HSP90 Inhibitors for Cancer Therapy and Overcoming Drug Resistance

Combination therapy involving HSP90 inhibitors for combating cancer: an overview of clinical and preclinical progress

The molecular chaperone heat shock protein 90 (HSP90) regulates multiple crucial signalling pathways in cancer by driving the maturation of key signalling components, thereby playing a crucial role in tumorigenesis and drug resistance in cancer. Inhibition of HSP90 results in metastable conformational collapse of its client proteins and their proteasomal degradation. Considerable efforts have been devoted to the development of small-molecule inhibitors targeting HSP90, and more than 20 inhibitors have been evaluated in clinical trials for cancer therapy. However, owing to disadvantages such as organ toxicity and drug resistance, only one HSP90 inhibitor has been approved for use in clinical settings. In recent years, HSP90 inhibitors used in combination with other anti-cancer therapies have shown remarkable potential in the treatment of cancer. HSP90 inhibitors work synergistically with various anti-cancer therapies, including chemotherapy, targeted therapy, radiation therapy and immunotherapy. HSP90 inhibitors can improve the pharmacological effects of the above-mentioned therapies and reduce treatment resistance. This review provides an overview of the use of combination therapy with HSP90 inhibitors and other anti-cancer therapies in clinical and preclinical studies reported in the past decade and summarises design strategies and prospects for these combination therapies. Altogether, this review provides a theoretical basis for further research and application of these combination therapies in the treatment of cancer.

Safety and efficacy of HSP90 inhibitor ganetespib for neoadjuvant treatment of stage II/III breast cancer

HSP90 inhibitors destabilize oncoproteins associated with cell cycle, angiogenesis, RAS-MAPK activity, histone modification, kinases and growth factors. We evaluated the HSP90-inhibitor ganetespib in combination with standard chemotherapy in patients with high-risk early-stage breast cancer. I-SPY2 is a multicenter, phase II adaptively randomized neoadjuvant (NAC) clinical trial enrolling patients with stage II-III breast cancer with tumors 2.5 cm or larger on the basis of hormone receptors (HR), HER2 and Mammaprint status. Multiple novel investigational agents plus standard chemotherapy are evaluated in parallel for the primary endpoint of pathologic complete response (pCR). Patients with HER2-negative breast cancer were eligible for randomization to ganetespib from October 2014 to October 2015. Of 233 women included in the final analysis, 140 were randomized to the standard NAC control; 93 were randomized to receive 150 mg/m2 ganetespib every 3 weeks with weekly paclitaxel over 12 weeks, followed by AC. Arms were balanced for hormone receptor status (51-52% HR-positive). Ganetespib did not graduate in any of the biomarker signatures studied before reaching maximum enrollment. Final estimated pCR rates were 26% vs. 18% HER2-negative, 38% vs. 22% HR-negative/HER2-negative, and 15% vs. 14% HR-positive/HER2-negative for ganetespib vs control, respectively. The predicted probability of success in phase 3 testing was 47% HER2-negative, 72% HR-negative/HER2-negative, and 19% HR-positive/HER2-negative. Ganetespib added to standard therapy is unlikely to yield substantially higher pCR rates in HER2-negative breast cancer compared to standard NAC, and neither HSP90 pathway nor replicative stress expression markers predicted response. HSP90 inhibitors remain of limited clinical interest in breast cancer, potentially in other clinical settings such as HER2-positive disease or in combination with anti-PD1 neoadjuvant chemotherapy in triple negative breast cancer.Trial registration: www.clinicaltrials.gov/ct2/show/NCT01042379.

Effects of Radiotherapy in Combination With Irinotecan and 17-AAG on Bcl-2 and Caspase 3 Gene Expression in Colorectal Cancer Cells

Introduction: In this study, the cytotoxic and anti-cancer effects of Irinotecan as a conventional chemotherapeutic agent compared to 17-(allyl amino)-17-demethoxygeldanamycin (17-AAG) as possible radiosensitizers in the HCT-116 cell line were investigated. Methods: HCT-116 cells were treated with various concentrations of irinotecan and 17-AAG and also irradiated with a 2-Gy of X-ray radiation. Then, the cell viability was examined by a water-soluble tetrazolium-1 assay after 24 hours. For single therapies and double and triple combination cases, IC50, 0.5×IC50 and 0.25×IC50 concentrations of each drug were selected respectively for a terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay and other tests. In treated and untreated cells, the caspase 3 and Bcl-2 gene expression ratios were evaluated by the real-time PCR method. Likewise, caspase 3 activity was detected with a colorimetric assay. Results: In all combined treatments, including 17-AAG- radiation, irinotecan - radiation, irinotecan -17-AAG, and irinotecan-17-AAG-radiation, decreased cellular viability and increased TUNEL positive cells were presented versus the control group (P<0.05). There were increased TUNEL positive cells in the triple combination, in concentrations of 0.25×IC50 of each drug, in comparison with single and double agent treatments. Moreover, in triple combination, the caspase 3 mRNA level and caspase 3 activity increased versus related single treatments. Likewise, in the irinotecan-17-AAG-radiation combined treatment and the 17-AAG-radiation double treatment, the Bcl-2 gene expression level decreased in comparison with single therapies. Conclusion: It can be indicated that the combination of chemo-radiotherapy versus single treatments has significant anti-cancer effects.

HSP90-dependent PUS7 overexpression facilitates the metastasis of colorectal cancer cells by regulating LASP1 abundance

BACKGROUND

Pseudouridine synthase (PUS) 7 is a member of the PUS family that catalyses pseudouridine formation. It has been shown to be involved in intellectual development and haematological malignancies. Nevertheless, the role and the underlying molecular mechanisms of PUS7 in solid tumours, such as colorectal cancer (CRC), remain unexplored. This study elucidated, for the first time, the role of PUS7 in CRC cell metastasis and the underlying mechanisms.

METHODS

We conducted immunohistochemistry, qPCR, and western blotting to quantify the expression of PUS7 in CRC tissues as well as cell lines. Besides, diverse in vivo and in vitro functional tests were employed to establish the function of PUS7 in CRC. RNA-seq and proteome profiling analysis were also applied to identify the targets of PUS7. PUS7-interacting proteins were further uncovered using immunoprecipitation and mass spectrometry.

RESULTS

Overexpression of PUS7 was observed in CRC tissues and was linked to advanced clinical stages and shorter overall survival. PUS7 silencing effectively repressed CRC cell metastasis, while its upregulation promoted metastasis, independently of the PUS7 catalytic activity. LASP1 was identified as a downstream effector of PUS7. Forced LASP1 expression abolished the metastasis suppression triggered by PUS7 silencing. Furthermore, HSP90 was identified as a client protein of PUS7, associated with the increased PUS7 abundance in CRC. NMS-E973, a specific HSP90 inhibitor, also showed higher anti-metastatic activity when combined with PUS7 repression. Importantly, in line with these results, in human CRC tissues, the expression of PUS7 was positively linked to the expression of HSP90 and LASP1, and patients co-expressing HSP90/PUS7/LASP1 showed a worse prognosis.

CONCLUSIONS

The HSP90-dependent PUS7 upregulation promotes CRC cell metastasis via the regulation of LASP1. Thus, targeting the HSP90/PUS7/LASP1 axis may be a novel approach for the treatment of CRC.

Exploiting DNA repair pathways for tumor sensitization, mitigation of resistance, and normal tissue protection in radiotherapy

More than half of cancer patients are treated with radiotherapy, which kills tumor cells by directly and indirectly inducing DNA damage, including cytotoxic DNA double-strand breaks (DSBs). Tumor cells respond to these threats by activating a complex signaling network termed the DNA damage response (DDR). The DDR arrests the cell cycle, upregulates DNA repair, and triggers apoptosis when damage is excessive. The DDR signaling and DNA repair pathways are fertile terrain for therapeutic intervention. This review highlights strategies to improve therapeutic gain by targeting DDR and DNA repair pathways to radiosensitize tumor cells, overcome intrinsic and acquired tumor radioresistance, and protect normal tissue. Many biological and environmental factors determine tumor and normal cell responses to ionizing radiation and genotoxic chemotherapeutics. These include cell type and cell cycle phase distribution; tissue/tumor microenvironment and oxygen levels; DNA damage load and quality; DNA repair capacity; and susceptibility to apoptosis or other active or passive cell death pathways. We provide an overview of radiobiological parameters associated with X-ray, proton, and carbon ion radiotherapy; DNA repair and DNA damage signaling pathways; and other factors that regulate tumor and normal cell responses to radiation. We then focus on recent studies exploiting DSB repair pathways to enhance radiotherapy therapeutic gain.

