Hsp-90-associated oncoproteins: multiple targets of geldanamycin and its analogs

The Myc Family and the Metastasis Suppressor NDRG1: Targeting Key Molecular Interactions with Innovative Therapeutics

Cancer is a leading cause of death worldwide, resulting in ∼10 million deaths in 2020. Major oncogenic effectors are the Myc proto-oncogene family, which consists of three members including c-Myc, N-Myc, and L-Myc. As a pertinent example of the role of the Myc family in tumorigenesis, amplification of MYCN in childhood neuroblastoma strongly correlates with poor patient prognosis. Complexes between Myc oncoproteins and their partners such as hypoxia-inducible factor-1α and Myc-associated protein X (MAX) result in proliferation arrest and pro-proliferative effects, respectively. Interactions with other proteins are also important for N-Myc activity. For instance, the enhancer of zest homolog 2 (EZH2) binds directly to N-Myc to stabilize it by acting as a competitor against the ubiquitin ligase, SCFFBXW7, which prevents proteasomal degradation. Heat shock protein 90 may also be involved in N-Myc stabilization since it binds to EZH2 and prevents its degradation. N-Myc downstream-regulated gene 1 (NDRG1) is downregulated by N-Myc and participates in the regulation of cellular proliferation via associating with other proteins, such as glycogen synthase kinase-3β and low-density lipoprotein receptor-related protein 6. These molecular interactions provide a better understanding of the biologic roles of N-Myc and NDRG1, which can be potentially used as therapeutic targets. In addition to directly targeting these proteins, disrupting their key interactions may also be a promising strategy for anti-cancer drug development. This review examines the interactions between the Myc proteins and other molecules, with a special focus on the relationship between N-Myc and NDRG1 and possible therapeutic interventions. SIGNIFICANCE STATEMENT: Neuroblastoma is one of the most common childhood solid tumors, with a dismal five-year survival rate. This problem makes it imperative to discover new and more effective therapeutics. The molecular interactions between major oncogenic drivers of the Myc family and other key proteins; for example, the metastasis suppressor, NDRG1, may potentially be used as targets for anti-neuroblastoma drug development. In addition to directly targeting these proteins, disrupting their key molecular interactions may also be promising for drug discovery.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Anti-aging: senolytics or gerostatics (unconventional view)

Senolytics are basically anti-cancer drugs, repurposed to kill senescent cells selectively. It is even more difficult to selectively kill senescent cells than to kill cancer cells. Based on lessons of cancer therapy, here I suggest how to exploit oncogene-addiction and to combine drugs to achieve selectivity. However, even if selective senolytic combinations will be developed, there is little evidence that a few senescent cells are responsible for organismal aging. I also discuss gerostatics, such as rapamycin and other rapalogs, pan-mTOR inhibitors, dual PI3K/mTOR inhibitors, which inhibit growth- and aging-promoting pathways. Unlike senolytics, gerostatics do not kill cells but slow down cellular geroconversion to senescence. Numerous studies demonstrated that inhibition of the mTOR pathways by any means (genetic, pharmacological and dietary) extends lifespan. Currently, only two studies demonstrated that senolytics (fisetin and a combination Dasatinib plus Quercetin) extend lifespan in mice. These senolytics slightly inhibit the mTOR pathway. Thus, life extension by these senolytics can be explained by their slight rapamycin-like (gerostatic) effects.

Heat shock proteins and exosomes in cancer theranostics

Heat shock proteins (HSPs) are a superfamily of molecular chaperones that were discovered through their ability to be induced by different stresses including heat shock. Other than their function as chaperones in proteins homeostasis, HSPs have been shown to inhibit different forms of cell death and to participate in cell proliferation and differentiation processes. Because cancer cells have to rewire their metabolism, they require a high amount of these stress-inducible chaperones for their survival. Therefore, HSPs are unusually abundant in cancer cells where they have oncogene-like functions. In cancer, HSPs have been involved in the regulation of apoptosis, immune responses, angiogenesis, metastasis and treatment resistance. Recently, HSPs have been shown to be secreted through exosomes by cancer cells. These tumor-derived exosomes can be used as circulating markers: HSP-exosomes have been reported as biomarkers of cancer dissemination, response to therapy and/or patient outcome. A new range of functions, mostly in modulation of anticancer immune responses, have been described for these extracellular HSPs. In this review, we will describe those recently reported functions of HSP-exosomes that makes them both targets for anticancer therapeutics and biomarkers for the monitoring of the disease. We will also discuss their emerging interest in cancer vaccines.

Identification of proteasome inhibitors using analysis of gene expression profiles

Inhibitors of the 20S proteasome such as bortezomib (Velcade_®) and carfilzomib (Kypriolis_®) are in clinical use for the treatment of patients with multiple myeloma and mantle cell lymphoma. In an attempt to identify novel inhibitors of the ubiquitin-proteasome system (UPS) we used the connectivity map (CMap) resource, based on alterations of gene expression profiles by perturbagens, and performed COMPARE analyses of drug sensitivity patterns in the NCI₆₀ panel. Cmap analysis identified a large number of small molecules with strong connectivity to proteasome inhibition, including both well characterized inhibitors of the 20S proteasome and molecules previously not described to inhibit the UPS. A number of these compounds have been reported to be cytotoxic to tumor cells and were tested for their ability to decrease processing of proteasome substrates. The antibiotic thiostrepton and the natural products celastrol and curcumin induced strong accumulation of polyubiquitinated proteasome substrates in exposed cells. Other compounds elicited modest increases of proteasome substrates, including the protein phosphatase inhibitor BCI-Cl and the farnesyltransferase inhibitor manumycin A, suggesting that these compounds inhibit proteasome function. Induction of chaperone expression in the absence of proteasome inhibition was observed by a number of compounds, suggesting other effects on the UPS. We conclude that the combination of bioinformatic analyses and cellular assays resulted in the identification of compounds with potential to inhibit the UPS.

Understanding p53 functions through p53 antibodies

TP53 is the most frequently mutated gene across all cancer types. Our understanding of its functions has evolved since its discovery four decades ago. Initially thought to be an oncogene, it was later realized to be a critical tumour suppressor. A significant amount of our knowledge about p53 functions have come from the use of antibodies against its various forms. The early anti-p53 antibodies contributed to the recognition of p53 accumulation as a common feature of cancer cells and to our understanding of p53 DNA-binding and transcription activities. They led to the concept that conformational changes can facilitate p53’s activity as a growth inhibitory protein. The ensuing p53 conformational-specific antibodies further underlined p53’s conformational flexibility, collectively forming the basis for current efforts to generate therapeutic molecules capable of altering the conformation of mutant p53. A subsequent barrage of antibodies against post-translational modifications on p53 has clarified p53’s roles further, especially with respect to the mechanistic details and context-dependence of its activity. More recently, the generation of p53 mutation-specific antibodies have highlighted the possibility to go beyond the general framework of our comprehension of mutant p53—and promises to provide insights into the specific properties of individual p53 mutants. This review summarizes our current knowledge of p53 functions derived through the major classes of anti-p53 antibodies, which could be a paradigm for understanding other molecular events in health and disease.

