HSP90 as a platform for the assembly of more effective cancer chemotherapy

New Pyrazole/Pyrimidine-Based Scaffolds as Inhibitors of Heat Shock Protein 90 Endowed with Apoptotic Anti-Breast Cancer Activity

Background/Objectives: Supported by a comparative study between conventional, grinding, and microwave techniques, a mild and versatile method based on the [1 + 3] cycloaddition of 2-((3-nitrophenyl)diazenyl)malononitrile to tether pyrazole and pyrimidine derivatives in good yields was used. Methods: The newly synthesized compounds were analyzed with IR, 13C NMR, 1H NMR, mass, and elemental analysis methods. The products show interesting precursors for their antiproliferative anti-breast cancer activity. Results: Pyrimidine-containing scaffold compounds 9 and 10 were the most active, achieving IC50 = 26.07 and 4.72 µM against the breast cancer MCF-7 cell line, and 10.64 and 7.64 µM against breast cancer MDA-MB231-tested cell lines, respectively. Also, compounds 9 and 10 showed a remarkable inhibitory activity against the Hsp90 protein with IC50 values of 2.44 and 7.30 µM, respectively, in comparison to the reference novobiocin (IC50 = 1.14 µM). Moreover, there were possible apoptosis and cell cycle arrest in the G1 phase for both tested compounds (supported by CD1, caspase-3,8, BAX, and Bcl-2 studies). Also, the binding interactions of compound 9 were confirmed through molecular docking, and simulation studies displayed a complete overlay into the Hsp90 protein pocket. Conclusions: Compounds 9 and 10 may have apoptotic antiproliferative action as Hsp90 inhibitors.

Intraperitoneal Administration of 17-DMAG as an Effective Treatment against Leishmania braziliensis Infection in BALB/c Mice: A Preclinical Study

BACKGROUND

Leishmaniasis is a significant global public health issue that is caused by parasites from Leishmania genus. With limited treatment options and rising drug resistance, there is a pressing need for new therapeutic approaches. Molecular chaperones, particularly Hsp90, play a crucial role in parasite biology and are emerging as promising targets for drug development.

OBJECTIVE

This study evaluates the efficacy of 17-DMAG in treating BALB/c mice from cutaneous leishmaniasis through in vitro and in vivo approaches.

MATERIALS AND METHODS

We assessed 17-DMAG's cytotoxic effect on bone marrow-derived macrophages (BMMΦ) and its effects against L. braziliensis promastigotes and intracellular amastigotes. Additionally, we tested the compound's efficacy in BALB/c mice infected with L. braziliensis via intraperitoneal administration to evaluate the reduction in lesion size and the decrease in parasite load in the ears and lymph nodes of infected animals.

RESULTS

17-DMAG showed selective toxicity [selective index = 432) towards Leishmania amastigotes, causing minimal damage to host cells. The treatment significantly reduced lesion sizes in mice and resulted in parasite clearance from ears and lymph nodes. It also diminished inflammatory responses and reduced the release of pro-inflammatory cytokines (IL-6, IFN-γ, TNF) and the regulatory cytokine IL-10, underscoring its dual leishmanicidal and anti-inflammatory properties.

CONCLUSIONS

Our findings confirm the potential of 17-DMAG as a viable treatment for cutaneous leishmaniasis and support further research into its mechanisms and potential applications against other infectious diseases.

Comprehensive analysis of resorcinyl-imidazole Hsp90 inhibitor design

Human Hsp90 chaperones are implicated in various aspects of cancer. Due to this, Hsp90 has been explored as potential target in cancer treatment. Initial attempts to use Hsp90 inhibitors in drug trials failed due to toxicity and inefficacy. The next generation of drugs were less toxic but still insufficiently effective in a clinical setting. Recently, a lot of effort is being put into understanding the consequences of Hsp90 isoform selective inhibition, expecting that this might hold the key in targeting Hsp90 for disease treatment. Here we investigate a series of compounds containing the aryl-resorcinol scaffold with a 5-membered ring as a promising class of new human Hsp90 inhibitors, reaching nanomolar affinity. We compare how the replacement of 5-membered ring, from thiadiazole to imidazole, as well as a variety of their substituents, influences the potency of these inhibitors for Hsp90 alpha and beta isoforms. To further elucidate the dissimilarity in ligand selectivity between the isoforms, a mutant protein was constructed and tested against the ligand library. In addition, we performed a series of molecular dynamics (MD) and docking simulations to further explain our experimental findings as well as evaluated key compounds in cell assays. Our results deepen the understanding of Hsp90 isoform ligand selectivity and serve as an informative base for further Hsp90 inhibitor optimization.

Pharmacophore Model-Based Virtual Screening Workflow for Discovery of Inhibitors Targeting Plasmodium falciparum Hsp90

Plasmodium falciparum causes the most lethal and widespread form of malaria. Eradication of malaria remains a priority due to the increasing number of cases of drug resistance. The heat shock protein 90 of P. falciparum (PfHsp90) is a validated drug target essential for parasite survival. Most PfHsp90 inhibitors bind at the ATP binding pocket found in its N-terminal domain, abolishing the chaperone's activities, which leads to parasite death. The challenge is that the NTD of PfHsp90 is highly conserved, and its disruption requires selective inhibitors that can act without causing off-target human Hsp90 activities. We endeavored to discover selective inhibitors of PfHsp90 using pharmacophore modeling, virtual screening protocols, induced fit docking (IFD), and cell-based and biochemical assays. The pharmacophore model (DHHRR), composed of one hydrogen bond donor, two hydrophobic groups, and two aromatic rings, was used to mine commercial databases for initial hits, which were rescored to 20 potential hits using IFD. Eight of these compounds displayed moderate to high activity toward P. falciparum NF54 (i.e., IC50s ranging from 6.0 to 0.14 μM) and averaged >10 in terms of selectivity indices toward CHO and HepG2 cells. Additionally, four compounds inhibited PfHsp90 with greater selectivity than a known inhibitor, harmine, and bound to PfHsp90 with weak to moderate affinity. Our findings support the use of a pharmacophore model to discover diverse chemical scaffolds such as FM2, FM6, F10, and F11 exhibiting anti-Plasmodium activities and serving as valuable new PfHsp90 inhibitors. Optimization of these hits may enable their development into potent leads for future antimalarial drugs.

Discovery of Quinacrine as a Potent Topo II and Hsp90 Dual-Target Inhibitor, Repurposing for Cancer Therapy

Topo II and Hsp90 are promising targets. In this study, we first verified the structural similarities between Topo IIα ATPase and Hsp90α N−ATPase. Subsequently, 720 compounds from the Food and Drug Administration (FDA) drug library and kinase library were screened using the malachite green phosphate combination with the Topo II-mediated DNA relaxation and MTT assays. Subsequently, the antimalarial drug quinacrine was found to be a potential dual−target inhibitor of Topo II and Hsp90. Mechanistic studies showed that quinacrine could specifically bind to the Topo IIα ATPase domain and inhibit the activity of Topo IIα ATPase without impacting DNA cleavage. Furthermore, our study revealed that quinacrine could bind Hsp90 N−ATPase and inhibit Hsp90 activity. Significantly, quinacrine has broad antiproliferation activity and remains sensitive to the multidrug−resistant cell line MCF−7/ADR and the atypical drug−resistant tumor cell line HL−60/MX2. Our study identified quinacrine as a potential dual−target inhibitor of Topo II and Hsp90, depending on the ATP−binding domain, positioning it as a hit compound for further structural modification.