Measuring Tumor Epichaperome Expression Using [124I] PU-H71 Positron Emission Tomography as a Biomarker of Response for PU-H71 Plus Nab-Paclitaxel in HER2-Negative Metastatic Breast Cancer

PURPOSE

Epichaperome network maintenance is vital to survival of tumors that express it. PU-H71 is an epichaperome inhibitor that binds to the ATP-binding site of HSP90 and has demonstrated antitumor activity in breast cancer xenograft models and clinical safety in patients. PU-positron emission tomography (PET) is a theragnostic imaging tool that allows visualization of the epichaperome target. In this phase Ib trial, we present safety and tolerability for PU-H71 plus nab-paclitaxel in HER2-negative patients with metastatic breast cancer (MBC) and the utility of PU-PET as a noninvasive predictive biomarker.

METHODS

We performed a 3 + 3 dose-escalation study with escalating PU-H71 doses and standard nab-paclitaxel. The primary objective was to establish safety and determine maximum tolerated dose (MTD)/recommended phase 2 dose. Secondary objectives were to assess pharmacokinetics and clinical efficacy. Patients could enroll in a companion PU-PET protocol to measure epichaperome expression before treatment initiation to allow exploratory correlation with treatment benefit.

RESULTS

Of the 12 patients enrolled, dose-limiting toxicity occurred in one patient (G3 neutropenic fever) at dose level 1; MTD of PU-H71 was 300 mg/m² plus nab-paclitaxel 260 mg/m² administered every 3 weeks. Common toxicities included diarrhea, fatigue, peripheral neuropathy, and nausea. PU-H71 systemic exposure was not altered by nab-paclitaxel administration. Two of 12 patients had partial response (overall response rate, 17%) and the clinical benefit rate was 42% (5 of 12). Time to progression was associated with baseline epichaperome positivity and PU-H71 peak standard uptake value (SUV), with more durable disease control observed with high epichaperome levels.

CONCLUSION

The combination of PU-H71 and nab-paclitaxel was well tolerated, with evidence of clinical activity. More durable disease control without progression was observed in patients with high baseline epichaperome expression. A phase II trial of this combination with PU-PET as a companion diagnostic for patient selection is currently planned.

Overcoming Limitations of Cisplatin Therapy by Additional Treatment With the HSP90 Inhibitor Onalespib

Rational

Cisplatin based cancer therapy is an affordable and effective standard therapy for several solid cancers, including lung, ovarian and head and neck cancers. However, the clinical use of cisplatin is routinely limited by the development of drug resistance and subsequent therapeutic failure. Therefore, methods of circumventing cisplatin resistance have the potential to increase therapeutic efficiency and dramatically increase overall survival. Cisplatin resistance can be mediated by alterations to the DNA damage response, where multiple components of the repair machinery have been described to be client proteins of HSP90. In the present study, we have investigated whether therapy with the novel HSP90 inhibitor onalespib can potentiate the efficacy of cisplatin and potentially reverse cisplatin resistance in ovarian and head and neck cancer cells.

Methods

Cell viability, cancer cell proliferation and migration capacity were evaluated in vitro on models of ovarian and head and neck cancer cells. Western blotting was used to assess the downregulation of HSP90 client proteins and alterations in downstream signaling proteins after exposure to cisplatin and/or onalespib. Induction of apoptosis and DNA damage response were evaluated in both monotherapy and combination therapy groups.

Results

Results demonstrate that onalespib enhances the efficiency of cisplatin in a dose-dependent manner. Tumor cells treated with both drugs displayed lower viability and a decreased migration rate compared to vehicle-control cells and cells treated with individual compounds. An increase of DNA double strand breaks was observed in both cisplatin and onalespib treated cells. The damage was highest and most persistent in the combination group, delaying the DNA repair machinery. Further, the cisplatin and onalespib co-treated cells had greater apoptotic activity compared to controls.

Conclusion

The results of this study demonstrate that the reduced therapeutic efficacy of cisplatin due to drug-resistance could be overcome by combination treatment with onalespib. We speculate that the increased apoptotic signaling, DNA damage as well as the downregulation of HSP90 client proteins are important mechanisms promoting increased sensitivity to cisplatin treatment.

HDAC11 deficiency disrupts oncogene-induced hematopoiesis in myeloproliferative neoplasms

Protein acetylation is an important contributor to cancer initiation. Histone deacetylase 6 (HDAC6) controls JAK2 translation and protein stability and has been implicated in JAK2-driven diseases best exemplified by myeloproliferative neoplasms (MPNs). By using novel classes of highly selective HDAC inhibitors and genetically deficient mouse models, we discovered that HDAC11 rather than HDAC6 is necessary for the proliferation and survival of oncogenic JAK2-driven MPN cells and patient samples. Notably, HDAC11 is variably expressed in primitive stem cells and is expressed largely upon lineage commitment. Although Hdac11is dispensable for normal homeostatic hematopoietic stem and progenitor cell differentiation based on chimeric bone marrow reconstitution, Hdac11 deficiency significantly reduced the abnormal megakaryocyte population, improved splenic architecture, reduced fibrosis, and increased survival in the MPLW515L-MPN mouse model during primary and secondary transplantation. Therefore, inhibitors of HDAC11 are an attractive therapy for treating patients with MPN. Although JAK2 inhibitor therapy provides substantial clinical benefit in MPN patients, the identification of alternative therapeutic targets is needed to reverse MPN pathogenesis and control malignant hematopoiesis. This study establishes HDAC11 as a unique type of target molecule that has therapeutic potential in MPN.

Identification of Isoform-Selective Ligands for the Middle Domain of Heat Shock Protein 90 (Hsp90)

The molecular chaperone heat shock protein 90 (Hsp90) is a current inhibition target for the treatment of diseases, including cancer. In humans, there are two major cytosolic isoforms of Hsp90 (Hsp90α and Hsp90β). Hsp90α is inducible and Hsp90β is constitutively expressed. Most Hsp90 inhibitors are pan-inhibitors that target both cytosolic isoforms of Hsp90. The development of isoform-selective inhibitors of Hsp90 may enable better clinical outcomes. Herein, by using virtual screening and binding studies, we report our work in the identification and characterisation of novel isoform-selective ligands for the middle domain of Hsp90β. Our results pave the way for further development of isoform-selective Hsp90 inhibitors.

What sustains the multidrug resistance phenotype beyond ABC efflux transporters? Looking beyond the tip of the iceberg

Identification of multidrug (MDR) efflux transporters that belong to the ATP-Binding Cassette (ABC) superfamily, represented an important breakthrough for understanding cancer multidrug resistance (MDR) and its possible overcoming. However, recent data indicate that drug resistant cells have a complex intracellular physiology that involves constant changes in energetic and oxidative-reductive metabolic pathways, as well as in the molecular circuitries connecting mitochondria, endoplasmic reticulum (ER) and lysosomes. The aim of this review is to discuss the key molecular mechanisms of cellular reprogramming that induce and maintain MDR, beyond the presence of MDR efflux transporters. We specifically highlight how cancer cells characterized by high metabolic plasticity - i.e. cells able to shift the energy metabolism between glycolysis and oxidative phosphorylation, to survive both the normoxic and hypoxic conditions, to modify the cytosolic and mitochondrial oxidative-reductive metabolism, are more prone to adapt to exogenous stressors such as anti-cancer drugs and acquire a MDR phenotype. Similarly, we discuss how changes in mitochondria dynamics and mitophagy rates, changes in proteome stability ensuring non-oncogenic proteostatic mechanisms, changes in ubiquitin/proteasome- and autophagy/lysosome-related pathways, promote the cellular survival under stress conditions, along with the acquisition or maintenance of MDR. After dissecting the complex intracellular crosstalk that takes place during the development of MDR, we suggest that mapping the specific adaptation pathways underlying cell survival in response to stress and targeting these pathways with potent pharmacologic agents may be a new approach to enhance therapeutic efficacy against MDR tumors.

