Metastatic castration-resistant prostate cancer: new therapies, novel combination strategies and implications for immunotherapy

Single-cell sequencing unveils the transcriptomic landscape of castration-resistant prostate cancer-associated fibroblasts and their association with prognosis and immunotherapy response

BACKGROUND

The tumor microenvironment (TME) is increasingly acknowledged as a determinant in the malignant transformation and progression of castration-resistant prostate cancer (CRPC). Cancer-associated fibroblasts (CAFs), as a pivotal stromal cellular component in TME, are implicated in tumor progression and immune escape. However, the molecular characteristics and biological functions of CRPC-CAFs in prostate cancer necessitate further investigation.

METHODS

We ascertained the differential transcriptomic profiles between CRPC-CAFs and PCa-CAFs through single-cell RNA-sequencing (scRNA-seq). Bulk RNA-seq data were employed to assess the prognostic implications of CRPC-CAFs in PCa. In addition, we examined the impact of CRPC-CAFs on the efficacy of immunotherapy and the composition of the tumor immune milieu. Furthermore, a subcutaneous PCa model was applied to determine the potential of TGF-β signaling blockade to augment the response to immunotherapeutic interventions.

RESULTS

We observed a pronounced increase in the proportion of CAFs in CRPC compared to those in primary PCa. The functional pathways implicated in TGF-β signaling and ECM remodeling were remarkably upregulated in CRPC-CAFs. Moreover, gene regulatory network analysis uncovered substantial differences in the transcription factor activity profiles between CRPC-CAFs and PCa-CAFs. The elevated CRPC-CAFs abundance was associated with diminished recurrence-free survival and immunotherapy insensitivity. Substantially elevated infiltration of inhibitory immune cells and upregulated expression levels of immunosuppressive molecules were observed in patients with high CRPC-CAFs abundance. Importantly, administration of anti-TGF-β therapy remarkably potentiated the efficacy of anti-PD-1 immunotherapy through upregulating the anti-tumor immune response in the PCa model.

CONCLUSION

Our results highlighted the impact of CRPC-CAFs on clinical prognosis and immunosuppressive tumor milieu, indicating that CRPC-CAFs may function as a promising therapeutic target for CRPC.

Chemotactic signaling pathways in prostate cancer: Implications in the tumor microenvironment and as potential therapeutic targets

Prostate cancer (PCa) stands as a significant global health concern, ranking among the leading causes of cancer deaths in men. While there are several treatment modalities for localized PCa, metastatic castration-resistant PCa (mCRPC) remains incurable. Despite therapeutic advancements showing promise in mCRPC, their impact on overall survival has been limited. This chapter explores the process by which tumors form, reviews our current understanding of PCa progression to mCRPC, and addresses the challenges of boosting anti-tumor immune responses in these tumors. It specifically discusses how chemotactic signaling affects the tumor microenvironment and its role in immune evasion and cancer progression. The chapter further examines the rationale of directly or indirectly targeting these pathways as adjuvant therapies for mCRPC, highlighting recent pre-clinical and clinical studies currently underway. The discussion emphasizes the potential of targeting specific chemokines and chemokine receptors as combination therapies with mainstream treatments for PCa and mCRPC to maximize long-term survival for this deadly disease.

Combined therapy targeting AR and EZH2 curbs castration-resistant prostate cancer enhancing anti-tumor T-cell response

Aim: Castration-resistant prostate cancer (CRPC) eventually becomes resistant to androgen receptor pathway inhibitors like enzalutamide. Immunotherapy also fails in CRPC. We propose a new approach to simultaneously revert enzalutamide resistance and rewire anti-tumor immunity. Methods: We investigated in vitro and in subcutaneous and spontaneous mouse models the effects of combining enzalutamide and GSK-126, a drug inhibiting the epigenetic modulator EZH2. Results: Enzalutamide and GSK-126 synergized to reduce CRPC growth, also restraining tumor neuroendocrine differentiation. The anti-tumor activity was lost in immunodeficient mice. Indeed, the combination treatment awoke cytotoxic activity and IFN-γ production of tumor-specific CD8+ T lymphocytes. Conclusion: These results promote the combination of enzalutamide and GSK-126 in CRPC, also offering new avenues for immunotherapy in prostate cancer.

PSMA-targeted low-molecular double conjugates for diagnostics and therapy

This review presents data on dual conjugates of therapeutic and diagnostic action for targeted delivery to prostate cancer cells. The works of the last ten years on this topic were analyzed. The mail attention focuses on low-molecular-weight conjugates directed to the prostate-specific membrane antigen (PSMA); the comparison of high and low molecular weight PSMA-targeted conjugates was made. The considered conjugates were divided in the review into two main classes: diagnostic bimodal conjugates (which are containing two fragments for different types of diagnostics), theranostic conjugates (containing both therapeutic and diagnostic agents); also bimodal high molecular weight therapeutic conjugates containing two therapeutic agents are briefly discussed. The data of in vitro and in vivo studies for PSMA-targeted double conjugates available by the beginning of 2021 have been analyzed.

