Discovery of 1H-Pyrazol-3(2H)-ones as Potent and Selective Inhibitors of Protein Kinase R-like Endoplasmic Reticulum Kinase (PERK)

Therapeutic Potential of Targeting the PERK Signaling Pathway in Ischemic Stroke

Many pathologic states can lead to the accumulation of unfolded/misfolded proteins in cells. This causes endoplasmic reticulum (ER) stress and triggers the unfolded protein response (UPR), which encompasses three main adaptive branches. One of these UPR branches is mediated by protein kinase RNA-like ER kinase (PERK), an ER stress sensor. The primary consequence of PERK activation is the suppression of global protein synthesis, which reduces ER workload and facilitates the recovery of ER function. Ischemic stroke induces ER stress and activates the UPR. Studies have demonstrated the involvement of the PERK pathway in stroke pathophysiology; however, its role in stroke outcomes requires further clarification. Importantly, considering mounting evidence that supports the therapeutic potential of the PERK pathway in aging-related cognitive decline and neurodegenerative diseases, this pathway may represent a promising therapeutic target in stroke. Therefore, in this review, our aim is to discuss the current understanding of PERK in ischemic stroke, and to summarize pharmacologic tools for translational stroke research that targets PERK and its associated pathways.

Activation of the integrated stress response by inhibitors of its kinases

Phosphorylation of the translation initiation factor eIF2α to initiate the integrated stress response (ISR) is a vital signalling event. Protein kinases activating the ISR, including PERK and GCN2, have attracted considerable attention for drug development. Here we find that the widely used ATP-competitive inhibitors of PERK, GSK2656157, GSK2606414 and AMG44, inhibit PERK in the nanomolar range, but surprisingly activate the ISR via GCN2 at micromolar concentrations. Similarly, a PKR inhibitor, C16, also activates GCN2. Conversely, GCN2 inhibitor A92 silences its target but induces the ISR via PERK. These findings are pivotal for understanding ISR biology and its therapeutic manipulations because most preclinical studies used these inhibitors at micromolar concentrations. Reconstitution of ISR activation with recombinant proteins demonstrates that PERK and PKR inhibitors directly activate dimeric GCN2, following a Gaussian activation-inhibition curve, with activation driven by allosterically increasing GCN2 affinity for ATP. The tyrosine kinase inhibitors Neratinib and Dovitinib also activate GCN2 by increasing affinity of GCN2 for ATP. Thus, the mechanism uncovered here might be broadly relevant to ATP-competitive inhibitors and perhaps to other kinases.

Control of immune cell function by the unfolded protein response

Initiating and maintaining optimal immune responses requires high levels of protein synthesis, folding, modification and trafficking in leukocytes, which are processes orchestrated by the endoplasmic reticulum. Importantly, diverse extracellular and intracellular conditions can compromise the protein-handling capacity of this organelle, inducing a state of 'endoplasmic reticulum stress' that activates the unfolded protein response (UPR). Emerging evidence shows that physiological or pathological activation of the UPR can have effects on immune cell survival, metabolism, function and fate. In this Review, we discuss the canonical role of the adaptive UPR in immune cells and how dysregulation of this pathway in leukocytes contributes to diverse pathologies such as cancer, autoimmunity and metabolic disorders. Furthermore, we provide an overview as to how pharmacological approaches that modulate the UPR could be harnessed to control or activate immune cell function in disease.

The integrated stress response in cancer progression: a force for plasticity and resistance

During their quest for growth, adaptation, and survival, cancer cells create a favorable environment through the manipulation of normal cellular mechanisms. They increase anabolic processes, including protein synthesis, to facilitate uncontrolled proliferation and deplete the tumor microenvironment of resources. As a dynamic adaptation to the self-imposed oncogenic stress, cancer cells promptly hijack translational control to alter gene expression. Rewiring the cellular proteome shifts the phenotypic balance between growth and adaptation to promote therapeutic resistance and cancer cell survival. The integrated stress response (ISR) is a key translational program activated by oncogenic stress that is utilized to fine-tune protein synthesis and adjust to environmental barriers. Here, we focus on the role of ISR signaling for driving cancer progression. We highlight mechanisms of regulation for distinct mRNA translation downstream of the ISR, expand on oncogenic signaling utilizing the ISR in response to environmental stresses, and pinpoint the impact this has for cancer cell plasticity during resistance to therapy. There is an ongoing need for innovative drug targets in cancer treatment, and modulating ISR activity may provide a unique avenue for clinical benefit.

Transcriptomic features reveal molecular signatures associated with recombinant adeno-associated virus production in HEK293 cells

The development of gene therapies based on recombinant adeno-associated viruses (rAAVs) has grown exponentially, so the current rAAV manufacturing platform needs to be more efficient to satisfy rising demands. Viral production exerts great demand on cellular substrates, energy, and machinery; therefore, viral production relies heavily on the physiology of the host cell. Transcriptomics, as a mechanism-driven tool, was applied to identify significantly regulated pathways and to study cellular features of the host cell for supporting rAAV production. This study investigated the transcriptomic features of two cell lines cultured in their respective media by comparing viral-producing cultures with non-producing cultures over time in parental human embryonic kidney cells (HEK293). The results demonstrate that the innate immune response signaling pathways of host cells (e.g., RIG-I-like receptor signaling pathway, Toll-like receptor signaling pathway, cytosolic DNA sensing pathway, JAK-STAT signaling pathway) were significantly enriched and upregulated. This was accompanied by the host cellular stress responses, including endoplasmic reticulum stress, autophagy, and apoptosis in viral production. In contrast, fatty acid metabolism and neutral amino acid transport were downregulated in the late phase of viral production. Our transcriptomics analysis reveals the cell-line independent signatures for rAAV production and serves as a significant reference for further studies targeting the productivity improvement in the future.

The Prohibitin-Binding Compound Fluorizoline Activates the Integrated Stress Response through the eIF2α Kinase HRI

Fluorizoline is a synthetic molecule that induces apoptosis, by selectively targeting prohibitins (PHBs), through induction of the BH3-only protein NOXA. This induction is transcriptionally regulated by the integrated stress response (ISR)-related transcription factors ATF3 and ATF4. Here, we evaluate the role of the four eIF2α kinases, to decipher which is responsible for the mechanism of ISR activation triggered by fluorizoline in HeLa and HAP1 cells. First, we demonstrated the involvement of the eIF2α kinases using ISR inhibitor (ISRIB) and by simultaneous downregulation of all four eIF2α kinases, as both approaches were able to increase cell resistance to fluorizoline-induced apoptosis. Furthermore, we confirmed that fluorizoline treatment results in endoplasmic reticulum (ER) stress, as evidenced by PERK activation. Despite PERK activation, this kinase was not directly involved in the ISR activation by fluorizoline. In this regard, we found that the eIF2α kinases are capable of compensating for each other's loss of function. Importantly, we demonstrated that the mitochondrial-stress-related eIF2α kinase HRI mediates ISR activation after fluorizoline treatment.

