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

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.

Clusterin and Its Isoforms in Oral Squamous Cell Carcinoma and Their Potential as Biomarkers: A Comprehensive Review

Oral squamous cell carcinoma (OSCC) is a prevalent type of head and neck cancer, ranked as the sixth most common cancer worldwide, accounting for approximately 300,000 new cases and 145,000 deaths annually. Early detection using biomarkers significantly increases the 5-year survival rate of OSCC by up to 80-90%. Clusterin (CLU), also known as apolipoprotein J, is a sulfated chaperonic glycoprotein expressed in all tissues and human fluids and has been reported to be a potential biomarker of OSCC. CLU has been implicated as playing a vital role in many biological processes such as apoptosis, cell cycle, etc. Abnormal CLU expression has been linked with the development and progression of cancers. Despite the fact that there are many studies that have reported the involvement of CLU and its isoforms in OSCC, the exact roles of CLU and its isoforms in OSCC carcinogenesis have not been fully explored. This article aims to provide a comprehensive review of the current understanding of CLU structure and genetics and its correlation with OSCC tumorigenesis to better understand potential diagnostic and prognostic biomarker development. The relationship between CLU and chemotherapy resistance in cancer will also be discussed to explore the therapeutic application of CLU and its isoforms in OSCC.

Dysregulation of HNF1B/Clusterin axis enhances disease progression in a highly aggressive subset of pancreatic cancer patients

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy and is largely refractory to available treatments. Identifying key pathways associated with disease aggressiveness and therapeutic resistance may characterize candidate targets to improve patient outcomes. We used a strategy of examining the tumors from a subset of PDAC patient cohorts with the worst survival to understand the underlying mechanisms of aggressive disease progression and to identify candidate molecular targets with potential therapeutic significance. Non-negative matrix factorization (NMF) clustering, using gene expression profile, revealed three patient subsets. A 142-gene signature specific to the subset with the worst patient survival, predicted prognosis and stratified patients with significantly different survival in the test and validation cohorts. Gene-network and pathway analysis of the 142-gene signature revealed dysregulation of Clusterin (CLU) in the most aggressive patient subset in our patient cohort. Hepatocyte nuclear factor 1 b (HNF1B) positively regulated CLU, and a lower expression of HNF1B and CLU was associated with poor patient survival. Mechanistic and functional analyses revealed that CLU inhibits proliferation, 3D spheroid growth, invasiveness and epithelial-to-mesenchymal transition (EMT) in pancreatic cancer cell lines. Mechanistically, CLU enhanced proteasomal degradation of EMT-regulator, ZEB1. In addition, orthotopic transplant of CLU-expressing pancreatic cancer cells reduced tumor growth in mice. Furthermore, CLU enhanced sensitivity of pancreatic cancer cells representing aggressive patient subset, to the chemotherapeutic drug gemcitabine. Taken together, HNF1B/CLU axis negatively regulates pancreatic cancer progression and may potentially be useful in designing novel strategies to attenuate disease progression in PDAC patients.

Clusterin and Related Scoring Index as Potential Early Predictors of Response to Sorafenib in Hepatocellular Carcinoma

Advanced hepatocellular carcinoma (HCC) remains a highly lethal malignancy, although several systemic therapeutic options are available, including sorafenib (SFN), which has been one of the standard treatment agents for almost a decade. As early prediction of response to SFN remains challenging, biomarkers that enable early prediction using a clinically feasible method are needed. Here, we report that the serum secretory form of clusterin (sCLU) protein and its related predictive index are potential beneficial biomarkers for early prediction of SFN response. Using high-throughput screening and subsequent multivariate analysis in the derivation cohort, we found that changes in the concentrations of CLU, vascular cell adhesion molecule-1 (VCAM1), and α-fetoprotein were significantly associated with response to SFN. Furthermore, we confirmed that an increase in CLU serum level 1 month after treatment initiation was significantly associated with shorter progression-free survival. In addition, "NR-index," which comprises these proteins, was evaluated as a tool for accurately predicting the efficacy of SFN and confirmed in the validation cohort. We also established SFN-resistant HepG2 cells (HepG2-SR) and found that sCLU significantly increased in HepG2-SR cells compared with normal HepG2 cells, and confirmed that HepG2-SR cells treated with SFN were resistant to apoptosis. The mechanism underlying activation of sCLU expression in acquired SFN resistance involves aberrant signaling and expression of Akt, mammalian target of rapamycin (mTOR), and a nutrient-related transcription factor, sterol regulatory element binding protein 1c (SREBP-1c). Furthermore, the PI3K and mTOR inhibitor BEZ235 markedly decreased sCLU expression in HepG2-SR cells. Conclusion: These results suggest that measurement of sCLU serum levels and the sCLU-related NR-index are promising clinical tools for the early prediction of SFN response in HCC. Additionally, sCLU-overexpressing HCC might be susceptible to mTOR inhibition.

Impact of STAT Proteins in Tumor Progress and Therapy Resistance in Advanced and Metastasized Prostate Cancer

Signal transducers and activators of transcription (STATs) are a family of transcription factors involved in several biological processes such as immune response, cell survival, and cell growth. However, they have also been implicated in the development and progression of several cancers, including prostate cancer (PCa). Although the members of the STAT protein family are structurally similar, they convey different functions in PCa. STAT1, STAT3, and STAT5 are associated with therapy resistance. STAT1 and STAT3 are involved in docetaxel resistance, while STAT3 and STAT5 are involved in antiandrogen resistance. Expression of STAT3 and STAT5 is increased in PCa metastases, and together with STAT6, they play a crucial role in PCa metastasis. Further, expression of STAT3, STAT5, and STAT6 was elevated in advanced and high-grade PCa. STAT2 and STAT4 are currently less researched in PCa. Since STATs are widely involved in PCa, they serve as potential therapeutic targets. Several inhibitors interfering with STATs signaling have been tested unsuccessfully in PCa clinical trials. This review focuses on the respective roles of the STAT family members in PCa, especially in metastatic disease and provides an overview of STAT-inhibitors evaluated in clinical trials.

Taxane resistance in prostate cancer is mediated by decreased drug-target engagement

Despite widespread use of taxanes, mechanisms of action and resistance in vivo remain to be established, and there is no way of predicting who will respond to therapy. This study examined prostate cancer (PCa) xenografts and patient samples to identify in vivo mechanisms of taxane action and resistance. Docetaxel drug-target engagement was assessed by confocal anti-tubulin immunofluorescence to quantify microtubule bundling in interphase cells and aberrant mitoses. Tumor biopsies from metastatic PCa patients obtained 2 to 5 days after their first dose of docetaxel or cabazitaxel were processed to assess microtubule bundling, which correlated with clinical response. Microtubule bundling was evident in PCa xenografts 2 to 3 days after docetaxel treatment but was decreased or lost with acquired resistance. Biopsies after treatment with leuprolide plus docetaxel showed extensive microtubule bundling as did biopsies obtained 2 to 3 days after initiation of docetaxel or cabazitaxel in 2 patients with castration-resistant PCa with clinical responses. In contrast, microtubule bundling in biopsies 2 to 3 days after the first dose of docetaxel was markedly lower in 4 nonresponding patients. These findings indicate that taxanes target both mitotic and interphase cells in vivo and that resistance is through mechanisms that impair drug-target engagement. Moreover, the findings suggest that microtubule bundling after initial taxane treatment may be a predictive biomarker for clinical response.

