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

Synthesis and Biological Evaluation of Methoxypolyethylene-Glycol-Substituted Abiraterone Derivatives as Potential Antiprostate Cancer Agents

Globally, prostate cancer is the most commonly diagnosed tumor and a cause of death in older men. Abiraterone, an orally administered irreversible CYP17 inhibitor, is employed to treat prostate cancer. However, abiraterone has several clinical limitations, such as poor water solubility, low dissolution rate, low bioavailability, and toxic side effects in the liver and kidney. Therefore, there is a need to identify high-efficiency and low-toxicity water-soluble abiraterone derivatives. In this work, we aimed to design and synthesize a series of abiraterone derivatives by methoxypoly(ethylene glycol) (mPEG) modification. Their antitumor activities and toxicology were analyzed in vitro and in vivo. The most potent compound, 2e, retained the principle of action on the CYP17 enzyme target and significantly improved the abiraterone water solubility, cell permeability, and blood safety. No significant abnormalities were observed in toxicology. mPEG-modification significantly improved abiraterone's antitumor activity and efficiency while reducing the associated toxic effects. The finding will provide a theoretical basis for future clinical application of mPEG-modified abiraterone.

Natural STAT3 Inhibitors for Cancer Treatment: A Comprehensive Literature Review

Cancer is one of the leading causes of mortality and morbidity worldwide, affecting millions of people physically and financially every year. Over time, many anticancer treatments have been proposed and studied, including synthetic compound consumption, surgical procedures, or grueling chemotherapy. Although these treatments have improved the daily life quality of patients and increased their survival rate and life expectancy, they have also shown significant drawbacks, including staggering costs, multiple side effects, and difficulty in compliance and adherence to treatment. Therefore, natural compounds have been considered a possible key to overcoming these problems in recent years, and thorough research has been done to assess their effectiveness. In these studies, scientists have discovered a meaningful interaction between several natural materials and signal transducer and activator of transcription 3 molecules. STAT3 is a transcriptional protein that is vital for cell growth and survival. Mechanistic studies have established that activated STAT3 can increase cancer cell proliferation and invasion while reducing anticancer immunity. Thus, inhibiting STAT3 signaling by natural compounds has become one of the favorite research topics and an attractive target for developing novel cancer treatments. In the present article, we intend to comprehensively review the latest knowledge about the effects of various organic compounds on inhibiting the STAT3 signaling pathway to cure different cancer diseases.

Circulating myeloid-derived suppressor cells and survival in prostate cancer patients: systematic review and meta-analysis

BACKGROUND

Immunotherapy has not achieved improvement of survival in prostate cancer patients. Myeloid-derived suppressor cells (MDSCs) in tumor microenvironment can hamper its efficacy. Some preclinical studies explored the role of MDSCs in prostate cancer development. We aimed to verify the availability of studies exploring the prognostic effect of circulating MDSCs in prostate cancer patients.

METHODS

We systematically selected studies for a meta-analysis, which compares survival between prostate cancer patients with high vs low circulating MDSC levels. We extracted or calculated hazard ratios (HRs) and relative 95% confidence intervals (CIs) in terms of overall survival (OS) from selected studies. We calculated the pooled HR and relative 95% CIs and estimated publication bias.

RESULTS

Among 133 studies retrieved from search on Pubmed, 5 eligible studies (236 prostate cancer patients) met inclusion criteria. High circulating MDSC levels are associated with a worse OS (HR = 2.19; 95%CI = 1.51-3.17). Heterogeneity was not significant (I2 = 0%; p = 0.64). Publication bias was also not significant (Egger's test, p = 0.09).

CONCLUSIONS

High levels of circulating MDSCs induce a worse OS in prostate cancer patients than in those with low levels. This finding supports the importance of MDSC detection and targeting also in prostate cancer patients.

STAT3 signaling in prostate cancer progression and therapy resistance: An oncogenic pathway with diverse functions

The categorization of cancers demonstrates that prostate cancer is the most common malignancy in men and it causes high death annually. Prostate cancer patients are diagnosed mainly via biomarkers such as PSA test and patients show poor prognosis. Prostate cancer cells rapidly diffuse into different parts of body and their metastasis is also a reason for death. Current therapies for prostate cancer patients include chemotherapy, surgery and radiotherapy as well as targeted therapy. The progression of prostate cancer cells is regulated by different factors that STAT3 signaling is among them. Growth factors and cytokines such as IL-6 can induce STAT3 signaling and it shows carcinogenic impact. Activation of STAT3 signaling occurs in prostate cancer and it promotes malignant behavior of tumor cells. Induction of STAT3 signaling increases glycolysis and proliferation of prostate cancer cells and prevents apoptosis. Furthermore, STAT3 signaling induces EMT mechanism in increasing cancer metastasis. Activation of STAT3 signaling stimulates drug resistance and the limitation of current works is lack of experiment related to role of STAT3 signaling in radio-resistance in prostate tumor. Calcitriol, capsazepine and β-elemonic are among the compounds capable of targeting STAT3 signaling and its inhibition in prostate cancer therapy. In addition to natural products, small molecules targeting STAT3 signaling have been developed in prostate cancer therapy.

