET) (Zhang et al. 2016; Pastorino et al. 2020), is based on the chemical structure of the natural substrate N-acetyl-L-aspartyl-L-glutamate (NAAG), which binds to the extracellular domain of PSMA (Bařinka et al. 2012). Glu-CO-Lys can be labelled through a linker (2Nal-Amb-Glu-Glu-PyTMA) with short half-life radioisotopes, such as Gallium-68 ([⁶⁸Ga]Ga-PSMA-11; half life: 67.71 min) and Fluorine-18 ([¹⁸F]PSMA-1007; half-life: 109.77 min); both of these radiopharmaceuticals have monographs published on European Pharmacopoeia (Ph. Eur.), under the authority of the European Directorate for the Quality of Medicine (EDQM) (European Pharmacopoeia 2024; European Pharmacopoeia, 2021). This study focuses on [¹⁸F]PSMA-1007 because [18¹⁸F]Fluoride, a positron (β +) emitting isotope in the form of two coincident 0.511 MeV γ rays, has more advantageous half-life and simple production than Gallium-68 (Ferrari and Treglia 2021; Saule et al. 2021). The uptake of [¹⁸F]PSMA-1007 by cancer cells, compared to 2-[18¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]-FDG), the gold standard in nuclear medicine, allows for better PET image resolution due to excretion through the hepatobiliary system rather than the urinary system (around 1.2% in the first two hours) (Mena et al. 2021). [ ¹⁸F]PSMA-1007 binds with high affinity to the enzymatic site of PSMA (Fig. 1) and subsequently undergoes endocytosis after binding: endocytosis leads to an accumulation of [¹⁸F]PSMA-1007 in PCa cells (Saule et al. 2021; Mena et al. 2021; Zhou et al. 2021), which are detected in PET/CT.

Fig. 1.

Scheme of PSMA: N-terminal cytoplasmic domain (H₂N), a transmembrane region and a C-terminal extracellular region (COOH), in which there is the catalytic domain that binds [¹⁸F]PSMA-1007 [Glu-CO-Lys(2Nal-Amb-Glu-Glu-PyTMA) + [¹⁸F]]

In this work, radiolabelling procedures to obtain radiopharmaceuticals must be carried out by healthcare professionals who have received specific training and have experience in the safe use and handling of radionuclides (Heston and Tafti 2025). Radioisotope [¹⁸F]Fluoride was produced via the ¹⁸O(p,n)¹⁸F reaction using a low volume (2,5 ml) of ¹⁸O-water target irradiated in a cyclotron for medical use; synthesis of [¹⁸F]PSMA-1007 was performed by nucleophilic substitution reactions (Ahmad Fadzil et al. 2025; Kollaard et al. 2021) using two different synthesis modules.

This study aims to assess production (radiochemical yield of synthesis—RCY) of [¹⁸F]PSMA-1007 using two automated synthesis platforms in accordance with the Guidelines on Good Radiopharmacy Practice (cGRPP) (Gillings et al. 2021) issued by the Radiopharmacy Committee of the European Association of Nuclear Medicine (EANM) (Gillings et al. 2020). It also compares the quality control (including pH, half-life, radionuclidic purity, chemical identity and radiochemical purity (RCP), bacterial endotoxins and sterility), in accordance with the current specific monograph (3116) of European Pharmacopoeia (Ph. Eur.) (European Pharmacopoeia 2024) focusing mainly on the chemical and radiochemical purity of [¹⁸F]PSMA-1007 produced by two different synthesis platforms.

While several automated synthesizers are commercially available for [¹⁸F]PSMA-1007 production, direct, head-to-head comparisons of their performance under identical production and quality control conditions are scarce in the literature. Such studies are crucial for evidence-based decision-making in radiopharmacy, as the choice of platform can impact yield, consistency, operational workflow, and cost. This study aims to provide a comparative assessment of the FASTlab2 and NEPTIS^® Perform platforms, evaluating not only the critical quality attributes as per the European Pharmacopoeia but also the synthesis efficiency and robustness across twenty production batches for each module.

