Analysis of expression of heat shock protein-90 (HSP90) and the effects of HSP90 inhibitor (17-AAG) in multiple myeloma

Targeting NKG2D/NKG2DL axis in multiple myeloma therapy

Immune effector cells in patients with multiple myeloma (MM) are at the forefront of many immunotherapy treatments, and several methods have been developed to fully utilise the antitumour potential of immune cells. T and NK cell-derived immune lymphocytes both expressed activating NK receptor group 2 member D(NKG2D). This receptor can identify eight distinct NKG2D ligands (NKG2DL), including major histocompatibility complex class I (MHC) chain-related protein A and B (MICA and MICB). Their binding to NKG2D triggers effector roles in T and NK cells. NKG2DL is polymorphic in MM cells. The decreased expression of NKG2DL on the cell surface is explained by multiple mechanisms of tumour immune escape. In this review, we discuss the mechanisms by which the NKG2D/NKG2DL axis regulates immune effector cells and strategies for promoting NKG2DL expression and inhibiting its release in multiple myeloma and propose therapeutic strategies that increase the expression of NKG2DL in MM cells while enhancing the activation and killing function of NK cells.

Predictive Value of Serum Heat Shock Protein 90α on the Prognosis of Patients with Lung Adenocarcinoma

Purpose

Heat shock protein 90α (HSP90α) is highly expressed in tumors, and predicts tumor progression. This study analyzed the correlation between the expression level of HSP90α in the serum and the prognosis of patients with lung adenocarcinoma.

Patients and methods

The medical records of patients with 228 lung adenocarcinoma from September 2015 to December 2021 were analyzed. HSP90α expression in the patients' serum was detected by ELISA and the cut-off value (93.76 ng/mL) was determined according to the ROC curve, then the patients were divided into high- and low-level groups. The differences in the medical records of the two groups were compared using the X² test, and Univariate and multivariate Cox regression analyses showed that serum HSP90α level were independent risk factors for both PFS and OS (P < 0.05).

Results

HSP90α was positively correlated with TNM staging (P < 0.01) by One-way analysis of variance. The results of the correlation analysis and the Kaplan-Meier survival curve showed that the expression levels of HSP90α and CEA of patients were positively correlated (R=0.54, P < 0.001), and patients with high HSP90α and CEA levels had the worst OS (P < 0.001).

Conclusion

HSP90α expression is negatively correlated with the prognosis of patients with lung adenocarcinoma and is a potential prognostic marker.

Transcriptomic analysis reveals that heat shock protein 90α is a potential diagnostic and prognostic biomarker for cancer

The molecular chaperone heat shock protein 90 (Hsp90) is highly expressed in tumor tissue according to many studies. However, there is no large-scale study investigating the expression of Hsp90 in pan-cancer so far, and the molecular mechanisms leading to aberrant Hsp90 expression are also largely unknown. To address these questions, we performed an in silico analysis of Hsp90 expression using mRNA sequencing data from The Cancer Genome Atlas study. The results were further validated using independent datasets. We found that the expression of HSP90AA1, a subtype of Hsp90, was much higher in hepatocellular carcinoma than in adjacent normal liver tissue. A large cancer panel with eight more cancer types revealed a similar trend except for prostate cancer, which had low HSP90AA1 expression in tumor tissue. Heat shock factor 1 followed a similar trend as HSP90AA1, with higher expression in cancer. HSP90AA1 expression was closely related to its copy numbers. Deletion of the HSP90AA1 locus in a subset of hepatocellular carcinoma led to low HSP90AA1 expression. In addition, higher HSP90AA1 expression was associated with poorer prognosis in hepatocellular carcinoma patients. In a multivariable analysis including tumor, node and metastasis stage, HSP90AA1 expression remained a negative prognostic factor, suggesting that the effect of HSP90AA1 was independent of tumor stage. In conclusion, we demonstrated that high HSP90AA1 expression was ubiquitous in cancer and that HSP90AA1 was a potential diagnostic and prognostic biomarker for hepatocellular carcinoma.

Heat shock proteins as a new, promising target of multiple myeloma therapy

Introduction: The results of therapy of the multiple myeloma (MM) patients remain unsatisfactory despite the constantly observed progress in treatment.Areas covered: It has been shown that mechanisms regulated by heat shock proteins (HSPs) play an important role in pathogenesis of MM and resistance developing to treatment, which constitute a protective shield against external damaging factors in healthy and cancerous cells.Expert opinion: Inhibiting these mechanisms seems to be the natural way of therapy in MM patients. In vitro studies have shown promising effects in the form of an increase in the apoptosis index of MM cells exposed to HSP inhibitors. The observations are very promising in the early stages of clinical trials with HSP inhibitors, such as tanespimycin, in the relapsed/refractory MM patients. Effects were more pronounced when combined with bortezomib. It seems that enriching the range of anti-myeloma drugs with HSP inhibitors may be the next step in the future of extending life of patients with multiple myeloma.

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

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

Consecutive Day HSP90 Inhibitor Administration Improves Efficacy in Murine Models of KIT-Driven Malignancies and Canine Mast Cell Tumors

PURPOSE

STA-1474, prodrug of the heat shock protein 90 inhibitor (HSP90i) ganetespib, previously demonstrated activity in canine preclinical models of cancer; interestingly, prolonged infusions were associated with improved biologic activity. The purpose of this study was to identify the ideal treatment schedule for HSP90i in preclinical models of KIT-driven malignancies and in dogs with spontaneous mast cell tumors (MCT), where KIT is a known driver.

EXPERIMENTAL DESIGN

In vitro and murine xenograft experiments and clinical studies in dogs with MCTs were used to define the effects of HSP90i-dosing regimen on client protein downregulation and antitumor activity.

RESULTS

Continuous HSP90 inhibition led to durable destabilization of client proteins in vitro; however, transient exposure required >10× drug for comparable effects. In vivo, KIT was rapidly degraded following a single dose of HSP90i but returned to baseline levels within a day. HSP90 levels increased and stabilized 16 hours after HSP90i and were not elevated following a subsequent near-term exposure, providing a functional pool of chaperone to stabilize proteins and a means for greater therapeutic activity upon HSP90i reexposure. HSP90i administered on days 1 and 2 (D1/D2) demonstrated increased biologic activity compared with D1 treatment in KIT or EGFR-driven murine tumor models. In a trial of dogs with MCT, D1/D2 dosing of HSP90i was associated with sustained KIT downregulation, 50% objective response rate and 100% clinical benefit rate compared with D1 and D1/D4 schedules.

CONCLUSIONS

These data provide further evidence that prolonged HSP90i exposure improves biologic activity through sustained downregulation of client proteins.

Synergistic effects of rmhTRAIL and 17-AAG on the proliferation and apoptosis of multiple myeloma cells

OBJECTIVE

This study aimed to investigate synergistic effects of recombinant mutant human tumor necrosis factor-related apoptosis-inducing ligand (rmhTRAIL) and heat-shock protein 90 (HSP90) inhibitor (geldanamycin derivative 17 -allylamino- 17-demethoxy -geldanamycin, 17-AAG) on the proliferation and apoptosis of multiple myeloma (MM) cells.