In Vitro Interaction of Geldanamycin with Triazoles and Echinocandins Against Common and Emerging Candida Species

The aim of this study was to determine the in vitro interactions of geldanamycin (Hsp90-inhibitor) with triazoles and echinocandins against common and emerging Candida species. Twenty clinically important Candida strains comprising C. auris, C. albicans, C. parapsilosis, and C. glabrata (each five strains) were included. In vitro interactions of geldanamycin with fluconazole, itraconazole, caspofungin and anidulafungin were determined using a checkerboard method. The results were interpreted as synergistic, indifferent and antagonistic based on the fractional inhibitory concentration index (FICI). In vitro combination of fluconazole with geldanamycin resulted in synergistic effect against C. albicans (100%), C. glabrata (80%) and C. parapsilosis (80%) (FICI range 0.009-0.5), while indifferent interactions were obtained against C. auris (FICI range 1.5-2). The overall minimum inhibitory concentration (MIC) range of fluconazole against C. albicans, C. glabrata and C. parapsilosis reduced from 16-256 to 0.25-64 mg/L when combined with geldanamycin. Regarding the synergistic effect of geldanamycin with itraconazole against all strains of C. albicans, C. glabrata and C. parapsilosis (FICI range 0.009-0.375), the MIC range of this antifungal was reduced from 0.125-32 mg/L when tested alone, to 0.03-1 mg/L. Combinations of geldanamycin with fluconazole and itraconazole against C. auris, as well as combination of geldanamycin with caspofungin and anidulafungin against all studied Candida species, resulted in indifferent effects. No antagonism was observed. Simultaneous targeting of Hsp90 and lanosterol 14-α demethylase seems an effective approach against C. albicans, C. glabrata and C. parapsilosis. However, this combination is ineffective against the emerging pathogen C. auris.

Overview of the Mutational Landscape in Primary Myelofibrosis and Advances in Novel Therapeutics

Primary Myelofibrosis is a BCR-ABL negative myeloproliferative neoplasm with a variety of hematological presentations, including thrombosis, bleeding diathesis and marrow fibrosis. It is estimated to have an incidence of 1.5 per 100,000 people each year. Although JAK2 or MPL mutations are seen in PMF, several other mutations have recently been documented, including mutations in CALR, epigenetic regulators like TET, ASXL1, and 13q deletions. The identification of these mutations has improved the ability to develop novel treatment options. These include JAK inhibitors like ruxolitinib, heat shock protein-90 inhibitors like ganetespib, histone deacetylase inhibitors including panobinostat, pracinostat, vorinostat and givinostat, hypomethylating agents like decitabine, hedgehog inhibitors like glasdegib, PI3K, AKT and mTOR inhibitors like everolimus as well as telomerase inhibitors like imtelstat. Research on novel therapeutic options is being actively pursued in order to expand treatment options for primary myelofibrosis however currently, there is no curative therapy other than allogenic hematopoietic stem cell transplantation (ASCT) which is possible in select patients.

Polymer mediated transport of the Hsp90 inhibitor LB76, a polar cyclic peptide, produces an Hsp90 cellular phenotype

LB76 is a cyclic peptide that shows great promise as a selective heat shock protein 90 (Hsp90) inhibitor. However despite strong binding to and inhibition of Hsp90 in cell lysate its polar structure prevents it from crossing the cell membrane. We have developed a pH responsive polymer nanoparticle that effectively encapsulates LB76 from solution without need for purification. The nanoparticle releases the molecule upon crossing the cell membrane. Treatment of human colon cancer HCT116 cells with nanoparticles laden with LB76 produces the typical phenotype associated with Hsp90 inhibition, providing evidence of a therapeutically active payload.

[HSP90 inhibitor 17-AAG plays an important role in JAK3/STAT5 signaling pathways in HTLV-1 infection cell line HUT-102]

Objective: To analyze whether heat-shock protein 90 (HSP90) be involved in a permanently abnormal activated JAK/STAT signaling in ATL cells in vitro. Methods: The effect of 17-AAG on proliferation of ATL cell lines HUT-102 was assessed using CCK8 at different time points. Cell apoptosis was measured by flow cytometry. The specific proteins HSP90, STAT5, p-STAT5 and JAK3 were detected by Western blotting. Results: Overexpression of HSP90 in HUT-102 cell lines was disclosed (P<0.05) , and constitutive activation of JAK3/STAT5 signaling was observed in HTLV-1-infected T-cell lines but not in normal PBMCs; Treatment of ATL cell lines with 17-AAG led to reduced cell proliferation, but there was no significant change in terms of cell proliferation when the concentration of 17-AAG between 2 000-8 000 nmol/L (P>0.05) . 17-AAG induced cell apoptosis in different time-points and concentrations. 17-AAG don't affect the expression of JAK3 gene. Conclusion: This study indicated that JAK3 as HSP90 client protein was aberrantly activated in HTLV-1-infected T-cell lines, leading to constitutive activation of p-STAT5 in JAK/STAT signal pathway, which demonstrated that HSP90-inhibitors 17-AAG inhibited the growth of HTLV-1-infected T-cell lines by reducing cell proliferation and inducing cell apoptosis.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

HSP90 promotes cell glycolysis, proliferation and inhibits apoptosis by regulating PKM2 abundance via Thr-328 phosphorylation in hepatocellular carcinoma

BACKGROUND

Heat shock protein 90 (HSP90) functions as a well-known onco-protein to regulate protein conformation, stability and degradation. Pyruvate kinase M2 (PKM2), a critical regulator of the metabolism, growth and metastasis of cancer cells, has been confirmed to be overexpressed in various human cancer including hepatocellular carcinoma (HCC). However, the molecular mechanisms underlying the oncogenic functions of HSP90 and PKM2 overexpression in HCC remain unknown.

METHODS

The expression of HSP90 and PKM2 in HCC specimens and cells were detected by immunoblotting and immunostaining. The interaction between HSP90 and PKM2 was confirmed by tandem affinity purification, co-immunoprecipitation and Glutathione S transferase (GST)-pulldown assay.

RESULTS

In this study, we found that HSP90 could bind to PKM2 and subsequently increased PKM2 abundance in HCC cells. Immunohistochemistry (IHC) staining showed that HSP90 level was positively correlated with PKM2 level in HCC tissues. Mechanistically, HSP90 was found to increase the phosphorylation of PKM2 at Thr-328. Protein kinase glycogen synthase kinase-3β (GSK-3β) formed a protein complex with HSP90 and PKM2, and directly mediated Thr-328 phosphorylation of PKM2 induced by HSP90. Thr-328 phosphorylation was critical for maintaining PKM2 stability and its biological functions in regulating glycolysis, mitochondria respiration, proliferation and apoptosis. Functionally, we found that HSP90 promoted the glycolysis and proliferation and inhibited apoptosis of HCC cells in a PKM2 dependent manner. In vivo experiments disclosed that PKM2 was required for the promoting effects of HSP90 on the growth of HCC cells in mice. Furthermore, we demonstrated that positive expression of HSP90 and PKM2 was correlated with poor clinicopathological features including high alpha fetoprotein (AFP) level, large tumor size, portal vein tumor thrombus (PVTT) and advanced tumor-node-metastasis (TNM) stage. Furthermore, we demonstrated that positive expression of HSP90 and PKM2, and a combination of these proteins could strongly predict the poor prognosis of HCC patients.

CONCLUSIONS

We suggest that HSP90 potentiates the glycolysis and proliferation, reduces the apoptosis and thus enhances the growth of HCC cells through PKM2.

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.

