Mukesh K. Pandey

An autoradiographic evaluation of AV-1451 Tau PET in dementia

BackgroundIt is essential to determine the specificity of AV-1451 PET for tau in brain imaging by using pathological comparisons. We performed autoradiography in autopsy-confirmed Alzheimer disease and other neurodegenerative disorders to evaluate the specificity of AV-1451 binding for tau aggregates.MethodsTissue samples were selected that had a variety of dementia-related neuropathologies including Alzheimer disease, primary age-related tauopathy, tangle predominant dementia, non-Alzheimer disease tauopathies, frontotemporal dementia, parkinsonism, Lewy body disease and multiple system atrophy (n = 38). Brain tissue sections were stained for tau, TAR DNA-binding protein-43, and α-synuclein and compared to AV-1451 autoradiography on adjacent sections.ResultsAV-1451 preferentially localized to neurofibrillary tangles, with less binding to areas enriched in neuritic pathology and less mature tau. The strength of AV-1451 binding with respect to tau isoforms in various neurodegenerative disorders was: 3R + 4R tau (e.g., AD) > 3R tau (e.g., Pick disease) or 4R tau. Only minimal binding of AV-1451 to TAR DNA-binding protein-43 positive regions was detected. No binding of AV-1451 to α-synuclein was detected. “Off-target” binding was seen in vessels, iron-associated regions, substantia nigra, calcifications in the choroid plexus, and leptomeningeal melanin.ConclusionsReduced AV-1451 binding in neuritic pathology compared to neurofibrillary tangles suggests that the maturity of tau pathology may affect AV-1451 binding and suggests complexity in AV-1451 binding. Poor association of AV-1451 with tauopathies that have preferential accumulation of either 4R tau or 3R tau suggests limited clinical utility in detecting these pathologies. In contrast, for disorders associated with 3R + 4R tau, such as Alzheimer disease, AV-1451 binds tau avidly but does not completely reflect the early stage tau progression suggested by Braak neurofibrillary tangle staging. AV-1451 binding to TAR DNA-binding protein-43 or TAR DNA-binding protein-43 positive regions can be weakly positive. Clinical use of AV-1451 will require a familiarity with distinct types of “off-target” binding.

Design, synthesis and evaluation of novel PEGylated curcumin analogs as potent Nrf2 activators in human bronchial epithelial cells

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a central transcription factor that regulates the anti-oxidant defense system and is considered as a modifier for several inflammatory diseases. Thus, activation of Nrf2 provides pivotal therapeutic target for developing therapy against these diseases. Herein, a chemo-enzymatic methodology is designed and developed to make PEGylated curcumins as water soluble drug candidates with enhanced aqueous solubility and bioavailability. For this, curcumin was judiciously converted to diester (1) using ethyl α-bromoacetate and potassium carbonate. The diester 1 in subsequent step was copolymerized with poly(ethylene glycol) using Candida antarctica lipase [CAL-B, Novozym 435] under solventless condition. C. antarctica selectively does trans-esterification and only catalyses reaction of the primary hydroxyls of poly(ethylene glycol). It does not affect the secondary enolic hydroxyls of curcumin, thus leaving behind the active group unaltered. A luciferase based reporter gene assay was used for primary screening for identifying a novel Nrf2 activator. Most of the PEGylated curcumin analogs strongly activate Nrf2 several folds higher than the free curcumin but copolymer 3a was identified as the most potent Nrf2 activator. Copolymer 3a induces Nrf2-driven NQO1 expression in a concentration dependent manner. Furthermore, a plausible mechanism for quantitative structure-activity relationship is also discussed.

Glycogen Synthase Kinase-3 (GSK-3)-Targeted Therapy and Imaging

Glycogen synthase kinase-3 (GSK-3) is associated with various key biological processes, including glucose regulation, apoptosis, protein synthesis, cell signaling, cellular transport, gene transcription, proliferation, and intracellular communication. Accordingly, GSK-3 has been implicated in a wide variety of diseases and specifically targeted for both therapeutic and imaging applications by a large number of academic laboratories and pharmaceutical companies. Here, we review the structure, function, expression levels, and ligand-binding properties of GSK-3 and its connection to various diseases. A selected list of highly potent GSK-3 inhibitors, with IC50 <20 nM for adenosine triphosphate (ATP)-competitive inhibitors and IC50 <5 μM for non-ATP-competitive inhibitors, were analyzed for structure activity relationships. Furthermore, ubiquitous expression of GSK-3 and its possible impact on therapy and imaging are also highlighted. Finally, a rational perspective and possible route to selective and effective GSK-3 inhibitors is discussed.

