Inducing apoptosis of cancer cells using small-molecule plant compounds that bind to GRP78

Eurycomanone inhibits osteosarcoma growth and metastasis by suppressing GRP78 expression

ETHNOPHARMACOLOGICAL RELEVANCE

Osteosarcoma (OS) is characterized by rapid growth and frequent pulmonary metastasis. Eurycoma longifolia Jack, a flowering plant primarily found in Southeast Asian countries, is commonly used in traditional herbal medicine. Its root extract is mainly used for against cancer, malaria, parasites and other conditions. The active compound in its root extract, eurycomanone (EUR), has been proven to inhibit lung and liver cancer proliferation.

AIM OF THE STUDY

Our research aimed to investigate the inhibitory effect and underlying molecular mechanism of EUR on OS growth and metastasis.

MATERIALS AND METHODS

In vitro experiments: western blotting (WB) screened 41 compounds that inhibited GRP78 expression and evaluated the protein levels of GRP78, PARP, cleaved-PARP, MMP2, and MMP9. Cell proliferation was evaluated using CCK-8, EdU, colony formation assay, and cell apoptosis was assessed by flow cytometry. Transwell, wound healing, and tube formation assays were performed to determine the effect of EUR on tumor invasion, migration, and angiogenesis, respectively. Quantitative real-time polymerase chain (qRT-PCR) and dual-luciferase activity assays detected GRP78 mRNA stability and transcription levels post-EUR and thapsigargin treatment. RNA-Seq identified signaling pathways inhibited by EUR. In vivo experiments: effects of EUR in mice were evaluated by H&E staining to detect lung metastasis and potential toxic effects in tissues. Immunohistochemical (IHC) staining detected the expression of Ki-67, CD31, and cleaved caspase-3 in tumors.

RESULTS

GRP78 is highly expressed in OS and correlated with poor prognosis. In vitro, eurycomanone (EUR) significantly downregulated GRP78 expression, inhibited cell proliferation, migration, invasion, tube formation, and induced apoptosis. Moreover, it enhanced trichostatin A (TSA) sensitivity and exhibited inhibitory effects on other cancer types. Mechanistically, EUR decreased GRP78 mRNA stability and transcription. In vivo, EUR inhibited proliferation and invasion in tibial and PDX models.

CONCLUSIONS

Our study demonstrated that EUR inhibits the growth and metastasis of OS by reducing GRP78 mRNA stability and inhibiting its transcription, which offers a novel approach for clinical treatment of OS.

Synthetic and Natural Inhibitors of Mortalin for Cancer Therapy

Upregulation of stress chaperone Mortalin has been closely linked to the malignant transformation of cells, tumorigenesis, the progression of tumors to highly aggressive stages, metastasis, drug resistance, and relapse. Various in vitro and in vivo assays have provided evidence of the critical role of Mortalin upregulation in promoting cancer cell characteristics, including proliferation, migration, invasion, and the inhibition of apoptosis, a consistent feature of most cancers. Given its critical role in several steps in oncogenesis and multi-modes of action, Mortalin presents a promising target for cancer therapy. Consequently, Mortalin inhibitors are emerging as potential anti-cancer drugs. In this review, we discuss various inhibitors of Mortalin (peptides, small RNAs, natural and synthetic compounds, and antibodies), elucidating their anti-cancer potentials.

Small molecules for impairing endoplasmic reticulum in cancer

The endoplasmic reticulum plays an important role in maintaining the protein homeostasis of cells as well as regulating Ca2+ storage. An increased load of unfolded proteins in the endoplasmic reticulum due to alterations in the cell's metabolic pathway leads to the activation of the unfolded protein response, also known as ER stress. ER stress plays a major role in maintaining the growth and survival of various cancer cells, but persistent ER stress can also lead to cell death and hence can be a therapeutic pathway in the treatment of cancer. In this review, we focus on different types of small molecules that impair different ER stress sensors, the protein degradation machinery, and chaperone proteins. We also review the metal complexes and other miscellaneous compounds inducing ER stress through multiple mechanisms. Finally, we discuss the challenges in this emerging area of research and the potential direction of research to overcome them towards next-generation ER-targeted cancer therapy.

The unfolded protein response machinery in glioblastoma genesis, chemoresistance and as a druggable target

BACKGROUND

The role of the unfolded protein response (UPR) has been progressively unveiled over the last decade and several studies have investigated its implication in glioblastoma (GB) development. The UPR restores cellular homeostasis by triggering the folding and clearance of accumulated misfolded proteins in the ER consecutive to endoplasmic reticulum stress. In case it is overwhelmed, it induces apoptotic cell death. Thus, holding a critical role in cell fate decisions.

METHODS

This article, reviews how the UPR is implicated in cell homeostasis maintenance, then surveils the evidence supporting the UPR involvement in GB genesis, progression, angiogenesis, GB stem cell biology, tumor microenvironment modulation, extracellular matrix remodeling, cell fate decision, invasiveness, and grading. Next, it concurs the evidence showing how the UPR mediates GB chemoresistance-related mechanisms.

RESULTS

The UPR stress sensors IRE1, PERK, and ATF6 with their regulator GRP78 are upregulated in GB compared to lower grade gliomas and normal brain tissue. They are activated in response to oncogenes and are implicated at different stages of GB progression, from its genesis to chemoresistance and relapse. The UPR arms can be effectors of apoptosis as mediators or targets.

CONCLUSION

Recent research has established the role of the UPR in GB pathophysiology and chemoresistance. Targeting its different sensors have shown promising in overcoming GB chomo- and radioresistance and inducing apoptosis.

Neuroprotective effects of flavonoids: endoplasmic reticulum as the target

The incidence of neurological disorders, particularly age-related neurodegenerative pathologies, exhibits an alarming upward trend, while current pharmacological interventions seldom achieve curative outcomes. Despite their diverse clinical presentations, neurological diseases often share a common pathological thread: the aberrant accumulation of misfolded proteins within the endoplasmic reticulum (ER). This phenomenon, known as ER stress, arises when the cell's intrinsic quality control mechanisms fail to cope with the protein-folding burden. Consequently, misfolded proteins accumulate in the ER lumen, triggering a cascade of cellular stress responses. Recognizing this challenge, researchers have intensified their efforts over the past two decades to explore natural compounds that could potentially slow or even reverse these devastating pathologies. Flavonoids constitute a vast and heterogeneous class of plant polyphenols, with over 10,000 identified from diverse natural sources such as wines, vegetables, medicinal plants, and organic products. Flavonoids are generally divided into six different subclasses: anthocyanidins, flavanones, flavones, flavonols, isoflavones, and flavonols. The diverse family of flavonoids, featuring a common phenolic ring backbone adorned with varying hydroxyl groups and additional modifications, exerts its antioxidant activity by inhibiting the formation of ROS, as evidenced by research. Also, studies suggest that polyphenols such as flavonoids can regulate ER stress through apoptosis and autophagy. By understanding these mechanisms, we can unlock the potential of flavonoids as novel therapeutic agents for neurodegenerative disorders. Therefore, this review critically examines the literature exploring the modulatory effects of flavonoids on various steps of the ER stress in neurological disorders.

Targeting HSP70 chaperones by rhein sensitizes liver cancer to artemisinin derivatives

BACKGROUND

Liver cancer is one of common types of cancer with poor prognosis and limited therapies. Heat shock proteins (HSP) are molecular chaperones that have important roles in tumorigenesis, and emerging as therapeutic targets. Artemisinin and rhein are natural agents from Artemisia annua L. and Rheum undulatum L., respectively. Both rhein and artemisinin have anticancer effects; however, the molecular targets of rhein remain to be identified. It is also unclear whether rhein can synergize with artemisinin derivatives to inhibit liver cancer.

PURPOSE

We aim to identify the targets of rhein in the treatment of hepatocarcinoma and determine the effects of combining rhein and artemisinin derivatives on liver cancer cells.

METHODS

The targets of rhein were detected by mass spectrometry and validated by rhein-proteins interaction assays. The effects of rhein on the chaperone activity of HSP72/HSC70/GRP78 were determined by luciferase refolding assays. Cell viability and apoptosis were determined by CCK8 and flow cytometry assays. For in vivo study, xenograft tumor models were established and treated with rhein and artesunate. Tumor growth was monitored regularly.

