Mixing water, sugar, and lipid: Conformations of isolated and micro-hydrated glycolipids in the gas phase.

Both sugars and lipids are important biomolecular building blocks with exceptional conformational flexibility and adaptability to their environment. Glycolipids bring together these two molecular components in the same assembly and combine the complexity of their conformational landscapes. In the present study, we have used selective double resonance vibrational spectroscopy, in combination with a computational approach, to explore the conformational preferences of two glycolipid models (3-0-acyl catechol and guaiacol α-D-glucopyranosides), either fully isolated in the gas phase or controlled interaction with a single water molecule. We could identify the preferred conformation and structures of the isolated and micro-hydrated species and evidence of the presence of a strong water pocket, which may influence the conformational flexibility of such systems, even in less controlled environments.

Design, Synthesis, and Evaluation of [18F]T-914 as a Novel Positron-Emission Tomography Tracer for Lysine-Specific Demethylase 1.

Histone methylation is associated with the pathophysiology of neurodevelopmental disorders. Lysine-specific demethylase 1 (LSD1) catalyzes histone demethylation in a flavin adenine dinucleotide (FAD)-dependent manner. Thus, inhibiting LSD1 enzyme activity could offer a novel way to treat neurodevelopmental disorders. Assessing LSD1 target engagement using positron-emission tomography (PET) imaging could aid in developing therapeutic LSD1 inhibitors. In this study, PET probes based on 4-(2-aminocyclopropyl)benzamide derivatives that bind irreversibly to FAD found in LSD1 were examined. By optimizing the profiles of brain penetrance and brain-penetrant metabolites, T-914 (1g) was identified as a suitable PET tracer candidate. PET studies in nonhuman primates demonstrated that [18F]1g had heterogeneous brain uptake, which corresponded to known LSD1 expression levels. Moreover, brain uptake of [18F]1g was reduced by coadministration of unlabeled 1g, demonstrating blockable binding. These data suggest that [18F]1g warrants further investigation as a potential PET tracer candidate for assessing target engagement of LSD1.

Design, Synthesis, and Evaluation of (2-Aminocyclopropyl)phenyl Derivatives as Novel Positron Emission Tomography Imaging Agents for Lysine-Specific Demethylase 1 in the Brain.

Dysregulation of histone H3 lysine 4 (H3K4) methylation is implicated in the pathogenesis of neurodevelopmental disorders. Lysine-specific demethylase 1 (LSD1) determines the methylation status of H3K4 through flavin adenine dinucleotide (FAD)-mediated histone demethylation. Therefore, LSD1 inhibition in the brain can be a novel therapeutic option for treating these disorders. Positron emission tomography (PET) imaging of LSD1 allows for investigating LSD1 expression levels under normal and disease conditions and validating target engagement of therapeutic LSD1 inhibitors. This study designed and synthesized (2-aminocyclopropyl)phenyl derivatives with irreversible binding to LSD1 as PET imaging agents for LSD1 in the brain. We optimized lipophilicity of the lead compound to minimize the risk of nonspecific binding and identified 1e with high selectivity over monoamine oxidase A and B, which are a family of FAD-dependent enzymes homologous to LSD1. PET imaging in a monkey showed a high uptake of [18F]1e to regions enriched with LSD1, indicating its specific binding to LSD1.

The Production, Quality Control, and Characterization of ZED8, a CD8-Specific 89Zr-Labeled Immuno-PET Clinical Imaging Agent.

Immuno-PET is a molecular imaging technique utilizing positron emission tomography (PET) to measure the biodistribution of an antibody species labeled with a radioactive isotope. When applied as a clinical imaging technique, an immuno-PET imaging agent must be manufactured with quality standards appropriate for regulatory approval. This paper describes methods relevant to the chemistry, manufacturing, and controls component of an immuno-PET regulatory filing, such as an investigational new drug application. Namely, the production, quality control, and characterization of the immuno-PET clinical imaging agent, ZED8, an 89Zr-labeled CD8-specific monovalent antibody as well as its desferrioxamine-conjugated precursor, CED8, is described and evaluated. PET imaging data in a human CD8-expressing tumor murine model is presented as a proof of concept that the imaging agent exhibits target specificity and comparable biodistribution across a range of desferrioxamine conjugate loads.

Preclinical In Vitro and In Vivo Characterization of Synaptic Vesicle 2A-Targeting Compounds Amenable to F-18 Labeling as Potential PET Radioligands for Imaging of Synapse Integrity.

