Development of a potential PET probe for HDAC6 imaging in Alzheimer’s disease

Enhanced autophagic clearance of amyloid-β via histone deacetylase 6-mediated V-ATPase assembly and lysosomal acidification protects against Alzheimer's disease in vitro and in vivo

JOURNAL/nrgr/04.03/01300535-202509000-00025/figure1/v/2024-11-05T132919Z/r/image-tiff Recent studies have suggested that abnormal acidification of lysosomes induces autophagic accumulation of amyloid-β in neurons, which is a key step in senile plaque formation. Therefore, restoring normal lysosomal function and rebalancing lysosomal acidification in neurons in the brain may be a new treatment strategy for Alzheimer's disease. Microtubule acetylation/deacetylation plays a central role in lysosomal acidification. Here, we show that inhibiting the classic microtubule deacetylase histone deacetylase 6 with an histone deacetylase 6 shRNA or thehistone deacetylase 6 inhibitor valproic acid promoted lysosomal reacidification by modulating V-ATPase assembly in Alzheimer's disease. Furthermore, we found that treatment with valproic acid markedly enhanced autophagy, promoted clearance of amyloid-β aggregates, and ameliorated cognitive deficits in a mouse model of Alzheimer's disease. Our findings demonstrate a previously unknown neuroprotective mechanism in Alzheimer's disease, in which histone deacetylase 6 inhibition by valproic acid increases V-ATPase assembly and lysosomal acidification.

Anti-Alzheimer effects of an HDAC6 inhibitor, WY118, alone and in combination of lithium chloride: Synergistic suppression of ferroptosis via the modulation of tau phosphorylation and MAPK signaling

Alzheimer's disease (AD) is a complex neurodegenerative disorder, and current therapies mainly offer symptomatic relief. Given that the pathophysiology of AD is multifaceted, a multimodal therapeutic strategy targeting multiple molecular pathways implicated in AD-related pathogenesis represents a pragmatic avenue for impeding the advancement of AD. In this study, we evaluated the anti-Alzheimer effects of an HDAC6 inhibitor WY118, both alone and in combination with lithium chloride (LiCl), a GSK-3β inhibitor, to synergistically suppress ferroptosis. The combination of compound WY118 and LiCl demonstrated significant synergistic effects in both cellular models of AD induced by glutamate and streptozotocin. The findings suggest that compound WY118, in particular in combination with LiCl, exhibits potent anti-Alzheimer effects by synergistically suppressing ferroptosis. Studies on the mechanism of action indicated that the combination treatment significantly reduced tau phosphorylation and inhibited p38 MAPK signaling. This combination therapy holds promise for developing more effective treatments for AD.

Effects of Bufexamac, a class IIb HDAC inhibitor, on behavior and neuropathological features in an Aβ-induced rat model of Alzheimer's disease

It has been suggested that Alzheimer's disease (AD), a progressive neurological condition, can potentially be treated through epigenetic means by targeting histone deacetylases (HDACs), enzymes that regulate gene expression. In this study, we investigated the molecular mechanisms of Bufexamac, in an animal model of AD. Bufexamac specifically targets Class IIb HDACs, which are particularly relevant in the context of neuroinflammation and neurodegeneration. This selectivity may reduce off-target effects commonly associated with broader-spectrum HDAC inhibitors, such as pan-HDAC inhibitors, which can affect multiple HDAC classes and potentially lead to undesirable side effects. Male rats injected with Aβ25-35 for AD-like symptoms were treated with 20 μg/rat Bufexamac for 8 days. Cognitive function, depression, and anxiety were assessed through behavioral tests, while Western blotting, H&E staining, and ELISA were used to detect protein expression, morphological changes, and enzyme activity. Bufexamac treatment markedly improved cognitive and behavioral impairments in Aβ-injected rats and regulated the key proteins related to neuroinflammation (GFAP, Iba1), histone, and α-tubulin acetylation. Simultaneously, it decreased the expression of proteins in the stromal interaction molecule (STIM) pathway. Furthermore, Bufexamac lowered the activity of monoamine oxidase enzymes, elevated the count of healthy neurons, and ameliorated neuronal structure in the hippocampus. Overall, these findings suggest that Bufexamac could be a more targeted therapy for AD than other non-selective HDAC inhibitors, which often have diverse functions and potential side effects. Bufexamac enhances cognitive function and alleviates depression and anxiety by regulating proteins related to neuroinflammation, histone, and α-tubulin acetylation, as well as modulating STIM levels and MAO activity.

