JNK Inhibition Protects Dopamine Neurons and Provides Behavioral Improvement in a Rat 6-hydroxydopamine Model of Parkinson's Disease

IRE1/JNK Is the Leading UPR Pathway in 6-OHDA-Induced Degeneration of Differentiated SH-SY5Y Cells

Parkinson's disease (PD) is a neurodegenerative disorder which affects dopaminergic neurons of the midbrain. Accumulation of α-synuclein or exposure to neurotoxins like 6-hydroxydopamine (6-OHDA) induces endoplasmic reticulum (ER) stress along with the unfolded protein response (UPR), which executes apoptosis via activation of PERK/CHOP or IRE1/JNK signaling. The present study aimed to determine which of these pathways is a major contributor to neurodegeneration in an 6-OHDA-induced in vitro model of PD. For this purpose, we have applied pharmacological PERK and JNK inhibitors (AMG44 and JNK V) in differentiated SH-SY5Y cells exposed to 6-OHDA. Inhibition of PERK and JNK significantly decreased genotoxicity and improved mitochondrial respiration, but only JNK inhibition significantly increased cell viability. Gene expression analysis revealed that the effect of JNK inhibition was dependent on a decrease in MAPK10 and XBP1 mRNA levels, whereas inhibition of either PERK or JNK significantly reduced the expression of DDIT3 mRNA. Western blot has shown that JNK inhibition strongly induced the XBP1s protein, and inhibition of each pathway attenuated the phosphorylation of eIF2α and JNK, as well as the expression of CHOP. Collectively, our data suggests that targeting the IRE1/JNK pathway of the UPR is a more effective option for PD treatment as it simultaneously affects more than one pro-apoptotic pathway.

Practical Three-Component Regioselective Synthesis of Drug-Like 3-Aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines as Potential Non-Covalent Multi-Targeting Inhibitors To Combat Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are one of the prominent health challenges facing contemporary society, and many efforts have been made to overcome and (or) control it. In this research paper, we described a practical one-pot two-step three-component reaction between 3,4-dihydronaphthalen-1(2H)-one (1), aryl(or heteroaryl)glyoxal monohydrates (2a-h), and hydrazine monohydrate (NH2NH2•H2O) for the regioselective preparation of some 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnoline derivatives (3a-h). After synthesis and characterization of the mentioned cinnolines (3a-h), the in silico multi-targeting inhibitory properties of these heterocyclic scaffolds have been investigated upon various Homo sapiens-type enzymes, including hMAO-A, hMAO-B, hAChE, hBChE, hBACE-1, hBACE-2, hNQO-1, hNQO-2, hnNOS, hiNOS, hPARP-1, hPARP-2, hLRRK-2(G2019S), hGSK-3β, hp38α MAPK, hJNK-3, hOGA, hNMDA receptor, hnSMase-2, hIDO-1, hCOMT, hLIMK-1, hLIMK-2, hRIPK-1, hUCH-L1, hPARK-7, and hDHODH, which have confirmed their functions and roles in the neurodegenerative diseases (NDs), based on molecular docking studies, and the obtained results were compared with a wide range of approved drugs and well-known (with IC50, EC50, etc.) compounds. In addition, in silico ADMET prediction analysis was performed to examine the prospective drug properties of the synthesized heterocyclic compounds (3a-h). The obtained results from the molecular docking studies and ADMET-related data demonstrated that these series of 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines (3a-h), especially hit ones, can really be turned into the potent core of new drugs for the treatment of neurodegenerative diseases (NDs), and/or due to the having some reactionable locations, they are able to have further organic reactions (such as cross-coupling reactions), and expansion of these compounds (for example, with using other types of aryl(or heteroaryl)glyoxal monohydrates) makes a new avenue for designing novel and efficient drugs for this purpose.

Physiological JNK3 Concentrations Are Higher in Motor-related and Disease-implicated Brain Regions of C57BL6/J Mice

The c-Jun N-terminal kinase 3 (JNK3) is a stress-responsive protein kinase primarily expressed in the central nervous system (CNS). JNK3 exhibits nuanced neurological activities, such as roles in behavior, circadian rhythms, and neurotransmission, but JNK3 is also implicated in cell death and neurodegeneration. Despite the critical role of JNK3 in neurophysiology and pathology, its localization in the brain is not fully understood due to a paucity of tools to distinguish JNK3 from other isoforms. While previous functional and histological studies suggest locales for JNK3 in the CNS, a comprehensive and higher resolution of JNK3 distribution and abundance remained elusive. Here, we sought to define the anatomical and cellular distribution of JNK3 in adult mouse brains. Data reveal the highest levels of JNK3 and pJNK3 were found in the cortex and the hippocampus. JNK3 possessed neuron-type selectivity as JNK3 was present in GABAergic, cholinergic, and dopaminergic neurons, but was not detectable in VGLUT-1-positive glutamatergic neurons and astrocytes in vivo . Intriguingly, higher JNK3 signals were found in motor neurons and relevant nuclei in the cortex, basal ganglia, brainstem, and spinal cord. While JNK3 was primarily observed in the cytosol of neurons in the cortex and the hippocampus, JNK3 appeared commonly within the nucleus in the brainstem. These distinctions suggest the potential for significant differences between JNK3 actions in distinct brain regions and cell types. Our results provide a significant improvement over previous reports of JNK3 spatial organization in the adult CNS and support continued investigation of JNK3's role in neurophysiology and pathophysiology.