Methods

Cyclotron production of [¹⁸F]Fluoride

[¹⁸F]Fluoride was obtained via the ¹⁸O(p,n)¹⁸F reaction from a medical-use cyclotron, GE PETtrace 800 series cyclotron (Uppsala, Sweden) (Hess et al. 2000; Zeisler et al. 2000), that provided a proton beam with a maximum energy of 16.5 MeV and maximum current of 100 µA on target (PETtrace 2024).

In detail, [¹⁸F]Fluoride production process was possible by irradiation of a small liquid target (2.5 ml), [¹⁸O]water target (> 98% purity; Marshall Isotope LTD, Kiryat Malakhi, Israel), using a 38 ± 2 μA proton beam for about 30 min to obtain [¹⁸F]Fluoride in aqueous solution, which was used in nucleophilic substitution reactions (Nye et al. 2006).

Production of [¹⁸F]PSMA-1007

Synthesis of [¹⁸F]PSMA-1007 was performed with two different platforms: a) FASTlab2 (Ge Healthcare, Uppsala, Sweden) synthesizer using a disposable cassette system (from Advanced Biochemical Compounds, ABX, Radeberg, Germany) that already had reagents and cartridges on board (He et al. 2014); b) NEPTIS® Perform (ORA – Optimized Radiochemical Applications, Neuville, Belgium) synthesizer using a disposable cassette system with reagents and cartridges (supplied by Advanced Biochemical Compounds, ABX, Radeberg, Germany), assembled by a dedicated technical staff. Cassette assembly was performed in a laminar flow hood, while the NEPTIS synthesizer has been prepared in a class A shielded laminar flow isolator (COMECER, Italy) to ensure the aseptic process and the radioprotection of the operator.

The manufacturer (ABX) declares, in the certificate of analysis attached to the reagents and disposable cassettes, that they have been tested for bioburden and bacterial endotoxins and have been manufactured under the quality management system referring to GMP standards for production of radiopharmaceutical preparations.

FASTlab2 synthesis procedure

[¹⁸F]Fluoride was transferred into the FASTlab2, specifically into the conical reservoir, in which the [¹⁸F]Fluoride ions were trapped on an anion exchange cartridge (QMA) and then remaining; [¹⁸O]water was recovered into [ ¹⁸O]water recovery vial (Cardinale et al. 2017a; Maisto et al. 2021). Afterwards, [¹⁸F]Fluoride ions were eluted from the QMA into the reaction vessel, using a solution containing 0.014 M tetrabutylammonium hydrogen carbonate (TBA·HCO₃) (Ahmad Fadzil et al. 2025). 2 mg of PSMA-1007 precursor (GMP) (Neels et al. 2018) was added into reaction vessel and here, at a temperature of 95°C the precursor underwent nucleophilic substitution; once the labelling has been completed, the solution came out of the reaction vessel, mixed with 10 ml of 5% ethanol and it passed through chromafix PS-H⁺ and tC18 cartridges. [ ¹⁸F]PSMA-1007, to ensure solid-phase extraction (SPE) (Cardinale et al. 2020), was trapped into tC18, while the remaining PSMA-1007 precursor was trapped into chromafix PS-H⁺ (a strong cation exchanger). Both cartridges were washed with 5% ethanol and then the [¹⁸F]PSMA-1007 purified was eluted with 30% ethanol from tC18 into a sterile single-use vial, supplied and certified by ABX, containing 530 mg of sodium ascorbate in 20 ml of Phosphate-buffered saline (PBS – pH 7.4) (Ahmad Fadzil et al. 2025; Cardinale et al. 2017a; Maisto et al. 2021). The final product (20 mL) was filtered using a 0.22 µm sterile filter unit (Millex-SG - Merck Life Science, Italy); [¹⁸F]PSMA-1007 synthesis steps took approximately 40 min (Table 1).

Table 1.