Activation of the integrated stress response (ISR) pathways in response to Ref-1 inhibition in human pancreatic cancer and its tumor microenvironment

Pancreatic cancer or pancreatic ductal adenocarcinoma (PDAC) is characterized by a profound inflammatory tumor microenvironment (TME) with high heterogeneity, metastatic propensity, and extreme hypoxia. The integrated stress response (ISR) pathway features a family of protein kinases that phosphorylate eukaryotic initiation factor 2 (eIF2) and regulate translation in response to diverse stress conditions, including hypoxia. We previously demonstrated that eIF2 signaling pathways were profoundly affected in response to Redox factor-1 (Ref-1) knockdown in human PDAC cells. Ref-1 is a dual function enzyme with activities of DNA repair and redox signaling, responds to cellular stress, and regulates survival pathways. The redox function of Ref-1 directly regulates multiple transcription factors including HIF-1α, STAT3, and NF-κB, which are highly active in the PDAC TME. However, the mechanistic details of the crosstalk between Ref-1 redox signaling and activation of ISR pathways are unclear. Following Ref-1 knockdown, induction of ISR was observed under normoxic conditions, while hypoxic conditions were sufficient to activate ISR irrespective of Ref-1 levels. Inhibition of Ref-1 redox activity increased expression of p-eIF2 and ATF4 transcriptional activity in a concentration-dependent manner in multiple human PDAC cell lines, and the effect on eIF2 phosphorylation was PERK-dependent. Treatment with PERK inhibitor, AMG-44 at high concentrations resulted in activation of the alternative ISR kinase, GCN2 and induced levels of p-eIF2 and ATF4 in both tumor cells and cancer-associated fibroblasts (CAFs). Combination treatment with inhibitors of Ref-1 and PERK enhanced cell killing effects in both human pancreatic cancer lines and CAFs in 3D co-culture, but only at high doses of PERK inhibitors. This effect was completely abrogated when Ref-1 inhibitors were used in combination with GCN2 inhibitor, GCN2iB. We demonstrate that targeting of Ref-1 redox signaling activates the ISR in multiple PDAC lines and that this activation of ISR is critical for inhibition of the growth of co-culture spheroids. Combination effects were only observed in physiologically relevant 3D co-cultures, suggesting that the model system utilized can greatly affect the outcome of these targeted agents. Inhibition of Ref-1 signaling induces cell death through ISR signaling pathways, and combination of Ref-1 redox signaling blockade with ISR activation could be a novel therapeutic strategy for PDAC treatment.

Endoplasmic Reticulum Stress and Mitochondrial Stress in Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a widespread and harmful disease closely linked to mitochondrial and endoplasmic reticulum stress (ERS). Globally, severe drug-induced hepatitis, cirrhosis, and liver cancer are the primary causes of liver-related morbidity and mortality. A hallmark of DILI is ERS and changes in mitochondrial morphology and function, which increase the production of reactive oxygen species (ROS) in a vicious cycle of mutually reinforcing stress responses. Several pathways are maladapted to maintain homeostasis during DILI. Here, we discuss the processes of liver injury caused by several types of drugs that induce hepatocyte stress, focusing primarily on DILI by ERS and mitochondrial stress. Importantly, both ERS and mitochondrial stress are mediated by the overproduction of ROS, destruction of Ca2+ homeostasis, and unfolded protein response (UPR). Additionally, we review new pathways and potential pharmacological targets for DILI to highlight new possibilities for DILI treatment and mitigation.

Identification of potent and selective inhibitors of PKR via virtual screening and traditional design

Protein Kinase RNA-activated (PKR) inhibition is thought to be relevant for immunology due to the potential to reduce macrophage and dendritic cell responses to bacteria and its signaling downstream of TNFα. PKR is also associated with neuroscience indications such as Alzheimer's disease due to its activation by the double stranded DNA (dsDNA) virus HSV1, a virus suggested to be important in the development of AD. Studies exploring the mechanistic role of PKR with existing tool molecules such as the tricyclic oxindole C16 are clouded by the poor selectivity profile of this ATP-competitive, Type I kinase inhibitor. Type II kinase leads such as the benzothiophene or pyrazolopyrimidine scaffolds from literature are equally poor in their selectivity profiles. As such, it became necessary to identify more potent and selective chemical matter to better understand PKR biology. A dual approach was taken. The first step of the strategy included virtual screening of the AbbVie compound collection. A combination of pharmacophore-based and GPU shape-based screening was pursued to identify selective chemical matter from promiscuous leads. The second step of the strategy followed traditional compound design. This step initiated from a literature lead with PKR cross reactivity. Combined, the two parallel efforts led to identification of more selective leads for investigation of PKR biology.

Chemical Chaperones to Inhibit Endoplasmic Reticulum Stress: Implications in Diseases

The endoplasmic reticulum (ER) is responsible for structural transformation or folding of de novo proteins for transport to the Golgi. When the folding capacity of the ER is exceeded or excessive accumulation of misfolded proteins occurs, the ER enters a stressed condition (ER stress) and unfolded protein responses (UPR) are triggered in order to rescue cells from the stress. Recovery of ER proceeds toward either survival or cell apoptosis. ER stress is implicated in many pathologies, such as diabetes, cardiovascular diseases, inflammatory diseases, neurodegeneration, and lysosomal storage diseases. As a survival or adaptation mechanism, chaperone molecules are upregulated to manage ER stress. Chemical versions of chaperone have been developed in search of drug candidates for ER stress-related diseases. In this review, synthetic or semi-synthetic chemical chaperones are categorized according to potential therapeutic area and listed along with their chemical structure and activity. Although only a few chemical chaperones have been approved as pharmaceutical drugs, a dramatic increase in literatures over the recent decades indicates enormous amount of efforts paid by many researchers. The efforts warrant clearer understanding of ER stress and the related diseases and consequently will offer a promising drug discovery platform with chaperone activity.

Molecular docking and molecular dynamics approach to identify potential compounds in Huperzia squarrosa for treating Alzheimer's disease

OBJECTIVES

Alzheimer's disease (AD) is a lingering progressive neurodegenerative disorder that causes patients to lose cognitive function. The enzyme Acetylcholinesterase (AChE), Butyrylcholinesterase (BuChE), Monoamine oxidase A (MAO A), Beta-secretase cleavage enzyme (BACE 1) and N-methyl-D-aspartate (NMDA) receptors play an important role in the pathogenesis of Alzheimer's disease. Therefore, inhibiting enzymes is an effective method to treat Alzheimer disease. In this study, we evaluated in silico inhibitory effects of AChE, BuChE, MAO A, BACE 1 and NMDA enzyme of Huperzia squarrosa's compounds.

METHODS

The three-dimensional (3D) of N-methyl-D-aspartate receptor (PDB ID: 1PBQ), enzyme β-secretase 1 (PDB ID: 4X7I), enzyme monoamine oxidase A (PDB ID: 2Z5X), enzyme butyrylcholinesterase (PDB ID: 4BDS) and enzyme acetylcholinesterase (PDB ID: 1EVE) were retrieved from the Protein Data Bank RCSB. Molecular docking was done by Autodock vina software and molecular dynamics (MD) simulation of the ligand-protein complex with the least binding energy pose was perfomed by MOE. Lipinski Rule of Five is used to compare compounds with drug-like and non-drug-like properties. Pharmacokinetic parameters of potential compounds were evaluated using the pkCSM tool.

RESULTS

Based on previous publication of Huperzia squarrosa, we have collected 15 compounds. In these compounds, huperzine B, huperzinine, lycoposerramine U N-oxide, 12-epilycodine N-oxide showed strongly inhibit the five AChE, BuChE, MAO A, BACE 1 and NMDA targets for Alzheimer's treatment. Lipinski rule of five and ADMET predict have shown that four above compounds have drug-likeness properties, good absorption ability and cross the blood-brain barrier, which have the most potential to become drugs for the treatment of Alzheimer's in the future. Furthermore, MD study showed that huperzine B and huperzinine have stability of the docking pose with NMDA target.