METHODS

MTT assays evaluated inhibitory effects of rmhTRAIL and 17-AAG in different concentrations and treatment durations on the proliferation of RPMI8226 and U266 cells. The half maximal inhibitory concentration was calculated using OriginPro7.5. Synergistic effects of rmhTRAIL and 17-AAG on apoptosis of MM cells were detected using flow cytometry at 24 and 48 h post-treatment. To evaluate synergistic effects of rmhTRAIL and 17-AAG, the Q-value was calculated using King's formula.

RESULTS

rmhTRAIL exhibited significant inhibitory effects on the proliferation of RPMI8226 cells in a dose- and time-dependent manner (>50%), whereas U266 cells were not sensitive to rmhTRAIL (<50%). 17-AAG inhibited the proliferation of RPMI8226 and U266 cells in a dose-dependent manner (>80%). Significant synergistic effects of rmhTRAIL and 17-AAG on the proliferation of RPMI8226 cells were revealed (Q-value > 1.15), whereas synergistic effects were not evident on the proliferation of U266 cells (Q-value < 1.15). rmhTRAIL and 17-AAG exhibited significant synergistic effects on apoptosis of RPMI8226 and U266 cells (Q-value > 1.15).

CONCLUSION

The combined application of rmhTRAIL and 17-AAG revealed favorable synergistic effects in the treatment of MM.

Evaluation of in vitro effects of various targeted drugs on plasma cells and putative neoplastic stem cells in patients with multiple myeloma

Multiple myeloma (MM) is a malignancy characterized by monoclonal paraproteinemia and tissue plasmocytosis. In advanced MM cytopenia and osteopathy may occur. Although several effective treatment strategies have been developed in recent years, there is still a need to identify new drug targets and to develop more effective therapies for patients with advanced MM. We examined the effects of 15 targeted drugs on growth and survival of primary MM cells and 5 MM cell lines (MM.1S, NCI-H929, OPM-2, RPMI-8226, U-266). The PI3-kinase blocker BEZ235, the pan-BCL-2 inhibitor obatoclax, the Hsp90-targeting drug 17AAG, and the Polo-like kinase-1 inhibitor BI2536, were found to exert major growth-inhibitory effects in all 5 MM cell lines tested. Moreover, these drugs suppressed the in vitro proliferation of primary bone marrow-derived MM cells and induced apoptosis at pharmacologic drug concentrations. Apoptosis-inducing effects were not only seen in the bulk of MM cells but also in MM stem cell-containing CD138⁻/CD20⁺/CD27⁺ memory B-cell fractions. Synergistic growth-inhibitory effects were observed in MM cell lines using various drug combinations, including 17AAG+BI2536 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+BEZ235 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+obatoclax in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+BEZ235 in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+obatoclax in MM.1S, OPM-2 and RPMI-8226 cells, and BEZ235+obatoclax in MM.1S and RPMI-8226 cells. Together, our data show that various targeted drugs induce profound and often synergistic anti-neoplastic effects in MM cells which may have clinical implications and may contribute to the development of novel treatment strategies in advanced MM.

Endoplasmic reticulum stress in the development of multiple myeloma and drug resistance

Multiple myeloma (MM) is a haematological malignancy of mature antibody‐secreting plasma cells. Currently, MM is incurable, but advances in drug treatments have increased patient lifespan. One of the characteristics of MM is the excessive production of monoclonal immunoglobulin (also referred to as paraprotein). This high level of protein production induces endoplasmic reticulum (ER) stress, and proteasomal degradation of the paraprotein is required to avoid ER stress‐induced cell death. Consequently, proteasomal inhibitors such as bortezomib have been particularly effective therapies. Unfortunately development of resistance to bortezomib is common. In this review, we address how control of endoplasmic reticulum stress is important in the development of MM and how the unfolded protein response and its associated stress response pathways are involved in the development of bortezomib resistance.

NKG2D and DNAM-1 Ligands: Molecular Targets for NK Cell-Mediated Immunotherapeutic Intervention in Multiple Myeloma

A pivotal strategy to improve NK cell-mediated antitumor activity involves the upregulation of activating ligands on tumor cells. Enhancement of NK cell-mediated recognition of multiple myeloma cells was reported by us and others showing increased surface expression of NKG2D and DNAM-1 ligands on tumor cells following treatment with a number of chemotherapeutic agents, such as genotoxic drugs or inhibitors of proteasome, histone deacetylases, GSK3, and HSP-90. These compounds have the capability to affect tumor survival but also to activate specific transduction pathways associated with the upregulation of different NK cell activating ligands on the tumor cells. Here, we will summarize and discuss the molecular pathways whereby these drugs can regulate the expression of NK cell activating ligands in multiple myeloma cells.

Recent advances in antimultiple myeloma drug development

Multiple myeloma (MM) is the second most common hematological malignancy and is characterized by the aberrant proliferation of terminally differentiated plasma B cells with impairment in apoptosis capacity. Particularly, osteolytic bone diseases and renal failure resulting from hyperparaproteinemia and hypercalcemia have been the major serious sequelae that are inextricably linked with MM tumor progression. Despite the introduction of new treatment regimens, problematic neuropathy, thrombocytopenia, drug resistance and high MM relapse rates continue to plague the current therapies. New chemical agents are in development on the basis of understanding several signaling pathways and molecular mechanisms like tumor necrosis factor-α, proteasome, PI3K and MARKs. This review focuses on the most recent patents and clinical trials in the development of new medicine for the treatment of multiple myeloma. Furthermore, the important signaling pathways involved in the proliferation, survival and apoptosis of myeloma cells will be discussed.

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

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

Drug resistance in multiple myeloma: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective therapeutic protocols, multiple myeloma still tends to be a hard-to-treat hematologic cancer. This hallmark of the disease is in fact a sequel to drug resistant phenotypes persisting initially or emerging in the course of treatment. Furthermore, the heterogeneous nature of multiple myeloma makes treating patients with the same drug challenging because finding a drugable oncogenic process common to all patients is not yet feasible, while our current knowledge of genetic/epigenetic basis of multiple myeloma pathogenesis is outstanding. Nonetheless, bone marrow microenvironment components are well known as playing critical roles in myeloma tumor cell survival and environment-mediated drug resistance happening most possibly in all myeloma patients. Generally speaking, however; real mechanisms underlying drug resistance in multiple myeloma are not completely understood. The present review will discuss the latest findings and concepts in this regard. It reviews the association of important chromosomal translocations, oncogenes (e.g. TP53) mutations and deranged signaling pathways (e.g. NFκB) with drug response in clinical and experimental investigations. It will also highlight how bone marrow microenvironment signals (Wnt, Notch) and myeloma cancer stem cells could contribute to drug resistance in multiple myeloma.

