Heat-shock protein 90 inhibitors as antitumor agents: a survey of the literature from 2005 to 2010

An update on the status of HSP90 inhibitors in cancer clinical trials

The evolutionary conserved molecular chaperone heat shock protein 90 (HSP90) plays an indispensable role in tumorigenesis by stabilizing client oncoproteins. Although the functionality of HSP90 is tightly regulated, cancer cells exhibit a unique dependence on this chaperone, leading to its overexpression, which has been associated with poor prognosis in certain malignancies. While various strategies targeting heat shock proteins (HSPs) involved in carcinogenesis have been explored, only inhibition of HSP90 has consistently and effectively resulted in proteasomal degradation of its client proteins. To date, a total of 22 HSP90 inhibitors (HSP90i) have been tested in 186 cancer clinical trials, as reported by clinicaltrials.gov. Among these trials, 60 % have been completed, 10 % are currently active, and 30 % have been suspended, terminated, or withdrawn. HSP90 inhibitors (HSP90i) have been used as single agents or in combination with other drugs for the treatment of various cancer types in clinical trials. Notably, improved clinical outcomes have been observed when HSP90i are used in combination therapies, as they exhibit a synergistic antitumor effect. However, as single agents, HSP90i have shown limited clinical activity due to drug-related toxicity or therapy resistance. Recently, active trials conducted in Japan evaluating TAS-116 (pimitespib) have demonstrated promising results with low toxicity as monotherapy and in combination with the immune checkpoint inhibitor nivolumab. Exploratory biomarker analyses performed in various trials have demonstrated target engagement that suggests the potential for identifying patient populations that may respond favorably to the therapy. In this review, we discuss the advances made in the past 5 years regarding HSP90i and their implications in anticancer therapeutics. Our focus lies in evaluating drug efficacy, prognosis forecast, pharmacodynamic biomarkers, and clinical outcomes reported in published trials. Through this comprehensive review, we aim to shed light on the progress and potential of HSP90i as promising therapeutic agents in cancer treatment.

Detailed curriculum vitae of HER2-targeted therapy

With the booming development of precision medicine, molecular targeted therapy has been widely used in clinical oncology treatment due to a smaller number of side effects and its superior accuracy compared to that of traditional strategies. Among them, human epidermal growth factor receptor 2 (HER2)-targeted therapy has attracted considerable attention and has been used in the clinical treatment of breast and gastric cancer. Despite excellent clinical effects, HER2-targeted therapy remains in its infancy due to its resulting inherent and acquired resistance. Here, a comprehensive overview of HER2 in numerous cancers is presented, including its biological role, involved signaling pathways, and the status of HER2-targeted therapy.

Synthesis and Biological Activity of 3-(Heteroaryl)quinolin-2(1H)-ones Bis-Heterocycles as Potential Inhibitors of the Protein Folding Machinery Hsp90

In the context of our SAR study concerning 6BrCaQ analogues as C-terminal Hsp90 inhibitors, we designed and synthesized a novel series of 3-(heteroaryl)quinolin-2(1H), of types 3, 4, and 5, as a novel class of analogues. A Pd-catalyzed Liebeskind-Srogl cross-coupling was developed as a convenient approach for easy access to complex purine architectures. This series of analogues showed a promising biological effect against MDA-MB231 and PC-3 cancer cell lines. This study led to the identification of the best compounds, 3b (IC₅₀ = 28 µM) and 4e, which induce a significant decrease of CDK-1 client protein and stabilize the levels of Hsp90 and Hsp70 without triggering the HSR response.

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.

Metabolites profiling and pharmacokinetics of troxipide and its pharmacodynamics in rats with gastric ulcer

Troxipide is widely used to treat gastric ulcer (GU) in the clinic. However, a lack of systematic metabolic, pharmacokinetic and pharmacological studies limits its clinical use. This study aimed to firstly explore the metabolic, pharmacokinetic and pharmacological mechanisms of troxipide in rats with GU compared to normal control (NC) rats. First, metabolic study was perormed by a highly selective, high-resolution mass spectrometry method. A total of 45 metabolites, including 9 phase I metabolites and 36 phase II metabolites, were identified based on MS/MS spectra. Subsequently, the pharmacokinetics results suggested that the Cmax, Ka, t1/2, AUC(0-t) and AUC(0-∞) of troxipide were significantly increased in rats with GU compared with NC rats. The Vz, K10 and absolute bioavailability of troxipide were obviously decreased in rats with GU compared with NC rats, and its tissue distribution (in the liver, lung and kidney) was significantly different between the two groups of rats. Additionally, the pharmacodynamic results suggested that the levels of biochemical factors (IL-17, IL-6, TNF-α, IFN-γ, AP-1, MTL, GAS, and PG-II) were significantly increased, the PG-Ӏ level was obviously decreased, and the protein expression levels of HSP-90, C-Cas-3 and C-PARP-1 were markedly increased in rats with GU compared with NC rats. The above results suggested that the therapeutic mechanisms underlying the metabolic, pharmacokinetic and pharmacological properties of troxipide in vivo in rats deserve further attention based on the importance of troxipide in the treatment of GU in this study, and these mechanisms could be targets for future studies.

