Geldanamycin induces heat shock protein expression through activation of HSF1 in K562 erythroleukemic cells

Geldanamycin ameliorates multiple organ dysfunction and microthrombosis in septic mice by inhibiting the formation of the neutrophil extracellular network by activating heat shock factor 1 HSF1

Sepsis and septic shock are common critical illnesses in the intensive care unit with a high mortality rate. Geldanamycin (GA) has a broad spectrum of antibacterial and antiviral activity and has inhibitory effects on various viruses. However, whether GA affects sepsis due to infections remains unknown. In this study, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen and creatinine in serum; neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 in the urine, cytokines (tumour necrosis factor alpha, interleukin-1β and interleukin-6) in the bronchoalveolar lavage fluid and myeloperoxidase in the lung tissues were measured using enzyme-linked immunosorbent assay kits. Pathological injury was measured by hematoxylin and eosin staining and neutrophils were measured by flow cytometry analysis; related expressions were analysed by qPCR, western blot and immunofluorescence assay. The results showed that GA significantly ameliorated cecum ligation and puncture (CLP)-triggered liver, kidney and lung injury in septic mice. In addition, we found that GA dose-dependently inhibited microthrombosis and alleviated coagulopathy in septic mice. Further molecular mechanism analysis suggests that GA may act through upregulation of heat shock factor 1 and tissue-type plasminogen activator. In conclusion, our study elucidated the protective effects of GA in a mouse model established using CLP, and the results reveal that GA may be a promising agent for sepsis.

Inhibition of Hsp90 during in vitro maturation under thermoneutral or heat shock conditions compromises the developmental competence of bovine oocytes

Heat shock protein 90 (Hsp90) is critical for cell homeostasis but its role on bovine oocyte maturation is not well known. We investigated the importance of Hsp90 for competence of bovine oocyte using 17-(allylamino)-17-demethoxygeldanamycin (17AAG), an inhibitor of Hsp90, during in vitro maturation (IVM). Three experiments evaluated the effect of 17AAG on developmental competence of oocytes matured in vitro under thermoneutral (38.5ºC) or heat shock (HS; 41.5ºC) temperatures. The first experiment found that the blastocyst rates were lower (P < 0.05) with 2 µM 17AAG compared with the untreated control (0 µM). The abundance of HSF1 transcripts was higher in oocytes matured with 2 µM than with 0 and 1 µM 17AAG, whereas the abundance of HSP90AA1 and HSPA1A transcripts was lower (P < 0.05) with 1 and 2 µM than with 0 µM. The second experiment found that 2 µM 17AAG for 12 or 24 h during IVM decreased (P < 0.05) the blastocysts rates. In the third experiment, the association of 2 μM 17AAG with HS for 12 h during IVM resulted in lower (P < 0.05) blastocysts rates than 17AAG, HS or untreated control. In conclusion, inhibition of Hsp90 during in vitro maturation compromises further embryo development; the association of Hsp90 inhibition with HS aggravates the deleterious effect of both on oocyte developmental competence.

In Silico Discovery and Optimisation of a Novel Structural Class of Hsp90 C-Terminal Domain Inhibitors

Hsp90 is a promising target for the development of novel agents for cancer treatment. The N-terminal Hsp90 inhibitors have several therapeutic limitations, the most important of which is the induction of heat shock response, which can be circumvented by targeting the allosteric binding site on the C-terminal domain (CTD) of Hsp90. In the absence of an Hsp90—CTD inhibitor co-crystal structure, the use of structure-based design approaches for the Hsp90 CTD is difficult and the structural diversity of Hsp90 CTD inhibitors is limited. In this study, we describe the discovery of a novel structural class of Hsp90 CTD inhibitors. A structure-based virtual screening was performed by docking a library of diverse compounds to the Hsp90β CTD binding site. Three selected virtual hits were tested in the MCF-7 breast cancer cell line, with compound TVS-23 showing antiproliferative activity with an IC₅₀ value of 26.4 ± 1.1 µM. We report here the optimisation, synthesis and biological evaluation of TVS-23 analogues. Several analogues showed significantly enhanced antiproliferative activities in MCF-7 breast cancer and SK-N-MC Ewing sarcoma cell lines, with 7l being the most potent (IC₅₀ = 1.4 ± 0.4 µM MCF-7; IC₅₀ = 2.8 ± 0.4 µM SK-N-MC). The results of this study highlight the use of virtual screening to expand the structural diversity of Hsp90 CTD inhibitors and provide new starting points for further development.

1-Mesityl-3-(3-Sulfonatopropyl) Imidazolium Protects Against Oxidative Stress and Delays Proteotoxicity in C. elegans

Due to the increase in life expectancy worldwide, age-related disorders such as neurodegenerative diseases (NDs) have become more prevalent. Conventional treatments comprise drugs that only attenuate some of the symptoms, but fail to arrest or delay neuronal proteotoxicity that characterizes these diseases. Due to their diverse biological activities, imidazole rings are intensively explored as powerful scaffolds for the development of new bioactive molecules. By using C. elegans, our work aims to explore novel biological roles for these compounds. To this end, we have tested the in vivo anti-proteotoxic effects of imidazolium salts. Since NDs have been largely linked to impaired antioxidant defense mechanisms, we focused on 1-Mesityl-3-(3-sulfonatopropyl) imidazolium (MSI), one of the imidazolium salts that we identified as capable of improving iron-induced oxidative stress resistance in wild-type animals. By combining mutant and gene expression analysis we have determined that this protective effect depends on the activation of the Heat Shock Transcription Factor (HSF-1), whereas it is independent of other canonical cytoprotective molecules such as abnormal Dauer Formation-16 (DAF-16/FOXO) and Skinhead-1 (SKN-1/Nrf2). To delve deeper into the biological roles of MSI, we analyzed the impact of this compound on previously established C. elegans models of protein aggregation. We found that MSI ameliorates β-amyloid-induced paralysis in worms expressing the pathological protein involved in Alzheimer’s Disease. Moreover, this compound also delays age-related locomotion decline in other proteotoxic C. elegans models, suggesting a broad protective effect. Taken together, our results point to MSI as a promising anti-proteotoxic compound and provide proof of concept of the potential of imidazole derivatives in the development of novel therapies to retard age-related proteotoxic diseases.

Quantitative Comparison of HSF1 Activators

The heat shock response (HSR) pathway is a highly conserved rescue mechanism, which protects the cells from harmful insults disturbing the cellular protein homeostasis via expression of chaperones. Furthermore, it was demonstrated to play crucial roles in various diseases like neurodegeneration and cancer. For neurodegenerative diseases, an overexpression of chaperones is a potential therapeutic approach to clear the cells from non-functional protein aggregates. Therefore, activators of the HSR pathway and its master regulator HSF1 are under close observation. There are numerous HSR activators published in the literature using different model systems, experimental designs, and readout assays. The aim of this work was to provide a quantitative comparison of a broad range of published activators using a newly developed HSF responsive dual-luciferase cell line. Contrary to natural target genes, which are regulated by multiple input pathways, the artificial reporter exclusively reacts to HSF activity. In addition, the results were compared to endogenous heat shock protein expression. As a result, great differences in the intensity of pathway activation were observed. In addition, a parallel viability assessment revealed high variability in the specificity of the drugs. Furthermore, the differences seen compared to published data indicate that some activators exhibit tissue-specific differences leading to interesting assumptions about the regulation of HSF1.

Natural compounds in the regulation of proteostatic pathways: An invincible artillery against stress, ageing, and diseases

Cells have different sets of molecules for performing an array of physiological functions. Nucleic acids have stored and carried the information throughout evolution, whereas proteins have been attributed to performing most of the cellular functions. To perform these functions, proteins need to have a unique conformation and a definite lifespan. These attributes are achieved by a highly coordinated protein quality control (PQC) system comprising chaperones to fold the proteins in a proper three-dimensional structure, ubiquitin-proteasome system for selective degradation of proteins, and autophagy for bulk clearance of cell debris. Many kinds of stresses and perturbations may lead to the weakening of these protective cellular machinery, leading to the unfolding and aggregation of cellular proteins and the occurrence of numerous pathological conditions. However, modulating the expression and functional efficiency of molecular chaperones, E3 ubiquitin ligases, and autophagic proteins may diminish cellular proteotoxic load and mitigate various pathological effects. Natural medicine and small molecule-based therapies have been well-documented for their effectiveness in modulating these pathways and reestablishing the lost proteostasis inside the cells to combat disease conditions. The present article summarizes various similar reports and highlights the importance of the molecules obtained from natural sources in disease therapeutics.

