AR-V7 in Metastatic Prostate Cancer: A Strategy beyond Redemption

Integrative Chinese-Western medicine strategy to overcome docetaxel resistance in prostate cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese Medicines (TCMs) have emerged as a promising complementary therapy in the management of prostate cancer (PCa), particularly in addressing resistance to Docetaxel (DTX) chemotherapy.

AIM OF THE REVIEW

This review aims to elucidate the mechanisms underlying the development of resistance to DTX in PCa and explore the innovative approach of integrating TCMs in PCa treatment to overcome this resistance. Key areas of investigation include alterations in microtubule proteins, androgen receptor and androgen receptor splice variant 7, ERG rearrangement, drug efflux mechanisms, cancer stem cells, centrosome clustering, upregulation of the PI3K/AKT signaling pathway, enhanced DNA damage repair capability, and the involvement of neurotrophin receptor 1/protein kinase C.

MATERIALS AND METHODS

With "Prostate cancer", "Docetaxel", "Docetaxel resistance", "Natural compounds", "Traditional Chinese medicine", "Traditional Chinese medicine compound", "Medicinal plants" as the main keywords, PubMed, Web of Science and other online search engines were used for literature retrieval.

RESULTS

Our findings underscore the intricate interplay of molecular alterations that collectively contribute to the resistance of PCa cells to DTX. Moreover, we highlight the potential of TCMs as a promising complementary therapy, showcasing their ability to counteract DTX resistance and enhance therapeutic efficacy.

CONCLUSION

The integration of TCMs in PCa treatment emerges as an innovative approach with significant potential to overcome DTX resistance. This review not only provides insights into the mechanisms of resistance but also presents new prospects for improving the clinical outcomes of patients with PCa undergoing DTX therapy. The comprehensive understanding of these mechanisms lays the foundation for future research and the development of more effective therapeutic interventions.

Reproducible preclinical models of androgen receptor driven human prostate cancer bone metastasis

BACKGROUND

Preclinical models recapitulating the metastatic phenotypes are essential for developing the next-generation therapies for metastatic prostate cancer (mPC). We aimed to establish a cohort of clinically relevant mPC models, particularly androgen receptor positive (AR+) bone metastasis models, from LuCaP patient-derived xenografts (PDX) that reflect the heterogeneity and complexity of mPC.

METHODS

PDX tumors were dissociated into single cells, modified to express luciferase, and were inoculated into NSG mice via intracardiac injection. The progression of metastases was monitored by bioluminescent imaging. Histological phenotypes of metastases were characterized by immunohistochemistry and immunofluorescence staining. Castration responses were further investigated in two AR-positive models.

RESULTS

Our PDX-derived metastasis (PDM) model collection comprises three AR+ adenocarcinomas (ARPC) and one AR- neuroendocrine carcinoma (NEPC). All ARPC models developed bone metastases with either an osteoblastic, osteolytic, or mixed phenotype, while the NEPC model mainly developed brain metastasis. Different mechanisms of castration resistance were observed in two AR+ PDM models with distinct genotypes, such as combined loss of TP53 and RB1 in one model and expression of AR splice variant 7 (AR-V7) expression in another model. Intriguingly, the castration-resistant tumors displayed inter- and intra-tumor as well as organ-specific heterogeneity in lineage specification.

CONCLUSION

Genetically diverse PDM models provide a clinically relevant system for biomarker identification and personalized medicine in metastatic castration-resistant prostate cancer.