Effect of a heat shock protein 90-specific inhibitor on the proliferation and apoptosis induced by VEGF-C in cervical cancer cells

The aim of the present study was to investigate the effect of heat shock protein 90 (Hsp90)-specific inhibitor geldanamycin (GA) on the proliferation and apoptosis induced by vascular endothelial growth factor-C (VEGF-C) in cervical cancer cells. HeLa cells (1×10⁶/ml) in the logarithmic growth phase were incubated without serum for 24 h. The cells were pretreated with kinase insert domain receptor antibody (KDR)-Ab (20 μg/ml), phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (3 μmol/l), mitogen-activated protein kinase (MAPK) inhibitor PD98059 (30 μmol/l) or Hsp90-specific inhibitor GA (10 μmol/l) for 30 min, and then treated with VEGF-C (50 ng/μl) for a further 24 h. The cells were harvested for MTT analysis, annexin V-FITC/propidium iodide double staining for early apoptosis and SDS-PAGE and western blot analysis in order to determine Hsp90, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax) and cyclin D1 expression. Treatment with VEGF-C alone induced Hsp90 protein expression in HeLa cells at all time-points. Hsp90 expression was increased 3.31-fold in VEGF-C treated HeLa cells, and this increase was attenuated in the treatment groups (2.17-, 1.69-, 1.82-fold in VEGF-C + KDR-Ab, VEGF-C + PD98059 and VEGF-C + LY294002, respectively). The proliferation of the VEGF-C-treated HeLa cells was increased ~2.13-fold, while that of the VEGF-C + GA-treated HeLa cells decreased 0.87-fold (P<0.05). Even low concentrations of GA (0.02 μmol/l) were found to inhibit the Bcl-2 and cyclin D1 protein expression induced by VEGF-C. Therefore, the results indicate that the Hsp90-specific inhibitor GA has a critical role in the proliferation and apoptosis induced by VEGF-C in cervical cancer cells.

AKT as a therapeutic target in multiple myeloma

INTRODUCTION

Multiple myeloma remains an incurable malignancy with poor survival. Novel therapeutic approaches capable of improving outcomes in patients with multiple myeloma are urgently required. AKT is a central node in the phosphatidylinositol-3-kinase/AKT/mammalian target of rapamycin signaling pathway with high expression in advanced and resistant multiple myeloma. AKT contributes to multiple oncogenic functions in multiple myeloma which may be exploited therapeutically. Promising preclinical data has lent support for pursuing further development of AKT inhibitors in multiple myeloma. Lead drugs are now entering the clinic.

AREAS COVERED

The rationale for AKT inhibition in multiple myeloma, pharmacological subtypes of AKT inhibitors in development, available results of clinical studies of AKT inhibitors and suitable drug partners for further development in combination with AKT inhibition in multiple myeloma are discussed.

EXPERT OPINION

AKT inhibitors are a welcome addition to the armamentarium against multiple myeloma and promising clinical activity is being reported from ongoing trials in combination with established and/or novel treatment approaches. AKT inhibitors may be set to improve patient outcomes when used in combination with synergistic drug partners.

Human heat shock protein-specific cytotoxic T lymphocytes display potent antitumour immunity in multiple myeloma

Tumour cell-derived heat shock proteins (HSPs) are used as vaccines for immunotherapy of cancer patients. However, it is proposed that the peptide chaperoned on HSPs, not HSPs themselves, elicited a potent immune response. Given that HSPs are highly expressed by most myeloma cells and vital to myeloma cell survival, we reasoned that HSPs themselves might be an ideal myeloma antigen. In the present study, we explored the feasibility of targeting HSPs themselves for treating multiple myeloma. We identified and chose HLA-A*0201-binding peptides from human HSPB1 (HSP27) and HSP90AA1 (HSP90), and confirmed their immunogenicity in HLA-A*0201 transgenic mice. Dendritic cells pulsed with HSPB1 and HSP90AA1 peptides were used to stimulate peripheral blood mononuclear cells from healthy volunteers and myeloma patients to generate HSP peptide-specific cytotoxic T lymphocytes (CTLs). HSP peptide-specific CTLs efficiently lysed HLA-A*0201(+) myeloma cells (established cell lines and primary plasma cells) but not HLA-A*0201(-) myeloma cells in vitro, indicating that myeloma cells naturally express HSP peptides in the context of major histocompatibility complex class I molecules. More importantly, HSP peptide-specific CTLs effectively reduced tumour burden in the xenograft mouse model of myeloma. Our study clearly demonstrated that HSPs might be novel tumour antigens for immunotherapy of myeloma.

Innate and Adaptive Responses to Heat Shock Proteins in Behcet's Disease

Behcet's disease (BD) is a systemic, chronic inflammatory disorder with both innate and adaptive immune responses. Heat shock proteins (HSP) are highly conserved molecules in different species with scavenger activity and involved in correct folding of newly synthesized proteins. T and B cell responses against HSPs are observed in BD patients in both αβ and γδ T-cell populations. 60-kD HSP (HSP60) is also shown to be recognized by pattern recognition receptors such as toll-like receptors (TLR) and is suggested to be an endogenous "danger" signal to the immune system with rapid inflammatory cytokine releases and enhancement of adaptive Th1-type responses. Elucidating the exact role of HSPs in BD pathogenesis might pave the way to less toxic therapeutic approaches to BD, such as antibacterial therapies and immunomodulation.

Targeting HSP90 and monoclonal protein trafficking modulates the unfolded protein response, chaperone regulation and apoptosis in myeloma cells

Multiple myeloma is characterized by the production of substantial quantities of monoclonal protein. We have previously demonstrated that select inhibitors of the isoprenoid biosynthetic pathway (IBP) induce apoptosis of myeloma cells via inhibition of Rab geranylgeranylation, leading to disruption of monoclonal protein trafficking and induction of the unfolded protein response (UPR) pathway. Heat-shock protein 90 (HSP90) inhibitors disrupt protein folding and are currently under clinical investigation in myeloma. The effects of combining IBP and HSP90 inhibitors on cell death, monoclonal protein trafficking, the UPR and chaperone regulation were investigated in monoclonal protein-producing cells. An enhanced induction of cell death was observed following treatment with IBP and HSP90 inhibitors, which occurred through both ER stress and non-ER stress pathways. The HSP90 inhibitor 17-AAG abrogated the effects of the IBP inhibitors on intracellular monoclonal protein levels and localization as well as induction of the UPR in myeloma cells. Disparate effects on chaperone expression were observed in myeloma vs amyloid light chain cells. Here we demonstrate that the novel strategy of targeting MP trafficking in concert with HSP90 enhances myeloma cell death via a complex modulation of ER stress, UPR, and cell death pathways.

Endoplasmic reticulum stress and the unfolded protein response: targeting the Achilles heel of multiple myeloma

Multiple myeloma is characterized by the malignant proliferating antibody-producing plasma cells in the bone marrow. Despite recent advances in therapy that improve the survival of patients, multiple myeloma remains incurable and therapy resistance is the major factor causing lethality. Clearly, more effective treatments are necessary. In recent years it has become apparent that, as highly secretory antibody-producing cells, multiple myeloma cells require an increased capacity to cope with unfolded proteins and are particularly sensitive to compounds targeting proteostasis such as proteasome inhibitors, which represent one of the most prominent new therapeutic strategies. Because of the increased requirement for dealing with secretory proteins within the endoplasmic reticulum, multiple myeloma cells are heavily reliant for survival on a set of signaling pathways, known as the unfolded protein response (UPR). Thus, directly targeting the UPR emerges as a new promising therapeutic strategy. Here, we provide an overview of the current understanding of the UPR signaling in cancer, and outline its important role in myeloma pathogenesis and treatment. We discuss new therapeutic approaches based on targeting the protein quality control machinery and particularly the IRE1α/XBP1 axis of the UPR.

