Antisense clusterin oligodeoxynucleotides increase the response of HER-2 gene amplified breast cancer cells to Trastuzumab

Decoding CLU (Clusterin): Conquering cancer treatment resistance and immunological barriers

One major obstacle in the treatment of cancer is the presence of proteins resistant to cancer therapy, which can impede the effectiveness of traditional approaches such as radiation and chemotherapy. This resistance can lead to disease progression and cause treatment failure. Extensive research is currently focused on studying these proteins to create tailored treatments that can circumvent resistance mechanisms. CLU (Clusterin), a chaperone protein, has gained notoriety for its role in promoting resistance to a wide range of cancer treatments, including chemotherapy, radiation therapy, and targeted therapy. The protein has also been discovered to have a role in regulating the immunosuppressive environment within tumors. Its ability to influence oncogenic signaling and inhibit cell death bolster cancer cells resistant against treatments, which poses a significant challenge in the field of oncology. Researchers are actively investigating to the mechanisms by which CLU exerts its resistance-promoting effects, with the ultimate goal of developing strategies to circumvent its impact and enhance the effectiveness of cancer therapies. By exploring CLU's impact on cancer, resistance mechanisms, tumor microenvironment (TME), and therapeutic strategies, this review aims to contribute to the ongoing efforts to improve cancer treatment outcomes.

Non-Coding RNAs: Foes or Friends for Targeting Tumor Microenvironment

Non-coding RNAs (ncRNAs) are a group of molecules critical for cell development and growth regulation. They are key regulators of important cellular pathways in the tumor microenvironment. To analyze ncRNAs in the tumor microenvironment, the use of RNA sequencing technology has revolutionized the field. The advancement of this technique has broadened our understanding of the molecular biology of cancer, presenting abundant possibilities for the exploration of novel biomarkers for cancer treatment. In this review, we will summarize recent achievements in understanding the complex role of ncRNA in the tumor microenvironment, we will report the latest studies on the tumor microenvironment using RNA sequencing, and we will discuss the potential use of ncRNAs as therapeutics for the treatment of cancer.

Clusterin inhibition mediates sensitivity to chemotherapy and radiotherapy in human cancer

Since its discovery in 1983, the protein clusterin (CLU) has been isolated from almost all human tissues and fluids and linked to the development of different physiopathological processes, including carcinogenesis and tumor progression. During the last few years, several studies have shown the cytoprotective role of secretory CLU in tumor cells, inhibiting their apoptosis and enhancing their resistance to conventional treatments including hormone depletion, chemotherapy, and radiotherapy. In an effort to determine the therapeutic potential that the inhibition of this protein could have on the development of new strategies for cancer treatment, numerous studies have been carried out in this field, with results, in most cases, satisfactory but sometimes contradictory. In this document, we summarize for the first time the current knowledge of the effects that CLU inhibition has on sensitizing tumor cells to conventional cancer treatments and discuss its importance in the development of new strategies against cancer.

Clusterin as a therapeutic target

INTRODUCTION

Clusterin (CLU) is a stress-activated, ATP-independent molecular chaperone, normally secreted from cells, that is up-regulated in Alzheimer disease and in many cancers. It plays important roles in protein homeostasis/proteostasis, inhibition of cell death pathways, and modulation of pro-survival signalling and transcriptional networks. Changes in the CLU gene locus are highly associated with Alzheimer disease, and many therapy-resistant cancers over-express CLU. The extensive post-translational processing and heterogeneous oligomerization of CLU have so far prevented any definitive structure determination. This in turn has meant that targeting CLU with small molecule inhibitors is challenging. Therefore, inhibiting CLU at the gene-expression level using siRNA or antisense is a valid approach to inhibit its function. Areas covered: This article reviews recent advances regarding the role of CLU in proteostasis, cellular trafficking, human diseases, and signalling pathways involved in oncogenesis. It addresses the rationale for CLU as a therapeutic target in cancer, and the current status of pre-clinical and clinical studies using CLU antisense inhibitor OGX011. Expert opinion: Discusses challenges facing the therapeutic targeting of CLU including rapid changes in the treatment landscape for prostate cancer with multiple new FDA approved drugs, selection of windows of intervention, and potential side effects when silencing CLU expression.

