Role of HSP90 in Cancer

HSP90 is a vital chaperone protein conserved across all organisms. As a chaperone protein, it correctly folds client proteins. Structurally, this protein is a dimer with monomer subunits that consist of three main conserved domains known as the N-terminal domain, middle domain, and the C-terminal domain. Multiple isoforms of HSP90 exist, and these isoforms share high homology. These isoforms are present both within the cell and outside the cell. Isoforms HSP90α and HSP90β are present in the cytoplasm; TRAP1 is present in the mitochondria; and GRP94 is present in the endoplasmic reticulum and is likely secreted due to post-translational modifications (PTM). HSP90 is also secreted into an extracellular environment via an exosome pathway that differs from the classic secretion pathway. Various co-chaperones are necessary for HSP90 to function. Elevated levels of HSP90 have been observed in patients with cancer. Despite this observation, the possible role of HSP90 in cancer was overlooked because the chaperone was also present in extreme amounts in normal cells and was vital to normal cell function, as observed when the drastic adverse effects resulting from gene knockout inhibited the production of this protein. Differences between normal HSP90 and HSP90 of the tumor phenotype have been better understood and have aided in making the chaperone protein a target for cancer drugs. One difference is in the conformation: HSP90 of the tumor phenotype is more susceptible to inhibitors. Since overexpression of HSP90 is a factor in tumorigenesis, HSP90 inhibitors have been studied to combat the adverse effects of HSP90 overexpression. Monotherapies using HSP90 inhibitors have shown some success; however, combination therapies have shown better results and are thus being studied for a more effective cancer treatment.

HSP90 Inhibitor, 17-DMAG, Alone and in Combination with Lapatinib Attenuates Acquired Lapatinib-Resistance in ER-positive, HER2-Overexpressing Breast Cancer Cell Line

Simple Summary

Lapatinib is a tyrosine kinase inhibitor widely used as a treatment for a Human Epidermal growth factor Receptor 2 (HER2) (+) breast cancer patients. However, when resistance is acquired through continued exposure, and it is associated with a poor prognosis for patients. In this study, we identified HSP90 as a common node for acquired resistance to lapatinib in two lapatinib resistant cell lines using proteomic analysis. Notably, in vitro and in vivo studies demonstrated synergy effect between lapatinib and an HSP90 inhibitor were observed in the estrogen receptor (+) HER2 (+) breast cancer cell only. These results could be a potential strategy for future clinical trials for HSP90 inhibitors in treatment—refractory HER2 (+) metastatic cancer patients

Abstract

Lapatinib, a Human Epidermal growth factor Receptor 2 (HER2)-targeting therapy in HER2-overexpressing breast cancer, has been widely used clinically, but the prognosis is still poor because most patients acquire resistance. Therefore, we investigated mechanisms related to lapatinib resistance to evaluate new therapeutic targets that may overcome resistance. Lapatinib-resistant cell lines were established using SKBR3 and BT474 cells. We evaluated cell viability and cell signal changes, gene expression and protein changes. In the xenograft mouse model, anti-tumor effects were evaluated using drugs. Analysis of the protein interaction network in two resistant cell lines with different lapatinib resistance mechanisms showed that HSP90 protein was commonly increased. When Heat Shock Protein 90 (HSP90) inhibitors were administered alone to both resistant cell lines, cell proliferation and protein expression were effectively inhibited. However, inhibition of cell proliferation and protein expression with a combination of lapatinib and HSP90 inhibitors showed a more synergistic effect in the LR-BT474 cell line than the LR-SKBR3 cell line, and the same result was exhibited with the xenograft model. These results suggest that HSP90 inhibitors in patients with lapatinib-resistant Estrogen Receptor (ER) (+) HER2 (+) breast cancer are promising therapeutics for future clinical trials.