Mebendazole's Conformational Space and Its Predicted Binding to Human Heat-Shock Protein 90

Recent experimental evidence suggests that mebendazole, a popular antiparasitic drug, binds to heat shock protein 90 (Hsp90) and inhibits acute myeloid leukemia cell growth. In this study we use quantum mechanics (QM), molecular similarity, and molecular dynamics (MD) calculations to predict possible binding poses of mebendazole to the adenosine triphosphate (ATP) binding site of Hsp90. Extensive conformational searches and minimization of the five mebendazole tautomers using the MP2/aug-cc-pVTZ theory level resulted in 152 minima. Mebendazole-Hsp90 complex models were subsequently created using the QM optimized conformations and protein coordinates obtained from experimental crystal structures that were chosen through similarity calculations. Nine different poses were identified from a total of 600 ns of explicit solvent, all-atom MD simulations using two different force fields. All simulations support the hypothesis that mebendazole is able to bind to the ATP binding site of Hsp90.

Virtual screening based identification of miltefosine and octenidine as inhibitors of heat shock protein 90

The molecular chaperone HSP90 facilitates the maturation of newly synthesized and unfolded proteins. The client proteins of HSP90 are involved in many processes of cancer occurrence and development, and therefore, HSP90 is considered as a promising target for the development of anticancer drugs. In contrast to N-terminal inhibitor, C-terminal inhibitor does not induce the pro-survival heat shock response. In order to get novel HSP90 C-terminal inhibitors and more evidences that HSP90 inhibitors could be applied in the therapy of cancer, we conducted a virtual screening toward HSP90 C-terminus from FDA-approved drugs. In this study, miltefosine and octenidine were identified as new HSP90 inhibitors. Miltefosine and octenidine exhibited strong and broad-spectrum anticancer activity and inhibited the proliferation of cancer cell by promoting apoptosis. Western blotting analysis revealed that miltefosine and octenidine significantly down-regulated the expression levels of HSP90 client proteins including p-AKT, CDK6, and ERK, and did not induce overexpression of heat shock proteins including HSP70 and HSP90 in MCF-7 cells. These results were in accordance with the characteristics of HSP90 C-terminal inhibitor. In conclusion, miltefosine and octenidine could disrupt the molecular chaperone function of HSP90, and thus, their strong and broad-spectrum anticancer activity is at least in part attributed to the inhibition activity against HSP90.

The disruption of protein-protein interactions with co-chaperones and client substrates as a strategy towards Hsp90 inhibition

The 90-kiloDalton (kD) heat shock protein (Hsp90) is a ubiquitous, ATP-dependent molecular chaperone whose primary function is to ensure the proper folding of several hundred client protein substrates. Because many of these clients are overexpressed or become mutated during cancer progression, Hsp90 inhibition has been pursued as a potential strategy for cancer as one can target multiple oncoproteins and signaling pathways simultaneously. The first discovered Hsp90 inhibitors, geldanamycin and radicicol, function by competitively binding to Hsp90's N-terminal binding site and inhibiting its ATPase activity. However, most of these N-terminal inhibitors exhibited detrimental activities during clinical evaluation due to induction of the pro-survival heat shock response as well as poor selectivity amongst the four isoforms. Consequently, alternative approaches to Hsp90 inhibition have been pursued and include C-terminal inhibition, isoform-selective inhibition, and the disruption of Hsp90 protein-protein interactions. Since the Hsp90 protein folding cycle requires the assembly of Hsp90 into a large heteroprotein complex, along with various co-chaperones and immunophilins, the development of small molecules that prevent assembly of the complex offers an alternative method of Hsp90 inhibition.

Development and Characterization of PLGA Nanoparticles Containing 17-DMAG, an Hsp90 Inhibitor

Leishmaniasis is a spectrum of neglected tropical diseases and its cutaneous form (CL) is characterized by papillary or ulcerated skin lesions that negatively impact patients' quality of life. Current CL treatments suffer limitations, such as severe side effects and high cost, making the search for new therapeutic alternatives an imperative. In this context, heat shock protein 90 (Hsp90) could present a novel therapeutic target, as evidence suggests that Hsp90 inhibitors, such as 17-Dimethylaminoethylamino-17-Demethoxygeldanamycin (17-DMAG), may represent promising chemotherapeutic agents against CL. As innovative input for formulation development of 17-DMAG, nano-based drug delivery systems could provide controlled release, targeting properties, and reduced drug toxicity. In this work, a double emulsion method was used to develop poly (lactic-co-glycolic acid) (PLGA) nanoparticles containing 17-DMAG. The nanoparticle was developed using two distinct protocols: Protocol 1 (P1) and Protocol 2 (P2), which differed concerning the organic solvent (acetone or dichloromethane, respectively) and procedure used to form double-emulsions (Ultra-Turrax® homogenization or sonication, respectively). The nanoparticles produced by P2 were comparatively smaller (305.5 vs. 489.0 nm) and more homogeneous polydispersion index (PdI) (0.129 vs. 0.33) than the ones made by P1. Afterward, the P2 was optimized and the best composition consisted of 2 mg of 17-DMAG, 100 mg of PLGA, 5% of polyethylene glycol (PEG 8000), 1.5 mL of the internal aqueous phase, 1% of polyvinyl alcohol (PVA), and 4 mL of the organic phase. Optimized P2 nanoparticles had a particle size of 297.2 nm (288.6-304.1) and encapsulation efficacy of 19.35% (15.42-42.18) by the supernatant method and 31.60% (19.9-48.79) by the filter/column method. Release kinetics performed at 37°C indicated that ~16% of the encapsulated 17-DMAG was released about to 72 h. In a separate set of experiments, a cell uptake assay employing confocal fluorescence microscopy revealed the internalization by macrophages of P2-optimized rhodamine B labeled nanoparticles at 30 min, 1, 2, 4, 6, 24, 48, and 72 h. Collectively, our results indicate the superior performance of P2 concerning the parameters used to assess nanoparticle development. Therefore, these findings warrant further research to evaluate optimized 17-DMAG-loaded nanoparticles (NP2-17-DMAG) for toxicity and antileishmanial effects in vitro and in vivo.

Hsp90 facilitates acquired drug resistance of tumor cells through cholesterol modulation however independent of tumor progression

Acquired multidrug resistance of cancer cells challenges the chemotherapeutic interventions. To understand the role of molecular chaperone, Hsp90 in drug adapted tumor cells, we have used in vitro drug adapted epidermoid tumor cells as a model system. We found that chemotherapeutic drug adaptation of tumor cells is mediated by induced activities of both Hsp90 and P-glycoprotein (P-gp). Although the high-affinity conformation of Hsp90 has correlated with the enhanced drug efflux activity, we did not observe a direct interaction between P-gp and Hsp90. The enrichment of P-gp and Hsp90 at the cholesterol-rich membrane microdomains is found obligatory for enhanced drug efflux activity. Since inhibition of cholesterol biosynthesis is not interfering with the drug efflux activity, it is presumed that the net cholesterol redistribution mediated by Hsp90 regulates the enhanced drug efflux activity. Our in vitro cholesterol and Hsp90 interaction studies have furthered our presumption that Hsp90 facilitates cholesterol redistribution. The drug adapted cells though exhibited anti-proliferative and anti-tumor effects in response to 17AAG treatment, drug treatment has also enhanced the drug efflux activity. Our findings suggest that drug efflux activity and metastatic potential of tumor cells are independently regulated by Hsp90 by distinct mechanisms. We expose the limitations imposed by Hsp90 inhibitors against multidrug resistant tumor cells.