Transcriptomics-Based Screening Identifies Pharmacological Inhibition of Hsp90 as a Means to Defer Aging

Aging strongly influences human morbidity and mortality. Thus, aging-preventive compounds could greatly improve our health and lifespan. Here we screened for such compounds, known as geroprotectors, employing the power of transcriptomics to predict biological age. Using age-stratified human tissue transcriptomes and machine learning, we generated age classifiers and applied these to transcriptomic changes induced by 1,309 different compounds in human cells, ranking these compounds by their ability to induce a “youthful” transcriptional state. Testing the top candidates in C. elegans, we identified two Hsp90 inhibitors, monorden and tanespimycin, which extended the animals’ lifespan and improved their health. Hsp90 inhibition induces expression of heat shock proteins known to improve protein homeostasis. Consistently, monorden treatment improved the survival of C. elegans under proteotoxic stress, and its benefits depended on the cytosolic unfolded protein response-inducing transcription factor HSF-1. Taken together, our method represents an innovative geroprotector screening approach and was able to identify a class that acts by improving protein homeostasis.

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Transcriptome-based age classifiers can distinguish young versus old tissues

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Application of age classifiers to drug-induced transcriptomes finds geroprotectors

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Validation of geroprotectors in C. elegans highlights Hsp90 inhibitors

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Hsp90 inhibitors act through HSF-1 to improve health and extend lifespan

Regulation of small heat-shock proteins by hetero-oligomer formation

Small heat-shock proteins (sHsps) compose the most widespread family of molecular chaperones. The human genome encodes 10 different sHsps (HspB1-10). It has been shown that HspB1 (Hsp27), HspB5 (αB-crystallin), and HspB6 (Hsp20) can form hetero-oligomers in vivo However, the impact of hetero-oligomerization on their structure and chaperone mechanism remains enigmatic. Here, we analyzed hetero-oligomer formation in human cells and in vitro using purified proteins. Our results show that the effect of hetero-oligomer formation on the composition of the sHsp ensembles and their chaperone activities depends strongly on the respective sHsps involved. We observed that hetero-oligomer formation between HspB1 and HspB5 leads to an ensemble that is dominated by species larger than the individual homo-oligomers. In contrast, the interaction of dimeric HspB6 with either HspB1 or HspB5 oligomers shifted the ensemble toward smaller oligomers. We noted that the larger HspB1-HspB5 hetero-oligomers are less active and that HspB6 activates HspB5 by dissociation to smaller oligomer complexes. The chaperone activity of HspB1-HspB6 hetero-oligomers, however, was modulated in a substrate-specific manner, presumably due to the specific enrichment of an HspB1-HspB6 heterodimer. These heterodimeric species may allow the tuning of the chaperone properties toward specific substrates. We conclude that sHsp hetero-oligomerization exerts distinct regulatory effects depending on the sHsps involved.

Homoharringtonine Combined with the Heat Shock Protein 90 Inhibitor IPI504 in the Treatment of FLT3-ITD Acute Myeloid Leukemia

As a heterogeneous group of clonal disorders, acute myeloid leukemia with internal tandem duplication of fms-like tyrosine kinase 3 (FLT3-ITD) mutation usually shows an inferior prognosis. In the present study, we found that homoharringtonine (HHT), a protein translation inhibitor of plant alkaloid in China, exhibited potent cytotoxic effect against FLT3-ITD (+) cell lines and primary leukemia cells, and a remarkable synergistic anti-leukemia action was demonstrated in vitro and in vivo in xenograft mouse models when co-treated with the heat shock protein 90 inhibitor IPI504. Mechanistically, HHT combined with IPI504 synergistically inhibited the growth of leukemia cells by inducing apoptosis and G1 phase arrest. This synergistic action resulted in a prominent reduction of total and phosphorylated FLT3 (p-FLT3) as well as inhibition of its downstream signaling molecules such as STAT5, AKT, ERK and 4E-BP1. Furthermore, co-treatment of HHT and IPI504 led to a synergistic or additive effect on 55.56%(10/18) of acute myeloid leukemia cases tested, including three relapsed/refractory patients. In conclusion, our findings indicate that the combination of HHT and HSP90 inhibitor provides an alternative way for the treatment of FLT3-ITD positive acute myeloid leukemia, especially for relapsed/refractory AML.

Role of Hsp90 and ATP in modulating apyrase activity and firefly luciferase kinetics

The present manuscript describes a novel bioassay consisting of apyrase and heat shock protein 90 (Hsp90) without additional co-chaperone supplementation; intended for high-throughput screening of anti-cancer drugs and prognosis of stress. In this regard, Hsp90 and adenosine 5'-triphosphate (ATP) mediated firefly luciferase (FLuc) kinetics was investigated using apyrase and FLuc as client proteins. Bioluminescent assay containing Hsp90, ATP, and apyrase led to complete loss of luminescence at 50 °C which indicates the protective role of Hsp90 against thermal denaturation. Similarly, the assay sample comprising Hsp90, ATP, and FLuc showed 2 fold increments in luminescence than their counterparts. Introduction of bovine serum albumin (BSA) to the pre-incubated assay mixture led to an initial rise in the luminescence (28%) in comparison to the sample containing Hsp90, ATP and FLuc. Therefore, FLuc based HTS assays are not suitable for clinical samples which may contain stabilizing agents. However, thermally denatured FLuc and apyrase could not regain their active conformation even when Hsp90 and ATP were introduced in the assay system. This observation justifies the role of Hsp90 to be protective rather than a reparation agent when acts without co-chaperones.

Hsp90 inhibition renders iNOS aggregation and the clearance of iNOS aggregates by proteasomes requires SPSB2

Inducible nitric oxide synthase (iNOS) plays important roles in cell injury and host defense. Our early study demonstrated that heat shock protein 90 (Hsp90) interacts with iNOS and this interaction enhances iNOS function. Recently, we reported that Hsp90 is also essential for iNOS gene transactivation. In the present study, we investigate the role of Hsp90 in controlling iNOS protein stability. In mouse macrophages, Hsp90 inhibition dissociated Hsp90 from iNOS and the latter subsequently formed aggregates. Aggregation deactivated iNOS. iNOS aggregates were cleared by the ubiquitin-proteasome system (UPS) inside cells. CHIP, an Hsp90-dependent E3 ligase, was previously implicated in iNOS turnover. However, CHIP knockdown had little effect on iNOS degradation in Hsp90-inhibited cells, indicating that other E3 ligases accounted for the clearance of iNOS aggregates. Further studies revealed that the SPRY domain-containing SOCS box protein 2 (SPSB2), an E3 ligase-recruiting protein, was essential for the ubiquitination of iNOS aggregates. SPSB2 knockdown or deleting the SPSB2-interacting domain on iNOS prevented the clearance of iNOS aggregates in Hsp90-inhibited cells. Thus, besides modulating iNOS function and gene transcription, Hsp90 is also essential for the protein stability of iNOS. Hsp90 blockade induces iNOS aggregation and SPSB2 is required for UPS degradation of iNOS aggregates.