Development of Carbon-11 Labeled Pyrimidine Derivatives as Novel Positron Emission Tomography (PET) Agents Enabling Brain Sigma-1 Receptor Imaging

The sigma-1 receptor (σ1R) is a stress-activated chaperone protein that has emerged as a significant therapeutic target for neurodegenerative disorders. Developing effective positron emission tomography (PET) imaging probes targeting σ1R is crucial for visualizing its distribution and function in the brain, as well as facilitating related drug development. In this study, two novel 11C-labeled PET probes based on the structure of a potent σ1R ligand Lan-0101 are designed and synthesized. PET imaging studies in mice reveal that [11C]CNY-01 exhibits good brain uptake and binding specificity. Subsequent evaluation in non-human primates further demonstrates that [11C]CNY-01 displays favorable brain penetration, slow clearance kinetics, and characteristics of irreversible binding to its target in blockage experiments. To assess the clinical potential of the probe, both in vitro experiments and in vivo PET imaging using [11C]CNY-01 are conducted in Alzheimer's disease (AD) transgenic mouse models. These studies reveal a significant decrease in σ1R expression in the brain under conditions of AD amyloid pathology and microglial activation, highlighting the probe's sensitivity to disease-related receptor changes. This work establishes [11C]CNY-01 as a promising tool for investigating the relationship between σ1R and neurological disorders, potentially advancing the understanding of σ1R's role in disease pathophysiology and therapeutic interventions.

A Novel Histone Deacetylase 6 Inhibitor, 4-FHA, Improves Scopolamine-Induced Cognitive and Memory Impairment in Mice

Although histone deacetylase 6 (HDAC6) is considered a therapeutic target for Alzheimer's disease (AD), its role in cholinergic dysfunction in AD patients remains unclear. This study investigated the effects of (E)-3-(2-(4-fluorostyryl)thiazol-4-yl)-N-hydroxypropanamide (4-FHA), a new synthetic HDAC6 inhibitor, on cognitive and memory impairments in a scopolamine-induced-AD mouse model. Behaviorally, 4-FHA improved scopolamine-induced memory impairments in the Y-maze, passive avoidance, and Morris water maze tests. In addition, 4-FHA ameliorated scopolamine-induced cognitive impairments in the novel object recognition and place recognition tests. Furthermore, 4-FHA increased acetylation of α-tubulin (a major HDAC6 substrate); the expression of BDNF; and the phosphorylation of ERK 1/2, CREB, and ChAT in the hippocampus of scopolamine-treated mice. In summary, according to our data 4-FHA, an HDAC6 inhibitor, improved the cognitive and memory deficits of the AD mouse model by normalizing BDNF signaling and synaptic transmission, suggesting that 4-FHA might be a potential therapeutic candidate for AD.

Development of an 18F-labeled 5-aroylindole derivative for histone deacetylase 6 imaging in spinocerebellar ataxia

Histone deacetylase 6 (HDAC6) is an enzyme crucial in epigenetic regulation and protein degradation, with implications in various cancers and neurodegenerative disorders. While HDAC6 is recognized as a promising therapeutic target for Parkinson's and Alzheimer's diseases, its involvement in spinocerebellar ataxias (SCAs) remains underexplored. Currently, there are no direct methods available for characterizing HDAC6 in the brains of living subjects. Positron emission tomography (PET) techniques offer a noninvasive approach to visualize HDAC6, potentially enhancing our understanding of its neuropathological roles. In this study, we present the synthesis and PET imaging of [18F]3, an 18F-labeled 5-aroylindole derivative, which exhibits favorable affinity for HDAC6. The synthesis of [18F]3 was achieved through microwave-assisted radiofluorination of a nitro-precursor, followed by hydroxamic acid formation. PET studies using [18F]3 in SCA17 transgenic mice revealed significantly increased radioactivity in the brain compared to wild-type mice, particularly evident in the cerebellum and hippocampus. These findings warrant the potential utility of 18F-labeled 5-aroylindole derivatives as PET radioligands for HDAC6 neuroimaging and advocate for further exploration in structural optimization endeavors.

PET imaging assist investigation of HDAC6 expression change in MDD and evaluating antidepressant efficacy of a newly developed HDAC6 inhibitor

The histone deacetylase 6 (HDAC6) is closely related to the pathogenesis of depression in epigenetic regulation. However, it remains unclear how HDAC6 expression changes in depression pathophysiology and whether it is a target for antidepressant treatment. Herein, we investigate the expression change of HDAC6 in major depressive disorder (MDD) and evaluate the efficacy of a novel HDAC6 inhibitor, PB200, using positron emission tomography (PET) imaging. PET imaging studies with an HDAC6 PET probe [18F]Bavarostat allied with in vitro experiments demonstrated significantly increased HDAC6 expression in the brains of MDD mice. To investigate if pharmacological inhibition of HDAC6 can exert antidepressant effects, a series of naphthyridine-based HDAC6 inhibitors were designed and synthesized, among which PB200 demonstrated high selectivity and inhibitory activity against HDAC6, favorable metabolic stability, and excellent brain uptake. Moreover, PB200 exhibited significant antidepressant effects by restoring abnormal HDAC6 expression level and alleviating neuroinflammation. These results imply that targeting HDAC6 shows promise as a therapeutic strategy for depression, and PB200 is a potential therapeutic option for treating MDD.

