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.

Objectives: To prove that our novel ethanolamine derivative (FDES) can normalize overall movement and exploratory activity of rats with traumatic brain injury (TBI) owing to its peculiar properties. Materials and methods: TBI was modeled using controlled cortical impact injury (CCI) model method. The resulting neurological deficit, efficacy of the novel agent and other reference agents used were assayed in tests which evaluated overall movements and exploratory behavior of the rats. Finally, scopolamine in equimolar dose was used to estimate the role of cholinergic system in the efficacy of our agent. The tests included: limb-placing, open field, elevated plus maze, cylinder, and beam walking tests. Results: Intraperitoneal administration of FDES at a dose of 10 mg/kg led to improvement of fore- and hind-limb functions of rats with traumatic brain injury as was shown in “Limb placing”, “Open field” “Cylinder” and “Beam walking” tests. The new agent had no effects on traumatized rats behavior in the “Elevated Plus Maze” test. Simultaneous co-administration of scopolamine with FDES reduced the beneficial effects of the latter in rats with trauma. Conclusion: The neuroprotective effects of new agent were manifested in the reduction of motor deficiencies, and exploratory activity in the CCI model rats. In comparison with choline alfoscerate and citicoline, FDES showed more beneficial effects as were observed in most of the tests, and did not negatively influence the traumatized rats psychologically. Notably, it is possible that the neuroprotective influence of the new agent is mediated by its actions on the cholinergic system.

The accumulation of α-synuclein aggregates (α-syn) in the human brain is an occurrence common to all α-synucleinopathies. Non-invasive detection of these aggregates in a living brain with a target-specific radiotracer is not yet possible. We have recently discovered that the inclusion of a methylenedioxy group in the structure of diarylbisthiazole (DABTA)-based tracers improves binding affinity and selectivity to α-syn. Subsequently, complementary in silico modeling and machine learning (ML) of tracer–protein interactions were employed to predict surface sites and structure–property relations for the binding of the ligands. Based on this observation, we developed a small focused library of DABTAs from which 4-(benzo[d][1,3]dioxol-5-yl)-4′-(3-[18F]fluoro-4-methoxyphenyl)-2,2′-bithiazole [18F]d2, 6-(4′-(3-[18F]fluoro-4-methoxyphenyl)-[2,2′-bithiazol]-4-yl)-[1,3]dioxolo[4,5-b]pyridine [18F]d4, 4-(benzo [d][1,3]dioxol-5-yl)-4′-(6-[18F]fluoropyridin-3-yl)-2,2′-bithiazole [18F]d6, and 6-(4′-(6-[18F]fluoropyridin-3-yl)-[2,2′-bithiazol]-4-yl)-[1,3]dioxolo[4,5-b]pyridine [18F]d8 were selected based on their high binding affinity to α-syn and were further evaluated. Binding assay experiments carried out with the non-radioactive versions of the above tracers d2, d4, d6, and d8 showed high binding affinity of the ligands to α-syn: 1.22, 0.66, 1.21, and 0.10 nM, respectively, as well as excellent selectivity over β-amyloid plaques (Aβ) and microtubular tau aggregates (>200-fold selectivity). To obtain the tracers, their precursors were radiolabeled either via an innovative ruthenium-mediated (SNAr) reaction ([18F]d2 and [18F]d4) or typical SNAr reaction ([18F]d6 and [18F]d8) with moderate-to-high radiochemical yields (13% – 40%), and high molar activity > 60 GBq/μmol. Biodistribution experiments carried out with the tracers in healthy mice revealed that [18F]d2 and [18F]d4 showed suboptimal brain pharmacokinetics: 1.58 and 4.63 %ID/g at 5 min post-injection (p.i.), and 1.93 and 3.86 %ID/g at 60 min p.i., respectively. However, [18F]d6 and [18F]d8 showed improved brain pharmacokinetics: 5.79 and 5.13 %ID/g at 5 min p.i.; 1.75 and 1.07 %ID/g at 60 min p.i.; and 1.04 and 0.58 %ID/g at 120 min p.i., respectively. The brain uptake kinetics of [18F]d6 and [18F]d8 were confirmed in a dynamic PET study. Both tracers also showed no brain radiometabolites at 20 min p.i. in initial in vivo stability experiments carried out in healthy mice. [18F]d8 seems very promising based on its binding properties and in vivo stability, thus encouraging further validation of its usefulness as a radiotracer for the in vivo visualization of α-syn in preclinical and clinical settings. Additionally, in silico and ML-predicted values correlated with the experimental binding affinity of the ligands.

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Background:The fundamental role that α-synuclein (aSyn) plays in the pathogenesis of neurodegenerative synucleinopathies is a well-accepted fact. Beyond the synucleinopathies, the abnormal deposition of aSyn is frequently seen in a variety of other neurodegenerative proteinopathies including Alzheimer's disease. We aimed to optimize the pharmacokinetics and the binding properties of disarylbisthiazoles (DABTAs) to aSyn fibrils and versus β-amyloid (Aβ) and tau (τ) fibrils as PET tracer for synucleinopathies and neurodegenerative comorbidities. Method:We have identified DABTAs as specific tracer for aSyn in this paper we improved brain uptake kinetics of them by the addition of nitrogen containing heteroaromatic rings in the scaffold. The binding affinity of these ligands were calculated prior using a combination of molecular dynamics and quantum/molecular mechanics.Furthermore, the physicochemical and pharmacokinetics of these DABTAs were modeled using machine learning methods. The radiolabeling via n.c.a one-or two-step F-18-fluorination was established. The DABTAs were further evaluated via experimental logD and binding assays, plasma stability, brain metabolite analyses, biodistribution, and for some dynamic PET-MRI scans. Result:In silico assays allowed to characterize and evaluate the binding affinity of the candidates, with some of the ligands showing promising affinity and selectivity over Aβ and τ fibrils (80-120-fold) based on these calculations. Experimentally, initial binding assays revealed that F-18-DABTA-3 (Log D 2.68), F-18-DABTA-4 (Log D 2.34), F18-DABTA-7 (LogD 2.88) and F18-DABTA-8 (LogD 2.65) showed good binding affinity to α-syn fibrils, with some even in the sub-nanomolar range. Further experiments are ongoing to verify these values. Biodistribution assays in healthy mice brain uptake at 5 mins p.i. ranged from 5.6 -7.3 %ID/g, with fast brain clearance at 60 mins and 120 mins (up to 0.96 %ID/g & 0.39 %ID/g respectively), with no significant defluorination. The metabolite analyses revealed almost no brain radiometabolites in 20 min. Conclusion:In silico study facilitated the development via a rational design of radioligands with desired characteristics. DABTA results show a lot of promises and encourage us to further investigate them by autoradiography, immunohistochemistry and in vivo imaging in NHP and human.