Comparison of [18F]-Tracers in Various Experimental Tumor Models by PET Imaging and Identification of an Early Response Biomarker for the Novel Microtubule Stabilizer Patupilone

Purpose: The suitability of [18F]FDG, [18F]FLT, [18F]FET, and [18F]FCH as non-invasive positron emission tomography (PET) biomarkers for monitoring response to chemotherapy was analyzed in various experimental tumor models. Procedures: Tracer uptake into three syngeneic rodent tumor models and ten human xenograft models was evaluated using semiquantitative analysis of small-animal PET data. Murine RIF-1 fibrosarcomas and [18F]FLT were selected to monitor the effects of the novel cytotoxic patupilone. Results: Except [18F]FCH, all tracers provided good tumor visualization. Highest [18F]FDG uptake was identified in syngeneic tumors. Xenograft models, however, showed low [18F]FDG SUVs and were better visualized by [18F]FLT. Monitoring the effects of patupilone on [18F]FLT uptake in RIF-1 tumors revealed a significant decrease of tracer uptake after 24h, which strongly negatively correlated with apoptosis. Conclusion: [18F]FLT PET of experimental tumors is a viable complement to [18F]FDG for preclinical drug development. [18F]FLT may be an excellent biomarker for patupilone-induced apoptosi

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

Cerebral mGluR5 availability contributes to elevated sleep need and behavioral adjustment after sleep deprivation.

Increased sleep time and intensity quantified as low-frequency brain electrical activity after sleep loss demonstrate that sleep need is homeostatically regulated, yet the underlying molecular mechanisms remain elusive. We here demonstrate that metabotropic glutamate receptors of subtype 5 (mGluR5) contribute to the molecular machinery governing sleep-wake homeostasis. Using positron emission tomography, magnetic resonance spectroscopy, and electroencephalography in humans, we find that increased mGluR5 availability after sleep loss tightly correlates with behavioral and electroencephalographic biomarkers of elevated sleep need. These changes are associated with altered cortical myo-inositol and glycine levels, suggesting sleep loss-induced modifications downstream of mGluR5 signaling. Knock-out mice without functional mGluR5 exhibit severe dysregulation of sleep-wake homeostasis, including lack of recovery sleep and impaired behavioral adjustment to a novel task after sleep deprivation. The data suggest that mGluR5 contribute to the brain's coping mechanisms with sleep deprivation and point to a novel target to improve disturbed wakefulness and sleep

Cerenkov Radiation Energy Transfer (CRET) Imaging: A Novel Method for Optical Imaging of PET Isotopes in Biological Systems

Positron emission tomography (PET) allows sensitive, non-invasive analysis of the distribution of radiopharmaceutical tracers labeled with positron (β(+))-emitting radionuclides in small animals and humans. Upon β(+) decay, the initial velocity of high-energy β(+) particles can momentarily exceed the speed of light in tissue, producing Cerenkov radiation that is detectable by optical imaging, but is highly absorbed in living organisms.To improve optical imaging of Cerenkov radiation in biological systems, we demonstrate that Cerenkov radiation from decay of the PET isotopes (64)Cu and (18)F can be spectrally coupled by energy transfer to high Stokes-shift quantum nanoparticles (Qtracker705) to produce highly red-shifted photonic emissions. Efficient energy transfer was not detected with (99m)Tc, a predominantly γ-emitting isotope. Similar to bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET), herein we define the Cerenkov radiation energy transfer (CRET) ratio as the normalized quotient of light detected within a spectral window centered on the fluorophore emission divided by light detected within a spectral window of the Cerenkov radiation emission to quantify imaging signals. Optical images of solutions containing Qtracker705 nanoparticles and [(18)F]FDG showed CRET ratios in vitro as high as 8.8±1.1, while images of mice with subcutaneous pseudotumors impregnated with Qtracker705 following intravenous injection of [(18)F]FDG showed CRET ratios in vivo as high as 3.5±0.3.Quantitative CRET imaging may afford a variety of novel optical imaging applications and activation strategies for PET radiopharmaceuticals and other isotopes in biomaterials, tissues and live animals

