Pharmacological induction of Hsp70 protects apoptosis-prone cells from doxorubicin: comparison with caspase-inhibitor- and cycle-arrest-mediated cytoprotection

Mediation of Ferroptosis Suppressor Protein 1 Expression via 4-Hydroxy-2-Nonenal Accumulation Contributes to Acquisition of Resistance to Apoptosis and Ferroptosis in Diffuse Large B-Cell Lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma. New therapeutic strategies are needed for the treatment of refractory DLBCL. 4-Hydroxy-2-nonenal (4-HNE) is a cytotoxic lipid peroxidation marker, which alters intracellular signaling and induces genetic mutations. Lipid peroxidation is associated with nonapoptotic cell death, called ferroptosis. However, the relationship between 4-HNE accumulation and feroptotic regulators in DLBCL has not been fully evaluated. Here, we aimed to evaluate the accumulation of lipid peroxide and the expression of ferroptosis suppressor protein 1 (FSP1) in DLBCL using immunohistochemistry. We found a significant increase in the expression of FSP1 in cases with nuclear 4-HNE accumulation (P = .021). Both nuclear and cytoplasmic 4-HNE accumulation and FSP1 positivity were independent predictors of worse prognosis. In vitro exposure to 4-HNE resulted in its concentration- and time-dependent intracellular accumulation and increased expression of FSP1. Furthermore, short-term (0.25 and 1.0 μM) or long-term (0.25 μM) exposure to 4-HNE induced resistance to not only apoptosis but also ferroptosis. Taken together, regulation of FSP1 through 4-HNE accumulation may attenuate resistance to cell death in treatment-resistant DLBCL and might help develop novel therapeutic strategies for refractory DLBCL.

Selective protection of normal cells from chemotherapy, while killing drug-resistant cancer cells

Cancer therapy is limited by toxicity in normal cells and drug-resistance in cancer cells. Paradoxically, cancer resistance to certain therapies can be exploited for protection of normal cells, simultaneously enabling the selective killing of resistant cancer cells by using antagonistic drug combinations, which include cytotoxic and protective drugs. Depending on the mechanisms of drug-resistance in cancer cells, the protection of normal cells can be achieved with inhibitors of CDK4/6, caspases, Mdm2, mTOR, and mitogenic kinases. When normal cells are protected, the selectivity and potency of multi-drug combinations can be further enhanced by adding synergistic drugs, in theory, eliminating the deadliest cancer clones with minimal side effects. I also discuss how the recent success of Trilaciclib may foster similar approaches into clinical practice, how to mitigate systemic side effects of chemotherapy in patients with brain tumors and how to ensure that protective drugs would only protect normal cells (not cancer cells) in a particular patient.

Synthesis and Biological Activity of 3-(Heteroaryl)quinolin-2(1H)-ones Bis-Heterocycles as Potential Inhibitors of the Protein Folding Machinery Hsp90

In the context of our SAR study concerning 6BrCaQ analogues as C-terminal Hsp90 inhibitors, we designed and synthesized a novel series of 3-(heteroaryl)quinolin-2(1H), of types 3, 4, and 5, as a novel class of analogues. A Pd-catalyzed Liebeskind-Srogl cross-coupling was developed as a convenient approach for easy access to complex purine architectures. This series of analogues showed a promising biological effect against MDA-MB231 and PC-3 cancer cell lines. This study led to the identification of the best compounds, 3b (IC50 = 28 µM) and 4e, which induce a significant decrease of CDK-1 client protein and stabilize the levels of Hsp90 and Hsp70 without triggering the HSR response.

Ethanol Enhances Hyperthermia-Induced Cell Death in Human Leukemia Cells

Ethanol has been shown to exhibit therapeutic properties as an ablative agent alone and in combination with thermal ablation. Ethanol may also increase sensitivity of cancer cells to certain physical and chemical antitumoral agents. The aim of our study was to assess the potential influence of nontoxic concentrations of ethanol on hyperthermia therapy, an antitumoral modality that is continuously growing and that can be combined with classical chemotherapy and radiotherapy to improve their efficiency. Human leukemia cells were included as a model in the study. The results indicated that ethanol augments the cytotoxicity of hyperthermia against U937 and HL60 cells. The therapeutic benefit of the hyperthermia/ethanol combination was associated with an increase in the percentage of apoptotic cells and activation of caspases-3, -8 and -9. Apoptosis triggered either by hyperthermia or hyperthermia/ethanol was almost completely abolished by a caspase-8 specific inhibitor, indicating that this caspase plays a main role in both conditions. The role of caspase-9 in hyperthermia treated cells acquired significance whether ethanol was present during hyperthermia since the alcohol enhanced Bid cleavage, translocation of Bax from cytosol to mitochondria, release of mitochondrial apoptogenic factors, and decreased of the levels of the anti-apoptotic factor myeloid cell leukemia-1 (Mcl-1). The enhancement effect of ethanol on hyperthermia-activated cell death was associated with a reduction in the expression of HSP70, a protein known to interfere in the activation of apoptosis at different stages. Collectively, our findings suggest that ethanol could be useful as an adjuvant in hyperthermia therapy for cancer.

Evaluation of the Role of Human DNAJAs in the Response to Cytotoxic Chemotherapeutic Agents in a Yeast Model System

Heat-shock proteins (HSPs) play a crucial role in maintaining protein stability for cell survival during stress-induced insults. Overexpression of HSPs in cancer cells results in antiapoptotic activity contributing to cancer cell survival and restricting the efficacy of cytotoxic chemotherapy, which continues to play an important role in the treatment of many cancers, including triple-negative breast cancer (TNBC). First-line therapy for TNBC includes anthracycline antibiotics, which are associated with serious dose-dependent side effects and the development of resistance. We previously identified YDJ1, which encodes a heat-shock protein 40 (HSP40), as an important factor in the cellular response to anthracyclines in yeast, with mutants displaying over 100-fold increased sensitivity to doxorubicin. In humans, the DNAJA HSP40s are homologues of YDJ1. To determine the role of DNAJAs in the cellular response to cytotoxic drugs, we investigated their ability to rescue ydj1Δ mutants from exposure to chemotherapeutic agents. Our results indicate that DNAJA1 and DNAJA2 provide effective protection, while DNAJA3 and DNAJA4 did not. The level of complementation was also dependent on the agent used, with DNAJA1 and DNAJA2 rescuing the ydj1Δ strain from doxorubicin, cisplatin, and heat shock. DNAJA3 and DNAJA4 did not rescue the ydj1Δ strain and interfered with the cellular response to stress when expressed in wild type background. DNAJA1 and DNAJA2 protect the cell from proteotoxic damage caused by reactive oxygen species (ROS) and are not required for repair of DNA double-strand breaks. These data indicate that the DNAJAs play a role in the protection of cells from ROS-induced cytotoxic stress.

Hsp105α suppresses Adriamycin-induced cell death via nuclear localization signal-dependent nuclear accumulation

Heat shock protein 105 (Hsp105) is a molecular chaperone, and the isoforms Hsp105α and Hsp105β exhibit distinct functions with different subcellular localizations. Hsp105β localizes in the nucleus and induces the expression of the major heat shock protein Hsp70, whereas cytoplasmic Hsp105α is less effective in inducing Hsp70 expression. Hsp105 shuttles between the cytoplasm and the nucleus; the subcellular localization is governed by the relative activities of the nuclear localization signal (NLS) and nuclear export signal (NES). Here, we show that nuclear accumulation of Hsp105α but not Hsp105β is involved in Adriamycin (ADR) sensitivity. Knockdown of Hsp105α induces cell death at low ADR concentration, at which ADR is less effective in inducing cell death in the presence of Hsp105α. Of note, Hsp105 is localized in the nucleus under these conditions, even though Hsp105β is not expressed, indicating that Hsp105α accumulates in the nucleus in response to ADR treatment. The exogenously expressed Hsp105α but not its NLS mutant localizes in the nucleus of ADR-treated cells. In addition, the expression level of the nuclear export protein chromosomal maintenance 1 (CRM1) was decreased by ADR treatment of cells, and CRM1 knockdown caused nuclear accumulation of Hsp105α both in the presence and absence of ADR. These results indicating that Hsp105α accumulates in the nucleus in a manner dependent on the NLS activity via the suppression of nuclear export. Our findings suggest a role of nuclear Hsp105α in the sensitivity against DNA-damaging agents in tumor cells.

