Down-regulation of heat shock protein 70 improves arsenic trioxide and 17-DMAG effects on constitutive signal transducer and activator of transcription 3 activity

Is It Still Possible to Think about HSP70 as a Therapeutic Target in Onco-Hematological Diseases?

The search for molecules to be targeted that are involved in apoptosis resistance/increased survival and pathogenesis of onco-hematological malignancies is ongoing since these diseases are still not completely understood. Over the years, a good candidate has been identified in the Heat Shock Protein of 70kDa (HSP70), a molecule defined as “the most cytoprotective protein ever been described”. HSP70 is induced in response to a wide variety of physiological and environmental insults, allowing cells to survive lethal conditions. This molecular chaperone has been detected and studied in almost all the onco-hematological diseases and is also correlated to poor prognosis and resistance to therapy. In this review, we give an overview of the discoveries that have led us to consider HSP70 as a therapeutic target for mono- or combination-therapies in acute and chronic leukemias, multiple myeloma and different types of lymphomas. In this excursus, we will also consider HSP70 partners, such as its transcription factor HSF1 or its co-chaperones whose druggability could indirectly affect HSP70. Finally, we will try to answer the question asked in the title of this review considering that, despite the effort made by research in this field, HSP70 inhibitors never reached the clinic.

Innovative challenge for the inhibition of hepatocellular carcinoma progression by combined targeting of HSP90 and STAT3/HIF-1α signaling

Hepatocellular carcinoma (HCC) is the third foremost cause of cancer-related deaths. HCC has a very bad prognosis because it is asymptomatic in the early stages, resulting in a late diagnosis, and it is highly resistant to conventional chemotherapy. Such chemotherapies have been proven disappointing because they provide extremely low survival benefits. This study discloses that the STAT3/HIF-1α is an auspicious therapeutic attack site for conceivable repression of HCC development. A site that can be targeted by simultaneous administration of a STAT3 inhibitor in the context of HSP90 inhibition. 17-DMAG binds to HSP90 and constrains its function, resulting in the degradation of HSP90 client proteins HIF-1α and STAT3. Hypoxia recruits STAT3/HIF-1α complex within the VEGF promoter. Additionally, it was acknowledged that STAT3 is an essential mediator of VEGF transcription by direct binding to its promoter. Furthermore, it induces HIF-1α stability and enhances its transcriptional activity. Herein, we revealed that the combination therapy using 17-DMAG and nifuroxazide, a STAT3 inhibitor, repressed the diethylnitrosamine-induced alterations in the structure of the liver. This effect was mediated via decreasing the levels of the HSP90 client proteins HIF-1α and pSTAT3 resulting in the suppression of the STAT3/HIF-1α complex transcriptional activity. To conclude, 17-DMAG/NFXZD combination therapy-induced disruption in the STAT3/HIF-1α loop led to a potential antiangiogenic activity and showed apoptotic potential by inhibiting autophagy and inducing ROS/apoptosis signaling. Additionally, this combination therapy exhibited promising survival prolongation in mice with HCC. Consequently, the use of 17-DMAG/NFXZD renders an inspirational perspective in managing HCC. However, further investigations are compulsory.

Cell Surface GRP94 as a Novel Emerging Therapeutic Target for Monoclonal Antibody Cancer Therapy

Glucose-regulated protein 94 (GRP94) is an endoplasmic reticulum (ER)-resident member of the heat shock protein 90 (HSP90) family. In physiological conditions, it plays a vital role in regulating biological functions, including chaperoning cellular proteins in the ER lumen, maintaining calcium homeostasis, and modulating immune system function. Recently, several reports have shown the functional role and clinical relevance of GRP94 overexpression in the progression and metastasis of several cancers. Therefore, the current review highlights GRP94’s physiological and pathophysiological roles in normal and cancer cells. Additionally, the unmet medical needs of small chemical inhibitors and the current development status of monoclonal antibodies specifically targeting GRP94 will be discussed to emphasize the importance of cell surface GRP94 as an emerging therapeutic target in monoclonal antibody therapy for cancer.

Chaperoning STAT3/5 by Heat Shock Proteins: Interest of Their Targeting in Cancer Therapy

While cells from multicellular organisms are dependent upon exogenous signals for their survival, growth, and proliferation, commitment to a specific cell fate requires the correct folding and maturation of proteins, as well as the degradation of misfolded or aggregated proteins within the cell. This general control of protein quality involves the expression and the activity of molecular chaperones such as heat shock proteins (HSPs). HSPs, through their interaction with the STAT3/STAT5 transcription factor pathway, can be crucial both for the tumorigenic properties of cancer cells (cell proliferation, survival) and for the microenvironmental immune cell compartment (differentiation, activation, cytokine secretion) that contributes to immunosuppression, which, in turn, potentially promotes tumor progression. Understanding the contribution of chaperones such as HSP27, HSP70, HSP90, and HSP110 to the STAT3/5 signaling pathway has raised the possibility of targeting such HSPs to specifically restrain STAT3/5 oncogenic functions. In this review, we present how HSPs control STAT3 and STAT5 activation, and vice versa, how the STAT signaling pathways modulate HSP expression. We also discuss whether targeting HSPs is a valid therapeutic option and which HSP would be the best candidate for such a strategy.

