Identification of a Putative α-synuclein Radioligand Using an in silico Similarity Search.

Purpose: Previous studies from our lab utilized an ultra-high throughput screening method to identify compound 1 as a small molecule that binds to alpha-synuclein (α-synuclein) fibrils. The goal of the current study was to conduct a similarity search of 1 to identify structural analogs having improved in vitro binding properties for this target that could be labeled with radionuclides for both in vitro and in vivo studies for measuring α-synuclein aggregates.

Methods: Using 1 as a lead compound in a similarity search, isoxazole derivative 15 was identified to bind to α-synuclein fibrils with high affinity in competition binding assays.

Novel Thienopyrimidine-Based PET Tracers for P2Y Receptor Imaging in the Brain.

The P2Y receptor (P2YR) is uniquely expressed on microglia in the brain, and its expression level directly depends on the microglial activation state. Therefore, P2YR provides a promising imaging marker for distinguishing the pro- and anti-inflammatory microglial phenotypes, both of which play crucial roles in neuroinflammatory diseases. In this study, three P2YR antagonists were selected from the literature, radiolabeled with carbon-11 or fluorine-18, and evaluated in healthy Wistar rats.

Towards PET imaging of the dynamic phenotypes of microglia.

There is increasing evidence showing the heterogeneity of microglia activation in neuroinflammatory and neurodegenerative diseases. It has been hypothesized that pro-inflammatory microglia are detrimental and contribute to disease progression, while anti-inflammatory microglia play a role in damage repair and remission. The development of therapeutics targeting the deleterious glial activity and modulating it into a regenerative phenotype relies heavily upon a clearer understanding of the microglia dynamics during disease progression and the ability to monitor therapeutic outcome in vivo.

Identification of a nanomolar affinity α-synuclein fibril imaging probe by ultra-high throughput screening.

Small molecules that bind with high affinity and specificity to fibrils of the α-synuclein (αS) protein have the potential to serve as positron emission tomography (PET) imaging probes to aid in the diagnosis of Parkinson's disease and related synucleinopathies. To identify such molecules, we employed an ultra-high throughput screening strategy using idealized pseudo-ligands termed exemplars to identify compounds for experimental binding studies. For the top hit from this screen, we used photo-crosslinking to confirm its binding site and studied the structure-activity relationship of its analogs to develop multiple molecules with nanomolar affinity for αS fibrils and moderate specificity for αS over Aβ fibrils.

PET imaging of P2XR in the experimental autoimmune encephalomyelitis model of multiple sclerosis using [C]SMW139.

Background: Non-invasive imaging of the activation status of microglia and the ability to identify a pro- or anti-inflammatory environment can provide valuable insights not only into pathogenesis of neuro-inflammatory and neurodegenerative diseases but also the monitoring of the efficacy of immunomodulatory therapies. P2XR is highly expressed on pro-inflammatory microglia and [C]SMW139, a specific P2XR tracer for positron emission tomography imaging, showed good pharmacokinetics, stability, and brain permeability in vivo. Our objective was to evaluate the potential of [C]SMW139 for PET imaging of neuroinflammation in vivo in the experimental autoimmune encephalomyelitis (EAE) model.

Synthesis and characterization of high affinity fluorogenic α-synuclein probes.

Fluorescent small molecules are powerful tools for imaging α-synuclein pathology in vitro and in vivo. In this work, we explore benzofuranone as a potential scaffold for the design of fluorescent α-synuclein probes. These compounds have high affinity for α-synuclein, show fluorescent turn-on upon binding to fibrils, and display different binding to Lewy bodies, Lewy neurites and glial cytoplasmic inclusion pathologies in post-mortem brain tissue.

The P2X receptor tracer [C]SMW139 as an in vivo marker of neuroinflammation in multiple sclerosis: a first-in man study.

Purpose: The novel PET tracer [C]SMW139 binds with high affinity to the P2X receptor, which is expressed on pro-inflammatory microglia. The purposes of this first in-man study were to characterise pharmacokinetics of [C]SMW139 in patients with active relapsing remitting multiple sclerosis (RRMS) and healthy controls (HC) and to evaluate its potential to identify in vivo neuroinflammation in RRMS.

Methods: Five RRMS patients and 5 age-matched HC underwent 90-min dynamic [C]SMW139 PET scans, with online continuous and manual arterial sampling to generate a metabolite-corrected arterial plasma input function.

Development of brain PET imaging agents: Strategies for imaging neuroinflammation in Alzheimer's disease.