Apoptosis and molecular targeting therapy in cancer

Apoptosis is the programmed cell death which maintains the healthy survival/death balance in metazoan cells. Defect in apoptosis can cause cancer or autoimmunity, while enhanced apoptosis may cause degenerative diseases. The apoptotic signals contribute into safeguarding the genomic integrity while defective apoptosis may promote carcinogenesis. The apoptotic signals are complicated and they are regulated at several levels. The signals of carcinogenesis modulate the central control points of the apoptotic pathways, including inhibitor of apoptosis (IAP) proteins and FLICE-inhibitory protein (c-FLIP). The tumor cells may use some of several molecular mechanisms to suppress apoptosis and acquire resistance to apoptotic agents, for example, by the expression of antiapoptotic proteins such as Bcl-2 or by the downregulation or mutation of proapoptotic proteins such as BAX. In this review, we provide the main regulatory molecules that govern the main basic mechanisms, extrinsic and intrinsic, of apoptosis in normal cells. We discuss how carcinogenesis could be developed via defective apoptotic pathways or their convergence. We listed some molecules which could be targeted to stimulate apoptosis in different cancers. Together, we briefly discuss the development of some promising cancer treatment strategies which target apoptotic inhibitors including Bcl-2 family proteins, IAPs, and c-FLIP for apoptosis induction.

Knockdown of clusterin expression increases the in vitro sensitivity of human prostate cancer cells to paclitaxel

Clusterin/apolipoprotein J is a secreted heterodimeric glycoprotein that is implicated in several pathophysiological processes, including tissue remodeling, reproduction, lipid transport, and apoptosis. Although previous studies demonstrated that clusterin is able to protect against apoptosis, the role of the clusterin in cellular proliferation remains elusive. To determine whether clusterin plays an important role in cellular proliferation, the function of clusterin was examined using a small interfering RNA (siRNA) in PC3 human prostate cancer cells. Transient transfection with clusterin siRNA resulted in significant suppression of clusterin mRNA and protein expression. Clusterin knockdown resulted in a decrease in protein expression of phospho-Akt and an increase in expression of proteins phosphatase type 2AC (PP2AC) and phosphorylation of p38. However, treatment with PP2AC siRNA exerted minimal effects on clusterin expression. Interestingly, clusterin mRNA expression was reduced in paclitaxel-treated cells, and the cytotoxic effect of paclitaxel was more potent when cells were incubated with clusterin siRNA. In addition, co-treatment with paclitaxel and clusterin siRNA significantly enhanced PP2AC levels. Taken together, these results indicate that clusterin plays a crucial role in PC3 cell proliferation and that clusterin depletion may contribute to enhanced sensitivity of PC3 cells to anticancer agents such as paclitaxel.

Proteomic analysis of acquired tamoxifen resistance in MCF-7 cells reveals expression signatures associated with enhanced migration

Introduction

Acquired tamoxifen resistance involves complex signaling events that are not yet fully understood. Successful therapeutic intervention to delay the onset of hormone resistance depends critically on mechanistic elucidation of viable molecular targets associated with hormone resistance. This study was undertaken to investigate the global proteomic alterations in a tamoxifen resistant MCF-7 breast cancer cell line obtained by long term treatment of the wild type MCF-7 cell line with 4-hydroxytamoxifen (4-OH Tam).

Methods

We cultured MCF-7 cells with 4-OH Tam over a period of 12 months to obtain the resistant cell line. A gel-free, quantitative proteomic method was used to identify and quantify the proteome of the resistant cell line. Nano-flow high-performance liquid chromatography coupled to high resolution Fourier transform mass spectrometry was used to analyze fractionated peptide mixtures that were isobarically labeled from the resistant and control cell lysates. Real time quantitative PCR and Western blots were used to verify selected proteomic changes. Lentiviral vector transduction was used to generate MCF-7 cells stably expressing S100P. Online pathway analysis was performed to assess proteomic signatures in tamoxifen resistance. Survival analysis was done to evaluate clinical relevance of altered proteomic expressions.