Molecular Imaging Reveals Antineuroinflammatory Effects of HDAC6 Inhibition in Stroke Models

Ischemic stroke is a devastating disease that causes neuronal death, neuroinflammation, and other cerebral damage. However, effective therapeutic strategies for ischemic stroke are still lacking. Histone deacetylase 6 (HDAC6) has been implicated in the pathogenesis of ischemic stroke, and the pharmacological inhibition of HDAC6 has shown promising neuroprotective effects. In this study, we utilized positron emission tomography (PET) imaging with the HDAC6-specific radioligand [18F]PB118 to investigate the dynamic changes of HDAC6 expression in the brain after ischemic injury. The results revealed a significant decline in [18F]PB118 uptake in the ipsilateral hemisphere on the first day after ischemia, followed by a gradual increase on days 4 and 7. To evaluate the therapeutic potential of HDAC6 inhibitors, we developed a novel brain-permeable and potent HDAC6 inhibitor, PB131, and assessed its neuroprotective effects in an ischemic stroke mouse model. PET imaging studies demonstrated that PB131 treatment alleviated the decline in [18F]PB118 uptake and reduced the infarct size in middle cerebral artery occlusion mice. Furthermore, PET imaging with the TSPO-specific radioligand [18F]FEPPA revealed that PB131 significantly suppressed neuroinflammation in the ischemic brain. These findings provide insights into the dynamic changes of HDAC6 in ischemic stroke and the potential of HDAC6 inhibitors as novel therapeutic agents for this condition.

Design, synthesis and biological activity of oxyevodiamine-based histone deacetylase 6 inhibitors

Histone deacetylase 6 (HDAC6) was a potential target for Alzheimer's disease (AD). In this study, a series of novel oxyevodiamine-based HDAC6 inhibitors with a variety of linker moieties were designed, synthesized and evaluated. Compound 12 with a benzyl linker was identified as a high potent and selective HDAC6 inhibitor. It inhibited HDAC6 with an IC50 value of 6.2 nM and was more than 200 fold selectivity over HDAC1. It also had lower cytotoxicity and higher anti-H2O2 activity in vitro comparing with other derivatives. Compound 12 might be a good lead as novel HDAC6 inhibitor for the treatment of AD.

Multimechanism biological profiling of tetrahydro-β-carboline analogues as selective HDAC6 inhibitors for the treatment of Alzheimer's disease

With the intensive research on the pathogenesis of Alzheimer's disease (AD), inhibition of HDAC6 appears to be a potential therapeutic approach for AD. In this paper, a series of tetrahydro-β-carboline derivatives with hydroxamic acid group were fast synthesized. Among all, the most potent 15 selectively inhibited HDAC6 with IC50 of 15.2 nM and markedly increased acetylated alpha-tubulin levels. In cellular assay, 15 showed excellent neurotrophic effect by increasing the expression of GAP43 and Beta-3 tubulin markers. Besides, 15 showed neuroprotective effects in PC12 or SH-SY5Y cells against H2O2 and 6-OHDA injury through activation of Nrf2, catalase and Prx II, and significantly reduced H2O2-induced reactive oxygen species (ROS) production. In vivo, 15 significantly attenuated zebrafish anxiety-like behaviour and memory deficits in a SCOP-induced zebrafish model of AD. To sum up, multifunctional 15 might be a good lead to develop novel tetrahydrocarboline-based agents for the treatment of AD.

Therapeutic indications for HDAC6 inhibitors in the peripheral and central nervous disorders

INTRODUCTION

Inhibition of the enzymatic function of HDAC6 is currently being explored in clinical trials ranging from peripheral neuropathies to cancers. Advances in selective HDAC6 inhibitor discovery allowed studying highly efficacious brain penetrant and peripheral restrictive compounds for treating PNS and CNS indications.

AREAS COVERED

This review explores the multifactorial role of HDAC6 in cells, the common pathological hallmarks of PNS and CNS disorders, and how HDAC6 modulates these mechanisms. Pharmacological inhibition of HDAC6 and genetic knockout/knockdown studies as a therapeutic strategy in PNS and CNS indications were analyzed. Furthermore, we describe the recent developments in HDAC6 PET tracers and their utility in CNS indications. Finally, we explore the advancements and challenges with HDAC6 inhibitor compounds, such as hydroxamic acid, fluoromethyl oxadiazoles, HDAC6 degraders, and thiol-based inhibitors.

EXPERT OPINION

Based on extensive preclinical evidence, pharmacological inhibition of HDAC6 is a promising approach for treating both PNS and CNS disorders, given its involvement in neurodegeneration and aging-related cellular processes. Despite the progress in the development of selective HDAC6 inhibitors, safety concerns remain regarding their chronic administration in PNS and CNS indications, and the development of novel compound classes and modalities inhibiting HDAC6 function offer a way to mitigate some of these safety concerns.

