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

Therapeutic Potential of Clusterin Inhibition in Human Cancer

Clusterin (CLU) protein is involved in various pathophysiological processes including carcinogenesis and tumor progression. In recent years, the role of the secretory isoform has been demonstrated in tumor cells, where it inhibits apoptosis and favors the acquisition of resistance to conventional treatments used to treat cancer. To determine the possible therapeutic potential of inhibiting this protein, numerous studies have been carried out in this field. In this article, we present the existing knowledge to date on the inhibition of this protein in different types of cancer and analyze the importance it could have in the development of new therapies targeted against this disease.

The role and function of CLU in cancer biology and therapy

Clusterin (CLU) is a highly evolutionary conserved glycoprotein with multiple isoform-specific functions and is widely distributed in different species. Accumulated evidence has shown the prominent role of CLU in regulating several essential physiological processes, including programmed cell death, metastasis, invasion, proliferation and cell growth via regulating diverse signaling pathways to mediate cancer progression in various cancers, such as prostate, breast, lung, liver, colon, bladder and pancreatic cancer. Several studies have revealed the potential benefit of inhibiting CLU in CLU inhibition-based targeted cancer therapies in vitro, in vivo or in human, suggesting CLU is a promising therapeutic target. This review discusses the multiple functions and mechanisms of CLU in regulating tumor progression of various cancers and summarizes the inhibitors of CLU used in CLU inhibition-based targeted cancer therapies.

The multiple roles and therapeutic potential of clusterin in non-small-cell lung cancer: a narrative review

Worldwide, lung cancer is the most common form of cancer, with an estimated 2.09 million new cases and 1.76 million of death cause in 2018. It is categorized into two subtypes, small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC). Although platinum-based chemotherapy or molecular targeted drugs is recommended for advanced stages of NSCLC patients, however, resistance to drug and chemotherapy are hindrances for patients to fully beneficial from these treatments. Clusterin (CLU), also known as apolipoprotein J, is a versatile chaperone molecule which produced by a wide array of tissues and found in most biologic fluids. There are studies reported high expression of CLU confers resistance to chemotherapy and radiotherapy in different lung cancer cell lines. By silencing CLU using Custirsen (OGX-011), a second-generation antisense oligonucleotide (ASO) that inhibits CLU production, not only could sensitized cells to chemo- and radiotherapy, also could decreased their metastatic potential. We will review here the extensive literature linking CLU to NSCLC, update the current state of research on CLU for better understanding of this unique protein and the development of more effective anti- CLU treatment.

Overexpression of secretory clusterin (sCLU) induces chemotherapy resistance in human gastric cancer cells by targeting miR-195-5p

Recent focus has turned to secretory clusterin (sCLU) as a key contributor to chemoresistance of anticancer agents, but the role of sCLU on chemotherapy drug response to gastric cancer cells is not fully understood. Previous research found that sCLU was overexpressed in the induced multidrug-resistant MGC-803/5-FU cell line, suggesting that sCLU upregulation was closely related to chemoresistance to anticancer agents. In the present study, we aimed to clarify the role and mechanisms of sCLU in regulating the chemoresistance of gastric cancer cells. Cell apoptosis and cell viability were evaluated by annexin V/propidium iodide staining and CCK8. Expression of sCLU and miR-195-5P was detected using quantitative RT-PCR assays. The expression of sCLU in gastric cancer tissues was detected by RT-PCR assays. Upregulating or downregulating sCLU or miR-195-5P in gastric cancer cells was used to evaluate the mechanisms of chemoresistance. We found that sCLU was significantly elevated in the MGC-803/5-FU and SGC-7901 cells, and the downregulating sCLU sensitized MGC-803/5-FU and SGC-7901 cells to cisplatin and Docetaxel by upregulation of miR-195-5P. Upregulating sCLU in MGC-803 and HGC-27 cells was resistant to cisplatin and Docetaxel by downregulating miR-195-5p. Targeting miR-195-5P reduced the sensitivity of MGC-803 cells to 5-FU, and miR-195-5P overexpression enhanced the sensitivity of MGC-803/5-FU cells to 5-FU. The overexpression of sCLU in gastric cancer tissues was associated with chemoresistance. Our findings suggest that overexpression of sCLU induced chemoresistance in gastric cancer cells by downregulating miR-195-5p, thus providing a potential target for the development of agents that targeting sCLU for gastric cancer therapy.

Clusterin as modulator of carcinogenesis: A potential avenue for targeted cancer therapy

Clusterin (CLU) is an evolutionary conserved molecular chaperone present in different human tissues and fluids and established to be a significant cancer regulator. It controls several cancer-associated cellular events, including cancer cell proliferation, stemness, survival, metastasis, epithelial-mesenchymal transition, therapy resistance, and inhibition of programmed cell death to support cancer growth and recurrence. This multifunctional role of CLU makes it an ideal target for cancer control. More importantly, genetic and antisense-mediated (OGX-011) inhibition of CLU enhances the anticancer potential of different FDA-approved chemotherapeutic drugs at the clinical level, improving patient's survival. In this review, we have discussed the detailed mechanism of CLU-mediated modulation of different cancer-associated signaling pathways. We have also provided updated information on the current preclinical and clinical findings that drive trials in various cancer types for potential targeted cancer therapy.

Targeting Clusterin Induces Apoptosis, Reduces Growth Ability and Invasion and Mediates Sensitivity to Chemotherapy in Human Osteosarcoma Cells

Objective:

The aim of the study was to investigate the expression of sCLU in relation to the clinicopathological features and prognosis of patients with untreated High-Grade Osteosarcoma (HGOS) and to evaluate sCLU as a target for osteosarcoma (OS) therapies.

Methods:

The expression of sCLU in 98 patients of HGOS enrolled from April 2005 to March 2015 at the affiliated hospital of Qingdao University was evaluated by immunohistochemistry. The sCLU expression, clinical data and survival were compared. siRNA-mediated sCLU gene silencing on cell apoptosis, viability, invasion and chemosensitivity to doxorubicin in U2OS cells in vitro was evaluated.

Results:

sCLU expression was found in 59 (60%) of the 98 patients. A positive correlation was observed between sCLU expression and metastatic disease (P = 0.036) and a negative correlation between sCLU expression and response to chemotherapy (P = 0.002). Targeting sCLU expression in U2OS cells induced significant reduction in cellular growth and higher rates of spontaneous endogenous apoptosis. In addition, targeting sCLU expression inhibited the invasion of U2OS cells. Furthermore, targeting sCLU expression significantly sensitized to chemotherapeutic drug, doxorubicin.