Results

Quantitative proteomic analysis revealed a wide breadth of signaling events during transition to acquired tamoxifen resistance. A total of 629 proteins were found significantly changed with 364 up-regulated and 265 down-regulated. Collectively, these changes demonstrated the suppressed state of estrogen receptor (ER) and ER-regulated genes, activated survival signaling and increased migratory capacity of the resistant cell line. The protein S100P was found to play a critical role in conferring tamoxifen resistance and enhanced cell motility.

Conclusions

Our data demonstrate that the adaptive changes in the proteome of tamoxifen resistant breast cancer cells are characterized by down-regulated ER signaling, activation of alternative survival pathways, and enhanced cell motility through regulation of the actin cytoskeleton dynamics. Evidence also emerged that S100P mediates acquired tamoxifen resistance and migration capacity.

Clusterin and chemoresistance

Resistance to anticancer agents is one of the primary impediments to effective cancer therapy. Chemoresistance occurs not only to clinically established therapeutic agents but also to novel targeted therapeutics. Both intrinsic and acquired mechanisms have been implicated in drug resistance but it remains controversial which mechanisms are responsible that lead to failure of therapy in cancer patients. Recent focus has turned to clusterin (CLU) as a key contributor to chemoresistance to anticancer agents. Its role has been documented in prostate cancer for paclitaxel/docetaxel resistance as well as in renal, breast, and lung tumor cells. Moreover, it is abnormally upregulated in numerous advanced stage and metastatic cancers spanning prostate, renal, bladder, breast, head and neck, colon, cervical, pancreatic, lung carcinomas, melanoma, and lymphoma. It is noteworthy that only the cytoplasmic/secretory clusterin form (sCLU), and not the nuclear form, is expressed in aggressive late stage tumors, which is in line with its antiapoptotic function. Most significantly, sCLU expression is documented to lead to broad-based resistance to other unrelated chemotherapeutic agents such as doxorubicin, cisplatin, etoposide, and camphothecin. Resistance to targeted death-inducing molecules, tumor necrosis factor, Fas and TRAIL, or histone deacetylase inhibitors can also be mediated by sCLU. Expression of sCLU may be an adaptive response to genotoxic and oxidative stresses but this adaptive response could pose a threat in malignant cells being treated with cytotoxic agents by enhancing their survival potential. The actual mechanisms for sCLU induction are unclear but STAT1 is required for its constitutive upregulation in docetaxel-resistant tumor cells. Known as a protein chaperone, sCLU appears to stabilize Ku70/Bax complexes, sequestering Bax from its ability to induce mitochondrial release of cytochrome c that triggers cell apoptosis. Thus, sCLU has a key role in preventing apoptosis induced by cytotoxic agents and has the potential to be targeted for cancer therapy.

The role of clusterin (CLU) in malignant transformation and drug resistance in breast carcinomas

Breast cancer is the main cause of cancer-related death among women in Western countries. Current research is focused on identifying antiapoptotic proteins which could be a possible target for novel chemotherapeutic drugs. Secretory clusterin (sCLU) is an extracellular chaperone that has been functionally implicated in DNA repair, cell-cycle regulation, apoptotic cell death and tumorigenesis. The implication of sCLU in carcinogenesis and the progression of breast carcinomas make it an interesting gene, worthy of investigation. It has been reported to present powerful antiapoptotic activity and to perform a prosurvival function with most therapeutic treatments for breast cancer. This review summarizes our current understanding of the role of CLU in tumorigenesis, progression, and response to treatment in breast carcinomas.

Peptides modulating conformational changes in secreted chaperones: from in silico design to preclinical proof of concept

Blocking conformational changes in biologically active proteins holds therapeutic promise. Inspired by the susceptibility of viral entry to inhibition by synthetic peptides that block the formation of helix-helix interactions in viral envelope proteins, we developed a computational approach for predicting interacting helices. Using this approach, which combines correlated mutations analysis and Fourier transform, we designed peptides that target gp96 and clusterin, 2 secreted chaperones known to shift between inactive and active conformations. In human blood mononuclear cells, the gp96-derived peptide inhibited the production of TNFalpha, IL-1beta, IL-6, and IL-8 induced by endotoxin by >80%. When injected into mice, the peptide reduced circulating levels of endotoxin-induced TNFalpha, IL-6, and IFNgamma by >50%. The clusterin-derived peptide arrested proliferation of several neoplastic cell lines, and significantly enhanced the cytostatic activity of taxol in vitro and in a xenograft model of lung cancer. Also, the predicted mode of action of the active peptides was experimentally verified. Both peptides bound to their parent proteins, and their biological activity was abolished in the presence of the peptides corresponding to the counterpart helices. These data demonstrate a previously uncharacterized method for rational design of protein antagonists.