BCN057 induces intestinal stem cell repair and mitigates radiation-induced intestinal injury

BACKGROUND

Radiation-induced gastrointestinal syndrome (RIGS) results from the acute loss of intestinal stem cells (ISC), impaired epithelial regeneration, and subsequent loss of the mucosal barrier, resulting in electrolyte imbalance, diarrhea, weight loss, sepsis, and mortality. The high radiosensitivity of the intestinal epithelium limits effective radiotherapy against abdominal malignancies and limits the survival of victims of nuclear accidents or terrorism. Currently, there is no approved therapy to mitigate radiation toxicity in the intestine. Here we demonstrate that BCN057, an anti-neoplastic small molecular agent, induces ISC proliferation and promotes intestinal epithelial repair against radiation injury.

METHODS

BCN057 (90 mg/kg body weight, subcutaneously) was injected into C57Bl6 male mice (JAX) at 24 h following abdominal irradiation (AIR) and was continued for 8 days post-irradiation. BCN057-mediated rescue of Lgr5-positive ISC was validated in Lgr5-EGFP-Cre-ERT2 mice exposed to AIR. The regenerative response of Lgr5-positive ISC was examined by lineage tracing assay using Lgr5-EGFP-ires-CreERT2-TdT mice with tamoxifen administration to activate Cre recombinase and thereby marking the ISC and their respective progeny. Ex vivo three-dimensional organoid cultures were developed from surgical specimens of human colon or from mice jejunum and were used to examine the radio-mitigating role of BCN057 on ISC ex vivo. Organoid growth was determined by quantifying the budding crypt/total crypt ratio. Statistical analysis was performed using Log-rank (Mantel-Cox) test and paired two-tail t test.

RESULTS

Treatment with BCN057 24 h after a lethal dose of AIR rescues ISC, promotes regeneration of the intestinal epithelium, and thereby mitigates RIGS. Irradiated mice without BCN057 treatment suffered from RIGS, resulting in 100% mortality within 15 days post-radiation. Intestinal organoids developed from mice jejunum or human colon demonstrated a regenerative response with BCN057 treatment and mitigated radiation toxicity. However, BCN057 did not deliver radio-protection to mouse or human colon tumor tissue.

CONCLUSION

BCN057 is a potential mitigator against RIGS and may be useful for improving the therapeutic ratio of abdominal radiotherapy. This is the first report demonstrating that a small molecular agent mitigates radiation-induced intestinal injury by inducing ISC self-renewal and proliferation.

A double-negative feedback loop between E2F3b and miR- 200b regulates docetaxel chemosensitivity of human lung adenocarcinoma cells

MicroRNAs (miRNAs) are non-coding small RNAs which negatively regulate gene expressions mainly through 3'-untranslated region (3'-UTR) binding of target mRNAs. Recent studies have highlighted the feedback loops between miRNAs and their target genes in physiological and pathological processes including chemoresistance of cancers. Our previous study identified miR-200b/E2F3 axis as a chemosensitivity restorer of human lung adenocarcinoma (LAD) cells. Moreover, E2F3b was bioinformatically proved to be a potential transcriptional regulator of pre-miR-200b gene promoter. The existance of this double-negative feedback minicircuitry comprising E2F3b and miR-200b was confirmed by chromatin immunoprecipitation (ChIP) assay, site-specific mutation and luciferase reporter assay. And the underlying regulatory mechanisms of this feedback loop on docetaxel resistance of LAD cells were further investigated by applying in vitro chemosensitivity assay, colony formation assay, flow cytometric analysis of cell cycle and apoptosis, as well as mice xenograft model. In conclusion, our results suggest that the double-negative feedback loop between E2F3b and miR-200b regulates docetaxel chemosensitivity of human LAD cells mainly through cell proliferation, cell cycle distribution and apoptosis.

Lipid bodies containing oxidatively truncated lipids block antigen cross-presentation by dendritic cells in cancer

Cross-presentation is a critical function of dendritic cells (DCs) required for induction of antitumor immune responses and success of cancer immunotherapy. It is established that tumor-associated DCs are defective in their ability to cross-present antigens. However, the mechanisms driving these defects are still unknown. We find that impaired cross-presentation in DCs is largely associated with defect in trafficking of peptide-MHC class I (pMHC) complexes to the cell surface. DCs in tumor-bearing hosts accumulate lipid bodies (LB) containing electrophilic oxidatively truncated (ox-tr) lipids. These ox-tr-LB, but not LB present in control DCs, covalently bind to chaperone heat shock protein 70. This interaction prevents the translocation of pMHC to cell surface by causing the accumulation of pMHC inside late endosomes/lysosomes. As a result, tumor-associated DCs are no longer able to stimulate adequate CD8 T cells responses. In conclusion, this study demonstrates a mechanism regulating cross-presentation in cancer and suggests potential therapeutic avenues.

Hsp90 inhibitor geldanamycin attenuates the cytotoxicity of sunitinib in cardiomyocytes via inhibition of the autophagy pathway

Sunitinib malate (sunitinib) is an orally available, multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activities. Although sunitinib is effective for the treatment of patients with gastrointestinal stromal tumor, advanced renal cell carcinoma, or pancreatic neuroendocrine tumor, adverse cardiac events associated with sunitinib administration have been reported. Here, we examined the effect of geldanamycin, an inhibitor of heat shock protein (Hsp) 90, on sunitinib-induced cytotoxicity in cardiomyocytes. First, we found that treatment with geldanamycin or other Hsp90 inhibitors (tanespimycin, ganetespib, or BIIB021) significantly attenuated sunitinib-induced cytotoxicity in rat H9c2 cardiomyocytes, suggesting a drug-class effect of Hsp90 inhibitors. We then examined the mechanisms underlying sunitinib-induced cytotoxicity and found that sunitinib induced autophagy in H9c2 cells and that pretreatment with geldanamycin inhibited the induction of autophagy by promoting degradation of the autophagy-related proteins Atg7, Beclin-1, and ULK1. Pharmacological assessment with autophagy inhibitors confirmed that geldanamycin attenuated the cytotoxicity of sunitinib by interfering with autophagy. In addition, we found that the molecular chaperone Hsp70, which is induced by geldanamycin, was not involved in the attenuation of sunitinib-induced cytotoxicity. Finally, to provide more clinically relevant data, we confirmed that geldanamycin attenuated sunitinib-induced cytotoxicity in human induced pluripotent stem cell-derived cardiomyocytes. Together, these data suggest that geldanamycin attenuates sunitinib-induced cytotoxicity in cardiomyocytes by inhibiting the autophagy pathway. Thus, the further investigation of combination or sequential treatment with an Hsp90 inhibitor and sunitinib is warranted as a potential strategy of attenuating the cardiotoxicity associated with sunitinib administration in the clinical setting.

Targeting the Hsp90 C-terminal domain to induce allosteric inhibition and selective client downregulation

BACKGROUND

Inhibition of Hsp90 is desirable due to potential downregulation of oncogenic clients. Early generation inhibitors bind to the N-terminal domain (NTD) but C-terminal domain (CTD) inhibitors are a promising class because they do not induce a heat shock response. Here we present a new structural class of CTD binding molecules with a unique allosteric inhibition mechanism.

METHODS

A hit molecule, NSC145366, and structurally similar probes were assessed for inhibition of Hsp90 activities. A ligand-binding model was proposed indicating a novel Hsp90 CTD binding site. Client protein downregulation was also determined.

