Mechanisms of androgen receptor activation in castration-resistant prostate cancer

Fenamates: Forgotten treasure for cancer treatment and prevention: Mechanisms of action, structural modification, and bright future

Fenamates as classical nonsteroidal anti-inflammatory agents are widely used for relieving pain. Preclinical studies and epidemiological data highlight their chemo-preventive and chemotherapeutic potential for cancer. However, comprehensive reviews of fenamates in cancer are limited. To accelerate the repurposing of fenamates, this review summarizes the results of fenamates alone or in combination with existing chemotherapeutic agents. This paper also explores targets of fenamates in cancer therapy, including COX, AKR family, AR, gap junction, FTO, TEAD, DHODH, TAS2R14, ion channels, and DNA. Besides, this paper discusses other mechanisms, such as regulating Wnt/β-catenin, TGF-β, p38 MAPK, and NF-κB pathway, and the regulation of the expressions of Sp, EGR-1, NAG-1, ATF-3, ErbB2, AR, as well as the modulation of the tumor immune microenvironment. Furthermore, this paper outlined the structural modifications of fenamates, highlighting their potential as promising leads for anticancer drugs.

Reciprocal regulation between RACGAP1 and AR contributes to endocrine therapy resistance in prostate cancer

BACKGROUND

Endocrine resistance driven by sustained activation of androgen receptor (AR) signaling pathway in advanced prostate cancer (PCa) is fatal. Characterization of mechanisms underlying aberrant AR pathway activation to search for potential therapeutic strategy is particularly important. Rac GTPase-activating protein 1 (RACGAP1) is one of the specific GTPase-activating proteins. As a novel tumor proto-oncogene, overexpression of RACGAP1 was related to the occurrence of various tumors.

METHODS

Bioinformatics methods were used to analyze the relationship of expression level between RACGAP1 and AR as well as AR pathway activation. qRT-PCR and western blotting assays were performed to assess the expression of AR/AR-V7 and RACGAP1 in PCa cells. Immunoprecipitation and immunofluorescence experiments were conducted to detect the interaction and co-localization between RACGAP1 and AR/AR-V7. Gain- and loss-of-function analyses were conducted to investigate the biological roles of RACGAP1 in PCa cells, using MTS and colony formation assays. In vivo experiments were conducted to evaluate the effect of RACGAP1 inhibition on the tumor growth.

RESULTS

RACGAP1 was a gene activated by AR, which was markedly upregulated in PCa patients with CRPC and enzalutamide resistance. AR transcriptionally activated RACGAP1 expression by binding to its promoter region. Reciprocally, nuclear RACGAP1 bound to the N-terminal domain (NTD) of both AR and AR-V7, blocking their interaction with the E3 ubiquitin ligase MDM2. Consequently, this prevented the degradation of AR/AR-V7 in a ubiquitin-proteasome-dependent pathway. Notably, the positive feedback loop between RACGAP1 and AR/AR-V7 contributed to endocrine therapy resistance of CRPC. Combination of enzalutamide and in vivo cholesterol-conjugated RIG-I siRNA drugs targeting RACGAP1 induced potent inhibition of xenograft tumor growth of PCa.

CONCLUSION

In summary, our results reveal that reciprocal regulation between RACGAP1 and AR/AR-V7 contributes to the endocrine resistance in PCa. These findings highlight the therapeutic potential of combined RACGAP1 inhibition and enzalutamide in treatment of advanced PCa.

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.

MDM2 regulates the stability of AR, AR-V7, and TM4SF3 proteins in prostate cancer

Androgen receptor (AR) and its constitutively active splice variant, AR Variant 7 (AR-V7), regulate genes essential for the development and progression of prostate cancer. Degradation of AR and AR-V7 by the ubiquitination proteasomal pathway is important for the regulation of both their protein stability. Our published results demonstrate that the interaction of TM4SF3 with either AR or AR-V7 leads to mutual stabilization due to a reduction in their ubiquitination and proteasomal degradation. These results led us to search for a common E3 ligase for AR, AR-V7, and TM4SF3. Depletion by siRNA of several E3 ligases identified MDM2 as the common E3 ligase. MDM2 inhibition by siRNA depletion or using a pharmacological inhibitor (MDM2i) of its E3 ligase activity led to elevated levels of endogenous AR, AR-V7, and TM4SF3 in prostate cancer cells. MDM2 knockdown in PC-3 cells, which do not express AR, also increased TM4SF3, demonstrating that MDM2 affects the TM4SF3 protein independent of AR. We further demonstrate that MDM2i treatment reduced the ubiquitination of AR and TM4SF3, suggesting that MDM2 can induce the ubiquitination of these proteins. Increased AR and AR-V7 protein levels induced by MDM2i treatment resulted in the expected increased expression of AR-regulated genes and enhanced proliferation and migration of both LNCaP and Enzalutamide-resistant CWR-22Rv1 prostate cancer cells. Thus, our study expands the known roles of MDM2 in prostate cancer to include its potential involvement in the important mutual stabilization that TM4SF3 exhibits when interacting with either AR or AR-V7.

Targeting PHB1 to inhibit castration-resistant prostate cancer progression in vitro and in vivo

BACKGROUND

Castration-resistant prostate cancer (CRPC) is currently the main challenge for prostate cancer (PCa) treatment, and there is an urgent need to find novel therapeutic targets and drugs. Prohibitin (PHB1) is a multifunctional chaperone/scaffold protein that is upregulated in various cancers and plays a pro-cancer role. FL3 is a synthetic flavagline drug that inhibits cancer cell proliferation by targeting PHB1. However, the biological functions of PHB1 in CRPC and the effect of FL3 on CRPC cells remain to be explored.

METHODS

Several public datasets were used to analyze the association between the expression level of PHB1 and PCa progression as well as outcome in PCa patients. The expression of PHB1 in human PCa specimens and PCa cell lines was examined by immunohistochemistry (IHC), qRT-PCR, and Western blot. The biological roles of PHB1 in castration resistance and underlying mechanisms were investigated by gain/loss-of-function analyses. Next, in vitro and in vivo experiments were conducted to investigate the anti-cancer effects of FL3 on CRPC cells as well as the underlying mechanisms.

RESULTS

PHB1 expression was significantly upregulated in CRPC and was associated with poor prognosis. PHB1 promoted castration resistance of PCa cells under androgen deprivation condition. PHB1 is an androgen receptor (AR) suppressive gene, and androgen deprivation promoted the PHB1 expression and its nucleus-cytoplasmic translocation. FL3, alone or combined with the second-generation anti-androgen Enzalutamide (ENZ), suppressed CRPC cells especially ENZ-sensitive CRPC cells both in vitro and in vivo. Mechanically, we demonstrated that FL3 promoted trafficking of PHB1 from plasma membrane and mitochondria to nucleus, which in turn inhibited AR signaling as well as MAPK signaling, yet promoted apoptosis in CRPC cells.

CONCLUSION

Our data indicated that PHB1 is aberrantly upregulated in CRPC and is involved in castration resistance, as well as providing a novel rational approach for treating ENZ-sensitive CRPC.