Exosomes in cancer theranostic: Diamonds in the rough

During the last 10 years, exosomes, which are small vesicles of 50-200 nm diameter of endosomal origin, have aroused a great interest in the scientific and clinical community for their roles in intercellular communication in almost all physiological and pathological processes. Most cells can potentially release these nanovesicles that share with the parent cell a similar lipid bilayer with transmembrane proteins and a panel of enclosed soluble proteins such as heat shock proteins and genetic material, thus acting as potential nanoshuttles of biomarkers. Exosomes surface proteins allow their targeting and capture by recipient cells, while the exosomes' content can modify the physiological state of recipient cells. Tumor derived exosomes by interacting with other cells of the tumor microenvironment modulate tumor progression, angiogenic switch, metastasis, and immune escape. Targeting tumor-derived exosomes might be an interesting approach in cancer therapy. Furthermore, because a key issue to improve cancer patients' outcome relies on earlier cancer diagnosis (metastases, as opposed to the primary tumor, are responsible for most cancer deaths) exosomes have been put forward as promising biomarker candidates for cancer diagnosis and prognosis. This review summarizes the roles of exosomes in cancer and clinical interest, focusing on the importance of exosomal heat shock proteins (HSP). The challenges of clinical translation of HSP-exosomes as therapeutic targets and biomarkers for early cancer detection are also discussed.

Oxymatrine on Hsp90a expression and apoptosis in a model of lung ischemia-reperfusion injury

The protective effects of oxymatrine (OMT) on apoptosis and heat shock protein 90a (Hsp90a) expression in a rabbit model of lung ischemia-reperfusion injury (LIRI) were investigated. The model of LIRI was established in rabbits and they were randomly divided into two groups: The control group (group C, n=10), and experimental group (further divided into groups E1, n=10; and group E2, n=10), to measure the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) activity in lung tissue homogenates at several time points (T₀, 0 min; T₁, 60 min; T₂, 120 min; T₃, 180 min; and T₄, 240 min), and to measures changes in lung tissue wet/dry weight ratio (W/D), apoptosis index (AI), and Hsp90a expression and organization at T₂, T₃ and T₄. Comparing group C with groups E1 and E2, the levels of SOD activity and MDA were not significantly different at T₀ and T₁ (P>0.05); W/D ratio and AI were significantly higher than in groups E1 and E2 (P<0.05, P<0.01); 120 min after LIR, MDA, W/D ratio, and AI were lower than in groups E1 and E2 (P<0.05, P<0.01). MDA, W/D ratio and AI were lower in E2 than in E1 (P<0.05), and SOD and Hsp90a expression increased (P<0.05). The ultrastructure in group E showed less injury compared with group C. In conclusion, by scavenging oxygen free radicals, OMT can inhibit apoptosis, increase Hsp90a expression, and reduce the injury caused by lung ischemia reperfusion.

Nuclear ERK5 inhibits progression of leukemic monocytes to macrophages by regulating the transcription factor PU.1 and heat shock protein HSP70

Differentiation therapy can supplement the therapy of APL, but other subtypes of AML are treated principally with cytotoxic agents, with few lasting remissions. While the induction of monocyte followed by macrophage differentiation by vitamin D derivatives (VDDs) is dramatic in cultured AML cells of all subtypes, attempts to translate this to the clinic have not been effective. Thus, better understanding of the mechanisms underlying VDD-induced differentiation may improve this approach. The key events in this form of differentiation include increased expression of CD11b, and the transcription factor PU.1 is known to be a part of this process. We show here that in the transition of monocytes to macrophages induced by a VDD, ERK5, a member of the MAPK family of signaling molecules, prevents PU.1 expression. However, upon ERK5 inhibition PU.1 protein is stabilized by HSP70.Thus, ERK5 may be a target for manipulation of the immunoregulatory actions of macrophages in cancer.

Non-benzoquinone geldanamycin analogs trigger various forms of death in human breast cancer cells

Background

Hsp90 proteins are important therapeutic targets for many anti-cancer drugs in clinical trials. Geldanamycin (GA) was identified as the first natural inhibitor of Hsp90, increasing evidence suggests that GA was not a good choice for clinical trials. In this study, we investigated two new non-benzoquinone geldanamycin analogs of Hsp90 inhibitors, DHQ3 and 17-demethoxy-reblastatin (17-DR), to explore the molecular mechanisms of their anti-cancer activity in vivo and vitro.

Methods

MTT and colony formation assays were used to measure cell viability. Flow cytometry, DAPI staining, ATP assay, electron microscopy, western blots, siRNAs transfection and immunofluorescence were used to determine the molecular mechanism of DHQ3- or 17-DR-induced different forms of death in human breast cancer MDA-MB-231 cells. Malachite green reagent was used to measure ATPase activity of the analogs.

Results

DHQ3 and 17-DR presented efficiently inhibitory effect in MDA-MB-231 cell lines, and DHQ3 induced necroptosis by activation of the RIP1-RIP3-MLKL necroptosis cascade. And DHQ3-induced cell death was inhibited by a necroptosis inhibitor, necrostatin-1 (Nec-1), but not by a caspase inhibitor z-VAD-fmk. On the other hand, 17-DR induced apoptosis in MDA-MB-231 cells, indicating a caspase-dependent killing mechanism. We further demonstrated that down-regulation of RIP1 and RIP3 by siRNA protected against DHQ3 but not 17-DR induced cell death. These results were confirmed by electron microscopy. DHQ3 and 17-DR induced the degradation of Hsp90 client proteins, and they showed strong antitumor effects in MDA-MB-231 cell-xenografted nude mice.

Conclusions

These findings supported that DHQ3 and 17-DR induce different forms of death in some cancer cell line via activation of different pathways. All of the results provided evidence for its anti-tumorigentic action with low hepatotoxicity in vivo, making them promising anti-breast cancer agents.

Mechanistic study of the anti-cancer effect of Gynostemma pentaphyllum saponins in the Apc(Min/+) mouse model

Gynostemma pentaphyllum saponins (GpS) have been shown to have anti-cancer activity. However, the underlying mechanisms remain unclear. In this study, we used the Apc(Min) (/+) colorectal cancer (CRC) mouse model to investigate the anti-cancer effect of GpS and we demonstrated that GpS treatment could significantly reduce the number and size of intestinal polyps in Apc(Min) (/+) mice. In order to identify the potential targets and mechanisms involved, a comparative proteomics analysis was performed and 40 differentially expressed proteins after GpS treatment were identified. Bioinformatics analyses suggested a majority of these proteins were involved in processes related to cellular redox homeostasis, and predicted Raf-1 as a potential target of GpS. The upregulation of two proteins known to be involved in redox homeostasis, peroxiredoxin-1 (Prdx1) and peroxiredoxin-2 (Prdx2), and the downregulation of Raf-1 were validated using Western blot analysis. After further investigation of the associated signaling networks, we postulated that the anti-cancer effect of GpS was mediated through the upregulation of Prdx1 and Prdx2, suppression of Ras, RAF/MEK/ERK/STAT, PI3K/AKT/mTOR signaling and modulation of JNK/p38 MAPK signaling. We also examined the potential combinatorial effect of GpS with the chemotherapeutic 5-fluorouracil (5-FU) and found that GpS could enhance the anti-cancer efficacy of 5-FU, further suppressing the number of polyps in Apc(Min/+) mice. Our findings highlight the potential of GpS as an anti-cancer agent, the potential mechanisms of its anti-cancer activities, and its effect as an adjuvant of 5-FU in the chemotherapy of CRC.