RESULTS

NSC145366 interacts with the Hsp90 CTD and has anti-proliferative activity in tumor cell lines (GI₅₀=0.2-1.9μM). NSC145366 increases Hsp90 oligomerization resulting in allosteric inhibition of NTD ATPase activity (IC₅₀=119μM) but does not compete with NTD or CTD-ATP binding. Treatment of LNCaP prostate tumor cells resulted in selective client protein downregulation including AR and BRCA1 but without a heat shock response. Analogs had similar potencies in ATPase and chaperone activity assays and variable effects on oligomerization. In silico modeling predicted a binding site at the CTD dimer interface distinct from the nucleotide-binding site.

CONCLUSIONS

A set of symmetrical scaffold molecules with bisphenol A cores induced allosteric inhibition of Hsp90. Experimental evidence and molecular modeling suggest that the binding site is independent of the CTD-ATP site and consistent with unique induction of allosteric effects.

GENERAL SIGNIFICANCE

Allosteric inhibition of Hsp90 via a mechanism used by the NSC145366-based probes is a promising avenue for selective oncogenic client downregulation.

Identification of a ternary protein-complex as a therapeutic target for K-Ras-dependent colon cancer

A cancer phenotype is driven by several proteins and targeting a cluster of functionally interdependent molecules should be more effective for therapeutic intervention. This is specifically important for Ras-dependent cancer, as mutated (MT) Ras is non-druggable and targeting its interaction with effectors may be essential for therapeutic intervention. Here, we report that a protein-complex activated by the Ras effector p38γ MAPK is a novel therapeutic target for K-Ras-dependent colon cancer. Unbiased proteomic screening and immune-precipitation analyses identified p38γ interaction with heat shock protein 90 (Hsp90) and K-Ras in K-Ras MT, but not wild-type (WT), colon cancer cells, indicating a role of this complex in Ras-dependent growth. Further experiments showed that this complex requires p38γ and Hsp90 activity to maintain MT, but not WT, K-Ras protein expression. Additional studies demonstrated that this complex is activated by p38γ-induced Hsp90 phosphorylation at S595, which is important for MT K-Ras stability and for K-Ras dependent growth. Of most important, pharmacologically inhibition of Hsp90 or p38γ activity disrupts the complex, decreases K-Ras expression, and selectively inhibits the growth of K-Ras MT colon cancer in vitro and in vivo. These results demonstrated that the p38γ-activated ternary complex is a novel therapeutic target for K-Ras-dependent colon cancer.

Protective effects of acteoside against X‑ray‑induced damage in human skin fibroblasts

To investigate the protective effects of acteoside against apoptosis induced by X-ray radiation in human skin fibroblasts (HSFs), the cells were divided into the following groups: Control group; X-ray radiation group; acteoside group, in which the confluent cells were preincubated with 50 μg/ml acteoside for 2 h followed by radiation; and positive control group, in which the cells were preincubated with 50 μg/ml paeoniflorin followed by radiation. For the radiation, HSF cells preincubated with acteoside or paeoniflorin were exposed to X-ray beams at a dose-rate of 3 Gy/min (16 Gy in total). Cell viability, apoptosis and intracellular alteration of redox were monitored by MTT and flow cytometry. Compared with the radiation group, the number of cells arrested at the G0/G1 phase was significantly reduced in the acteoside and paeoniflorin groups, respectively (P<0.05). X-ray radiation induced marked apoptosis in HSF cells and acteoside reversed this effect. Compared with the radiation group, the generation of intracellular reactive oxygen species (ROS) was abrogated by pre-incubation with acteoside or paeoniflorin (P<0.05). In addition, the upregulation of pro-caspase-3 induced by radiation was reversed by acteoside or paeoniflorin. Radiation could induce upregulation of Bax and downregulation of Bcl-2; however, it was reversed completely after administration of acteoside or paeoniflorin. Furthermore, the enhanced expression of ERK and JNK induced by radiation was reversed by acteoside or paeoniflorin. Acteoside could protect the cells from X-ray induced damage through enhancing the scavenging activity of ROS, decreasing the Bax/Bcl-2 ratio and downregulating the activity of procaspase-3, as well as modulating the mitogen-activated protein kinase signaling pathways.

A small molecule inhibitor of ATPase activity of HSP70 induces apoptosis and has antitumor activities

The heat shock protein HSP70 plays antiapoptotic and oncogenic roles, and thus its inhibition has been recognized as a potential avenue for anticancer therapy. Here we describe the small molecule, apoptozole (Az), which inhibits the ATPase activity of HSP70 by binding to its ATPase domain and, as a result, induces an array of apoptotic phenotypes in cancer cells. Affinity chromatography provides evidence that Az binds HSP70 but not other types of heat shock proteins including HSP40, HSP60, and HSP90. We also demonstrate that Az induces cancer cell death via caspase-dependent apoptosis by disrupting the interaction of HSP70 with APAF-1. Animal studies indicate that Az treatment retards tumor growth in a xenograft mouse model without affecting mouse viability. These studies suggest that Az will aid the development of new cancer therapies and serve as a chemical probe to gain a better understanding of the diverse functions of HSP70.

Antitumor activity of the combination of an HSP90 inhibitor and a PI3K/mTOR dual inhibitor against cholangiocarcinoma

The PI3K/Akt/mTOR pathway is overactivated and heat shock protein (HSP) 90 is overexpressed in common cancers. We hypothesized that targeting both pathways can kill intrahepatic cholangiocarcinoma (CCA) cells. HSP90 and PTEN protein expression was evaluated by immunohistochemical staining of samples from 78 patients with intrahepatic CCA. CCA cell lines and a thioacetamide (TAA)-induced CCA animal model were treated with NVP-AUY922 (an HSP90 inhibitor) and NVP-BEZ235 (a PI3K/mTOR inhibitor) alone or in combination.

Both HSP90 overexpression and loss of PTEN were poor prognostic factors in patients with intrahepatic CCA. The combination of the HSP90 inhibitor NVP-AUY922 and the PI3K/mTOR inhibitor NVP-BEZ235 was synergistic in inducing cell death in CCA cells. A combination of NVP-AUY922 and NVP-BEZ235 caused tumor regression in CCA rat animal model. This combination not only inhibited the PI3K/Akt/mTOR pathway but also induced ROS, which may exacerbate the vicious cycle of ER stress. Our data suggest simultaneous targeting of the PI3K/mTOR and HSP pathways for CCA treatment.

Sublethal concentrations of 17-AAG suppress homologous recombination DNA repair and enhance sensitivity to carboplatin and olaparib in HR proficient ovarian cancer cells

The promise of PARP-inhibitors(PARPis) in the management of epithelial ovarian cancer(EOC) is tempered by the fact that approximately 50% of patients with homologous recombination (HR)-proficient tumors do not respond well to these agents. Combination of PARPis with agents that inhibit HR may represent an effective strategy to enhance their activity in HR-proficient tumors. Using a bioinformatics approach, we identified that heat shock protein 90 inhibitors(HSP90i) may suppress HR and thus revert HR-proficient to HR-deficient tumors. Analysis of publicly available gene expression data showed that exposure of HR-proficient breast cancer cell lines to HSP90i 17-AAG(17-allylamino-17-demethoxygeldanamycin) downregulated HR, ATM and Fanconi Anemia pathways. In HR-proficient EOC cells, 17-AAG suppressed HR as assessed using the RAD51 foci formation assay and this was further confirmed using the Direct Repeat-GFP reporter assay. Furthermore, 17-AAG downregulated BRCA1 and/or RAD51 protein levels, and induced significantly more γH2AX activation in combination with olaparib compared to olaparib alone. Finally, sublethal concentrations of 17-AAG sensitized HR-proficient EOC lines to olaparib and carboplatin but did not affect sensitivity of the HR-deficient OVCAR8 line arguing that the 17-AAG mediated sensitization is dependent on suppression of HR. These results provide a preclinical rationale for using a combination of olaparib/17-AAG in HR-proficient EOC.