Strategy and clinical application of up-regulating cross presentation by DCs in anti-tumor therapy

The cross presentation of exogenous antigen (Ag) by dendritic cells (DCs) facilitates a diversified mode of T-cell activation, orchestrates specific humoral and cellular immunity, and contributes to an efficient anti-tumor immune response. DCs-mediated cross presentation is subject to both intrinsic and extrinsic factors, including the homing and phenotype of DCs, the spatiotemporal trafficking and degradation kinetics of Ag, and multiple microenvironmental clues, with many details largely unexplored. Here, we systemically review the current mechanistic understanding and regulation strategies of cross presentation by heterogeneous DC populations. We also provide insights into the future exploitation of DCs cross presentation for a better clinical efficacy in anti-tumor therapy.

Near infrared light activated upconversion nanoparticles (UCNP) based photodynamic therapy of prostate cancers: An in vitro study

Photodynamic therapy (PDT), has a potential to cure cancerous prostate tissue with minimal side effects. Traditional PDT, however, mostly utilized visible (VIS) light range with direct application of hydrophobic photosensitizers which may not be adequate in clinical practice for especially deep-seated cancer cells because of poor penetration of VIS wavelengths. Here, we report near infrared light (NIR) induced and dual photosensitizers (PS) encapsulated PDT strategy to reduce prostate cancer cells - PC3. The designed nanoplatform (MC540/ZnPc-UCNP@Au), in this study, include upconversion nanoparticles (UCNP) synthesis to convert NIR light into multiple VIS wavelengths, porous silica coating to upload dual photosensitizers (MC540/ZnPc), and gold (Au) functionalization to enhance PDT treatment. High chemical stabilization provided MC540/ZnPc-UCNP@Au show excellent biocompatibility, and efficient PDT treatment for prostate cancer cells. In fact, the fluorescence of the synthesized nanoplatforms, upon NIR light excitation, can produce considerable amount of ROS in 5 min, as it is well matched with the absorption of MC540, ZnPc and Au nanoparticles (np). In addition, the easy visualization of cellular internalized/adsorbed nanoplatforms reveal the in situ cell imaging possibility for diagnosis. Based on the evidence of the results, NIR light activated MC540/ZnPc-UCNP@Au may offer a PDT technique for the treatment of prostate cancer.

Castration-Induced Downregulation of SPARC in Stromal Cells Drives Neuroendocrine Differentiation of Prostate Cancer

Fatal neuroendocrine differentiation (NED) of castration-resistant prostate cancer is a recurrent mechanism of resistance to androgen deprivation therapies (ADT) and antiandrogen receptor pathway inhibitors (ARPI) in patients. The design of effective therapies for neuroendocrine prostate cancer (NEPC) is complicated by limited knowledge of the molecular mechanisms governing NED. The paucity of acquired genomic alterations and the deregulation of epigenetic and transcription factors suggest a potential contribution from the microenvironment. In this context, whether ADT/ARPI induces stromal cells to release NED-promoting molecules and the underlying molecular networks are unestablished. Here, we utilized transgenic and transplantable mouse models and coculture experiments to unveil a novel tumor-stroma cross-talk that is able to induce NED under the pressure of androgen deprivation. Castration induced upregulation of GRP78 in tumor cells, which triggers miR29-b-mediated downregulation of the matricellular protein SPARC in the nearby stroma. SPARC downregulation enabled stromal cells to release IL6, a known inducer of NED. A drug that targets GRP78 blocked NED in castrated mice. A public, human NEPC gene expression dataset showed that Hspa5 (encoding for GRP78) positively correlates with hallmarks of NED. Finally, prostate cancer specimens from patients developing local NED after ADT showed GRP78 upregulation in tumor cells and SPARC downregulation in the stroma. These results point to GRP78 as a potential therapeutic target and to SPARC downregulation in stromal cells as a potential early biomarker of tumors undergoing NED. SIGNIFICANCE: Tumor-stroma cross-talk promotes neuroendocrine differentiation in prostate cancer in response to hormone therapy via a GRP78/SPARC/IL6 axis, providing potential therapeutic targets and biomarkers for neuroendocrine prostate cancer.

The long non-coding RNA GHSROS reprograms prostate cancer cell lines toward a more aggressive phenotype

It is now appreciated that long non-coding RNAs (lncRNAs) are important players in orchestrating cancer progression. In this study we characterized GHSROS, a human lncRNA gene on the opposite DNA strand (antisense) to the ghrelin receptor gene, in prostate cancer. The lncRNA was upregulated by prostate tumors from different clinical datasets. Transcriptome data revealed that GHSROS alters the expression of cancer-associated genes. Functional analyses in vitro showed that GHSROS mediates tumor growth, migration and survival, and resistance to the cytotoxic drug docetaxel. Increased cellular proliferation of GHSROS-overexpressing PC3, DU145, and LNCaP prostate cancer cell lines in vitro was recapitulated in a subcutaneous xenograft model. Conversely, in vitro antisense oligonucleotide inhibition of the lncRNA reciprocally regulated cell growth and migration, and gene expression. Notably, GHSROS modulates the expression of PPP2R2C, the loss of which may drive androgen receptor pathway-independent prostate tumor progression in a subset of prostate cancers. Collectively, our findings suggest that GHSROS can reprogram prostate cancer cells toward a more aggressive phenotype and that this lncRNA may represent a potential therapeutic target.