Understanding variants of unknown significance and classification of genomic alterations

Despite recent efforts to issue clinical guidelines outlining strategies to define the pathogenicity of genomic variants, there is currently no standardized framework for which to make these assertions. This review does not present a step-by-step methodology, but rather takes a holistic approach to discuss many aspects which should be taken into consideration when determining variant pathogenicity. Categorization should be curated to reflect relevant findings within the scope of the specific medical context. Functional characterization should evaluate all available information, including results from literature reviews, different classes of genomic data repositories, and applicable computational predictive algorithms. This article further proposes a multidimensional view to infer pathogenic status from many genomic measurements across multiple axes. Notably, tumor suppressors and oncogenes exhibit fundamentally different biology which helps refine the importance of effects on splicing, mutation interactions, copy number thresholds, rearrangement annotations, germline status, and genome-wide signatures. Understanding these relevant datapoints with thoughtful perspective could aid in the reclassification of variants of unknown significance (VUS), which are ambiguously understood and currently have uncertain clinical implications. Ongoing assessments of VUS examining these relevant biological axes could lead to more accurate classification of variant pathogenicity interpretation in diagnostic oncology.

Novel Androgen Receptor Splice Variant 7 in Gynecologic Tumors

Androgen receptor splicing variant 7 (AR-V7) is a truncated variant of the AR mRNA that may be a predictive biomarker for AR-targeted therapy. AR-V7 has been described in prostate, breast, salivary duct, and hepatocellular carcinomas as well as mammary and extra-mammary Paget disease. We report 2 gynecologic cancers occurring in the lower uterine segment and ovary and both harboring AR-V7 by targeted RNA sequencing. The uterine tumor was an undifferentiated carcinoma consisting of epithelioid cells and focally spindled cells arranged in sheets, nests, and cords associated with brisk mitotic activity and tumor necrosis. The ovarian tumor consisted of glands with cribriform and solid architecture and uniform cytologic atypia. ER and PR were positive in the ovarian tumor and negative in the uterine tumor. Both were positive for AR and negative for HER2, GATA3, and NKX3.1. DNA methylation profiling showed epigenetic similarity of the AR-V7-positive gynecologic cancers to AR-V7-positive breast cancers rather than to prostate cancers. AR-V7 may underpin rare gynecologic carcinomas with undifferentiated histology or cribriform growth reminiscent of prostatic adenocarcinoma and breast invasive ductal carcinoma.

Advances in sequencing and omics studies in prostate cancer: unveiling molecular pathogenesis and clinical applications

Background

Prostate cancer (PCa) is one of the most threatening health problems for the elderly males. However, our understanding of the disease has been limited by the research technology for a long time. Recently, the maturity of sequencing technology and omics studies has been accelerating the studies of PCa, establishing themselves as an essential impetus in this field.

Methods

We assessed Web of Science (WoS) database for publications of sequencing and omics studies in PCa on July 3rd, 2023. Bibliometrix was used to conduct ulterior bibliometric analysis of countries/affiliations, authors, sources, publications, and keywords. Subsequently, purposeful large amounts of literature reading were proceeded to analyze research hotspots in this field.

Results

3325 publications were included in the study. Research associated with sequencing and omics studies in PCa had shown an obvious increase recently. The USA and China were the most productive countries, and harbored close collaboration. CHINNAIYAN AM was identified as the most influential author, and CANCER RESEARCH exhibited huge impact in this field. Highly cited publications and their co-citation relationships were used to filtrate literatures for subsequent literature reading. Based on keyword analysis and large amounts of literature reading, 'the molecular pathogenesis of PCa' and 'the clinical application of sequencing and omics studies in PCa' were summarized as two research hotspots in the field.

Conclusion

Sequencing technology had a deep impact on the studies of PCa. Sequencing and omics studies in PCa helped researchers reveal the molecular pathogenesis, and provided new possibilities for the clinical practice of PCa.

Targeting androgen biosynthesis in prostate cancer: implications on endocrine physiology

PURPOSE OF REVIEW

Targeting specific steroidogenic enzymes is effective in decreasing testosterone synthesis, resulting in significant antitumor effects in prostate cancer. Such treatments result in disruptions of complicated and intertwining pathways with systemic physiologic consequences via effects on the adrenal gland and renin-angiotensin-aldosterone axis. This review highlights some of these aspects that need to be taken into consideration when treating patients with androgen biosynthesis inhibitors.

