Phase I pharmacokinetic-pharmacodynamic study of 17-(allylamino)-17-demethoxygeldanamycin (17AAG, NSC 330507), a novel inhibitor of heat shock protein 90, in patients with refractory advanced cancers

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 Among these trials, 60 % have been completed, 10 % are currently active, and 30 % have been suspended, terminated, or withdrawn.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.

Pharmacokinetics, Dose-Proportionality, and Tolerability of Intravenous Tanespimycin (17-AAG) in Single and Multiple Doses in Dogs: A Potential Novel Treatment for Canine Visceral Leishmaniasis

In the New World, dogs are considered the main reservoir of visceral leishmaniasis (VL). Due to inefficacies in existing treatments and the lack of an efficient vaccine, dog culling is one of the main strategies used to control disease, making the development of new therapeutic interventions mandatory. We previously showed that Tanespimycin (17-AAG), a Hsp90 inhibitor, demonstrated potential for use in leishmaniasis treatment. The present study aimed to test the safety of 17-AAG in dogs by evaluating plasma pharmacokinetics, dose-proportionality, and the tolerability of 17-AAG in response to a dose-escalation protocol and multiple administrations at a single dose in healthy dogs. Two protocols were used: Study A: four dogs received variable intravenous (IV) doses (50, 100, 150, 200, or 250 mg/m2) of 17-AAG or a placebo (n = 4/dose level), using a cross-over design with a 7-day "wash-out" period; Study B: nine dogs received three IV doses of 150 mg/m2 of 17-AAG administered at 48 h intervals. 17-AAG concentrations were determined by a validated high-performance liquid chromatographic (HPLC) method: linearity (R2 = 0.9964), intra-day precision with a coefficient of variation (CV) ≤ 8%, inter-day precision (CV ≤ 20%), and detection and quantification limits of 12.5 and 25 ng/mL, respectively. In Study A, 17-AAG was generally well tolerated. However, increased levels of liver enzymes-alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT)-and bloody diarrhea were observed in all four dogs receiving the highest dosage of 250 mg/m2. After single doses of 17-AAG (50-250 mg/m2), maximum plasma concentrations (Cmax) ranged between 1405 ± 686 and 9439 ± 991 ng/mL, and the area under the curve (AUC) plotting plasma concentration against time ranged between 1483 ± 694 and 11,902 ± 1962 AUC 0-8 h μg/mL × h, respectively. Cmax and AUC parameters were dose-proportionate between the 50 and 200 mg/m2 doses. Regarding Study B, 17-AAG was found to be well tolerated at multiple doses of 150 mg/m2. Increased levels of liver enzymes-ALT (28.57 ± 4.29 to 173.33 ± 49.56 U/L), AST (27.85 ± 3.80 to 248.20 ± 85.80 U/L), and GGT (1.60 ± 0.06 to 12.70 ± 0.50 U/L)-and bloody diarrhea were observed in only 3/9 of these dogs. After the administration of multiple doses, Cmax and AUC 0-48 h were 5254 ± 2784 μg/mL and 6850 ± 469 μg/mL × h in plasma and 736 ± 294 μg/mL and 7382 ± 1357 μg/mL × h in tissue transudate, respectively. In conclusion, our results demonstrate the potential of 17-AAG in the treatment of CVL, using a regimen of three doses at 150 mg/m2, since it presents the maintenance of high concentrations in subcutaneous interstitial fluid, low toxicity, and reversible hepatotoxicity.

Modulation of the tumor microenvironment and mechanism of immunotherapy-based drug resistance in breast cancer

Breast cancer, the most frequent female malignancy, is often curable when detected at an early stage. The treatment of metastatic breast cancer is more challenging and may be unresponsive to conventional therapy. Immunotherapy is crucial for treating metastatic breast cancer, but its resistance is a major limitation. The tumor microenvironment (TME) is vital in modulating the immunotherapy response. Various tumor microenvironmental components, such as cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs), are involved in TME modulation to cause immunotherapy resistance. This review highlights the role of stromal cells in modulating the breast tumor microenvironment, including the involvement of CAF-TAM interaction, alteration of tumor metabolism leading to immunotherapy failure, and other latest strategies, including high throughput genomic screening, single-cell and spatial omics techniques for identifying tumor immune genes regulating immunotherapy response. This review emphasizes the therapeutic approach to overcome breast cancer immune resistance through CAF reprogramming, modulation of TAM polarization, tumor metabolism, and genomic alterations.

Phase Ib study of HSP90 inhibitor, onalespib (AT13387), in combination with paclitaxel in patients with advanced triple-negative breast cancer

Background

Heat shock protein 90 (HSP90) is a molecular chaperone required for stabilization of client proteins over-activated in triple-negative breast cancer (TNBC). Over-expression of HSP90 client proteins has been implicated in paclitaxel resistance. Onalespib (AT13387) is a potent inhibitor of HSP90 that could improve paclitaxel efficacy when administered in combination.

Design

This phase Ib trial administered onalespib with paclitaxel in patients with advanced TNBC to assess safety and establish a recommended phase II dose (RP2D).

Objectives

The primary objectives were determining the dose-limiting toxicities and maximum tolerated dose of combination therapy. Secondary objectives included pharmacokinetic (PK) analysis and determination of overall response rate (ORR), duration of response (DOR), and progression-free survival (PFS).

Methods

Patients with advanced TNBC were treated with standard dose intravenous paclitaxel in combination with intravenous onalespib at doses ranging from 120 to 260 mg/m2 administered on days 1, 8, and 15 of a 28-day cycle using a standard 3 + 3 design. A total of 15 patients were enrolled to dose expansion cohort at RP2D to confirm safety profile.

Results

Thirty-one patients were enrolled in the study, of which over 90% had received prior taxane therapy. Paclitaxel was given for metastatic disease in 23% of patients. Adverse events (AEs) included anemia (grade 3: 20%), lymphopenia (grade 3: 17%), and neutropenia (grade 3: 33%, grade 4: 4%). The most frequent grade ⩾3 non-hematologic AE was diarrhea (7%). The established RP2D was 260 mg/m2 onalespib when given with paclitaxel at 80 mg/m2. PK analysis revealed a modest drug interaction profile for onalespib in the combination regimen. ORR was 20%. Three patients achieved complete responses, all of whom had received prior taxane therapy. Median DOR was 5.6 months; median PFS was 2.9 months.

Conclusion

Combination treatment with onalespib and paclitaxel had an acceptable toxicity profile and RP2D was determined to be 260 mg/m2 of onalespib. Combination therapy showed antitumor activity in patients with advanced TNBC.

Trial registration

Onalespib and paclitaxel in treating patients with advanced TNBC https://clinicaltrials.gov/ct2/show/NCT02474173.