Conclusions:

The overexpression of sCLU was significantly correlated with metastasis and chemosensitivity in patients with HGOS. sCLU may be a promising therapeutic or chemopreventive target for human OS treatment.

sCLU as prognostic biomarker and therapeutic target in osteosarcoma

Osteosarcoma (OS) is the most common primary malignant bone tumor. Secretory apolipoprotein J/clusterin (sCLU) is overexpressed in many cancers; however, its role in OS has not been previously investigated. The objectives of this study were to address this question and also to assess the clinical value of sCLU as a prognostic biomarker and therapeutic target by comparing sCLU expression in human OS (n = 106), normal bone (n = 16), fibrous dysplasia (n = 9), and ossifying myositis (n = 11) tissues and by evaluating the effect of sCLU silencing on OS growth, invasion, and chemosensitivity in vitro and in vivo. We found that sCLU was highly expressed in OS tissue specimens, which was positively correlated with metastatic disease and negatively correlated with response to chemotherapy. sCLU knockdown in KHOS cells inhibited proliferation and invasion and increased apoptosis as well as sensitivity to the chemotherapy drug gemcitabine (Gem). In a mouse xenograft model, sCLU depletion suppressed lung metastasis and enhanced the effects of Gem, thereby slowing KHOS tumor growth. These results indicate that sCLU overexpression is a biomarker for malignant transformation of OS and that therapeutic strategies targeting sCLU may be an effective treatment for OS.

Highlights

● Secretory apolipoprotein J/clusterin (sCLU) is overexpressed in osteosarcoma (OS).

● sCLU overexpression is associated with metastasis and chemoresistance.

● Silencing sCLU inhibits metastasis and enhances chemosensitivity in OS cells.

sCLU is a biomarker for metastatic OS and a potential therapeutic target.

Clusterin in Alzheimer's Disease: Mechanisms, Genetics, and Lessons From Other Pathologies

Clusterin (CLU) or APOJ is a multifunctional glycoprotein that has been implicated in several physiological and pathological states, including Alzheimer's disease (AD). With a prominent extracellular chaperone function, additional roles have been discussed for clusterin, including lipid transport and immune modulation, and it is involved in pathways common to several diseases such as cell death and survival, oxidative stress, and proteotoxic stress. Although clusterin is normally a secreted protein, it has also been found intracellularly under certain stress conditions. Multiple hypotheses have been proposed regarding the origin of intracellular clusterin, including specific biogenic processes leading to alternative transcripts and protein isoforms, but these lines of research are incomplete and contradictory. Current consensus is that intracellular clusterin is most likely to have exited the secretory pathway at some point or to have re-entered the cell after secretion. Clusterin's relationship with amyloid beta (Aβ) has been of great interest to the AD field, including clusterin's apparent role in altering Aβ aggregation and/or clearance. Additionally, clusterin has been more recently identified as a mediator of Aβ toxicity, as evidenced by the neuroprotective effect of CLU knockdown and knockout in rodent and human iPSC-derived neurons. CLU is also the third most significant genetic risk factor for late onset AD and several variants have been identified in CLU. Although the exact contribution of these variants to altered AD risk is unclear, some have been linked to altered CLU expression at both mRNA and protein levels, altered cognitive and memory function, and altered brain structure. The apparent complexity of clusterin's biogenesis, the lack of clarity over the origin of the intracellular clusterin species, and the number of pathophysiological functions attributed to clusterin have all contributed to the challenge of understanding the role of clusterin in AD pathophysiology. Here, we highlight clusterin's relevance to AD by discussing the evidence linking clusterin to AD, as well as drawing parallels on how the role of clusterin in other diseases and pathways may help us understand its biological function(s) in association with AD.

Clusterin, a Novel DEC1 Target, Modulates DNA Damage-Mediated Cell Death

Differentiated embryonic chondrocyte expressed gene 1 (DEC1, also known as Sharp2/Stra13/BHLHE40) is a basic helix-loop-helix transcription factor that plays an important role in circadian rhythms, cell proliferation, apoptosis, cellular senescence, hypoxia response, and epithelial-to-mesenchymal transition of tumor cells. Secretory clusterin (sCLU) is a cytoprotective protein that guards against genotoxic stresses. Here, clusterin (CLU) was identified as a novel target gene of DEC1 and suppresses DNA damage-induced cell death in tumor cells. Mechanistically, based on chromatin immunoprecipitation and luciferase assays, DEC1 binds to and activates the promoter of the CLU gene. DEC1 and DNA-damaging agents induce sCLU expression, whereas DEC1 knockdown decreases the expression of sCLU upon DNA damage. Moreover, the data demonstrate that DEC1 inhibits, whereas sCLU knockdown enhances, DNA damage-induced cell death in MCF7 breast cancer cells. Given that DEC1 and sCLU are frequently overexpressed in breast cancers, these data provide mechanistic insight into DEC1 as a prosurvival factor by upregulating sCLU to reduce the DNA damage-induced apoptotic response. Together, this study reveals sCLU as a novel target of DEC1 which modulates the sensitivity of the DNA damage response.Implications: DEC1 and sCLU are frequently overexpressed in breast cancer, and targeting the sCLU-mediated cytoprotective signaling pathway may be a novel therapeutic approach. Mol Cancer Res; 16(11); 1641-51. ©2018 AACR.

Secretory Clusterin Mediates Oxaliplatin Resistance via the Gadd45a/PI3K/Akt Signaling Pathway in Hepatocellular Carcinoma

Purpose: Systemic therapy has often been used for patients with advanced hepatocellular carcinoma (HCC). However, due to drug resistance, the use of cytotoxic chemotherapy in the treatment of patients with advanced HCC has typically demonstrated low response rates. Secretory clusterin (sCLU) is expressed in aggressive late-stage tumors and associated with resistance to chemotherapy, including that in HCC cases. The present research aimed to investigate the biological role of sCLU in HCC.

Methods: sCLU expression in HCC and normal tissues was examined using immunohistochemical staining, followed by analysis of the correlation between sCLU expression and clinical indicators. In addition, the role and internal mechanism of sCLU in cell proliferation and apoptosis were investigated in HCC cells.

Results: sCLU expression was significantly upregulated in HCC tissues; and was associated with histological grade and poor overall survival. The levels of sCLU were significantly increased in Bel7402, SMMC7721 and resistant HCC cells (Bel7404-OR). Inhibiting the activity of sCLU enhanced the chemosensitivity of Bel7402 and SMMC7721 cells. Downregulation of sCLU could increase the expression of Gadd45a in HCC cells. Overexpression of sCLU contributed to drug resistance in Bel7402, SMMC7721 and Bel7404-OR cells; whereas, overexpression of Gadd45a alone overcame drug resistance in the cells above. No significant expression changes of sCLU and Gadd45a were observed in HCC cells after the interference of a selective inhibitor of the PI3K/Akt signaling pathway. However, regulation of the expression of Gadd45a could influence the phosphorylation level of Akt; and further regulate the expression of Bcl-2 and Bax proteins involved in the mitochondrial apoptosis pathways.

Conclusions: The results demonstrate that sCLU/Gadd45a/PI3K/Akt signaling represents a novel pathway that could regulate drug resistance in a one-way manner in HCC cells.

