Prostate cancer stem cells

Translating preclinical insights into clinical strategies: Targeting cancer stem cells and stemness in prostate cancer

CSCs represent a unique group within the tumor microenvironment (TME) elevating the tumorigenesis. The cause of cancer recurrence can also be investigated in the function of CSCs possessing self-renewing capabilities and differentiation into various types of cells. Prostate cancer (PCa) is a malignant disease of the urogenital system characterized by aggressive behavior and heterogeneous nature due to the dysregulation of molecular pathways and the interactions among cells within the TME. The PCa can quickly become resistant to standard chemotherapy and other kinds of therapies such as radiotherapy along with ability to mediate immune evasion. The focus of biology has been on the molecular and cellular alterations in PCa. The CSCs have been recognized as potential biomarkers for predicting the outcome of prostate PCa. Furthermore, a positive correlation exists between CSCs and the metastatic growth and stemness of PCa. The existence of hypoxia enhances the stemness of PCa, and CSCs play a role in dormancy. Genomic and epigenetic elements, including non-coding RNAs, can influence CSCs and the advancement of PCa. Additionally, therapeutic agents and nanotechnology methods aimed at targeting CSCs have been developed to inhibit CSCs in PCa treatment.

m6A-modified circABCC4 promotes stemness and metastasis of prostate cancer by recruiting IGF2BP2 to increase stability of CCAR1

Prostate cancer (PCa) is a malignant tumor of the urinary system. CircABCC4 has been demonstrated to promote the development of PCa; however, its regulatory mechanisms in PCa progression remain largely unknown. We found that circABCC4 was highly expressed in PCa tissues and cells, and elevated circABCC4 level indicated a poor overall survival of PCa patients. METTL3 overexpression increased circABCC4 expression via m6A modification in PCa cells. Functionally, knockdown of circABCC4 or METTL3 repressed PCa cell stemness, migration, and invasion in vitro and delayed PCa cancer growth and metastasis in vivo. circABCC4 knockdown-mediated inhibition in PCa cell stemness and metastasis could be counteracted by overexpression of wild-type circABCC4 with m6A sites. Mechanistically, circABCC4 recruited IGF2BP2 protein to CCAR1 mRNA, thereby enhancing CCAR1 mRNA stability and subsequent activation of the Wnt/β-catenin pathway. Overexpression of CCAR1 counteracted the inhibitory effect of circABCC4 silencing on PCa cell stemness and metastasis. These results revealed that m6A-modified circABCC4 by METTL3 facilitated PCa cell stemness and metastasis by interacting with IGF2BP2 to increase the stability and expression of CCAR and subsequent expression of Wnt/β-catenin target genes. Our findings suggest circABCC4 as a promising therapeutic target for PCa.

Eradicating the tumor "seeds": nanomedicines-based therapies against cancer stem cells

OBJECTIVES

Cancer stem cells (CSCs), a small subpopulation of cells with high tumorigenesis and strong intrinsic drug resistance, exhibit self-renewal and differentiation abilities. CSCs play a crucial role in tumor progression, drug resistance, recurrence and metastasis,and conventional therapy is not enough to eradicate them. Therefore, developing novel therapies targeting CSCs to increase drug sensitivity and preventing relapse is essential. The objective of this review is to present nanotherapies that target and eradicate the tumor "seeds".

EVIDENCE ACQUISITION

Evidence was collected and sorted from the literature ranging from 2000 to 2022, using appropriate keywords and key phrases as search terms within scientific databases such as Web of Science, PubMed and Google Scholar.

RESULTS

Nanoparticle drug delivery systems have been successfully applied to gain longer circulation time, more precise targeting capability and better stability during cancer treatment. Nanotechnology-based strategies that have been used to target CSCs, include (1) encapsulating small molecular drugs and genes by nanotechnology, (2) targeting CSC signaling pathways, (3) utilizing nanocarriers targeting for specific markers of CSCs, (4) improving photothermal/ photodynamic therapy (PTT/PDT), 5)targeting the metabolism of CSCs and 6) enhancing nanomedicine-aided immunotherapy.

CONCLUSION

This review summarizes the biological hallmarks and markers of CSCs, and the nanotechnology-based therapies to kill them. Nanoparticle drug delivery systems are appropriate means for delivering drugs to tumors through enhanced permeability and retention (EPR) effect. Furthermore, surface modification with special ligands or antibodies improves the recognition and uptake of tumor cells or CSCs. It is expected that this review can offer insights into features of CSCs and the exploration of targeting nanodrug delivery systems.

