Prostate Cancer Stem Cells: Clinical Aspects and Targeted Therapies

In-silico analysis unveiling the role of cancer stem cells in immunotherapy resistance of immune checkpoint-high pancreatic adenocarcinoma

Although immune checkpoint (IC) inhibition is a major treatment modality in cancer-immunotherapy, multiple cancers show low response. Our in-silico exploration by mining cancer datasets using R2, available clinical trial data, and Kaplan-Meier analysis from GEPIA depicted that unlike low-responder (LR) cancers, high-responder (HR) cancers furnish higher IC expression, that upon lowering may provide better prognosis. Contrastingly, pancreatic adenocarcinoma (PAAD) demonstrated high IC expression but low immunotherapy-response. Infiltration scores from TIMER2.0 revealed higher pro-tumor immune subsets and cancer-associated fibroblasts (CAFs) while depicting lower anti-tumor immune subsets in PAAD as compared to HR lung adenocarcinoma (LUAD). Additionally, bioinformatic tool cBioportal showed lesser tumor mutational burden, mismatch repair deficiency and greater percent of driver mutations in TP53, KRAS and CDKN2A in PAAD, supporting its higher immunotherapy-resistance than LUAD. Our search for the 'key' immunotherapy response-deciding factor(s) revealed cancer stem cells (CSCs), the known contributors of therapy-resistance and immuno-evasion, to be positively correlated with above-mentioned driver mutations, pro-tumor immune and CAF subsets; and that PAAD furnished higher expression of CSC genes than LUAD. UMAP/tSNE analyses revealed that high CSC signature is positively correlated with immunotherapy-resistance genes and pro-cancer immune cells, while negatively with cytotoxic-T cells in PAAD. Our in-silico study explains the low immunotherapy-response in high IC-expressing PAAD, wherein CSC plays a pivotal role. Further exploration portrayed correlation of CSCs with immunotherapy-resistance in other LR and HR cancers too, substantiating the need for personalized CSC evaluation and targeting for successful immunotherapy outcomes.

Integrated Bioinformatic Analyses Reveal Thioredoxin as a Putative Marker of Cancer Stem Cells and Prognosis in Prostate Cancer

Objectives

Prostate cancer stem cells (CSCs) play an important role in cancer cell survival, proliferation, metastasis, and recurrence; thus, removing CSCs is important for complete cancer removal. However, the mechanisms underlying CSC functions remain largely unknown, making it difficult to develop new anticancer drugs targeting CSCs. Herein, we aimed to identify novel factors that regulate stemness and predict prognosis.

Methods

We reanalyzed 2 single-cell RNA sequencing data of prostate cancer (PCa) tissues using Seurat. We used gene set enrichment analysis (GSEA) to estimate CSCs and identified common upregulated genes in CSCs between these datasets. To investigate whether its expression levels change over CSC differentiation, we performed a trajectory analysis using monocle 3. In addition, GSEA helped us understand how the identified genes regulate stemness. Finally, to assess their clinical significance, we used the Cancer Genome Atlas database to evaluate their impact on prognosis.

Results

The expression of thioredoxin (TXN), a redox enzyme, was approximately 1.2 times higher in prostate CSCs than in PCa cells (P < 1 × 10-10), and TXN expression decreased over CSC differentiation. In addition, GSEA suggested that intracellular signaling pathways, including MYC, may be involved in stemness regulation by TXN. Furthermore, TXN expression correlated with poor prognosis (P < .05) in PCa patients with high stemness.

Conclusions

Despite the limited sample size in our study and the need for further in vitro and in vivo experiments to demonstrate whether TXN functionally regulates prostate CSCs, our findings suggest that TXN may serve as a novel therapeutic target against CSCs. Moreover, TXN expression in CSCs could be a useful marker for predicting the prognosis of PCa patients.

Targeting CD44 and EpCAM with Antibody Dye Conjugates for the Photoimmunotherapy of Prostate Cancer

BACKGROUND/OBJECTIVES

Photoimmunotherapy (PIT) is an innovative approach for the targeted therapy of cancer. In PIT, photosensitizer dyes are conjugated to tumor-specific antibodies for targeted delivery into cancer cells. Upon irradiation with visible light, the photosensitizer dye is activated and induces cancer-specific cell death. In the present article, we describe the PIT of prostate cancer (PC) as a therapeutic option for the targeted treatment of localized prostate cancer.