Subcellular localization of the J-protein Sis1 regulates the heat shock response

Cells exposed to heat shock induce a conserved gene expression program, the heat shock response (HSR), encoding protein homeostasis (proteostasis) factors. Heat shock also triggers proteostasis factors to form subcellular quality control bodies, but the relationship between these spatial structures and the HSR is unclear. Here we show that localization of the J-protein Sis1, a cofactor for the chaperone Hsp70, controls HSR activation in yeast. Under nonstress conditions, Sis1 is concentrated in the nucleoplasm, where it promotes Hsp70 binding to the transcription factor Hsf1, repressing the HSR. Upon heat shock, Sis1 forms an interconnected network with other proteostasis factors that spans the nucleolus and the surface of the endoplasmic reticulum. We propose that localization of Sis1 to this network directs Hsp70 activity away from Hsf1 in the nucleoplasm, leaving Hsf1 free to induce the HSR. In this manner, Sis1 couples HSR activation to the spatial organization of the proteostasis network.

Inhibition of heat shock protein 90 alleviates cholestatic liver injury by decreasing IL-1β and IL-18 expression

Severe cholestatic liver injury diseases, such as obstructive jaundice and the subsequent acute obstructive cholangitis, are induced by biliary tract occlusion. Heat shock protein 90 (HSP90) inhibitors have been demonstrated to be protective for various organs. The potential of HSP90 inhibitors in the treatment of cholestatic liver injury, however, remains unclear. In the present study, rat models of bile duct ligation (BDL) were established, the HSP90 inhibitor 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG) was administered, and its ability to ameliorate the cholestasis-induced liver injuries was evaluated. In the BDL rat models and clinical samples, increased HSP90 expression was observed to be associated with cholestatic liver injury. Furthermore, 17-DMAG alleviated cholestasis-induced liver injury in the rat models, as revealed by the assessment of pathological changes and liver function. In addition, 17-DMAG protected hepatocytes against cholestatic injury in vitro. Further assays indicated that 17-DMAG administration prevented cholestasis-induced liver injury in the rats by decreasing the expression of interleukin (IL)-1β and IL-18. Moreover, 17-DMAG also decreased the cholestasis-induced upregulation of IL-1β and IL-18 in liver sinusoidal endothelial cells in vitro. In conclusion, the HSP90 inhibitor 17-DMAG is able to prevent liver injury in rats with biliary obstruction, and this phenomenon is associated with the reduction of IL-1β and IL-18 expression.

The Compound Expression of HSP90 and INOS in the Testis of Diabetic Rats as Cellular and Pathologic Adverse Effects of Diabetes

Introduction

Diabetes is increasingly prevalent at global level and associated with various impacts including the male reproductive system.

Aims

This research is aimed at investigating the influence of diabetes on the localization and expression of HSP90 and iNOS in the testicular tissue of diabetic rats.

Methods

A diabetic model was developed through a single injection of alloxan monohydrate intraperitoneally (purchased from Sigma-Aldrich) 120 mg/kg body weight following fasting for 12 hrs. The experiment involved two groups, the control and diabetic groups with 10 albino rats in each group. Diabetes was considered if glucose concentration was ≥200 mg/dl. The experiment duration was for one month. After the experiment had finished, all rats were terminated and prepared for routine histological and immunohistochemical examination.

Results

The results revealed that diabetes caused morphological changes at histological level in testicular tissue. Immunohistochemical examination showed that diabetes significantly upregulated the expression of both HSP90 and iNOS in the testicular tissue of diabetic rats as compared with that of the control group (p < 0.001).

Conclusion

Diabetes may induce adverse health effects on the male reproduction through upregulation of HSP90 and iNOS in the testicular tissue of diabetic rats.

Regulation of Hsf1 and the Heat Shock Response

The heat shock response (HSR) is characterized by the induction of molecular chaperones following a sudden increase in temperature. In eukaryotes, the HSR comprises the set of genes controlled by the transcription factor Hsf1. The HSR is induced by defects in co-translational protein folding, ribosome biogenesis, organellar targeting of nascent proteins, and protein degradation by the ubiquitin proteasome system. Upon heat shock, these processes may be endogenous sources of polypeptide ligands that activate the HSR. Mechanistically, these ligands are thought to titrate the chaperone Hsp70 away from Hsf1, releasing Hsf1 to induce the full arsenal of cellular chaperones to restore protein homeostasis. In metazoans, this cell-autonomous feedback loop is modulated by the microenvironment and neuronal cues to enable tissue-level and organism-wide coordination.

Inhibition of HSP90 and Activation of HSF1 Diminish Macrophage NLRP3 Inflammasome Activity in Alcohol-Associated Liver Injury

BACKGROUND

Activation of NLRP3 in liver macrophages contributes to alcohol-associated liver disease (ALD). Molecular chaperone heat shock protein (HSP) 90 facilitates NLRP3 inflammasome activity during infections and inflammatory diseases. We previously reported that HSP90 is induced in ALD and regulates proinflammatory cytokines, tumor necrosis factor alpha, and IL-6. Whether HSP90 affects IL-1β and IL-18 regulated by NLRP3 inflammasome in ALD is unknown. Here, we hypothesize that HSP90 modulated NLRP3 inflammasome activity and affects IL-1β and IL-18 secretion in ALD.

METHODS

The expression of HSP90AA1 and NLRP3 inflammasome genes was evaluated in human alcoholic livers and in mouse model of ALD. The importance of HSP90 on NLRP3 inflammasome activation in ALD was evaluated by administering HSP90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) to mice subjected to ALD, and in vitro to bone marrow-derived macrophages (BMDM) stimulated with LPS and ATP. The effect of activation of HSF1/HSPA1A axis during HSP90 inhibition or direct activation during heat shock of BMDMs on NLRP3 activity and secretion of downstream cytokines was evaluated.

RESULTS

We found positive correlation between induction of HSP90 and NLRP3 inflammasome genes in human alcoholic cirrhotic livers. Administration of 17-DMAG in mouse model of ALD significantly down-regulated NLRP3 inflammasome-mediated caspase-1 (CASP-1) activity and cytokine secretion, with reduction in ALD. 17-DMAG-mediated decrease in NLRP3 was restricted to liver macrophages. Using BMDMs, we show that inhibition of HSP90 prevented CASP-1 activity, and Gasdermin D (GSDMD) cleavage, important in release of active IL-1β and IL-18. Interestingly, activation of the heat shock factor 1 (HSF1)/HSPA1A axis, either during HSP90 inhibition or by heat shock, decreased NLRP3 inflammasome activity and reduced secretion of cytokines.

CONCLUSION

Our studies indicate that inhibition of HSP90 and activation of HSF1/HSPA1A reduce IL-1β and IL-18 via decrease in NLRP3/CASP-1 and GSDMD activity in ALD.

Degradation of proteins by PROTACs and other strategies

Blocking the biological functions of scaffold proteins and aggregated proteins is a challenging goal. PROTAC proteolysis-targeting chimaera (PROTAC) technology may be the solution, considering its ability to selectively degrade target proteins. Recent progress in the PROTAC strategy include identification of the structure of the first ternary eutectic complex, extra-terminal domain-4-PROTAC-Von-Hippel-Lindau (BRD4-PROTAC-VHL), and PROTAC ARV-110 has entered clinical trials for the treatment of prostate cancer in 2019. These discoveries strongly proved the value of the PROTAC strategy. In this perspective, we summarized recent meaningful research of PROTAC, including the types of degradation proteins, preliminary biological data in vitro and in vivo, and new E3 ubiquitin ligases. Importantly, the molecular design, optimization strategy and clinical application of candidate molecules are highlighted in detail. Future perspectives for development of advanced PROTAC in medical fields have also been discussed systematically.