A Brain-Penetrating Hsp90 Inhibitor NXD30001 Inhibits Glioblastoma as a Monotherapy or in Combination With Radiation

Glioblastoma multiforme (GBM) is a highly heterogeneous disease, which is initiated and sustained by various molecular alterations in an array of signal transduction pathways. Heat-shock protein 90 (Hsp90) is a molecular chaperone and is critically implicated in folding and activation of a diverse group of client proteins, many of which are key regulators for glioblastoma biology. We here assessed the anti-neoplastic efficacy of a novel brain-penetrating Hsp90 inhibitor NXD30001 as a monotherapy and combined with radiation in vitro and in vivo. Our results demonstrated that NXD30001 potently inhibited neurosphere formation, growth, and survival of CD133+ GBM cells with the half maximal inhibitory concentration at low nanomolar range, but CD133- GBM cells were less sensitive to NXD30001. NXD30001 also increased radio-sensitivity in glioblastoma stem cells (GSCs) at suboptimal concentrations. Moreover, NXD30001 dose-dependently decreased phosphorylation levels of multiple Hsp90 client proteins which play key roles in GBM, such as EGFR, Akt, c-Myc, and Notch1. In addition, NXD30001 could impair DNA damage response and endoplasmic reticulum stress response after radiotherapy by alteration of the related proteins expression. In a murine orthotopic model of human glioblastoma, NXD30001 marvelously induced tumor regression and extended median survival of tumor-bearing mice by approximately 20% when compared with the vehicle group (37 d vs 31 d, P<0.05). Radiotherapy solely increased median survival of tumor-bearing mice from 31 d to 38 d (P<0.05), while NXD30001 combined with radiation further extended survival to 43 d (P<0.05). We concluded that GSCs are more sensitive to NXD30001 than non-stem GBM cells, and NXD30001 in combination with radiation exerts better inhibitive effect in GBM progression than monotherapy.

HSP90α combined with AFP and TK1 improved the diagnostic value for hepatocellular carcinoma

Aim: We investigated the effect of the combination of heat shock protein 90α (HSP90α), alpha-fetoprotein (AFP) and thymidine kinase 1 (TK1) in the diagnosis of hepatocellular carcinoma (HCC). Methods & results: A total of 409 patients with HCC, 101 patients with benign liver disorder and 78 healthy individuals were retrospectively analyzed. HSP90α level was higher in HCC patients than in controls. The expression of HSP90α showed a positive correlation with tumor stage, differentiation, lymph node metastasis and tumor thrombus formation. The combination of HSP90α, AFP and TK1 improved the diagnostic sensitivity (89.24%) and the area under the receiver operating characteristic curve (0.919). Conclusion: The detection of HSP90α, AFP and TK1 is more efficient than a single tumor marker for the diagnosis of HCC.

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.

The HSP90 inhibitor NVP-AUY922 inhibits growth of HER2 positive and trastuzumab-resistant breast cancer cells

As HER2 is a client protein of the molecular chaperone Hsp90, targeting Hsp90 may be beneficial in HER2-positive breast cancer. In this study, the activity of the Hsp90 inhibitor NVP-AUY922 was assessed in HER2 overexpressing breast cancer cell lines, including two cell line models of acquired trastuzumab-resistance. The seven HER2-positive breast cancer cell lines tested showed significant sensitivity to NVP-AUY922 in vitro, with IC₅₀ values between 6 and 17 nM. Combining NVP-AUY922 with chemotherapy did not improve response. NVP-AUY922 in combination with trastuzumab, significantly enhanced growth inhibition in three of the seven cell lines tested. In conclusion, our data shows that NVP-AUY922 displays potent anti-cancer activity in HER2-positive and trastuzumab-resistant breast cancer cells, and supports further testing of NVP-AUY922 in patients with HER2-positive breast cancer.