Apolipoprotein J in Alzheimer's Disease: Shedding Light on Its Role with Cell Signaling Pathway Perspective and Possible Therapeutic Approaches

Apolipoprotein J (ApoJ), or clusterin, is one of the main apolipoproteins in the brain. It is synthesized and released from astrocytes in a healthy brain, and its expression increases in neurodegenerative disorders. Genetic evidence has suggested an association between ApoJ polymorphism and the risk of Alzheimer's disease (AD)-it is now considered the third main genetic risk factor for late-onset AD. However, the role of ApoJ overexpression in the state of disorder, toxicity, or protection is not yet clear. Since ApoJ plays different roles in AD, we review the function of ApoJ using different cell signaling pathways in AD and outline its paradoxical roles in AD. ApoJ helps in amyloid-beta (Aβ) clearance. Vice versa, ApoJ gene knock-out causes fibrillary Aβ reduction and prevents Aβ-induced neuron cell death. Understanding ApoJ, through various cellular signaling pathways, creates a new perspective on AD's cellular principles. The overall message is that ApoJ can be a valuable tool in controlling AD.

Mechanisms of docetaxel resistance in prostate cancer: The key role played by miRNAs

One of the main problems with the treatment of metastatic prostate cancer is that, despite an initial positive response, the majority of patients develop resistance and progress. In particular, the resistance to docetaxel, the gold standard therapy for metastatic prostate cancer since 2010, represents one of the main factors responsible for the failure of prostate cancer therapy. According to the present knowledge, different processes contribute to the appearance of docetaxel resistance and non-coding RNA seems to play a relevant role in them. In this review, a comprehensive overview of the miRNA network involved in docetaxel resistance is described, highlighting the pathway/s affected by their activity.

What sustains the multidrug resistance phenotype beyond ABC efflux transporters? Looking beyond the tip of the iceberg

Identification of multidrug (MDR) efflux transporters that belong to the ATP-Binding Cassette (ABC) superfamily, represented an important breakthrough for understanding cancer multidrug resistance (MDR) and its possible overcoming. However, recent data indicate that drug resistant cells have a complex intracellular physiology that involves constant changes in energetic and oxidative-reductive metabolic pathways, as well as in the molecular circuitries connecting mitochondria, endoplasmic reticulum (ER) and lysosomes. The aim of this review is to discuss the key molecular mechanisms of cellular reprogramming that induce and maintain MDR, beyond the presence of MDR efflux transporters. We specifically highlight how cancer cells characterized by high metabolic plasticity - i.e. cells able to shift the energy metabolism between glycolysis and oxidative phosphorylation, to survive both the normoxic and hypoxic conditions, to modify the cytosolic and mitochondrial oxidative-reductive metabolism, are more prone to adapt to exogenous stressors such as anti-cancer drugs and acquire a MDR phenotype. Similarly, we discuss how changes in mitochondria dynamics and mitophagy rates, changes in proteome stability ensuring non-oncogenic proteostatic mechanisms, changes in ubiquitin/proteasome- and autophagy/lysosome-related pathways, promote the cellular survival under stress conditions, along with the acquisition or maintenance of MDR. After dissecting the complex intracellular crosstalk that takes place during the development of MDR, we suggest that mapping the specific adaptation pathways underlying cell survival in response to stress and targeting these pathways with potent pharmacologic agents may be a new approach to enhance therapeutic efficacy against MDR tumors.

The Multiple Roles and Therapeutic Potential of Molecular Chaperones in Prostate Cancer

Prostate cancer (PCa) is one of the most common cancer types in men worldwide. Heat shock proteins (HSPs) are molecular chaperones that are widely implicated in the pathogenesis, diagnosis, prognosis, and treatment of many cancers. The role of HSPs in PCa is complex and their expression has been linked to the progression and aggressiveness of the tumor. Prominent chaperones, including HSP90 and HSP70, are involved in the folding and trafficking of critical cancer-related proteins. Other members of HSPs, including HSP27 and HSP60, have been considered as promising biomarkers, similar to prostate-specific membrane antigen (PSMA), for PCa screening in order to evaluate and monitor the progression or recurrence of the disease. Moreover, expression level of chaperones like clusterin has been shown to correlate directly with the prostate tumor grade. Hence, targeting HSPs in PCa has been suggested as a promising strategy for cancer therapy. In the current review, we discuss the functions as well as the role of HSPs in PCa progression and further evaluate the approach of inhibiting HSPs as a cancer treatment strategy.

Clusterin enhances AKT2-mediated motility of normal and cancer prostate cells through a PTEN and PHLPP1 circuit

Clusterin (CLU) is a chaperone-like protein with multiple functions. sCLU is frequently upregulated in prostate tumor cells after chemo- or radiotherapy and after surgical or pharmacological castration. Moreover, CLU has been documented to modulate the cellular homolog of murine thymoma virus akt8 oncogene (AKT) activity. Here, we investigated how CLU overexpression influences phosphatidylinositol 3'-kinase (PI3K)/AKT signaling in human normal and cancer epithelial prostate cells. Human prostate cells stably transfected with CLU were broadly profiled by reverse phase protein array (RPPA), with particular emphasis on the PI3K/AKT pathway. The effect of CLU overexpression on normal and cancer cell motility was also tested. Our results clearly indicate that CLU overexpression enhances phosphorylation of AKT restricted to isoform 2. Mechanistically, this can be explained by the finding that the phosphatase PH domain leucine-rich repeat-containing protein phosphatase 1 (PHLPP1), known to dephosphorylate AKT2 at S474, is markedly downregulated by CLU, whereas miR-190, a negative regulator of PHLPP1, is upregulated. Moreover, we found that phosphatase and tensin homolog (PTEN) was heavily phosphorylated at the inhibitory site S380, contributing to the hyperactivation of AKT signaling. By keeping AKT2 phosphorylation high, CLU dramatically enhances the migratory behavior of prostate epithelial cell lines with different migratory and invasive phenotypes, namely prostate normal epithelial 1A (PNT1A) and prostatic carcinoma 3 (PC3) cells. Altogether, our results unravel for the first time a circuit by which CLU can switch a low migration phenotype toward a high migration phenotype, through miR-190-dependent downmodulation of PHLPP1 expression and, in turn, stabilization of AKT2 phosphorylation.

Glyceryl trinitrate‑induced cytotoxicity of docetaxel‑resistant prostatic cancer cells is associated with differential regulation of clusterin

Metastatic castration resistant prostate cancer (mCRPC) relapse due to acquired resistance to chemotherapy, such as docetaxel, remains a major threat to patient survival. Resistance of mCRPC to docetaxel can be associated with elevated levels of soluble clusterin (sCLU) and growth differentiation factor‑15 (GDF‑15). Any strategies aiming to modulate sCLU and/or GDF‑15 in docetaxel‑resistant prostate cancer cells present a therapeutic interest. The present study reports the cytotoxic effect of a nitric oxide donor, glyceryl trinitrate (GTN), on docetaxel‑resistant mCRPC human cell lines and demonstrates that GTN displays greater inhibition of cell viability toward docetaxel‑resistant mCRPC cells than on mCRPC cells. It is also demonstrated that GTN modulates the level of expression of clusterin (CLU) which is dependent of GDF‑15, two markers associated with docetaxel resistance in prostate cancer. The results indicate that GTN represses the level of expression of the cytoprotective isoform of CLU (sCLU) and can increase the level of expression of the cytotoxic isoform (nuclear CLU) in docetaxel resistant cells. Furthermore, it was observed that GTN differentially regulates the level of the precursor form of GDF‑15 between resistant and parental cells, and that recombinant GDF‑15 can modulate the expression of CLU isoforms and counteract GTN‑induced cytotoxicity in resistant cells. A link was established between GDF‑15 and the expression of CLU isoforms. The present study thus revealed GTN as a potential therapeutic strategy to overcome docetaxel‑resistant mCRPC.