RESULTS

Mass spectrometry analysis of rhein-binding proteins in HepG2 cells revealed that HSP72, HSC70 and GRP78 were more profoundly pulled down by rhein-crosslinked sepharose 4B beads compared to the control beads. Further experiments demonstrated that rhein directly interacted with HSP72/HSC70/GRP78 proteins, and inhibit their activity of refolding denatured luciferase. Meanwhile, rhein induced proteasomal degradation of HIF1α and β-catenin. Artesunate or dihydroartemisinin in combination with knockdown of both HSP72 and HSC70 significantly inhibited cell viability. The HSP70/HSC70/GRP78 inhibitors VER-155,008 and rhein phenocopied HSP72/HSC70 knockdown, synergizing with artesunate or dihydroartemisinin to inhibit hepatocarcinoma cell viability. Combinatorial treatment with rhein and artemisinin derivatives significantly induced hepatocarcinoma cell apoptosis, and inhibited tumor growth in vivo.

CONCLUSIONS

The current study demonstrates that rhein is a novel HSP72/HSC70/GRP78 inhibitor that suppresses the chaperone activity of HSP70s. Dual inhibition of HSP72 and HSC70 can enhance the sensitivity of hepatocarcinoma cells to artemisinin derivatives. Combined treatment with artemisinin derivative and rhein significantly inhibits hepatocarcinoma. Artemisinin derivatives in combination with dual inhibition of HSP72 and HSC70 represents a new approach to improve cancer therapy.

Cellular stress responses as modulators of drug cytotoxicity in pharmacotherapy of glioblastoma

Despite the extensive efforts to find effective therapeutic strategies, glioblastoma (GBM) remains a therapeutic challenge with dismal prognosis of survival. Over the last decade the role of stress responses in GBM therapy has gained a great deal of attention, since depending on the duration and intensity of these cellular programs they can be cytoprotective or promote cancer cell death. As such, initiation of the UPR, autophagy or oxidative stress may either impede or facilitate drug-mediated cell killing. In this review, we summarize the mechanisms that regulate ER stress, autophagy, and oxidative stress during GBM development and progression to later discuss the involvement of these stress pathways in the response to different treatments. We also discuss how a precise understanding of the molecular mechanisms regulating stress responses evoked by different pharmacological agents could decisively contribute to the design of novel and more effective combinational treatments against brain malignancies.

Recent advances in small molecule and peptide inhibitors of glucose-regulated protein 78 for cancer therapy

Glucose-regulated protein 78 (GRP78) is one of key endoplasmic reticulum (ER) chaperone proteins that regulates the unfolded protein response (UPR) to maintain ER homeostasis. As a core factor in the regulation of the UPR, GRP78 takes a critical part in the cellular processes required for tumorigenesis, such as proliferation, metastasis, anti-apoptosis, immune escape and chemoresistance. Overexpression of GRP78 is closely correlated with tumorigenesis and poor prognosis in various malignant tumors. Targeting GRP78 is regarded as a potentially promising therapeutic strategy for cancer therapy. Although none of the GRP78 inhibitors have been approved to date, there have been several studies of GRP78 inhibitors. Herein, we comprehensively review the structure, physiological functions of GRP78 and the recent progress of GRP78 inhibitors, and discuss the structures, in vitro and in vivo efficacies, and merits and demerits of these inhibitors to inspire further research. Additionally, the feasibility of GRP78-targeting proteolysis-targeting chimeras (PROTACs), disrupting GRP78 cochaperone interactions, or covalent inhibition are also discussed as novel strategies for drugs discovery targeting GRP78, with the hope that these strategies can provide new opportunities for targeted GRP78 antitumor therapy.

Targeting histone deacetylase-3 blocked epithelial-mesenchymal plasticity and metastatic dissemination in gastric cancer

BACKGROUND AND PURPOSE

Histone deacetylase (HDAC) inhibitors (HDIs) can modulate the epithelial-mesenchymal transition (EMT) progression and inhibit the migration and invasion of cancer cells. Emerging as a novel class of anti-cancer drugs, HDIs are attracted much attention in the field of drug discovery. This study aimed to discern the underlying mechanisms of Honokiol in preventing the metastatic dissemination of gastric cancer cells by inhibiting HDAC3 activity/expression.

EXPERIMENTAL APPROACH

Clinical pathological analysis was performed to determine the relationship between HDAC3 and tumor progression. The effects of Honokiol on pharmacological characterization, functional, transcriptional activities, organelle structure changes, and molecular signaling were analyzed using binding assays, differential scanning calorimetry, luciferase reporter assay, HDAC3 activity, ER stress response element activity, transmission electron microscopy, immune-blotting, and Wnt/β-catenin activity assays. The in vivo effects of Honokiol on peritoneal dissemination were determined by a mouse model and detected by PET/CT tomography.

KEY RESULTS

HDAC3 over-expression was correlated with poor prognosis. Honokiol significantly abolished HDAC3 activity (Y298) via inhibition of NFκBp65/CEBPβ signaling, which could be reversed by the over-expression of plasmids of NFκBp65/CEBPβ. Treatments with 4-phenylbutyric acid (a chemical chaperone) and calpain-2 gene silencing inhibited Honokiol-inhibited NFκBp65/CEBPβ activation. Honokiol increased ER stress markers and inhibited EMT-associated epithelial markers, but decreased Wnt/β-catenin activity. Suppression of HDAC3 by both Honokiol and HDAC3 gene silencing decreased cell migration and invasion in vitro and metastasis in vivo.

CONCLUSIONS AND IMPLICATIONS

Honokiol acts by suppressing HDAC3-mediated EMT and metastatic signaling. By prohibiting HDAC3, metastatic dissemination of gastric cancer may be blocked. Conceptual model showing the working hypothesis on the interaction among Honokiol, HDAC3, and ER stress in the peritoneal dissemination of gastric cancer. Honokiol targeting HDAC3 by ER stress cascade and mitigating the peritoneal spread of gastric cancer. Honokiol-induced ER stress-activated calpain activity targeted HDAC3 and blocked Tyr298 phosphorylation, subsequently blocked cooperating with EMT transcription factors and cancer progression. The present study provides evidence to demonstrate that HDAC3 is a positive regulator of EMT and metastatic growth of gastric cancer cells. The findings here imply that overexpressed HDAC3 is a potential therapeutic target for honokiol to reverse EMT and prevent gastric cancer migration, invasion, and metastatic dissemination. • Honokiol significantly abolished HDAC3 activity on catalytic tyrosine 298 residue site. In addition, Honokiol-induced ER stress markedly inhibited HDAC3 expression via inhibition of NFκBp65/CEBPβ signaling. • HDAC3, which is a positive regulator of metastatic gastric cancer cell growth, can be significantly inhibited by Honokiol. • Opportunities for HDAC3 inhibition may be a potential therapeutic target for preventing gastric cancer metastatic dissemination.

Unveiling the dark side of glucose-regulated protein 78 (GRP78) in cancers and other human pathology: a systematic review

Glucose-Regulated Protein 78 (GRP78) is a chaperone protein that is predominantly expressed in the lumen of the endoplasmic reticulum. GRP78 plays a crucial role in protein folding by assisting in the assembly of misfolded proteins. Under cellular stress conditions, GRP78 can translocate to the cell surface (csGRP78) were it interacts with different ligands to initiate various intracellular pathways. The expression of csGRP78 has been associated with tumor initiation and progression of multiple cancer types. This review provides a comprehensive analysis of the existing evidence on the roles of GRP78 in various types of cancer and other human pathology. Additionally, the review discusses the current understanding of the mechanisms underlying GRP78's involvement in tumorigenesis and cancer advancement. Furthermore, we highlight recent innovative approaches employed in downregulating GRP78 expression in cancers as a potential therapeutic target.