Adrenal Steroids and Resistance to Hormonal Blockade of Prostate and Breast Cancer

Prostate cancer and breast cancer are sex-steroid-dependent diseases that are driven in major part by gonadal sex steroids. Testosterone (T) is converted to 5α-dihydrotestosterone, both of which stimulate the androgen receptor (AR) and prostate cancer progression. Estradiol is the major stimulus for estrogen receptor-α (ERα) and proliferation of ERα-expressing breast cancer. However, the human adrenal provides an alternative source for sex steroids. A number of different androgens are produced by the adrenals, the most abundant of which is dehydroepiandrosterone (DHEA) and DHEA sulfate. These precursor steroids are subject to metabolism by peripherally expressed enzymes that are responsible for the synthesis of potent androgens and estrogens. In the case of prostate cancer, the regulation of one of these enzymatic steps occurs at least in part by way of a germline-encoded missense in 3β-hydroxysteroid dehydrogenase-1 (3βHSD1), which regulates potent androgen biosynthesis and clinical outcomes in men with advanced prostate cancer treated with gonadal T deprivation. The sex steroids that drive prostate cancer and breast cancer require a common set of enzymes for their generation. However, the pathways diverge once 3-keto, Δ4-androgens are generated and these steroids are either turned into potent androgens by steroid-5α-reductase, or into estrogens by aromatase. Alternative steroid receptors have also emerged as disease- and treatment-resistance modifiers, including a role for AR in breast cancer and glucocorticoid receptor both in breast and prostate cancer. In this review, we integrate the commonalities of adrenal steroid physiology that regulate both prostate and breast cancer while recognizing the clear distinctions between these diseases.

Ser815 Phosphorylation stabilizes the androgen receptor homodimer and stimulates ER-stress induced cell death

Androgen receptor, which regulates diverse biological processes for cell fate decisions, forms a homodimer in the cytoplasm and is monomerized by activation for nuclear translocation. Ser815 phosphorylated AR is expressed in mature prostates, with levels decreased by castration in mice or prostate cancer progression in humans. Here, we have examined the functional and biological roles of phosphorylation. AR phosphorylation at Ser815 stabilized homodimer formation in the cytoplasm, interrupting DHT-response nuclear translocation. cDNA microarray studies in castrated mouse prostates implied castration attenuates ER stress responses, suggesting AR phosphorylation acts on ER stress responses. In addition, AR Ser815Asp phospho-mimetic mutant expression augmented ER stress-induced death in PC-3 cells. These results suggested that phosphorylation at AR Ser815 modulates AR functions for maintaining the prostate.

The epigenetic function of androgen receptor in prostate cancer progression

Androgen and androgen deprivation (castration) therapies, including androgen receptor antagonists, are clinically used to treat patients with prostate cancer. However, most hormone-dependent prostate cancer patients progress into a malignant state with loss of hormone-dependency, known as castration (drug)-resistant prostate cancer (CRPC), after prolong androgen-based treatments. Even in the CRPC state with irreversible malignancy, androgen receptor (AR) expression is detectable. An epigenetic transition to CRPC induced by the action of AR-mediated androgen could be speculated in the patients with prostate cancer. Androgen receptors belongs to the nuclear receptor superfamily with 48 members in humans, and acts as a ligand-dependent transcriptional factor, leading to local chromatin reorganization for ligand-dependent gene regulation. In this review, we discussed the transcriptional/epigenetic regulatory functions of AR, with emphasis on the clinical applications of AR ligands, AR protein co-regulators, and AR RNA coregulator (enhancer RNA), especially in chromatin reorganization, in patients with prostate cancer.

JAG1 Intracellular Domain Enhances AR Expression and Signaling and Promotes Stem-like Properties in Prostate Cancer Cells

JAG1 expression is upregulated in high-grade metastatic prostate carcinomas and associated with poor disease-free survival of patients with prostate cancer. Intriguingly, all JAG1-positive prostate carcinomas express JICD although JICD function in prostate cancer (PC) cells is poorly understood. In this study, we found that JICD overexpression increased the expression levels of AR, especially AR-Vs, in PC cell lines and significantly enhanced androgen-independent and androgen-dependent function of ARs. Interestingly, JICD overexpression upregulated the expression of the PCSC marker CD133 in PC cells as the expression of self-renewal markers; namely, NANOG and OCT3/4 increased. In addition, JICD overexpression highly increased the expression of anti-apoptotic BCL-XL protein, while it little affected the expression of apoptotic BIM protein. In 3D cell culture assays, the spheres formed by JICD-overexpressing PC subline cells (C4-2 and CWR22Rv1) were larger than those formed by control (EV) subline cells with undifferentiated morphology. Although JICD overexpression caused quiescence in cell proliferation, it activated the expression of components in PCSC-related signaling pathways, increased PC cell mobility, and promoted in vivo xenograft mouse tumorigenesis. Therefore, JICD may play a crucial role in enhancing androgen independence and promoting stem-like properties in PC cells and should be considered a novel target for CRPC and PCSC diagnostic therapy.

Antagonistic action of a synthetic androgen ligand mediated by chromatin remodeling in a human prostate cancer cell line

The clinical use of androgen receptor (AR) antagonists has been successful in treating prostate cancer patients, inducing remission of androgen-dependent tumors. However, a couple of years after treatment, prostate tumors transition into an androgen-independent state with altered gene expression profiles, but the molecular basis is not understood. Since the AR antagonists trigger this transition, we assessed whether AR antagonists induce chromatin reorganization in an androgen-dependent prostate cancer cell line (LNCaP). Treatment of LNCaP cells with two clinically used AR antagonists (bicalutamide [Bic] and enzalutamide [Enz]) expectedly resulted in antagonistic effects on cell proliferation, AR transactivation, and dihydrotestosterone (DHT)-induced expression of AR target genes. Thus, the antagonists expectedly acted to antagonize the transactivation function of AR activated by androgen binding. By ChIP-qPCR assay, AR bound to Bic, but not Enz, was recruited to an endogenous consensus AR-binding site within the kallikrein-related peptidase 3 gene promoter after treatment with Bic, similar to the effect of DHT. By ATAC-seq analysis of the cells after long-term treatment for 5 days, Bic and dihydrotestosterone DHT induced different chromatin reorganization patterns and gene expression profiles, suggesting that Bic exhibited a distinct action from that by DHT. Thus, these results suggest that the action of a known AR antagonist is mediated by chromatin reorganization in a prostate cancer cell line.

Natural Product-Based Studies for the Management of Castration-Resistant Prostate Cancer: Computational to Clinical Studies

Background: With prostate cancer being the fifth-greatest cause of cancer mortality in 2020, there is a dire need to expand the available treatment options. Castration-resistant prostate cancer (CRPC) progresses despite androgen depletion therapy. The mechanisms of resistance are yet to be fully discovered. However, it is hypothesized that androgens depletion enables androgen-independent cells to proliferate and recolonize the tumor. Objectives: Natural bioactive compounds from edible plants and herbal remedies might potentially address this need. This review compiles the available cheminformatics-based studies and the translational studies regarding the use of natural products to manage CRPC. Methods: PubMed and Google Scholar searches for preclinical studies were performed, while ClinicalTrials.gov and PubMed were searched for clinical updates. Studies that were not in English and not available as full text were excluded. The period of literature covered was from 1985 to the present. Results and Conclusion: Our analysis suggested that natural compounds exert beneficial effects due to their broad-spectrum molecular disease-associated targets. In vitro and in vivo studies revealed several bioactive compounds, including rutaecarpine, berberine, curcumin, other flavonoids, pentacyclic triterpenoids, and steroid-based phytochemicals. Molecular modeling tools, including machine and deep learning, have made the analysis more comprehensive. Preclinical and clinical studies on resveratrol, soy isoflavone, lycopene, quercetin, and gossypol have further validated the translational potential of the natural products in the management of prostate cancer.

Profiling of Androgen-Dependent Enhancer RNAs Expression in Human Prostate Tumors: Search for Malignancy Transition Markers

Introduction

Although the ability of androgens to promote prostate cancer development has been known for decades, the molecular mechanisms of androgen receptor (AR) signaling in the tumorigenesis remain unclear. Enhancer RNAs (eRNAs) transcribed from strong enhancers, or super-enhancers (SEs), have recently emerged as a novel class of regulatory non-coding RNAs (ncRNAs) that facilitate transcription, including that of androgen target genes, through chromatin looping to position enhancers proximate to the promoters. The aim of this study was to assess androgen-dependent transcription in prostate tumors of eRNAs (designated as KLK3eRNAs) from the SE of the KLK3 gene encoding the prostate-specific antigen (PSA) protein, a clinical marker of prostate carcinogenesis.