Chaperone-assisted E3 ligase CHIP: A double agent in cancer

The carboxy-terminus of Hsp70-interacting protein (CHIP) is a ubiquitin ligase and co-chaperone belonging to Ubox family that plays a crucial role in the maintenance of cellular homeostasis by switching the equilibrium of the folding-refolding mechanism towards the proteasomal or lysosomal degradation pathway. It links molecular chaperones viz. HSC70, HSP70 and HSP90 with ubiquitin proteasome system (UPS), acting as a quality control system. CHIP contains charged domain in between N-terminal tetratricopeptide repeat (TPR) and C-terminal Ubox domain. TPR domain interacts with the aberrant client proteins via chaperones while Ubox domain facilitates the ubiquitin transfer to the client proteins for ubiquitination. Thus, CHIP is a classic molecule that executes ubiquitination for degradation of client proteins. Further, CHIP has been found to be indulged in cellular differentiation, proliferation, metastasis and tumorigenesis. Additionally, CHIP can play its dual role as a tumor suppressor as well as an oncogene in numerous malignancies, thus acting as a double agent. Here, in this review, we have reported almost all substrates of CHIP established till date and classified them according to the hallmarks of cancer. In addition, we discussed about its architectural alignment, tissue specific expression, sub-cellular localization, folding-refolding mechanisms of client proteins, E4 ligase activity, normal physiological roles, as well as involvement in various diseases and tumor biology. Further, we aim to discuss its importance in HSP90 inhibitors mediated cancer therapy. Thus, this report concludes that CHIP may be a promising and worthy drug target towards pharmaceutical industry for drug development.

Cellular Senescence in Idiopathic Pulmonary Fibrosis

Cellular senescence (CS) is increasingly implicated in the etiology of age-related diseases. While CS can facilitate physiological processes such as tissue repair and wound healing, senescent cells also contribute to pathophysiological processes involving macromolecular damage and metabolic dysregulation that characterize multiple morbid and prevalent diseases, including Alzheimer’s disease, osteoarthritis, atherosclerotic vascular disease, diabetes mellitus, and idiopathic pulmonary fibrosis (IPF). Preclinical studies targeting senescent cells and the senescence-associated secretory phenotype (SASP) with “senotherapeutics” have demonstrated improvement in age-related morbidity associated with these disease states. Despite promising results from these preclinical trials, few human clinical trials have been conducted. A first-in-human, open-label, pilot study of the senolytic combination of dasatinib and quercetin (DQ) in patients with IPF showed improved physical function and mobility. In this review, we will discuss our current understanding of cellular senescence, its role in age-associated diseases, with a specific focus on IPF, and potential for senotherapeutics in the treatment of fibrotic lung diseases.

UBQLN2-HSP70 axis reduces poly-Gly-Ala aggregates and alleviates behavioral defects in the C9ORF72 animal model

Expansion of a hexanucleotide repeat GGGGCC (G4C2) in the intron of the C9ORF72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9-ALS/FTD). Transcripts carrying G4C2 repeat expansions generate neurotoxic dipeptide repeat (DPR) proteins, including poly-Gly-Ala (poly-GA), which tends to form protein aggregates. Here, we demonstrate that UBQLN2, another ALS/FTD risk factor, is recruited to reduce poly-GA aggregates and alleviate poly-GA-induced neurotoxicity. UBQLN2 could recognize HSP70 ubiquitination, which facilitates the UBQLN2-HSP70-GA complex formation and promotes poly-GA degradation. ALS/FTD-related UBQLN2 mutants fail to bind HSP70 and clear poly-GA aggregates. Disruption of the interaction between UBQLN2 and HSP70 inhibits poly-GA aggregation in C9-ALS/FTD iPSC-derived neurons. Finally, enhancing HSP70 by the chemical compound 17AAG at the adult stage mitigates behavioral defects in poly-GA animals. Our findings suggest a critical role of the UBQLN2-HSP70 axis in protein aggregate clearance in C9-ALS/FTD.

Design, Synthesis and In Vitro Investigation of Novel Basic Celastrol Carboxamides as Bio-Inspired Leishmanicidal Agents Endowed with Inhibitory Activity against Leishmania Hsp90

The natural triterpene celastrol (CE) is here used as lead compound for the design and synthesis of a panel of eleven CE carboxamides that were tested in vitro for their growth inhibitory activity against Leishmania infantum and L.tropica parasites. Among them, in vitro screening identified four basic CE carboxamides endowed with nanomolar leishmanicidal activity, against both the promastigotes and the intramacrophage Leishmania amastigotes forms. These compounds also showed low toxicity toward two human (HMEC-1 and THP-1) and one murine (BMDM) cell lines. Interestingly, the most selective CE analogue (compound 3) was also endowed with the ability to inhibit the ATPase activity of the Leishmania protein chaperone Hsp90 as demonstrated by the in vitro assay conducted on a purified, full-length recombinant protein. Preliminary investigations by comparing it with the naturally occurring Hsp90 active site inhibitor Geldanamycin (GA) in two different in vitro experiments were performed. These promising results set the basis for a future biochemical investigation of the mode of interaction of celastrol and CE-inspired compounds with Leishmania Hsp90.

Direct targeting of HSP90 with daurisoline destabilizes β-catenin to suppress lung cancer tumorigenesis

Lung cancer is the most frequent cancer worldwide with a poor prognosis. Identification of novel cancer targets and useful therapeutic strategies without toxicity are urgently needed. In this study, we screened natural products for anticancer bioactivity in a library consisting of 429 small molecules. We demonstrated for the first time that daurisoline, a constituent of Rhizoma Menispermi, repressed lung cancer cell proliferation by inducing cell cycle arrest at the G1 phase. Furthermore, daurisoline was found not only to suppress the growth of lung tumor xenografts in animals without obvious side effects, but also to inhibit cell migration and invasion. Mechanistically, quantitative proteomics and bioinformatics analyses, Western blotting and qRT-PCR confirmed that daurisoline exerted its anticancer effects by inhibiting the expression levels of β-catenin and its downstream targets c-myc and cyclin D1. Furthermore, our data from Drug Affinity Responsive Target Stability (DARTS), isothermal titration calorimetry (ITC) and a series of functional assays demonstrated that daurisoline could target HSP90 directly and disrupt its interaction with β-catenin, therefore increasing the ubiquitin-mediated proteasomal degradation of β-catenin. This study reveals that daurisoline could be a promising therapeutic strategy for the treatment of lung cancer.

