Simplified and highly-reliable automated production of [18F]FSPG for clinical studies

Abstract

Background: (S)-4-(3-¹⁸F-Fluoropropyl)-L-Glutamic Acid ([¹⁸F]FSPG) is a positron emission tomography (PET) tracer that specifically targets the cystine/glutamate antiporter (xc^-), which is frequently overexpressed in cancer and several neurological disorders. Pilot studies examining the dosimetry and biodistribution of [¹⁸F]FSPG in healthy volunteers and tumor detection in patients with non-small cell lung cancer, hepatocellular carcinoma, and brain tumors showed promising results. In particular, low background uptake in the brain, lung, liver, and bowel was observed that further leads to excellent imaging contrasts of [¹⁸F]FSPG PET. However, reliable production-scale cGMP-compliant automated procedures for [¹⁸F]FSPG production are still lacking to further increase the utility and clinical adoption of this radiotracer. Herein, we report the optimized automated approaches to produce [¹⁸F]FSPG through two commercially available radiosynthesizers capable of supporting centralized and large-scale production for clinical use.

Results: Starting with activity levels of 60-85 GBq, the fully-automated process to produce [¹⁸F]FSPG took less than 45 min with average radiochemical yields of 22.56 ± 0.97% and 30.82 ± 1.60% (non-decay corrected) using TRACERlab™ FXFN and FASTlab™, respectively. The radiochemical purities were > 95% and the formulated [¹⁸F]FSPG solution was determined to be sterile and colorless with the pH of 6.5-7.5. No radiolysis of the product was observed up to 8 h after final batch formulation.

Conclusions: In summary, cGMP-compliant radiosyntheses and quality control of [¹⁸F]FSPG have been established on two commercially available synthesizers leveraging high activity concentration and radiochemical purity. While the clinical trials using [¹⁸F]FSPG PET are currently underway, the automated approaches reported herein will accelerate the clinical adoption of this radiotracer and warrant centralized and large-scale production of [¹⁸F]FSPG.

Keywords: Automation; PET; Radiopharmaceutical; [18F]FSPG.

Fig. 1

Chemical structure of (4S)-4-(3-fluoropropyl)L-glutamate as the reference standard of [¹⁸F]FSPG

Fig. 2

Chemical structure of the precursor to produce [¹⁸F]FSPG

Fig. 3

Radiosynthesis scheme and detailed flow chart of producing [¹⁸F]FSPG

Fig. 4

Schematic overview of the [¹⁸F]FSPG radiosynthesis on the GE TRACERlab™ FXFN module. The numbers denoted in RED, represented the designation of item and position of reagents and consumables indicated on Table 1

Fig. 5

GE TRACERlab™ FXFN module set-up of reagents and cartridge/filter assembly for the radiosynthesis of [¹⁸F]FSPG

Fig. 6

Assembling the Oasis^® MCX cartridge/Glass membrane filter set (a) and the Alumina N Cartridge/Superclean™ ENVI-Carb™ assembly (b). The assemblies were installed and activated only on the day of the synthesis

Fig. 7

Schematic FASTlab cassette layouts for the radiosynthesis of [¹⁸F]FSPG. The numbers denoted in RED represent the designation of item and position of reagents and consumables indicated on Table 2

Fig. 8

GE FASTlab™ set-up of reagents and cartridges for the radiosynthesis of [¹⁸F]FSPG

Fig. 9

Five (5) point calibration of FSPG reference standard complexation with OPA reagent by HPLC analysis. The blue regression curve represents the molar concentration, whereas the red curve represents the mass concentration, measured against the peak area

Fig. 10

Illustration of UV chromatograms of FSPG reference standard after reaction with OPA reagent by HPLC analysis. Per the method described previously (in “Quality control method” section), the OPA peak elutes around 7 min and FSPG standard elutes at the 13 min region

Fig. 11

Radio-HPLC chromatograms of [¹⁸F]FSPG after reaction with OPA reagent. Per the method described previously (in “Quality control method” section), [¹⁸F]FSPG peak elutes at the 13 min region. The indicated chromatograms verified that [¹⁸F]FSPG remained stable for 8 h after final batch formulation