Phosphodiesterase-4 Inhibition in Parkinson's Disease: Molecular Insights and Therapeutic Potential

Clinicians and researchers are exploring safer and novel treatment strategies for treating the ever-prevalent Parkinson's disease (PD) across the globe. Several therapeutic strategies are used clinically for PD, including dopamine replacement therapy, DA agonists, MAO-B blockers, COMT blockers, and anticholinergics. Surgical interventions such as pallidotomy, particularly deep brain stimulation (DBS), are also employed. However, they only provide temporal and symptomatic relief. Cyclic adenosine monophosphate (cAMP) is one of the secondary messengers involved in dopaminergic neurotransmission. Phosphodiesterase (PDE) regulates cAMP and cGMP intracellular levels. PDE enzymes are subdivided into families and subtypes which are expressed throughout the human body. PDE4 isoenzyme- PDE4B subtype is overexpressed in the substantia nigra of the brain. Various studies have implicated multiple cAMP-mediated signaling cascades in PD, and PDE4 is a common link that can emerge as a neuroprotective and/or disease-modifying target. Furthermore, a mechanistic understanding of the PDE4 subtypes has provided perceptivity into the molecular mechanisms underlying the adverse effects of phosphodiesterase-4 inhibitors (PDE4Is). The repositioning and development of efficacious PDE4Is for PD have gained much attention. This review critically assesses the existing literature on PDE4 and its expression. Specifically, this review provides insights into the interrelated neurological cAMP-mediated signaling cascades involving PDE4s and the potential role of PDE4Is in PD. In addition, we discuss existing challenges and possible strategies for overcoming them.

Discovery of Novel Indazole Chemotypes as Isoform-Selective JNK3 Inhibitors for the Treatment of Parkinson's Disease

c-Jun N-terminal kinases (JNKs) are involved in the pathogenesis of various diseases. In particular, JNK3 and not JNK1/2 is primarily expressed in the brain and plays a key role in mediating neurodegenerative diseases like Parkinson's disease (PD). Due to the sequence similarity of JNK isoforms, developing isoform-selective JNK3 inhibitors to evaluate their biological functions and therapeutic potential in PD has become a challenge. Herein, docking-based virtual screening and structure-activity relationship studies identified 25c with excellent inhibitory activity against JNK3 (IC₅₀ = 85.21 nM) and exhibited an over 100-fold isoform selectivity for JNK3 over JNK1/2 and remarkable kinase selectivity. 25c showed neuroprotective effects on in vitro and in vivo PD models by selectively inhibiting JNK3. Meanwhile, 25c showed an ideal blood-brain barrier permeability and low toxicity. Overall, this study provided a valuable molecular tool for investigating the role of JNK3 in PD and a solid foundation for developing JNK3-targeted drugs in PD treatment.

Neuroprotective Effects of the DPP4 Inhibitor Vildagliptin in In Vivo and In Vitro Models of Parkinson's Disease

Parkinson’s disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the midbrain. Restoration of nigrostriatal dopamine neurons has been proposed as a potential therapeutic strategy for PD. Because currently used PD therapeutics only help relieve motor symptoms and do not treat the cause of the disease, highly effective drugs are needed. Vildagliptin, a dipeptidyl peptidase 4 (DPP4) inhibitor, is an anti-diabetic drug with various pharmacological properties including neuroprotective effects. However, the detailed effects of vildagliptin against PD are not fully understood. We investigated the effects of vildagliptin on PD and its underlying molecular mechanisms using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model and a 1-methyl-4-phenylpyridium (MPP⁺)-induced cytotoxicity model. Vildagliptin (50 mg/kg) administration significantly attenuated MPTP-induced motor deficits as evidenced by rotarod, pole, and nest building tests. Immunohistochemistry and Western blot analysis revealed that vildagliptin increased tyrosine hydroxylase-positive cells in the SNpc and striatum, which was reduced by MPTP treatment. Furthermore, vildagliptin activated MPTP-decreased PI3k/Akt and mitigated MPTP-increased ERK and JNK signaling pathways in the striatum. Consistent with signaling transduction in the mouse striatum, vildagliptin reversed MPP⁺-induced dephosphorylation of PI3K/Akt and phosphorylation of ERK and JNK in SH-SY5Y cells. Moreover, vildagliptin attenuated MPP⁺-induced conversion of LC3B-II in SH-SY5Y cells, suggesting its role in autophagy inhibition. Taken together, these findings indicate that vildagliptin has protective effects against MPTP-induced motor dysfunction by inhibiting dopaminergic neuronal apoptosis, which is associated with regulation of PI3k/Akt, ERK, and JNK signaling transduction. Our findings suggest vildagliptin as a promising repurposing drug to treat PD.