Comparison of several commonly used detection indicators of cell senescence

Cell senescence is the state of irreversible growth arrest that can be triggered by a variety of different cellular stresses. Currently, the commonly used detection indicators involved in the study of cell senescence include senescence-associated β-galactosidase, Clusterin, Telomeres/Telomerase, senescence-associated heterochromatin foci, senescence-associated secretory phenotype, senescence marker protein-30, tumor suppressor genes p53 and p16, and other indicators such as Ki67 and decoy receptor 2. These indicators are widely used in the study of cell senescence, each with its own characteristics, advantages, and disadvantages. This review summarizes several commonly used cell senescence indicators and compares their accuracy, credibility, specificity, and the scope of their potential application.

Glucocorticoids Induce Stress Oncoproteins Associated with Therapy-Resistance in African American and European American Prostate Cancer Cells

Glucocorticoid receptor (GR) is emerging as a key driver of prostate cancer (PCa) progression and therapy resistance in the absence of androgen receptor (AR) signaling. Acting as a bypass mechanism, GR activates AR-regulated genes, although GR-target genes contributing to PCa therapy resistance remain to be identified. Emerging evidence also shows that African American (AA) men, who disproportionately develop aggressive PCa, have hypersensitive GR signaling linked to cumulative stressful life events. Using racially diverse PCa cell lines (MDA-PCa-2b, 22Rv1, PC3, and DU145) we examined the effects of glucocorticoids on the expression of two stress oncoproteins associated with PCa therapy resistance, Clusterin (CLU) and Lens Epithelium-Derived Growth Factor p75 (LEDGF/p75). We observed that glucocorticoids upregulated LEDGF/p75 and CLU in PCa cells. Blockade of GR activation abolished this upregulation. We also detected increased GR transcript expression in AA PCa tissues, compared to European American (EA) tissues, using Oncomine microarray datasets. These results demonstrate that glucocorticoids upregulate the therapy resistance-associated oncoproteins LEDGF/p75 and CLU, and suggest that this effect may be enhanced in AA PCa. This study provides an initial framework for understanding the contribution of glucocorticoid signaling to PCa health disparities.

RNA sequencing reveals upregulation of a transcriptomic program associated with stemness in metastatic prostate cancer cells selected for taxane resistance

Patients with metastatic castration-resistant prostate cancer (mCRPC) develop resistance to conventional therapies including docetaxel (DTX). Identifying molecular pathways underlying DTX resistance is critical for developing novel combinatorial therapies to prevent or reverse this resistance. To identify transcriptomic signatures associated with acquisition of chemoresistance we profiled gene expression in DTX-sensitive and -resistant mCRPC cells using RNA sequencing (RNA-seq). PC3 and DU145 cells were selected for DTX resistance and this phenotype was validated by immunoblotting using DTX resistance markers (e.g. clusterin, ABCB1/P-gp, and LEDGF/p75). Overlapping genes differentially regulated in the DTX-sensitive and -resistant cells were ranked by Gene Set Enrichment Analysis (GSEA) and validated to correlate transcript with protein expression. GSEA revealed that genes associated with cancer stem cells (CSC) (e.g., NES, TSPAN8, DPPP, DNAJC12, and MYC) were highly ranked and comprised 70% of the top 25 genes differentially upregulated in the DTX-resistant cells. Established markers of epithelial-to-mesenchymal transition (EMT) and CSCs were used to evaluate the stemness of adherent DTX-resistant cells (2D cultures) and tumorspheres (3D cultures). Increased formation and frequency of cells expressing CSC markers were detected in DTX-resistant cells. DU145-DR cells showed a 2-fold increase in tumorsphere formation and increased DTX resistance compared to DU145-DR 2D cultures. These results demonstrate the induction of a transcriptomic program associated with stemness in mCRPC cells selected for DTX resistance, and strengthen the emerging body of evidence implicating CSCs in this process. In addition, they provide additional candidate genes and molecular pathways for potential therapeutic targeting to overcome DTX resistance.

Oral administration of withaferin A inhibits carcinogenesis of prostate in TRAMP model

We previously reported that withaferin A (WA), a natural compound, deters prostate cancer by inhibiting AKT while inducing apoptosis. In the current study, we examined its chemopreventive efficacy against carcinogenesis in the prostate using the transgenic adenocarcinoma of mouse prostate (TRAMP) model. Two distinct sets of experiments were conducted. To determine whether WA delays tumor progression, it was given before cancer onset, at week 6, and until week 44. To determine its effect after the onset of prostate cancer, it was given from weeks 12 to 35. In both strategies, oral administration of WA effectively suppressed tumor burden when compared to vehicle-treated animals. No toxicity was seen in treated animals at gross pathological examination. Western blot analysis and immunohistochemistry of tumor sections revealed that in TRAMP controls, AKT and pAKT were highly expressed while nuclear FOXO3a and Par-4 were downregulated. On the contrary, treated mice showed inhibition of AKT signaling and activation of FOX03a-Par-4-induced cell death. They also displayed inhibition of mesenchymal markers such as β-catenin, vimentin, and snail as well as upregulation of E-cadherin. Because expressions of the angiogenic markers factor VIII and retic were downregulated, an anti-angiogenic role of WA is suggested. Overall, our results suggest that WA could be a promising anti-cancer agent that effectively inhibits carcinogenesis of the prostate.

O-linked N-acetylglucosamine transferase enhances secretory clusterin expression via liver X receptors and sterol response element binding protein regulation in cervical cancer

O-linked N-acetylglucosamine transferase (OGT) expression is increased in various cancer types, indicating the potential importance of O-GlcNAcylation in tumorigenesis. Secretory clusterin (sCLU) is involved in cancer cell proliferation and drug resistance, and recently, liver X receptors (LXRs) and sterol response element binding protein-1 (SREBP-1) were reported to regulate sCLU transcription. Here, we found that sCLU is significantly increased in cervical cancer cell lines, which have higher expression levels of O-GlcNAc and OGT than keratinocytes. OGT knockdown decreased expression of LXRs, SREBP-1 and sCLU through hypo-O-GlcNAcylation of LXRs. Additionally, treatment with Thiamet G, O-GlcNAcase OGA inhibitor, increased expression of O-GlcNAcylation and sCLU, and high glucose increased levels of LXRs, SREBP-1 and sCLU in HeLa cells. Moreover, OGT knockdown induced G₀/G₁ phase cell cycle arrest and late apoptosis in cisplatin-treated HeLa cells, and decreased viability compared to OGT intact HeLa cells. Taken together, these findings suggest that OGT, O-GlcNAcylated LXRs, and SREBP-1 increase sCLU expression in cervical cancer cells, which contributes to drug resistance.

ProCAID: a phase I clinical trial to combine the AKT inhibitor AZD5363 with docetaxel and prednisolone chemotherapy for metastatic castration resistant prostate cancer

Background Docetaxel and prednisolone chemotherapy (DP) extends survival in metastatic castration resistant prostate cancer (mCRPC). However, emergent clinical resistance is almost inevitable. AKT pathway activation is highly prevalent in mCRPC contributing to disease progression and DP resistance. AZD5363 is a potent oral pan-AKT inhibitor with pre-clinical data indicating activity in mCRPC and synergy with docetaxel. Methods This phase I trial was to determine an AZD5363 recommended phase II dose (RP2D) for combination with DP. Eligibility criteria included chemotherapy naive mCRPC, PSA or radiographic disease progression and ECOG performance status 0 or 1. Treatment comprised DP (75 mg/m2, IV, day 1 and 5 mg BID, PO, day 1-21 respectively for ten cycles) and AZD5363 to disease progression for all patients. We utilised a 3 + 3 dose escalation design to determine a maximum tolerated dose according to defined dose limiting toxicity criteria assessed using CTCAE version 4.03. Planned AZD5363 dose levels were 320 mg (DL1), 400 mg (DL2) and 480 mg (DL3), BID, PO, 4 days on/3 days off, from day 2 of each cycle. Results 10 patients were treated. Dose limiting toxicities affected 2 patients (grade 3 rash ≥5 days; grade 3 diarrhoea) in DL2. The commonest grade 3 or 4, AZD5363 related, symptomatic adverse events were rash and diarrhoea. Hyperglycaemia affected all patients but was self-limiting. PSA reduction to <50% at 12 weeks occurred in 7 patients. Conclusions The RP2D for AZD5363 is 320 mg BID, 4 days on/3 days off, in combination with full dose DP for mCRPC.