An activated JAK/STAT3 pathway and CD45 expression are associated with sensitivity to Hsp90 inhibitors in multiple myeloma

The molecular chaperone Hsp90 is required to maintain the activity of many signaling proteins, including members of the JAK/STAT and the PI3K pathways. Inhibitors of Hsp90 (Hsp90-Is) demonstrated varying activity against multiple myeloma (MM) in clinical trials. We aimed to determine which signaling pathways that account for the differential sensitivity to the Hsp90-I 17DMAG on a panel of MM cell lines and freshly obtained MM cells. Three CD45(+) cell lines with an activated JAK/STAT3 pathway were sensitive to 17DMAG and underwent prominent apoptosis upon treatment, while the majority of CD45(-) cell lines, that were dependent on the activated PI3K pathway, were more resistant to the drug. Culturing the most resistant cell line, LP1, in the presence of IL-6 resulted in up-regulation of CD45 and pSTAT3, and sensitized to 17DMAG-induced apoptosis, primarily in the induced CD45(+) sub-population of cells. The high CD45 expressers among primary myeloma cells also expressed significantly higher levels of pSTAT3, as compared to the low CD45 expressers. Ex vivo treatment of primary myeloma cells with 17DMAG resulted in a stronger caspase3 activation in tumor samples with the prevalence of high CD45 expressers. STAT3 activity was efficiently inhibited by Hsp90-Is in both cell lines and primary cells suggesting an importance of STAT3 inactivation for the pro-apoptotic effects of HSP90-Is. Indeed, over-expression of STAT3C, a variant with an increased DNA binding activity, in U266 cells protected them from 17DMAG-induced cell death. The down-regulation of the STAT3 target gene Mcl-1 at both the mRNA and protein levels following 17DMAG treatment was significantly attenuated in STAT3C-expressing cells, and transient over-expression of Mcl-1 protected U266 cells from 17DMAG-induced cell death. The finding that CD45(+) MM cells with an IL-6-activated JAK/STAT3 pathway are particularly sensitive to Hsp90-Is as compared to the low CD45 expressers may provide a rational basis for selection of MM patients amenable to Hsp90-I treatment.

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

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Effect of inhibition of the ubiquitin-proteasome system and Hsp90 on growth and survival of rhabdomyosarcoma cells in vitro

Background

The ubiquitin-proteasome system (UPS) and the heat shock response (HSR) are two critical regulators of cell homeostasis, as their inhibition affects growth and survival of normal cells, as well as stress response and invasiveness of cancer cells. We evaluated the effects of the proteasome inhibitor Bortezomib and of 17-DMAG, a competitive inhibitor of Hsp90, in rhabdomyosarcoma (RMS) cells, and analyzed the efficacy of single-agent exposures with combination treatments.

Methods

To assess cytotoxicity induced by Bortezomib and 17-DMAG in RMS cells, viability was measured by MTT assay after 24, 48 and 72 hours. Western blotting and immunofluorescence analyses were carried out to elucidate the mechanisms of action. Apoptosis was measured by FACS with Annexin-V-FITC and Propidium Iodide.

Results

Bortezomib and 17-DMAG, when combined at single low-toxic concentrations, enhanced growth inhibition of RMS cells, with signs of autophagy that included intensive cytoplasmic vacuolization and conversion of cytosolic LC3-I protein to its autophagosome-associated form. Treatment with lysosomal inhibitor chloroquine facilitates apoptosis, whereas stimulation of autophagy by rapamycin prevents LC3-I conversion and cell death, suggesting that autophagy is a resistance mechanism in RMS cells exposed to proteotoxic drugs. However, combination treatment also causes caspase-dependent apoptosis, PARP cleavage and Annexin V staining, as simultaneous inhibition of both UPS and HSR systems limits cytoprotective autophagy, exacerbating stress resulting from accumulation of misfolded proteins.

Conclusion

The combination of proteasome inhibitor Bortezomib with Hsp90 inhibitor 17-DMAG, appears to have important therapeutic advantages in the treatment of RMS cells compared with single-agent exposure, because compensatory survival mechanisms that occur as side effects of treatment may be prevented.

DangER: protein ovERload. Targeting protein degradation to treat myeloma

Myeloma is a malignancy of the antibody-producing plasma cells and, as such, these cells synthesize large quantities of unfolded or misfolded immunoglobulin. The build-up of excess protein triggers a number of downstream signal transduction cascades, including endoplasmic reticulum stress and autophagy. As a result, myeloma cells are uniquely reliant on these and other protein handling pathways for their survival. Strategies aimed at targeting this vulnerability have proved successful with the proteasome inhibitor, bortezomib, already licensed for clinical use. In addition to the proteasome, various other points within the protein handling pathways are also the subject of drug discovery projects, with some already progressing into clinical trials. These include compounds directed against heat shock proteins, the unfolded protein response and pathways both upstream and downstream of the proteasome. More recently, the role of autophagy has been recognized in myeloma. In this review, we discuss the various pathways used by myeloma cells for survival, with particular emphasis on the emerging role and conundrum of autophagy, as well as highlighting pre-clinical research on novel inhibitors targeting protein handling pathways.

Anti-tumor activity against multiple myeloma by combination of KW-2478, an Hsp90 inhibitor, with bortezomib

Heat shock protein 90 (Hsp90) is a promising target for anti-tumor therapy. We previously reported the anti-tumor activity of a novel Hsp90 inhibitor, KW-2478, in multiple myeloma (MM) as a single agent. In this study, we examined the combinational effect of KW-2478 and bortezomib, a proteasome inhibitor, in vitro and in vivo. In vitro, KW-2478 enhanced bortezomib-induced cell growth inhibition, both in MM cell lines and primary patient MM cells. The combination of KW-2478 and bortezomib also induced caspase activation in MM cell lines. Interestingly, the combination synergistically enhanced the expression of Hsp70B, a homolog of Hsp70, in human MM cells and peripheral blood mononuclear cells, indicating Hsp70B could be a surrogate biomarker for the combination of Hsp90 and proteasome inhibitors. In vivo, the combination of KW-2478 with bortezomib showed synergistic anti-tumor activity without significant body weight loss in a subcutaneously inoculated human myeloma model. Furthermore, the combination also showed synergistic reduction of tumor burden in bone marrow in an orthotopic myeloma model. Our results strongly suggest that combination of KW-2478 with bortezomib could exhibit enhanced anti-tumor activity against human myeloma.