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

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

A phase I trial of ganetespib in combination with paclitaxel and trastuzumab in patients with human epidermal growth factor receptor-2 (HER2)-positive metastatic breast cancer

BACKGROUND

Targeted therapies in HER2-positive metastatic breast cancer significantly improve outcomes but efficacy is limited by therapeutic resistance. HER2 is an acutely sensitive Heat Shock Protein 90 (HSP90) client and HSP90 inhibition can overcome trastuzumab resistance. Preclinical data suggest that HSP90 inhibition is synergistic with taxanes with the potential for significant clinical activity. We therefore tested ganetespib, a HSP90 inhibitor, in combination with paclitaxel and trastuzumab in patients with trastuzumab-refractory HER2-positive metastatic breast cancer.

METHODS

In this phase I dose-escalation study, patients with trastuzumab-resistant HER2-positive metastatic breast cancer received weekly trastuzumab (2 mg/kg) and paclitaxel (80 mg/m²) on days 1, 8, 15, and 22 of a 28-day cycle with escalating doses of ganetespib (100 mg/m², 150 mg/m², and a third cohort of 125 mg/m² if needed) on days 1, 8, and 15. Therapy was continued until disease progression or toxicity. The primary objective was to establish the safety and maximum tolerated dose and/or recommended phase II dose (RP2D) of this therapy. The secondary objectives included evaluation of the effects of ganetespib on the pharmacokinetics of paclitaxel, and to make a preliminary assessment of the efficacy of the combination therapy.

RESULTS

Dose escalation was completed for the two main cohorts without any observed dose-limiting toxicities. Nine patients received treatment. The median prior lines of anti-HER2 therapy numbered three (range 2-4), including prior pertuzumab in 9/9 patients and ado-trastuzumab emtansine (T-DM1) in 8/9 patients. The most common grade 1/2 adverse events (AEs) were diarrhea, fatigue, anemia, and rash. There were no grade 4 AEs related to ganetespib. The overall response rate was 22% (2/9 patients had partial response) and stable disease was seen in 56% (5/9 patients). The clinical benefit rate was 44% (4/9 patients). The median progression-free survival was 20 weeks (range 8-55).

CONCLUSION

The RP2D of ganetespib is 150 mg/m² in combination with weekly paclitaxel plus trastuzumab. The combination was safe and well tolerated. Despite prior taxanes, pertuzumab, and T-DM1, clinical activity of this triplet regimen in this heavily pretreated cohort is promising and warrants further study in HER2-positive metastatic breast cancer.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02060253 . Registered 30 January 2014.

Maximizing the Therapeutic Potential of HSP90 Inhibitors

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

PI3K/AKT/mTOR pathway inhibitors: the ideal combination partners for breast cancer therapies?

Activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway is common in breast cancer. PI3K pathway activation has been associated with tumor growth and progression, and thus is a promising target for breast cancer therapy. Agents targeting the PI3K pathway can restore sensitivity to standard breast cancer therapies, including endocrine, HER2-targeted agents and chemotherapy, by suppressing PI3K pathway activation, which is central to the development of therapeutic resistance. The combination of endocrine therapy and PI3K pathway (mTOR) inhibition has proven clinical benefit, and novel combination strategies involving PI3K pathway inhibitors and other investigational targeted therapies are now being explored clinically in patients with breast cancer.

89Zr-trastuzumab and 89Zr-bevacizumab PET to evaluate the effect of the HSP90 inhibitor NVP-AUY922 in metastatic breast cancer patients

PURPOSE

HSP90 chaperones have key client proteins that are involved in all hallmarks of breast cancer growth and progression. The primary aim of this clinical trial was to evaluate the feasibility of using (89)Zr-trastuzumab PET (for HER2-positive breast cancer) or (89)Zr-bevacizumab PET [for estrogen receptor (ER)-positive breast cancer] to determine in vivo degradation of client proteins caused by the novel HSP90 inhibitor NVP-AUY922.

EXPERIMENTAL DESIGN

Of note, 70 mg/m(2) NVP-AUY922 was administered intravenously in a weekly schedule to patients with advanced HER2 or ER-positive breast cancer. Biomarker analysis consisted of serial PET imaging with 2[18F]fluoro-2-deoxy-D-glucose (FDG), (89)Zr-trastuzumab, or (89)Zr-bevacizumab. Response evaluation was performed according to RECIST1.0. FDG, (89)Zr-trastuzumab, and (89)Zr-bevacizumab distributions were scored visually and quantitatively by calculating the maximum standardized uptake values (SUVmax). In blood samples, serial HSP70 levels, extracellular form of HER2 (HER2-ECD), and pharmacokinetic and pharmacodynamic parameters were measured.