Targeting aerobic glycolysis and HIF-1alpha expression enhance imiquimod-induced apoptosis in cancer cells

Tumor cells rely on aerobic glycolysis to maintain unconstrained cell growth and proliferation. Imiquimod (IMQ), a synthetic Toll-like receptor (TLR) 7/8 ligand, exerts anti-tumor effects directly by inducing cell death in cancer cells and/or indirectly by activating cellular immune responses against tumor cells. However, whether IMQ modulates glucose metabolism pathways remains unclear. In this study, we demonstrated that IMQ can enhance aerobic glycolysis by up-regulating HIF-1α expression at the transcriptional and translational levels via ROS mediated STAT3- and Akt-dependent pathways, independent of TLR7/8 signaling. The genetic silencing of HIF-1α not only repressed IMQ-induced aerobic glycolysis but also sensitized cells to IMQ-induced apoptosis due to faster ATP and Mcl-1 depletion. Moreover, the glucose analog 2-DG and the Hsp90 inhibitor 17-AAG, which destabilizes the HIF-1α protein, synergized with IMQ to induce tumor cell apoptosis in vitro and significantly inhibited tumor growth in vivo. Thus, we hypothesize that the IMQ-induced up-regulation of HIF-1α and aerobic glycolysis is a protective response to the metabolic stress generated by IMQ treatment, and thus, co-treatment with inhibitors of HIF-1α and/or glycolysis may be a useful therapeutic strategy to enhance the anti-tumor effects of IMQ in clinical settings.

Exogenously delivered heat shock protein 70 displaces its endogenous analogue and sensitizes cancer cells to lymphocytes-mediated cytotoxicity

Hsp70 chaperone is known to stimulate anti-tumour immunity in a variety of cancer models. Here we demonstrated that the addition of purified recombinant Hsp70 to the culture medium facilitated cancer cell cytolysis by lymphocytes. Importantly, exogenous Hsp70 triggered secretion of the intracellular Hsp70 to a cell surface and extracellular milieu, which played a role in cytolysis because down-regulation of the endogenous Hsp70 reduced both its presence at the cell surface and the lymphocyte-mediated cytolysis. Inhibitors that target both the ATPase and the peptide-binding domains of Hsp70 molecule potently decreased its anti-tumor effect. Using a variety of cell transport markers and inhibitors, we showed that the exchange of exogenous and intracellular Hsp70 is supported by classical and non-classical transport pathways, with a particular role of lipid rafts in the chaperone's intracellular transport. In conclusion, exogenous Hsp70 can eject endogenous Hsp70, thus exerting anticancer activity.

Up-regulation of neogenin-1 increases cell proliferation and motility in gastric cancer

Although elevated expression of neogenin-1 has been detected in human gastric cancer tissue, its role in gastric tumorigenesis remains unclear due to the lack of neogenin-1 studies in cancer. Therefore, we demonstrated here the function and regulatory mechanism of neogenin-1 in gastric cancer. Neogenin-1 ablation decreased proliferation and migration of gastric cancer cells, whereas its over-expression reversed these effects. Xenografted analyses using gastric cancer cells displayed statistically significant inhibition of tumor growth by neogenin-1 depletion. Interestingly, galectin-3 interacted with HSF-1 directly, which facilitated nuclear-localization and binding on neogenin-1 promoter to drive its transcription and gastric cancer cell motility. The galectin-3-increased gastric cancer cell motility was down-regulated by HSF-1 depletion. Moreover, the parallel expression patterns of galectin-3 and neogenin-1, as well as those of HSF-1 and neogenin-1, were detected in the malignant tissues of gastric cancer patients. Taken together, high-expression of neogenin-1 promotes gastric cancer proliferation and motility and its expression is regulated by HSF-1 and galectin-3 interaction. In addition, we propose further studies for neogenin-1 and its associated pathways to provide them as a proper target for gastric cancer therapy.

Hsp70 regulates the doxorubicin-mediated heart failure in Hsp70-transgenic mice

The aim of this study was to investigate the potential protective effect of the Hsp70 protein in the cardiac dysfunction induced by doxorubicin (DOX) and the mechanisms of its action. For this purpose, we used both wild-type mice (F1/F1) and Hsp70-transgenic mice (Tg/Tg) overexpressing human HSP70. Both types were subjected to chronic DOX administration (3 mg/kg intraperitoneally every week for 10 weeks, with an interval from weeks 4 to 6). Primary cell cultures isolated from embryos of these mice were also studied. During DOX administration, the mortality rate as well as weight reduction were lower in Tg/Tg compared to F1/F1 mice (P < 0.05). In vivo cardiac function assessment by transthoracic echocardiography showed that the reduction in left ventricular systolic function observed after DOX administration was lower in Tg/Tg mice (P < 0.05). The study in primary embryonic cell lines showed that the apoptosis after incubation with DOX was reduced in cells overexpressing Hsp70 (Tg/Tg), while the apoptotic pathway that was activated by DOX administration involved activated protein factors such as p53, Bax, caspase-9, caspase-3, and PARP-1. In myocardial protein extracts from identical mice with DOX-induced heart failure, the particular activated apoptotic pathway was confirmed, while the presence of Hsp70 appeared to inhibit the apoptotic pathway upstream of the p53 activation. Our results, in this DOX-induced heart failure model, indicate that Hsp70 overexpression in Tg/Tg transgenic mice provides protection from myocardial damage via an Hsp70-block in p53 activation, thus reducing the subsequent apoptotic mechanism.

Necroptosis is associated with low procaspase-8 and active RIPK1 and -3 in human glioma cells

Necroptosis is a regulated necrotic cell death that involves receptor-interacting protein kinases RIPK1 and RIPK3. Here, we report that edelfosine triggers a rapid and massive cell death in human glioblastoma cells with characteristics of necrosis. Only a minor proportion of edelfosine-treated cells underwent caspase-dependent apoptosis. Autophagy and a rapid influx of extracellular calcium into the cells had little impact on cell death. Levels of procaspase-8 were very low in necroptosis-prone glioma cells compared with the levels in other cancer cell types that underwent apoptosis upon edelfosine treatment. The RIPK1-dependent necroptosis inhibitors necrostatin-1 (Nec-1) and Nec-1s as well as siRNA-mediated silencing of RIPK3 inhibited edelfosine-induced necroptosis, resulting in increased caspase-dependent apoptosis in edelfosine-treated glioblastoma U118 cells. Inhibition of the RIPK3 substrate MLKL with necrosulfonamide also increased apoptosis in edelfosine-treated cells. These data support a major role for RIPK1 and RIPK3 in the induction of necrotic cell death and in the switch from necrosis to apoptosis following edelfosine treatment. These results indicate that the ether lipid edelfosine exerts a rapid necroptotic cell death in apoptosis-reluctant glioblastoma cells, suggesting that induction of necroptosis could constitute a new approach for glioblastoma therapy.

HSP-90 inhibitor ganetespib is synergistic with doxorubicin in small cell lung cancer

Small cell lung cancer (SCLC) at advanced stage is considered an incurable disease. Despite good response to initial chemotherapy, the responses in SCLC patients with metastatic disease are of short duration and resistance inevitably occurs. Although several target-specific drugs have altered the paradigm of treatment for many other cancers, we have yet to witness a revolution of the same magnitude in SCLC treatment. Anthracyclines, such as doxorubicin, have definite activity in this disease, and ganetespib has shown promising activity in preclinical models but underwhelming activity as a single agent in SCLC patients. Using SCLC cell lines, we demonstrated that ganetespib (IC50: 31 nM) was much more potent than 17-allylamino-17-demethoxygeldanamycin (17-AAG), a geldanamycin derivative (IC50: 16 μM). Ganetespib inhibited SCLC cell growth via induction of persistent G2/M arrest and Caspase 3-dependent cell death. MTS assay revealed that ganetespib synergized with both doxorubicin and etoposide, two topoisomerase II inhibitors commonly used in SCLC chemotherapy. Expression of receptor-interacting serine/threonine-protein kinase 1 (RIP1), a protein that may function as a pro-survival scaffold protein or a pro-death kinase in TNFR1-activated cells, was induced by doxorubicin and downregulated by ganetespib. Depletion of RIP1 by either RIP1 small interfering RNA (siRNA) or ganetespib sensitized doxorubicin-induced cell death, suggesting that RIP1 may promote survival in doxorubicin-treated cells and that ganetespib may synergize with doxorubicin in part through the downregulation of RIP1. In comparison to ganetespib or doxorubicin alone, the ganetespib+doxorubicin combination caused significantly more growth regression and death of human SCLC xenografts in immunocompromised mice. We conclude that ganetespib and doxorubicin combination exhibits significant synergy and is efficacious in inhibiting SCLC growth in vitro and in mouse xenograft models. Our preclinical study suggests that ganetespib and doxorubicin combination therapy may be an effective strategy for SCLC treatment, which warrants clinical testing.