Materials and Methods

The androgen-induced KLK3eRNAs were identified in the LNCaP human prostate cancer cell line. The expressions of these KLK3eRNAs together with KLK3 and AR mRNA transcripts were assessed by qRT-PCR in prostate tumor samples from five prostate cancer patients.

Results

Androgen-induced KLK3eRNAs have been identified in the LNCaP cells, and their expression was further analyzed in tumors of prostate cancer patients. Transcripts of the tested KLK3eRNAs have been detected in all clinical samples, but their expression patterns differed between individual tumor specimens. We found a statistically significant correlation between the levels of the KLK3 and AR mRNAs with those of the previously reported KLK3eRNAs, while such correlation was not observed for novel KLK3eRNAs described in our recent report.

Conclusion

Presented data suggest that prostate tumor development may associate with epigenetic reorganization in the KLK3 genomic regulatory elements reflected by changes of the KLK3eRNA expression. Our findings support a potential of eRNAs profiling to be used as diagnostic marker.

Drosophila Accessory Gland: A Complementary In Vivo Model to Bring New Insight to Prostate Cancer

Prostate cancer is the most common cancer in aging men. Despite recent progress, there are still few effective treatments to cure its aggressive and metastatic stages. A better understanding of the molecular mechanisms driving disease initiation and progression appears essential to support the development of more efficient therapies and improve patient care. To do so, multiple research models, such as cell culture and mouse models, have been developed over the years and have improved our comprehension of the biology of the disease. Recently, a new model has been added with the use of the Drosophila accessory gland. With a high level of conservation of major signaling pathways implicated in human disease, this functional equivalent of the prostate represents a powerful, inexpensive, and rapid in vivo model to study epithelial carcinogenesis. The purpose of this review is to quickly overview the existing prostate cancer models, including their strengths and limitations. In particular, we discuss how the Drosophila accessory gland can be integrated as a convenient complementary model by bringing new understanding in the mechanisms driving prostate epithelial tumorigenesis, from initiation to metastatic formation.

Resistance to Antiandrogens in Prostate Cancer: Is It Inevitable, Intrinsic or Induced?

Increasingly sophisticated therapies for chemical castration dominate first-line treatments for locally advanced prostate cancer. However, androgen deprivation therapy (ADT) offers little prospect of a cure, as resistant tumors emerge rather rapidly, normally within 30 months. Cells have multiple mechanisms of resistance to even the most sophisticated drug regimes, and both tumor cell heterogeneity in prostate cancer and the multiple salvage pathways result in castration-resistant disease related genetically to the original hormone-naive cancer. The timing and mechanisms of cell death after ADT for prostate cancer are not well understood, and off-target effects after long-term ADT due to functional extra-prostatic expression of the androgen receptor protein are now increasingly being recorded. Our knowledge of how these widely used treatments fail at a biological level in patients is deficient. In this review, I will discuss whether there are pre-existing drug-resistant cells in a tumor mass, or whether resistance is induced/selected by the ADT. Equally, what is the cell of origin of this resistance, and does it differ from the treatment-naïve tumor cells by differentiation or dedifferentiation? Conflicting evidence also emerges from studies in the range of biological systems and species employed to answer this key question. It is only by improving our understanding of this aspect of treatment and not simply devising another new means of androgen inhibition that we can improve patient outcomes.

α-Actinin-4 Promotes the Progression of Prostate Cancer Through the Akt/GSK-3β/β-Catenin Signaling Pathway

The first-line treatment for prostate cancer (PCa) is androgen ablation therapy. However, prostate tumors generally recur and progress to androgen-independent PCa (AIPC) within 2–3 years. α-Actinin-4 (ACTN4) is an actin-binding protein that belongs to the spectrin gene superfamily and acts as an oncogene in various cancer types. Although ACTN4 is involved in tumorigenesis and the epithelial–mesenchymal transition of cervical cancer, the role of ACTN4 in PCa remains unknown. We found that the ACTN4 expression level increased during the transition from androgen-dependent PCa to AIPC. ACTN4 overexpression resulted in enhanced proliferation and motility of PCa cells. Increased β-catenin due to ACTN4 promoted the transcription of genes involved in proliferation and metastasis such as CCND1 and ZEB1. ACTN4-overexpressing androgen-sensitive PCa cells were able to grow in charcoal-stripped media. In contrast, ACTN4 knockdown using si-ACTN4 and ACTN4 nanobody suppressed the proliferation, migration, and invasion of AIPC cells. Results of the xenograft experiment revealed that the mice injected with LNCaP^ACTN4 cells exhibited an increase in tumor mass compared with those injected with LNCaP^Mock cells. These results indicate that ACTN4 is involved in AIPC transition and promotes the progression of PCa.

A new compound targets the AF-1 of androgen receptor and decreases its activity and protein levels in prostate cancer cells

Increased expression levels of constitutively active androgen receptor splice variants (AR-Vs) cause alterations in AR signaling, resulting in drug resistance and failed hormone therapy among patients with advanced prostate cancers. Several available compounds targeting the androgen axis and AR signaling have not demonstrated efficacy in preventing prostate cancer recurrence. Here, we investigated whether a new agent, 6-[6-ethoxy-5-ispropoxy-3,4-dihydroisoquinolin-2[1H)-yl]-N-[6-methylpyridin-2-yl]nicotinamide (EIQPN), has the potential for treating advanced prostate cancer. EIQPN interacted with the AR-activation fragment-1 (AF-1) domain and blocked its androgen-independent activity, robustly decreased the protein levels of AR and variants in prostate cancer cells by inducing AR protein degradation, and inhibited the androgen-independent proliferation of various AR-positive prostate cancer cells. In xenograft mouse models, EIQPN blocked the tumor growth of androgen-independent prostate cancer cells. Overall, these findings indicate that EIQPN could serve as a novel therapeutic agent for advanced recurrent prostate cancers.

Coordinated AR and microRNA regulation in prostate cancer

The androgen receptor (AR) remains a key driver of prostate cancer (PCa) progression, even in the advanced castrate-resistant stage, where testicular androgens are absent. It is therefore of critical importance to understand the molecular mechanisms governing its activity and regulation during prostate tumourigenesis. MicroRNAs (miRs) are small ∼22 nt non-coding RNAs that regulate target gene, often through association with 3′ untranslated regions (3′UTRs) of transcripts. They display dysregulation during cancer progression, can function as oncogenes or tumour suppressors, and are increasingly recognised as targets or regulators of hormonal action. Thus, understanding factors which modulate miRs synthesis is essential. There is increasing evidence for complex and dynamic bi-directional cross-talk between the multi-step miR biogenesis cascade and the AR signalling axis in PCa. This review summarises the wealth of mechanisms by which miRs are regulated by AR, and conversely, how miRs impact AR's transcriptional activity, including that of AR splice variants. In addition, we assess the implications of the convergence of these pathways on the clinical employment of miRs as PCa biomarkers and therapeutic targets.