RECENT FINDINGS

Targeting CYP17A1, a key enzyme involved in androgen biosynthesis, is a well established treatment in prostate cancer. More recently, efforts are underway to target a gatekeeper enzyme of steroidogenesis, CYP11A1. This enzyme mediates conversion of cholesterol to pregnenolone, the first step in steroid hormone biogenesis. Studies are beginning to demonstrate antitumor effects of ODM-208, a CYP11A1 inhibitor in prostate cancer. Although anticipated to have a therapeutic role in prostate cancer, there are potential downstream effects of CYP11A1 targeting arising from suppression of the entire adrenal cortex, including long-term adrenal insufficiency and possibly cardiovascular dysregulation.

SUMMARY

Agents targeting androgen biosynthesis can have systemic implications. Balancing management of prostate cancer with better understanding of the mechanisms associated with potential side effects will allow for patients to obtain improved antitumor benefit while mitigating against treatment-associated adverse effects.

Discovery of an Aldo-Keto reductase 1C3 (AKR1C3) degrader

Aldo-keto reductase 1C3 (AKR1C3) is a protein upregulated in prostate cancer, hematological malignancies, and other cancers where it contributes to proliferation and chemotherapeutic resistance. Androgen receptor splice variant 7 (ARv7) is the most common mutation of the AR receptor that confers resistance to clinical androgen receptor signalling inhibitors in castration-resistant prostate cancer. AKR1C3 interacts with ARv7 promoting stabilization. Herein we report the discovery of the first-in-class AKR1C3 Proteolysis-Targeting Chimera (PROTAC) degrader. This first-generation degrader potently reduced AKR1C3 expression in 22Rv1 prostate cancer cells with a half-maximal degradation concentration (DC50) of 52 nM. Gratifyingly, concomitant degradation of ARv7 was observed with a DC50 = 70 nM, along with degradation of the AKR1C3 isoforms AKR1C1 and AKR1C2 to a lesser extent. This compound represents a highly useful chemical tool and a promising strategy for prostate cancer intervention.

Evaluation of AR, AR-V7, and p160 family as biomarkers for prostate cancer: insights into the clinical significance and disease progression

PURPOSE

To assess the role of the p160 family, AR, and AR-V7 in different initial presentations of prostate cancer and their association with clinical endpoints related to tumor progression.

METHODS

The study sample comprises 155 patients who underwent radical prostatectomy and 11 healthy peripheral zone biopsies as the control group. Gene expression was quantified by qPCR from the tissue specimens. The statistical analysis investigated correlations between gene expression levels, associations with disease presence, and clinicopathological features. Additionally, ROC curves were applied for distinct PCa presentations, and time-to-event analysis was used for clinical endpoints.

RESULTS

The AR-V7 diagnostic performance for any PCa yielded an AUC of 0.77 (p < 0.05). For locally advanced PCa, the AR-V7 AUC was 0.65 (p < 0.05). Moreover, the metastasis group had a higher expression of SRC-1 than the non-metastatic group (p < 0.05), showing a shorter time to metastasis in the over-expressed group (p = 0.005). Patients with disease recurrence had super-expression of AR levels (p < 0.0005), with a shorter time-to-recurrence in the super-expression group (p < 0.0001).

CONCLUSION

Upregulation of SRC-1 indicates a higher risk of progression to metastatic disease in a shorter period, which warrants further research to be applied as a clinical tool. Additionally, AR may be used as a predictor for PCa recurrence. Furthermore, AR-V7 may be helpful as a diagnostic tool for PCa and locally advanced cancer, comparable with other investigated tools.