Liposomal co-delivery-based quantitative evaluation of chemosensitivity enhancement in breast cancer stem cells by knockdown of GRP78/CLU

Resistance to chemotherapy is a key factor in the inefficacy of various forms of treatments for cancer. In the present study, chemo-resistant proteins, including glucose-regulated protein 78 (GRP78)/clusterin (CLU) targeted 1,2-dioleoyloxy-3-trimethylammoniumpropane (DOTAP) liposomes, were developed as a delivery system for co-delivery of camptothecin (CPT) and GRP78 siRNA/CLU siRNA. Their drug/gene co-deliveries were quantitatively assessed in cancer stem cells (CSC) and MCF-7 cells. DOTAP-CPT/siRNA were prepared via electrostatic interaction on GRP78 siRNA or CLU siRNA. The size and ζ-potential of liposomes and lipoplexes were measured by dynamic light scattering techniques and electrophoretic light scattering spectrophotometry. The lipoplexes formation was tested by using gel electrophoresis. Immunofluorescence analysis showed that the expression level of CLU and GRP78 were significantly elevated in CSC compared to MCF-7 cells. Transfection and drug-delivery efficiency of DOTAP-CPT/siRNA were quantitatively compared with Lipofectamine 2000. Compared to free CPT, DOTAP-CPT-siCLU delivery in CSC and MCF-7 cells increased transfection efficiency and chemo-sensitivity by 4.1- and 5.9-fold, respectively. On the other hand, DOTAP-CPT-siGRP78 delivery increased transfection efficiency and chemo sensitivity by 4.4- and 6.2-fold in CSC and MCF-7 cells, respectively, compared to free CPT. It is significant that 3 ± 1.2-fold increase in transfection efficiency was achieved by lipofectamine. Consequently, an increase in anti-cancer/gene silencing efficacy was quantitatively observed as an effect of DOTAP-CPT/siRNA treatment, which was relatively higher than lipofectamine treatment. Conclusively, our experimental data quantitatively demonstrate that using DOTAP-CPT-siRNA specifically targeting (CSCs) chemo-resistant protein in vitro offers substantial potential for synergistic anti-cancer therapy.

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.

Clusterin knockdown sensitizes prostate cancer cells to taxane by modulating mitosis

Clusterin (CLU) is a stress‐activated molecular chaperone that confers treatment resistance to taxanes when highly expressed. While CLU inhibition potentiates activity of taxanes and other anti‐cancer therapies in preclinical models, progression to treatment‐resistant disease still occurs implicating additional compensatory survival mechanisms. Taxanes are believed to selectively target cells in mitosis, a complex mechanism controlled in part by balancing antagonistic roles of Cdc25C and Wee1 in mitosis progression. Our data indicate that CLU silencing induces a constitutive activation of Cdc25C, which delays mitotic exit and hence sensitizes cancer cells to mitotic‐targeting agents such as taxanes. Unchecked Cdc25C activation leads to mitotic catastrophe and cell death unless cells up‐regulate protective mechanisms mediated through the cell cycle regulators Wee1 and Cdk1. In this study, we show that CLU silencing induces a constitutive activation of Cdc25C via the phosphatase PP2A leading to relief of negative feedback inhibition and activation of Wee1‐Cdk1 to promote survival and limit therapeutic efficacy. Simultaneous inhibition of CLU‐regulated cell cycle effector Wee1 may improve synergistic responses of biologically rational combinatorial regimens using taxanes and CLU inhibitors.

Downregulation of clusterin mediates sensitivity to protein kinase inhibitors in breast cancer cells

The efficacy of protein kinase inhibitors (PKIs) has been shown in clinical assays for cancer, but as isolated agents, they only have a modest effect. One of the most important characteristics of mitogen-activated PKIs is their ability to decrease the apoptotic threshold of cancer cells, sensitizing them to the action of other antiapoptotic agents. The secretory clusterin protein is an inhibitor of apoptosis with a cytoprotective function. We describe the use of clusterin-specific antisense oligonucleotides and siRNA to sensitize breast carcinoma cells to several PKIs. MCF-7 and MDA-MB-231 cells were treated with antisense oligonucleotide or siRNA to clusterin and the following PKIs: H-89, chelerythrine and genistein. The three inhibitors used in this study upregulated clusterin expression and treatments that included antisense oligonucleotide or siRNA to clusterin reduced the number of viable cells more effectively than did treatment with the drugs alone. Therefore, treatment with such combinations may benefit patients with breast cancer.

PACAP inhibits tumor growth and interferes with clusterin in cervical carcinomas

Secretory clusterin (sCLU), an anti-apoptotic protein, is overexpressed in many tumors and enhances tumorigenesis and chemo-resistance. However, the regulation mechanism controlling the sCLU maturation process or activity remains undetermined. In this study, we found PACAP as a negative regulator of CLU. Overexpression of the PACAP gene in cervical cancer cell lines lacking PACAP expression significantly inhibited cell growth and induced apoptosis. We further demonstrated that interaction of PACAP with CLU significantly downregulated CLU expression and secretion, inhibited the Akt-Raf-ERK pathway, and suppressed the growth of human tumor xenografts in nude mice. This novel inhibitory function of PACAP may be applicable for developing novel molecular therapies for tumors with increased sCLU expression.

Secreted clusterin (sCLU) regulates cell proliferation and chemosensitivity to cisplatin by modulating ERK1/2 signals in human osteosarcoma cells

Background

Several studies have shown that secreted clusterin (sCLU) up-regulation in multi-drug resistant osteosarcoma (OS) cells relates to enhanced drug resistance. Furthermore, sCLU silencing directed against sCLU induces significant reduction of cellular growth and sensitizes OS cells to chemotherapy. However, the molecular mechanisms underlying the effect of sCLU on OS cells are not known.

Methods

To evaluate the roles and possible mechanisms of sCLU in chemoresistance of OS cells to cisplatin (DPP), we utilized RNA interference to knockdown sCLU expression in the sCLU-rich U-2 OS cells and to overexpress sCLU in the sCLU-poorer KH OS cells, and further assessed the cell viability and chemosensitivity to DDP as well as possible signaling transduction pathways.

Results

The data showed that sCLU depletion inhibited growth and sensitized sCLU-rich U-2 OS cells to cisplatin in vitro and in vivo by inducing inactivation of ERK1/2, and sCLU overexpression promoted growth and increased resistance of sCLU-less KH OS cells to cisplatin in vitro and in vivo by activation of ERK1/2.

Conclusions

The data also suggests critical roles of sCLU in OS cell chemoresistance to DPP and raises the possibility of sCLU depletion as a promising approach to OS therapy.

Downregulating sCLU enhances the sensitivity of hepatocellular carcinoma cells to gemcitabine by activating the intrinsic apoptosis pathway

PURPOSE

The purpose of this study was to investigate whether the therapeutic activity of gemcitabine (GCB) in hepatocellular carcinoma (HCC) could be increased by the down-regulation of secretory clusterin (sCLU), a glycoprotein that is considered to play a cytoprotective role in the resistance to chemotherapy.