A Mechanistic High-Content Analysis Assay Using a Chimeric Androgen Receptor That Rapidly Characterizes Androgenic Chemicals

Human health is at risk from environmental exposures to a wide range of chemical toxicants and endocrine-disrupting chemicals (EDCs). As part of understanding this risk, the U.S. Environmental Protection Agency (EPA) has been pursuing new high-throughput in vitro assays and computational models to characterize EDCs. EPA models have incorporated our high-content analysis-based green fluorescent protein estrogen receptor (GFP-ER): PRL-HeLa assay, which allows direct visualization of ER binding to DNA regulatory elements. Here, we characterize a modified functional assay based on the stable expression of a chimeric androgen receptor (ARER), wherein a region containing the native AR DNA-binding domain (DBD) was replaced with the ERα DBD (amino acids 183-254). We demonstrate that the AR agonist dihydrotestosterone induces GFP-ARER nuclear translocation, PRL promoter binding, and transcriptional activity at physiologically relevant concentrations (<1 nM). In contrast, the AR antagonist bicalutamide induces only nuclear translocation of the GFP-ARER receptor (at μM concentrations). Estradiol also fails to induce visible chromatin binding, indicating androgen specificity. In a screen of reference chemicals from the EPA and the Agency for Toxic Substances and Disease Registry, the GFP-ARER cell model identified and mechanistically grouped activity by known (anti-)androgens based on the ability to induce nuclear translocation and/or chromatin binding. Finally, the cell model was used to identify potential (anti-)androgens in environmental samples in collaboration with the Houston Ship Channel/Galveston Bay Texas A&M University EPA Superfund Research Program. Based on these data, the chromatin-binding, in vitro assay-based GFP-ARER model represents a selective tool for rapidly identifying androgenic activity associated with drugs, chemicals, and environmental samples.

Abiraterone acetate treatment lowers 11-oxygenated androgens

CONTEXT

The human adrenal is the dominant source of androgens in castration-resistant prostate cancer (CRPC) and classic 21-hydroxylase deficiency (21OHD). Abiraterone, derived from the prodrug abiraterone acetate (AA), inhibits the activity of cytochrome P450 17-hydroxylase/17,20-lyase (CYP17A1), the enzyme required for all androgen biosynthesis. AA treatment effectively lowers testosterone and androstenedione in 21OHD and CRPC patients. The 11-oxygenated androgens are major adrenal-derived androgens, yet little is known regarding the effects of AA administration on 11-oxygenated androgens.

OBJECTIVE

To test the hypothesis that AA therapy decreases 11-oxygenated androgens.

DESIGN

Samples were obtained from 21OHD or CRPC participants in AA or AA plus prednisone (AAP)-treatment studies, respectively.

METHODS

We employed liquid chromatography-tandem mass spectrometry (LC-MS/MS) to measure the 11-oxygenated androgens, 11β-hydroxyandrostenedione, 11-ketoandrostenedione, 11β-hydroxytestosterone, and 11-ketotestosterone, in plasma or serum samples from six 21OHD and six CRPC patients before and after treatment with AA or AAP, respectively.

RESULTS

In CRPC patients, administration of AAP (1000 mg/day AA with prednisone and medical castration) lowered all four 11-oxygenated androgens to below the lower limits of quantitation (<0.1-0.3 nmol/L), equivalent to 64-94% reductions from baseline. In 21OHD patients, administration of AA (100-250 mg/day for 6 days) reduced all 11-oxygenated androgens by on average 56-77% from baseline.

CONCLUSIONS

We conclude that AA and AAP therapies markedly reduce the production of the adrenal-derived 11-oxygenated androgens, both in patients with high (21OHD) or normal (CRPC) 11-oxygenated androgens at baseline, respectively. Reduction of 11-oxygenated androgens is an important aspect of AA and AAP pharmacology.

Using medical claims database to develop a population disease progression model for leuprorelin-treated subjects with hormone-sensitive prostate cancer

Androgen deprivation therapy (ADT) is a widely used treatment for patients with hormone-sensitive prostate cancer (PCa). However, duration of treatment response varies, and most patients eventually experience disease progression despite treatment. Leuprorelin is a luteinizing hormone-releasing hormone (LHRH) agonist, a commonly used form of ADT. Prostate-specific antigen (PSA) is a biomarker for monitoring disease progression and predicting treatment response and survival in PCa. However, time-dependent profile of tumor regression and growth in patients with hormone-sensitive PCa on ADT has never been fully characterized. In this analysis, nationwide medical claims database provided by Humana from 2007 to 2011 was used to construct a population-based disease progression model for patients with hormone-sensitive PCa on leuprorelin. Data were analyzed by nonlinear mixed effects modeling utilizing Monte Carlo Parametric Expectation Maximization (MCPEM) method in NONMEM. Covariate selection was performed using a modified Wald’s approximation method with backward elimination (WAM-BE) proposed by our group. 1113 PSA observations from 264 subjects with malignant PCa were used for model development. PSA kinetics were well described by the final covariate model. Model parameters were well estimated, but large between-patient variability was observed. Hemoglobin significantly affected proportion of drug-resistant cells in the original tumor, while baseline PSA and antiandrogen use significantly affected treatment effect on drug-sensitive PCa cells (Ds). Population estimate of Ds was 3.78 x 10⁻² day^-1. Population estimates of growth rates for drug-sensitive (Gs) and drug-resistant PCa cells (G_R) were 1.96 x 10⁻³ and 6.54 x 10⁻⁴ day^-1, corresponding to a PSA doubling time of 354 and 1060 days, respectively. Proportion of the original PCa cells inherently resistant to treatment was estimated to be 1.94%. Application of population-based disease progression model to clinical data allowed characterization of tumor resistant patterns and growth/regression rates that enhances our understanding of how PCa responds to ADT.

Natural Compounds in Prostate Cancer Prevention and Treatment: Mechanisms of Action and Molecular Targets

Prostate cancer (PCa) represents a major cause of cancer mortality among men in developed countries. Patients with recurrent disease initially respond to androgen-deprivation therapy, but the tumor eventually progresses into castration-resistant PCa; in this condition, tumor cells acquire the ability to escape cell death and develop resistance to current therapies. Thus, new therapeutic approaches for PCa management are urgently needed. In this setting, natural products have been extensively studied for their anti-PCa activities, such as tumor growth suppression, cell death induction, and inhibition of metastasis and angiogenesis. Additionally, numerous studies have shown that phytochemicals can specifically target the androgen receptor (AR) signaling, as well as the PCa stem cells (PCSCs). Interestingly, many clinical trials have been conducted to test the efficacy of nutraceuticals in human subjects, and they have partially confirmed the promising results obtained in vitro and in preclinical models. This article summarizes the anti-cancer mechanisms and therapeutic potentials of different natural compounds in the context of PCa prevention and treatment.

Psychosocial Stress, Glucocorticoid Signaling, and Prostate Cancer Health Disparities in African American Men

Recent advances in our understanding of racial disparities in prostate cancer (PCa) incidence and mortality that disproportionately affect African American (AA) men have provided important insights into the psychosocial, socioeconomic, environmental, and molecular contributors. There is, however, limited mechanistic knowledge of how the interplay between these determinants influences prostate tumor aggressiveness in AA men and other men of African ancestry. Growing evidence indicates that chronic psychosocial stress in AA populations leads to sustained glucocorticoid signaling through the glucocorticoid receptor (GR), with negative physiological and pathological consequences. Compelling evidence indicates that treatment of castration-resistant prostate cancer (CRPC) with anti-androgen therapy activates GR signaling. This enhanced GR signaling bypasses androgen receptor (AR) signaling and transcriptionally activates both AR-target genes and GR-target genes, resulting in increased prostate tumor resistance to anti-androgen therapy, chemotherapy, and radiotherapy. Given its enhanced signaling in AA men, GR-together with specific genetic drivers-may promote CRPC progression and exacerbate tumor aggressiveness in this population, potentially contributing to PCa mortality disparities. Ongoing and future CRPC clinical trials that combine standard of care therapies with GR modulators should assess racial differences in therapy response and clinical outcomes in order to improve PCa health disparities that continue to exist for AA men.