Fluorescent probes for bioimaging of potential biomarkers in Parkinson's disease

This review comprehensively summarizes various types of fluorescent probes for PD and their applications for detection of various PD biomarkers.

Thiophene-Pyrazolourea Derivatives as Potent, Orally Bioavailable, and Isoform-Selective JNK3 Inhibitors

Potent JNK3 isoform selective inhibitors were developed from a thiophenyl-pyrazolourea scaffold. Through structure activity relationship (SAR) studies utilizing enzymatic and cell-based assays, and in vitro and in vivo drug metabolism and pharmacokinetic (DMPK) studies, potent and highly selective JNK3 inhibitors with oral bioavailability and brain penetrant capability were developed. Inhibitor 17 was a potent and isoform selective JNK3 inhibitor (IC₅₀ = 35 nM), had significant inhibition to only JNK3 in a panel profiling of 374 wild-type kinases, had high potency in functional cell-based assays, had high stability in human liver microsome (t _1/2 = 66 min) and a clean CYP-450 inhibition profile, and was orally bioavailable and brain penetrant. Moreover, cocrystal structures of compounds 17 and 27 in human JNK3 were solved at 1.84 Å, which showed that these JNK3 isoform selective inhibitors bound to the ATP pocket, had interactions in both hydrophobic pocket-I and hydrophobic pocket-II.

Clinically Precedented Protein Kinases: Rationale for Their Use in Neurodegenerative Disease

Kinases are an intensively studied drug target class in current pharmacological research as evidenced by the large number of kinase inhibitors being assessed in clinical trials. Kinase-targeted therapies have potential for treatment of a broad array of indications including central nervous system (CNS) disorders. In addition to the many variables which contribute to identification of a successful therapeutic molecule, drug discovery for CNS-related disorders also requires significant consideration of access to the target organ and specifically crossing the blood-brain barrier (BBB). To date, only a small number of kinase inhibitors have been reported that are specifically designed to be BBB permeable, which nonetheless demonstrates the potential for success. This review considers the potential for kinase inhibitors in the context of unmet medical need for neurodegenerative disease. A subset of kinases that have been the focus of clinical investigations over a 10-year period have been identified and discussed individually. For each kinase target, the data underpinning the validity of each in the context of neurodegenerative disease is critically evaluated. Selected molecules for each kinase are identified with information on modality, binding site and CNS penetrance, if known. Current clinical development in neurodegenerative disease are summarized. Collectively, the review indicates that kinase targets with sufficient rationale warrant careful design approaches with an emphasis on improving brain penetrance and selectivity.

Molecular docking of C-Jun-N-Terminal Kinase (Jnk) with amino-pyrimidine derivatives

It is of interest to document the molecular docking of C-Jun-N-Terminal Kinase (Jnk) (known structure with PDB ID: 1PMN) with amino-pyrimidine derivatives in the context of Alzheimer's Disease (AD). We report the optimal binding features (binding energy, interacting residues, inter atomic hydrogen bonding patterns) of 11 amino-pyrimidine derivatives with Jnk for further consideration.

Impact of Brain Insulin Signaling on Dopamine Function, Food Intake, Reward, and Emotional Behavior

PURPOSE OF REVIEW

Dietary obesity is primarily attributed to an imbalance between food intake and energy expenditure. Adherence to lifestyle interventions reducing weight is typically low. As a result, obesity becomes a chronic state with increased co-morbidities such as insulin resistance and diabetes. We review the effects of brain insulin action and dopaminergic signal transmission on food intake, reward, and mood as well as potential modulations of these systems to counteract the obesity epidemic.

RECENT FINDINGS

Central insulin and dopamine action are interlinked and impact on food intake, reward, and mood. Brain insulin resistance causes hyperphagia, anxiety, and depressive-like behavior and compromises the dopaminergic system. Such effects can induce reduced compliance to medical treatment. Insulin receptor sensitization and dopamine receptor agonists show attenuation of obesity and improvement of mental health in rodents and humans. Modulating brain insulin and dopamine signaling in obese patients can potentially improve therapeutic outcomes.