The use of zebrafish model in prostate cancer therapeutic development and discovery

Zebrafish is now among the leading in vivo model for cancer research, including prostate cancer. They are an alternative economic model being used to study cancer development, proliferation, and metastasis. They can also be effectively utilized for the development of cancer drugs at all levels, including target validation, and high-throughput screening for possible lead molecules. In this review, we provide a comprehensive overview of the role of zebrafish as an in vivo model in prostate cancer research. Globally, prostate cancer is a leading cause of death in men. Although many molecular mechanisms have been identified as playing a role in the pathogenesis of prostate cancer, there is still a significant need to understand the initial events of the disease. Furthermore, current treatments are limited by the emergence of severe toxicities and multidrug resistance. There is an essential need for economical and relevant research tools to improve our understanding and overcome these problems. This review provides a comprehensive summary of studies that utilized zebrafish for different aims in prostate cancer research. We discuss the use of zebrafish in prostate cancer cell proliferation and metastasis, defining signaling pathways, drug discovery and therapeutic development against prostate cancer, and toxicity studies. Finally, this review highlights limitations in this field and future directions to efficiently use zebrafish as a robust model for prostate cancer therapeutics development.

Prognostic and Therapeutic Significance of Androgen Receptor in Patients with Gastric Cancer

Purpose

The clinical studies carried out in the last few decades unequivocally introduced activated androgen receptor (AR) as a pathogenic feature of human malignancies which not only endows cancer cells with survival advantage, but also may be exploited for anticancer interventions.

Patients and Methods

In this study, we have investigated the expression profile of AR and EMT-related genes in fresh gastric cancer (GC), adjacent nontumor and normal gastric tissues, as well as the effect and molecular mechanisms of AR inhibition in GC cell lines.

Results

Amongst 60 GC patients, 66.7% overexpressed AR that was remarkably correlated with the overexpression of Snail, β-catenin, Twist1, and STAT3. AR overexpression was also remarkably associated with unfavorable outcome (HR=3.478, P=0.001); however, multivariate Cox regression analysis indicated that it was not an independent prognostic factor (HR=2.089, P=0.056). This study has investigated simultaneous assessment of AR and EMT-related genes expression and indicated that concurrent overexpression of AR and Snail is an independent unfavorable factor for GC overall survival after adjustment with other variables (HR=2.382, P=0.021). Interestingly, the inhibition of AR signaling by potent AR antagonist enzalutamide suppressed cell growth, migration and invasion of GC cells via regulation of apoptosis-, cell cycle-, and EMT-related gene expressions.

Conclusion

Our findings have clinical importance proposing AR as an important prognostic factor involved in GC progression and metastasis, and submit AR inhibition as an appealing therapeutic approach for GC patients, either as a single agent or in a combined-modal strategy.

ACK1-AR and AR-HOXB13 signaling axes: epigenetic regulation of lethal prostate cancers

The androgen receptor (AR) is a critical transcription factor in prostate cancer (PC) pathogenesis. Its activity in malignant cells is dependent on interactions with a diverse set of co-regulators. These interactions fluctuate depending on androgen availability. For example, the androgen depletion increases the dependence of castration-resistant PCs (CRPCs) on the ACK1 and HOXB13 cell survival pathways. Activated ACK1, an oncogenic tyrosine kinase, phosphorylates cytosolic and nuclear proteins, thereby avoiding the inhibitory growth consequences of androgen depletion. Notably, ACK1-mediated phosphorylation of histone H4, which leads to epigenetic upregulation of AR expression, has emerged as a critical mechanism of CRPC resistance to anti-androgens. This resistance can be targeted using the ACK1-selective small-molecule kinase inhibitor (R)- 9b. CRPCs also deploy the bromodomain and extra-terminal domain protein BRD4 to epigenetically increase HOXB13 gene expression, which in turn activates the MYC target genes AURKA/AURKB. HOXB13 also facilitates ligand-independent recruitment of the AR splice variant AR-V7 to chromatin, compensating for the loss of the chromatin remodeling protein, CHD1, and restricting expression of the mitosis control gene HSPB8. These studies highlight the crosstalk between AR-ACK1 and AR-HOXB13 pathways as key mediators of CRPC recurrence.

A Multimodal Theranostic Nanoformulation That Dramatically Enhances Docetaxel Efficacy Against Castration Resistant Prostate Cancer

In this work, a multifunctional hierarchical nanoformulation composed of biodegradable chitosan (CS) coated poly (lactic-co-glycolic acid) (PLGA) nanocarriers loaded with docetaxel (Doc) and interleukin-8 (IL-8) small interfering RNA (siRNA) electrostatically bound to upconversion nanoparticles (UCNPs), is developed to treat castration-resistant prostate cancer (CRPC). This theranostic nanoformulation facilitates simultaneous delivery of chemotherapy and gene therapy, as well as a bimodal optical and magnetic resonance imaging agent that could enable image-guided combination therapy. Poly-d-lysine coated NaYF₄; Yb20%, Er2%@NaYF₄; Gd50% core@shell UCNPs are effective siRNA transfection agents, and Er³⁺ doping provides upconversion imaging capabilities, while Gd³⁺ doping enables magnetic resonance contrast enhancement. These properties are maintained upon encapsulation in PLGA-CS. PLGA-CS nanocarriers containing Doc and UCNP-siRNA are 235 ± 5 nm with a zeta potential of +17 ± 4 meV, and have a high Doc encapsulation efficiency of 57 ± 6%. Compared to free Doc, this PLGA-CS nanoformulation containing Doc and UCNP-siRNA exhibits a dramatic decrease in IC₅₀ of ~14,000 fold (p < 0.001) through combination therapy in human PC-3 prostate cancer cells. This biocompatible, multimodal, theranostic nanoformulation demonstrates paradigm-shifting enhancement in anticancer activity over free Doc, with unique potential for use in image-guided combination therapy to treat CRPC.

