Following Metabolism in Living Microorganisms by Hyperpolarized ¹H NMR

Dissolution dynamic nuclear polarization (dDNP) is used to enhance the sensitivity of nuclear magnetic resonance (NMR), enabling monitoring of metabolism and specific enzymatic reactions in vivo. dDNP involves rapid sample dissolution and transfer to a spectrometer/scanner for subsequent signal detection. So far, most biologically oriented dDNP studies have relied on hyperpolarizing long-lived nuclear spin species such as ¹³C in small molecules. While advantages could also arise from observing hyperpolarized ¹H, short relaxation times limit the utility of prepolarizing this sensitive but fast relaxing nucleus. Recently, it has been reported that ¹H NMR peaks in solution-phase experiments could be hyperpolarized by spontaneous magnetization transfers from bound ¹³C nuclei following dDNP. This work demonstrates the potential of this sensitivity-enhancing approach to probe the enzymatic process that could not be suitably resolved by ¹³C dDNP MR. Here we measured, in microorganisms, the action of pyruvate decarboxylase (PDC) and pyruvate formate lyase (PFL)enzymes that catalyze the decarboxylation of pyruvate to form acetaldehyde and formate, respectively. While ¹³C NMR did not possess the resolution to distinguish the starting pyruvate precursor from the carbonyl resonances in the resulting products, these processes could be monitored by ¹H NMR at 500 MHz. These observations were possible in both yeast and bacteria in minute-long kinetic measurements where the hyperpolarized ¹³C enhanced, via ¹³C → ¹H cross-relaxation, the signals of protons binding to the ¹³C over the course of enzymatic reactions. In addition to these spontaneous heteronuclear enhancement experiments, single-shot acquisitions based on <i>J</i>-driven ¹³C → ¹H polarization transfers were also carried out. These resulted in higher signal enhancements of the ¹H resonances but were not suitable for multishot kinetic studies. The potential of these ¹H-based approaches for measurements in vivo is briefly discussed

Positive Linear Regression of Auditory Cortical Deactivation with Cognitive Performance (MMSE) in All Participants

<div><p>Left: results are superimposed on a standard MRI template. Yellow indicates a significant relationship of cerebral deactivation with the MMSE: (A) axial slice, cranial aspect; (B) coronal slice, dorsal aspect (results are displayed at <i>p</i> < 0.005, for illustration purposes).</p> <p>Right: Regression analysis (red indicates regression line) of the fitted and adjusted rCBF response (blue points, arbitrary units) to active navigation in relation to the MMSE score at the position of the significant cluster (Talairach coordinates <i>x,</i> −56; <i>y,</i> −14; <i>z,</i> −2; <i>p</i> < 0.001, uncorrected).</p></div

Deactivation in Control Individuals and Patients with MCI and AD

<p>Results are superimposed on a standard MRI template. Yellow indicates significant cerebral deactivations during active navigation: (A) axial slices, cranial aspect; (B) coronal slices, dorsal aspect (results are displayed at <i>p <</i> 0.005, for illustration purposes).</p

rCBF Changes in Control Individuals and Patients with MCI and AD during Navigation Task

<p>Results are surface-rendered and superimposed on a standard MRI template. Green indicates significant increase of rCBF, and red indicates significant decrease of rCBF during active navigation (results are displayed at <i>p</i> < 0.001).</p

Experimental Setup

<div><p>(A) Experimental setup, showing a participant in the PET scanner during performance of a navigation task in the VR environment.</p> <p>(B) Snapshot of the visual impression of the test condition in the virtual environment at the start point of the navigation task.</p></div

Auditory Cortical Deactivation

<p>Areas of significant deactivation in healthy volunteers (<i>p</i> < 0.001) during navigation are demonstrated in black on a glass-brain display. The probabilistic volume of A1 according to Penhune et al. [<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0020288#pmed-0020288-b21" target="_blank">21</a>] is outlined in green (right hemisphere) and red (left hemisphere). Aspects are (A) left lateral, (B) cranial, (C) right lateral, and (D) dorsal.</p

Additional file 1: of Synthesis and preclinical evaluation of novel 18F-labeled Glu-urea-Glu-based PSMA inhibitors for prostate cancer imaging: a comparison with 18F-DCFPyl and 18F-PSMA-1007

Supporting information contains the description of the chemical synthesis and radiolabeling of all compounds investigated in this study, the methods and results for the determination of the PSMA binding affinities (IC50) and internalization studies, the metabolite analyses and the time-activity curves for the blood pool derived from dynamic small-animal PET. (PDF 911kb

Table1_Simultaneous 18-FDG PET and MR imaging in lower extremity arterial disease.docx

BackgroundSimultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is a novel hybrid imaging method integrating the advances of morphological tissue characterization of MRI with the pathophysiological insights of PET applications.AimThis study evaluated the use of simultaneous 18-FDG PET/MR imaging for characterizing atherosclerotic lesions in lower extremity arterial disease (LEAD).MethodsEight patients with symptomatic stenoses of the superficial femoral artery (SFA) under simultaneous acquisition of 18-FDG PET and contrast-enhanced MRI using an integrated whole-body PET/MRI scanner. Invasive plaque characterization of the SFA was performed by intravascular imaging using optical coherence tomography. Histological analysis of plaque specimens was performed after directional atherectomy.ResultsMRI showed contrast enhancement at the site of arterial stenosis, as assessed on T2-w and T1-w images, compared to a control area of the contralateral SFA (0.38 ± 0.15 cm vs. 0.23 ± 0.11 cm; 1.77 ± 0.19 vs. 1.57 ± 0.15; p-value  1) at the level of symptomatic stenosis was observed in all but one patient. Contrast medium-induced MR signal enhancement was detected in all plaques, whereas FDG uptake in PET imaging was increased in lesions with active fibroatheroma and reduced in fibrocalcified lesions.ConclusionIn this multimodal imaging study, we report the feasibility and challenges of simultaneous PET/MR imaging of LEAD, which might offer new perspectives for risk estimation.</p