CONCLUSIONS

In this study, we found two natural compounds in Huperzia squarrosa including Huperzine B and Huperzinine have drug-likeness properties, good absorption ability and cross the blood-brain barrier, which have potential to become drugs for the treatment of Alzheimer's in the future.

Decoding endoplasmic reticulum stress signals in cancer cells and antitumor immunity

The tumor microenvironment (TME) provokes endoplasmic reticulum (ER) stress in malignant cells and infiltrating immune populations. Sensing and responding to ER stress is coordinated by the unfolded protein response (UPR), an integrated signaling pathway governed by three ER stress sensors: activating transcription factor (ATF6), inositol-requiring enzyme 1α (IRE1α), and protein kinase R (PKR)-like ER kinase (PERK). Persistent UPR activation modulates malignant progression, tumor growth, metastasis, and protective antitumor immunity. Hence, therapies targeting ER stress signaling can be harnessed to elicit direct tumor killing and concomitant anticancer immunity. We highlight recent findings on the role of the ER stress responses in onco-immunology, with an emphasis on genetic vulnerabilities that render tumors highly sensitive to therapeutic UPR modulation.

Optimization of a Novel Mandelamide-Derived Pyrrolopyrimidine Series of PERK Inhibitors

The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of three endoplasmic reticulum (ER) transmembrane sensors of the unfolded protein response (UPR) responsible for regulating protein synthesis and alleviating ER stress. PERK has been implicated in tumorigenesis, cancer cell survival as well metabolic diseases such as diabetes. The structure-based design and optimization of a novel mandelamide-derived pyrrolopyrimidine series of PERK inhibitors as described herein, resulted in the identification of compound 26, a potent, selective, and orally bioavailable compound suitable for interrogating PERK pathway biology in vitro and in vivo, with pharmacokinetics suitable for once-a-day oral dosing in mice.

Ablation of the endoplasmic reticulum stress kinase PERK induces paraptosis and type I interferon to promote anti-tumor T cell responses

Activation of unfolded protein responses (UPRs) in cancer cells undergoing endoplasmic reticulum (ER) stress promotes survival. However, how UPR in tumor cells impacts anti-tumor immune responses remains poorly described. Here, we investigate the role of the UPR mediator pancreatic ER kinase (PKR)-like ER kinase (PERK) in cancer cells in the modulation of anti-tumor immunity. Deletion of PERK in cancer cells or pharmacological inhibition of PERK in melanoma-bearing mice incites robust activation of anti-tumor T cell immunity and attenuates tumor growth. PERK elimination in ER-stressed malignant cells triggers SEC61β-induced paraptosis, thereby promoting immunogenic cell death (ICD) and systemic anti-tumor responses. ICD induction in PERK-ablated tumors stimulates type I interferon production in dendritic cells (DCs), which primes CCR2-dependent tumor trafficking of common-monocytic precursors and their intra-tumor commitment into monocytic-lineage inflammatory Ly6C+CD103+ DCs. These findings identify how tumor cell-derived PERK promotes immune evasion and highlight the potential of PERK-targeting therapies in cancer immunotherapy.

Potent GCN2 Inhibitor Capable of Reversing MDSC-Driven T Cell Suppression Demonstrates In Vivo Efficacy as a Single Agent and in Combination with Anti-Angiogenesis Therapy

General control nonderepressible 2 (GCN2) protein kinase is a cellular stress sensor within the tumor microenvironment (TME), whose signaling cascade has been proposed to contribute to immune escape in tumors. Herein, we report the discovery of cell-potent GCN2 inhibitors with excellent selectivity against its closely related Integrated Stress Response (ISR) family members heme-regulated inhibitor kinase (HRI), protein kinase R (PKR), and (PKR)-like endoplasmic reticulum kinase (PERK), as well as good kinome-wide selectivity and favorable PK. In mice, compound 39 engages GCN2 at levels ≥80% with an oral dose of 15 mg/kg BID. We also demonstrate the ability of compound 39 to alleviate MDSC-related T cell suppression and restore T cell proliferation, similar to the effect seen in MDSCs from GCN2 knockout mice. In the LL2 syngeneic mouse model, compound 39 demonstrates significant tumor growth inhibition (TGI) as a single agent. Furthermore, TGI mediated by anti-VEGFR was enhanced by treatment with compound 39 demonstrating the complementarity of these two mechanisms.

Predicting compound-protein interaction using hierarchical graph convolutional networks

Motivation

Convolutional neural networks have enabled unprecedented breakthroughs in a variety of computer vision tasks. They have also drawn much attention from other domains, including drug discovery and drug development. In this study, we develop a computational method based on convolutional neural networks to tackle a fundamental question in drug discovery and development, i.e. the prediction of compound-protein interactions based on compound structure and protein sequence. We propose a hierarchical graph convolutional network (HGCN) to encode small molecules. The HGCN aggregates a molecule embedding from substructure embeddings, which are synthesized from atom embeddings. As small molecules usually share substructures, computing a molecule embedding from those common substructures allows us to learn better generic models. We then combined the HGCN with a one-dimensional convolutional network to construct a complete model for predicting compound-protein interactions. Furthermore we apply an explanation technique, Grad-CAM, to visualize the contribution of each amino acid into the prediction.

Results

Experiments using different datasets show the improvement of our model compared to other GCN-based methods and a sequence based method, DeepDTA, in predicting compound-protein interactions. Each prediction made by the model is also explainable and can be used to identify critical residues mediating the interaction.

Post-treatment with apocynin at a lower dose regulates the UPR branch of eIF2α and XBP-1 pathways after stroke

Stroke leads to disturbance in the physiology of the ER (Endoplasmic Reticulum) that triggers UPR (Unfolded Protein Response) pathways aimed to compensate neuronal cell damage. However, sustained UPR causes stressful conditions in the ER lumen forming abnormal protein aggregates. Stroke-induced oxidative stress also amalgamates with UPR to safeguard and ensure the proper functioning of brain cells. Thus we tested the effect of apocynin (a potent antioxidant) post-treatment in experimental stroke on the outcome of ER stress and UPR branch pathways. We administered a low dose of apocynin at 1 mg/kg (intraperitoneal) to adult Sprague-Dawley rats subjected to Middle Cerebral Artery Occlusion (MCAO) for two-time points. The first dose immediately after re-establishing the blood flow and another at 6 h of reperfusion. Apocynin post-treatment significantly reduced ROS (Reactive Oxygen Species) generation at an early reperfusion time point of 4 h. It preserved neuronal morphology, dendritic spine density, reduced protein aggregation, and brain damage after 24 h of reperfusion. Apocynin post-treatment regulates the two UPR branch pathways in our experimental paradigm. 1) Down-regulation of eIF2α (Eukaryotic Initiation Factor 2α) phosphorylation, and CHOP (C/EBP homologous protein) 2) by reducing the XBP-1 (X-Box binding Protein-1) mRNA splicing downstream to PERK (Protein Kinase RNA-Like ER Kinase) and IRE1α (Inositol Requiring Enzyme 1alpha) UPR pathways, respectively. Bioinformatics prediction showed that apocynin has binding sites for PERK (Protein Kinase RNA-Like ER Kinase) and IRE1α proteins. The amino acid residues interacting with apocynin were Cys891 and Gln889 (for PERK), and the amino acids Ser726, Arg722, and Ala719 (for IRE1α) lying within their activation loop. Overall, these studies indicate that apocynin post-treatment might regulate ER stress/UPR pathways and minimize stroke brain damage, thus having implications for developing newer strategies for stroke treatment.