Assessing the Potential of Small Peptides for Altering Expression Levels of the Iron-Regulatory Genes FTH1 and TFRC and Enhancing Androgen Receptor Inhibitor Activity in In Vitro Prostate Cancer Models

Recent research highlights the key role of iron dyshomeostasis in the pathogenesis of prostate cancer (PCa). PCa cells are heavily dependent on bioavailable iron, which frequently results in the reprogramming of iron uptake and storage pathways. Although advanced-stage PCa is currently incurable, bioactive peptides capable of modulating key iron-regulatory genes may constitute a means of exploiting a metabolic adaptation necessary for tumor growth. Recent annual increases in PCa incidence have been reported, highlighting the urgent need for novel treatments. We examined the ability of LNCaP, PC3, VCaP, and VCaP-EnzR cells to form colonies in the presence of androgen receptor inhibitors (ARI) and a series of iron-gene modulating oligopeptides (FT-001-FT-008). The viability of colonies following treatment was determined with clonogenic assays, and the expression levels of FTH1 (ferritin heavy chain 1) and TFRC (transferrin receptor) were determined with quantitative polymerase chain reaction (PCR). Peptides and ARIs combined significantly reduced PCa cell growth across all phenotypes, of which two peptides were the most effective. Colony growth suppression generally correlated with the magnitude of concurrent increases in FTH1 and decreases in TFRC expression for all cells. The results of this study provide preliminary insight into a novel approach at targeting iron dysmetabolism and sensitizing PCa cells to established cancer treatments.

Pinostilbene inhibits full-length and splice variant of androgen receptor in prostate cancer

Prostate cancer is the most prevalent cancer in men worldwide and is promoted by the sex hormone androgen. Expression of androgen from the testis can be significantly reduced through castration. However, as most prostate cancer patients acquire castration resistance, additional therapeutic solutions are necessary. Although anti-androgens, such as enzalutamide, have been used to treat castration-resistant prostate cancer (CRPC), enzalutamide-resistant CRPC (Enz-resistant CRPC) has emerged. Therefore, development of novel treatments for Enz-resistant CRPC is urgent. In this study, we found a novel anti-androgen called pinostilbene through screening with a GAL4-transactivation assay. We confirmed that pinostilbene directly binds to androgen receptor (AR) and inhibits its activation and translocalization. Pinostilbene treatment also reduced the protein level and downstream gene expression of AR. Furthermore, pinostilbene reduced the protein level of AR variant 7 in the Enz-resistant prostate cancer cell line 22Rv1 and inhibited cell viability and proliferation. Our results suggest that pinostilbene has the potential to treat Enz-resistant CRPC.

Molecular basis and therapeutic targets in prostate cancer: A comprehensive review

Prostate cancer is one of the most significant causes of morbidity and mortality in male patients. The incidence increases with age, and it is higher among African Americans. The occurrence of prostate cancer is associated with many risk factors, including genetic and hereditary predisposition. The most common genetic syndromes associated with prostate cancer risk are BRCA-associated hereditary breast and ovarian cancer (HBOC) and Lynch syndrome. Local-regional therapy, i.e., surgery is beneficial in early-stage prostate cancer management. Advanced and metastatic prostate cancers require systemic therapies, including hormonal inhibition, chemotherapy, and targeted agents. Most prostate cancers can be treated by targeting the androgen-receptor pathway and decreasing androgen production or binding to androgen receptors (AR). Castration-resistant prostate cancer (CRPC) usually involves the PI3K/AKT/mTOR pathway and requires targeted therapy. Specific molecular therapy can target mutated cell lines in which DNA defect repair is altered, caused by mutations of BRCA2, partner and localizer of BRCA2 (PALB2), and phosphatase and tensin homolog (PTEN) or the transmembrane protease serine 2-ERG (TMPRSS2-ERG) fusion. Most benefits were demonstrated in cyclin dependent-kinase 12 (CDK12) mutated cell lines when treated with anti-programmed cell death protein 1 (PD1) therapy. Therapies targeting p53 and AKT are the subject of ongoing clinical trials. Many genetic defects are listed as diagnostic, prognostic, and clinically actionable markers in prostate cancer. Androgen receptor splice variant 7 (AR-V7) is an important oncogenic driver and an early diagnostic and prognostic marker, as well as a therapeutic target in hormone-resistant CRPC. This review summarizes the pathophysiological mechanisms and available targeted therapies for prostate cancer.