METHODS

The expression of sCLU was detected in HCC tumor tissues and cell lines. A cell viability and apoptosis assay were performed in parental HCC cells or the same cells transfected with sCLU shRNA and treated with or without GCB. The potential downstream pathways were investigated using the Human Apoptosis RT(2) Profiler™ PCR Array.

RESULTS

The expression levels of sCLU in HCC tissues were significantly higher than in adjacent non-tumor liver tissues and were associated with the histological grade and transarterial chemoembolization. sCLU overexpression was also found in three HCC cell lines and hepatocytes. The depletion of sCLU synergistically increased GCB sensitivity in Bel7402 and SMMC7721 cells and induced cell apoptosis. Based on the PCR array analysis, sCLU depletion also resulted in the up-regulation of BNIP1, GADD45A, TNFRSF10A, and TRADD and down-regulation of AKT1 in Bel7402 and SMMC7721 cells compared with the parental controls. These results were further supported by a Western blot analysis, which showed increased GADD45a protein expression and the decreased expression of phosphorylated AKT. GADD45a overexpression also increased the sensitivity to GCB in the Bel7402 and SMMC7721 cells.

CONCLUSION

Targeting sCLU may be a useful method to enhance the cytotoxic effect of GCB in hepatocellular carcinoma.

Insulin-like growth factor-I induces CLU expression through Twist1 to promote prostate cancer growth

Clusterin (CLU) is cytoprotective molecular chaperone that is highly expressed in castrate-resistant prostate cancer (CRPC). CRPC is also characterized by increased insulin-like growth factor (IGF)-I responsiveness which induces prostate cancer survival and CLU expression. However, how IGF-I induces CLU expression and whether CLU is required for IGF-mediated growth signaling remain unknown. Here we show that IGF-I induced CLU via STAT3-Twist1 signaling pathway. In response to IGF-I, STAT3 was phosphorylated, translocated to the nucleus and bound to the Twist1 promoter to activate Twist1 transcription. In turn, Twist1 bound to E-boxes on the CLU promoter and activated CLU transcription. Inversely, we demonstrated that knocking down Twist1 abrogated IGF-I induced CLU expression, indicating that Twist1 mediated IGF-I-induced CLU expression. When PTEN knockout mice were crossed with lit/lit mice, the resultant IGF-I deficiency suppressed Twist1 as well as CLU gene expression in mouse prostate glands. Moreover, both Twist1 and CLU knockdown suppressed prostate cancer growth accelerated by IGF-I, suggesting the relevance of this signaling not only in an in vitro, but also in an in vivo. Collectively, this study indicates that IGF-I induces CLU expression through sequential activation of STAT3 and Twist1, and suggests that this signaling cascade plays a critical role in prostate cancer pathogenesis.

Clusterin: a key player in cancer chemoresistance and its inhibition

Clusterin is a heterodimeric disulfide-linked glycoprotein (449 amino acids) isolated in the rat prostate after castration. It is widely distributed in different tissues and highly conserved in species. There are two isoforms (1 and 2) with antagonistic actions regarding apoptosis. Clusterin is implicated in a number of biological processes, including lipid transport, membrane recycling, cell adhesion, programmed cell death, and complement cascade, representing a truly multifunctional protein. Isoform 2 is overexpressed under cellular stress conditions and protects cells from apoptosis by impeding Bax actions on the mitochondrial membrane and exerts other protumor activities, like phosphatidylinositol 3-kinase/protein kinase B pathway activation, modulation of extracellular signal-regulated kinase 1/2 signaling and matrix metallopeptidase-9 expression, increased angiogenesis, modulation of the nuclear factor kappa B pathway, among others. Its overexpression should be considered as a nonspecific cellular response to a wide variety of tissue insults like cytotoxic chemotherapy, radiation, excess of free oxygen radicals, androgen or estrogen deprivation, etc. A review of the recent literature strongly suggests potential roles for custirsen in particular, and proapoptosis treatments in general, as novel modalities in cancer management. Inhibition of clusterin is known to increase the cytotoxic effects of chemotherapeutic agents, and custirsen, a second-generation antisense oligonucleotide that blocks clusterin, is being tested in a Phase III clinical trial after successful results were achieved in Phase II studies. A major issue in cancer evolution that remains unanswered is whether clusterin represents a driving force of tumorigenesis or a late phenomenon after chemotherapy. This review presents preclinical data that encourages trials in various types of cancer other than advanced castration-resistance prostate cancer and discusses briefly the appropriate timing for clusterin inhibition in the clinical context.

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.

Star-branched amphiphilic PLA-b-PDMAEMA copolymers for co-delivery of miR-21 inhibitor and doxorubicin to treat glioma

The combined treatment of chemotherapeutant and microRNA (miR) has been proven to be a viable strategy for enhancing chemosensitivity due to its synergistic effect for tumor therapy. However, the co-delivery of drugs and genes remains a major challenge as they lack efficient co-delivery carriers. In this study, three amphiphilic star-branched copolymers comprising polylactic acid (PLA) and polydimethylaminoethyl methacrylate (PDMAEMA) with AB3, (AB3)2,and (AB3)3 molecular architectures were synthesized respectively by a combination of ring-opening polymerization, atom transfer radical polymerization, and click chemistry via an "arm-first" approach. The star copolymers possessed a low critical micelle concentration (CMC) and formed nano-sized micelles with positive surface charges in water as well as exhibiting a much lower cytotoxicity than PEI 25 kDa. Nevertheless, their gene transfection efficiency and tumor inhibition ability showed a remarkable dependence on their molecular architecture. The (AB3)3 architecture micelle copolymer exhibited the highest transfection efficiency, about 2.5 times higher than PEI. In addition, after co-delivering DOX and miR-21 inhibitor (miR-21i) into LN229 glioma cells, the micelles could mediate escaping miR-21i from lysosome degradation and the release of DOX to the nucleus, which significantly decreased the miR-21 expression. Moreover, co-delivery of DOX and miR-21i surprisingly exhibited an anti-proliferative efficiency compared with DOX or the miR-21i treatment alone. These results demonstrated that amphiphilic star-branched copolymers are highly promising for their combinatorial delivery of genes and hydrophobic therapeutants.