Cancer Stem Cells are Actually Stem Cells with Disordered Differentiation: the Monophyletic Origin of Cancer

Cancer stem cells (CSCs) play an important role in cancer development. Based on advancements in CSC research, we propose a monophyletic model of cancer. This model is based on the idea that CSCs are stem cells with disordered differentiation whose original purpose was to repair damaged tissues. Inflammatory responses and damage repair signals are crucial for the creation and maintenance of CSCs. Normal quiescent stem cells are activated by environmental stimulation, such as an inflammatory response, and undergo cell division and differentiation. In the initial stage of cancer development, stem cell differentiation leads to heteromorphism due to the accumulation of gene mutations, resulting in the development of metaplasia or precancerosis. In the second stage, accumulated mutations induce poor differentiation and lead to cancer development. The monophyletic model illustrates the evolution, biological behavior, and hallmarks of CSCs, proposes a concise understanding of the origin of cancer, and may encourage a novel therapeutic approach.

Stem Cells as Target for Prostate cancer Therapy: Opportunities and Challenges

Cancer stem cells (CSCs) and cells in a cancer stem cell-like (CSCL) state have proven to be responsible for tumor initiation, growth, and relapse in Prostate Cancer (PCa) and other cancers; therefore, new strategies are being developed to target such cellular populations. TLR3 activation-based immunotherapy using Polyinosinic:Polycytidylic acid (PIC) has been proposed to be used as a concomitant strategy to first-line treatment. This strategy is based on the induction of apoptosis and an inflammatory response in tumor cells. In combination with retinoids like 9cRA, this treatment can induce CSCs differentiation and apoptosis. A limitation in the use of this combination is the common decreased expression of TLR3 and its main positive regulator p53. observed in many patients suffering of different cancer types such as PCa. Importantly, human exposure to certain toxicants, such as iAs, not only has proven to enrich CSCs population in an in vitro model of human epithelial prostate cells, but additionally, it can also lead to a decreased p53, TLR3 and RA receptor (RARβ), expression/activation and thus hinder this treatment efficacy. Therefore, here we point out the relevance of evaluating the TLR3 and P53 status in PCa patients before starting an immunotherapy based on the use of PIC +9cRA to determine whether they will be responsive to treatment. Additionally, the use of strategies to overcome the lower TLR3, RARβ or p53 expression in PCa patients, like the inclusion of drugs that increase p53 expression, is encouraged, to potentiate the use of PIC+RA based immunotherapy in these patients.

The vulnerable primed cancer stem cells in disguise: demystifying the role of Maspin

Epithelial-specific Maspin is widely known as a tumor suppressor. However, while the level of maspin expression is inversely correlated with tumor grade and stage, emerging clinical evidence shows a correlation between seemingly better differentiated tumor cells that express Maspin in both the nucleus and the cytoplasm, (n + c)Maspin, with a poor prognosis of many types of cancer. Biological studies demonstrate that Maspin plays an essential role in stem cell differentiation. In light of the recently established characterization of primed stem cells (P-SCs) in development, we propose, for the first time, that cancer stem cells (CSCs) also need to undergo priming (P-CSCs) before their transition to various progeny phenotypes. We envisage major differences in the steady state kinetics between P-SCs and P-CSCs. We further propose that P-CSCs of carcinoma are both marked and regulated by (n + c)Maspin. The concept of P-CSCs helps explain the apparent dichotomous relationships of (n + c)Maspin expression with cancer diagnosis and prognosis, and is supported by the evidence from mechanistic studies. We believe that the potential utility of (n + c)Maspin as a molecular marker of P-CSCs may significantly accelerate the advancement in our understanding of the genesis of tumor phenotypic plasticity in response to changes of tumor microenvironments (TME) or drug treatments. The vulnerabilities of the cellular state of (n + c)Maspin-expressing P-CSCs are also discussed as the rationale for future development of P-CSC-targeted chemotherapeutic and immunotherapeutic strategies.

Phage display screening identifies a prostate specific antigen (PSA)-/lo prostate cancer cell specific peptide to retard castration resistance of prostate cancer

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To our knowledge, this is the first study to identify a peptide (named as “TAP1”) that specifically binds with PSA^−/lo prostate cancer cells.