The Major Heat Shock Proteins, Hsp70 and Hsp90, in 2-Methoxyestradiol-Mediated Osteosarcoma Cell Death Model

2-Methoxyestradiol is one of the natural 17β-estradiol derivatives and a potential novel anticancer agent currently being under evaluation in advanced phases of clinical trials. However, the mechanism of anticancer action of 2-methoxyestradiol has not been yet fully established. In our previous studies we have demonstrated that 2-methoxyestradiol selectively induces the expression and nuclear translocation of neuronal nitric oxide synthase in osteosarcoma 143B cells. Heat shock proteins (Hsps) are factors involved in the regulation of expression and activity of nitric oxide synthases. Herein, we chose osteosarcoma cell lines differed in metastatic potential, metastatic 143B and highly metastatic MG63.2 cells, in order to further investigate the anticancer mechanism of 2-methoxyestradiol. The current study aimed to determine the role of major heat shock proteins, Hsp90 and Hsp70 in 2-methoxyestradiol-induced osteosarcoma cell death. We focused on the implication of Hsp90 and Hsp70 in control under expression of neuronal nitric oxide synthase, localization of the enzyme, and further generation of nitro-oxidative stress. To give the insight into the role of Hsp90 in regulation of anticancer efficacy of 2-methoxyestradiol, we used geldanamycin as a potent Hsp90 inhibitor. Herein, we evidenced that inhibition of Hsp90 controls the protein expression of 2-methoxyestradiol-induced neuronal nitric oxide synthase and inhibits enzyme nuclear translocation. We propose that decreased level of neuronal nitric oxide synthase protein after a combined treatment with 2-methoxyestradiol and geldanamycin is directly associated with the accompanying upregulation of Hsp70 and downregulation of Hsp90. This interaction resulted in abrogation of anticancer efficacy of 2-methoxyestradiol by geldanamycin.

Natural heat shock protein 90 inhibitors in cancer and inflammation

Heat shock protein (HSP)90 is the most abundant HSPs, which are chaperone molecules whose major roles are cell protection and maintenance by means of aiding the folding, the stabilization and the remodeling of a wide range of proteins. A few hundreds of proteins depend on HSP90 chaperone activity, including kinases and transcriptional factors that play essential roles in cancer and inflammation, so that HSP90-targeted therapies have been considered as a potential strategy for the treatment of cancer and inflammatory-associated diseases. HSP90 inhibition by natural, semi-synthetic and synthetic compounds have yield promising results in pre-clinical studies and clinical trials for different types of cancers and inflammation. Natural products are a huge source of biologically active compounds widely used in drug development due to the great diversity of their metabolites which are capable to modulate several protein functions. HSP90 inhibitors have been isolated from bacteria, fungi and vegetal species. These natural compounds have a noteworthy ability to modulate HSP90 activity as well as serve as scaffolds for the development of novel synthetic or semi-synthetic inhibitors. Over a hundred clinical trials have evaluated the effect of HSP90 inhibitors as adjuvant treatment against different types of tumors and, currently, new studies are being developed to gain sight on novel promising and more effective approaches for cancer treatment. In this review, we present the naturally occurring HSP90 inhibitors and analogues, discussing their anti-cancer and anti-inflammatory effects.

Identification of Novel Response and Predictive Biomarkers to Hsp90 Inhibitors Through Proteomic Profiling of Patient-derived Prostate Tumor Explants

Inhibition of the heat shock protein 90 (Hsp90) chaperone is a promising therapeutic strategy to target expression of the androgen receptor (AR) and other oncogenic drivers in prostate cancer cells. However, identification of clinically-relevant responses and predictive biomarkers is essential to maximize efficacy and treatment personalization. Here, we combined mass spectrometry (MS)-based proteomic analyses with a unique patient-derived explant (PDE) model that retains the complex microenvironment of primary prostate tumors. Independent discovery and validation cohorts of PDEs (n = 16 and 30, respectively) were cultured in the absence or presence of Hsp90 inhibitors AUY922 or 17-AAG. PDEs were analyzed by LC-MS/MS with a hyper-reaction monitoring data independent acquisition (HRM-DIA) workflow, and differentially expressed proteins identified using repeated measure analysis of variance (ANOVA; raw p value <0.01). Using gene set enrichment, we found striking conservation of the most significantly AUY922-altered gene pathways between the discovery and validation cohorts, indicating that our experimental and analysis workflows were robust. Eight proteins were selectively altered across both cohorts by the most potent inhibitor, AUY922, including TIMP1, SERPINA3 and CYP51A (adjusted p < 0.01). The AUY922-mediated decrease in secretory TIMP1 was validated by ELISA of the PDE culture medium. We next exploited the heterogeneous response of PDEs to 17-AAG in order to detect predictive biomarkers of response and identified PCBP3 as a marker with increased expression in PDEs that had no response or increased in proliferation. Also, 17-AAG treatment led to increased expression of DNAJA1 in PDEs that exhibited a cytostatic response, revealing potential drug resistance mechanisms. This selective regulation of DNAJA1 was validated by Western blot analysis. Our study establishes "proof-of-principle" that proteomic profiling of drug-treated PDEs represents an effective and clinically-relevant strategy for identification of biomarkers that associate with certain tumor-specific responses.

Small molecule inhibitor screening identifified HSP90 inhibitor 17-AAG as potential therapeutic agent for gallbladder cancer

Gallbladder cancer (GBC) is a lethal cancer with poor prognosis associated with high invasiveness and poor response to chemotherapy and radiotherapy. New therapeutic approaches are urgently needed in order to improve survival and response rates of GBC patients. We screened 130 small molecule inhibitors on a panel of seven GBC cell lines and identified the HSP90 inhibitor 17-AAG as one of the most potent inhibitory drugs across the different lines. We tested the antitumor efficacy of 17-AAG and geldanamycin (GA) in vitro and in a subcutaneous preclinical tumor model NOD-SCID mice. We also evaluated the expression of HSP90 by immunohistochemistry in human GBC tumors.In vitro assays showed that 17-AAG and GA significantly reduced the expression of HSP90 target proteins, including EGFR, AKT, phospho-AKT, Cyclin B1, phospho-ERK and Cyclin D1. These molecular changes were consistent with reduced cell viability and cell migration and promotion of G2/M cell cycle arrest and apoptosis observed in our in vitro studies.In vivo, 17-AAG showed efficacy in reducing subcutaneous tumors size, exhibiting a 69.6% reduction in tumor size in the treatment group compared to control mice (p < 0.05).The HSP90 immunohistochemical staining was seen in 182/209 cases of GBC (87%) and it was strongly expressed in 70 cases (33%), moderately in 58 cases (28%), and weakly in 54 cases (26%).Our pre-clinical observations strongly suggest that the inhibition of HSP90 function by HSP90 inhibitors is a promising therapeutic strategy for gallbladder cancer that may benefit from new HSP90 inhibitors currently in development.

Investigation of quercetin and hyperoside as senolytics in adult human endothelial cells

Quercetin has been reported to act as a senolytic by selectively removing senescent endothelial cells, and thus it would seem quercetin could revolutionize the field of gerontology. However, given quercetin's narrow therapeutic index reported in work done with human umbilical vein endothelial cells (HUVECs), we hypothesized that quercetin is not innocuous for non-senescent adult human vascular endothelial cells at concentrations that have been reported to be safe for proliferating HUVECs. Furthermore, we investigated quercetin 3-D-galactoside (Q3G; hyperoside), an inactive quercetin derivative that needs to be cleaved by beta-galactosidase overexpressed in senescent cells to release quercetin, as a potential safer senolytic. We compared the effectiveness of quercetin and Q3G in primary human coronary artery endothelial cells (HCAEC), which are adult microvascular cells. We found that quercetin caused cell death in non-senescent endothelial cells at a concentration that has been reported to selectively remove senescent cells, and that Q3G was not cytotoxic to either young or senescent cells. Thus, in primary adult human endothelial cells, quercetin and Q3G are not senolytics. Earlier work reporting positive results was done with HUVECs, and given their origin and the disparate findings from the current study, these may not be the best cells for evaluating potential senolytics in clinically relevant endothelial cells.

