High affinity radiopharmaceuticals based upon lansoprazole for PET imaging of aggregated tau in Alzheimer's disease and progressive supranuclear palsy: synthesis, preclinical evaluation, and lead selection

Strategies of positron emission tomography (PET) tracer development for imaging of tau and α-synuclein in neurodegenerative disorders

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by the presence of extracellular amyloid plaques consisting of β-amyloid peptides (Aβ) and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau (pTau) protein in the brain. Genetic and animal studies strongly indicate that Aβ, tau and neuroinflammation play important roles in the pathogenesis of AD. Several staging models showed that NFTs correlated well with the disease progression. Positron emission tomography (PET) imaging has become a widely used non-invasive technique to image NFTs for early diagnosis of AD. Despite the remarkable progress made over the past few years, tau PET imaging is still challenging due to the nature of tau pathology and the technical aspects of PET imaging. Tau pathology often coexists with other proteinopathies, such as Aβ plaques and α-synuclein aggregates. Distinguishing tau-specific signals from other overlapping pathologies is difficult, especially in the context of AD, where multiple protein aggregates are present, as well as the spectrum of different tau isoforms (3R and 4R) and conformations. Moreover, tracers should ideally have optimal pharmacokinetic properties to penetrate the blood-brain barrier (BBB) while maintaining specificity, low toxicity, low non-specific binding, rapid uptake and clearance from the brain, and formation of no radiolabeled metabolites in the brain. On the other hand, Parkinson's disease (PD) is a progressive neurodegenerative movement disorder characterized by the abnormal accumulations of α-synuclein in neurons. Heterogeneity and the unclear pathogenesis of PD hinder early and accurate diagnosis of the disease for therapeutic development in clinical use. In this review, while referring to existing reviews, we focus on the design strategies and current progress in tau (NFTs) targeting new PET tracers for AD; evolution of non-AD tau targeting PET tracers for applications including progressive supranuclear paralysis (PSP) and corticobasal degeneration (CBD); new PET tracer development for α-synuclein aggregate imaging in PD and giving an outlook for future PET tracer development.

Isotopologues of potassium 2,2,2-trifluoroethoxide for applications in positron emission tomography and beyond

The 2,2,2-trifluoroethoxy group increasingly features in drugs and potential tracers for biomedical imaging with positron emission tomography (PET). Herein, we describe a rapid and transition metal-free conversion of fluoroform with paraformaldehyde into highly reactive potassium 2,2,2-trifluoroethoxide (CF3CH2OK) and demonstrate robust applications of this synthon in one-pot, two-stage 2,2,2-trifluoroethoxylations of both aromatic and aliphatic precursors. Moreover, we show that these transformations translate easily to fluoroform that has been labeled with either carbon-11 (t1/2 = 20.4 min) or fluorine-18 (t1/2 = 109.8 min), so allowing the appendage of complex molecules with a no-carrier-added 11C- or 18F- 2,2,2-trifluoroethoxy group. This provides scope to create candidate PET tracers with radioactive and metabolically stable 2,2,2-trifluoroethoxy moieties. We also exemplify syntheses of isotopologues of potassium 2,2,2-trifluoroethoxide and show their utility for stable isotopic labeling which can be of further benefit for drug discovery and development.

Peptidoglycan-Targeted [18F]3,3,3-Trifluoro-d-alanine Tracer for Imaging Bacterial Infection

Imaging is increasingly used to detect and monitor bacterial infection. Both anatomic (X-rays, computed tomography, ultrasound, and MRI) and nuclear medicine ([111In]-WBC SPECT, [18F]FDG PET) techniques are used in clinical practice but lack specificity for the causative microorganisms themselves. To meet this challenge, many groups have developed imaging methods that target pathogen-specific metabolism, including PET tracers integrated into the bacterial cell wall. We have previously reported the d-amino acid derived PET radiotracers d-methyl-[11C]-methionine, d-[3-11C]-alanine, and d-[3-11C]-alanine-d-alanine, which showed robust bacterial accumulation in vitro and in vivo. Given the clinical importance of radionuclide half-life, in the current study, we developed [18F]3,3,3-trifluoro-d-alanine (d-[18F]-CF3-ala), a fluorine-18 labeled tracer. We tested the hypothesis that d-[18F]-CF3-ala would be incorporated into bacterial peptidoglycan given its structural similarity to d-alanine itself. NMR analysis showed that the fluorine-19 parent amino acid d-[19F]-CF3-ala was stable in human and mouse serum. d-[19F]-CF3-ala was also a poor substrate for d-amino acid oxidase, the enzyme largely responsible for mammalian d-amino acid metabolism and a likely contributor to background signals using d-amino acid derived PET tracers. In addition, d-[19F]-CF3-ala showed robust incorporation into Escherichia coli peptidoglycan, as detected by HPLC/mass spectrometry. Based on these promising results, we developed a radiosynthesis of d-[18F]-CF3-ala via displacement of a bromo-precursor with [18F]fluoride followed by chiral stationary phase HPLC. Unexpectedly, the accumulation of d-[18F]-CF3-ala by bacteria in vitro was highest for Gram-negative pathogens in particular E. coli. In a murine model of acute bacterial infection, d-[18F]-CF3-ala could distinguish live from heat-killed E. coli, with low background signals. These results indicate the viability of [18F]-modified d-amino acids for infection imaging and indicate that improved specificity for bacterial metabolism can improve tracer performance.

A closer look at amyloid ligands, and what they tell us about protein aggregates

The accumulation of amyloid fibrils is characteristic of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease. Detecting these fibrils with fluorescent or radiolabelled ligands is one strategy for diagnosing and better understanding these diseases. A vast number of amyloid-binding ligands have been reported in the literature as a result. To obtain a better understanding of how amyloid ligands bind, we have compiled a database of 3457 experimental dissociation constants for 2076 unique amyloid-binding ligands. These ligands target Aβ, tau, or αSyn fibrils, as well as relevant biological samples including AD brain homogenates. From this database significant variation in the reported dissociation constants of ligands was found, possibly due to differences in the morphology of the fibrils being studied. Ligands were also found to bind to Aβ(1-40) and Aβ(1-42) fibrils with similar affinities, whereas a greater difference was found for binding to Aβ and tau or αSyn fibrils. Next, the binding of ligands to fibrils was shown to be largely limited by the hydrophobic effect. Some Aβ ligands do not fit into this hydrophobicity-limited model, suggesting that polar interactions can play an important role when binding to this target. Finally several binding site models were outlined for amyloid fibrils that describe what ligands target what binding sites. These models provide a foundation for interpreting and designing site-specific binding assays.

CenTauR: Toward a universal scale and masks for standardizing tau imaging studies

INTRODUCTION

Recently, an increasing number of tau tracers have become available. There is a need to standardize quantitative tau measures across tracers, supporting a universal scale. We developed several cortical tau masks and applied them to generate a tau imaging universal scale.

