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(R)-[(18)F]MH.MZ ([(18)F]MH.MZ) is a promising positron emission tomography (PET) radiotracer for in vivo study of the 5-HT(2A) receptor. To facilitate clinical trials a fully automated radiosynthesis procedure for [(18)F]MH.MZ was developed using commercially available materials on the iPhase Flexlab module. The overall synthesis time was 100 minutes with a radiochemical yield of 7 ± 0.9% (n=3). The radiochemical purity was greater than 99% for [(18)F]MH.MZ with a molar activity of 361 ± 57 GBq/μmol (n=3). The protocol described herein reliably provides [(18)F]MH.MZ that meets all relevant release criteria for a GMP radiopharmaceutical.

L-ergothioneine (ERGO) is a potent antioxidant with cytoprotective effects. To study ERGO biodistribution and detect oxidative stress in vivo, we report an efficient and reproducible preparation of [(11)C]-labeled ERGO PET radioligand based on protecting the histidine carboxylic group with a methyl ester. Overall, this new protection approach using methyl ester improved the chemical yield of a 4-step reaction from 14% to 24% compared to the previous report using t-butyl ester. The [(11)C]CH(3) methylation of the precursor provided the desired product with 55 ± 10% radiochemical purity and a molar activity of 450 ± 200 TBq/mmol. The [(11)C]ERGO radioligand was able to detect threshold levels of oxidative stress in a preclinical animal model of Alzheimer’s disease.

Ergothioneine (ERGO) is a rare amino acid mostly found in fungi, including mushrooms, with recognized antioxidant activity to protect tissues from damage by reactive oxygen species (ROS) components. Prior to this publication, the biodistribution of ERGO has been performed solely in vitro using extracted tissues. The aim of this study was to develop a feasible chemistry for the synthesis of an ERGO PET radioligand, [11C]ERGO, to facilitate in vivo study. The radioligand probe was synthesized with identical structure to ERGO by employing an orthogonal protection/deprotection approach. [11C]methylation of the precursor was performed via [11C]CH3OTf to provide [11C]ERGO radioligand. The [11C]ERGO was isolated by RP-HPLC with a molar activity of 690 TBq/mmol. To demonstrate the biodistribution of the radioligand, we administered approximately 37 MBq/0.1 mL in 5XFAD mice, a mouse model of Alzheimer’s disease via the tail vein. The distribution of ERGO in the brain was monitored using 90-min dynamic PET scans. The delivery and specific retention of [11C]ERGO in an LPS-mediated neuroinflammation mouse model was also demonstrated. For the pharmacokinetic study, the concentration of the compound in the serum started to decrease 10 min after injection while starting to distribute in other peripheral tissues. In particular, a significant amount of the compound was found in the eyes and small intestine. The radioligand was also distributed in several regions of the brain of 5XFAD mice, and the signal remained strong 30 min post-injection. This is the first time the biodistribution of this antioxidant and rare amino acid has been demonstrated in a preclinical mouse model in a highly sensitive and non-invasive manner.

INTRODUCTION: The natural amino acid L-Glutamine (Gln) is essential for both cell growth and proliferation. In addition to glucose, cancer cells utilize Gln as a carbon source for ATP production, biosynthesis, and as a defense against reactive oxygen species. The utilization of [(11)C]Gln has been previously reported as a biomarker for tissues with an elevated demand for Gln, however, the previous reports for the preparation of [(11)C]Gln were found to be lacking several crucial aspects necessary for transition to human production. Namely, the presence of unreacted precursor and the use of noncommercialized, custom built, reaction platforms. Herein, we report the development and utilization of methodology for the automated production of [(11)C]Gln that meets institutional criteria for human use. METHODS: The preparation of [(11)C]Gln was carried out on the the GE FX(2)N platform. Briefly, after trapping of [(11)C]HCN with a solution of CsHCO(3) in DMF, the [(11)C]CsCN was reacted with a commercially available precursor. This intermediate was then purified by HPLC and deprotected/hydrolyzed under acidic conditions. Following pH adjustment, the product was filtered to give the desired [(11)C]Gln as a sterile injectable. The resulting product was then analyzed for quality assurance. RESULTS: Automated production by this method reliably provides over 3.7 GBq (100 mCi) of [(11)C]Gln. The resulting final drug product was found to have a >99% radiochemical purity