Role of Mitogen Activated Protein Kinase Signaling in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by insufficient dopamine production due to the loss of 50% to 70% of dopaminergic neurons. A shortage of dopamine, which is predominantly produced by the dopaminergic neurons within the substantia nigra, causes clinical symptoms such as reduction of muscle mass, impaired body balance, akinesia, bradykinesia, tremors, postural instability, etc. Lastly, this can lead to a total loss of physical movement and death. Since no cure for PD has been developed up to now, researchers using cell cultures and animal models focus their work on searching for potential therapeutic targets in order to develop effective treatments. In recent years, genetic studies have prominently advocated for the role of improper protein phosphorylation caused by a dysfunction in kinases and/or phosphatases as an important player in progression and pathogenesis of PD. Thus, in this review, we focus on the role of selected MAP kinases such as JNKs, ERK1/2, and p38 MAP kinases in PD pathology.

Small Molecules Identified from a Quantitative Drug Combinational Screen Resensitize Cisplatin's Response in Drug-Resistant Ovarian Cancer Cells

Drug resistance to chemotherapy occurs in many ovarian cancer patients resulting in failure of treatment. Exploration of drug resistance mechanisms and identification of new therapeutics that overcome the drug resistance can improve patient prognosis. Following a quantitative combination screen of 6060 approved drugs and bioactive compounds in a cisplatin-resistant A2780-cis ovarian cancer cell line, 38 active compounds with IC₅₀s under 1 μM suppressed the growth of cisplatin-resistant ovarian cancer cells. Among these confirmed compounds, CUDC-101, OSU-03012, oligomycin A, VE-821, or Torin2 in a combination with cisplatin restored cisplatin's apoptotic response in the A2780-cis cells, while SR-3306, GSK-923295, SNX-5422, AT-13387, and PF-05212384 directly suppressed the growth of A2780-cis cells. One of the mechanisms for overcoming cisplatin resistance in these cells is mediated by the inhibition of epidermal growth factor receptor (EGFR), though not all the EGFR inhibitors are equally active. The increased levels of total EGFR and phosphorylated-EGFR (p-EGFR) in the A2780-cis cells were reduced after the combined treatment of cisplatin with EGFR inhibitors. In addition, a knockdown of EGFR mRNA reduced cisplatin resistance in the A2780-cis cells. Therefore, the top active compounds identified in this work can be studied further as potential treatments for cisplatin-resistant ovarian cancer. The quantitative combinational screening approach is a useful method for identifying effective compounds and drug combinations against drug-resistant cancer cells.

New insights into the structural dynamics of the kinase JNK3

In this work, we study the dynamics and the energetics of the all-atom structure of a neuronal-specific serine/threonine kinase c-Jun N-terminal kinase 3 (JNK3) in three states: unphosphorylated, phosphorylated, and ATP-bound phosphorylated. A series of 2 µs atomistic simulations followed by a conformational landscape mapping and a principal component analysis supports the mechanistic understanding of the JNK3 inactivation/activation process and also indicates key structural intermediates. Our analysis reveals that the unphosphorylated JNK3 undergoes the ‘open-to-closed’ movement via a two-step mechanism. Furthermore, the phosphorylation and ATP-binding allow the JNK3 kinase to attain a fully active conformation. JNK3 is a widely studied target for small-drugs used to treat a variety of neurological disorders. We believe that the mechanistic understanding of the large-conformational changes upon the activation of JNK3 will aid the development of novel targeted therapeutics.

Neuroprotective Effects of Proanthocyanidins, Natural Flavonoids Derived From Plants, on Rotenone-Induced Oxidative Stress and Apoptotic Cell Death in Human Neuroblastoma SH-SY5Y Cells

Proanthocyanidins (PA) are natural flavonoids widely present in many vegetables, fruits, nuts and seeds, and especially in grape seed. In the present study, we examined the neuroprotective effects of PA and the underlying molecular mechanism in rotenone model of Parkinson's disease (PD). We found that pretreatment with PA significantly reduced rotenone-induced oxidative stress in human neuroblastoma SH-SY5Y dopaminergic cells. In addition, PA markedly enhanced cell viability against rotenone neurotoxicity and considerably blocked rotenone-induced activation of caspase-9, caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP), biochemical features of apoptosis. Further study demonstrated that the anti-apoptotic effect of PA was mediated by suppressing p38, JNK, and ERK signaling, and inhibitors of these three signaling pathways reproduced the protective effect of PA separately. In summary, our results demonstrated that PA mitigated rotenone-induced ROS generation and antagonized apoptosis in SH-SY5Y cells by inhibiting p38, JNK, and ERK signaling pathways, and it may provide a new insight of PA in PD therapy.