METHOD

One thousand forty-five participants underwent tau scans with either 18F-flortaucipir, 18F-MK6240, 18F-PI2620, 18F-PM-PBB3, 18F-GTP1, or 18F-RO948. The universal mask was generated from cognitively unimpaired amyloid beta (Aβ)- subjects and Alzheimer's disease (AD) patients with Aβ+. Four additional regional cortical masks were defined within the constraints of the universal mask. A universal scale, the CenTauRz, was constructed.

RESULTS

None of the regions known to display off-target signal were included in the masks. The CenTauRz allows robust discrimination between low and high levels of tau deposits.

DISCUSSION

We constructed several tau-specific cortical masks for the AD continuum and a universal standard scale designed to capture the location and degree of abnormality that can be applied across tracers and across centers. The masks are freely available at https://www.gaain.org/centaur-project.

The Sensitivity of Tau Tracers for the Discrimination of Alzheimer's Disease Patients and Healthy Controls by PET

Hyperphosphorylated tau aggregates, also known as neurofibrillary tangles, are a hallmark neuropathological feature of Alzheimer's disease (AD). Molecular imaging of tau by positron emission tomography (PET) began with the development of [18F]FDDNP, an amyloid β tracer with off-target binding to tau, which obtained regional specificity through the differing distributions of amyloid β and tau in AD brains. A concerted search for more selective and affine tau PET tracers yielded compounds belonging to at least eight structural categories; 18F-flortaucipir, known variously as [18F]-T807, AV-1451, and Tauvid®, emerged as the first tau tracer approved by the American Food and Drug Administration. The various tau tracers differ concerning their selectivity over amyloid β, off-target binding at sites such as monoamine oxidase and neuromelanin, and degree of uptake in white matter. While there have been many reviews of molecular imaging of tau in AD and other conditions, there has been no systematic comparison of the fitness of the various tracers for discriminating between AD patient and healthy control (HC) groups. In this narrative review, we endeavored to compare the binding properties of the various tau tracers in vitro and the effect size (Cohen's d) for the contrast by PET between AD patients and age-matched HC groups. The available tracers all gave good discrimination, with Cohen's d generally in the range of two-three in culprit brain regions. Overall, Cohen's d was higher for AD patient groups with more severe illness. Second-generation tracers, while superior concerning off-target binding, do not have conspicuously higher sensitivity for the discrimination of AD and HC groups. We suppose that available pharmacophores may have converged on a maximal affinity for tau fibrils, which may limit the specific signal imparted in PET studies.

Fluorine-18: Radiochemistry and Target-Specific PET Molecular Probes Design

The positron emission tomography (PET) molecular imaging technology has gained universal value as a critical tool for assessing biological and biochemical processes in living subjects. The favorable chemical, physical, and nuclear characteristics of fluorine-18 (97% β+ decay, 109.8 min half-life, 635 keV positron energy) make it an attractive nuclide for labeling and molecular imaging. It stands that 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) is the most popular PET tracer. Besides that, a significantly abundant proportion of PET probes in clinical use or under development contain a fluorine or fluoroalkyl substituent group. For the reasons given above, 18F-labeled radiotracer design has become a hot topic in radiochemistry and radiopharmaceutics. Over the past decades, we have witnessed a rapid growth in 18F-labeling methods owing to the development of new reagents and catalysts. This review aims to provide an overview of strategies in radiosynthesis of [18F]fluorine-containing moieties with nucleophilic [18F]fluorides since 2015.

Quantitative analysis of regional distribution of tau pathology with 11C-PBB3-PET in a clinical setting

PURPOSE

The recent developments of tau-positron emission tomography (tau-PET) enable in vivo assessment of neuropathological tau aggregates. Among the tau-specific tracers, the application of 11C-pyridinyl-butadienyl-benzothiazole 3 (11C-PBB3) in PET shows high sensitivity to Alzheimer disease (AD)-related tau deposition. The current study investigates the regional tau load in patients within the AD continuum, biomarker-negative individuals (BN) and patients with suspected non-AD pathophysiology (SNAP) using 11C-PBB3-PET.

MATERIALS AND METHODS

A total of 23 memory clinic outpatients with recent decline of episodic memory were examined using 11C-PBB3-PET. Pittsburg compound B (11C-PIB) PET was available for 17, 18F-flurodeoxyglucose (18F-FDG) PET for 16, and cerebrospinal fluid (CSF) protein levels for 11 patients. CSF biomarkers were considered abnormal based on Aβ42 (< 600 ng/L) and t-tau (> 450 ng/L). The PET biomarkers were classified as positive or negative using statistical parametric mapping (SPM) analysis and visual assessment. Using the amyloid/tau/neurodegeneration (A/T/N) scheme, patients were grouped as within the AD continuum, SNAP, and BN based on amyloid and neurodegeneration status. The 11C-PBB3 load detected by PET was compared among the groups using both atlas-based and voxel-wise analyses.

RESULTS

Seven patients were identified as within the AD continuum, 10 SNAP and 6 BN. In voxel-wise analysis, significantly higher 11C-PBB3 binding was observed in the AD continuum group compared to the BN patients in the cingulate gyrus, tempo-parieto-occipital junction and frontal lobe. Compared to the SNAP group, patients within the AD continuum had a considerably increased 11C-PBB3 uptake in the posterior cingulate cortex. There was no significant difference between SNAP and BN groups. The atlas-based analysis supported the outcome of the voxel-wise quantification analysis.

CONCLUSION

Our results suggest that 11C-PBB3-PET can effectively analyze regional tau load and has the potential to differentiate patients in the AD continuum group from the BN and SNAP group.

Positron Emission Tomography in Animal Models of Tauopathies

The microtubule-associated protein tau (MAPT) plays an important role in Alzheimer's disease and primary tauopathy diseases. The abnormal accumulation of tau contributes to the development of neurotoxicity, inflammation, neurodegeneration, and cognitive deficits in tauopathy diseases. Tau synergically interacts with amyloid-beta in Alzheimer's disease leading to detrimental consequence. Thus, tau has been an important target for therapeutics development for Alzheimer's disease and primary tauopathy diseases. Tauopathy animal models recapitulating the tauopathy such as transgenic, knock-in mouse and rat models have been developed and greatly facilitated the understanding of disease mechanisms. The advance in PET and imaging tracers have enabled non-invasive detection of the accumulation and spread of tau, the associated microglia activation, metabolic, and neurotransmitter receptor alterations in disease animal models. In vivo microPET studies on mouse or rat models of tauopathy have provided significant insights into the phenotypes and time course of pathophysiology of these models and allowed the monitoring of treatment targeting at tau. In this study, we discuss the utilities of PET and recently developed tracers for evaluating the pathophysiology in tauopathy animal models. We point out the outstanding challenges and propose future outlook in visualizing tau-related pathophysiological changes in brain of tauopathy disease animal models.

