Spinocerebellar ataxia type 4 is caused by a GGC expansion in the ZFHX3 gene and is associated with prominent dysautonomia and motor neuron signs.

BACKGROUND: Spinocerebellar ataxia 4 (SCA4), characterized in 1996, features adult-onset ataxia, polyneuropathy, and linkage to chromosome 16q22.1; its underlying mutation has remained elusive. OBJECTIVE: To explore the radiological and neuropathological abnormalities in the entire neuroaxis in SCA4 and search for its mutation. METHODS: Three Swedish families with undiagnosed ataxia went through clinical, neurophysiological, and neuroimaging tests, including PET studies and genetic investigations. In four cases, neuropathological assessments of the neuroaxis were performed. Genetic testing included short read whole genome sequencing, short tandem repeat analysis with ExpansionHunter de novo, and long read sequencing. RESULTS: Novel features for SCA4 include dysautonomia, motor neuron affection, and abnormal eye movements. We found evidence of anticipation; neuroimaging demonstrated atrophy in the cerebellum, brainstem, and spinal cord. [18F]FDG-PET demonstrated brain hypometabolism and [11C]Flumazenil-PET reduced binding in several brain lobes, insula, thalamus, hypothalamus, and cerebellum. Moderate to severe loss of Purkinje cells in the cerebellum and of motor neurons in the anterior horns of the spinal cord along with pronounced degeneration of posterior tracts was also found. Intranuclear, mainly neuronal, inclusions positive for p62 and ubiquitin were sparse but widespread in the CNS. This finding prompted assessment for nucleotide expansions. A polyglycine stretch encoding GGC expansions in the last exon of the zink finger homeobox 3 gene was identified segregating with disease and not found in 1000 controls. CONCLUSIONS: SCA4 is a neurodegenerative disease caused by a novel GGC expansion in the coding region of ZFHX3, and its spectrum is expanded to include dysautonomia and neuromuscular manifestations.

Validation of a good manufacturing practice procedure for the production of [11C]AZD4747, a CNS penetrant KRASG12c inhibitor.

AZD4747 is a KRASG12C inhibitor recently shown to cross the non-human primate blood-brain barrier efficiently. In the current study, a GMP-compliant production of [11C]AZD4747 was developed to enable PET studies in human subjects. The validated procedure afforded [11C]AZD4747 as an injectable solution in good radioactivity yield (1656 ± 532 MBq), excellent radiochemical purity (100%), and a molar activity of 77 ± 13 GBq/µmol at the end of the synthesis, which took 46 ± 1 min from the end of the bombardment. Quality control on the final product was performed satisfactorily and met all acceptance criteria.

Labeling of Bruton's Tyrosine Kinase (BTK) Inhibitor [11C]BIO-2008846 in Three Different Positions and Measurement in NHP Using PET.

Bruton's tyrosine kinase (BTK) is pivotal in B-cell signaling and a target for potential anti-cancer and immunological disorder therapies. Improved selective reversible BTK inhibitors are in demand due to the absence of direct BTK engagement measurement tools. Promisingly, PET imaging can non-invasively evaluate BTK expression. In this study, radiolabeled BIO-2008846 ([11C]BIO-2008846-A), a BTK inhibitor, was used for PET imaging in NHPs to track brain biodistribution. Radiolabeling BIO-2008846 with carbon-11, alongside four PET scans on two NHPs each, showed a homogeneous distribution of [11C]BIO-2008846-A in NHP brains. Brain uptake ranged from 1.8% ID at baseline to a maximum of 3.2% post-pretreatment. The study found no significant decrease in regional VT values post-dose, implying minimal specific binding of [11C]BIO-2008846-A compared to free and non-specific components in the brain. Radiometabolite analysis revealed polar metabolites with 10% unchanged radioligand after 30 min. The research highlighted strong brain uptake despite minor distribution variability, confirming passive diffusion kinetics dominated by free and non-specific binding.

Synthesis of [11C]BIIB104, an α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic-Acid-Positive Allosteric Modulator, and Evaluation of the Bio-Distribution in Non-Human Primate Brains Using Positron Emission Tomography.

The aim of this study was to measure the brain penetrance and kinetics of BIIB104, a first-in-class AMPA receptor potentiator developed for cognitive impairment associated with schizophrenia. It was recently halted in phase 2 clinical development, and there are a lack of tools to directly measure AMPA receptor engagement. To achieve this, the drug candidate was radiolabeled with carbon-11, and its brain penetrance and kinetics were measured in non-human primates via dynamic PET scans. Radiolabeling was achieved through a three-step nucleophilic [11C]cyanation reaction in one pot, resulting in the high radioactivity and radiochemical purity (>99%) of [11C]BIIB104. The study found that [11C]BIIB104 entered the non-human primate brains at 4-5% ID at peak, with a homogeneous distribution. However, a mild regional heterogeneity was observed in the thalamus. The lack of conclusive evidence for a change in regional values after BIIB104 dosing suggests that any specific binding component of BIIB104 is negligible compared to the free and non-specific components in the living brain. Overall, the study demonstrated high brain uptake with minor variability in [11C]BIIB104 distribution across various brain regions, its kinetics were consistent with those of passive diffusion, and the dominating components were the free concentration and non-specific binding. This information is valuable for understanding the potential effects and mechanisms of BIIB104 in the brain.