Understanding the Hsp90 N-terminal Dynamics: Structural and Molecular Insights into the Therapeutic Activities of Anticancer Inhibitors Radicicol (RD) and Radicicol Derivative (NVP-YUA922)

Heat shock protein 90 (Hsp90) is a crucial component in carcinogenesis and serves as a molecular chaperone that facilitates protein maturation whilst protecting cells against temperature-induced stress. The function of Hsp90 is highly dependent on adenosine triphosphate (ATP) binding to the N-terminal domain of the protein. Thus, inhibition through displacement of ATP by means of competitive binding with a suitable organic molecule is considered an attractive topic in cancer research. Radicicol (RD) and its derivative, resorcinylic isoxazole amine NVP-AUY922 (NVP), have shown promising pharmacodynamics against Hsp90 activity. To date, the underlying binding mechanism of RD and NVP has not yet been investigated. In this study, we provide a comprehensive understanding of the binding mechanism of RD and NVP, from an atomistic perspective. Density functional theory (DFT) calculations enabled the analyses of the compounds' electronic properties and results obtained proved to be significant in which NVP was predicted to be more favorable with solvation free energy value of -23.3 kcal/mol and highest stability energy of 75.5 kcal/mol for a major atomic delocalization. Molecular dynamic (MD) analysis revealed NVP bound to Hsp90 (NT-NVP) is more stable in comparison to RD (NT-RD). The Hsp90 protein exhibited a greater binding affinity for NT-NVP (-49.4 ± 3.9 kcal/mol) relative to NT-RD (-28.9 ± 4.5 kcal/mol). The key residues influential in this interaction are Gly 97, Asp 93 and Thr 184. These findings provide valuable insights into the Hsp90 dynamics and will serve as a guide for the design of potent novel inhibitors for cancer treatment.

Synergistic activity of Hsp90 inhibitors and anticancer agents in pancreatic cancer cell cultures

Heat shock protein 90 (Hsp90) is a widely investigated target for anticancer therapy. The experimental Hsp90 inhibitors ICPD47 and ICPD62 demonstrated anticancer activity against colorectal, osteosarcoma and cervical cancer cell lines. However, their anticancer activity has not been investigated against pancreatic cancer cell lines yet, and there are no data about synergistic activity of these compounds in combination with clinically used anticancer agents. Pancreatic cancer cell lines, MIA PaCa-2 and PANC-1 were exposed to ICPD47 and ICPD62 alone and in combinations with antimetabolites gemcitabine (GEM), 5-fluorouracil (5-FU) and topoisomerase inhibitor doxorubicin (DOX). Effects on cell viability were determined by MTT assay. The synergistic activity was evaluated using Chou-Talalay method. Also, 3D cell cultures were formed using 3D Bioprinting method and the activity of each compound and their combinations was examined by measuring the size change of spheroids. The strongest synergistic activities were determined in combinations using all ratios of ICPD47 with GEM and ICPD62 with GEM in MIA PaCa-2 cell line (combination index <0.5). The combinations of ICPD47 with 5-FU and ICPD47 with GEM in a ratio of 1:5 showed the greatest effect on tumour spheroid growth in both cell lines. The ICPD47 in combination with mild hyperthermia showed significant results, where the EC₅₀ value in PANC-1 cell line dropped from 4.04 ± 0.046 to 1.68 ± 0.004 µM. The ICPD47 and ICPD62 under the same conditions could act synergistically with GEM, 5-FU and DOX and is worth of further investigations, and studies of synergistic effect is a promising path for more efficient anticancer therapies.

Structural characterization and biological properties of silver(I) tris(pyrazolyl)methane sulfonate

The water-soluble 1D helical coordination polymer [Ag(Tpms)]_n (1) [Tpms = tris(pyrazolyl)methane sulfonate, ^-O₃SC(pz)₃; pz = pyrazolyl] was synthesized and fully characterized, its single-crystal X-ray diffraction analysis revealing the ligand acting as a bridging chelate N₃-donor ligand. The antiproliferative potential of 1 was performed on two human tumour cell lines, A2780 and HCT116, and in normal fibroblasts, with a much higher effect in the former cell line (IC₅₀ of 0.04 μM) as compared to the latter cell line and to normal fibroblasts. Compound 1 does not alter cell cycle progression but interferes with the adherence of A2780 cells triggering cell apoptosis. Apoptosis appears to occur via the extrinsic pathway (no changes in mitochondria membrane potential, reactive oxygen species (ROS) and pro-apoptotic (B-cell lymphoma 2 (BCL-2) associated protein (BAX))/anti-apoptotic (BCL-2) ratio) being this hypothesis also supported by the presence of silver mainly in the supernatants of A2780 cells. Results also indicated that cell death via autophagy was triggered. Proteomic analysis allowed us to confirm that compound 1 is able to induce a stress response in A2780 cells that is related with its antiproliferative activity and the trigger of apoptosis.

Alcohol Modulates the Biogenesis and Composition of Microglia-Derived Exosomes

Exosomes are small extracellular vesicles that have emerged as an important tool for intercellular communication. In the central nervous system, exosomes can mediate glia and neuronal communication. Once released from the donor cell, exosomes can act as discrete vesicles and travel to distant and proximal recipient cells to alter cellular function. Microglia cells secrete exosomes due to stress stimuli of alcohol abuse. The goal of this study was to investigate the effects of alcohol exposure on the biogenesis and composition of exosomes derived from microglia cell line BV-2. The BV-2 cells were cultured in exosome-free media and were either mock treated (control) or treated with 50 mM or 100 mM of alcohol for 48 and 72 h. Our results demonstrated that alcohol significantly impacted BV-2 cell morphology, viability, and protein content. Most importantly, our studies revealed that exosome biogenesis and composition was affected by alcohol treatment.

Penicisulfuranol A, a novel C-terminal inhibitor disrupting molecular chaperone function of Hsp90 independent of ATP binding domain

The goal of this study is to explore the mechanism of a heat shock protein 90 (Hsp90) C-terminal inhibitor, Penicisulfuranol A (PEN-A), for cancer therapy. PEN-A was produced by a mangrove endophytic fungus Penicillium janthinellum and had a new structure with a rare 3H-spiro [benzofuran-2, 2'-piperazine] ring system. PEN-A caused depletion of multiple Hsp90 client proteins without induction of heat shock protein 70 (Hsp70). Subsequently, it induced apoptosis and inhibited xerograph tumor growth of HCT116 cells in vitro and in vivo. Mechanism studies showed that PEN-A was bound to C-terminus of Hsp90 at the binding site different from ATP binding domain. Therefore, it inhibited dimerization of Hsp90 C-terminus, depolymerization of ADH protein by C-terminus of Hsp90, and interaction of co-chaperones with Hsp90. These inhibitory effects of PEN-A were similar to those of novobiocin, an inhibitor binding to interaction site for ATP of C-terminus of Hsp90. Furthermore, our study revealed that disulfide bond was essential moiety for inhibition activity of PEN-A on Hsp90. This suggested that PEN-A may be bound to cysteine residues near amino acid region which was responsible for dimerization of Hsp90. All results indicate that PEN-A is a novel C-terminal inhibitor of Hsp90 and worthy for further study in the future not only for drug development but also for unraveling the bioactivities of Hsp90.