The use of molecular-based risk stratification and pharmacogenomics for outcome prediction and personalized therapeutic management of multiple myeloma

Despite improvement in therapeutic efficacy, multiple myeloma (MM) remains incurable with a median survival of approximately 10 years. Gene-expression profiling (GEP) can be used to elucidate the molecular basis for resistance to chemotherapy through global assessment of molecular alterations that exist at diagnosis, after therapeutic treatment and that evolve during tumor progression. Unique GEP signatures associated with recurrent chromosomal translocations and ploidy changes have defined molecular classes with differing clinical features and outcomes. When compared to other stratification systems the GEP70 test remained a significant predictor of outcome, reduced the number of patients classified with a poor prognosis, and identified patients at increased risk of relapse despite their standard clinico-pathologic and genetic findings. GEP studies of serial samples showed that risk increases over time, with relapsed disease showing GEP shifts toward a signature of poor outcomes. GEP signatures of myeloma cells after therapy were prognostic for event-free and overall survival and thus may be used to identify novel strategies for overcoming drug resistance. This brief review will focus on the use of GEP of MM to define high-risk myeloma, and elucidate underlying mechanisms that are beginning to change clinical decision-making and inform drug design.

Tanespimycin as antitumor therapy

BACKGROUND

The 90 kDa heat shock protein (HSP90), which facilitates proper folding and stability of numerous signaling molecules involved in growth control, cell survival, and development, has been implicated in malignant processes. Like its parent compound geldanamycin, tanespimycin binds to HSP90 and causes antineoplastic effects in vitro and in vivo.

MATERIALS AND METHODS

All relevant published papers identified through searches of PubMed and abstracts from major recent hematology and oncology meetings were reviewed as of October 2009.

RESULTS

Different formulations and schedules of tanespimycin monotherapy and combination therapy have been tested in several phase I studies in patients with solid tumors or multiple myeloma (MM). No responses have been reported in studies of tanespimycin monotherapy in patients with metastatic melanoma. Tanespimycin given in combination with trastuzumab in patients with metastatic breast cancer induced a partial response in 24% of patients. Single-agent tanespimycin showed activity in MM and in combination with bortezomib, 27% of patients achieved minor response or better (48% bortezomib-naive patients, 22% bortezomib-pretreated patients, 13% bortezomib-refractory patients).

CONCLUSION

Tanespimycin represents a promising new agent for the treatment of relapsed/refractory MM. Results of ongoing and future trials will determine the role of tanespimycin both in MM and other malignancies, including breast cancer.

HSP90 inhibitors as therapy for multiple myeloma

The heat shock protein 90 (HSP90) family of proteins are ubiquitous molecular chaperones that are intricately involved in folding, activation, maturation, and assembly of many proteins that include essential mediators of signal transduction and cell cycle progression. They are abundant in eukaryotic cells and localized to the cytoplasm and mitochondria as well as the endoplasmic reticulum under normal conditions, making up 1% to 2% of all cellular proteins. HSP90 proteins have increased expression in a number of malignancies, including multiple myeloma. HSP90 inhibition can influence multiple oncogenic pathways and proteins involved in myeloma, therefore making it an attractive target for drug development in this disease. This article serves as an overview of the pre-clinical data and clinical trial data on HSP90 inhibitors in multiple myeloma.

Tanespimycin and bortezomib combination treatment in patients with relapsed or relapsed and refractory multiple myeloma: results of a phase 1/2 study

This open-label, dose escalation, multicentre phase 1/2 trial was undertaken to determine the safety and tolerability of the heat shock protein 90 (HSP90) inhibitor tanespimycin (100-340 mg/m(2) )+ bortezomib (0·7-1·3 mg/m(2) ) given on days 1, 4, 8 and 11 in each 21-d cycle. Phase 2 expansion occurred at the highest tested dose of tanespimycin at 340 mg/m(2) and bortezomib at 1·3 mg/m(2) . Seventy-two patients (median age, 60 years) with relapsed or relapsed and refractory multiple myeloma (MM) were enrolled; 63 patients (89%) completed the study. Tanespimycin in combination with bortezomib was well tolerated; few patients experienced significant neutropenia, constipation and anorexia (<10%), and no patients developed severe peripheral neuropathy. Among 67 efficacy-evaluable patients, there were 2 (3%) complete responses and 8 (12%) partial responses, for an objective response rate (ORR) of 27%, including 8 (12%) minimal responses. Response rates were highest among bortezomib-naive patients and proved durable in all patient subgroups, including those with bortezomib-refractory disease. Pharmacodynamic analyses indicated that tanespimycin plus bortezomib effectively inhibited the proteasome, as evidenced by decreased 20S proteasome activity, and inhibited HSP90, as reflected by increased HSP70 expression. The results of this study support additional studies of this combination approach in MM.

Inhibition of heat shock protein 90 (HSP90) as a therapeutic strategy for the treatment of myeloma and other cancers

Heat shock protein 90 (HSP90) is a molecular chaperone that is induced in response to cellular stress and stabilizes client proteins involved in cell cycle control and proliferative/anti-apoptotic signalling. HSP90 is overexpressed in a range of cancers, and may contribute to tumour cell survival by stabilizing aberrant signalling proteins and by interfering with apoptosis. Tanespimycin, an HSP90 inhibitor, reduces tumour cell survival in vitro. In multiple myeloma (MM), HSP90 inhibition affects multiple client proteins that contribute to tumour cell survival, including the IGF1 receptor and the IL-6 receptor, and elements of the PI3/Akt, STAT3, and MAPK signalling pathways. HSP90 inhibition also abrogates the protective effect of bone marrow stromal cells and inhibits angiogenesis and osteoclastogenesis. Tanespimycin acts synergistically with the proteasome inhibitor bortezomib in MM cells and tumour explants, possibly reducing their ability to resist bortezomib-induced stress to the endoplasmic reticulum. The combination of tanespimycin and bortezomib has demonstrated significant and durable responses with acceptable toxicity in a phase I/II study in patients with relapsed and relapsed/refractory MM. HSP90 inhibition is a promising strategy in MM especially in combination with bortezomib; additional studies will further evaluate optimal dosings of candidate drugs and schedules, as well as confirm efficacy in comparative phase III trials.

Novel therapeutic strategies in multiple myeloma: role of the heat shock protein inhibitors

Despite advances in understanding the molecular pathogenesis of multiple myeloma and promising new therapies, almost all patients eventually relapse with resistant disease. There is therefore a strong rationale for combining novel therapies that target intrinsic molecular pathways mediating multiple myeloma cell resistance. One such protein family is the heat shock proteins (HSP), especially the HSP90 family. Heat shock protein inhibitors have been identified as promising cancer treatments as, while they only inhibit a single biologic function, the chaperone-protein association, their effect is widespread as it results in the destruction of numerous client proteins. This article reviews the preclinical and clinical data, which support the testing of HSP90 inhibitors as cancer drugs and update the reader on the current status of the ongoing clinical trials of HSP90 inhibitors in multiple myeloma.