Insights and Perspectives on the Role of Proteostasis and Heat Shock Proteins in Fungal Infections

Fungi are a diverse group of eukaryotic organisms that infect humans, animals, and plants. To successfully colonize their hosts, pathogenic fungi must continuously adapt to the host's unique environment, e.g., changes in temperature, pH, and nutrient availability. Appropriate protein folding, assembly, and degradation are essential for maintaining cellular homeostasis and survival under stressful conditions. Therefore, the regulation of proteostasis is crucial for fungal pathogenesis. The heat shock response (HSR) is one of the most important cellular mechanisms for maintaining proteostasis. It is activated by various stresses and regulates the activity of heat shock proteins (HSPs). As molecular chaperones, HSPs participate in the proteostatic network to control cellular protein levels by affecting their conformation, location, and degradation. In recent years, a growing body of evidence has highlighted the crucial yet understudied role of stress response circuits in fungal infections. This review explores the role of protein homeostasis and HSPs in fungal pathogenicity, including their contributions to virulence and host-pathogen interactions, as well as the concerted effects between HSPs and the main proteostasis circuits in the cell. Furthermore, we discuss perspectives in the field and the potential for targeting the components of these circuits to develop novel antifungal therapies.

GRP78 Activity Moderation as a Therapeutic Treatment against Obesity

Glucose-regulated protein 78 (GRP78), a molecular chaperone, is overexpressed in patients suffering from obesity, fatty liver, hyperlipidemia and diabetes. GRP78, therefore, can be not only a biomarker to predict the progression and prognosis of obesity and metabolic diseases but also a potential therapeutic target for anti-obesity treatment. In this paper, GRP78 inhibitors targeting its ATPase domain have been reviewed. Small molecules and proteins that directly bind GRP78 have been described. Putative mechanisms of GRP78 in regulating lipid metabolism were also summarized so as to investigate the role of GRP78 in obesity and other related diseases and provide a theoretical basis for the development and design of anti-obesity drugs targeting GRP78.

The application prospects of honokiol in dermatology

Honokiol is one of the natural extracts of Magnolia officinalis. It is a small molecule, lipophilic compound with extensive biological effects. It has been used in the treatment of multisystem diseases, including digestive diseases, endocrine diseases, nervous system diseases, and various tumors. This paper reviews the biological effects of honokiol on the treatment of skin diseases in recent years, including anti-microbial, anti-oxidant, anti-inflammatory, anti-tumor, anti-fibrosis, anti-allergy, photo-protection, and immunomodulation. Most current researches are focused on the effects of anti-melanoma and photo-protection. Therefore, we summarized the specific mechanisms about these two effects. On the other side of treating skin diseases, the advantages of topical drugs cannot be replaced. As a small molecule fat-soluble compound, honokiol is suitable for external use. We reviewed the advantages and disadvantages of the topical mixed cream and various improved methods. These improvements include physical and chemical penetration enhancers, drug carriers, and chemical derivatives. In conclusion, honokiol has a wide range of effects, and its topical preparation provides a safe and effective way for treating skin diseases.

Emerging role of LETM1/GRP78 axis in lung cancer

The selective autophagy of damaged mitochondria is called mitophagy. Mitochondrial dysfunction, mitophagy, and apoptosis have been suggested to be interrelated in various human lung carcinomas. Leucine zipper EF-hand-containing transmembrane protein-1 (LETM1) was cloned in an attempt to identify candidate genes for Wolf-Hirschhorn syndrome. LETM1 plays a role in mitochondrial morphology, ion homeostasis, and cell viability. LETM1 has also been shown to be overexpressed in different human cancer tissues, including lung cancer. In the current study, we have provided clear evidence that LETM1 acts as an anchoring protein for the mitochondria-associated ER membrane (MAM). Fragmented mitochondria have been found in lung cancer cells with LETM1 overexpression. In addition, a reduction of mitochondrial membrane potential and significant accumulation of microtubule-associated protein 1 A/1B-light chain 3 punctate, which localizes with Red-Mito, was found in LETM1-overexpressed cells, suggesting that mitophagy is upregulated in these cells. Interestingly, glucose-regulated protein 78 kDa (GRP78; an ER chaperon protein) and glucose-regulated protein 75 kDa (GRP75) were posited to interact with LETM1 in the immunoprecipitated LETM1 of H460 cells. This interaction was enhanced in cells treated with carbonyl cyanide m-chlorophenylhydrazone, a chemical mitophagy inducer. Treatment of cells with honokiol (a GRP78 inhibitor) blocked LETM1-mediated mitophagy, and CRISPR/Cas9-mediated GRP75 knockout inhibited LETM1-induced autophagy. Thus, GRP78 interacts with LETM1. Taken together, these observations support the notion that the complex formation of LETM1/GRP75/GRP78 might be an important step in MAM formation and mitophagy, thus regulating mitochondrial quality control in lung cancer.

Natural Compounds as Promising Adjuvant Agents in The Treatment of Gliomas

In humans, glioblastoma is the most prevalent primary malignant brain tumor. Usually, glioblastoma has specific characteristics, such as aggressive cell proliferation and rapid invasion of surrounding brain tissue, leading to a poor patient prognosis. The current therapy-which provides a multidisciplinary approach with surgery followed by radiotherapy and chemotherapy with temozolomide-is not very efficient since it faces clinical challenges such as tumor heterogeneity, invasiveness, and chemoresistance. In this respect, natural substances in the diet, integral components in the lifestyle medicine approach, can be seen as potential chemotherapeutics. There are several epidemiological studies that have shown the chemopreventive role of natural dietary compounds in cancer progression and development. These heterogeneous compounds can produce anti-glioblastoma effects through upregulation of apoptosis and autophagy; allowing the promotion of cell cycle arrest; interfering with tumor metabolism; and permitting proliferation, neuroinflammation, chemoresistance, angiogenesis, and metastasis inhibition. Although these beneficial effects are promising, the efficacy of natural compounds in glioblastoma is limited due to their bioavailability and blood-brain barrier permeability. Thereby, further clinical trials are necessary to confirm the in vitro and in vivo anticancer properties of natural compounds. In this article, we overview the role of several natural substances in the treatment of glioblastoma by considering the challenges to be overcome and future prospects.

Peroxidase from foxtail millet bran exerts anti-colorectal cancer activity via targeting cell-surface GRP78 to inactivate STAT3 pathway

Molecular targeted therapy has become an emerging promising strategy in cancer treatment, and screening the agents targeting at cancer cell specific targets is very desirable for cancer treatment. Our previous study firstly found that a secretory peroxidase of class III derived from foxtail millet bran (FMBP) exhibited excellent targeting anti-colorectal cancer (CRC) activity in vivo and in vitro, whereas its underlying target remains unclear. The highlight of present study focuses on the finding that cell surface glucose-regulated protein 78 (csGRP78) abnormally located on CRC is positively correlated with the anti-CRC effects of FMBP, indicating it serves as a potential target of FMBP against CRC. Further, we demonstrated that the combination of FMBP with the nucleotide binding domain (NBD) of csGRP78 interfered with the downstream activation of signal transducer and activator of transcription 3 (STAT3) in CRC cells, thus promoting the intracellular accumulation of reactive oxygen species (ROS) and cell grown inhibition. These phenomena were further confirmed in nude mice tumor model. Collectively, our study highlights csGRP78 acts as an underlying target of FMBP against CRC, uncovering the clinical potential of FMBP as a targeted agent for CRC in the future.

A Benzenesulfonamide-Based Mitochondrial Uncoupler Induces Endoplasmic Reticulum Stress and Immunogenic Cell Death in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecologic malignancies and requires new therapeutic strategies to improve clinical outcomes. EOC metastasizes in the abdominal cavity through dissemination in the peritoneal fluid and ascites, efficiently adapt to the nutrient-deprived microenvironment, and resist current chemotherapeutic agents. Accumulating evidence suggests that mitochondrial oxidative phosphorylation is critical for the adaptation of EOC cells to this otherwise hostile microenvironment. Although chemical mitochondrial uncouplers can impair mitochondrial functions and thereby target multiple, essential pathways for cancer cell proliferation, traditional mitochondria uncouplers often cause toxicity that precludes their clinical application. In this study, we demonstrated that a mitochondrial uncoupler, specifically 2,5-dichloro-N-(4-nitronaphthalen-1-yl)benzenesulfonamide, hereinafter named Y3, was an antineoplastic agent in ovarian cancer models. Y3 treatment activated AMP-activated protein kinase and resulted in the activation of endoplasmic reticulum stress sensors as well as growth inhibition and apoptosis in ovarian cancer cells in vitro Y3 was well tolerated in vivo and effectively suppressed tumor progression in three mouse models of EOC, and Y3 also induced immunogenic cell death of cancer cells that involved the release of damage-associated molecular patterns and the activation of antitumor adaptive immune responses. These findings suggest that mitochondrial uncouplers hold promise in developing new anticancer therapies that delay tumor progression and protect patients with ovarian cancer against relapse.