Synthesis and Evaluation of a Fluorine-18 Radioligand for Imaging Huntingtin Aggregates by Positron Emission Tomographic Imaging

Mutations in the huntingtin gene (HTT) triggers aggregation of huntingtin protein (mHTT), which is the hallmark pathology of neurodegenerative Huntington's disease (HD). Development of a high affinity 18F radiotracer would enable the study of Huntington's disease pathology using a non-invasive imaging modality, positron emission tomography (PET) imaging. Herein, we report the first synthesis of fluorine-18 imaging agent, 6-(5-((5-(2,2-difluoro-2-(fluoro-18F)ethoxy)pyridin-2-yl)methoxy)benzo[d]oxazol-2-yl)-2-methylpyridazin-3(2H)-one ([18F]1), a radioligand for HD and its preclinical evaluation in vitro (autoradiography of post-mortem HD brains) and in vivo (rodent and non-human primate brain PET). [18F]1 was synthesized in a 4.1% RCY (decay corrected) and in an average molar activity of 16.5 ± 12.5 GBq/μmol (445 ± 339 Ci/mmol). [18F]1 penetrated the blood-brain barrier of both rodents and primates, and specific saturable binding in post-mortem brain slices was observed that correlated to mHTT aggregates identified by immunohistochemistry.

Advances in [18F]Trifluoromethylation Chemistry for PET Imaging

Positron emission tomography (PET) is a preclinical and clinical imaging technique extensively used to study and visualize biological and physiological processes in vivo. Fluorine-18 (¹⁸F) is the most frequently used positron emitter for PET imaging due to its convenient 109.8 min half-life, high yield production on small biomedical cyclotrons, and well-established radiofluorination chemistry. The presence of fluorine atoms in many drugs opens new possibilities for developing radioligands labelled with fluorine-18. The trifluoromethyl group (CF₃) represents a versatile structural motif in medicinal and pharmaceutical chemistry to design and synthesize drug molecules with favourable pharmacological properties. This fact also makes CF₃ groups an exciting synthesis target from a PET tracer discovery perspective. Early attempts to synthesize [¹⁸F]CF₃-containing radiotracers were mainly hampered by low radiochemical yields and additional challenges such as low radiochemical purity and molar activity. However, recent innovations in [¹⁸F]trifluoromethylation chemistry have significantly expanded the chemical toolbox to synthesize fluorine-18-labelled radiotracers. This review presents the development of significant [¹⁸F]trifluoromethylation chemistry strategies to apply [¹⁸F]CF₃-containing radiotracers in preclinical and clinical PET imaging studies. The continuous growth of PET as a crucial functional imaging technique in biomedical and clinical research and the increasing number of CF₃-containing drugs will be the primary drivers for developing novel [¹⁸F]trifluoromethylation chemistry strategies in the future.

The Risk of Epilepsy after Long-term Proton Pump Inhibitor Therapy

BACKGROUND

Prescription-event monitoring studies have reported incident epilepsy or seizures in proton pump inhibitor (PPI) recipients. We examined the risk of epilepsy after prolonged PPI exposure and determine what age group was at higher risk of epilepsy.

METHODS

We performed a case-control study nested within a sample of Taiwan National Health Insurance beneficiaries (n = 1,000,000). PPI users with subsequent epilepsy were selected as the case cohort. Controls were PPI users without subsequent epilepsy, matched for age, sex, PPI use indication, enrollment time, end point time, follow-up period, overall systemic health, and comorbidities. The total dose of PPI was defined as the cumulative defined daily dose (cDDD). Prolonged PPI use was defined as a cDDD > 365. A logistic regression analysis was performed. Population attributable risk was calculated.

RESULTS

Epilepsy occurred 4.13 years after the initiation of PPI use. PPI users with the highest risk of incident epilepsy received a cDDD > 365 [odds ratio = 1.63, 95% confidence interval = 1.37-1.95], followed by 121-365 cDDD (1.33, 1.18-1.51) and 31-120 cDDD (1.15, 1.02-1.29), compared to those receiving a cDDD ≤ 30, after adjusting for potential confounders. Prolonged PPI use increased the risk of epilepsy in all age groups, and the risk was highest for those older than 80 years (3.11, 1.67-5.79). The population attributable risk was 12.2% (> 365 cDDD vs ≤ 30 cDDD).

DISCUSSION

Prolonged PPI therapy was associated with an increased risk of epilepsy, particularly in the elderly population.

Clinical Relevance of [18F]Florbetaben and [18F]FDG PET/CT Imaging on the Management of Patients with Dementia

PET of β-Amyloid plaques (Aβ) using [¹⁸F]florbetaben ([¹⁸F]FBB) and [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) increasingly aid clinicians in early diagnosis of dementia, including Alzheimer’s disease (AD), frontotemporal disease, dementia with Lewy bodies, and vascular dementia. The aim of this retrospective analysis was to evaluate clinical relevance of [¹⁸F]FBB, [¹⁸F]FDG PET and complimentary CSF measurements in patients with suspected dementia. In this study, 40 patients with clinically suspected or history of dementia underwent (1) measurement of Aβ peptides, total tau, and p-tau protein levels in the cerebrospinal fluid (CSF) compared with healthy controls (HC); (2) clinical and neuropsychological assessment, which included Consortium to Establish a Registry for Alzheimer’s Disease neuropsychological assessment battery (CERAD-NAB); (3) [¹⁸F]FBB and [¹⁸F]FDG PET imaging within an average of 3 weeks. The subjects were within 15 days stratified using PET, CSF measurements as HC, mild cognitive impaired (MCI) and dementia including Alzheimer´s disease. The predictive dementia-related cognitive decline values were supporting the measurements. PET images were evaluated visually and quantitatively using standard uptake value ratios (SUVR). Twenty-one (52.5%) subjects were amyloid-positive (Aβ+), with a median neocortical SUVR of 1.80 for AD versus 1.20 relative to the respective 19 (47.5 %) amyloid-negative (Aβ-) subjects. Moreover, the [¹⁸F]FDG and [¹⁸F]FBB confirmed within a sub-group of 10 patients a good complimentary role by correlation between amyloid pathology and brain glucose metabolism in 8 out of 10 subjects. The results suggest the clinical relevance for [¹⁸F]FBB combined with [¹⁸F]FDG PET retention and CFS measurements serving the management of our patients with dementia. Therefore, [¹⁸F]FBB combined with [¹⁸F]FDG PET is a helpful tool for differential diagnosis, and supports the patients’ management as well as treatment.