Development of a New Positron Emission Tomography Imaging Radioligand Targeting RIPK1 in the Brain and Characterization in Alzheimer's Disease

Targeting receptor-interacting protein kinase 1 (RIPK1) has emerged as a promising therapeutic stratagem for neurodegenerative disorders, particularly Alzheimer's disease (AD). A positron emission tomography (PET) probe enabling brain RIPK1 imaging can provide a powerful tool to unveil the neuropathology associated with RIPK1. Herein, the development of a new PET radioligand, [11C]CNY-10 is reported, which may enable brain RIPK1 imaging. [11C]CNY-10 is radiosynthesized with a high radiochemical yield (41.8%) and molar activity (305 GBq/µmol). [11C]CNY-10 is characterized by PET imaging in rodents and a non-human primate, demonstrating good brain penetration, binding specificity, and a suitable clearance kinetic profile. It is performed autoradiography of [11C]CNY-10 in human AD and healthy control postmortem brain tissues, which shows strong radiosignal in AD brains higher than healthy controls. Subsequently, it is conducted further characterization of RIPK1 in AD using [11C]CNY-10-based PET studies in combination with immunohistochemistry leveraging the 5xFAD mouse model. It is found that AD mice revealed RIPK1 brain signal significantly higher than WT control mice and that RIPK1 is closely related to amyloid plaques in the brain. The studies enable further translational studies of [11C]CNY-10 for AD and potentially other RIPK1-related human studies.

HDAC6 modulates the cognitive behavioral function and hippocampal tissue pathological changes of APP/PS1 transgenic mice through HSP90-HSF1 pathway

The aim of this study was to investigate histone deacetylase 6 (HDAC6) modifies the heat shock protein 90 (HSP90) and heat shock transcription factor 1 (HSF1) affect the levels of pathological markers such as Aβ oligomers (Aβo) and Tau phosphorylation (p-Tau) in APP/PS1 double transgenic mice hippocampal tissues or HT22 neurons as well as the changes in cognitive behavioral functions of mice. (1) APP/PS1 transgenic mice (6 months old, 25 ~ 30 g) were randomly assigned to 5 experimental groups, C57BL/6J mice (6 months old, 25 ~ 30 g) were used as 4 control groups, with 8 mice in each group. All mice underwent intracerebroventricular (i.c.v.) cannulation, and the experimental groups were administered with normal saline (APP + NS group), HDAC6 agonist tubastatin A hydrochloride (TSA) (APP + TSA group) or HDAC6 agonist theophylline (Theo) (APP + Theo group), HSP90 inhibitor Ganetespib (Gane) (APP + Gane group), or a combination of pre-injected Gane by TSA (APP + Gane + TSA group); the control group received i.c.v. injections of Gane (Gane group), TSA (TSA group), Theo (Theo group) or NS (NS group), respectively. (2) Mouse hippocampal neurons HT22 were randomly divided into a control group (Control) and an Aβ1-42 intervention group (Aβ). Within the Aβ group, further divisions were made for knockdown HSP90 (Aβ + siHSP90 group), overexpression HSP90 (Aβ + OE-HSP90 group), knockdown HSF1(Aβ + siHSF1 group) and knockdown HSF1 followed by overexpression HSP90 (Aβ + siHSF1 + OE-HSP90 group), resulting in a total of 6 groups. Morris water maze test was used to evaluate the cognitive behavior of the mice. Western blot and immunohistochemistry or immunofluorescence were performed to detect the levels of HDAC6, HSP90, HSF1, Aβ1-42, Tau protein, and p-Tau in the hippocampal tissue or HT22 cells. qRT-PCR was used to measure the levels of hdac6, hsp90, and hsf1 mRNA in the hippocampus or nerve cells. (1) The levels of HDAC6, Aβ1-42 and p-Tau were elevated, while HSP90 and HSF1 were decreased in the hippocampal tissue of APP/PS1 transgenic mice (all P < 0.01). Inhibiting HDAC6 upregulated the expressions of HSP90 and HSF1 in the hippocampal tissue of APP/PS1 mice, while decreasing the levels of Aβ1-42 and p-Tau as well as improving the spatial cognitive behavior in mice (P < 0.05 or P < 0.01). The opposite effects were observed upon HDAC6 activation. However, inhibiting HSP90 reduced the expression of HSF1 (P < 0.01) and increased the levels of Aβ1-42 and p-Tau (P < 0.05 or P < 0.01) but did not significantly affect the expression of HDAC6 (P > 0.05). No significant changes were observed in the aforementioned indicators in the 4 control groups (P > 0.05). (2) In the Aβ1-42 intervention group, HDAC6 and Aβ1-42, p-Tau expression levels were elevated, while HSP90 and HSF1 expressions were all decreased, and cell viability was reduced (P < 0.05 or P < 0.01). Overexpression of HSP90 upregulated HSF1 expression, decreased the levels of Aβ1-42 and p-Tau, and increased cell viability (P < 0.05 or P < 0.01). Knocking down HSP90 had the opposite effect; and knocking down HSF1 increased the levels of Aβ1-42 and p-Tau and decreased cells viability (all P < 0.01), but did not result in significant changes in the expression levels of HSP90 (P > 0.05). Inhibiting HDAC6 can upregulate the expressions of HSP90 and HSF1 but reduce the levels of Aβ1-42 and p-Tau in the hippocampus of APP/PS1 mice and improvement of cognitive behavioral function in mice; Overexpression of HSP90 can increase HSF1 but decrease Aβ1-42 and p-Tau levels in the hippocampal neurons and increase cell activity. It is suggested that HDAC6 may affect the formation of Aβ oligomers and the changes in Tau protein phosphorylation levels in the hippocampus of AD transgenic mouse as well as the alterations in cognitive behavioral functions by regulating the HSP90-HSF1 pathway.