The translation elongation factor eEF1A1 couples transcription to translation during heat shock response

Translation elongation factor eEF1A has a well-defined role in protein synthesis. In this study, we demonstrate a new role for eEF1A: it participates in the entire process of the heat shock response (HSR) in mammalian cells from transcription through translation. Upon stress, isoform 1 of eEF1A rapidly activates transcription of HSP70 by recruiting the master regulator HSF1 to its promoter. eEF1A1 then associates with elongating RNA polymerase II and the 3'UTR of HSP70 mRNA, stabilizing it and facilitating its transport from the nucleus to active ribosomes. eEF1A1-depleted cells exhibit severely impaired HSR and compromised thermotolerance. In contrast, tissue-specific isoform 2 of eEF1A does not support HSR. By adjusting transcriptional yield to translational needs, eEF1A1 renders HSR rapid, robust, and highly selective; thus, representing an attractive therapeutic target for numerous conditions associated with disrupted protein homeostasis, ranging from neurodegeneration to cancer.

Proteotoxicity is not the reason for the dependence of cancer cells on the major chaperone Hsp70

Several years ago a hypothesis was proposed that the survival of cancer cells depend on elevated expression of molecular chaperones because these cells are prone to proteotoxic stress. A critical prediction of this hypothesis is that depletion of chaperones in cancer cells should lead to proteotoxicity. Here, using the major chaperone Hsp70 as example, we demonstrate that its depletion does not trigger proteotoxic stress, thus refuting the model. Accordingly, other functions of chaperones, e.g., their role in cell signaling, might define the requirements for chaperones in cancer cells, which is critical for rational targeting Hsp70 in cancer treatment.

Selective inhibition of Leishmania donovani by active extracts of wild mushrooms used by the tribal population of India: An in vitro exploration for new leads against parasitic protozoans

The study was intended at evaluating the anti-proliferating effect of mushrooms used in traditional folklore of Santal tribal population in India against Leishmania donovani (MHOM/IN/83/AG83). A total of eighteen extracts, three estracts from each mushroom [(80% ethanol extracted; Fa), (water-soluble polysaccharide fraction; Fb), (polyphenolic fraction; Fc)], from six wild mushrooms were obtained. These extracts were tested against the promastigotes and amastigotes for their antileishmanial capacity. Fa fractions (250 μg/mL) of Astraeus hygrometricus and Tricholoma giganteum significantly inhibited the growth of L. donovani promastigotes and interfered in lipid biosynthesis. Moreover, both fractions induced apoptosis in promastigotes. Water soluble Fb fractions of A. hygrometricus, Russula laurocerasi, Russula albonigra, Termitomyces eurhizus, Russula delica and polyphenolic Fc fraction of R. laurocerasi were found to inhibit the replication of intracellular amastigotes in macrophages dose dependently. Significantly, 50% inhibitory concentration of the active extracts against intracellular amastigotes induced release of nitric oxide and IL-12 in murine macrophages and dendritic cells assay and also found considerably non-toxic on murine splenocytes. Results of this study can be used as a basis for further phytochemical and pharmacological investigations in the effort for search of novel anti-leishmanial leads.

Geldanamycin-induced osteosarcoma cell death is associated with hyperacetylation and loss of mitochondrial pool of heat shock protein 60 (hsp60)

Osteosarcoma is one of the most malignant tumors of childhood and adolescence that is often resistant to standard chemo- and radio-therapy. Geldanamycin and geldanamycin analogs have been recently studied as potential anticancer agents for osteosarcoma treatment. Here, for the first time, we have presented novel anticancer mechanisms of geldanamycin biological activity. Moreover, we demonstrated an association between the effects of geldanamycin on the major heat shock proteins (HSPs) and the overall survival of highly metastatic human osteosarcoma 143B cells. We demonstrated that the treatment of 143B cells with geldanamycin caused a subsequent upregulation of cytoplasmic Hsp90 and Hsp70 whose activity is at least partly responsible for cancer development and drug resistance. On the other hand, geldanamycin induced upregulation of Hsp60 gene expression, and a simultaneous loss of hyperacetylated Hsp60 mitochondrial protein pool resulting in decreased viability and augmented cancer cell death. Hyperacetylation of Hsp60 seems to be associated with anticancer activity of geldanamycin. In light of the fact that mitochondrial dysfunction plays a critical role in the apoptotic signaling pathway, the presented data may support a hypothesis that Hsp60 can be another functional part of mitochondria-related acetylome being a potential target for developing novel anticancer strategies.

HSP27 expression levels are associated with the sensitivity of hepatocellular carcinoma cells to 17-allylamino-17-demethoxygeldanamycin

AIMS, MATERIALS & METHODS: As heat-shock proteins are associated with tumor proliferation, differentiation, invasion and metastasis, we investigated whether targeting Hsp90 with the geldanamycin derivative 17-allylamino-17-demethoxygeldanamycin (17AAG) can inhibit the viability of hepatocellular carcinoma cell lines with various levels of metastatic potential. In addition, we investigated whether the use of Hsp27-siRNA can decrease resistance to 17AAG.

RESULTS

Although 17AAG upregulated the expression of heat-shock proteins, it did not affect the expression of Hsp90 client proteins in normal hepatocytes. Hsp90 inhibition by 17AAG degraded its client proteins in both low- and high-metastatic potential cell lines. siRNA inhibited Hsp27 expression in cell lines and improved the sensitivity of 17AAG.

CONCLUSION

17AAG inhibited the viability of hepatocellular carcinoma cells by degrading Hsp90 client proteins. The sensitivity of cells to 17AAG is associated with the level of Hsp27 expression.

Wt p53 impairs response to chemotherapy: make lemonade to spare normal cells

As published recently in Cancer Cell, p53 impairs the apoptotic response to chemotherapy and clinical outcome in breast cancer. I discuss that, while treating tumors lacking wt p53, this phenomenon can be exploited to protect normal cells from chemotherapy because all normal cells have wt p53. Also, several therapeutic paradigms can be reassessed, including the role of cellular senescence in cancer therapy.

Hsp70 is a novel posttranscriptional regulator of gene expression that binds and stabilizes selected mRNAs containing AU-rich elements

The AU-rich elements (AREs) encoded within many mRNA 3' untranslated regions (3'UTRs) are targets for factors that control transcript longevity and translational efficiency. Hsp70, best known as a protein chaperone with well-defined peptide-refolding properties, is known to interact with ARE-like RNA substrates in vitro. Here, we show that cofactor-free preparations of Hsp70 form direct, high-affinity complexes with ARE substrates based on specific recognition of U-rich sequences by both the ATP- and peptide-binding domains. Suppressing Hsp70 in HeLa cells destabilized an ARE reporter mRNA, indicating a novel ARE-directed mRNA-stabilizing role for this protein. Hsp70 also bound and stabilized endogenous ARE-containing mRNAs encoding vascular endothelial growth factor (VEGF) and Cox-2, which involved a mechanism that was unaffected by an inhibitor of its protein chaperone function. Hsp70 recognition and stabilization of VEGF mRNA was mediated by an ARE-like sequence in the proximal 3'UTR. Finally, stabilization of VEGF mRNA coincided with the accumulation of Hsp70 protein in HL60 promyelocytic leukemia cells recovering from acute thermal stress. We propose that the binding and stabilization of selected ARE-containing mRNAs may contribute to the cytoprotective effects of Hsp70 following cellular stress but may also provide a novel mechanism linking constitutively elevated Hsp70 expression to the development of aggressive neoplastic phenotypes.