Megakaryocytes Mediate Hyperglycemia-Induced Tumor Metastasis

High blood glucose has long been established as a risk factor for tumor metastasis, yet the molecular mechanisms underlying this association have not been elucidated. Here we describe that hyperglycemia promotes tumor metastasis via increased platelet activity. Administration of glucose, but not fructose, reprogrammed the metabolism of megakaryocytes to indirectly prime platelets into a prometastatic phenotype with increased adherence to tumor cells. In megakaryocytes, a glucose metabolism-related gene array identified the mitochondrial molecular chaperone glucose-regulated protein 75 (GRP75) as a trigger for platelet activation and aggregation by stimulating the Ca²⁺-PKCα pathway. Genetic depletion of Glut1 in megakaryocytes blocked MYC-induced GRP75 expression. Pharmacologic blockade of platelet GRP75 compromised tumor-induced platelet activation and reduced metastasis. Moreover, in a pilot clinical study, drinking a 5% glucose solution elevated platelet GRP75 expression and activated platelets in healthy volunteers. Platelets from these volunteers promoted tumor metastasis in a platelet-adoptive transfer mouse model. Together, under hyperglycemic conditions, MYC-induced upregulation of GRP75 in megakaryocytes increases platelet activation via the Ca²⁺-PKCα pathway to promote cancer metastasis, providing a potential new therapeutic target for preventing metastasis. SIGNIFICANCE: This study provides mechanistic insights into a glucose-megakaryocyte-platelet axis that promotes metastasis and proposes an antimetastatic therapeutic approach by targeting the mitochondrial protein GRP75.

Natural Compounds in Glioblastoma Therapy: Preclinical Insights, Mechanistic Pathways, and Outlook

Simple Summary

Glioblastoma (GBM) is a tumor of the brain or spinal cord with poor clinical prognosis. Current interventions, such as chemotherapy and surgical tumor resection, are constrained by tumor invasion and cancer drug resistance. Dietary natural substances are therefore evaluated for their potential as agents in GBM treatment. Various substances found in fruits, vegetables, and other natural products restrict tumor growth and induce GBM cell death. These preclinical effects are promising but remain constrained by natural substances’ varying pharmacological properties. While many of the reviewed substances are available as over-the-counter supplements, their anti-GBM efficacy should be corroborated by clinical trials moving forward.

Abstract

Glioblastoma (GBM) is an aggressive, often fatal astrocyte-derived tumor of the central nervous system. Conventional medical and surgical interventions have greatly improved survival rates; however, tumor heterogeneity, invasiveness, and chemotherapeutic resistance continue to pose clinical challenges. As such, dietary natural substances—an integral component of the lifestyle medicine approach to chronic diseases—are examined as potential chemotherapeutic agents. These heterogenous substances exert anti-GBM effects by upregulating apoptosis and autophagy, inducing cell cycle arrest, interfering with tumor metabolism, and inhibiting proliferation, neuroinflammation, chemoresistance, angiogenesis, and metastasis. Although these beneficial effects are promising, natural substances’ efficacy in GBM is constrained by their bioavailability and blood–brain barrier permeability; various chemical formulations are proposed to improve their pharmacological properties. Many of the reviewed substances are available as over-the-counter dietary supplements, underscoring their viability as lifestyle interventions. However, clinical trials remain necessary to substantiate the in vitro and in vivo properties of natural substances.

The Hydroxyquinoline Analogue YUM70 Inhibits GRP78 to Induce ER Stress-Mediated Apoptosis in Pancreatic Cancer

GRP78 (glucose-regulated protein, 78 kDa) is a key regulator of endoplasmic reticulum (ER) stress signaling. Cancer cells are highly proliferative and have high demand for protein synthesis and folding, which results in significant stress on the ER. To respond to ER stress and maintain cellular homeostasis, cells activate the unfolded protein response (UPR) that promotes either survival or apoptotic death. Cancer cells utilize the UPR to promote survival and growth. In this study, we describe the discovery of a series of novel hydroxyquinoline GRP78 inhibitors. A representative analogue, YUM70, inhibited pancreatic cancer cell growth in vitro and showed in vivo efficacy in a pancreatic cancer xenograft model with no toxicity to normal tissues. YUM70 directly bound GRP78 and inactivated its function, resulting in ER stress-mediated apoptosis. A YUM70 analogue conjugated with BODIPY showed colocalization of the compound with GRP78 in the ER. Moreover, a YUM70-PROTAC (proteolysis targeting chimera) was synthesized to force degradation of GRP78 in pancreatic cancer cells. YUM70 showed a strong synergistic cytotoxicity with topotecan and vorinostat. Together, our study demonstrates that YUM70 is a novel inducer of ER stress, with preclinical efficacy as a monotherapy or in combination with topoisomerase and HDAC inhibitors in pancreatic cancer. SIGNIFICANCE: This study identifies a novel ER stress inducer that binds GRP78 and inhibits pancreatic cancer cell growth in vitro and in vivo, demonstrating its potential as a therapeutic agent for pancreatic cancer.

Targeting unfolded protein response: a new horizon for disease control

Unfolded protein response (UPR) is an evolutionarily conserved pathway triggered during perturbation of endoplasmic reticulum (ER) homeostasis in response to the accumulation of unfolded/misfolded proteins under various stress conditions like viral infection, diseased states etc. It is an adaptive signalling cascade with the main purpose of relieving the stress from the ER, which may otherwise lead to the initiation of cell death via apoptosis. ER stress if prolonged, contribute to the aetiology of various diseases like cancer, type II diabetes, neurodegenerative diseases, viral infections etc. Understanding the role of UPR in disease progression will help design pharmacological drugs targeting the sensors of signalling cascade acting as potential therapeutic agents against various diseases. The current review aims at highlighting the relevance of different pathways of UPR in disease progression and control, including the available pharmaceutical interventions responsible for ameliorating diseased state via modulating UPR pathways.

GDF-15: Diagnostic, prognostic, and therapeutic significance in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the commonest primary malignant brain tumor and has a remarkably weak prognosis. According to the aggressive form of GBM, understanding the accurate molecular mechanism associated with GBM pathogenesis is essential. Growth differentiation factor 15 (GDF-15) belongs to transforming growth factor-β superfamily with important roles to control biological processes. It affects cancer growth and progression, drug resistance, and metastasis. It also can promote stemness in many cancers, and also can stress reactions control, bone generation, hematopoietic growth, adipose tissue performance, and body growth, and contributes to cardiovascular disorders. The role GDF-15 to develop and progress cancer is complicated and remains unclear. GDF-15 possesses tumor suppressor properties, as well as an oncogenic effect. GDF-15 antitumorigenic and protumorigenic impacts on tumor development are linked to the cancer type and stage. However, the GDF-15 signaling and mechanism have not yet been completely identified because of no recognized cognate receptor.