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TAP1 inhibited PCa growth both in vitro and in vivo.

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TAP1 also improved the anti-tumor effect of the anti-androgens and chemotherapeutic agents in vitro.

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The effects of TAP1 might at least in part by shortening the lengths of telomeres and decreasing the expression of HOXB9 and TGF-β2.

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Our results indicated that therapeutic peptides that specifically target prostate cancer stem cell might be a very valuable and promising approach to overcome chemoresistance and prevent recurrence in patients with PCa.

Patients with prostate cancer (PCa) will eventually progress to castrate-resistant prostate cancer (CRPC) after androgen deprivation therapy (ADT) treatment. Prostate-specific antigen (PSA)^−/lo cells which harbor self-renewing long-term tumor-propagating cells that can be enriched using ALDH+CD44+α2β1+ and can initiate tumor development may represent a critical source of CRPC cells. Our purpose was to find a peptide that specifically targets PSA^−/lo PCa cells to retard the development of CRPC. PSA⁺ and PSA^−/lo cells were successfully separated from LNCaP xenograft tumors after prostate- PSAP-GFP vector infection and FACS. A variety of PSA^−/lo cells specifically targeting peptide (named as “TAP1” targeted affinity peptide 1) was identified by using phage display library screening. The highest binding rate in TAP1 binding cell subpopulations are identified to be among ALDH⁺CD44⁺CXCR4⁺CD24⁺ cells. TAP1 significantly inhibited PCa growth both in vitro and in vivo. TAP1 significantly improved the anti-proliferation effect of the anti-androgens (Charcoal dextran-stripped serum (CDSS)+Bicalutamide, Enzalutamide) and chemotherapeutic agents (Abiraterone, Docetaxel, Etoposide) in vitro. TAP1 treatment shortens the length of telomeres in ALDH⁺CD44⁺CXCR4⁺CD24⁺ cells and significantly reduces the expression of Homeobox B9 (HOXB9) and TGF-β2. In conclusion, PSA^−/lo PCa cell-specific targeting peptide (TAP1) that suppressed PCa cell growth both in vitro and in vivo and improved the drug sensitivities of anti-androgens and chemotherapeutic agents at least through shortening the length of telomere and reducing the expression of HOXB9 and TGF-β2. Therapeutic peptides that specifically target prostate cancer stem cell might be a very valuable and promising approach to overcome chemoresistance and prevent recurrence in patients with PCa.

Prostate-specific antigen dynamics predict individual responses to intermittent androgen deprivation

Intermittent androgen deprivation therapy (IADT) is an attractive treatment for biochemically recurrent prostate cancer (PCa), whereby cycling treatment on and off can reduce cumulative dose and limit toxicities. We simulate prostate-specific antigen (PSA) dynamics, with enrichment of PCa stem-like cell (PCaSC) during treatment as a plausible mechanism of resistance evolution. Simulated PCaSC proliferation patterns correlate with longitudinal serum PSA measurements in 70 PCa patients. Learning dynamics from each treatment cycle in a leave-one-out study, model simulations predict patient-specific evolution of resistance with an overall accuracy of 89% (sensitivity = 73%, specificity = 91%). Previous studies have shown a benefit of concurrent therapies with ADT in both low- and high-volume metastatic hormone-sensitive PCa. Model simulations based on response dynamics from the first IADT cycle identify patients who would benefit from concurrent docetaxel, demonstrating the feasibility and potential value of adaptive clinical trials guided by patient-specific mathematical models of intratumoral evolutionary dynamics.

MicroRNAs, Hypoxia and the Stem-Like State as Contributors to Cancer Aggressiveness

MicroRNAs (miRNAs) are small non-coding RNA molecules that play key regulatory roles in cancer acting as both oncogenes and tumor suppressors. Due to their potential roles in improving cancer prognostic, predictive, diagnostic and therapeutic approaches, they have become an area of intense research focus in recent years. Several studies have demonstrated an altered expression of several miRNAs under hypoxic condition and even shown that the hypoxic microenvironment drives the selection of a more aggressive cancer cell population through cellular adaptations referred as the cancer stem-like cell. These minor fractions of cells are characterized by their self-renewal abilities and their ability to maintain the tumor mass, suggesting their crucial roles in cancer development. This review aims to highlight the interconnected role between miRNAs, hypoxia and the stem-like state in contributing to the cancer aggressiveness as opposed to their independent contributions, and it is based in four aggressive tumors, namely glioblastoma, cervical, prostate, and breast cancers.