The STAT3 inhibitor GPB730 enhances the sensitivity to enzalutamide in prostate cancer cells

Enzalutamide is a second-generation anti-androgen which has shown increased survival in patients with metastatic prostate cancer. However, some patients do not respond to this therapy or will develop resistance to treatment over time. Signal Transducer and Activator of Transcription 3 (STAT3) is known to be involved in castration-resistant prostate cancer and to interact with androgen receptor (AR)-signaling. This study aims to investigate the combination enzalutamide and the small molecule STAT3 inhibitor GPB730 for enhanced therapeutic effect in advanced prostate cancer in vitro. The prostate cancer cell lines LNCaP (androgen dependent) and C4-2 (androgen insensitive) were used. The effect of enzalutamide and GPB730, alone and in combination, was investigated on viability and IC₅₀ values calculated. Enzalutamide and GPB730 treated LNCaP and C4-2 cells were subjected to western blot and QPCR analyses in order to investigate the expression of AR, STAT3 and down-stream targets. C4-2 were less sensitive to growth inhibition by enzalutamide than LNCaP cells. GPB730 enhanced the growth inhibitory effect of enzalutamide in LNCaP and C4-2 cells. The addition of GPB730 to enzalutamide decreased the IC₅₀ values for enzalutamide by 3.3-fold for LNCaP and by 12-fold for C4-2. In C4-2 cells, GPB730 alone decreased PSA expression and enhanced the enzalutamide induced decrease in NKX3.1 expression. GPB730 and enzalutamide in combination enhanced inhibition of c-myc and survivin expression. This study suggests that enzalutamide may be combined with the STAT3 inhibitor GPB730 in order to enhance the efficacy of enzalutamide, offering a new therapeutic approach in advanced prostate cancer.

From Therapy Resistance to Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second most common malignancy among men worldwide. Although early-stage disease is curable, advanced stage PCa is mostly incurable and eventually becomes resistant to standard therapeutic options. Different genetic and epigenetic alterations are associated with the development of therapy resistant PCa, with specific players being particularly involved in this process. Therefore, identification and targeting of these molecules with selective inhibitors might result in anti-tumoral effects. Herein, we describe the mechanisms underlying therapy resistance in PCa, focusing on the most relevant molecules, aiming to enlighten the current state of targeted therapies in PCa. We suggest that selective drug targeting, either alone or in combination with standard treatment options, might improve therapeutic sensitivity of resistant PCa. Moreover, an individualized analysis of tumor biology in each PCa patient might improve treatment selection and therapeutic response, enabling better disease management.

Association of STAT3, PTPRT, TNK2-AS1, LINC-ROR Genes Expression Level with Prostate Cancer and Benign Prostatic Hyperplasia

Background: Prostate cancer (PCa) and benign prostate hyperplasia (BPH) are highly prevalent heterogeneous disorders among men. Since angiogenesis is the key step in cancer progression, the deregulation of genes involved in this process may play a role in cancer development. Objectives: We evaluated the expression level of 4 angiogenesis-related genes including signal transducer and activator of transcription 3 (STAT3), protein tyrosine phosphatase receptor type T (PTPRT), TNK2 antisense RNA 1 (TNK2-AS1), and long intergenic non-protein coding rna-regulator of reprogramming (LINC-ROR) in patients with PCa and BPH. Methods: The expression level of STAT3, PTPRT, TNK2-AS1, and LINC-ROR genes in tumoral and adjacent non-cancerous tissue (ANCT) samples of 50 PCa patients and tissue samples from 50 BPH patients were evaluated, using the real-time PCR method. The statistical analysis was performed to evaluate the association between genes expression and clinicopathological characteristics of patients with PCa. Results: The expression level of STAT3 and LINC-ROR was upregulated in tumoral tissues compared to ANCTs (P < 0.0001 for both). Only the expression level of STAT3 in PCa was higher than in BPH tissues (P = 0.001). The elevated expression of STAT3 was associated with the higher grade group of the tumor (P = 0.03). Also, the high expression level of PTPRT and LINC-ROR genes was associated with a higher stage of cancer in patients with PCa (P = 0.002, P = 0.0001 respectively). The STAT3 gene transcript level had an excellent diagnostic power for discrimination between tumoral tissue and the ANCTs with an area under the curve (AUC) of 0.93. Conclusions: The higher expression of STAT3 and LINC-ROR suggested a role in the pathogenesis of PCa in higher stages. Also, STAT3 expression level could be suggested as a potential biomarker for PCa in combination with PSA level.

Myeloid-Derived Suppressor Cells in Prostate Cancer: Present Knowledge and Future Perspectives

Several lines of research are being investigated to better understand mechanisms implicated in response or resistance to immune checkpoint blockade in prostate cancer (PCa). Myeloid-derived suppressor cells (MDSCs) have emerged as a major mediator of immunosuppression in the tumor microenvironment that promotes progression of various tumor types. The main mechanisms underlying MDSC-induced immunosuppression are currently being explored and strategies to enhance anti-tumor immune response via MDSC targeting are being tested. However, the role of MDSCs in PCa remains elusive. In this review, we aim to summarize and present the state-of-the-art knowledge on current methodologies to phenotypically and metabolically characterize MDSCs in PCa. We describe how these characteristics may be linked with MDSC function and may influence the clinical outcomes of patients with PCa. Finally, we briefly discuss emerging strategies being employed to therapeutically target MDSCs and potentiate the long-overdue improvement in the efficacy of immunotherapy in patients with PCa.

Minimally modified low-density lipoprotein upregulates mouse mesenteric arterial 5-HT1B receptor in vivo via activation of the JAK2/STAT3 pathway

OBJECTIVES

To explore whether minimally modified low-density lipoprotein (mmLDL) upregulates mesenteric arterial 5-hydroxytryptamine 1B (5-HT_1B) receptor expression by activating the JAK2/STAT3 signaling pathway.