Non-secreted clusterin isoforms are translated in rare amounts from distinct human mRNA variants and do not affect Bax-mediated apoptosis or the NF-κB signaling pathway

Clusterin, also known as apolipoprotein J, is expressed from a variety of tissues and implicated in pathological disorders such as neurodegenerative diseases, ischemia and cancer. In contrast to secretory clusterin (sCLU), which acts as an extracellular chaperone, the synthesis, subcellular localization and function(s) of intracellular CLU isoforms is currently a matter of intense discussion. By investigating human CLU mRNAs we here unravel mechanisms leading to the synthesis of distinct CLU protein isoforms and analyze their subcellular localization and their impact on apoptosis and on NF-κB-activity. Quantitative PCR-analyses revealed the expression of four different stress-inducible CLU mRNA variants in non-cancer and cancer cell lines. In all cell lines variant 1 represents the most abundant mRNA, whereas all other variants collectively account for no more than 0.34% of total CLU mRNA, even under stressed conditions. Overexpression of CLU cDNAs combined with in vitro mutagenesis revealed distinct translational start sites including a so far uncharacterized non-canonical CUG start codon. We show that all exon 2-containing mRNAs encode sCLU and at least three non-glycosylated intracellular isoforms, CLU_1‑449, CLU_21‑449 and CLU_34‑449, which all reside in the cytosol of unstressed and stressed HEK‑293 cells. The latter is the only form expressed from an alternatively spliced mRNA variant lacking exon 2. Functional analysis revealed that none of these cytosolic CLU forms modulate caspase-mediated intrinsic apoptosis or significantly affects TNF-α-induced NF-κB-activity. Therefore our data challenge some of the current ideas regarding the physiological functions of CLU isoforms in pathologies.

Potential use of custirsen to treat prostate cancer

Over the last few years, five agents have demonstrated a survival benefit over a comparator treatment or placebo in the treatment of metastatic castration-resistant prostate cancer and have been approved by the US Food and Drug Administration: sipuleucel-T (a dendritic cell immunotherapy); cabazitaxel; abiraterone acetate and enzalutamide (both hormonal agents); and radium 223 (an alpha emitter). The development of these agents pivoted on whether patients had been treated with docetaxel, which remains the first-line chemotherapy of choice. To date, no combination of docetaxel and another active agent has demonstrated superiority to docetaxel alone despite numerous Phase III trials. Clusterin is a cytoprotective chaperone protein that is upregulated in response to various anticancer therapies. When overexpressed, clusterin interferes with apoptotic signaling, thereby promoting cell survival and conferring broad-spectrum resistance in cancer cell lines. Custirsen (OGX-011) is a second-generation 2'-methoxyethyl modified phosphorothioate antisense oligonucleotide that inhibits expression of clusterin. This review presents the preclinical and clinical data that provided the rationale for the combination of custirsen with chemotherapy in ongoing Phase III trials.

Reduction in serum clusterin is a potential therapeutic biomarker in patients with castration-resistant prostate cancer treated with custirsen

Elevated levels of clusterin (CLU), a stress-induced and secreted cytoprotective chaperone, are associated with advanced tumor stage, metastasis, treatment resistance, and adverse outcome in several cancers. Custirsen, a second-generation antisense oligonucleotide, inhibits CLU production in tumor cells and reduces serum CLU levels. A Phase 2 study evaluated custirsen in combination with second-line chemotherapy in men with metastatic castration-resistant prostate cancer (mCRPC) who had progressed while on or within 6 months of first-line docetaxel-based chemotherapy. Exploratory analyses evaluated serum CLU levels during custirsen treatment and correlative clinical effects on prostate-specific antigen (PSA) response, overall survival, and any relationship between serum CLU and PSA. Men with mCRPC were treated with mitoxantrone/prednisone/custirsen (MPC, n = 22) or docetaxel retreatment/prednisone/custirsen (DPC plus DPC-Assigned, n = 45) in an open-label, multicenter study. Subject-specific profiles of PSA and serum CLU levels during treatment were characterized using statistical modeling to compute subject-specific summary measures; these measures were analyzed for relationship to survival using proportional hazard regression. Estimated individual serum CLU response profiles were scored as below or at/above the median level for the population through 100 days postrandomization. Median survival was longer for subjects scoring below the median serum CLU level compared with subjects at/above the median level, respectively (MPC: 15.1 months vs. 6.2 months; DPC-Pooled: 17.0 months vs. 12.1 months). Lowered serum CLU levels during custirsen treatment when in combination with either chemotherapy regimen were predictive of longer survival in mCRPC. These results support further evaluation of serum CLU as a therapeutic biomarker.

Clusterin confers resistance to TNF-alpha-induced apoptosis in breast cancer cells through NF-kappaB activation and Bcl-2 overexpression

Secretory clusterin (sClu) is an anti-apoptotic protein that plays a role in protecting cells from Tumour-necrosis factor (TNF)-alpha-induced apoptosis. The aim of the present study was to investigate the molecular mechanisms underlying the effect of sClu on TNF-alpha-induced apoptosis in breast cancer cells. The wild-type p53 expressing MCF-7 cell line was engineered to overexpress sClu (MCF-7/sClu), whereas the MDA-MB-231 cell line with mutant p53 was transfected with a sClu silencing siRNA (MDA-MB-231/sClu siRNA). The effects of clusterin overexpression and downregulation on apoptosis and sensitivity to TNF-alpha were examined in vitro. Our results showed that TNF-alpha treatment increased Bcl-2 mRNA and protein levels in breast cancer cells, suggesting that Bcl-2 is directly regulated by nuclear factor-kappaB (NF-kappaB) in response to TNF-alpha. The induction of Bcl-2 was mediated by the p65 subunit of NF-kappaB. siRNA-mediated silencing of Bcl-2 led to a significant increase in TNF-alpha-induced apoptosis. Silencing of sClu in MDA-MB-231/sClu siRNA cells abrogated TNF-alpha-mediated NF-kappaB activation and Bcl-2 overexpression, and rendered the MDA-MB-231/sClu siRNA cells significantly more sensitive to TNF-alpha-mediated apoptosis than the parental cells. Furthermore, overexpression of sClu in MCF-7/sClu cells promoted TNF-alpha-mediated NF-kappaB activity and Bcl-2 overexpression, and rendered the MCF-7/Clu cells significantly more resistant to TNF-alpha-mediated apoptosis. Inhibition of NF-kappaB activity or p65 and Bcl-2 expression reversed these effects. The present results suggested that sClu confers breast cancer cells resistance to TNF-alpha-induced apoptosis through NF-kappaB activation and Bcl-2 overexpression.

Cotransin induces accumulation of a cytotoxic clusterin variant that cotranslationally rerouted to the cytosol

Although clusterin (CLU) was originally identified as a secreted glycoprotein that plays cytoprotective role, several intracellular CLU variants have been recently identified in the diverse pathological conditions. The mechanistic basis of these variants is now believed to be alternative splicing and retrotranslocation. Here, we uncovered, an unglycosylated and signal sequence-unprocessed, CLU variant in the cytosol. This variant proved to be a product that cotranslationally rerouted to the cytosol during translocation. Cytosolic CLU was prone to aggregation at peri-nuclear region of cells and induced cell death. Signal sequence is shown to be an important determinant for cytosolic CLU generation and aggregation. These results provide not only a new mechanistic insight into the cytosolic CLU generation but also an idea for therapeutic mislocalization of CLU as a strategy for cancer treatment.