[Hsp90AB1 Protein is Overexpressed in Non-small Cell Lung Cancer Tissues and Associated with Poor Prognosis in Lung Adenocarcinoma Patients]

BACKGROUND

Heat shock protein 90 kDa alpha, class B member 1 (Hsp90AB1) is highly conserved ATP-dependent molecular chaperone, and over-expressed in a variety of tumor cells. Some molecules that play important roles in tumor development signaling pathways such as epidermal growth factor receptor (EGFR), human epidermal growth factor receptor-2 (HER2) are Hsp90AB1 client proteins. Hsp90AB1 interact with these client proteins and participate in a variety of pathophysiological processes of cells. The aim of this study is to detect the expression of Hsp90AB1 in non-small cell lung cancer (NSCLC) tissues, and explore its clinical significance.

METHODS

The expression of Hsp90AB1 in 213 NSCLC tissues and 147 normal lung tissues was detected by tissue microarray and immunohistochemical staining method, and the relationship of Hsp90AB1 expression with clinicopathological parameters and prognosis of NSCLC patients were analyzed.

RESULTS

The expression level of Hsp90AB1 in lung cancer tissues (positive rate of 54.0%) was significantly higher than that in normal lung tissue (positive rate of 0.0%, P<0.001). The positive expression rate of Hsp90AB1 in lung adenocarcinoma tissues (61.2%) was significantly higher than that in lung squamous cell carcinoma tissues (37.9%)(P=0.002), and its over-expression was associated with poor prognosis in lung adenocarcinoma patients (P=0.032). The expression level of Hsp90AB1 had no significant correlation with clinical stage, lymph node metastasis, pathological grade or other factors (P>0.05).

CONCLUSIONS

Hsp90AB1 protein was over-expressed in NSCLC tissues, and was associated with lung cancer pathological type and overall survival in lung adenocarcinoma patients.

In vitro and in vivo anti-malarial activity of novel harmine-analog heat shock protein 90 inhibitors: a possible partner for artemisinin

Background

The emergence of artemisinin-resistant Plasmodium falciparum strains poses a serious challenge to the control of malaria. This necessitates the development of new anti-malarial drugs. Previous studies have shown that the natural beta-carboline alkaloid harmine is a promising anti-malarial agent targeting the P. falciparum heat-shock protein 90 (PfHsp90). The aim of this study was to test the anti-malarial activity of harmine analogues.

Methods

Forty-two harmine analogues were synthesized and the binding of these analogues to P. falciparum heat shock protein 90 was investigated. The in vitro anti-malarial activity of two of the analogues, 17A and 21A, was evaluated using a 72-h growth inhibition assay. The in vivo anti-malarial activity was tested in Plasmodium berghei infection of BALB/c mice. The potential of 21A for a combination treatment with artemisinin was evaluated using in vivo combination study with dihydro-artemisinin in BALB/c mice. Cytotoxicity of the harmine analogues was tested in vitro using HepG2 and HeLa cell lines.

Results

17A and 21A bound to PfHsp90 with average IC₅₀ values of 12.2 ± 2.3 and 23.1 ± 8.8 µM, respectively. They also inhibited the P. falciparum W2 strain with average IC₅₀ values of 4.2 ± 1.3 and 5.7 ± 1.7 µM, respectively. In vivo, three daily injections of P. berghei-infected BALB/c mice with 100 mg/kg of either 17A or 21A showed significant reduction in parasitaemia with a 51.5 and 56.1% reduction, respectively. Mice treated with 17A and 21A showed a median survival time of 11 and 14 days, respectively, while the vehicle control mice survived a median of only 8.5 days. A dose-ranging experiment with 21A showed that the compound has a dose-dependent anti-malarial effect. Furthermore, treatment of infected mice with a combination of 21A and dihydroartemisinin (DHA) showed a dramatic reduction in parasitaemia compared to treatment with DHA alone.

Conclusion

A novel and non-toxic harmine analogue has been synthesized which binds to PfHsp90 protein, inhibits P. falciparum in vitro at micromolar concentration, reduces parasitaemia and prolongs survival of P. berghei-infected mice with an additive anti-malarial effect when combined with DHA.

Identification of epipolythiodioxopiperazines HDN-1 and chaetocin as novel inhibitor of heat shock protein 90

The molecular chaperone heat shock protein 90 (Hsp90) has emerged as an important target for cancer treatment. HDN-1, an epipolythiopiperazine-2, 5-diones (ETPs) compound, was here identified as a new Hsp90 inhibitor. HDN-1 bound directly to C-terminus of Hsp90α, resulting in a potential conformational change that interfered with the binding of 17-AAG and novobiocin to Hsp90α. In contrast, association of 17-AAG, novobiocin or ATP with Hsp90α did not prevent the binding HDN-1 to Hsp90α. HDN-1 in combination with 17-AAG exhibited an enhanced inhibitory effect on non-small lung cancer cell proliferation. Molecular docking analyses revealed that HDN-1 bound to Hsp90α at C-terminal 526–570 region. In addition, HDN-1 degraded multiple oncoproteins and promoted EGF-induced wild type and mutated EGFR downregulation. Notably, chaetocin, used as a SUV39H1 inhibitor with similar structure to HDN-1, bound to Hsp90 and degraded Hsp90 client proteins and SUV39H1 as did HDN-1. These results indicate that HDN-1 and chaetocin are inhibitors of Hsp90 and that SUV39H1 is a novel client protein of Hsp90.

CPUY201112, a novel synthetic small-molecule compound and inhibitor of heat shock protein Hsp90, induces p53-mediated apoptosis in MCF-7 cells

Heat-shock protein 90 (Hsp90) is highly expressed in many tumor cells and is associated with the maintenance of malignant phenotypes. Targeting Hsp90 has had therapeutic success in both solid and hematological malignancies, which has inspired more studies to identify new Hsp90 inhibitors with improved clinical efficacy. Using a fragment-based approach and subsequent structural optimization guided by medicinal chemistry principles, we identified the novel compound CPUY201112 as a potent Hsp90 inhibitor. It binds to the ATP-binding pocket of Hsp90 with a kinetic dissociation (K_d) constant of 27 ± 2.3 nM. It also exhibits potent in vitro antiproliferative effects in a range of solid tumor cells. In MCF-7 cells with high Hsp90 expression, CPUY201112 induces the degradation of Hsp90 client proteins including HER-2, Akt, and c-RAF. We prove that treating MCF-7 cells with CPUY201112 results in cell cycle arrest and apoptosis through the wild-type (wt) p53 pathway. CPUY201112 also synergizes with Nutlin-3a to induce cancer cell apoptosis. CPUY201112 significantly inhibited the growth of MCF-7 xenografts in nude mice without apparent body weight loss. These results demonstrate that CPUY201112 is a novel Hsp90 inhibitor with potential use in treating wild-type p53 related cancers.

Biomarkers That Predict Sensitivity to Heat Shock Protein 90 Inhibitors

INTRODUCTION

Heat shock protein (HSP) 90, a viable target for cancer treatment, mediates the maturation and stabilization of client oncoproteins. HSP90 inhibitors (HSP90i) are potentially active in a variety of tumors, but therapeutic benefit is confirmed in only a small subset. We explored potential biomarkers across multiple studies of HSP90i in advanced solid tumors.

PATIENTS AND METHODS

Archived tumor specimens from patients treated with HSP90i in 7 different phase I/II trials at Memorial Sloan Kettering Cancer Center were identified. Tumor tissue was tested using immunohistochemistry; estrogen, progesterone, and androgen receptors ≥ 1% positive and < 1% negative; HSP90 and HSP70: 0, 1 + negative, and 2+, 3 + positive; phosphatase and tensin homolog: 0 negative, 1 reduced, and 2 positive; HER2: 0, 1 + negative, 2 + equivocal, 3 + positive; and epidermal growth factor receptor: 0 negative, and 1+, 2+, 3 + positive. The expression of the biomarker panel was correlated with clinical benefit (CB) (defined by overall response [ORR] or CB by the "8-week" scan) using Fisher exact test.