Synergistic Activity of Deguelin and Fludarabine in Cells from Chronic Lymphocytic Leukemia Patients and in the New Zealand Black Murine Model

B-cell chronic lymphocytic leukemia (CLL) remains an incurable disease, and despite the improvement achieved by therapeutic regimes developed over the last years still a subset of patients face a rather poor prognosis and will eventually relapse and become refractory to therapy. The natural rotenoid deguelin has been shown to induce apoptosis in several cancer cells and cell lines, including primary human CLL cells, and to act as a chemopreventive agent in animal models of induced carcinogenesis. In this work, we show that deguelin induces apoptosis in vitro in primary human CLL cells and in CLL-like cells from the New Zealand Black (NZB) mouse strain. In both of them, deguelin dowregulates AKT, NFκB and several downstream antiapoptotic proteins (XIAP, cIAP, BCL2, BCL-X_L and survivin), activating the mitochondrial pathway of apoptosis. Moreover, deguelin inhibits stromal cell-mediated c-Myc upregulation and resistance to fludarabine, increasing fludarabine induced DNA damage. We further show that deguelin has activity in vivo against NZB CLL-like cells in an experimental model of CLL in young NZB mice transplanted with spleen cells from aged NZB mice with lymphoproliferation. Moreover, the combination of deguelin and fludarabine in this model prolonged the survival of transplanted mice at doses of both compounds that were ineffective when administered individually. These results suggest deguelin could have potential for the treatment of human CLL.

Identification of epipolythiodioxopiperazines HDN-1 and chaetocin as novel inhibitor of heat shock protein 90

The molecular chaperone heat shock protein 90 (Hsp90) has emerged as an important target for cancer treatment. HDN-1, an epipolythiopiperazine-2, 5-diones (ETPs) compound, was here identified as a new Hsp90 inhibitor. HDN-1 bound directly to C-terminus of Hsp90α, resulting in a potential conformational change that interfered with the binding of 17-AAG and novobiocin to Hsp90α. In contrast, association of 17-AAG, novobiocin or ATP with Hsp90α did not prevent the binding HDN-1 to Hsp90α. HDN-1 in combination with 17-AAG exhibited an enhanced inhibitory effect on non-small lung cancer cell proliferation. Molecular docking analyses revealed that HDN-1 bound to Hsp90α at C-terminal 526–570 region. In addition, HDN-1 degraded multiple oncoproteins and promoted EGF-induced wild type and mutated EGFR downregulation. Notably, chaetocin, used as a SUV39H1 inhibitor with similar structure to HDN-1, bound to Hsp90 and degraded Hsp90 client proteins and SUV39H1 as did HDN-1. These results indicate that HDN-1 and chaetocin are inhibitors of Hsp90 and that SUV39H1 is a novel client protein of Hsp90.

Causes and consequences of protein folding stress in aneuploid cells

Imbalanced chromosomal content, or aneuploidy, strongly affects the physiology of eukaryotic cells. The consequences of these effects are frequently detrimental, in particular in Metazoans. In humans, aneuploidy has been causatively linked to pathological conditions such as spontaneous abortions, trisomy syndromes and cancer. However, only in recent years have we witnessed an unraveling of the complex phenotypes that are caused by aneuploidy. Importantly, it has become apparent that aneuploidy evokes global and uniform changes that cannot be explained by the altered expression of the specific genes located on aneuploid chromosomes. Recent discoveries show that aneuploidy negatively affects protein folding; in particular, the functions of the molecular chaperone Heat Shock Protein 90 (HSP90) and the upstream regulator of heat shock-induced transcription, Heat Shock Factor 1 (HSF1), are impaired. Here we discuss the possible causes and consequences of this impairment and propose that the protein folding stress instigated by aneuploidy may be a common feature of conditions as variable as cancer and trisomy syndromes.

Receptor ligand-triggered resistance to alectinib and its circumvention by Hsp90 inhibition in EML4-ALK lung cancer cells

Alectinib is a new generation ALK inhibitor with activity against the gatekeeper L1196M mutation that showed remarkable activity in a phase I/II study with echinoderm microtubule associated protein-like 4 (EML4)--anaplastic lymphoma kinase (ALK) non-small cell lung cancer (NSCLC) patients. However, alectinib resistance may eventually develop. Here, we found that EGFR ligands and HGF, a ligand of the MET receptor, activate EGFR and MET, respectively, as alternative pathways, and thereby induce resistance to alectinib. Additionally, the heat shock protein 90 (Hsp90) inhibitor suppressed protein expression of ALK, MET, EGFR, and AKT, and thereby induced apoptosis in EML4-ALK NSCLC cells, even in the presence of EGFR ligands or HGF. These results suggest that Hsp90 inhibitors may overcome ligand-triggered resistance to new generation ALK inhibitors and may result in more successful treatment of NSCLC patients with EML4-ALK.

Identification of a ternary protein-complex as a therapeutic target for K-Ras-dependent colon cancer

A cancer phenotype is driven by several proteins and targeting a cluster of functionally interdependent molecules should be more effective for therapeutic intervention. This is specifically important for Ras-dependent cancer, as mutated (MT) Ras is non-druggable and targeting its interaction with effectors may be essential for therapeutic intervention. Here, we report that a protein-complex activated by the Ras effector p38γ MAPK is a novel therapeutic target for K-Ras-dependent colon cancer. Unbiased proteomic screening and immune-precipitation analyses identified p38γ interaction with heat shock protein 90 (Hsp90) and K-Ras in K-Ras MT, but not wild-type (WT), colon cancer cells, indicating a role of this complex in Ras-dependent growth. Further experiments showed that this complex requires p38γ and Hsp90 activity to maintain MT, but not WT, K-Ras protein expression. Additional studies demonstrated that this complex is activated by p38γ-induced Hsp90 phosphorylation at S595, which is important for MT K-Ras stability and for K-Ras dependent growth. Of most important, pharmacologically inhibition of Hsp90 or p38γ activity disrupts the complex, decreases K-Ras expression, and selectively inhibits the growth of K-Ras MT colon cancer in vitro and in vivo. These results demonstrated that the p38γ-activated ternary complex is a novel therapeutic target for K-Ras-dependent colon cancer.

The effect of 17-allylamino-17-demethoxygeldanamycin alone or in combination with paclitaxel on anaplastic thyroid carcinoma cells

The effect of 17-allylamino-17-demethoxygeldanamycin (17-AAG), an hsp90 inhibitor, alone or in combination with paclitaxel on survival of anaplastic thyroid carcinoma (ATC) was evaluated. In 8505C and CAL62 cells, after treatment of 17-AAG, cell viability decreased, and the percentage of dead cells increased. 17-AAG did not cause cleavage of caspase-3 protein, and change expression of IAPs. Pretreatment of z-VAD-fmk did not alter cell viability and the percentage of dead cells. In 17-AAG-treated cells, knockdown of p53 rescued growth inhibition, while cycloheximide attenuated cell death. When cells were treated with both 17-AAG and paclitaxel, all of the combination index values were higher than 1, indicating antagonism between 17-AAG and paclitaxel. In 17-AAG- and paclitaxel-treated cells, compared with paclitaxel alone-treated cells, the protein levels of hsp90, hsp70, and hsc70 increased. In conclusion, our results suggest that 17-AAG induces non-apoptotic cell death requiring de novo protein synthesis in ATC cells. Moreover, these results demonstrate that 17-AAG antagonizes paclitaxel with concomitant alterations in hsp90 client proteins in ATC cells.

