Inhibition of HSP90 by AUY922 Preferentially Kills Mutant KRAS Colon Cancer Cells by Activating Bim through ER Stress

ER stress and the unfolded protein response in gastrointestinal stem cells and carcinogenesis

Endoplasmic reticulum (ER) stress and the adaptive response that follows, termed the unfolded protein response (UPR), are crucial molecular mechanisms to maintain cellular integrity by safeguarding proper protein synthesis. Next to being important in protein homeostasis, the UPR is intricate in cell fate decisions such as proliferation, differentiation, and stemness. In the intestine, stem cells are critical in governing epithelial homeostasis and they are the cell of origin of gastrointestinal malignancies. In this review, we will discuss the role of ER stress and the UPR in the gastrointestinal tract, focusing on stem cells and carcinogenesis. Insights in mechanisms that connect ER stress and UPR with stemness and carcinogenesis may broaden our understanding in the development of cancer throughout the gastrointestinal tract and how we can exploit these mechanisms to target these malignancies.

Combination therapy with HSP90 inhibitors and piperlongumine promotes ROS-mediated ER stress in colon cancer cells

Colon cancer is a major cause of cancer-related death. Despite recent improvements in the treatment of colon cancer, new strategies to improve the overall survival of patients are urgently needed. Heat shock protein 90 (HSP90) is widely recognized as a promising target for treating various cancers, including colon cancer. However, no HSP90 inhibitor has been approved for clinical use due to limited efficacy. In this study, we evaluated the antitumor activities of HSP90 inhibitors in combination with piperlongumine in colon cancer cells. We show that combination treatment with HSP90 inhibitors and piperlongumine displayed strong synergistic interaction in colon cancer cells. These agents synergize by promoting ER stress, JNK activation, and DNA damage. This process is fueled by oxidative stress, which is caused by the accumulation of reactive oxygen species. These studies nominated piperlongumine as a promising agent for HSP90 inhibitor-based combination therapy against colon cancer.

RAS-mediated tumor stress adaptation and the targeting opportunities it presents

Cellular stress is known to function in synergistic cooperation with oncogenic mutations during tumorigenesis to drive cancer progression. Oncogenic RAS is a strong inducer of a variety of pro-tumorigenic cellular stresses, and also enhances the ability of cells to tolerate these stresses through multiple mechanisms. Many of these oncogenic, RAS-driven, stress-adaptive mechanisms have also been implicated in tolerance and resistance to chemotherapy and to therapies that target the RAS pathway. Understanding how oncogenic RAS shapes cellular stress adaptation and how this functions in drug resistance is of vital importance for identifying new therapeutic targets and therapeutic combinations to treat RAS-driven cancers.

AUY922 induces retinal toxicity through attenuating TRPM1

Background

Ocular adverse events are common dose-limiting toxicities in cancer patients treated with HSP90 inhibitors, such as AUY922; however, the pathology and molecular mechanisms that mediate AUY922-induced retinal toxicity remain undescribed.

Methods

The impact of AUY922 on mouse retinas and cell lines was comprehensively investigated using isobaric tags for relative and absolute quantitation (iTRAQ)‑based proteomic profiling and pathway enrichment analysis, immunohistochemistry and immunofluorescence staining, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, MTT assay, colony formation assay, and western blot analysis. The effect of AUY922 on the Transient Receptor Potential cation channel subfamily M member 1 (TRPM1)-HSP90 chaperone complex was characterized by coimmunoprecipitation. TRPM1-regulated gene expression was analyzed by RNAseq analysis and gene set enrichment analysis (GSEA). The role of TRPM1 was assessed using both loss-of-function and gain-of-function approaches.

