Hyperpolarized Xenon-129 Chemical Exchange Saturation Transfer (HyperCEST) Molecular Imaging: Achievements and Future Challenges.

Molecular magnetic resonance imaging (MRI) is an emerging field that is set to revolutionize our perspective of disease diagnosis, treatment efficacy monitoring, and precision medicine in full concordance with personalized medicine. A wide range of hyperpolarized (HP) 129Xe biosensors have been recently developed, demonstrating their potential applications in molecular settings, and achieving notable success within in vitro studies. The favorable nuclear magnetic resonance properties of 129Xe, coupled with its non-toxic nature, high solubility in biological tissues, and capacity to dissolve in blood and diffuse across membranes, highlight its superior role for applications in molecular MRI settings. The incorporation of reporters that combine signal enhancement from both hyperpolarized 129Xe and chemical exchange saturation transfer holds the potential to address the primary limitation of low sensitivity observed in conventional MRI. This review provides a summary of the various applications of HP 129Xe biosensors developed over the last decade, specifically highlighting their use in MRI. Moreover, this paper addresses the evolution of in vivo applications of HP 129Xe, discussing its potential transition into clinical settings.

R3-Noria-methanesulfonate: A Molecular Cage with Superior Hyperpolarized Xenon-129 MRI Contrast.

Hyperpolarized (HP) xenon-129 (129Xe) magnetic resonance imaging (MRI) has the potential to be used as a molecular imaging modality. For this purpose, numerous supramolecular cages have been developed and evaluated in the past. Herein, we report a novel and unique macrocycle that can be successfully utilized for xenon MRI, the resorcinarene trimer methanesulfonate (R3-Noria-MeSO3H). This molecule is capable of two different contrast mechanisms for xenon-MRI, resulting from an increase in the effective spin-spin relaxation and hyperpolarized chemical exchange saturation transfer (HyperCEST). We have demonstrated a superior negative contrast caused by R3-Noria-MeSO3H on HP 129Xe MRI at 3.0 T as well as HyperCEST imaging of the studied macrocycle. Additionally, we have found that the complex aggregation behaviors of R3-Noria-methanesulfonate and its impact on xenon-129 relaxivity are an area for future study.

Cucurbit[6]uril Hyperpolarized Chemical Exchange Saturation Transfer Pulse Sequence Parameter Optimization and Detectability Limit Assessment at 3.0T.

The front cover artwork is provided by Prof. Mitchell S. Albert's group at Lakehead University. The image shows the hyperpolarized chemical exchange saturation transfer (HyperCEST) effect in cucurbit[6]uril molecular biosensors within a blood vessel. Read the full text of the Research Article at 10.1002/cphc.202300346.

Cucurbit[6]uril Hyperpolarized Chemical Exchange Saturation Transfer Pulse Sequence Parameter Optimization and Detectability Limit Assessment at 3.0T.

Molecular imaging is the future of personalized medicine; however, it requires effective contrast agents. Hyperpolarized chemical exchange saturation transfer (HyperCEST) can boost the signal of Hyperpolarized 129 Xe MRI and render it a molecular imaging modality of high efficiency. Cucurbit[6]uril (CB6) has been successfully employed in vivo as a contrast agent for HyperCEST MRI, however its performance in a clinical MRI scanner has yet to be optimized. In this study, MRI pulse sequence parameter optimization was first performed in CB6 solutions in phosphate-buffered saline (PBS), and subsequently in whole sterile citrated bovine blood. The performance of four different depolarization pulse shapes (sinusoidal, 3-lobe sinc (3LS), rectangular (block), and hyperbolic secant (hypsec) was optimized. The detectability limits of CB6 in a clinical 3.0T MRI scanner was assessed using the optimized pulse sequences. The 3LS depolarization pulses performed best, and demonstrated 24 % depletion in a 25 µM solution of CB6 in PBS. It performed similarly in blood. The CB6 detectability limit was found to be 100 µM in citrated bovine blood with a correspondent HyperCEST depletion of 30 % ±9 %. For the first time, the HP 129 Xe HyperCEST effect was observed in red blood cells (RBC) and had a similar strength as HyperCEST in plasma.

A PDK-1 allosteric agonist improves spatial learning and memory in a ßAPP/PS-1 transgenic mouse-high fat diet intervention model of Alzheimer's disease.