Preclinical validation of a novel brain-penetrant PET ligand for visualization of histone deacetylase 6: a potential imaging target for neurodegenerative diseases

PURPOSE

Histone deacetylase 6 (HDAC6) has emerged as a therapeutic target for neurodegenerative diseases such as Alzheimer's disease. Noninvasive imaging of HDAC6 in the brain by positron emission tomography (PET) would accelerate research into its roles in these diseases. We recently discovered an 18F-labeled derivative of the selective HDAC6 inhibitor SW-100 ([18F]FSW-100) as a potential candidate for brain HDAC6 radioligand. As a mandatory step prior to clinical translation, we performed preclinical validation of [18F]FSW-100.

METHODS

Process validation of [18F]FSW-100 radiosynthesis for clinical use and assessment of preclinical toxicity and radiation dosimetry estimated from mouse distribution data were performed. In vitro selectivity of FSW-100 for 28 common receptors in the brain and HDAC isoforms was characterized. [18F]FSW-100 PET imaging was performed in non-human primates in a conscious state to estimate the feasibility of HDAC6 imaging in humans.

RESULTS

Three consecutive validation runs of the automated radiosynthesis gave [18F]FSW-100 injections with radiochemical yields of 12%, and the injections conformed to specified quality control criteria for batch release. No acute toxicity was observed for non-radiolabeled FSW-100 or radioactivity decayed [18F]FSW-100 injection, and the former was negative in the Ames test. The whole-body effective dose estimated from biodistribution in mice was within the range of that of previously reported 18F-radioligands in humans. In vitro selectivity against common receptors and other HDAC isoforms was confirmed. [18F]FSW-100 demonstrated good penetration in monkey brain, and in vivo blocking studies suggested that the uptake was specific.

CONCLUSION

These results support the clinical utility of [18F]FSW-100 for in vivo imaging of HDAC6 in the brain.

Role of histone modifications in neurogenesis and neurodegenerative disease development

Progressive neuronal dysfunction and death are key features of neurodegenerative diseases; therefore, promoting neurogenesis in neurodegenerative diseases is crucial. With advancements in proteomics and high-throughput sequencing technology, it has been demonstrated that histone post-transcriptional modifications (PTMs) are often altered during neurogenesis when the brain is affected by disease or external stimuli and that the degree of histone modification is closely associated with the development of neurodegenerative diseases. This review aimed to show the regulatory role of histone modifications in neurogenesis and neurodegenerative diseases by discussing the changing patterns and functional significance of histone modifications, including histone methylation, acetylation, ubiquitination, phosphorylation, and lactylation. Finally, we explored the control of neurogenesis and the development of neurodegenerative diseases by artificially modulating histone modifications.

Step-by-step optimisation of the radiosynthesis of the brain HDAC6 radioligand [18F]FSW-100 for clinical applications

BACKGROUND

Histone deacetylase 6 (HDAC6) is an emerging target for the treatment and diagnosis of proteinopathies. [18F]FSW-100 was recently developed as a promising brain-penetrating radioligand for HDAC6 PET imaging and the process validation of [18F]FSW-100 radiosynthesis for clinical use is complete, but no detailed synthetic strategy nor process optimisation has been reported. Here, we describe the optimisation of several processes in [18F]FSW-100 radiosynthesis, including the 18F-fluorination reaction, semipurification of the 18F-intermediate, and purification of the product by high-performance liquid chromatography (HPLC), to achieve a radiochemical yield (RCY) adequate for clinical applications of the radioligand. Our findings will aid optimisation of radiosynthesis processes in general.

RESULTS

In the 18F-fluorination reaction, the amount of copper reagent was reduced without reducing the nonisolated RCY of the intermediate (50%), thus reducing the risk of copper contamination in the product injection solution. Optimising the solid-phase extraction (SPE) conditions for semipurification of the intermediate improved its recovery efficiency. The addition of anti-radiolysis reagents to the mobile phase for the HPLC purification of [18F]FSW-100 increased its activity yield in radiosynthesis using a high [18F]fluoride radioactivity of approximately 50 GBq. The SPE-based formulation method and additives for the injection solution were optimised, and the resulting [18F]FSW-100 injection solution was stable for over 2 h with a radiochemical purity of greater than 95%.

CONCLUSIONS

Of all the reconsidered processes, we found that optimisation of the SPE-based semipurification of the intermediate and of the mobile phase for HPLC purification in particular improved the RCY of [18F]FSW-100, doubling it compared to that of the original protocol. The radioactivity of [18F]FSW-100 synthesized using the optimized protocol was sufficient for multiple doses for a clinical study.