Combination of the natural product capsaicin and docetaxel synergistically kills human prostate cancer cells through the metabolic regulator AMP-activated kinase

Background

Current chemotherapy for castration-resistant prostate cancer is established on taxane-based compounds like docetaxel. However, eventually, the development of toxic side effects and resistance limits the therapeutic benefit being the major concern in the treatment of prostate cancer. Combination therapies in many cases, enhance drug efficacy and delay the appearance of undesired effects, representing an important option for the treatment of castration-resistant prostate cancer. In this study, we tested the efficacy of the combination of docetaxel and capsaicin, the pungent ingredient of hot chili peppers, on prostate cancer cells proliferation.

Methods

Prostate cancer LNCaP and PC3 cell lines were used in this study. Levels of total and phosphorylated forms of Akt, mTOR, S6, LKB1, AMPK and ACC were determined by Western blot. AMPK, LKB1 and Akt knock down was performed by siRNA. PTEN was overexpressed by transient transfection with plasmids. Xenograft prostate tumors were induced in nude mice and treatments (docetaxel and capsaicin) were administered intraperitoneally. Statistical analyses were performed with GraphPad software. Combination index was calculated with Compusyn software.

Results

Docetaxel and capsaicin synergistically inhibited the growth of LNCaP and PC3 cells, with a combination index lower than 1 for most of the combinations tested. Co-treatment with docetaxel and capsaicin notably decreased Akt and its downstream targets mTOR and S6 phosphorylation. Overexpression of PTEN phosphatase abrogated the synergistic antiproliferative effect of docetaxel and capsaicin. The combined treatment also increased the phosphorylation of AMP-activated kinase (AMPK) and the phosphorylation of its substrate ACC. In addition, pharmacological inhibition of AMPK with dorsomorphin (compound C) as well as knock down by siRNA of AMPK or its upstream kinase LKB1, abolished the synergy of docetaxel and capsaicin. Mechanistically, we showed that the synergistic anti-proliferative effect may be attributed to two independent effects: Inhibition of the PI3K/Akt/mTOR signaling pathway by one side, and AMPK activation by the other. In vivo experiments confirmed the synergistic effects of docetaxel and capsaicin in reducing the tumor growth of PC3 cells.

Conclusion

Combination of docetaxel and capsaicin represents a therapeutically relevant approach for the treatment of Prostate Cancer.

Paclitaxel-Loaded Core-Shell Magnetic Nanoparticles and Cold Atmospheric Plasma Inhibit Non-Small Cell Lung Cancer Growth

Nanoparticle-based drug delivery allows effective and sustained delivery of therapeutic agents to solid tumors and has completely changed how cancer is treated. As a new technology for medical applications, cold atmospheric plasma (CAP) shows a great potential in selective cancer treatment. The aim of this work is to develop a new dual cancer treatment approach by integrating CAP with novel paclitaxel (PTX)-loaded nanoparticles for targeting A549 cells. For this purpose, PTX-loaded core-shell magnetic nanoparticles were prepared through coaxial electrospraying, and various characteristics were investigated. Biodegradable poly(lactic- co-glycolic acid) was selected as the polymer shell to encapsulate the anticancer therapeutics. Results demonstrated a uniform size distribution and high drug encapsulation efficiency of the electrosprayed nanoparticles, which had sustained release characteristics and a variety of excellent properties. An in vitro study showed that PTX-loaded nanoparticles and CAP synergistically inhibited the growth of A549 cells more effectively than when each was used individually. We also found that CAP could induce the PTX-loaded nanoparticles in tumor cells to increase the effective drug concentration to a level that might be conducive to reduce drug resistance. Therefore, the integration of PTX-encapsulated nanoparticles and CAP provides a promising tool for the development of a new non-small cell lung cancer treatment strategy.

Bags versus flasks: a comparison of cell culture systems for the production of dendritic cell-based immunotherapies

In recent years, cell-based therapies targeting the immune system have emerged as promising strategies for cancer treatment. This review summarizes manufacturing challenges related to production of antigen presenting cells as a patient-tailored cancer therapy. Understanding cell-material interactions is essential because in vitro cell culture manipulations to obtain mature antigen-producing cells can significantly alter their in vivo performance. Traditional antigen-producing cell culture protocols often rely on cell adhesion to surface-treated hydrophilic polystyrene flasks. More recent commercial and investigational cancer immunotherapy products were manufactured using suspension cell culture in closed hydrophobic fluoropolymer bags. The shift to closed cell culture systems can decrease risks of contamination by individual operators, as well as facilitate scale-up and automation. Selecting closed cell culture bags over traditional open culture systems entails different handling procedures and processing controls, which can affect product quality. Changes in culture vessels also entail changes in vessel materials and geometry, which may alter the cell microenvironment and resulting cell fate decisions. Strategically designed culture systems will pave the way for the generation of more sophisticated and highly potent cell-based cancer vaccines. As an increasing number of cell-based therapies enter the clinic, the selection of appropriate cell culture vessels and materials becomes a critical consideration that can impact the therapeutic efficacy of the product, and hence clinical outcomes and patient quality of life.