Synthesis of [18F]PS13 and Evaluation as a PET Radioligand for Cyclooxygenase-1 in Monkey

Cyclooxygenase-1 (COX-1) and its isozyme COX-2 are key enzymes in the syntheses of prostanoids. Imaging of COX-1 and COX-2 selective radioligands with positron emission tomography (PET) may clarify how these enzymes are involved in inflammatory conditions and assist in the discovery of improved anti-inflammatory drugs. We have previously labeled the selective high-affinity COX-1 ligand, 1,5-bis(4-methoxyphenyl)-3-(2,2,2-trifluoroethoxy)-1H-1,2,4-triazole (PS13), with carbon-11 (t1/2 = 20.4 min). This radioligand ([11C]PS13) has been successful for PET imaging of COX-1 in monkey and human brain and in periphery. [11C]PS13 is being used in clinical investigations. Alternative labeling of PS13 with fluorine-18 (t1/2 = 109.8 min) is desirable to provide a longer-lived radioligand in high activity that might be readily distributed among imaging centers. However, labeling of PS13 in its 1,1,1-trifluoroethoxy group is a radiochemical challenge. Here we assess two labeling approaches based on nucleophilic addition of cyclotron-produced [18F]fluoride ion to gem-difluorovinyl precursors, either to label PS13 in one step or to produce [18F]2,2,2-trifluoroethyl p-toluenesulfonate for labeling a hydroxyl precursor. From the latter two-step approach, we obtained [18F]PS13 ready for intravenous injection in a decay-corrected radiochemical yield of 7.9% and with a molar activity of up to 7.9 GBq/μmol. PET imaging of monkey brain with [18F]PS13 shows that this radioligand can specifically image and quantify COX-1 without radiodefluorination but with some radioactivity uptake in skull, ascribed to red bone marrow. The development of a new procedure for labeling PS13 with fluorine-18 at a higher molar activity is, however, desirable to suppress occupancy of COX-1 by carrier at baseline.

PET Agents in Dementia: An Overview

This article presents an overview of imaging agents for PET that have been applied for research and diagnostic purposes in patients affected by dementia. Classified by the target which the agents visualize, seven groups of tracers can be distinguished, namely radiopharmaceuticals for: (1) Misfolded proteins (ß-amyloid, tau, α-synuclein), (2) Neuroinflammation (overexpression of translocator protein), (3) Elements of the cholinergic system, (4) Elements of monoamine neurotransmitter systems, (5) Synaptic density, (6) Cerebral energy metabolism (glucose transport/ hexokinase), and (7) Various other proteins. This last category contains proteins involved in mechanisms underlying neuroinflammation or cognitive impairment, which may also be potential therapeutic targets. Many receptors belong to this category: AMPA, cannabinoid, colony stimulating factor 1, metabotropic glutamate receptor 1 and 5 (mGluR1, mGluR5), opioid (kappa, mu), purinergic (P2X7, P2Y12), sigma-1, sigma-2, receptor for advanced glycation endproducts, and triggering receptor expressed on myeloid cells-1, besides several enzymes: cyclooxygenase-1 and 2 (COX-1, COX-2), phosphodiesterase-5 and 10 (PDE5, PDE10), and tropomyosin receptor kinase. Significant advances in neuroimaging have been made in the last 15 years. The use of 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (FDG) for quantification of regional cerebral glucose metabolism is well-established. Three tracers for ß-amyloid plaques have been approved by the Food and Drug Administration and European Medicines Agency. Several tracers for tau neurofibrillary tangles are already applied in clinical research. Since many novel agents are in the preclinical or experimental stage of development, further advances in nuclear medicine imaging can be expected in the near future. PET studies with established tracers and tracers for novel targets may result in early diagnosis and better classification of neurodegenerative disorders and in accurate monitoring of therapy trials which involve these targets. PET data have prognostic value and may be used to assess the response of the human brain to interventions, or to select the appropriate treatment strategy for an individual patient.

Binding of omeprazole to protein targets identified by monoclonal antibodies

Omeprazole is the most commonly used proton pump inhibitor (PPI), a class of medications whose therapeutic mechanism of action involves formation of a disulfide linkage to cysteine residues in the H+/K+ ATPase pump on gastric secretory cells. Covalent linkage between the sole sulfur group of omeprazole and selected cysteine residues of the pump protein results in inhibition of acid secretion in the stomach, an effect that ameliorates gastroesophageal reflux and peptic ulcer disease. PPIs, though useful for specific conditions when used transiently, are associated with diverse untoward effects when used long term. The mechanisms underlying these potential off-target effects remain unclear. PPIs may, in fact, interact with non-canonical target proteins (non-pump molecules) resulting in unexpected pathophysiological effects, but few studies describe off-target PPI binding. Here, we describe successful cloning of monoclonal antibodies against protein-bound omeprazole. We developed and used monoclonal antibodies to characterize the protein target range of omeprazole, stability of omeprazole-bound proteins, and the involvement of cysteines in binding of omeprazole to targets. We demonstrate that a wide range of diverse proteins are targeted by omeprazole. Protein complexes, detected by Western blotting, are resistant to heat, detergents, and reducing agents. Reaction of omeprazole occurs with cysteine-free proteins, is not fully inhibited by cysteine alkylation, occurs at neutral pH, and induces protein multimerization. At least two other clinically used PPIs, rabeprazole and tenatoprazole, are capable of binding to proteins in a similar fashion. We conclude that omeprazole binds to multiple proteins and is capable of forming highly stable complexes that are not dependent on disulfide linkages between the drug and protein targets. Further studies made possible by these antibodies may shed light on whether PPI-protein complexes underlie off-target untoward effects of chronic PPI use.

Molecular Imaging of Fluorinated Probes for Tau Protein and Amyloid-β Detection

Alzheimer’s disease (AD) is the most common form of dementia and results in progressive neurodegeneration. The incidence rate of AD is increasing, creating a major public health issue. AD is characterized by neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein and senile plaques composed of amyloid-β (Aβ). Currently, a definitive diagnosis of AD is accomplished post-mortem. Thus, the use of molecular probes that are able to selectively bind to NFTs or Aβ can be valuable tools for the accurate and early diagnosis of AD. The aim of this review is to summarize and highlight fluorinated molecular probes that can be used for molecular imaging to detect either NFTs or Aβ. Specifically, fluorinated molecular probes used in conjunction with ¹⁹F MRI, PET, and fluorescence imaging will be explored.

Synthesis and evaluation of NLRP3-inhibitory sulfonylurea [11C]MCC950 in healthy animals

The diaryl sulfonylurea MCC950/CRID3 is a potent NLRP3 inhibitor (IC₅₀ = 8 nM) and, in animal models, MCC950 protects against numerous NLRP3-related neurodegenerative disorders. To evaluate the brain uptake and investigate target engagement of MCC950, we synthesised [¹¹C-urea]MCC950 via carrier added [¹¹C]CO₂ fixation chemistry (activity yield = 237 MBq; radiochemical purity >99%; molar activity = 7 GBq/µmol; radiochemical yield (decay-corrected from [¹¹C]CO₂) = 1.1%; synthesis time from end-of-bombardment = 31 min; radiochemically stable for >1 h). Despite preclinical efficacy in neurodegeneration studies, preclinical positron emission tomography (PET) imaging studies in mouse, rat and rhesus monkey revealed poor brain uptake of low molar activity [¹¹C]MCC950 and rapid washout. In silico prediction tools suggest efflux transporter liabilities for MCC950 at microdoses, and this information should be taken into account when developing next generation NLRP3 inhibitors and/or PET radiotracers.