METHODS

We conjugated the silicon phthalocyanine dye WB692-CB2 to recombinant cysteine-modified anti-CD44 and anti-EpCAM antibodies via a maleimide linker and tested the antibody dye conjugates for PIT on PC cells and prostate cancer stem cell (PCSC)-like cells.

RESULTS

The anti-CD44 and anti-EpCAM antibody dye conjugates showed specific binding and high cytotoxicity against PC and PCSC-like cells following irradiation with red light. Combined treatment with both conjugates led to enhanced cytotoxic effects.

CONCLUSIONS

PIT with our dye WB692-CB2 can serve as an effective focal therapy against prostate cancer, preserving the prostate gland and minimizing side effects. It can be employed during radical prostatectomy (RP) to treat residual tumor cells or lymph node metastases in areas where further surgical intervention is not feasible. Utilizing multiple conjugates against antigens expressed on differentiated PC and PCSC-like cells, such as CD44 and EpCAM, could be an effective method to eradicate residual cancer cells in heterogeneous tumors. This approach could reduce the risk of local recurrence after RP and thus increase the therapeutic outcome of PC patients.

Doublecortin-like kinase 1 promotes stem cell-like properties through the Hippo-YAP pathway in prostate cancer

Background: Doublecortin-like kinase 1 (DCLK1) has been revealed to be involved in modulating cancer stemness and tumor progression, but its role in prostate cancer (PCa) remains obscure. Castration-resistant and metastatic PCa exhibit aggressive behaviors, and current therapeutic approaches have shown limited beneficial effects on the overall survival rate of patients with advanced PCa. This study aimed to investigate the biological role and potential molecular mechanism of DCLK1 in the progression of PCa. Methods: The role of DCLK1 in maintaining PCa stem cell-like properties was explored via gain- and loss-of-function studies, including colony formation assays, sphere formation assays and measurement of stemness-related marker expression. A set of transcriptomic data for patients with PCa was downloaded from The Cancer Genome Atlas to analyze the correlations between DCLK1 and Hippo pathway gene expression. The mechanism by which DCLK1 regulates Hippo signaling and cancer stemness was further investigated in vitro by methods such as Western blot analysis, quantitative real-time PCR analysis, immunofluorescence staining, and luciferase reporter assays and in vivo by animal studies. Results: The gain- and loss-of-function studies demonstrated that upregulating DCLK1 promoted but downregulating DCLK1 suppressed aspects of the PCa stem cell-like phenotype, including colony formation, sphere formation and the expression of stemness-related markers (c-Myc, OCT4, CD44, NANOG, SOX2, and KLF4). Importantly, bioinformatics analysis indicated that DCLK1 is closely correlated with the Hippo signaling pathway in PCa. Further in vitro assays revealed that DCLK1 inhibits the Hippo signaling pathway, leading to yes-associated protein (YAP) activation via large tumor suppressor homolog 1 (LATS1). Moreover, the effect of DCLK1 on abolishing stemness traits in PCa was observed after treatment with verteporfin, a small molecule inhibitor of YAP. Consistent with the in vitro findings, the in vivo findings confirmed that DCLK1 promoted the tumorigenicity and stem cell-like traits of PCa cells via Hippo-YAP signaling. Conclusion: DCLK1 promotes stem cell-like characteristics by inducing LATS1-mediated YAP signaling activation, ultimately leading to PCa tumor growth and progression. Thus, our findings identify an attractive candidate for the development of cancer stem cell-targeted therapies to improve treatment outcomes in advanced PCa.

Nuclear receptor TLX functions to promote cancer stemness and EMT in prostate cancer via its direct transactivation of CD44 and stem cell-regulatory transcription factors

BACKGROUND

Prostate cancer stem cells (PCSCs) play crucial roles in therapy-resistance and metastasis in castration-resistant prostate cancer (CRPC). Certain functional link between cancer stemness and epithelial-mesenchymal transition (EMT) is involved in CRPC. However, up-stream regulators controlling these two processes in PCSCs are still poorly understood. Recently, we have shown that orphan nuclear receptor TLX can promote tumour initiation and progression in CRPC by repressing androgen receptor and oncogene-induced senescence.