Transition from androgenic to neurosteroidal action of 5α-androstane-3α, 17β-diol through the type A γ-aminobutyric acid receptor in prostate cancer progression

Androgen ablation is the standard of care prescribed to patients with advanced or metastatic prostate cancer (PCa) to slow down disease progression. Unfortunately, a majority of PCa patients under androgen ablation progress to castration-resistant prostate cancer (CRPC). Several mechanisms including alternative intra-prostatic androgen production and androgen-independent androgen receptor (AR) activation have been proposed for CRPC progression. Aldo-keto reductase family 1 member C3 (AKR1C3), a multi-functional steroid metabolizing enzyme, is specifically expressed in the cytoplasm of PCa cells; and positive immunoreactivity of the type A γ-aminobutyric acid receptor (GABA_AR), an ionotropic receptor and ligand-gated ion channel, is detected on the membrane of PCa cells. We studied a total of 72 radical prostatectomy cases by immunohistochemistry, and identified that 21 cases exhibited positive immunoreactivities for both AKR1C3 and GABA_AR. In the dual positive cancer cases, AKR1C3 and GABA_AR subunit α₁ were either expressed in the same cells or in neighboring cells. Among several possible substrates, AKR1C3 reduces 5α-dihydrotesterone (DHT) to form 5α-androstane-3α, 17β-diol (3α-diol). 3α-diol is a neurosteroid that acts as a positive allosteric modulator of the GABA_AR in the central nervous system (CNS). We examined the hypothesis that 3α-diol-regulated pathological effects in the prostate are GABA_AR-dependent, but are independent of the AR. In GABA_AR-positive, AR-negative human PCa PC-3 cells, 3α-diol significantly stimulated cell growth in culture and the in ovo chorioallantoic membrane (CAM) xenograft model. 3α-diol also up-regulated expression of the epidermal growth factor (EGF) family of growth factors and activation of EGF receptor (EGFR) and Src as measured by quantitative polymerase chain reaction and immunoblotting, respectively. Inclusion of GABA_AR antagonists reversed 3α-diol-stimulated tumor cell growth, expression of EGF family members, and activation of EGFR and Src to the level observed in untreated cells. Results from the present study suggest that 3α-diol may act as an alternative intra-prostatic neurosteroid that activates AR-independent PCa progression. The involvement of AKR1C3-mediated steroid metabolisms in modulating GABA_AR activation and promoting PCa progression requires continued studies.

MED15 overexpression in prostate cancer arises during androgen deprivation therapy via PI3K/mTOR signaling

Androgen deprivation therapy (ADT) is the main therapeutic option for advanced prostate cancer (PCa). After initial regression, most tumors develop into castration-resistant PCa (CRPC). Previously, we found the Mediator complex subunit MED15 to be overexpressed in CRPC and to correlate with clinical outcome. Therefore, we investigated whether MED15 is implicated in the signaling changes taking place during progression to CRPC. Immunohistochemistry (IHC) for MED15 on matched samples from the same patients before and after ADT reveals significantly increased MED15 expression after ADT in 72%. A validation cohort comprising samples before and after therapy confirmed our observations. Protein analysis for pAKT and pSMAD3 shows that MED15 correlates with PI3K and TGFß activities, respectively, and that hyper-activation of both pathways simultaneously correlates with highest levels of MED15. We further show that MED15 protein expression increases in LNCaP cells under androgen deprivation, and via EGF mediated PI3K activation. PI3K/mTOR and TGFß-receptor inhibition results in decreased MED15 expression. MED15 knockdown reduces LNCaP cell viability and induces apoptosis during androgen deprivation, while cell cycle is not affected. Collectively, MED15 overexpression arises during ADT via hyper-activation of PI3K/mTOR signaling, thus MED15 may serve as a predictive marker for response to PI3K/mTOR inhibitors. Furthermore, MED15 is potentially a therapeutic target for the treatment of CRPC.

