A Novel Near-Infrared Fluorescence Probe THK-565 Enables In Vivo Detection of Amyloid Deposits in Alzheimer's Disease Mouse Model

PURPOSE

Noninvasive imaging of protein aggregates in the brain is critical for the early diagnosis, disease monitoring, and evaluation of the effectiveness of novel therapies for Alzheimer's disease (AD). Near-infrared fluorescence (NIRF) imaging with specific probes is a promising technique for the in vivo detection of protein deposits without radiation exposure. Comprehensive screening of fluorescent compounds identified a novel compound, THK-565, for the in vivo imaging of amyloid-β (Aβ) deposits in the mouse brain. This study assessed whether THK-565 could detect amyloid-β deposits in vivo in the AD mouse model.

PROCEDURES

The fluorescent properties of THK-565 were evaluated in the presence and absence of Aβ fibrils. APP knock-in (APP-KI) mice were used as an animal model of AD. In vivo NIRF images were acquired after the intravenous administration of THK-565 and THK-265 in mice. The binding selectivity of THK-565 to Aβ was evaluated using brain slices obtained from these mouse models.

RESULTS

The fluorescence intensity of the THK-565 solution substantially increased by mixing with Aβ fibrils. The maximum emission wavelength of the complex of THK-565 and Aβ fibrils was 704 nm, which was within the optical window range. THK-565 selectively bound to amyloid deposits in brain sections of APP-KI mice After the intravenous administration of THK-565, the fluorescence signal in the head of APP-KI mice was significantly higher than that of wild-type mice and higher than that after administration of THK-265. Ex vivo analysis confirmed that the THK-565 signal corresponded to Aβ immunostaining in the brain sections of these mice.

CONCLUSIONS

A novel NIRF probe, THK-565, enabled the in vivo detection of Aβ deposits in the brains of the AD mouse model, suggesting that NIRF imaging with THK-565 could non-invasively assess disease-specific pathology in AD.

Preclinical Characterization of the Tau PET Tracer [18F]SNFT-1: Comparison of Tau PET Tracers

Tau PET tracers are expected to be sufficiently sensitive to track the progression of age-related tau pathology in the medial temporal cortex. The tau PET tracer N-(4-[18F]fluoro-5-methylpyridin-2-yl)-7-aminoimidazo[1,2-a]pyridine ([18F]SNFT-1) has been successfully developed by optimizing imidazo[1,2-a]pyridine derivatives. We characterized the binding properties of [18F]SNFT-1 using a head-to-head comparison with other reported 18F-labeled tau tracers. Methods: The binding affinity of SNFT-1 to tau, amyloid, and monoamine oxidase A and B was compared with that of the second-generation tau tracers MK-6240, PM-PBB3, PI-2620, RO6958948, JNJ-64326067, and flortaucipir. In vitro binding properties of 18F-labeled tau tracers were evaluated through the autoradiography of frozen human brain tissues from patients with diverse neurodegenerative disease spectra. Pharmacokinetics, metabolism, and radiation dosimetry were assessed in normal mice after intravenous administration of [18F]SNFT-1. Results: In vitro binding assays demonstrated that [18F]SNFT-1 possesses high selectivity and high affinity for tau aggregates in Alzheimer disease (AD) brains. Autoradiographic analysis of tau deposits in medial temporal brain sections from patients with AD showed a higher signal-to-background ratio for [18F]SNFT-1 than for the other tau PET tracers and no significant binding with non-AD tau, α-synuclein, transactiviation response DNA-binding protein-43, and transmembrane protein 106B aggregates in human brain sections. Furthermore, [18F]SNFT-1 did not bind significantly to various receptors, ion channels, or transporters. [18F]SNFT-1 showed a high initial brain uptake and rapid washout from the brains of normal mice without radiolabeled metabolites. Conclusion: These preclinical data suggest that [18F]SNFT-1 is a promising and selective tau radiotracer candidate that allows the quantitative monitoring of age-related accumulation of tau aggregates in the human brain.

Evaluation of 18F labeled glial fibrillary acidic protein binding nanobody and its brain shuttle peptide fusion proteins using a neuroinflammation rat model

Astrogliosis is a crucial feature of neuroinflammation and is characterized by the significant upregulation of glial fibrillary acidic protein (GFAP) expression. Hence, visualizing GFAP in the living brain of patients with damaged central nervous system using positron emission tomography (PET) is of great importance, and it is expected to depict neuroinflammation more directly than existing neuroinflammation imaging markers. However, no PET radiotracers for GFAP are currently available. Therefore, neuroimaging with antibody-like affinity proteins could be a viable strategy for visualizing imaging targets that small molecules rarely recognize, such as GFAP, while we need to overcome the challenges of slow clearance and low brain permeability. The E9 nanobody, a small-affinity protein with high affinity and selectivity for GFAP, was utilized in this study. E9 was engineered by fusing a brain shuttle peptide that facilitates blood-brain barrier permeation via two different types of linker domains: E9-GS-ApoE (EGA) and E9-EAK-ApoE (EEA). E9, EGA and EEA were radiolabeled with fluorine-18 using cell-free protein radiosynthesis. In vitro autoradiography showed that all radiolabeled proteins exhibited a significant difference in neuroinflammation in the brain sections created from a rat model constructed by injecting lipopolysaccharide (LPS) into the unilateral striatum of wildtype rats, and an excess competitor displaced their binding. However, exploratory in vivo PET imaging and ex vivo biodistribution studies in the rat model failed to distinguish neuroinflammatory lesions within 3 h of 18F-EEA intravenous injection. This study contributes to a better understanding of the characteristics of small-affinity proteins fused with a brain shuttle peptide for further research into the use of protein molecules as PET tracers for imaging neuropathology.