METHODS

PCSCs were isolated from various prostate cancer cell lines and clinical tumour tissues using multiple methods for various in vitro and in vivo oncogenic growth analyses. Direct targets of TLX involved in stemness and EMT regulation were determined by specific reporter gene assays and ligand-driven modulation of TLX activity.

RESULTS

PCSCs isolated from various sources exhibited increased expression of TLX. Functional and molecular characterisation showed that TLX could function to promote cancer stemness and EMT in prostate cancer cells via its direct transactivation of CD44, SOX2, POU5F1 and NANOG, which share certain functional crosstalk in these two cellular processes.

CONCLUSIONS

TLX could act as a key up-stream regulator in transcriptional control of stemness and EMT in PCSCs, which contribute to their tumorigenicity, castration-resistance and metastasis potentials in advanced prostate cancer.

Molecular mechanisms and targeted therapy for the metastasis of prostate cancer to the bones (Review)

The incidence of prostate cancer (PCa) is increasing, making it one of the prevalent malignancies among men. Metastasis of PCa to the bones poses the greatest danger to patients, potentially resulting in treatment ineffectiveness and mortality. At present, the management of patients with bone metastasis focuses primarily on providing palliative care. Research has indicated that the spread of PCa to the bones occurs through the participation of numerous molecules and their respective pathways. Gaining knowledge regarding the molecular processes involved in bone metastasis may result in the development of innovative and well‑tolerated therapies, ultimately enhancing the quality of life and prognosis of patients. The present article provides the latest overview of the molecular mechanisms involved in the formation of bone metastatic tumors from PCa. Additionally, the clinical outcomes of targeted drug therapies for bone metastasis are thoroughly analyzed. Finally, the benefits and difficulties of targeted therapy for bone metastasis of PCa are discussed, aiming to offer fresh perspectives for treatment.

Application and new findings of scRNA-seq and ST-seq in prostate cancer

Prostate cancer is a malignant tumor of the male urological system with the highest incidence rate in the world, which seriously threatens the life and health of middle-aged and elderly men. The progression of prostate cancer involves the interaction between tumor cells and tumor microenvironment. Understanding the mechanisms of prostate cancer pathogenesis and disease progression is important to guide diagnosis and therapy. The emergence of single-cell RNA sequencing (scRNA-seq) and spatial transcriptome sequencing (ST-seq) technologies has brought breakthroughs in the study of prostate cancer. It makes up for the defects of traditional techniques such as fluorescence-activated cell sorting that are difficult to elucidate cell-specific gene expression. This review summarized the heterogeneity and functional changes of prostate cancer and tumor microenvironment revealed by scRNA-seq and ST-seq, aims to provide a reference for the optimal diagnosis and treatment of prostate cancer.

Secreted factors from M1 macrophages drive prostate cancer stem cell plasticity by upregulating NANOG, SOX2, and CD44 through NFκB-signaling

The inflammatory tumor microenvironment (TME) is a key driver for tumor-promoting processes. Tumor-associated macrophages are one of the main immune cell types in the TME and their increased density is related to poor prognosis in prostate cancer. Here, we investigated the influence of pro-inflammatory (M1) and immunosuppressive (M2) macrophages on prostate cancer lineage plasticity. Our findings reveal that M1 macrophage secreted factors upregulate genes related to stemness while downregulating genes associated with androgen response in prostate cancer cells. The expression of cancer stem cell (CSC) plasticity markers NANOG, KLF4, SOX2, OCT4, and CD44 was stimulated by the secreted factors from M1 macrophages. Moreover, AR and its target gene PSA were observed to be suppressed in LNCaP cells treated with secreted factors from M1 macrophages. Inhibition of NFκB signaling using the IKK16 inhibitor resulted in downregulation of NANOG, SOX2, and CD44 and CSC plasticity. Our study highlights that the secreted factors from M1 macrophages drive prostate cancer cell plasticity by upregulating the expression of CSC plasticity markers through NFκB signaling pathway.