A Promising Serum Autoantibody Marker, Anti-Heat Shock Protein 90α, for Cholangiocarcinoma

The present study was designed to investigate cholangiocarcinoma (CCA) antibodies in hamster serum. Hamster CCA cell lines were processed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A candidate biomarker was confirmed by immunoprecipitation and western blot, and was further analyzed using ELISA and sera from normal control hamsters, hamsters with opisthorchiasis and hamsters with various stages of CCA, as well as from CCA patients and healthy individuals. One candidate marker was identified as HSP90α, as indicated by a high level of anti-HSP90α in hamster CCA sera. It was found that the levels of anti-HSP90α were specifically elevated in the sera of hamsters with CCA compared with other groups and progressively increased with the clinical stage. At the cut-off point of 0.4850 on the receiver operating characteristic curve, anti-HSP90α could discriminate CCA from healthy control groups with a sensitivity of 76.2%, specificity of 71.4% and total accuracy 75.5%. In the present study, we have shown that anti-HSP90α may be a potential useful serum biomarker to discriminate CCA cases from healthy persons.

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.

Targeting heat-shock protein 90 with ganetespib for molecularly targeted therapy of gastric cancer

Gastric cancer (GC) remains the fifth most common cancer worldwide. Heat-shock protein 90 (HSP90) has become an attractive therapeutic target in treating cancers, because of its abnormally high expression in cancers. Several successful cases of HSP90 inhibitors capable of inhibiting GC inspired us to try ganetespib, a clinically promising and actively investigated second-generation HSP90 inhibitor in GC treatment. In our study, we show that ganetespib markedly reduced the growth of MGC-803 and also significantly inhibited the growth of SGC-7901 and MKN-28 in a dose-dependent manner. It induced G2/M cell-cycle arrest and apoptosis in all three cell lines, together with the related markers affected significantly. Mechanistically, ganetespib caused pronounced decrease of expression of classic HSP90 client proteins. Specifically, it greatly affected epidermal growth factor receptor (EGFR) signaling cascades by markedly decreasing the levels of total EGFR and EGFR on cell membranes. EGFR knockdown also induced cell-cycle arrest and apoptosis accompanied with a decrease of several EGFR downstream proteins. These results strongly support that EGFR signaling greatly contributes to the ganetespib inhibitory effects. Besides, we found that the responses of GC cell lines to ganetespib correlated well with their EGFR expression levels: MGC-803, as well as AGS and BGC-803, with higher EGFR expression responded to ganetespib better, whereas SGC-7901 and MKN-28 with lower EGFR levels were much less sensitive to ganetespib. Although SGC-7901 and MKN-28 were not very sensitive to ganetespib, ganetespib worked synergistically with radiation and cisplatin in killing them. Importantly, ganetespib significantly inhibited the growth of xenograft tumors in vivo as a single agent or in combination with cisplatin. Results of hematoxylin/eosin staining, TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) assays, and immunohistochemistry staining of phosphorylated cyclin-dependent kinase 1 (pCDK1), EGFR and Ki-67 revealed significant differences in ganetespib-treated tumors. Collectively, our data suggest that ganetespib, as a new potent treatment option, can be used for the molecularly targeted therapy of GC patients according to their expression profiles of EGFR.

Protein chaperones: a composition of matter review (2008 - 2013)

INTRODUCTION

Heat shock proteins (Hsps) are proteins with important functions in regulating disease phenotypes. Historically, Hsp90 has first received recognition as a target in cancer, with consequent efforts extending its potential role to other diseases. Hsp70 has also attracted interest as a therapeutic target for its role as a co-chaperone to Hsp90 as well as its own anti-apoptotic roles.

AREAS COVERED

Herein, patents from 2008 to 2013 are reviewed to identify those that disclose composition of matter claimed to inhibit Hsp90 or Hsp70.

EXPERT OPINION

For Hsp90, there has been considerable creativity in the discovery of novel pharmacophores that fall outside the three initially discovered scaffolds (i.e., ansamycins, resorcinols and purines). Nonetheless, much of the patent literature appears to build on previously reported structure activity relationship through slight modifications of Hsp90 inhibitor space by finding weaknesses in existing patents. The major goal of future development of Hsp90 inhibitors is not necessarily identifying better molecules but rather understanding how to rationally use these agents in the clinic. The development of Hsp70 inhibitors has lagged behind. It will require a more concerted effort from the drug discovery community in order to begin to realize the potential of this target.