Imaging biomarkers in neurodegeneration: current and future practices

There is an increasing role for biological markers (biomarkers) in the understanding and diagnosis of neurodegenerative disorders. The application of imaging biomarkers specifically for the in vivo investigation of neurodegenerative disorders has increased substantially over the past decades and continues to provide further benefits both to the diagnosis and understanding of these diseases. This review forms part of a series of articles which stem from the University College London/University of Gothenburg course "Biomarkers in neurodegenerative diseases". In this review, we focus on neuroimaging, specifically positron emission tomography (PET) and magnetic resonance imaging (MRI), giving an overview of the current established practices clinically and in research as well as new techniques being developed. We will also discuss the use of machine learning (ML) techniques within these fields to provide additional insights to early diagnosis and multimodal analysis.

PET Radiopharmaceuticals for Alzheimer's Disease and Parkinson's Disease Diagnosis, the Current and Future Landscape

Ironically, population aging which is considered a public health success has been accompanied by a myriad of new health challenges, which include neurodegenerative disorders (NDDs), the incidence of which increases proportionally to age. Among them, Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common, with the misfolding and the aggregation of proteins being common and causal in the pathogenesis of both diseases. AD is characterized by the presence of hyperphosphorylated τ protein (tau), which is the main component of neurofibrillary tangles (NFTs), and senile plaques the main component of which is β-amyloid peptide aggregates (Aβ). The neuropathological hallmark of PD is α-synuclein aggregates (α-syn), which are present as insoluble fibrils, the primary structural component of Lewy body (LB) and neurites (LN). An increasing number of non-invasive PET examinations have been used for AD, to monitor the pathological progress (hallmarks) of disease. Notwithstanding, still the need for the development of novel detection tools for other proteinopathies still remains. This review, although not exhaustively, looks at the timeline of the development of existing tracers used in the imaging of Aβ and important moments that led to the development of these tracers.

Evaluation of [18F]-N-Methyl lansoprazole as a Tau PET Imaging Agent in First-in-Human Studies

Development of positron emission tomography (PET) imaging agents capable of quantifying tau aggregates in neurodegenerative disorders such as Alzheimer's disease (AD) is of enormous importance in the field of dementia research. The aim of the present study was to conduct first-in-man imaging studies with the potential novel tau imaging agent [¹⁸F]N-methyl lansoprazole ([¹⁸F]NML). Herein we report validation of the synthesis of [¹⁸F]NML for clinical use by labeling the trifluoromethyl group via radiofluorination of the corresponding gem-difluoro enol ether precursor. This is the first use of this method for clinical production of PET radiotracers and confirmed that it can be readily implemented at multiple production facilities to provide [¹⁸F]NML in good noncorrected radiochemical yield (3.4 ± 1.5 GBq, 4.6% ± 2.6%) and molar activity (120.1 ± 186.3 GBq/μmol), excellent radiochemical purity (>97%), and suitable for human use (n = 15). With [¹⁸F]NML in hand, we conducted rodent biodistribution, estimates of human dosimetry, and preliminary evaluation of [¹⁸F]NML in human subjects at two imaging sites. Healthy controls (n = 4) and mildly cognitively impaired (MCI) AD patients (n = 6) received [¹⁸F]NML (tau), [¹⁸F]AV1451 (tau), and [¹⁸F]florbetaben or [¹⁸F]florbetapir (amyloid) PET scans. A single progressive supranuclear palsy (PSP) patient also received [¹⁸F]NML and [¹⁸F]AV1451 PET scans. [¹⁸F]NML showed good brain uptake, reasonable pharmacokinetics, and appropriate imaging characteristics in healthy controls. The mean ± SD of the administered mass of [¹⁸F/¹⁹F]NML was 2.01 ± 2.17 μg (range, 0.16-8.27 μg) and the mean administered activity was 350 ± 62 MBq (range, 199-403 MBq). There were no adverse or clinically detectable pharmacologic effects in any of the 11 subjects, and no significant changes in vital signs were observed. However, despite high affinity for tau in vitro, brain retention in MCI/AD and PSP patients was low, and there was no evidence of specific signals in vivo that corresponded to tau. Although it is still unclear why clinical translation of the radiotracer was unsuccessful, we nevertheless conclude that further development of [¹⁸F]NML as a tau PET imaging agent is not warranted at this time.

Tau-positron emission tomography correlates with neuropathology findings

INTRODUCTION

Comparison of tau (flortaucipir) positron emission tomography (FTP-PET) to autopsy is important to demonstrate the relationship of FTP-PET to neuropathologic findings.

METHODS

Autopsies were performed on 26 participants who had antemortem FTP-PET. FTP-PET standardized uptake value ratios (SUVRs) were compared to autopsy diagnoses and Braak tangle stage. Quantitative tau burden was compared to regional FTP-PET signal.

RESULTS

Participants with Braak stages of IV or greater had elevated FTP-PET signal. FTP-PET was elevated in participants with Alzheimer's disease. An FTP-PET SUVR cut point of 1.29 was determined to be optimal. Quantitative measurements of hippocampal and temporal lobe tau burden were highly correlated to FTP-PET signal (rho's from 0.61 to 0.70, P ≤ .02).

DISCUSSION

Elevated FTP-PET reflects Braak IV or greater neuropathology. Participants with primary age-related tauopathy and hippocampal sclerosis did not show elevated FTP-PET signal. Secondary neuropathologic diagnoses of Alzheimer's disease neuropathologic change can lead to borderline elevated FTP-PET signal.

Fluselenamyl: Evaluation of radiation dosimetry in mice and pharmacokinetics in brains of non-human primate

INTRODUCTION

To allow quantitative assessment of therapeutic efficacy for therapeutic interventions (either approved or undergoing FDA approvals) for either inhibiting or reducing development of Aβ pathophysiology in vivo, ¹⁸F-labelled tracers, such as Florbetapir, Florbetaben, and Flutemetamol have been approved. Previously, we have reported on development and preclinical validation of ¹⁸F-Fluselenamyl, comprising traits of translatable Aβ imaging agents. Herein, we report the dosimetry data for ¹⁸F-Fluselenamyl to provide radiation dose deposited within organs and determine effective dose (ED) for human studies, while also evaluating its pharmacokinetics in the nonhuman primate brains.

METHODS

To evaluate safety profiles of ¹⁸F-Fluselenamyl for enabling its deployment as a PET imaging agent for monitoring Aβ pathophysiology in vivo, we estimated the human radiation dosimetry extrapolated from rodent biodistribution data obtained by standard method of organ dissection. Animal biodistribution studies were performed in FVB/NCR mice (20 males, 20 females), following tail-vein injection of the tracer. Following euthanasia of mice, organs were harvested, counted, radiation dose to each organ and whole body was determined using the standard MIRD methodology. For evaluation of pharmacokinetics in non-human primates, following intravenous injection of the tracer, dynamic PET scan of rhesus monkey brains were performed, and co-registered with MR for anatomical reference. Parametric images of tracer transport rate constant and distribution volume relative to cerebellum were generated using a simplified reference tissue model and a spatially-constraint linear regression algorithm.