Antitumor activity of the combination of an HSP90 inhibitor and a PI3K/mTOR dual inhibitor against cholangiocarcinoma

The PI3K/Akt/mTOR pathway is overactivated and heat shock protein (HSP) 90 is overexpressed in common cancers. We hypothesized that targeting both pathways can kill intrahepatic cholangiocarcinoma (CCA) cells. HSP90 and PTEN protein expression was evaluated by immunohistochemical staining of samples from 78 patients with intrahepatic CCA. CCA cell lines and a thioacetamide (TAA)-induced CCA animal model were treated with NVP-AUY922 (an HSP90 inhibitor) and NVP-BEZ235 (a PI3K/mTOR inhibitor) alone or in combination.

Both HSP90 overexpression and loss of PTEN were poor prognostic factors in patients with intrahepatic CCA. The combination of the HSP90 inhibitor NVP-AUY922 and the PI3K/mTOR inhibitor NVP-BEZ235 was synergistic in inducing cell death in CCA cells. A combination of NVP-AUY922 and NVP-BEZ235 caused tumor regression in CCA rat animal model. This combination not only inhibited the PI3K/Akt/mTOR pathway but also induced ROS, which may exacerbate the vicious cycle of ER stress. Our data suggest simultaneous targeting of the PI3K/mTOR and HSP pathways for CCA treatment.

Sublethal concentrations of 17-AAG suppress homologous recombination DNA repair and enhance sensitivity to carboplatin and olaparib in HR proficient ovarian cancer cells

The promise of PARP-inhibitors(PARPis) in the management of epithelial ovarian cancer(EOC) is tempered by the fact that approximately 50% of patients with homologous recombination (HR)-proficient tumors do not respond well to these agents. Combination of PARPis with agents that inhibit HR may represent an effective strategy to enhance their activity in HR-proficient tumors. Using a bioinformatics approach, we identified that heat shock protein 90 inhibitors(HSP90i) may suppress HR and thus revert HR-proficient to HR-deficient tumors. Analysis of publicly available gene expression data showed that exposure of HR-proficient breast cancer cell lines to HSP90i 17-AAG(17-allylamino-17-demethoxygeldanamycin) downregulated HR, ATM and Fanconi Anemia pathways. In HR-proficient EOC cells, 17-AAG suppressed HR as assessed using the RAD51 foci formation assay and this was further confirmed using the Direct Repeat-GFP reporter assay. Furthermore, 17-AAG downregulated BRCA1 and/or RAD51 protein levels, and induced significantly more γH2AX activation in combination with olaparib compared to olaparib alone. Finally, sublethal concentrations of 17-AAG sensitized HR-proficient EOC lines to olaparib and carboplatin but did not affect sensitivity of the HR-deficient OVCAR8 line arguing that the 17-AAG mediated sensitization is dependent on suppression of HR. These results provide a preclinical rationale for using a combination of olaparib/17-AAG in HR-proficient EOC.

Targeting aerobic glycolysis and HIF-1alpha expression enhance imiquimod-induced apoptosis in cancer cells

Tumor cells rely on aerobic glycolysis to maintain unconstrained cell growth and proliferation. Imiquimod (IMQ), a synthetic Toll-like receptor (TLR) 7/8 ligand, exerts anti-tumor effects directly by inducing cell death in cancer cells and/or indirectly by activating cellular immune responses against tumor cells. However, whether IMQ modulates glucose metabolism pathways remains unclear. In this study, we demonstrated that IMQ can enhance aerobic glycolysis by up-regulating HIF-1α expression at the transcriptional and translational levels via ROS mediated STAT3- and Akt-dependent pathways, independent of TLR7/8 signaling. The genetic silencing of HIF-1α not only repressed IMQ-induced aerobic glycolysis but also sensitized cells to IMQ-induced apoptosis due to faster ATP and Mcl-1 depletion. Moreover, the glucose analog 2-DG and the Hsp90 inhibitor 17-AAG, which destabilizes the HIF-1α protein, synergized with IMQ to induce tumor cell apoptosis in vitro and significantly inhibited tumor growth in vivo. Thus, we hypothesize that the IMQ-induced up-regulation of HIF-1α and aerobic glycolysis is a protective response to the metabolic stress generated by IMQ treatment, and thus, co-treatment with inhibitors of HIF-1α and/or glycolysis may be a useful therapeutic strategy to enhance the anti-tumor effects of IMQ in clinical settings.

Up-regulation of neogenin-1 increases cell proliferation and motility in gastric cancer

Although elevated expression of neogenin-1 has been detected in human gastric cancer tissue, its role in gastric tumorigenesis remains unclear due to the lack of neogenin-1 studies in cancer. Therefore, we demonstrated here the function and regulatory mechanism of neogenin-1 in gastric cancer. Neogenin-1 ablation decreased proliferation and migration of gastric cancer cells, whereas its over-expression reversed these effects. Xenografted analyses using gastric cancer cells displayed statistically significant inhibition of tumor growth by neogenin-1 depletion. Interestingly, galectin-3 interacted with HSF-1 directly, which facilitated nuclear-localization and binding on neogenin-1 promoter to drive its transcription and gastric cancer cell motility. The galectin-3-increased gastric cancer cell motility was down-regulated by HSF-1 depletion. Moreover, the parallel expression patterns of galectin-3 and neogenin-1, as well as those of HSF-1 and neogenin-1, were detected in the malignant tissues of gastric cancer patients. Taken together, high-expression of neogenin-1 promotes gastric cancer proliferation and motility and its expression is regulated by HSF-1 and galectin-3 interaction. In addition, we propose further studies for neogenin-1 and its associated pathways to provide them as a proper target for gastric cancer therapy.

Down-regulation of MSH2 expression by Hsp90 inhibition enhances cytotoxicity affected by tamoxifen in human lung cancer cells

The anti-estrogen tamoxifen has been used worldwide as an adjuvant hormone therapeutic agent in the treatment of breast cancer. However, the molecular mechanism of tamoxifen-induced cytotoxicity in non-small cell lung cancer (NSCLC) cells has not been identified. Human MutS homolog 2 (MSH2), a crucial element of the highly conserved DNA mismatch repair system, and expression of MSH2 have been down-regulated by Hsp90 function inhibition in human lung cancer. Therefore, in this study, we examined whether MSH2 plays a role in the tamoxifen and Hsp90 inhibitor-induced cytotoxic effect on NSCLC cells. The results showed that treatment with tamoxifen increased MSH2 mRNA and protein levels. The combination treatment with PI3K inhibitors (LY294002 or wortmannin) or knockdown AKT expression by specific small interfering RNA could decrease tamoxifen-induced MSH2 expression. Both knocking down MSH2 expression and co-treatment of PI3K inhibitors enhanced the cytotoxicity and cell growth inhibition of tamoxifen. Compared to a single agent alone, tamoxifen combined with an Hsp90 inhibitor resulted in cytotoxicity and cell growth inhibition synergistically in NSCLC cells, accompanied with reduced MSH2 expression. These findings may have implications for the rational design of future drug regimens incorporating tamoxifen and Hsp90 inhibitors for the treatment of NSCLC.