RESULTS

Adequate tissue was available for 51 of 158 patients (32%), including 10 different solid tumors. Of these, 71% (36 of 51) and 51% (26 of 51) patients met the criteria to assess CB by best ORR or by the "8-week scan" assessment, respectively. Breast was the most frequent tumor. The mean duration of HSP90i therapy was 55 days (range, 16-411 days). There were 16 responses (4 partial response; 12 stable disease); 13 of 16 responses strongly correlated with HER2-positive status (P = .001).

CONCLUSION

Our findings suggest HER2 as a sensitive client and perhaps the only effective biomarker for sensitivity to these HSP90i.

17-AAG suppresses growth and invasion of lung adenocarcinoma cells via regulation of the LATS1/YAP pathway

The large tumour suppressor 1 (LATS1) signalling network has been proved to be an essential regulator within the cell, participating in multiple cellular phenotypes. However, it is unclear concerning the clinical significance of LATS1 and the regulatory mechanisms of 17-Allylamino-17- demethoxygeldanamycin (17-AAG) in lung adenocarcinoma (LAC). The aim of the present study was to investigate the correlation of LATS1 and yes-associated protein (YAP) expression with clinicopathological characteristics in LAC patients, and the effects of 17-AAG on biological behaviours of LAC cells. Subcutaneous LAC tumour models were further established to observe the tumour growth in nude mice. The results showed that the positive expression of LATS1 was significantly lowered (26.7% versus 68.0%, P < 0.001), while that of YAP was elevated (76.0% versus 56.0%, P + 0.03) in LAC tissues compared to the adjacent non-cancerous tissues; LAST1 expression was negatively correlated with YAP expression (r + 0.432, P < 0.001) and lymphatic invasion of the tumour (P + 0.015). In addition, 17-AAG inhibited proliferation and invasion, and induced cell apoptosis and cycle arrest in LAC cells together with increased expression of E-cadherin and p-LATS1, and decreased expression of YAP and connective tissue growth factor. Tumour volumes and weight were much smaller in 17-AAG-treated groups than those in untreated group (P < 0.01). Taken together, our findings indicate that decreased expression of LATS1 is associated with lymphatic invasion of LAC, and 17-AAG suppresses growth and invasion of LAC cells via regulation of the LATS1/YAP pathway in vitro and in vivo, suggesting that we may provide a promising therapeutic strategy for the treatment of human LAC.

Response of head and neck squamous cell carcinoma cells carrying PIK3CA mutations to selected targeted therapies

IMPORTANCE

The PIK3CA mutation is one of the most common mutations in head and neck squamous cell carcinoma (HNSCC). Through this research we attempt to elicit the role of oncogene dependence and effects of targeted therapy on this PIK3CA mutation.

OBJECTIVES

(1) To determine the role of oncogene dependence on PIK3CA-one of the more common and targetable oncogenes in HNSCC, and (2) to evaluate the consequence of this oncogene on the effectiveness of newly developed targeted therapies.

DESIGN, SETTING, AND PARTICIPANTS

This was a cell culture-based, in vitro study performed at an academic research laboratory assessing the viability of PIK3CA-mutated head and neck cell lines when treated with targeted therapy.

EXPOSURES

PIK3CA-mutated head and neck cell lines were treated with 17-AAG, GDC-0941, trametinib, and BEZ-235.

MAIN OUTCOMES AND MEASURES

Assessment of cell viability of HNSCC cell lines characterized for PIK3CA mutations or SCC25 cells engineered to express the PIK3CA hotspot mutations E545K or H1047R.

RESULTS

Surprisingly, in engineered cell lines, the hotspot E545K and H1047R mutations conferred increased, rather than reduced, IC50 assay measurements when treated with the respective HSP90, PI3K, and MEK inhibitors, 17-AAG, GDC-0941, and trametinib, compared with the SCC25 control cell lines. When treated with BEZ-235, H1047R-expressing cell lines showed increased sensitivity to inhibition compared with control, whereas those expressing E545K showed slightly increased sensitivity of unclear significance.

CONCLUSIONS AND RELEVANCE

(1) The PIK3CA mutations within our engineered cell model did not lead to enhanced oncogene-dependent cell death when treated with direct inhibition of the PI3K enzyme yet did show increased sensitivity compared with control with dual PI3K/mTOR inhibition. (2) Oncogene addiction to PIK3CA hotspot mutations, if it occurs, is likely to evolve in vivo in the context of additional molecular changes that remain to be identified. Additional study is required to develop new model systems and approaches to determine the role of targeted therapy in the treatment of PI3K-overactive HNSCC tumors.

Ganetespib: research and clinical development

Under stressful conditions, the heat shock protein 90 (HSP90) molecular chaperone protects cellular proteins (client proteins) from degradation via the ubiquitin-proteasome pathway. HSP90 expression is upregulated in cancers, and this contributes to the malignant phenotype of increased proliferation and decreased apoptosis and maintenance of metastatic potential via conservation of its client proteins, including human epidermal growth factor receptor 2, anaplastic lymphoma kinase, androgen receptor, estrogen receptor, Akt, Raf-1, cell cycle proteins, and B-cell lymphoma 2 among others. Hence, inhibition of HSP90 leads to the simultaneous degradation of its many clients, thereby disrupting multiple oncogenic signaling cascades. This has sparked tremendous interest in the development of HSP90 inhibitors as an innovative anticancer strategy. Based on the wealth of compelling data from preclinical studies, a number of HSP90 inhibitors have entered into clinical testing. However, despite enormous promise and anticancer activity reported to date, none of the HSP90 inhibitors in development has been approved for cancer therapy, and the full potential of this class of agents is yet to be realized. This article provides a review on ganetespib, a small molecule HSP90 inhibitor that is currently under evaluation in a broad range of cancer types in combination with other therapeutic agents with the hope of further enhancing its efficacy and overcoming drug resistance. Based on our current understanding of the complex HSP90 machinery combined with the emerging data from these key clinical trials, ganetespib has the potential to be the first-in-class HSP90 inhibitor to be approved as a new anticancer therapy.

The HSP90 Inhibitor Ganetespib Radiosensitizes Human Lung Adenocarcinoma Cells

The molecular chaperone HSP90 is involved in stabilization and function of multiple client proteins, many of which represent important oncogenic drivers in NSCLC. Utilization of HSP90 inhibitors as radiosensitizing agents is a promising approach. The antitumor activity of ganetespib, HSP90 inhibitor, was evaluated in human lung adenocarcinoma (AC) cells for its ability to potentiate the effects of IR treatment in both in vitro and in vivo. The cytotoxic effects of ganetespib included; G2/M cell cycle arrest, inhibition of DNA repair, apoptosis induction, and promotion of senescence. All of these antitumor effects were both concentration- and time-dependent. Both pretreatment and post-radiation treatment with ganetespib at low nanomolar concentrations induced radiosensitization in lung AC cells in vitro. Ganetespib may impart radiosensitization through multiple mechanisms: such as down regulation of the PI3K/Akt pathway; diminished DNA repair capacity and promotion of cellular senescence. In vivo, ganetespib reduced growth of T2821 tumor xenografts in mice and sensitized tumors to IR. Tumor irradiation led to dramatic upregulation of β-catenin expression in tumor tissues, an effect that was mitigated in T2821 xenografts when ganetespib was combined with IR treatments. These data highlight the promise of combining ganetespib with IR therapies in the treatment of AC lung tumors.

Novel therapies for myelofibrosis

Myelofibrosis (MF), including primary, post-essential thrombocythemia and post-polycythemia vera MF, associates with a reduced quality of life and shortened life expectancy. Dysregulation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is prominent, even in the absence of the JAK2(V617F) mutation. Therefore, all symptomatic MF patients may potentially derive benefit from JAK inhibitors. Despite the efficacy of JAK inhibitors in controlling signs and symptoms of MF, they do not eradicate the disease. Therefore, JAK inhibitors are currently being tested in combination with other novel therapies, a strategy which may be more effective in reducing disease burden, either by overcoming JAK inhibitor resistance or targeting additional mechanisms of pathogenesis. Additional targets include modulators of epigenetic regulation, pathways that work downstream from JAK/STAT (i.e. mammalian target of rapamycin/AKT/phosphoinositide 3-kinase) heat shock protein 90, hedgehog signaling, pro-fibrotic factors, abnormal megakaryocytes and telomerase. In this review, we discuss novel MF therapeutic strategies.