Comparison of [¹⁸F]PSMA-1007 synthesis using two different modules

[18F]PSMA-1007	FASTlab2	NEPTIS-Perform
Module	Disposable cassette ready to use	Disposable cassette to assembled
[18F] Phase transfer TBA·HCO3	0.014 M	0.075 M
Precursor (mg)	2	1.6
Solvent Evaporation	Heating	Heating
Labelling (°C)	95	105
Product purification	SPE	SPE
Final volume (ml)	20	20
Processing time (min)	40	45

NEPTIS^® Perform synthesis procedure

Unlike the FASTlab2 module, the disposable cassette was prepared by the operator under a laminar flow hood, specifically: the ready-to-use reagent vials were loaded onto the cassette skeleton; 5.5 mL of ethanol was added to the water bag (100 mL); 1.6 mg of PSMA-1007 precursor (GMP) (Neels et al. 2018) was dissolved in 2 mL of dimethyl sulfoxide (DMSO); a single-use vial, supplied and certified by ABX, containing 400 mg of sodium ascorbate was dissolved with 3 mL of PBS (pH 7.4). All reagents were loaded onto the cassette, which had previously been placed in the synthesis module.

[¹⁸F]Fluoride was transferred into the conical column reservoir, in which the [¹⁸F]Fluoride ions were trapped on an anion exchange cartridge (QMA); [¹⁸O]water was recovered into [¹⁸O]water recovery vial (He et al. 2014). [¹⁸F]Fluoride ions were eluted into the reaction vessel, using a solution containing 0.075 M tetrabutylammonium hydrogen carbonate (TBA·HCO₃); after the evaporation phase of residual solvents promoted by high temperatures, PSMA-1007 precursor was added to the reaction vessel, where the nucleophilic substitution reaction took place, at a temperature of 105°C. At the end of labelling, the product passed through Chromafix PS-H + and tC18 to remove chemical and radiochemical impurities (Neels et al. 2018). The product was finally eluted with 5 mL of 30% EtOH solution into the product vial, passing through a sterile Millex-Cathivex GV 0.22-µm filter (Millex-SG -Merck Life Science, Italy) and diluted with 3 mL of PBS + 400 mg sodium ascorbate and brought to a volume of 20 mL with 12 mL of PBS (Naka et al. 2020; Cardinale et al. 2017b). Synthesis steps took approximately 45 min (Table 1).

[¹⁸F]PSMA-1007 quality control

Acceptance criteria, specifications and release timing were chosen in compliance with the current general texts and related monograph (3116) of the Ph. Eur. (European Pharmacopoeia 2024). pH was verified using pH indicator strips (VWR Chemicals, Italy, increment 0.5 pH unit); radionuclidic purity by gamma-ray spectrometry (GammaVision - Ortec, Illinois, USA) with principal gamma photons of 0.511 MeV; liquid chromatography was performed on an Ultimate 3000 system (HPLC: High Performance Liquid Chromatography): equipped with a UV variable wavelength detector RS300 (Thermo Fischer Scientific, Germany) and a radiometric detector (GABI, Raytest, Germany). The system was controlled by Chromeleon software version 7.2 SR5 (Dionex Sunnyvale, CA, USA); the column was a C18 solid core octadecylsilyl silica gel for chromatography (2.7 μm), 0.15 m—4.6 mm (Restek Corporation, USA). Chromatography was performed using a mobile phase A: 1000 mL of a 3.12 g·L⁻¹ solution of sodium dihydrogen phosphate (from Sigma Aldrich, USA) added with 10.0 mL of a 90 g·L⁻¹ solution of phosphoric acid (Merck Life Science, Italy) and adjusted to pH 2.5 ± 0.1 with phosphoric acid; a mobile phase B: acetonitrile from Sigma Aldrich, USA; the flow rate was set at 1.3 mL·min-1, UV wavelength at 225 nm, column oven at 30 °C. The gradient elution was programmed as follows: 77% A and 23% B for 2 min; from 77% A to 70% A and from 23% B to 30% B over 12 min; then from 70% A to 40% A and from 30% B to 60% B over 3 min; and finally 40% A and 60% B for 4 min (European Pharmacopoeia, 2020, European Pharmacopoeia. Osmolality, 2024). Thin-layer chromatography was performed using a TLC silica gel plate (Aluminum TLC plate, silica gel coated with flourescent indicator F₂₅₄; 5 × 10 cm, Merck Life Science, Italy). The solvent for development of TLC plate was a solution of water from Milli-Q Millipore system and acetonitrile (Sigma Aldrich) (40:60 v/v); plate was developed over 2/3 of its length and was then analyzed with a radio-TLC scanner (Elysia-Raytest, Germany). The RCP was calculated using the formula recommended by Ph.eur.: Radiochemical Purity = (100 – B) x T; where B is the percentage of [¹⁸F]Fluoride base on TLC analysis, and T is the ratio of [¹⁸F]PSMA-1007 radioactivity to the total radioactivity detected by HPLC (European Pharmacopoeia 2024). Determination of residual solvent (ethanol - DMSO) in the final formulation was carried out by gas chromatography (GC 6850 Series II, Agilent, USA) controlled by Raytest Iberica software (Barcelona, Spain): the column was a GC Column “5cg HP-Fast GC Residual Solvent Column” 30 m, 0.53 mm, 1.0um (Agilent Technologies, Germany), carrier gas was helium, the flame ionization detector (FID) was set at 300 °C and oven temperature was programmed from 33 °C to 160 °C in 10 min. Although not required by the specific monograph, we also determined osmolality using an OSMO1 osmometer (Advanced Instruments, Norwood, USA). Bacterial endotoxins were investigated by Endosafe Nexgen-PTS technology (Charles River, Massachusetts, USA) on a 1:40 diluted sample. The sterility instead was verified by an external service (ISZLER: Experimental Zooprophylactic Institute of Lombardia and Emilia-Romagna): the radiopharmaceutical was released for human use before the completion of this test (European Pharmacopoeia 2024).

