Synthesis and biological evaluation of radioiodinated benzoxazole and benzothiazole derivatives for imaging myelin in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system that results from destruction of the myelin sheath. Due to heterogeneity of the symptoms and course of MS, periodic monitoring of disease activity is important for diagnosis and treatment. In the present study, we synthesized four radioiodinated benzoxazole (BO) and benzothiazole (BT) derivatives, and evaluated their utility as novel myelin imaging probes for single photon emission computed tomography (SPECT). In a biodistribution study using normal mice, three compounds ([125I]BO-1, [125I]BO-2, and [125I]BT-2) displayed moderate brain uptake (2.7, 2.9, and 2.8% ID/g, respectively) at 2 min postinjection. On ex vivo autoradiography using normal mice, [125I]BO-2 showed the most preferable ratio of radioactivity accumulation in white matter (myelin-rich region) versus gray matter (myelin-deficient region). In addition, the radioactivity of [125I]BO-2 was reduced in the lysophosphatidylcholine-induced demyelination region. In conclusion, [123I]BO-2 demonstrated the fundamental characteristics of a myelin imaging probe for SPECT.

Pre-clinical evaluation of 99mTc-labeled chalcone derivative for amyloid-β imaging post-head trauma

Aβ42 plaque formation is one of the preliminary pathologic events that occur post traumatic brain injury (TBI) which is also among the most noteworthy hallmarks of AD. Their pre symptomatic detection is therefore vital for better disease management. Chalcone-picolinic acid chelator derivative, 6-({[(6-carboxypyridin-2-yl)methyl](2-{4-[(2E)-3-[4-(dimethyl amino)phenyl]prop-2-enoyl]phenoxy}ethyl)amino}methyl)pyridine-2-carboxylic acid, Py-chal was synthesized to selectively identify amyloid plaques formed post head trauma using SPECT imaging by stable complexation to 99mTc with > 97% efficiency without compromising amyloid specificity. The binding potential of the Py-chal ligand to amyloid plaques remained high as confirmed by in vitro binding assay and photophysical spectra. Further, the Py-chal complex stained amyloid aggregates in the brain sections of rmTBI mice model. In vivo scintigraphy in TBI mice model displayed high uptake followed by high retention while the healthy rabbits displayed higher brain uptake followed by a rapid washout attributed to absence of amyloid plaques. Higher uptake in brain of TBI model was also confirmed by ex vivo biodistribution analysis wherein brain uptake of 3.38 ± 0.2% ID/g at 2 min p.i. was observed for TBI mice model. This was followed by prolonged retention and more than twofold higher activity as compared to sham mice brain. This preliminary data suggests the specificity of the radiotracer for amyloid detection post head trauma and applicability of 99mTc labeled Py-chal complex for TBI-induced β-amyloid SPECT imaging.

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.

Promising heterocycle-based scaffolds in recent (2019-2021) anti-Alzheimer's drug design and discovery

Alzheimer's disease (AD) is one of the neurodegenerative diseases that led to morbidity and mortality world-wide. It is a complex disease whose etiology is not completely known that leads to difficulty in prevent or cure of the AD. Also, there are only few approved drugs for AD treatment. Apart from deaths due to AD, expenditure of treatment and care of AD patients is higher than that of treatment of HIV and cancer diseases combined. Hence, it leads to an economic burden also. Although research is being carried out on designing drugs for AD, most of them have ended up in poor inhibitors with high toxicity. Hence, researchers should shoulder a great responsibility of discovery of efficient drugs for AD treatment. In the field of drug discovery, heterocycles played an important role. Also, most of the heterocyclic scaffolds have been used in design of potent anti-AD agents. In view of this, heterocyclic molecules reported recently are compiled and evaluated comprehensively. Especially, the molecules which exhibited pronounced activity are emphasized and described with respect to structure-activity relationship (SAR) in brief.

A Patent Review on the Current Developments of Benzoxazoles in Drug Discovery

The benzoxazole moiety is widely found in various natural compounds, which are often found to be biologically active. Due to its versatile biological properties, benzoxazole has been incorporated as an essential pharmacophore and substructure in many medicinal compounds. In the past years, numerous benzoxazole derivatives have been synthesised and evaluated for their biological potential. The wide range in therapeutic potential of benzoxazole derivatives is related to the favourable interactions of the benzoxazole moiety with different protein targets. Herein we review the biological activities of benzoxazole derivatives patented within the past six years. Using the Lens database, granted patents issued from 2015 to 2020 were retrieved. The patented benzoxazole derivatives demonstrated excellent activity against various protein targets and diseases, with some reaching clinical trial stage. Pharmacological and medicinal aspects of patented benzoxazole derivatives are discussed. The recent development and drawbacks are also reviewed.