Phase II trial of OGX-011 in combination with docetaxel in metastatic breast cancer

PURPOSE

Clusterin is an antiapoptotic protein activated in response to cellular stress. OGX-011 is a second-generation antisense oligonucleotide that inhibits clusterin expression. The primary objective of this phase II trial was to assess the safety and efficacy of the combination of OGX-011 and docetaxel for metastatic breast cancer.

EXPERIMENTAL DESIGN

Women with measurable metastatic breast cancer and <or=1 chemotherapy regimen were eligible. Three loading doses of OGX-011 640 mg i.v. followed by weekly OGX-011 and docetaxel 75 mg/m(2) (every 3 weeks) were given. A two-stage design was used with a hypothesis of H(0) <or=35% and H(a) >or=55%. Objective response in >or=6 of the first 14 patients was required for the trial to continue to the second stage.

RESULTS

Fifteen patients were enrolled. A median of six cycles were delivered (range, 2-10). Five partial responses were confirmed for a 33% response rate (95% confidence interval, 11.8-61.6%) with a further 9 (60%) patients showing stable disease. The median duration of stable disease was 9.3 months. The median time to progression was 8 months (95% confidence interval, 5.62-9.43 months). Toxic effects were similar to those with single agent docetaxel. Although serum clusterin decreased on treatment, there was no relationship observed between the magnitude of decrease and response.

CONCLUSION

The combination of OGX-011 and docetaxel at 75 mg/m(2) is well tolerated and clinical activity was seen in these patients with metastatic breast cancer, but there was an insufficient number of responses to meet the criteria for proceeding to the second stage of accrual.

Anticlusterin treatment of breast cancer cells increases the sensitivities of chemotherapy and tamoxifen and counteracts the inhibitory action of dexamethasone on chemotherapy-induced cytotoxicity

INTRODUCTION

Overexpression of the apoptosis-related protein clusterin is associated with breast cancer development and tumor progression. We describe the use of clusterin-specific antisense oligonucleotides and antibodies to sensitize breast carcinoma cells to anticancer drugs routinely used in breast cancer therapy.

METHODS

MCF-7 and MDA-MB-231 cells were treated with the oligonucleotide or antibody, chemotherapeutic agents (doxorubicin or paclitaxel), tamoxifen, or with combinations of these.

RESULTS

Treatments that include antisense clusterin oligonucleotide or antibody to clusterin have been shown to reduce the number of viable cells more effectively than treatment with the drugs alone. We also demonstrate that dexamethasone pretreatment of breast cancer cell lines inhibits chemotherapy-induced cytotoxicity and is associated with the transcriptional induction of clusterin. However, anticlusterin treatment increases chemotherapy-induced cytotoxicity, even in the presence of glucocorticoids, suggesting a possible role for these proteins in glucocorticoid-mediated survival.

CONCLUSION

These data suggest that combined treatment with antibodies to clusterin or antisense clusterin oligodeoxynucleotides and paclitaxel, doxorubicin, or tamoxifen could be a novel and attractive strategy to inhibit the progression of breast carcinoma by regulation of the clusterin function. Moreover, glucocorticoid activation in breast cancer cells regulates survival signaling by the direct transactivation of genes like clusterin which encode proteins that decrease susceptibility to apoptosis. Given the widespread clinical administration of dexamethasone before chemotherapy, understanding glucocorticoid-induced survival mechanisms is essential for achieving optimal therapeutic responses.

