HSP90 inhibition: two-pronged exploitation of cancer dependencies

Anti-cancer properties of Sansalvamide A, its derivatives, and analogs: an updated review

As peptide-based therapies gain recognition for their potential anti-cancer activity, cyclic peptides like Sansalvamide A, a marine-derived cyclic depsipeptide, have emerged as a potential anti-cancer agent due to their potent activity against various cancer types in preclinical studies. This review offers a comprehensive overview of Sansalvamide A, including its sources, structure-activity relationship, and semi-synthetic derivatives. The review also aims to outline the mechanisms through which Sansalvamide A and its analogs exert their anti-proliferative effects and to discuss the need for enhancements in pharmacokinetic profiles for better clinical utility. An extensive literature search was conducted, focusing on studies that detailed the anti-cancer activity of Sansalvamide A, its pharmacokinetics, and mechanistic pathways. Data from both in vitro and in vivo studies were collated and analyzed. Sansalvamide A and its analogs demonstrated significant anti-cancer activity across various cancer models, mediated through Hsp 90 inhibition, Topoisomerase inhibition, and G0/G1 cell cycle arrest. However, their pharmacokinetic properties were identified as a significant limitation, requiring improvement for effective clinical translation. Despite its notable anti-cancer effects, the utility of Sansalvamide A is currently limited by its pharmacokinetic characteristics. Therefore, while Sansalvamide A exhibits promise as an anti-cancer agent, there is a compelling need for further clinical and toxicological studies and optimization of its pharmacokinetic profile to fully exploit its therapeutic potential alongside modern cancer therapies.

Stress biology: Complexity and multifariousness in health and disease

Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.

Binding Mechanism of Inhibitors to Heat Shock Protein 90 Investigated by Multiple Independent Molecular Dynamics Simulations and Prediction of Binding Free Energy

The heat shock protein (HSP90) has been an import target of drug design in the treatment of human disease. An exploration of the conformational changes in HSP90 can provide useful information for the development of efficient inhibitors targeting HSP90. In this work, multiple independent all-atom molecular dynamics (AAMD) simulations followed by calculations of the molecular mechanics generalized Born surface area (MM-GBSA) were performed to explore the binding mechanism of three inhibitors (W8Y, W8V, and W8S) to HSP90. The dynamics analyses verified that the presence of inhibitors impacts the structural flexibility, correlated movements, and dynamics behavior of HSP90. The results of the MM-GBSA calculations suggest that the selection of GB models and empirical parameters has important influences on the predicted results and verify that van der Waals interactions are the main forces that determine inhibitor-HSP90 binding. The contributions of separate residues to the inhibitor-HSP90 binding process indicate that hydrogen-bonding interactions (HBIs) and hydrophobic interactions play important roles in HSP90-inhibitor identifications. Moreover, residues L34, N37, D40, A41, D79, I82, G83, M84, F124, and T171 are recognized as hot spots of inhibitor-HSP90 binding and provide significant target sites of for the design of drugs related to HSP90. This study aims to contribute to the development of efficient inhibitors that target HSP90 by providing an energy-based and theoretical foundation.

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.

PKM2 Regulates HSP90-Mediated Stability of the IGF-1R Precursor Protein and Promotes Cancer Cell Survival during Hypoxia

Simple Summary

Generally, IGF-1R is overexpressed in most solid tumors, and its expression is significantly associated with poor prognosis in cancer patients. However, IGF-1R gene amplification events are extremely rare in tumors. It is, therefore, necessary to define the mechanism underlying IGR-1R overexpression to elucidate potential therapeutic targets. Our study, specifically, aimed to define the potential mechanisms associated with PKM2 function in regulating IGF-1R protein expression. PKM2 was found to be a non-metabolic protein that regulates HSP90 binding to and stabilizing the precursor IGF-1R protein, thereby promoting the basal level of mature IGF-1R protein. Consequently, PKM2 knockdown inhibits the activation of AKT, a downstream effector of IGF-1R signaling, and increases apoptosis during hypoxia. Our findings reveal a novel mechanism for regulating IGF-1R protein expression, thus suggesting PKM2 as a potential therapeutic target in cancers associated with aberrant IGF signaling.

Abstract

Insulin-like growth factor-1 receptor (IGF-1R), an important factor in promoting cancer cell growth and survival, is commonly upregulated in cancer cells. However, amplification of the IGF1R gene is extremely rare in tumors. Here, we have provided insights into the mechanisms underlying the regulation of IGF-1R protein expression. We found that PKM2 serves as a non-metabolic protein that binds to and increases IGF-1R protein expression by promoting the interaction between IGF-1R and heat-shock protein 90 (HSP90). PKM2 depletion decreases HSP90 binding to IGF-1R precursor, thereby reducing IGF-1R precursor stability and the basal level of mature IGF-1R. Consequently, PKM2 knockdown inhibits the activation of AKT, the key downstream effector of IGF-1R signaling, and increases apoptotic cancer cell death during hypoxia. Notably, we clinically verified the PKM2-regulated expression of IGF-1R through immunohistochemical staining in a tissue microarray of 112 lung cancer patients, demonstrating a significant positive correlation (r = 0.5208, p < 0.0001) between PKM2 and IGF-1R expression. Together, the results of a previous report demonstrated that AKT mediates PKM2 phosphorylation at serine-202; these results suggest that IGF-1R signaling and PKM2 mutually regulate each other to facilitate cell growth and survival, particularly under hypoxic conditions, in solid tumors with dysregulated IGF-1R expression.

Heat Shock Protein 90 Inhibitor Effects on Pancreatic Cancer Cell Cultures

OBJECTIVES

Pancreatic ductal adenocarcinoma is one of the deadliest cancers for which few curative therapies are available to date. Heat shock protein 90 (Hsp90) inhibitors have shown activity against numerous cancers in vitro; therefore, we tested whether they could be used to target pancreatic ductal adenocarcinoma.

METHODS

Inhibitors of Hsp90 ATPase activity were applied on low-passage pancreatic cell line cultures (Panc10.05, Panc215, A6L) in a dose-response manner, and the inhibitor in vitro effect on cell growth was evaluated. Seven of novel Hsp90 inhibitors based on resorcinol fragment and 5 commercially available Hsp90 inhibitors (17-AAG, AT-13387, AUY-922, ganetespib, and rifabutin) as well as control compound triptolide were tested yielding IC50 values in 2- and 3-dimensional assays.

RESULTS

The novel Hsp90 inhibitors exhibited strong effects on all 3 tested pancreatic cell line cultures (Panc10.05, Panc215, A6L) reaching the IC50 of 300 to 600 nM in 2- and 3-dimensional assays.

CONCLUSIONS

Novel Hsp90 inhibitors can be developed as antipancreatic cancer agents. Their chemical structures are simpler, and they are likely to exhibit lower side effects than the much more complex inhibitors used as controls.