Diabetes mellitus (DM), peripheral insulin resistance (IR) and obesity are clear risk factors for Alzheimer's disease. Several anti-diabetic drugs and insulin have been tested in rodents and humans with MCI or AD, yielding promising but inconclusive results. The PDK-1/Akt axis, essential to the action of insulin, has not however been pharmacologically interrogated to a similar degree. Our previous cell culture and in vitro studies point to such an approach. Double transgenic APPsw/PSENdE9 mice, a model for Alzheimer's disease, were used to test the oral administration of PS48, a PDK-1 agonist, on preventing the expected decline in learning and memory in the Morris Water Maze (MWM). Mice were raised on either standard (SD) or high fat (HFD) diets, dosed beginning 10 months age and tested at an advanced age of 14 months. PS48 had positive effects on learning the spatial location of a hidden platform in the TG animals, on either SD or HFD, compared to vehicle diet and WT animals. On several measures of spatial memory following successful acquisition (probe trials), the drug also proved significantly beneficial to animals on either diet. The PS48 treatment-effect size was more pronounced in the TG animals on HFD compared to on SD in several of the probe measures. HFD produced some of the intended metabolic effects of weight gain and hyperglycemia, as well as accelerating cognitive impairment in the TG animals. PS48 was found to have added value in modestly reducing body weights and improving OGTT responses in TG groups although results were not definitive. PS48 was well tolerated without obvious clinical signs or symptoms and did not itself affect longevity. These results recommend a larger preclinical study before human trial.

Development and Application of a Supramolecular Brønsted Acid Catalyst Based on the Noria Macrocycle.

The synthesis of derivatives of the Noria macrocycle and the structurally similar macrocycle, R3, each containing 12 sulfonic acid groups, is reported. Herein, we demonstrate their utility as reusable Brønsted acid catalysts for the Biginelli synthesis of dihydropyrimidinones and the Pechmann synthesis of coumarins. We also demonstrate that the supramolecular structure directs the reagents to interact with the sulfonic acid catalytic sites, thus increasing the catalyst's efficiency compared to other monomeric, macrocyclic, and polymeric sulfonic acid catalysts.

Development of Spray-Dried Cyclodextrin-Based Pediatric Anti-HIV Formulations.

The human immunodeficiency virus (HIV) impacts up to 37 million people globally, of which 1.8 million are children. To date, there is no cure for HIV, although treatment options such as antiretroviral therapy (ART) are available. ART, which involves a patient taking a combination of antiretrovirals, is being used to treat HIV clinically. Despite the effectiveness of ART, there is currently no palatable pediatric formulation to treat HIV in children, which has hindered patient compliance and overall treatment efficacy. In addition, anti-HIV therapeutics are often poorly water-soluble, and hence have poor bioavailability. In the present study, we developed a pediatric-friendly formulation for anti-HIV therapeutics with improved dissolution characteristics of the therapeutic agents. Lopinavir (LPV) and ritonavir (RTV), available as FDA-approved fixed-dose combination products, were chosen as model ART drugs, and the formulation and processing parameters of spray-dried cyclodextrin (CD)-based LPV and RTV complexes were studied. Results showed that the spray-dried complexes exhibited enhanced dissolution profiles in comparison to pure drugs, particularly spray-dried ß-CD complexes, which showed the most favorable dissolution profiles. This current formulation with enhanced dissolution and taste-masking ability through the use of cyclodextrin has the potential to address the unmet need for the development of suitable pediatric formulations.

Impact of chronic stylet-feeder infestation on folivore-induced signaling and defenses in a conifer.

Our understanding of how conifers respond biochemically to multiple simultaneous herbivore attacks is lacking. Eastern hemlock (Tsuga canadensis; 'hemlock') is fed on by hemlock woolly adelgid (Adelges tsugae; 'adelgid') and by later-instar gypsy moth (Lymantria dispar; 'gypsy moth') caterpillars. The adelgid is a stylet-feeding insect that causes a salicylic acid (SA)-linked response in hemlock, and gypsy moth larvae are folivores that presumably cause a jasmonic acid (JA)-linked response. This system presents an opportunity to study how invasive herbivore-herbivore interactions mediated through host biochemical responses. We used a factorial field experiment to challenge chronically adelgid-infested hemlocks with gypsy moth caterpillars. We quantified 17 phytohormones, 26 phenolic and terpene metabolites, and proanthocyanidin, cell wall-bound (CW-bound) phenolic, and lignin contents. Foliage infested with adelgid only accumulated gibberellins and SA; foliage challenged by gypsy moth only accumulated JA phytohormones. Gypsy moth folivory on adelgid-infested foliage reduced the accumulation of JA phytohormones and increased the SA levels. Both herbivores increased CW-bound phenolics and gypsy moth increased lignin content when feeding alone but not when feeding on adelgid-infested foliage. Our study illustrates the importance of understanding the biochemical mechanisms and signaling antagonism underlying tree responses to multiple stresses and of disentangling local and systemic stress signaling in trees.