In vivo [18F]THK-5351 imaging detected reactive astrogliosis in argyrophilic grain disease with comorbid pathology: A clinicopathological study

Quantification of in vivo reactive astrogliosis, which represents neural inflammation and remodeling in the brain, is an emerging methodology for the evaluation of patients with neurodegenerative diseases. [18F]THK-5351 is a positron emission tomography (PET) tracer for monoamine oxidase B (MAO-B), a molecular marker of reactive astrogliosis. We performed in vivo [18F]THK-5351 PET in a patient who at autopsy was found to have argyrophilic grain disease (AGD) with comorbid pathology to visualize reactive astrogliosis for the first time. We aimed to validate an imaging-pathology correlation using [18F]THK-5351 PET and the autopsy brain. The patient, a 78-year-old man, was pathologically diagnosed with AGD combined with limbic-predominant age-related transactive response DNA-binding protein of 43 kDa encephalopathy and Lewy body disease without Alzheimer disease-related neuropathological changes. Reactive astrogliosis in the postmortem brain was abundant in the inferior temporal gyrus, insular gyrus, entorhinal cortex, and ambient gyrus where premortem [18F]THK-5351 signals were high. We found a proportional correlation between the amount of reactive astrogliosis in the postmortem brain and the in vivo [18F]THK-5351 standardized uptake value ratio (r = 0.8535, p = 0.0004). These results indicated that reactive astrogliosis in AGD with comorbid pathology could be identified and quantified by in vivo MAO-B imaging.

[In vivo imaging of astrogliosis by PET]

Glial cells are non-neuronal cells that make up the central nervous system, including astrocytes, oligodendrocytes, microglia, and ependymal cells, which play an important role in brain homeostasis. However, activated microglia and reactive astrocytes cause neuroinflammation, which is closely related to neurodegeneration. Neuronal loss, gliosis, and accumulation of misfolded proteins are commonly observed in the brain of many neurodegenerative diseases at autopsy. Therefore, in vivo imaging of glial cell responses by positron emission tomography (PET) would be useful not only for understanding pathological processes, but also for differential diagnosis and evaluation of disease-modifying therapeutics targeting glial cells. The gold standard marker for reactive astrocytes is glial fibrillary acidic protein (GFAP), but no specific ligands are available. To date, there are two targets of reactive astrocytes that are under intense investigation: Monoamine oxidase-B (MAO-B) and imidazoline₂ binding site (I₂BS). PET radiopharmaceuticals for MAO-B and I₂BS have been developed and are under clinical investigation. In this chapter, we review the MAO-B and I₂BS as molecular targets for imaging reactive astrocytes and introduce the PET tracers and their clinical studies.

Imaging of Reactive Astrogliosis by Positron Emission Tomography

Many neurodegenerative diseases are neuropathologically characterized by neuronal loss, gliosis, and the deposition of misfolded proteins such as β-amyloid (Aβ) plaques and tau tangles in Alzheimer’s disease (AD). In postmortem AD brains, reactive astrocytes and activated microglia are observed surrounding Aβ plaques and tau tangles. These activated glial cells secrete pro-inflammatory cytokines and reactive oxygen species, which may contribute to neurodegeneration. Therefore, in vivo imaging of glial response by positron emission tomography (PET) combined with Aβ and tau PET would provide new insights to better understand the disease process, as well as aid in the differential diagnosis, and monitoring glial response disease-specific therapeutics. There are two promising targets proposed for imaging reactive astrogliosis: monoamine oxidase-B (MAO-B) and imidazoline2 binding site (I2BS), which are predominantly expressed in the mitochondrial membranes of astrocytes and are upregulated in various neurodegenerative conditions. PET tracers targeting these two MAO-B and I2BS have been evaluated in humans. [18F]THK-5351, which was originally designed to target tau aggregates in AD, showed high affinity for MAO-B and clearly visualized reactive astrocytes in progressive supranuclear palsy (PSP). However, the lack of selectivity of [18F]THK-5351 binding to both MAO-B and tau, severely limits its clinical utility as a biomarker. Recently, [18F]SMBT-1 was developed as a selective and reversible MAO-B PET tracer via compound optimization of [18F]THK-5351. In this review, we summarize the strategy underlying molecular imaging of reactive astrogliosis and clinical studies using MAO-B and I2BS PET tracers.

The Role of Chirality of [18F]SMBT-1 in Imaging of Monoamine Oxidase-B

(S)-(2-Methylpyrid-5-yl)-6-[(3-[¹⁸F]fluoro-2-hydroxy)propoxy]quinoline ([¹⁸F]SMBT-1) was recently developed as a novel class of selective and reversible monoamine oxidase-B (MAO-B) tracers for in vivo imaging of reactive astrogliosis via positron emission tomography. To investigate the effect of the chirality of [¹⁸F]SMBT-1 on tracer performance, we synthesized (S)-[¹⁸F]6 ([¹⁸F]SMBT-1) and (R)-[¹⁸F]6 and compared their binding properties, pharmacokinetics, and metabolism. (S)-6 showed higher binding affinity to MAO-B and lower binding affinity to MAO-A than (R)-6, demonstrating a higher selectivity ratio (MAO-B/MAO-A). A pharmacokinetic study in mice demonstrated that both (S)-[¹⁸F]6 and (R)-[¹⁸F]6 showed sufficient initial brain uptake. However, (S)-[¹⁸F]6 was cleared significantly faster from the body. An abundant sulfoconjugate metabolite M2 was observed in plasma for (S)-[¹⁸F]6 but not for (R)-[¹⁸F]6. In vitro sulfation assays confirmed that (S)-6 was more reactive than (R)-6, consistent with the in vivo findings. Mefenamic acid, a selective sulfotransferase 1A1 (SULT1A1) inhibitor, strongly inhibited the in vitro sulfation of (S)-6 by mouse liver fractions, human liver cytosol fractions, and human recombinant SULT1A1 enzyme. Genetic polymorphisms of SULT1A1 did not affect the sulfation of (S)-6 in vitro. In conclusion, (S)-[¹⁸F]6 had a more favorable binding affinity and binding selectivity for MAO-B than (R)-[¹⁸F]6. Additionally, (S)-[¹⁸F]6 also possessed better pharmacological and metabolic properties than (R)-[¹⁸F]6. These results suggest that (S)-[¹⁸F]6 ([¹⁸F]SMBT-1) is a promising candidate for application in the imaging of MAO-B in vivo.