Novel Small Molecule Hsp90/Cdc37 Interface Inhibitors Indirectly Target K-Ras-Signaling

The ATP-competitive inhibitors of Hsp90 have been tested predominantly in kinase addicted cancers; however, they have had limited success. A mechanistic connection between Hsp90 and oncogenic K-Ras is not known. Here, we show that K-Ras selectivity is enabled by the loss of the K-Ras membrane nanocluster modulator galectin-3 downstream of the Hsp90 client HIF-1α. This mechanism suggests a higher drug sensitivity in the context of KRAS mutant, HIF-1α-high and/or Gal3-high cancer cells, such as those found, in particular, in pancreatic adenocarcinoma. The low toxicity of conglobatin further indicates a beneficial on-target toxicity profile for Hsp90/Cdc37 interface inhibitors. We therefore computationally screened >7 M compounds, and identified four novel small molecules with activities of 4 μM-44 μM in vitro. All of the compounds were K-Ras selective, and potently decreased the Hsp90 client protein levels without inducing the heat shock response. Moreover, they all inhibited the 2D proliferation of breast, pancreatic, and lung cancer cell lines. The most active compounds from each scaffold, furthermore, significantly blocked 3D spheroids and the growth of K-Ras-dependent microtumors. We foresee new opportunities for improved Hsp90/Cdc37 interface inhibitors in cancer and other aging-associated diseases.

The Development of Hsp90β-Selective Inhibitors to Overcome Detriments Associated with pan-Hsp90 Inhibition

The 90 kD heat shock proteins (Hsp90) are molecular chaperones that are responsible for the folding of select proteins, many of which are directly associated with cancer progression. Consequently, inhibition of the Hsp90 protein folding machinery results in a combinatorial attack on numerous oncogenic pathways. Seventeen small-molecule inhibitors of Hsp90 have entered clinical trials for the treatment of cancer, all of which bind the Hsp90 N-terminus and exhibit pan-inhibitory activity against all four Hsp90 isoforms, which may lead to adverse effects. The development of Hsp90 isoform-selective inhibitors represents an alternative approach toward the treatment of cancer and may limit some of these detriments. Described herein, is a structure-based approach to develop isoform-selective inhibitors of Hsp90β, which induces the degradation of select Hsp90 clients without concomitant induction of Hsp90 levels. Together, these initial studies support the development of Hsp90β-selective inhibitors as a method for overcoming the detriments associated with pan-inhibition.

HSP90 Inhibition Enhances Cancer Immunotherapy by Modulating the Surface Expression of Multiple Immune Checkpoint Proteins

Cancer immunotherapies, including immune checkpoint blockade, have the potential to significantly impact treatments for diverse tumor types. At present, response failures and immune-related adverse events remain significant issues, which could be addressed using optimized combination therapies. Through a cell-based chemical screen of ∼200,000 compounds, we identified that HSP90 inhibitors robustly decrease PD-L1 surface expression, through a mechanism that appears to involve the regulation of master transcriptional regulators (i.e., STAT-3 and c-Myc). Interestingly, HSP90 inhibitors were found to also modulate the surface expression of additional checkpoint proteins (i.e., PD-L2). In the MC-38 syngeneic mouse tumor model, HSP90 inhibition was found to dramatically reduce PD-L1 surface expression on isolated live tumor cells and, consistent with recent findings, was found to increase the number of activated CD8+ T cells within the tumor microenvironment. These findings provide further rationale to explore HSP90 inhibitors as part of combination immunotherapies for the treatment of cancer.

An updated patent review of anticancer Hsp90 inhibitors (2013-present)

INTRODUCTION

Heat shock protein 90 (Hsp90) is one of the most critical chaperones amenable to mediating the folding and maturation of more than 300 client proteins. In normal cells, Hsp90 chaperone cycle is required for regulating multiple cellular processes to maintain homeostasis. However, extremely overexpressed Hsp90 in neoplastic cells results in the dysregulation of client proteins, many of which are indispensable to the accumulation of cancer hallmarks, such as infinite proliferation and increased invasiveness. Consequently, modulation of Hsp90 activity has been considered as a potential strategy for cancer treatment.

AREAS COVERED

This review recapitulated recent patents' progress in the development of Hsp90 inhibitors with potent antitumor activities during 2013 to present. Besides, the structural-activity relationships of the patented inhibitors and their structural similarity were also discussed.

EXPERT OPINION

Hsp90, as an anticancer target, has been investigated for several decades. The first generation of Hsp90 inhibitors exhibited potent antitumor activities in preclinical trials but were trapped in different phases of clinical trials. The second generation of Hsp90 inhibitors has been identified with increased specificity and security through structure modification. Moreover, these inhibitors may offer opportunities for studies of Hsp90 chaperone and development of Hsp90 inhibition therapy.

Solution structure of the Hop TPR2A domain and investigation of target druggability by NMR, biochemical and in silico approaches

Heat shock protein 90 (Hsp90) is a molecular chaperone that plays an important role in tumour biology by promoting the stabilisation and activity of oncogenic 'client' proteins. Inhibition of Hsp90 by small-molecule drugs, acting via its ATP hydrolysis site, has shown promise as a molecularly targeted cancer therapy. Owing to the importance of Hop and other tetratricopeptide repeat (TPR)-containing cochaperones in regulating Hsp90 activity, the Hsp90-TPR domain interface is an alternative site for inhibitors, which could result in effects distinct from ATP site binders. The TPR binding site of Hsp90 cochaperones includes a shallow, positively charged groove that poses a significant challenge for druggability. Herein, we report the apo, solution-state structure of Hop TPR2A which enables this target for NMR-based screening approaches. We have designed prototype TPR ligands that mimic key native 'carboxylate clamp' interactions between Hsp90 and its TPR cochaperones and show that they block binding between Hop TPR2A and the Hsp90 C-terminal MEEVD peptide. We confirm direct TPR-binding of these ligands by mapping 1H-15N HSQC chemical shift perturbations to our new NMR structure. Our work provides a novel structure, a thorough assessment of druggability and robust screening approaches that may offer a potential route, albeit difficult, to address the chemically challenging nature of the Hop TPR2A target, with relevance to other TPR domain interactors.

A Chemical Biology Approach to the Chaperome in Cancer-HSP90 and Beyond

Cancer is often associated with alterations in the chaperome, a collection of chaperones, cochaperones, and other cofactors. Changes in the expression levels of components of the chaperome, in the interaction strength among chaperome components, alterations in chaperome constituency, and in the cellular location of chaperome members, are all hallmarks of cancer. Here we aim to provide an overview on how chemical biology has played a role in deciphering such complexity in the biology of the chaperome in cancer and in other diseases. The focus here is narrow and on pathologic changes in the chaperome executed by enhancing the interaction strength between components of distinct chaperome pathways, specifically between those of HSP90 and HSP70 pathways. We will review chemical tools and chemical probe-based assays, with a focus on HSP90. We will discuss how kinetic binding, not classical equilibrium binding, is most appropriate in the development of drugs and probes for the chaperome in disease. We will then present our view on how chaperome inhibitors may become potential drugs and diagnostics in cancer.