JAB1/COPS5 is a putative oncogene that controls critical oncoproteins deregulated in prostate cancer

Recent evidence support that the c-Jun activation domain-binding protein 1 (JAB1)/COPS5 has an oncogenic function in various tissues. We show that JAB1 amplification in human prostate cancer (PCa) correlates with reduced overall survival and disease-free progression. Immunohistochemical staining shows enhanced expression of JAB1 in the cytoplasmic compartment of PCa cells compared to the normal prostate epithelium, indicating the activity/function of JAB1 is altered in PCa. To test the function of JAB1 in PCa, we efficiently silenced JAB1 expression using four unique shRNAs in three PCa cell lines (LNCaP, C4-2, and PC-3) and an immortalized prostate epithelial cell line, RWPE-1. Our data clearly show that silencing JAB1 robustly suppresses the growth of PCa cells, but not RWPE-1 cells, suggesting that PCa cells become addicted to JAB1. To study the potential mechanism by which JAB1 controls PCa growth, we profiled gene expression changes by whole transcriptome microarray analysis of C4-2 cells silenced for JAB1 using a pool of 3 shRNAs compared to scrambled shRNA control. We identified 1268 gene changes ≥1.5 fold by silencing JAB1 in C4-2. Western blot confirmation and bioinformatics pathway analyses support that PCa cells become addicted to JAB1 through controlling the following signaling pathways: cell cycle, p53 signaling, DNA replication, TGF-β/BMP, MAPK, TNF, and steroid hormone biosynthesis. We propose that UGT2B28, UGT2B10, UGT2B11, Skp2, EZH2, MDM2, BIRC5 (Survivin), UBE2C, and Smads 1/5/8, which are all associated with the abovementioned key oncogenic pathways, may play critical roles in the putative oncogenic function of JAB1 in PCa.

PEG10 Promoter-Driven Expression of Reporter Genes Enables Molecular Imaging of Lethal Prostate Cancer

The retrotransposon-derived paternally expressed gene 10 (PEG10) protein is ordinarily expressed at high levels in the placenta. Recently, it was discovered that PEG10 isoforms promote the progression of prostate cancer to a highly lethal androgen receptor (AR)-negative phenotype. The presence of PEG10 in other subtypes of prostate cancer has not been explored and a utility for PEG10 overexpression has not been developed. Here, we found that in addition to AR-null disease, PEG10 was also expressed in prostate cancer with constitutively active AR-splice variants. A molecular genetic imaging strategy for noninvasive imaging of AR-splice variant prostate cancer was developed by utilizing the cancer specificity of the PEG10 promoter to drive the expression of reporter genes. Plasmid insertion of a PEG10 promoter sequence optimized for enhanced output upstream of a reporter gene allowed detection of prostate cancer by near-infrared and positron emission tomography imaging after systemic administration of the plasmid in vivo. PEG10 expressing subcutaneous xenograft and intratibial tumor models were imaged by both modalities using this molecular genetic imaging strategy. This study demonstrates a preclinical proof-of-concept that the PEG10 promoter is a powerful and specific tool that can be utilized for noninvasive detection of aggressive prostate cancer subtypes. SIGNIFICANCE: PEG10 is expressed by prostate cancer with constitutively active AR-splice variants that can be exploited for noninvasive molecular imaging of this aggressive prostate cancer subytpe.

HSD3B1 Genotypes Conferring Adrenal-Restrictive and Adrenal-Permissive Phenotypes in Prostate Cancer and Beyond

Castration-resistant prostate cancer (PCa) almost invariably occurs after androgen deprivation therapy for metastatic disease and is driven in part by androgen synthesis within the tumor. 3β-hydroxysteroid dehydrogenase isoenzyme-1 catalyzes the conversion of adrenal precursor steroids into potent androgens essential for PCa progression. A common 1245 A→C missense-encoding single nucleotide polymorphism in HSD3B1 (rs1047303), the gene that encodes this enzyme, leads to a more stable protein that is resistant to degradation and thus increased production of potent androgens from adrenal precursors, facilitating castration-resistant PCa development. Consistent with this mechanism, this adrenal-permissive HSD3B1(1245C) genotype is associated with inferior outcomes after androgen deprivation therapy for advanced PCa, and increased sensitivity to pharmacologic blockade of adrenal precursors in metastatic disease. Herein, we review current knowledge of the mechanisms conferred by HSD3B1 genotype to alter androgen physiology and accelerate development of castration-resistant disease and its associations with clinical PCa outcomes. In light of its effect on steroid physiology, we also discuss its potential associations with non-PCa phenotypes.

Gene Expression Profiling Analysis Reveals Putative Phytochemotherapeutic Target for Castration-Resistant Prostate Cancer

Prostate cancer is the leading cause of cancer death among men globally, with castration development resistant contributing significantly to treatment failure and death. By analyzing the differentially expressed genes between castration-induced regression nadir and castration-resistant regrowth of the prostate, we identified soluble guanylate cyclase 1 subunit alpha as biologically significant to driving castration-resistant prostate cancer. A virtual screening of the modeled protein against 242 experimentally-validated anti-prostate cancer phytochemicals revealed potential drug inhibitors. Although, the identified four non-synonymous somatic point mutations of the human soluble guanylate cyclase 1 gene could alter its form and ligand binding ability, our analysis identified compounds that could effectively inhibit the mutants together with wild-type. Of the identified phytochemicals, (8′R)-neochrome and (8′S)-neochrome derived from the Spinach (Spinacia oleracea) showed the highest binding energies against the wild and mutant proteins. Our results identified the neochromes and other phytochemicals as leads in pharmacotherapy and as nutraceuticals in management and prevention of castration-resistance prostate cancers.

Epigenetic Control of Gene Expression in the Normal and Malignant Human Prostate: A Rapid Response Which Promotes Therapeutic Resistance

A successful prostate cancer must be capable of changing its phenotype in response to a variety of microenvironmental influences, such as adaptation to treatment or successful proliferation at a particular metastatic site. New cell phenotypes emerge by selection from the large, genotypically heterogeneous pool of candidate cells present within any tumor mass, including a distinct stem cell-like population. In such a multicellular model of human prostate cancer, flexible responses are primarily governed not only by de novo mutations but appear to be dominated by a combination of epigenetic controls, whose application results in treatment resistance and tumor relapse. Detailed studies of these individual cell populations have resulted in an epigenetic model for epithelial cell differentiation, which is also instructive in explaining the reported high and inevitable relapse rates of human prostate cancers to a multitude of treatment types.

Histone demethylase KDM7A controls androgen receptor activity and tumor growth in prostate cancer

Prostate cancer can be controlled by androgen-hormone treatment until the cancer becomes refractory. It is believed that hormone sensitivity is largely dependent on androgen receptor (AR) activity. Here, we found the histone demethylase KDM7A which demethylates histone H3K27 to be overexpressed in enzalutamide resistant castration-resistant prostate cancer cell line C4-2b, and investigated the molecular mechanism whereby androgen receptor activity is regulated by KDM7A. We engineered AR-positive LNCaP cells to stably express a short-hairpin RNA against KDM7A mRNA from a lentiviral vector. By measuring AR downstream gene expression after androgen stimulation, we found that a KDM7A-deficient cell line showed lower AR downstream gene expression compared to a control cell. KDM7A knock-down in LNCaP cell line caused decreased cell proliferation. Western blot analysis with modified-histone antibody revealed that the KDM7A-knock-down LNCaP cell line had increased H3K27 di-methylation. We confirmed KDM7A binding on AR target-gene promoters after hormone stimulation in chromatin-immunoprecipitation experiments. And increased H3K27 di-methylation was observed in KDM7A knock-down LNCaP stable cell. Treatment with KDM7A inhibitor, TC-E 5002, reduced proliferation and induced apoptosis of prostate cancer cells. Finally, we observed that the KDM7A protein was significantly upregulated in prostate cancer tissue, and that this difference correlated with the Gleason score. These data suggested that KDM7A is potentially a good therapeutic target for prostate cancer drugs and can be used as potentially a good prognostic indicator for prostate cancer and related treatment strategies.