Brain penetrant kinase inhibitors: Learning from kinase neuroscience discovery

A recent review of kinase inhibitors in clinical trials for brain cancer noted differences in the properties of these compounds relative to the mean property parameters associated with drugs marketed for CNS-associated conditions. However, many of these kinase drugs arose from opportunistic observations of brain activity, rather than design or flow schemes focused on optimizing CNS penetration. Thus, this digest examines kinase inhibitors that have been developed specifically for neurodegenerative indications such as Alzheimer's or Parkinson's disease, and considers design, flow scheme, and the physicochemical properties associated with compounds that have demonstrated brain penetrance.

Reciprocal signals between microglia and neurons regulate α-synuclein secretion by exophagy through a neuronal cJUN-N-terminal kinase-signaling axis

Background

Secretion of proteopathic α-synuclein (α-SNC) species from neurons is a suspected driving force in the propagation of Parkinson’s disease (PD). We have previously implicated exophagy, the exocytosis of autophagosomes, as a dominant mechanism of α-SNC secretion in differentiated PC12 or SH-SY5Y nerve cells. Here we have examined the regulation of exophagy associated with different forms of nerve cell stress relevant to PD.

Results

We identify cJUN-N-terminal kinase (JNK) activity as pivotal in the secretory fate of autophagosomes containing α-SNC. Pharmacological inhibition or genetic (shRNA) knockdown of JNK2 or JNK3 decreases α-SNC secretion in differentiated PC12 and SH-SY5Y cells, respectively. Conversely, expression of constitutively active mitogen-activated protein kinase kinase 7 (MKK7)-JNK2 and -JNK3 constructs augment secretion. The transcriptional activity of cJUN was not required for the observed effects. We establish a causal relationship between increased α-SNC release by exophagy and JNK activation subsequent to lysosomal fusion deficiency (overexpression of Lewy body-localized protein p25α or bafilomycin A1). JNK activation following neuronal ER or oxidative stress was not correlated with exophagy, but of note, we demonstrate that reciprocal signaling between microglia and neurons modulates α-SNC secretion. NADPH oxidase activity of microglia cell lines was upregulated by direct co-culture with α-SNC-expressing PC12 neurons or by passive transfer of nerve cell-conditioned medium. Conversely, inflammatory factors secreted from activated microglia increased JNK activation and α-SNC secretion several-fold in PC12 cells. While we do not identify these factors, we extend our observations by showing that exposure of neurons in monoculture to TNFα, a classical pro-inflammatory mediator of activated microglia, is sufficient to increase α-SNC secretion in a mechanism dependent on JNK2 or JNK3. In continuation hereof, we show that also IFNβ and TGFβ increase the release of α-SNC from PC12 neurons.

Conclusions

We implicate stress kinases of the JNK family in the regulation of exophagy and release of α-SNC following endogenous or exogenous stimulation. In a wider scope, our results imply that microglia not only inflict bystander damage to neurons in late phases of inflammatory brain disease but may also be active mediators of disease propagation.

Modulation of c-Jun N-terminal kinase signaling and specific glucocorticoid receptor phosphorylation in the treatment of major depression

Glucocorticoid resistance is a common finding in major depressive disorder. Increased glucocorticoid receptor (GR) phosphorylation at serine 226 is associated with increased glucocorticoid resistance. Previously we have demonstrated that depressed patients exhibit higher levels of GR phosphorylated at serine 226 compared to healthy controls. The enzyme that is involved in this specific GR phosphorylation is c-Jun N-terminal kinase (JNK). We propose that modulation of glucocorticoid phosphorylation at serine 226, by targeting JNK signaling pathway, could be a potential strategy for antidepressant treatment. We base this assumption on the results of previous research that examined GR phosphorylation and JNK signaling in animal models and human studies. We also discuss the potential challenges in targeting JNK signaling pathway in depression.

Pyridopyrimidinone Derivatives as Potent and Selective c-Jun N-Terminal Kinase (JNK) Inhibitors

A novel series of 2-aminopyridopyrimidinone based JNK (c-jun N-terminal kinase) inhibitors were discovered and developed. Structure-activity relationships (SARs) were systematically developed utilizing biochemical and cell based assays and in vitro and in vivo drug metabolism and pharmacokinetic (DMPK) studies. Through the optimization of lead compound 1, several potent and selective JNK inhibitors with high oral bioavailability were developed. Inhibitor 13 was a potent JNK3 inhibitor (IC50 = 15 nM), had high selectivity against p38 (IC50 > 10 μM), had high potency in functional cell based assays, and had high stability in human liver microsome (t 1/2 = 76 min), a clean CYP-450 inhibition profile, and excellent oral bioavailability (%F = 87). Moreover, cocrystal structures of compounds 13 and 22 in JNK3 were solved at 2.0 Å. These structures elucidated the binding mode (Type-I binding) and can pave the way for further inhibitor design of this pyridopyrimidinone scaffold for JNK inhibition.