Fibronectin is a stress responsive gene regulated by HSF1 in response to geldanamycin

Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended.

Heat Shock Protein 90 Modulates Lipid Homeostasis by Regulating the Stability and Function of Sterol Regulatory Element-binding Protein (SREBP) and SREBP Cleavage-activating Protein

Sterol regulatory element-binding proteins (SREBPs) are the key transcription factors that modulate lipid biosynthesis. SREBPs are synthesized as endoplasmic reticulum-bound precursors that require proteolytic activation in the Golgi apparatus. The stability and maturation of precursor SREBPs depend on their binding to SREBP cleavage-activating protein (SCAP), which escorts the SCAP-SREBP complex to the Golgi apparatus. In this study, we identified heat shock protein (HSP) 90 as a novel SREBP regulator that binds to and stabilizes SCAP-SREBP. In HepG2 cells, HSP90 inhibition led to proteasome-dependent degradation of SCAP-SREBP, which resulted in the down-regulation of SREBP target genes and the reduction in intracellular triglyceride and cholesterol levels. We also demonstrated in vivo that HSP90 inhibition decreased SCAP-SREBP protein, down-regulated SREBP target genes, and reduced lipids levels in mouse livers. We propose that HSP90 plays an indispensable role in SREBP regulation by stabilizing the SCAP-SREBP complex, facilitating the activation of SREBP to maintain lipids homeostasis.

HSP90 inhibition overcomes ibrutinib resistance in mantle cell lymphoma

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib induces responses in 70% of patients with relapsed and refractory mantle cell lymphoma (MCL). Intrinsic resistance can occur through activation of the nonclassical NF-κB pathway and acquired resistance may involve the BTK C481S mutation. Outcomes after ibrutinib failure are dismal, indicating an unmet medical need. We reasoned that newer heat shock protein 90 (HSP90) inhibitors could overcome ibrutinib resistance by targeting multiple oncogenic pathways in MCL. HSP90 inhibition induced the complete degradation of both BTK and IκB kinase α in MCL lines and CD40-dependent B cells, with downstream loss of MAPK and nonclassical NF-κB signaling. A proteome-wide analysis in MCL lines and an MCL patient-derived xenograft identified a restricted set of targets from HSP90 inhibition that were enriched for factors involved in B-cell receptor and JAK/STAT signaling, the nonclassical NF-κB pathway, cell-cycle regulation, and DNA repair. Finally, multiple HSP90 inhibitors potently killed MCL lines in vitro, and the clinical agent AUY922 was active in vivo against both patient-derived and cell-line xenografts. Together, these findings define the HSP90-dependent proteome in MCL. Considering the disappointing clinical activity of HSP90 inhibitors in other contexts, trials in patients with MCL will be essential for defining the efficacy of and mechanisms of resistance after ibrutinib failure.

HSP90 and Immune Modulation in Cancer

Heat-shock protein 90 (HSP90) is a highly conserved molecular chaperone that plays prominent functional roles in nearly all aspects of cell biology. As a chaperone, it interacts with literally hundreds of "clients," many of which are important drivers, regulators, and promoters of cancer. Thus, HSP90 is a high-value target in the development of anticancer therapeutics. Despite its popularity, our overall knowledge of HSP90 in immune function has lagged behind its well-recognized tumor-supportive roles. The use of inhibitors of HSP90 as chemical biological probes has been invaluable in revealing important roles for the chaperone in multiple aspects of immune function. Given this critical link, we must now consider the question of how immune outcomes may be affected by the HSP90 inhibitors currently in clinical development for the treatment of cancer. This chapter will review some of the immunological aspects of HSP90 function in terms of its intracellular and extracellular roles in antigen presentation, immune effector cell tasks, and regulation of inflammatory processes. This review will further examine the value of HSP90 inhibitors within the context of cancer immunotherapy and will discuss how these drugs might be optimally utilized in combination with immune stimulatory approaches against cancer.

Small-Molecule-Mediated Degradation of the Androgen Receptor through Hydrophobic Tagging

Androgen receptor (AR)-dependent transcription is a major driver of prostate tumor cell proliferation. Consequently, it is the target of several antitumor chemotherapeutic agents, including the AR antagonist MDV3100/enzalutamide. Recent studies have shown that a single AR mutation (F876L) converts MDV3100 action from an antagonist to an agonist. Here we describe the generation of a novel class of selective androgen receptor degraders (SARDs) to address this resistance mechanism. Molecules containing hydrophobic degrons linked to small-molecule AR ligands induce AR degradation, reduce expression of AR target genes and inhibit proliferation in androgen-dependent prostate cancer cell lines. These results suggest that selective AR degradation may be an effective therapeutic prostate tumor strategy in the context of AR mutations that confer resistance to second-generation AR antagonists.

Alternative approaches to Hsp90 modulation for the treatment of cancer

Hsp90 is responsible for the conformational maturation of newly synthesized polypeptides (client proteins) and the re-maturation of denatured proteins via the Hsp90 chaperone cycle. Inhibition of the Hsp90 N-terminus has emerged as a clinically relevant strategy for anticancer chemotherapeutics due to the involvement of clients in a variety of oncogenic pathways. Several immunophilins, co-chaperones and partner proteins are also necessary for Hsp90 chaperoning activity. Alternative strategies to inhibit Hsp90 function include disruption of the C-terminal dimerization domain and the Hsp90 heteroprotein complex. C-terminal inhibitors and Hsp90 co-chaperone disruptors prevent cancer cell proliferation similar to N-terminal inhibitors and destabilize client proteins without induction of heat shock proteins. Herein, current Hsp90 inhibitors, the chaperone cycle, and regulation of this cycle will be discussed.

Phase II trial of gemcitabine and tanespimycin (17AAG) in metastatic pancreatic cancer: a Mayo Clinic Phase II Consortium study

OBJECTIVES

Heat Shock Protein 90 (HSP90) is a molecular chaperone that stabilizes many oncogenic proteins. HSP90 inhibitors may sensitize tumors to cytotoxic agents by causing client protein degradation. Gemcitabine, which has modest activity in pancreas cancer, activates Chk1, a client protein of HSP90. This phase II trial was designed to determine whether 17AAG could enhance the clinical activity of gemcitabine through degradation of Chk1 in patients with stage IV pancreatic cancer.

METHODS

A multicenter, prospective study combining gemcitabine and 17AAG enrolled patients with stage IV pancreatic adenocarcinoma, adequate liver and kidney function, ECOG performance status 0-2, and no prior chemotherapy for metastatic disease. The primary goal was to achieve a 60 % overall survival at 6 months. Sixty-six patients were planned for accrual, with an interim analysis after 25 patients enrolled.

RESULTS

After a futility analysis to achieve the endpoint, accrual was halted with 21 patients enrolled. No complete or partial responses were seen. Forty percent of patients were alive at 6 months. Median overall survival was 5.4 months. Tolerability was moderate, with 65 % of patients having ≥ grade 3 adverse events (AE), and 15 % having grade 4 events.

CONCLUSIONS

The lack of clinical activity suggests that targeting Chk1 by inhibiting HSP90 is not important in pancreatic cancer sensitivity to gemcitabine alone. Further studies of HSP90 targeted agents with gemcitabine alone are not warranted.

Cucurbitacin D Is a Disruptor of the HSP90 Chaperone Machinery

Heat shock protein 90 (Hsp90) facilitates the maturation of many newly synthesized and unfolded proteins (clients) via the Hsp90 chaperone cycle, in which Hsp90 forms a heteroprotein complex and relies upon cochaperones, immunophilins, etc., for assistance in client folding. Hsp90 inhibition has emerged as a strategy for anticancer therapies due to the involvement of clients in many oncogenic pathways. Inhibition of chaperone function results in client ubiquitinylation and degradation via the proteasome, ultimately leading to tumor digression. Small molecule inhibitors perturb ATPase activity at the N-terminus and include derivatives of the natural product geldanamycin. However, N-terminal inhibition also leads to induction of the pro-survival heat shock response (HSR), in which displacement of the Hsp90-bound transcription factor, heat shock factor-1, translocates to the nucleus and induces transcription of heat shock proteins, including Hsp90. An alternative strategy for Hsp90 inhibition is disruption of the Hsp90 heteroprotein complex. Disruption of the Hsp90 heteroprotein complex is an effective strategy to prevent client maturation without induction of the HSR. Cucurbitacin D, isolated from Cucurbita texana, and 3-epi-isocucurbitacin D prevented client maturation without induction of the HSR. Cucurbitacin D also disrupted interactions between Hsp90 and two cochaperones, Cdc37 and p23.