Polyfluoroalkylated antipyrines in Pd-catalyzed transformations

In the direct C–H arylation with arylhalogenides in the presence of Pd(OAc)₂, trifluoromethyl-containing antipyrine reacts very slowly and incompletely owing to the low nucleophilicity of its C4 center. However, it was effective in modifying polyfluoroalkyl-substituted 4-bromo- and 4-iodo antipyrines by the Suzuki and Sonogashira reactions. It was established that using Pd₂(dba)₃ as catalyst and XPhos as phosphine ligand was the optimal catalytic system for the synthesis of 4-aryl- and 4-phenylethynyl-3-polyfluoroalkyl-antipyrines. Moreover, iodo-derivatives as the initial reagents were found to be more advantageous compared to bromo-containing analogs. It was found that 4-phenylethynyl-5-CF₃-antipyrine has a moderate activity against the influenza virus A/Puerto Rico/8/34 (H1N1) and 4-iodo-5-CF₃-antipyrine reveals a weak activity against the vaccine virus (strain Copenhagen) and bovine diarrhea virus (strain VC-1).

Peculiarities of heterocyclic systems with electron-withdrawing groups (polyfluoroalkyl-containing antipyrines) in Pd-catalyzed C–H arylation and cross-coupling reactions.

Pharmacological targeting of endoplasmic reticulum stress in disease

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress, resulting in activation of the unfolded protein response (UPR) that aims to restore protein homeostasis. However, the UPR also plays an important pathological role in many diseases, including metabolic disorders, cancer and neurological disorders. Over the last decade, significant effort has been invested in targeting signalling proteins involved in the UPR and an array of drug-like molecules is now available. However, these molecules have limitations, the understanding of which is crucial for their development into therapies. Here, we critically review the existing ER stress and UPR-directed drug-like molecules, highlighting both their value and their limitations.

Proteotoxic Stress as an Exploitable Vulnerability in Cells with Hyperactive AKT

Hyperactivity of serine-threonine kinase AKT is one of the most common molecular abnormalities in cancer, where it contributes to poor outcomes by facilitating the growth and survival of malignant cells. Despite its well-documented anti-apoptotic effects, hyperactivity of AKT is also known to be stressful to a cell. In an attempt to better elucidate this phenomenon, we observed the signs of proteotoxic stress in cells that harbor hyperactive AKT or have lost its principal negative regulator, PTEN. The activity of HSF1 was predictably elevated under these circumstances. However, such cells proved more sensitive to various regimens of heat shock, including the conditions that were well-tolerated by syngeneic cells without AKT hyperactivity. The sensitizing effect of hyperactive AKT was also seen in HSF1-deficient cells, suggesting that the phenomenon does not require the regulation of HSF1 by this kinase. Notably, the elevated activity of AKT was accompanied by increased levels of XBP1, a key component of cell defense against proteotoxic stress. Interestingly, the cells harboring hyperactive AKT were also more dependent on XBP1 for their growth. Our observations suggest that proteotoxic stress conferred by hyperactive AKT represents a targetable vulnerability, which can be exploited by either elevating the stress above the level tolerated by such cells or by eliminating the factors that enable such tolerance.

Endoplasmic Reticulum Quality Control in Immune Cells

The endoplasmic reticulum quality control (ERQC) system, including endoplasmic reticulum-associated degradation (ERAD), the unfolded protein response (UPR), and autophagy, presides over cellular protein secretion and maintains proteostasis in mammalian cells. As part of the immune system, a variety of proteins are synthesized and assembled correctly for the development, activation, and differentiation of immune cells, such as dendritic cells (DCs), macrophages, myeloid-derived-suppressor cells (MDSCs), B lymphocytes, T lymphocytes, and natural killer (NK) cells. In this review, we emphasize the role of the ERQC in these immune cells, and also discuss how the imbalance of ER homeostasis affects the immune response, thereby suggesting new therapeutic targets for immunotherapy.

Unfolded Protein Response Inhibition Reduces Middle East Respiratory Syndrome Coronavirus-Induced Acute Lung Injury

Tissue- and cell-specific expression patterns are highly variable within and across individuals, leading to altered host responses after acute virus infection. Unraveling key tissue-specific response patterns provides novel opportunities for defining fundamental mechanisms of virus-host interaction in disease and the identification of critical tissue-specific networks for disease intervention in the lung. Currently, there are no approved therapeutics for Middle East respiratory syndrome coronavirus (MERS-CoV) patients, and little is understood about how lung cell types contribute to disease outcomes. MERS-CoV replicates equivalently in primary human lung microvascular endothelial cells (MVE) and fibroblasts (FB) and to equivalent peak titers but with slower replication kinetics in human airway epithelial cell cultures (HAE). However, only infected MVE demonstrate observable virus-induced cytopathic effect. To explore mechanisms leading to reduced MVE viability, donor-matched human lung MVE, HAE, and FB were infected, and their transcriptomes, proteomes, and lipidomes were monitored over time. Validated functional enrichment analysis demonstrated that MERS-CoV-infected MVE were dying via an unfolded protein response (UPR)-mediated apoptosis. Pharmacologic manipulation of the UPR in MERS-CoV-infected primary lung cells reduced viral titers and in male mice improved respiratory function with accompanying reductions in weight loss, pathological signatures of acute lung injury, and times to recovery. Systems biology analysis and validation studies of global kinetic transcript, protein, and lipid data sets confirmed that inhibition of host stress pathways that are differentially regulated following MERS-CoV infection of different tissue types can alleviate symptom progression to end-stage lung disease commonly seen following emerging coronavirus outbreaks.

Discovery of 2-amino-3-amido-5-aryl-pyridines as highly potent, orally bioavailable, and efficacious PERK kinase inhibitors

The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of the three endoplasmic reticulum (ER) transmembrane sensors of the unfolded protein response (UPR) that regulates protein synthesis, alleviates cellular ER stress and has been implicated in tumorigenesis and prolonged cancer cell survival. In this study, we report a series of 2-amino-3-amido-5-aryl-pyridines that we have identified as potent, selective, and orally bioavailable PERK inhibitors. Amongst the series studied herein, compound (28) a (R)-2-Amino-5-(4-(2-(3,5-difluorophenyl)-2-hydroxyacetamido)-2-ethylphenyl)-N-isopropylnicotinamide has demonstrated potent biochemical and cellular activity, robust pharmacokinetics and 70% oral bioavailability in mice. Given these data, this compound (28) was studied in the 786-O renal cell carcinoma xenograft model. We observed dose-dependent, statistically significant tumor growth inhibition, supporting the use of this tool compound in additional mechanistic studies.

Endoplasmic reticulum stress signals in the tumour and its microenvironment

Protein handling, modification and folding in the endoplasmic reticulum (ER) are tightly regulated processes that determine cell function, fate and survival. In several tumour types, diverse oncogenic, transcriptional and metabolic abnormalities cooperate to generate hostile microenvironments that disrupt ER homeostasis in malignant and stromal cells, as well as infiltrating leukocytes. These changes provoke a state of persistent ER stress that has been demonstrated to govern multiple pro-tumoural attributes in the cancer cell while dynamically reprogramming the function of innate and adaptive immune cells. Aberrant activation of ER stress sensors and their downstream signalling pathways have therefore emerged as key regulators of tumour growth and metastasis as well as response to chemotherapy, targeted therapies and immunotherapy. In this Review, we discuss the physiological inducers of ER stress in the tumour milieu, the interplay between oncogenic signalling and ER stress response pathways in the cancer cell and the profound immunomodulatory effects of sustained ER stress responses in tumours.