RESULTS

The critical organ in humans has been determined to be the gall bladder with a gender average radiation absorbed dose of 0.079 mGy/MBq with an effective dose of 0.017 mSv/MBq and 0.020 mSv/MBq, in males and females, respectively. Therefore, these data provide preliminary projections on human dosimetry derived from rodent estimates, thereby defining safe imaging conditions for further validations in human subjects. Additionally, the tracer penetrated the non-human primate brain and excreted to background levels at later-time points thus pointing to the potential for high signal/noise ratios during noninvasive imaging. Tissue time activity curves (TACs) also show fast initial uptake with maximum projection of activity at 2-6 min post administration followed by clearance of activity at later time-points from cortex, cerebellum, and white matter of nonhuman primate brain. Parametric images confirmed that the ¹⁸F-Fluselenamyl has relative high transport rate constant at striatum, thalamus, and cortex.

CONCLUSIONS

The data obtained from radiation dosimetry studies in mice indicate that ¹⁸F-Fluselenamyl can be safely used for further evaluation in humans. Additionally, ¹⁸F-Fluselenamyl demonstrated ability to traverse the blood brain barrier (BBB) and indicated high initial influx, followed by clearance to background levels in non-human primate brains. Combined information indicates that ¹⁸F-Fluselenamyl would be a potential candidate for detecting amyloid plaques in the living human brain.

Proton Pump Inhibitors and Radiofrequency Ablation for Treatment of Barrett's Esophagus

Gastroesophageal Reflux Disease (GERD) is characterized by acid and bile reflux in the distal oesophagus, and this may cause the development of reflux esophagitis and Barrett's oesophagus (BE). The natural histological course of untreated BE is non-dysplastic or benign BE (ND), then lowgrade (LGD) and High-Grade Dysplastic (HGD) BE, with the expected increase in malignancy transfer to oesophagal adenocarcinoma (EAC). The gold standard for BE diagnostics involves high-resolution white-light endoscopy, followed by uniform endoscopy findings description (Prague classification) with biopsy performance according to Seattle protocol. The medical treatment of GERD and BE includes the use of proton pump inhibitors (PPIs) regarding symptoms control. It is noteworthy that long-term use of PPIs increases gastrin level, which can contribute to transfer from BE to EAC, as a result of its effects on the proliferation of BE epithelium. Endoscopy treatment includes a wide range of resection and ablative techniques, such as radio-frequency ablation (RFA), often concomitantly used in everyday endoscopy practice (multimodal therapy). RFA promotes mucosal necrosis of treated oesophagal region via high-frequency energy. Laparoscopic surgery, partial or total fundoplication, is reserved for PPIs and endoscopy indolent patients or in those with progressive disease. This review aims to explain distinct effects of PPIs and RFA modalities, illuminate certain aspects of molecular mechanisms involved, as well as the effects of their concomitant use regarding the treatment of BE and prevention of its transfer to EAC.

AD molecular: Imaging tau aggregates with positron emissions tomography

Pathologic aggregates of tau protein are observed in several neurodegenerative diseases and are used to diagnose and stage disease postmortem. Recent advances in positron emission tomography radioligands allow for the detection of aggregated tau proteins in living persons. This chapter describes the development and characterization of several positron emission tomography radioligands used to detect tau pathophysiology in vivo, and how these ligands are being used in clinical aging and neurodegenerative disease research with a focus on imaging tau aggregates in Alzheimer's disease.

Chemistry for Positron Emission Tomography: Recent Advances in 11 C-, 18 F-, 13 N-, and 15 O-Labeling Reactions

Positron emission tomography (PET) is a molecular imaging technology that provides quantitative information about function and metabolism in biological processes in vivo for disease diagnosis and therapy assessment. The broad application and rapid advances of PET has led to an increased demand for new radiochemical methods to synthesize highly specific molecules bearing positron-emitting radionuclides. This Review provides an overview of commonly used labeling reactions through examples of clinically relevant PET tracers and highlights the most recent developments and breakthroughs over the past decade, with a focus on 11 C, 18 F, 13 N, and 15 O.

Evaluation of the Feasibility of Screening Tau Radiotracers Using an Amyloid Biomathematical Screening Methodology

The purpose of this study is to evaluate the feasibility of extending a previously developed amyloid biomathematical screening methodology to support the screening of tau radiotracers during compound development. 22 tau-related PET radiotracers were investigated. For each radiotracer, in silico MLogP, V _x, and in vitro K _D were input into the model to predict the in vivo K ₁, k ₂, and BP_ND under healthy control (HC), mild cognitive impaired (MCI), and Alzheimer's disease (AD) conditions. These kinetic parameters were used to simulate the time activity curves (TACs) in the target regions of HC, MCI, and AD and a reference region. Standardized uptake value ratios (SUVR) were determined from the integrated area under the TACs of the target region over the reference region within a default time window of 90-110 min. The predicted K ₁, k ₂, and BP_ND values were compared with the clinically observed values. The TACs and SUVR distributions were also simulated with population variations and noise. Finally, the clinical usefulness index (CUI) ranking was compared with clinical comparison results. The TACs and SUVR distributions differed for tau radiotracers with lower tau selectivity. The CUI values ranged from 0.0 to 16.2, with 6 out of 9 clinically applied tau radiotracers having CUI values higher than the recommend CUI value of 3.0. The differences between the clinically observed TACs and SUVR results showed that the evaluation of the clinical usefulness of tau radiotracer based on single target binding could not fully reflect in vivo tau binding. The screening methodology requires further study to improve the accuracy of screening tau radiotracers. However, the higher CUI rankings of clinically applied tau radiotracers with higher signal-to-noise ratio supported the use of the screening methodology in radiotracer development by allowing comparison of candidate radiotracers with clinically applied radiotracers based on SUVR, with respect to binding to a single target.

Synthesis and Derivatization of 1,1-[18 F]Difluorinated Alkenes

A general method for the synthesis of 1,1-[¹⁸ F]difluorinated alkenes from [¹⁸ F]fluoride is reported. This transformation is highly regioselective giving the desired ¹⁸ F-fluoroalkenes with radiochemical purities of up to 77 % within 20 minutes and a molar activity (A_m ) of 1 GBq μmol^-1 . The transformations are operationally simple to perform and were readily translated onto a commercial automated synthesis unit. The resultant 1,1-[¹⁸ F]difluorinated alkene motif is prevalent in numerous drug molecules, and this is the first general method to synthesize this motif with fluorine-18. ¹⁸ F-fluorinated alkenes are excellent building blocks and participate in a number of post-labeling transformations to access a range of ¹⁸ F-perfluorinated functional groups that have never before been radiolabeled with non-carrier-added [¹⁸ F]fluoride. This method considerably expands the range of ¹⁸ F-motifs accessible to radiochemists.