Upregulation of sphingosine-1-phosphate receptor 1 (S1PR1) expression in multiple sclerosis (MS) lesions is associated with neuroinflammatory response. This study investigated the correlation between neuroinflammation and S1PR1 expression in the spinal cord of an experimental autoimmune encephalomyelitis (EAE) rat model of MS, using the S1PR1 positron emission tomography (PET) radiotracer [(11)C]TZ3321.MicroPET imaging studies of [(11)C]TZ3321 were performed to measure uptake of [(11)C]TZ3321 in the spinal cord of EAE rats. Immunohistochemical staining was performed to confirm the overexpression of S1PR1 and other inflammatory biomarkers.MicroPET imaging demonstrated a 20-30 % increase in [(11)C]TZ3321 uptake in the lumbar spinal cord of EAE rats versus sham controls at 35-60 min post injection. The increased uptake of [(11)C]TZ3321 was correlated with the overexpression of S1PR1 in the lumbar spinal cord of EAE rats that was confirmed by immunohistochemical staining. Upregulated S1PR1 expression was associated with glial cell activation and immune cell infiltration.MicroPET imaging modality with a specific radioligand [(11)C]TZ3321 is able to assess the expression of S1PR1 in EAE rat lumbar spinal cord. This may provide a new approach to the assessment of neuroinflammatory response in MS and other inflammatory diseases.

A series of seventeen hydroxyl-containing sphingosine 1-phosphate receptor 1 (S1PR1) ligands were designed and synthesized. Their in vitro binding potencies were determined using [(32)P]S1P competitive binding assays. Compounds 10a, 17a, 17b, and 24 exhibited high S1PR1 binding potencies with IC(50) values ranging from 3.9 to 15.4 nM and also displayed high selectivity for S1PR1 over other S1P receptor subtypes (IC(50) > 1000 nM for S1PR2–5). The most potent compounds 10a, 17a, 17b, and 24 were subsequently radiolabeled with F-18 in high yields and purities. MicroPET studies in cynomolgus macaque showed that [(18)F]10a, [(18)F]17a, and [(18)F]17b but not [(18)F]24 crossed the blood brain barrier and had high initial brain uptake. Further validation of [(18)F]10a, [(18)F]17a, and [(18)F]17b in preclinical models of neuroinflammation is warranted to identify a suitable PET radioligand to quantify S1PR1 expression in vivo as a metric of an inflammatory response.

Thirteen new sphingosine-1-phosphate receptor 1 (S1PR1) ligands were designed and synthesized by replacing azetidine-3-carboxylic acid moiety of compound 4 with new polar groups. The in vitro binding potency of these new analogs toward S1PR1 was determined. Out of 13 new compounds, four compounds 9a, 10c, 12b, and 16b displayed high S1PR1 binding potency with IC50 values of 13.2 ± 3.2, 14.7 ± 1.7, 9.7 ± 1.6, and 6.3 ± 1.3 nM, respectively; further binding studies of these four ligands toward S1PR2-5 suggested they are highly selective for S1PR1 over other S1PRs. The radiosynthesis of the lead radiotracer [18F]12b was achieved with good radiochemical yield (∼14.1%), high radiochemical purity (>98%), and good specific activity (∼54.1 GBq/μmol, decay corrected to the end of synthesis, EOS). Ex vivo autoradiography and initial biodistribution studies in rodents were performed, suggesting that [18F]12b was able to penetrate the blood-brain barrier (BBB) with high brain uptake (0.71% ID/g at 60 min post-injection) and no defluorination was observed. In vitro autoradiography study in brain slices of lipopolysaccharides (LPS)-induced neuroinflammation mice indicated that SEW2871, a specific S1PR1 ligand was able to reduce the uptake of [18F]12b, suggesting [18F]12b has S1PR1 specific binding. These initial results suggested that [18F]12b has potential to be an F-18 labeled radiotracer for imaging S1PR1 in the brain of the animal in vivo.

Sphingosine-1-phosphate receptors (S1PRs) are important regulators of vascular permeability, inflammation, angiogenesis and vascular maturation. Identifying a specific S1PR PET radioligand is imperative, but it is hindered by the complexity and variability of current for binding affinity measurement procedures. Herein, we report a streamlined protocol for radiosynthesis of [(32)P]S1P with good radiochemical yield (36-50%) and high radiochemical purity (>99%). We also report a reproducible procedure for determining the binding affinity for compounds targeting S1PRs in vitro.