Comparative evaluation process of the two synthesis platforms

Before the administration to the patients, five validation syntheses for each module (FASTlab2 – NEPTIS^® Perform) were performed to verify the production process and the quality control, in accordance with the specifications published on the Ph. Eur. current monograph (European Pharmacopoeia 2024). This study shows the comparative evaluation of radiochemical purity and yield of [¹⁸F]PSMA-1007 performed on twenty syntheses for each module, performed after the validation process.

All quantitative data are presented as mean ± standard deviation. The differences in radiochemical yield, RCP, ethanol residual, and other continuous parameters between the two synthesis platforms were analyzed using an unpaired two-tailed Student’s t-test for normally distributed (Hₐ: µ FASTlab2 > µ NEPTIS). A p-value of less than 0.05 was considered statistically significant. All statistical analyses were performed using jamovi, version 2.6 [The jamovi project (2025)].

Results

Comparative analysis of [¹⁸F]PSMA-1007 production with the two systems (NEPTIS^® Perform vs FASTlab2)

Twenty syntheses of [¹⁸F]PSMA-1007 per module, as mentioned in the previous paragraph, were performed in order to evaluate and compare the data, summarised in Table 2. This table shows the average production data using two different synthesis platforms, specifically: the average activity of [¹⁸F]Fluoride at the end of beam (EOB) was 38541 ± 4296 MBq for FASTlab2 and 41237 ± 3991 MBq for NEPTIS^® Perform: these data do not come from direct measurement with a dose calibrator but estimated using the proton beam parameters (beam current and irradiation time). [¹⁸F]Fluoride activity captured in QMA between FASTlab2 and NEPTIS was measured with a Geiger-Muller detector (installed and calibrated into the modules) and it registered 39335 ± 2954 MBq vs. 40566 ± 1516 MBq; [¹⁸F]Fluoride activity transported from QMA to the reaction vessel was 36704 ± 2791 MBq for FASTlab2 vs. 39079 ± 1863 MBq); the average activity of [¹⁸F]Fluoride remaining in the reaction vessel after labelling was 2501 ± 170 MBq for FASTlab2 versus 2324 ± 333 MBq. The average activity of [¹⁸F]PSMA-1007 produced at the end of synthesis (EOS) was significantly higher (p-value < 0.001) for the FASTlab2 module (20122 ± 1564 MBq) than for NEPTIS (13588 ± 1658 MBq), reflected in the decay-corrected radiochemical yield (%) and molar activity (GBq/µmol) at EOS values: 43.7 ± 3% and 350 ± 42.3 GBq/µmol (time of synthesis: 40 min) versus 28.5 ± 3.1% and 245.2 ± 72 GBq/µmol (time of synthesis: 45 min). As it can be deduce from these data, the activity of [¹⁸F]Fluoride captured in the QMA cartridge of the two different modules is comparable, however, there was an absolute difference of 15.2 ± 3% in RCY between the two synthesis platforms to the advantage of FASTlab2 (p-value < 0.001 – Table 2, Fig. 2).