Tau PET imaging in neurodegenerative tauopathies-still a challenge

The accumulation of pathological misfolded tau is a feature common to a collective of neurodegenerative disorders known as tauopathies, of which Alzheimer's disease (AD) is the most common. Related tauopathies include progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), Down's syndrome (DS), Parkinson's disease (PD), and dementia with Lewy bodies (DLB). Investigation of the role of tau pathology in the onset and progression of these disorders is now possible due the recent advent of tau-specific ligands for use with positron emission tomography (PET), including first- (e.g., [¹⁸F]THK5317, [¹⁸F]THK5351, [¹⁸F]AV1451, and [¹¹C]PBB3) and second-generation compounds [namely [¹⁸F]MK-6240, [¹⁸F]RO-948 (previously referred to as [¹⁸F]RO69558948), [¹⁸F]PI-2620, [¹⁸F]GTP1, [¹⁸F]PM-PBB3, and [¹⁸F]JNJ64349311 ([¹⁸F]JNJ311) and its derivative [¹⁸F]JNJ-067)]. In this review we describe and discuss findings from in vitro and in vivo studies using both initial and new tau ligands, including their relation to biomarkers for amyloid-β and neurodegeneration, and cognitive findings. Lastly, methodological considerations for the quantification of in vivo ligand binding are addressed, along with potential future applications of tau PET, including therapeutic trials.

Synthesis and Initial In Vivo Evaluation of [11C]AZ683-A Novel PET Radiotracer for Colony Stimulating Factor 1 Receptor (CSF1R)

Positron emission tomography (PET) imaging of Colony Stimulating Factor 1 Receptor (CSF1R) is a new strategy for quantifying both neuroinflammation and inflammation in the periphery since CSF1R is expressed on microglia and macrophages. AZ683 has high affinity for CSF1R (Ki = 8 nM; IC50 = 6 nM) and >250-fold selectivity over 95 other kinases. In this paper, we report the radiosynthesis of [11C]AZ683 and initial evaluation of its use in CSF1R PET. [11C]AZ683 was synthesized by 11C-methylation of the desmethyl precursor with [11C]MeOTf in 3.0% non-corrected activity yield (based upon [11C]MeOTf), >99% radiochemical purity and high molar activity. Preliminary PET imaging with [11C]AZ683 revealed low brain uptake in rodents and nonhuman primates, suggesting that imaging neuroinflammation could be challenging but that the radiopharmaceutical could still be useful for peripheral imaging of inflammation.

Image-Guided Development of Heterocyclic Sulfoxides as Ligands for Tau Neurofibrillary Tangles: From First-in-Man to Second-Generation Ligands

Positron emission tomography (PET) imaging of misfolded protein aggregates that form in neurodegenerative processes of the brain is key to providing a robust marker for improved diagnosis and evaluation of treatments. We report the development of advanced radiotracer candidates based on the sulfoxide scaffold found in proton pump inhibitors (lansoprazole, prevacid) with inherent affinity to neurofibrillary tangles in Alzheimer's disease and related disorders (e.g., dementia with Lewy bodies and the frontotemporal degeneration syndrome). First-in-man results obtained with [¹⁸F]lansoprazole and N-methyl-[¹⁸F]lansoprazole were used to guide the design of a set of 24 novel molecules with suitable properties for neuroimaging with PET. Compounds were synthesized and characterized pharmacologically, and the binding affinity of the compounds to synthetic human tau-441 fibrils was determined. Selectivity of binding was assessed using α-synuclein and β-amyloid fibrils to address the key misfolded proteins of relevance in dementia. To complete the pharmacokinetic profiling in vitro, plasma protein binding and lipophilicity were investigated. Highly potent and selective new radiotracer candidates were identified for further study.

Small Molecule PET Tracers in Drug Discovery

The process of discovering and developing a new pharmaceutical is a long, difficult, and risky process that requires numerous resources. Molecular imaging techniques such as PET have recently become a useful tool for making decisions along a drug candidate's development timeline. PET is a translational, noninvasive imaging technique that provides quantitative information about a potential drug candidate and its target at the molecular level. Using this technique provides decisional information to ensure that the right drug candidate is being chosen, for the right target, at the right dose within the right patient population. This review will focus on small molecule PET tracers and how they are used within the drug discovery process. PET provides key information about a drug candidate's pharmacokinetic and pharmacodynamic properties in both preclinical and clinical studies. PET is being used in all phases of the drug discovery and development process, and the goal of these studies are to accelerate the process in which drugs are developed.

Proton Pump Inhibitors and Dementia: Physiopathological Mechanisms and Clinical Consequences

Alzheimer's disease (AD) is the most common type of dementia, mainly encompassing cognitive decline in subjects aged ≥65 years. Further, AD is characterized by selective synaptic and neuronal degeneration, vascular dysfunction, and two histopathological features: extracellular amyloid plaques composed of amyloid beta peptide (Aβ) and neurofibrillary tangles formed by hyperphosphorylated tau protein. Dementia and AD are chronic neurodegenerative conditions with a complex physiopathology involving both genetic and environmental factors. Recent clinical studies have shown that proton pump inhibitors (PPIs) are associated with risk of dementia, including AD. However, a recent case-control study reported decreased risk of dementia. PPIs are a widely indicated class of drugs for gastric acid-related disorders, although most older adult users are not treated for the correct indication. Although neurological side effects secondary to PPIs are rare, several preclinical reports indicate that PPIs might increase Aβ levels, interact with tau protein, and affect the neuronal microenvironment through several mechanisms. Considering the controversy between PPI use and dementia risk, as well as both cognitive and neuroprotective effects, the aim of this review is to examine the relationship between PPI use and brain effects from a neurobiological and clinical perspective.

Automated synthesis of PET radiotracers by copper-mediated 18 F-fluorination of organoborons: Importance of the order of addition and competing protodeborylation

In this paper, we describe the use of Cu-mediated [18 F]fluorodeboronation for the automated production of positron emission tomography radiotracers suitable for clinical use. Two recurrent issues with the method, low radiochemical conversion on automation and protoarene byproduct purification issues, have been successfully addressed. The new method was utilized to produce sterile injectable doses of [18 F]-(±)-IPMICF17, a positron emission tomography radiotracer for tropomyosin receptor kinase B/C, using an automated synthesis module. The product was isolated in 1.9 ± 0.1% isolated radiochemical yield, excellent radiochemical purity (>99%), and high specific activity (5294 ± 1227 Ci/mmol). Quality control testing confirmed that doses were suitable for clinical use.

Elevated medial temporal lobe and pervasive brain tau-PET signal in normal participants

INTRODUCTION

Medial temporal lobe (MTL) uptake on tau-positron emission tomography (PET) is seen not only in Alzheimer's disease (AD) dementia but also in the aging population. The relationship of these findings to the development of AD dementia needs to be better understood.

METHODS

Tau-PET with AV-1451 was performed on 576 cognitively unimpaired (CU) participants aged 50-94 years. The number of CUs with and without abnormal MTL regions and those with or without extra-MTL abnormalities was determined. Left and right regions were compared within each subject.

RESULTS

Of CUs, 58% (334/576) had abnormal tau-PET findings. MTL abnormalities were present in 41% (238/576) of subjects.