siRNA-based approaches for castration-resistant prostate cancer therapy targeting the androgen receptor signaling pathway

Androgen deprivation therapy is a common treatment method for metastatic prostate cancer through lowering androgen levels; however, this therapy frequently leads to the development of castration-resistant prostate cancer (CRPC). This is attributed to the activation of the androgen receptor (AR) signaling pathway. Current treatments targeting AR are often ineffective mostly due to AR gene overexpression and mutations, as well as the presence of splice variants that accelerate CRPC progression. Thus there is a critical need for more specific medication to treat CRPC. Small interfering RNAs have shown great potential as a targeted therapy. This review discusses prostate cancer progression and the role of AR signaling in CRPC, and proposes siRNA-based targeted therapy as a promising strategy for CRPC.

Novel Inhibitors of androgen receptor's DNA binding domain identified using an ultra-large virtual screening

Androgen receptor (AR) inhibition remains the primary strategy to combat the progression of prostate cancer (PC). However, all clinically used AR inhibitors target the ligand-binding domain (LBD), which is highly susceptible to truncations through splicing or mutations that confer drug resistance. Thus, there exists an urgent need for AR inhibitors with novel modes of action. We thus launched a virtual screening of an ultra-large chemical library to find novel inhibitors of the AR DNA-binding domain (DBD) at two sites: protein-DNA interface (P-box) and dimerization site (D-box). The compounds selected through vigorous computational filtering were then experimentally validated. We identified several novel chemotypes that effectively suppress transcriptional activity of AR and its splice variant V7. The identified compounds represent previously unexplored chemical scaffolds with a mechanism of action that evades the conventional drug resistance manifested through LBD mutations. Additionally, we describe the binding features required to inhibit AR DBD at both P-box and D-box target sites.

Genetic and epigenetic features of neuroendocrine prostate cancer and their emerging applications

Prostate cancer is the second most prevalent cancer in men globally. De novo neuroendocrine prostate cancer (NEPC) is uncommon at initial diagnosis, however, (treatment-induced) t-NEPC emerges in up to 25% of prostate adenocarcinoma (PRAD) cases treated with androgen deprivation, carrying a drastically poor prognosis. The transition from PRAD to t-NEPC is underpinned by several key genetic mutations; TP53, RB1, and MYCN are the main genes implicated, bearing similarities to other neuroendocrine tumours. A broad range of epigenetic alterations, such as aberrations in DNA methylation, histone post-translational modifications, and non-coding RNAs, may drive lineage plasticity from PRAD to t-NEPC. The clinical diagnosis of NEPC is hampered by a lack of accessible biomarkers; recent advances in liquid biopsy techniques assessing circulating tumour cells and ctDNA in NEPC suggest that the advent of non-invasive means of monitoring progression to NEPC is on the horizon. Such techniques are vital for NEPC management; diagnosis of t-NEPC is crucial for implementing effective treatment, and precision medicine will be integral to providing the best outcomes for patients.

Novel signatures of prostate cancer progression and therapeutic resistance

INTRODUCTION

The extensive heterogeneity of prostate cancer (PCa) and multilayered complexity of progression to castration-resistant prostate cancer (CRPC) have contributed to the challenges of accurately monitoring advanced disease. Profiling of the tumor microenvironment with large-scale transcriptomic studies have identified gene signatures that predict biochemical recurrence, lymph node invasion, metastases, and development of therapeutic resistance through critical determinants driving CRPC.