Serum- and Glucocorticoid-Inducible Kinase 1 Confers Protection in Cell-Based and in In Vivo Neurotoxin Models via the c-Jun N-Terminal Kinase Signaling Pathway

Serum glucocorticoid kinase 1 (SGK1) has been shown to be protective in models of Parkinson's disease, but the details by which it confers benefit is unknown. The current study was designed to investigate the details by which SGK1 confers neuroprotection. To do this we employed a cellular neurodegeneration model to investigate c-Jun N-terminal kinase (JNK) signaling and endoplasmic reticulum (ER) stress induced by 6-hydroxydopamine. SGK1-expressing adenovirus was created and used to overexpress SGK1 in SH-SY5Y cells, and dexamethasone was used to increase endogenous expression of SGK1. Oxidative stress, mitochondrial dysfunction, and cell death were monitored to test the protective effect of SGK1. To investigate the effect of SGK1 overexpression in vivo, SGK1-expressing adenovirus was injected into the striatum of mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and protection of dopaminergic neurons was quantitatively assessed by tyrosine hydroxylase immunohistochemistry. SGK1 overexpression was found to decrease reactive oxygen species generation, alleviate mitochondrial dysfunction, and rescue cell death in vitro and in vivo by inactivating mitogen-activated protein kinase kinase 4 (MKK4), JNK, and glycogen synthase kinase 3β (GSK3β) and thereby decreasing ER and oxidative stress. These results suggest that therapeutic strategies for activation of SGK1 may have the potential to be neuroprotective by deactivating the JNK and GSK3β pathways.

Structural basis and biological consequences for JNK2/3 isoform selective aminopyrazoles

Three JNK isoforms, JNK1, JNK2, and JNK3 have been reported and unique biological function has been ascribed to each. It is unknown if selective inhibition of these isoforms would confer therapeutic or safety benefit. To probe JNK isoform function we designed JNK2/3 inhibitors that have >30-fold selectivity over JNK1. Utilizing site-directed mutagenesis and x-ray crystallography we identified L144 in JNK3 as a key residue for selectivity. To test whether JNK2/3 selective inhibitors protect human dopaminergic neurons against neurotoxin-induced mitochondrial dysfunction, we monitored reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP). The results showed that JNK2/3 selective inhibitors protected against 6-hydroxydopamine-induced ROS generation and MMP depolarization. These results suggest that it was possible to develop JNK2/3 selective inhibitors and that residues in hydrophobic pocket I were responsible for selectivity. Moreover, the findings also suggest that inhibition of JNK2/3 likely contributed to protecting mitochondrial function and prevented ultimate cell death.

Inhibitors of c-Jun N-terminal kinases: an update

The c-Jun N-terminal kinases (JNKs) are serine/threonine kinases implicated in the pathogenesis of various diseases. Recent advances in the development of novel inhibitors of JNKs will be reviewed. Significant progress in the design of JNK inhibitors displaying selectivity versus other kinases has been achieved within the past 4 years. However, the development of isoform selective JNK inhibitors is still an open task.

Design and synthesis of highly potent and isoform selective JNK3 inhibitors: SAR studies on aminopyrazole derivatives

The c-jun N-terminal kinase 3 (JNK3) is expressed primarily in the brain. Numerous reports have shown that inhibition of JNK3 is a promising strategy for treatment of neurodegeneration. The optimization of aminopyrazole-based JNK3 inhibitors with improved potency, isoform selectivity, and pharmacological properties by structure–activity relationship (SAR) studies utilizing biochemical and cell-based assays, and structure-based drug design is reported. These inhibitors had high selectivity over JNK1 and p38α, minimal cytotoxicity, potent inhibition of 6-OHDA-induced mitochondrial membrane potential dissipation and ROS generation, and good drug metabolism and pharmacokinetic (DMPK) properties for iv dosing. 26n was profiled against 464 kinases and was found to be highly selective hitting only seven kinases with >80% inhibition at 10 μM. Moreover, 26n showed good solubility, good brain penetration, and good DMPK properties. Finally, the crystal structure of 26k in complex with JNK3 was solved at 1.8 Å to explore the binding mode of aminopyrazole based JNK3 inhibitors.