Reflections and Outlook on Targeting HSP90, HSP70 and HSF1 in Cancer: A Personal Perspective

This personal perspective focuses on small-molecule inhibitors of proteostasis networks in cancer-specifically the discovery and development of chemical probes and drugs acting on the molecular chaperones HSP90 and HSP70, and on the HSF1 stress pathway. Emphasis is on progress made and lessons learned and a future outlook is provided. Highly potent, selective HSP90 inhibitors have proved invaluable in exploring the role of this molecular chaperone family in biology and disease pathology. Clinical activity was observed, especially in non small cell lung cancer and HER2 positive breast cancer. Optimal use of HSP90 inhibitors in oncology will likely require development of creative combination strategies. HSP70 family members have proved technically harder to drug. However, recent progress has been made towards useful chemical tool compounds and these may signpost future clinical drug candidates. The HSF1 stress pathway is strongly validated as a target for cancer therapy. HSF1 itself is a ligandless transcription factor that is extremely challenging to drug directly. HSF1 pathway inhibitors have been identified mostly by phenotypic screening, including a series of bisamides from which a clinical candidate has been identified for treatment of ovarian cancer, multiple myeloma and potentially other cancers.

Ligand Binding, Unbinding, and Allosteric Effects: Deciphering Small-Molecule Modulation of HSP90

The molecular chaperone HSP90 oversees the functional activation of a large number of client proteins. Because of its role in multiple pathways linked to cancer and neurodegeneration, drug discovery targeting HSP90 has been actively pursued. Yet, a number of inhibitors failed to meet expectations due to induced toxicity problems. In this context, allosteric perturbation has emerged as an alternative strategy for the pharmacological modulation of HSP90 functions. Specifically, novel allosteric stimulators showed the interesting capability of accelerating HSP90 closure dynamics and ATPase activities while inducing tumor cell death. Here, we gain atomistic insight into the mechanisms of allosteric ligand recognition and their consequences on the functional dynamics of HSP90, starting from the fully unbound state. We integrate advanced computational sampling methods based on FunnelMetadynamics, with the analysis of internal dynamics of the structural ensembles visited during the simulations. We observe several binding/unbinding events, and from these, we derive an accurate estimation of the absolute binding free energy. Importantly, we show that different binding poses induce different dynamics states. Our work for the first time explicitly correlates HSP90 responses to binding/unbinding of an allosteric ligand to the modulation of functionally oriented protein motions.

Effects of purine-scaffold inhibitors on HUVECs: Involvement of the purinergic pathway and interference with ATP. Implications for preventing the adverse effects of extracellular Grp94

Background

Extracellular Glucose-regulated protein94 (Grp94) is linked to pathological conditions disrupting the obligatory intracellular location of this Heat Shock Protein (HSP). In plasma, Grp94 is linked to IgG in complexes that drive adverse effects on vascular cells and are biomarker of gastro-intestinal cancer. By blocking ATP site in different HSPs, purine-scaffold inhibitors are used as promising anti-cancer compounds, but their effects on vasculature are not known.

Methods

We tested the capacity of two purine-scaffold inhibitors, PU-H71 and PU-WS13, to prevent the binding of Grp94 to IgG and to antagonize the effects of Grp94 and native Grp94-IgG complexes on HUVECs in different experimental conditions.

Results

PU-H71 and PU-WS13 blocked Grp94 and the formation of Grp94-IgG complexes in absence of cells. Instead, in presence of HUVECs rather than Grp94 PU-inhibitors targeted cells causing stimulation of Akt and VEGF pathways and displaying angiogenic-like effects similar to, although less intense than that provoked by Grp94 and Grp94-IgG complexes. Unlike Grp94 and Grp94-IgG complexes, PU-inhibitors also activated the purinergic pathway and increased the expression of the ATP receptor P2X7. Effects of PU-inhibitors on HUVECs were reversed by ATP and in presence of ATP PU-inhibitors were again able to block Grp94.

Conclusions

PU-inhibitors can display direct effects on endothelial cells by targeting the ATP receptor P2X7. In absence of ATP, PU-inhibitors preferentially bind to cells rather than Grp94. ATP antagonizes the PU-inhibitor binding to cells thus restoring the capacity to block Grp94 and Grp94-IgG complex formation. Results have implications for enhancing the therapeutic efficacy of PU-inhibitors against circulating pathogenic Grp94.

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Extracellular Grp94 forms pathogenic complexes with IgG.

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PU-inhibitors block the Grp94-IgG complex formation in absence of cells.

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PU-inhibitors target cells and activate the purinergic pathway.

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Effects of PU-inhibitors on cells are reversed by ATP.

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ATP restores the capacity of PU-inhibitors to block the Grp94-IgG complex formation.

Hsp90 Inhibitor SNX-2112 Enhances TRAIL-Induced Apoptosis of Human Cervical Cancer Cells via the ROS-Mediated JNK-p53-Autophagy-DR5 Pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent cancer cell apoptosis-inducing factor that can induce apoptosis in a variety of cancer cells. However, resistance to TRAIL in cancer cells is a huge obstacle in creating effective TRAIL-targeted clinical therapies. Thus, agents that can either enhance the effect of TRAIL or overcome its resistance are needed. In this study, we combined TRAIL with SNX-2112, an Hsp90 inhibitor we previously developed, to explore the effect and mechanism that SNX-2112 enhanced TRAIL-induced apoptosis in cervical cancer cells. Our results showed that SNX-2112 markedly enhanced TRAIL-induced cytotoxicity in HeLa cells, and this combination was found to be synergistic. Additionally, we found that SNX-2112 sensitized TRAIL-mediated apoptosis caspase-dependently in TRAIL-resistant HeLa cells. Mechanismly, SNX-2112 downregulated antiapoptosis proteins, including Bcl-2, Bcl-XL, and FLIP, promoted the accumulation of reactive oxygen species (ROS), and increased the expression levels of p-JNK and p53. ROS scavenger NAC rescued SNX-2112/TRAIL-induced apoptosis and suppressed SNX-2112-induced p-JNK and p53. Moreover, SNX-2112 induced the upregulation of death-receptor DR5 in HeLa cells. The silencing of DR5 by siRNA significantly decreased cell apoptosis by the combined effect of SNX-2112 and TRAIL. In addition, SNX-2112 inhibited the Akt/mTOR signaling pathway and induced autophagy in HeLa cells. The blockage of autophagy by bafilomycin A1 or Atg7 siRNA abolished SNX-2112-induced upregulation of DR5. Meanwhile, ROS scavenger NAC, JNK inhibitor SP600125, and p53 inhibitor PFTα were used to verify that autophagy-mediated upregulation of DR5 was regulated by the SNX-2112-stimulated activation of the ROS-JNK-p53 signaling pathway. Thus, the combination of SNX-2112 and TRAIL may provide a novel strategy for the treatment of human cervical cancer by overcoming cellular mechanisms of apoptosis resistance.

Iron-oxide nanoparticles target intracellular HSP90 to induce tumor radio-sensitization

BACKGROUND

Nanoparticle-based therapies have emerged as a promising approach to overcome limitations of conventional chemotherapy. Present study investigates the potential of oleic acid-functionalized iron-oxide nanoparticles (MN-OA) to enhance the radiation response of fibrosarcoma tumor and elucidates its underlying mechanism.

METHODS

Various cellular and molecular assays (e.g. MTT, clonogenic, cell cycle analysis, cell death, DNA damage/repair) and tumor growth kinetics were employed to investigate the mechanism of MN-OA induced radio-sensitization.