Results

Here, we show that the treatment with AUY922 induced retinal damage and cell apoptosis, dysregulated the photoreceptor and retinal pigment epithelium (RPE) layers, and reduced TRPM1 expression. Proteomic profiling and functional annotation of differentially expressed proteins reveals that those related to stress responses, protein folding processes, regulation of apoptosis, cell cycle and growth, reactive oxygen species (ROS) response, cell junction assembly and adhesion regulation, and proton transmembrane transport were significantly enriched in AUY922-treated cells. We found that AUY922 triggered caspase-3-dependent cell apoptosis, increased ROS production and inhibited cell growth. We determined that TRPM1 is a bona fide HSP90 client and characterized that AUY922 may reduce TRPM1 expression by disrupting the CDC37-HSP90 chaperone complex. Additionally, GSEA revealed that TRPM1-regulated genes were associated with retinal morphogenesis in camera-type eyes and the JAK-STAT cascade. Finally, gain-of-function and loss-of-function analyses validated the finding that TRPM1 mediated the cell apoptosis, ROS production and growth inhibition induced by AUY922.

Conclusions

Our study demonstrates the pathology of AUY922-induced retinal toxicity in vivo. TRPM1 is an HSP90 client, regulates photoreceptor morphology and function, and mediates AUY922-induced cytotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00751-5.

The Hydroxyquinoline Analogue YUM70 Inhibits GRP78 to Induce ER Stress-Mediated Apoptosis in Pancreatic Cancer

GRP78 (glucose-regulated protein, 78 kDa) is a key regulator of endoplasmic reticulum (ER) stress signaling. Cancer cells are highly proliferative and have high demand for protein synthesis and folding, which results in significant stress on the ER. To respond to ER stress and maintain cellular homeostasis, cells activate the unfolded protein response (UPR) that promotes either survival or apoptotic death. Cancer cells utilize the UPR to promote survival and growth. In this study, we describe the discovery of a series of novel hydroxyquinoline GRP78 inhibitors. A representative analogue, YUM70, inhibited pancreatic cancer cell growth in vitro and showed in vivo efficacy in a pancreatic cancer xenograft model with no toxicity to normal tissues. YUM70 directly bound GRP78 and inactivated its function, resulting in ER stress-mediated apoptosis. A YUM70 analogue conjugated with BODIPY showed colocalization of the compound with GRP78 in the ER. Moreover, a YUM70-PROTAC (proteolysis targeting chimera) was synthesized to force degradation of GRP78 in pancreatic cancer cells. YUM70 showed a strong synergistic cytotoxicity with topotecan and vorinostat. Together, our study demonstrates that YUM70 is a novel inducer of ER stress, with preclinical efficacy as a monotherapy or in combination with topoisomerase and HDAC inhibitors in pancreatic cancer. SIGNIFICANCE: This study identifies a novel ER stress inducer that binds GRP78 and inhibits pancreatic cancer cell growth in vitro and in vivo, demonstrating its potential as a therapeutic agent for pancreatic cancer.

Cooperative treatment effectiveness of ATR and HSP90 inhibition in Ewing's sarcoma cells

INTRODUCTION

Ewing's sarcoma is an aggressive childhood malignancy whose outcome has not substantially improved over the last two decades. In this study, combination treatments of the HSP90 inhibitor AUY922 with either the ATR inhibitor VE821 or the ATM inhibitor KU55933 were investigated for their effectiveness in Ewing's sarcoma cells.

METHODS

Effects were determined in p53 wild-type and p53 null Ewing's sarcoma cell lines by flow cytometric analyses of cell death, mitochondrial depolarization and cell-cycle distribution as well as fluorescence and transmission electron microscopy. They were molecularly characterized by gene and protein expression profiling, and by quantitative whole proteome analysis.

RESULTS

AUY922 alone induced DNA damage, apoptosis and ER stress, while reducing the abundance of DNA repair proteins. The combination of AUY922 with VE821 led to strong apoptosis induction independent of the cellular p53 status, yet based on different molecular mechanisms. p53 wild-type cells activated pro-apoptotic gene transcription and underwent mitochondria-mediated apoptosis, while p53 null cells accumulated higher levels of DNA damage, ER stress and autophagy, eventually leading to apoptosis. Impaired PI3K/AKT/mTOR signaling further contributed to the antineoplastic combination effects of AUY922 and VE821. In contrast, the combination of AUY922 with KU55933 did not produce a cooperative effect.