TLR9 agonist protects mice from radiation-induced gastrointestinal syndrome

Purpose

Radiation-induced gastrointestinal syndrome (RIGS) is due to the clonogenic loss of crypt cells and villi depopulation, resulting in disruption of mucosal barrier, bacterial invasion, inflammation and sepsis. Intestinal macrophages could recognize invading bacterial DNA via TLR9 receptors and transmit regenerative signals to the neighboring crypt. We therefore investigated whether systemic administration of designer TLR9 agonist could ameliorate RIGS by activating TLR9.

Methods and Materials

Male C57Bl6 mice were distributed in four experimental cohorts, whole body irradiation (WBI) (8.4–10.4 Gy), TLR9 agonist (1 mg/kg s.c.), 1 h pre- or post-WBI and TLR9 agonist+WBI+iMyd88 (pretreatment with inhibitory peptide against Myd88). Animals were observed for survival and intestine was harvested for histological analysis. BALB/c mice with CT26 colon tumors in abdominal wall were irradiated with 14 Gy single dose of whole abdominal irradiation (AIR) for tumor growth study.

Results

Mice receiving pre-WBI TLR9 agonist demonstrated improvement of survival after 10.4 Gy (p<0.03), 9.4 Gy (p<0.008) and 8.4 Gy (p<0.002) of WBI, compared to untreated or iMyd88-treated controls. Post-WBI TLR9 agonist mitigates up to 8.4 Gy WBI (p<0.01). Histological analysis and xylose absorption test demonstrated significant structural and functional restitution of the intestine in WBI+TLR9 agonist cohorts. Although, AIR reduced tumor growth, all animals died within 12 days from RIGS. TLR9 agonist improved the survival of mice beyond 28 days post-AIR (p<0.008) with significant reduction of tumor growth (p<0.0001).

Conclusions

TLR9 agonist treatment could serve both as a prophylactic or mitigating agent against acute radiation syndrome and also as an adjuvant therapy to increase the therapeutic ratio of abdominal Radiation Therapy for Gastro Intestinal malignancies.

ATP analog enhances the actions of a heat shock protein 90 inhibitor in multiple myeloma cells

Heat shock protein (HSP) 90 regulates client oncoprotein maturation. The chaperone function of HSP90 is blocked by 17-N-allylamino-17-demethoxygeldanamycin (17-AAG), although it results in transcription and translation of antiapoptotic HSP proteins. Using three myeloma cell lines, we tested whether inhibition of transcription/translation of HSP or client proteins will enhance 17-AAG-mediated cytotoxicity. 8-Chloro-adenosine (8-Cl-Ado), currently in clinical trials, inhibits bioenergy production, mRNA transcription, and protein translation and was combined with 17-AAG. 17-AAG treatment resulted in HSP transcript and protein level elevation. In the combination, 8-Cl-Ado did not abrogate HSP mRNA and protein induction. HSP90 requires ATP to stabilize client proteins; hence, expression of signal transducer and activator of transcription 3 (STAT3), Raf-1, and Akt was analyzed. 17-AAG alone resulted in <10% change in STAT3, Raf-1, and Akt protein levels, whereas no change was observed for 4E-BP1. In contrast, the combination treatment resulted in a >50% decrease in client protein levels and marked hypophosphorylation of 4E-BP1. 8-Cl-Ado alone resulted in a <30% decrease of client proteins and 4E-BP1 hypophosphorylation. 8-Cl-Ado combined with 17-AAG resulted in more than additive cytotoxicity. In conclusion, 8-Cl-Ado, which targets transcription, translation, and cellular bioenergy, enhanced 17-AAG-mediated cytotoxicity in myeloma cells.

Development and characterization of a novel C-terminal inhibitor of Hsp90 in androgen dependent and independent prostate cancer cells

Background

The molecular chaperone, heat shock protein 90 (Hsp90) has been shown to be overexpressed in a number of cancers, including prostate cancer, making it an important target for drug discovery. Unfortunately, results with N-terminal inhibitors from initial clinical trials have been disappointing, as toxicity and resistance resulting from induction of the heat shock response (HSR) has led to both scheduling and administration concerns. Therefore, Hsp90 inhibitors that do not induce the heat shock response represent a promising new direction for the treatment of prostate cancer. Herein, the development of a C-terminal Hsp90 inhibitor, KU174, is described, which demonstrates anti-cancer activity in prostate cancer cells in the absence of a HSR and describe a novel approach to characterize Hsp90 inhibition in cancer cells.

Methods

PC3-MM2 and LNCaP-LN3 cells were used in both direct and indirect in vitro Hsp90 inhibition assays (DARTS, Surface Plasmon Resonance, co-immunoprecipitation, luciferase, Western blot, anti-proliferative, cytotoxicity and size exclusion chromatography) to characterize the effects of KU174 in prostate cancer cells. Pilot in vivo efficacy studies were also conducted with KU174 in PC3-MM2 xenograft studies.

Results

KU174 exhibits robust anti-proliferative and cytotoxic activity along with client protein degradation and disruption of Hsp90 native complexes without induction of a HSR. Furthermore, KU174 demonstrates direct binding to the Hsp90 protein and Hsp90 complexes in cancer cells. In addition, in pilot in-vivo proof-of-concept studies KU174 demonstrates efficacy at 75 mg/kg in a PC3-MM2 rat tumor model.

Conclusions

Overall, these findings suggest C-terminal Hsp90 inhibitors have potential as therapeutic agents for the treatment of prostate cancer.

Small interfering RNA targeting heat shock protein 70 enhances chemosensitivity in human bladder cancer cells

OBJECTIVES

To evaluate the expression levels of heat shock protein 70 (HSP70) in human urothelial cancer of the bladder and to assess the therapeutic effects of treatment with small interfering RNA (siRNA) targeting HSP70 on human bladder cancer KoTCC-1 cells.

MATERIALS AND METHODS

HSP70 expression in bladder cancer specimens obtained from 235 patients were evaluated by immunohistochemical staining. We then analyzed changes in the growth and chemosensitivity of KoTCC-1 cells following treatment with HSP70 siRNA.

RESULTS

Expression levels of HSP70 protein in bladder cancer specimens were significantly related to major prognostic indicators, including pathologic stage and tumor grade. Treatment of KoTCC-1 with HSP70 siRNA resulted in a dose-dependent inhibition of HSP70 expression. HSP70 siRNA significantly inhibited the growth of KoTCC-1 compared with that after treatment with scrambled control siRNA. Among several chemotherapeutic agents, the most powerful synergistic cytotoxic effect was observed when KoTCC-1 was treated with gemcitabine plus HSP70 siRNA, which induced more than 50% reduction in the IC50 of gemcitabine. Furthermore, a significant increase in the subG0-G1 fraction of KoTCC-1 and the DNA fragmentation was observed only after combined treatment with HSP70 siRNA and sublethal doses of gemcitabine, but not after treatment with either agent alone. Similarly, caspase-3 and caspase-9, but not caspase-8, in KoTCC-1 were synergistically activated by combined treatment with gemcitabine and HSP70 siRNA.

CONCLUSIONS

Silencing of HSP70 expression using siRNA could be an attractive therapeutic strategy for bladder cancer by inducing inhibition of tumor growth as well as enhancing chemosensitivity.

Proteotoxic stress targeted therapy (PSTT): induction of protein misfolding enhances the antitumor effect of the proteasome inhibitor bortezomib

Proteotoxic stress (PS) is generated in cells under a variety of conditions involving accumulation of misfolded proteins. To avoid the toxicity of unmitigated PS, cells activate the heat shock response (HSR). HSR involves upregulation of factors such as ubiquitin and the non-housekeeping chaperone Hsp70 which assist with metabolism of aberrant proteins. The PS-HSR axis is a potential anticancer treatment target since many tumor cells display constitutive PS and dependence on HSR due to their rapid rates of proliferation and translation. In fact, induction of PS via stimulation of protein misfolding (hyperthermia), inhibition of proteasomes (bortezomib) or inhibition of Hsp90 (geldanamycin) have all been considered or used for cancer treatment. We found that combination of bortezomib with an inducer of protein misfolding (hyperthermia or puromycin) resulted in enhanced PS. HSR was also induced, but could not mitigate the elevated PS and the cells died via largely p53-independent apoptosis. Thus, combination treatments were more cytotoxic in vitro than the component single treatments. Consistent with this, combination of non-toxic doses of puromycin with bortezomib significantly increased the antitumor activity of bortezomib in a mouse model of multiple myeloma. These results provide support for using combination treatments that disrupt the balance of PS and HSR to increase the therapeutic index of anticancer therapies.

