The Multifaceted Roles of STAT3 Signaling in the Progression of Prostate Cancer

Preclinical Characterization of 3β-(N-Acetyl l-cysteine methyl ester)-2aβ,3-dihydrogaliellalactone (GPA512), a Prodrug of a Direct STAT3 Inhibitor for the Treatment of Prostate Cancer

The transcription factor STAT3 is a potential target for the treatment of castration-resistant prostate cancer. Galiellalactone (1), a direct inhibitor of STAT3, prevents the transcription of STAT3 regulated genes. In this study we characterized 6 (GPA512, Johansson , M. ; Sterner , O. Patent WO 2015/132396 A1, 2015 ), a prodrug of 1. In vitro studies showed that 6 is rapidly converted to 1 in plasma and is stable in a buffer solution. The pharmacokinetics of 6 following a single oral dose indicated that the prodrug was rapidly absorbed and converted to 1 with a tmax of 15 min. Oral administration of 6 in mice increased the plasma exposure of the active parent compound 20-fold compared to when 1 was dosed orally. 6 treated mice bearing DU145 xenograft tumors had significantly reduced tumor growth compared to untreated mice. The favorable druglike properties and safety profile of 6 warrant further studies of 6 for the treatment of castration-resistant prostate cancer.

Anti-inflammatory therapies in TRAMP mice: delay in PCa progression

The aim of this study was to characterize the structural and molecular biology as well as evaluate the immediate and late responses of prostatic cancer in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model after treatment with goniothalamin (GTN) and celecoxib. The treated mice received GTN (150 mg/kg, gavage) or celecoxib (10 mg/kg, gavage) from 8 to 12 weeks of age. They were killed at different ages: the immediate-response groups at 12 weeks and the late-response groups at 22 weeks. The ventral prostate was collected for light microscopy, immunohistochemistry, western blotting, TUNEL, and ELISA. Morphological analyses indicated that GTN treatment delayed the progression of prostatic adenocarcinoma, leading to a significant decrease of prostatic lesion frequency in both experimental period responses to this treatment, mainly high-grade prostatic intraepithelial neoplasia and well-differentiated adenocarcinoma. Also, the celecoxib treatment showed a particular decrease in the proliferative processes (PCNA) in both the experimental periods. Despite celecoxib diminishing the COX2 and IGFR1 levels, GTN presented higher action spectrum considering the decrease of a greater molecular number involved in the proliferative and inflammatory processes in prostatic cancer. Goniothalamin attenuated the pro-inflammatory response in TRAMP prostatic microenvironment, delaying prostate cancer (PCa) progression. Celecoxib treatment was efficient in the regulation of COX2 in the TRAMP mice, mainly in the advanced disease grade. Finally, we concluded that inflammatory process control in early grades of PCa was crucial for the downregulation of the signaling pathways involved in the proliferative processes in advanced cancer grades.

EC-70124, a Novel Glycosylated Indolocarbazole Multikinase Inhibitor, Reverts Tumorigenic and Stem Cell Properties in Prostate Cancer by Inhibiting STAT3 and NF-κB

Cancer stem cells (CSC) contribute to disease progression and treatment failure in prostate cancer because of their intrinsic resistance to current therapies. The transcription factors NF-κB and STAT3 are frequently activated in advanced prostate cancer and sustain expansion of prostate CSCs. EC-70124 is a novel chimeric indolocarbazole compound generated by metabolic engineering of the biosynthetic pathways of glycosylated indolocarbazoles, such as staurosporine and rebeccamycin. In vitro kinome analyses revealed that EC-70124 acted as a multikinase inhibitor with potent activity against IKKβ and JAK2. In this study, we show that EC-70124 blocked concomitantly NF-κB and STAT3 in prostate cancer cells and particularly prostate CSCs, which exhibited overactivation of these transcription factors. Phosphorylation of IkB and STAT3 (Tyr705), the immediate targets of IKKβ and JAK2, respectively, was rapidly inhibited in vitro by EC-70124 at concentrations that were well below plasma levels in mice. Furthermore, the drug blocked activation of NF-κB and STAT3 reporters and suppressed transcription of their target genes. Treatment with EC-70124 impaired proliferation and colony formation in vitro and delayed development of prostate tumor xenografts. Notably, EC-70124 had profound effects on the prostate CSC subpopulation both in vitro and in vivo Thus, EC-70124 is a potent inhibitor of the NF-κB and STAT3 signaling pathways and blocked tumor growth and maintenance of prostate CSCs. EC-70124 may provide the basis for developing new therapeutic strategies that combine agents directed to the CSC component and the bulk tumor cell population for treatment of advanced prostate cancer. Mol Cancer Ther; 15(5); 806-18. ©2016 AACR.