Neuroinflammation is thought to play a key role in the development and progression of neurodegenerative diseases such as Alzheimer's disease. Positron emission tomography (PET) is an in vivo imaging technique capable of studying the biochemical processes which provide the molecular basis of disease. PET imaging of neuroinflammation, which is characterized by the activation of glial cells in the central nervous system (CNS), has been traditionally studied using radiotracers targeting the translocator protein 18kDa (TSPO).

Identification of new molecular targets for PET imaging of the microglial anti-inflammatory activation state.

Microglia are potential targets for therapeutic intervention in neurological and neurodegenerative diseases affecting the central nervous system. In order to assess the efficacy of therapies aimed to reduce the tissue damaging activities of microglia and/or to promote the protective potential of these cells, suitable pre-clinical and clinical tools for the analysis of microglia activities and dynamics are required. The aim of this work was to identify new translational markers of the anti-inflammatory / protective state of microglia for the development of novel PET tracers.

Identification of the allosteric P2X receptor antagonist [C]SMW139 as a PET tracer of microglial activation.

The P2X receptor plays a significant role in microglial activation, and as a potential drug target, the P2X receptor is also an interesting target in positron emission tomography. The current study aimed at the development and evaluation of a potent tracer targeting the P2X receptor, to which end four adamantanyl benzamide analogues with high affinity for the human P2X receptor were labelled with carbon-11. All four analogues could be obtained in excellent radiochemical yield and high radiochemical purity and molar activity, and all analogues entered the rat brain.

PET Imaging of Microglial Activation-Beyond Targeting TSPO.

Neuroinflammation, which involves microglial activation, is thought to play a key role in the development and progression of neurodegenerative diseases and other brain pathologies. Positron emission tomography is an ideal imaging technique for studying biochemical processes in vivo, and particularly for studying the living brain. Neuroinflammation has been traditionally studied using radiotracers targeting the translocator protein 18 kDa, but this comes with certain limitations.

Purinergic receptors P2Y12R and P2X7R: potential targets for PET imaging of microglia phenotypes in multiple sclerosis.

Background: Microglia are major players in the pathogenesis of multiple sclerosis (MS) and may play a dual role in disease progression. The activation status of microglia in vivo is highly dynamic and occurs as a continuum, with the pro-inflammatory and anti-inflammatory phenotypes on either end of this spectrum. Little is known about in vivo dynamics of microglia phenotypes in MS due to the lack of diagnostic tools.

Pharmacological Evaluation of Novel Bioisosteres of an Adamantanyl Benzamide P2X Receptor Antagonist.

Adamantanyl benzamide 1 was identified as a potent P2XR antagonist but failed to progress further due to poor metabolic stability. We describe the synthesis and SAR of a series of bioisosteres of benzamide 1 to explore improvements in the pharmacological properties of this lead. Initial efforts investigated a series of heteroaromatic bioisosteres, which demonstrated improved physicochemical properties but reduced P2XR antagonism.

Imaging of neuroinflammation in Alzheimer's disease, multiple sclerosis and stroke: Recent developments in positron emission tomography.

Neuroinflammation is thought to play a pivotal role in many diseases affecting the brain, including Alzheimer's disease, multiple sclerosis and stroke. Neuroinflammation is characterised predominantly by microglial activation, which can be visualised using positron emission tomography (PET). Traditionally, translocator protein 18kDa (TSPO) is the target for imaging of neuroinflammation using PET.

Synthesis and initial preclinical evaluation of the P2X7 receptor antagonist [¹¹C]A-740003 as a novel tracer of neuroinflammation.

Neuroinflammation, in particular activation of microglia, is thought to play an important role in the progression of neurodegenerative diseases. In activated microglia, the purinergic P2X7 receptor is upregulated. A-740003, a highly affine and selective P2X7 receptor antagonist, is a promising candidate for the development of a radiotracer for imaging of neuroinflammation by positron emission tomography.

(11) C-labeled and (18) F-labeled PET ligands for subtype-specific imaging of histamine receptors in the brain.

The signaling molecule histamine plays a key role in the mediation of immune reactions, in gastric secretion, and in the sensory system. In addition, it has an important function as a neurotransmitter in the central nervous system, acting in pituitary hormone secretion, wakefulness, motor and cognitive functions, as well as in itch and nociception. This has raised interest in the role of the histaminergic system for the treatment and diagnosis of various pathologies such as allergy, sleeping and eating disorders, neurodegeneration, neuroinflammation, mood disorders, and pruritus.