Non-immunosuppressive triazole-based small molecule induces anticancer activity against human hormone-refractory prostate cancers: the role in inhibition of PI3K/AKT/mTOR and c-Myc signaling pathways

A series of triazole-based small molecules that mimic FTY720-mediated anticancer activity but minimize its immunosuppressive effect have been produced. SPS-7 is the most effective derivative displaying higher activity than FTY720 in anti-proliferation against human hormone-refractory prostate cancer (HRPC). It induced G1 arrest of cell cycle and subsequent apoptosis in thymidine block-mediated synchronization model. The data were supported by a decrease of cyclin D1 expression, a dramatic increase of p21 expression and an associated decrease in RB phosphorylation. c-Myc overexpression replenished protein levels of cyclin D1 indicating that c-Myc was responsible for cell cycle regulation. PI3K/Akt/mTOR signaling pathways through p70S6K- and 4EBP1-mediated translational regulation are critical to cell proliferation and survival. SPS-7 significantly inhibited this translational pathway. Overexpression of Myr-Akt (constitutively active Akt) completely abolished SPS-7-induced inhibitory effect on mTOR/p70S6K/4EBP1 signaling and c-Myc protein expression, suggesting that PI3K/Akt serves as a key upstream regulator. SPS-7 also demonstrated substantial anti-tumor efficacy in an in vivo xenograft study using PC-3 mouse model. Notably, FTY720 but not SPS-7 induced a significant immunosuppressive effect as evidenced by depletion of marginal zone B cells, down-regulation of sphingosine-1-phosphate receptors and a decrease in peripheral blood lymphocytes. In conclusion, the data suggest that SPS-7 is not an immunosuppressant while induces anticancer effect against HRPC through inhibition of Akt/mTOR/p70S6K pathwaysthat down-regulate protein levels of both c-Myc and cyclin D1, leading to G1 arrest of cell cycle and subsequent apoptosis. The data also indicate the potential of SPS-7 since PI3K/Akt signalingis responsive for the genomic alterations in prostate cancer.

Immunotherapy for Prostate Cancer: Where We Are Headed

Prostate cancer is one of the most common malignant neoplasms in men worldwide, and is the fifth cause of cancer-related death. In recent years, a new generation of therapies have been approved for the management of metastatic disease. Moreover, the development of new immunotherapeutic drugs has become a novel frontier for the treatment of several tumor types; to date, numerous studies have investigated their potential activity, including in prostate cancer. In this article, we discuss the role of emerging immunotherapeutic drugs in prostate cancer patients.

Prostate Cancer Cells Express More Androgen Receptor (AR) Following Androgen Deprivation, Improving Recognition by AR-Specific T Cells

Androgen deprivation is the primary therapy for recurrent prostate cancer, and agents targeting the androgen receptor (AR) pathway continue to be developed. Because androgen-deprivation therapy (ADT) has immmunostimulatory effects as well as direct antitumor effects, AR-targeted therapies have been combined with other anticancer therapies, including immunotherapies. Here, we sought to study whether an antigen-specific mechanism of resistance to ADT (overexpression of the AR) may result in enhanced AR-specific T-cell immune recognition, and whether this might be strategically combined with an antitumor vaccine targeting the AR. Androgen deprivation increased AR expression in human and murine prostate tumor cells in vitro and in vivo The increased expression persisted over time. Increased AR expression was associated with recognition and cytolytic activity by AR-specific T cells. Furthermore, ADT combined with vaccination, specifically a DNA vaccine encoding the ligand-binding domain of the AR, led to improved antitumor responses as measured by tumor volumes and delays in the emergence of castrate-resistant prostate tumors in two murine prostate cancer models (Myc-CaP and prostate-specific PTEN-deficient mice). Together, these data suggest that ADT combined with AR-directed immunotherapy targets a major mechanism of resistance, overexpression of the AR. This combination may be more effective than ADT combined with other immunotherapeutic approaches. Cancer Immunol Res; 5(12); 1074-85. ©2017 AACR.

Myeloid-derived cells in prostate cancer progression: phenotype and prospective therapies

Prostate cancer is the second most common cause of cancer mortality in men in the United States. As is the case for other tumor types, accumulating evidence suggests an important role for myeloid-derived cells in the promotion and progression of prostate cancer. Here, we briefly describe myeloid-derived cells that interact with tumor cells and what is known about their immune suppressive function. We next discuss new evidence for tumor cell-mediated myeloid infiltration via the PI3K/PTEN/AKT signaling pathway and an alternative mechanism for immune evasion that may be regulated by an endoplasmic reticulum stress response. Finally, we discuss several interventions that target myeloid-derived cells to treat prostate cancer.

Bone-Targeted Imaging and Radionuclide Therapy in Prostate Cancer

Although selective metabolic and receptor-based molecular agents will surely be included in the future of prostate cancer diagnosis and therapy, currently available inorganic compounds-such as ¹⁸F-NaF for the diagnosis of bony disease and ²²³RaCl₂ for the therapy of bone metastases-were recently shown to be superior to standard ^99mTc-phosphonates for diagnosis and ¹⁵³Sm-ethylenediaminetetramethylene phosphonate or ⁸⁹SrCl₂ for therapy. The advantages of ¹⁸F-NaF include improved lesion detection and, when used in combination with CT, improved diagnostic confidence and specificity. In addition to being the first approved α-emitter, ²²³RaCl₂ is the first radiopharmaceutical to show an increase in overall survival, a decrease in skeletal events, palliation of bone pain, and a low profile of adverse reactions (which are mild and manageable). The management of metastatic bone disease with ²²³RaCl₂ is uniquely satisfying, as patients can be monitored directly during their monthly treatment visits.