First-in-human evaluation of 18F-SMBT-1, a novel 18F-labeled MAO-B PET tracer for imaging reactive astrogliosis

Background: Reactive gliosis changes, characterized by reactive astrocytes and activated microglia, contribute greatly to neurodegeneration throughout the course of Alzheimer's disease (AD). Reactive astrocytes overexpress monoamine oxidase-B (MAO-B). We characterized the clinical performance of ¹⁸F-SMBT-1, a novel MAO-B PET tracer as a potential surrogate marker of reactive astrogliosis. Methods: Seventy-seven participants -53 controls (CN), 7 mild cognitively impaired (MCI), 7 AD patients, and 10 young controls (YCN)- were recruited for the different aspects of the study. Older participants underwent 3D-MPRAGE MRI and Aβ, tau, and ¹⁸F-SMBT-1 imaging with PET. To ascertain ¹⁸F-SMBT-1 selectivity to MAO-B, 9 participants underwent two ¹⁸F-SMBT-1 scans, before and after receiving 5mg selegiline twice daily for 5 days. To compare selectivity, ¹⁸F-THK5351 studies were also conducted before and after selegiline. Aβ burden was expressed in Centiloids. ¹⁸F-SMBT-1 outcomes were expressed as standard uptake value, as well as tissue ratios and binding parameters using the subcortical white matter as reference region. Results: ¹⁸F-SMBT-1 showed robust entry into the brain and reversible binding kinetics, with high tracer retention in basal ganglia, intermediate in cortical regions, and lowest in cerebellum and white matter which tightly follows the known regional brain distribution of MAO-B (R2=0.84). More than 85% of ¹⁸F-SMBT-1 signal was blocked by selegiline across the brain and, in contrast to ¹⁸F-THK5351, no residual cortical activity was observed after the selegiline regimen, indicating high selectivity for MAO-B and low non-specific binding. ¹⁸F-SMBT-1 also captured the known MAO-B increases with age, with an annual rate of change (~2.6%/yr), similar to the in vitro rates of change (~1.9%/yr). Quantitative and semiquantitative measures of ¹⁸F-SMBT-1 binding were highly associated (R2>0.94), suggesting a simplified tissue ratio approach could be used to generate outcome measures. Conclusion: ¹⁸F-SMBT-1 is a highly selective MAO-B tracer, with low non-specific binding, high entry into the brain and displaying reversible kinetics. Moreover, ¹⁸F-SMBT-1 brain distribution matches the reported in vitro distribution and captures the known MAO-B increases with age, suggesting ¹⁸F-SMBT-1 can potentially be used as a surrogate marker of reactive astrogliosis. Further validation of these findings with ¹⁸F-SMBT-1 will require examination of a much larger series, including participants with MCI and AD.

Assessing reactive astrogliosis with 18F-SMBT-1 across the Alzheimer's disease spectrum

Background: Neuroinflammatory reaction in Alzheimer's disease (AD) brains involves reactive astrocytes which overexpress monoamine oxidase-B (MAO-B). ¹⁸F-SMBT-1 is a novel F-18 PET tracer highly selective for MAO-B. We characterized the clinical performance of ¹⁸F-SMBT-1 PET across the Alzheimer's disease (AD) continuum as a potential surrogate marker of reactive astrogliosis Methods: We assessed ¹⁸F-SMBT-1 PET regional binding in 77 volunteers (76±5.5 y.o.; 41F/36M) across the AD continuum: 57 cognitively unimpaired controls (CN, 44 Aβ- & 13 Aβ+), 12 mild cognitively impaired (MCI, 9 Aβ- & 3 Aβ+), and 8 AD dementia patients (6 Aβ+ and 2 Aβ-). All participants also underwent Aβ and tau PET imaging, 3T MRI and neuropsychological evaluation. Tau imaging results were expressed in standard uptake value ratios (SUVR) using the cerebellar cortex as reference region, while Aβ burden was expressed in Centiloids. ¹⁸F-SMBT-1 outcomes were expressed as SUVR using the subcortical white matter as reference region. Results: ¹⁸F-SMBT-1 yielded high contrast images at steady state (60-80 min after injection). When compared to Aβ-CN, there were no significant differences in ¹⁸F-SMBT-1 binding in the Aβ-MCI group. Conversely, ¹⁸F-SMBT-1 binding was significantly higher in several cortical regions in the Aβ+AD group, but also was significantly lower in mesial temporal and basal ganglia. Most importantly, ¹⁸F-SMBT-1 binding was significantly higher in the same regions in Aβ+CN when compared to Aβ-CN. When all clinical groups were considered together, ¹⁸F-SMBT-1 was highly correlated with Aβ burden, and much less with tau burden. While in most cortical regions ¹⁸F-SMBT-1 was not correlated with brain volumetrics, regions known for high MAO-B concentrations presented a direct association with hippocampal and grey matter volumes, while the occipital lobe was directly associated with white matter hyperintensities. ¹⁸F-SMBT-1 binding was inversely correlated with MMSE and AIBL PACC in some neocortical regions such as the frontal cortex, lateral temporal and supramarginal gyrus. Conclusion: Cross-sectional human PET studies with ¹⁸F-SMBT-1, showed that Aβ+AD, but most importantly, Aβ+CN have significantly higher regional ¹⁸F-SMBT-1 binding than Aβ- CN. Moreover, in several regions in the brain, ¹⁸F-SMBT-1 retention was highly associated with Aβ load. These findings suggest that increased ¹⁸F-SMBT-1 binding is detectable at the preclinical stages of Aβ accumulation, providing strong support for its use as surrogate marker of astrogliosis in the AD continuum.

[Imaging of neuropathology by PET tracers]

Alzheimer's disease (AD) is one of the most common causes of dementia in the world. Neurodegeneration, gliosis, and misfolded proteins such as amyloid plaques and tau tangles are neuropathological hallmarks in AD. In vivo imaging of these neuropathological lesions would be good biomarkers to understand pathophysiology as well as surrogate markers for clinical trials. We developed THK tau radiotracers including [¹⁸F]THK-5351 and tested them in humans. Validations studies identified monoamine oxidase-B (MAO-B) as the off-target binding substrate of [¹⁸F]THK-5351. Since the elevation of MAO-B, which is highly expressed in reactive astrocytes, were observed in various neurological conditions, MAO-B would be a promising target for imaging reactive astrogliosis. In fact, [¹⁸F]THK-5351 PET studies demonstrated that high tracer uptake in site susceptible regions to occur astrogliosis in various neurological disorders. However, the lack of binding selectivity affects the interpretation of PET images. Therefore, we performed lead optimization from [¹⁸F]THK-5351 generating a selective and reversible MAO-B PET tracer, [¹⁸F]SMBT-1. These translational and reverse translational studies, from the development of PET tracers to validation of PET images, led to the generation of new biomarkers. In this review, we will introduce the development of [¹⁸F]THK-5351, identification of off-target binding substrates, imaging-autopsy validations, new tracer development ([¹⁸F]SMBT-1), and finally recent clinical studies of [¹⁸F]SMBT-1.