Antisense oligonucleotides: from design to therapeutic application

1. An antisense oligonucleotide (ASO) is a short strand of deoxyribonucleotide analogue that hybridizes with the complementary mRNA in a sequence-specific manner via Watson-Crick base pairing. Formation of the ASO-mRNA heteroduplex either triggers RNase H activity, leading to mRNA degradation, induces translational arrest by steric hindrance of ribosomal activity, interferes with mRNA maturation by inhibiting splicing or destabilizes pre-mRNA in the nucleus, resulting in downregulation of target protein expression. 2. The ASO is not only a useful experimental tool in protein target identification and validation, but also a highly selective therapeutic strategy for diseases with dysregulated protein expression. 3. In the present review, we discuss various theoretical approaches to rational design of ASO, chemical modifications of ASO, ASO delivery systems and ASO-related toxicology. Finally, we survey ASO drugs in various current clinical studies.

Multiple pathways regulating the anti-apoptotic protein clusterin in breast cancer

Cancer chemotherapy inhibits tumor growth, in part, by triggering apoptosis, and anti-apoptotic proteins reduce the effectiveness of chemotherapy. Clusterin, a chaperone-like protein that binds to apoptotic and DNA repair proteins, is induced by chemotherapy and promotes tumor cell survival. Histone deacetylase inhibitors (HDIs) such as sodium butyrate and suberoylanilide hydroxamic acid (SAHA) are pharmacological agents that induce differentiation and apoptosis in cancer cells by altering chromatin structure, and we have found that combinations of chemotherapeutic drugs such as doxorubicin and HDIs efficiently induce apoptosis, even though they paradoxically induce high levels of clusterin. The hyper-expressed form of clusterin localizes to mitochondria, inhibits cytochrome c release, and is inhibited by the proteasome. When HDIs are used as single agents, clusterin suppresses cytochrome c release and apoptosis. However, doxorubicin/HDI-induced apoptosis is not inhibited by clusterin, and clusterin-resistant apoptosis corresponds with markers of the extrinsic/receptor-mediated apoptotic pathway. Thus, chemotherapy-HDI combinations are capable of overcoming an innate anti-apoptotic pathway of tumor cells, suggesting that chemotherapy-HDI combinations have potential for treating advanced stage breast cancer.

Clusterin expression and univariate analysis of overall survival in human breast cancer

The aim of this research is to investigate the significance of clusterin (CLU) expression as a risk factor for breast cancer through tissue microarray technology and univariate analysis of overall survival. Formalin-fixed, paraffin-embedded tissues from 158 cases of breast cancer and 31 cases of normal adjacent tissues assembled into a tissue microarray. Cytoplasmic CLU expression in tumor tissues was measured by immunochemistry. Survival analysis was used to investigate the relationship between CLU expression and prognosis, tumor volume, pathological classification, and recurrence. Survival time of patients with CLU expression, lymph node metastasis, and limited post-surgery chemotherapy (<6 cycles of treatment) was significantly shorter than that of patients with no detectable CLU expression (P=0.000), without lymph node metastasis (P=0.000) and more comprehensive post-surgery chemotherapy (>/=6 cycles of treatment) (P=0.035). CLU expression in tumor cells was higher than in normal adjacent breast epithelial cells (P=0.03). The CLU expression staining coefficient of cancer tissues with lymph node metastasis was higher than those without lymph node metastasis (P=0.000). Cytoplasmic CLU expression was found to be a prognostic factor for human breast cancer.

Challenge and promise: roles for clusterin in pathogenesis, progression and therapy of cancer

Clusterin (CLU) has been implicated in various cell functions involved in carcinogenesis and tumour progression. There are two known CLU protein isoforms generated in human cells. A nuclear form of CLU protein (nCLU) is proapoptotic, and a secretory form (sCLU) is prosurvival. CLU expression has been associated with tumorigenesis of various malignancies, including tumours of prostate, colon, and breast. Furthermore, CLU expression is modulated by many factors that are believed to regulate tumour growth and/or apoptosis, including 1,25-dihydroxyvitamin D3, transforming growth factor beta-1, ultraviolet radiation, and IR. sCLU upregulation appears to be a general molecular stress response. Presently, preliminary results indicate that therapeutic modalities targeting CLU may be effective in cancer treatment. However, such strategies should make sure that nCLU is not eliminated or reduced. This review summarizes our present understanding of the importance of CLU in various physiological functions including tumour growth, and discusses its relevance to future cancer therapy.