Small interfering RNA targeted to secretory clusterin blocks tumor growth, motility, and invasion in breast cancer

Clusterin/apolipoprotein J (Clu) is a ubiquitously expressed secreted heterodimeric glycoprotein that is implicated in several physiological processes. It has been reported that the elevated level of secreted clusterin (sClu) protein is associated with poor survival in breast cancer patients and can induce metastasis in rodent models. In this study, we investigated the effects of sClu inhibition with small interfering RNAs (siRNAs) on cell motility, invasion, and growth in vitro and in vivo. MDA-MB-231 cells were transfected with pSuper-siRNA/sClu. Cell survival and proliferation were examined by 3-(4,5-dimethyl-thiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and clonogenic survival assay. The results showed that sClu silencing significantly inhibited the proliferation of MDA-MB-231 cells. The invasion and migration ability were also dramatically decreased, which was detected by matrigel assays. TUNEL staining and caspase-3 activity assay demonstrated that sClu silencing also could increase the apoptosis rate of cells, resulting in the inhibition of cell growth. We also determined the effects of sClu silencing on tumor growth and metastatic progression in an orthotopic breast cancer model. The results showed that orthotopic primary tumors derived from MDA-MB-231/pSuper sClu siRNA cells grew significantly slower than tumors derived from parental MDA-MB-231 or MDA-MB-231/pSuper scramble siRNA cells, and metastasize less to the lungs. These data suggest that secretory clusterin plays a significant role in tumor growth and metastatic progression. Knocking-down sClu gene expression may provide a valuable method for breast cancer therapy.

Antisense oligonucleotide against clusterin regulates human hepatocellular carcinoma invasion through transcriptional regulation of matrix metalloproteinase-2 and E-cadherin

Secreted clusterin (sCLU) has been shown to be overexpressed in metastatic hepatocellular carcinoma (HCC) tissue, and its overexpression in HCC cells increases cell migration and the formation of liver metastatic tumor nodules in vivo. In this study, we tested the hypothesis that sCLU plays a role in the invasiveness of human HCC and may be associated with its metastatic spread. HCCLM3, a human hepatocellular carcinoma cell line, was transiently transfected with an antisense oligonucleotide (ASO) against sCLU (OGX-011). HepG2 liver hepatocellular cells were transiently transfected with the pc.DNA3.1-sCLU plasmid to overexpress sCLU, and subsequently evaluated for effects on invasion and the expression of molecules involved in invasion. We observed that suppression of the sCLU gene significantly reduced the invasive capability of the highly invasive HCCLM3 cells, and vice versa in the low invasive HepG2 cell line. The results revealed that knockdown of sCLU by OGX-011 resulted in a significant increase in the expression of E-cadherin and a decrease in matrix metalloproteinase-2 (MMP-2) gene transcription. Overexpression of sCLU by transfection with pc.DNA3.1-sCLU significantly decreased the expression of E-cadherin and increased MMP-2 gene transcription. These data were further verified by reverse transcription-PCR and Western blot analysis. A significant reduction in MMP-2 expression and an increase in E-cadherin expression in sCLU-knockdown HCCLM3 cells were observed, as well as a significant increase in MMP-2 expression and a decrease in E-cadherin expression in HepG2 cells overexpressing sCLU. These data indicate a role for sCLU in augmenting MMP-2 transcription and decreasing E-cadherin expression. Our data show the involvement of sCLU in human HCC invasion, and demonstrate that silencing sCLU gene expression inhibits the invasion of human HCC cells by inhibiting MMP-2 expression and promoting E-cadherin expression. Thus, OGX-011 could be an effective therapeutic agent for HCC.

mda-7/IL-24 differentially regulates soluble and nuclear clusterin in prostate cancer

Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24), a unique member of the IL-10 gene family, displays a broad range of antitumor properties including cancer-specific induction of apoptosis, inhibition of tumor angiogenesis, and modulation of anti-tumor immune responses. Here, we identify clusterin (CLU) as a MDA-7/IL-24 interacting protein in DU-145 cells and investigate the role of MDA-7/IL-24 in regulating CLU expression and mediating the antitumor properties of mda-7/IL-24 in prostate cancer. Ad.mda-7 decreased expression of soluble CLU (sCLU) and increased expression of nuclear CLU (nCLU). In the initial phase of Ad.mda-7 infection sCLU expression increased and CLU interacted with MDA-7/IL-24 producing a cytoprotective effect. Infection of stable clones of DU-145 prostate cancer cells expressing sCLU with Ad.mda-7 resulted in generation of nCLU that correlated with decreased cell viability and increased apoptosis. In the presence of mda-7/IL-24, sCLU-DU-145 cells displayed G(2)/M phase arrest followed by apoptosis. Similarly, Ad.mda-7 infection decreased cell migration by altering cytoskeleton in sCLU-DU-145 cells. Ad.mda-7-treated sCLU-DU-145 cells displayed a significant reduction in tumor growth in mouse xenograft models and reduced angiogenesis when compared to the vector control group. Tumor tissue lysates demonstrated enhanced nCLU generated from sCLU with increased apoptosis in the presence of MDA-7/IL-24. Our findings reveal novel aspects relative to the role of sCLU/nCLU in regulating the anticancer properties of MDA-7/IL-24 that may be exploited for developing enhanced therapies for prostate cancer.

Secreted CLU is associated with the initiation of triple-negative breast cancer

Triple-negative breast cancer, which is negative for the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2, represents about 15-26% of all breast cancer cases. However, because of its genotype, a triple-negative disease accounts for a remarkable metastasis and mortality. Moreover, no targeted treatment is available because the molecular mechanism of triple-negative breast cancer initiation is still unclear. Secreted clusterin (sCLU) is associated with the refractory to anti-estrogen in breast cancer cells. We investigated the sCLU expression in 384 human breast cancer cases, including 61 triple-negative cases, as well as the relationship between sCLU and clinical pathological characteristics. Triple-negative patients (75.4%) were positive for sCLU based on immunohistochemical analysis, and sCLU expression in this subtype was proven related to a larger tumor size, an axillary node status, and a higher clinical stage. Furthermore, we used a spontaneous breast cancer mouse strain with a triple-negative genotype to detect the sCLU dynamic expression in breast cancer oncogenesis using western blot and real-time polymerase chain reaction. The sCLU mRNA and protein expression in the tumor and hyperplastic epithelium were upregulated and reached a peak compared with those of a normal mammary gland. These results suggest that sCLU is involved in the initiation of triple-negative breast cancer, which is beneficial for the clinical trial design of an anti-CLU treatment for triple-negative breast cancer.

Effects of female sex hormones on clusterin expression and paclitaxel resistance in endometrial cancer cell lines

OBJECTIVE

We have analyzed the association between clusterin expression in endometrial cancer cells and their resistance to paclitaxel. We also analyzed whether the effects of female sex hormones on clusterin expression by these cell lines affect their resistance to paclitaxel.

METHODS

The expression of estrogen receptors α and β, progesterone receptors AB and B, and clusterin mRNA and protein was assayed in the ECC-1 and KLE endometrial cancer cell lines by RT-PCR and Western blotting, respectively. The IC(50) of paclitaxel was measured in each cell line by XTT assay. Using clusterin siRNA, we analyzed the association between clusterin expression and paclitaxel IC(50) in each cell line. We also examined the effects of hormone treatment on cellular resistance to paclitaxel.