Inhibition of heat shock protein 90 alleviates steatosis and macrophage activation in murine alcoholic liver injury

BACKGROUND & AIMS

Heat shock protein 90 (hsp90) is an emerging therapeutic target in chronic liver diseases. Hsp90 plays an important role in liver immune cell activation; however its role in alcoholic liver disease (ALD) remains elusive. Here we hypothesize that hsp90 is crucial in alcohol induced steatosis and pro-inflammatory cytokine production. To test this hypothesis, we employed a pharmacological inhibitor of hsp90, 17-DMAG (17-Dimethylamino-ethylamino-17-demethoxygeldanamycin) in an in vivo mouse model of acute and chronic alcoholic liver injury.

METHODS

C57BL/6 mice were given either a single dose of ethanol via oral gavage (acute) or chronically fed alcohol for 2 weeks followed by oral gavage (chronic-binge). 17-DMAG was administered during or at the end of feeding. Liver injury parameters, inflammatory cytokines and lipid metabolism genes were analysed.

RESULTS

Our results reveal increased expression of hsp90 in human and mouse alcoholic livers. In vivo inhibition of hsp90, using 17-DMAG, not only prevented but also alleviated alcoholic liver injury, determined by lower serum ALT, AST and reduced hepatic triglycerides. Mechanistic analysis showed that 17-DMAG decreased alcohol mediated oxidative stress, reduced serum endotoxin, decreased inflammatory cells, and diminished sensitization of liver macrophages to LPS, resulting in downregulation of CD14, NFκB inhibition, and decreased pro-inflammatory cytokine production. Hsp90 inhibition decreased fatty acid synthesis genes via reduced nuclear SREBP-1 and favoured fatty acid oxidation genes via PPARα.

CONCLUSIONS

Inhibition of hsp90 decreased alcohol induced steatosis and pro-inflammatory cytokines and inhibited alcoholic liver injury. Hsp90 is therefore relevant in human alcoholic cirrhosis and a promising therapeutic target in ALD.

Advances in therapeutics for neurodegenerative tauopathies: moving toward the specific targeting of the most toxic tau species

Neurodegenerative disease is one of the greatest health concerns today and with no effective treatment in sight, it is crucial that researchers find a safe and successful therapeutic. While neurofibrillary tangles are considered the primary tauopathy hallmark, more evidence continues to come to light to suggest that soluble, intermediate tau aggregates--tau oligomers--are the most toxic species in disease. These intermediate tau species may also be responsible for the spread of pathology, suggesting that oligomeric tau may be the best therapeutic target. Here, we summarize results for the modulation of tau by molecular chaperones, small molecules and aggregation inhibitors, post-translational modifications, immunotherapy, other techniques, and future directions.

Heat shock protein 90 is a potential therapeutic target for ameliorating skeletal muscle abnormalities in Parkinson's disease

Previous studies have confirmed that heat shock protein 90 overexpression can lead to dopaminergic neuronal death. This study was designed to further investigate what effects are produced by heat shock protein 90 after endurance exercise training. Immunohistochemistry results showed that exercise training significantly inhibited heat shock protein 90 overexpression in the soleus and gastrocnemius in Parkinson's disease rats, which is a potential therapeutic target for ameliorating skeletal muscle abnormalities in Parkinson's disease.

The anti-inflammatory effects of a high-frequency oligodeoxynucleotide from the genomic DNA of Lactobacillus casei

Genomic DNA has been identified as an anti-inflammatory component of Lactobacillus species, the effects of which are mediated through toll-like receptor (TLR) 9. In this study, we identified 14 novel anti-inflammatory oligodeoxynucleotide (ODN) from the genomic DNA of Lactobacillus casei by measuring their effects on the secretion of interleukin (IL)-8 (CXCL8) in the human epithelial colorectal adenocarcinoma cell line Caco-2 cells. The ODN TTTTGCCG strongly decreased IL-8 secretion. In the genomic DNA of Lactobacillus species, the frequency of TTTTGCCG was highest in the genomic DNA of L. casei and similar among strains of L. casei. Decreases in inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 expressions in macrophage-like differentiated THP-1 cells confirmed the anti-inflammatory effect of TTTTGCCG. Furthermore, oral administration of TTTTGCCG ameliorated dextran sodium sulfate (DSS)-induced murine colitis and DSS-induced increased expression of inflammatory factor mRNAs, such as macrophage inflammatory protein (MIP)-2 (CXCL2), iNOS, and COX-2. The anti-inflammatory effect of TTTTGCCG was mainly regulated by an increase in heat shock protein (Hsp) 70 expression in the epithelium. TLR9 and Hsp90 may primarily mediate the anti-inflammatory effect of TTTTGCCG on Hsp70 signaling.

Chronic treatment with 17-DMAG improves balance and coordination in a new mouse model of Machado-Joseph disease

Machado-Joseph disease (MJD) or spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease currently with no treatment. We describe a novel mouse model of MJD which expresses mutant human ataxin-3 at near endogenous levels and manifests MJD-like motor symptoms that appear gradually and progress over time. CMVMJD135 mice show ataxin-3 intranuclear inclusions in the CNS and neurodegenerative changes in key disease regions, such as the pontine and dentate nuclei. Hsp90 inhibition has shown promising outcomes in some neurodegenerative diseases, but nothing is known about its effects in MJD. Chronic treatment of CMVMJD mice with Hsp90 inhibitor 17-DMAG resulted in a delay in the progression of their motor coordination deficits and, at 22 and 24 weeks of age, was able to rescue the uncoordination phenotype to wild-type levels; in parallel, a reduction in neuropathology was observed in treated animals. We observed limited induction of heat-shock proteins with treatment, but found evidence that 17-DMAG may be acting through autophagy, as LC3-II (both at mRNA and protein levels) and beclin-1 were induced in the brain of treated animals. This resulted in decreased levels of the mutant ataxin-3 and reduced intranuclear aggregation of this protein. Our data validate this novel mouse model as a relevant tool for the study of MJD pathogenesis and for pre-clinical studies, and show that Hsp90 inhibition is a promising therapeutic strategy for MJD.

Contesting the dogma of an age-related heat shock response impairment: implications for cardiac-specific age-related disorders

Ageing is associated with the reduced performance of physiological processes and has been proposed as a major risk factor for disease. An age-related decline in stress response pathways has been widely documented in lower organisms. In particular, the heat shock response (HSR) becomes severely compromised with age in Caenorhabditis elegans. However, a comprehensive analysis of the consequences of ageing on the HSR in higher organisms has not been documented. We used both HS and inhibition of HSP90 to induce the HSR in wild-type mice at 3 and 22 months of age to investigate the extent to which different brain regions, and peripheral tissues can sustain HSF1 activity and HS protein (HSP) expression with age. Using chromatin immunoprecipitation, quantitative reverse transcription polymerase chain reaction, western blotting and enzyme linked immunosorbent assay (ELISA), we were unable to detect a difference in the level or kinetics of HSP expression between young and old mice in all brain regions. In contrast, we did observe an age-related reduction in chaperone levels and HSR-related proteins in the heart. This could result in a decrease in the protein folding capacity of old hearts with implications for age-related cardiac disorders.