Table 2.

Comparison of average data relating to 20 syntheses of [¹⁸F]PSMA-1007 for each platform used

Platform	EOB (MBq)	18F QMA (MBq)	18F React (MBq)	18F React Residual (MBq)	[18F]PSMA-1007 EOS (MBq)	Molar activity EOS (GBb/µmol)	Decay corrected yield RCY (%)	Student’s t (RCY%)
Fastlab2	38541 ± 4296	39335 ± 2954	36704 ± 2791	2501 ± 170	20122 ± 1564	350.5 ± 42.3	43.7 ± 3	p-value < 0.001*
Neptis	41237 ± 3991	40566 ± 1516	39079 ± 1863	2324 ± 333	13588 ± 1658	245.2 ± 72	28.5 ± 3.1

^*Independent Samples T-Test calculated on Decay corrected yield (%) data only (Hₐ: µ FASTlab2 > µ NEPTIS)

Fig. 2.

[¹⁸F]PSMA-1007 Yield corrected to decay (%) distribution comparison among FASTlab2 and NEPTIS syntheses results

Comparative analysis of quality control of [¹⁸F]PSMA-1007 (NEPTIS^® Perform vs FASTlab2)

Quality control of the radiopharmaceutical before administration to the patients was performed on the 10 validation syntheses (five for each module), following the current monograph (3116) of the Ph. Eur. (European Pharmacopoeia 2024).

Also the data from the 20 syntheses of this comparative study (listed between the two platforms used) and each single production, as evidenced, meets the requirements set by Ph. Eur. (Table 3).

Table 3.

[¹⁸F]PSMA-1007 monograph release criteria and comparison test results between NEPTIS®-Perform and FASTlab2

Parameter	Release criteria (monograph 3116 Ph. Eur)	FASTlab2	NEPTIS-Perform	Student’s t*
Visual inspection	Clear, colorless	Clear, colorless	Clear, colorless
pH	4.5–8.5	7.0	7.0
Radiochem. Purity (HPLC)	≥ 91%	96.58 ± 1.25	95.86 ± 0.79	p-value 0.054
Radiochem. Impurities (TLC)	≤ 5% (18F-Fluorine)	0.62 ± 0.53	0.61 ± 0.37	p-value 0.468
Ethanol Residual (GC)	< 10% v/v	8.46 ± 0.61	7.88 ± 0.85	p-value 0.006
Osmolality (mOsm/kg)	Not required	1920 ± 103	1798 ± 66.2
Radionuclidic Identity (T1/2)	105–115 min	111.52 ± 3.18	108.94 ± 2.48
Radionucl. Identity – Gray Spectrometer	Princ. Photons: 0.511 MeV	√	√
Endotoxins	< 175 IU·V−1	< 175 IU·V−1	< 175 IU·V−1
Sterility	Sterile	√	√
Stability	Not required	verified for up to 8 h	verified for up to 8 h

^*Independent Samples T-Test calculated on RCP (%) and Ethanol Residual data only (Hₐ: µ FASTlab2 > µ NEPTIS)

The radiopharmaceutical appeared clear and colourless; the pH fell within the acceptance criteria (4.5–8.5) with an average of 7.0; RCP was verified by HPLC with a radiometric detector and must be at least ≥ 91% of total radioactivity: both synthesis modules produce a radiopharmaceutical that met these criteria (95.86 ± 0.79% NEPTIS vs 96.58 ± 1.25% FASTlab2). Radiopharmaceutical RCP was also verified by TLC and with both modules it met the acceptability criteria ([¹⁸F]Fluoride ≤ 5%), 0.61 ± 0.37% vs 0.62 ± 0.5% (Fig. 3).