Hsp90 inhibitor as a sensitizer of cancer cells to different therapies (review)

Hsp90 is a molecular chaperone that maintains the structural and functional integrity of various client proteins involved in signaling and many other functions of cancer cells. The natural inhibitors, ansamycins influence the Hsp90 chaperone function by preventing its binding to client proteins and resulting in their proteasomal degradation. N- and C-terminal inhibitors of Hsp90 and their analogues are widely tested as potential anticancer agents in vitro, in vivo as well as in clinical trials. It seems that Hsp90 competitive inhibitors target different tumor types at nanomolar concentrations and might have therapeutic benefit. On the contrary, some Hsp90 inhibitors increased toxicity and resistance of cancer cells induced by heat shock response, and through the interaction of survival signals, that occured as side effects of treatments, could be very effectively limited via combination of therapies. The aim of our review was to collect the data from experimental and clinical trials where Hsp90 inhibitor was combined with other therapies in order to prevent resistance as well as to potentiate the cytotoxic and/or antiproliferative effects.

Enhanced antitumor activity of erlotinib in combination with the Hsp90 inhibitor CH5164840 against non-small-cell lung cancer

Inhibition of heat shock protein 90 (Hsp90) can lead to degradation of multiple client proteins, which are involved in tumor progression. Epidermal growth factor receptor (EGFR) is one of the most potent oncogenic client proteins of Hsp90. Targeted inhibition of EGFR has shown clinical efficacy in the treatment of patients with non-small-cell lung cancer (NSCLC). However, primary and acquired resistance to the existing EGFR inhibitors is a major clinical problem. In the present study, we investigated the effect of the novel Hsp90 inhibitor CH5164840 on the antitumor activity of erlotinib. The NSCLC cell lines and xenograft models were treated with CH5164840 and erlotinib to examine their mechanisms of action and cell growth inhibition. We found that CH5164840 showed remarkable antitumor activity against NSCLC cell lines and xenograft models. The addition of CH5164840 enhanced the antitumor activity of erlotinib against NCI-H292 EGFR-overexpressing xenograft models. Phosphorylation of Stat3 increased with erlotinib treatment in NCI-H292 cells, which was abrogated by Hsp90 inhibition. Furthermore, in a NCI-H1975 T790M mutation erlotinib-resistant model, CH5164840 enhanced the antitumor activity of erlotinib despite the low efficacy of erlotinib treatment alone. In addition, ERK signaling was effectively suppressed by combination treatment with erlotinib and CH5164840 in a NCI-H1975 erlotinib-resistant model. Taken together, these data indicate that CH5164840 has potent antitumor activity and is highly effective in combination with erlotinib against NSCLC tumors with EGFR overexpression and mutations. Our results support the therapeutic potential of CH5164840 as a Hsp90 inhibitor for combination therapy with EGFR-targeting agents against EGFR-addicted NSCLC.

A first in human, safety, pharmacokinetics, and clinical activity phase I study of once weekly administration of the Hsp90 inhibitor ganetespib (STA-9090) in patients with solid malignancies

Background

This phase I study investigated the maximum tolerated dose (MTD), safety, pharmacokinetics and antitumor activity of ganetespib in patients with solid malignancies.

Methods

Patients were enrolled in cohorts of escalating ganetespib doses, given as 1 hour IV infusion, once weekly for 3 weeks, followed by a 1-week rest until disease progression or unacceptable toxicity. Endpoints included safety, pharmacokinetic and pharmacodynamic parameters and preliminary clinical activity.

Results

Fifty-three patients were treated at doses escalating from 7 to 259 mg/m². The most common adverse events were Grade 1 and 2 diarrhea, fatigue, nausea or vomiting. Dose-limiting toxicities (DLT) observed were: one Grade 3 amylase elevation (150 mg/m²), one Grade 3 diarrhea and one Grade 3 and one Grade 4 asthenia (259 mg/m²). The MTD was 216 mg/m² and the recommended phase 2 dose was established at 200 mg/m² given IV at Days 1, 8, and 15 every 4 weeks. There was a linear relationship between dose and exposure. Plasma HSP70 protein levels remained elevated for over a week post treatment. Disease control rate (objective response and stable disease at ≥ 16 weeks) was 24.4%.

Conclusions

Ganetespib is well tolerated as a weekly infusion for 3 of every 4 weeks cycle. The recommended phase II dose is 200 mg/m², and is associated with an acceptable tolerability profile.