Non-Coding RNAs in Castration-Resistant Prostate Cancer: Regulation of Androgen Receptor Signaling and Cancer Metabolism

Hormone-refractory prostate cancer frequently relapses from therapy and inevitably progresses to a bone-metastatic status with no cure. Understanding of the molecular mechanisms conferring resistance to androgen deprivation therapy has the potential to lead to the discovery of novel therapeutic targets for type of prostate cancer with poor prognosis. Progression to castration-resistant prostate cancer (CRPC) is characterized by aberrant androgen receptor (AR) expression and persistent AR signaling activity. Alterations in metabolic activity regulated by oncogenic pathways, such as c-Myc, were found to promote prostate cancer growth during the development of CRPC. Non-coding RNAs represent a diverse family of regulatory transcripts that drive tumorigenesis of prostate cancer and various other cancers by their hyperactivity or diminished function. A number of studies have examined differentially expressed non-coding RNAs in each stage of prostate cancer. Herein, we highlight the emerging impacts of microRNAs and long non-coding RNAs linked to reactivation of the AR signaling axis and reprogramming of the cellular metabolism in prostate cancer. The translational implications of non-coding RNA research for developing new biomarkers and therapeutic strategies for CRPC are also discussed.

Interleukin-6 as a potential molecular target in esophageal squamous cell carcinoma

Knowledge of potential tumor markers may improve chemotherapeutic efficacy. Interleukin-6 (IL-6) expression in local tumor tissues is associated with cancer progression and poor prognosis in variety of cancer types. The aim of the present study was to investigate the role and potential application of IL-6 in determining the prognosis of esophageal carcinoma. KYSE170 and TE13 esophageal cancer cell lines were used to conduct cell- and animal-based experiments investigating biological changes and tumor behavior. Immunohistochemical analysis revealed that 70–80% of cancer cells exhibited positive staining for IL-6, compared with <15% of non-malignant epithelial cells. These immunohistochemical results were consistent with the mRNA expression levels detetced. The IL-6 silencing vector significantly reduced invasion and proliferation of the two cell lines and attenuated tumor growth in xenograft mouse models (P<0.05). The IL-6 silencing vector markedly reduced the presence of Ki-67 (a typical proliferation marker) and microvessel density, indicating that downregulation of IL-6 levels may greatly affect tumor growth and inhibition. The IL-6 silencing vector increased E-cadherin and matrix metalloproteinase (MMP)-9 expression levels in the two esophageal carcinoma cell lines. This vector also regulated the release of IL-6 in cell supernatant and serum in KYSE170- and TE13-tumor-bearing mice. The secretion of vascular endothelial growth factor and cluster of differentiation 31 (a nuclear protein) immunoreactive molecules were also reduced by the IL-6 silencing vector. Therefore, IL-6 may be an important trigger in the progression of angiogenesis and endothelial tube formation within the tumor, and targeting IL-6 may be a promising strategy for the treatment of esophageal cancer.