Unnarmicin D, an Anti-inflammatory Cyanobacterial Metabolite with δ and µ Opioid Binding Activity Discovered via a Pipeline Approach Designed to Target Neurotherapeutics.

To combat the bottlenecks in drug discovery and development, a pipeline to identify neuropharmacological candidates using in silico, in vitro, and receptor specific assays was devised. The focus of this pipeline was to identify metabolites with the ability to reduce neuroinflammation, due to the implications that chronic neuroinflammation has in chronic pain and neurodegenerative diseases. A library of pure compounds isolated from the cyanobacterium Trichodesmium thiebautii was evaluated using this method. In silico analysis of drug likelihood and in vitro permeability analysis using the parallel artificial membrane permeability assay (PAMPA) highlighted multiple metabolites of interest from the library. Murine BV-2 microglia were used in conjunction with the Griess assay to determine if metabolites could reduce lipopolysaccharide induced neuroinflammation followed by analysis of pro-inflammatory cytokine concentrations in the supernatant of the treated cell cultures. The nontoxic metabolite unnarmicin D was further evaluated due to its moderate permeability in the PAMPA assay, promising ADME data, modulation of all cytokines tested, and prediction as an opioid receptor ligand. Molecular modeling of unnarmicin D to the µ and δ opioid receptors showed strong theoretical binding potential to the µ opioid receptor. In vitro binding assays validated this pipeline showing low micromolar binding affinity for the µ opioid receptor launching the potential for further analysis of unnarmicin D derivatives for the treatment of pain and neuroinflammation related diseases.

Cyclodextrin-Based Contrast Agents for Medical Imaging.

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides consisting of multiple glucose subunits. CDs are widely used in host-guest chemistry and biochemistry due to their structural advantages, biocompatibility, and ability to form inclusion complexes. Recently, CDs have become of high interest in the field of medical imaging as a potential scaffold for the development of a large variety of the contrast agents suitable for magnetic resonance imaging, ultrasound imaging, photoacoustic imaging, positron emission tomography, single photon emission computed tomography, and computed tomography. The aim of this review is to summarize and highlight the achievements in the field of cyclodextrin-based contrast agents for medical imaging.

Decacationic Pillar[5]arene: A New Scaffold for the Development of 129Xe MRI Imaging Agents.

A decacationic water-soluble pillar[5]arene possessing a nonsolvated hydrophobic core has been designed and synthesized. This supramolecular host is capable of binding xenon, as evidenced by hyperCEST depletion experiments. Fluorescence-based studies also demonstrate that xenon binds into the cavity of the pillararene with an association constant of 4.6 × 103 M-1. These data indicate that the water-soluble pillararene is a potential scaffold for building contrast agents that can be detected by xenon-129 magnetic resonance imaging.

FeCl2-Mediated Rearrangement of Allylic Alcohols.

A mild, one-pot procedure to produce 3-substituted allylic alcohols from α,ß-unsaturated ketones is described. The addition of an organolithium nucleophile produces a tertiary allylic alcohol as an intermediate, which undergoes a 1,3-OH-migration assisted by FeCl2. The proposed mechanism indicates that a syn-facial migration occurs for the major product. Yields as high as 98% for the one-pot reaction are reported.

Cyclodextrin-Based Pseudorotaxanes: Easily Conjugatable Scaffolds for Synthesizing Hyperpolarized Xenon-129 Magnetic Resonance Imaging Agents.