Deciphering the molecular pathways of apoptosis using purified fractions from leaf extract of Basella alba through studying the regulation of apoptosis related genes

Apoptosis plays a pivotal role in the exclusion of abnormal cells without any ruin of surrounding healthy cells. Generally, it occurs through an orderly and autonomously process which is controlled by proper function of various genes. Therefore, the current experiments detect the expression level/pattern of those genes to confirm the involvement of extrinsic and intrinsic pathway using Basella alba leaf (BAL). Several fractions after gel filtration chromatography of BAL extract have been pooled to evaluates its apoptosis induction potentiality on Ehrlich's Ascites Carcinoma (EAC) cells through conducting a number of bio-assays such as cell growth inhibition assay, fluorescence and optical microscopy, DNA fragmentation assay and gene expression analysis etc. The pooled fractions of BAL showed 12-56% inhibitory effect on EAC cell line at the concentration range of 25-400 μg/ml that was determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. They also exhibited excellent cell growth inhibition at in vivo and in vitro condition when treated with 10, 20 and 40 mg/kg day. After administration of six consequent days, significant morphological features of apoptosis were observed in EAC cells under both fluorescence and optical microscope which was further supported by DNA fragmentation assay. The polymerase chain reaction amplification of bax, bcl-2 (B-cell lymphoma 2), p53, tumor necrosis factor-α, Fas, NF-kβ (Nuclear factor-Kappa-B), PARP-1 (Poly (ADP-ribose) polymerase), Cyt-c cas-8, cas-9 and cas-3 revealed that the experimental sample able to induce apoptosis in both extrinsic and intrinsic pathways through altering the gene expression. The current findings suggest that sample from BAL occupy wonderful competence to induce cell apoptosis and become an ideal resource for cancer treatment.

Characterizing Cell Stress and GRP78 in Glioma to Enhance Tumor Treatment

Glioblastoma (GBM) is the most common primary brain tumor, carrying a very poor prognosis, with median overall survival at about 12 to 15 months despite surgical resection, chemotherapy with temozolomide (TMZ), and radiation therapy. GBM recurs in the vast majority of patients, with recurrent tumors commonly displaying increase in resistance to standard of care chemotherapy, TMZ, as well as radiotherapy. One of the most commonly cited mechanisms of chemotherapeutic and radio-resistance occurs via the glucose-regulated protein 78 (GRP78), a well-studied mediator of the unfolded protein response (UPR), that has also demonstrated potential as a biomarker in GBM. Overexpression of GRP78 has been directly correlated with malignant tumor characteristics, including higher tumor grade, cellular proliferation, migration, invasion, poorer responses to TMZ and radiation therapy, and poorer patient outcomes. GRP78 expression is also higher in GBM tumor cells upon recurrence. Meanwhile, knockdown or suppression of GRP78 has been shown to sensitize cells to TMZ and radiation therapy. In light of these findings, various novel developing therapies are targeting GRP78 as monotherapies, combination therapies that enhance the effects of TMZ and radiation therapy, and as treatment delivery modalities. In this review, we delineate the mechanisms by which GRP78 has been noted to specifically modulate glioblastoma behavior and discuss current developing therapies involving GRP78 in GBM. While further research is necessary to translate these developing therapies into clinical settings, GRP78-based therapies hold promise in improving current standard-of-care GBM therapy and may ultimately lead to improved patient outcomes.

Preliminary Virtual Screening Studies to Identify GRP78 Inhibitors Which May Interfere with SARS-CoV-2 Infection

SARS-CoV-2 Spike protein was predicted by molecular docking to bind the host cell surface GRP78, which was suggested as a putative good molecular target to inhibit Covid-19. We aimed to confirm that GRP78 gene expression was increased in blood of SARS-CoV-2 (+) versus SARS-CoV-2 (-) pneumonia patients. In addition, we aimed to identify drugs that could be repurposed to inhibit GRP78, thus with potential anti-SARS-CoV-2 activity. Gene expression studies were performed in 10 SARS-CoV-2 (-) and 24 SARS-CoV-2 (+) pneumonia patients. A structure-based virtual screen was performed with 10,761 small molecules retrieved from DrugBank, using the GRP78 nucleotide binding domain and substrate binding domain as molecular targets. Results indicated that GRP78 mRNA levels were approximately four times higher in the blood of SARS-CoV-2 (+) versus SARS-CoV-2 (-) pneumonia patients, further suggesting that GRP78 might be a good molecular target to treat Covid-19. In addition, a total of 409 compounds were identified with potential as GRP78 inhibitors. In conclusion, we found preliminary evidence that further proposes GRP78 as a possible molecular target to treat Covid-19 and that many clinically approved drugs bind GRP78 as an off-target effect. We suggest that further work should be urgently carried out to confirm if GRP78 is indeed a good molecular target and if some of those drugs have potential to be repurposed for SARS-CoV-2 antiviral activity.

Synthesis and Studies of the Inhibitory Effect of Hydroxylated Phenylpropanoids and Biphenols Derivatives on Tyrosinase and Laccase Enzymes

The impaired activity of tyrosinase and laccase can provoke serious concerns in the life cycles of mammals, insects and microorganisms. Investigation of inhibitors of these two enzymes may lead to the discovery of whitening agents, medicinal products, anti-browning substances and compounds for controlling harmful insects and bacteria. A small collection of novel reversible tyrosinase and laccase inhibitors with a phenylpropanoid and hydroxylated biphenyl core was prepared using naturally occurring compounds and their activity was measured by spectrophotometric and electrochemical assays. Biosensors based on tyrosinase and laccase enzymes were constructed and used to detect the type of protein-ligand interaction and half maximal inhibitory concentration (IC50). Most of the inhibitors showed an IC50 in a range of 20-423 nM for tyrosinase and 23-2619 nM for laccase. Due to the safety concerns of conventional tyrosinase and laccase inhibitors, the viability of the new compounds was assayed on PC12 cells, four of which showed a viability of roughly 80% at 40 µM. In silico studies on the crystal structure of laccase enzyme identified a hydroxylated biphenyl bearing a prenylated chain as the lead structure, which activated strong and effective interactions at the active site of the enzyme. These data were confirmed by in vivo experiments performed on the insect model Tenebrio molitur.

Function and mutual interaction of BiP-, PERK-, and IRE1α-dependent signalling pathways in vascular tumours

Spontaneously regressing infantile haemangiomas and aggressive angiosarcomas are vascular tumours with excessive angiogenesis. When analysing haemangiomas and angiosarcomas immunohistochemically with respect to their chaperone profiles we found that angiosarcomas have significantly elevated protein levels of binding immunoglobulin protein (BIP) and PERK with concomitant attenuated IRE1α levels, whereas haemangioma tissue exhibits the same pattern as embryonal skin tissue. We show that BiP is essential for the maintenance of VEGFR2 protein, which is expressed in the endothelium of both tumour types. When studying the effects of BiP, the IRE1α/Xbp1 -, and PERK/ATF4-signalling pathways on the migration and tube-forming potential of endothelial cells, we show that downregulation of BiP, as well as inhibition of the kinase activity of IRE1α, inhibit in vitro angiogenesis. Downregulation of PERK (PKR-like kinase; PKR = protein kinase R) levels promotes Xbp1 splicing in endoplasmic reticulum (ER)-stressed cells, indicating that in angiosarcoma the elevated PERK levels might result in high levels of unspliced Xbp1, which have been reported to promote cell proliferation and increase tumour malignancy. The data presented in this study revealed that in addition to BiP or PERK, the kinase domains of IRE1α and Xbp1 could be potential targets for the development of novel therapeutic approaches for treating angiosarcomas and to control tumour angiogenesis. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Glucose-Regulated Protein 78 Interacts with Zika Virus Envelope Protein and Contributes to a Productive Infection

Zika virus (ZIKV; Flaviviridae) is a mosquito-borne flavivirus shown to cause fetal abnormalities collectively known as congenital Zika syndrome and Guillain-Barré syndrome in recent outbreaks. Currently, there is no specific treatment or vaccine available, and more effort is needed to identify cellular factors in the viral life cycle. Here, we investigated interactors of ZIKV envelope (E) protein by combining protein pull-down with mass spectrometry. We found that E interacts with the endoplasmic reticulum (ER) resident chaperone, glucose regulated protein 78 (GRP78). Although other flaviviruses are known to co-opt ER resident proteins, including GRP78, to enhance viral infectivity, the role ER proteins play during the ZIKV life cycle is yet to be elucidated. We showed that GRP78 levels increased during ZIKV infection and localised to sites coincident with ZIKV E staining. Depletion of GRP78 using specific siRNAs significantly reduced reporter-virus luciferase readings, viral protein synthesis, and viral titres. Additionally, GRP78 depletion reduced the ability of ZIKV to disrupt host cell translation and altered the localisation of viral replication factories, though there was no effect on viral RNA synthesis. In summary, we showed GRP78 is a vital host-factor during ZIKV infection, which may be involved in the coordination of viral replication factories.