Characterization and First Human Investigation of FIBT, a Novel Fluorinated Aβ Plaque Neuroimaging PET Radioligand

Imidazo­[2,1-<i>b</i>]­benzothiazoles (IBTs) are a promising novel class of amyloid positron emission tomography (PET) radiopharmaceuticals for diagnosis of neurodegenerative disorders like Alzheimer’s disease (AD). Their good in vivo imaging properties have previously been shown in preclinical studies. Among IBTs, fluorinated [¹⁸F]­FIBT was selected for further characterization and advancement toward use in humans. [¹⁸F]­FIBT characteristics were analyzed in relation to Pittsburgh compound B (PiB) as reference ligand. [¹⁸F]­FIBT and [³H]­PiB were coinjected to an APP/PS1 mouse for ex vivo dual-label autoradiographic correlation. Acute dose toxicity of FIBT was examined in two groups of healthy mice. Preexisting in vivo stability and biodistribution studies in mice were complemented with analogous studies in rats. [¹⁸F]­FIBT was titrated against postmortem human AD brain homogenate in a saturation binding assay previously performed with [³H]­PiB. Binding of [¹⁸F]­FIBT to human AD brain was further analyzed by in vitro incubation of human AD brain sections in comparison to [¹¹C]­PiB in relation to standard immunohistochemistry. Finally, [¹⁸F]­FIBT was administered to two human subjects for a dynamic 90 min PET/MR brain investigation. Ex vivo autoradiography confirmed good uptake of [¹⁸F]­FIBT to mouse brain and its excellent correlation to [³H]­PiB binding. No toxicity of FIBT could be found in mice at a concentration of 33.3 nmol/kg. As in mice, [¹⁸F]­FIBT was showing high in vivo stability in rats and comparable regional brain biodistribution dynamics to [³H]­PiB. Radioligand saturation binding confirmed at least one high-affinity binding component of [¹⁸F]­FIBT around 1 nM. Good binding of FIBT relative to PiB was further confirmed in binding assays and autoradiographies using post-mortem AD brain. First use of [¹⁸F]­FIBT in humans successfully yielded clinical [¹⁸F]­FIBT PET/MR images with very good contrast. In summary, [¹⁸F]­FIBT has been characterized to be a new lead compound with improved binding characteristics and pharmacokinetics on its own as well as in comparison to PiB. A pilot human PET investigation provided high-quality images with a plausible tracer distribution pattern. Detailed clinical investigations are needed to confirm these first results and to explore the specific qualities of [¹⁸F]­FIBT PET for dementia imaging in relation to established ligands

Molecular Design of ⁶⁸Ga- and ⁸⁹Zr-Labeled Anticalin Radioligands for PET-Imaging of PSMA-Positive Tumors

Anticalin proteins directed against the prostate-specific membrane antigen (PSMA), optionally having tailored plasma half-life using PASylation technology, show promise as radioligands for PET-imaging of xenograft tumors in mice. To investigate their suitability, the short-circulating unmodified Anticalin was labeled with 68Ga (τ1/2 = 68 min), using the NODAGA chelator, whereas the half-life extended PASylated Anticalin was labeled with 89Zr (τ1/2 = 78 h), using either the linear chelator deferoxamine (Dfo) or a cyclic derivative, fusarinine C (FsC). Different PSMA targeting Anticalin versions (optionally carrying the PASylation sequence) were produced carrying a single exposed N- or C-terminal Cys residue and site-specifically conjugated with the different radiochelators via maleimide chemistry. These protein conjugates were labeled with radioisotopes having distinct physical half-lives and, subsequently, applied for PET-imaging of subcutaneous LNCaP xenograft tumors in CB17 SCID mice. Uptake of the protein tracers into tumor versus healthy tissues was assessed by segmentation of PET data as well as biodistribution analyses. PET-imaging with both the 68Ga-labeled plain Anticalin and the 89Zr-labeled PASylated Anticalin allowed clear delineation of the xenograft tumor. The radioligand A3A5.1-PAS(200)-FsC·89Zr, having an extended plasma half-life, led to a higher tumor uptake 24 h p.i. compared to the 68Ga·NODAGA-Anticalin imaged 60 min p.i. (2.5% ID/g vs 1.2% ID/g). Pronounced demetallation was observed for the 89Zr·Dfo-labeled PASylated Anticalin, which was ∼50% lower in the case of the cyclic radiochelator FsC (p < 0.0001). Adjusting the plasma half-life of Anticalin radioligands using PASylation technology is a viable approach to increase radioisotope accumulation within the tumor. Furthermore, 89Zr-ImmunoPET-imaging using the FsC radiochelator is superior to that using Dfo. Our strategy for the half-life adjustment of a tumor-targeting Anticalin to match the physical half-life of the applied radioisotope illustrates the potential of small binding proteins as an alternative to antibodies for PET-imaging