Evaluation of the effect of hyperthermia and electron radiation on prostate cancer stem cells

The aim of this study was to investigate the effect of hyperthermia, 6 MeV electron radiation and combination of these treatments on cancer cell line DU145 in both monolayer culture and spheroids enriched for prostate cancer stem cells (CSCs). Flowcytometric analysis of the expression of molecular markers CD133⁺/CD44⁺ was carried out to determine the prostate CSCs in cell line DU145 grown as spheroids in serum-free medium. Following monolayer and spheroid culture, DU145 cells were treated with different doses of hyperthermia, electron beam and combination of them. The survival and self-renewing of the cells were evaluated by colony formation assay (CFA) and spheroid formation assay (SFA). Flowcytometry results indicated that the percentage of CD133⁺/CD44⁺ cells in spheroid culture was 13.9-fold higher than in the monolayer culture. The SFA showed significant difference between monolayer and spheroid culture for radiation treatment (6 Gy) and hyperthermia (60 and 90 min). The CFA showed significantly enhanced radiosensitivity in DU145 cells grown as monolayer as compared to spheroids, but no effect of hyperthermia. In contrast, for the combination of radiation and hyperthermia the results of CFA and SFA showed a reduced survival fraction in both cultures, with larger effects in monolayer than in spheroid culture. Thus, hyperthermia may be a promising approach in prostate cancer treatment that enhances the cytotoxic effect of electron radiation. Furthermore, determination and characterization of radioresistance and thermoresistance of CSCs in the prostate tumor is the key to develop more efficient therapeutic strategies.

Cell surface Thomsen-Friedenreich proteome profiling of metastatic prostate cancer cells reveals potential link with cancer stem cell-like phenotype

The tumor-associated Thomsen-Friedenreich glycoantigen (TF-Ag) plays an important role in hematogenous metastasis of multiple cancers. The LTQ Orbitrap LC-MS/MS mass spectrometry analysis of cell surface TF-Ag proteome of metastatic prostate cancer cells reveals that several cell surface glycoproteins expressing this carbohydrate antigen in prostate cancer (CD44, α2 integrin, β1 integrin, CD49f, CD133, CD59, EphA2, CD138, transferrin receptor, profilin) are either known as stem cell markers or control important cancer stem-like cell functions. This outcome points to a potential link between TF-Ag expression and prostate cancer stem-like phenotype. Indeed, selecting prostate cancer cells for TF-Ag expression resulted in the enrichment of cells with stem-like properties such as enhanced clonogenic survival and growth, prostasphere formation under non-differentiating and differentiating conditions, and elevated expression of stem cell markers such as CD44 and CD133. Further, the analysis of the recent literature demonstrates that TF-Ag is a common denominator for multiple prostate cancer stem-like cell populations identified to date and otherwise characterized by distinct molecular signatures. The current paradigm suggests that dissemination of tumor cells with stem-like properties to bone marrow that occurred before surgery and/or radiation therapy is largely responsible for disease recurrence years after radical treatment causing a massive clinical problem in prostate cancer. Thus, developing means for destroying disseminated prostate cancer stem-like cells is an important goal of modern cancer research. The results presented in this study suggest that multiple subpopulation of putative prostate cancer stem-like cells characterized by distinct molecular signatures can be attacked using a single target commonly expressed on these cells, the TF-Ag.

Therapies for castration-resistant prostate cancer in a new era: The indication of vintage hormonal therapy, chemotherapy and the new medicines

When advanced prostate cancer recurred during hormonal therapy and became the castration-resistant prostate cancer, "vintage hormonal therapy," such as antiandrogen alternating therapy or estrogen-related hormonal therapy, was widely carried out in Japan until 2013. This vintage hormonal therapy controlled the progression of castration-resistant prostate cancer. When castration-resistant prostate cancer relapses during these therapies, chemotherapy using docetaxel has been carried out subsequently. Since new hormonal therapies using abiraterone acetate and enzalutamide, which improve the prognosis of castration-resistant prostate cancer, became available in Japan from 2014, therapeutic options for castration-resistant prostate cancer have increased. Furthermore, the improvement of the further prognosis is promising by using cabazitaxel for docetaxel-resistant castration-resistant prostate cancer and radium-223 for castration-resistant prostate cancer with bone metastasis. An increase in therapeutic options gives rise to many questions, including best timing to use them and the indication. Furthermore, physicians have to consider the treatment for the recurrence after having carried out chemotherapy. We want to argue the difference in hormonal therapy between Japan and Western countries, and problems when carrying out new treatments, and the importance of imaging in the present review article.