DISCUSSION

MTL tau-PET signal is often associated with abnormal extra-MTL tau-PET signal in CU participants and may represent neurofibrillary tangle development that could identify participants most likely to develop AD dementia. Tau-PET signal exclusively outside of the MTL is seen in 17% of CU participants and could be the initial findings in participants in different AD dementia pathways. Significant (P < .001) differences in tau-standardized uptake value ratio between sides were noted in 26 of 41 examined brain regions implicating further study of side-specific deficits.

Widespread brain tau and its association with ageing, Braak stage and Alzheimer's dementia

See Herholz (doi:10.1093/brain/awx340) for a scientific commentary on this article.Autopsy data have proposed that a topographical pattern of tauopathy occurs in the brain with the development of dementia due to Alzheimer's disease. We evaluated the findings of tau-PET to better understand neurofibrillary tangle development as it is seen in cognitively unimpaired and impaired individuals. The evolution of Alzheimer's disease tauopathy in cognitively unimpaired individuals needs to be examined to better understand disease pathogenesis. Tau-PET was performed in 86 cognitively impaired individuals who all had abnormal amyloid levels and 601 cognitively unimpaired individuals. Tau-PET findings were assessed for relationships with clinical diagnosis, age, and regional uptake patterns relative to Braak stage. Regional and voxel-wise analyses were performed. Topographical findings from tau-PET were characterized using hierarchical clustering and clinical characteristic-based subcategorization. In older cognitively unimpaired individuals (≥50 years), widespread, age-related elevated tau signal was seen among those with normal or abnormal amyloid status as compared to younger cognitively unimpaired individuals (30-49 years). More frequent regional tau signal elevation throughout the brain was seen in cognitively unimpaired individuals with abnormal versus normal amyloid. Elevated tau signal was seen in regions that are considered high Braak Stage in cognitively unimpaired and cognitively impaired individuals. Hierarchical clustering and clinical characteristic-based categorizations both showed different patterns of tau signal between groups such as greater tau signal in frontal regions in younger onset Alzheimer's disease dementia participants (most of whom had a dysexecutive clinical presentation). Tau-PET signal increases modestly with age throughout the brain in cognitively unimpaired individuals and elevated tau is seen more often when amyloid brain accumulation is present. Tau signal patterns in cognitively unimpaired correspond to early Braak stage but also suggest tangle involvement in extra-medial temporal and extra-temporal regions that are considered more advanced in the Braak scheme even when amyloid negative. Our findings also suggest the possibility of widespread development of early tangle pathology rather than a pattern defined exclusively by adjacent, region-to-region spread, prior to onset of clinical symptoms. Distinct patterns of neurofibrillary tangle deposition in younger-onset Alzheimer's disease dementia versus older-onset Alzheimer's disease dementia provide evidence for variability in regional tangle deposition patterns and demonstrate that different disease phenotypes have different patterns of tauopathy. Pathological correlation with imaging is needed to assess the implications of these observations.

New advances in tau imaging in parkinsonism

Currently, the differential diagnosis between atypical parkinsonisms and classical idiopathic Parkinson's disease can be quite difficult because of the significant overlap of clinical presentation and symptoms. Neurodegenerative conditions, including progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and frontotemporal dementia (FTD), are primarily characterized by accumulation of tau protein in the brain. Recent imaging developments for tau pathology may provide a promising tool for the assessment of diagnosis, prognosis, and progression of these neurodegenerative disorders. This review will survey PET studies to describe the recent advances in the imaging of tau pathology in PSP, CBD, and FTD.

Association Between Proton Pump Inhibitor Use and Cognitive Function in Women

BACKGROUND & AIMS

Studies have reported associations between proton pump inhibitor (PPI) use and dementia. However, data are lacking on long-term PPI use and cognitive function. We therefore examined associations between PPI use and performance in tests of cognitive function. Because of shared clinical indications, we examined associations for H2 receptor antagonists (H2RAs) as a secondary aim.

METHODS

We used prospectively collected data on medication use and other potential risk factors from 13,864 participants in the Nurses' Health Study II who had completed a self-administered computerized neuropsychological test battery. Multivariable linear regression models were used to examine associations between medication use and composite scores of psychomotor speed and attention, learning and working memory, and overall cognition.

RESULTS

We observed a modest association between duration of PPI use and scores for psychomotor speed and attention (mean score difference for PPI use of 9-14 years vs never users, -0.06; 95% confidence interval, -0.11 to 0.00; P_trend = .03). After controlling for H2RA use, the magnitude of this score difference was attenuated. Among individuals who did not use PPIs regularly, duration of H2RA use was associated with poorer cognitive scores, with the strongest association apparent for learning and working memory (mean score difference for H2RA users of 9-14 years vs never users, -0.20; 95% confidence interval, -0.32 to -0.08; P_trend < .001).

CONCLUSIONS

In an analysis of data from the Nurses' Health Study II, we did not observe a convincing association between PPI use and cognitive function. Our data do not support the suggestion that PPI use increases dementia risk. Because our primary hypothesis related to PPI use, our findings for H2RAs should be interpreted with caution.

Detection and Characterization of Small Molecule Interactions with Fibrillar Protein Aggregates Using Microscale Thermophoresis

Neurodegenerative diseases such as Parkinson's and Alzheimer's disease share the pathological hallmark of fibrillar protein aggregates. The specific detection of these protein aggregates by positron emission tomography (PET) in the patient brain can yield valuable information for diagnosis and disease progression. However, the identification of novel small compounds that bind fibrillar protein aggregates has been a challenge. In this study, microscale thermophoresis (MST) was applied to assess the binding affinity of known small molecule ligands of α-synuclein fibrils, which were also tested in parallel in a thioflavin T fluorescence competition assay for further validation. In addition, a MST assay was also developed for the detection of the interaction between a variety of small molecules and tau fibrils. The results of this study demonstrate that MST is a powerful and practical methodology to quantify interactions between small molecules and protein fibrillar aggregates, which suggests that it can be applied for the identification and development of PET radioligands and potentially of therapeutic candidates for protein misfolding diseases.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

Development of tau PET Imaging Ligands and their Utility in Preclinical and Clinical Studies

The pathological features of Alzheimer's disease are senile plaques which are aggregates of β-amyloid peptides and neurofibrillary tangles in the brain. Neurofibrillary tangles are aggregates of hyperphosphorylated tau proteins, and these induce various other neurodegenerative diseases, such as progressive supranuclear palsy, corticobasal degeneration, frontotemporal lobar degeneration, frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and chronic traumatic encephalopathy. In the case of Alzheimer's disease, the measurement of neurofibrillary tangles associated with cognitive decline is suitable for differential diagnosis, disease progression assessment, and to monitor the effects of therapeutic treatment. This review discusses considerations for the development of tau ligands for imaging and summarizes the results of the first-in-human and preclinical studies of the tau tracers that have been developed thus far. The development of tau ligands for imaging studies will be helpful for differential diagnosis and for the development of therapeutic treatments for tauopathies including Alzheimer's disease.