RESULTS

Sixteen patients (ten HER2-positive and six ER-positive tumors) were included. One partial response was observed; seven patients showed stable disease. SUVmax change in individual tumor lesions on baseline versus 3 weeks (89)Zr-trastuzumab PET was heterogeneous and related to size change on CT after 8 weeks treatment (r(2) = 0.69; P = 0.006). Tumor response on (89)Zr-bevacizumab PET and FDG-PET was not correlated with CT response.

CONCLUSIONS

NVP-AUY922 showed proof-of-concept clinical response in HER2-amplified metastatic breast cancer. Early change on (89)Zr-trastuzumab PET was positively associated with change in size of individual lesions assessed by CT.

Visualising dual downregulation of insulin-like growth factor receptor-1 and vascular endothelial growth factor-A by heat shock protein 90 inhibition effect in triple negative breast cancer

PURPOSE

Triple negative breast cancer (TNBC) is biologically characterised by heterogeneous presence of molecular pathways underlying it. Insulin-like growth factor receptor-1 (IGF-1R) expression and vascular endothelial growth factor-A (VEGF-A) have been identified as key factors in these pathways in TNBC. In this study, we aimed at in vivo PET imaging the effect of heat shock protein (Hsp) 90 inhibition by means of NVP-AUY922 on these pathways, with zirconium-89 ((89)Zr) labelled antibodies targeting IGF-1R and VEGF-A.

MATERIALS AND METHODS

In vitro NVP-AUY922 effects on cellular IGF-1R expression and VEGF-A secretion were determined in MCF-7 and MDA-MB-231 cell lines. Moreover human TNBC bearing MDA-MB-231 mice received 50mg/kg NVP-AUY922 or vehicle q3d intraperitoneally for 21days. PET scans with (89)Zr-MAB391 and (89)Zr-bevacizumab for visualisation of IGF-1R and VEGF-A were performed before and during treatment. Ex vivo biodistribution and correlative tissue analyses were performed.

RESULTS

NVP-AUY922 treatment reduced IGF-1R expression and VEGF-A excretion in both cell lines. Hsp90 inhibition lowered tumour uptake on (89)Zr-MAB391-PET by 37.3% (P<0.01) and on (89)Zr-bevacizumab-PET by 44.4% (P<0.01). This was confirmed by ex vivo biodistribution with a reduction of 41.3% injected dose (ID)/g for (89)Zr-MAB391 and 37.8% ID/g for (89)Zr-bevacizumab, while no differences were observed for other tissues. This coincided with reduced IGF-1R expression and mean vessel density in the NVP-AUY922 treated tumours.

CONCLUSION

(89)Zr-MAB391 and (89)Zr-bevacizumab PET reflect effect of Hsp90 inhibitors and can therefore potentially be used to monitor therapeutic effects of Hsp90 inhibitor therapy in TNBC.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

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.

First-in-human phase I dose-escalation study of the HSP90 inhibitor AUY922 in patients with advanced solid tumors

PURPOSE

A phase I study was conducted with the primary objective of determining the maximum tolerated dose (MTD) of AUY922 in patients with advanced solid tumors. Secondary objectives included characterization of the safety, pharmacokinetic, and pharmacodynamic profiles.

PATIENTS AND METHODS

Patients with advanced solid tumors received 1-hour i.v. infusions of AUY922 once a week in a 28-day cycle. An adaptive Bayesian logistic regression model that employed observed dose-limiting toxicities (DLT) in the first treatment cycle was used to guide dose-escalation decisions, with the established MTD to be used in phase II studies.