Multidrug-resistant cancer cells and cancer stem cells hijack cellular systems to circumvent systemic therapies, can natural products reverse this?

Chemotherapy is one of the most effective and broadly used approaches for cancer management and many modern regimes can eliminate the bulk of the cancer cells. However, recurrence and metastasis still remain a major obstacle leading to the failure of systemic cancer treatments. Therefore, to improve the long-term eradication of cancer, the cellular and molecular pathways that provide targets which play crucial roles in drug resistance should be identified and characterised. Multidrug resistance (MDR) and the existence of tumor-initiating cells, also referred to as cancer stem cells (CSCs), are two major contributors to the failure of chemotherapy. MDR describes cancer cells that become resistant to structurally and functionally unrelated anti-cancer agents. CSCs are a small population of cells within cancer cells with the capacity of self-renewal, tumor metastasis, and cell differentiation. CSCs are also believed to be associated with chemoresistance. Thus, MDR and CSCs are the greatest challenges for cancer chemotherapy. A significant effort has been made to identify agents that specifically target MDR cells and CSCs. Consequently, some agents derived from nature have been developed with a view that they may overcome MDR and/or target CSCs. In this review, natural products-targeting MDR cancer cells and CSCs are summarized and clustered by their targets in different signaling pathways.

Downregulation of microRNA‑574 in cancer stem cells causes recurrence of prostate cancer via targeting REL

miR‑574‑5p has been reported involved in the pathogenesis of numerous human malignancies such as colorectal and lung cancer. In this study, we aimed to explore the roles of REL and miR‑574 in the recurrence of prostate cancer (PCa) and to identify the underlying molecular mechanisms. Our literature search found that miR‑574 is regulated in cancer stem cells (CSCs), and next we used the microRNA (miRNA) database (www.mirdb.org) to find REL as a target of miR‑574. Luciferase assay was performed to verify the miRNA/target relationship. Oligo-transfection, real‑time PCR and western blot analysis were used to support the conclusions. We validated REL to be the direct gene via luciferase reporter assay system, and real‑time PCR and western blot analysis were also conducted to study the mRNA and protein expression level of REL between different groups (recurrence and non‑recurrence) or cells treated with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors, indicating the negative regulatory relationship between miR‑574 and REL. We also investigated the relative viability of prostate CSCs when transfected with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors to validate miR‑574 to be positively interfering with the viability of prostate CSCs. We then investigated the relative apoptosis of prostate CSCs when transfected with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors. The results showed miR‑574 inhibited apoptosis. In conclusion, miR‑574 might be a novel prognostic and therapeutic target in the management of PCa recurrence.

Ecotropic viral integration site 1, a novel oncogene in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed non-cutaneous cancer in men in the western world. Mutations in tumor suppressor genes and in oncogenes are important for PCa progression, whereas the role of stem cell proteins in prostate carcinogenesis is insufficiently examined. This study investigates the role of the transcriptional regulator Ecotropic Viral Integration site 1 (EVI1), known as an essential modulator of hematopoietic and leukemic stem cell biology, in prostate carcinogenesis. We show that in healthy prostatic tissue, EVI1 expression is confined to the prostate stem cell compartment located at the basal layer, as identified by the stem cell marker CD44. Instead, in a PCa progression cohort comprising 219 samples from patients with primary PCa, lymph node and distant metastases, EVI1 protein was heterogeneously distributed within samples and high expression is associated with tumor progression (P<0.001), suggesting EVI1 induction as a driver event. Functionally, short hairpin RNA-mediated knockdown of EVI1 inhibited proliferation, cell cycle progression, migratory capacity and anchorage-independent growth of human PCa cells, while enhancing their apoptosis sensitivity. Interestingly, modulation of EVI1 expression also strongly regulated stem cell properties (including expression of the stem cell marker SOX2) and in vivo tumor initiation capacity. Further emphasizing a functional correlation between EVI1 induction and tumor progression, upregulation of EVI1 expression was noted in experimentally derived docetaxel-resistant PCa cells. Importantly, knockdown of EVI1 in these cells restored sensitivity to docetaxel, in part by downregulating anti-apoptotic BCL2. Together, these data indicate EVI1 as a novel molecular regulator of PCa progression and therapy resistance that may control prostate carcinogenesis at the stem cell level.