METHODS

Mice were randomly divided into the following groups: the normal saline (NS), LDL, mmLDL, mmLDL+galiellactone (GL, a JAK2/STAT3 pathway inhibitor), and mmLDL+DMSO groups. The dose-response curve of mesenteric arterial ring constriction after administration of 5-carboxamidotryptamine (5-CT), an agonist of 5-HT_1B, was recorded with a microvascular tensiometer. JAK2, p-JAK2, STAT3, p-STAT3, and 5-HT_1B receptor protein expression levels were determined by Western blotting. 5-HT_1B receptor mRNA levels were measured by RT-PCR. 5-HT_1B receptor protein expression was determined by immunofluorescence.

RESULTS

Injection of mmLDL into the tail vein significantly increased the contractile dose-response curve after 5-CT stimulation, as the E_max was 82.15 ± 6.15% in the NS group and 171.88 ± 5.78% in the mmLDL group (P < 0.01); significantly elevated 5-HT_1B receptor mRNA and protein expression levels; and significantly increased p-JAK2 and p-STAT3 protein expression levels. After intraperitoneal injection of GL, the vasoconstrictive response was significantly reduced compared with that in the mmLDL group, as the E_max was decreased to 97.14 ± 1.20% (P < 0.01); 5-HT_1B receptor mRNA and protein expression levels were significantly reduced; STAT3 phosphorylation and p-JAK2 and p-STAT3 protein expression were not significantly changed; and 5-HT_1B receptor expression was altered via inhibition of p-STAT3 binding to DNA, which suppressed transcription.

CONCLUSIONS

mmLDL can upregulate 5-HT_1B receptor expression in mouse mesenteric arteries by activating the JAK2/STAT3 signaling pathway.

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.

STAT3 transcription factor as target for anti-cancer therapy

STATs constitute a large family of transcription activators and transducers of signals that have an important role in many cell functions as regulation of proliferation and differentiation of the cell also regulation of apoptosis and angiogenesis. STAT3 as a member of that family, recently was discovered to have a vital role in progression of different types of cancers. The activation of STAT3 was observed to regulate multiple gene functions during cancer-like cell proliferation, differentiation, apoptosis, metastasis, inflammation, immunity, cell survival, and angiogenesis. The inhibition of STAT3 activation has been an important target for cancer therapy. Inhibitors of STAT3 have been used for a long time for treatment of many types of cancers like leukemia, melanoma, colon, and renal cancer. In this review article, we summarize and discuss different drugs inhibiting the action of STAT3 and used in treatment of different types of cancer.

STAT3 inhibition with galiellalactone effectively targets the prostate cancer stem-like cell population

Cancer stem cells (CSCs) are a small subpopulation of quiescent cells with the potential to differentiate into tumor cells. CSCs are involved in tumor initiation and progression and contribute to treatment failure through their intrinsic resistance to chemo- or radiotherapy, thus representing a substantial concern for cancer treatment. Prostate CSCs’ activity has been shown to be regulated by the transcription factor Signal Transducer and Activator of Transcription 3 (STAT3). Here we investigated the effect of galiellalactone (GL), a direct STAT3 inhibitor, on CSCs derived from prostate cancer patients, on docetaxel-resistant spheres with stem cell characteristics, on CSCs obtained from the DU145 cell line in vitro and on DU145 tumors in vivo. We found that GL significantly reduced the viability of docetaxel-resistant and patient-derived spheres. Moreover, CSCs isolated from DU145 cells were sensitive to low concentrations of GL, and the treatment with GL suppressed their viability and their ability to form colonies and spheres. STAT3 inhibition down regulated transcriptional targets of STAT3 in these cells, indicating STAT3 activity in CSCs. Our results indicate that GL can target the prostate stem cell niche in patient-derived cells, in docetaxel-resistant spheres and in an in vitro model. We conclude that GL represents a promising therapeutic approach for prostate cancer patients, as it reduces the viability of prostate cancer-therapy-resistant cells in both CSCs and non-CSC populations.

Knockdown of GSG2 inhibits prostate cancer progression in vitro and in vivo

Prostate cancer (PCa) is the second leading cause of cancer related death among men worldwide. The present study aimed to investigate the role of germ cell-specific gene 2 protein (GSG2), also termed histone H3 phosphorylated by GSG2 at threonine 3, in the development and progression of PCa. GSG2 expression levels in PCa tissues and para carcinoma tissues was detected by immunohistochemistry. The GSG2 knockdown cell model was constructed by lentivirus infec tion, and the knockdown efficiency was verified by qPCR and WB. In addition, the effects of shGSG2 on cell proliferation, colony formation and apoptosis were evaluated by Celigo cell counting assay, Giemsa staining and flow cytometry, respec tively. Tumor development in nude mice was also detected. GSG2 expression was upregulated in PCa tissues and human PCa cell lines PC 3 and DU 145. High expression of GSG2 in tumor samples was associated with progressed tumors. GSG2 knockdown suppressed cell proliferation and colony forma tion, but promoted apoptosis, which was also verified in vivo. The results of the present study revealed that GSG2 upregula tion was associated with PCa progression; GSG2 knockdown inhibited cell proliferation and colony formation and induced apoptosis, and may therefore serve as a potential therapeutic target for PCa therapy.