Structural basis for species-selective targeting of Hsp90 in a pathogenic fungus

New strategies are needed to counter the escalating threat posed by drug-resistant fungi. The molecular chaperone Hsp90 affords a promising target because it supports survival, virulence and drug-resistance across diverse pathogens. Inhibitors of human Hsp90 under development as anticancer therapeutics, however, exert host toxicities that preclude their use as antifungals. Seeking a route to species-selectivity, we investigate the nucleotide-binding domain (NBD) of Hsp90 from the most common human fungal pathogen, Candida albicans. Here we report structures for this NBD alone, in complex with ADP or in complex with known Hsp90 inhibitors. Encouraged by the conformational flexibility revealed by these structures, we synthesize an inhibitor with >25-fold binding-selectivity for fungal Hsp90 NBD. Comparing co-crystals occupied by this probe vs. anticancer Hsp90 inhibitors revealed major, previously unreported conformational rearrangements. These insights and our probe's species-selectivity in culture support the feasibility of targeting Hsp90 as a promising antifungal strategy.

Hydroxybiphenylamide GroEL/ES Inhibitors Are Potent Antibacterials against Planktonic and Biofilm Forms of Staphylococcus aureus

We recently reported the identification of a GroEL/ES inhibitor (1, N-(4-(benzo[ d]thiazol-2-ylthio)-3-chlorophenyl)-3,5-dibromo-2-hydroxybenzamide) that exhibited in vitro antibacterial effects against Staphylococcus aureus comparable to vancomycin, an antibiotic of last resort. To follow up, we have synthesized 43 compound 1 analogs to determine the most effective functional groups of the scaffold for inhibiting GroEL/ES and killing bacteria. Our results identified that the benzothiazole and hydroxyl groups are important for inhibiting GroEL/ES-mediated folding functions, with the hydroxyl essential for antibacterial effects. Several analogs exhibited >50-fold selectivity indices between antibacterial efficacy and cytotoxicity to human liver and kidney cells in cell culture. We found that MRSA was not able to easily generate acute resistance to lead inhibitors in a gain-of-resistance assay and that lead inhibitors were able to permeate through established S. aureus biofilms and maintain their bactericidal effects.

Adapting to stress - chaperome networks in cancer

In this Opinion article, we aim to address how cells adapt to stress and the repercussions chronic stress has on cellular function. We consider acute and chronic stress-induced changes at the cellular level, with a focus on a regulator of cellular stress, the chaperome, which is a protein assembly that encompasses molecular chaperones, co-chaperones and other co-factors. We discuss how the chaperome takes on distinct functions under conditions of stress that are executed in ways that differ from the one-on-one cyclic, dynamic functions exhibited by distinct molecular chaperones. We argue that through the formation of multimeric stable chaperome complexes, a state of chaperome hyperconnectivity, or networking, is gained. The role of these chaperome networks is to act as multimolecular scaffolds, a particularly important function in cancer, where they increase the efficacy and functional diversity of several cellular processes. We predict that these concepts will change how we develop and implement drugs targeting the chaperome to treat cancer.

DCZ3112, a novel Hsp90 inhibitor, exerts potent antitumor activity against HER2-positive breast cancer through disruption of Hsp90-Cdc37 interaction

Hsp90 regulates the stability of oncoproteins important in tumor development and progression, and represents a potential therapeutic target. However, all Hsp90 inhibitors currently in clinical trials target Hsp90 ATPase activity and exhibit low selectivity and high toxicity. In this study, we discovered a new Hsp90 inhibitor, DCZ3112, with a novel mechanism of action. DCZ3112 directly bound to the N-terminal domain of Hsp90 and inhibited Hsp90-Cdc37 interaction without inhibiting ATPase activity. DCZ3112 inhibited the proliferation predominantly in HER2-positive breast cancer cells, including those resistant to the classical Hsp90 inhibitor geldanamycin, which mainly targets ATPase. DCZ3112 produced synergistic in vitro activity in inhibiting cell proliferation, inducing G₁-phase arrest and apoptosis, and reducing AKT and ERK phosphorylation. Consistent with this, DCZ3112 alone inhibited the growth of HER2-positive BT-474 xenografts, and exhibited enhanced antitumor activity when combined with the anti-HER2 antibody trastuzumab. Importantly, DCZ3112 also significantly inhibited the growth of trastuzumab-resistant BT-474 cells, and combined treatment retained synergistic antitumor activity. Thus, our findings show that disrupting Hsp90-Cdc37 interaction may represent a promising strategy against HER2-positive breast cancer, especially those with acquired resistance to trastuzumab.

c-FLIP is a target of the E3 ligase deltex1 in gastric cancer

The ubiquitin E3 ligase DELTEX1 (DTX1) is specifically downregulated in gastric cancer tissues, and expression of DTX1 is linked to better prognoses and survival in gastric cancer. Cellular FLICE inhibitory protein (c-FLIP) is known for its pivotal role in the resistance of cancer cells to death receptor-induced cell death. Here, we show that DTX1 is an E3 ligase for c-FLIP in gastric cancer cells. DTX1 promoted c-FLIP downregulation. Overexpression of DTX1 sensitized gastric cancer cells to TRAIL-induced apoptosis, whereas DTX1-knockdown attenuated apoptosis induction. DTX1 binds c-FLIP_L and directs it into the endosome-lysosomal pathway for proteasome-independent degradation. Moreover, induction of DTX1 in AGS cells by geldanamycin conferred susceptibility of those cells to TRAIL-induced apoptosis. Our results reveal a tumor-suppressive role for DTX1 and suggest a new approach to increasing TRAIL efficacy by raising DTX1 levels in gastric cancer therapy. DTX1 also enhanced c-FLIP degradation and FasL-induced and TRAIL-induced apoptosis in T cells, suggesting that DTX1 constitutes one of the physiological mechanisms regulating c-FLIP stability.

Chetracins E and F, cytotoxic epipolythiodioxopiperazines from the marine-derived fungus Acrostalagmus luteoalbus HDN13-530

Three epipolythiodioxopiperazines with two new ones were isolated from a marine-derived fungus, and all of them exhibited extensive cytotoxicity.

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.

Therapeutic potency of heat-shock protein-90 pharmacological inhibitors in the treatment of gastrointestinal cancer, current status and perspectives

Objectives

Heat-shock protein-90 (HSP90) chaperone machinery is critical to the folding, stability and activity of several client proteins including many responsible for tumour initiation, progression and metastasis. Overexpression of HSP90 is correlated with poor prognosis of GI cancer.