Synthesis and SAR of novel isoxazoles as potent c-jun N-terminal kinase (JNK) inhibitors

The design and synthesis of isoxazole 3 is described, a potent JNK inhibitor with two fold selectivity over p38. Optimization of this scaffold led to compounds 27 and 28 which showed greatly improved selectivity over p38 by maintaining the JNK3 potency of compound 3. Extensive SAR studies will be described as well as preliminary in vivo data of the two lead compounds.

Dynamic changes in chromatin conformation at the TNF transcription start site in T helper lymphocyte subsets

Tumor necrosis factor (TNF) is one of the key primary response genes in the immune system that can be activated by a variety of stimuli. Previous analysis of chromatin accessibility to DNaseI demonstrated open chromatin conformation of the TNF proximal promoter in T cells. Here, using chromatin probing with restriction enzyme EcoNI and micrococcal nuclease we show that in contrast to the proximal promoter, the TNF transcription start site remains in a closed chromatin configuration in primary T helper (Th) cells, but acquires an open state after activation or polarization under Th1 and Th17 conditions. We further demonstrate that transcription factor c-Jun plays a pivotal role in the maintenance of open chromatin conformation at the transcription start site of the TNF gene.

A small molecule bidentate-binding dual inhibitor probe of the LRRK2 and JNK kinases

Both JNK and LRRK2 are associated with Parkinson's disease (PD). Here we report a reasonably selective and potent kinase inhibitor (compound 6) that bound to both JNK and LRRK2 (a dual inhibitor). A bidentate-binding strategy that simultaneously utilized the ATP hinge binding and a unique protein surface site outside of the ATP pocket was applied to the design and identification of this kind of inhibitor. Compound 6 was a potent JNK3 and modest LRRK2 dual inhibitor with an enzyme IC50 value of 12 nM and 99 nM (LRRK2-G2019S), respectively. Compound 6 also exhibited good cell potency, inhibited LRRK2:G2019S-induced mitochondrial dysfunction in SHSY5Y cells, and was demonstrated to be reasonably selective against a panel of 116 kinases from representative kinase families. Design of such a probe molecule may help enable testing if dual JNK and LRRK2 inhibitions have added or synergistic efficacy in protecting against neurodegeneration in PD.

Mitogen-activated protein kinase phosphatase (MKP)-1 as a neuroprotective agent: promotion of the morphological development of midbrain dopaminergic neurons

A greater understanding of the mechanisms that promote the survival and growth of dopaminergic neurons is essential for the advancement of cell replacement therapies for Parkinson's disease (PD). Evidence supports a role for the mitogen-activated protein kinase p38 in the demise of dopaminergic neurons, while mitogen-activated protein kinase phosphatase-1 (MKP-1), which negatively regulates p38 activity, has not yet been investigated in this context. Here, we show that MKP-1 is expressed in dopaminergic neurons cultured from E14 rat ventral mesencephalon (VM). When dopaminergic neurons were transfected to overexpress MKP-1, they displayed a more complex morphology than their control counterparts in vitro. Specifically, MKP-1-transfection induced significant increases in neurite length and branching with a maximum increase observed in primary branches. We demonstrate that inhibition of dopaminergic neurite growth induced by treatment of rat VM neurons with the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in vitro is mediated by p38 and is concomitant with a significant and selective decrease in MKP-1 expression in these neurons. We further show that overexpression of MKP-1 in dopaminergic neurons contributes to neuroprotection against the effects of 6-OHDA. Collectively, we report that MKP-1 can promote the growth and elaboration of dopaminergic neuronal processes and can help protect them from the neurotoxic effects of 6-OHDA. Thus, we propose that strategies aimed at augmenting MKP-1 expression or activity may be beneficial in protecting dopaminergic neurons and may provide potential therapeutic approaches for PD.

Blocking c-Jun N-terminal kinase (JNK) translocation to the mitochondria prevents 6-hydroxydopamine-induced toxicity in vitro and in vivo