Chetomin, a Hsp90/HIF1α pathway inhibitor, effectively targets lung cancer stem cells and non-stem cells

Non-small cell lung cancer (NSCLC) remains recalcitrant to effective treatment due to tumor relapse and acquired resistance. Cancer stem cells (CSCs) are believed to be one mechanism for relapse and resistance and are consequently considered promising drug targets. We report that chetomin, an active component of Chaetomium globosum, blocks heat shock protein 90/hypoxia-inducible factor 1 alpha (Hsp90/HIF1α) pathway activity. Chetomin also attenuated sphere-forming, a stem cell-like characteristic, of NSCLC CSCs (at ~ nM range) and the proliferation of non-CSCs NSCLC cultures and chemoresistant sublines (at ~ μM range). At these concentrations, chetomin exerted a marginal influence on noncancerous cells originating from several organs. Chetomin markedly decreased in vivo tumor formation in a spontaneous Kras ^LA1 lung cancer model, flank xenograft models, and a tumor propagation flank implanted model at doses that did not produce an observable toxicity to the animals. Chetomin blocked Hsp90/HIF1α pathway activity via inhibiting the Hsp90-HIF1α binding interaction without affecting Hsp90 or Hsp70 protein levels. This study advocates chetomin as a Hsp90/HIF1α pathway inhibitor and a potent, nontoxic NSCLC CSC-targeting molecule.

Approaches to develop therapeutics to treat frontotemporal dementia

Frontotemporal degeneration (FTD) is a complex disease presenting as a spectrum of clinical disorders with progressive degeneration of frontal and temporal brain cortices and extensive neuroinflammation that result in personality and behavior changes, and eventually, death. There are currently no effective therapies for FTD. While 60-70% of FTD patients are sporadic cases, the other 30-40% are heritable (familial) cases linked to mutations in several known genes. We focus here on FTD caused by mutations in the GRN gene, which encodes a secreted protein, progranulin (PGRN), that has diverse roles in regulating cell survival, immune responses, and autophagy and lysosome function in the brain. FTD-linked mutations in GRN reduce brain PGRN levels that lead to autophagy and lysosome dysfunction, TDP43 accumulation, excessive microglial activation, astrogliosis, and neuron death through still poorly understood mechanisms. PGRN insufficiency has also been linked to Alzheimer's disease (AD), and so the development of therapeutics for GRN-linked FTD that restore PGRN levels and function may have broader application for other neurodegenerative diseases. This review focuses on a strategy to increase PGRN to functional, healthy levels in the brain by identifying novel genetic and chemical modulators of neuronal PGRN levels. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Traditional and Novel Mechanisms of Heat Shock Protein 90 (HSP90) Inhibition in Cancer Chemotherapy Including HSP90 Cleavage

HSP90 is a molecular chaperone that increases the stability of client proteins. Cancer cells show higher HSP90 expression than normal cells because many client proteins play an important role in the growth and survival of cancer cells. HSP90 inhibitors mainly bind to the ATP binding site of HSP90 and inhibit HSP90 activity, and these inhibitors can be distinguished as ansamycin and non-ansamycin depending on the structure. In addition, the histone deacetylase inhibitors inhibit the activity of HSP90 through acetylation of HSP90. These HSP90 inhibitors have undergone or are undergoing clinical trials for the treatment of cancer. On the other hand, recent studies have reported that various reagents induce cleavage of HSP90, resulting in reduced HSP90 client proteins and growth suppression in cancer cells. Cleavage of HSP90 can be divided into enzymatic cleavage and non-enzymatic cleavage. Therefore, reagents inducing cleavage of HSP90 can be classified as another class of HSP90 inhibitors. We discuss that the cleavage of HSP90 can be another mechanism in the cancer treatment by HSP90 inhibition.

Spotlight on 17-AAG as an Hsp90 inhibitor for molecular targeted cancer treatment

Hsp90 is a ubiquitous chaperone with important roles in the organization and maturation of client proteins that are involved in the progression and survival of cancer cells. Multiple oncogenic pathways can be affected by inhibition of Hsp90 function through degradation of its client proteins. That makes Hsp90 a therapeutic target for cancer treatment. 17-allylamino-17-demethoxy-geldanamycin (17-AAG) is a potent Hsp90 inhibitor that binds to Hsp90 and inhibits its chaperoning function, which results in the degradation of Hsp90's client proteins. There have been several preclinical studies of 17-AAG as a single agent or in combination with other anticancer agents for a wide range of human cancers. Data from various phases of clinical trials show that 17-AAG can be given safely at biologically active dosages with mild toxicity. Even though 17-AAG has suitable pharmacological potency, its low water solubility and high hepatotoxicity could significantly restrict its clinical use. Nanomaterials-based drug delivery carriers may overcome these drawbacks. In this paper, we review preclinical and clinical research on 17-AAG as a single agent and in combination with other anticancer agents. In addition, we highlight the potential of using nanocarriers and nanocombination therapy to improve therapeutic effects of 17-AAG.

Targeted cancer therapy through 17-DMAG as an Hsp90 inhibitor: Overview and current state of the art

Heat shock protein 90 (Hsp90) is an evolutionary preserved molecular chaperone which mediates many cellular processes such as cell transformation, proliferation, and survival in normal and stress conditions. Hsp90 plays an important role in folding, maturation, stabilization and activation of Hsp90 client proteins which all contribute to the development, and proliferation of cancer as well as other inflammatory diseases. Functional inhibition of Hsp90 can have a massive effect on various oncogenic and inflammatory pathways, and will result in the degradation of their client proteins. This turns it into an interesting target in the treatment of different malignancies. 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) as a semi-synthetic derivative of geldanamycin, has several advantages over 17-Allylamino-17-demethoxygeldanamycin (17-AAG) such as higher water solubility, good bioavailability, reduced metabolism, and greater anti-tumour capability. 17-DMAG binds to the Hsp90, and inhibits its function which eventually results in the degradation of Hsp90 client proteins. Here, we reviewed the pre-clinical data and clinical trial data on 17-DMAG as a single agent, in combination with other agents and loaded on nanomaterials in various cancers and inflammatory diseases.

Panaxynol, a natural Hsp90 inhibitor, effectively targets both lung cancer stem and non-stem cells

Cancer stem-like cells (CSCs) contribute to tumor recurrence and chemoresistance. Hence, strategies targeting CSCs are crucial for effective anticancer therapies. Here, we demonstrate the capacities of the non-saponin fraction of Panax ginseng and its active principle panaxynol to inhibit Hsp90 function and viability of both non-CSC and CSC populations of NSCLC in vitro and in vivo. Panaxynol inhibited the sphere forming ability of NSCLC CSCs at nanomolar concentrations, and micromolar concentrations of panaxynol suppressed the viability of NSCLC cells (non-CSCs) and their sublines carrying acquired chemoresistance with minimal effect on normal cells derived from various organs. Orally administered panaxynol significantly reduced lung tumorigenesis in Kras^G12D/+ transgenic mice and mice carrying NSCLC xenografts without detectable toxicity. Mechanistically, panaxynol disrupted Hsp90 function by binding to the N-terminal and C-terminal ATP-binding pockets of Hsp90 without increasing Hsp70 expression. These data suggest the potential of panaxynol as a natural Hsp90 inhibitor targeting both the N-terminal and C-terminal of Hsp90 with limited toxicities.