RESULTS

Mouse (WEHI-164) and human (HT-1080) fibrosarcoma cells treated with MN-OA and gamma-radiation (2 Gy) showed a significant decrease in the cell proliferation. Combination treatment showed significant decrease in clonogenic survival of WEHI-164 cells and was found to induce cell cycle arrest, apoptosis and mitotic catastrophe. The mechanism of radio-sensitization was found to involve binding of MN-OA with HSP90, resulting in down-regulation of its client proteins, involved in cell cycle progression (Cyclin B1 and CDC2) and DNA-double strand break repair (e.g. RAD51 and BRCA1). Consistently, longer persistence of DNA damage in cells treated with MN-OA and radiation was observed in the form of γ-H2AX foci. The efficacy and mechanism of MN-OA-induced radio-sensitization was also validated in an immuno-competent murine fibrosarcoma model.

CONCLUSION

This study reveals the key role of HSP90 in the mechanism of tumor radio-sensitization by MN-OA.

GENERAL SIGNIFICANCE

Present work provides a deeper understanding about the mechanism of MN-OA-induced tumor radiosensitization, highlighting the role of HSP90 protein. In addition to diagnostic and magnetic hyperthermia abilities, present remarkable radiosensitizing activity of MN-OA would further excite the clinicians to test its anti-cancer potential.

An update on the discovery and development of selective heat shock protein inhibitors as anti-cancer therapy

INTRODUCTION

Over the years, not a single HSP inhibitor has progressed into the post-market phase of drug development despite the success recorded in various pre-clinical and clinical studies. The inability of existing drugs to specifically target oncogenic HSPs has majorly accounted for these setbacks. Recent combinatorial strategies that incorporated computer-aided drug design (CADD) techniques are geared towards the development of highly specific HSP inhibitors with increased activities and minimal toxicities. Areas covered: In this review, strategic therapeutic approaches that have recently aided the development of selective HSP inhibitors were highlighted. Also, the significant contributions of CADD techniques over the years were discussed in detail. This article further describes promising computational paradigms and their applications towards the discovery of highly specific inhibitors of oncogenic HSPs. Expert opinion: The recent shift towards highly selective and specific HSP inhibition has shown great promise as evidenced by the development of paralog/isoform-selective HSP drugs. It could be further augmented with computer-aided drug design strategies, which incorporate reliable methods that would greatly enhance the design and optimization of novel inhibitors with improved activities and minimal toxicities.

Dynamics revelation of conformational changes and binding modes of heat shock protein 90 induced by inhibitor associations

Heat shock protein 90 (Hsp90) has been an attractive target of potential drug design for antitumor treatment. The current work integrates molecular dynamics (MD) simulations, calculations of binding free energy, and principal component (PC) analysis with scanning of inhibitor-residue interaction to probe the binding modes of inhibitors YK9, YKJ and YKI to Hsp90 and identify the hot spot of the inhibitor-Hsp90 binding. The results suggest that the introductions of two groups G1 and G2 into YKJ and YKI strengthen the binding ability of YKJ and YKI to Hsp90 compared to YK9. PC analysis based MD trajectories prove that inhibitor bindings exert significant effects on the conformational changes, internal dynamics and motion modes of Hsp90, especially for the helix α2 and the loops L1 and L2. The calculations of residue-based free energy decomposition and scanning of the inhibitor-Hsp90 interaction suggest that six residues L107, G108, F138, Y139, W162 and F170 construct the common hot spot of the inhibitor-residue interactions. Moreover the substitutions of the groups G1 and G2 in YKJ and YKI lead to two additional hydrogen bonding interactions and multiple hydrophobic interactions for bindings of YKJ and YKI to Hsp90. This work is also expected to contribute theoretical hints for the design of potent inhibitors toward Hsp90.

Heat shock protein 90 inhibitors augment endogenous wild-type p53 expression but down-regulate the adenovirally-induced expression by inhibiting a proteasome activity

Heat shock protein 90 (HSP90) inhibitors suppressed MDM4 functions which mediated p53 ubiquitination, and blocked a chaperon function which influenced expression of the client proteins. We examined cytotoxic effects of the inhibitors, 17-allylamino-17-demetheoxygeldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17-DMAG), on mesothelioma and investigated combinatory effects of the inhibitors and adenoviruses expressing the wild-type p53 gene (Ad-p53). A majority of mesothelioma lacks p14 and p16 expression, which leads to defective p53 pathway despite bearing the wild-type p53 genotype. The HSP90 inhibitors up-regulated endogenous wild-type p53 expression and induced cell death. Furthermore, the inhibitors increased the endogenous p53 levels that were induced by cisplatin. Nevertheless, the HSP90 inhibitors suppressed Ad-p53-induced exogenous p53 expression primarily at a posttranscriptional level and inhibited the Ad-p53-mediated cell death. HSP90 inhibitors suppressed ubiquitination processes which were involved in p53 degradation, but a proteasome inhibitor, MG-132, prevented the HSP90 inhibitors-induced p53 down-regulation. In contrast, an inhibitor for HSP70 with a chaperon function, pifithrin-μ, did not produce the p53 down-regulation. The HSP90 inhibitors did not suppress expression of Ad receptor molecules but rather increased expression of green fluorescence protein transduced by the same Ad vector. These data collectively indicated that an HSP90 inhibitor possessed a divalent action on p53 expression, as an activator for endogenous wild-type p53 through inhibited ubiquitination and a negative regulator of exogenously over-expressed p53 through the proteasome pathway.

Hsp90 N- and C-terminal double inhibition synergistically suppresses Bcr-Abl-positive human leukemia cells

Heat shock protein 90 (Hsp90) contains amino (N)–terminal domain, carboxyl(C)-terminal domain, and middle domains, which activate Hsp90 chaperone function cooperatively in tumor cells. One terminal occupancy might influence another terminal binding with inhibitor. The Bcr-Abl kinase is one of the Hsp90 clients implicated in the pathogenesis of chronic myeloid leukemia (CML). Present studies demonstrate that double inhibition of the N- and C-terminal termini can disrupt Hsp90 chaperone function synergistically, but not antagonistically, in Bcr-Abl-positive human leukemia cells. Furthermore, both the N-terminal inhibitor 17-AAG and the C-terminal inhibitor cisplatin (CP) have the capacity to suppress progenitor cells; however, only CP is able to inhibit leukemia stem cells (LSCs) significantly, which implies that the combinational treatment is able to suppress human leukemia in different mature states.

Structure-guided design of an Hsp90β N-terminal isoform-selective inhibitor

The 90 kDa heat shock protein (Hsp90) is a molecular chaperone responsible for folding proteins that are directly associated with cancer progression. Consequently, inhibition of the Hsp90 protein folding machinery results in a combinatorial attack on numerous oncogenic pathways. Seventeen small-molecule inhibitors of Hsp90 have entered clinical trials, all of which bind the Hsp90 N-terminus and exhibit pan-inhibitory activity against all four Hsp90 isoforms. pan-Inhibition of Hsp90 appears to be detrimental as toxicities have been reported alongside induction of the pro-survival heat shock response. The development of Hsp90 isoform-selective inhibitors represents an alternative approach towards the treatment of cancer that may limit some of the detriments. Described herein is a structure-based approach to design isoform-selective inhibitors of Hsp90β, which induces the degradation of select Hsp90 clients without concomitant induction of Hsp90 levels. Together, these initial studies support the development of Hsp90β-selective inhibitors as a method to overcome the detriments associated with pan-inhibition.