Signal Transducer and Activator of Transcription Protein 3 (STAT3): An Update on its Direct Inhibitors as Promising Anticancer Agents

BACKGROUND

Since Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor which plays an important role in multiple aspects of cancer, including progression and migration, and it is constitutively activated in various human tumors, STAT3 inhibition has emerged as a validated strategy for the treatment of several malignancies. The aim of this review is to provide an update on the identification of new promising direct inhibitors targeting STAT3 domains, as potential anticancer agents.

METHODS

A thorough literature search focused on recently reported STAT3 direct inhibitors was undertaken. We considered the relevant developments regarding the STAT3 domains, which have been identified as potential drug targets.

RESULTS

In detail, 135 peer-reviewed papers and 7 patents were cited; the inhibitors we took into account targeted the DNA binding domain (compounds were grouped into natural derivatives, small molecules, peptides, aptamers and oligonucleotides), the SH2 binding domain (natural, semi-synthetic and synthetic compounds) and specific residues, like cysteines (natural, semi-synthetic, synthetic compounds and dual inhibitors) and tyrosine 705.

CONCLUSION

The huge number of direct STAT3 inhibitors recently identified demonstrates a strong interest in the investigation of this target, although it represents a challenging task considering that no drug targeting this enzyme is currently available for anticancer therapy. Notably, many studies on the available inhibitors evidenced that some of them possess a dual mechanism of action.

The STAT3 inhibitor galiellalactone inhibits the generation of MDSC-like monocytes by prostate cancer cells and decreases immunosuppressive and tumorigenic factors

BACKGROUND

The transcription factor signal transducer and activator of transcription 3 (STAT3) is implicated in cancer drug resistance, metastasis, and immunosuppression and has been identified as a promising therapeutic target for new anticancer drugs. Myeloid-derived suppressor cells (MDSCs) play a major role in the suppression of antitumor immunity and STAT3 is involved in the accumulation, generation, and function of MDSCs. Thus, targeting STAT3 holds the potential of reversing immunosuppression in cancer. This study aims to investigate the effect of the small molecule STAT3 inhibitor galiellalactone on prostate cancer cell- induced generation of MDSCs from monocytes and the effect on immunosuppressive factors and inflammatory cytokines.

METHODS

Primary human monocytes were cocultured with prostate cancer cells (DU145, PC3, and LNCaP-IL6) or with conditioned medium (CM) from prostate cancer cells in the presence or absence of the STAT3 inhibitor galiellalactone. Monocytes were analyzed by flow cytometry for an MDSC-like phenotype (CD14⁺ HLA-DR^-/lo ). The secretion and gene expression of immunosuppressive factors and inflammatory cytokines from prostate cancer cells and monocytes were investigated.

RESULTS

Galiellalactone blocked the prostate cancer cell-induced generation of MDSC-like monocytes with an immunosuppressive phenotype ex vivo. Monocytes cultured with CM from prostate cancer cells showed increased expression of phosphorylated STAT3. Prostate cancer cells increased the expression of interleukin1β (IL1β), IL10, and IL6 in monocytes which was inhibited by galiellalactone. In addition, galiellalactone decreased indoleamine 2,3-dioxygenase gene expression in monocytes. Galiellalactone reduced the levels of IL8 and granulocyte macrophage-colony stimulating factor in prostate cancer cells per se.

CONCLUSION

The STAT3 inhibitor galiellalactone may prevent the prostate cancer cell-induced generation of MDSCs and reverse the immunosuppressive mechanisms caused by the interplay between prostate cancer cells and MDSCs. This is a potential new immunotherapeutic approach for the treatment of prostate cancer.

The Tumor Immune Contexture of Prostate Cancer

One in seven men in North America is expected to be diagnosed with prostate cancer (PCa) during their lifetime (1, 2). While a wide range of treatment options including surgery, radiation, androgen deprivation and chemotherapy have been in practice for the last few decades, there are limited treatment options for metastatic and treatment resistant disease. Immunotherapy targeting T-cell associated immune checkpoints such as CTLA-4, PD-L1, and PD-1 have not yet proven to be efficacious in PCa. Tumor mutational burden, mutations in DNA damage repair genes, immune cell composition and density in combination with their spatial organization, and expression of immune checkpoint proteins are some of the factors influencing the success of immune checkpoint inhibitor therapies. The paucity of these features in PCa potentially makes them unresponsive to contemporary immune checkpoint inhibition. In this review, we highlight the hallmark events in the PCa tumor immune microenvironment and provide insights into the current state of knowledge in this field with a focus on the role of tumor cell intrinsic events that potentially regulate immune related events and determine therapeutic outcomes. We surmise that the cumulative impact of factors such as the pre-treatment immune status, PTEN expression, DNA damage repair gene mutations, and the effects of conventionally used treatments on the anti-tumor immune response should be considered in immunotherapy trial design in PCa.

Enantioselective syntheses and application of 4-epi-galiellalactone and the corresponding activity-based probe: from strained bicycles to strained tricycles

The [6,5,5] tricyclic fungal metabolite galiellalactone is a Michael acceptor that has been demonstrated to be a covalent inhibitor for Signal Transducer and Activator of Transcription 3 (STAT3). Recognizing the ring strain associated with the skeleton of this natural product, we utilized 1R-5S-bicyclo[3.1.0]hexan-2-one as the starting material and developed two novel approaches to accomplish the enantioselective total synthesis of the C4 epimer of galiellalactone in 5 and 7 steps, respectively, which capitalized on an efficient radical cyclization/fragmentation cascade reaction. Furthermore, an activity-based probe of 4-epi-galiellalactone with a terminal alkyne tag was successfully prepared to enable the experiments of activity-based protein profiling (ABPP). Through western blot and proteomic analysis, we not only confirmed the known target STAT3, but also identified a new target protein ataxin-7, which formed a covalent bond with the probe in intact cells via the Cys-129 residue.