Cancer stem cell markers in prostate cancer: an immunohistochemical study of ALDH1, SOX2 and EZH2

The aims of this study were to investigate the immunohistochemical expression and potential prognostic significance of putative cancer stems cell markers ALDH1, EZH2 and SOX2 in prostate cancer.A total of 142 consecutive radical prostatectomies submitted to one laboratory with a diagnosis of prostatic adenocarcinoma between 2008 and 2012 were retrieved and retrospectively studied. Immunohistochemistry for the three markers was performed in each case and both univariate and multivariate analyses were undertaken to evaluate the correlation between the staining patterns and known histopathological prognostic features.ALDH1 showed a statistically significant association with tumour stage p < 0.001), extraprostatic extension (p < 0.001) and lymphovascular invasion (p = 0.001). EZH2 correlated with Gleason score (p = 0.044) and lymph node metastases (p = 0.023). SOX2 showed a statistically significant correlation with lymphovascular invasion only (p = 0.018) in both univariate and multivariate analyses.Cancer stem cell markers are variably expressed in prostate adenocarcinoma and immunohistochemical staining for ALDH1 and EZH2 may have a role in predicting tumour aggressiveness before treatment of prostate cancer.

Surgical cytoreduction of the primary tumor reduces metastatic progression in a mouse model of prostate cancer

Metastatic prostate cancer (mPCa) is one of the most prevalent cancers in men worldwide. The main cause of death in these patients is androgen-resistant metastatic disease. Surgery of the primary tumor has been avoided in these patients as there is no strong evidence that supports a beneficial effect. From the biological point of view, it appears rational to hypothesize that the primary tumor may contribute to the establishment and growth of metastases. Considering this, we propose that cytoreductive surgery (CS) in advanced metastatic stage slows the progression of metastatic disease. To test this, we used a mouse model of resectable orthotopic prostate cancer (PCa) and performed CS. After surgery, metastases were smaller and less numerous in the treated mice; an effect that was observable until the end of the experiment. These results suggest that CS alone delays the progression of metastatic disease and that although this effect may be temporary, it may translate to prolonged survival, especially when used with adjuvant therapy.

The update of prostatic ductal adenocarcinoma

Since initially described in 1967, prostatic ductal adenocarcinoma (PDA) has engendered a series of controversies on its origin, histological features, and biological behavior. Owing to the improvement of molecular biological technique, there are some updated findings on the characteristics of PDA. In the current review, we will mainly analyze its origin, clinical manifestations, morphological features, differential diagnosis, immunophenotype and molecular genetics, with the purpose of enhancing recognition of this tumor and making a correct diagnosis and treatment choice.

Suppression of prostate cancer progression by cancer cell stemness inhibitor napabucasin

A small population of cells with stem cell-like properties in prostate cancer (PCa), called prostate cancer stem cells (PrCSCs) or prostate stemness-high cancer cells, displays highly tumorigenic and metastatic features and may be responsible for the therapy resistance. A small molecule, napabucasin (BBI608), recently have been identified with suppression of stemness-high cancer cells in a variety of cancers. However, the effects of napabucasin on PCa cells as well as PrCSCs isolated from PCa cells have not yet been defined. The effect of napabucasin on PCa cells in cell proliferation, colony formation, and cell migration in vitro were measured by MTS, colony formation assay, and Transwell, respectively. Flow cytometry was employed to evaluate cell cycle and cell apoptosis, and the effect on tumorigenesis in vivo was examined by tumor growth assays. Furthermore, the role of napabucasin on self-renewal and survival of PrCSCs was evaluated by their ability to grow spheres and cell viability assay, respectively. Western Blot and qRT-PCR were used to determine the effect of napabucasin on the expressions of stemness markers. Decrease in cell viability, colony formation, migration, and survival with cell cycle arrest, higher sensitivity to docetaxel in vitro, and repressed tumorigenesis in vivo was observed upon napabucasin treatment. More importantly, napabucasin can obviously inhibit spherogenesis and even kill PrCSCs in vitro. Downregulation of stemness markers was observed after PrCSCs were treated with napabucasin. This study demonstrates that napabucasin may be a novel approach in the treatment of advanced PCa, specifically for castration-resistant prostate cancer (CRPC).