PURPOSE: Current synaptic vesicle 2A (SV2A) positron emission tomography (PET) imaging agents include the nanomolar affinity probes [11C]UCB-J and [18F]UCB-H derived from the anti-epileptic drug levitaracetam (Keppra®). An industry-utilized "de-risking" approach was used to carry out initial pharmacological characterization and to assess potential next-generation candidates amenable to F-18 radiolabeling for preliminary evaluation. PROCEDURES: Radioligand binding methods were employed in mammalian brain homogenates to determine the SV2A affinity (Kd) and maximal binding capacity (Bmax) of [3H]UCB-J. Novel leads were then screened to identify compounds minimally with comparable binding affinities with UCB-J in order to select a F-18-labeled candidate for subsequent in vivo assessment in rat. In parallel, mammalian brain tissue section autoradiography was performed to assess specific SV2A distribution. RESULTS: [3H]UCB-J bound with high affinity to a single population of sites in the rat brain (Kd = 2.6 ± 0.25 nM; Bmax = 810 ± 25 fmol/mg protein) and control human cortex (Kd = 2.9 ± 0.54 nM; Bmax = 10,000 ± 640 fmol/mg protein). Distribution of specific SV2A binding was shown to be homogeneous throughout the rodent brain and primarily in gray matter regions of rodent and human brain sections. Analog screening identified MNI-1038, MNI-1126/SDM-8, and SDM-2 as having comparable binding affinities with the currently available PET ligands. Subsequent [18F]MNI-1126/[18F]SDM-8 dynamic micro-PET imaging in rats revealed in vivo uptake and accumulation in the brain with favorable kinetics. Chase studies using 30 mg/kg levetiracetam confirmed that in vivo brain uptake of [18F]MNI-1126/[18F]SDM-8 was reversible. CONCLUSIONS: Taken together, these data suggest [18F]MNI-1126/[18F]SDM-8 (since renamed as [18F]SynVesT-1) characterized via an in vitro screening cascade provided a measurable in vivo SV2A specific signal in the rodent brain. This tracer as well as the close analog [18F]SDM-2 (since renamed as [18F]SynVesT-2) is currently undergoing further evaluation in preclinical and clinical studies.

Development and In Vivo Preclinical Imaging of Fluorine-18-Labeled Synaptic Vesicle Protein 2A (SV2A) PET Tracers.

PURPOSE: Synaptic vesicle protein 2A (SV2A) serves as a biomarker of synaptic density and positron emission tomography (PET) imaging of SV2A could provide a tool to assess progression of neurodegenerative diseases. Two tracers have primarily been reported and characterized in vivo: [11C]UCB-J and [18F]UCB-H. In early human studies, [11C]UCB-J showed promising results, while its F-18-labeled analogue [18F]UCB-H showed suboptimal specific signal in comparison to [11C]UCB-J. Considering the limited use of [11C]UCB-J to facilities with a cyclotron, having a F-18 variant would facilitate large, multicenter imaging trials. We have screened several F-18 derivatives of UCB-J in non-human primates and identified a promising F-18 PET candidate, [18F]MNI-1126, with additional investigations of the racemate [18F]MNI-1038, affording a signal comparable to [11C]UCB-J. PROCEDURES: F-18 derivatives of UCB-J and UCB-H were synthesized and administered to non-human primates for microPET imaging. Following screenings, [18F]MNI-1038 (racemate) and [18F]MNI-1126 (R-enantiomer) were identified with the highest signal and favorable kinetics and were selected for further imaging. Kinetic modeling with one- and two-tissue compartmental models, and linear methods were applied to PET data using metabolite-corrected arterial input function. Pre-block scans with levetiracetam (LEV, 10, 30 mg/kg, iv) were performed to determine the tracers' in vivo specificity for SV2A. Two whole-body PET studies were performed with [18F]MNI-1038 in one male and one female rhesus, and radiation absorbed dose estimates and effective dose (ED, ICRP-103) were estimated with OLINDA/EXM 2.0. RESULTS: All compounds screened displayed very good brain penetration, with a plasma-free fraction of ~ 40 %. [18F]MNI-1126 and [18F]MNI-1038 showed uptake and distribution the most consistent with UCB-J, while the other derivatives showed suboptimal results, with similar or lower uptake than [18F]UCB-H. VT of [18F]MNI-1126 and [18F]MNI-1038 was high in all gray matter regions (within animal averages ~ 30 ml/cm3) and highly correlated with [11C]UCB-J (r > 0.99). Pre-blocking of [18F]MNI-1126 or [18F]MNI-1038 with LEV showed robust occupancy across all gray matter regions, similar to that reported with [11C]UCB-J (~ 85 % at 30 mg/kg, ~ 65 % at 10 mg/kg). Using the centrum semiovale as a reference region, BPND of [18F]MNI-1126 reached values of up to ~ 30 to 40 % higher than those reported for [11C]UCB-J. From whole-body imaging average ED of [18F]MNI-1038 was estimated to be 22.3 µSv/MBq, with tracer being eliminated via both urinary and hepatobiliary pathways. CONCLUSIONS: We have identified a F-18-labeled tracer ([18F]MNI-1126) that exhibits comparable in vivo characteristics and specificity for SV2A to [11C]UCB-J in non-human primates, which makes [18F]MNI-1126 a promising PET radiotracer for imaging SV2A in human trials.