Prostate cancer stem cells and their targeted therapies

Prostate cancer (PCa) is the most common malignancy among men worldwide. Through androgen receptor signaling inhibitor (ARSI) treatment, patients eventually succumb to castration-resistant prostate cancer (CRPC). For this, the prostate cancer stem cells (PCSCs), as a minor population of tumor cells that can promote tumor relapse, ARSI resistance, and disease progression, are gaining attention. Therefore, specific therapy targeting PCSCs has momentum. This study reviewed the identification and characterization of PCSCs and PCSC-based putative biomarkers and summarized their mechanisms of action. We further discussed clinical trials of novel therapeutic interventions focused on PCSC-related pathways, the PCSC microenvironment, cutting-edge miRNA therapy, and immunotherapy approaches from a mechanistic standpoint. This review provides updated insights into PCSC plasticity, identifying new PCSC biomarkers and optimized treatments for patients with advanced PCa.

Cell Membrane-Camouflaged Chitosan-Polypyrrole Nanogels Co-Deliver Drug and Gene for Targeted Chemotherapy and Bone Metastasis Inhibition of Prostate Cancer

The development of functional nanoplatforms to improve the chemotherapy outcome and inhibit distal cancer cell metastasis remains an extreme challenge in cancer management. In this work, a human-derived PC-3 cancer cell membrane-camouflaged chitosan-polypyrrole nanogel (CH-PPy NG) platform, which can be loaded with chemotherapeutic drug docetaxel (DTX) and RANK siRNA for targeted chemotherapy and gene silencing-mediated metastasis inhibition of late-stage prostate cancer in a mouse model, is reported. The prepared NGs with a size of 155.8 nm show good biocompatibility, pH-responsive drug release profile, and homologous targeting specificity to cancer cells, allowing for efficient and precise drug/gene co-delivery. Through in-vivo antitumor treatment in a xenografted PC-3 mouse tumor model, it is shown that such a CH-PPy NG-facilitated co-delivery system allows for effective chemotherapy to slow down the tumor growth rate, and effectively inhibits the metastasis of prostate cancer to the bone via downregulation of the RANK/RANKL signaling pathway. The created CH-Ppy NGs may be utilized as a promising platform for enhanced chemotherapy and anti-metastasis treatment of prostate cancer.

Embryonic microenvironment suppresses YY1 and YY1-related genes in prostate cancer stem cells

Yin yang 1 (YY1), a transcription factor, plays crucial roles in cell fate specification, differentiation, and pluripotency during embryonic development. It is also involved in tumorigenesis, drug resistance, metastasis, and relapse caused by cancer stem cells (CSCs), particularly in prostate cancer (PCa). Targeting YY1 could potentially eliminate prostate CSCs (PCSCs) and provide novel therapeutic approaches. PCa tissues often exhibit elevated YY1 expression levels, especially in high-grade cases. Notably, high-grade PCa tissues from 58 PCa patients and CD133high/CD44high PCSCs isolated from DU145 PCa cell line by FACS both showed significantly increased YY1 expression as observed through immunofluorescence staining, respectively. To investigate the embryonic microenvironment impact on YY1 expression in CSC populations, firstly PCSCs were microinjected into the inner cell mass of blastocysts and then PCSCs were co-cultured with blastocysts. Next Generation Sequencing was used to analyze alterations in YY1 and related gene expressions. Interestingly, exposure to the embryonic microenvironment significantly reduced the expressions of YY1, YY2, and other relevant genes in PCSCs. These findings emphasize the tumor-suppressing effects of the embryonic environment by downregulating YY1 and YY1-related genes in PCSCs, thus providing promising strategies for PCa therapy. Through elucidating the mechanisms involved in embryonic reprogramming and its effects on YY1 expression, this research offers opportunities for further investigation into focused therapies directed against PCSCs, therefore enhancing the outcomes of PCa therapy. As a result, PCa tumors may benefit from YY1 and associated genes as a novel therapeutic target.

Nuclear receptor NURR1 functions to promote stemness and epithelial-mesenchymal transition in prostate cancer via its targeting of Wnt/β-catenin signaling pathway