Targeting HSP 90 induces apoptosis and inhibits critical survival and proliferation pathways in multiple myeloma

The second most commonly diagnosed hematologic malignancy, multiple myeloma, affects predominantly older patients (>60s) and is characterized by paraprotein in the serum or urine. Clinical manifestations include anemia, hypercalcaemia, progressive renal impairment, and osteolytic bone destruction. Despite promising new therapies, multiple myeloma eventually relapses in almost all patients. HSP are ubiquitous and highly conserved in prokaryotes and eukaryote organisms. Exposure to a broad range of stimuli results in increased HSP protein expression. These chaperone proteins are involved in protein transportation, prevent protein aggregation, and ensure correct folding of nascent and stress-accumulated misfolded proteins. In cancer, HSP expression is dysregulated, resulting in elevated expression, which promotes cancer by preventing programmed cell death and supporting autonomous cells growth, ultimately leading to resistance to heat, chemotherapy, and other stresses. Client proteins of HSP90 such as AKT, p53, MEK, STAT3, and Bcr-Abl are vital in tumor progression, including multiple myeloma, and their maturation and stability is dependent on HSP90. Therefore, inhibition of HSP90 via a HSP90 inhibitor (such as NVP-HSP990) should interrupt multiple signaling pathways essential for oncogenesis and growth in multiple myeloma. Our study showed that NVP-HSP990 triggered apoptosis in a panel of human multiple myeloma cells, induced cell-cycle arrest, PARP cleavage, downregulation of client proteins, the inability to reactivate phospho-STAT3 following exogenous IL-6 stimulation, and it synergized with azacytidine and bortezomib in cell lines and primary multiple myeloma samples. The mechanism of HSP90 inhibition in multiple myeloma warrants further evaluation.

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.

Do liposomal apoptotic enhancers increase tumor coagulation and end-point survival in percutaneous radiofrequency ablation of tumors in a rat tumor model?

PURPOSE

To characterize effects of combining radiofrequency (RF) ablation with proapoptotic intravenous liposome-encapsulated paclitaxel and doxorubicin on tumor destruction, apoptosis and heat-shock protein (HSP) production, intratumoral drug accumulation, and end-point survival.

MATERIALS AND METHODS

R3230 mammary adenocarcinomas (n = 177) were implanted in 174 rats in this animal care committee-approved study. Tumors received (a) no treatment, (b) RF ablation, (c) paclitaxel, (d) RF ablation followed by paclitaxel (RF ablation-paclitaxel), (e) paclitaxel before RF ablation (paclitaxel-RF ablation), (f) RF ablation followed by doxorubicin (RF ablation-doxorubicin), (g) paclitaxel followed by doxorubicin without RF ablation (paclitaxel-doxorubicin), or (h) paclitaxel before RF ablation, followed by doxorubicin (paclitaxel-RF ablation-doxorubicin). Tumor coagulation area and diameter were compared at 24-96 hours after treatment. Intratumoral paclitaxel uptake with and without RF ablation were compared. Immunohistochemical staining revealed cleaved caspase-3 and 70-kDa HSP (HSP70) expression. Tumors were randomized into eight treatment arms for Kaplan-Meier analysis of defined survival end-point (3.0-cm diameter).

RESULTS

Paclitaxel-RF ablation increased tumor coagulation over RF ablation or paclitaxel (mean, 14.0 mm ± 0.9 [standard deviation], 6.7 mm ± 0.6, 2.5 mm ± 0.6, respectively; P < .001). Paclitaxel-RF ablation-doxorubicin had similar tumor coagulation (P < .05), compared with paclitaxel-RF ablation, at 24 and 96 hours. Mean intratumoral paclitaxel accumulation for paclitaxel-RF ablation (6.76 μg/g ± 0.35) and RF ablation-paclitaxel (9.28 μg/g ± 0.87) increased over that for paclitaxel (0.63 μg/g ± 0.25, P < .001). Paclitaxel substantially increased apoptosis and decreased HSP70 expression at coagulation margin. Mean end-point survival for paclitaxel-RF ablation-doxorubicin (56.8 days ± 25.3) was greater, compared with that for paclitaxel-RF ablation or RF ablation-paclitaxel (17.6 days ± 2.5), RF ablation-doxorubicin (30.3 days ± 4.9, P < .002), or paclitaxel-doxorubicin (27.9 days ± 4.1, P < .001).

CONCLUSION

Selecting adjuvant liposomal chemotherapies (paclitaxel, doxorubicin) to target cellular apoptosis and HSP production effectively increases RF ablation-induced tumor coagulation and end-point survival, and combined multidrug approach results in even better outcomes.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100500/-/DC1.

Early effects of doxorubicin in perfused heart: transcriptional profiling reveals inhibition of cellular stress response genes

Doxorubicin (DXR) belongs to the most efficient anticancer drugs. However, its clinical application is limited by the risk of severe cardiac-specific toxicity, for which an efficient treatment is missing. Underlying molecular mechanisms are not sufficiently understood so far, but nonbiased, systemic approaches can yield new clues to develop targeted therapies. Here, we applied a genome-wide transcriptome analysis to determine the early cardiac response to DXR in a model characterized earlier, that is, rat heart perfusion with 2 muM DXR, leading to only mild cardiac dysfunction. Single-gene and gene set enrichment analysis of DNA microarrays yielded robust data on cardiac transcriptional reprogramming, including novel DXR-responsive pathways. Main characteristics of transcriptional reprogramming were 1) selective upregulation of individual genes or gene sets together with widespread downregulation of gene expression; 2) repression of numerous transcripts involved in cardiac stress response and stress signaling; 3) modulation of genes with cardiac remodeling capacity; 4) upregulation of "energy-related" pathways; and 5) similarities to the transcriptional response of cancer cells. Some early responses like the induction of glycolytic and Krebs cycle genes may have compensatory function. Only minor changes in the cardiac energy status or the respiratory activity of permeabilized cardiac fibers have been observed. Other responses potentially contribute to acute and also chronic toxicity, in particular, those in stress-responsive and cardiac remodeling transcripts. We propose that a blunted response to stress and reduced "danger signaling" is a prime component of toxic DXR action and can drive cardiac cells into pathology.

Anti-malaria drug blocks proteotoxic stress response: anti-cancer implications

The number of physical conditions and chemical agents induce accumulation of misfolded proteins creating proteotoxic stress. This leads to activation of adaptive pro-survival pathway, known as heat shock response (HSR), resulting in expression of additional chaperones. Several cancer treatment approaches, such as proteasome inhibitor Bortezomib and hsp90 inhibitor geldanamycin, involve activation of proteotoxic stress. Low efficacy of these therapies is likely due to the protective effects of HSR induced in treated cells, making this pathway an attractive target for pharmacological suppression. We found that the anti-malaria drugs quinacrine (QC) and emetine prevented HSR in cancer cells, as judged by induction of hsp70 expression. As opposed to emetine, which inhibited general translation, QC did not affect protein synthesis, but rather suppressed inducible HSF1-dependent transcription of the hsp70 gene in a relatively selective manner. The treatment of tumor cells in vitro with a combination of non-toxic concentrations of QC and proteotoxic stress inducers resulted in rapid induction of apoptosis. The effect was similar if QC was substituted by siRNA against hsp70, suggesting that the HSR inhibitory activity of QC was responsible for cell sensitization to proteotoxic stress inducers. QC was also found to enhance the antitumor efficacy of proteotoxic stress inducers in vivo: combinatorial treatment with 17-DMAG + QC resulted in suppression of tumor growth in two mouse syngeneic models. These results reveal that QC is an inhibitor of HSF1-mediated HSR. As such, this compound has significant clinical potential as an adjuvant in therapeutic strategies aimed at exploiting the cytotoxic potential of proteotoxic stress.