Heat shock proteins at the crossroads between cancer and Alzheimer's disease

Heat shock proteins 70 and heat shock proteins 90 (Hsp70/90) have been implicated in many crucial steps of carcinogenesis: stabilizing oncogenic proteins, inhibiting programmed cell death and replicative senescence, induction of tumor angiogenesis, and activation of the invasion and metastasis. Plenty of cancer related proteins have the ability of regulating the expression of Hsp70/90 through heat shock factor 1. Cancer and Alzheimer's disease (AD) have plenty of overlapping regions in molecular genetics and cell biology associated with Hsp70/90. The Hsp70, as a protein stabilizer, has a cellular protection against neurodegeneration of the central nervous system, while Hsp90 promote neurodegenerative disorders indirectly through regulating the expression of Hsp70 and other chaperones. All these make existing anticancer drugs target Hsp70/90 which might be used in AD therapy.

M. P, Chattopadhyay S, Chattopadhyay S. Heat shock protein 90 positively regulates Chikungunya virus replication by stabilizing viral non-structural protein nsP2 during infection

Background

The high morbidity and socio-economic loss associated with the recent massive global outbreak of Chikungunya virus (CHIKV) emphasize the need to understand the biology of the virus for developing effective antiviral therapies.

Methods and Findings

In this study, an attempt was made to understand the molecular mechanism involved in Heat shock protein 90 (Hsp90) mediated regulation of CHIKV infection in mammalian cells using CHIKV prototype strain (S 27) and Indian outbreak strain of 2006 (DRDE-06). Our results showed that Hsp90 is required at a very early stage of viral replication and Hsp90 inhibitor Geldanamycin (GA) can abrogate new virus particle formation more effectively in the case of S 27 than that of DRDE-06. Further analysis revealed that CHIKV nsP2 protein level is specifically reduced by GA treatment as well as HSP90-siRNA transfection; however, viral RNA remains unaltered. Immunoprecipitation analysis showed that nsP2 interacts with Hsp90 during infection; however this interaction is reduced in the presence of GA. In addition, our analysis on Hsp90 associated PI3K/Akt/mTOR signaling pathway demonstrated that CHIKV infection stabilizes Raf1 and activates Hsp90 client protein Akt, which in turn phosphorylates mTOR. Subsequently, this phosphorylation leads to the activation of two important downstream effectors, S6K and 4EBP1, which may facilitate translation of viral as well as cellular mRNAs. Hence, the data suggests that CHIKV infection is regulated by Hsp90 associated Akt phosphorylation and DRDE-06 is more efficient than S 27 in enhancing the activation of host signaling molecules for its efficient replication and virus production.

Conclusion

Hsp90 positively regulates Chikungunya virus replication by stabilizing CHIKV-nsP2 through its interaction during infection. The study highlights the possible molecular mechanism of GA mediated inhibition of CHIKV replication and differential effect of this drug on S 27 and DRDE-06, which will be informative for developing effective anti-CHIKV therapies in future.

Geldanamycin and Its Derivatives Inhibit the Growth of Myeloma Cells and Reduce the Expression of the MET Receptor

Introduction. Geldanamycin (GA) is an ansamycin antibiotic that exhibits potent anti-neoplastic properties. The aim of this study was to assess the impact of GA and its derivatives on the growth and invasiveness of myeloma cell lines and CD138+ cells derived from the bone marrow of patients with multiple myeloma. Materials and methods. We evaluated cell proliferation, survival, apoptosis, cell cycle of myeloma cells, and the expression of cell surface proteins after incubation with geldanamycin or its derivatives. Results. GA and its analogs have an effect on myeloma cells by inhibiting their growth in a time and dose-dependent manner. Myeloma cell lines demonstrated decreased proliferation after incubation with 10 nM of GA or 100 nM GA analogs. The first significant effects of GA on U266 cells was observed after 24 hours. After 24 hours, U266 cells incubated with 100 nM GA were in both early and late stages of apoptosis; 17AEP and 17DMAG caused apoptosis of similar intensity to GA. It has been observed that GA and its derivatives cause caspase-3 activation. Analysis of the activity of AKT and MAP 42/44 kinases was performed by incubating U266 cells for 24 and 48 hours in100 nM of GA and its derivatives. After 24 hours incubation, no significant changes in protein expression were observed, while after 48 hours, the strongest changes were seen in AKT protein expression after incubation with GA and 17AEP-GA. In studies of the cell cycle, it was found that 100 nM 17AEP-GA and 17-DMAP-GA cause cell cycle abnormalities. We observed a nearly two-fold increase in U266 cells in the G1 phase and a simultaneous decrease in the percentage of cells in the G2/M phase, indicating that cells were halted in the G1 phase. In the case of the INA6 cells, proliferation was halted in both the G1 and G2/M phases. Conclusions. GA and the analogues that we tested can inhibit myeloma cell growth by induction of apoptosis and blockage of cell cycle progression, and have an effect on the down-regulation of the MET receptor. The GA derivatives tested, despite their modifications still retain strong anticancer properties. Specifically, two analogues of GA, 17AEP-GA and 17DMAG due to their properties can be more effective and safer chemotherapeutic agents than 17AAG, which is currently used and described in literature.

Combined pharmacological induction of Hsp70 suppresses prion protein neurotoxicity in Drosophila

Prion diseases are rare and aggressive neurodegenerative disorders caused by the accumulation of misfolded, toxic conformations of the prion protein (PrP). Therapeutic strategies directed at reducing the levels of PrP offer the best chance of delaying or halting disease progression. The challenge, though, is to define pharmacologic targets that result in reduced PrP levels. We previously reported that expression of wild type hamster PrP in flies induces progressive locomotor dysfunction and accumulation of pathogenic PrP conformations, while co-expression of human Hsp70 delayed these changes. To validate the therapeutic potential of Hsp70, we treated flies with drugs known to induce Hsp70 expression, including the Hsp90 inhibitor 17-DMAG and the glucocorticoid dexamethasone. Although the individual treatment with these compounds produced no significant benefits, their combination significantly increased the level of inducible Hsp70, decreased the level of total PrP, reduced the accumulation of pathogenic PrP conformers, and improved locomotor activity. Thus, the combined action of two pharmacological activators of Hsp70 with distinct targets results in sustained high levels of inducible Hsp70 with improved behavioral output. These findings can have important therapeutic applications for the devastating prion diseases and other related proteinopathies.