Addressing taxane resistance in metastatic castration-resistant prostate cancer: a focus on chaperone proteins

Despite the significant survival benefit of taxane therapy in metastatic castration-resistant prostate cancer (mCRPC), all patients inevitably develop treatment resistance. An understanding of resistance mechanisms has led to new therapies for prostate cancer (cabazitaxel, abiraterone and enzalutamide), all of which have improved survival following first-line docetaxel. Another treatment, currently in development, targets the prosurvival molecule clusterin. Custirsen, an antisense molecule that inhibits clusterin production, has shown promise in combination with docetaxel in mCRPC patients at risk for poor outcomes. Although optimal sequence and combination of available therapies is unclear, the heterogeneity of mCRPC suggests a continuing need for personalized treatment regimens and improved abilities to predict which patients will respond to the available treatment options.

Mechanisms of resistance in castration-resistant prostate cancer (CRPC)

Despite advances in prostate cancer diagnosis and management, morbidity from prostate cancer remains high. Approximately 20% of men present with advanced or metastatic disease, while 29,000 men continue to die of prostate cancer each year. Androgen deprivation therapy (ADT) has been the standard of care for initial management of advanced or metastatic prostate cancer since Huggins and Hodges first introduced the concept of androgen-dependence in 1972, but progression to castration-resistant prostate cancer (CRPC) occurs within 2-3 years of initiation of ADT. CRPC, previously defined as hormone-refractory prostate cancer, is now understood to still be androgen dependent. Multiple mechanisms of resistance help contribute to the progression to castration resistant disease, and the androgen receptor (AR) remains an important driver in this progression. These mechanisms include AR amplification and hypersensitivity, AR mutations leading to promiscuity, mutations in coactivators/corepressors, androgen-independent AR activation, and intratumoral and alternative androgen production. More recently, identification of AR variants (ARVs) has been established as another mechanism of progression to CRPC. Docetaxel chemotherapy has historically been the first-line treatment for CRPC, but in recent years, newer agents have been introduced that target some of these mechanisms of resistance, thereby providing additional survival benefit. These include AR signaling inhibitors such as enzalutamide (Xtandi, ENZA, MDV-3100) and CYP17A1 inhibitors such as abiraterone acetate (Zytiga). Ultimately, these agents will also fail to suppress CRPC. While some of the mechanisms by which these agents fail are unique, many share similarities to the mechanisms contributing to CRPC progression. Understanding these mechanisms of resistance to ADT and currently approved CRPC treatments will help guide future research into targeted therapies.

HMGB1 induction of clusterin creates a chemoresistant niche in human prostate tumor cells

Development of chemoresistance, especially to docetaxel (DTX), is the primary barrier to the cure of castration-resistant prostate cancer but its mechanism is obscure. Here, we report a seminal crosstalk between dying and residual live tumor cells during treatment with DTX that can result in outgrowth of a chemoresistant population. Survival was due to the induction of secretory/cytoplasmic clusterin (sCLU), which is a potent anti-apoptotic protein known to bind and sequester Bax from mitochondria, to prevent caspase 3 activation. sCLU induction in live cells depended on HMGB1 release from dying cells. Supernatants from DTX-treated DU145 tumor cells, which were shown to contain HMGB1, effectively induced sCLU from newly-plated DU145 tumor cells and protected them from DTX toxicity. Addition of anti-HMBG1 to the supernatant or pretreatment of newly-plated DU145 tumor cells with anti-TLR4 or anti-RAGE markedly abrogated sCLU induction and protective effect of the supernatant. Mechanistically, HMGB1 activated NFκB to promote sCLU gene expression and prevented the translocation of activated Bax to mitochondria to block cell death. Importantly, multiple currently-used chemotherapeutic drugs could release HMGB1 from tumor cells. These results suggest that acquisition of chemoresistance may involve the HMGB1/TLR4-RAGE/sCLU pathway triggered by dying cells to provide survival advantage to remnant live tumor cells.

Targeting molecular resistance in castration-resistant prostate cancer

Multiple mechanisms of resistance contribute to the inevitable progression of hormone-sensitive prostate cancer to castration-resistant prostate cancer (CRPC). Currently approved therapies for CRPC include systemic chemotherapy (docetaxel and cabazitaxel) and agents targeting the resistance pathways leading to CRPC, including enzalutamide and abiraterone. While there is significant survival benefit, primary and secondary resistance to these therapies develops rapidly. Up to one-third of patients have primary resistance to enzalutamide and abiraterone; the remaining patients eventually progress on treatment. Understanding the mechanisms of resistance resulting in progression as well as identifying new targetable pathways remains the focus of current prostate cancer research. We review current knowledge of mechanisms of resistance to the currently approved treatments, development of adjunctive therapies, and identification of new pathways being targeted for therapeutic purposes.

Antiandrogens Inhibit ABCB1 Efflux and ATPase Activity and Reverse Docetaxel Resistance in Advanced Prostate Cancer

PURPOSE

Previous studies show that inhibition of ABCB1 expression overcomes acquired docetaxel resistance in C4-2B-TaxR cells. In this study, we examined whether antiandrogens, such as bicalutamide and enzalutamide, could inhibit ABCB1 activity and overcome resistance to docetaxel.

EXPERIMENTAL DESIGN

ABCB1 efflux activity was determined using a rhodamine efflux assay. ABCB1 ATPase activity was determined by Pgp-Glo assay systems. The effects of the antiandrogens bicalutamide and enzalutamide on docetaxel sensitivity were determined by cell growth assays and tumor growth in vivo.

RESULTS

We found that bicalutamide and enzalutamide inhibit ABCB1 ATP-binding cassette transporter activity through blocking ABCB1 efflux activity. Bicalutamide inhibited ABCB1 efflux activity by 40%, whereas enzalutamide inhibited ABCB1 efflux activity by approximately 60%. Both bicalutamide and enzalutamide inhibit ABCB1 ATPase activity. In addition, bicalutamide and enzalutamide inhibit ABCB1 efflux activity and desensitize docetaxel-resistant and androgen receptor (AR)-negative DU145 cells. Combination of bicalutamide with docetaxel had a significant antitumor effect in both AR-positive and AR-negative docetaxel-resistant xenograft models, suggesting that bicalutamide desensitizes docetaxel-resistant cells to docetaxel treatment independent of AR status.

CONCLUSIONS

We identified a novel mechanism of action for antiandrogens such as bicalutamide and enzalutamide as inhibitors of ABCB1 efflux and ATPase activity. Bicalutamide and enzalutamide desensitize docetaxel-resistant prostate cancer cells to docetaxel treatment independent of AR status. These studies may lead to the development of combinational therapies with bicalutamide/enzalutamide and docetaxel as effective regimens to treat advanced prostate cancer independent of AR status, and possibly other types of 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.