Because oxidative stress and mitochondrial dysfunction are well known contributors to Parkinson disease (PD), we set out to investigate the role mitochondrial JNK plays in the etiology of 6-hydroxydopamine-induced (6-OHDA) oxidative stress, mitochondrial dysfunction, and neurotoxicity in SHSY5Y cells and neuroprotection and motor behavioral protection in vivo. To do this, we utilized a cell-permeable peptide of the outer mitochondrial membrane protein, Sab (SH3BP5), as an inhibitor of JNK mitochondrial translocation. In vitro studies showed that 6-OHDA induced JNK translocation to the mitochondria and that inhibition of mitochondrial JNK signaling by Tat-Sab(KIM1) protected against 6-OHDA-induced oxidative stress, mitochondrial dysfunction, and neurotoxicity. Administration of Tat-Sab(KIM1) via an intracerebral injection into the mid-forebrain bundle increased the number of tyrosine hydroxylase immunoreactive neurons in the substantia nigra pars compacta by 2-fold (p < 0.05) in animals lesioned with 6-OHDA, compared with animals treated only with 6-OHDA into the nigrostriatal pathway. In addition, Tat-Sab(KIM1) decreased the d-amphetamine-induced unilateral rotations associated with the lesion by 30% (p < 0.05). Steady-state brain levels of Tat-Sab(KIM1) at day 7 were 750 nm, which was ∼3.4-fold higher than the IC(50) for this peptide versus Sab protein. Collectively, these data suggest that 6-OHDA induced JNK translocation to the mitochondria and that blocking this translocation reduced oxidative stress, mitochondrial dysfunction, and neurotoxicity both in vitro and in vivo. Moreover, the data suggest that inhibitors that block association of JNKs with the mitochondria may be useful neuroprotective agents for the treatment of Parkinson disease.

Metabotropic glutamate receptor 4 (mGlu4)-positive allosteric modulators for the treatment of Parkinson's disease: historical perspective and review of the patent literature

INTRODUCTION

Metabotropic glutamate receptor 4 (mGlu(4)) is a group III GPCR and has been demonstrated to play a major role in a number of therapeutic areas within the CNS. As the orthosteric site of all glutamate receptors is highly conserved, modulating mGlu(4) via allosteric modulation has emerged as a very attractive mode-of-action and has been validated preclinically in a number of animal models for Parkinson's disease, anxiety, pain, and neuroinflammation.

AREAS COVERED

In this review, the patent literature for mGlu(4)-positive allosteric modulators over the past 4 years will be provided. Patents from all companies are discussed and an overview of the chemical matter and relevant biological properties will be given.

EXPERT OPINION

Although there has yet to be an mGlu(4)-positive allosteric modulator progressed into clinical trials, there is a wealth of preclinical data from the primary literature that shows the promise of this emerging target. A number of academic and industry laboratories have recently published exciting patent data covering a multitude of chemical matter. Positive allosteric modulation of mGlu(4) remains one of the more attractive non-dopaminergic therapies for Parkinson's disease, as well as emerging data for other indications such as pain, neuroinflammation, schizophrenia and diabetes, which could potentially make mGlu(4) a significant therapeutic target going forward.

Discovery of potent and selective covalent inhibitors of JNK

The mitogen-activated kinases JNK1/2/3 are key enzymes in signaling modules that transduce and integrate extracellular stimuli into coordinated cellular response. Here, we report the discovery of irreversible inhibitors of JNK1/2/3. We describe two JNK3 cocrystal structures at 2.60 and 2.97 Å resolution that show the compounds form covalent bonds with a conserved cysteine residue. JNK-IN-8 is a selective JNK inhibitor that inhibits phosphorylation of c-Jun, a direct substrate of JNK, in cells exposed to submicromolar drug in a manner that depends on covalent modification of the conserved cysteine residue. Extensive biochemical, cellular, and pathway-based profiling establish the selectivity of JNK-IN-8 for JNK and suggests that the compound will be broadly useful as a pharmacological probe of JNK-dependent signal transduction. Potential lead compounds have also been identified for kinases, including IRAK1, PIK3C3, PIP4K2C, and PIP5K3.

Oxidative toxicity in neurodegenerative diseases: role of mitochondrial dysfunction and therapeutic strategies

Besides fluorine, oxygen is the most electronegative element with the highest reduction potential in biological systems. Metabolic pathways in mammalian cells utilize oxygen as the ultimate oxidizing agent to harvest free energy. They are very efficient, but not without risk of generating various oxygen radicals. These cells have good antioxidative defense mechanisms to neutralize these radicals and prevent oxidative stress. However, increased oxidative stress results in oxidative modifications in lipid, protein, and nucleic acids, leading to mitochondrial dysfunction and cell death. Oxidative stress and mitochondrial dysfunction have been implicated in many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and stroke-related brain damage. Research has indicated mitochondria play a central role in cell suicide. An increase in oxidative stress causes mitochondrial dysfunction, leading to more production of reactive oxygen species and eventually mitochondrial membrane permeabilization. Once the mitochondria are destabilized, cells are destined to commit suicide. Therefore, antioxidative agents alone are not sufficient to protect neuronal loss in many neurodegenerative diseases. Combinatorial treatment with antioxidative agents could stabilize mitochondria and may be the most suitable strategy to prevent neuronal loss. This review discusses recent work related to oxidative toxicity in the central nervous system and strategies to treat neurodegenerative diseases.