O-GlcNAcase Expression is Sensitive to Changes in O-GlcNAc Homeostasis

O-linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification involving an attachment of a single β-N-acetylglucosamine moiety to serine or threonine residues in nuclear and cytoplasmic proteins. Cellular O-GlcNAc levels are regulated by two enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which add and remove the modification, respectively. The levels of O-GlcNAc can rapidly change in response to fluctuations in the extracellular environment; however, O-GlcNAcylation returns to a baseline level quickly after stimulus removal. This process termed O-GlcNAc homeostasis appears to be critical to the regulation of many cellular functions including cell cycle progress, stress response, and gene transcription. Disruptions in O-GlcNAc homeostasis are proposed to lead to the development of diseases, such as cancer, diabetes, and Alzheimer's disease. O-GlcNAc homeostasis is correlated with the expression of OGT and OGA. We reason that alterations in O-GlcNAc levels affect OGA and OGT transcription. We treated several human cell lines with Thiamet-G (TMG, an OGA inhibitor) to increase overall O-GlcNAc levels resulting in decreased OGT protein expression and increased OGA protein expression. OGT transcript levels slightly declined with TMG treatment, but OGA transcript levels were significantly increased. Pretreating cells with protein translation inhibitor cycloheximide did not stabilize OGT or OGA protein expression in the presence of TMG; nor did TMG stabilize OGT and OGA mRNA levels when cells were treated with RNA transcription inhibitor actinomycin D. Finally, we performed RNA Polymerase II chromatin immunoprecipitation at the OGA promoter and found that RNA Pol II occupancy at the transcription start site was lower after prolonged TMG treatment. Together, these data suggest that OGA transcription was sensitive to changes in O-GlcNAc homeostasis and was potentially regulated by O-GlcNAc.

Geldanamycin-induced osteosarcoma cell death is associated with hyperacetylation and loss of mitochondrial pool of heat shock protein 60 (hsp60)

Osteosarcoma is one of the most malignant tumors of childhood and adolescence that is often resistant to standard chemo- and radio-therapy. Geldanamycin and geldanamycin analogs have been recently studied as potential anticancer agents for osteosarcoma treatment. Here, for the first time, we have presented novel anticancer mechanisms of geldanamycin biological activity. Moreover, we demonstrated an association between the effects of geldanamycin on the major heat shock proteins (HSPs) and the overall survival of highly metastatic human osteosarcoma 143B cells. We demonstrated that the treatment of 143B cells with geldanamycin caused a subsequent upregulation of cytoplasmic Hsp90 and Hsp70 whose activity is at least partly responsible for cancer development and drug resistance. On the other hand, geldanamycin induced upregulation of Hsp60 gene expression, and a simultaneous loss of hyperacetylated Hsp60 mitochondrial protein pool resulting in decreased viability and augmented cancer cell death. Hyperacetylation of Hsp60 seems to be associated with anticancer activity of geldanamycin. In light of the fact that mitochondrial dysfunction plays a critical role in the apoptotic signaling pathway, the presented data may support a hypothesis that Hsp60 can be another functional part of mitochondria-related acetylome being a potential target for developing novel anticancer strategies.

The anticancer drug AUY922 generates a proteomics fingerprint that is highly conserved among structurally diverse Hsp90 inhibitors

AUY922 is a potent synthetic Hsp90 antagonist that is moving steadily through clinical trials against a small range of cancers. To identify protein markers that might measure the drug's effects, and to gain understanding of mechanisms by which AUY922 might inhibit the proliferation of leukemia cells, we characterized AUY922's impacts on the proteomes of cultured Jurkat cells. We describe a robust and readily assayed proteomics fingerprint that AUY922 shares with the flagship Hsp90 inhibitors 17-DMAG and radicicol. We also extend our proteomics findings, demonstrating that an unrelated antagonist of protein folding potentiates the antiproliferative effects of AUY922. Results provide a set of candidate biomarkers for responses to AUY922 in leukemia cells and suggest new modalities for enhancing AUY922's anticancer activities.

HSP90 inhibitor 17-AAG selectively eradicates lymphoma stem cells

Cancer stem cells (CSC; also called tumor-initiating cells) comprise tumor cell subpopulations that preserve the properties of quiescence, self-renewal, and differentiation of normal stem cells. In addition, CSCs are therapeutically important because of their key contributions toward drug resistance. The hypoxia-inducible transcription factor HIF1α is critical for CSC maintenance in mouse lymphoma. In this study, we showed that low concentrations of the HSP90 inhibitor 17-AAG eliminate lymphoma CSCs in vitro and in vivo by disrupting the transcriptional function of HIF1α, a client protein of HSP90. 17-AAG preferentially induced apoptosis and eliminated the colony formation capacity of mouse lymphoma CSCs and human acute myeloid leukemia (AML) CSCs. However, low concentrations of 17-AAG failed to eliminate highly proliferative lymphoma and AML cells (non-CSCs), in which the AKT-GSK3 signaling pathway is constitutively active. The heat shock transcription factor HSF1 is highly expressed in non-CSCs, but it was weakly expressed in lymphoma CSCs. However, siRNA-mediated attenuation of HSF1 abrogated the colony formation ability of both lymphoma and AML CSCs. This study supports the use of 17-AAG as a CSC targeting agent and, in addition, shows that HSF1 is an important target for elimination of both CSCs and non-CSCs in cancer.

Anti-tumor activity of the HSP90 inhibitor SNX-2112 in pediatric cancer cell lines

BACKGROUND

HSP90 plays a central role in stabilizing client proteins involved in malignant processes. SNX-2112 is an orally administered potent HSP90 inhibitor that has demonstrated pre-clinical anti-tumor activity in adult malignancies. As many childhood tumors depend upon HSP90 client proteins, we sought to test the pre-clinical efficacy of SNX-2112 in a panel of pediatric cancer cell lines both as a single-agent and in combination with cisplatin (CP).

PROCEDURE

Eight cell lines (from osteosarcoma, neuroblastoma, hepatoblastoma, and lymphoma) were studied. Short- and long-term effects of SNX-2112 were assessed by MTT and clonogenic assays. Cell cycling was measured using flow cytometry. Status of HSC70, HSP72, AKT1, C-Raf, and PARP was assessed by immunoblotting. Efficacy of SNX-2112 in combination with CP was assessed using median-effect analysis.

RESULTS

Cell lines studied demonstrated sensitivity to SNX-2112 with IC(50) values ranging from 10-100 nM. Low dose treatments (12 nM) resulted in a cytostatic response with a minimal increase in sub-G1 content. A higher dose (70 nM) exhibited a more prolonged inhibition and larger sub-G1 accumulation. Observed levels of AKT1 and C-Raf were markedly reduced over time along with an increase in PARP cleavage. In concurrently administered combination treatments, SNX-2112 and CP synergistically inhibited cell growth.

CONCLUSIONS

SNX-2112 showed marked single-agent activity in pediatric cancer cell lines with downstream effects on HSP90 client proteins. The combination of SNX-2112 and CP showed synergistic activity in two cell lines tested. Further studies of HSP90 inhibitors such as SNX-2112 as a single agent or in combination with chemotherapy are warranted in pediatric cancer.

Inhibition of heat shock protein (molecular weight 90 kDa) attenuates proinflammatory cytokines and prevents lipopolysaccharide-induced liver injury in mice

Endotoxin-mediated proinflammatory cytokines play a significant role in the pathogenesis of acute and chronic liver diseases. Heat shock protein 90 (molecular weight, 90 kDa) (hsp90) functions as an important chaperone of lipopolysaccharide (LPS) signaling and is required for the production of proinflammatory cytokines. We hypothesized that inhibition of hsp90 would prevent LPS-induced liver injury by decreasing proinflammatory cytokines. C57BL/6 mice were injected intraperitoneally with an hsp90 inhibitor, 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG), and LPS. Parameters of liver injury, proinflammatory cytokines, and associated mechanisms were studied by in vivo and in vitro experiments. Inhibition of hsp90 by 17-DMAG prevented LPS-induced increases in serum alanine aminotransferase activity and significantly reduced serum tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) protein as well as messenger RNA (mRNA) in liver. Enhanced DNA-binding activity of heat shock transcription factor 1 (HSF1) and induction of target gene heat shock protein 70 (molecular weight, 70 kDa) confirmed hsp90 inhibition in liver. 17-DMAG treatment decreased cluster of differentiation 14 mRNA and LPS-induced nuclear factor kappa light-chain enhancer of activated B cells (NFκB) DNA binding without affecting Toll-like receptor 4 mRNA in liver. Mechanistic studies revealed that 17-DMAG-mediated inhibition of TNFα showed no effect on LPS-induced NFκB promoter-driven reporter activity, but significantly decreased TNFα promoter-driven reporter activity. Chromatin immunoprecipitation assays showed that 17-DMAG enhanced HSF1 binding to the TNFα promoter, but not the IL-6 promoter, suggesting HSF1 mediated direct inhibition of TNFα, but not IL-6. We show that HSF1 indirectly regulates IL-6 by the induction of another transcription factor, activating transcription factor 3. Inhibition of HSF1, using small interfering RNA, prevented 17-DMAG-mediated down-regulation of NFκB-binding activity, TNFα, and IL-6 induction, supporting a repressive role for HSF1 on proinflammatory cytokine genes during hsp90 inhibition.