Heat Shock Protein (HSP) Drug Discovery and Development: Targeting Heat Shock Proteins in Disease

Heat shock proteins (HSPs) present as a double edged sword. While they play an important role in maintaining protein homeostasis in a normal cell, cancer cells have evolved to co-opt HSP function to promote their own survival. As a result, HSPs such as HSP90 have attracted a great deal of interest as a potential anticancer target. These efforts have resulted in over 20 distinct compounds entering clinical evaluation for the treatment of cancer. However, despite the potent anticancer activity demonstrated in preclinical models, to date no HSP90 inhibitor has obtained regulatory approval. In this review we discuss the unique challenges faced in targeting HSPs that have likely contributed to their lack of progress in the clinic and suggest ways to overcome these so that the enormous potential of these compounds to benefit patients can finally be realized. We also provide a guideline for the future development of HSP-targeted agents based on the many lessons learned during the last two decades in developing HSP90 inhibitors.

Induced protein degradation: an emerging drug discovery paradigm

Small-molecule drug discovery has traditionally focused on occupancy of a binding site that directly affects protein function, and this approach typically precludes targeting proteins that lack such amenable sites. Furthermore, high systemic drug exposures may be needed to maintain sufficient target inhibition in vivo, increasing the risk of undesirable off-target effects. Induced protein degradation is an alternative approach that is event-driven: upon drug binding, the target protein is tagged for elimination. Emerging technologies based on proteolysis-targeting chimaeras (PROTACs) that exploit cellular quality control machinery to selectively degrade target proteins are attracting considerable attention in the pharmaceutical industry owing to the advantages they could offer over traditional small-molecule strategies. These advantages include the potential to reduce systemic drug exposure, the ability to counteract increased target protein expression that often accompanies inhibition of protein function and the potential ability to target proteins that are not currently therapeutically tractable, such as transcription factors, scaffolding and regulatory proteins.

Pharmacologic inhibition of Hsp90 to prevent GLT-1 degradation as an effective therapy for epilepsy

Sha et al. report that Hsp90β, which is up-regulated in astrocytes of human epileptogenic tissue, interacts with GLT-1 and recruits it to 20S proteasome for degradation. The Hsp90 inhibitor 17AAG exhibits beneficial effects in a model of temporal lobe epilepsy.

The glutamate transporter GLT-1 is critical for the maintenance of low interstitial glutamate concentrations. Loss of GLT-1 is commonly observed in neurological disorders, including temporal lobe epilepsy (TLE). Despite the hypothesis that targeting the mechanisms of GLT-1 deficiency may be a novel strategy for treating drug-resistant epilepsy, the underlying molecular cascade remains largely unknown. Here, we show that Hsp90β is up-regulated in reactive astrocytes of the epileptic hippocampus in patients with TLE and mouse models of epilepsy. Inhibition of Hsp90, but not Hsp70, increased GLT-1 levels. Mechanistically, Hsp90β recruits GLT-1 to the 20S proteasome, thereby promoting GLT-1 degradation. Hsp90 inhibitor prevents GLT-1 degradation by disrupting the association between Hsp90β and GLT-1. Using a model of TLE, we demonstrated that long-term systemic administration of 17AAG dramatically suppressed spontaneous recurrent seizures and ameliorated astrogliosis. Overall, these results suggest that up-regulation of GLT-1 by inhibiting Hsp90β in reactive astrocytes may be a potential therapeutic target for the treatment of epilepsy and excitotoxicity.

Heat Shock Protein 90 Regulates Subcellular Localization of Smads in Mv1Lu Cells

Heat shock protein 90 (HSP90) regulates the stability of various proteins and plays an essential role in cellular homeostasis. Many client proteins of HSP90 are involved in cell growth, survival, and migration; processes that are generally accepted as participants in tumorigenesis. HSP90 is also up-regulated in certain tumors. Indeed, the inhibition of HSP90 is known to be effective in cancer treatment. Recently, studies showed that HSP90 regulates transforming growth factor β1 (TGF-β1)-induced transcription by increasing the stability of the TGF-β receptor. TGF-β signaling also has been implicated in cancer, suggesting the possibility that TGF-β1 and HSP90 function cooperatively during the cancer cell progression. Here in this paper, we investigated the role of HSP90 in TGF-β1-stimulated Mv1Lu cells. Treatment of Mv1Lu cells with the HSP90 inhibitor, 17-allylamino-demethoxy-geldanamycin (17AAG), or transfection with truncated HSP90 (ΔHSP90) significantly reduced TGF-β1-induced cell migration. Pretreatment with 17AAG or transfection with ΔHSP90 also reduced the levels of phosphorylated Smad2 and Smad3. In addition, the HSP90 inhibition interfered the nuclear localization of Smads induced by constitutively active Smad2 (S2EE) or Smad3 (S3EE). We also found that the HSP90 inhibition decreased the protein level of importin-β1 which is known to regulate R-Smad nuclear translocation. These data clearly demonstrate a novel function of HSP90; HSP90 modulates TGF-β signaling by regulating Smads localization. Overall, our data could provide a detailed mechanism linking HSP90 and TGF-β signaling. The extension of our understanding of HSP90 would offer a better strategy for treating cancer.

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

Background

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

Methods

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

Results

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

Conclusions

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

Effects of treatment with an Hsp90 inhibitor in tumors based on 15 phase II clinical trials

Heat shock protein (Hsp)90 serves as a chaperone protein that promotes the proper folding of proteins involved in a variety of signal transduction processes involved in cell growth. Hsp90 inhibitors, which inhibit the activity of critical client proteins, have emerged as the accessory therapeutic agents for multiple human cancer types. To better understand the effects of Hsp90 inhibitors in cancer treatment, the present study reviewed 15 published phase II clinical trials to investigate whether Hsp90 inhibitors will benefit patients with cancer. Information of complete response, partial response, stable disease, objective response and objective response rate was collected to evaluate clinical outcomes. Overall, Hsp90 inhibitors are effective against a variety of oncogene-addicted cancers, including those that have developed resistance to specific receptors.

A cytosolic heat shock protein 90 and cochaperone CDC37 complex is required for RIP3 activation during necroptosis

Receptor-interacting protein kinase 3, RIP3, and a pseudokinase mixed lineage kinase-domain like protein, MLKL, constitute the core components of the necroptosis pathway, which causes programmed necrotic death in mammalian cells. Latent RIP3 in the cytosol is activated by several upstream signals including the related kinase RIP1, which transduces signals from the tumor necrosis factor (TNF) family of cytokines. We report here that RIP3 activation following the induction of necroptosis requires the activity of an HSP90 and CDC37 cochaperone complex. This complex physically associates with RIP3. Chemical inhibitors of HSP90 efficiently block necroptosis by preventing RIP3 activation. Cells with knocked down CDC37 were unable to respond to necroptosis stimuli. Moreover, an HSP90 inhibitor that is currently under clinical development as a cancer therapy was able to prevent systemic inflammatory response syndrome in rats treated with TNF-α. HSP90 and CDC37 cochaperone complex-mediated protein folding is thus an important part of the RIP3 activation process during necroptosis.