Metabolism of no-carrier-added 2-[18F]fluoro-L-tyrosine in rats

Background: Several fluorine-18 labelled fluoroamino acids have been evaluated as tracers for the quantitative assessment of cerebral protein synthesis in vivo by positron emission tomography (PET). Among these, 2-[18F]fluoro-L-tyrosine (2-[18F]Tyr) has been studied in mice at a low specific activity. Its incorporation into proteins is fast and metabolism via other pathways is limited. The present in vivo study was carried out in normal awake rats using no-carrier-added 2-[18F]Tyr. Under normal physiological conditions, we have studied the incorporation into proteins and the metabolism of the tracer in different brain areas. Methods: No-carrier-added 2-[18F]Tyr was administered to awake rats equipped with chronic arterial and venous catheters. The time course of the plasma activity was studied by arterial blood sampling. The biodistribution of the activity in the main organs was studied at the end of the experiment. The distribution of radioactive species in plasma and brain regions was studied by acidic precipitation of the proteins and HPLC analysis of the supernatant. Results: The absolute uptake of radioactivity in brain regions was homogenous. In awake rats, nocarrier-added 2-[18F]Tyr exhibits a fast and almost quantitative incorporation into the proteins fractions of cerebellum and cortex. In striatum, this incorporation into proteins and the unchanged fraction of the tracer detected by HPLC could be lower than in other brain regions. Conclusion: This study confirms the potential of 2-[18F]fluoro-L-tyrosine as a tracer for the assessment of the rate of protein synthesis by positron emission tomography. The observed metabolism suggests a need for a correction for the appearance of metabolites, at least in plasma

Synthesis of fluorosugar reagents for the construction of well-defined fluoroglycoproteins.

2-Deoxy-2-fluoroglycosyl iodides are privileged glycosyl donors for the stereoselective preparation of 1-Nu-β-fluorosugars, which are useful reagents for chemical site-selective protein glycosylation. Ready access to such β-fluorosugars enables the mild and efficient construction of well-defined fluoroglycoproteins.We thank the European Commission (Marie Curie CIG, O.B. and G.J.L.B.), MICINN, Spain (Juan de la Cierva Fellowship, O.B.), MINECO, Spain (CTQ2011-22872BQU) and Generalitat de Catalunya (M.S.) for generous financial support. We also thank Mr. Adrià Cardona-Benages (URV) for technical assis-tance. G.J.L.B. thanks the Royal Society (University Research Fellowship), Fundação para a Ciência a Tecnologia, Portugal (FCT Investigator), and the EPSRC for funding.This is the final version of the article. It first appeared from ACS via http://pubs.acs.org/doi/abs/10.1021/acs.orglett.5b01259

Recent advances in organic synthesis using light-mediated n-heterocyclic carbene catalysis

The combination of photocatalysis with other ground state catalytic systems have attracted much attention recently due to the enormous synthetic potential offered by a dual activation mode. The use of N-heterocyclic carbene (NHC) as organocatalysts emerged as an important synthetic tool. Its ability to harness umpolung reactivity by the formation of the Breslow intermediate has been employed in the synthesis of thousands of biologically important compounds. However, the available coupling partners are relatively restricted, and its combination with other catalytic systems might improve its synthetic versatility. Thus, merging photoredox and N-heterocyclic carbene (NHC) catalysis has emerged recently as a powerful strategy to develop new transformations and give access to a whole new branch of synthetic possibilities. This review compiles the NHC catalyzed methods mediated by light, either in the presence or absence of an external photocatalyst, that have been described so far, and aims to give an accurate overview of the potential of this activation modeL.M. acknowledges the Autonomous Community of Madrid (CAM) for the financial support (PEJD-2019-PRE/AMB-16640 and SI1/PJI/ 2019-00237) and for an “Atracción de Talento Investigador” contract (2017-T2/AMB-5037

Metabotropic glutamate receptor 5 as a potential target for smoking cessation

Rationale Most habitual smokers find it difficult to quit smoking because they are dependent upon the nicotine present in tobacco smoke. Tobacco dependence is commonly treated pharmacologically using nicotine replacement therapy or drugs, such as varenicline, that target the nicotinic receptor. Relapse rates, however, remain high and there remains a need to develop novel non-nicotinic pharmacotherapies for the dependence that are more effective than existing treatments. Objective The purpose of this paper is to review the evidence from preclinical and clinical studies that drugs that antagonise the metabotropic glutamate receptor 5 (mGluR5) in the brain are likely to be efficacious as treatments for tobacco dependence. Results Imaging studies reveal that chronic exposure to tobacco smoke reduces the density of mGluR5s in human brain. Preclinical results demonstrate that negative allosteric modulators (NAMs) at mGluR5 attenuate both nicotine self-administration and the reinstatement of responding evoked by exposure to conditioned cues paired with nicotine delivery. They also attenuate the effects of nicotine on brain dopamine pathways implicated in addiction. Conclusions Although mGluR5 NAMs attenuate most of the key facets of nicotine dependence they potentiate the symptoms of nicotine withdrawal. This may limit their value as smoking cessation aids. The NAMs that have been employed most widely in preclinical studies of nicotine dependence have too many \u201coff target\u201d effects to be used clinically. However newer mGluR5 NAMs have been developed for clinical use in other indications. Future studies will determine if these agents can also be used effectively and safely to treat tobacco dependence