DTX3L and ARTD9 inhibit IRF1 expression and mediate in cooperation with ARTD8 survival and proliferation of metastatic prostate cancer cells

Background

Prostate cancer (PCa) is one of the leading causes of cancer-related mortality and morbidity in the aging male population and represents the most frequently diagnosed malignancy in men around the world. The Deltex (DTX)-3-like E3 ubiquitin ligase (DTX3L), also known as B-lymphoma and BAL-associated protein (BBAP), was originally identified as a binding partner of the diphtheria-toxin-like macrodomain containing ADP-ribosyltransferase-9 (ARTD9), also known as BAL1 and PARP9. We have previously demonstrated that ARTD9 acts as a novel oncogenic survival factor in high-risk, chemo-resistant, diffuse large B cell lymphoma (DLBCL). The mono-ADP-ribosyltransferase ARTD8, also known as PARP14 functions as a STAT6-specific co-regulator of IL4-mediated proliferation and survival in B cells.

Methods

Co-expression of DTX3L, ARTD8, ARTD9 and STAT1 was analyzed in the metastatic PCa (mPCa) cell lines PC3, DU145, LNCaP and in the normal prostate luminal epithelial cell lines HPE and RWPE1. Effects on cell proliferation, survival and cell migration were determined in PC3, DU145 and/or LNCaP cells depleted of DTX3L, ARTD8, ARTD9, STAT1 and/or IRF1 compared to their proficient control cells, respectively. In further experiments, real-time RT-PCR, Western blot, immunofluorescence and co-immunoprecipitations were conducted to evaluate the physical and functional interactions between DTX3L, ARTD8 and ARTD9.

Results

Here we could identify DTX3L, ARTD9 and ARTD8 as novel oncogenic survival factors in mPCa cells. Our studies revealed that DTX3L forms a complex with ARTD8 and mediates together with ARTD8 and ARTD9 proliferation, chemo-resistance and survival of mPCa cells. In addition, DTX3L, ARTD8 and ARTD9 form complexes with each other. Our study provides first evidence that the enzymatic activity of ARTD8 is required for survival of mPCa cells. DTX3L and ARTD9 act together as repressors of the tumor suppressor IRF1 in mPCa cells. Furthermore, the present study shows that DTX3L together with STAT1 and STAT3 is implicated in cell migration of mPCa cells.

Conclusions

Our data strongly indicate that a crosstalk between STAT1, DTX3L and ARTD-like mono-ADP-ribosyltransferases mediates proliferation and survival of mPCa cells. The present study further suggests that the combined targeted inhibition of STAT1, ARTD8, ARTD9 and/or DTX3L could increase the efficacy of chemotherapy or radiation treatment in prostate and other high-risk tumor types with an increased STAT1 signaling.

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.

RNA sequencing identifies multiple fusion transcripts, differentially expressed genes, and reduced expression of immune function genes in BRAF (V600E) mutant vs BRAF wild-type papillary thyroid carcinoma

CONTEXT

The BRAF V600E mutation (BRAF-MUT) confers an aggressive phenotype in papillary thyroid carcinoma, but unidentified additional genomic abnormalities may be required for full phenotypic expression.

OBJECTIVE

RNA sequencing (RNA-Seq) was performed to identify genes differentially expressed between BRAF-MUT and BRAF wild-type (BRAF-WT) tumors and to correlate changes to patient clinical status.

DESIGN

BRAF-MUT and BRAF-WT tumors were identified in patients with T1N0 and T2-3N1 tumors evaluated in a referral medical center. Gene expression levels were determined (RNA-Seq) and fusion transcripts were detected. Multiplexed capture/detection and digital counting of mRNA transcripts (nCounter, NanoString Technologies) validated RNA-Seq data for immune system-related genes.

PATIENTS

BRAF-MUT patients included nine women, three men; nine were TNM stage I and three were stage III. Three (25%) had tumor infiltrating lymphocytes. BRAF-WT included five women, three men; all were stage I, and five (62.5%) had tumor infiltrating lymphocytes.

RESULTS

RNA-Seq identified 560 of 13 085 genes differentially expressed between BRAF-MUT and BRAF-WT tumors. Approximately 10% of these genes were related to MetaCore immune function pathways; 51 were underexpressed in BRAF-MUT tumors, whereas 4 (HLAG, CXCL14, TIMP1, IL1RAP) were overexpressed. The four most differentially overexpressed immune genes in BRAF-WT tumors (IL1B; CCL19; CCL21; CXCR4) correlated with lymphocyte infiltration. nCounter confirmed the RNA-Seq expression level data. Eleven different high-confidence fusion transcripts were detected (four interchromosomal; seven intrachromosomal) in 13 of 20 tumors. All in-frame fusions were validated by RT-PCR.

CONCLUSION

BRAF-MUT papillary thyroid cancers have reduced expression of immune/inflammatory response genes compared with BRAF-WT tumors and correlate with lymphocyte infiltration. In contrast, HLA-G and CXCL14 are overexpressed in BRAF-MUT tumors. Sixty-five percent of tumors had between one and three fusion transcripts. Functional studies will be required to determine the potential role of these newly identified genomic abnormalities in contributing to the aggressiveness of BRAF-MUT and BRAF-WT tumors.

Phosphoproteomic profiling identifies focal adhesion kinase as a mediator of docetaxel resistance in castrate-resistant prostate cancer

Docetaxel remains the standard-of-care for men diagnosed with metastatic castrate-resistant prostate cancer (CRPC). However, only approximately 50% of patients benefit from treatment and all develop docetaxel-resistant disease. Here, we characterize global perturbations in tyrosine kinase signaling associated with docetaxel resistance and thereby develop a potential therapeutic strategy to reverse this phenotype. Using quantitative mass spectrometry-based phosphoproteomics, we identified that metastatic docetaxel-resistant prostate cancer cell lines (DU145-Rx and PC3-Rx) exhibit increased phosphorylation of focal adhesion kinase (FAK) on Y397 and Y576, in comparison with parental controls (DU145 and PC3, respectively). Bioinformatic analyses identified perturbations in pathways regulating focal adhesions and the actin cytoskeleton and in protein-protein interaction networks related to these pathways in docetaxel-resistant cells. Treatment with the FAK tyrosine kinase inhibitor (TKI) PF-00562271 reduced FAK phosphorylation in the resistant cells, but did not affect cell viability or Akt phosphorylation. Docetaxel administration reduced FAK and Akt phosphorylation, whereas cotreatment with PF-00562271 and docetaxel resulted in an additive attenuation of FAK and Akt phosphorylation and overcame the chemoresistant phenotype. The enhanced efficacy of cotreatment was due to increased autophagic cell death, rather than apoptosis. These data strongly support that enhanced FAK activation mediates chemoresistance in CRPC, and identify a potential clinical niche for FAK TKIs, where coadministration with docetaxel may be used in patients with CRPC to overcome chemoresistance.