Ubiquitin B: an essential mediator of trichostatin A-induced tumor-selective killing in human cancer cells

Although histone deacetylase inhibitors (HDACis) are emerging as a new class of anticancer agents, the mechanism of tumor-selective killing by HDACi is not well understood. We used suppression of mortality by antisense rescue technique (SMART) to screen the key genes responsible for the tumor-selective killing by trichostatin A (TSA). Twenty-four genes were identified, the most significant of which was ubiquitin B (UbB). The expression of UbB was selectively upregulated by TSA in tumor cells, but not non-malignant cells. Further observation indicated that TSA induced a substantial dissipation of mitochondrial transmembrane potential, release of cytochrome c into the cytosol, and proteolytic cleavage of caspases-3/9 in HeLa cells, which was apparently mediated by ubiquitylation and the subsequent degradation of mitochondrial membrane proteins including BCL-2 and MCL-1. In contrast, knockdown of UbB expression inhibited the TSA-induced apoptotic cascade by abolishing TSA-induced ubiquitylation and the subsequent degradation of mitochondrial membrane proteins. Furthermore, apicidine, another HDACi, exhibited activity similar to that of TSA. Interestingly, TSA induced UbB-dependent proteasomal degradation of BCR-ABL fusion protein in K562 leukemic cells. Thus, our findings highlight the essential role of UbB and UbB-dependent proteasomal protein degradation in HDACi-induced tumor selectivity. The mechanism provides a novel starting point for dissecting the molecular mechanism underlying the tumor selectivity of HDACi.

Synergistic action of the novel HSP90 inhibitor NVP-AUY922 with histone deacetylase inhibitors, melphalan, or doxorubicin in multiple myeloma

Heat shock protein 90 (HSP90) is a promising target for tumor therapy. The novel HSP90 inhibitor NVP-AUY922 has preclinical activity in multiple myeloma, however, little is known about effective combination partners to design clinical studies. Multiple myeloma cell lines, OPM-2, RPMI-8226, U-266, LP-1, MM1.S, and primary myeloma cells were exposed to NVP-AUY922 and one of the combination partners histone deacetylase inhibitor NVP-LBH589, suberoylanilide hydroxamic acid (SAHA), melphalan, or doxorubicin, either simultaneously or in sequential patterns. Effects on cell proliferation and apoptosis were determined. Synergistic effects were evaluated using the method of Chou and Talalay. Combined sequential incubation with NVP-AUY922 and SAHA showed that best synergistic effects were achieved with 24 h preincubation with SAHA followed by another 48 h of combination treatment. Combination of NVP-AUY922 with SAHA, NVP-LBH589, melphalan, or doxorubicin resulted in synergistic inhibition of viability, with strong synergy (combination index < 0.3) in the case of melphalan. Importantly, resistance of the RPMI-8226 cell line and relative resistance of some primary myeloma cells against NVP-AUY922 could be overcome by combination treatment. These data show impressive synergistic action of the novel HSP90 inhibitor NVP-AUY922 with melphalan, doxorubicin, NVP-LBH589, and SAHA in multiple myeloma and build the frame work for clinical trials.

Kinome-wide RNAi studies in human multiple myeloma identify vulnerable kinase targets, including a lymphoid-restricted kinase, GRK6

A paucity of validated kinase targets in human multiple myeloma has delayed clinical deployment of kinase inhibitors in treatment strategies. We therefore conducted a kinome-wide small interfering RNA (siRNA) lethality study in myeloma tumor lines bearing common t(4;14), t(14;16), and t(11;14) translocations to identify critically vulnerable kinases in myeloma tumor cells without regard to preconceived mechanistic notions. Fifteen kinases were repeatedly vulnerable in myeloma cells, including AKT1, AK3L1, AURKA, AURKB, CDC2L1, CDK5R2, FES, FLT4, GAK, GRK6, HK1, PKN1, PLK1, SMG1, and TNK2. Whereas several kinases (PLK1, HK1) were equally vulnerable in epithelial cells, others and particularly G protein-coupled receptor kinase, GRK6, appeared selectively vulnerable in myeloma. GRK6 inhibition was lethal to 6 of 7 myeloma tumor lines but was tolerated in 7 of 7 human cell lines. GRK6 exhibits lymphoid-restricted expression, and from coimmunoprecipitation studies we demonstrate that expression in myeloma cells is regulated via direct association with the heat shock protein 90 (HSP90) chaperone. GRK6 silencing causes suppression of signal transducer and activator of transcription 3 (STAT3) phosphorylation associated with reduction in MCL1 levels and phosphorylation, illustrating a potent mechanism for the cytotoxicity of GRK6 inhibition in multiple myeloma (MM) tumor cells. As mice that lack GRK6 are healthy, inhibition of GRK6 represents a uniquely targeted novel therapeutic strategy in human multiple myeloma.

Heat shock protein-90 inhibitors increase MHC class I-related chain A and B ligand expression on multiple myeloma cells and their ability to trigger NK cell degranulation

Modulation of the host immune system represents a promising therapeutic approach against cancer, including multiple myeloma. Recent findings indicate that the NK group 2D (NKG2D)- and DNAX accessory molecule-1 (DNAM-1)-activating receptors play a prominent role in tumor recognition and elimination by cytotoxic lymphocytes, suggesting that the levels of NKG2D and DNAM-1 ligand expression on tumor cells may be a critical factor to improve the immune response against cancer. In this study, we tested the effect of 17-allylaminogeldanamycin and radicicol, drugs targeting the heat shock protein-90 (HSP-90) chaperone protein and displaying antimyeloma activity, on the expression of NKG2D and DNAM-1 ligands in human myeloma cell lines. We demonstrate that HSP-90 inhibitors are able to up-regulate both MHC class I chain-related (MIC) A and MICB protein surface and mRNA expression in human myeloma cell lines, without any significant effect on the basal expression of the DNAM-1 ligand poliovirus receptor CD155, or induction of nectin-2 and UL16-binding proteins. Activation of the transcription factor heat shock factor-1 by HSP-90 inhibitors is essential for the up-regulation of MICA/MICB expression and knockdown of heat shock factor-1 using small hairpin RNA interference blocks this effect. Moreover, in vitro and in vivo binding of heat shock factor-1 to MICA and MICB promoters indicates that it may enhance NKG2D ligand expression at the transcriptional level. Finally, exposure to HSP-90 inhibitors renders myeloma cells more efficient to activate NK cell degranulation and a blocking Ab specific for NKG2D significantly reduces this effect. Thus, these results provide evidence that targeting NKG2D ligands expression may be an additional mechanism supporting the antimyeloma activity of HSP-90 inhibitors and suggest their possible immunotherapeutic value.

The use of novel agents in the treatment of relapsed and refractory multiple myeloma

Although outcomes for patients with multiple myeloma (MM) have improved over the past decade, the disease remains incurable and even patients who respond well to induction therapy ultimately relapse and require additional treatment. Conventional chemotherapy and high-dose therapy with stem cell transplantation (SCT) have historically been utilized in the management of relapsed MM, but in recent years the immunomodulatory drugs (IMiDs) thalidomide and lenalidomide, as well as the proteasome inhibitor bortezomib, have assumed a primary role in this setting. This review focuses on the role of thalidomide, lenalidomide and bortezomib in relapsed and refractory MM, with additional discussion dedicated to emerging drugs in relapsed MM that may prove beneficial to patients with this disease.