Synthesis and Preliminary Evaluation of 18-18F-Fluoro-4-Thia-Oleate as a PET Probe of Fatty Acid Oxidation

Fatty acid oxidation (FAO) is a major energy-providing process with important implications in cardiovascular, oncologic, neurologic, and metabolic diseases. A novel 4-thia oleate analog, 18-18F-fluoro-4-thia-oleate (18F-FTO), was evaluated in relationship to the previously developed palmitate analog 16-18F-fluoro-4-thia-palmitate (18F-FTP) as an FAO probe. Methods: 18F-FTO was synthesized from a corresponding bromoester. Biodistribution and metabolite analysis studies were performed in rats. Preliminary small-animal PET studies were performed with 18F-FTO and 18F-FTP in rats. Results: A practical synthesis of 18F-FTO was developed, providing a radiotracer of high radiochemical purity (>99%). In fasted rats, myocardial uptake of 18F-FTO (0.70 ± 0.30% dose kg [body mass]/g [tissue mass]) was similar to that of 18F-FTP at 30 min after injection. At 2 h, myocardial uptake of 18F-FTO was maintained, whereas 18F-FTP uptake in the heart was 82% reduced. Similar to 18F-FTP, 18F-FTO uptake by the heart was approximately 80% reduced at 30 min by pretreatment of rats with the CPT-I inhibitor etomoxir. Folch-type extraction analyses showed 70–90% protein-bound fractions in the heart, liver, and skeletal muscle, consistent with efficient trafficking of 18F-FTO to the mitochondrion with subsequent metabolism to protein-bound species. Preliminary small-animal PET studies showed rapid blood clearance and avid extraction of 18F-FTO and of 18F-FTP into the heart and liver. Images of 18F-FTO accumulation in the rat myocardium were clearly superior to those of 18F-FTP. Conclusion: 18F-FTO is shown to be a promising metabolically trapped FAO probe that warrants further evaluation.

Production of 89Zr via the 89Y(p,n)89Zr reaction in aqueous solution: Effect of solution composition on in-target chemistry

OBJECTIVE The existing solid target production method of radiometals requires high capital and operational expenditures, which limit the production of radiometals to the small fraction of cyclotron facilities that are equipped with solid target systems. Our objective is to develop a robust solution target method, which can be applicable to a wide array of radiometals and would be simply and easily adopted by existing cyclotron facility for the routine production of radiometals. METHOD We have developed a simplified, solution target approach for production of (89)Zr using a niobium target by 14 MeV energy proton bombardment of aqueous solutions of yttrium salts via the (89)Y(p,n)(89)Zr nuclear reaction. The production conditions were optimized, following a detailed mechanistic study of the gas evolution. RESULTS Although the solution target approach avoided the expense and complication of solid target processing, rapid radiolytic formation of gases in the target represents a major impediment in the success of solution target. To address this challenge we performed a systematic mechanistic study of gas evolution. Gas evolution was found to be predominantly due to decomposition of water to molecular hydrogen and oxygen. The rate of gas evolutions varied >40-fold depending on solution composition even under the same irradiation condition. With chloride salts, the rate of gas evolution increased in the order rank Na<Ca<Y. However, the trend was reversed with the corresponding nitrate salts, and further addition of nitric acid to the irradiating solution minimized gas evolution. At optimized condition, (89)Zr was produced in moderate yield (4.36 ± 0.48 MBq/μA • h) and high effective specific activity (464 ± 215 MBq/μg) using the solution target approach (2.75 M yttrium nitrate, 1.5 N HNO3, 2h irradiation at 20 μA). CONCLUSION The novel findings on substrate dependent, radiation-induced water decomposition provide fundamental data for the development and optimization of conditions for solution targets. The developed methodology of irradiation of nitrate salts in dilute nitric acid solutions can be translated to the production of a wide array of radiometals like (64)Cu, (68)Ga and (86)Y, and is well suited for short-lived isotopes.