Apigenin inhibits prostate cancer progression in TRAMP mice via targeting PI3K/Akt/FoxO pathway

Forkhead box O (FoxO) transcription factors play an important role as tumor suppressor in several human malignancies. Disruption of FoxO activity due to loss of phosphatase and tensin homolog and activation of phosphatidylinositol-3 kinase (PI3K)/Akt are frequently observed in prostate cancer. Apigenin, a naturally occurring plant flavone, exhibits antiproliferative and anticarcinogenic activities through mechanisms, which are not fully defined. In the present study, we show that apigenin suppressed prostate tumorigenesis in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice through the PI3K/Akt/FoxO-signaling pathway. Apigenin-treated TRAMP mice (20 and 50 μg/mouse/day, 6 days/week for 20 weeks) exhibited significant decrease in tumor volumes of the prostate as well as completely abolished distant organ metastasis. Apigenin treatment resulted in significant decrease in the weight of genitourinary apparatus (P < 0.0001), dorsolateral (P < 0.0001) and ventral prostate (P < 0.028), compared with the control group. Apigenin-treated mice showed reduced phosphorylation of Akt (Ser473) and FoxO3a (Ser253), which correlated with its increased nuclear retention and decreased binding of FoxO3a with 14-3-3. These events lead to reduced proliferation as assessed by Ki-67 and cyclin D1, along with upregulation of FoxO-responsive proteins BIM and p27/Kip1. Complementing in vivo results, similar observations were noted in human prostate cancer LNCaP and PC-3 cells after apigenin treatment. Furthermore, binding of FoxO3a with p27/Kip1 was markedly increased after 10 and 20 μM apigenin treatment resulting in G0/G1-phase cell cycle arrest, which was consistent with the effects elicited by PI3K/Akt inhibitor, LY294002. These results provide convincing evidence that apigenin effectively suppressed prostate cancer progression, at least in part, by targeting the PI3K/Akt/FoxO-signaling pathway.

Vitamin k2, a naturally occurring menaquinone, exerts therapeutic effects on both hormone-dependent and hormone-independent prostate cancer cells

In recent years, several studies have shown that vitamin k2 (VK2) has anticancer activity in a variety of cancer cells. The antitumor effects of VK2 in prostate cancer are currently not known. In the present study, we sought to characterize the anticancer potential of VK2 in both androgen-dependent and -independent prostate cancer cells. Our investigations show that VK2 is able to suppress viability of androgen-dependent and androgen-independent prostate cancer cells via caspase-3 and -8 dependent apoptosis. We also show that VK2 treatment reduces androgen receptor expression and PSA secretion in androgen-dependent prostate cancer cells. Our results also implicate VK2 as a potential anti-inflammatory agent, as several inflammatory genes are downregulated in prostate cancer cells following treatment with VK2. Additionally, AKT and NF-kB levels in prostate cancer cells are reduced significantly when treated with VK2. These findings correlated with the results of the Boyden chamber and angiogenesis assay, as VK2 treatment reduced cell migration and angiogenesis potential of prostate cancer cells. Finally, in a nude mice model, VK2 administration resulted in significant inhibition of both androgen-dependent and androgen-independent tumor growth. Overall, our results suggest that VK2 may be a potential therapeutic agent in the treatment of prostate cancer.

Inhibition of ABCB1 expression overcomes acquired docetaxel resistance in prostate cancer

Docetaxel is the first-line standard treatment for castration-resistant prostate cancer. However, relapse eventually occurs due to the development of resistance to docetaxel. To unravel the mechanism of acquired docetaxel resistance, we established docetaxel-resistant prostate cancer cells, TaxR, from castration-resistant C4-2B prostate cancer cells. The IC50 for docetaxel in TaxR cells was about 70-fold higher than parental C4-2B cells. Global gene expression analysis revealed alteration of expression of a total of 1,604 genes, with 52% being upregulated and 48% downregulated. ABCB1, which belongs to the ATP-binding cassette (ABC) transporter family, was identified among the top upregulated genes in TaxR cells. The role of ABCB1 in the development of docetaxel resistance was examined. Knockdown of ABCB1 expression by its specific shRNA or inhibitor resensitized docetaxel-resistant TaxR cells to docetaxel treatment by enhancing apoptotic cell death. Furthermore, we identified that apigenin, a natural product of the flavone family, inhibits ABCB1 expression and resensitizes docetaxel-resistant prostate cancer cells to docetaxel treatment. Collectively, these results suggest that overexpression of ABCB1 mediates acquired docetaxel resistance and targeting ABCB1 expression could be a potential approach to resensitize docetaxel-resistant prostate cancer cells to docetaxel treatment.

The mechanism of DAB2IP in chemoresistance of prostate cancer cells

PURPOSE

The docetaxel-based chemotherapy is the standard of care for castration-resistant prostate cancer (CRPC), inevitably, patients develop resistance and decease. Until now, the mechanism and predictive marker for chemoresistance are poorly understood.

EXPERIMENTAL DESIGN

Immortalized normal prostate and cancer cell lines stably manipulated with different DAB2IP expression levels were used and treated with chemotherapeutic drugs commonly used in prostate cancer therapy. Cell proliferation was measured using MTT assay; Western blot, quantitative PCR, and luciferase reporter assays were used to analyze Clusterin gene regulation by DAB2IP. Immunohistochemical analysis was conducted for evaluating DAB2IP, Clusterin and Egr-1 expression in human prostate cancer tissue.

RESULTS

DAB2IP Knockdown (KD) cells exhibited resistance to several chemotherapeutic drugs, whereas increased DAB2IP in C4-2 cells restored the drug sensitivity. Parallel, DAB2IP KD cells exhibited higher expression of Clusterin, an antiapoptotic factor, whereas elevated DAB2IP in C4-2 cells decreased Clusterin expression. Functionally, knocking down Clusterin by short-hairpin RNA or antisense oligonucleotide OGX-011 decreased drug resistance, whereas overexpressing Clusterin in C4-2 D2 enhanced drug resistance. Mechanistically, DAB2IP blocked the cross-talk between Wnt/β-catenin and IGF-I signaling, leading to the suppression of Egr-1 that is responsible for Clusterin expression. A similar result was observed in the prostate of DAB2IP knockout animals. In addition, we observed a significantly inverse correlation between DAB2IP and Egr-1 or Clusterin expression from clinical tissue microarray.

CONCLUSIONS

This study unveils a new regulation of the Egr-1/Clusterin signaling network by DAB2IP. Loss of DAB2IP expression in CRPC cells signifies their chemoresistance. Clusterin is a key target for developing more effective CRPC therapy.

Targeting the apoptosis pathway in prostate cancer

Important inroads have been made in the understanding and treatment of metastatic prostate cancer in recent years. However, the need for agents targeting novel pathways remains ever present. One such area with promise is through apoptosis or programmed cell death. Many perturbations within the apoptotic process have been associated with treatment resistance and progression in castration-resistant prostate cancer; thus, therapeutic potential exists with agents that can restore an effective apoptotic response to cellular stressors. This article focuses on agents in clinical development targeting apoptosis through the intrinsic and extrinsic pathways. We review the current status of agents that intervene at the Bcl2 checkpoints, humanized antibodies to death receptors, agents that target the inhibitors of apoptosis proteins, mimetics of small mitochondria-derived activator of caspases, and antisense therapies targeting cytoprotective chaperones. Although single-agent activity has been demonstrated with some of these agents, the clinical development path forward will see them coupled with standard hormonal therapy and chemotherapy. OGX-011 (custirsen), which inhibits expression of the cytoprotective chaperone protein clusterin, is the most mature of these agents and is being tested in combination with chemotherapy in phase III clinical trials for castration-resistant prostate cancer, and results are eagerly awaited.

Custirsen (OGX-011): a second-generation antisense inhibitor of clusterin in development for the treatment of prostate cancer

Clusterin is a stress-induced cytoprotective chaperone that confers broad-spectrum treatment resistance and is overexpressed across a number of cancers. custirsen (OGX-011) is a promising novel second-generation antisense inhibitor of clusterin in clinical development. This article describes the mechanism of action and safety profile of OGX-011 and details the Phase I and II results in human solid organ malignancies. Two Phase III registration trials are currently under recruitment evaluating OGX-011 in combination with chemotherapy in patients with metastatic castration-resistant prostate cancer. These studies not only have the potential to significantly alter the standard of care in prostate cancer, but would also endorse a new class of targets and targeted therapy approach for cancer.