New treatment strategy for patients with EGFR-mutant lung cancer

SUMMARY Activating EGFR mutations in non-small-cell lung cancer were discovered in 2004. Patients harboring these mutations, who have been treated with EGFR–tyrosine kinase inhibitor (TKI), are expected to live longer than 2 years. However, lung cancer eventually progresses and the patients die of the disease. Thus, alternative treatments are needed for EGFR-mutated lung cancer. Here, we review the alternative treatments for patients with activating EGFR mutation. Combinations of available EGFR–TKIs (gefitinib or erlotinib) with chemotherapy and newer EGFR–TKIs (second-generation or third-generation EGFR–TKIs) have been developed as treatments for obtaining a more durable response or overcoming the acquired resistance to current EGFR–TKIs. In addition, new drugs other than EGFR–TKIs have also been developed. Their targets include EGFR itself and downstream signals of EGFR pathway, among others. However, these therapies cannot reach clinically striking effects so far. Greater efforts are needed to achieve an increased response, overcome resistance and prolong overall survival.

Heat-shock protein 90 inhibitors synergistically enhance melanoma differentiation-associated gene-7-mediated cell killing of human pancreatic carcinoma

Pancreatic cancer is one of the intractable diseases and an effective therapeutic strategy is required to improve the prognosis. We examined possible antitumor effects of adenoviruses expressing melanoma differentiation-associated gene-7/interleukin-24 (Ad-mda-7) and a heat-shock protein 90 (Hsp90) inhibitor to human pancreatic carcinoma cells. Ad-mda-7 and an Hsp90 inhibitor, geldanamycin (GA), produced cytotoxic effects, and a combinatory use of Ad-mda-7 and GA further achieved synergistic effects. Administration of N-acetyl-L-cysteine, an inhibitor of reactive oxygen species, eliminated Ad-mda-7- and GA-mediated cytotoxicity. Ad-mda-7 augmented phosphorylated AKT levels but GA did not influence the phosphorylation. GA-treated cells showed cleavage of poly-(ADP-ribose) polymerase but not caspase-3, and upregulated Hsp70 and LC3A/B II levels, whereas Ad-mda-7-treated cells did not. GA treatments augmented ubiquitination and markedly increased melanoma differentiation-associated gene-7 (MDA-7) expression levels. These findings suggest that Ad-mda-7-mediated cytotoxicity is dependent on reactive oxygen species but independent of apoptosis or autophagy, and that GA-mediated cytotoxicity was linked with caspase-independent apoptosis and/or autophagy. A mechanism underlying the combinatory effects of Ad-mda-7 and GA remained complex and the synergism is attributable to multiple factors including increased MDA-7 protein stability by GA.

HSP27 expression levels are associated with the sensitivity of hepatocellular carcinoma cells to 17-allylamino-17-demethoxygeldanamycin

AIMS, MATERIALS & METHODS: As heat-shock proteins are associated with tumor proliferation, differentiation, invasion and metastasis, we investigated whether targeting Hsp90 with the geldanamycin derivative 17-allylamino-17-demethoxygeldanamycin (17AAG) can inhibit the viability of hepatocellular carcinoma cell lines with various levels of metastatic potential. In addition, we investigated whether the use of Hsp27-siRNA can decrease resistance to 17AAG.

RESULTS

Although 17AAG upregulated the expression of heat-shock proteins, it did not affect the expression of Hsp90 client proteins in normal hepatocytes. Hsp90 inhibition by 17AAG degraded its client proteins in both low- and high-metastatic potential cell lines. siRNA inhibited Hsp27 expression in cell lines and improved the sensitivity of 17AAG.

CONCLUSION

17AAG inhibited the viability of hepatocellular carcinoma cells by degrading Hsp90 client proteins. The sensitivity of cells to 17AAG is associated with the level of Hsp27 expression.

Geldanamycin, a ligand of heat shock protein 90, inhibits herpes simplex virus type 2 replication both in vitro and in vivo

Previously, we discovered geldanamycin, a ligand of heat shock protein 90, effectively inhibited herpes simplex virus type 1 replication in vitro and in vivo (mouse encephalitis model). In this study, we demonstrate that geldanamycin has very strong activities against herpes simplex virus type 2 in vitro and in vivo (mouse vagina model). In mouse vagina model, administration of geldanamycin suspension to vagina after virus infection protected the infected mice from death and increased the average survival days in a dose-dependent manner. Geldanamycin also significantly reduced virus shedding from mouse vagina. All geldanamycin-treated groups were statistically significant when compared with the infected control group. The high-dose group of geldanamycin (5.72 mg kg⁻¹) was better than acyclovir group (2.86 mg kg⁻¹). All geldanamycin vaginal administration mock-infected groups did not show significant body weight loss. Although geldanamycin has strong antiviral activities against various DNA and RNA viruses, geldanamycin is not suitable for systemic administration because of its high toxicity. We consider that geldanamycin is a candidate of topical usage for the treatment of herpes simplex virus type infections.

Heat shock proteins and heat shock factor 1 in carcinogenesis and tumor development: an update

Heat shock proteins (HSP) are a subset of the molecular chaperones, best known for their rapid and abundant induction by stress. HSP genes are activated at the transcriptional level by heat shock transcription factor 1 (HSF1). During the progression of many types of cancer, this heat shock transcriptional regulon becomes co-opted by mechanisms that are currently unclear, although evidently triggered in the emerging tumor cell. Concerted activation of HSF1 and the accumulation of HSPs then participate in many of the traits that permit the malignant phenotype. Thus, cancers of many histologies exhibit activated HSF1 and increased HSP levels that may help to deter tumor suppression and evade therapy in the clinic. We review here the extensive work that has been carried out and is still in progress aimed at (1) understanding the oncogenic mechanisms by which HSP genes are switched on, (2) determining the roles of HSF1/HSP in malignant transformation and (3) discovering approaches to therapy based on disrupting the influence of the HSF1-controlled transcriptome in cancer.

The heat shock protein 90 inhibitor, AT13387, displays a long duration of action in vitro and in vivo in non-small cell lung cancer

A ubiquitously expressed chaperone, heat shock protein 90 (HSP90) is of considerable interest as an oncology target because tumor cells and oncogenic proteins are acutely dependent on its activity. AT13387 (2,4-dihydroxy-5-isopropyl-phenyl)-[5-(4-methyl-piperazin-1-ylmethyl)-1,3-dihydro-isoindol-2-yl] methanone, l-lactic acid salt) a novel, high-affinity HSP90 inhibitor, which is currently being clinically tested, has shown activity against a wide array of tumor cell lines, including lung cancer cell lines. This inhibitor has induced the degradation of specific HSP90 client proteins for up to 7 days in tumor cell lines in vitro. The primary driver of cell growth (mutant epidermal growth factor receptors) was particularly sensitive to HSP90 inhibition. The long duration of client protein knockdown and suppression of phospho-signaling seen in vitro after treatment with AT13387 was also apparent in vivo, with client proteins and phospho-signaling suppressed for up to 72 h in xenograft tumors after treatment with a single dose of AT13387. Pharmacokinetic analyses indicated that while AT13387 was rapidly cleared from blood, its retention in tumor xenografts was markedly extended, and it was efficacious in a range of xenograft models. AT13387's long duration of action enabled, in particular, its efficacious once weekly administration in human lung carcinoma xenografts. The use of longer-acting HSP90 inhibitors, such as AT13387, on less frequent dosing regimens has the potential to maintain antitumor efficacy as well as minimize systemic exposure and unwanted effects on normal tissues.