AREAS COVERED

This review encompasses understanding of the role of different molecular determinants of PCa progression to lethal disease including the phenotypic dynamic of cell plasticity, EMT-MET interconversion, and signaling-pathways driving PCa cells to advance and metastasize. The value of liquid biopsies encompassing circulating tumor cells and extracellular vesicles to detect disease progression and emergence of therapeutic resistance in patients progressing to lethal disease is discussed. Relevant literature was added from PubMed portal.

EXPERT OPINION

Despite progress in the tumor-targeted therapeutics and biomarker discovery, distant metastasis and therapeutic resistance remain the major cause of mortality in patients with advanced CRPC. No single signature can encompass the tremendous phenotypic and genomic heterogeneity of PCa, but rather multi-threaded omics-derived and phenotypic markers tailored and validated into a multimodal signature.

Emergent dynamics of underlying regulatory network links EMT and androgen receptor-dependent resistance in prostate cancer

Advanced prostate cancer patients initially respond to hormone therapy, be it in the form of androgen deprivation therapy or second-generation hormone therapies, such as abiraterone acetate or enzalutamide. However, most men with prostate cancer eventually develop hormone therapy resistance. This resistance can arise through multiple mechanisms, such as through genetic mutations, epigenetic mechanisms, or through non-genetic pathways, such as lineage plasticity along epithelial-mesenchymal or neuroendocrine-like axes. These mechanisms of hormone therapy resistance often co-exist within a single patient's tumor and can overlap within a single cell. There exists a growing need to better understand how phenotypic heterogeneity and plasticity results from emergent dynamics of the regulatory networks governing androgen independence. Here, we investigated the dynamics of a regulatory network connecting the drivers of androgen receptor (AR) splice variant-mediated androgen independence and those of epithelial-mesenchymal transition. Model simulations for this network revealed four possible phenotypes: epithelial-sensitive (ES), epithelial-resistant (ER), mesenchymal-resistant (MR) and mesenchymal-sensitive (MS), with the latter phenotype occurring rarely. We observed that well-coordinated "teams" of regulators working antagonistically within the network enable these phenotypes. These model predictions are supported by multiple transcriptomic datasets both at single-cell and bulk levels, including in vitro EMT induction models and clinical samples. Further, our simulations reveal spontaneous stochastic switching between the ES and MR states. Addition of the immune checkpoint molecule, PD-L1, to the network was able to capture the interactions between AR, PD-L1, and the mesenchymal marker SNAIL, which was also confirmed through quantitative experiments. This systems-level understanding of the driver of androgen independence and EMT could aid in understanding non-genetic transitions and progression of such cancers and help in identifying novel therapeutic strategies or targets.

Mechanisms of Prostate Cancer Cells Survival and Their Therapeutic Targeting

Prostate cancer (PCa) is today the second most common cancer in the world, with almost 400,000 deaths annually. Multiple factors are involved in the etiology of PCa, such as older age, genetic mutations, ethnicity, diet, or inflammation. Modern treatment of PCa involves radical surgical treatment or radiation therapy in the stages when the tumor is limited to the prostate. When metastases develop, the standard procedure is androgen deprivation therapy, which aims to reduce the level of circulating testosterone, which is achieved by surgical or medical castration. However, when the level of testosterone decreases to the castration level, the tumor cells adapt to the new conditions through different mechanisms, which enable their unhindered growth and survival, despite the therapy. New knowledge about the biology of the so-called of castration-resistant PCa and the way it adapts to therapy will enable the development of new drugs, whose goal is to prolong the survival of patients with this stage of the disease, which will be discussed in this review.