Heat shock protein 90β stabilizes focal adhesion kinase and enhances cell migration and invasion in breast cancer cells

Focal adhesion kinase (FAK) acts as a regulator of cellular signaling and may promote cell spreading, motility, invasion and survival in malignancy. Elevated expression and activity of FAK frequently correlate with tumor cell metastasis and poor prognosis in breast cancer. However, the mechanisms by which the turnover of FAK is regulated remain elusive. Here we report that heat shock protein 90β (HSP90β) interacts with FAK and the middle domain (amino acids 233-620) of HSP90β is mainly responsible for this interaction. Furthermore, we found that HSP90β regulates FAK stability since HSP90β inhibitor 17-AAG triggers FAK ubiquitylation and subsequent proteasome-dependent degradation. Moreover, disrupted FAK-HSP90β interaction induced by 17-AAG contributes to attenuation of tumor cell growth, migration, and invasion. Together, our results reveal how HSP90β regulates FAK stability and identifies a potential therapeutic strategy to breast cancer.

Novel small-molecule therapy of Hodgkin lymphoma

The treatment of Hodgkin lymphoma continues to be based on combination chemotherapy and radiation therapy. Although this treatment strategy produces a high cure rate, short- and long-term toxic effects continue to be problematic for young cured patients. In this review we focus on emerging novel therapies using small molecules that target specific survival pathways in the cancer cells. This approach is aimed at improving the cure rate while reducing treatment-related toxicity.

White matter loss in a mouse model of periventricular leukomalacia is rescued by trophic factors

Periventricular leukomalacia (PVL) is the most frequent cause of cerebral palsy and other intellectual disabilities, and currently there is no treatment. In PVL, glutamate excitotoxicity (GME) leads to abnormal oligodendrocytes (OLs), myelin deficiency, and ventriculomegaly. We have previously identified that the combination of transferrin and insulin growth factors (TSC1) promotes endogenous OL regeneration and remyelination in the postnatal and adult rodent brain. Here, we produced a periventricular white matter lesion with a single intracerebral injection of N-methyl-d-aspartate (NMDA). Comparing lesions produced by NMDA alone and those produced by NMDA + TSC1 we found that: NMDA affected survival and reduced migration of OL progenitors (OLPs). In contrast, mice injected with NMDA + TSC1 proliferated twice as much indicating that TSC1 supported regeneration of the OLP population after the insult. Olig2-mRNA expression showed 52% OLP survival in mice receiving a NMDA injection and increased to 78% when TSC1 + NMDA were injected simultaneously and ventricular size was reduced by TSC1. Furthermore, in striatal slices TSC1 reduced the inward currents induced by NMDA in medium-sized spiny neurons, demonstrating neuroprotection. Thus, white matter loss after excitotoxicity can be partially rescued as TSC1 conferred neuroprotection to preexisting OLP and regeneration via OLP proliferation. Furthermore, we showed that early TSC1 administration maximizes neuroprotection.

An improved route to 19-substituted geldanamycins as novel Hsp90 inhibitors--potential therapeutics in cancer and neurodegeneration

19-Substituted geldanamycin derivatives are efficient Hsp90 inhibitors, without the toxicity associated with the other benzoquinone ansamycins, thus giving them potential for use as molecular therapeutics in cancer and neurodegeneration. Here a new method of synthesising these important compounds is reported, eliminating the need for toxic metals and metalloids.

Phase I study of tanespimycin in combination with bortezomib in patients with advanced solid malignancies

PURPOSE

To determine the maximum tolerated dose (MTD) and characterize the dose-limiting toxicities (DLT) of tanespimycin when given in combination with bortezomib.

EXPERIMENTAL DESIGN

Phase I dose-escalating trial using a standard cohort "3+3" design performed in patients with advanced solid tumors. Patients were given tanespimycin and bortezomib twice weekly for 2 weeks in a 3 week cycle (days 1, 4, 8, 11 every 21 days).

RESULTS

Seventeen patients were enrolled in this study, fifteen were evaluable for toxicity, and nine patients were evaluable for tumor response. The MTD was 250 mg/m(2) of tanespimycin and 1.0 mg/m(2) of bortezomib when used in combination. DLTs of abdominal pain (13 %), complete atrioventricular block (7 %), fatigue (7 %), encephalopathy (7 %), anorexia (7 %), hyponatremia (7 %), hypoxia (7 %), and acidosis (7 %) were observed. There were no objective responses. One patient had stable disease.

CONCLUSIONS

The recommended phase II dose for twice weekly 17-AAG and PS341 are 250 mg/m(2) and 1.0 mg/m(2), respectively, on days 1, 4, 8 and 11 of a 21 day cycle.

A rat retinal damage model predicts for potential clinical visual disturbances induced by Hsp90 inhibitors

In human trials certain heat shock protein 90 (Hsp90) inhibitors, including 17-DMAG and NVP-AUY922, have caused visual disorders indicative of retinal dysfunction; others such as 17-AAG and ganetespib have not. To understand these safety profile differences we evaluated histopathological changes and exposure profiles of four Hsp90 inhibitors, with or without clinical reports of adverse ocular effects, using a rat retinal model. Retinal morphology, Hsp70 expression (a surrogate marker of Hsp90 inhibition), apoptotic induction and pharmacokinetic drug exposure analysis were examined in rats treated with the ansamycins 17-DMAG and 17-AAG, or with the second-generation compounds NVP-AUY922 and ganetespib. Both 17-DMAG and NVP-AUY922 induced strong yet restricted retinal Hsp70 up-regulation and promoted marked photoreceptor cell death 24h after the final dose. In contrast, neither 17-AAG nor ganetespib elicited photoreceptor injury. When the relationship between drug distribution and photoreceptor degeneration was examined, 17-DMAG and NVP-AUY922 showed substantial retinal accumulation, with high retina/plasma (R/P) ratios and slow elimination rates, such that 51% of 17-DMAG and 65% of NVP-AUY922 present at 30 min post-injection were retained in the retina 6h post-dose. For 17-AAG and ganetespib, retinal elimination was rapid (90% and 70% of drugs eliminated from the retina at 6h, respectively) which correlated with lower R/P ratios. These findings indicate that prolonged inhibition of Hsp90 activity in the eye results in photoreceptor cell death. Moreover, the results suggest that the retina/plasma exposure ratio and retinal elimination rate profiles of Hsp90 inhibitors, irrespective of their chemical class, may predict for ocular toxicity potential.