Key findings

Pharmacological inhibitors of HSP90 suppress tumorigenic effects of HSP90 by suppressing angiogenesis, survival, metastasis and drug resistance in GI cancer. This review summarizes the role of HSP90 inhibitors in the treatment of GI cancer.

Summary

We have presented different antitumour mechanisms of HSP90 inhibitors in cancer treatment. Suppression of HSP90 signalling via specific and novel pharmacological inhibitors is a potentially novel therapeutic approach for patients with GI cancer for a better understanding and hence a better management of this disease.

Proteins regulating the intercellular transfer and function of P-glycoprotein in multidrug-resistant cancer

Chemotherapy is an essential part of anticancer treatment. However, the overexpression of P-glycoprotein (P-gp) and the subsequent emergence of multidrug resistance (MDR) hampers successful treatment clinically. P-gp is a multidrug efflux transporter that functions to protect cells from xenobiotics by exporting them out from the plasma membrane to the extracellular space. P-gp inhibitors have been developed in an attempt to overcome P-gp-mediated MDR; however, lack of specificity and dose limiting toxicity have limited their effectiveness clinically. Recent studies report on accessory proteins that either directly or indirectly regulate P-gp expression and function and which are necessary for the establishment of the functional phenotype in cancer cells. This review discusses the role of these proteins, some of which have been recently proposed to comprise an interactive complex, and discusses their contribution towards MDR. We also discuss the role of other pathways and proteins in regulating P-gp expression in cells. The potential for these proteins as novel therapeutic targets provides new opportunities to circumvent MDR clinically.

HSP90 inhibitor NVP-AUY922 induces cell apoptosis by disruption of the survivin in papillary thyroid carcinoma cells

Heat shock protein 90 (HSP90) is a molecular chaperone required for maintaining the stability and function of signal proteins that plays an important role in promoting the growth and survival of cancer cells. The incidence of papillary thyroid carcinoma (PTC) has been increasing in recent years. The effect of the novel non-geldanamycin HSP90 inhibitor NVP-AUY922 on apoptosis of papillary thyroid carcinoma cells has not been investigated. The influence of AUY922 on the survival of PTC cell lines K1 and IHH4 was evaluated. Cell viability was determined by cell counting kit method. Cell apoptosis was assessed by flow cytometry and western blotting and the potential mechanism was evaluated by western blotting and immunoprecipitation. Overexpression plasmid was transfected by Lipofectamine 2000 method. In K1 and IHH4 cell lines, after the treatment of AUY922, cell viability decreased, and the proportion of apoptosis cells increased. AUY922 caused the cleavage of PARP and caspase-3 proteins, and altered expression of survivin, which was a client protein of HSP90. In AUY922-treated cells, overexpression of survivin attenuated growth inhibition and cell apoptosis. The results indicate that AUY922 induces apoptotic cell death in PTC cells. Moreover, our findings demonstrate that AUY922 induced apoptosis by downregulating the expression of survivin protein in PTC cells.

Secreted heat shock protein 90 promotes prostate cancer stem cell heterogeneity

Heat-shock protein 90 (Hsp90), a highly conserved molecular chaperone, is frequently upregulated in tumors, and remains an attractive anti-cancer target. Hsp90 is also found extracellularly, particularly in tumor models. Although extracellular Hsp90 (eHsp90) action is not well defined, eHsp90 targeting attenuates tumor invasion and metastasis, supporting its unique role in tumor progression. We herein investigated the potential role of eHsp90 as a modulator of cancer stem-like cells (CSCs) in prostate cancer (PCa). We report a novel function for eHsp90 as a facilitator of PCa stemness, determined by its ability to upregulate stem-like markers, promote self-renewal, and enhance prostasphere growth. Moreover, eHsp90 increased the side population typically correlated with the drug-resistant phenotype. Intriguingly, tumor cells with elevated surface eHsp90 exhibited a marked increase in stem-like markers coincident with increased expression of the epithelial to mesenchymal (EMT) effector Snail, indicating that surface eHsp90 may enrich for a unique CSC population. Our analysis of distinct effectors modulating the eHsp90-dependent CSC phenotyperevealed that eHsp90 is a likely facilitator of stem cell heterogeneity. Taken together, our findings provide unique functional insights into eHsp90 as a modulator of PCa plasticity, and provide a framework towards understanding its role as a driver of tumor progression.

Paralog Specific Hsp90 Inhibitors - A Brief History and a Bright Future

BACKGROUND

The high sequence and structural homology among the hsp90 paralogs - Hsp90α, Hsp90β, Grp94, and Trap-1 - has made the development of paralog-specific inhibitors a challenging proposition.

OBJECTIVE

This review surveys the state of developments in structural analysis, compound screening, and structure-based design that have been brought to bear on this problem.

RESULTS

First generation compounds that selectively bind to Hsp90, Grp94, or Trap-1 have been identified.

CONCLUSION

With the proof of principle firmly established, the prospects for further progress are bright.

Bcl-2 overexpression contributes to laryngeal carcinoma cell survival by forming a complex with Hsp90β

Laryngeal carcinoma (LC) is one of the most common malignant tumors of all head and neck squamous cell carcinomas (HNSCCs). However, the molecular mechanism and genetic basis of the development of LC have not been fully elucidated. To explore the possible mechanism, targeted proteomic analysis was performed on Bcl-2-associated proteins from LC cells. According to our results, 35 proteins associated with Bcl-2 were identified and Hsp90β was confirmed by co-immunoprecipitation and western blot analysis. Protein‑protein interaction (PPI) analysis indicated that Bcl-2‑Hsp90β interactions may be involved in the anti-apoptotic progression of LC. Further results revealed that disruption of the Bcl-2-Hsp90β interaction inhibited the anti-apoptotic ability of Bcl-2 and decreased the caspase activation in LC, which has broad implications for the better understanding of tumor formation, tumor cell survival and development of metastasis due to Bcl-2. Collectively, we report the mechanism by which Bcl-2 functions in LC as an anti-apoptotic factor in relation to its association with proteins and potentially identify a Bcl-2/Hsp90β axis as a novel target for LC therapy.

Molecular Chaperone HSP90 Is Necessary to Prevent Cellular Senescence via Lysosomal Degradation of p14ARF

The tumor suppressor function of p14ARF is regulated at a posttranslational level via mechanisms yet to be fully understood. Here, we report the identification of an unconventional p14ARF degradation pathway induced by the chaperone HSP90 in association with the E3 ubiquitin ligase C-terminus of HSP70-interacting protein (CHIP). The ternary complex of HSP90, CHIP, and p14ARF was required to induce the lysosomal degradation of p14ARF by an ubiquitination-independent but LAMP2A-dependent mechanism. Depletion of HSP90 or CHIP induced p14ARF-dependent senescence in human fibroblasts. Premature senescence observed in cells genetically deficient in CHIP was rescued in cells that were doubly deficient in CHIP and p14ARF. Notably, non-small cell lung cancer cells (NSCLC) positive for p14ARF were sensitive to treatment with the HSP90 inhibitor geldanamycin. Furthermore, overexpression of HSP90 and CHIP with a concomitant loss of p14ARF correlated with poor prognosis in patients with NSCLC. Our findings identify a relationship between p14ARF and its chaperones that suggest new therapeutic strategies in cancers that overexpress HSP90. Cancer Res; 77(2); 343-54. ©2016 AACR.