Heterochiral Assembly of Amphiphilic Peptides Inside the Mitochondria for Supramolecular Cancer Therapeutics

Self-assembly of peptides containing both l- and d-isomers often results in nanostructures with enhanced properties compared to their enantiomeric analogues, such as faster kinetics of formation, higher mechanical strength, and enzymatic stability. However, occurrence and consequences of the heterochiral assembly in the cellular microenvironment are unknown. In this study, we monitored heterochiral assembly of amphiphilic peptides inside the cell, specifically mitochondria of cancer cells, resulting in nanostructures with refined morphological and biological properties owing to the superior interaction between the backbones of opposite chirality. We have designed a mitochondria penetrating tripeptide containing a diphenyl alanine building unit, named as Mito-FF due to their mitochondria targeting ability. The short peptide amphiphile, Mito-FF co-assembled with its mirror pair, Mito-ff, induced superfibrils of around 100 nm in diameter and 0.5-1 μm in length, while enantiomers formed only narrow fibers of 10 nm in diameter. The co-administration of Mito-FF and Mito-ff in the cell induced drastic mitochondrial disruption both in vitro and in vivo. The experimental and theoretical analyses revealed that pyrene capping played a major role in inducing superfibril morphology upon the co-assembly of racemic peptides. This work shows the impact of chirality control over the peptide self-assembly inside the biological system, thus showing a potent strategy for fabricating promising peptide biomaterials by considering chirality as a design modality.

Discovery of novel series of 2-substituted benzo[d]oxazol-5-amine derivatives as multi-target directed ligands for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is associated with multifactorial neuropathological conditions, which include cholinergic deficit, amyloid-beta plaques formation, loss of neuronal plasticity and neuronal death. Treating such multifactorial conditions with a single target directed approach is considered to be inadequate. Accordingly, multi-target directed ligand (MTDL) strategy has been evolved as an auspicious approach for the treatment of AD. In light of that, a library of 2-substituted benzo[d]oxazol-5-amine derivatives (29-39; 86-107) was designed using the scaffold hopping guided MTDLs strategy, synthesized and evaluated through various in-vitro and in-vivo biological studies. The optimal compound 92 exhibited potent inhibitory activities against AChE (IC₅₀ = 0.052 ± 0.010 μM), BuChE (IC₅₀ = 1.085 ± 0.035 μM), and significant amyloid-beta aggregation (20 μM) inhibition. The compound possessed better blood-brain barrier permeability (Pe = 10.80 ± 0.055 × 10^-6 cm s^-1) in PAMPA assay and neuro protective properties (40 μM) on SH-SY5Y neuroblastoma cell lines. Furthermore, in-vivo behavioural studies were performed on Y-maze test (scopolamine-induced amnesia model) and Morris water maze test (Aβ_1-42 induced ICV rat model). The compound 92, at a dose of 10 mg/kg oral administration, demonstrated a substantial improvement of the cognitive and special memory impairment. In summary, both in-vitro and in-vivo investigations evidenced that compound 92 was a potential lead for the discovery of safe and effective disease-modifying agents for AD.

99mTc-labeled Small Molecules for Diagnosis of Alzheimer’s Disease: Past, Recent and Future Perspectives

Background:

Alzheimer’s disease (AD) is an age-related progressive neurodegenerative disease. Its prominent hallmarks are extracellular deposition of β-amyloids (amyloid plaques), intracellular neurofibrillary tangles (NTFs), neurodegeneration and finally loss of cognitive function. Hence, AD diagnosis in the early stage and monitoring of the disease are of great importance.

Methods:

In this review article, we have reviewed recent efforts for design, synthesis and evaluation of 99mTc labeled small molecule for AD imaging purposes.

Results:

These small molecules include derivatives of Congo red, benzothiazole, benzofuran, benzoxazole, naphthalene, biphenyl, chalcone, flavone, aurone, stilbene, curcumin, dibenzylideneacetone, quinoxaline, etc. The different aspects of 99mTc-labeled small molecules including chemical structure, their affinity toward amyloid plaques, BBB permeation and in vivo/vitro stability will be discussed.

Conclusion:

The findings of this review confirm the importance of 99mTc-labeled small molecules for AD imaging. Future studies based on the pharmacophore of these designed compounds are needed for improvement of these molecules for clinical application.