Dysregulated activation of Wnt/β-catenin signaling pathway is a frequent or common event during advanced progression of multiple cancers. With this signaling activation, it enhances their tumorigenic growth and facilitates metastasis and therapy resistance. Advances show that this signaling pathway can play dual regulatory roles in the control of cellular processes epithelial-mesenchymal transition (EMT) and cancer stemness in cancer progression. Aberrant activation of Wnt/β-catenin signaling pathway is shown to be common in prostate cancer and also castration-resistant prostate cancer (CRPC). However, the transcriptional regulators of this pathway in prostate cancer are still not well characterized. NURR1 (NR4A2) is an orphan nuclear receptor and plays an important role in the development of dopaminergic neurons. Previously, we have shown that NURR1 exhibits an upregulation in isolated prostate cancer stem-like cells (PCSCs) and a xenograft model of CRPC. In this study, we further confirmed that NURR1 exhibited an upregulation in prostate cancer and also enhanced expression in prostate cancer cell lines. Functional and molecular analyses showed that NURR1 could act to promote both in vitro (cancer stemness and EMT) and also in vivo oncogenic growth of prostate cancer cells (metastasis and castration resistance) via its direct transactivation of CTNNB1 (β-catenin) and activation of β-catenin to mediate the activation of Wnt/β-catenin signaling pathway. Moreover, we also demonstrated that NURR1 activity in prostate cancer cells could be modulated by small molecules, implicating that NURR1 could be a potential therapeutic target for advanced prostate cancer management.

Biomolecular fingerprints of the effect of zoledronic acid on prostate cancer stem cells: Comparison of 2D and 3D cell culture models

Revealing the potential of candidate drugs against different cancer types without disrupting normal cells depends on the drug mode of action. In the current study, the drug response of prostate cancer stem cells (PCSCs) to zoledronic acid (ZOL) grown in two-dimensional (2D) and three-dimensional (3D) culture systems was compared using Fourier transform-infrared (FT-IR) spectroscopy which is a vibrational spectroscopic technique, supporting by biochemical assays and imaging techniques. Based on our data, in 2D cell culture conditions, the ZOL treatment of PCSCs isolated according to both C133 and CD44 cell surface properties induced early/late apoptosis and suppressed migration ability. The CD133 gene expression and protein levels were altered, depending on culture systems. CD133 expression was significantly reduced in 2D cells upon ZOL treatment. FT-IR data revealed that the integrity, fluidity, and ordering/disordering states of the cell membrane and nucleic acid content were altered in both 2D and 3D cells after ZOL treatment. Regular protein structures decrease in 2D cells while glycogen and protein contents increase in 3D cells, indicating a more pronounced cytotoxic effect of ZOL for 2D cells. Untreated 3D PCSCs exhibited an even different spectral profile associated with IR signals of lipids, proteins, nucleic acids, and glycogen in comparison to untreated 2D cells. Our study revealed significant differences in the drug response and cellular constituents between 2D and 3D cells. Exploring molecular targets and/or drug-action mechanisms is significant in cancer treatment approaches; thus, FT-IR spectroscopy can be successfully applied as a novel drug-screening method in clinical research.

Integrative multi-omics analysis unveils stemness-associated molecular subtypes in prostate cancer and pan-cancer: prognostic and therapeutic significance

BACKGROUND

Prostate cancer (PCA) is the fifth leading cause of cancer-related deaths worldwide, with limited treatment options in the advanced stages. The immunosuppressive tumor microenvironment (TME) of PCA results in lower sensitivity to immunotherapy. Although molecular subtyping is expected to offer important clues for precision treatment of PCA, there is currently a shortage of dependable and effective molecular typing methods available for clinical practice. Therefore, we aim to propose a novel stemness-based classification approach to guide personalized clinical treatments, including immunotherapy.

METHODS

An integrative multi-omics analysis of PCA was performed to evaluate stemness-level heterogeneities. Unsupervised hierarchical clustering was used to classify PCAs based on stemness signature genes. To make stemness-based patient classification more clinically applicable, a stemness subtype predictor was jointly developed by using four PCA datasets and 76 machine learning algorithms.

RESULTS

We identified stemness signatures of PCA comprising 18 signaling pathways, by which we classified PCA samples into three stemness subtypes via unsupervised hierarchical clustering: low stemness (LS), medium stemness (MS), and high stemness (HS) subtypes. HS patients are sensitive to androgen deprivation therapy, taxanes, and immunotherapy and have the highest stemness, malignancy, tumor mutation load (TMB) levels, worst prognosis, and immunosuppression. LS patients are sensitive to platinum-based chemotherapy but resistant to immunotherapy and have the lowest stemness, malignancy, and TMB levels, best prognosis, and the highest immune infiltration. MS patients represent an intermediate status of stemness, malignancy, and TMB levels with a moderate prognosis. We further demonstrated that these three stemness subtypes are conserved across pan-tumor. Additionally, the 9-gene stemness subtype predictor we developed has a comparable capability to 18 signaling pathways to make tumor diagnosis and to predict tumor recurrence, metastasis, progression, prognosis, and efficacy of different treatments.