DANCR Promotes Metastasis and Proliferation in Bladder Cancer Cells by Enhancing IL-11-STAT3 Signaling and CCND1 Expression

The prognosis for patients with bladder cancer (BCa) with lymph node (LN) metastasis is poor, and it is not improved by current treatments. Long noncoding RNAs (lncRNAs) are involved in the pathology of various tumors, including BCa. However, the role of Differentiation antagonizing non-protein coding RNA (DANCR) in BCa LN metastasis remains unclear. In this study, we discover that DANCR was significantly upregulated in BCa tissues and cases with LN metastasis. DANCR expression was positively correlated with LN metastasis status, tumor stage, histological grade, and poor patient prognosis. Functional assays demonstrated that DANCR promoted BCa cell migration, invasion, and proliferation in vitro and enhanced tumor LN metastasis and growth in vivo. Mechanistic investigations revealed that DANCR activated IL-11-STAT3 signaling and increased cyclin D1 and PLAU expression via guiding leucine-rich pentatricopeptide repeat containing (LRPPRC) to stabilize mRNA. Moreover, oncogenesis facilitated by DANCR was attenuated by anti-IL-11 antibody or a STAT3 inhibitor (BP-1-102). In conclusion, our findings indicate that DANCR induces BCa LN metastasis and proliferation via an LRPPRC-mediated mRNA stabilization mechanism. DANCR may serve as a multi-potency target for clinical intervention in LN-metastatic BCa.

Dual androgen receptor (AR) and STAT3 inhibition by a compound targeting the AR amino-terminal domain

Prostate cancer (PCa) often recurs as incurable castration-resistant prostate cancer (CRPC) after the failure of androgen deprivation therapy. CRPC development relies on androgen receptor (AR) signaling. The IL6/STAT3 pathway is also a key driver of CRPC. The crosstalk between IL6/STAT3 and the AR pathways provides opportunities to explore next-generation agents to treat PCa. Through screening of around 600 natural compounds in our newly established prostate tumorigenesis model, potential STAT3 signaling inhibitors were found and additionally examined for effects on AR signaling. The small molecular compound 154 exhibited dual effects on IL6/STAT3 and AR pathways. We show here that compound 154 inhibits AR and STAT3 transcriptional activity, reduces the expression of phosphorylation of STAT3 (Y705) and downregulates the mRNA levels of AR target genes. Compound 154 also inhibits protein expression of AR and AR splice variants (ARv567es and AR-V7) without altering AR mRNA levels. Compound 154 binds to AR directly, but not to STAT3 and is identified as an antagonist of the AR amino-terminal domain (NTD) by disrupting protein-protein interactions between STAT3 and the AR NTD. Moreover, compound 154 does not reduce AR nuclear translocation. Compound 154 possesses the potential to become a leading compound in novel therapies against CRPC.

The STAT3 Inhibitor Galiellalactone Reduces IL6-Mediated AR Activity in Benign and Malignant Prostate Models

IL6/STAT3 signaling is associated with endocrine therapy resistance in prostate cancer, but therapies targeting this pathway in prostate cancer were unsuccessful in clinical trials so far. The mechanistic explanation for this phenomenon is currently unclear; however, IL6 has pleiotropic effects on a number of signaling pathways, including the androgen receptor (AR). Therefore, we investigated IL6-mediated AR activation in prostate cancer cell lines and ex vivo primary prostate tissue cultures in order to gain a better understanding on how to inhibit this process for future clinical trials. IL6 significantly increased androgen-dependent AR activity in LNCaP cells but importantly did not influence AR activity at castrate androgen levels. To identify the underlying mechanism, we investigated several signaling pathways but only found IL6-dependent changes in STAT3 signaling. Biochemical inhibition of STAT3 with the small-molecule inhibitor galiellalactone significantly reduced AR activity in several prostate and breast cancer cell lines. We confirmed the efficacy of galiellalactone in primary tissue slice cultures from radical prostatectomy samples. Galiellalactone significantly reduced the expression of the AR target genes PSA (P < 0.001), TMPRSS2 (P < 0.001), and FKBP5 (P = 0.003) in benign tissue cultures (n = 24). However, a high heterogeneity in the response of the malignant samples was discovered, and only a subset of tissue samples (4 out of 10) had decreased PSA expression upon galiellalactone treatment. Taken together, this finding demonstrates that targeting the IL6/STAT3 pathway with galiellalactone is a viable option to decrease AR activity in prostate tissue that may be applied in a personalized medicine approach.