Molecular Imaging of Alzheimer's Disease-Related Sigma-1 Receptor in the Brain a Novel Ru-Mediated Aromatic 18F-deoxyfluorination Probe

Sigma-1 receptor (σ1R) is an intracellular protein implicated in a spectrum of neurodegenerative conditions, notably Alzheimer's disease (AD). Positron emission tomography (PET) imaging of brain σ1R could provide a powerful tool for better understanding the underlying pathomechanism of σ1R in AD. In this study, we successfully developed a 18F-labeled σ1R radiotracer [18F]CNY-05 via an innovative ruthenium (Ru)-mediated 18F-deoxyfluorination method. [18F]CNY-05 exhibited preferable brain uptake, high specific binding, and slightly reversible pharmacokinetics within the PET scanning time window. PET imaging of [18F]CNY-05 in nonhuman primates (NHP) indicated brain permeability, metabolic stability, and safety. Moreover, autoradiography and PET studies of [18F]CNY-05 in the AD mouse model found a significantly decreased brain uptake compared to that in wild-type mice. Collectively, we have provided a novel 18F-radiolabeled σ1R PET probe, which enables visualizing brain σ1R in health and neurological diseases.

Design and Discovery of Novel NLRP3 Inhibitors and PET Imaging Radiotracers Based on a 1,2,3-Triazole-Bearing Scaffold

The NOD-like receptor (NLR) family pyrin-domain-containing 3 (NLRP3) inflammasome, an essential component of the innate immune system, has been emerging as a viable drug target and a potential biomarker for human diseases. In our efforts to develop novel small molecule NLRP3 inhibitors, a 1-(5-chloro-2-methoxybenzyl)-4-phenyl-1H-1,2,3-triazole scaffold was designed via a rational approach based on our previous leads. Structure-activity relationship studies and biophysical studies identified a new lead compound 8 as a potent (IC50: 0.55 ± 0.16 μM), selective, and direct NLRP3 inhibitor. Positron emission tomography (PET) imaging studies of [11C]8 demonstrated its rapid and high brain uptake as well as fast washout in mice and rhesus macaque. Notably, plasma kinetic analysis of this radiotracer from the PET/magnetic resonance imaging studies in rhesus macaque suggested radiometabolic stability. Collectively, our data not only encourage further studies of this lead compound but also warrant further optimization to generate additional novel NLRP3 inhibitors and suitable central nervous system PET radioligands with translational promise.

Structure-Based Discovery of A Small Molecule Inhibitor of Histone Deacetylase 6 (HDAC6) that Significantly Reduces Alzheimer's Disease Neuropathology

Histone deacetylase 6 (HDAC6) is one of the key histone deacetylases (HDACs) that regulates various cellular functions including clearance of misfolded protein and immunological responses. Considerable evidence suggests that HDAC6 is closely related to amyloid and tau pathology, the two primary hallmarks of Alzheimer's disease (AD). It is still unclear whether HDAC6 expression changes with amyloid deposition in AD during disease progression or HDAC6 may be regulating amyloid phagocytosis or neuroinflammation or other neuropathological changes in AD. In this work, the pathological accumulation of HDAC6 in AD brains over age as well as the relationship of its regulatory activity - with amyloid pathogenesis and pathophysiological alterations is aimed to be enlightened using the newly developed HDAC6 inhibitor (HDAC6i) PB118 in microglia BV2 cell and 3D-AD human neural culture model. Results suggest that the structure-based rational design led to biologically compelling HDAC6i PB118 with multiple mechanisms that clear Aβ deposits by upregulating phagocytosis, improve tubulin/microtubule network by enhancing acetyl α-tubulin levels, regulate different cytokines and chemokines responsible for inflammation, and significantly reduce phospho-tau (p-tau) levels associated with AD. These findings indicate that HDAC6 plays key roles in the pathophysiology of AD and potentially serves as a suitable pharmacological target through chemical biology-based drug discovery in AD.

Development and Pharmacochemical Characterization Discover a Novel Brain-Permeable HDAC11-Selective Inhibitor with Therapeutic Potential by Regulating Neuroinflammation in Mice

Recent studies have shown that the epigenetic protein histone deacetylase 11 (HDAC11) is highly expressed in the brain and critically modulates neuroimmune functions, making it a potential therapeutic target for neurological disorders. Herein, we report the development of PB94, which is a novel HDAC11 inhibitor. PB94 exhibited potency and selectivity against HDAC11 with IC50 = 108 nM and >40-fold selectivity over other HDAC isoforms. Pharmacokinetic/pharmacodynamic evaluation indicated that PB94 possesses promising drug-like properties. Additionally, PB94 was radiolabeled with carbon-11 as [11C]PB94 for positron emission tomography (PET), which revealed significant brain uptake and metabolic properties suitable for drug development in live animals. Furthermore, we demonstrated that neuropathic pain was associated with brain upregulation of HDAC11 and that pharmacological inhibition of HDAC11 by PB94 ameliorated neuropathic pain in a mouse model. Collectively, our findings support further development of PB94 as a selective HDAC11 inhibitor for neurological indications, including pain.