CONCLUSIONS

The three stemness subtypes we identified have the potential to be a powerful tool for clinical tumor molecular classification in PCA and pan-cancer, and to guide the selection of immunotherapy or other sensitive treatments for tumor patients.

Unmasking the Deceptive Nature of Cancer Stem Cells: The Role of CD133 in Revealing Their Secrets

Cancer remains a leading cause of death globally, and its complexity poses a significant challenge to effective treatment. Cancer stem cells and their markers have become key players in tumor growth and progression. CD133, a marker in various cancer types, is an active research area as a potential therapeutic target. This article explores the role of CD133 in cancer treatment, beginning with an overview of cancer statistics and an explanation of cancer stem cells and their markers. The rise of CD133 is discussed, including its structure, functions, and occurrence in different cancer types. Furthermore, the article covers CD133 as a therapeutic target, focusing on gene therapy, immunotherapy, and approaches to affect CD133 expression. Nanoparticles such as gold nanoparticles and nanoliposomes are also discussed in the context of CD133-targeted therapy. In conclusion, CD133 is a promising therapeutic target for cancer treatment. As research in this area progresses, it is hoped that CD133-targeted therapies will offer new and effective treatment options for cancer patients in the future.

Cancer Stem Cells and Prostate Cancer: A Narrative Review

Cancer stem cells (CSCs) are a small and elusive subpopulation of self-renewing cancer cells with the remarkable ability to initiate, propagate, and spread malignant disease. In the past years, several authors have focused on the possible role of CSCs in PCa development and progression. PCa CSCs typically originate from a luminal prostate cell. Three main pathways are involved in the CSC development, including the Wnt, Sonic Hedgehog, and Notch signaling pathways. Studies have observed an important role for epithelial mesenchymal transition in this process as well as for some specific miRNA. These studies led to the development of studies targeting these specific pathways to improve the management of PCa development and progression. CSCs in prostate cancer represent an actual and promising field of research.

State-of-the-art therapeutic strategies for targeting cancer stem cells in prostate cancer

The development of new therapeutic strategies is on the increase for prostate cancer stem cells, owing to current standardized therapies for prostate cancer, including chemotherapy, androgen deprivation therapy (ADT), radiotherapy, and surgery, often failing because of tumor relapse ability. Ultimately, tumor relapse develops into advanced castration-resistant prostate cancer (CRPC), which becomes an irreversible and systemic disease. Hence, early identification of the intracellular components and molecular networks that promote prostate cancer is crucial for disease management and therapeutic intervention. One of the potential therapeutic methods for aggressive prostate cancer is to target prostate cancer stem cells (PCSCs), which appear to be a primary focal point of cancer metastasis and recurrence and are resistant to standardized therapies. PCSCs have also been documented to play a major role in regulating tumorigenesis, sphere formation, and the metastasis ability of prostate cancer with their stemness features. Therefore, the current review highlights the origin and identification of PCSCs and their role in anti-androgen resistance, as well as stemness-related signaling pathways. In addition, the review focuses on the current advanced therapeutic strategies for targeting PCSCs that are helping to prevent prostate cancer initiation and progression, such as microRNAs (miRNAs), nanotechnology, chemotherapy, immunotherapy, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene-editing system, and photothermal ablation (PTA) therapy.

Anti-Cancer Stem-Cell-Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second-most commonly diagnosed cancer in men around the world. It is treated using a risk stratification approach in accordance with the National Comprehensive Cancer Network (NCCN) in the United States. The main treatment options for early PCa include external beam radiation therapy (EBRT), brachytherapy, radical prostatectomy, active surveillance, or a combination approach. In those with advanced disease, androgen deprivation therapy (ADT) is considered as a first-line therapy. However, the majority of cases eventually progress while receiving ADT, leading to castration-resistant prostate cancer (CRPC). The near inevitable progression to CRPC has spurred the recent development of many novel medical treatments using targeted therapies. In this review, we outline the current landscape of stem-cell-targeted therapies for PCa, summarize their mechanisms of action, and discuss avenues of future development.