Targeting heat-shock-protein 90 (Hsp90) by natural products: geldanamycin, a show case in cancer therapy

Covering 2005 to 2013. In this review recent progress in the development of heat shock proteins (Hsp90) in oncogenesis is illuminated. Particular emphasis is put on inhibitors such as geldanamycin and analogues that serve as a natural product show case. Hsp90 has emerged as an important target in cancer therapy and/or against pathogenic cells which elicit abnormal Hsp patterns. Competition for ATP by geldanamycin and related compounds abrogate the chaperone function of Hsp90. In this context, this account pursues three topics in detail: a) Hsp90 and its biochemistry, b) Hsp90 and its role in oncogenesis and c) strategies to create compound libraries of structurally complex inhibitors like geldanamycin on which SAR studies and the development of drugs that are currently in different stages of clinical testing rely.

Hsp90 inhibitors in breast cancer: a systematic review

PURPOSE

Pharmacological inhibition of Hsp90 shows great promise in breast cancer treatment. This is the first systematic review to synthesize all available data and to evaluate the efficacy and safety of Hsp90 inhibitors in breast cancer.

METHODS

This study was performed in accordance with the PRISMA guidelines. Eligible articles were identified by a search of MEDLINE and ClinicalTrials.gov databases, using a predefined combination of the terms "breast", "cancer", "Hsp90", "inhibitors".

RESULTS

Overall, 19 articles (190 patients) were eligible. The greatest clinical activity has been observed on the field of HER2-positive metastatic breast cancer. However, accumulating data suggest that Hsp90 inhibitors may play a significant role in the treatment of triple negative and aromatase inhibitor-resistant breast cancer.

CONCLUSION

In the last decade, the development of Hsp90 inhibitors has moved forward rapidly; however, no phase III trials have been conducted and none agent has been approved for use in the clinical practice.

Drug targets from genetics: α-synuclein

One of the critical issues in Parkinson disease (PD) research is the identity of the specific toxic, pathogenic moiety. In PD, mutations in α-synuclein (αsyn) or multiplication of the SNCA gene encoding αsyn, result in a phenotype of cellular inclusions, cell death, and brain dysfunction. While the historical point of view has been that the macroscopic aggregates containing αsyn are the toxic species, in the last several years evidence has emerged that suggests instead that smaller soluble species--likely oligomers containing misfolded αsyn--are actually the toxic moiety and that the fibrillar inclusions may even be a cellular detoxification pathway and less harmful. If soluble misfolded species of αsyn are the toxic moieties, then cellular mechanisms that degrade misfolded αsyn would be neuroprotective and a rational target for drug development. In this review we will discuss the fundamental mechanisms underlying αsyn toxicity including oligomer formation, oxidative stress, and degradation pathways and consider rational therapeutic strategies that may have the potential to prevent or halt αsyn induced pathogenesis in PD.

Discovery and development of heat shock protein 90 inhibitors as anticancer agents: a review of patented potent geldanamycin derivatives

INTRODUCTION

There has been research on anticancer strategies which focus on disrupting a single malignant protein. One of the strategies is the inhibition of one protein, heat shock protein 90 (Hsp90). There are many reasons why Hsp90 protein is targeted by anticancer agents: maintenance of cellular homeostasis in organisms involves Hsp90 and its client proteins; moreover, Hsp90 complex is involved in regulating several signal transduction pathways and plays an important role in the maturation of lots of tumor-promoting client proteins. Geldanamycin (GM), the first benzoquinone ansamycin, has shown anticancer activity by binding to Hsp90. Currently, several GM derivatives such as 17-AAG, 17-(2-dimethylaminoethyl)amino-17-demethoxygeldanamycin, IPI-493, and IPI-504 are being progressively developed toward clinical application.

AREAS COVERED

Several research groups have studied GM and its derivatives to develop novel and potent Hsp90 inhibitors for the treatment of cancer. The crystal structure of Hsp90 was utilized to undergo structural optimization of GM derivatives. A wide variety of structural modifications were performed and some of the derivatives are now in clinical studies. The aim of this review was to summarize and analyze the structure-activity relationships of GM derivatives and the focus is on patented novel and pharmaceutically efficacious derivatives published from 1971 to 2012.

EXPERT OPINION

Hsp90 inhibitors offer an effective therapeutic approach for treatment of cancer. To date, the clinical results of 17-AAG, IPI-493, and IPI-504 suggest that these GM derivatives could be used either alone or in combination with other marketed medications for the treatment of cancer patients. As there are not any marketed Hsp90 inhibitors, inhibiting Hsp90 chaperone function remains as a promising strategy that still requires further research.

Open-label, dose-escalation, safety, pharmacokinetic, and pharmacodynamic study of intravenously administered CNF1010 (17-(allylamino)-17-demethoxygeldanamycin [17-AAG]) in patients with solid tumors

BACKGROUND

17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) is a benzoquinone ansamycin that binds to and inhibits the Hsp90 family of molecular chaperones leading to the proteasomal degradation of client proteins critical in malignant cell proliferation and survival. We have undertaken a Phase 1 trial of CNF1010, an oil-in-water nanoemulsion of 17-AAG.

METHODS

Patients with advanced solid tumors and adequate organ functions received CNF1010 by 1-h intravenous (IV) infusion, twice a week, 3 out of 4 weeks. Doses were escalated sequentially in single-patient (6 and 12 mg/m(2)/day) and three-to-six-patient (≥25 mg/m(2)/day) cohorts according to a modified Fibonacci's schema. Plasma pharmacokinetic (PK) profiles and biomarkers, including Hsp70 in PBMCs, HER-2 extracellular domain, and IGFBP2 in plasma, were performed.

RESULTS

Thirty-five patients were treated at doses ranging from 6 to 225 mg/m(2). A total of 10 DLTs in nine patients (2 events of fatigue, 83 and 175 mg/m(2); shock, abdominal pain, ALT increased, increased transaminases, and pain in extremity at 175 mg/m(2); extremity pain, atrial fibrillation, and metabolic encephalopathy at 225 mg/m(2)) were noted. The PK profile of 17-AAG after the first dose appeared to be linear up to 175 mg/m(2), with a dose-proportional increase in C max and AUC0-inf. Hsp70 induction in PBMCs and inhibition of serum HER-2 neu extracellular domain indicated biological effects of CNF1010 at doses >83 mg/m(2).

CONCLUSION

The maximum tolerated dose was not formally established. Hsp70 induction in PBMCs and inhibition of serum HER-2 neu extracellular domain indicated biological effects. The CNF1010 clinical program is no longer being pursued due to the toxicity profile of the drug and the development of second-generation Hsp90 molecules.

Learning from nature: advances in geldanamycin- and radicicol-based inhibitors of Hsp90

Natural products have been fundamental in the development of new therapeutic agents predicated on the inhibition of heat shock protein 90 (Hsp90). This Perspective describes the influential role of the benzoquinone ansamycin geldanamycin and the resorcylic acid macrolactone radicicol not only in driving forward drug discovery programs but also in inspiring organic chemists to develop innovative methodology for the synthesis of natural products and analogues with improved properties.