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

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

Establishment and characterization of arsenic trioxide resistant KB/ATO cells

Arsenic trioxide (ATO) is used as a chemotherapeutic agent for the treatment of acute promyelocytic leukemia. However, increasing drug resistance is reducing its efficacy. Therefore, a better understanding of ATO resistance mechanism is required. In this study, we established an ATO-resistant human epidermoid carcinoma cell line, KB/ATO, from its parental KB-3-1 cells. In addition to ATO, KB/ATO cells also exhibited cross-resistance to other anticancer drugs such as cisplatin, antimony potassium tartrate, and 6-mercaptopurine. The arsenic accumulation in KB/ATO cells was significantly lower than that in KB-3-1 cells. Further analysis indicated that neither application of P-glycoprotein inhibitor, breast cancer resistant protein (BCRP) inhibitor, or multidrug resistance protein 1 (MRP1) inhibitor could eliminate ATO resistance. We found that the expression level of ABCB6 was increased in KB/ATO cells. In conclusion, ABCB6 could be an important factor for ATO resistance in KB/ATO cells. The ABCB6 level may serve as a predictive biomarker for the effectiveness of ATO therapy.

Protein stabilization improves STAT3 function in autosomal dominant hyper-IgE syndrome

Autosomal dominant hyper-IgE syndrome (AD-HIES) is caused by dominant-negative mutations in STAT3; however, the molecular basis for mutant STAT3 allele dysfunction is unclear and treatment remains supportive. We hypothesized that AD-HIES mutations decrease STAT3 protein stability and that mutant STAT3 activity can be improved by agents that increase chaperone protein activity. We used computer modeling to characterize the effect of STAT3 mutations on protein stability. We measured STAT3 protein half-life (t_1/2) and determined levels of STAT3 phosphorylated on tyrosine (Y) 705 (pY-STAT3) and mRNA levels of STAT3 gene targets in Epstein-Barr virus-transformed B (EBV) cells, human peripheral blood mononuclear cells (PBMCs), and mouse splenocytes incubated without or with chaperone protein modulators-HSF1A, a small-molecule TRiC modulator, or geranylgeranylacetone (GGA), a drug that upregulates heat shock protein (HSP) 70 and HSP90. Computer modeling predicted that 81% of AD-HIES mutations are destabilizing. STAT3 protein t_1/2 in EBV cells from AD-HIES patients with destabilizing STAT3 mutations was markedly reduced. Treatment of EBV cells containing destabilizing STAT3 mutations with either HSF1A or GGA normalized STAT3 t_1/2, increased pY-STAT3 levels, and increased mRNA levels of STAT3 target genes up to 79% of control. In addition, treatment of human PBMCs or mouse splenocytes containing destabilizing STAT3 mutations with either HSF1A or GGA increased levels of cytokine-activated pY-STAT3 within human CD4⁺ and CD8⁺ T cells and numbers of IL-17-producing CD4⁺ mouse splenocytes, respectively. Thus, most AD-HIES STAT3 mutations are destabilizing; agents that modulate chaperone protein function improve STAT3 stability and activity in T cells and may provide a specific treatment.

Contribution of chaperones to STAT pathway signaling

Aberrant STAT signaling is associated with the development and progression of many cancers and immune related diseases. Recent findings demonstrate that proteostasis modulators under clinical investigation for cancer therapy have a significant impact on STAT signaling, which may be critical for mediating their anti-cancer effects. Chaperones are critical for protein folding, stability and function and, thus, play an essential role in the maintenance of proteostasis. In this review we discuss the role of chaperones in STAT and tyrosine kinase (TK) protein folding, modulation of STAT and TK activity, and degradation of TKs. We highlight the important role of chaperones in STAT signaling, and how this knowledge has provided a framework for the development of new therapeutic avenues of targeting STAT signaling related pathologies.