Hyperpolarized (HP) xenon-129 (Xe) magnetic resonance (MR) imaging has the potential to detect biological analytes with high sensitivity and high resolution when coupled with xenon-encapsulating molecular probes. Despite the development of numerous HP Xe probes, one of the challenges that has hampered the translation of these agents from in vitro demonstration to in vivo testing is the difficulty in synthesizing the Xe-encapsulating cage molecule. In this study, we demonstrate that a pseudorotaxane, based on a γ-cyclodextrin macrocycle, is easily synthesized in one step and is detectable using HyperCEST-enhanced 129Xe MR spectroscopy.

In vivo detection of cucurbit[6]uril, a hyperpolarized xenon contrast agent for a xenon magnetic resonance imaging biosensor.

The Hyperpolarized gas Chemical Exchange Saturation Transfer (HyperCEST) Magnetic Resonance (MR) technique has the potential to increase the sensitivity of a hyperpolarized xenon-129 MRI contrast agent. Signal enhancement is accomplished by selectively depolarizing the xenon within a cage molecule which, upon exchange, reduces the signal in the dissolved phase pool. Herein we demonstrate the in vivo detection of the cucurbit[6]uril (CB6) contrast agent within the vasculature of a living rat. Our work may be used as a stepping stone towards using the HyperCEST technique as a molecular imaging modality.

HyperCEST detection of cucurbit[6]uril in whole blood using an ultrashort saturation Pre-pulse train.

Xenon based biosensors have the potential to detect and localize biomarkers associated with a wide variety of diseases. The development and nuclear magnetic resonance (NMR) characterization of cage molecules which encapsulate hyperpolarized xenon is imperative for the development of these xenon biosensors. We acquired (129) Xe NMR spectra, and magnetic resonance images and a HyperCEST saturation map of cucurbit[6]uril (CB6) in whole bovine blood. We observed a mean HyperCEST depletion of 84% (n = 5) at a concentration of 5 mM and 74% at 2.5 mM. Additionally, we collected these data using a pulsed HyperCEST saturation pre-pulse train with a SAR of 0.025 W/kg which will minimize any potential RF heating in animal or human tissue. Copyright © 2016 John Wiley & Sons, Ltd.

Transition-metal free umpolung carbon-nitrogen vs. carbon-chlorine bond formation.

The formation of carbon-nitrogen (C-N) bonds via an umpolung substitution reaction has been achieved at -78 °C without the need for catalysts, ligands, or additives. The scope is limited to aryl Grignard reagents with N-chloroamines. The findings in this manuscript serve as a reference point for all C-N bond formation involving N-chloroamines and organometallic reagents. Knowing the yields of uncatalyzed reactions will be useful when determining the success of future catalytic methods.

Oxidative Cross-Coupling of sp(3)- and sp(2)-Hybridized C-H Bonds: Vanadium-Catalyzed Aminomethylation of Imidazo[1,2-a]pyridines.

The vanadium-catalyzed oxidative coupling of substituted 2-arylimidiazo[1,2-a]pyridines to N-methylmorpholine oxide, which acts as both a coupling partner and an oxidant, has been achieved. This reaction was applied to various substituted imidiazo[1,2-a]pyridine and indole substrates, resulting in yields as high as 90%. Mechanistic investigations indicate that the reaction may proceed via a Mannich-type process. This work demonstrates how oxidative aminomethylation can be used as a useful method to introduce tertiary amines into heterocycles, thus providing an alternative method for conventional Mannich-type reactions.

Regioselective C-H bond amination by aminoiodanes.

A new approach for the direct amination of 2-phenylpyridine derivatives using a diphthalimide-iodane and copper triflate has been developed. A series of different 2-phenylpyridine derivatives were aminated with yields up to 88%. Mechanistic investigations indicate that the reaction proceeds via a copper-mediated single electron transfer.

Synthesis of a ß-CCT-lanthanide conjugate for binding the dopamine transporter.

The development of a ß-CCT-lanthanide conjugate that binds the dopamine transporter (DAT) with high affinity (K(d) = 303 nM) is described. Contrast agents such as the one described herein could be used as molecular probes to directly study the binding of small molecules to receptors such as DAT via MRI, PET or SPECT.

Regioselective gold-catalyzed oxidative C-N bond formation.

A novel protocol for the regioselective intermolecular amination of various arenes has been developed. By using an I(III) oxidant in the presence of a Au(I) catalyst, a direct and novel route for regioselectively accessing a variety of substituted aniline moieties has been achieved with yields as high as 90%. Mechanistic insight suggests that regioselectivity can be predicted based on electrophilic aromatic metalation patterns.