Trial registration

NCT00687934

Discovery of survivin inhibitors and beyond: FL118 as a proof of concept

Survivin, a novel antiapoptotic protein molecule, plays a central role in cancer cell survival/proliferation networks and has therefore become a therapeutic target for cancer drug discovery efforts. There are two strategies for discovering survivin inhibitors. One is based on survivin interactions within the cell and the other strategy is based on blocking survivin expression. Survivin inhibitors developed by the first strategy would disrupt a particular survivin function. These survivin inhibitors could also be useful tools for delineating the mechanism of action of survivin. The second strategy may use a reporter system of the survivin gene to screen drug libraries. To date, two molecules, YM155 and FL118, have been identified using this strategy. These two examples provide a proof of concept that screens for inhibitors of survivin expression using survivin gene reporter assays as surrogate markers will uncover versatile small molecules that not only inhibit survivin but also inhibit other essential cancer survival/proliferation-associated targets and/or signaling pathways. This review provides an overview of current information in the area relevant to survivin inhibitors that may facilitate future studies.

Radicicol, an Hsp90 inhibitor, inhibits intestinal inflammation and leakage in abdominal sepsis

BACKGROUND

Intestinal injury is a key feature in sepsis. Inhibitors of heat shock protein 90 (Hsp90) have been shown to exert protective effects in models of inflammation. Herein, we hypothesized that Hsp90 might regulate intestinal inflammation and leakage in abdominal sepsis.

MATERIALS AND METHODS

Male C57BL/6 mice were pretreated with radicicol (60 mg/kg), which is a specific inhibitor of Hsp90, prior to cecal ligation and puncture (CLP). Intravital fluorescence microscopy was used to quantify leukocyte-endothelium interactions in the colonic microcirculation 6 h after CLP. Colonic tissue was harvested to determine levels of myeloperoxidase, tumor necrosis factor-α and CXC chemokines. Intestinal injury was examined by histology. Intestinal barrier function was quantified by leakage of fluorescein isothiocyanate-dextran from the vascular system out into the abdominal cavity after intravenous injection.

RESULTS

We found that radicicol significantly decreased CLP-induced leukocyte rolling and adhesion in colonic venules. Inhibition of Hsp90 reduced colonic levels of myeloperoxidase by 24% in septic animals. Moreover, radicicol significantly decreased CLP-provoked formation of CXC chemokines but had no significant effect on tumor necrosis factor-α levels in the colon. Notably, Hsp90 inhibition significantly attenuated intestinal tissue injury evoked by CLP. Lastly, it was found that radicicol reduced sepsis-induced intestinal leakage by 43%.

CONCLUSION

Our novel findings suggest that targeting Hsp90 protects against intestinal inflammation and leakage and might be a useful strategy to ameliorate intestinal failure in polymicrobial sepsis.

Enzymatic glycosylation of nonbenzoquinone geldanamycin analogs via Bacillus UDP-glycosyltransferase

Geldanamycin (GM) is a naturally occurring anticancer agent isolated from several strains of Streptomyces hygroscopicus. However, its potential clinical utility is compromised by its severe toxicity and poor water solubility. For this reason, considerable efforts are under way to make new derivatives that have both good clinical efficacy and high water solubility. On the other hand, glycosylation is often a step that improves the water solubility and/or biological activity in many natural products of biosynthesis. Here, we report the facile production of glucose-conjugated nonbenzoquinone GM analogs using the Bacillus UDP-glycosyltransferase BL-C. Five aglycon substrates containing nonbenzoquinone aromatic rings were chosen to validate the in vitro glycosylation reaction. Putative glucoside compounds were determined through the presence of a product peak(s) and were also verified using LC/MS analyses. Further, the chemical structures of new glucoside compounds 6 and 7 were elucidated using spectroscopy data. These glucoside compounds showed a dramatic improvement in water solubility compared with that of the original aglycon, nonbenzoquinone GM.

Fluorine- and rhenium-containing geldanamycin derivatives as leads for the development of molecular probes for imaging Hsp90

Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone responsible for protein quality control in cells. Hsp90 has been shown to be overexpressed in many human cancers. This has prompted extensive research on Hsp90 inhibitors as novel anticancer agents and, more recently, the development of molecular probes for imaging Hsp90 expression in vivo. This work describes the development of various fluorine-containing and rhenium-containing geldanamycin derivatives as leads for the development of corresponding (18)F-labeled and (99m)Tc-labeled PET and SPECT probes for molecular imaging of Hsp90 expression. All compounds were evaluated in an in vitro ATPase activity assay using Hsp90 isoform Hsp82p. Fluorobenzoylated geldanamycin derivative 5 displayed comparable inhibitory potency like parent compound geldanamycin.