Modulating the Activity of Androgen Receptor for Treating Breast Cancer

The androgen receptor (AR) is a steroid hormone receptor widely detected in breast cancer. Evidence suggests that the AR might be a tumor suppressor in estrogen receptor alpha-positive (ERα+ve) breast cancer but a tumor promoter in estrogen receptor alpha-negative (ERα-ve) breast cancer. Modulating AR activity could be a potential strategy for treating breast cancer. For ERα+ve breast cancer, activation of the AR had been demonstrated to suppress the disease. In contrast, for ERα-ve breast cancer, blocking the AR could confer better prognosis to patients. These studies support the feasibility of utilizing AR modulators as anti-cancer drugs for different subtypes of breast cancer patients. Nevertheless, several issues still need to be addressed, such as the lack of standardization in the determination of AR positivity and the presence of AR splice variants. In future, the inclusion of the AR status in the breast cancer report at the time of diagnosis might help improve disease classification and treatment decision, thereby providing additional treatment strategies for breast cancer.

The role of cyclins in the development and progression of prostate cancer

The role of cyclins in hormone-dependent neoplasms is crucial in the development of the disease that is resistant to first-line therapy, as the example of breast cancer shows. However, in prostate cancer, cyclins are studied to a lesser extent. There are some well-described molecular pathways, including cyclins A1 and D1 signaling, however the role of other cyclins, e.g., D2, D3, E, and H, still requires further investigation. Recent studies indicate that cyclins regulate various cellular processes, not only the cell cycle. Furthermore, they remain in cross-talk with many other signaling pathways, e.g., MAPK/ERK, PI3K/Akt, and Notch. The androgen signaling axis, which is pivotal in prostate cancer progression, interferes with cyclin pathways at many levels. This article summarizes current knowledge on the influence of cyclins on prostate cancer progression by describing interactions between the androgen receptor and cyclins, as well as mechanisms underlying the development of resistance to currently used therapies.

Overcoming Obstacles in Liquid Biopsy Developments for Prostate Cancer

Prostate cancer is one of the most common malignancies in men. Over time, it can metastasize and become lethal once it exhausts hormonal therapies and transitions into castration-resistant prostate cancer (CRPC). Several therapies have been recently approved for advanced prostate cancer, but identifying biomarkers for current treatments and searching for more effective treatments are urgently needed. Liquid biopsy is a powerful tool for isolating genetic material, proteins, and whole tumor cells from the blood. In recent decades, this technology has rapidly advanced, allowing for better insights into the pathogenesis and treatment response in different stages of prostate cancer. In this review, we summarize important clinical studies involving liquid biopsies in prostate cancer with a focus on advanced disease, notably regarding circulating tumor DNA, circulating tumor cells, and exosomes. We highlight the progress and the challenges that still exist for these technologies. Finally, we discuss promising avenues that will further expand the importance of liquid biopsy in the care for prostate cancer patients.

Androgen receptor variant-7 regulation by tenascin-c induced src activation

BACKGROUND

Bone metastatic prostate cancer does not completely respond to androgen-targeted therapy and generally evolves into lethal castration resistant prostate cancer (CRPC). Expression of AR-V7- a constitutively active, ligand independent splice variant of AR is one of the critical resistant mechanisms regulating metastatic CRPC. TNC is an extracellular matrix glycoprotein, crucial for prostate cancer progression, and associated with prostate cancer bone metastases. In this study, we investigated the mechanisms that regulate AR-V7 expression in prostate cancer cells interacting with osteogenic microenvironment including TNC.

METHODS

Prostate cancer/preosteoblast heterotypical organoids were evaluated via immunofluorescence imaging and gene expression analysis using RT-qPCR to assess cellular compartmentalization, TNC localization, and to investigate regulation of AR-V7 in prostate cancer cells by preosteoblasts and hormone or antiandrogen action. Prostate cancer cells cultured on TNC were assessed using RT-qPCR, Western blotting, cycloheximide chase assay, and immunofluorescence imaging to evaluate (1) regulation of AR-V7, and (2) signaling pathways activated by TNC. Identified signaling pathway induced by TNC was targeted using siRNA and a small molecular inhibitor to investigate the role of TNC-induced signaling activation in regulation of AR-V7. Both AR-V7- and TNC-induced signaling effectors were targeted using siRNA, and TNC expression assessed to evaluate potential feedback regulation.