18F-THK5351 Positron Emission Tomography Imaging in Neurodegenerative Tauopathies

Introduction: We aimed to determine whether in vivo tau deposits and monoamine oxidase B (MAO-B) detection using ¹⁸F-THK5351 positron emission tomography (PET) can assist in the differential distribution in patients with corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), and Alzheimer's disease (AD) and whether ¹⁸F-THK5351 retention of lesion sites in CBS and PSP can correlate with clinical parameters. Methods: ¹⁸F-THK5351 PET was performed in 35 participants, including 7, 9, and 10 patients with CBS, PSP, and AD, respectively, and 9 age-matched normal controls. In CBS and PSP, cognitive and motor functions were assessed using the Montreal Cognitive Assessment, Addenbrooke's Cognitive Examination-Revised, and Frontal Assessment Battery, Unified Parkinson's Disease Rating Scale Motor Score, and PSP Rating Scale. Results: ¹⁸F-THK5351 retention was observed in sites susceptible to disease-related pathologies in CBS, PSP, and AD. ¹⁸F-THK5351 uptake in the precentral gyrus clearly differentiated patients with CBS from those with PSP and AD. Furthermore, ¹⁸F-THK5351 uptake in the inferior temporal gyrus clearly differentiated patients with AD from those with CBS and PSP. Regional ¹⁸F-THK5351 retention was associated with the cognitive function in CBS and PSP. Conclusion: Measurement of the tau deposits and MAO-B density in the brain using ¹⁸F-THK5351 may be helpful for the differential diagnosis of tauopathies and for understanding disease stages.

Sequential variation of super periodic structures emerged in Bi-layered perovskite pillar-matrix epitaxial nanocomposite films with spinel ferrites

The phase stability of Aurivillius bismuth-layer structured Bi5Ti3FeO15 (BTFO15) has been investigated in an epitaxial pillar-matrix nanocomposite system with spinel ferrites.

A concentration-based microscale method for 18F-nucleophilic substitutions and its testing on the one-pot radiosynthesis of [18F]FET and [18F]fallypride

When applied to a radiosynthesis, a microscale approach can help to save precursor and improve yields. Thus, a 5-10 μL microscale method based on a concentration procedure was developed and applied to the radiosynthesis of [¹⁸F]FET and [¹⁸F]fallypride. In spite of using an amount of precursor ca. 100 times smaller, radiochemical yields were comparable or even higher than those reported in literature. Because of the very low reaction volumes, the possible effects of concentrated dose of activity and carrier fluoride were also investigated.

18F-SMBT-1: A Selective and Reversible PET Tracer for Monoamine Oxidase-B Imaging

Reactive astrocytes play a key role in the pathogenesis of various neurodegenerative diseases. Monoamine oxidase-B (MAO-B) is one of the promising targets for the imaging of astrogliosis in the human brain. A novel selective and reversible MAO-B tracer, (S)-(2-methylpyrid-5-yl)-6-[(3-¹⁸F-fluoro-2-hydroxy)propoxy]quinoline (¹⁸F-SMBT-1), was successfully developed via lead optimization from the first-generation tau PET tracer ¹⁸F-THK-5351. Methods: SMBT-1 was radiolabeled with ¹⁸F using the corresponding precursor. The binding affinity of radiolabeled compounds to MAO-B was assessed using saturation and competitive binding assays. The binding selectivity of ¹⁸F-SMBT-1 to MAO-B was evaluated by autoradiography of frozen human brain tissues. The pharmacokinetics and metabolism were assessed in normal mice after intravenous administration of ¹⁸F-SMBT-1. A 14-d toxicity study after the intravenous administration of ¹⁸F-SMBT-1 was performed using rats and mice. Results: In vitro binding assays demonstrated a high binding affinity of ¹⁸F-SMBT-1 to MAO-B (dissociation constant, 3.7 nM). In contrast, it showed low binding affinity to MAO-A and protein aggregates such as amyloid-β and tau fibrils. Autoradiographic analysis showed higher amounts of ¹⁸F-SMBT-1 binding in the Alzheimer disease brain sections than in the control brain sections. ¹⁸F-SMBT-1 binding was completely displaced with the reversible MAO-B inhibitor lazabemide, demonstrating the high selectivity of ¹⁸F-SMBT-1 for MAO-B. Furthermore, ¹⁸F-SMBT-1 showed a high uptake by brain, rapid washout, and no radiolabeled metabolites in the brain of normal mice. ¹⁸F-SMBT-1 showed no significant binding to various receptors, ion channels, or transporters, and no toxic effects related to its administration were observed in mice and rats. Conclusion: ¹⁸F-SMBT-1 is a promising and selective MAO-B PET tracer candidate, which would be useful for quantitative monitoring of astrogliosis in the human brain.

FRI0580 DISCORDANCE BETWEEN OBJECTIVE ELBOW ASSESSMENT AND PATIENTS REPORTED OUTCOMES (PROS) AFTER TOTAL ELBOW ARTHROPLASTY IN PATIENTS WITH RHEUMATOID ARTHRITIS

Background:

Patient-reported outcomes (PROs) have become widespread in daily clinical evaluation in patients with rheumatoid arthritis (RA). However, there are few reports for the relationship or discordance between the subjective assessment by the physician and the objective assessment by the patient with RA in surgical treatment.

Objectives:

We examined the relationship or discordance about the PROs in patients with RA who underwent total elbow arthroplasty (TEA).

Methods:

We retrospectively identified 53 elbows of 48 patients with RA who underwent TEA at Okayama University Hospital, collected from January 2012 to December 2016.