Knockdown of the cytoprotective chaperone, clusterin, chemosensitizes human breast cancer cells both in vitro and in vivo

Clusterin is a stress-associated cytoprotective chaperone up-regulated by various apoptotic triggers in many cancers and confers treatment resistance when overexpressed. The objectives of this study were to evaluate clusterin expression levels in human breast cancer and to determine whether antisense oligonucleotides or double-stranded small interfering RNAs (siRNA) targeting the clusterin gene enhance apoptosis induced by paclitaxel. Clusterin immunostaining was evaluated in a tissue microarray of 379 spotted breast cancers. The effect of hormone withdrawal, paclitaxel treatment, clusterin antisense oligonucleotide (OGX-011), and siRNA treatments on clusterin expression was examined in MCF-7 and MDA-MB-231 cells. Northern, quantitative real-time PCR, and Western analyses were used to measure change in clusterin mRNA and protein levels. The effect of OGX-011 or siRNA clusterin treatment on chemosensitivity to paclitaxel was done in both cell lines in vitro, whereas the ability of OGX-011 to chemosensitize in vivo was evaluated in athymic mice bearing MCF-7 tumors. Clusterin was expressed in 62.5% of tumors within the tissue microarray. Clusterin expression increased after estrogen withdrawal and paclitaxel treatment in vitro in MCF-7 cells. OGX-011 or siRNA clusterin decreased clusterin levels by >90% in a dose-dependent, sequence-specific manner and significantly enhanced chemosensitivity to paclitaxel in vitro. When combined, OGX-011 or siRNA clusterin reduced the IC50 by 2-log compared with paclitaxel alone. In vivo administration of OGX-011 enhanced the effects of paclitaxel to significantly delay MCF-7 tumor growth. These data identify clusterin as a valid therapeutic target and provides preclinical proof-of-principle to test OGX-011 in multimodality therapies for breast cancer.

cDNA microarray analysis of isogenic paclitaxel- and doxorubicin-resistant breast tumor cell lines reveals distinct drug-specific genetic signatures of resistance

cDNA microarray analysis is a highly useful tool for the classification of tumors and for prediction of patient prognosis to specific cancers based on this classification. However, to date, there is little evidence that microarray approaches can be used to reliably predict patient response to specific chemotherapy drugs or regimens. This is likely due to an inability to differentiate between genes affecting patient prognosis and genes that play a role in response to specific drugs. Thus, it would be highly useful to identify genes whose expression correlates with tumor cell sensitivity to specific chemotherapy agents in a drug-specific manner. Using cDNA microarray analysis of wildtype MCF-7 breast tumor cells and isogenic paclitaxel-resistant (MCF-7(TAX)) or doxorubicin-resistant (MCF-7(DOX)) derivative cell lines, we have uncovered drug-specific changes in gene expression that accompany the establishment of paclitaxel or doxorubicin resistance. These changes in gene expression were confirmed by quantitative reverse transcription polymerase chain reaction and immunoblotting experiments, with a confirmation rate of approximately 91-95%. The genes identified may prove highly useful for prediction of response to paclitaxel or doxorubicin in patients with breast cancer. To our knowledge this is the first report of drug-specific genetic signatures of resistance to paclitaxel or doxorubicin, based on a comparison of gene expression between isogenic wildtype and drug-resistant tumor cell lines. Moreover, this study provides significant insight into the wide variety of mechanisms through which resistance to these agents may be acquired in breast cancer.

Antisense therapy for cancer

Improved understanding of the molecular mechanisms that mediate cancer progression and therapeutic resistance has identified many therapeutic gene targets that regulate apoptosis, proliferation and cell signalling. Antisense oligonucleotides offer one approach to target genes involved in cancer progression, especially those that are not amenable to small-molecule or antibody inhibition. Better chemical modifications of antisense oligonucleotides increase resistance to nuclease digestion, prolong tissue half-lives and improve scheduling. Indeed, recent clinical trials confirm the ability of this class of drugs to significantly suppress target-gene expression. The current status and future directions of several antisense drugs that have potential clinical use in cancer are reviewed.