Pharmacological Manipulation of Translation as a Therapeutic Target for Chronic Pain

Dysfunction in regulation of mRNA translation is an increasingly recognized characteristic of many diseases and disorders, including cancer, diabetes, autoimmunity, neurodegeneration, and chronic pain. Approximately 50 million adults in the United States experience chronic pain. This economic burden is greater than annual costs associated with heart disease, cancer, and diabetes combined. Treatment options for chronic pain are inadequately efficacious and riddled with adverse side effects. There is thus an urgent unmet need for novel approaches to treating chronic pain. Sensitization of neurons along the nociceptive pathway causes chronic pain states driving symptoms that include spontaneous pain and mechanical and thermal hypersensitivity. More than a decade of preclinical research demonstrates that translational mechanisms regulate the changes in gene expression that are required for ongoing sensitization of nociceptive sensory neurons. This review will describe how key translation regulation signaling pathways, including the integrated stress response, mammalian target of rapamycin, AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase-interacting kinases, impact the translation of different subsets of mRNAs. We then place these mechanisms of translation regulation in the context of chronic pain states, evaluate currently available therapies, and examine the potential for developing novel drugs. Considering the large body of evidence now published in this area, we propose that pharmacologically manipulating specific aspects of the translational machinery may reverse key neuronal phenotypic changes causing different chronic pain conditions. Therapeutics targeting these pathways could eventually be first-line drugs used to treat chronic pain disorders. SIGNIFICANCE STATEMENT: Translational mechanisms regulating protein synthesis underlie phenotypic changes in the sensory nervous system that drive chronic pain states. This review highlights regulatory mechanisms that control translation initiation and how to exploit them in treating persistent pain conditions. We explore the role of mammalian/mechanistic target of rapamycin and mitogen-activated protein kinase-interacting kinase inhibitors and AMPK activators in alleviating pain hypersensitivity. Modulation of eukaryotic initiation factor 2α phosphorylation is also discussed as a potential therapy. Targeting specific translation regulation mechanisms may reverse changes in neuronal hyperexcitability associated with painful conditions.

Small molecule strategies to harness the unfolded protein response: where do we go from here?

The unfolded protein response (UPR) plays a central role in regulating endoplasmic reticulum (ER) and global cellular physiology in response to pathologic ER stress. The UPR is comprised of three signaling pathways activated downstream of the ER membrane proteins IRE1, ATF6, and PERK. Once activated, these proteins initiate transcriptional and translational signaling that functions to alleviate ER stress, adapt cellular physiology, and dictate cell fate. Imbalances in UPR signaling are implicated in the pathogenesis of numerous, etiologically-diverse diseases, including many neurodegenerative diseases, protein misfolding diseases, diabetes, ischemic disorders, and cancer. This has led to significant interest in establishing pharmacologic strategies to selectively modulate IRE1, ATF6, or PERK signaling to both ameliorate pathologic imbalances in UPR signaling implicated in these different diseases and define the importance of the UPR in diverse cellular and organismal contexts. Recently, there has been significant progress in the identification and characterization of UPR modulating compounds, providing new opportunities to probe the pathologic and potentially therapeutic implications of UPR signaling in human disease. Here, we describe currently available UPR modulating compounds, specifically highlighting the strategies used for their discovery and specific advantages and disadvantages in their application for probing UPR function. Furthermore, we discuss lessons learned from the application of these compounds in cellular and in vivo models to identify favorable compound properties that can help drive the further translational development of selective UPR modulators for human disease.

The Unfolded Protein Response Mediator PERK Governs Myeloid Cell-Driven Immunosuppression in Tumors through Inhibition of STING Signaling

The primary mechanisms supporting immunoregulatory polarization of myeloid cells upon infiltration into tumors remain largely unexplored. Elucidation of these signals could enable better strategies to restore protective anti-tumor immunity. Here, we investigated the role of the intrinsic activation of the PKR-like endoplasmic reticulum (ER) kinase (PERK) in the immunoinhibitory actions of tumor-associated myeloid-derived suppressor cells (tumor-MDSCs). PERK signaling increased in tumor-MDSCs, and its deletion transformed MDSCs into myeloid cells that activated CD8⁺ T cell-mediated immunity against cancer. Tumor-MDSCs lacking PERK exhibited disrupted NRF2-driven antioxidant capacity and impaired mitochondrial respiratory homeostasis. Moreover, reduced NRF2 signaling in PERK-deficient MDSCs elicited cytosolic mitochondrial DNA elevation and, consequently, STING-dependent expression of anti-tumor type I interferon. Reactivation of NRF2 signaling, conditional deletion of STING, or blockade of type I interferon receptor I restored the immunoinhibitory potential of PERK-ablated MDSCs. Our findings demonstrate the pivotal role of PERK in tumor-MDSC functionality and unveil strategies to reprogram immunosuppressive myelopoiesis in tumors to boost cancer immunotherapy.

2-Aminoquinazolines by Chan–Evans–Lam Coupling of Guanidines with (2-Formylphenyl)boronic Acids

A new method is presented for the synthesis of 2-aminoquinazolines, which is based on a Chan–Evans–Lam coupling of (2-formylphenyl)boronic acids with guanidines. Relatively mild conditions involving the use of inexpensive CuI as a catalyst and methanol as a solvent permit the application of the method to a wide range of substrates. Nonsubstituted, N-monosubstituted, and N,N-disubstituted guanidines can be used as reactants to give the corresponding 2-aminoquinazolines in moderate yields from readily available (2-formylphenyl)boronic acids.

Targeting Adaptive IRE1α Signaling and PLK2 in Multiple Myeloma: Possible Anti-Tumor Mechanisms of KIRA8 and Nilotinib

BACKGROUND

Inositol-requiring enzyme 1α (IRE1α), along with protein kinase R-like endoplasmic reticulum kinase (PERK), is a principal regulator of the unfolded protein response (UPR). Recently, the 'mono'-specific IRE1α inhibitor, kinase-inhibiting RNase attenuator 6 (KIRA6), demonstrated a promising effect against multiple myeloma (MM). Side-stepping the clinical translation, a detailed UPR phenotype in patients with MM and the mechanisms of how KIRA8 works in MM remains unclear.

METHODS

We characterized UPR phenotypes in the bone marrow of patients with newly diagnosed MM. Then, in human MM cells we analyzed the possible anti-tumor mechanisms of KIRA8 and a Food and Drug Administration (FDA)-approved drug, nilotinib, which we recently identified as having a strong inhibitory effect against IRE1α activity. Finally, we performed an RNA-sequence analysis to detect key IRE1α-related molecules against MM.

RESULTS

We illustrated the dominant induction of adaptive UPR markers under IRE1α over the PERK pathway in patients with MM. In human MM cells, KIRA8 decreased cell viability and induced apoptosis, along with the induction of C/EBP homologous protein (CHOP); its combination with bortezomib exhibited more anti-myeloma effects than KIRA8 alone. Nilotinib exerted a similar effect compared with KIRA8. RNA-sequencing identified Polo-like kinase 2 (PLK2) as a KIRA8-suppressed gene. Specifically, the IRE1α overexpression induced PLK2 expression, which was decreased by KIRA8. KIRA8 and PLK2 inhibition exerted anti-myeloma effects with apoptosis induction and the regulation of cell proliferation. Finally, PLK2 was pathologically confirmed to be highly expressed in patients with MM.