We collected clinical data for the grip strength, range of motion, the Mayo Elbow Performance Scale (MEPS) as objective assessments, and the Patient-Related Elbow Evaluation (PREE), Disability of the Arm, Shoulder, and Hand (DASH) Japanese version and Hand20 as subjective assessments.

For statistical analysis, we performed t-tests for pre- and post-operative physical findings and subjective evaluations, and Spearman rank correlation to examine the relationship between objective and subjective assessments.

Results:

The mean age of the patients at the time of arthroplasty was 63 years, the average disease duration was 23 years, and the average postoperative observation period was 32 months. The average DAS28-CRP was 3.01, and biological uses were 18 cases.

The range of motion of the elbow joint and the grip strength was significantly improved postoperatively. All outcome assessments improved significantly except for HAQ (see table1).

There was significantly correlated PREE with DASH, Hand20, and MEPS preoperatively. Postoperative PREE showed a significant and robust correlation in postoperative DASH, Hand20, whereas not associated with postoperative MEPS (see table2).

To investigate the discordance between PREE and MEPS after TEA, we focused on changes in each item of PREE. Pain- and reach-related items improved postoperatively. But, it was difficult to improve in items affected by hand and finger functions, such as “tie shoelaces.”

To explore the effects of finger and hand functions on postoperative assessments, we performed multiple regression analyses. Both preoperative grip strength (unstandardized coefficient [Β] =-0.07; 95%CI -0.148 to -0.006, t value=-2.18, P=0.03) and preoperative Hand20 (B = 0.27, 95%CI 0.029 - 0.518, t=2.25, p=0.02) were significant predictors of postoperative PREE.

Conclusion:

Surprisingly, the PROs of patients and the surgeon’s evaluations correlated well before surgery but resulted in discordance after TEA. We improved elbow functions by TEA, but since rheumatoid arthritis was a polyarticular disorder, improvement of a single joint function did not improve utterly subjective assessment in patients with RA. We found that the upper limb functions after TEA were significantly affected by preoperative finger and hand function. A rheumatologist should consider the dysfunctions of finger and hand when planning for elbow surgery in patients with RA.

Table 1.

Pre- and postoperative range of motion of elbow and forearm, grip strength, and measurement

CharacteristicPreoperativePostoperativeP valueElbow flexion, degree116 ± 19134 ± 9< 0.001- extension-34 ± 21-25 ± 160.005- total arc82 ± 32109 ± 19< 0.001Grip power, mmHg106 ± 66130 ± 740.007DASH50.5 ± 20.535.8 ± 25.4< 0.001Hand2060.4 ± 19.138.9 ± 29.6< 0.001PREE55.6 ± 18.818.5 ± 17.1< 0.001- pain29.7 ± 11.36.5 ± 7.9< 0.001- function25.9 ± 11.512.0 ± 11.9< 0.001- specific function56.9 ± 25.525.4 ± 25.3< 0.001- usual function20.8 ± 11.310.5 ± 11.3< 0.001HAQ-DI1.06 ± 0.701.07 ± 0.800.607MEPS51.3 ± 16.697.9 ± 3.6< 0.001Table 2.

Spearman’s correlation coefficients for pre- and postoperative PREE score*

QuestionnairePreoperative Correlation estimateP valuePostoperative Correlation estimateP valueDASH0.56< 0.00010.84< 0.0001Hand200.58< 0.00010.84< 0.0001MEPS- 0.39< 0.01-0.27N.S.

Disclosure of Interests:

ryozo harada: None declared, Keiichiro Nishida Grant/research support from: K. Nishida has received scholarship donation from CHUGAI PHARMACEUTICAL Co., Eisai Co., Mitsubishi Tanabe Pharma and AbbVie GK., Speakers bureau: K. Nishida has received speaking fees from CHUGAI PHARMACEUTICAL Co., Eli Lilly, Janssen Pharmaceutical K.K., Eisai Co. and AYUMI Pharmaceutical Corporation., Yoshihisa Nasu: None declared, Ryuichi Nakahara: None declared

[Radiolabeled proteins for the development of biopharmaceuticals]

Positron emission tomography (PET) is a molecular imaging technique that visualizes pathophysiology in the body using radiotracers at tracer doses (~μg). PET would provide the information regarding not only pharmacokinetics of radiolabeled compounds, but also target engagements, patient selection, and biomarkers. Previously small molecules are widely used as radiotracers, but recently biopharmaceuticals are launched, providing a novel type radiotracer. In general, antibodies are radiolabeled by long physiological half-lives radionuclides such as Cu-64 and Zr-89 because of their slow pharmacokinetics. However, shorter half-lives radiolabeled tracers (C-11 and F-18) might be suitable on the point view of radiation. Now small protein ligands such as affibodies (~7 kDa) are developed as a radiotracer. We are trying to develop a novel approach to label proteins for PET imaging, which are based on radiolabeled amino acids and cell-free protein synthesis system. In this review, we introduced the topics of protein-based PET tracers.

Pharmacokinetic-Pharmacodynamic-Efficacy Modeling of ONO-7579, a Novel Pan-Tropomyosin Receptor Kinase Inhibitor, in a Murine Xenograft Tumor Model

