Improved Syntheses of the Mglu₅ Antagonists MMPEP and MTEP Using Sonogashira Cross-Coupling.

The Sonogashira cross-coupling, a key step in the syntheses of the mGlu₅ antagonists MMPEP and MTEP, provided an improved three-step method for the preparation of MMPEP in 62% overall yield. Using Spartan molecular modeling kit an explanation for the failure to employ analogues method in the synthesis of MTEP was sought. The DFT calculations indicated that meaningful isolated yields were obtained when the HOMO energy of the aryl halide was lower than the HOMO energy of the respective alkyne

ATN profile classification across two independent prospective cohorts

BACKGROUND The ATN model represents a research framework used to describe in subjects the presence or absence of Alzheimer's disease (AD) pathology through biomarkers. The aim of this study was to describe the prevalence of different ATN profiles using quantitative imaging biomarkers in two independent cohorts, and to evaluate the pertinence of ATN biomarkers to identify comparable populations across independent cohorts. METHODS A total of 172 subjects from the Geneva Memory Clinic and 113 volunteers from a study on healthy aging at the University Hospital of Zurich underwent amyloid (A) and tau (T) PET, as well as T1-weigthed MRI scans using site-specific protocols. Subjects were classified by cognition (cognitively unimpaired, CU, or impaired, CI) based on clinical assessment by experts. Amyloid data converted into the standardized centiloid scale, tau PET data normalized to cerebellar uptake, and hippocampal volume expressed as a ratio over total intracranial volume ratio were considered as biomarkers for A, T, and neurodegeneration (N), respectively. Positivity for each biomarker was defined based on previously published thresholds. Subjects were then classified according to the ATN model. Differences among profiles were tested using Kruskal-Wallis ANOVA, and between cohorts using Wilcoxon tests. RESULTS Twenty-nine percent of subjects from the Geneva cohorts were classified with a normal (A-T-N-) profile, while the Zurich cohort included 64% of subjects in the same category. Meanwhile, 63% of the Geneva and 16% of the Zurich cohort were classified within the AD continuum (being A+ regardless of other biomarkers' statuses). Within cohorts, ATN profiles were significantly different for age and mini-mental state examination scores, but not for years of education. Age was not significantly different between cohorts. In general, imaging A and T biomarkers were significantly different between cohorts, but they were no longer significantly different when stratifying the cohorts by ATN profile. N was not significantly different between cohorts. CONCLUSION Stratifying subjects into ATN profiles provides comparable groups of subjects even when individual recruitment followed different criteria

Synthesis, radiolabelling and in vitro and in vivo evaluation of a novel fluorinated ABP688 derivative for the PET imaging of metabotropic glutamate receptor subtype 5

(E)-3-(Pyridin-2-ylethynyl)cyclohex-2-enone O-(2-(3-18F-fluoropropoxy)ethyl) oxime ([18F]-PSS223) was evaluated in vitro and in vivo to establish its potential as a PET tracer for imaging metabotropic glutamate receptor subtype 5 (mGluR5). [18F]-PSS223 was obtained in 20% decay corrected radiochemical yield whereas the non-radioactive PSS223 was accomplished in 70% chemical yield in a SN2 reaction of common intermediate mesylate 8 with potassium fluoride. The in vitro binding affinity of [18F]-PSS223 was measured directly in a Scatchard assay to give Kd = 3.34 ± 2.05 nM. [18F]-PSS223 was stable in PBS and rat plasma but was significantly metabolized by rat liver microsomal enzymes, but to a lesser extent by human liver microsomes. Within 60 min, 90% and 20% of [18F]-PSS223 was metabolized by rat and human microsome enzymes, respectively. In vitro autoradiography on horizontal rat brain slices showed heterogeneous distribution of [18F]-PSS223 with the highest accumulation in brain regions where mGluR5 is highly expressed (hippocampus, striatum and cortex). Autoradiography in vitro under blockade conditions with ABP688 confirmed the high specificity of [18F]-PSS223 for mGluR5. Under the same blocking conditions but using the mGluR1 antagonist, JNJ16259685, no blockade was observed demonstrating the selectivity of [18F]-PSS223 for mGluR5 over mGluR1. Despite favourable in vitro properties of [18F]-PSS223, a clear-cut visualization of mGluR5- rich brain regions in vivo in rats was not possible mainly due to a fast clearance from the brain and low metabolic stability of [18F]-PSS223