RESULTS

Paclitaxel IC(50) was significantly higher in KLE cells, which expressed higher levels of clusterin, than in ECC-1 cells, which expressed lower levels of clusterin. Conversely, incubation with clusterin siRNA significantly decreased the viability of KLE cells (P<0.001), but did not alter the viability of ECC-1 cells. Incubation with estrogen tended to increase the level of clusterin expression in these endometrial cancer cell lines, although the level of clusterin expression did not correlate with that of estrogen receptors. Incubation with progesterone did not alter the levels of expression of clusterin and clusterin receptor. Incubation with estrogen and paclitaxel significantly increased the viability of ECC-1 (P<0.001) but not KLE cells.

CONCLUSION

Estrogen increases the paclitaxel resistance of endometrial cancer cell lines, by increasing clusterin expression.

Randomized phase II trial of Custirsen (OGX-011) in combination with docetaxel or mitoxantrone as second-line therapy in patients with metastatic castrate-resistant prostate cancer progressing after first-line docetaxel: CUOG trial P-06c

PURPOSE

Clusterin (CLU) is an antiapoptotic, stress-induced protein conferring treatment resistance when overexpressed. This study tested custirsen, a CLU inhibitor, in patients with metastatic castration-resistant prostate cancer (mCRPC) progressing during or within 6 months of initial docetaxel therapy.

PATIENTS AND METHODS

Men were randomized to receive either docetaxel + prednisone + custirsen (DPC) or mitoxantrone + prednisone + custirsen (MPC).

RESULTS

Forty-two patients received study treatment. Toxicity was similar in both arms. Twenty patients treated with DPC received a median of 8 cycles; overall survival (OS) was 15.8 months. Median time to pain progression (TTPP) was 10.0 months; 10 of 13 (77%) evaluable patients had pain responses. Three of 13 (23%) evaluable patients had objective partial responses. Prostate-specific antigen (PSA) declines of 90% or more, 50% or more, and 30% or more occurred in 4 (20%), 8 (40%), and 11 (55%) patients, respectively. Twenty-two patients treated with MPC received a median of 6 cycles; OS was 11.5 months. The median TTPP was 5.2 months; 6 of 13 (46%) evaluable patients had pain responses. No objective responses were observed. PSA declines of 50% or more and 30% or more occurred in 6 (27%) and 7 (32%) patients, respectively. Low serum CLU levels during treatment showed superior survival for patients based on modeling with proportional hazard regression with a time-dependent covariate and different landmarks.

CONCLUSIONS

Custirsen plus either docetaxel or mitoxantrone was feasible in patients with progressive mCRPC following first-line docetaxel therapy. Pain relief was higher than expected, with interesting correlations between serum CLU and survival. A phase III trial evaluating the pain palliation benefit of custirsen with taxane therapy is ongoing.

Clusterin confers gemcitabine resistance in pancreatic cancer

Objective

To measure clusterin expression in pancreatic cancer tissues and cell lines and to evaluate whether clusterin confers resistance to gmcitabine in pancreatic cancer cells.

Methods

Immunohistochemistry for clusterin was performed on 50 primary pancreatic cancer tissues and 25 matched backgrounds, and clusterin expression in 5 pancreatic cancer cell lines was quantified by Western blot and PT-PCR. The correlation between clusterin expression level and gmcitabine IC50 in pancreatic cancer cell lines was evaluated. The effect of an antisense oligonucleotide (ASO) against clusterin(OGX-011) on gmcitabine resistance was evaluated by MTT assays. Xenograft model was used to demonstrate tumor growth.

Results

Pancreatic cancer tissues expressed significantly higher levels of clusterin than did normal pancreatic tissues (P < 0.01). Clusterin expression levels were correlated with gmcitabine resistance in pancreatic cancer cell lines, and OGX-011 significantly decreased BxPc-3 cells resistance to gmcitabine (P < 0.01). In vivo systemic administration of AS clusterin and gmcitabine significantly decreased the s.c. BxPC-3 tumor volume compared with mismatch control ODN plus gmcitabine.

Conclusion

Our finding that clusterin expression was significantly higher in pancreatic cancer than in normal pancreatic tissues suggests that clusterin may confer gmcitabine resistance in pancreatic cancer cells.

ATM-dependent IGF-1 induction regulates secretory clusterin expression after DNA damage and in genetic instability

Secretory clusterin (sCLU) is a stress-induced, pro-survival glycoprotein elevated in early-stage cancers, in particular in APC/Min-defective colon cancers. sCLU is upregulated after exposure to various cytotoxic agents, including ionizing radiation (IR), leading to a survival advantage. We found that stimulation of insulin-like growth factor-1 (IGF-1) and IGF-1R protein kinase signaling was required for sCLU induction after IR exposure. Here, we show that activation of Ataxia telangiectasia-mutated kinase (ATM) by endogenous or exogenous forms of DNA damage was required to relieve basal repression of IGF-1 transcription by the p53/NF-YA complex, leading to sCLU expression. Although p53 levels were stabilized and elevated after DNA damage, dissociation of NF-YA, and thereby p53, from the IGF-1 promoter resulted in IGF-1 induction, indicating that NF-YA was rate limiting. Cells with elevated endogenous DNA damage (deficient in H2AX, MDC1, NBS1, mTR or hMLH1) or cells exposed to DNA-damaging agents had elevated IGF-1 expression, resulting in activation of IGF-1R signaling and sCLU induction. In contrast, ATM-deficient cells were unable to induce sCLU after DNA damage. Our results integrate DNA damage resulting from genetic instability, IR, or chemotherapeutic agents, to ATM activation and abrogation of p53/NF-YA-mediated IGF-1 transcriptional repression, that induces IGF-1-sCLU expression. Elucidation of this pathway should uncover new mechanisms for cancer progression and reveal new targets for drug development to overcome resistance to therapy.

Clusterin immunoexpression and its clinical significance in patients with non-small cell lung cancer

Clusterin is an enigmatic glycoprotein with a nearly ubiquitous tissue distribution. It plays important roles in various pathophysiological processes, including tissue remodeling, reproduction, lipid transport, complement regulation, and apoptosis. Clusterin appears to have two main isoforms that result from alternative splicing. The secreted and nuclear forms of clusterin have been reported to play different roles in human malignancies. The purpose of this study was to examine clusterin immunoexpression and its clinical significance in a group of Chinese patients with non-small cell lung cancer (NSCLC). Tissue samples from the primary tumors of 121 patients with completely resected NSCLC were obtained. Clusterin protein expression was evaluated by immunohistochemical staining with an antibody against all clusterin isoforms. Staining patterns were observed and graded based on intensity and density and were correlated with clinical and pathological data. Both cytoplasmic and nuclear clusterin immunostaining patterns were observed. Clusterin staining was observed only in the cytoplasm in 70 patients (57.9%), only in the nucleus in 27 patients (22.3%), and in both the cytoplasm and nucleus in 16 patients (13.2%). A significant association was observed between positive cytoplasmic clusterin expression and histologic type as indicated by adenocarcinomas that were more likely to have clusterin staining only in the cytoplasm. Clusterin immunostaining was neither associated with recurrence-free survival (RFS) nor overall survival of patients by univariate or multivariate analysis. For patients undergoing chemotherapy, those with only cytoplasmic clusterin staining had worse survival than other patients. In conclusion, both cytoplasmic and nuclear immunostaining patterns of clusterin were detected in the tumors of patients with NSCLC. Adenocarcinomas were more likely to have only cytoplasmic staining. The immunoexpression of clusterin was not associated with prognosis, and cytoplasm-only immunostaining of clusterin was inversely correlated with chemosensitivity in this group of patients.