Dual targeting of heat shock proteins 90 and 70 promotes cell death and enhances the anticancer effect of chemotherapeutic agents in bladder cancer

Heat shock proteins (HSPs), which are molecular chaperones that stabilize numerous vital proteins, may be attractive targets for cancer therapy. The aim of the present study was to investigate the possible anticancer effect of single or dual targeting of HSP90 and HSP70 and the combination treatment with HSP inhibitors and chemotherapeutic agents in bladder cancer cells. The expression of HSP90 and the anticancer effect of the HSP90 inhibitor 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) coupled with cisplatin, docetaxel, or gemcitabine were examined using immunohistochemistry, quantitative real-time PCR, cell growth, flow cytometry, immunoblots and caspase-3/7 assays. The expression of HSP70 under HSP90 inhibition and the additive effect of HSP70 inhibitor pifithrin-μ (PFT-μ) were examined by the same assays and transmission electron microscopy. HSP90 was highly expressed in bladder cancer tissues and cell lines. 17-AAG enhanced the antiproliferative and apoptotic effects of each chemotherapeutic agent. 17-AAG also suppressed Akt activity but induced the upregulation of HSP70. PFT-μ enhanced the effect of 17-AAG or chemotherapeutic agents; the triple combination of 17-AAG, PFT-μ and a chemotherapeutic agent showed the most significant anticancer effect on the T24 cell line. The combination of 17-AAG and PFT-μ markedly suppressed Akt and Bad activities. With HSP90 suppression, HSP70 overexpression possibly contributes to the avoidance of cell death and HSP70 may be a key molecule for overcoming resistance to the HSP90 inhibitor. The dual targeting of these two chaperones and the combination with conventional anticancer drugs could be a promising therapeutic option for patients with advanced bladder cancer.

Synergism between clofarabine and decitabine through p53R2: a pharmacodynamic drug-drug interaction modeling

Clofarabine (CLO), a purine nucleoside analog with promising efficacy in acute myeloid leukemia (AML), inhibits the ribonucleotidereductase, p53R2. We have shown that p53R2 mRNA is up-regulated by decitabine (DEC), another drug with promising activity in AML. We developed a pharmacodynamic model to characterize the interaction between CLO and DEC on an AML cell line and down-regulated p53R2 protein to understand its role. These results confirm a role for p53R2 in both CLO and DEC mechanism of action, demonstrate synergism between these two drugs in this AML model and support the use of this combination in a future clinical trial.

HSP90 inhibition by 17-DMAG reduces inflammation in J774 macrophages through suppression of Akt and nuclear factor-κB pathways

OBJECTIVE

This study was designed to determine whether inhibition of heat shock protein 90 (HSP90) reduces pro-inflammatory mediator production by decreasing the nuclear factor (NF)-κB and Akt signaling pathways in immune-stimulated macrophages.

METHODS

J774A.1 murine macrophages were treated with the HSP90 inhibitor 17-DMAG (0.01, 0.1 or 1 μM) prior to immune stimulation with lipopolysaccharide and interferon-γ. Expression of Akt, inhibitor of κB kinase (IKK), and heat shock proteins were measured in whole cell lysates by Western blotting. Phosphorylated Akt and inhibitor of κB (IκB) were measured in whole cell lysates by ELISA. Cell supernatants were analyzed for interleukin (IL)-6, tumor necrosis factor (TNF)-α and nitric oxide (NO). Translocation of NF-κB and heat shock factor (HSF)-1 was assessed by immunofluorescence.

RESULTS

Treating cells with 17-DMAG reduced expression of Akt and IKK in immune-stimulated cells. 17-DMAG reduced nuclear translocation of NF-κB and reduced immune-stimulated production of IL-6, TNF-α and NO, but did not decrease inducible nitric oxide synthase expression.

CONCLUSIONS

Our studies show that the immune-mediated NF-κB inflammatory cascade is blocked by the HSP90 inhibitor 17-DMAG. Due to the broad interaction of HSP90 with many pro-inflammatory kinase cascades, inhibition of HSP90 may provide a novel approach to reducing chronic inflammation.

Phase 1 study of arsenic trioxide, high-dose cytarabine, and idarubicin to down-regulate constitutive signal transducer and activator of transcription 3 activity in patients aged <60 years with acute myeloid leukemia

BACKGROUND

Constitutive activation of signal transducer and activator of transcription-3 (STAT3) was detected in blasts from approximately 50% of patients with acute myeloid leukemia (AML) and was correlated with an adverse outcome. In vitro treatment of AML blasts with arsenic trioxide (ATO) down-regulated STAT3 activity within 6 hours associated with a reduced viability within 48 hours.

METHODS

A phase 1 clinical trial to evaluate the biologically effective dose and/or the maximally tolerated dose (MTD) of ATO in vivo in conjunction with high-dose cytarabine (Hidac) and idarubicin (Ida) in patients with AML aged <60 years was conducted. Data were compared with 117 historic AML patients who had received treatment with Hidac/Ida.

RESULTS

In total, 61 patients were enrolled onto 11 different dose levels (from 0.01 to 0.65 mg/kg ideal body weight). The MTD was 0.5 mg/kg. Compared with historic controls, patients who received ATO/Hidac/Ida, although they had similar pretreatment characteristics, had better overall survival (P = .039).

CONCLUSIONS

ATO priming may have improved the outcome of patients aged <60 years with AML who received Hidac/Ida. The current data suggested that ATO may enhance the effect of chemotherapy. The authors concluded that further studies of this novel combination are warranted.