Fragment-based discovery of hydroxy-indazole-carboxamides as novel small molecule inhibitors of Hsp90

Inhibitors of the Hsp90 molecular chaperone are showing considerable promise as potential molecular therapeutic agents for the treatment of cancer. Here we describe the identification of novel small molecular weight inhibitors of Hsp90 using a fragment based approach. Fragments were selected by docking, tested in a biochemical assay and the confirmed hits were crystallized. Information gained from X-ray structures of these fragments and other chemotypes was used to drive the fragment evolution process. Optimization of these high μM binders resulted in 3-benzylindazole derivatives with significantly improved affinity and anti-proliferative effects in different human cancer cell lines.

Isoxazolo(aza)naphthoquinones: a new class of cytotoxic Hsp90 inhibitors

A series of 3-aryl-naphtho[2,3-d]isoxazole-4,9-diones and some of their 6-aza analogues were synthesized and found to inhibit the heat shock protein 90 (Hsp90). The compounds were tested for their binding to Hsp90 and for their effects on Hsp90 client proteins expression in a series of human tumour cell lines. Representative compounds (7f, 10c) downregulated the Hsp90 client proteins EGFR, Akt, Cdk4, Raf-1, and survivin, and upregulated Hsp70. Most of the compounds, in particular the alkylated 3-pyridyl derivatives, exhibited potent antiproliferative activity, down to two-digit nanomolar range. Preliminary results indicated in vivo activity of 7f against human epithelial carcinoma A431 model growing as tumour xenograft in nude mice, thus supporting the therapeutic potential of this novel series of Hsp90 inhibitors.

Anti-inflammatory properties and pharmacological induction of Hsp70 after brain injury

The 70-kDa heat shock protein (Hsp70) is thought to protect the brain from a variety of insults. Although the mechanism has been largely limited to its chaperone functions, recent work indicates that Hsp70 also modulates inflammatory pathways. Brain injury and ischemia are associated with an immune response that is largely innate. Hsp70 appears to suppress this response and lead to improved neurological outcome. However, most of this work has relied on the use of genetic mutant models or Hsp70 overexpression using gene transfer or heat stress, thus limiting its translational utility. A few compounds have been studied by various disciplines which, through their ability to inhibit Hsp90, can cause induction of Hsp70. The investigation of Hsp70-inducing pharmacological compounds has obvious clinical implications in terms of potential therapies to mitigate neuroinflammation and lead to neuroprotection from stroke or traumatic brain injury. This review will focus on the inflammation modulating properties of Hsp70, and the current literature surrounding the pharmacological induction in acute neurological injury models with comments on potential applications at the clinical level.

Hsp90 molecular chaperone inhibitors: are we there yet?

Heat shock protein (Hsp) 90 is an ATP-dependent molecular chaperone that is exploited by malignant cells to support activated oncoproteins, including many cancer-associated kinases and transcription factors, and it is essential for oncogenic transformation. Originally viewed with skepticism, Hsp90 inhibitors are now being actively pursued by the pharmaceutical industry, with 17 agents having entered clinical trials. Investigators established Hsp90's druggability using the natural products geldanamycin and radicicol, which mimic the unusual ATP structure adopted in the chaperone's N-terminal nucleotide-binding pocket and cause potent and selective blockade of ATP binding/hydrolysis, inhibit chaperone function, deplete oncogenic clients, and show antitumor activity. Preclinical data obtained with these natural products have heightened interest in Hsp90 as a drug target, and 17-allylamino-17-demethoxygeldanamycin (17-AAG, tanespimycin) has shown clinical activity (as defined by Response Evaluation Criteria in Solid Tumors) in HER2+ breast cancer. Many optimized synthetic, small-molecule Hsp90 inhibitors from diverse chemotypes are now in clinical trials. Here, we review the discovery and development of Hsp90 inhibitors and assess their potential. There has been significant learning from studies of the basic biology of Hsp90, as well as translational drug development involving this chaperone, enhanced by the use of Hsp90 inhibitors as chemical probes. Success will likely lie in treating cancers that are addicted to particular driver oncogene products (e.g., HER2, ALK, EGFR, and BRAF) that are sensitive Hsp90 clients, as well as malignancies (especially multiple myeloma) in which buffering of proteotoxic stress is critical for survival. We discuss approaches for enhancing the effectiveness of Hsp90 inhibitors and highlight new chaperone and stress-response pathway targets, including HSF1 and Hsp70.