The orally available and novel small molecule ONO-7579 (N-{2-[4-(2-amino-5-chloropyridin-3-yl)phenoxy]pyrimidin-5-yl}-N'-[2-(methanesulfonyl)-5-(trifluoromethyl)phenyl]urea) is a highly potent and selective pan-tropomyosin receptor kinase (TRK) inhibitor. The objective of the present study was to characterize the pharmacokinetic (PK), pharmacodynamic (PD), and antitumor efficacy relationships of ONO-7579 in mice xenografted with a human colorectal cancer cell line, KM12 (harboring the tropomyosin 3 (TPM3) -neurotrophic tyrosine receptor kinase 1 fusion gene), via a PK/PD modeling approach. Plasma and tumor concentrations of ONO-7579, tumor levels of phosphorylated TPM3-TRKA (pTRKA), and tumor volumes in the murine model were measured with a single or multiple dose of ONO-7579 (0.06-0.60 mg/kg) administered once daily. The PK/PD/efficacy models were developed in a sequential manner. Changes in plasma concentrations of ONO-7579 were described with an oral one-compartment model. Tumor concentrations of ONO-7579 were higher than plasma concentrations, and changes in ONO-7579 tumor concentrations were described with an additional tumor compartment that had no influence on plasma concentrations. pTRKA in tumors was described with a direct E_max model, and the tumor ONO-7579 concentration causing 50% of the maximum effect was estimated to be 17.6 ng/g. In addition, a pTRKA-driven tumor growth inhibition model indicated that ONO-7579 started to sharply increase the antitumor effect at pTRKA inhibition rates >60% and required >91.5% to reduce tumors. In conclusion, the developed PK/PD/efficacy models revealed a "switch-like" relationship between pTRKA inhibition rate and antitumor effect in a murine KM12 xenograft model, demonstrating that pTRKA in tumors could serve as an effective biomarker for scheduling the dose regimen in early-stage clinical studies. SIGNIFICANCE STATEMENT: In recent years, clinical development of TRK inhibitors in patients with neurotrophic tyrosine receptor kinase fusion-positive solid tumors has been accelerated. This research found that phosphorylated TRKA was a useful biomarker for explaining the antitumor efficacy of TRK inhibitors using a pharmacokinetic/pharmacodynamic modeling approach in xenograft mice. This finding suggests a rational dosing regimen in early-stage clinical studies for ONO-7579 (N-{2-[4-(2-amino-5-chloropyridin-3-yl)phenoxy]pyrimidin-5-yl}-N'-[2-(methanesulfonyl)-5-(trifluoromethyl)phenyl]urea), a novel pan-TRK inhibitor.

Pulsed laser deposition with rapid beam deflection by a galvanometer mirror scanner

A pulsed laser deposition system with rapid beam deflection (RBD-PLD) by a galvanometer mirror scanner has been developed for alternating ablation of multiple targets with a single laser instrument. In this system, the alternating deposition of different target materials is carried out by scanning the laser beam between the positionally fixed targets with a galvanometer mirror instead of mechanically switching the target positions on a fixed optical path of the laser beam as is done in conventional pulsed laser deposition (PLD) systems. Thus, the "wait" time required for switching target materials to be deposited, which typically takes several seconds in a conventional system, can be made as short as a few milliseconds. We demonstrate some of the advantages of this PLD system in several technologically important aspects of thin film synthesis: (1) fast fabrication of binary alloy films, (2) preparation of natural composition spread libraries, (3) effect of the target switching time on the deposition of volatile compounds, (4) control of the degree of mixing of two different materials in a film, and (5) efficient growth of compositionally graded thin films.

Brain histamine H1 receptor occupancy after oral administration of desloratadine and loratadine

Some histamine H1 receptor (H1R) antagonists induce adverse sedative reactions caused by blockade of histamine transmission in the brain. Desloratadine is a second-generation antihistamine for treatment of allergic disorders. Its binding to brain H1Rs, which is the basis of sedative property of antihistamines, has not been examined previously in the human brain by positron emission tomography (PET). We examined brain H1R binding potential ratio (BPR), H1R occupancy (H1RO), and subjective sleepiness after oral desloratadine administration in comparison to loratadine. Eight healthy male volunteers underwent PET imaging with [11C]-doxepin, a PET tracer for H1Rs, after a single oral administration of desloratadine (5 mg), loratadine (10 mg), or placebo in a double-blind crossover study. BPR and H1RO in the cerebral cortex were calculated, and plasma concentrations of loratadine and desloratadine were measured. Subjective sleepiness was quantified by the Line Analogue Rating Scale (LARS) and the Stanford Sleepiness Scale (SSS). BPR was significantly lower after loratadine administration than after placebo (0.504 ± 0.074 vs 0.584 ± 0.059 [mean ± SD], P < 0.05), but BPR after desloratadine administration was not significantly different from BPR after placebo (0.546 ± 0.084 vs 0.584 ± 0.059, P = 0.250). The plasma concentration of loratadine was negatively correlated with BPR in subjects receiving loratadine, but that of desloratadine was not correlated with BPR. Brain H1ROs after desloratadine and loratadine administration were 6.47 ± 10.5% and 13.8 ± 7.00%, respectively (P = 0.103). Subjective sleepiness did not significantly differ among subjects receiving the two antihistamines and placebo. At therapeutic doses, desloratadine did not bind significantly to brain H1Rs and did not induce any significant sedation.

Longitudinal changes in 18 F-THK5351 positron emission tomography in corticobasal syndrome

BACKGROUND AND PURPOSE

Corticobasal syndrome (CBS) is pathologically characterized by tau deposits in neuronal and glial cells and by reactive astrogliosis. In several neurodegenerative disorders, ¹⁸ F-THK5351 has been observed to bind to reactive astrocytes expressing monoamine oxidase B. In this study, the aim was to investigate the progression of disease-related pathology in the brains of patients with CBS using positron emission tomography with ¹⁸ F-THK5351.

METHODS

Baseline and 1-year follow-up imaging were acquired using magnetic resonance imaging and positron emission tomography with ¹⁸ F-THK5351 in 10 subjects: five patients with CBS and five age-matched normal controls (NCs).

RESULTS

The 1-year follow-up scan images revealed that ¹⁸ F-THK5351 retention had significantly increased in the superior parietal gyrus of the patients with CBS compared with the NCs. The median increases in ¹⁸ F-THK5351 accumulation in the patients with CBS were 6.53% in the superior parietal gyrus, 4.34% in the precentral gyrus and 4.33% in the postcentral gyrus. In contrast, there was no significant increase in the regional ¹⁸ F-THK5351 retention in the NCs.

CONCLUSIONS

Longitudinal increases in ¹⁸ F-THK5351 binding can be detected over a short interval in the cortical sites of patients with CBS. A monoamine oxidase B binding radiotracer could be useful in monitoring the progression of astrogliosis in CBS.

Involvement of the Precuneus/Posterior Cingulate Cortex Is Significant for the Development of Alzheimer's Disease: A PET (THK5351, PiB) and Resting fMRI Study

Background: Imaging studies in Alzheimer’s disease (AD) have yet to answer the underlying questions concerning the relationship among tau retention, neuroinflammation, network disruption and cognitive decline. We compared the spatial retention patterns of ¹⁸F-THK5351 and resting state network (RSN) disruption in patients with early AD and healthy controls.