CONCLUSION

Our study reveals that HSP90 and ATR inhibitor combination treatment may be an effective therapeutic approach for Ewing's sarcoma irrespective of the p53 status.

DCZ5248, a novel dual inhibitor of Hsp90 and autophagy, exerts antitumor activity against colon cancer

Hsp90 is a potential therapeutic target for tumor, as it maintains the stability of a variety of proteins related to tumor development and progression. Autophagy is a self-degradation process to maintain cellular homeostasis and autophagy inhibitors can suppress tumor growth. In this study, we identified DCZ5248, a triazine derivative, was a dual inhibitor of both Hsp90 and late-autophagy with potent antitumor activity against colon cancer cells in vitro and in vivo. We showed that DCZ5248 (0.1-10 μM) induced dose-dependent degradation of Hsp90 client proteins (AKT, CDK4, CDK6 and RAF-1) in HCT 116 colon cancer cells through a proteasome-dependent pathway. Meanwhile, DCZ5248 (0.3 μM) induced cytoplasmic vacuole formation, LC3 II conversion, p62 protein upregulation, and inhibited autophagy at the late stage in the colon cancer cell lines tested. We further revealed that the inhibition of autophagy was achieved by impairing lysosomal functions through induction of lysosomal acidification and attenuation of lysosomal cathepsin activity. The modulation of autophagy by DCZ5248 was independent of Hsp90 inhibition as the autophagy inhibition was not blocked by Hsp90 knockdown. Importantly, inhibition of both Hsp90 function and autophagy by DCZ5248 induced G1-phase cell cycle arrest, apoptosis, and exerted potent antitumor activity against colon cancer cells both in vitro and in vivo. These findings demonstrate that DCZ5248 is a novel dual inhibitor of Hsp90 and autophagy with potential for colon cancer therapy.

The Function and Prognostic Significance of Cripto-1 in Colorectal Cancer

Cripto-1 is a plasma membrane protein which is not expressed in adult tissue, but some tumors are accompanied by re-activation. We studied the clinical and biological significance of Cripto-1 in colorectal cancer. Cripto-1 was positive in 68 out of 192 cases (35%) by immunohistochemistry. Cripto-1 expression was correlated with worse prognosis and was an independent prognostic factor. Cripto-1-silenced colorectal cancer cell lines had reduced cell proliferation, migration, and activation of Akt and MAPK signaling pathways in vitro, and decreased tumor growth and lymph node metastasis in vivo. Cripto-1 could be a useful prognostic biomarker and therapeutic target in colorectal cancer.

Inhibition of Heat Shock Protein 90 as a Novel Platform for the Treatment of Cancer

Heat shock protein 90 (Hsp90) plays an essential role in various physiological and pathological processes. It activates client proteins to participate in tumor progression. Blocking Hsp90 could enable effective antitumor effects in many tumor types, such as multiple myeloma and colon cancer. Recently, it has motivated an interest in Hsp90 inhibitors that bind to the N-terminal or C-terminal ATP pocket as antitumor drugs. We reviewed the data from experimental and clinical trials on Hsp90 inhibitors in the treatment of different malignancies to explore and summarize their antitumor mechanisms.

Regulation of the EGFR Pathway by HSP90 Is Involved in the Pathogenesis of Cushing's Disease

PURPOSE

To investigate the role of heat-shock protein Hsp90 in adrenocorticotropic hormone (ACTH)-secreting cells, and to explore the potential clinical application of an inhibitor of Hsp90, 17-N-allylamino-17-demethoxygeldanamycin(17-AAG) in corticotropinomas [also known as "Cushing's disease" (CD)].