RESULTS

Utilizing heterotypical organoids, we show that TNC is an integral component of prostate cancer interaction with preosteoblasts. Interaction with preosteoblasts upregulated both TNC and AR-V7 expression in prostate cancer cells which was suppressed by testosterone but elevated by antiandrogen enzalutamide. Interestingly, the results demonstrate that TNC-induced Src activation regulated AR-V7 expression, post-translational stability, and nuclear localization in prostate cancer cells. Treatment with TNC neutralizing antibody, Src knockdown, and inhibition of Src kinase activity repressed AR-V7 transcript and protein. Reciprocally, both activated Src and AR-V7 were observed to upregulate autocrine TNC gene expression in prostate cancer cells.

CONCLUSION

Overall, the findings reveal that prostate cancer cell interactions with the cellular and ECM components in the osteogenic microenvironment plays critical role in regulating AR-V7 associated with metastatic CRPC. Video Abstract.

Prostate Cancer Stem Cells: Clinical Aspects and Targeted Therapies

Despite decades of research and successful improvements in diagnosis and therapy, prostate cancer (PC) remains a major challenge. In recent years, it has become clear that PC stem cells (PCSCs) are the driving force in tumorigenesis, relapse, metastasis, and therapeutic resistance of PC. In this minireview, we discuss the impact of PCSCs in the clinical practice. Moreover, new therapeutic approaches to combat PCSCs are presented with the aim to achieve an improved outcome for patients with PC.

Biomarkers for Predicting Abiraterone Treatment Outcome and Selecting Alternative Therapies in Castration-Resistant Prostate Cancer

Approximately one‐third of patients with metastatic castration‐resistant prostate cancer (CRPC) exhibited primary abiraterone resistance. To identify alternative treatment for abiraterone nonresponders, we performed drug discovery analyses using the L1000 database using differentially expressed genes identified in tumor biopsies and patient‐derived xenograft (PDX) tumors between abiraterone responders and nonresponders enrolled in PROMOTE trial. This approach identified 3 drugs, including topoisomerase II (TOP2) inhibitor mitoxantrone, CDK4/6 inhibitor palbociclib, and pan‐CDK inhibitor PHA‐793887. These drugs significantly suppressed the growth of abiraterone‐resistant cell lines and PDX models. Moreover, we identified 11 genes targeted by all 3 drugs that were associated with worse outcomes in both the PROMOTE and Stand Up To Cancer cohorts. This 11‐gene panel might also function as biomarkers to select the 3 alternative therapies for this subgroup of patients with CRPC, warranting further clinical investigation.

Impact of STAT Proteins in Tumor Progress and Therapy Resistance in Advanced and Metastasized Prostate Cancer

Signal transducers and activators of transcription (STATs) are a family of transcription factors involved in several biological processes such as immune response, cell survival, and cell growth. However, they have also been implicated in the development and progression of several cancers, including prostate cancer (PCa). Although the members of the STAT protein family are structurally similar, they convey different functions in PCa. STAT1, STAT3, and STAT5 are associated with therapy resistance. STAT1 and STAT3 are involved in docetaxel resistance, while STAT3 and STAT5 are involved in antiandrogen resistance. Expression of STAT3 and STAT5 is increased in PCa metastases, and together with STAT6, they play a crucial role in PCa metastasis. Further, expression of STAT3, STAT5, and STAT6 was elevated in advanced and high-grade PCa. STAT2 and STAT4 are currently less researched in PCa. Since STATs are widely involved in PCa, they serve as potential therapeutic targets. Several inhibitors interfering with STATs signaling have been tested unsuccessfully in PCa clinical trials. This review focuses on the respective roles of the STAT family members in PCa, especially in metastatic disease and provides an overview of STAT-inhibitors evaluated in clinical trials.