Hypoxia promotes conversion to a stem cell phenotype in prostate cancer cells by activating HIF-1α/Notch1 signaling pathway

PURPOSE

The hypoxic tumor microenvironment and the maintenance of stem cells are relevant to the malignancy of prostate cancer (PCa). However, whether HIF-1α in the hypoxic microenvironment mediates the transformation of prostate cancer to a stem cell phenotype and the mechanism have not been elucidated.

MATERIALS AND METHODS

Prostate cancer stem cells (PCSCs) from PC-3 cell lines were examined for the expression of CD44, CD133, ALDH1, HIF-1α, Notch1, and HES1. We observed the effect of knockdown HIF-1α in vitro and mice models and evaluated the impact of HIF-1α on the Notch1 pathway as well as stem cell dedifferentiation. The effects on sphere formation, cell proliferation, apoptosis, cell cycle, and invasive metastasis were evaluated.

RESULTS

In our study, hypoxia upregulated HIF-1α expression and induced a stem cell phenotype through activation of the Notch1 pathway, leading to enhanced proliferation, invasion, and migration of PCa PC-3 cells. The knockdown of HIF-1α significantly inhibited cell dedifferentiation and the ability to proliferate, invade and metastasize. However, the inhibitory effect of knocking down HIF-1α was reversed by Jagged1, an activator of the Notch1 pathway. These findings were further confirmed in vivo, where hypoxia could enhance the tumorigenicity of xenograft tumors by upregulating the expression of HIF-1α to activate the Notch1 pathway. In addition, the expression of HIF-1α and Notch1 was significantly increased in human PCa tissues, and high expression of HIF-1α correlated with the malignancy of PCa.

CONCLUSION

In a hypoxic environment, HIF-1α promotes PCa cell dedifferentiation to stem-like cell phenotypes by activating the Notch1 pathway and enhancing the proliferation and invasive capacity of PC-3 cells.

Stem cells from a malignant rat prostate cell line generate prostate cancers in vivo: a model for prostate cancer stem cell propagated tumor growth

Cancer stem cells (CSCs) are resistant to conventional cancer therapies, permitting the repopulation of new tumor growth and driving disease progression. Models for testing prostate CSC-propagated tumor growth are presently limited yet necessary for therapeutic advancement. Utilizing the congenic nontumorigenic NRP152 and tumorigenic NRP154 rat prostate epithelial cell lines, the present study investigated the self-renewal, differentiation, and regenerative abilities of prostate stem/progenitor cells and developed a CSC-based PCa model. NRP154 cells expressed reduced levels of tumor suppressor caveolin-1 and increased p-Src as compared to NRP152 cells. Gene knockdown of caveolin-1 in NRP152 cells upregulated p-Src, implicating their role as potential oncogenic mediators in NRP154 cells. A FACS-based Hoechst exclusion assay revealed a side population of stem-like cells (0.1%) in both NRP152 and NRP154 cell lines. Using a 3D Matrigel culture system, stem cells from both cell lines established prostaspheres at a 0.1% efficiency through asymmetric self-renewal and rapid proliferation of daughter progenitor cells. Spheres derived from both cell lines contained CD117⁺ and CD133⁺ stem cell subpopulations and basal progenitor cell subpopulations (p63⁺ and CK5⁺) but were negative for luminal cell CK8 markers at day 7. While some NRP152 sphere cells were androgen receptor (AR) positive at this timepoint, NRP154 cells were AR^- up to 30 days of 3D culture. The regenerative capacity of the stem/progenitor cells was demonstrated by in vivo tissue recombination with urogenital sinus mesenchyme (UGM) and renal grafting in nude mice. While stem/progenitor cells from NRP152 spheroids generated normal prostate structures, CSCs and progeny cells from NRP154 tumoroids generated tumor tissues that were characterized by immunohistochemistry. Atypical hyperplasia and prostatic intraepithelial neoplasia (PIN) lesions progressed to adenocarcinoma with kidney invasion over 4 months. This provides clear evidence that prostate CSCs can repopulate new tumor growth outside the prostate gland that rapidly progresses to poorly differentiated adenocarcinoma with invasive capabilities. The dual in vitro/in vivo CSC model system presented herein provides a novel platform for screening therapeutic agents that target prostate CSCs for effective combined treatment protocols for local and advanced disease stages.