Targeting Transcription Factors for Cancer Treatment

Transcription factors are involved in a large number of human diseases such as cancers for which they account for about 20% of all oncogenes identified so far. For long time, with the exception of ligand-inducible nuclear receptors, transcription factors were considered as “undruggable” targets. Advances knowledge of these transcription factors, in terms of structure, function (expression, degradation, interaction with co-factors and other proteins) and the dynamics of their mode of binding to DNA has changed this postulate and paved the way for new therapies targeted against transcription factors. Here, we discuss various ways to target transcription factors in cancer models: by modulating their expression or degradation, by blocking protein/protein interactions, by targeting the transcription factor itself to prevent its DNA binding either through a binding pocket or at the DNA-interacting site, some of these inhibitors being currently used or evaluated for cancer treatment. Such different targeting of transcription factors by small molecules is facilitated by modern chemistry developing a wide variety of original molecules designed to specifically abort transcription factor and by an increased knowledge of their pathological implication through the use of new technologies in order to make it possible to improve therapeutic control of transcription factor oncogenic functions.

Interleukin-30/IL27p28 Shapes Prostate Cancer Stem-like Cell Behavior and Is Critical for Tumor Onset and Metastasization

Prostate cancer stem-like cells (PCSLC) are believed to be responsible for prostate cancer onset and metastasis. Autocrine and microenvironmental signals dictate PCSLC behavior and patient outcome. In prostate cancer patients, IL30/IL27p28 has been linked with tumor progression, but the mechanisms underlying this link remain mostly elusive. Here, we asked whether IL30 may favor prostate cancer progression by conditioning PCSLCs and assessed the value of blocking IL30 to suppress tumor growth. IL30 was produced by PCSLCs in human and murine prostatic intraepithelial neoplasia and displayed significant autocrine and paracrine effects. PCSLC-derived IL30 supported PCSLC viability, self-renewal and tumorigenicity, expression of inflammatory mediators and growth factors, tumor immune evasion, and regulated chemokine and chemokine receptor genes, primarily via STAT1/STAT3 signaling. IL30 overproduction by PCSLCs promoted tumor onset and development associated with increased proliferation, vascularization, and myeloid cell recruitment. Furthermore, it promoted PCSLC dissemination to lymph nodes and bone marrow by upregulating the CXCR5/CXCL13 axis, and drove metastasis to lungs through the CXCR4/CXCL12 axis. These mechanisms were drastically hindered by IL30 knockdown or knockout in PCSLCs. Collectively, these results mark IL30 as a key driver of PCSLC behavior. Targeting IL30 signaling may be a potential therapeutic strategy against prostate cancer progression and recurrence.Significance: IL30 plays an important role in regulating prostate cancer stem-like cell behavior and metastatic potential, therefore targeting this cytokine could hamper prostate cancer progression or recurrence. Cancer Res; 78(10); 2654-68. ©2018 AACR.

Interleukin-6 and prostate cancer: Current developments and unsolved questions

Interleukin (IL)-6 is a pro-inflammatory cytokine that is expressed in prostate tumors and in the stromal tumor micro-enviroment. It is known to regulate proliferation, apoptosis, angiogenesis, and differentiation. The signaling pathway of Janus kinase and signal transducer and activator of transcription (STAT)3, which is activated by IL-6, is in the focus of scientific investigations for improved treatment approaches. Different effects of IL-6 and/or STAT3 on tumor cell growth have been observed in human and murine prostate cancer (PCa) models. Experimental therapies have been proposed in order to block the IL-6/STAT3 signaling pathway. In this context, the anti-IL-6 antibody siltuximab (CNTO 328) has been demonstrated to inhibit growth of prostate tumors in vitro and in vivo and delays progression towards castration resistance. However, clinically, the anti-IL-6 antibody was not successful as a monotherapy in phase II studies in patients with metastatic PCa. IL-6 is implicated in regulation of cellular stemness by increasing phosphorylation of STAT3. The cytokine has also a role in development of resistance to the non-steroidal anti-androgen enzalutamide. Endogenous inhibitors of IL-6 are suppressors of cytokine signaling and protein inhibitors of activated STAT. Although they inhibit signal transduction through STAT3, they may also exhibit anti-apoptotic effects. On the basis of complexity of IL-6 action in PCa, an individualized approach is needed to identify patients who will benefit from anti-IL-6 therapy in combination with standard treatments.

Molecular determinants of prostate cancer metastasis

Metastatic cancer remains largely incurable and fatal. The general course of cancer, from the initiation of primary tumor formation and progression to metastasis, is a multistep process wherein tumor cells at each step must display specific phenotypic features. Distinctive capabilities required for primary tumor initiation and growth form the foundation, and sometimes may remain critical, for subsequent metastases. These phenotypic features must remain easily malleable during the acquisition of additional capabilities unique and essential to the metastatic process such as dissemination to distant tissues wherein tumor cells interact with foreign microenvironments. Thus, the metastatic phenotype is a culmination of multiple genetic and epigenetic alterations and subsequent selection for favorable traits under the pressure of ever-changing tumor microenvironments. Although our understanding of the molecular programs that drive cancer metastasis are incomplete, increasing evidence suggests that successful metastatic colonization relies on the dissemination of cancer stem cells (CSCs) with tumor-regenerating capacity and adaptive programs for survival in distant organs. In the past 2-3 years, a myriad of novel molecular regulators and determinants of prostate cancer metastasis have been reported, and in this Perspective, we comprehensively review this body of literature and summarize recent findings regarding cell autonomous molecular mechanisms critical for prostate cancer metastasis.