Induction of clusterin by AKT--role in cytoprotection against docetaxel in prostate tumor cells

Clusterin (CLU), in its cytoplasmic form, is abundant in many advanced cancers and has been established to be cytoprotective against chemotherapeutic agents including docetaxel. However, little is known of the mechanism of its induction. Here, we provide evidence that AKT plays a critical role in upregulating cytoplasmic/secretory sCLU, which is responsible for docetaxel resistance. Western blot analysis indicated that docetaxel-resistant sublines derived from DU145 and PC3 prostate tumor cell lines displayed a markedly increased phospho-AKT level closely accompanied by heightened sCLU expression when compared with parental cells. To examine if AKT has a role in sCLU expression, AKT blockade was done by treatment with a specific inhibitor, API-2, or dominant-negative AKT transduction before analysis of sCLU gene expression. Loss of AKT function resulted in loss of sCLU and was accompanied by chemosensitization to docetaxel and increased cell death via a caspase-3-dependent pathway. To confirm that AKT affected resistance to docetaxel through sCLU and not through other mediators, tumor cells were first transfected with full-length CLU for overexpression and then treated with the AKT inhibitor API-2. We found that once sCLU was overexpressed, API-2 could not chemosensitize the tumor cells to docetaxel. Thus, the chemoresistance to docetaxel is mediated by sCLU and it can be induced by AKT. Lastly, AKT was found to mediate sCLU induction via signal transducer and activator of transcription 1 activation, which we have earlier shown to drive sCLU gene expression. These results identify a previously unrecognized pathway linking AKT to cytoprotection by sCLU in tumor cells.

Clusterin facilitates COMMD1 and I-kappaB degradation to enhance NF-kappaB activity in prostate cancer cells

Secretory clusterin (sCLU) is a stress-activated, cytoprotective chaperone that confers broad-spectrum cancer treatment resistance, and its targeted inhibitor (OGX-011) is currently in phase II trials for prostate, lung, and breast cancer. However, the molecular mechanisms by which sCLU inhibits treatment-induced apoptosis in prostate cancer remain incompletely defined. We report that sCLU increases NF-kappaB nuclear translocation and transcriptional activity by serving as a ubiquitin-binding protein that enhances COMMD1 and I-kappaB proteasomal degradation by interacting with members of the SCF-betaTrCP E3 ligase family. Knockdown of sCLU in prostate cancer cells stabilizes COMMD1 and I-kappaB, thereby sequestrating NF-kappaB in the cytoplasm and decreasing NF-kappaB transcriptional activity. Comparative microarray profiling of sCLU-overexpressing and sCLU-knockdown prostate cancer cells confirmed that the expression of many NF-kappaB-regulated genes positively correlates with sCLU levels. We propose that elevated levels of sCLU promote prostate cancer cell survival by facilitating degradation of COMMD1 and I-kappaB, thereby activating the canonical NF-kappaB pathway.

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.

Clusterin as a predictor for chemoradiotherapy sensitivity and patient survival in esophageal squamous cell carcinoma

Clusterin (CLU) is frequently overexpressed and correlates closely with chemotherapy and radiotherapy resistance and poor prognosis in many human cancers. However, the significance of CLU expression in chemoradiotherapy (CRT) sensitivity and its effect on the prognosis of esophageal squamous cell carcinoma (ESCC) are still unknown. In the present study, we used the methods of immunohistochemistry and terminal deoxyuridine triphosphate nick-end labeling assay to examine the expression status of CLU and apoptotic index in 110 pretreated biopsy specimens of ESCC patients treated with definitive CRT. High expression of CLU was observed in 42.7% of epithelium and 50.0% of stroma in ESCC. A significant association of high CLU stromal expression with large tumor size (P = 0.012) and locoregional progression (P = 0.001) was observed, and high epithelial expression of CLU showed a significant correlation with the lack of complete response (P = 0.028) and low apoptotic index (P = 0.001). Univariate analysis revealed that high CLU stromal expression was associated with poor locoregional progression-free survival, distant progression-free survival, and overall survival. Furthermore, ESCC patients with high CLU expression in both epithelium and stroma have the shortest survival time among the subgroups of different CLU expression status. In multivariate analysis, CLU stromal expression was evaluated as an independent prognostic factor for locoregional progression-free survival, distant progression-free survival, and overall survival. These findings suggest an important role for CLU, especially in stroma, in ESCC progression, and that high CLU epithelial expression might be a promising predictor of ESCC resistance to CRT.

Transcriptome profiling of a TGF-beta-induced epithelial-to-mesenchymal transition reveals extracellular clusterin as a target for therapeutic antibodies

Transforming growth factor (TGF)-beta plays a dual role in tumorigenesis, switching from acting as a growth inhibitory tumor suppressor early in the process, to a tumor promoter in late-stage disease. Since TGF-beta's prometastatic role may be linked to its ability to induce tumor cell epithelial-to-mesenchymal transition (EMT), we explored TGF-beta's EMT-promoting pathways by analysing the transcriptome changes occurring in BRI-JM01 mammary tumor epithelial cells undergoing a TGF-beta-induced EMT. We found the clusterin gene to be the most highly upregulated throughout most of the TGF-beta time course, and showed that this results in an increase of the secreted form of clusterin. By monitoring several hallmark features of EMT, we demonstrated that antibodies targeting secreted clusterin inhibit the TGF-beta-induced EMT of BRI-JM01 cells, as well as the invasive phenotype of several other breast and prostate tumor cell lines (4T1, NMuMG, MDA-MB231LM2 and PC3), without affecting the proliferation of these cells. These results indicate that secreted clusterin is a functionally important EMT mediator that lies downstream within TGF-beta's EMT-promoting transcriptional cascade, but not within its growth-inhibitory pathways. To further investigate the role played by secreted clusterin in tumor metastasis, we assessed the effect of several anti-clusterin monoclonal antibodies in vivo using a 4T1 syngeneic mouse breast cancer model and found that these antibodies significantly reduce lung metastasis. Taken together, our results reveal a role for secreted clusterin as an important extracellular promoter of EMT, and suggest that antibodies targeting clusterin may inhibit tumor metastasis without reducing the beneficial growth inhibitory effects of TGF-beta.

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.