miR-21 regulates tumor progression through the miR-21-PDCD4-Stat3 pathway in human salivary adenoid cystic carcinoma

miR-21, which is a putative tumor onco-miR and frequently overexpressed microRNA in various tumors, has been linked to tumor progression through targeting of tumor-suppressor genes. In this study, we sought to determine whether miR-21 has any role on tumor progression of salivary adenoid cystic carcinoma (SACC) and the possible mechanisms. We found that the level of miR-21 expression was significantly higher in SACC than that in normal salivary tissues, and it is also higher in tumors with metastasis than that without metastasis. Using an anti-miR-21 inhibitor in an in vitro model, downregulation of miR-21 significantly decreased the capacity of invasion and migration of SACC cells, whereas a pre-miR-21 increased the capacity of invasion and migration of SACC cells. To explore the potential mechanisms by which miR-21 regulate invasion and migration, we identified one direct miR-21 target gene, programmed cell death 4 (PDCD4), which has been implicated in invasion and metastasis. The suppression of miR-21 in metastatic SACC-LM cells significantly increased the report activity of PDCD4 promoter and the expression of PDCD4 protein. This subsequently resulted in downregulation of the p-STAT3 protein. The level of miR-21 expression positively related to the expression of PDCD4 protein and negatively related to the expression of p-STAT3 protein in SACC specimens, respectively, indicating the potential role of the STAT3-miR-21-PDCD4 pathway in these tumors. Dysregulation of miR-21 has an important role in tumor growth and invasion by targeting PDCD4. Therefore, suppression of miR-21 may provide a potential approach for the treatment of advanced SACC patients.

Constitutive activation of STAT3 in breast cancer cells: A review

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in numerous cancer types, including more than 40% of breast cancers. In contrast to tight regulation of STAT3 as a latent transcription factor in normal cells, its signaling in breast cancer oncogenesis is multifaceted. Signaling through the IL-6/JAK/STAT3 pathway initiated by the binding of IL-6 family of cytokines (i.e., IL-6 and IL-11) to their receptors have been implicated in breast cancer development. Receptors with intrinsic kinase activity such as EGFR and VEGFR directly or indirectly induce STAT3 activation in various breast cancer types. Aberrant STAT3 signaling promotes breast tumor progression through deregulation of the expression of downstream target genes which control proliferation (Bcl-2, Bcl-xL, Survivin, Cyclin D1, c-Myc and Mcl-1), angiogenesis (Hif1α and VEGF) and epithelial-mesenchymal transition (Vimentin, TWIST, MMP-9 and MMP-7). These multiple modes of STAT3 regulation therefore make it a central linking point for a multitude of signaling processes. Extensive efforts to target STAT3 activation in breast cancer had no remarkable success in the past because the highly interconnected nature of STAT3 signaling introduces lack of selectivity in pathway identification for STAT3 targeted molecular therapies or because its role in tumorigenesis may not be as critical as it was thought. This review provides a full spectrum of STAT3's involvement in breast cancer by consolidating the knowledge about its role in breast cancer development at multiple levels: its differential regulation by different receptor signaling pathways, its downstream target genes, and modification of its transcriptional activity by its coregulatory transcription factors.

Role of STAT3 pathway in genitourinary tumors

The STAT3 is often dysregulated in genitourinary tumors. In prostate cancer, STAT3 activation correlates with Gleason score and pathological stage and modulates cancer stem cells and epithelial-mesenchymal transition. In addition, STAT3 promotes the progression from carcinoma in situ to invasive bladder cancer and modulates renal cell carcinoma angiogenesis by increasing the expression of HIF1α and VEGF. STAT3 is also involved in the response to tyrosine kinase inhibitors sunitinib and axitinib, in patients with metastatic renal cell carcinoma, and to second-generation androgen receptor inhibitor enzalutamide in patients with advanced prostate cancer. In this review, we describe the role of STAT3 in genitourinary tumors, thus describing its potential for future therapeutic strategies.

Metformin represses androgen-dependent and androgen-independent prostate cancers by targeting androgen receptor

BACKGROUND

Metformin has been reported to inhibit the growth of different types of cancers, including prostate cancer. We were interested to understand if the effect of metformin on prostate cancer is AR-dependent and, if so, whether metformin could act synergistically with the other anti-AR agents to serve as a therapeutic regimen with high efficacy and low toxicity.