CONCLUSION

Hsp90 inhibition in vivo reduces proinflammatory cytokines and prevents LPS-induced liver injury likely through repressive action of HSF1. Our results suggest a novel application for 17-DMAG in alleviating LPS-induced liver injury.

Inhibition of the heat shock response by PI103 enhances the cytotoxicity of arsenic trioxide

Heat shock factor 1 (HSF1) is a key regulator of the cytoprotective and anti-apoptotic heat shock response and can be activated by arsenite. Inhibition of HSF1 activation may therefore enhance the cytotoxicity of arsenic trioxide (ATO). We show that ATO induced HSF1 phosphorylation at serine 326 (S326) and induced HSF1-dependent expression of heat shock proteins (HSPs) 27 and 70 in cultured cells. HSF1 significantly reduced cell sensitivity to ATO by reducing apoptosis. Disruption of HSF1 function not only reduced ATO induction of HSP27 and 70 but also enhanced ATO cytotoxicity by elevating apoptosis. These results reveal that HSF1 activation and the resulting induction of HSPs may protect cells from ATO cytotoxicity. The diminished expression of HSPs and hypersensitivity to ATO in cells stably depleted of HSF1 was rescued by ectopic expression of wild-type HSF1 but not an S326A substitution mutant, indicating that phosphorylation at S326 was critical for the protective effect of HSF1. Simultaneous treatment of cells with ATO and PI103, an inhibitor of members of the phosphatidylinositol 3-kinase (PI3K) family, suppressed not only ATO-induced expression of an HSP70 promoter-reporter construct and endogenous HSP70 but also phosphorylation of HSF1 S326. PI103 considerably reduced HSF1 transactivation in ATO-treated cells but had only a limited effect on HSF1 nuclear translocation and DNA binding. Furthermore, PI103 enhanced ATO cytotoxicity in an HSF1-dependent manner. Thus, inhibition of S326 phosphorylation by PI103 blocks the transactivation of HSF1 and may consequently suppress ATO induction of the heat shock response and sensitize cells to ATO.

Systematic identification of the HSP90 candidate regulated proteome

HSP90 is a central player in the folding and maturation of many proteins. More than two hundred HSP90 clients have been identified by classical biochemical techniques including important signaling proteins with high relevance to human cancer pathways. HSP90 inhibition has thus become an attractive therapeutic concept and multiple molecules are currently in clinical trials. It is therefore of fundamental biological and medical importance to identify, ideally, all HSP90 clients and HSP90 regulated proteins. To this end, we have taken a global and a chemical proteomic approach in geldanamycin treated cancer cell lines using stable isotope labeling with amino acids in cell culture and quantitative mass spectrometry. We identified >6200 proteins in four different human cell lines and ~1600 proteins showed significant regulation upon drug treatment. Gene ontology and pathway/network analysis revealed common and cell-type specific regulatory effects with strong connections to unfolded protein binding and protein kinase activity. Of the 288 identified protein kinases, 98 were geldanamycin treatment including >50 kinases not formerly known to be regulated by HSP90. Protein turn-over measurements using pulsed stable isotope labeling with amino acids in cell culture showed that protein down-regulation by HSP90 inhibition correlates with protein half-life in many cases. Protein kinases show significantly shorter half lives than other proteins highlighting both challenges and opportunities for HSP90 inhibition in cancer therapy. The proteomic responses of the HSP90 drugs geldanamycin and PU-H71 were highly similar suggesting that both drugs work by similar molecular mechanisms. Using HSP90 immunoprecipitation, we validated several kinases (AXL, DDR1, TRIO) and other signaling proteins (BIRC6, ISG15, FLII), as novel clients of HSP90. Taken together, our study broadly defines the cellular proteome response to HSP90 inhibition and provides a rich resource for further investigation relevant for the treatment of cancer.

HSP90 inhibition by 17-DMAG reduces inflammation in J774 macrophages through suppression of Akt and nuclear factor-κB pathways

OBJECTIVE

This study was designed to determine whether inhibition of heat shock protein 90 (HSP90) reduces pro-inflammatory mediator production by decreasing the nuclear factor (NF)-κB and Akt signaling pathways in immune-stimulated macrophages.

METHODS

J774A.1 murine macrophages were treated with the HSP90 inhibitor 17-DMAG (0.01, 0.1 or 1 μM) prior to immune stimulation with lipopolysaccharide and interferon-γ. Expression of Akt, inhibitor of κB kinase (IKK), and heat shock proteins were measured in whole cell lysates by Western blotting. Phosphorylated Akt and inhibitor of κB (IκB) were measured in whole cell lysates by ELISA. Cell supernatants were analyzed for interleukin (IL)-6, tumor necrosis factor (TNF)-α and nitric oxide (NO). Translocation of NF-κB and heat shock factor (HSF)-1 was assessed by immunofluorescence.

RESULTS

Treating cells with 17-DMAG reduced expression of Akt and IKK in immune-stimulated cells. 17-DMAG reduced nuclear translocation of NF-κB and reduced immune-stimulated production of IL-6, TNF-α and NO, but did not decrease inducible nitric oxide synthase expression.

CONCLUSIONS

Our studies show that the immune-mediated NF-κB inflammatory cascade is blocked by the HSP90 inhibitor 17-DMAG. Due to the broad interaction of HSP90 with many pro-inflammatory kinase cascades, inhibition of HSP90 may provide a novel approach to reducing chronic inflammation.

Downregulation of the Hsp90 system causes defects in muscle cells of Caenorhabditis elegans

The ATP-dependent molecular chaperone Hsp90 is required for the activation of a variety of client proteins involved in various cellular processes. Despite the abundance of known client proteins, functions of Hsp90 in the organismal context are not fully explored. In Caenorhabditis elegans, Hsp90 (DAF-21) has been implicated in the regulation of the stress-resistant dauer state, in chemosensing and in gonad formation. In a C. elegans strain carrying a DAF-21 mutation with a lower ATP turnover, we observed motility defects. Similarly, a reduction of DAF-21 levels in wild type nematodes leads to reduced motility and induction of the muscular stress response. Furthermore, aggregates of the myosin MYO-3 are visible in muscle cells, if DAF-21 is depleted, implying a role of Hsp90 in the maintenance of muscle cell functionality. Similar defects can also be observed upon knockdown of the Hsp90-cochaperone UNC-45. In life nematodes YFP-DAF-21 localizes to the I-band and the M-line of the muscular ultrastructure, but the protein is not stably attached there. The Hsp90-cofactor UNC-45-CFP contrarily can be found in all bands of the nematode muscle ultrastructure and stably associates with the UNC-54 containing A-band. Thus, despite the physical interaction between DAF-21 and UNC-45, apparently the two proteins are not always localized to the same muscular structures. While UNC-45 can stably bind to myofilaments in the muscular ultrastructure, Hsp90 (DAF-21) appears to participate in the maintenance of muscle structures as a transiently associated diffusible factor.