CONCLUSION

Dominant activation of adaptive IRE1α was established in patients with MM. Both KIRA8 and nilotinib exhibited anti-myeloma effects, which were enhanced by bortezomib. Adaptive IRE1α signaling and PLK2 could be potential therapeutic targets and biomarkers in MM.

Endoplasmic reticulum stress in the dorsal root ganglia regulates large-conductance potassium channels and contributes to pain in a model of multiple sclerosis

Neuropathic pain is a common symptom of multiple sclerosis (MS) and current treatment options are ineffective. In this study, we investigated whether endoplasmic reticulum (ER) stress in dorsal root ganglia (DRG) contributes to pain hypersensitivity in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Inflammatory cells and increased levels of ER stress markers are evident in post-mortem DRGs from MS patients. Similarly, we observed ER stress in the DRG of mice with EAE and relieving ER stress with a chemical chaperone, 4-phenylbutyric acid (4-PBA), reduced pain hypersensitivity. In vitro, 4-PBA and the selective PERK inhibitor, AMG44, normalize cytosolic Ca²⁺ transients in putative DRG nociceptors. We went on to assess disease-mediated changes in the functional properties of Ca²⁺ -sensitive BK-type K⁺ channels in DRG neurons. We found that the conductance-voltage (GV) relationship of BK channels was shifted to a more positive voltage, together with a more depolarized resting membrane potential in EAE cells. Our results suggest that ER stress in sensory neurons of MS patients and mice with EAE is a source of pain and that ER stress modulators can effectively counteract this phenotype.

The IRE1 and PERK arms of the unfolded protein response promote survival of rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma, is associated with a low 5-year survival and harsh treatment side effects, underscoring an urgent need for therapy. The unfolded protein response (UPR) is activated in response to endoplasmic reticulum (ER) stress, where three ER stress receptors, IRE1, PERK and ATF6, aim to restore cellular homeostasis. The UPR is pro-tumourigenic in many cancers. In this study, we investigate basal UPR activity in RMS. Basal activation of IRE1 and PERK was observed in RMS cell lines, which was diminished upon addition of the IRE1 RNase inhibitor, MKC8866, or PERK inhibitor, AMGEN44. UPR inhibition caused a reduction in cell viability, cell proliferation and inhibition of long-term colony formation in both subtypes of RMS. Alveolar RMS (ARMS) subtype was highly sensitive to IRE1 inhibition, whereas embryonal RMS (ERMS) subtypes responded more markedly to PERK inhibition. Further investigation revealed a robust activation of senescence upon UPR inhibition. For the first time, the UPR is implicated in RMS biology and phenotype, and inhibition of UPR signalling reduces cell growth, suggesting that the UPR may be a promising target in RMS.

Insight into potent leads for alzheimer's disease by using several artificial intelligence algorithms

Several proteins including S-nitrosoglutathione reductase (GSNOR), complement Factor D, complement 3b (C3b) and Protein Kinase R-like Endoplasmic Reticulum Kinase (PERK), have been demonstrated to be involved in pathogenesis pathways for Alzheimer's disease (AD) and considered as potential treatment targets to AD. Based on the concept of multitargets, a network pharmacology-based approach was employed to investigate potential Traditional Chinese Medicine (TCM) candidates that can dock well with GSNOR, C3b, Factor D and PERK proteins. To predict the bioactivities of candidates, Artificial Intelligence (AI) algorithms composed of seven machine learning algorithms and a deep learning model were performed to validate the docking results. Furthermore, in this study, we propose a novel combined method for efficiently exploring the predicted results of AI algorithms. Besides, Comparative force field analysis (CoMFA) and comparative similarity indices analysis (CoMSIA) were performed to construct predicted models. The results show that the square correlation coefficients (R²) of all models are almost higher than 0.75, which also acquire good achievements on the test set. Moreover, the binding stability of the potential inhibitors were evaluated using 100 ns of MD simulation. Collectively, this study elucidate that the herbs Ardisia japonica, Ligusticum chuanxiong, Lippia nodiflora and Mirabilis jalapa containing 2,2'-[benzene-1,4-diylbis(methanediyloxybenzene-4,1-diyl)]bis(oxoacetic acid), Glyasperin B, Nodifloridin A, Miraxanthin III and l-Valine-l-valine anhydride might be a potential medicine formula for AD.

Endorepellin evokes an angiostatic stress signaling cascade in endothelial cells

Endorepellin, the C-terminal fragment of the heparan sulfate proteoglycan perlecan, influences various signaling pathways in endothelial cells by binding to VEGFR2. In this study, we discovered that soluble endorepellin activates the canonical stress signaling pathway consisting of PERK, eIF2α, ATF4, and GADD45α. Specifically, endorepellin evoked transient activation of VEGFR2, which, in turn, phosphorylated PERK at Thr980 Subsequently, PERK phosphorylated eIF2α at Ser51, upregulating its downstream effector proteins ATF4 and GADD45α. RNAi-mediated knockdown of PERK or eIF2α abrogated the endorepellin-mediated up-regulation of GADD45α, the ultimate effector protein of this stress signaling cascade. To functionally validate these findings, we utilized an ex vivo model of angiogenesis. Exposure of the aortic rings embedded in 3D fibrillar collagen to recombinant endorepellin for 2-4 h activated PERK and induced GADD45α vis à vis vehicle-treated counterparts. Similar effects were obtained with the established cellular stress inducer tunicamycin. Notably, chronic exposure of aortic rings to endorepellin for 7-9 days markedly suppressed vessel sprouting, an angiostatic effect that was rescued by blocking PERK kinase activity. Our findings unravel a mechanism by which an extracellular matrix protein evokes stress signaling in endothelial cells, which leads to angiostasis.

Targeting the Unfolded Protein Response in Hormone-Regulated Cancers

Cancer cells exploit many of the cellular adaptive responses to support their survival needs. One of these is the unfolded protein response (UPR), a highly conserved signaling pathway that is mounted in response to endoplasmic reticulum (ER) stress. Recent work showed that steroid hormones, in particular estrogens and androgens, regulate the canonical UPR pathways in breast cancer (BCa) and prostate cancer (PCa). In addition, UPR has pleiotropic effects in advanced disease and development of therapy resistance. These findings implicate the UPR pathway as a novel target in hormonally regulated cancers in the clinic. Here, we review the potential therapeutic value of recently developed small molecule inhibitors of UPR in hormone regulated cancers.

Molecular modeling provides a structural basis for PERK inhibitor selectivity towards RIPK1

Molecular modelling explains the lack of selectivity for inhibitors GSK2606414 and GSK2656157, as compared to inhibitor AMG44.

microRNAs in Cardiovascular Disease: Small Molecules but Big Roles

microRNAs (miRNAs) are an evolutionarily conserved class of small single-stranded noncoding RNAs. The aberrant expression of specific miRNAs has been implicated in the development and progression of diverse cardiovascular diseases. For many decades, miRNA therapeutics has flourished, taking advantage of the fact that miRNAs can modulate gene expression and control cellular phenotypes at the posttranscriptional level. Genetic replacement or knockdown of target miRNAs by chemical molecules, referred to as miRNA mimics or inhibitors, has been used to reverse their abnormal expression as well as their adverse biological effects in vitro and in vivo in an effort to fully implement the therapeutic potential of miRNA-targeting treatment. However, the limitations of the chemical structure and delivery systems are hindering progress towards clinical translation. Here, we focus on the regulatory mechanisms and therapeutic trials of several representative miRNAs in the context of specific cardiovascular diseases; from this basic perspective, we evaluate chemical modifications and delivery vectors of miRNA-based chemical molecules and consider the underlying challenges of miRNA therapeutics as well as the clinical perspectives on their applications.