Fig. 3.

[¹⁸F]PSMA-1007 Radiochemical purity distribution comparison among NEPTIS and FASTlab2, analyzed with HPLC (%RCP of [¹⁸F]PSMA-1007) and TLC method (%.¹⁸F-Fluorine)

To avoid exceeding the threshold of 10% v/v ethanol according to Ph. Eur. (< 10% V/V and < 2.5 g·dose⁻¹), the final product was formulated at 20 ml with PBS (pH 7.4); it was analyzed by gas chromatography: 7.88 ± 0.85% with NEPTIS vs 8.46 ± 0.61% with FASTlab2 (Fig. 4) (Serdons et al. 2008; European Pharmacopoeia 2020). Ethanol within the preparation contributes to increasing the number of osmotically active particles; Table 3 shows % ethanol data and the osmolality (mOsm/kg) of the radiopharmaceutical solution: 7.88 ± 0.85% ethanol corresponds to 1798 ± 66.2 mOsm/kg; 8.46 ± 0.61% corresponds to 1920 ± 103 mOsm/kg. To give value to this data comparison, we prepared a 10% ethanol solution in PBS (v/v) and we performed gas chromatography and osmometric analyses: out of 10 repetitions, we obtained 10 ± 0.27% ethanol and osmolality equal to 2150 ± 20.6 mOsm/kg (European Pharmacopoeia. Osmolality, 2024).

Fig. 4.

Comparative analysis of ethanol residual (%) in [¹⁸F]PSMA-1007 productions among NEPTIS and FASTlab2, analyzed by gas chromatography

Radionuclide identity (T1/2) fell within the acceptance criteria (105–115 min) with both modules; checking of radionuclide identity using a gray spectrometer, detected, as required by the monograph, the emission of principal photons at 0.511 MeV.

The level of bacterial endotoxins is under the limit of 175 IU·V⁻¹ and all preparations were sterile, regardless of the system used. We also verified and validated the stability of the radiopharmaceutical [¹⁸F]PSMA-1007: the vial containing the final product was stored at room temperature in a shielded isolator, an aliquot was taken at T₀ from the end of the synthesis, and quality control was performed by verifying all the parameters indicated in the specific monograph (European Pharmacopoeia 2024). Subsequently, a new aliquot was taken every hour after T₀ and the quality control was rechecked; the study was conducted up to 8 h post-synthesis (from T₀ to T₈), demonstrating that all parameters met the criteria of the Ph. Eur. (European Pharmacopoeia 2024), especially that radiopharmaceutical RCP remained consistently above 91% with both synthesis platforms. This data is very significant because a decrease in RCP can diminish over and affect the quality of PET/CT diagnostic images, risking subjecting the patient to ionising radiation without diagnostic benefit (Fahey and Stabin 2014).

Discussion

Radiopharmaceutical [¹⁸F]PSMA-1007, a marker for prostate nuclear imaging, is based on PSMA inhibitor [Glu-CO-Lys(2Nal-Amb-Glu-Glu-PyTMA)] bound to the radioisotope Fluorine-18 (Zhang et al. 2016; Pastorino et al. 2020). In this study, we compared two synthesis platforms, specifically FASTlab2 and NEPTIS^® Perform, evaluating the production processes through radiochemical yields and the quality control process, assessing the parameters required by the current Ph. Eur. monograph (European Pharmacopoeia 2024), with a focus on RCP.