Hsp90: still a viable target in prostate cancer

Heat shock protein 90 (Hsp90) is a molecular chaperone that regulates the maturation, activation and stability of critical signaling proteins that drive the development and progression of prostate cancer, including the androgen receptor. Despite robust preclinical data demonstrating anti-tumor activity of first-generation Hsp90 inhibitors in prostate cancer, poor clinical responses initially cast doubt over the clinical utility of this class of agent. Recent advances in compound design and development, use of novel preclinical models and further biological insights into Hsp90 structure and function have now stimulated a resurgence in enthusiasm for these drugs as a therapeutic option. This review highlights how the development of new-generation Hsp90 inhibitors with improved physical and pharmacological properties is unfolding, and discusses the potential contexts for their use either as single agents or in combination, for men with metastatic prostate cancer.

Recent advances in novel targeted therapies for HER2-positive breast cancer

The monoclonal antibody trastuzumab has improved the outcomes of patients with breast cancer that overexpresses the human epidermal growth factor receptor 2 (HER2). However, despite this advancement, many tumors develop resistance and novel approaches are needed. Recently, a greater understanding of cellular biology has translated into the development of novel anti-HER2 agents with varying mechanisms of action. The small molecule tyrosine kinase inhibitor lapatinib has demonstrated activity in HER2-positive metastatic breast cancer (MBC) and in the preoperative setting. Pertuzumab is a monoclonal antibody with a distinct binding site from trastuzumab, which inhibits receptor dimerization. In recent studies, the addition of pertuzumab to combination therapy has led to improvements in progression-free survival in patients with HER2-positive MBC and higher response rates in the preoperative setting. An alternative approach is the use of novel antibody-drug conjugates such as trastuzumab-emtansine, which recently demonstrated activity in MBC. Neratinib, a pan-HER tyrosine kinase inhibitor, which irreversibly inhibits HER1 and HER2, also has proven activity in MBC. A range of compounds is being developed to attempt to overcome trastuzumab resistance by targeting heat shock protein 90, a molecular chaperone required for the stabilization of cellular proteins. Furthermore, agents are being developed to inhibit the mammalian target of rapamycin, a downstream component of the PTEN/PI3K pathway, which has been implicated in trastuzumab resistance. Finally, there are emerging data indicating that combinations of anti-HER2 agents may circumvent resistance mechanisms and improve patient outcomes. In this review, recent data on these emerging agents and novel combinations for HER2-positive breast cancer are discussed.

Use of pharmacokinetic/pharmacodynamic biomarkers to support rational cancer drug development

The process of drug development in oncology has struggled to alter at a pace in keeping with the rapid discovery and testing of agents that act on a wide variety of molecular targets. The rational development of such agents requires an understanding of drug effect(s) on their purported target. It is likely that testing these drugs in a framework designed to examine cytotoxic agents will fail to establish their full potential. We discuss how data gained from biomarker investigation might impact on drug development and provide examples that highlight the development, validation and use of pharmacokinetic, and especially pharmacodynamic biomarkers as drug development moves from the laboratory into clinical testing. The challenges of performing assays to satisfy regulatory requirements have been the subject of much debate. We recommend the implementation of appropriate, fit-for-purpose biomarkers in clinical trials of all new cancer drugs.

The heat shock protein 90 inhibitor 17-AAG suppresses growth and induces apoptosis in human cholangiocarcinoma cells

The aim of this study was to investigate the effects of 17-Allylamino-17-demethoxygeldanamycin (17-AAG), a heat shock protein 90 (HSP90) inhibitor, on the proliferation, cell cycle, and apoptosis of human cholangiocarcinoma (CCA) cells. Cell proliferation and cell cycle distribution were measured by the MTT assay and flow cytometry analysis, respectively. Induction of apoptosis was determined by flow cytometry and Hoechst staining. The expressions of cleaved poly ADP-ribose polymerase (PARP), Bcl-2, Survivin, and Cyclin B1 were detected by Western blot analysis. The activity of caspase-3 was also examined. We found that 17-AAG inhibited cell growth and induced G2/M cell cycle arrest and apoptosis in CCA cells together with the down-regulation of Bcl-2, Survivin and Cyclin B1, and the up-regulation of cleaved PARP. Moreover, increased caspase-3 activity was also observed in CCA cells treated with 17-AAG. In conclusion, our data suggest that the inhibition of HSP90 function by 17-AAG may provide a promising therapeutic strategy for the treatment of human CCA.

17AEP-GA, an HSP90 antagonist, is a potent inhibitor of glioblastoma cell proliferation, survival, migration and invasion

Glioblastoma multiforme (GBM) is the most frequent and the most malignant human brain tumor. The expression of receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF) is strongly increased in GBM, where they promote tumor proliferation, cell survival, migration, invasion and angiogenesis. We used geldanamycins (GAs) (inhibitors of HSP90) in order to block glioblastoma growth and HGF-dependent cell migration and invasion. The effect of GAs on three GBM cell lines was tested and we found their antiproliferative effect on tumor cells. The maximum level of inhibition reached 70%. After treatment with GAs, cells also became apoptotic as determined by Annexin V-positive staining and activation of the caspase-3 pathway. We examined the expression and activity of the MET receptor on GBM cell lines and we observed phosphorylation of AKT and MAPK after HGF stimulation by western blot analysis. Since GBM cells express high level of MET receptor and were shown to respond to HGF by increased motility we tested if GAs could negatively affect GBM cell movement. In our study, we found that GAs inhibited the chemotaxis of glioblastoma cells toward the hepatocyte growth factor gradient. The GAs also blocked migration of tumor cells through a Matrigel layer in invasion assays. The strongest inhibitory effect was observed for GA and its analog, 17AEP-GA. Based on our results, GAs, particularly 17AEP-GA, could be considered as a new potential agent to treat glioblastoma multiforme.

17-allylamino-17-(demethoxy)geldanamycin (17-AAG) is a potent and effective inhibitor of human cytomegalovirus replication in primary fibroblast cells

The 90 % human cytomegalovirus inhibitory concentration of 17-allylamino-17-(demethoxy)geldanamycin (17-AAG) was 0.1 nM and 50 % cytotoxicity required at least a 10 μM concentration. Three molecular targets may explain the antiviral activities of this compound. These are (1) heat shock protein maturation complexes, (2) host cell cycle progression and (3) phosphatidylinositol 3-kinase signaling. However, the data suggested a mechanism of action where 17-AAG blocked immediate-early protein transactivation.

A phase I trial of docetaxel and pulse-dose 17-allylamino-17-demethoxygeldanamycin in adult patients with solid tumors

PURPOSE

To define maximum tolerated dose (MTD), clinical toxicities, and pharmacokinetics of 17-allylamino-17-demethoxygeldanamycin (17-AAG) when administered in combination with docetaxel once every 21 days in patients with advanced solid tumor malignancies.