Profiling protein markers associated with the sensitivity to concurrent chemoradiotherapy in human cervical carcinoma

Concurrent chemoradiotherapy (CCRT) is recently recommended as the primary and standard treatment modality for cervical cancer. The aim of this study is to investigate the protein biomarkers associated with CCRT sensitivity, so as to better understand the mechanisms underlying CCRT resistance. Fresh tumor tissues from five cases for each group of CCRT-highly sensitive (CCRT-HS) and CCRT-lowly sensitive (CCRT-LS) were analyzed by 2-D electrophoresis coupled with MALDI-TOF-MS, followed by Western blot for four candidate proteins including S100A9, galectin-7, nuclear matrix protein-238 (NMP-238), and heat shock protein-70 (HSP-70). In randomly selected CCRT-HS (n = 60) and CCRT-LS (n = 35) cases, these four differentially expressed proteins were detected by tissue microarray with immunohistochemistry staining to explore the association between these interested proteins and CCRT sensitivity. Nineteen proteins differentially expressed more than four times between two groups were identified. An association was revealed between CCRT sensitivity and increased S100A9 and galectin-7, but decreased NMP-238 and HSP-70 expression (p < 0.001, respectively). Although none of these four protein markers could be used as an independent predictive factor, a recurrence prediction model was generated by combining S100A9, galectin-7, NMP-238, and HSP-70 as a full predictive factor. The proteomic analysis combined with tissue microarray provides us a dramatic tool in predicting CCRT response. The increased expression of S100A9 and galectin-7, but decreased expression of NMP-238 and HSP-70, suggests a significantly increased sensitivity to CCRT in cervical cancer.

Hsp72 chaperone function is dispensable for protection against stress-induced apoptosis

In addition to its role as a molecular chaperone, heat shock protein 72 (Hsp72) protects cells against a wide range of apoptosis inducing stresses. However, it is unclear if these two roles are functionally related or whether Hsp72 inhibits apoptosis by a mechanism independent of chaperone activity. The N-terminal adenosine triphosphatase domain, substrate-binding domain and the C-terminal EEVD regulatory motif of Hsp72 are all essential for chaperone activity. In this study, we show that Hsp72 mutants with a functional substrate-binding domain but lacking chaperone activity retain their ability to protect cells against apoptosis induced by heat and tumor necrosis factor alpha. In contrast, a deletion mutant lacking a functional substrate-binding domain has no protective capacity. The ability of the Hsp72 substrate-binding domain to inhibit apoptosis independent of the regulatory effects of the adenosine triphosphate-binding domain indicates that the inhibition of apoptosis may involve a stable binding interaction with a regulatory substrate rather than Hsp72 chaperone activity.

Transcription inhibition of heat shock proteins: a strategy for combination of 17-allylamino-17-demethoxygeldanamycin and actinomycin d

The heat shock protein (HSP) 90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) is currently in clinical trials because of its unique mechanism of action and antitumor activity. However, 17-AAG triggers the transcription and elevation of antiapoptotic HSP90, HSP70, and HSP27, which lead to chemoresistance in tumor cells. We hypothesized that inhibiting HSP90, HSP70, and HSP27 transcription may enhance 17-AAG-induced cell death in multiple myeloma cell lines. Actinomycin D (Act D), a clinically used agent and transcription inhibitor, was combined with 17-AAG. The concentrations for 17-AAG and Act D were selected based on the target actions and plasma levels during therapy. Inducible and constitutive HSP27, HSP70, and HSP90 mRNA and protein levels were measured by real-time reverse transcription-PCR and immunoblot assays. Compared with no treatment, Act D alone decreased HSP mRNA levels in MM.1S and RPMI-8226 cell lines. Combining Act D with 17-AAG did not attenuate 17-AAG-mediated increases in transcript levels of inducible HSP70; however, constitutive HSP mRNA levels were decreased. In contrast to its effect on mRNA levels, Act D was able to abrogate 17-AAG-mediated increases in all HSP protein levels. The cytotoxicity of combined Act D and 17-AAG was assessed. Treatment with Act D alone caused <40% cell death, whereas the combination of 17-AAG and Act D resulted in an increase of cell death in both multiple myeloma cell lines. In conclusion, these results indicate that 17-AAG-mediated induction of HSP70 and HSP27 expression can be attenuated by Act D and therefore can potentially improve the clinical treatment of multiple myeloma.

The heat shock protein 90 inhibitor IPI-504 induces apoptosis of AKT-dependent diffuse large B-cell lymphomas

Heat shock protein 90 (HSP90) is a molecular chaperone that stabilizes critical client proteins in multiple cancers. Gene expression profiling was utilized to characterize HSP90 isoform expression in primary human diffuse large B-cell lymphomas (DLBCLs). HSP90 alpha and beta isoforms were differentially expressed in subsets of tumours defined by their transcriptional profiles. Thereafter, we assessed the activity of the HSP90 inhibitor, IPI-504, in an extensive panel of DLBCL cell lines. IPI-504, which interacts with the conserved ATP-binding site in both HSP90 isoforms, inhibited proliferation and induced apoptosis in the majority of DLBCL cell lines at low micromolar concentrations. IPI-504-sensitive cell lines expressed high levels of the HSP90 client protein, pAKT, and exhibited dose-dependent decreases in pAKT levels following IPI-504 treatment and significantly reduced proliferation following AKT RNAi. Furthermore, the combination of low-dose (<1 micromol/l) IPI-504 and the AKT/Pi3K pathway inhibitor, LY24009, was synergistic in IPI-504-sensitive DLBCL cell lines. Low-dose IPI-504 was also synergistic with the chemotherapeutic agent, doxorubicin. The HSP90 inhibitor IPI-504 warrants further investigation in DLBCL alone and in combination with identified client protein inhibitors and active chemotherapeutic agents.

Heat shock protein 20 interacting with phosphorylated Akt reduces doxorubicin-triggered oxidative stress and cardiotoxicity

Doxorubicin (DOX) is a widely used antitumor drug, but its application is limited because of its cardiotoxic side effects. Heat shock protein (Hsp)20 has been recently shown to protect cardiomyocytes against apoptosis, induced by ischemia/reperfusion injury or by prolonged beta-agonist stimulation. However, it is not clear whether Hsp20 would exert similar protective effects against DOX-induced cardiac injury. Actually, DOX treatment was associated with downregulation of Hsp20 in the heart. To elucidate the role of Hsp20 in DOX-triggered cardiac toxicity, Hsp20 was first overexpressed ex vivo by adenovirus-mediated gene delivery. Increased Hsp20 levels conferred higher resistance to DOX-induced cell death, compared to green fluorescent protein control. Furthermore, cardiac-specific overexpression of Hsp20 in vivo significantly ameliorated acute DOX-triggered cardiomyocyte apoptosis and animal mortality. Hsp20 transgenic mice also showed improved cardiac function and prolonged survival after chronic administration of DOX. The mechanisms underlying these beneficial effects were associated with preserved Akt phosphorylation/activity and attenuation of DOX-induced oxidative stress. Coimmunoprecipitation studies revealed an interaction between Hsp20 and phosphorylated Akt. Accordingly, BAD phosphorylation was preserved, and cleaved caspase-3 was decreased in DOX-treated Hsp20 transgenic hearts, consistent with the antiapoptotic effects of Hsp20. Parallel ex vivo experiments showed that either infection with a dominant-negative Akt adenovirus or preincubation of cardiomyocytes with the phosphatidylinositol 3-kinase inhibitors significantly attenuated the protective effects of Hsp20. Taken together, our findings indicate that overexpression of Hsp20 inhibits DOX-triggered cardiac injury, and these beneficial effects appear to be dependent on Akt activation. Thus, Hsp20 may constitute a new therapeutic target in ameliorating the cardiotoxic effects of DOX treatment in cancer patients.