METHODS

Culture of mouse pituitary tumor [AtT-20/D16v-F2 (ATCC^® CRL-1795™)] cells and human pituitary ACTH-secreting tumor cells were employed. Hepatocellular carcinoma cell line (HLE) was used to evaluate EGFR inhibition by 17-AAG. Cell viability was evaluated using a commercial kit. The ACTH level was measured by a radioimmunoassay. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to measure expression of proopiomelanocortin (POMC) mRNA. Western blotting was done to measure protein levels.

RESULTS

17-AAG suppressed the viability and proliferation, and promoted the apoptosis, of AtT-20/D16v-F2 cells. 17-AAG suppressed the synthesis and secretion of ACTH in AtT-20/D16v-F2 cells and down-regulated POMC transcription. 17-AAG acted in a similar pattern upon treatment with human pituitary ACTH-secreting tumor cells. Inhibition by 17-AAG was stronger in human pituitary ACTH-secreting tumor cells carrying the ubiquitin-specific protease-8 (USP8) mutant in comparison with cells carrying wild-type USP8.

CONCLUSIONS

The HSP90 inhibitor 17-AAG reduced the viability and secretory function of human pituitary ACTH-secreting tumor cells, and tumor cells carrying the USP8 mutant were more sensitive to 17-AAG than tumor cells carrying wild-type USP8. 17-AAG could be a potential treatment option for CD.

Estrogen therapy induces an unfolded protein response to drive cell death in ER+ breast cancer

Estrogens have been shown to elicit anticancer effects against estrogen receptor α (ER)-positive breast cancer. We sought to determine the mechanism underlying the therapeutic response. Response to 17β-estradiol was assessed in ER+ breast cancer models with resistance to estrogen deprivation: WHIM16 patient-derived xenografts, C7-2-HI and C4-HI murine mammary adenocarcinomas, and long-term estrogen-deprived MCF-7 cells. As another means to reactivate ER, the anti-estrogen fulvestrant was withdrawn from fulvestrant-resistant MCF-7 cells. Transcriptional, growth, apoptosis, and molecular alterations in response to ER reactivation were measured. 17β-estradiol treatment and fulvestrant withdrawal induced transcriptional activation of ER, and cells adapted to estrogen deprivation or fulvestrant were hypersensitive to 17β-estradiol. ER transcriptional response was followed by an unfolded protein response and apoptosis. Such apoptosis was dependent upon the unfolded protein response, p53, and JNK signaling. Anticancer effects were most pronounced in models exhibiting genomic amplification of the gene encoding ER (ESR1), suggesting that engagement of ER at high levels is cytotoxic. These data indicate that long-term adaptation to estrogen deprivation or ER inhibition alters sensitivity to ER reactivation. In such adapted cells, 17β-estradiol treatment and anti-estrogen withdrawal hyperactivate ER, which drives an unfolded protein response and subsequent growth inhibition and apoptosis. 17β-estradiol treatment should be considered as a therapeutic option for anti-estrogen-resistant disease, particularly in patients with tumors harboring ESR1 amplification or ER overexpression. Furthermore, therapeutic strategies that enhance an unfolded protein response may increase the therapeutic effects of ER reactivation.

Co-inhibition of BET and proteasome enhances ER stress and Bim-dependent apoptosis with augmented cancer therapeutic efficacy