The molecular chaperone apolipoprotein J/clusterin as a sensor of oxidative stress: implications in therapeutic approaches - a mini-review

BACKGROUND

Organisms are constantly exposed to physiological and environmental stresses and therefore require an efficient surveillance of genome and proteome quality in order to prevent disruption of homeostasis. Central to the intra- and extracellular proteome surveillance system are the molecular chaperones that contribute to both proteome maintenance and clearance. The conventional protein product of the apolipoprotein J/clusterin (CLU) gene is a heterodimeric secreted glycoprotein (also termed as sCLU) with a ubiquitous expression in human tissues. CLU exerts a small heat shock protein-like stress-induced chaperone activity and has been functionally implicated in numerous physiological processes as well as in ageing and most age-related diseases including tumorigenesis, neurodegeneration, and cardiovascular and metabolic syndromes.

OBJECTIVE

The CLU gene is differentially regulated by a wide variety of stimuli due to the combined presence of many distinct regulatory elements in its promoter that make it an extremely sensitive cellular biosensor of environmental and/or oxidative stress. Downstream to CLU gene induction, the CLU protein seems to actively intervene in pathological states of increased oxidative injury due to its chaperone-related property to inhibit protein aggregation and precipitation (a main feature of oxidant injury), as well as due to its reported distribution in both extra- and, most likely, intracellular compartments.

CONCLUSION

On the basis of these findings, CLU has emerged as a unique regulator of cellular proteostasis. Nevertheless, it seemingly exerts a dual function in pathology. For instance, in normal cells and during early phases of carcinogenesis, CLU may inhibit tumor progression as it contributes to suppression of proteotoxic stress. In advanced neoplasia, however, it may offer a significant survival advantage in the tumor by suppressing many therapeutic stressors and enhancing metastasis. This review will critically present a synopsis of recent novel findings that relate to the function of this amazing molecule and support the notion that CLU is a biosensor of oxidative injury; a common link between ageing and all pathologies where CLU has been implicated. Potential future perspectives, implications and opportunities for translational research and the development of new therapies will be discussed.

The use of LC-MS to identify differentially expressed proteins in docetaxel-resistant prostate cancer cell lines

Docetaxel is a taxane-derived chemotherapy drug that has been approved for treatment of prostate cancer. While docetaxel is frequently used as a treatment for hormone-refractory prostate cancer, a subset of patients either do not respond to this treatment or those that do respond eventually become resistant to the drug over time. Resistance to docetaxel is complex and multi-factoral and further understanding of the cellular biochemistry underlying resistance is vital to improve treatment efficacy. To identify proteins altered in the resistant phenotype, three parental cell lines DU145, 22RV1 and PC-3, as well as their docetaxel resistant sub-lines, were subjected to quantitative label-free LC-MS proteomic profiling. A total of 189 significant (p < 0.05) protein abundance changes were identified in the DU145 resistant sub-lines, 254 in the 22RV1 sub-lines, and 51 and 72 in the 8 and 12 nM resistant PC-3 sub-lines, respectively. From these, 29 proteins demonstrated a significant (p < 0.05) fold change across two or more resistant variants. These included proteins indicative of an epithelial-to-mesenchemyl transition as well as altered heat shock response elements.

Epithelial-to-mesenchymal transition leads to docetaxel resistance in prostate cancer and is mediated by reduced expression of miR-200c and miR-205

Docetaxel is a standard chemotherapy for patients with metastatic prostate cancer. However, the response is rather limited and not all of the patients benefit from this treatment. To uncover key mechanisms of docetaxel insensitivity in prostate cancer, we have established docetaxel-resistant sublines. In this study, we report that docetaxel-resistant cells underwent an epithelial-to-mesenchymal transition during the selection process, leading to diminished E-cadherin levels and up-regulation of mesenchymal markers. Screening for key regulators of an epithelial phenotype revealed a significantly reduced expression of microRNA (miR)-200c and miR-205 in docetaxel-resistant cells. Transfection of either microRNA (miRNA) resulted in re-expression of E-cadherin. Functional assays confirmed reduced adhesive and increased invasive and migratory abilities. Furthermore, we detected an increased subpopulation with stem cell-like properties in resistant cells. Tissue microarray analysis revealed a reduced E-cadherin expression in tumors after neoadjuvant chemotherapy. Low E-cadherin levels could be linked to tumor relapse. The present study uncovers epithelial-to-mesenchymal transition as a hallmark of docetaxel resistance. Therefore, we suggest that this mechanism is at least in part responsible for chemotherapy failure, with implications for the development of novel therapeutics.

Knockdown of clusterin sensitizes pancreatic cancer cells to gemcitabine chemotherapy by ERK1/2 inactivation

OBJECTIVES

To study the hypothesis that gemcitabine treatment augments the chemoresistance to gemcitabine by clusterin (sCLU) upregulation. Clusterin inhibition could augment the chemosensitivity of human pancreatic cancer cells by inhibition of clusterin-dependent pERK1/2 activation.

METHODS

Clusterin was silenced by serial concentration of OGX-011 transfection in pancreatic cancer MIAPaCa-2 and BxPC-3 cell lines, then treated with serial concentration of gemcitabine. After the cells were treated with OGX-011 for 8 h, the cells were then treated with 5 μM ERK inhibitor PD98059 for 18 h or transfected with a wt-pERK-expressing plasmid into these cells for 24 h, after which the cells were treated with 1.0 uM gemcitabine for 24-72 h. Cell proliferation was determined by MTT. Apoptosis was quantified by flow cytometry,.sCLU and pERK1/2 production was analyzed by western blot, and sCLU mRNA was analyzed by RT-PCR. Xenograft of established tumors was used to evaluate primary tumor growth and apoptosis after treatment with gemcitabine alone or in combination with OGX-011. Phosphorylated ERK1/2 and sCLU levels in tumor tissues were measured by TUNEL analysis.

RESULTS

As detected by MTT and FACS assay, a combination of gemcitabine + OGX-011 reflected the chemotherapeutic sensitivity and increased the gemcitabine -induced apoptosis in MIAPaCa-2 and BxPC-3 cells. Western blotting and RT-PCR analysis revealed that the expression of clusterin was higher in gemcitabine -resistant MIAPaCa-2 cells, however, decreased significantly after pretreatment with OGX-011. Furthermore, the OGX-011 or combination of gemcitabine + OGX-011 decreased the gemcitabine -induced activation of pERK1/2. wt-pERK-re-expression decreased OGX-011+ gemcitabine -induced apoptosis. Finally, OGX-011 in combination with gemcitabine substantially decreased the in vivo tumor growth and promoted apoptosis. Taken together, clusterin confers gmcitabine resistance in pancreatic cancer cells.

CONCLUSIONS

Knockdown of clusterin by OGX-011 transfection sensitizes pancreatic cancer cells to gemcitabine by inhibition of gemcitabine -induced clusterin-pERK1/2 activation.

Clusterin inhibition using OGX-011 synergistically enhances antitumour activity of sorafenib in a human renal cell carcinoma model

BACKGROUND

The objective of this study was to investigate whether the therapeutic activity of sorafenib could be enhanced by combining with OGX-011, an antisense oligodeoxynucleotide (ODN) targeting clusterin, in renal cell carcinoma (RCC).

METHODS

We investigated the effects of combined treatment with OGX-011 and sorafenib on a human RCC ACHN model both in vitro and in vivo.