Imaging Tumour ATB0,+ Transport Activity by PET with the Cationic Amino Acid O -2((2-[18F]fluoroethyl)methyl-amino)ethyltyrosine

Purpose: The concentrative amino acid transporter ATB0,+ (SLC6A14) is under evaluation as a target for anticancer therapy. An ATB0,+-selective positron emission tomography (PET) probe could advance preclinical drug development. We characterised the cationic tyrosine analogue O-2((2-[18F]fluoroethyl)methyl-amino)ethyltyrosine ([18F]FEMAET) as a PET probe for ATB0,+ activity. Procedures: Cell uptake was studied in vitro. ATB0,+ expression was quantified by real-time PCR. [18F]FEMAET accumulation in xenografts was investigated by small animal PET with mice. Results: [18F]FEMAET accumulated in PC-3 and NCI-H69 cancer cells in vitro. As expected for ATB0,+ transport, uptake was inhibited by LAT/ATB0,+ inhibitors and dibasic amino acids, and [18F]FEMAET efflux was only moderately stimulated by extracellular amino acids. ATB0,+ was expressed in PC-3 and NCI-H69 but not MDA-MB-231 xenografts. PET revealed accumulation in PC-3 and NCI-H69 xenografts and significant reduction by ATB0,+ inhibition. Uptake was negligible in MDA-MB-231 xenografts. Conclusion: ATB0,+ activity can be imaged in vivo by PET with [18F]FEMAET

Synthesis and preliminary biological evaluation of O -2((2-[18F]fluoroethyl)methylamino)ethyltyrosine ([18F]FEMAET) as a potential cationic amino acid PET tracer for tumor imaging

Amino acid transport is an attractive target for oncologic imaging. Despite a high demand of cancer cells for cationic amino acids, their potential as PET probes remains unexplored. Arginine, in particular, is involved in a number of biosynthetic pathways that significantly influence carcinogenesis and tumor biology. Cationic amino acids are transported by several cationic transport systems including, ATB0,+ (SLC6A14), which is upregulated in certain human cancers including cervical, colorectal and estrogen receptor-positive breast cancer. In this work, we report the synthesis and preliminary biological evaluation of a new cationic analog of the clinically used PET tumor imaging agent O-(2-[18F]fluroethyl)-l-tyrosine ([18F]FET), namely O-2((2-[18F]fluoroethyl)methylamino)ethyltyrosine ([18F]FEMAET). Reference compound and precursor were prepared by multi-step approaches. Radiosynthesis was achieved by no-carrier-added nucleophilic [18F]fluorination in 16-20% decay-corrected yields with radiochemical purity >99%. The new tracer showed good stability in vitro and in vivo. Cell uptake assays demonstrated that FEMAET and [18F]FEMAET accumulate in prostate cancer (PC-3) and small cell lung cancer cells (NCI-H69), with an energy-dependent mechanism. Small animal PET imaging with NCI-H69 xenograft-bearing mice revealed good tumor visualization comparable to [18F]FET and low brain uptake, indicating negligible transport across the blood-brain barrier. In conclusion, the non-natural cationic amino acid PET probe [18F]FEMAET accumulates in cancer cells in vitro and in vivo with possible involvement of ATB0,+

Role of sex hormones in modulating myocardial perfusion and coronary flow reserve