Knock down of heat shock protein 27 (HspB1) induces degradation of several putative client proteins

Hsp27 belongs to the heat shock protein family and displays chaperone properties in stress conditions by holding unfolded polypeptides, hence avoiding their inclination to aggregate. Hsp27 is often referenced as an anti-cancer therapeutic target, but apart from its well-described ability to interfere with different stresses and apoptotic processes, its role in non-stressed conditions is still not well defined. In the present study we report that three polypeptides (histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3) were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. In addition, these proteins interacted with Hsp27 complexes of different native size. Altogether, these findings suggest that HDAC6, STAT2 and procaspase-3 are client proteins of Hsp27. Hence, in non stressed cancerous cells, the structural organization of Hsp27 appears to be a key parameter in the regulation by this chaperone of the level of specific polypeptides through client-chaperone type of interactions.

Heterozygous yeast deletion collection screens reveal essential targets of Hsp90

Hsp90 is an essential eukaryotic chaperone with a role in folding specific “client” proteins such as kinases and hormone receptors. Previously performed homozygous diploid yeast deletion collection screens uncovered broad requirements for Hsp90 in cellular transport and cell cycle progression. These screens also revealed that the requisite cellular functions of Hsp90 change with growth temperature. We present here for the first time the results of heterozygous deletion collection screens conducted at the hypothermic stress temperature of 15°C. Extensive bioinformatic analyses were performed on the resulting data in combination with data from homozygous and heterozygous screens previously conducted at normal (30°C) and hyperthermic stress (37°C) growth temperatures. Our resulting meta-analysis uncovered extensive connections between Hsp90 and (1) general transcription, (2) ribosome biogenesis and (3) GTP binding proteins. Predictions from bioinformatic analyses were tested experimentally, supporting a role for Hsp90 in ribosome stability. Importantly, the integrated analysis of the 15°C heterozygous deletion pool screen with previously conducted 30°C and 37°C screens allows for essential genetic targets of Hsp90 to emerge. Altogether, these novel contributions enable a more complete picture of essential Hsp90 functions.

Subtype and pathway specific responses to anticancer compounds in breast cancer

Breast cancers are comprised of molecularly distinct subtypes that may respond differently to pathway-targeted therapies now under development. Collections of breast cancer cell lines mirror many of the molecular subtypes and pathways found in tumors, suggesting that treatment of cell lines with candidate therapeutic compounds can guide identification of associations between molecular subtypes, pathways, and drug response. In a test of 77 therapeutic compounds, nearly all drugs showed differential responses across these cell lines, and approximately one third showed subtype-, pathway-, and/or genomic aberration-specific responses. These observations suggest mechanisms of response and resistance and may inform efforts to develop molecular assays that predict clinical response.

Choice of biological source material supersedes oxidative stress in its influence on DJ-1 in vivo interactions with Hsp90

DJ-1 is a small but relatively abundant protein of unknown function that may undergo stress-dependent cellular translocation and has been implicated in both neurodegenerative diseases and cancer. As such, DJ-1 may be an excellent study object to elucidate the relative influence of the cellular context on its interactome and for exploring whether acute exposure to oxidative stressors alters its molecular environment. Using quantitative mass spectrometry, we conducted comparative DJ-1 interactome analyses from in vivo cross-linked brains or livers and from hydrogen peroxide-treated or naïve embryonic stem cells. The analysis identified a subset of glycolytic enzymes, heat shock proteins 70 and 90, and peroxiredoxins as interactors of DJ-1. Consistent with a role of DJ-1 in Hsp90 chaperone biology, we document destabilization of Hsp90 clients in DJ-1 knockout cells. We further demonstrate the existence of a C106 sulfinic acid modification within DJ-1 and thereby establish that this previously inferred modification also exists in vivo. Our data suggest that caution has to be exerted in interpreting interactome data obtained from a single biological source material and identify a role of DJ-1 as an oxidative stress sensor and partner of a molecular machinery notorious for its involvement in cell fate decisions.

Thermo-targeted drug delivery of geldanamycin to hyperthermic tumor margins with diblock elastin-based biopolymers

The tumor margins are the barrier to hepatocellular carcinoma (HCC) eradication for tumors>3 cm. Indeed, inadequately treated tumor margins commonly result in local and regional HCC recurrence with increased size and mass. Tumor recurrence is a common problem with chemotherapy, radiotherapy, thermal ablation, and/or surgical resection, by the inability to properly treat the tumor core and the tumor margins. Here we present novel thermosensitive biopolymer-drug conjugates for thermo-targeted chemotherapy at hyperthermic isotherms produced by focal, locoregional thermal ablation. The chemotherapeutic target is heat shock protein 90 (HSP90), a key molecular chaperone of several, and potent pro-oncogenic pathways including Akt, Raf-1, and mutated p53 that is upregulated in HCC. To inhibit HSP90, we have chosen geldanamycin (GA), a potent HSP90 inhibitor. GA has gained significant attention for its low IC50 ~ 1 nM and inhibition of Akt and Raf-1, amongst other critical pro-oncogenic pathways. Despite such evidence, clinical trials of GA have not shown promise due to off-target toxicity and poor formulation design. Here, we propose using diblock elastin-based biopolymers as a Ringsdorf macromolecular GA solubilizer--a new generation containing functional poly(Asp)/(Glu) blocks for facile drug conjugation and an ELP block for thermo-targeting of hyperthermic ablative margins. GA release is controlled by pH-sensitive, covalent hydrazone bonds with the biopolymer backbone to avoid systemic toxicity and off-target effects. The resultant biopolymer-conjugates form stable nanoconstructs and display tunable, acute phase transitions at high temperatures. Drug release kinetics are favorable with or without the presence of serum. Thermo-targeted chemotherapy and synchronous thermal ablation provide a unique opportunity for simultaneous destruction of the HCC ablative margins and tumor core for focal, locoregional control of HCC.

Functional interaction of heat shock protein 90 and Beclin 1 modulates Toll-like receptor-mediated autophagy

Autophagy is one of the downstream effector mechanisms for elimination of intracellular microbes following activation of the Toll-like receptors (TLRs). Although the detailed molecular mechanism for this cellular process is still unclear, Beclin 1, a key molecule for autophagy, has been suggested to play a role. Heat shock protein 90 (Hsp90) is a molecular chaperone that regulates the stability of signaling proteins. Herein, we show that Hsp90 forms a complex with Beclin 1 through an evolutionarily conserved domain to maintain the stability of Beclin 1. In monocytic cells, geldanamycin (GA), an Hsp90 inhibitor, effectively promoted proteasomal degradation of Beclin 1 in a concentration-dependent (EC(50) 100 nM) and time-dependent (t(50) 2 h) manner. In contrast, KNK437/Hsp inhibitor I had no effect. Hsp90 specifically interacted with Beclin 1 but not with other adapter proteins in the TLR signalsome. Treatment of cells with GA inhibited TLR3- and TLR4-mediated autophagy. In addition, S. typhimurium infection-induced autophagy was blocked by GA treatment. This further suggested a role of the Hsp90/Beclin 1 in controlling autophagy in response to microbial infections. Taken together, our data revealed that by maintaining the homeostasis of Beclin 1, Hsp90 plays a novel role in TLR-mediated autophagy.