Phenylacetyl-/Trolox- Amides: Synthesis, Sigma-1, HDAC-6, and Antioxidant Activities

In search of novel multi-mechanistic approaches for treating Alzheimer's disease (AD), we have embarked on synthesizing single small molecules for probing contributory roles of the following combined disease targets: sigma-1 (σ-1), class IIb histone deacetylase-6 (HDAC-6), and oxidative stress (OS). Herein, we report the synthesis and partial evaluation of 20 amides (i.e., phenylacetic and Trolox or 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid derivatives). Target compounds were conveniently synthesized via amidation by either directly reacting acyl chlorides with amines or condensing acids with amines in the presence of coupling agents 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b] pyridinium 3-oxide hexafluorophosphate (HATU) or 1,1'-carbonyldiimidazole (CDI). Overall, this project afforded compound 8 as a promising lead with σ-1 affinity (Ki = 2.1 μM), HDAC-6 (IC50 = 17 nM), and antioxidant (1.92 Trolox antioxidant equivalents or TEs) activities for optimization in ensuing structure-activity relationship (SAR) studies.

Deciphering the Mysterious Relationship between the Cross-Pathogenetic Mechanisms of Neurodegenerative and Oncological Diseases

The relationship between oncological pathologies and neurodegenerative disorders is extremely complex and is a topic of concern among a growing number of researchers around the world. In recent years, convincing scientific evidence has accumulated that indicates the contribution of a number of etiological factors and pathophysiological processes to the pathogenesis of these two fundamentally different diseases, thus demonstrating an intriguing relationship between oncology and neurodegeneration. In this review, we establish the general links between three intersecting aspects of oncological pathologies and neurodegenerative disorders, i.e., oxidative stress, epigenetic dysregulation, and metabolic dysfunction, examining each process in detail to establish an unusual epidemiological relationship. We also focus on reviewing the current trends in the research and the clinical application of the most promising chemical structures and therapeutic platforms that have a modulating effect on the above processes. Thus, our comprehensive analysis of the set of molecular determinants that have obvious cross-functional pathways in the pathogenesis of oncological and neurodegenerative diseases can help in the creation of advanced diagnostic tools and in the development of innovative pharmacological strategies.

Blood tau-PT217 contributes to the anesthesia/surgery-induced delirium-like behavior in aged mice

INTRODUCTION

Blood phosphorylated tau at threonine 217 (tau-PT217) is a newly established biomarker for Alzheimer's disease and postoperative delirium in patients. However, the mechanisms and consequences of acute changes in blood tau-PT217 remain largely unknown.

METHODS

We investigated the effects of anesthesia/surgery on blood tau-PT217 in aged mice, and evaluated the associated changes in B cell populations, neuronal excitability in anterior cingulate cortex, and delirium-like behavior using positron emission tomography imaging, nanoneedle technology, flow cytometry, electrophysiology, and behavioral tests.

RESULTS

Anesthesia/surgery induced acute increases in blood tau-PT217 via enhanced generation in the lungs and release from B cells. Tau-PT217 might cross the blood-brain barrier, increasing neuronal excitability and inducing delirium-like behavior. B cell transfer and WS635, a mitochondrial function enhancer, mitigated the anesthesia/surgery-induced changes.

DISCUSSION

Acute increases in blood tau-PT217 may contribute to brain dysfunction and postoperative delirium. Targeting B cells or mitochondrial function may have therapeutic potential for preventing or treating these conditions.

Design, synthesis, and anti-inflammatory activity characterization of novel brain-permeable HDAC6 inhibitors

Targeting histone deacetylase 6 (HDAC6) has emerged as a promising therapeutic approach for anti-inflammation and related biological pathways, including inflammatory events associated with the brain. In this study, in order to develop brain-permeable HDAC6 inhibitors for anti-neuroinflammation, we report here the design, synthesis, and characterization of a number of N-heterobicyclic analogues that can inhibit HDAC6 with high specificity and strong potency. Among our analogues, PB131 exhibits potent binding affinity and selectivity against HDAC6, with an IC50 value of 1.8 nM and more than 116-fold selectivity over other HDAC isoforms. In addition, PB131 shows good brain penetration, binding specificity, and reasonable biodistribution through our positron emission tomography (PET) imaging studies of [18F]PB131 in mice. Furthermore, we characterized the efficacy of PB131 on regulating neuroinflammation using the mouse microglia model BV2 cells in vitro and the LPS-induced inflammation mouse model in vivo. These data not only indicate the anti-inflammatory activity of our novel HDAC6 inhibitor PB131, but also strengthen the biological functions of HDAC6 and further extend the therapeutic approach inhibiting HDAC6. Our findings show that PB131 displays good brain permeability, high specificity, and strong potency toward inhibiting HDAC6 and is a potential HDAC6 inhibitor for inflammation-related disease treatment, especially neuroinflammation.