Resorcinol-Based Grp94-Selective Inhibitors

Glucose regulated protein 94 (Grp94) is the endoplasmic reticulum resident of the 90 kDa heat shock protein (Hsp90) family and represents a promising therapeutic target for the treatment of several diseases. Grp94 is the most unique member of the 90 kDa heat shock protein family due to a five amino acid insertion into its primary sequence, which creates hydrophobic subpockets exclusive to Grp94 that can be utilized for selective inhibition. The first resorcinol-based Grp94-selective inhibitor to take advantage of the hydrophobic S2 subpocket has been developed and shown to manifest low nanomolar affinity and ∼10-fold selectivity for Grp94. Furthermore, these Grp94-selective inhibitors manifest low micromolar GI₅₀ values against multiple myeloma cells, supporting Grp94 as an emerging target for the treatment of this disease.

Second Generation Grp94-Selective Inhibitors Provide Opportunities for the Inhibition of Metastatic Cancer

Glucose regulated protein 94 (Grp94) is the endoplasmic reticulum (ER) resident isoform of the 90 kDa heat shock protein (Hsp90) family and its inhibition represents a promising therapeutic target for the treatment of many diseases. Modification of the first generation cis-amide bioisostere imidazole to alter the angle between the resorcinol ring and the benzyl side chain via cis-amide replacements produced compounds with improved Grp94 affinity and selectivity. Structure-activity relationship studies led to the discovery of compound 30, which exhibits 540 nm affinity and 73-fold selectivity towards Grp94. Grp94 is responsible for the maturation and trafficking of proteins associated with cell signaling and motility, including select integrins. The Grp94-selective inhibitor 30 was shown to exhibit potent anti-migratory effects against multiple aggressive and metastatic cancers.

HSP90 inhibitor AUY922 can reverse Fulvestrant induced feedback reaction in human breast cancer cells

Hormone therapy has become one of the main strategies for breast cancer, however, many estrogen receptor (ER) positive patients end in tumor collapse due to initial or acquired resistance to hormone treatment, which includes Fulvestrant. Here we report that ErbB receptors and downstream PI3K/AKT and ERK pathway have been reactivated after treatment of Fulvestrant in ER positive MCF‐7 and T47D cells, which are related to Fulvestrant resistance. HSP90 is a universally expressed chaperone protein and plays a vital role in both normal and cancer cells, HSP90 inhibitor AUY922 can reverse this feedback reactivation effect of Fulvestrant by targeting multiple proteins related in ErbB receptors, PI3K/AKT and ERK pathway, which is much better than single targeting inhibitors. We also consolidate these effects in human fresh breast tumors. Combination of AUY922 and Fulvestrant may become a promising therapy strategy in breast cancer treatment.

Recognition of enzymes lacking bound cofactor by protein quality control

Protein biogenesis is tightly linked to protein quality control (PQC). The role of PQC machinery in recognizing faulty polypeptides is becoming increasingly understood. Molecular chaperones and cytosolic and vacuolar degradation systems collaborate to detect, repair, or hydrolyze mutant, damaged, and mislocalized proteins. On the other hand, the contribution of PQC to cofactor binding-related enzyme maturation remains largely unexplored, although the loading of a cofactor represents an all-or-nothing transition in regard to the enzymatic function and thus must be surveyed carefully. Combining proteomics and biochemical analysis, we demonstrate here that cells are able to detect functionally immature wild-type enzymes. We show that PQC-dedicated ubiquitin ligase C-terminal Hsp70-interacting protein (CHIP) recognizes and marks for degradation not only a mutant protein but also its wild-type variant as long as the latter remains cofactor free. A distinct structural feature, the protruding C-terminal tail, which appears in both the mutant and wild-type polypeptides, contributes to recognition by CHIP. Our data suggest that relative insufficiency of apoprotein degradation caused by cofactor shortage can increase amyloidogenesis and aggravate protein aggregation disorders.

5'-N-ethylcarboxamidoadenosine is not a paralog-specific Hsp90 inhibitor

The molecular chaperone Hsp90 facilitates the folding and modulates activation of diverse substrate proteins. Unlike other heat shock proteins such as Hsp60 and Hsp70, Hsp90 plays critical regulatory roles by maintaining active states of kinases, many of which are overactive in cancer cells. Four Hsp90 paralogs are expressed in eukaryotic cells: Hsp90α/β (in the cytosol), Grp94 (in the endoplasmic reticulum), Trap1 (in mitochondria). Although numerous Hsp90 inhibitors are being tested in cancer clinical trials, little is known about why different Hsp90 inhibitors show specificity among Hsp90 paralogs. The paralog specificity of Hsp90 inhibitors is likely fundamental to inhibitor efficacy and side effects. In hopes of gaining insight into this issue we examined NECA (5'-N-ethylcarboxamidoadenosine), which has been claimed to be an example of a highly specific ligand that binds to one paralog, Grp94, but not cytosolic Hsp90. To our surprise we find that NECA inhibits many different Hsp90 proteins (Grp94, Hsp90α, Trap1, yeast Hsp82, bacterial HtpG). NMR experiments demonstrate that NECA can bind to the N-terminal domains of Grp94 and Hsp82. We use ATPase competition experiments to quantify the inhibitory power of NECA for different Hsp90 proteins. This scale: Hsp82 > Hsp90α > HtpG ≈ Grp94 > Trap1, ranks Grp94 as less sensitive to NECA inhibition. Because NECA is primarily used as an adenosine receptor agonist, our results also suggest that cell biological experiments utilizing NECA may have confounding effects from cytosolic Hsp90 inhibition.

D3R grand challenge 2015: Evaluation of protein-ligand pose and affinity predictions

The Drug Design Data Resource (D3R) ran Grand Challenge 2015 between September 2015 and February 2016. Two targets served as the framework to test community docking and scoring methods: (1) HSP90, donated by AbbVie and the Community Structure Activity Resource (CSAR), and (2) MAP4K4, donated by Genentech. The challenges for both target datasets were conducted in two stages, with the first stage testing pose predictions and the capacity to rank compounds by affinity with minimal structural data; and the second stage testing methods for ranking compounds with knowledge of at least a subset of the ligand-protein poses. An additional sub-challenge provided small groups of chemically similar HSP90 compounds amenable to alchemical calculations of relative binding free energy. Unlike previous blinded Challenges, we did not provide cognate receptors or receptors prepared with hydrogens and likewise did not require a specified crystal structure to be used for pose or affinity prediction in Stage 1. Given the freedom to select from over 200 crystal structures of HSP90 in the PDB, participants employed workflows that tested not only core docking and scoring technologies, but also methods for addressing water-mediated ligand-protein interactions, binding pocket flexibility, and the optimal selection of protein structures for use in docking calculations. Nearly 40 participating groups submitted over 350 prediction sets for Grand Challenge 2015. This overview describes the datasets and the organization of the challenge components, summarizes the results across all submitted predictions, and considers broad conclusions that may be drawn from this collaborative community endeavor.