Titanium dioxide nanoparticles induce endoplasmic reticulum stress-mediated apoptotic cell death in liver cancer cells

Objective

Titanium oxide (TiO₂) acts as a photosensitizer in photodynamic therapy by mediating reactive oxygen species (ROS)-induced endoplasmic reticulum (ER) stress. This study aimed to investigate the effect of TiO₂ on ER stress in liver cancer cells.

Methods

Normal human liver and human hepatocarcinoma cell lines were incubated with various concentrations of TiO₂ nanotubes for 48 hours. Cell growth, apoptosis, cell cycle, and cellular ROS were detected. Expression levels of ER stress sensors (PERK and ATF6) and Bax were evaluated by western blot. The effect of TiO₂ on liver cancer growth was also investigated in mice in vivo.

Results

TiO₂ inhibited cell growth, increased apoptosis and cellular ROS levels, and arrested the cell cycle in G1 stage in liver cancer cells. TiO₂ also increased PERK, ATF6, and Bax expression levels in liver cancer cells in dose-dependent manners. TiO₂ had no significant effect on cell growth, apoptosis, ROS level, cell cycle distribution, or PERK, ATF6, or Bax expression in normal liver cells. TiO₂ administration reduced tumor volume and increased PERK, Bax, and ATF6 expression levels in tumor tissues in vivo.

Conclusions

TiO₂ nanoparticles increased ROS-induced ER stress and activated the PERK/ATF6/Bax axis in liver cancer cells in vitro and in vivo.

Honokiol: A Review of Its Anticancer Potential and Mechanisms

Cancer is characterised by uncontrolled cell division and abnormal cell growth, which is largely caused by a variety of gene mutations. There are continuous efforts being made to develop effective cancer treatments as resistance to current anticancer drugs has been on the rise. Natural products represent a promising source in the search for anticancer treatments as they possess unique chemical structures and combinations of compounds that may be effective against cancer with a minimal toxicity profile or few side effects compared to standard anticancer therapy. Extensive research on natural products has shown that bioactive natural compounds target multiple cellular processes and pathways involved in cancer progression. In this review, we discuss honokiol, a plant bioactive compound that originates mainly from the Magnolia species. Various studies have proven that honokiol exerts broad-range anticancer activity in vitro and in vivo by regulating numerous signalling pathways. These include induction of G0/G1 and G2/M cell cycle arrest (via the regulation of cyclin-dependent kinase (CDK) and cyclin proteins), epithelial-mesenchymal transition inhibition via the downregulation of mesenchymal markers and upregulation of epithelial markers. Additionally, honokiol possesses the capability to supress cell migration and invasion via the downregulation of several matrix-metalloproteinases (activation of 5' AMP-activated protein kinase (AMPK) and KISS1/KISS1R signalling), inhibiting cell migration, invasion, and metastasis, as well as inducing anti-angiogenesis activity (via the down-regulation of vascular endothelial growth factor (VEGFR) and vascular endothelial growth factor (VEGF)). Combining these studies provides significant insights for the potential of honokiol to be a promising candidate natural compound for chemoprevention and treatment.

Proteostasis In The Endoplasmic Reticulum: Road to Cure

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER-mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

Analyzing pharmacological intervention points: A method to calculate external stimuli to switch between steady states in regulatory networks

Once biological systems are modeled by regulatory networks, the next step is to include external stimuli, which model the experimental possibilities to affect the activity level of certain network’s nodes, in a mathematical framework. Then, this framework can be interpreted as a mathematical optimal control framework such that optimization algorithms can be used to determine external stimuli which cause a desired switch from an initial state of the network to another final state. These external stimuli are the intervention points for the corresponding biological experiment to obtain the desired outcome of the considered experiment. In this work, the model of regulatory networks is extended to controlled regulatory networks. For this purpose, external stimuli are considered which can affect the activity of the network’s nodes by activation or inhibition. A method is presented how to calculate a selection of external stimuli which causes a switch between two different steady states of a regulatory network. A software solution based on Jimena and Mathworks Matlab is provided. Furthermore, numerical examples are presented to demonstrate application and scope of the software on networks of 4 nodes, 11 nodes and 36 nodes. Moreover, we analyze the aggregation of platelets and the behavior of a basic T-helper cell protein-protein interaction network and its maturation towards Th0, Th1, Th2, Th17 and Treg cells in accordance with experimental data.

Organisms can be seen as molecular networks being able to react on external stimuli. Experiments are performed to understand the underlying regulating mechanisms within the molecular network. A common purpose for these efforts is to reveal mechanisms with which the molecular networks can be affected to achieve a desired behavior. To cover the complexity of life these models of molecular networks often need to be quite huge and need to have many cross connections between the different agents of the network that regulate the behavior of the network. A useful tool to structure this complexity are mathematical methods. Once the model based on experiments is set up the experimental data can be further processed by mathematical methods. As experiments are cumbersome, the present work provides a framework that can be used to systematically figure out intervention points in molecular networks to cause a desired effect. In this way promising intervention strategies can be obtained. For instance the process of obtaining new drugs for pharmacological modulation can be shortened as in the best case the calculated intervention strategy just has to be validated with one experiment and the time consuming procedure of searching an intervention strategy with several experiments can be saved.

Pharmaceutical Topical Delivery of Poorly Soluble Polyphenols: Potential Role in Prevention and Treatment of Melanoma

Melanoma is regarded as the fifth and sixth most common cancer in men and women, respectively, and it is estimated that one person dies from melanoma every hour in the USA. Unfortunately, the treatment of melanoma is difficult because of its aggressive metastasis and resistance to treatment. The treatment of melanoma continues to be a challenging issue due to the limitations of available treatments such as a low response rate, severe adverse reactions, and significant toxicity. Natural polyphenols have attracted considerable attention from the scientific community due to their chemopreventive and chemotherapeutic efficacy. It has been suggested that poorly soluble polyphenols such as curcumin, resveratrol, quercetin, coumarin, and epigallocatechin-3-gallate may have significant benefits in the treatment of melanoma due to their antioxidant, anti-inflammatory, antiproliferative, and chemoprotective efficacies. The major obstacles for the use of polyphenolic compounds are low stability and poor bioavailability. Numerous nanoformulations, including solid lipid nanoparticles, polymeric nanoparticles, micelles, and liposomes, have been formulated to enhance the bioavailability and stability, as well as the therapeutic efficacy of polyphenols. This review will provide an overview of poorly soluble polyphenols that have been reported to have antimetastatic efficacy in melanomas.

Unraveling the molecular mechanisms and the potential chemopreventive/therapeutic properties of natural compounds in melanoma

Melanoma is the most fatal form of skin cancer. Current therapeutic approaches include surgical resection, chemotherapy, targeted therapy and immunotherapy. However, these treatment strategies are associated with development of drug resistance and severe side effects. In recent years, natural compounds have also been extensively studied for their anti-melanoma effects, including tumor growth inhibition, apoptosis induction, angiogenesis and metastasis suppression and cancer stem cell elimination. Moreover, a considerable number of studies reported the synergistic activity of phytochemicals and standard anti-melanoma agents, as well as the enhanced effectiveness of their synthetic derivatives and novel formulations. However, clinical data confirming these promising effects in patients are still scanty. This review emphasizes the anti-tumor mechanisms and potential application of the most studied natural products for melanoma prevention and treatment.

Pharmacological effectors of GRP78 chaperone in cancers

The protein chaperone GRP78 is a master regulator of endoplasmic reticulum (ER) functions and is frequently over-expressed at the surface of cancer cells where it contributes to chemo-resistance. It represents a well-studied ER stress marker but an under-explored target for new drug development. This review aims to untangle the structural and functional diversity of GRP78 modulators, covering over 130 natural products, synthetic molecules, specific peptides and monoclonal antibodies that target GRP78. Several approaches to promote or to incapacitate GRP78 are presented, including the use of oligonucleotides and specific cell-delivery peptides often conjugated to cytotoxic payloads to design GRP78-targeted therapeutics. A repertoire of drugs that turn on/off GRP78 is exposed, including molecules which bind directly to GRP78, principally to its ATP site. There exist many options to regulate positively or negatively the expression of the chaperone, or to interfere with its cellular trafficking. This review provides a molecular cartography of GRP78 pharmacological effectors and adds weight to the notion that GRP78 repressors could represent promising anticancer therapeutics, notably as regards limiting chemo-resistance of cancer cells. The potential of GRP78-targeting drugs in other therapeutic modalities is also evoked.