A phase 1 study of IPI-504 (retaspimycin hydrochloride) in patients with relapsed or relapsed and refractory multiple myeloma

Abstract A phase 1 study of IPI-504 (retaspimycin hydrochloride) administered intravenously twice weekly for 2 weeks at 22.5, 45, 90, 150, 225, 300 or 400 mg/m(2) followed by 10 days off-treatment was conducted to determine the safety and maximum tolerated dose (MTD) of IPI-504 in patients with relapsed or relapsed/refractory multiple myeloma (MM). Anti-tumor activity and pharmacokinetics were also evaluated. Eighteen patients (mean age 60.5 years; median 9 prior therapies) were enrolled. No dose-limiting toxicities (DLTs) were reported for IPI-504 doses up to 400 mg/m(2). The most common treatment-related adverse event was grade 1 infusion site pain (four patients). All other treatment-related events were assessed as grade 1 or 2 in severity. The area under the curve (AUC) increased with increasing dose, and the mean half-life was approximately 2-4 h for IPI-504 and its metabolites. Four patients had stable disease, demonstrating modest single-agent activity in relapsed or relapsed/refractory MM.

Altered chromatin architecture underlies progressive impairment of the heat shock response in mouse models of Huntington disease

Huntington disease (HD) is a devastating neurodegenerative disorder for which there are no disease-modifying treatments. Previous studies have proposed that activation of the heat shock response (HSR) via the transcription factor heat shock factor 1 (HSF1) may be of therapeutic benefit. However, the effect of disease progression on the HSR and the therapeutic potential of this pathway are currently unknown. Here, we used a brain-penetrating HSP90 inhibitor and physiological, molecular, and behavioral readouts to demonstrate that pharmacological activation of HSF1 improves huntingtin aggregate load, motor performance, and other HD-related phenotypes in the R6/2 mouse model of HD. However, the beneficial effects of this treatment were transient and diminished with disease progression. Molecular analyses to understand the transient nature of these effects revealed altered chromatin architecture, reduced HSF1 binding, and impaired HSR accompanied disease progression in both the R6/2 transgenic and HdhQ150 knockin mouse models of HD. Taken together, our findings reveal that the HSR, a major inducible regulator of protein homeostasis and longevity, is disrupted in HD. Consequently, pharmacological induction of HSF1 as a therapeutic approach to HD is more complex than was previously anticipated.

To fold or not to fold: modulation and consequences of Hsp90 inhibition

BACKGROUND

The 90-kDa heat-shock proteins (Hsp90) have rapidly evolved into promising therapeutic targets for the treatment of several diseases, including cancer and neurodegenerative diseases. Hsp90 is a molecular chaperone that aids in the conformational maturation of nascent polypeptides, as well as the rematuration of denatured proteins.

DISCUSSION

Many of the Hsp90-dependent client proteins are associated with cellular growth and survival and, consequently, inhibition of Hsp90 represents a promising approach for the treatment of cancer. Conversely, stimulation of heat-shock protein levels has potential therapeutic applications for the treatment of neurodegenerative diseases that result from misfolded and aggregated proteins.

CONCLUSION

Hsp90 modulation exhibits the potential to treat unrelated disease states, from cancer to neurodegenerative diseases, and, thus, to fold or not to fold, becomes a question of great value.

Modulation of Hsf1 activity by novobiocin and geldanamycin

Since Hsp90 is a known modulator of HSF1 activity, we examined the effects of two pharmacological inhibitors of Hsp90, novobiocin and geldanamycin, on HSF1 DNA-binding activity in the Xenopus oocyte model system. Novobiocin exhibits antiproliferative activity in culture cells and interacts with a C-terminal ATP-binding pocket on Hsp90, inhibiting Hsp90 autophosphorylation. Treatment of oocytes with novobiocin followed by heat shock results in a dose-dependent decrease in HSF1 DNA-binding and transcriptional activity. Immunoprecipitation experiments demonstrate novobiocin does not alter HSF1 activity through dissociation of Hsp90 from either monomeric or trimerized HSF1, suggesting that the effect of novobiocin on HSF1 is mediated through alterations in Hsp90 autophosphorylation. Geldanamycin binds the N-terminal ATPase site of Hsp90 and inhibits chaperone activity. Geldanamycin treatment of oocytes resulted in a dose-dependent increase in stability of active HSF1 trimers during submaximal heat shock and a delay in disassembly of trimers during recovery. The results suggest that Hsp90 chaperone activity is required for disassembly of HSF1 trimers. The data obtained with novobiocin suggests the C-terminal ATP-binding activity of Hsp90 is required for the initial steps of HSF1 trimerization, whereas the effects of geldanamycin suggest N-terminal ATPase and chaperone activities are required for disassembly of activated trimers. These data provide important insight into the molecular mechanisms by which pharmacological inhibitors of Hsp90 affect the heat shock response.

Phase I study of 17-allylamino-17 demethoxygeldanamycin, gemcitabine and/or cisplatin in patients with refractory solid tumors

PURPOSE

To determine the maximum tolerated dose (MTD) and characterize the dose-limiting toxicities (DLT) of 17-AAG, gemcitabine and/or cisplatin. Levels of the proteins Hsp90, Hsp70 and ILK were measured in peripheral blood mononuclear cell (PMBC) lysates to assess the effects of 17-AAG.

EXPERIMENTAL DESIGN

Phase I dose-escalating trial using a "3 + 3" design performed in patients with advanced solid tumors. Once the MTD of gemcitabine + 17-AAG + cisplatin was determined, dose escalation of 17-AAG with constant doses of gemcitabine and cisplatin was attempted. After significant hematologic toxicity occurred, the protocol was amended to evaluate three cohorts: gemcitabine and 17-AAG; 17-AAG and cisplatin; and gemcitabine, 17-AAG and cisplatin with modified dosing.

RESULTS

The 39 patients enrolled were evaluable for toxicity and response. The MTD for cohort A was 154 mg/m(2) of 17-AAG, 750 mg/m(2) of gemcitabine, and 40 mg/m(2) of cisplatin. In cohort A, DLTs were observed at the higher dose level and included neutropenia, hyperbilirubinemia, dehydration, GGT elevation, hyponatremia, nausea, vomiting, and thrombocytopenia. The MTD for cohort C was 154 mg/m(2) of 17-AAG and 750 mg/m(2) of gemcitabine, with one DLT observed (alkaline phosphatase elevation) observed. In cohort C, DLTs of thrombocytopenia, fever and dyspnea were seen at the higher dose level. The remaining cohorts were closed to accrual due to toxicity. Six patients experienced partial responses. Mean Hsp90 levels were decreased and levels of Hsp70 were increased compared to baseline.

CONCLUSIONS

17-AAG in combination with gemcitabine and cisplatin demonstrated antitumor activity, but significant hematologic toxicities were encountered. 17-AAG combined with gemcitabine is tolerable and has demonstrated evidence of activity at the MTD. The recommended phase II dose is defined as 154 mg/m(2) of 17-AAG and 750 mg/m(2) of gemcitabine, and is currently being investigated in phase II studies in ovarian and pancreatic cancers. There is no recommended phase II dose for the cisplatin-containing combinations.

Triptolide therapy for neuroblastoma decreases cell viability in vitro and inhibits tumor growth in vivo

BACKGROUND

Heat shock protein (Hsp)-70 is overexpressed in several human malignancies, and its inhibition has been shown to kill cancer cells. Our objectives were to assess the effectiveness of triptolide, an Hsp-70 inhibitor, in treating neuroblastoma in vitro and in vivo, and to measure the associated effects on Hsp-70 levels and apoptosis markers.

METHODS

After exposing N2a and SKNSH cell lines to triptolide, cell viability was assessed. Caspase-3 and -9 activities were measured and annexin staining performed to determine if cell death occurred via apoptosis. Hsp-70 protein and mRNA levels were determined using Western blot and real-time polymerase chain reaction. In an orthotopic tumor model, mice received daily triptolide injections and were humanely killed at study completion with tumor measurement.

RESULTS

Triptolide treatment resulted in dose- and time-dependent N2a cell death and dose-dependent SKNSH killing. Triptolide exposure was associated with dose-dependent increases in caspase activity and annexin staining. Triptolide decreased Hsp-70 protein and mRNA levels in a dose-dependent fashion. Mice receiving triptolide therapy had significantly smaller tumors than controls.

CONCLUSION

Triptolide therapy decreased neuroblastoma cell viability in vitro and inhibited tumor growth in vivo. Our studies suggest that triptolide killed cells via apoptosis and in association with inhibition of Hsp-70 expression. Triptolide may provide a novel therapy for neuroblastoma.