Identification of Novel, Potent, and Orally Available GCN2 Inhibitors with Type I Half Binding Mode

General control nonderepressible 2 (GCN2) is a master regulator kinase of amino acid homeostasis and important for cancer survival in the tumor microenvironment under amino acid depletion. We initiated studies aiming at the discovery of novel GCN2 inhibitors as first-in-class antitumor agents and conducted modification of the substructure of sulfonamide derivatives with expected type I half binding on GCN2. Our synthetic strategy mainly corresponding to the αC-helix allosteric pocket of GCN2 led to significant enhancement in potency and a good pharmacokinetic profile in mice. In addition, compound 6d, which showed slow dissociation in binding on GCN2, demonstrated antiproliferative activity in combination with the asparagine-depleting agent asparaginase in an acute lymphoblastic leukemia (ALL) cell line, and it also displayed suppression of GCN2 pathway activation with asparaginase treatment in the ALL cell line and mouse xenograft model.

ER stress and UPR activation in glioblastoma: identification of a noncanonical PERK mechanism regulating GBM stem cells through SOX2 modulation

Patients with aggressive brain tumors, named glioblastoma multiforme (GBM), have a poor prognoses. Here we explored if the ER stress/unfolded protein response (UPR) is involved in the pathophysiology of GBM and may provide novel therapeutic targets. Immunohistochemical analyses of a tissue microarray containing primary GBM specimens showed strong variability in expression of the UPR markers GRP78/BiP, XBP1, and ATF4. Interestingly, high ATF4 expression was associated with poor overall survival suggesting involvement of PERK signaling in GBM progression. In vitro experiments using patient-derived neurospheres, enriched for GBM stem cells (GSCs), showed high sensitivity for the ER stressor thapsigargin (Tg) mainly via PERK signaling. In contrast, neurospheres-derived differentiated GBM cells were less sensitive likely due to lower UPR activity as indicated by comparative transcriptional profiling. Tg and Tunicamycin strongly reduced neurosphere forming ability of GSCs that was linked with potent PERK-dependent downregulation of SOX2 protein. Interestingly, SOX2 downregulation occurred directly via PERK, not requiring downstream activation of the PERK-UPR pathway. Moreover, PERK inactivation resulted in aberrant serum-induced differentiation of GBM neurospheres accompanied by persistent SOX2 expression, delayed upregulation of GFAP and reduced cell adherence. In conclusion, we provide evidence that PERK signaling contributes to the prognoses of primary GBM patients and identified PERK as a novel regulator of SOX2 expression and GSC differentiation. The role of PERK appeared to be pleiotropic involving UPR-dependent, as well as novel identified noncanonical mechanisms regulating SOX2. ER stress and PERK modulation appear to provide promising therapeutic targets for therapy in GBM.

Dual role of Endoplasmic Reticulum Stress-Mediated Unfolded Protein Response Signaling Pathway in Carcinogenesis

Cancer constitutes a grave problem nowadays in view of the fact that it has become one of the main causes of death worldwide. Poor clinical prognosis is presumably due to cancer cells metabolism as tumor microenvironment is affected by oxidative stress. This event triggers adequate cellular response and thereby creates appropriate conditions for further cancer progression. Endoplasmic reticulum (ER) stress occurs when the balance between an ability of the ER to fold and transfer proteins and the degradation of the misfolded ones become distorted. Since ER is an organelle relatively sensitive to oxidative damage, aforementioned conditions swiftly cause the activation of the unfolded protein response (UPR) signaling pathway. The output of the UPR, depending on numerous factors, may vary and switch between the pro-survival and the pro-apoptotic branch, and hence it displays opposing effects in deciding the fate of the cancer cell. The role of UPR-related proteins in tumorigenesis, such as binding the immunoglobulin protein (BiP) and inositol-requiring enzyme-1α (IRE1α), activating transcription factor 6 (ATF6) or the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), has already been specifically described so far. Nevertheless, due to the paradoxical outcomes of the UPR activation as well as gaps in current knowledge, it still needs to be further investigated. Herein we would like to elicit the actual link between neoplastic diseases and the UPR signaling pathway, considering its major branches and discussing its potential use in the development of a novel, anti-cancer, targeted therapy.

Pharmacological targeting of the unfolded protein response for disease intervention

Accumulation of unfolded proteins at the endoplasmic reticulum (ER) is a salient attribute of many human diseases including obesity, liver disorders, cancer, diabetes and neurodegeneration. To restore ER proteostasis, cells activate the unfolded protein response (UPR), a signaling pathway that imposes adaptive programs or triggers apoptosis of damaged cells. The UPR is critical to sustain the normal function of specialized secretory cells (i.e., pancreatic β cells and B lymphocytes) and to control the production of lipids and cholesterol in the liver. In the context of disease, adaptive UPR responses have been linked to the growth of solid tumors, whereas chronic ER stress contributes to cell dysfunction in brain diseases, metabolic syndromes, among other conditions. Here we discuss recent developments in the design and optimization of novel compounds to manipulate UPR signaling and their efficacy in various disease models.

Visible-Light Induced Radical Perfluoroalkylation/Cyclization Strategy To Access 2-Perfluoroalkylbenzothiazoles/Benzoselenazoles by EDA Complex

A novel and practical fluoroalkyl radical-initiated cascade reaction was developed to access diverse 2-fluoroalkylbenzothiazoles by reacting various fluoroalkyl radical sources, including perfluoroalkyl iodide (IC _nF_{2 n+1}, n = 3-8, 10), ICF(CF₃)₂, ICF₂COOEt, ICF₂CF₂Cl, or ICF₂CF₂Br, tetramethylethane-1,2-diamine (TMEDA), and 2-isocyanoaryl thioethers in tetrahydrofuran under nitrogen atmosphere and blue-light irradiation conditions. Furthermore, this one-pot protocol could well be expanded to access various 2-fluoroalkylbenzoselenazoles starting from (2-isocyanophenyl)(methyl)selane, perfluoroalkyl iodides (IC _nF_{2 n+1}, n = 3-8) or ICF₂COOEt and TMEDA.

The unfolded protein response modulators GSK2606414 and KIRA6 are potent KIT inhibitors

IRE1, PERK, and ATF6 are the three transducers of the mammalian canonical unfolded protein response (UPR). GSK2606414 is a potent inhibitor of PERK, while KIRA6 inhibits the kinase activity of IRE1. Both molecules are frequently used to probe the biological roles of the UPR in mammalian cells. In a direct binding assay, GSK2606414 bound to the cytoplasmic domain of KIT with dissociation constants (K_d) value of 664 ± 294 nM whereas KIRA6 showed a K_d value of 10.8 ± 2.9 µM. In silico docking studies confirmed a compact interaction of GSK2606414 and KIRA6 with KIT ATP binding pocket. In cultured cells, GSK2606414 inhibited KIT tyrosine kinase activity at nanomolar concentrations and in a PERK-independent manner. Moreover, in contrast to other KIT inhibitors, GSK2606414 enhanced KIT endocytosis and its lysosomal degradation. Although KIRA6 also inhibited KIT at nanomolar concentrations, it did not prompt KIT degradation, and rescued KIT from GSK2606414-mediated degradation. Consistent with KIT inhibition, nanomolar concentrations of GSK2606414 and KIRA6 were sufficient to induce cell death in a KIT signaling-dependent mast cell leukemia cell line. Our data show for the first time that KIT is a shared target for two seemingly unrelated UPR inhibitors at concentrations that overlap with PERK and IRE1 inhibition. Furthermore, these data underscore discrepancies between in vitro binding measurements of kinase inhibitors and inhibition of the tyrosine kinase receptors in living cells.