Triptolide Inhibits the AR Signaling Pathway to Suppress the Proliferation of Enzalutamide Resistant Prostate Cancer Cells

Enzalutamide is a second-generation androgen receptor (AR) antagonist for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Unfortunately, AR dysfunction means that resistance to enzalutamide will eventually develop. Thus, novel agents are urgently needed to treat this devastating disease. Triptolide (TPL), a key active compound extracted from the Chinese herb Thunder God Vine (Tripterygium wilfordii Hook F.), possesses anti-cancer activity in human prostate cancer cells. However, the effects of TPL against CRPC cells and the underlying mechanism of any such effect are unknown. In this study, we found that TPL at low dose inhibits the transactivation activity of both full-length and truncated AR without changing their protein levels. Interestingly, TPL inhibits phosphorylation of AR and its CRPC-associated variant AR-V7 at Ser515 through XPB/CDK7. As a result, TPL suppresses the binding of AR to promoter regions in AR target genes along with reduced TFIIH and RNA Pol II recruitment. Moreover, TPL at low dose reduces the viability of prostate cancer cells expressing AR or AR-Vs. Low-dose TPL also shows a synergistic effect with enzalutamide to inhibit CRPC cell survival in vitro, and enhances the anti-cancer effect of enzalutamide on CRPC xenografts with minimal side effects. Taken together, our data demonstrate that TPL targets the transactivation activity of both full-length and truncated ARs. Our results also suggest that TPL is a potential drug for CRPC, and can be used in combination with enzalutamide to treat CRPC.

Androgen receptor-dependent and -independent mechanisms driving prostate cancer progression: Opportunities for therapeutic targeting from multiple angles

Despite aggressive treatment for localized cancer, prostate cancer (PC) remains a leading cause of cancer-related death for American men due to a subset of patients progressing to lethal and incurable metastatic castrate-resistant prostate cancer (CRPC). Organ-confined PC is treated by surgery or radiation with or without androgen deprivation therapy (ADT), while options for locally advanced and disseminated PC include radiation combined with ADT, or systemic treatments including chemotherapy. Progression to CRPC results from failure of ADT, which targets the androgen receptor (AR) signaling axis and inhibits AR-driven proliferation and survival pathways. The exact mechanisms underlying the transition from androgen-dependent PC to CRPC remain incompletely understood. Reactivation of AR has been shown to occur in CRPC despite depletion of circulating androgens by ADT. At the same time, the presence of AR-negative cell populations in CRPC has also been identified. While AR signaling has been proposed as the primary driver of CRPC, AR-independent signaling pathways may represent additional mechanisms underlying CRPC progression. Identification of new therapeutic strategies to target both AR-positive and AR-negative PC cell populations and, thereby, AR-driven as well as non-AR-driven PC cell growth and survival mechanisms would provide a two-pronged approach to eliminate CRPC cells with potential for synthetic lethality. In this review, we provide an overview of AR-dependent and AR-independent molecular mechanisms which drive CRPC, with special emphasis on the role of the Jak2-Stat5a/b signaling pathway in promoting castrate-resistant growth of PC through both AR-dependent and AR-independent mechanisms.

Adipocytes promote prostate cancer stem cell self-renewal through amplification of the cholecystokinin autocrine loop

Obesity has long been linked with prostate cancer progression, although the underlying mechanism is still largely unknown. Here, we report that adipocytes promote the enrichment of prostate cancer stem cells (CSCs) through a vicious cycle of autocrine amplification. In the presence of adipocytes, prostate cancer cells actively secrete the peptide hormone cholecystokinin (CCK), which not only stimulates prostate CSC self-renewal, but also induces cathepsin B (CTSB) production of the adipocytes. In return, CTSB facilitates further CCK secretion by the cancer cells. More importantly, inactivation of CCK receptor not only suppresses CTSB secretion by the adipocytes, but also synergizes the inhibitory effect of CTSB inhibitor on adipocyte-promoted prostate CSC self-renewal. In summary, we have uncovered a novel mechanism underlying the mutual interplay between adipocytes and prostate CSCs, which may help explaining the role of adipocytes in prostate cancer progression and provide opportunities for effective intervention.

The Effect of F877L and T878A Mutations on Androgen Receptor Response to Enzalutamide

Treatment-induced mutations in the ligand-binding domain of the androgen receptor (AR) are known to change antagonists into agonists. Recently, the F877L mutation has been described to convert enzalutamide into an agonist. This mutation was seen to co-occur in the endogenous AR allele of LNCaP cells, next to the T878A mutation. Here, we studied the effects of enzalutamide on the F877L and T878A mutants, as well as the double-mutant AR (F877L/T878A). Molecular modeling revealed favorable structural changes in the double-mutant AR that lead to a decrease in steric clashes for enzalutamide. Ligand-binding assays confirmed that the F877L mutation leads to an increase in relative binding affinity for enzalutamide, but only the combination with the T878A mutation resulted in a strong agonistic activity. This correlated with changes in coregulator recruitment and chromatin interactions. Our data show that enzalutamide is only a very weak partial agonist of the AR F877L, and a strong partial agonist of the double-mutant AR. Mol Cancer Ther; 15(7); 1702-12. ©2016 AACR.