In vitro and in vivo anti-diabetic and hepatoprotective effects of edible pods of Parkia roxburghii and quantification of the active constituent by HPLC-PDA

ETHNOPHARMACOLOGICAL RELEVANCE

Parkia roxburghii G. Don. is a traditional medicinal plant and its pods are extensively used as food and medicine. It is believed by the traditional healers to have medicinal properties to treat diabetes, hypertension and urinary tract infections (Jamaluddin et al., 1994).

MATERIALS AND METHODS

The methanolic extract of pods of P roxburghii and fractions were screened for their α-glucosidase and α-amylase inhibitory activity. Anti-hyperglycemic effects were studied on streptozotocin (45mg/kg b.w.) induced diabetes in albino rats (seven groups, n=7 n=6), using different doses for 14 days. Plasma glucose concentration (HbA1c) was analysed using whole blood, while SGOT, SGPT, TG, TC and uric acid were analysed using serum, employing commercial kits. Quantitative analysis of the major active constituent was carried out by HPLC-PDA.

RESULTS

Bioactivity guided chemical investigation of the edible pods of P roxburghii identified sub-fraction EA-Fr 5 which significantly inhibited α-glucosidase (IC50 0.39±0.06 µgmL(-1)), reduced the blood glucose level to normal, and lowered the elevated levels of liver function enzymes SGOT and SGPT in STZ-induced diabetic rats. EA-Fr 5 was found to contain epigallocatechin gallate (1) and hyperin (2) which exhibited significantly higher α-glucosidase inhibitory potency with IC50 0.51±0.09 and 0.71±0.03µM respectively. EA-Fr 5 contained 379.82±2.90mg/g of EGCG, the major active constituent which manifests a broad spectrum of biological activities.

CONCLUSION

The present investigation for the first time reports the occurrence of EGCG and hyperin in P roxburghii and substantiates the traditional use of pods of P roxburghii as dietary supplement for management of diabetes with significantly promising α-glucosidase inhibitory potency and anti-hyperglycemic as well as hepatoprotective effects.

Colorectal cancer cells display chaperone dependency for the unconventional prefoldin URI1

Chaperone dependency of cancer cells is an emerging trait that relates to the need of transformed cells to cope with the various stresses associated with the malignant state. URI1 (unconventional prefoldin RPB5 interactor 1) encodes a member of the prefoldin (PFD) family of molecular chaperones that acts as part of a heterohexameric PFD complex, the URI1 complex (URI1C), to promote assembly of multiprotein complexes involved in cell signaling and transcription processes. Here, we report that human colorectal cancer (CRCs) cell lines demonstrate differential dependency on URI1 and on the URI1 partner PFD STAP1 for survival, suggesting that this differential vulnerability of CRC cells is directly linked to URI1C chaperone function. Interestingly, in URI1-dependent CRC cells, URI1 deficiency is associated with non-genotoxic p53 activation and p53-dependent apoptosis. URI1-independent CRC cells do not exhibit such effects even in the context of wildtype p53. Lastly, in tumor xenografts, the conditional depletion of URI1 in URI1-dependent CRC cells was, after tumor establishment, associated with severe inhibition of subsequent tumor growth and activation of p53 target genes. Thus, a subset of CRC cells has acquired a dependency on the URI1 chaperone system for survival, providing an example of 'non-oncogene addiction' and vulnerability for therapeutic targeting.

Inhibition of Heat Shock Protein 90 Prevents HIV Rebound

HIV evades eradication because transcriptionally dormant proviral genomes persist in long-lived reservoirs of resting CD4(+) T cells and myeloid cells, which are the source of viral rebound after cessation of antiretroviral therapy. Dormant HIV genomes readily produce infectious virus upon cellular activation because host transcription factors activated specifically by cell stress and heat shock mediate full-length HIV transcription. The molecular chaperone heat shock protein 90 (Hsp90) is overexpressed during heat shock and activates inducible cellular transcription factors. Here we show that heat shock accelerates HIV transcription through induction of Hsp90 activity, which activates essential HIV-specific cellular transcription factors (NF-κB, NFAT, and STAT5), and that inhibition of Hsp90 greatly reduces gene expression mediated by these factors. More importantly, we show that Hsp90 controls virus transcription in vivo by specific Hsp90 inhibitors in clinical development, tanespimycin (17-(allylamino)-17-demethoxygeldanamycin) and AUY922, which durably prevented viral rebound in HIV-infected humanized NOD scid IL-2Rγ(-/-) bone marrow-liver-thymus mice up to 11 weeks after treatment cessation. Despite the absence of rebound viremia, we were able to recover infectious HIV from PBMC with heat shock. Replication-competent virus was detected in spleen cells from these nonviremic Hsp90 inhibitor-treated mice, indicating the presence of a tissue reservoir of persistent infection. Our novel findings provide in vivo evidence that inhibition of Hsp90 activity prevents HIV gene expression in replication-competent cellular reservoirs that would typically cause rebound in plasma viremia after antiretroviral therapy cessation. Alternating or supplementing Hsp90 inhibitors with current antiretroviral therapy regimens could conceivably suppress rebound viremia from persistent HIV reservoirs.

Synthesis and Biological Evaluation of Novobiocin Core Analogues as Hsp90 Inhibitors

Development of heat shock protein 90 (Hsp90) C-terminal inhibitors has emerged as an exciting strategy for the treatment of cancer. Previous efforts have focused on modifications to the natural products novobiocin and coumermycin. Moreover, variations in both the sugar and amide moieties have been extensively studied, whereas replacements for the coumarin core have received less attention. Herein, 24 cores were synthesized with varying distances and angles between the sugar and amide moieties. Compounds that exhibited good anti-proliferative activity against multiple cancer cell lines and Hsp90 inhibitory activity, were those that placed the sugar and amide moieties between 7.7 and 12.1 Å apart along with angles of 180°.

Heat Shock Protein Augmentation of Angelica gigas Nakai Root Hot Water Extract on Adipogenic Differentiation in Murine 3T3-L1 Preadipocytes

There is a high association of heat shock on the alteration of energy and lipid metabolism. The alterations associated with thermal stress are composed of gene expression changes and adaptation through biochemical responses. Previous study showed that Angelica gigas Nakai (AGN) root extract promoted adipogenic differentiation in murine 3T3-L1 preadipocytes under the normal temperature condition. However, its effect in heat shocked 3T3-L1 cells has not been established. In this study, we investigated the effect of AGN root hot water extract in the adipogenic differentiation of murine 3T3-L1 preadipocytes following heat shock and its possible mechanism of action. Thermal stress procedure was executed within the same stage of preadipocyte confluence (G0) through incubation at 42°C for one hour and then allowed to recover at normal incubation temperature of 37°C for another hour before AGN treatment for both cell viability assay and Oil Red O. Cell viability assay showed that AGN was able to dose dependently (0 to 400 μg/mL) increase cell proliferation under normal incubation temperature and also was able to prevent cytotoxicity due to heat shock accompanied by cell proliferation. Confluent preadipocytes were subjected into heat shock procedure, recovery and then AGN treatment prior to stimulation with the differentiation solution. Heat shocked preadipocytes exhibited reduced differentiation as supported by decreased amount of lipid accumulation in Oil Red O staining and triglyceride measurement. However, those heat shocked preadipocytes that then were given AGN extract showed a dose dependent increase in lipid accumulation as shown by both evaluation procedures. In line with these results, real-time polymerase chain reaction (RT-PCR) and Western blot analysis showed that AGN increased adipogenic differentiation by upregulating heat shock protection related genes and proteins together with the adipogenic markers. These findings imply the potential of AGN in heat shock amelioration among 3T3-L1 preadipocytes through heat shock factor and proteins augmentation and enhanced adipogenic marker expression.