Design, synthesis and anti-inflammatory evaluation of PEGylated 4-methyl and 4,8-dimethylcoumarins

Aberrant interaction between the leukocyte and the endothelial cell (EC) resulting from the deregulated expression of cell adhesion molecules (CAMs) on the endothelium results in uncontrolled inflammation leading to various inflammatory disorders. The existing drugs used to modulate the cytokine-induced expression of cell molecules have severe side effects. Therefore, there is an unmet therapeutic need to develop potent and safe drugs to treat inflammatory disorders. In the present study, novel PEGylated and non-PEGylated 4-methyl and 4,8-dimethylcoumarin derivatives were designed, synthesized and, evaluated for ICAM-1 inhibitory activity. The PEGylated coumarins were synthesized in two different ways. In the first approach, diesters of 4-methyl and 4,8-dimethylcoumarin were co-polymerized, separately with poly(ethylene glycol) using Candida antarctica lipase under solventless conditions. In the other approach, 4-methyl and 4,8-dimethylcoumarins were suitably converted to their bromo analogues and were tethered to already synthesized PEGylated polymers. Synthesized derivatives were evaluated for anti-inflammatory activities with respect to their ability to inhibit the TNF-alpha induced ICAM-1 (intercellular cell adhesion molecule-1) on human endothelial cells. It was found that PEGylated 4-methyl and 4,8-dimethylcoumarin derivatives were more effective than their non-PEGylated analogues to inhibit ICAM-1 expression. The present study opens new vista for PEGylated non-steroidal anti-inflammatory compounds and their further investigations.

Design and Synthesis of Novel Pegylated 4‐Methylcoumarins

Coumarins are well known for their antioxidant and anti‐edema activities. Their antioxidant property gets enhanced with a methyl group at the C‐4 position of the pyran ring. To increase the antioxidant potential and their hydrophilicity, a lipase (Novozyme 435) catalyzed copolymerization of 4‐methylcoumarin diesters and polyethylene glycols (PEGs) has been carried out to give novel copolymers.

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 Alzheimers 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 Alzheimers 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 Alzheimers 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 Alzheimers disease dementia versus older-onset Alzheimers 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.

Novel PEGylated Amphiphilic Copolymers as Nanocarriers for Drug Delivery: Synthesis, Characterization and Curcumin Encapsulation

Amphiphilic polymers can self assemble into micellar nano-particles and can be effectively used as nano carriers for drug delivery. A number of macromolecular delivery systems are under investigation to improve the efficacy of prospective drugs. In this study, seven new co-polymers were synthesized under mild reaction conditions in bulk (without solvent) by chemoenzymatic approach using Candida antarctica lipase (Novozyme 435) and molecular sieves, subsequently these polymers were treated with different long chain bromoalkanes and acid chlorides for attachment of the lipophilic moieties to the backbone polymer via an ether or an ester linkage, respectively in order to make them amphiphilic. These synthesized nano-particles demonstrated high drug loading capacity and have the potential to encapsulate hydrophobic drugs.

Microwave-assisted radiosynthesis of [18F]fluorinated fatty acid analogs

UNLABELLED Microwave reactors remain largely underutilized in the field of positron emission tomography (PET) chemistry. This is particularly unfortunate since microwave synthesis elegantly addresses two of the most critical issues of PET radiochemistry with short-lived radionuclides: reaction rate and side-product formation. In this study, we investigate the efficiency of synthesis of terminally [(18)F]fluorinated fatty acid analogs using a commercial microwave reactor in comparison with conventional heating (CH). METHODS The labeling precursors were methyl esters of terminally substituted alkyl bromides and iodides. Duration and temperatures of the [(18)F]fluorination reaction were varied. Chemical and radiochemical purities, and radiochemical yields were investigated for conventional (CH) and microwave-assisted (MW) radiosyntheses. RESULTS The results demonstrate that microwave heating enhanced [(18)F]fluoride incorporation to >95% (up to 55% improvement), while reducing reaction times to 2 min (∼ 10-fold reduction) or temperatures to 55-60 °C (20 °C reduction). Overall decay-corrected radiochemical yields of purified [(18)F]fluoro fatty acids were higher (MW = 49.0 ± 4.5%, CH = 23.6 ± 3.5%, P < .05) with microwave heating and side-products were notably fewer. CONCLUSION For routine synthesis of [(18)F]fluoro fatty acid analogs, microwave heating is faster, milder, cleaner, less variable and higher yielding than CH and therefore the preferred reaction method.