Targeting Heat-Shock Protein 90 (HSP90) as a Complementary Strategy to Immune Checkpoint Blockade for Cancer Therapy

The demonstration that immune checkpoint blockade can meaningfully improve outcomes for cancer patients has revolutionized the field of immuno-oncology. New biologic agents targeting specific checkpoints have shown remarkable durability in terms of patient response and, importantly, exhibit clinical activity across a range of human malignancies, including many that have traditionally proven refractory to other immunotherapies. In this rapidly evolving area, a key consideration relates to the identification of novel combinatorial strategies that exploit existing or investigational cancer therapies in order to optimize patient outcomes and the proportion of individuals able to derive benefit from this approach. In this regard, heat-shock protein 90 (HSP90) represents an important emerging target for cancer therapy because its inactivation results in the simultaneous blockade of multiple signaling pathways and can sensitize tumor cells to other anticancer agents. Within the context of immunology, HSP90 plays a dual regulatory role, with its functional inhibition resulting in both immunosuppressive and immunostimulatory effects. In this Cancer Immunology at the Crossroads overview, the anticancer activity profile of targeted HSP90 inhibitors is discussed along with their paradoxical roles in immunology. Overall, we explore the rationale for combining the modalities of HSP90 inhibition and immune checkpoint blockade in order to augment the antitumor immune response in cancer.

Anthracyclines/trastuzumab: new aspects of cardiotoxicity and molecular mechanisms

Anticancer drugs continue to cause significant reductions in left ventricular ejection fraction resulting in congestive heart failure. The best-known cardiotoxic agents are anthracyclines (ANTHs) such as doxorubicin (DOX). For several decades cardiotoxicity was almost exclusively associated with ANTHs, for which cumulative dose-related cardiac damage was the use-limiting step. Human epidermal growth factor (EGF) receptor 2 (HER2; ErbB2) has been identified as an important target for breast cancer. Trastuzumab (TRZ), a humanized anti-HER2 monoclonal antibody, is currently recommended as first-line treatment for patients with metastatic HER2(+) tumors. The use of TRZ may be limited by the development of drug intolerance, such as cardiac dysfunction. Cardiotoxicity has been attributed to free-iron-based, radical-induced oxidative stress. Many approaches have been promoted to minimize these serious side effects, but they are still clinically problematic. A new approach to personalized medicine for cancer that involves molecular screening for clinically relevant genomic alterations and genotype-targeted treatments is emerging.

The heat shock protein 90 inhibitor BIIB021 suppresses the growth of T and natural killer cell lymphomas

Epstein-Barr virus (EBV), which infects not only B cells but also T and natural killer (NK) cells, is associated with a variety of lymphoid malignancies. Because EBV-associated T and NK cell lymphomas are refractory and resistant to conventional chemotherapy, there is a continuing need for new effective therapies. EBV-encoded “latent membrane protein 1” (LMP1) is a major oncogene that activates nuclear factor kappa B (NF-κB), c-Jun N-terminal kinase (JNK), and phosphatidylinositol 3-kinase signaling pathways, thus promoting cell growth and inhibiting apoptosis. Recently, we screened a library of small-molecule inhibitors and isolated heat shock protein 90 (Hsp90) inhibitors as candidate suppressors of LMP1 expression. In this study, we evaluated the effects of BIIB021, a synthetic Hsp90 inhibitor, against EBV-positive and -negative T and NK lymphoma cell lines. BIIB021 decreased the expression of LMP1 and its downstream signaling proteins, NF-κB, JNK, and Akt, in EBV-positive cell lines. Treatment with BIIB021 suppressed proliferation in multiple cell lines, although there was no difference between the EBV-positive and -negative lines. BIIB021 also induced apoptosis and arrested the cell cycle at G1 or G2. Further, it down-regulated the protein levels of CDK1, CDK2, and cyclin D3. Finally, we evaluated the in vivo effects of the drug; BIIB021 inhibited the growth of EBV-positive NK cell lymphomas in a murine xenograft model. These results suggest that BIIB021 has suppressive effects against T and NK lymphoma cells through the induction of apoptosis or a cell cycle arrest. Moreover, BIIB021 might help to suppress EBV-positive T or NK cell lymphomas via the down-regulation of LMP1 expression.

Preclinical development of novel Rac1-GEF signaling inhibitors using a rational design approach in highly aggressive breast cancer cell lines

Rho GTPases play a key role in the regulation of multiple essential cellular processes, including actin dynamics, gene transcription and cell cycle progression. Aberrant activation of Rac1, a member of Rho family of small GTPases, is associated with tumorigenesis, cancer progression, invasion and metastasis. Particularly, Rac1 is overexpressed and hyperactivated in highly aggressive breast cancer. Thus, Rac1 appears to be a promising and relevant target for the development of novel anticancer drugs. We identified the novel Rac1 inhibitor ZINC69391 through a docking-based virtual library screening targeting Rac1 activation by GEFs. This compound was able to block Rac1 interaction with its GEF Tiam1, prevented EGF-induced Rac1 activation and inhibited cell proliferation, cell migration and cell cycle progression in highly aggressive breast cancer cell lines. Moreover, ZINC69391 showed an in vivo antimetastatic effect in a syngeneic animal model. We further developed the novel analog 1A-116 by rational design and showed to be specific and more potent than the parental compound in vitro and interfered Rac1-P-Rex1 interaction. We also showed an enhanced in vivo potency of 1A-116 analog. These results show that we have developed novel Rac1 inhibitors that may be used as a novel anticancer therapy.

Raf-interactome in tuning the complexity and diversity of Raf function

Raf kinases have been intensely studied subsequent to their discovery 30 years ago. The Ras-Raf-mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase/mitogen-activated protein kinase (Ras-Raf-MEK-ERK/MAPK) signaling pathway is at the heart of the signaling networks that control many fundamental cellular processes and Raf kinases takes centre stage in the MAPK pathway, which is now appreciated to be one of the most common sources of the oncogenic mutations in cancer. The dependency of tumors on this pathway has been clearly demonstrated by targeting its key nodes; however, blockade of the central components of the MAPK pathway may have some unexpected side effects. Over recent years, the Raf-interactome or Raf-interacting proteins have emerged as promising targets for protein-directed cancer therapy. This review focuses on the diversity of Raf-interacting proteins and discusses the mechanisms by which these proteins regulate Raf function, as well as the implications of targeting Raf-interacting proteins in the treatment of human cancer.

Integrative quantitative proteomics unveils proteostasis imbalance in human hepatocellular carcinoma developed on nonfibrotic livers

Proteomics-based clinical studies represent promising resources for the discovery of novel biomarkers or for unraveling molecular mechanisms underlying particular diseases. Here, we present a discovery study of hepatocellular carcinoma developed on nonfibrotic liver (nfHCC) that combines complementary quantitative iTRAQ-based proteomics and phosphoproteomics approaches. Using both approaches, we compared a set of 24 samples (18 nfHCC versus six nontumor liver tissue). We identified 43 proteins (67 peptides) differentially expressed and 32 peptides differentially phosphorylated between the experimental groups. The functional analysis of the two data sets pointed toward the deregulation of a protein homeostasis (proteostasis) network including the up-regulation of the Endoplasmic Reticulum (ER) resident HSPA5, HSP90B1, PDIA6, and P4HB and of the cytosolic HSPA1B, HSP90AA1, HSPA9, UBC, CNDP2, TXN, and VCP as well as the increased phosphorylation of the ER resident calnexin at Ser583. Antibody-based validation approaches (immunohistochemistry, immunoblot, Alphascreen(®), and AMMP(®)) on independent nfHCC tumor sets (up to 77 samples) confirmed these observations, thereby indicating a common mechanism occurring in nfHCC tumors. Based on these results we propose that adaptation to proteostasis imbalance in nfHCC tumors might confer selective advantages to those tumors. As such, this model could provide an additional therapeutic opportunity for those tumors arising on normal liver by targeting the tumor proteostasis network. Data are available via ProteomeXchange with identifier PXD001253.