First, regarding the choice of radioisotope: in the literature, PSMA inhibitors used as markers for prostate nuclear medicine are mainly linked to Fluorine-18 or Gallium-68 (Soydal et al. 2023; Hoffmann et al. 2022a, 2022b); Fluorine-18 was chosen due to its more advantageous half-life and the availability, in our centre, of two synthesis platforms with disposable cassette systems. [¹⁸F]Fluoride, aqueous solution, as described by Hess et al. 2000 (Nye et al. 2006), was obtained via the ¹⁸O(p,n)¹⁸F reaction from a small cyclotron for medical use, while the synthesis of radiopharmaceutical [¹⁸F]PSMA-1007 was established on two different synthesis modules, both based on nucleophilic substitution reaction and purification of the final product by Solid Phase Extraction. Both platforms use two different single-use cassette systems that ensure a high degree of simplicity in preparation and safety for the operator in accordance with the Guidelines on Good Radiopharmacy Practice (cGRPP). Compliance with GMP for cassettes and reagents is guaranteed by the manufacturer (ABX), but only qualified personnel carry out the synthesis process. As already mentioned in the Methods section, FASTlab2 synthesizer uses a disposable cassette system that already has reagents and cartridges on board; NEPTIS system requires that the operator, working under a laminar flow hood, prepare reagent vials and cartridges, following the procedures recommended by ABX, and load them onto the cassette. These operations mean that the NEPTIS system has a more complex workflow, but a skilled technical team ensures that every batch of the radiopharmaceutical produced is sterile (as can be seen in Table 3).

There are also methodological differences in the synthesis of [¹⁸F]PSMA-1007, depending on the module used, as described in the Methods section and in Table 1: with both systems [ ¹⁸F]Fluoride ions are eluted from QMA with TBA·HCO3, but in different concentration (0.014 M for FASTlab2 and 0.075 M for NEPTIS); residual solvents are evaporated by heating; 2 mg of PSMA precursor is used in FASTlab2 system while 1.6 mg in NEPTIS system; the labelling procedure in the reaction vessel takes place at 95°C for the first system and at 105°C for the second; purification takes place in solid-phase extraction and, in both cases, the final formulation is made with PBS (pH 7.4) at a total volume of 20 ml. These minimal variations especially in labelling temperature and precursor concentration, could lead to differences in RCY and molar activity between the two systems (Fig. 2 and Table 2); as can be seen instead from the HPLC analysis (Table 3), do not affect the RCP of the radiopharmaceutical produced with both synthesis modules. Our work therefore was focused on the RCY, which showed an imbalance to the advantage of FASTlab2 (average data of 43.7 ± 3% versus 28.5 ± 3.1%) with an absolute difference between the modules of 15.2%. A statistical evaluation was performed on these data by applying a Student’s t-Test to indipendence variable, assuming that yield of synthesis data from FASTlab2 are higher than NEPTIS: the test showed statistical significance with a p-value < 0.001 (Table 2). The standard deviation, 3% in both cases, indicates linearity in the synthesis yield regardless of the batch of PSMA precursor used.

The radiopharmaceutical produced with the FASTlab2 module showed a significantly higher RCY, which led us to analyse the possible factors that determined this difference: the same beam parameters and the same target were used by cyclotron for the production of [¹⁸F]Fluoride; despite using different concentrations of TBA·HCO3, there were no significant differences in the phase transfer (Table 2); we did not detect any leakage within the module (especially into NEPTIS) by monitoring, during the synthesis process, the Geiger-Muller detectors located inside the module and in the shielded isolator. As described by Naka et al. 2020, there are other aspects to consider: the possibility that the final product may be absorbed by the materials used, but silicone tubing were used for both systems; or the eventuality that there were differences in SPE purification, but we have no experimental data to assert this.

The comparison of the RCP of [¹⁸F]PSMA-1007, as shown in Table 3 and Fig. 3, did not reveal any statistical significant differences based on the synthesis module used. In fact, the data derived from TLC analysis show comparable results (NEPTIS^® vs FASTlab2 TLC: 0.61 ± 0.37 vs 0.62 ± 0.53; p-value 0.468, Table 3), while the HPLC analyses showed a tendency to a superior purity with the FASTlab2 platform with a p-value very near to statistical significance (NEPTIS^® vs FASTlab2 HPLC: 95.86 ± 0.79%; HPLC 96.58 ± 1.25%; p-value 0.054, Table 3). These data are consistent with other studies (Katzschmann et al. 2021; Ioppolo et al. 2023) and suggest that the different RCY between the two systems does not affect the RCP of the radiopharmaceutical.