The molecular characterization and clinical management of multiple myeloma in the post-genome era

Cancer-causing mutations disrupt coordinated, precise programs of gene expression that govern cell growth and differentiation. Microarray-based gene-expression profiling (GEP) is a powerful tool to globally analyze these changes to study cancer biology and clinical behavior. Despite overwhelming genomic chaos in multiple myeloma (MM), expression patterns within tumor samples are remarkably stable and reproducible. Unique expression patterns associated with recurrent chromosomal translocations and ploidy changes defined molecular classes with differing clinical features and outcomes. Combined molecular techniques also dissected two distinct, reproducible forms of hyperdiploid disease and have molecularly defined MM with high risk for poor clinical outcome. GEP is now used to risk-stratify patients with newly diagnosed MM. Groups with high-risk features are evident in all GEP-defined MM classes, and GEP studies of serial samples showed that risk increases over time, with relapsed disease showing dramatic GEP shifts toward a signature of poor outcomes. This suggests a common mechanism of disease evolution and potentially reflects preferential expansion of therapy-resistant cells. Correlating GEP-defined disease class and risk with outcomes of therapeutic regimens reveals class-specific benefits for individual agents, as well as mechanistic insights into drug sensitivity and resistance. Here, we review modern genomics contributions to understanding MM pathogenesis, prognosis, and therapy.

Emerging treatments for multiple myeloma: beyond immunomodulatory drugs and bortezomib

The successful clinical development of thalidomide, bortezomib, and lenalidomide not only transformed the therapeutic management of multiple myeloma (MM) but also catalyzed a renewed interest in the development of additional classes of novel agents for this disease. This review focuses on a series of new therapeutics that have shown promising preclinical results, as well as encouraging safety profiles and early evidence of anti-MM activity in clinical studies, either alone or in combination with other, conventional or novel, anti-MM treatments. These agents include second-generation proteasome inhibitors and immunomodulatory agents, as well as members of other therapeutic classes, such as histone deacetylase inhibitors (HDAC), heat shock protein 90 (Hsp90) inhibitors, and the alkylphospholipid Akt inhibitor perifosine.

Targeted therapies in multiple myeloma

Increasing knowledge of the biology of multiple myeloma led the way for the development of novel drugs that have changed the management of the disease. New treatments target not only to the malignant plasma cell but also target the interactions of myeloma cells with their microenvironment. Several preclinical studies have identified potential targets and drugs are developed that act on pathways crucial for myeloma cell survival, proliferation, migration and drug resistance. The identification of active agents in the laboratory is followed by rationally designed clinical studies that validate these drugs, either as single agents or in combinations with other active drugs. These novel agents may be either small molecules or monoclonal antibodies targeting receptors, kinase activity of receptors or key molecules within critical pathways, intracellular maintenance mechanisms and immune modulation.

New drugs in multiple myeloma

PURPOSE OF REVIEW

Advances in the understanding of multiple myeloma pathogenesis have led to the development of innovative targeted therapies and improved management of this aggressive hematological neoplasia. This review will focus on the clinical trials that have reinforced the use of these new agents. Also, we will briefly take a look at the newer drugs making their way out of the laboratory and into early phase studies.

RECENT FINDINGS

During the past decade new multiple myeloma therapies featuring bortezomib and lenalidomide have come to light, whereas known agents such as thalidomide and arsenic trioxide have been reintroduced as key factors in multiple myeloma management. These new agents and their combinations have shown increased response rates and have added more options for patients with multiple myeloma whose disease has become resistant to conventional therapy. With these drug therapies has come a more targeted approach to treatment enabling not only improved antimyeloma efficacy but also the use of decreased dosing enhancing the safety and tolerability of these regimens. Newer agents including the histone deacetylase, hsp90, mammalian target of rapamycin and Akt inhibitors are showing promise preclinically and are now being assessed in phase I/II trials.

SUMMARY

This new antimultiple myeloma arsenal has shown its worth in both the relapsed/refractory and frontline setting and provides valuable options for patients with this debilitating disease.

The novel HSP90 inhibitor STA-9090 exhibits activity against Kit-dependent and -independent malignant mast cell tumors

OBJECTIVE

Mutations of the receptor tyrosine kinase Kit occur in several human and canine cancers. While Kit inhibitors have activity in the clinical setting, they possess variable efficacy against particular forms of mutant Kit and drug resistance often develops over time. Inhibitors of heat shock protein 90 (HSP90), a chaperone for which Kit is a client protein, have demonstrated activity against human cancers and evidence suggests they downregulate several mutated and imatinib-resistant forms of Kit. The purpose of this study was to evaluate a novel HSP90 inhibitor, STA-9090, against wild-type (WT) and mutant Kit in canine bone marrow-derived cultured mast cells (BMCMCs), malignant mast cell lines, and fresh malignant mast cells.

MATERIALS AND METHODS

BMCMCs, cell lines, and fresh malignant mast cells were treated with STA-9090, 17-AAG, and SU11654 and evaluated for loss in cell viability, cell death, alterations in HSP90 and Kit expression/signaling, and Kit mutation. STA-9090 activity was tested in a canine mastocytoma xenograft model.

RESULTS

Treatment of BMCMCs, cell lines, and fresh malignant cells with STA-9090 induced growth inhibition, apoptosis that was caspase-3/7-dependent, and downregulation of phospho/total Kit and Akt, but not extracellular signal-regulated kinase (ERK) or phosphoinositide-3 kinase (PI-3K). Loss of Kit cell-surface expression was also observed. Furthermore, STA-9090 exhibited superior activity to 17-AAG and SU11654, and was effective against malignant mast cells expressing either WT or mutant Kit. Lastly, STA-9090 inhibited tumor growth in a canine mastocytoma mouse xenograft model.

CONCLUSIONS

STA-9090 exhibits broad activity against mast cells expressing WT or mutant Kit, suggesting it may be an effective agent in the clinical setting against mast cell malignancies.

Signalling profile and antitumour activity of the novel Hsp90 inhibitor NVP-AUY922 in multiple myeloma

We as well as others have recently shown that Hsp90 is overexpressed in multiple myeloma (MM) and critically contributes to tumour cell survival. Pharmacologic blockade of Hsp90 has consistently been found to induce MM cell death. However, most data have been obtained with MM cell lines whereas knowledge about the molecular effects of pharmacologic Hsp90 blockade in primary tumour cells is limited. Furthermore, these investigations have so far focused on geldanamycin derivatives. We analysed the biochemical effects of a novel diarylisoxazole-based Hsp90 inhibitor (NVP-AUY922) on signalling pathways and cell death in a large set of primary MM tumour samples and in MM cell lines. Treated cells displayed the molecular signature and pharmacodynamic properties for abrogation of Hsp90 function, such as downregulation of multiple survival pathways and strong upregulation of Hsp70. NVP-AUY922 treatment efficiently induced MM cell apoptosis and revealed both sensitive and resistant subgroups. Sensitivity was not correlated with TP53 mutation or Hsp70 induction levels and stromal cells from the bone marrow microenvironment were unable to abrogate NVP-AUY922-induced apoptosis of MM cells. Thus, NVP-AUY922 may be a promising drug for treatment of MM and clinical studies are warranted.