Synergetic cytotoxic activity toward breast cancer cells enhanced by the combination of Antp-TPR hybrid peptide targeting Hsp90 and Hsp70-targeted peptide

Background

Heat shock protein (Hsp) 90 and Hsp70 are indispensable for cell survival under conditions of stress. They bind to client proteins to assist in protein stabilization, translocation of polypeptides across the cell membrane, and recovery of proteins from aggregates in the cell. Therefore, these proteins have recently emerged as important targets in the treatment of cancer. We previously reported that the newly designed Antp-TPR hybrid peptide targeting Hsp90 induced cytotoxic activity to cancer cells both in vitro and in vivo.

Methods

To further improve the cytotoxic activity of Antp-TPR toward cancer cells, we investigated the effect of a Hsp70-targeted peptide, which was made cell-permeable by adding the polyarginine with a linker sequence, on the cytotoxic activity of Antp-TPR in breast cancer cell lines.

Results

It was revealed that Antp-TPR in the presence of a Hsp70-targeted peptide induced effective cytotoxic activity toward breast cancer cells through the descrease of Hsp90 client proteins such as p53, Akt, and cRaf. Moreover, the combined treatment with these peptides did not induce the up-regulation of Hsp70 protein, as determined by western blotting, a promoter assay using a luminometer, and single-cell level imaging with the LV200 system, although a small-molecule inhibitor of Hsp90, 17-allylamino-demethoxygeldanamycin (17-AAG), did induce the up-regulation of this protein. We also found that treatment with Antp-TPR, Hsp70-targeted peptide, or a combination of the two did not induce an increase in the glutathione concentrations in the cancer cells.

Conclusion

These findings suggest that targeting both Hsp90 and Hsp70 with Antp-TPR and Hsp70-targeted peptide is an attractive approach for selective cancer cell killing that might provide potent and selective therapeutic options for the treatment of cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-615) contains supplementary material, which is available to authorized users.

Preclinical antitumor activity of SST0116CL1: a novel heat shock protein 90 inhibitor

4-Amino substituted resorcino-isoxazole (SST0116CL1) (property of Sigma-Tau Research Switzerland S.A.) is a potent, second generation, small-molecule heat shock protein 90 inhibitor (Hsp90i). SST0116CL1 binds to the ATP binding pocket of Hsp90, and interferes with Hsp90 chaperone function thus resulting in client protein degradation and tumor growth inhibition. The aim of the study was to assess SST0116CL1 in various solid and haematological tumors. The antitumor properties of SST0116CL1 were assessed using in vitro cell proliferation and client protein degradation assays and in vivo different tumor xenograft models. Pharmacokinetic (PK) data were also generated in tumor-bearing mice to gain an understanding of optimal dosing schedules and regimens. SST0116CL1 was shown to inhibit recombinant Hsp90α and to induce the destabilization of different client proteins, often overexpressed and constitutively activated in different types of hematological or solid human tumors. In preclinical in vivo studies, it was revealed to induce antitumor effects in murine models of leukemia and of gastric and ovarian carcinoma. A modulation of PD biomarkers in terms of downregulation of Hsp90 client proteins in tumor-bearing mice was found. SST0116CL1 is a new clinical candidate for cancer therapy. The antitumor property of SST0116CL1, likely due to direct inhibition of the Hsp90 enzymatic activity, may prove to be a critical attribute as the compound enters phase I clinical trials.

Host factor-targeted hepatitis B virus therapies

In this review we will focus on host factors known to impact hepatitis B virus (HBV) replication as current or potential targets for therapeutic intervention. Some immunotherapeutic strategies will be discussed because they have the potential to activate interferon-mediated clearance of HBV, but attention will also be paid to host machinery and proteins that silence covalently closed circular DNA, destabilize viral RNA, or disrupt entry and trafficking of HBV virions. Many of these are in the early stages of development, but may represent novel avenues to reduce HBV burden when combined with nucleos(t)ide analogues.

Chemically accessible hsp90 inhibitor that does not induce a heat shock response

Recent cancer therapies have focused on targeting biology networks through a single regulatory protein. Heat shock protein 90 (hsp90) is an ideal oncogenic target as it regulates over 400 client proteins and cochaperones. However, clinical inhibitors of hsp90 have had limited success; the primary reason being that they induce a heat shock response. We describe the synthesis and biological evaluation of a new hsp90 inhibitor, SM253. The previous generation on which SM253 is based (SM145) has poor overall synthetic yields, low solubility, and micromolar cytotoxicity. By comparison SM253 has relatively high overall yields, good aqueous solubility, and is more cytotoxic than its parent compound. Verification that hsp90 is SM253's target was accomplished using pull-down and protein folding assays. SM253 is superior to both SM145 and the clinical candidate 17-AAG as it decreases proteins related to the heat shock response by 2-fold, versus a 2-4-fold increase observed when cells are treated with 17-AAG.

Identification of two novel HSP90 proteins in Babesia orientalis: molecular characterization, and computational analyses of their structure, function, antigenicity and inhibitor interaction

Background

HSP90 protects the cells from heat stress and facilitates protein maturation and stability. The full genome sequences of piroplasms contain two putative HSP90 proteins, which are yet uncharacterized. To this end, the two putative HSP90 proteins of Babesia orientalis were identified and characterized by molecular and in silico methods.

Methods

The two putative proteins in B. orientalis genome showing homology with putative HSP90 of other piroplasms were cloned and sequenced. A computational analysis was carried out to predict the antigenic determinants, structure and function of these proteins. The interactions of two HSP90 isoforms with respective inhibitors were also examined through docking analysis.

Results

The length of BoHSP90-A gene (amplified from gDNA) was 2706 bp with one intron from position 997 to 1299 bp. This gene amplified from cDNA corresponded to full length CDS with an open reading frame (ORF) of 2403 bp encoding a 800 amino acid (AA) polypeptide with a predicted size of 91.02 kDa. The HSP90-B gene was intronless with an ORF of 2349 bp, and predicted polypeptide comprised of 797 AA with a size of 90.59 kDa. The AA sequences of these two proteins of B. orientalis were the most identical to those of B. bovis. The BoHSP90-A and BoHSP90-B were recognized as 90 kDa in the parasite lysate by the rabbit antisera raised against the recombinant BoHSP90 proteins. The anti-B. orientalis buffalo serum reacted with the rBoHSP90s expressed in E. coli, indicating that these proteins might be secreted by the parasite before entry into host cells. The overall structure and functional analyses showed several domains involved in ATPase activity, client protein binding and HSP90 dimerization. Likewise, several HSP90 inhibitors showed binding to ATP binding pockets of BoHSP90-A and BoHSP90-B, as observed through protein structure-ligand interaction analysis.

Conclusions

The two putative HSP90 proteins in B. orientalis were recognized as 90 kDa. The rBoHSP90-A and rBoHSP90-B were reacted with the B. orientalis infected buffalo serum. The computational structure and functional analyses revealed that these two proteins may have chaperonic activity. The protein structure-ligand interaction analyses indicated that these two proteins had many drug target sites.

Novel myelofibrosis treatment strategies: potential partners for combination therapies

Of the myeloproliferative neoplasms (MPNs), myelofibrosis (MF) is associated with the greatest symptom burden and poorest prognosis and is characterized by constitutional symptoms, cytopenias, splenomegaly and bone marrow fibrosis. A hallmark of MF is dysregulation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway that has led to the development of JAK inhibitors targeting this pathway. Calreticulin gene mutations have recently been identified in JAK2 mutation-negative patients with MF. Identification of JAK inhibitor resistance and broad contributions to MF disease pathogenesis from epigenetic deregulators, pathways that work in concert with JAK/STAT (that is, mammalian target of rapamycin/AKT/phosphoinositide 3-kinase, RAS/RAF/MEK, PIM kinase), fibrosis-promoting factors and the MF megakaryocyte, suggest that numerous options may be partnered with a JAK inhibitor. Therefore, we will discuss logical and potential partners for combination therapies for the treatment of patients with MF.

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.