METHODS

Cell viabilities and apoptosis were determined by MTT assay and annexin V-FITC staining, respectively, when the two human prostate cancer cell lines, the androgen-dependent LNCaP and the androgen-independent 22RV1 were treated with metformin alone or in combination with bicalutamide. Quantitative RT-PCR and western blotting assays were conducted to examine metformin effects on AR mRNA and protein levels, respectively. Chromatin immunoprecipitation (ChIP) assays were conducted to confirm the recruitment of AR to the ARE(s) located on the promoter region of the AR target gene PSA.

RESULTS

Metformin treatment reduced cell viability and enhanced apoptosis for both cell lines and additive effects were observed when LNCaP cells were treated with combined metformin and bicalutamide. Metformin down-regulated full-length AR protein in LNCaP cells. Both full-length and the truncated AR (AR-v7) were down-regulated by metformin in CWR22Rv1 cells. In both LNCaP and CWR22Rv1 cells, metformin repressed AR signaling pathway not by affecting AR protein degradation/stability, but rather through down-regulating the levels of AR mRNAs.

CONCLUSIONS

Metformin represses prostate cancer cell viability and enhances apoptosis by targeting the AR signaling pathway. Combinations of metformin and other anti-AR agents pose a potentially promising therapeutic approach for treatment of prostate cancers, especially the castrate-resistant prostate cancer, with high efficacy and low toxicity.

The STAT3 Inhibitor Galiellalactone Effectively Reduces Tumor Growth and Metastatic Spread in an Orthotopic Xenograft Mouse Model of Prostate Cancer

Signal transducer and activator of transcription 3 (STAT3) is known to be involved in the progression of prostate cancer (PCa) and is a key factor in drug resistance and tumor immunoescape. As a result, it represents a promising target for PCa therapy. We studied the effects of the STAT3 inhibitor galiellalactone (GL) on tumor growth and metastatic spread in vitro and in vivo. The effect of GL on cell viability, apoptosis, and invasion was studied in vitro using androgen-independent DU145 and DU145-Luc cell lines. For in vivo studies, mice were injected orthotopically with DU145-Luc cells and treated with daily intraperitoneal injections of GL for 6 wk. GL significantly reduced the growth of the primary tumor and the metastatic spread of PCa cells to regional and distal lymph nodes in vivo. Treatment with GL also resulted in decreased cell proliferation and increased apoptosis compared with controls. In vitro, GL reduces the viability and invasive abilities of DU145-Luc cells and induces apoptosis. Our results showed that tumor growth and early metastatic dissemination of PCa can be significantly reduced by GL, indicating its potential use as a therapeutic compound in advanced metastatic PCa.

PATIENT SUMMARY

In this study, we tested the STAT3 inhibitor galiellalactone (GL) in an animal model of PCa. We found that mice treated with GL had smaller primary tumors and decreased lymph node metastases compared with mice treated with vehicle. GL has potential for treating advanced metastatic PCa.

Investigational therapies targeting signal transducer and activator of transcription 3 for the treatment of cancer

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3) mediates the expression of a variety of genes in response to cell stimuli and thus plays a key role in several cellular processes such as cell growth and apoptosis. Deregulation of the STAT3 activity has been shown in many malignancies, including breast, head and neck, prostate, pancreas, ovarian and brain cancers and melanoma. Thus, STAT3 may represent an ideal target for cancer therapy.

AREAS COVERED

The authors review recent data on the role of STAT3 in tumor initiation and progression, as well as the ongoing clinical trials in cancer patients. The content includes information derived from trial databases, regulatory authorities and scientific literature.

EXPERT OPINION

Targeting STAT3 activation leads to the inhibition of tumor growth and metastasis both in vitro and in vivo without affecting normal cells; this suggests that STAT3 could be a valid molecular target for cancer therapy. Extensive clinical research is trying to find anti-STAT3 agents with high single-agent activity. The identification and development of novel drugs that can target deregulated STAT3 activation effectively is both a scientific and clinical challenge that needs to be addressed in the near future.