EXPERIMENTAL DESIGN

Docetaxel was administered over 1 h at doses of 55, 70, and 75 mg/m(2). 17-AAG was administered over 1-2 h, following the completion of the docetaxel infusion, at escalating doses ranging from 80 to 650 mg/m(2) in 12 patient cohorts. Serum was collected for pharmacokinetic and pharmacodynamic studies during cycle 1. Docetaxel, 17-AAG, and 17-AG levels were determined by high-performance liquid chromatography. Biologic effects of 17-AAG were monitored in peripheral blood mononuclear cells by immunoblot.

RESULTS

Forty-nine patients received docetaxel and 17-AAG. The most common all-cause grade 3 and 4 toxicities were leukopenia, lymphopenia, and neutropenia. An MTD was not defined; however, three dose-limiting toxicities were observed, including 2 incidences of neutropenic fever and 1 of junctional bradycardia. Dose escalation was halted at docetaxel 75 mg/m(2)-17-AAG 650 mg/m(2) due to delayed toxicities attributed to patient intolerance of the DMSO-based 17-AAG formulation. Of 46 evaluable patients, 1 patient with lung cancer experienced a partial response. Minor responses were observed in patients with lung, prostate, melanoma, and bladder cancers. A correlation between reduced docetaxel clearance and 17-AAG dose level was observed.

CONCLUSIONS

The combination of docetaxel and 17-AAG was well tolerated in adult patients with solid tumors, although patient intolerance to the DMSO formulation precluded further dose escalation. The recommended phase II dose is docetaxel 70 mg/m(2) and 17-AAG 500 mg/m(2).

Cytotoxic activity to acute myeloid leukemia cells by Antp-TPR hybrid peptide targeting Hsp90

We previously reported that Antp-TPR hybrid peptide inhibited the interaction of Hsp90 with TPR2A and had selective cytotoxic activity discriminating between normal and cancer cells to induce cancer cell death. In this study, we investigated the cytotoxic activity of Antp-TPR peptide toward acute myeloid leukemia (AML) cells. It was demonstrated that Antp-TPR peptide induced AML cell death in cell lines such as U937, K562, THP-1, and HL-60 via activation of caspases 3 and 7, and disruption of mitochondrial membrane potential. Conversely, Antp-TPR peptide did not reduce the viability of normal cells including peripheral blood mononuclear cells (PBMCs), although both geldanamycin and 17-AAG, small-molecule inhibitors of Hsp90, mediated cytotoxicity to these normal cells at low concentrations. In addition, mutation analysis of TPR peptide demonstrated that the highly conserved amino acids Lys and Arg were critical to the cytotoxic activity. These results indicated that Antp-TPR hybrid peptide would provide potent and selective therapeutic options in the treatment of AML.

Advances in the clinical development of heat shock protein 90 (Hsp90) inhibitors in cancers

Hsp90 is an ATP dependent molecular chaperone protein which integrates multiple oncogenic pathways. As such, Hsp90 inhibition is a promising anti-cancer strategy. Several inhibitors that act on Hsp90 by binding to its N-terminal ATP pocket have entered clinical evaluation. Robust pre-clinical data suggested anti-tumor activity in multiple cancer types. Clinically, encouraging results have been demonstrated in melanoma, acute myeloid leukemia, castrate refractory prostate cancer, non-small cell lung carcinoma and multiple myeloma. In breast cancer, proof-of-concept was demonstrated by first generation Hsp90 inhibitors in combination with trastuzumab mainly in human epidermal growth factor receptor 2 (HER2)+metastatic breast cancer. There are a multitude of second generation Hsp90 inhibitors currently under investigation. To date, however, there is no FDA approved Hsp90 inhibitor nor standardized assay to ascertain Hsp90 inhibition. This review summarizes the current status of both first and second generation Hsp90 inhibitors based on their chemical classification and stage of clinical development. It also discusses the pharmacodynamic assays currently implemented in clinic as well as other novel strategies aimed at enhancing the effectiveness of Hsp90 inhibitors. Ultimately, these efforts will aid in maximizing the full potential of this class of agents. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

A phase II study of 17-allylamino-17-demethoxygeldanamycin in metastatic or locally advanced, unresectable breast cancer

Heat shock protein 90 (Hsp90) is an attractive target for breast cancer treatment, as it is required for the proper folding and stabilization of several proteins known to be involved in breast cancer growth and development. These proteins include the epidermal growth factor receptor, human epidermal growth factor receptor 2 (HER2), estrogen receptor (ER), progesterone receptor (PR), and src. 17-Allylamino-17-demethoxygeldanamycin (17-AAG) is an intravenous Hsp90 inhibitor in development for breast cancer treatment. We conducted a phase II study of 17-AAG 220 mg/m(2) on days 1, 4, 8, and 11 every 21 days in patients with metastatic and locally advanced breast cancer. Since we expected the molecular effects of Hsp90 inhibition to extend beyond just ER, PR, and HER2 down regulation and to impact a variety of other cellular proteins, patients were not selected based on ER, PR, or HER2 status. Eleven patients, including 6 patients with triple negative breast cancer, were enrolled and treated. There were no responses and 3 patients had stable disease as their best response. Five patients developed grade 3/4 toxicities, which were primarily hepatic and pulmonary. Based on these results, we do not recommend further study of 17-AAG at this dosing schedule or in unselected breast cancer patients.

A phase II study of gemcitabine in combination with tanespimycin in advanced epithelial ovarian and primary peritoneal carcinoma

OBJECTIVE

To evaluate the efficacy and biological effects of the gemcitabine/tanespimycin combination in patients with advanced ovarian and peritoneal cancer. To assess the effect of tanespimycin on tumor cells, levels of the chaperone proteins HSP90 and HSP70 were examined in peripheral blood mononuclear cells (PBMC) and paired tumor biopsy lysates.

METHODS

Two-cohort phase II clinical trial. Patients were grouped according to prior gemcitabine therapy. All participants received tanespimycin 154 mg/m(2) on days 1 and 9 of cycle 1 and days 2 and 9 of subsequent cycles. Patients also received gemcitabine 750 mg/m(2) on day 8 of the first treatment cycle and days 1 and 8 of subsequent cycles.

RESULTS

The tanespimycin/gemcitabine combination induced a partial response in 1 gemcitabine naïve patient and no partial responses in gemcitabine resistant patients. Stable disease was seen in 6 patients (2 gemcitabine naïve and 4 gemcitabine resistant). The most common toxicities were hematologic (anemia and neutropenia) as well as nausea and vomiting. Immunoblotting demonstrated limited upregulation of HSP70 but little or no change in levels of most client proteins in PBMC and paired tumor samples.

CONCLUSIONS

Although well tolerated, the tanespimycin/gemcitabine combination exhibited limited anticancer activity in patients with advanced epithelial ovarian and primary peritoneal carcinoma, perhaps because of failure to significantly downregulate the client proteins at clinically achievable exposures.