AR Pathway Is Involved in the Regulation of CX43 in Prostate Cancer

CX43 plays a critical role in tumor progression. Previous studies imply that AR pathway may be involved in regulation of CX43. This study was focused on determining the relationship between AR pathway and CX43. The result showed that the expression of CX43 in malignant cells was higher than that in normal cells, and in nonmalignant and malignant cells, not only is the expression level of CX43 different, but the localization of CX43 can also be changed. After androgen stimulation and inhibition of AR pathway, expression of CX43 can also be changed. Thus, AR pathway plays an important role in regulation of CX43 expression in prostate cancer cells. AR may be the upstream signal of CX43.

Maintenance Therapy Containing Metformin and/or Zyflamend for Advanced Prostate Cancer: A Case Series

Metformin is derived from galegine, a natural ingredient, and recent studies have suggested that metformin could enhance the antitumor effects of hormone ablative therapy or chemotherapy and reduce prostate cancer-specific mortality. Zyflamend is a combination of herbal extracts that reduces inflammation and comprises turmeric, holy basil, green tea, oregano, ginger, rosemary, Chinese goldthread, hu zhang, barberry, and basil skullcap. We propose a maintenance regimen with metformin and/or Zyflamend that targets cancer stem cells and the tumor microenvironment to keep the cancer dormant and prevent it from activation from dormancy. Herein, we report the clinical course of four patients who experienced a clinical response after treatment with metformin and/or Zyflamend.

Infiltrating T cells promote prostate cancer metastasis via modulation of FGF11→miRNA-541→androgen receptor (AR)→MMP9 signaling

Early clinical studies suggested infiltrating T cells might be associated with poor outcomes in prostate cancer (PCa) patients. The detailed mechanisms how T cells contribute to PCa progression, however, remained unclear. Here, we found PCa cells have a better capacity to recruit more CD4(+) T cells than the surrounding normal prostate cells via secreting more chemokines-CXCL9. The consequences of more recruited CD4(+) T cells to PCa might then lead to enhance PCa cell invasion. Mechanism dissection revealed that infiltrating CD4(+) T cells might function through the modulation of FGF11→miRNA-541 signals to suppress PCa androgen receptor (AR) signals. The suppressed AR signals might then alter the MMP9 signals to promote the PCa cell invasion. Importantly, suppressed AR signals via AR-siRNA or anti-androgen Enzalutamide in PCa cells also enhanced the recruitment of T cells and the consequences of this positive feed back regulation could then enhance the PCa cell invasion. Targeting these newly identified signals via FGF11-siRNA, miRNA-541 inhibitor or MMP9 inhibitor all led to partially reverse the enhanced PCa cell invasion. Results from in vivo mouse models also confirmed the in vitro cell lines in co-culture studies. Together, these results concluded that infiltrating CD4(+) T cells could promote PCa metastasis via modulation of FGF11→miRNA-541→AR→MMP9 signaling. Targeting these newly identified signals may provide us a new potential therapeutic approach to better battle PCa metastasis.

Functional characteristics of cancer stem cells and their role in drug resistance of prostate cancer

Cancer stem cells (CSCs) have the ability to self-renew and differentiate to give rise to heterogeneous phenotype of the tumor cells. It is believed that these cells are involved in metastasis, recurrence and therapy resistance in various cancers. CSCs have been identified in prostate cancer (PCa), one of the most diagnosed malignancies in men over the world, for which chemotherapy resistance is a major problem in the treatment of castration-resistant advanced stages. Molecular signatures, gene expression and functional features have been reported for PCa CSCs. Most data come from cell lines which may not represent the actual tumor. In the present work, a CSCs enriched population obtained from PCa explants was functionally characterized and analyzed for drug resistance. Tumorsphere cultures positive for ABCG2 transporter, CD133, CD44, cytokeratins 5 and 18 (CK5 and CK18) and negatives for androgen receptor (AR) and prostate-specific antigen (PSA) showed higher clonogenic capacity, holoclone-forming ability, colony-forming capacity in soft agar and lower proliferative and apoptotic rate than control adherent cell cultures. Furthermore, exposing tumorsphere cultures to ABCG2 substrate drugs resulted in a high survival rate compared with control PCa cells. This high drug resistance was decreased using a selective inhibitor of ABCG2. According to these results, tumorspheres from PCa explants showed a functional stem phenotype and a marked drug resistance, probably mediated by high expression of the ABCG2 transporter, which might be considered as a suitable therapeutic target for CSCs.