Methods: We enrolled 23 ¹¹C-Pittsburgh compound B (PiB)-positive patients with early AD and 24 ¹¹C-PiB-negative participants as healthy controls. All participants underwent resting state functional MRI and ¹⁸F-THK5351 PET scans. We used scaled subprofile modeling/principal component analysis (SSM/PCA) to reduce the complexity of multivariate data and to identify patterns that exhibited the largest statistical effects (variances) in THK5351 concentration in AD and healthy controls.

Findings: SSM/PCA identified a significant spatial THK5351 pattern composed by mainly three clusters including precuneus/posterior cingulate cortex (PCC), right and left dorsolateral prefrontal cortex (DLPFC) which accounted for 23.6% of the total subject voxel variance of the data and had 82.6% sensitivity and 79.1% specificity in discriminating AD from healthy controls. There was a significant relationship between the intensity of the ¹⁸F-THK5351 covariation pattern and cognitive scores in AD. The spatial patterns of ¹⁸F-THK5351 uptake showed significant similarity with intrinsic functional connectivity, especially in the PCC network. Seed-based connectivity analysis from the PCC showed significant decrease in connectivity over widespread brain regions in AD patients. An evaluation of an autopsied AD patient with Braak V showed that ¹⁸F-THK5351 retention corresponded to tau deposition, monoamine oxidase-B (MAO-B) and astrogliosis in the precuneus/PCC.

Interpretation: We identified an AD-specific spatial pattern of ¹⁸F-THK5351 retention in the precuneus/PCC, an important connectivity hub region in the brain. Disruption of the functional connections of this important network hub may play an important role in developing dementia in AD.

Corrigendum: Imaging Protein Misfolding in the Brain Using β-Sheet Ligands

[This corrects the article DOI: 10.3389/fnins.2018.00585.].

Imaging Protein Misfolding in the Brain Using β-Sheet Ligands

Neurodegenerative diseases characterized by pathological protein accumulation in cells are termed “proteinopathies.” Although various protein aggregates share cross-β-sheet structures, actual conformations vary among each type of protein deposit. Recent progress in the development of radiotracers for positron emission tomography (PET) has enabled the visualization of protein aggregates in living brains. Amyloid PET tracers have been developed, and are widely used for the diagnosis of Alzheimer’s disease and non-invasive assessment of amyloid burden in clinical trials of anti-dementia drugs. Furthermore, several tau PET tracers have been successfully developed and used in the clinical studies. However, recent studies have identified the presence of off-target binding of radiotracers in areas of tau deposition, suggesting that concomitant neuroinflammatory changes might affect tracer binding. In contrast to amyloid and tau PET, there are no established tracers for imaging Lewy bodies in the human brain. In this review, we describe lessons learned from the development of PET tracers and discuss the future direction of tracer development for protein misfolding diseases.

The development and validation of tau PET tracers: current status and future directions

Purpose

To provide an overview on positron emission tomography (PET) imaging of tau pathology in Alzheimer’s disease (AD) and other neurodegenerative disorders.

Results

Different classes of tau tracers such as flortaucipir, THK5317, and PBB3 have been developed and utilized in previous clinical studies. In AD, the topographical distribution of tracer binding follows the known distribution of neurofibrillary tangles and is closely associated with neurodegeneration as well as the clinical phenotype of dementia. Significant retention of tracers has also been observed in the frequent site of the 4-repeat (4R) tau isoform deposits in non-AD tauopathies, such as in progressive supranuclear palsy. However, in vitro binding studies indicate that most tau tracers are less sensitive to straight tau filaments, in contrast to their high binding affinity to paired helical filaments of tau (PHF-tau). The first-generation of tau tracers shows off-target binding in the basal ganglia, midbrain, thalamus, choroid plexus, and venous sinus. Off-target binding of THK5351 to monoamine oxidase B (MAO-B) has been observed in disease-associated brain regions linked to neurodegeneration and is associated with astrogliosis in areas of misfolded protein accumulation. The second generation of tau tracers, such as [¹⁸F]MK-6240, is highly selective to PHF-tau with little off-target binding and have enabled the reliable assessment of PHF-tau burden in aging and AD.

Conclusions

Tau PET tracers have enabled in vivo quantification of PHF-tau burden in human brains. Tau PET can help in understanding the underlying cause of dementia symptoms, and in patient selection for clinical trials of anti-dementia therapies.

Neuroimaging-pathological correlations of [18F]THK5351 PET in progressive supranuclear palsy

Recent positron emission tomography (PET) studies have demonstrated the accumulation of tau PET tracer in the affected region of progressive supranuclear palsy (PSP) cases. To confirm the binding target of radiotracer in PSP, we performed an imaging-pathology correlation study in two autopsy-confirmed PSP patients who underwent [¹⁸F]THK5351 PET before death. One patient with PSP Richardson syndrome showed elevated tracer retention in the globus pallidus and midbrain. In a patient with PSP-progressive nonfluent aphasia, [¹⁸F]THK5351 retention also was observed in the cortical areas, particularly the temporal cortex. Neuropathological examination confirmed PSP in both patients. Regional [¹⁸F]THK5351 standardized uptake value ratio (SUVR) in antemortem PET was significantly correlated with monoamine oxidase-B (MAO-B) level, reactive astrocytes density, and tau pathology at postmortem examination. In in vitro autoradiography, specific THK5351 binding was detected in the area of antemortem [¹⁸F]THK5351 retention, and binding was blocked completely by a reversible selective MAO-B inhibitor, lazabemide, in brain samples from these patients. In conclusion, [¹⁸F]THK5351 PET signals reflect MAO-B expressing reactive astrocytes, which may be associated with tau accumulation in PSP.