SRPK1 inhibition in prostate cancer: A novel anti-angiogenic treatment through modulation of VEGF alternative splicing

Prostate cancer remains one of the leading causes of cancer death in men around the world, regardless of intense research and development of novel therapies in the last 10 years. One of the new avenues that has been tested - inhibition of angiogenesis - has been disappointing so far in clinical studies in spite of strong evidence that determinants of angiogenesis (e.g. vascular endothelial growth factor) are strongly associated with disease progression. One of the reasons for these outcomes may be our poor understanding of the biology of angiogenesis in prostate cancer (and probably other cancers as well) resulting in inhibition of both detrimental and favourable molecules. We discuss here novel targeted and more specific approaches to inhibit angiogenesis in prostate cancer as well as a completely new therapeutic modality to do this - modulation of alternative splicing - that may be applicable to other molecules/biological processes as well.

Diagnosis of prostatic carcinoma on multiparametric magnetic resonance imaging using shearlet transform

This paper presents a method to diagnose prostate cancer on multiparametric magnetic resonance imaging (Mp-MRI) using the shearlet transform. The objective is classification of benign and malignant regions on transverse relaxation time weighted (T2W), dynamic contrast enhanced (DCE), and apparent diffusion coefficient (ADC) images. Compared with conventional wavelet filters, shearlet has inherent directional sensitivity, which makes it suitable for characterizing small contours of cancer cells. By applying a multi-scale decomposition, the shearlet transform captures visual information provided by edges detected at different orientations and multiple scales in each region of interest (ROI) of the images. ROIs are represented by histograms of shearlet coefficients (HSC) and then used as features in Support Vector Machines (SVM) to classify ROIs as benign or malignant. Experimental results show that our method can recognize carcinoma in T2W, DCE, and ADC with overall sensitivity of 92%, 100%, and 89%, respectively. Hence, application of shearlet transform may further increase utility of Mp-MRI for prostate cancer diagnosis.

Beyond the Immune Suppression: The Immunotherapy in Prostate Cancer

Prostate cancer (PCa) is the second most common cancer in men. As well in many other human cancers, inflammation and immune suppression have an important role in their development. We briefly describe the host components that interact with the tumor to generate an immune suppressive environment involved in PCa promotion and progression. Different tools provide to overcome the mechanisms of immunosuppression including vaccines and immune checkpoint blockades. With regard to this, we report results of most recent clinical trials investigating immunotherapy in metastatic PCa (Sipuleucel-T, ipilimumab, tasquinimod, Prostvac-VF, and GVAX) and provide possible future perspectives combining the immunotherapy to the traditional therapies.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

SYK is a candidate kinase target for the treatment of advanced prostate cancer

Improved targeted therapies are needed to combat metastatic prostate cancer. Here, we report the identification of the spleen kinase SYK as a mediator of metastatic dissemination in zebrafish and mouse xenograft models of human prostate cancer. Although SYK has not been implicated previously in this disease, we found that its expression is upregulated in human prostate cancers and associated with malignant progression. RNAi-mediated silencing prevented invasive outgrowth in vitro and bone colonization in vivo, effects that were reversed by wild-type but not kinase-dead SYK expression. In the absence of SYK expression, cell surface levels of the progression-associated adhesion receptors integrin α2β1 and CD44 were diminished. RNAi-mediated silencing of α2β1 phenocopied SYK depletion in vitro and in vivo, suggesting an effector role for α2β1 in this setting. Notably, pharmacologic inhibitors of SYK kinase currently in phase I-II trials for other indications interfered similarly with the invasive growth and dissemination of prostate cancer cells. Our findings offer a mechanistic rationale to reposition SYK kinase inhibitors for evaluation in patients with metastatic prostate cancer.

Serine-arginine protein kinase 1 (SRPK1) inhibition as a potential novel targeted therapeutic strategy in prostate cancer

Angiogenesis is required for tumour growth and is induced principally by VEGF-A. VEGF-A pre-mRNA is alternatively spliced at the terminal exon to produce two families of isoforms, pro- and anti-angiogenic, only the former of which is upregulated in prostate cancer. In renal epithelial cells and colon cancer cells, the choice of VEGF splice isoforms is controlled by the splicing factor SRSF1, phosphorylated by SRPK1. Immunohistochemistry staining of human samples revealed a significant increase in SRPK1 expression both in prostate intra-epithelial neoplasia lesions as well as malignant adenocarcinoma compared to benign prostate tissue. We therefore tested the hypothesis that the selective upregulation of pro-angiogenic VEGF in prostate cancer may be under the control of SRPK1 activity. A switch in the expression of VEGF₁₆₅ towards the anti-angiogenic splice isoform, VEGF₁₆₅b, was seen in PC-3 cells with SRPK1 knock-down (KD). PC-3 SRPK1-KD cells resulted in tumours that grew more slowly in xenografts, with decreased microvessel density. No effect was seen as a result of SRPK1-KD on growth, proliferation, migration and invasion capabilities of PC-3 cells in vitro. Small molecule inhibitors of SRPK1 switched splicing towards the anti-angiogenic isoform VEGF₁₆₅b in PC3 cells and decreased tumour growth when administered intraperitoneally in an orthotopic mouse model of prostate cancer. Our study suggests that modulation of SRPK1 and subsequent inhibition of tumour angiogenesis by regulation of VEGF splicing can alter prostate tumour growth and supports further studies into the use of SRPK1 inhibition as a potential anti-angiogenic therapy in prostate cancer.