Elaboration of the Effective Multi-Target Therapeutic Platform for the Treatment of Alzheimer's Disease Based on Novel Monoterpene-Derived Hydroxamic Acids

Novel monoterpene-based hydroxamic acids of two structural types were synthesized for the first time. The first type consisted of compounds with a hydroxamate group directly bound to acyclic, monocyclic and bicyclic monoterpene scaffolds. The second type included hydroxamic acids connected with the monoterpene moiety through aliphatic (hexa/heptamethylene) or aromatic linkers. An in vitro analysis of biological activity demonstrated that some of these molecules had powerful HDAC6 inhibitory activity, with the presence of a linker area in the structure of compounds playing a key role. In particular, it was found that hydroxamic acids containing a hexa- and heptamethylene linker and (-)-perill fragment in the Cap group exhibit excellent inhibitory activity against HDAC6 with IC₅₀ in the submicromolar range from 0.56 ± 0.01 µM to 0.74 ± 0.02 µM. The results of the study of antiradical activity demonstrated the presence of moderate ability for some hydroxamic acids to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2ROO^• radicals. The correlation coefficient between the DPPH radical scavenging activity and oxygen radical absorbance capacity (ORAC) value was R² = 0.8400. In addition, compounds with an aromatic linker based on para-substituted cinnamic acids, having a monocyclic para-menthene skeleton as a Cap group, 35a, 38a, 35b and 38b, demonstrated a significant ability to suppress the aggregation of the pathological β-amyloid peptide 1-42. The 35a lead compound with a promising profile of biological activity, discovered in the in vitro experiments, demonstrated neuroprotective effects on in vivo models of Alzheimer's disease using 5xFAD transgenic mice. Together, the results obtained demonstrate a potential strategy for the use of monoterpene-derived hydroxamic acids for treatment of various aspects of Alzheimer's disease.

Microtubule acetylation dyshomeostasis in Parkinson's disease

The inter-neuronal communication occurring in extensively branched neuronal cells is achieved primarily through the microtubule (MT)-mediated axonal transport system. This mechanistically regulated system delivers cargos (proteins, mRNAs and organelles such as mitochondria) back and forth from the soma to the synapse. Motor proteins like kinesins and dynein mechanistically regulate polarized anterograde (from the soma to the synapse) and retrograde (from the synapse to the soma) commute of the cargos, respectively. Proficient axonal transport of such cargos is achieved by altering the microtubule stability via post-translational modifications (PTMs) of α- and β-tubulin heterodimers, core components constructing the MTs. Occurring within the lumen of MTs, K40 acetylation of α-tubulin via α-tubulin acetyl transferase and its subsequent deacetylation by HDAC6 and SIRT2 are widely scrutinized PTMs that make the MTs highly flexible, which in turn promotes their lifespan. The movement of various motor proteins, including kinesin-1 (responsible for axonal mitochondrial commute), is enhanced by this PTM, and dyshomeostasis of neuronal MT acetylation has been observed in a variety of neurodegenerative conditions, including Alzheimer's disease and Parkinson's disease (PD). PD is the second most common neurodegenerative condition and is closely associated with impaired MT dynamics and deregulated tubulin acetylation levels. Although the relationship between status of MT acetylation and progression of PD pathogenesis has become a chicken-and-egg question, our review aims to provide insights into the MT-mediated axonal commute of mitochondria and dyshomeostasis of MT acetylation in PD. The enzymatic regulators of MT acetylation along with their synthetic modulators have also been briefly explored. Moving towards a tubulin-based therapy that enhances MT acetylation could serve as a disease-modifying treatment in neurological conditions that lack it.

Abdallah M, M. Mukhtar R, Moutasim F, Rafie Ahmed A, Edris A, Ibraheem W, Makki AA, M. Elshamly E, Elhag R, Osman W, A. Mothana R, Alzain AA. Identification of Novel Natural Dual HDAC and Hsp90 Inhibitors for Metastatic TNBC Using e-Pharmacophore Modeling, Molecular Docking, and Molecular Dynamics Studies

Breast cancer (BC) is one of the main types of cancer that endangers women's lives. The characteristics of triple-negative breast cancer (TNBC) include a high rate of recurrence and the capacity for metastasis; therefore, new therapies are urgently needed to combat TNBC. Dual targeting HDAC6 and Hsp90 has shown good synergistic effects in treating metastatic TNBC. The goal of this study was to find potential HDAC6 and Hsp90 dual inhibitors. Therefore, several in silico approaches have been used. An e-pharmacophore model generation based on the HDAC6-ligand complex and subsequently a pharmacophore-based virtual screening on 270,450 natural compounds from the ZINC were performed, which resulted in 12,663 compounds that corresponded to the obtained pharmacophoric hypothesis. These compounds were docked into HDAC6 and Hsp90. This resulted in the identification of three compounds with good docking scores and favorable free binding energy against the two targets. The top three compounds, namely ZINC000096116556, ZINC000020761262, and ZINC000217668954, were further subjected to ADME prediction and molecular dynamic simulations, which showed promising results in terms of pharmacokinetic properties and stability. As a result, these three compounds can be considered potential HDAC6 and Hsp90 dual inhibitors and are recommended for experimental evaluation.