Beyond immune checkpoint blockade: new approaches to targeting host-tumor interactions in prostate cancer: report from the 2014 Coffey-Holden prostate cancer academy meeting

INTRODUCTION

The 2014 Coffey-Holden Prostate Cancer Academy Meeting, held in La Jolla, CA from June 26 to 29, 2014, was themed: "Beyond Immune Checkpoint Blockade: New Approaches to Targeting Host-Tumor Interactions in Prostate Cancer."

METHODS

Sponsored by the Prostate Cancer Foundation (PCF), this annual, invitation-only meeting is structured as an action-tank, and brought together 72 investigators with diverse academic backgrounds to discuss the most relevant topics in the fields of prostate cancer immunotherapy and the tumor microenvironment.

RESULTS

The questions addressed at the meeting included: mechanisms underlying the successes and failures of prostate cancer immunotherapies, how to trigger an effective immune response against prostate cancer, the tumor microenvironment and its role in therapy resistance and tumor metastasis, clinically relevant prostate cancer mouse models, how host-tumor interactions affect current therapies and tumor phenotypes, application of principles of precision medicine to prostate cancer immunotherapy, optimizing immunotherapy clinical trial design, and complex multi-system interactions that affect prostate cancer and immune responses including the effects of obesity and the potential role of the host microbiome.

DISCUSSION

This article highlights the most significant recent progress and unmet needs that were discussed at the meeting toward the goal of speeding the development of optimal immunotherapies for the treatment of prostate cancer.

Dual high expression of STAT3 and cyclinD1 is associated with poor prognosis after curative resection of esophageal squamous cell carcinoma

BACKGROUND

Signal transducer of activator of transcription 3 (STAT3) and cyclinD1 are overexpressed in various human cancers, and their overexpression positively correlates to tumor progression and poor prognosis. However, the clinical significance of dual high expression of these two proteins in esophageal squamous cell carcinoma (ESCC) has yet to be determined.

METHODS

The expression of STAT3 and cyclinD1 was analyzed in tissue microarrays containing tumor and adjacent tissue samples from 82 patients who had undergone curative resection for histologically proven ESCC. Kaplan-Meier plots and Cox proportional hazards regression model were used to analyze the prognostic value of STAT3 and cyclinD1 expression.

RESULTS

We discovered that expressions of STAT3 and cyclinD1 in cancer tissues were significantly higher than that in adjacent tissues. High expression of STAT3 and cyclinD1 was associated with malignant behaviors. Moreover, the expression of STAT3 was positively associated with the expression of cyclinD1. High STAT3 or cyclinD1 expression alone was associated with lower overall survival (OS) rates. Furthermore, dual high expression of STAT3 and cyclinD1 expression predict even worse survival outcome in both univariate and multivariate analysis.

CONCLUSION

STAT3 and cyclinD1 correlate with more aggressive tumor behavior in ESCC. When STAT3 and cyclinD1 are considered together, they serve as effective prognostic markers in patients with surgically resected ESCC.

A behavioral study of healthy and cancer genes by modeling electrical network

In recent years, gene network modeling is gaining popularity in genomics to monitor the activity profile of genes. More specifically, the objective of the network modeling concept is to study the genetic behavior associated with disease. Previous researchers have designed network model at nucleotide level which produces more complexity for designing circuits mostly in case of gene expression studies. Whereas the authors have designed the present network model, based on amino acid level which is simpler as well as more appropriate for prediction of the genetic abnormality. In the present concept, SISO continuous and discrete system models of genes are realized using Foster network. The model is designed based on hydropathy index value of amino acids to study the biological system behavior. The time and phase response in continuous (s) domain and pole-zero distribution in discrete (z) domain are used as measurement metric in the present study. The simulated responses of the system show genetic instability for cancer genes which truly reflects the medical reports. The proposed modeling concept can be used, to accurately identify or separate out the diseased genes from healthy genes.