Treatment with the WNT5A-mimicking peptide Foxy-5 effectively reduces the metastatic spread of WNT5A-low prostate cancer cells in an orthotopic mouse model

Prostate cancer patients with high WNT5A expression in their tumors have been shown to have more favorable prognosis than those with low WNT5A expression. This suggests that reconstitution of Wnt5a in low WNT5A-expressing tumors might be an attractive therapeutic approach. To explore this idea, we have in the present study used Foxy-5, a WNT5A mimicking peptide, to investigate its impact on primary tumor and metastasis in vivo and on prostate cancer cell viability, apoptosis and invasion in vitro. We used an in vivo orthotopic xenograft mouse model with metastatic luciferase-labeled WNT5A-low DU145 cells and metastatic luciferase-labeled WNT5A-high PC3prostate cancer cells. We provide here the first evidence that Foxy-5 significantly inhibits the initial metastatic dissemination of tumor cells to regional and distal lymph nodes by 90% and 75%, respectively. Importantly, this effect was seen only with the WNT5A-low DU145 cells and not with the WNT5A-high PC3 cells. The inhibiting effect in the DU145-based model occurred despite the fact that no effects were observed on primary tumor growth, apoptosis or proliferation. These findings are consistent with and supported by the in vitro data, where Foxy-5 specifically targets invasion without affecting apoptosis or viability of WNT5A-low prostate cancer cells. To conclude, our data indicate that the WNT5A-mimicking peptide Foxy-5, which has been recently used in a phase 1 clinical trial, is an attractive candidate for complimentary anti-metastatic treatment of prostate cancer patients with tumors exhibiting absent or low WNT5A expression.

Total glucosides of paeony inhibits lipopolysaccharide-induced proliferation, migration and invasion in androgen insensitive prostate cancer cells

Previous studies demonstrated that inflammatory microenvironment promoted prostate cancer progression. This study investigated whether total glucosides of paeony (TGP), the active constituents extracted from the root of Paeonia Lactiflora Pall, suppressed lipopolysaccharide (LPS)-stimulated proliferation, migration and invasion in androgen insensitive prostate cancer cells. PC-3 cells were incubated with LPS (2.0 μg/mL) in the absence or presence of TGP (312.5 μg /mL). As expected, cells at S phase and nuclear CyclinD1, the markers of cell proliferation, were increased in LPS-stimulated PC-3 cells. Migration activity, as determined by wound-healing assay and transwell migration assay, and invasion activity, as determined by transwell invasion assay, were elevated in LPS-stimulated PC-3 cells. Interestingly, TGP suppressed LPS-stimulated PC-3 cells proliferation. Moreover, TGP inhibited LPS-stimulated migration and invasion of PC-3 cells. Additional experiment showed that TGP inhibited activation of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK)/p38 in LPS-stimulated PC-3 cells. Correspondingly, TGP attenuated upregulation of interleukin (IL)-6 and IL-8 in LPS-stimulated PC-3 cells. In addition, TGP inhibited nuclear translocation of signal transducer and activator of transcription 3 (STAT3) in LPS-stimulated PC-3 cells. These results suggest that TGP inhibits inflammation-associated STAT3 activation and proliferation, migration and invasion in androgen insensitive prostate cancer cells.

MiR-320a effectively suppresses lung adenocarcinoma cell proliferation and metastasis by regulating STAT3 signals

MicroRNAs play important roles in tumorigenesis of various types of cancers. MiR-320a can inhibits cell proliferation of some cancers, but the biologic roles of miR-320a in lung cancer need to be further studied. Here, we investigated the roles of miR-320a in suppressing the proliferation of lung adenocarcinoma cells. MiR-320a treatment was found to effectively suppress LTEP-a-2 and A549 cell proliferation, and induce more apoptotic cells with irradiation treatment compared with control treatment. Our results also showed that miR-320a, as a novel miRNA, directly regulated signal transducer and activator of transcription 3 (STAT3) and its signals, such as Bcl^-2, Bax, and Caspase 3. The siRNA-inhibited STAT3 levels further proved its roles in regulating STAT3 signals. Moreover, miR-320a treatment effectively suppressed cancer cell growth in mice xenografts compared with controls, and significantly inhibited cell migration in vitro and in vivo. Our findings collectively demonstrated that miR-320a, by directly regulating STAT3 signals, not only suppressed cell proliferation and metastasis, but also enhanced irradiation-induced apoptosis of adenocarcinomia cells.

The Effects and Mechanism of YK-4-279 in Combination with Docetaxel on Prostate Cancer

Background: Docetaxel is the first-line treatment for castration-resistant prostate cancer (CRPC). The limited survival benefit associated with the quick emergence of resistance and systemic toxicity diminishes its efficacy in high-dose monotherapy. YK-4-279 is a small molecule inhibitor of ETV1 that plays an important role in the progression of prostate cancer. The aim of this study was to evaluate the hypothesis that the combination of docetaxel and YK-4-279 will have a synergistic effect on inhibiting growth and accelerating apoptosis in human prostate cancer cells. Methods: Cell growth assessed using CCK-8 and trypan blue exclusion assays. Cell apoptosis was determined by morphological assessment in cells stained with propidium iodide. Standard scratch migration and Matrigel-coated transwell invasion assays were used to assess cell migration and invasion, respectively. Western blotting was used to investigate the levels of ETV1, AR, PSA, p-STAT3, survivin, Bcl-2, and p-Akt in prostate cancer cells. Results: The combination of low-dose docetaxel and YK-4-279 synergistically inhibited growth and induced apoptosis in human prostate cancer cells. The combination also more efficiently suppressed the migration and invasion of LNCaP and PC-3 cells. The combination of low-dose docetaxel and YK-4-279 caused a stronger decrease in the levels of ETV1, AR, PSA, p-STAT3, survivin, Bcl-2, and p-Akt in LNCaP cells and of p-Akt, Bcl-2, and p-STAT3 in PC-3 cells compared with either drug alone. Conclusions: These data suggest that the combination of docetaxel and YK-4-279 may be an effective approach for inhibiting the growth and metastasis of prostate cancer. This could permit a decrease in the docetaxel dose necessary for patients with CRPC and thereby lower its systemic toxicity.

