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Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use.

ABSTRACT: (4S)-4-(3-[18F]Fluoropropyl)-L-glutamic acid ([18F]FSPG) is a positron emission tomography (PET) imaging agent for measuring the system xC- transporter activity. It has been used for the detection of various cancers and metastasis in clinical trials. [18F]FSPG is also a promising diagnostic tool for evaluation of multiple sclerosis, drug resistance in chemotherapy, inflammatory brain diseases, and infectious lesions. Due to the very short half-life (110 min) of 18F nuclide, [18F]FSPG needs to be produced on a daily basis; therefore, fast and efficient synthesis and analytical methods for quality control must be established to assure the quality and safety of [18F]FSPG for clinical use. To manufacture cGMP-compliant [18F]FSPG, all four nonradioactive stereoisomers of FSPG were prepared as reference standards for analysis. (2S,4S)-1 and (2R,4R)-1 were synthesized starting from protected L- and D-glutamate derivatives in three steps, whereas (2S,4R)-1 and (2R,4S)-1 were prepared in three steps from protected (S)- and (R)-pyroglutamates. A chiral HPLC method for simultaneous determination of four FSPG stereoisomers was developed by using a 3-cm Chirex 3126 column and a MeCN/CuSO4(aq) mobile phase. In this method, (2R,4S)-1, (2S,4S)-1, (2R,4R)-1, and (2S,4R)-1 were eluted in sequence with sufficient resolution in less than 25 min without derivatization. Scale-up synthesis of intermediates for the production of [18F]FSPG in high optical purity was achieved via stereo-selective synthesis or resolution by recrystallization. The enantiomeric excess of intermediates was determined by HPLC using a Chiralcel OD column and monitored at 220 nm. The nonradioactive precursor with >98% ee can be readily distributed to other facilities for the production of [18F]FSPG. Based on the above accomplishments, cGMP-compliant [18F]FSPG met the acceptance criteria in specifications and was successfully manufactured for human use. It has been routinely prepared and used in several pancreatic ductal adenocarcinoma metastasis-related clinical trials.

SUBMITTER: Shih KT

PROVIDER: S-EPMC7735610 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use.

Shih Kai-Ting KT Huang Ya-Yao YY Yang Chia-Ying CY Cheng Mei-Fang MF Tien Yu-Wen YW Shiue Chyng-Yann CY Yen Rouh-Fang RF Hsin Ling-Wei LW

PloS one 20201214 12

(4S)-4-(3-[18F]Fluoropropyl)-L-glutamic acid ([18F]FSPG) is a positron emission tomography (PET) imaging agent for measuring the system xC- transporter activity. It has been used for the detection of various cancers and metastasis in clinical trials. [18F]FSPG is also a promising diagnostic tool for evaluation of multiple sclerosis, drug resistance in chemotherapy, inflammatory brain diseases, and infectious lesions. Due to the very short half-life (110 min) of 18F nuclide, [18F]FSPG needs to be ...[more]

PMID: 33315962

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Project description:PURPOSE:(S)-4-(3-[18F]Fluoropropyl)-L-glutamic acid (18F-FSPG) is a novel radiopharmaceutical for Positron Emission Tomography (PET) imaging. It is a glutamate analogue that can be used to measure xC- transporter activity. This study was performed to assess the feasibility of 18F-FSPG for imaging orthotopic brain tumors in small animals and the translation of this approach in human subjects with intracranial malignancies. EXPERIMENTAL DESIGN:For the small animal study, GS9L glioblastoma cells were implanted into brains of Fischer rats and studied with 18F-FSPG, the 18F-labeled glucose derivative 18F-FDG and with the 18F-labeled amino acid derivative 18F-FET. For the human study, five subjects with either primary or metastatic brain cancer were recruited (mean age 50.4 years). After injection of 300 MBq of 18F-FSPG, 3 whole-body PET/Computed Tomography (CT) scans were obtained and safety parameters were measured. The three subjects with brain metastases also had an 18F-FDG PET/CT scan. Quantitative and qualitative comparison of the scans was performed to assess kinetics, biodistribution, and relative efficacy of the tracers. RESULTS:In the small animals, the orthotopic brain tumors were visualized well with 18F-FSPG. The high tumor uptake of 18F-FSPG in the GS9L model and the absence of background signal led to good tumor visualization with high contrast (tumor/brain ratio: 32.7). 18F-FDG and 18F-FET showed T/B ratios of 1.7 and 2.8, respectively. In the human pilot study, 18F-FSPG was well tolerated and there was similar distribution in all patients. All malignant lesions were positive with 18F-FSPG except for one low-grade primary brain tumor. In the 18F-FSPG-PET-positive tumors a similar T/B ratio was observed as in the animal model. CONCLUSIONS:18F-FSPG is a novel PET radiopharmaceutical that demonstrates good uptake in both small animal and human studies of intracranial malignancies. Future studies on larger numbers of subjects and a wider array of brain tumors are planned. TRIAL REGISTRATION:ClinicalTrials.gov NCT01186601.