Agents that inhibit bromodomain and extra-terminal domain (BET) protein have been actively tested in the clinic as potential anticancer drugs. Proteasome inhibitors such as carfilzomib (CFZ) are FDA-approved for the treatment of patients with advanced multiple myeloma and have been tested against other cancers. The current study focuses on the combination of a BET inhibitor (e.g., JQ1) and a proteasome inhibitor (e.g., CFZ) as a novel cancer therapeutic strategy and the underlying mechanisms. The tested combination (JQ1 with CFZ) synergistically decreased cell survival and enhanced apoptosis in vitro and inhibited tumor growth in vivo. The dramatic induction of apoptosis was accompanied by enhanced elevation of Bim and ER stress. Bim knockout significantly attenuated apoptosis induced by the combination, suggesting a critical role of Bim induction in mediating the enhanced induction of apoptosis by BET and proteasome co-inhibition. The combination significantly increased Bim mRNA levels with limited effect on Bim protein stability, suggesting a primary transcriptional regulation of enhanced Bim expression. Our findings warrant further investigation of this combinatorial strategy as an effective regimen against cancer in the clinic.

Reactivation of ERK and Akt confers resistance of mutant BRAF colon cancer cells to the HSP90 inhibitor AUY922

Oncogenic mutations of BRAF occur in approximately 10% of colon cancers and are associated with their resistance to clinically available therapeutic drugs and poor prognosis of the patients. Here we report that colon cancer cells with mutant BRAF are also resistant to the heat shock protein 90 (HSP90) inhibitor AUY922, and that this is caused by rebound activation of ERK and Akt. Although AUY922 triggered rapid reduction in ERK and Akt activation in both wild-type and mutant BRAF colon cancer cells, activation of ERK and Akt rebounded shortly in the latter leading to resistance of the cells to AUY922-induced apoptosis. Reactivation of ERK was associated with the persistent expression of mutant BRAF, which, despite being a client of HSP90, was only partially degraded by AUY922, whereas reactivation of Akt was related to the activity of the HSP90 co-chaperone, cell division cycle 37 (CDC37), in that knockdown of CDC37 inhibited Akt reactivation in mutant colon cancer cells treated with AUY922. In support, as a HSP90 client protein, Akt was only diminished by AUY922 in wild-type but not mutant BRAF colon cancer cells. Collectively, these results reveal that reactivation of ERK and Akt associated respectively with the activity of mutant BRAF and CDC37 renders mutant BRAF colon cancer cells resistant to AUY922, with implications of co-targeting mutant BRAF and/or CDC37 and HSP90 in the treatment of mutant BRAF colon cancers.

Therapeutic potency of heat-shock protein-90 pharmacological inhibitors in the treatment of gastrointestinal cancer, current status and perspectives

Objectives

Heat-shock protein-90 (HSP90) chaperone machinery is critical to the folding, stability and activity of several client proteins including many responsible for tumour initiation, progression and metastasis. Overexpression of HSP90 is correlated with poor prognosis of GI cancer.

Key findings

Pharmacological inhibitors of HSP90 suppress tumorigenic effects of HSP90 by suppressing angiogenesis, survival, metastasis and drug resistance in GI cancer. This review summarizes the role of HSP90 inhibitors in the treatment of GI cancer.

Summary

We have presented different antitumour mechanisms of HSP90 inhibitors in cancer treatment. Suppression of HSP90 signalling via specific and novel pharmacological inhibitors is a potentially novel therapeutic approach for patients with GI cancer for a better understanding and hence a better management of this disease.

miR-17-92基因簇在肿瘤发生发展中作用的研究进展

肿瘤是威胁全世界人类健康和影响社会经济的重要因素. 近年来, 随着经济的发展, 肿瘤的发病率呈明显上升趋势, 但是其病因尚未完全阐明. 越来越多的证据显示肿瘤的发生和遗传因素有关, 随着病理生理学和遗传学的发展, 许多学者认为生物标志物可以预测癌症甚至指导临床治疗. 微小RNA(microRNA, miRNA)是非编码小分子RNA, 在发育、生理、病理过程以及肿瘤发生等环节中起着重要的调节作用. miR-17-92基因簇是研究较为深入、最有特点的miRNA, 被认为是原癌基因miRNA的代表, 在多种肿瘤的发生发展中起着至关重要的作用. 本文就miR-17-92基因簇在肿瘤发生发展中的作用及功能进行综述.