RESULTS

One hundred and one patients were enrolled and explored at doses in the range of 2 to 70 mg/m(2). DLTs occurred in 8 patients (22-70 mg/m(2)) and included diarrhea, asthenia/fatigue, anorexia, atrial flutter, and visual symptoms. At 70 mg/m(2), the AUY922 concentration achieved was consistent with active concentrations in a range of xenograft models. There was evidence of target inhibition in peripheral blood mononuclear cells (HSP70 induction) and tumor (client protein depletion and reduction of metabolic activity by (18)F-FDG PET). The recommended phase II dose (RP2D) of 70 mg/m(2) was proposed on the basis of toxicity and pharmacokinetic and pharmacodynamic profiles.

CONCLUSIONS

At the RP2D of 70 mg/m(2), AUY922 exhibited acceptable tolerability, and phase II single-agent and combination studies have been initiated in patients with HER2-positive breast, gastric, and non-small cell lung cancers.

Inhibition of HSP90 with AUY922 induces synergy in HER2-amplified trastuzumab-resistant breast and gastric cancer

HSP90 enables the activation of many client proteins of which the most clinically validated is HER2. NVP-AUY922, a potent HSP90 inhibitor, is currently in phase II clinical trials. To explore its potential clinical use in HER2-amplified breast and gastric cancers, we evaluated the effect of AUY922 alone and in combination with trastuzumab in both trastuzumab-sensitive and -resistant models. A panel of 16 human gastric and 45 breast cancer cell lines, including 16 HER2-amplified (3 and 13, respectively) cells, was treated with AUY922 over various concentrations. In both breast and gastric cancer, we used cell lines and xenograft models with conditioned trastuzumab-resistance to investigate the efficacy of AUY922 alongside trastuzumab. Effects of this combination on downstream markers were analyzed via Western blot analysis. AUY922 exhibited potent antiproliferative activity in the low nanomolar range (<40 nmol/L) for 59 of 61 cell lines. In both histologies, HER2-amplified cells expressed greater sensitivity to AUY than HER2-negative cells. In conditioned trastuzumab-resistant models, AUY922 showed a synergistic effect with trastuzumab. In vitro, the combination induced greater decreases in HER2, a G2 cell-cycle arrest, and increased apoptosis. In a trastuzumab-resistant gastric cancer xenograft model, the combination of AUY922 and trastuzumab showed greater antitumor efficacy than either drug alone. These data suggest that AUY922 in combination with trastuzumab has unique efficacy in trastuzumab-resistant models. The combination of HSP90 inhibition and direct HER2 blockade represents a novel approach to the treatment of HER2-amplified cancers and clinical trials based on the above data are ongoing.

Targeting the molecular chaperone heat shock protein 90 (HSP90): lessons learned and future directions

Due to the critical role of heat shock protein 90 (HSP90) in regulating the stability, activity and intracellular sorting of its client proteins involved in multiple oncogenic processes, HSP90 inhibitors are promising therapeutic agents for cancer treatment. In cancer cells, HSP90 client proteins play a major role in oncogenic signal transduction (i.e., mutant epidermal growth factor receptor), angiogenesis (i.e., vascular endothelial growth factor), anti-apoptosis (i.e., AKT), and metastasis (i.e., matrix metalloproteinase 2 and CD91), processes central to maintaining the cancer phenotype. Thus, HSP90 has emerged as a viable target for antitumor drug development, and several HSP90 inhibitors have transitioned to clinical trials. HSP90 inhibitors include geldanamycin and its derivatives (i.e., tanespimycin, alvespimycin, IPI-504), synthetic and small molecule inhibitors (i.e., AUY922, AT13387, STA9090, MPC3100), other inhibitors of HSP90 and its isoforms (i.e., shepherdin and 5'-N-ethylcarboxamideadenosine). With more than 200 "client" proteins, many of them meta-stable and oncogenic, HSP90 inhibition can affect an array of tumors. Here we review the molecular structure of HSP90, structural features of HSP90 inhibition, pharmacodynamic effects and tumor responses in clinical trials of HSP90 inhibitors. We also discuss lessons learned from completed clinical trials of HSP90 inhibitors, and future directions for these promising therapeutic agents.

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).