Cotargeting HSP90 and Its Client Proteins for Treatment of Prostate Cancer

Castration-resistant prostate cancer (CRPC) is the later stage of prostate cancer when the disease has stopped responding to androgen deprivation therapy (ADT). It has been established that androgen receptor (AR) reactivation is responsible for the recurrence of prostate cancer after ADT. Thus, targeting different pathways that regulate AR stability and activity should be a promising strategy for treatment of CRPC. Heat shock proteins (HSP) are chaperones that modify stability and activity of their client proteins. HSP90, a major player in the HSP family, regulates stability of many proteins, including AR and Polo-like kinase 1 (Plk1), a critical regulator of many cell-cycle events. Further, HSP90 is overexpressed in different cancers, including prostate cancer. Herein, we show that cotreatment of prostate cancer with AR antagonist enzalutamide and HSP90 inhibitor leads to more severe cell death due to a synergistic reduction of AR protein. Interestingly, we show that overexpression of Plk1 rescued the synergistic effect and that cotargeting HSP90 and Plk1 also leads to more severe cell death. Mechanistically, we show that E3 ligase CHIP, in addition to targeting AR, is responsible for the degradation of Plk1 as well. These findings suggest that cotargeting HSP90 and some of its client proteins may be a useful strategy in treatment of CRPC. Mol Cancer Ther; 15(9); 2107-18. ©2016 AACR.

Mapping the Hsp90 Genetic Network Reveals Ergosterol Biosynthesis and Phosphatidylinositol-4-Kinase Signaling as Core Circuitry Governing Cellular Stress

Candida albicans is a leading human fungal pathogen that causes life-threatening systemic infections. A key regulator of C. albicans stress response, drug resistance, morphogenesis, and virulence is the molecular chaperone Hsp90. Targeting Hsp90 provides a powerful strategy to treat fungal infections, however, the therapeutic utility of current inhibitors is compromised by toxicity due to inhibition of host Hsp90. To identify components of the Hsp90-dependent circuitry governing virulence and drug resistance that are sufficiently divergent for selective targeting in the pathogen, we pioneered chemical genomic profiling of the Hsp90 genetic network in C. albicans. Here, we screen mutant collections covering ~10% of the genome for hypersensitivity to Hsp90 inhibition in multiple environmental conditions. We identify 158 HSP90 chemical genetic interactors, most of which are important for growth only in specific environments. We discovered that the sterol C-22 desaturase gene ERG5 and the phosphatidylinositol-4-kinase (PI4K) gene STT4 are HSP90 genetic interactors under multiple conditions, suggesting a function upstream of Hsp90. By systematic analysis of the ergosterol biosynthetic cascade, we demonstrate that defects in ergosterol biosynthesis induce cellular stress that overwhelms Hsp90's functional capacity. By analysis of the phosphatidylinositol pathway, we demonstrate that there is a genetic interaction between the PI4K Stt4 and Hsp90. We also establish that Stt4 is required for normal actin polarization through regulation of Wal1, and suggest a model in which defects in actin remodeling induces stress that creates a cellular demand for Hsp90 that exceeds its functional capacity. Consistent with this model, actin inhibitors are synergistic with Hsp90 inhibitors. We highlight new connections between Hsp90 and virulence traits, demonstrating that Erg5 and Stt4 enable activation of macrophage pyroptosis. This work uncovers novel circuitry regulating Hsp90 functional capacity and new effectors governing drug resistance, morphogenesis and virulence, revealing new targets for antifungal drug development.

Novobiocin Analogues That Inhibit the MAPK Pathway

Heat shock protein 90 (Hsp90) inhibition by modulation of its N- or C-terminal binding site has become an attractive strategy for the development of anticancer chemotherapeutics. The first Hsp90 C-terminus inhibitor, novobiocin, manifested a relatively high IC50 value of ∼700 μM. Therefore, investigation of the novobiocin scaffold has led to analogues with improved antiproliferative activity (nanomolar concentrations) against several cancer cell lines. During these studies, novobiocin analogues that do not inhibit Hsp90 were identified; however, these analogues demonstrated potent antiproliferative activity. Compound 2, a novobiocin analogue, was identified as a MAPK pathway signaling disruptor that lacked Hsp90 inhibitory activity. In addition, structural modifications of compound 2 were identified that segregated Hsp90 inhibition from MAPK signaling disruption. These studies indicate that compound 2 represents a novel scaffold for disruption of MAPK pathway signaling and may serve as a useful structure for the generation of new anticancer agents.

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.

Potential Prognostic Value of Histone Deacetylase 6 and Acetylated Heat-Shock Protein 90 in Early-Stage Breast Cancer

Purpose

Histone deacetylase 6 (HDAC6) is an enzyme that deacetylates heat-shock protein 90 (HSP90). Many studies have investigated the role of HDAC6 and HSP90 in tumorigenesis and in the prognosis of cancer patients. This study aimed to evaluate the prognostic value of HDAC6 and acetylated HSP90 (acetyl-HSP90) in a cohort of breast cancer patients.

Methods

Immunohistochemical analysis of 314 surgical specimens obtained from patients with invasive breast cancer was carried out to assess standard pathologic factors and the expression of HDAC6 and acetyl-HSP90. Statistical analyses were performed to determine the association between HDAC6, acetyl-HSP90, and conventional clinicopathological factors, and the prognostic values of these factors were evaluated.

Results

HDAC6 expression did not show any correlation with other clinicopathological factors, but acetyl-HSP90 was significantly correlated with histologic grade (p=0.001) and the Ki-67 index (p=0.015). HDAC6 and acetyl-HSP90 expression were significantly associated with each other (p=0.047). Although HDAC6 was not prognostic for disease-free survival (DFS), some patients with high expression of HDAC6 experienced recurrence 5 years after diagnosis, while there was no recurrent disease after 5 years in those with low expression. Acetyl-HSP90 was significantly associated with the DFS of all patients (p=0.016) and with high HDAC6 expression (p=0.017), but not with low expression.

Conclusion

Expression of HDAC6 and acetyl-HSP90 are correlated. HDAC6 is proposed to be a possible predictive marker of late recurrence, and acetyl-HSP90 has prognostic value in predicting the DFS of breast cancer patients.

Accessory proteins for heterotrimeric G-proteins in the kidney

Heterotrimeric G-proteins play a fundamentally important role in regulating signal transduction pathways in the kidney. Accessory proteins are being identified as direct binding partners for heterotrimeric G-protein α or βγ subunits to promote more diverse mechanisms by which G-protein signaling is controlled. In some instances, accessory proteins can modulate the signaling magnitude, localization, and duration following the activation of cell membrane-associated receptors. Alternatively, accessory proteins complexed with their G-protein α or βγ subunits can promote non-canonical models of signaling activity within the cell. In this review, we will highlight the expression profile, localization and functional importance of these newly identified accessory proteins to control the function of select G-protein subunits under normal and various disease conditions observed in the kidney.