miR-211 and MITF modulation by Bcl-2 protein in melanoma cells

Melanoma, the most lethal form of skin cancer, is frequently associated with alterations in several genes, among which the Bcl-2 oncogene plays an important role in progression, chemosensitivity and angiogenesis. Also microRNA (miRNA) are emerging as modulators of melanoma development and progression, and among them, miR-211, located within the melastatin-1/TRPM1 (transient receptor potential cation channel, subfamily M, member 1 protein) gene, is prevalently expressed in the melanocyte lineage and acts as oncosuppressor. Using several human melanoma cell lines and their Bcl-2 stably overexpressing derivatives, we evaluated whether there was a correlation between expression of Bcl-2 and miR-211. Western blot analysis and quantitative real-time polymerase chain reaction demonstrated reduced expression of pri-miR-211, miR-211, TRPM1, and MLANA levels, after Bcl-2 overexpression, associated with increased expression of well-known miR-211 target genes. Overexpression of mature miR-211 in Bcl-2 overexpressing cells rescued Bcl-2 ability to increase cell migration. A decreased nuclear localization of microphthalmia-associated transcription factor (MITF), a co-regulator of both miR-211 and TRPM1, and a reduced MITF recruitment at the TRPM1 and MLANA promoters were also evidenced in Bcl-2 overexpressing cells by immunofluorescence and chromatin immunoprecipitation experiments, respectively. Reduction of Bcl-2 expression by small interference RNA confirmed the ability of Bcl-2 to modulate miR-211 and TRPM1 expression. © 2015 Wiley Periodicals, Inc.

Maximizing the Therapeutic Potential of HSP90 Inhibitors

HSP90 is required for maintaining the stability and activity of a diverse group of client proteins, including protein kinases, transcription factors, and steroid hormone receptors involved in cell signaling, proliferation, survival, oncogenesis, and cancer progression. Inhibition of HSP90 alters the HSP90-client protein complex, leading to reduced activity, misfolding, ubiquitination, and, ultimately, proteasomal degradation of client proteins. HSP90 inhibitors have demonstrated significant antitumor activity in a wide variety of preclinical models, with evidence of selectivity for cancer versus normal cells. In the clinic, however, the efficacy of this class of therapeutic agents has been relatively limited to date, with promising responses mainly observed in breast and lung cancer, but no major activity seen in other tumor types. In addition, adverse events and some significant toxicities have been documented. Key to improving these clinical outcomes is a better understanding of the cellular consequences of inhibiting HSP90 that may underlie treatment response or resistance. This review considers the recent progress that has been made in the study of HSP90 and its inhibitors and highlights new opportunities to maximize their therapeutic potential.

Temporal Phosphoproteome Dynamics Induced by an ATP Synthase Inhibitor Citreoviridin

Citreoviridin, one of toxic mycotoxins derived from fungal species, can suppress lung cancer cell growth by inhibiting the activity of ectopic ATP synthase, but has limited effect on normal cells. However, the mechanism of citreoviridin triggering dynamic molecular responses in cancer cells remains unclear. Here, we performed temporal phosphoproteomics to elucidate the dynamic changes after citreoviridin treatment in cells and xenograft model. We identified a total of 829 phosphoproteins and demonstrated that citreoviridin treatment affects protein folding, cell cycle, and cytoskeleton function. Furthermore, response network constructed by mathematical modeling shows the relationship between the phosphorylated heat shock protein 90 β and mitogen-activated protein kinase signaling pathway. This work describes that citreoviridin suppresses cancer cell growth and mitogen-activated protein kinase/extracellular signal-regulated kinase signaling by site-specific dephosphorylation of HSP90AB1 on Serine 255 and provides perspectives in cancer therapeutic strategies.

Histone deacetylase inhibitors prevent pulmonary endothelial hyperpermeability and acute lung injury by regulating heat shock protein 90 function

Transendothelial hyperpermeability caused by numerous agonists is dependent on heat shock protein 90 (Hsp90) and leads to endothelial barrier dysfunction (EBD). Inhibition of Hsp90 protects and restores transendothelial permeability. Hyperacetylation of Hsp90, as by inhibitors of histone deacetylase (HDAC), suppresses its chaperone function and mimics the effects of Hsp90 inhibitors. In this study we assessed the role of HDAC in mediating lipopolysaccharide (LPS)-induced transendothelial hyperpermeability and acute lung injury (ALI). We demonstrate that HDAC inhibition protects against LPS-mediated EBD. Inhibition of multiple HDAC by the general inhibitors panobinostat or trichostatin provided protection against LPS-induced transendothelial hyperpermeability, acetylated and suppressed Hsp90 chaperone function, and attenuated RhoA activity and signaling crucial to endothelial barrier function. Treatment with the HDAC3-selective inhibitor RGFP-966 or the HDAC6-selective inhibitor tubastatin A provided partial protection against LPS-mediated transendothelial hyperpermeability. Similarly, knock down of HDAC3 and HDAC6 by specific small-interfering RNAs provided significant protection against LPS-induced EBD. Furthermore, combined pharmacological inhibition of both HDAC3 and -6 attenuated the inflammation, capillary permeability, and structural abnormalities associated with LPS-induced ALI in mice. Together these data indicate that HDAC mediate increased transendothelial hyperpermeability caused by LPS and that inhibition of HDAC protects against LPS-mediated EBD and ALI by suppressing Hsp90-dependent RhoA activity and signaling.

Discovery of an L-alanine ester prodrug of the Hsp90 inhibitor, MPC-3100

Various types of Hsp90 inhibitors have been and continue to undergo clinical investigation. One development candidate is the purine-based, synthetic Hsp90 inhibitor 1 (MPC-3100), which successfully completed a phase I clinical study. However, further clinical development of 1 was hindered by poor solubility and consequent formulation issues and promoted development of a more water soluble prodrug. Towards this end, numerous pro-moieties were explored in vitro and in vivo. These studies resulted in identification of L-alanine ester mesylate, 2i (MPC-0767), which exhibited improved aqueous solubility, adequate chemical stability, and rapid bioconversion without the need for solubilizing excipients. Based on improved physical characteristics and favorable PK and PD profiles, 2i mesylate was selected for further development. A convergent, scalable, chromatography-free synthesis for 2i mesylate was developed to support further clinical evaluation.

Prediction of dual agents as an activator of mutant p53 and inhibitor of Hsp90 by docking, molecular dynamic simulation and virtual screening

Heat shock protein90s (Hsp90s) play a crucial role in the development of cancer, and their inhibitors are a main target for tumor suppression. P53 also is a tumor suppressor, but in cancer cells, mutations in the p53 gene lead to the inactivation and accumulation of protein. For instance, the ninth p53 cancer mutation, Y220C, destabilizes the p53 core domain. Small molecules have been assumed to bind to Y220C DNA-binding domain and reactivate cellular mutant p53 functions. In this study, one of the mutant p53 activators is suggested as an Hsp90 inhibitor according to a pyrazole scaffold. To confirm a new ligand as a dual agent, molecular docking and molecular dynamic simulations were performed on both proteins (p53 and Hsp90). Molecular dynamic simulations were also conducted to evaluate the obtained results on the other two pyrazole structures, one known as Hsp90 inhibitor and the other as the reported mutant p53 activator. The findings indicate that the new ligand was stable in the active site of both proteins. Finally, a virtual screening was performed on ZINC database, and a set of new dual agents was proposed according to the new ligand scaffold.