Project description:Although the growth and proliferation of most tumors is fueled by glucose, some tumors are more likely to metabolize glutamine. In particular, tumor cells with the upregulated c-Myc gene are generally reprogrammed to utilize glutamine. We have developed new 3-fluoropropyl analogs of glutamine, namely [(18)F](2S,4R)- and [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 3 and 4, to be used as probes for studying glutamine metabolism in these tumor cells. Optically pure isomers labeled with (18)F and (19)F (2S,4S) and (2S,4R)-4-(3-fluoropropyl)glutamine were synthesized via different routes and isolated in high radiochemical purity (≥95%). Cell uptake studies of both isomers showed that they were taken up efficiently by 9L tumor cells with a steady increase over a time frame of 120 min. At 120 min, their uptake was approximately two times higher than that of l-[(3)H]glutamine ([(3)H]Gln). These in vitro cell uptake studies suggested that the new probes are potential tumor imaging agents. Yet, the lower chemical yield of the precursor for 3, as well as the low radiochemical yield for 3, limits the availability of [(18)F](2S,4R)-4-(3-fluoropropyl)glutamine, 3. We, therefore, focused on [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4. The in vitro cell uptake studies suggested that the new probe, [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, is most sensitive to the LAT transport system, followed by System N and ASC transporters. A dual-isotope experiment using l-[(3)H]glutamine and the new probe showed that the uptake of [(3)H]Gln into 9L cells was highly associated with macromolecules (>90%), whereas the [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, was not (<10%). This suggests a different mechanism of retention. In vivo PET imaging studies demonstrated tumor-specific uptake in rats bearing 9L xenographs with an excellent tumor to muscle ratio (maximum of ∼8 at 40 min). [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, may be useful for testing tumors that may metabolize glutamine related amino acids.

Project description:PURPOSE:Non-invasive imaging is central to hepatocellular carcinoma (HCC) diagnosis; however, conventional modalities are limited by smaller tumors and other chronic diseases that are often present in patients with HCC, such as cirrhosis. This pilot study evaluated the feasibility of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) positron emission tomography (PET)/X-ray computed tomography (CT) to image HCC. [18F]FSPG PET/CT was compared to standard-of-care (SOC) magnetic resonance imaging (MRI) and CT, and [11C]acetate PET/CT, commonly used in this setting. We report the largest cohort of HCC patients imaged to date with [18F]FSPG PET/CT and present the first comparison to [11C]acetate PET/CT and SOC imaging. This study represents the first in a US HCC population, which is distinguished by different underlying comorbidities than non-US populations. PROCEDURES:xC- transporter RNA and protein levels were evaluated in HCC and matched liver samples from The Cancer Genome Atlas (n = 16) and a tissue microarray (n = 83). Eleven HCC patients who underwent prior MRI or CT scans were imaged by [18F]FSPG PET/CT, with seven patients also imaged with [11C]acetate PET/CT. RESULTS:xC- transporter RNA and protein levels were elevated in HCC samples compared to background liver. Over 50 % of low-grade HCCs and ~70 % of high-grade tumors exceeded background liver protein expression. [18F]FSPG PET/CT demonstrated a detection rate of 75 %. [18F]FSPG PET/CT also identified an HCC devoid of typical MRI enhancement pattern. Patients scanned with [18F]FSPG and [11C]acetate PET/CT exhibited a 90 and 70 % detection rate, respectively. In dually positive tumors, [18F]FSPG accumulation consistently resulted in significantly greater tumor-to-liver background ratios compared with [11C]acetate PET/CT. CONCLUSIONS:[18F]FSPG PET/CT is a promising modality for HCC imaging, and larger studies are warranted to examine [18F]FSPG PET/CT impact on diagnosis and management of HCC. [18F]FSPG PET/CT may also be useful for phenotyping HCC tumor metabolism as part of precision cancer medicine.

Dataset Information

Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use.

Publications

Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use.

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