Alteration of Androgen Receptor Protein Stability by Triptolide in LNCaP Cells

Background and Objective: Although triptolide was effective for prostate cancer (PCa), the mechanism is still unclear. Androgen receptor (AR) plays a large role in the development and progression of PCa, even after castration. The present study aimed at investigating the effects of triptolide on AR protein stability and the possible mechanism. Materials and Methods: By blocking protein synthesis with cycloheximide (CHX), the effect of triptolide on AR protein stability was investigated with western blot assay. The potential role of calpains in triptolide reduced AR protein stability was investigated with calpain inhibitor and Ca²⁺ chelator. Results: Triptolide down-regulated AR protein level when protein synthesis was blocked by CHX, demonstrating the decrease of AR protein stability. The AR protein level was restored when the cells were co-treated with triptolide and calpain inhibitor or Ca²⁺ chelator, indicating the important role of calpains. Conclusions: The results indicate that triptolide can activate calpain via promoting intracellular Ca²⁺ accumulation, and thus decrease the stability of AR protein, subsequently resulting in the breakdown of the AR protein in LNCaP cells. This work provides an experimental basis and evidence to elucidate the anti-PCa mechanisms of triptolide.

PC-1 works in conjunction with E3 ligase CHIP to regulate androgen receptor stability and activity

The androgen receptor (AR) is not only a ligand-dependent transcription factor, but also functions as a licensing factor, a component of DNA replication, which is degraded during mitosis. Furthermore, the deregulation of AR activity is involved in the initiation of prostate cancer and contributes to castration resistant prostate cancer (CRPC). While AR degradation is known to occur primarily through a proteasome-mediated pathway, very little is known about how this process is regulated, especially in M phase. PC-1 is an androgen-responsive factor and expresses specificity in prostate cancer, with higher expression noted at G2/M. In this study, PC-1 was shown to interact with AR and E3 ligase CHIP (Carboxy-terminus of Hsc70 Interacting Protein) and to enhance AR/CHIP interactions, thereby decreasing AR stability. Moreover, PC-1 was found to act in conjunction with CHIP in the decreasing of AR via ubiquitination, with the subsequent degradation predominantly occurring during M phase. PC-1 was also found to repress AR transcriptional activity in androgen-dependent and androgen-independent prostate cancer cells and attenuate the growth inhibition of AR. In conclusion, these findings should provide new clues regarding the modulation of AR turnover and activity via PC-1 and reveals an essential role of PC-1 in AR signaling.

Degarelix treatment is compatible with diabetes and antithrombotic therapy in patients with prostate cancer

Introduction

Therapeutically induced androgen deficiency (AD) is a standard treatment for patients with prostate cancer, but it is often associated with various adverse effects (AEs) that may lead to discontinuation. Some AEs may depend on the patient's health condition, while others may be due to complications of the drug delivery method. Degarelix is a gonadotropin-releasing hormone (GnRH) antagonist widely used for the treatment of androgen-dependent prostate cancer. This study aimed to ascertain the following: 1) the compatibility of degarelix treatment with diabetes and 2) any specific causal associations of degarelix injections with increased blood clotting and antithrombotic therapy requirements.

Patients and methods

The medical records of 162 patients with prostate cancer who had undergone degarelix treatment were retrospectively examined. The association of a medical history of diabetes and anticoagulant co-treatment with degarelix treatment discontinuation was analyzed statistically.

Results

Rapid and significant decreases in prostate-specific antigen (PSA) levels during the course of degarelix treatment were detected for patients with prostate cancer regardless of clinical state. During the 27 months of treatment, 68 subjects (48%) ceased degarelix treatment, owing to several reasons, mainly financial issues. Among these subjects, 19 had diabetes, while 35 were treated with antithrombotics. Extensive statistical analysis indicated that there were no causal associations between degarelix treatment discontinuation and preexisting diabetes or antithrombotic therapy.

Conclusion

Our study suggests that preexisting diabetes and antithrombotic therapy were not significant factors for the discontinuation of degarelix treatment in patients with prostate cancer.

Androgen Signaling in Prostate Cancer

The androgen-signaling axis plays a pivotal role in the pathogenesis of prostate cancer. Since the landmark discovery by Huggins and Hodges, gonadal depletion of androgens has remained a mainstay of therapy for advanced disease. However, progression to castration-resistant prostate cancer (CRPC) typically follows and is largely the result of restored androgen signaling. Efforts to understand the mechanisms behind CRPC have revealed new insights into dysregulated androgen signaling and intratumoral androgen synthesis, which has ultimately led to the development of several novel androgen receptor (AR)-directed therapies for CRPC. However, emergence of resistance to these newer agents has also galvanized new directions in investigations of prereceptor and postreceptor AR regulation. Here, we review our current understanding of AR signaling as it pertains to the biology and natural history of prostate cancer.

Direct Metabolic Interrogation of Dihydrotestosterone Biosynthesis from Adrenal Precursors in Primary Prostatectomy Tissues

Purpose: A major mechanism of castration-resistant prostate cancer (CRPC) involves intratumoral biosynthesis of dihydrotestosterone (DHT) from adrenal precursors. We have previously shown that adrenal-derived androstenedione (AD) is the preferred substrate over testosterone (T) for 5α-reductase expressed in metastatic CRPC, bypassing T as an obligate precursor to DHT. However, the metabolic pathway of adrenal-derived DHT biosynthesis has not been rigorously investigated in the setting of primary disease in the prostate.Experimental Design: Seventeen patients with clinically localized prostate cancer were consented for fresh tissues after radical prostatectomy. Prostate tissues were cultured ex vivo in media spiked with an equimolar mixture of AD and T, and stable isotopic tracing was employed to simultaneously follow the enzymatic conversion of both precursor steroids into nascent metabolites, detected by liquid chromatography-tandem mass spectrometry. CRPC cell line models and xenograft tissues were similarly assayed for comparative analysis. A tritium-labeled steroid radiotracing approach was used to validate our findings.Results: Prostatectomy tissues readily 5α-reduced both T and AD. Furthermore, 5α-reduction of AD was the major directionality of metabolic flux to DHT. However, AD and T were comparably metabolized by 5α-reductase in primary prostate tissues, contrasting the preference exhibited by CRPC in which AD was favored over T. 5α-reductase inhibitors effectively blocked the conversion of AD to DHT.Conclusions: Both AD and T are substrates of 5α-reductase in prostatectomy tissues, resulting in two distinctly nonredundant metabolic pathways to DHT. Furthermore, the transition to CRPC may coincide with a metabolic switch toward AD as the favored substrate. Clin Cancer Res; 23(20); 6351-62. ©2017 AACR.