The Arabian camel Camelus dromedarius heat shock protein 90α: cDNA cloning, characterization and expression

Heat shock protein 90 (Hsp90) is a highly conserved ubiquitous molecular chaperone contributing to assisting folding, maintenance of structural integrity and proper regulation of a subset of cytosolic proteins. In the present study, a heat shock protein 90α full length coding cDNA was isolated and cloned from the Arabian one-humped camel by reverse transcription polymerase chain reaction (RT-PCR). The full length cDNA sequence was submitted to NCBI GeneBank under the accession number KF612338. The sequence analysis of the Arabian camel Hsp90α cDNA showed 2202bp encoding a protein of 733 amino acids with estimated molecular mass of 84.827kDa and theoretical isoelectric point (pI) of 5.31. Blast search analysis revealed that the C. dromedarius Hsp90α shared high similarity with other known Hsp90α. Comparative analyses of camel Hsp90α protein sequence with other mammalian Hsp90s showed high identity (85-94%). Heterologous expression of camel Hsp90α cDNA in E. coli JM109 (DE3) gave a fusion protein band of 86.0kDa after induction with IPTG for 4h.

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.

Sensitization of chemo-resistant human chronic myeloid leukemia stem-like cells to Hsp90 inhibitor by SIRT1 inhibition

Development of effective therapeutic strategies to eliminate cancer stem-like cells (CSCs), which play a major role in drug resistance and disease recurrence, is critical to improve cancer treatment outcomes. The current investigation was undertaken to examine the effectiveness of the combination treatment of Hsp90 inhibitor and SIRT1 inhibitor in inhibiting the growth of chemo-resistant stem-like cells isolated from human chronic myeloid leukemia K562 cells. Inhibition of SIRT1 by use of SIRT1 siRNA or SIRT1 inhibitors (amurensin G and EX527) effectively potentiated sensitivity of Hsp90 inhibitors (17-AAG and AUY922) in CD44(high) K562 stem-like cells expressing high levels of CSC-related molecules including Oct4, CD34, β-catenin, c-Myc, mutant p53 (mut p53), BCRP and P-glycoprotein (P-gp) as well as CD44. SIRT1 depletion caused significant down-regulation of heat shock factor 1 (HSF1)/heat shock proteins (Hsps) as well as these CSC-related molecules, which led to the sensitization of CD44(high) K562 cells to Hsp90 inhibitor by SIRT1 inhibitor. Moreover, 17-AAG-mediated activation of HSF1/Hsps and P-gp-mediated efflux, major causes of Hsp90 inhibitor resistance, was suppressed by SIRT1 inhibitor in K562-CD44(high) cells. Our data suggest that combined treatment with Hsp90 inhibitor and SIRT1 inhibitor could be an effective therapeutic approach to target CSCs that are resistant to current therapies.

Natural Product Inspired N-Terminal Hsp90 Inhibitors: From Bench to Bedside?

The 90 kDa heat shock proteins (Hsp90) are responsible for the conformational maturation of nascent polypeptides and the rematuration of denatured proteins. Proteins dependent upon Hsp90 are associated with all six hallmarks of cancer. Upon Hsp90 inhibition, protein substrates are degraded via the ubiquitin-proteasome pathway. Consequentially, inhibition of Hsp90 offers a therapeutic opportunity for the treatment of cancer. Natural product inhibitors of Hsp90 have been identified in vitro, which have served as leads for the development of more efficacious inhibitors and analogs that have entered clinical trials. This review highlights the development of natural product analogs, as well as the development of clinically important inhibitors that arose from natural products.

Molecular chaperone Hsp90 is a therapeutic target for noroviruses

Human noroviruses (HuNoV) are a significant cause of acute gastroenteritis in the developed world, and yet our understanding of the molecular pathways involved in norovirus replication and pathogenesis has been limited by the inability to efficiently culture these viruses in the laboratory. Using the murine norovirus (MNV) model, we have recently identified a network of host factors that interact with the 5' and 3' extremities of the norovirus RNA genome. In addition to a number of well-known cellular RNA binding proteins, the molecular chaperone Hsp90 was identified as a component of the ribonucleoprotein complex. Here, we show that the inhibition of Hsp90 activity negatively impacts norovirus replication in cell culture. Small-molecule-mediated inhibition of Hsp90 activity using 17-DMAG (17-dimethylaminoethylamino-17-demethoxygeldanamycin) revealed that Hsp90 plays a pleiotropic role in the norovirus life cycle but that the stability of the viral capsid protein is integrally linked to Hsp90 activity. Furthermore, we demonstrate that both the MNV-1 and the HuNoV capsid proteins require Hsp90 activity for their stability and that targeting Hsp90 in vivo can significantly reduce virus replication. In summary, we demonstrate that targeting cellular proteostasis can inhibit norovirus replication, identifying a potential novel therapeutic target for the treatment of norovirus infections.

IMPORTANCE

HuNoV are a major cause of acute gastroenteritis around the world. RNA viruses, including noroviruses, rely heavily on host cell proteins and pathways for all aspects of their life cycle. Here, we identify one such protein, the molecular chaperone Hsp90, as an important factor required during the norovirus life cycle. We demonstrate that both murine and human noroviruses require the activity of Hsp90 for the stability of their capsid proteins. Furthermore, we demonstrate that targeting Hsp90 activity in vivo using small molecule inhibitors also reduces infectious virus production. Given the considerable interest in the development of Hsp90 inhibitors for use in cancer therapeutics, we identify here a new target that could be explored for the development of antiviral strategies to control norovirus outbreaks and treat chronic norovirus infection in immunosuppressed patients.

Development of a mitochondria-targeted Hsp90 inhibitor based on the crystal structures of human TRAP1

The mitochondrial pool of Hsp90 and its mitochondrial paralogue, TRAP1, suppresses cell death and reprograms energy metabolism in cancer cells; therefore, Hsp90 and TRAP1 have been suggested as target proteins for anticancer drug development. Here, we report that the actual target protein in cancer cell mitochondria is TRAP1, and current Hsp90 inhibitors cannot effectively inactivate TRAP1 because of their insufficient accumulation in the mitochondria. To develop mitochondrial TRAP1 inhibitors, we determined the crystal structures of human TRAP1 complexed with Hsp90 inhibitors. The isopropyl amine of the Hsp90 inhibitor PU-H71 was replaced with the mitochondria-targeting moiety triphenylphosphonium to produce SMTIN-P01. SMTIN-P01 showed a different mode of action from the nontargeted PU-H71, as well as much improved cytotoxicity to cancer cells. In addition, we determined the structure of a TRAP1-adenylyl-imidodiphosphate (AMP-PNP) complex. On the basis of comparative analysis of TRAP1 structures, we propose a molecular mechanism of ATP hydrolysis that is crucial for chaperone function.

Biological relevance of Hsp90-binding immunophilins in cancer development and treatment

Immunophilins are a family of intracellular receptors for immunosuppressive drugs. Those immunophilins that are related to immunosuppression are the smallest proteins of the family, i.e., FKBP12 and CyPA, whereas the other members of the family have higher molecular weight because the show additional domains to the drug-binding site. Among these extra domains, the TPR-domain is perhaps the most relevant because it permits the interaction of high molecular weight immunophilins with the 90-kDa heat-shock protein, Hsp90. This essential molecular chaperone regulates the biological function of several protein-kinases, oncogenes, protein phosphatases, transcription factors and cofactors . Hsp90-binding immunophilins where first characterized due to their association with steroid receptors. They regulate the cytoplasmic transport and the subcellular localization of these and other Hsp90 client proteins, as well as transcriptional activity, cell proliferation, cell differentiation and apoptosis. Hsp90-binding immunophilins are frequently overexpressed in several types of cancers and play a key role in cell survival. In this article we analyze the most important biological actions of the best characterized Hsp90-binding immunophilins in both steroid receptor function and cancer development and discuss the potential use of these immunophilins for therapeutic purposes as potential targets of specific small molecules.