Histamine elicits glutamate release from cultured astrocytes

Astrocytes play key roles in regulating brain homeostasis and neuronal activity. This is, in part, accomplished by the ability of neurotransmitters in the synaptic cleft to bind astrocyte membrane receptors, activating signalling cascades that regulate concentration of intracellular Ca²⁺ ([Ca²⁺]_i) and gliotransmitter release, including ATP and glutamate. Gliotransmitters contribute to dendrite formation and synaptic plasticity, and in some cases, exacerbate neurodegeneration. The neurotransmitter histamine participates in several physiological processes, such as the sleep-wake cycle and learning and memory. Previous studies have demonstrated the expression of histamine receptors on astrocytes, but until now, only a few studies have examined the effects of histamine on astrocyte intracellular signalling and gliotransmitter release. Here, we used the human astrocytoma cell line 1321N1 to study the role of histamine in astrocyte intracellular signalling and gliotransmitter release. We found that histamine activated astrocyte signalling through histamine H₁ and H₂ receptors, leading to distinct cellular responses. Activation of histamine H₁ receptors caused concentration-dependent release of [Ca²⁺]_i from internal stores and concentration-dependent increase in glutamate release. Histamine H₂ receptor activation increased cyclic adenosine monophosphate (cAMP) levels and phosphorylation of transcription factor cAMP response-element binding protein. Taken together, these data emphasize a role for histamine in neuron-glia communication.

Newly-Developed Positron Emission Mammography (PEM) Device for the Detection of Small Breast Cancer

Positron emission mammography (PEM) has higher detection sensitivity for breast cancer compared with whole-body positron emission tomography (PET) due to higher spatial resolution. We have developed a new PEM device with high resolution over a wide field of view. This PEM device comprises novel scintillation crystals, praseodymium-doped lutetium aluminum garnet (Pr:LuAG). In the present study, the clinical use of the newly developed PEM for the detection of small breast cancer was compared with that of the conventional PET-computed tomography (PET/CT). Eighty-two patients with breast cancer less than 20 mm (UICC T1) participated in this study, including 23 patients with T1a or T1b breast cancer (less than 10 mm). Histologically-proved lesions were examined by PET/CT and PEM on the same day after injection of [¹⁸F]fluoro-2-deoxy-2-fluoro-D-glucose ([¹⁸F]FDG), a marker of glycolytic activity. The newly developed PEM showed better sensitivity of cancer detection compared with PET/CT especially in case of the small T1a or T1b lesions. Moreover, when the conventional PET/CT and new PEM were combined, the detection sensitivity with [¹⁸F]FDG molecular imaging for T1 (N = 82) and T1a plus T1b breast cancer (N = 23) were 90% and 70%, respectively. The uptake of [¹⁸F]FDG was proportional to the histological malignancy of breast cancer. Using the newly-developed PEM with [¹⁸F]FDG, we are able to identify and characterize exactly the small breast tumors less than 10 mm in combination with the conventional PET/CT. These data indicate that PEM and PET/CT are synergic and complementary for the detection of small breast cancer.

Heparan sulfate in pancreatic β-cells contributes to normal glucose homeostasis by regulating insulin secretion

Heparan sulfate (HS), a linear polysaccharide, is involved in diverse biological functions of various tissues. HS is expressed in pancreatic β-cells and may be involved in β-cell functions. However, the importance of HS for β-cell function remains unknown. Here, we generated mice with β-cell-specific deletion of Ext1 (βExt1CKO), which encodes an enzyme essential for HS synthesis, to investigate the detailed roles of HS in β-cell function. βExt1CKO mice decreased body weights compared with control mice, despite increased food intake. Additionally, βExt1CKO mice showed impaired glucose tolerance associated with decreased insulin secretion upon glucose challenge. Glucose-induced insulin secretion (GIIS) from isolated βExt1CKO islets was also significantly reduced, highlighting the contribution of HS to insulin secretion and glucose homeostasis. The gene expression essential for GIIS was decreased in βExt1CKO islets. Pdx1 and MafA were downregulated in βExt1CKO islets, indicating that HS promoted β-cell development and maturation. BrdU- or Ki67-positive β-cells were reduced in βExt1CKO pancreatic sections, suggesting the involvement of HS in the proliferation of β-cells. Moreover, insufficient vascularization in βExt1CKO islets may contribute to central distribution of α-cells. These data demonstrate HS plays diverse roles in β-cells, and that loss of HS leads to insufficient insulin secretion and dysregulation of glucose homeostasis.

18F-Labeled 2-Arylquinoline Derivatives for Tau Imaging: Chemical, Radiochemical, Biological and Clinical Features

Alzheimer's disease is the most common form of dementia among older people. Misfolding and aggregation of proteins (amyloid-β and tau) in the brain is the primary cause of neurodegeneration in the disease. Non-invasive detection of amyloid-β deposition can be realized using positron emission tomography probes, but a proportion of Aβ-positive subjects do not present with cognitive dysfunction, suggesting limitations in assessment using this method. Non-invasive detection of tau deposits in the brain can be used to diagnose, monitor, and predict Alzheimer's disease progression. Tau positron emission tomography radiolabelled probes such as T807, THK-5117, and PBB3 can image the pathology of the disease in vivo. The 18F-labeled tau imaging agents 18F-THK-5351, 18F-T807 (18F-AV-1451), and 18F-RO6958948 are presently under evaluation in clinical studies and clinical trials worldwide. This imaging methodology could be applied to enable preclinical diagnoses and disease-modifying drugs for Alzheimer's disease. In this review, we provide an overview of the pathology and potential imaging of tau in Alzheimer's disease, development of a THK series among tau tracers, and the chemical, radiochemical, biological, and clinical features of tau probes.

Correlations of 18F-THK5351 PET with Postmortem Burden of Tau and Astrogliosis in Alzheimer Disease

Clinical PET studies using ¹⁸F-THK5351 have demonstrated significant tracer retention in sites susceptible to tau burden in Alzheimer disease (AD). However, the in vivo PET signal to reflect tau aggregates remains controversial. Methods: We examined the spatial pattern of tracer binding, amyloid-β, tau, and gliosis in an autopsy-confirmed AD patient who underwent ¹⁸F-THK5351 and ¹¹C-Pittsburgh compound B PET before death. Results: Regional in vivo ¹⁸F-THK5351 retention was significantly correlated with the density of tau aggregates in the neocortex and monoamine oxidase-B in the whole brain, but not correlated with that of insoluble amyloid-β. Furthermore, significant association was observed between the density of tau aggregates, monoamine oxidase-B, and glial fibrillary acidic protein, suggesting that neocortical tau would strongly influence the formation of reactive astrocytes. Conclusion:¹⁸F-THK5351 PET may have limited utility as a biomarker of tau pathology in AD; however, it could be used to monitor the neuroinflammatory processes in the living brain.