Somatic Mutation Analyses in Studies of the Clonal Evolution and Diagnostic Targets of Prostate Cancer

Prostate cancer (PC) is the most common uro-oncological disease in the global population and still requires a more efficient laboratory diagnosis. Point mutations of oncogenes and tumor sup-pressor genes are the most frequent molecular genetic events in carcinogenesis. The mutations are re-sponsible, to a great extent, for the clonal evolution of cancer and can be considered as primary candi-date molecular markers of PC. Using next-generation sequencing to analyze the mutations in PC, the main molecular PC subtypes were identified, which depended on the presence of fusion genes and FOXA1, CHD1, and SPOP point mutations; other driver mutations responsible for the progression of PC subclones were also characterized. This review summarizes the data on early PC genetic markers (an mtDNA deletion, and TMPRSS2:ERG expression), as well as these somatic mutations at later stages of PC. Emphasis is placed on a switch in AR synthesis to a constitutively active variant and the point muta-tions that facilitate PC transition to a castration-refractory state that is resistant to new AR inhibitors. Based on the current whole-exome sequencing data, the frequencies and localizations of the somatic mu-tations that may provide new genetic diagnostic markers and drug targets are described.

Steroid hormone receptors and prostate cancer: role of structural dynamics in therapeutic targeting

Steroid hormone receptors (SHRs) act in cell type- and gene-specific manner through interactions with coregulatory proteins to regulate numerous physiological and pathological processes at the level of gene regulation. Binding of steroid receptor modulator (SRM) ligand leads to allosteric changes in SHR to exert positive or negative effects on the expression of target genes. Due, in part, to the fact that current SRMs generally target ligand binding domain (LBD)/AF2 and neglect intrinsically disordered (ID) N-terminal domain (NTD)/AF1, clinically relevant SRMs lack selectivity and are also prone to the development of resistance over time. Therefore, to maximize the efficacy of SHR-based therapeutics, the possibility of developing unique modulators that act to control AF1 activity must be considered. Recent studies targeting androgen receptor's (AR's) ID AF1 domain for the castration-resistant prostate cancer has provided the possibility of therapeutically targeting ID NTD/AF1 surfaces by allosteric modulations to achieve desired effects. In this review article, we discuss how inter- and intra- molecular allosteric regulations controlled by AR's structural flexibility and dynamics particularly the ID NTD/AF1 is an emerging area of investigation, which could be exploited for drug development and therapeutic targeting of prostate cancer.

Src promotes castration-recurrent prostate cancer through androgen receptor-dependent canonical and non-canonical transcriptional signatures

Progression of prostate cancer (PC) to castration-recurrent growth (CRPC) remains dependent on sustained expression and transcriptional activity of the androgen receptor (AR). A major mechanism contributing to CRPC progression is through the direct phosphorylation and activation of AR by Src-family (SFK) and ACK1 tyrosine kinases. However, the AR-dependent transcriptional networks activated by Src during CRPC progression have not been elucidated. Here, we show that activated Src (Src527F) induces androgen-independent growth in human LNCaP cells, concomitant with its ability to induce proliferation/survival genes normally induced by dihydrotestosterone (DHT) in androgen-dependent LNCaP and VCaP cells. Src induces additional gene signatures unique to CRPC cell lines, LNCaP-C4-2 and CWR22Rv1, and to CRPC LuCaP35.1 xenografts. By comparing the Src-induced AR-cistrome and/or transcriptome in LNCaP to those in CRPC and LuCaP35.1 tumors, we identified an 11-gene Src-regulated CRPC signature consisting of AR-dependent, AR binding site (ARBS)-associated genes whose expression is altered by DHT in LNCaP[Src527F] but not in LNCaP cells. The differential expression of a subset (DPP4, BCAT1, CNTNAP4, CDH3) correlates with earlier PC metastasis onset and poorer survival, with the expression of BCAT1 required for Src-induced androgen-independent proliferation. Lastly, Src enhances AR binding to non-canonical ARBS enriched for FOXO1, TOP2B and ZNF217 binding motifs; cooperative AR/TOP2B binding to a non-canonical ARBS was both Src- and DHT-sensitive and correlated with increased levels of Src-induced phosphotyrosyl-TOP2B. These data suggest that CRPC progression is facilitated via Src-induced sensitization of AR to intracrine androgen levels, resulting in the engagement of canonical and non-canonical ARBS-dependent gene signatures.

The fluorescent two-hybrid assay for live-cell profiling of androgen receptor modulators

The androgen receptor (AR) is an important target for drug therapies combating prostate cancer. However, various acquired mutations within the AR sequence often render this receptor resistant to treatment. Ligand-induced interaction between the N- and C-termini of the AR marks the initial step in the AR signaling cascade and can thus serve as an early read-out for analysis of potential antagonists of wt and mutant AR. To measure changes of the N/C interaction in the wt and mutant AR variants upon the addition of inhibitors, we applied our recently developed Fluorescent Two-Hybrid (F2H) assay. The F2H method enables real-time monitoring and quantitative analysis of the interactions between GFP- and RFP-tagged proteins in live mammalian cells, where GFP-tagged proteins are tethered to a specific nuclear location. This anchoring approach provides a local signal enrichment suitable for direct visualization of protein-protein interactions as co-localizations by conventional epifluorescence microscopy. Since the F2H assay is fully reversible, we could monitor dynamics of AR N/C interactions in living cells in real time upon agonistic, as well as antagonistic treatments. In dose-response F2H experiments, we compared the potencies of abiraterone, bicalutamide, enzalutamide, flutamide, and galeterone/TOK-001 to prevent the dihydrotestosterone-induced N/C interaction in wt AR. We further applied the newly developed F2H assay to analyze how the AR N/C interaction is affected by the clinically relevant mutations W741L, F876L, T877A and F876L/T877A. We conclude that F2H is a reliable and technically undemanding approach for straightforward screening of new AR modulators, as well as for monitoring their activity in real time in living cells.

Castration Resistance in Prostate Cancer Is Mediated by the Kinase NEK6

In prostate cancer, the development of castration resistance is pivotal in progression to aggressive disease. However, understanding of the pathways involved remains incomplete. In this study, we performed a high-throughput genetic screen to identify kinases that enable tumor formation by androgen-dependent prostate epithelial (LHSR-AR) cells under androgen-deprived conditions. In addition to the identification of known mediators of castration resistance, which served to validate the screen, we identified a mitotic-related serine/threonine kinase, NEK6, as a mediator of androgen-independent tumor growth. NEK6 was overexpressed in a subset of human prostate cancers. Silencing NEK6 in castration-resistant cancer cells was sufficient to restore sensitivity to castration in a mouse xenograft model system. Tumors in which castration resistance was conferred by NEK6 were predominantly squamous in histology with no evidence of AR signaling. Gene expression profiling suggested that NEK6 overexpression stimulated cytoskeletal, differentiation, and immune signaling pathways and maintained gene expression patterns normally decreased by castration. Phosphoproteome profiling revealed the transcription factor FOXJ2 as a novel NEK6 substrate, with FOXJ2 phosphorylation associated with increased expression of newly identified NEK6 transcriptional targets. Overall, our studies establish NEK6 signaling as a central mechanism mediating castration-resistant prostate cancer. Cancer Res; 77(3); 753-65. ©2016 AACR.

Recent Advances in Drug Design and Drug Discovery for Androgen- Dependent Diseases

This article summarizes the importance of different targets such as 5α-reductase, 17β-HSD, CYP17A, androgen receptor and protein kinase A for the treatment of prostate cancer and benign prostatic hyperplasia. It is a well known fact that dihydrotestosterone (DHT) is associated with the development of androgen-dependent afflictions. At the present time, several research groups are attempting to develop new steroidal and non-steroidal molecules with the purpose of inhibiting the synthesis and biological response of DHT. This review also discusses the most recent studies reported in the literature that describe the therapeutic potential of novel compounds, as well as the new drugs, principally inhibitors of 5α-reductase.