The role of heat shock protein 90 in migration and proliferation of vascular smooth muscle cells in the development of atherosclerosis

The molecular chaperone heat shock protein 90 (HSP90) is overexpressed in plaques of atherosclerosis patients, and is associated with plaque instability. However, the role of HSP90 in atherosclerosis remains unclear. The present study investigated the effects of HSP90 inhibition on migration and proliferation of vascular smooth muscle cells (VSMCs) and involvement in atherosclerosis. To examine the role of HSP90 in VSMC migration, VSMCs were treated with the specific HSP90 inhibitors, 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) and STA-9090. Results of a chemotaxis assay showed that the HSP90 inhibitors suppress migration of VSMCs. HSP90 inhibition also prevented invasion and sprout formation of VSMCs via inhibition of matrix metalloproteinase-2 proteolytic activity. Results of a flow cytometric analysis showed that HSP90 inhibition induces cell cycle arrest via regulation of cyclin D3, PCNA and pRb. To investigate the role of HSP90 in the development of atherosclerosis, low-density lipoprotein receptor (LDLR) deficient mice were fed with a high cholesterol diet for 4weeks and treated with 17-AAG for 8weeks. HSP90 inhibition suppressed migration of VSMCs into atherosclerotic plaque lesions in high cholesterol diet-stimulated LDLR(-/-) mice. Inhibition of HSP90 attenuates formation of atherosclerotic plaques via suppression of VSMC migration and proliferation, indicating that HSP90 inhibitors can be used as therapeutic agents for atherosclerosis and in stent restenosis.

Triazole Containing Novobiocin and Biphenyl Amides as Hsp90 C-Terminal Inhibitors

Hsp90 C-terminal inhibitors are advantageous for the development of new cancer chemotherapeutics due to their ability to segregate client protein degradation from induction of the prosurvival heat shock response, which is a major detriment associated with Hsp90 N-terminal inhibitors under clinical investigation. Based upon prior SAR trends, a 1,2,3-triazole side chain was placed in lieu of the aryl side chain and attached to both the coumarin and biphenyl scaffold. Antiproliferative studies against SKBr3 and MCF-7 breast cancer cell lines demonstrated these triazole-containing compounds to exhibit improved activity. These compounds were shown to manifest Hsp90 inhibitory activity through Western blot analysis and represent a new scaffold upon which more potent inhibitors can be pursued.

A phase II open-label study of ganetespib, a novel heat shock protein 90 inhibitor for patients with metastatic breast cancer

BACKGROUND

Ganetespib is a small molecule, nongeldanamycin HSP90 inhibitor with potent inhibitory effects on HSP90-dependent oncoproteins of relevance to breast cancer pathogenesis. We therefore tested ganetespib in an unselected cohort of patients with MBC.

PATIENTS AND METHODS

Patients were treated with single agent ganetespib at 200 mg/m(2) once weekly for 3 weeks, on a 28-day cycle. Therapy was continued until disease progression. The primary end point was ORR using Reponse Evaluation Criteria in Solid Tumors version 1.1.

RESULTS

Twenty-two patients were enrolled with a median age of 51(range, 38-70) years and a median Eastern Cooperative Oncology Group performance status of 0 (range, 0-1). Most patients had at least 2 previous lines of chemotherapy in the metastatic setting. Most common toxicities, largely grade 1/2, were diarrhea, fatigue, nausea, and hypersensitivity reaction. The ORR in this unselected population was 9%, with all responses coming from the subset of patients with HER2-positive MBC (2/13; 15%). One patient with TNBC had objective tumor regression in the lung metastases. The clinical benefit rate (complete response + partial response + stable disease > 6 months) was 9%, median progression-free survival was 7 weeks (95% confidence interval [CI], 7-19), and median overall survival was 46 weeks (95% CI, 27-not applicable).

CONCLUSION

The study did not meet the prespecified criteria for ORR in the first stage of the Simon 2-stage model in this heavily pretreated unselected population of MBC. However, activity was observed in trastuzumab-refractory HER2-positive and TNBC. Ganetespib was well tolerated and responses in more targeted populations harboring specific HSP90-dependent oncoproteins justifies its further study, particularly as part of rational combinations.

Antiviral strategies for hepatitis E virus

The hepatitis E virus is a common cause of acute hepatitis. Contrary to hepatitis B and C, hepatitis E is mostly a mild infection, although it has a high mortality in pregnant women and can evolve to chronicity in immunocompromised patients. Ribavirin and pegylated interferon-α are the only available therapies, but both have side effects that are not acceptable for prophylaxis or treatment of mild infections. In addition, these drugs cannot be used for all patient types (e.g. in case of pregnancy, specific organ transplants or co-morbidities) and in resource-poor settings. Hence there is an urgent need for better antiviral treatments that are efficacious and safe, also during pregnancy. In this review, a concise introduction to the virus and disease is provided, followed by a discussion of the available assay systems and potential molecular targets (viral proteins and host factors) for the development of inhibitors of HEV replication. Finally, directions for future research are presented.

The spectral properties of (-)-epigallocatechin 3-O-gallate (EGCG) fluorescence in different solvents: dependence on solvent polarity

(-)-Epigallocatechin 3-O-gallate (EGCG) a molecule found in green tea and known for a plethora of bioactive properties is an inhibitor of heat shock protein 90 (HSP90), a protein of interest as a target for cancer and neuroprotection. Determination of the spectral properties of EGCG fluorescence in environments similar to those of binding sites found in proteins provides an important tool to directly study protein-EGCG interactions. The goal of this study is to examine the spectral properties of EGCG fluorescence in an aqueous buffer (AB) at pH=7.0, acetonitrile (AN) (a polar aprotic solvent), dimethylsulfoxide (DMSO) (a polar aprotic solvent), and ethanol (EtOH) (a polar protic solvent). We demonstrate that EGCG is a highly fluorescent molecule when excited at approximately 275 nm with emission maxima between 350 and 400 nm depending on solvent. Another smaller excitation peak was found when EGCG is excited at approximately 235 nm with maximum emission between 340 and 400 nm. We found that the fluorescence intensity (FI) of EGCG in AB at pH=7.0 is significantly quenched, and that it is about 85 times higher in an aprotic solvent DMSO. The Stokes shifts of EGCG fluorescence were determined by solvent polarity. In addition, while the emission maxima of EGCG fluorescence in AB, DMSO, and EtOH follow the Lippert-Mataga equation, its fluorescence in AN points to non-specific solvent effects on EGCG fluorescence. We conclude that significant solvent-dependent changes in both fluorescence intensity and fluorescence emission shifts can be effectively used to distinguish EGCG in aqueous solutions from EGCG in environments of different polarity, and, thus, can be used to study specific EGCG binding to protein binding sites where the environment is often different from aqueous in terms of polarity.

Hsp90 inhibitor 17-DMAG decreases expression of conserved herpesvirus protein kinases and reduces virus production in Epstein-Barr virus-infected cells

All eight human herpesviruses have a conserved herpesvirus protein kinase (CHPK) that is important for the lytic phase of the viral life cycle. In this study, we show that heat shock protein 90 (Hsp90) interacts directly with each of the eight CHPKs, and we demonstrate that an Hsp90 inhibitor drug, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), decreases expression of all eight CHPKs in transfected HeLa cells. 17-DMAG also decreases expression the of the endogenous Epstein-Barr virus protein kinase (EBV PK, encoded by the BGLF4 gene) in lytically infected EBV-positive cells and inhibits phosphorylation of several different known EBV PK target proteins. Furthermore, 17-DMAG treatment abrogates expression of the human cytomegalovirus (HCMV) kinase UL97 in HCMV-infected human fibroblasts. Importantly, 17-DMAG treatment decreased the EBV titer approximately 100-fold in lytically infected AGS-Akata cells without causing significant cellular toxicity during the same time frame. Increased EBV PK expression in 17-DMAG-treated AGS-Akata cells did not restore EBV titers, suggesting that 17-DMAG simultaneously targets multiple viral and/or cellular proteins required for efficient viral replication. These results suggest that Hsp90 inhibitors, including 17-DMAG, may be a promising group of drugs that could have profound antiviral effects on herpesviruses.