Exploring the Interactions between two Ligands, UCB-J and UCB-F, and Synaptic Vesicle Glycoprotein 2 Isoforms.

In silico modeling was applied to study the efficiency of two ligands, namely, UCB-J and UCB-F, to bind to isoforms of the synaptic vesicle glycoprotein 2 (SV2) that are involved in the regulation of synaptic function in the nerve terminals, with the ultimate goal to understand the selectivity of the interaction between UCB-J and UCB-F to different isoforms of SV2. Docking and large-scale molecular dynamics simulations were carried out to unravel various binding patterns, types of interactions, and binding free energies, covering hydrogen bonding and nonspecific hydrophobic interactions, water bridge, π-π, and cation-π interactions. The overall preference for bonding types of UCB-J and UCB-F with particular residues in the protein pockets can be disclosed in detail. A unique interaction fingerprint, namely, hydrogen bonding with additional cation-π interaction with the pyridine moiety of UCB-J, could be established as an explanation for its high selectivity over the SV2 isoform A (SV2A). Other molecular details, primarily referring to the presence of π-π interactions and hydrogen bonding, could also be analyzed as sources of selectivity of the UCB-F tracer for the three isoforms. The simulations provide atomic details to support future development of new selective tracers targeting synaptic vesicle glycoproteins and their associated diseases.

Advancements in Microfluidic Cassette-Based iMiDEV™ Technology for Production of L-[11C]Methionine and [11C]Choline.

Microfluidic technology is a highly efficient technique used in positron emission tomography (PET) radiochemical synthesis. This approach enables the precise control of reactant flows and reaction conditions, leading to improved yields and reduced synthesis time. The synthesis of two radiotracers, L-[11C]methionine and [11C]choline, was performed, using a microfluidic cassette and an iMiDEVTM module by employing a dose-on-demand approach for the synthesis process. We focused on optimizing the precursor amounts and radiosynthesis on the microfluidic cassette. L-[11C]methionine and [11C]choline were synthesized using a microreactor filled with a suitable resin for the radiochemical reaction. Trapping of the [11C]methyl iodide, its reaction, and solid-phase extraction purification were performed on a microreactor, achieving radiochemical yields of >80% for L-[11C]methionine and >60% for [11C]choline (n = 3). The total synthesis time for both the radiotracers was approximately 20 min. All quality control tests complied with the European Pharmacopeia standards. The dose-on-demand model allows for real-time adaptation to patient schedules, making it suitable for preclinical and clinical settings. Precursor optimization enhanced the cost efficiency without compromising the yield. The importance of dose-on-demand synthesis and optimized precursor utilization to produce L-[11C]methionine and [11C]choline was emphasized in this study. The results demonstrated the feasibility of dose-on-demand adaptations for clinical applications with reduced precursor quantities and high radiochemical yields.

High Contrast PET Imaging of Subcortical and Allocortical Amyloid-ß in Early Alzheimer's Disease Using [11C]AZD2184.

Background: Deposits of amyloid-ß (Aß) appear early in Alzheimer's disease (AD). Objective: The aim of the present study was to compare the presence of cortical and subcortical Aß in early AD using positron emission tomography (PET). Methods: Eight cognitively unimpaired (CU) subjects, 8 with mild cognitive impairment (MCI) and 8 with mild AD were examined with PET and [11C]AZD2184. A data driven cut-point for Aß positivity was defined by Gaussian mixture model of isocortex binding potential (BPND) values. Results: Sixteen subjects (3 CU, 5 MCI and 8 AD) were Aß-positive. BPND was lower in subcortical and allocortical regions compared to isocortex. Fifteen of the 16 Aß-positive subjects displayed Aß binding in striatum, 14 in thalamus and 10 in allocortical regions. Conclusions: Aß deposits appear to be widespread in early AD. It cannot be excluded that deposits appear simultaneously throughout the whole brain which has implications for improved diagnostics and disease monitoring.

Radiosynthesis and Evaluation of 11C-Labeled Isoindolone-Based Positive Allosteric Modulators for Positron Emission Tomography Imaging of Metabotropic Glutamate Receptor 2.

The metabotropic glutamate receptor 2 (mGluR2) has emerged as a potential therapeutic target for the treatment of various neurological diseases, prompting substantial interest in the development of mGluR2-targeted drug candidates. As part of our medicinal chemistry program, we synthesized a series of isoindolone derivatives and assessed their potential as mGluR2 positive allosteric modulators (PAMs). Notably, AZ12559322 exhibited high affinity (K i mGluR2 = 1.31 nM) and an excellent in vitro binding specificity of 89% while demonstrating selectivity over other mGluR subtypes (>4000-fold). Autoradiography with the radiolabeled counterpart, [3H]AZ12559322, revealed a heterogeneous accumulation with the highest binding in mGluR2-rich brain regions. Radioligand binding was significantly reduced by pretreatment with nonradioactive mGluR2 PAMs in brains of rats and nonhuman primates. Although positron emission tomography imaging of [11C]AZ12559322 (6a) revealed low brain uptake in a nonhuman primate, this study provides valuable guidance to further design novel isoindolone-based mGluR2 PAMs with improved brain exposure.