Another parameter analyzed using gas chromatography is the percentage of ethanol (v/v) in the final preparation: in accordance with the studies of Cardinale et al. 2020 (Cardinale et al. 2020) and Ioppolo et al. 2023 (Ioppolo et al. 2023) it stands at 8.46 ± 0.61% with FASTlab2 vs 7.88 ± 0.85% with NEPTIS^® (p-value 0.006, Table 3). We compared the data derived from gas chromatography analysis with osmolality analysis: resulting in 7.88 ± 0.85% ethanol which corresponds to 1798 ± 66.2 mOsm/kg, 8.46 ± 0.61% which corresponds to 1920 ± 103 mOsm/kg. This type of analysis is not required by the monograph, but we have included it in order to monitor this parameter as well (evaluation required in the specific chapter of the Ph.Eur (European Pharmacopoeia. Osmolality, 2024)). Product stability has been confirmed, for both systems, over 8 h post-production through RCP analysis via HPLC and TLC; moreover, all productions were sterile (Table 3), conforming to the safety of the production process.

The aim of this study was to compare data derived from 40 productions of [¹⁸F]PSMA-1007 (20 from FASTlab2, 20 from NEPTIS) and from the relative quality control (in accordance with the current specific monograph (3116) of the Ph. Eur. (European Pharmacopoeia 2024)). The only significant differences found concern: the higher RCY with FASTlab2, which is acceptable considering the half-life of the Fluorine-18 radioisotope (109.77 min) and the availability of a cassette system ready to use (FASTlab2) vs a cassette system prepared by the operator (NEPTIS). No cost assessments of the two systems were made because this was not the objective of our work, which was to verify the degree of radiochemical purity and safety of the radiopharmaceutical.

Conclusion

In this work, we described the synthesis of the radiopharmaceutical [¹⁸F]PSMA-1007 using two different synthesis platforms (FASTlab2 and NEPTIS^® Perform), both single-use cassettes that use the nucleophilic substitution strategy starting from the same precursor molecule (different milligrams and labelling temperatures), with final purification of the product in solid-phase extraction (SPE). [¹⁸F]PSMA-1007 productions, despite minimal differences in synthesis conditions between the two systems, have ensured reproducibility and stable activity yields; quality control met the acceptance criteria defined by the specific monograph of the current European Pharmacopoeia, in particular high radiochemical purity verified through HPLC and TLC analysis. Based on this study, we can state that with FASTlab2 there is a higher risk of obtaining ethanol residual data very close to the Ph.Eur limit (10% v/v) and that with NEPTIS^® Perform showed a lower RCY; however, these differences are negligible for our production activities and for patient safety.

In conclusion, both the FASTlab2 and NEPTIS® Perform platforms are capable of reliably producing [¹⁸F]PSMA-1007 that complies with the quality standards of the European Pharmacopoeia. The choice between them should be guided by local clinical and operational priorities. The FASTlab2 system is superior in terms of RCY, providing more usable activity per production run. The NEPTIS® Perform system, while yielding less, produces a final product with marginally lower ethanol content. Therefore, the definition of ‘better’ is context-dependent.

Abbreviations

cGRPP

Guidelines on good radiopharmacy practice

EANM

European association of nuclear medicine

Ph. Eur

European pharmacopoeia

GMP

Good manufacturing practices

EOB

End of beam

EOS

End of synthesis

HPLC

High performance liquid chromatography

TLC

Thin-layer chromatography

Author contributions

MC, MS have drafted the first version of the manuscript. LS, CR have implemented the cyclotron section; GLV supervised instrumentation details; GB and LC has contributed to the discussion section; EM interpreted and approved the writing about quality control’s process; RR, PB and FD have reviewed the statistical analysis. All authors provided critical review, read, and approved the final manuscript. BF supervised the writing of the manuscript.

Funding

No funding was received by any of the authors.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Given the nature of the study, no specific ethical approval was required.

Consent for publication

Not applicable.

Competing interests

All the authors declare that they have no conflict of interest.