Targeting Akt and heat shock protein 90 produces synergistic multiple myeloma cell cytotoxicity in the bone marrow microenvironment

PURPOSE

We hypothesized that targeting both Akt and heat shock protein (HSP) 90 would induce cytotoxic activity against multiple myeloma (MM) cells and target the bone marrow (BM) microenvironment to inhibit angiogenesis, osteoclast formation, as well as migration and adhesion of MM cells.

EXPERIMENTAL DESIGN

MM cell lines were incubated with perifosine (5 and 10 micromol/L) and 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG; 50 and 100 nmol/L) alone and in combination.

RESULTS

The combination of Akt inhibitor perifosine and HSP90 inhibitor 17-DMAG was synergistic in inducing MM cell cytotoxicity, evidenced by inhibition of DNA synthesis and induction of apoptosis. In addition, perifosine and 17-DMAG almost completely inhibited osteoclast formation: perifosine interfered with both early and late stages of osteoclast progenitor development, whereas 17-DMAG targeted only early stages. We next showed that combined therapy overcomes tumor growth and resistance induced by BM stromal cells and endothelial cells as well as the proliferative effect of exogenous interleukin-6, insulin-like growth factor-I, and vascular endothelial growth factor. Moreover, the combination also induced apoptosis and growth inhibition in endothelial cells and inhibited angiogenesis. Finally, we showed that the two agents prevented migration of MM cells toward stromal-derived factor-1 and vascular endothelial growth factor, which are present in the BM milieu, and also prevented adhesion of MM cells to fibronectin.

CONCLUSIONS

This study provides the preclinical framework for treatment protocols targeting both the Akt and HSP pathways in MM.

The heat-shock protein 90 inhibitor, geldanamycin, induces apoptotic cell death in Epstein-Barr virus-positive NK/T-cell lymphoma by Akt down-regulation

NK/T-cell lymphoma (NKTL) is strongly associated with latent Epstein-Barr virus (EBV) infection. Recently, latent membrane protein 1 (LMP1), an EBV oncoprotein, was reported to activate the phosphatidylinositol-3 kinase (PI3K)/Akt pathway for cell survival. Because geldanamycin (GA) and its derivative, 17-allylamino-17-demethoxygeldanamycin (17-AAG), exhibit anti-tumour activity by degrading HSP90 client proteins, including Akt, we investigated the effect of GA and 17-AAG on the survival of NKTL cell lines. EBV-positive NKTL cell lines, Hank-1 and NK-YS, and an EBV-negative NK leukaemia cell line, NK-L, were treated with PI3K and Akt inhibitors, GA, and 17-AAG, and were subjected to apoptosis and cell viability assays, and immunoblot analysis. EBV-positive B-lymphoblastoid cell lines IM9 and LMP1-transfected IM9 (IM9-LMP1) were also included. Hank-1 and NK-YS cell viability was compromised and apoptosis was induced by LY294002 (PI3K inhibitor) or Akt inhibitor II. GA or 17-AAG administration resulted in the apoptosis of NKTL cells, accompanied by Akt and pAkt down-regulation, caspase 3 activation, and mitochondrial membrane potential disruption. The intrinsic level of pAkt was higher in EBV-positive NKTL cells than in EBV-negative NK-L, and GA or 17-AAG decreased the viability of NKTL cells more efficiently than NK-L. Moreover, IM9-LMP1 was more sensitive to Akt inhibitor II or HSP90 inhibitors than IM9. Importantly, GA showed little effect on the viability of normal peripheral NK cells as non-neoplastic counterparts for comparison. In conclusion, this study suggests that the PI3K/Akt pathway is frequently activated in EBV-positive NKTL and that therapeutic modalities based on targeting the PI3K/Akt pathway with HSP90 inhibitors could be useful for achieving NKTL control.

From the bench to the bedside: emerging new treatments in multiple myeloma

Within the last decade, several novel classes of anti-myeloma therapeutics have become available. The clinical successes achieved by thalidomide, lenalidomide, and the proteasome inhibitor bortezomib, and in particular the ability of these agents to lead to major clinical responses in patients resistant to conventional or high-dose chemotherapy, have highlighted the importance of expanding further the spectrum of classes of agents utilized for the treatment of myeloma. Herein, we review the current status for the development of novel anti-myeloma agents, with emphasis on classes of therapeutics which have already translated into clinical trials or those in advanced stages of preclinical development. These include second-generation proteasome inhibitors (NPI-0052 and PR-171), heat shock protein 90 (hsp90) inhibitors, 2-methoxyestradiol, histone deacetylase (HDAC) inhibitors (e.g. SAHA and LBH589), fibroblast growth factor receptor 3 (FGF-R3) inhibitors, insulin-like growth factor 1 receptor (IGF-1R) inhibitors, mTOR inhibitors, monoclonal antibodies, and agents specifically targeting the tumor microenvironment, such as defibrotide.

HSP90 inhibitor 17AAG causes apoptosis in ATRA-resistant acute promyelocytic leukemia cells

The effects of a novel heat shock protein inhibitor, 17AAG, on established APL cell lines (NB4 and R1) were analyzed. 17AAG induces apoptosis in APL cell lines both sensitive (NB4) and resistant (R1) to ATRA after 72 h of incubation. Apoptosis occurs by a mechanism different than ATRA-mediated response, as the cells do not undergo differentiation before apoptosis. Analysis of bax and bcl-2 shows that pro-apoptotic (bax) and anti-apoptotic (bcl-2) proteins are decreased in expression after incubation with 17AAG. We believe this data supports potential clinical use of agents that target HSP90 in APL patients failing conventional therapy.

Development of 17-allylamino-17-demethoxygeldanamycin hydroquinone hydrochloride (IPI-504), an anti-cancer agent directed against Hsp90

Heat shock protein 90 (Hsp90) is an emerging therapeutic target of interest for the treatment of cancer. Its role in protein homeostasis and the selective chaperoning of key signaling proteins in cancer survival and proliferation pathways has made it an attractive target of small molecule therapeutic intervention. 17-Allylamino-17-demethoxygeldanamycin (17-AAG), the most studied agent directed against Hsp90, suffers from poor physical-chemical properties that limit its clinical potential. Therefore, there exists a need for novel, patient-friendly Hsp90-directed agents for clinical investigation. IPI-504, the highly soluble hydroquinone hydrochloride derivative of 17-AAG, was synthesized as an Hsp90 inhibitor with favorable pharmaceutical properties. Its biochemical and biological activity was profiled in an Hsp90-binding assay, as well as in cancer-cell assays. Furthermore, the metabolic profile of IPI-504 was compared with that of 17-AAG, a geldanamycin analog currently in clinical trials. The anti-tumor activity of IPI-504 was tested as both a single agent as well as in combination with bortezomib in myeloma cell lines and in vivo xenograft models, and the retention of IPI-504 in tumor tissue was determined. In conclusion, IPI-504, a potent inhibitor of Hsp90, is efficacious in cellular and animal models of myeloma. It is synergistically efficacious with the proteasome inhibitor bortezomib and is preferentially retained in tumor tissues relative to plasma. Importantly, it was observed that IPI-504 interconverts with the known agent 17-AAG in vitro and in vivo via an oxidation-reduction equilibrium, and we demonstrate that IPI-504 is the slightly more potent inhibitor of Hsp90.