Unfolded Protein Response as a Therapeutic Target in Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide. Despite overwhelming socioeconomic impact and mounting clinical needs, our understanding of the underlying pathophysiology remains incomplete. Multiple forms of cardiovascular disease involve an acute or chronic disturbance in cardiac myocytes, which may lead to potent activation of the Unfolded Protein Response (UPR), a cellular adaptive reaction to accommodate protein-folding stress. Accumulation of unfolded or misfolded proteins in the Endoplasmic Reticulum (ER) elicits three signaling branches of the UPR, which otherwise remain quiescent. This ER stress response then transiently suppresses global protein translation, augments production of protein-folding chaperones, and enhances ER-associated protein degradation, with an aim to restore cellular homeostasis. Ample evidence has established that the UPR is strongly induced in heart disease. Recently, the mechanisms of action and multiple pharmacological means to favorably modulate the UPR are emerging to curb the initiation and progression of cardiovascular disease. Here, we review the current understanding of the UPR in cardiovascular disease and discuss existing therapeutic explorations and future directions.

Emerging role of Unfolded Protein Response (UPR) mediated proteotoxic apoptosis in diabetes

Endoplasmic reticulum (ER) is a crucial single membrane organelle that acts as a quality control system for cellular proteins as it is intricately involved in their synthesis, folding and trafficking to the respective targets. Type 2 diabetes is characterized by enhanced blood glucose level that promotes insulin resistance and hampers cellular glucose metabolism. Hyperglycemia provokes mitochondrial ROS production and glycation of proteins which exert a tremendous load on ER for conventional refolding of misfolded/unfolded and nascent proteins that perturb ER homeostasis resulting in apoptotic cell death. Impairment in ER functions is suspected to be through specific ER membrane-bound proteins known as Unfolded Protein Response (UPR) sensor proteins. Conformational changes in these proteins induce oligomerization and cross-autophosphorylation which facilitate processes required for the restoration of ER homeostatic imbalance. Multiple studies have reported the involvement of UPR mediated autophagy and apoptotic pathways in the progression of metabolic disorders including diabetes, cardiac ischemia/reperfusion injury and hypoxia-mediated cell death. In this review, the involvement of UPR pathways in the progression of diabetes associated complications have been addressed, which underscores molecular crosstalks during neuropathy, nephropathy, hepatic injury and retinopathy. A better understanding of these molecular interventions may reveal advanced therapeutic approaches for preventing diabetic comorbidities. The article also highlights the importance of phytochemicals that are emerging as novel ER stress inhibitors and are being explored for targeted interaction in preventing cell death responses during diabetes.

Triazolo[4,5-d]pyrimidines as Validated General Control Nonderepressible 2 (GCN2) Protein Kinase Inhibitors Reduce Growth of Leukemia Cells

Cellular stress signals activate adaptive signaling pathways of the mammalian integrated stress response (ISR), of which the unfolded protein response (UPR) is a subset. These pathways converge at the phosporylation of eIF2α. Drug-like, potent and selective chemical inhibitors (valid chemical probes) targeting major ISR kinases have been previously identified, with the exception of GCN2. We synthesized and evaluated a series of GCN2 inhibitors based on a triazolo[4,5-d]pyrimidine scaffold. Several compounds potently inhibited GCN2 in vitro and displayed good selectivity over the related kinases PERK, HRI, and IRE1. The compounds inhibited phosporylation of eIF2α in HEK293T cells with an IC₅₀ < 150 nM, validating them as chemical probes for cellular studies. These probes were screened against the National Cancer Institute NCI-60 human cancer cell line panel. Uniform growth inhibition was observed in the leukemia group of cell lines. Growth inhibition in the most sensitive cell lines coincided with high GCN2 mRNA expression levels. Oncomine analysis revealed high GCN2 expression accompanied by lower asparagine synthetase (ASNS) expression in patient-derived acute lymphoblastic leukemias with B-Cell origins (B-ALL) as well. Notably, asparaginase, which depletes amino acids and triggers GCN2 activity, is a licensed, first-line B-ALL treatment. Thus, we hypothesize that leukemias exhibiting high GCN2 expression and low ASNS expression may be susceptible to pharmacologic GCN2 inhibition.

The Unfolded Protein Response in Breast Cancer

In 2018, in the US alone, it is estimated that 268,670 people will be diagnosed with breast cancer, and that 41,400 will die from it. Since breast cancers often become resistant to therapies, and certain breast cancers lack therapeutic targets, new approaches are urgently required. A cell-stress response pathway, the unfolded protein response (UPR), has emerged as a promising target for the development of novel breast cancer treatments. This pathway is activated in response to a disturbance in endoplasmic reticulum (ER) homeostasis but has diverse physiological and disease-specific functions. In breast cancer, UPR signalling promotes a malignant phenotype and can confer tumours with resistance to widely used therapies. Here, we review several roles for UPR signalling in breast cancer, highlighting UPR-mediated therapy resistance and the potential for targeting the UPR alone or in combination with existing therapies.

PERK signalling pathway mediates single prolonged stress-induced dysfunction of medial prefrontal cortex neurons

Post-traumatic stress disorder (PTSD) is characterized with abnormal learning and memory. Impairments in learning and memory are closely associated with apoptosis in the medial prefrontal cortex (mPFC). We previously examined the endoplasmic reticulum (ER) stress was involved in the apoptosis in the mPFC of PTSD. The PERK pathway plays the important role in the ER stress-induced apoptosis. The aim of the present study was to explore the role of PERK pathway in neuronal apoptosis in the mPFC of rat models of PTSD. We used the single prolonged stress (SPS) to mimic PTSD in rats and studied the effects of the PERK pathway in mPFC. Learning and memory behavior were examined by Morris water maze and novel object recognition tests. Apoptosis in mPFC was detected by TUNEL staining. Our results showed decreased learning memory and increased apoptosis of mPFC neurons in rats exposed to SPS. SPS exposure upregulate mRNA expressions of PERK, p-PERK, eIF2α, p-eIF2α, nuclear ATF4 and C/EBP-homologous protein (CHOP) in mPFC neurons, but the protein levels of these molecules showed difference in magnitude and time course. GSK2606414 (an antagonist of PERK) treatment successfully reversed the above changes. These results suggested that the PERK pathway mediated SPS-induced neural apoptosis in the mPFC. These findings will be helpful in understanding mPFC-related pathogenesis of PTSD.

Phenylpyridine-2-ylguanidines and rigid mimetics as novel inhibitors of TNFα overproduction: Beneficial action in models of neuropathic pain and of acute lung inflammation

4-phenylpyridin-2-yl-guanidine (5b): a new inhibitor of the overproduction of pro-inflammatory cytokines (TNFα and Il1β) was identified from a high-throughput screening of a chemical library on human peripheral blood mononuclear cells (PBMCs) after LPS stimulation. Derivatives, homologues and rigid mimetics of 5b were designed and synthesized, and their cytotoxicity and ability to inhibit TNFα overproduction were evaluated. Among them, compound 5b and its mimetic 12 (2-aminodihydroquinazoline) showed similar inhibitory activities, and were evaluated in vivo in models of lung inflammation and neuropathic pain in mice. In particular, compound 12 proved to be active (5 mg/kg, ip) in both models.