WOMEN IN CANCER THEMATIC REVIEW: New roles for nuclear receptors in prostate cancer

Prostate cancer has, for decades, been treated by inhibiting androgen signalling. This is effective in the majority of patients, but inevitably resistance develops and patients progress to life-threatening metastatic disease - hence the quest for new effective therapies for 'castrate-resistant' prostate cancer (CRPC). Studies into what pathways can drive tumour recurrence under these conditions has identified several other nuclear receptor signalling pathways as potential drivers or modulators of CRPC.The nuclear receptors constitute a large (48 members) superfamily of transcription factors sharing a common modular functional structure. Many of them are activated by the binding of small lipophilic molecules, making them potentially druggable. Even those for which no ligand exists or has yet been identified may be tractable to activity modulation by small molecules. Moreover, genomic studies have shown that in models of CRPC, other nuclear receptors can potentially drive similar transcriptional responses to the androgen receptor, while analysis of expression and sequencing databases shows disproportionately high mutation and copy number variation rates among the superfamily. Hence, the nuclear receptor superfamily is of intense interest in the drive to understand how prostate cancer recurs and how we may best treat such recurrent disease. This review aims to provide a snapshot of the current knowledge of the roles of different nuclear receptors in prostate cancer - a rapidly evolving field of research.

Global analysis of transcription in castration-resistant prostate cancer cells uncovers active enhancers and direct androgen receptor targets

Androgen receptor (AR) is a male sex steroid-activated transcription factor (TF) that plays a critical role in prostate cancers, including castration-resistant prostate cancers (CRPC) that typically express amplified levels of the AR. CRPC-derived VCaP cells display an excessive number of chromatin AR-binding sites (ARBs) most of which localize to distal inter- or intragenic regions. Here, we analyzed direct transcription programs of the AR in VCaP cells using global nuclear run-on sequencing (GRO-seq) and integrated the GRO-seq data with the ARB and VCaP cell-specific TF-binding data. Androgen immediately activated transcription of hundreds of protein-coding genes, including IGF-1 receptor and EGF receptor. Androgen also simultaneously repressed transcription of a large number of genes, including MYC. As functional enhancers have been postulated to produce enhancer-templated non-coding RNAs (eRNAs), we also analyzed the eRNAs, which revealed that only a fraction of the ARBs reside at functional enhancers. Activation of these enhancers was most pronounced at the sites that also bound PIAS1, ERG and HDAC3, whereas binding of HDAC3 and PIAS1 decreased at androgen-repressed enhancers. In summary, our genome-wide data of androgen-regulated enhancers and primary target genes provide new insights how the AR can directly regulate cellular growth and control signaling pathways in CPRC cells.

Redirecting abiraterone metabolism to fine-tune prostate cancer anti-androgen therapy

Abiraterone blocks androgen synthesis and prolongs survival in castration-resistant prostate cancer, which is otherwise driven by intratumoral androgen synthesis^1,2. Abiraterone is metabolized in patients to D4A, which has even greater anti-tumor activity and structural similarities to endogenous steroidal 5α-reductase substrates, such as testosterone³. Here, we show that D4A is converted to at least 3 5α-reduced and 3 5β-reduced metabolites. The initial 5α-reduced metabolite, 3-keto-5α-abi, is more abundant than D4A in patients with prostate cancer taking abiraterone, and is an androgen receptor (AR) agonist, which promotes prostate cancer progression. In a clinical trial of abiraterone alone, followed by abiraterone plus dutasteride (a 5α-reductase inhibitor), 3-keto-5α-abi and downstream metabolites are depleted, while D4A concentrations rise, effectively blocking production of a tumor-promoting metabolite and permitting D4A accumulation. Furthermore, dutasteride does not deplete three 5β-reduced metabolites, which were also clinically detectable, demonstrating the specific biochemical effects of pharmacologic 5α-reductase inhibition on abiraterone metabolism. Our findings suggest a previously unappreciated and biochemically specific method of clinically fine-tuning abiraterone metabolism to optimize therapy.

Targeting intratumoral androgens: statins and beyond

While initially effective, androgen deprivation therapy (ADT) is not curative, and nearly all men with advanced prostate cancer will eventually progress to the more resistant, and ultimately lethal form of the disease, so called castration-resistant prostate cancer (CRPC). The maintenance of androgens within the prostate cancer microenvironment likely represents one of the key mechanisms by which this transition from hormone-sensitive to CRPC occurs. This can be accomplished either through intratumoral androgen biosynthesis or the active transport of androgens and androgenic precursors into the tumor microenvironment. More recently, preclinical and clinical data supported therapeutic strategies that seek to target these two mechanisms, either through the use of drugs that impair androgen biosynthesis (e.g. inhibiting the steroidogenic enzymes CYP17 and AKR1C3 with abiraterone and indomethacin, respectively) or drugs that inhibit the SLCO transporters responsible for importing androgens (e.g. statins).

Androgen-glucocorticoid interactions in the era of novel prostate cancer therapy

Great strides have been made in the treatment of castration-resistant prostate cancer (CRPC) with the development of new antiandrogens (enzalutamide) and more potent androgen synthesis inhibitors (abiraterone) that have both improved patient outcomes. These new drugs have also helped unravel the complex biology of androgen-androgen receptor driven prostate cancer and brought into prominence various mechanisms triggering the development of drug resistance and tumour cell survival despite use of androgen deprivation therapy (ADT). The complex role of glucocorticoids in the treatment, management and progression of patients with CRPC is integral to these advances. Historically, glucocorticoid treatment has resulted in both subjective and objective responses in patients with advanced-stage prostate cancer. With the use of these new therapeutic agents, however, unexpected glucocorticoid-related mechanisms that can cause iatrogenic stimulation of prostate cancer growth have emerged, which might contribute to drug resistance and disease progression despite optimal ADT. For example, the upregulation of glucocorticoid receptors (GRs) during enzalutamide therapy results in glucocorticoid-GR-mediated regulation of androgen target genes, leading to escape from enzalutamide blockade. Thus, understanding the biological role of glucocorticoids in patients with prostate cancer is of major importance in the era of new and evolving antiandrogen therapies.

Persistent androgen receptor addiction in castration-resistant prostate cancer

It is now understood that persistent activation of the androgen receptor (AR) signaling pathway often underlies the development of castration-resistant prostate cancer (CRPC). This realization led to renewed interest in targeting the AR and ultimately to the development of the potent next-generation AR-directed agents abiraterone and enzalutamide. While these drugs prolong survival in men with CRPC, they are unfortunately not curative. Perhaps not surprisingly, evidence points to persistent AR signaling as one of the key drivers by which resistances to these agents develops. In this context, activation of the AR signaling program can occur through a number of molecular adaptations, including alterations leading to persistent canonical AR signaling (e.g., AR amplification/overexpression, elucidations/concentration of intratumoral androgens), activation of the AR program via feedback pathways (e.g., AKT/mTOR/Pi3K, HER2/Neu), and activation of the AR program via mutation or substitution (e.g., AR ligand binding domain mutation; AR splice variants; glucocorticoid receptor signaling). This review will provide an overview of the more clinical relevant (i.e., druggable) pathways that have been implicated in the emergence of drug resistance in men with CRPC and highlight some of the ongoing efforts towards developing therapeutics to impair these mechanisms.

The Tumor Macroenvironment: Cancer-Promoting Networks Beyond Tumor Beds

During tumor progression, alterations within the systemic tumor environment, or macroenvironment, result in the promotion of tumor growth, tumor invasion to distal organs, and eventual metastatic disease. Distally produced hormones, commensal microbiota residing within mucosal surfaces, myeloid cells and even the bone marrow impact the systemic immune system, tumor growth, and metastatic spread. Understanding the reciprocal interactions between the cells and soluble factors within the macroenvironment and the primary tumor will enable the design of specific therapies that have the potential to prevent dissemination and metastatic spread. This chapter will summarize recent findings detailing how the primary tumor and systemic tumor macroenvironment coordinate malignant progression.