Hypoxia promotes radioresistance of CD133-positive Hep-2 human laryngeal squamous carcinoma cells in vitro

Hypoxia promotes the radioresistance of laryngeal carcinomas and CD133 is one of the markers expressed by tumor-initiating, human laryngeal carcinoma cells. In order to investigate whether CD133-positive Hep-2 cells exhibit a radioresistant phenotype and to determine whether hypoxia promotes this phenotype, we performed a series of experiments. Hep-2 cells, and Hep-2 cells stably expressing hypoxia-inducible factor (HIF)-targeted small interfering RNA (siRNA) were cultured under hypoxic and normoxic conditions and were treated with varying doses of γ-rays (0, 5, 10, 15 and 20 Gy). MTT and cell cycle assays were subsequently performed. Using fluorescence-activated cell sorting (FACS), CD133-positive Hep-2 cells and CD133-positive HIF-siRNA Hep-2 cells were isolated. These cells were grown as spheres under hypoxic and normoxic conditions for MTT and soft agar colony formation assays. The expression levels of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), survivin, p53 and ataxia-telangiectasia mutated (ATM) were also assayed using flow cytometry. The data showed that the growth of Hep-2 cells exposed to hypoxic conditions and treated with 10 Gy radiation (group A) was less compared to that of groups B-D (P<0.05). In addition, more cells in group A were arrested in the G1 phase of the cell cycle compared to groups B-D (P<0.05). The percentage of CD133+ cells detected after radiation increased and was the highest for group A (P<0.05). In sphere formation assays, significantly more CD133+ cells grew in spheres than CD133- cells (P<0.001). Moreover, sphere formation was the highest for CD133+ Hep-2 cells grown under hypoxic conditions and exposed to irradiation (group E) (P<0.05). Lastly, expression of DNA-PKcs and survivin for group E was the highest (P<0.05), while ATM and p53 levels remained largely unchanged (P>0.05). In conclusion, CD133-positive Hep-2 cells exhibited a radioresistant phenotype that was enhanced with hypoxia. Furthermore, an increase in DNA-PK activity was associated with this enhancement.

Hypoxia-inducing factors as master regulators of stemness properties and altered metabolism of cancer- and metastasis-initiating cells

Accumulating lines of experimental evidence have revealed that hypoxia-inducible factors, HIF-1α and HIF-2α, are key regulators of the adaptation of cancer- and metastasis-initiating cells and their differentiated progenies to oxygen and nutrient deprivation during cancer progression under normoxic and hypoxic conditions. Particularly, the sustained stimulation of epidermal growth factor receptor (EGFR), insulin-like growth factor-1 receptor (IGF-1R), stem cell factor (SCF) receptor KIT, transforming growth factor-β receptors (TGF-βRs) and Notch and their downstream signalling elements such as phosphatidylinositol 3′-kinase (PI3K)/Akt/molecular target of rapamycin (mTOR) may lead to an enhanced activity of HIFs. Moreover, the up-regulation of HIFs in cancer cells may also occur in the hypoxic intratumoral regions formed within primary and secondary neoplasms as well as in leukaemic cells and metastatic prostate and breast cancer cells homing in the hypoxic endosteal niche of bone marrow. The activated HIFs may induce the expression of numerous gene products such as induced pluripotency-associated transcription factors (Oct-3/4, Nanog and Sox-2), glycolysis- and epithelial-mesenchymal transition (EMT) programme-associated molecules, including CXC chemokine receptor 4 (CXCR4), snail and twist, microRNAs and angiogenic factors such as vascular endothelial growth factor (VEGF). These gene products in turn can play critical roles for high self-renewal ability, survival, altered energy metabolism, invasion and metastases of cancer cells, angiogenic switch and treatment resistance. Consequently, the targeting of HIF signalling network and altered metabolic pathways represents new promising strategies to eradicate the total mass of cancer cells and improve the efficacy of current therapies against aggressive and metastatic cancers and prevent disease relapse.