Role of Endoplasmic Reticulum Stress in the Anticancer Activity of Natural Compounds

Cancer represents a serious global health problem, and its incidence and mortality are rapidly growing worldwide. One of the main causes of the failure of an anticancer treatment is the development of drug resistance by cancer cells. Therefore, it is necessary to develop new drugs characterized by better pharmacological and toxicological profiles. Natural compounds can represent an optimal collection of bioactive molecules. Many natural compounds have been proven to possess anticancer effects in different types of tumors, but often the molecular mechanisms associated with their cytotoxicity are not completely understood. The endoplasmic reticulum (ER) is an organelle involved in multiple cellular processes. Alteration of ER homeostasis and its appropriate functioning originates a cascade of signaling events known as ER stress response or unfolded protein response (UPR). The UPR pathways involve three different sensors (protein kinase RNA(PKR)-like ER kinase (PERK), inositol requiring enzyme1α (IRE1) and activating transcription factor 6 (ATF6)) residing on the ER membranes. Although the main purpose of UPR is to restore this organelle's homeostasis, a persistent UPR can trigger cell death pathways such as apoptosis. There is a growing body of evidence showing that ER stress may play a role in the cytotoxicity of many natural compounds. In this review we present an overview of different plant-derived natural compounds, such as curcumin, resveratrol, green tea polyphenols, tocotrienols, and garcinia derivates, that exert their anticancer activity via ER stress modulation in different human cancers.

Thermodynamic and computational analyses reveal the functional roles of the galloyl group of tea catechins in molecular recognition

Catechins, biologically active polyphenols in green tea, exhibit various biological activities, such as anticancer and antiviral activities, arising from interactions with functional proteins. However, the molecular details of these interactions remain unclear. In this study, we investigated the interactions between human serum albumin (HSA) and various catechins, including some with a galloyl group, by means of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), and docking simulations. Our results indicate that the galloyl group was important for recognition by HSA and was responsible for enthalpic gains derived from a larger buried surface area and more van der Waals contacts. Thus, our thermodynamic and computational analyses suggest that the galloyl group plays important functional roles in the specific binding of catechins to proteins, implying that the biological activities of these compounds may be due in part to the physicochemical characteristics of the galloyl group.

Leukocyte Differentiation by Histidine-Rich Glycoprotein/Stanniocalcin-2 Complex Regulates Murine Glioma Growth through Modulation of Antitumor Immunity

The plasma-protein histidine-rich glycoprotein (HRG) is implicated in phenotypic switching of tumor-associated macrophages, regulating cytokine production and phagocytotic activity, thereby promoting vessel normalization and antitumor immune responses. To assess the therapeutic effect of HRG gene delivery on CNS tumors, we used adenovirus-encoded HRG to treat mouse intracranial GL261 glioma. Delivery of Ad5-HRG to the tumor site resulted in a significant reduction in glioma growth, associated with increased vessel perfusion and increased CD45⁺ leukocyte and CD8⁺ T-cell accumulation in the tumor. Antibody-mediated neutralization of colony-stimulating factor-1 suppressed the effects of HRG on CD45⁺ and CD8⁺ infiltration. Using a novel protein interaction-decoding technology, TRICEPS-based ligand receptor capture (LRC), we identified Stanniocalcin-2 (STC2) as an interacting partner of HRG on the surface of inflammatory cells in vitro and colocalization of HRG and STC2 in gliomas. HRG reduced the suppressive effects of STC2 on monocyte CD14⁺ differentiation and STC2-regulated immune response pathways. In consequence, Ad5-HRG-treated gliomas displayed decreased numbers of IL35⁺ Treg cells, providing a mechanistic rationale for the reduction in GL261 growth in response to Ad5-HRG delivery. We conclude that HRG suppresses glioma growth by modulating tumor inflammation through monocyte infiltration and differentiation. Moreover, HRG acts to balance the regulatory effects of its partner, STC2, on inflammation and innate and/or acquired immunity. HRG gene delivery therefore offers a potential therapeutic strategy to control antitumor immunity. Mol Cancer Ther; 17(9); 1961-72. ©2018 AACR.

Mitochondria-Targeted Honokiol Confers a Striking Inhibitory Effect on Lung Cancer via Inhibiting Complex I Activity

We synthesized a mitochondria-targeted honokiol (Mito-HNK) that facilitates its mitochondrial accumulation; this dramatically increases its potency and efficacy against highly metastatic lung cancer lines in vitro, and in orthotopic lung tumor xenografts and brain metastases in vivo. Mito-HNK is >100-fold more potent than HNK in inhibiting cell proliferation, inhibiting mitochondrial complex ?, stimulating reactive oxygen species generation, oxidizing mitochondrial peroxiredoxin-3, and suppressing the phosphorylation of mitoSTAT3. Within lung cancer brain metastases in mice, Mito-HNK induced the mediators of cell death and decreased the pathways that support invasion and proliferation. In contrast, in the non-malignant stroma, Mito-HNK suppressed pathways that support metastatic lesions, including those involved in inflammation and angiogenesis. Mito-HNK showed no toxicity and targets the metabolic vulnerabilities of primary and metastatic lung cancers. Its pronounced anti-invasive and anti-metastatic effects in the brain are particularly intriguing given the paucity of treatment options for such patients either alone or in combination with standard chemotherapeutics.

Glucose-regulated protein 78 substrate-binding domain alters its conformation upon EGCG inhibitor binding to nucleotide-binding domain: Molecular dynamics studies

Glucose-regulated protein 78 (GRP78), is overexpressed in glioblastoma, other tumors and during viral and bacterial infections, and so, it is postulated to be a key drug target. EGCG, an ATP-competitive natural inhibitor, inhibits GRP78 effect in glioblastoma. Structural basis of its action on GRP78 nucleotide-binding domain and selectivity has been investigated. We were interested in exploring the large-scale conformational movements travelling to substrate-binding domain via linker region. Conformational effects of EGCG inhibitor as well as ATP on full length GRP78 protein were studied using powerful MD simulations. Binding of EGCG decreases mobility of residues in SBDα lid region as compared to ATP-bound state and similar to apo state. The decreased mobility may prevent its opening and closing over SBDβ. This hindrance to SBDα subdomain movement, in turn, may reduce the binding of substrate peptide to SBDβ. EGCG binding folds the protein stably as opposed to ATP binding. Several results from EGCG binding simulations are similar to that of the apo state. Key insights from these results reveal that after EGCG binding upon competitive inhibition with ATP, GRP78 conformation may revert to that of inactive, apo state. Further, SBD may adopt a semi-open conformation unable to facilitate association of substrates.

Effects of the Green Tea Polyphenol Epigallocatechin-3-Gallate on Glioma: A Critical Evaluation of the Literature

The review discusses the effects of Epigallocatechin-3-gallate Gallate (EGCG) on glioma as a basis for future research on clinical application of EGCG. Epidemiological studies on the effects of green tea or EGCG on the risk of glioma is inconclusive due to the limited number of studies, the inclusion of all tea types in these studies, and the focus on caffeine rather than EGCG. In vivo experiments using EGCG monotherapy are inconclusive. Nevertheless, EGCG induces cell death, prevents cellular proliferation, and limits invasion in multiple glioma cell lines. Furthermore, EGCG enhances the efficacy of anti-glioma therapies, including irradiation, temozolomide, carmustine, cisplatin, tamoxifen, and TNF-related apoptosis-inducing ligand, but reduces the effect of bortezomib. Pro-drugs, co-treatment, and encapsulation are being investigated to enhance clinical applicability of EGCG. Mechanisms of actions of EGCG have been partly elucidated. EGCG has both anti-oxidant and oxidant properties. EGCG inhibits pro-survival proteins, such as telomerase, survivin, GRP78, PEA15, and P-gp. EGCG inhibits signaling of PDGFR, IGF-1R, and 67LR. EGCG reduces invasiveness of cancer cells by inhibiting the activities of various metalloproteinases, cytokines, and chemokines. Last, EGCG inhibits some NADPH-producing enzymes, thus disturbing redox status and metabolism of glioma cells. In conclusion, EGCG may be a suitable adjuvant to potentiate anti-glioma therapies.