RESULTS

Although clusterin expression was increased by sorafenib, additional treatment of ACHN with OGX-011 significantly blocked the upregulation of clusterin induced by sorafenib. Despite the lack of a significant effect on the growth of ACHN, OGX-011 synergistically enhanced the sensitivity to sorafenib, reducing the IC(50) by >50%. Apoptotic changes were intensively detected in ACHN after combined treatment with OGX-011 and a sublethal dose of sorafenib, but not either agent alone. Furthermore, this combined treatment resulted in the marked downregulation of phosphorylated Akt and p44/42 mitogen-activated protein kinase in ACHN compared with treatment with either agent alone. In vivo systemic administration of OGX-011 plus sorafenib significantly decreased the ACHN tumour volume compared with control ODN plus sorafenib.

CONCLUSION

Combined use with OGX-011 may be useful in enhancing the cytotoxic effect of sorafenib on RCC by inducing apoptosis and inactivating major signal transduction pathways.

Zinc sensing receptor signaling, mediated by GPR39, reduces butyrate-induced cell death in HT29 colonocytes via upregulation of clusterin

Zinc enhances epithelial proliferation, protects the digestive epithelial layer and has profound antiulcerative and antidiarrheal roles in the colon. Despite the clinical significance of this ion, the mechanisms linking zinc to these cellular processes are poorly understood. We have previously identified an extracellular Zn²⁺ sensing G-protein coupled receptor (ZnR) that activates Ca²⁺ signaling in colonocytes, but its molecular identity as well as its effects on colonocytes' survival remained elusive. Here, we show that Zn²⁺, by activation of the ZnR, protects HT29 colonocytes from butyrate induced cell death. Silencing of the G-protein coupled receptor GPR39 expression abolished ZnR-dependent Ca²⁺ release and Zn²⁺-dependent survival of butyrate-treated colonocytes. Importantly, GPR39 also mediated ZnR-dependent upregulation of Na⁺/H⁺ exchange activity as this activity was found in native colon tissue but not in tissue obtained from GPR39 knock-out mice. Although ZnR-dependent upregulation of Na⁺/H⁺ exchange reduced the cellular acid load induced by butyrate, it did not rescue HT29 cells from butyrate induced cell death. ZnR/GPR39 activation however, increased the expression of the anti-apoptotic protein clusterin in butyrate-treated cells. Furthermore, silencing of clusterin abolished the Zn²⁺-dependent survival of HT29 cells. Altogether, our results demonstrate that extracellular Zn²⁺, acting through ZnR, regulates intracellular pH and clusterin expression thereby enhancing survival of HT29 colonocytes. Moreover, we identify GPR39 as the molecular moiety of ZnR in HT29 and native colonocytes.

Clusterin attenuates the development of renal fibrosis

Upregulation of clusterin occurs in several renal diseases and models of nephrotoxicity, but whether this promotes injury or is a protective reaction to injury is unknown. Here, in the mouse unilateral ureteral obstruction model, obstruction markedly increased the expression of clusterin, plasminogen activator inhibitor-1 (PAI-1), type I collagen, and fibronectin. Compared with wild-type mice, clusterin-deficient mice exhibited higher levels of PAI-1, type I collagen, and fibronectin and accelerated renal fibrosis in response to obstruction. In cultured rat tubular epithelium-like cells, adenovirus-mediated overexpression of clusterin inhibited the expression of TGF-β-stimulated PAI-1, type I collagen, and fibronectin. Clusterin inhibited TGF-β-stimulated Smad3 activity via inhibition of Smad3 phosphorylation and its nuclear translocation. Moreover, intrarenal delivery of adenovirus-expressing clusterin upregulated expression of clusterin in tubular epithelium-like cells and attenuated obstruction-induced renal fibrosis. In conclusion, clusterin attenuates renal fibrosis in obstructive nephropathy. These results suggest that upregulation of clusterin during renal injury is a protective response against the development of renal fibrosis.

Clusterin is a potential molecular predictor for ovarian cancer patient's survival: targeting clusterin improves response to paclitaxel

Background

Clusterin is a cytoprotective chaperone protein involved in numerous physiological processes, carcinogenesis, tumor growth and tissue remodelling. The purpose of this study was to investigate whether clusterin (CLU), an antiapoptotic molecule, could be a potential predictor molecule for ovarian cancer and whether or not targeting this molecule can improve survival of ovarian cancer patients.

Methods

Clusterin expression was compared between ten primary and their recurrent tumors from same patients immunohistochemically. We analyzed prognostic significance of CLU expression in another 47 ovarian cancer tissue samples by immunohistochemistry. We used small interference RNA to knock down CLU in the chemo-resistant ovarian cancer cell lines. KF-TX and SKOV-3-TX, paclitaxel-resistant ovarian cancer cells, were established from parental KF and SKOV-3 chemo-sensitive cell lines, respectively. Either siRNA or second generation antisense oligodeoxynucleotide against CLU (OGX-011), which is currently evaluated in clinical phase II trials in other cancer s, was used to modulate sensitivity to paclitaxel (TX) in ovarian cancer cells in vitro. Cellular viability assay, FACS analysis and annexin V staining were used to evaluate the comparative effect of CLU knocking down in ovarian cancer cells.

Results

Immunohistochemical analysis of CLU expression in primary ovarian cancer tissue specimens and their recurrent counterparts from same patients demonstrated higher expression of CLU in the recurrent resistant tumors compared with their primary tumors. High expression of CLU by immunohistochemistry among 47 surgical tissue specimens of early-stage (stage I/II) ovarian cancer, who underwent complete cytoreduction as a primary surgery, significantly related to poor survival, while none of other clinicopathological factors analyzed were related to survival in this patient cohort. Secretory CLU (s-CLU; 60 KDa) expression was upregulated in TX-resistant ovarian cancer cells compared to parental cells. Transfection of siRNA or OGX-011 clearly reduced CLU expression. Cell viability assay, FACS analysis and annexin V staining demonstrated that targeting CLU expression by siRNA or OGX-011 sensitized ovarian cancer cells to TX.

Conclusion

We conclude that CLU could be a potential molecular target to predict survival while targeting this s-CLU may improve survival of patients with ovarian cancer.

A novel chemoimmunomodulating property of docetaxel: suppression of myeloid-derived suppressor cells in tumor bearers

PURPOSE

Myeloid-derived suppressor cells (MDSC) accumulate in tumor-bearing hosts and are associated with immune suppression. To date, there have only been few studies that evaluate the direct effect of chemotherapeutic agents on MDSCs. Agents that inhibit MDSCs may be useful in the treatment of patients with various cancers.

EXPERIMENTAL DESIGN

We investigated the in vivo effects of docetaxel on immune function in 4T1-Neu mammary tumor-bearing mice to examine if a favorable immunomodulatory effect accompanies tumor suppression. Primary focus was on the differentiation status of MDSCs and their ability to modulate T-cell responses.

RESULTS

Docetaxel administration significantly inhibited tumor growth in 4T1-Neu tumor-bearing mice and considerably decreased MDSC proportion in the spleen. The treatment also selectively increased CTL responses. Docetaxel-pretreated MDSCs cocultured with OT-II splenocytes in the presence of OVA(323-339) showed OT-II-specific CD4 activation and expansion in vitro. In characterizing the phenotype of MDSCs for M1 (CCR7) and M2 [mannose receptor (CD206)] markers, MDSCs from untreated tumor bearers were primarily MR(+) with few CCR7(+) cells. Docetaxel treatment polarized MDSCs toward an M1-like phenotype, resulting in 40% of MDSCs expressing CCR7 in vivo and in vitro, and macrophage differentiation markers such as MHC class II, CD11c, and CD86 were upregulated. Interestingly, docetaxel induced cell death selectively in MR(+) MDSCs while sparing the M1-like phenotype. Finally, inhibition of signal transducer and activator of transcription 3 may in part be responsible for the observed results.

CONCLUSIONS

These findings suggest potential clinical benefit for the addition of docetaxel to current immunotherapeutic protocols.