Metformin inhibits castration-induced EMT in prostate cancer by repressing COX2/PGE2/STAT3 axis

Castration is the standard therapeutic treatment for advanced prostate cancer but with limited benefit due to the profound relapse and metastasis. Activation of inflammatory signaling pathway and initiation of epithelial-mesenchymal transition (EMT) are closely related to drug resistance, tumor relapseas well as metastasis. In this study, we demonstrated that metformin is capable of inhibiting prostate cancer cell migration and invasion by repressing EMT evidenced by downregulating the mesenchymal markers N-cadherin, Vimentin, and Twist and upregulating the epithelium E-cadherin. These effects have also been observed in our animal model as well as prostate cancer patients. In addition, we showed the effects of metformin on the expression of genes involved in EMT through repressing the levels of COX2, PGE2 and phosphorylated STAT3. Furthermore, inactivating COX2 abolishes metformin's regulatory effects and exogenously administered PGE2 is capable of enhancing STAT3 phosphorylation and expression of EMT biomarker. We propose that metformin represses prostate cancer EMT and metastasis through targeting the COX2/PGE2/STAT3 axis. These findings suggest that metformin by itself or in combination with other anticancer drugs could be used as an anti-metastasis therapy.

Galiellalactone induces cell cycle arrest and apoptosis through the ATM/ATR pathway in prostate cancer cells

Galiellalactone (GL) is a fungal metabolite that presents antitumor activities on prostate cancer in vitro and in vivo. In this study we show that GL induced cell cycle arrest in G₂/M phase, caspase-dependent apoptosis and also affected the microtubule organization and migration ability in DU145 cells. GL did not induce double strand DNA break but activated the ATR and ATM-mediated DNA damage response (DDR) inducing CHK1, H2AX phosphorylation (fH2AX) and CDC25C downregulation. Inhibition of the ATM/ATR activation with caffeine reverted GL-induced G₂/M cell cycle arrest, apoptosis and DNA damage measured by fH2AX. In contrast, UCN-01, a CHK1 inhibitor, prevented GL-induced cell cycle arrest but enhanced apoptosis in DU145 cells. Furthermore, we found that GL did not increase the levels of intracellular ROS, but the antioxidant N-acetylcysteine (NAC) completely prevented the effects of GL on fH2AX, G₂/M cell cycle arrest and apoptosis. In contrast to NAC, other antioxidants such as ambroxol and EGCG did not interfere with the activity of GL on cell cycle. GL significantly suppressed DU145 xenograft growth in vivo and induced the expression of fH2AX in the tumors. These findings identify for the first time that GL activates DDR in prostate cancer.

Expression of STAT3 in Prostate Cancer Metastases

STAT3 and its upstream activator IL6R have been implicated in the progression of prostate cancer and are possible future therapeutic targets. We analyzed 223 metastatic samples from rapid autopsies of 71 patients who had died of castration-resistant prostate cancer (CRPC) to study protein and gene expression of pSTAT3 and IL6R. Immunohistochemical analysis revealed that 95% of metastases were positive for pSTAT3 and IL6R, with varying expression levels. Bone metastases showed significantly higher expression of both pSTAT3 and IL6R in comparison to lymph node and visceral metastases. STAT3 mRNA levels were significantly higher in bone than in lymph node and visceral metastases, whereas no significant difference in IL6R mRNA expression was observed. Our study strongly supports the suggested view of targeting STAT3 as a therapeutic option in patients with metastatic CRPC.

PATIENT SUMMARY

We studied the levels of two proteins (pSTAT3 and IL6R) in metastases from patients who died from castration-resistant prostate cancer. We found high levels of pSTAT3and IL6R in bone metastases, suggesting that these proteins could be used as targets for new anticancer drugs.

A comprehensive review of genomic landscape, biomarkers and treatment sequencing in castration-resistant prostate cancer

Hormone-naïve prostate cancer and its castration-resistant state (CRPC) are clinically and genetically heterogeneous diseases. From initiation of prostate carcinogenesis to its evolution towards therapeutic resistance, various combinations of genetic and epigenetic events occur. Schematically, progression to CRPC could be divided in two distinct pathways, either dependent or independent of the androgen receptor activity. Nevertheless, because the better knowledge of the genetic landscape of CRPC is under way, limited clinical applications are available at the moment, underlying the usefulness of prognostic and predictive biomarkers in daily practice. Despite the promising prognostic value of circulating tumor cells, no biomarker has been currently validated as a surrogate for overall survival in CRPC patients. Inversely, considerable interest has been generated with the recent finding of the splice variant AR-V7 that allows to predict resistance to abiraterone acetate and enzalutamide. However, other predictive biomarkers would be necessary to accurately guide personalized sequencing of CRPC treatment, which now includes numerous possibilities based on the six validated drugs, without accounting for those currently under investigation in the ongoing randomized controlled trials. As a consequence, only rational sequencing, which consists in choosing an agent that is not expected to have cross-resistance with previous therapy, can be currently advised.

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.