Identification, characterization and HPLC quantification of formulation-related impurities of honokiol, an antitumor natural drug candidate in clinical trials

Natural products and their derivatives have historically been invaluable as a source of therapeutic agents. Honokiol, as a well-known natural product in Chinese herbal medicine Houpu, is finally being studied in a Phase I clinical trial (CTR20170822) in patients with Advanced Non-Small Cell Lung Cancer (NSCLS) in China this year. During the honokiol liposome formulation process, five major impurities were present in the range of 0.05-0.1% based on the HPLC analysis. These five major impurities were obtained from the forced degradation product of honokiol through countercurrent chromatography and prep-HPLC. The structure were elucidated with ¹H NMR, ¹³C NMR, 2D NMR and MS spectral data. The proposed HPLC method was validated for specificity, linearity (concentration range 0.01-1.62, 0.003-0.96, 0.05-7.98, 0.04-6.52, 0.03-5.18 μg/ml for impurities I-V respectively, R2 > 0.9988), accuracy (99.11-100.67%), precision (CV < 1.6%), and sensitivity (LOD 3.3, 0.1, 16.7, 13.3, 10.0 ng/ml for impurities I-V respectively). The validated method was employed in the further study of the honokiol drug substance.

Epigallocatechin-3-gallate enhances ER stress-induced cancer cell apoptosis by directly targeting PARP16 activity

Poly(ADP-ribose) polymerases (PARPs) are ADP-ribosylating enzymes and play important roles in a variety of cellular processes. Most small-molecule PARP inhibitors developed to date have been against PARP1, a poly-ADP-ribose transferase, and suffer from poor selectivity. PARP16, a mono-ADP-ribose transferase, has recently emerged as a potential therapeutic target, but its inhibitor development has trailed behind. Here we newly characterized epigallocatechin-3-gallate (EGCG) as a potential inhibitor of PARP16. We found that EGCG was associated with PARP16 and dramatically inhibited its activity in vitro. Moreover, EGCG suppressed the ER stress-induced phosphorylation of PERK and the transcription of unfolded protein response-related genes, leading to dramatically increase of cancer cells apoptosis under ER stress conditions, which was dependent on PARP16. These findings newly characterized EGCG as a potential inhibitor of PARP16, which can enhance the ER stress-induced cancer cell apoptosis, suggesting that a combination of EGCG and ER stress-induced agents might represent a novel approach for cancer therapy or chemoprevention.

Endoplasmic Reticulum Stress, Unfolded Protein Response, and Cancer Cell Fate

Perturbation of endoplasmic reticulum (ER) homeostasis results in a stress condition termed "ER stress" determining the activation of a finely regulated program defined as unfolded protein response (UPR) and whose primary aim is to restore this organelle's physiological activity. Several physiological and pathological stimuli deregulate normal ER activity causing UPR activation, such as hypoxia, glucose shortage, genome instability, and cytotoxic compounds administration. Some of these stimuli are frequently observed during uncontrolled proliferation of transformed cells, resulting in tumor core formation and stage progression. Therefore, it is not surprising that ER stress is usually induced during solid tumor development and stage progression, becoming an hallmark of such malignancies. Several UPR components are in fact deregulated in different tumor types, and accumulating data indicate their active involvement in tumor development/progression. However, although the UPR program is primarily a pro-survival process, sustained and/or prolonged stress may result in cell death induction. Therefore, understanding the mechanism(s) regulating the cell survival/death decision under ER stress condition may be crucial in order to specifically target tumor cells and possibly circumvent or overcome tumor resistance to therapies. In this review, we discuss the role played by the UPR program in tumor initiation, progression and resistance to therapy, highlighting the recent advances that have improved our understanding of the molecular mechanisms that regulate the survival/death switch.

HSPA5 Gene encoding Hsp70 chaperone BiP in the endoplasmic reticulum

The HSPA5 gene encodes the binding immunoglobulin protein (BiP), an Hsp70 family chaperone localized in the ER lumen. As a highly conserved molecular chaperone, BiP assists in a wide range of folding processes via its two structural domains, a nucleotide-binding domain (NBD) and substrate-binding domain (SBD). BiP is also an essential component of the translocation machinery for protein import into the ER, a regulator for Ca²⁺ homeostasis in the ER, as well as a facilitator of ER-associated protein degradation (ERAD) via retrograde transportation of aberrant proteins across the ER membrane. When unfolded/misfolded proteins in the ER overwhelm the capacity of protein folding machinery, BiP can initiate the unfolded protein response (UPR), decrease unfolded/misfolded protein load, induce autophagy, and crosstalk with apoptosis machinery to assist in the cell survival decision. Post-translational modifications (PTMs) of BiP have been shown to regulate BiP's activity, turnover, and availability upon different extrinsic or intrinsic stimuli. As a master regulator of ER function, BiP is associated with cancer, cardiovascular disease, neurodegenerative disease, and immunological diseases. BiP has been targeted in cancer therapies and shows promise for application in other relevant diseases.

Isochaihulactone-induced DDIT3 causes ER stress-PERK independent apoptosis in glioblastoma multiforme cells

The endoplasmic reticulum (ER) is a major site of cellular homeostasis regulation. Under the ER stress condition, Glioblastoma multiform (GBM) cells activate the unfolded protein response. In this study, we discovered isochaihulactone, a natural compound extracted from the Chinese traditional herb Nan-Chai-Hu, which can disrupt ER homeostasis in GBM cell lines. It can induce DNA damage inducible transcript 3 (DDIT3) expression which is independent of 78 kDa glucose-regulated protein (GRP78) and protein kinase RNA-like endoplasmic reticulum kinase (PERK) expression. Flow cytometry results revealed that isochaihulactone trigger the cell cycle arrest at G2/M phase and apoptosis in GBM cells. Isochaihulactone induced DDIT3 led to the expression of NAG-1. The in vivo study showed that isochaihulactone suppressed tumor growth, and DDIT3 and Caspase3 overexpressed in the xenograft model, which is consistent with the in vitro study. Overall, the data revealed that isochaihulactone disrupted ER homeostasis in cancer cells by increasing DDIT3 and NAG-1 expression. Our finding also provides a therapeutic strategy by using isochaihulactone for GBM treatment.

Honokiol Decreases Lung Cancer Metastasis through Inhibition of the STAT3 Signaling Pathway

Lung cancer is the leading cause of cancer death in the United States. Metastasis to lymph nodes and distal organs, especially brain, leads to severe complications and death. Preventing lung cancer development and metastases is an important strategy to reduce lung cancer mortality. Honokiol (HNK), a natural compound present in the extracts of magnolia bark, has a favorable bioavailability profile and recently has been shown to readily cross the blood-brain barrier. In the current study, we evaluated the antimetastatic effects of HNK in both the lymph node and brain mouse models of lung tumor metastasis. We tested the efficacy of HNK in preventing 18 H2030-BrM3 cell (brain-seeking human lung tumor cells) migration to lymph node or brain. In an orthotopic mouse model, HNK significantly decreased lung tumor growth compared with the vehicle control group. HNK also significantly reduced the incidence of lymph node metastasis and the weight of mediastinal lymph nodes. In a brain metastasis model, HNK inhibits metastasis of lung cancer cells to the brain to approximately one third of that observed in control mice. We analyzed HNK's mechanism of action, which indicated that its effect is mediated primarily by inhibiting the STAT3 pathway. HNK specifically inhibits STAT3 phosphorylation irrespective of the mutation status of EGFR, and knockdown of STAT3 abrogated both the antiproliferative and the antimetastatic effects of HNK. These observations suggest that HNK could provide novel chemopreventive or therapeutic options for preventing both lung tumor progression and lung cancer metastasis. Cancer Prev Res; 10(2); 133-41. ©2016 AACR.