BACKGROUND A growing body of evidence highlights sex differences in the diagnostic accuracy of cardiovascular imaging modalities. Nonetheless, the role of sex hormones in modulating myocardial perfusion and coronary flow reserve (CFR) is currently unclear. The aim of our study was to assess the impact of female and male sex hormones on myocardial perfusion and CFR. METHODS Rest and stress myocardial perfusion imaging (MPI) was conducted by small animal positron emission tomography (PET) with [$^{18}$F]flurpiridaz in a total of 56 mice (7-8 months old) including gonadectomized (Gx) and sham-operated males and females, respectively. Myocardial [$^{18}$F]flurpiridaz uptake (% injected dose per mL, % ID/mL) was used as a surrogate for myocardial perfusion at rest and following intravenous regadenoson injection, as previously reported. Apparent coronary flow reserve (CFR$_{App}$) was calculated as the ratio of stress and rest myocardial perfusion. Left ventricular (LV) morphology and function were assessed by cardiac magnetic resonance (CMR) imaging. RESULTS Orchiectomy resulted in a significant decrease of resting myocardial perfusion (Gx vs. sham, 19.4 ± 1.0 vs. 22.2 ± 0.7 % ID/mL, p = 0.034), while myocardial perfusion at stress remained unchanged (Gx vs. sham, 27.5 ± 1.2 vs. 27.3 ± 1.2 % ID/mL, p = 0.896). Accordingly, CFR$_{App}$ was substantially higher in orchiectomized males (Gx vs. sham, 1.43 ± 0.04 vs. 1.23 ± 0.05, p = 0.004), and low serum testosterone levels were linked to a blunted resting myocardial perfusion (r = 0.438, p = 0.020) as well as an enhanced CFR$_{App}$ (r = -0.500, p = 0.007). In contrast, oophorectomy did not affect myocardial perfusion in females. Of note, orchiectomized males showed a reduced LV mass, stroke volume, and left ventricular ejection fraction (LVEF) on CMR, while no such effects were observed in oophorectomized females. CONCLUSION Our experimental data in mice indicate that sex differences in myocardial perfusion are primarily driven by testosterone. Given the diagnostic importance of PET-MPI in clinical routine, further studies are warranted to determine whether testosterone levels affect the interpretation of myocardial perfusion findings in patients

Tauvid™: The First FDA-Approved PET Tracer for Imaging Tau Pathology in Alzheimer’s Disease

Tauvid has been approved by the U.S. Food and Drug Administration (FDA) in 2020 for positron emission tomography (PET) imaging of adult patients with cognitive impairments undergoing evaluation for Alzheimer's disease (AD) based on tau pathology. Abnormal aggregation of tau proteins is one of the main pathologies present in AD and is receiving increasing attention as a diagnostic and therapeutic target. In this review, we summarised the production and quality control of Tauvid, its clinical application, pharmacology and pharmacokinetics, as well as its limitation due to off-target binding. Moreover, a brief overview on the second-generation of Tau PET tracers is provided. The approval of Tauvid marks a step forward in the field of AD research and opens up opportunities for second-generation tau tracers to advance tau PET imaging in the clinic

Radioligands for positron emission tomography imaging of cannabinoid type 2 receptor

The cannabinoid type 2 (CB2) receptor is an immunomodulatory receptor mainly expressed in peripheral cells and organs of the immune system. The expression level of CB2 in the central nervous system under physiological conditions is negligible, however under neuroinflammatory conditions an upregulation of CB2 protein or mRNA mainly colocalized with activated microglial cells has been reported. Consequently, CB2 agonists have been confirmed to play a role in neuroprotective and anti-inflammatory processes. A suitable positron emission tomography radioligand for imaging CB2 would provide an invaluable research tool to explore the role of CB2 receptor expression in inflammatory disorders. In this review, we provide a summary of so far published CB2 radioligands as well as their in vitro and in vivo binding characteristics

Remote Effects Modulating the Spin Equilibrium of the Resting State of Cytochrome P450cam –An Investigation Using Active Site Analogues

The crystal structure of the resting state of cytochrome P450cam (CYP101), a heme thiolate protein, shows a cluster of six water molecules in the substrate binding pocket, one of which is coordinating to iron(III) as sixth ligand. The resting state is low-spin and changes to high-spin when substrate camphor binds and H2O is removed. In contrast to the protein, previously synthesised enzyme models such as H2O[BOND]FeIII(porph)(ArS−) were shown to be purely high-spin. Iron(S−)porphyrins with different distal sites mimicking proposed remote effects have been prepared and studied by cw-EPR. The results indicate that the low-spin of the resting state of P450cam is due to the fact that the water molecule coordinating to iron has an OH−-like character because of hydrogen bonding and polarisation of the water cluster, respectively