Resistance to HSP90 inhibition involving loss of MCL1 addiction

Inhibition of the chaperone heat-shock protein 90 (HSP90) induces apoptosis, and it is a promising anti-cancer strategy. The mechanisms underpinning apoptosis activation following HSP90 inhibition and how they are modified during acquired drug resistance are unknown. We show for the first time that, to induce apoptosis, HSP90 inhibition requires the cooperation of multi BH3-only proteins (BID, BIK, PUMA) and the reciprocal suppression of the pro-survival BCL-2 family member MCL1, which occurs via inhibition of STAT5A. A subset of tumour cell lines exhibit dependence on MCL1 expression for survival and this dependence is also associated with tumour response to HSP90 inhibition. In the acquired resistance setting, MCL1 suppression in response to HSP90 inhibitors is maintained; however, a switch in MCL1 dependence occurs. This can be exploited by the BH3 peptidomimetic ABT737, through non-BCL-2-dependent synthetic lethality.

Hsp90 inhibition induces both protein-specific and global changes in the ubiquitinome

Inhibition of the essential chaperone Hsp90 with drugs causes a global perturbation of protein folding and the depletion of direct substrates of Hsp90, also called clients. Ubiquitination and proteasomal degradation play a key role in cellular stress responses, but the impact of Hsp90 inhibition on the ubiquitinome has not been characterized on a global scale. We used stable isotope labeling and antibody-based peptide enrichment to quantify more than 1500 protein sites modified with a Gly-Gly motif, the remnant of ubiquitination, in human T-cells treated with an Hsp90 inhibitor. We observed rapid changes in GlyGly-modification sites, with strong increases for some Hsp90 clients but also decreases for a majority of cellular proteins. A comparison with changes in total protein levels and protein synthesis and decay rates from a previous study revealed a complex picture with different regulatory patterns observed for different protein families. Overall the data support the notion that for Hsp90 clients GlyGly-modification correlates with targeting by the ubiquitin-proteasome system and decay, while for other proteins levels of GlyGly-modification appear to be mainly influenced by their synthesis rates. Therefore a correct interpretation of changes in ubiquitination requires knowledge of multiple parameters. Data are available via ProteomeXchange with identifier PXD001549.

BIOLOGICAL SIGNIFICANCE

Proteostasis, i.e. the capacity of the cell to maintain proper synthesis and maturation of proteins, is a fundamental biological process and its perturbations have far-reaching medical implications e.g. in cancer or neurodegenerative diseases. Hsp90 is an essential chaperone responsible for the correct maturation and stability of a number of key proteins. Inhibition of Hsp90 triggers a global stress response caused by accumulation of misfolded chains, which have to be either refolded or eliminated by protein degradation pathways such as the Ubiquitin-Proteasome System (UPS). We present the first global assessment of the changes in the ubiquitinome, the subset of ubiquitin-modified proteins, following Hsp90 inhibition in human T-cells. The results provide clues on how cells respond to a specific proteostasis challenge. Furthermore, our data also suggest that basal ubiquitination levels for most proteins are influenced by synthesis rates. This has broad significance as it implies that a proper interpretation of data on ubiquitination levels necessitates simultaneous knowledge of other parameters.

The heat shock protein 90 inhibitor, (-)-epigallocatechin gallate, has anticancer activity in a novel human prostate cancer progression model

(-)-Epigallocatechin gallate (EGCG), a major tea polyphenol, elicits anticancer effects. However, the mechanism of action is not fully understood. Our laboratory previously showed that EGCG inhibits heat shock protein 90 (HSP90). We used nontumorigenic (NT), tumorigenic, and metastatic cancer cells from a novel human prostate cancer progression model to test the hypotheses that certain stages are more or less sensitive to EGCG and that sensitivity is related to HSP90 inhibition. Treatment of cells with EGCG, novobiocin, or 17-AAG resulted in more potent cytotoxic effects on tumorigenic and metastatic cells than NT cells. When tumorigenic or metastatic cells were grown in vivo, mice supplemented with 0.06% EGCG in drinking water developed significantly smaller tumors than untreated mice. Furthermore, EGCG prevented malignant transformation in vivo using the full prostate cancer model. To elucidate the mechanism of EGCG action, we performed binding assays with EGCG-Sepharose, a C-terminal HSP90 antibody, and HSP90 mutants. These experiments revealed that EGCG-Sepharose bound more HSP90 from metastatic cells compared with NT cells and binding occurred through the HSP90 C-terminus. In addition, EGCG bound HSP90 mutants that mimic both complexed and uncomplexed HSP90. Consistent with HSP90 inhibitory activity, EGCG, novobiocin, and 17-AAG induced changes in HSP90-client proteins in NT cells and larger differences in metastatic cells. These data suggest that EGCG may be efficacious for the treatment of prostate cancer because it preferentially targets cancer cells and inhibits a molecular chaperone supportive of the malignant phenotype.

Design, structure-activity relationship, and in vivo characterization of the development candidate NVP-HSP990

Utilizing structure-based drug design, a novel dihydropyridopyrimidinone series which exhibited potent Hsp90 inhibition, good pharmacokinetics upon oral administration, and an excellent pharmacokinetic/pharmacodynamic relationship in vivo was developed from a commercial hit. The exploration of this series led to the selection of NVP-HSP990 as a development candidate.

Mode of cell death induced by the HSP90 inhibitor 17-AAG (tanespimycin) is dependent on the expression of pro-apoptotic BAX

Inhibitors of the molecular chaperone heat shock protein 90 (HSP90) are of considerable current interest as targeted cancer therapeutic agents because of the ability to destabilize multiple oncogenic client proteins. Despite their resulting pleiotropic effects on multiple oncogenic pathways and hallmark traits of cancer, resistance to HSP90 inhibitors is possible and their ability to induce apoptosis is less than might be expected. Using an isogenic model for BAX knockout in HCT116 human colon carcinoma cells, we demonstrate the induction of BAX-dependent apoptosis at pharmacologically relevant concentrations of the HSP90 inhibitor 17-AAG both in vitro and in tumor xenografts in vivo. Removal of BAX expression by homologous recombination reduces apoptosis in vitro and in vivo but allows a lower level of cell death via a predominantly necrotic mechanism. Despite reducing apoptosis, the loss of BAX does not alter the overall sensitivity to 17-AAG in vitro or in vivo. The results indicate that 17-AAG acts predominantly to cause a cytostatic antiproliferative effect rather than cell death and further suggest that BAX status may not alter the overall clinical response to HSP90 inhibitors. Other agents may be required in combination to enhance tumor-selective killing by these promising drugs. In addition, there are implications for the use of apoptotic endpoints in the assessment of the activity of molecularly targeted agents.