AUY922 effectively overcomes MET- and AXL-mediated resistance to EGFR-TKI in lung cancer cells

The activation of bypass signals, such as MET and AXL, has been identified as a possible mechanism of EGFR-TKI resistance. Because various oncoproteins depend on HSP90 for maturation and stability, we investigated the effects of AUY922, a newly developed non-geldanamycin class HSP90 inhibitor, in lung cancer cells with MET- and AXL-mediated resistance. We established resistant cell lines with HCC827 cells harboring an exon 19-deletion mutation in of the EGFR gene via long-term exposure to increasing concentrations of gefitinib and erlotinib (HCC827/GR and HCC827/ER, respectively). HCC827/GR resistance was mediated by MET activation, whereas AXL activation caused resistance in HCC827/ER cells. AUY922 treatment effectively suppressed proliferation and induced cell death in both resistant cell lines. Accordingly, the downregulation of EGFR, MET, and AXL led to decreased Akt activation. The inhibitory effects of AUY922 on each receptor were confirmed in gene-transfected LK2 cells. AUY922 also effectively controlled tumor growth in xenograft mouse models containing HCC827/GR and HCC827/ER cells. In addition, AUY922 reduced invasion and migration by both types of resistant cells. Our study findings thus show that AUY922 is a promising therapeutic option for MET- and AXL-mediated resistance to EGFR-TKI in lung cancer.

Reaction design, discovery, and development as a foundation to function-oriented synthesis

Convergent C-C bond-forming reactions define the fabric of organic synthesis and, when applied in complex molecule synthesis, can have a profound impact on efficiency by decreasing the longest linear sequence of transformations required to convert simple starting materials to complex targets. Despite their well-appreciated strategic significance, campaigns in natural product synthesis typically embrace only a small suite of reactivity to achieve such bond construction (i.e., nucleophilic addition to polarized π-bonds, nucleophilic substitution, cycloaddition, and metal-catalyzed "cross-coupling"), therefore limiting the sites at which convergent coupling chemistry can be strategically employed. In our opinion, it is far too often that triumphs in the field are defined by chemical sequences that do not address the challenges associated with discovery, development, and production of natural product-inspired agents. We speculated that advancing an area of chemical reactivity not represented in the few well-established strategies for convergent C-C bond formation may lead to powerful new retrosynthetic relationships that could simplify approaches to the syntheses of a variety of different classes of natural products. Our studies ultimately embraced the pursuit of strategies to control the course of metallacycle-mediated "cross-coupling" between substrates containing sites of simple π-unsaturation (ubiquitous functionality in organic chemistry including alkenes, alkynes, allenes, aldehydes, and imines, among others). In just eight years since our initial publication in this area, we have defined over 20 stereoselective intermolecular C-C bond-forming reactions that provide access to structural motifs of relevance for the synthesis of polyketides, fatty acids, alkaloids, and terpenes, while doing so in a direct and stereoselective fashion. These achievements continue to serve as the foundation of my group's activity in natural product and function-oriented synthesis, where our achievements in reaction development are challenged in the context of complex targets. Among our early efforts, we achieved the most concise synthesis of a benzoquinone ansamycin ever described (macbecin I), and moved beyond this achievement to explore the role of our chemistry in function-oriented synthesis targeting the discovery of natural product-inspired Hsp90 inhibitors. These later efforts have led to the discovery of a uniquely selective benzoquinone ansamycin-inspired Hsp90 inhibitor that lacks the problematic quinone present in the natural series. This achievement was made possible by a concise chemical synthesis pathway that had at its core the application of metallacycle-mediated cross-coupling chemistry.

Heat shock protein 90 targeting therapy: state of the art and future perspective

Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone that plays a role in stabilizing and activating more than 200 client proteins. It is required for the stability and function of numerous oncogenic signaling proteins that determine the hallmarks of cancer. Since the initial discovery of the first Hsp90 inhibitor in the 1970s, multiple phase II and III clinical trials of several Hsp90 inhibitors have been undertaken. This review provides an overview of the current status on clinical trials of Hsp90 inhibitors and future perspectives on novel anticancer strategies using Hsp90 inhibitors.

Proteomic analysis of mitochondria in respiratory epithelial cells infected with human respiratory syncytial virus and functional implications for virus and cell biology

OBJECTIVES

The aim of this study was to quantitatively characterise the mitochondrial proteome of airway epithelial cells infected with human respiratory syncytial virus (HRSV), a major cause of paediatric illness.

METHODS

Quantitative proteomics, underpinned by stable isotope labelling with amino acids in cell culture, coupled to LC-MS/MS, was applied to mitochondrial fractions prepared from HRSV-infected and mock-infected cells 12 and 24 h post-infection. Datasets were analysed using ingenuity pathway analysis, and the results were validated and characterised using bioimaging, targeted inhibition and gene depletion.

KEY FINDINGS

The data quantitatively indicated that antiviral signalling proteins converged on mitochondria during HRSV infection. The mitochondrial receptor protein Tom70 was found to act in an antiviral manner, while its chaperone, Hsp90, was confirmed to be a positive viral factor. Proteins associated with different organelles were also co-enriched in the mitochondrial fractions from HRSV-infected cells, suggesting that alterations in organelle dynamics and membrane associations occur during virus infection.

CONCLUSIONS

Protein and pathway-specific alterations occur to the mitochondrial proteome in a spatial and temporal manner during HRSV infection, suggesting that this organelle may have altered functions. These could be targeted as part of potential therapeutic strategies to disrupt virus biology.

Heat shock protein 90 inhibitors in the treatment of cancer: current status and future directions

INTRODUCTION

Heat shock protein 90 (HSP90) serves as a critical facilitator for oncogene addiction. There has been augmenting enthusiasm in pursuing HSP90 as an anticancer strategy. In fact, since the initial serendipitous discovery that geldanamycin (GM) inhibits HSP90, the field has rapidly moved from proof-of-concept clinical studies with GM derivatives to novel second-generation inhibitors.

AREAS COVERED

The authors highlight the current status of the second-generation HSP90 inhibitors in clinical development. Herein, the authors note the lessons learned from the completed clinical trials of first- and second-generation inhibitors and describe various assays attempting to serve for a more rational implementation of these agents to cancer treatment. Finally, the authors discuss the future perspectives for this promising class of agents.

EXPERT OPINION

The knowledge gained thus far provides perhaps only a glimpse at the potential of HSP90 for which there is still much work to be done. Lessons from the clinical trials suggest that HSP90 therapy would advance at a faster pace if patient selection and tumor pharmacokinetics of these drugs were better understood and applied to their clinical development. It is also evident that combining HSP90 inhibitors with other potent anticancer therapies holds great promise not only due to synergistic antitumor activity but also due to the potential of prolonging or preventing the development of drug resistance.