Biologic and clinical significance of androgen receptor variants in castration resistant prostate cancer

A Comprehensive Review and Androgen Deprivation Therapy and Its Impact on Alzheimer's Disease Risk in Older Men with Prostate Cancer

Prostate cancer (PCa) is one of the most prevalent malignancies affecting males worldwide. Despite reductions in mortality rates due to advances in early identification and treatment methods, PCa remains a major health concern. Recent research has shed light on a possible link between PCa and Alzheimer's disease (AD), which is a significant neurological ailment that affects older males all over the world. Androgen deprivation therapy (ADT), a cornerstone therapeutic method used in conjunction with radiation and palliative care in advanced metastatic PCa cases, is critical for disease management. Evidence reveals a relationship between ADT and cognitive impairment. Hormonal manipulation may cause long-term cognitive problems through processes such as amyloid beta (Aβ) aggregation and neurofibrillary tangles (NFTs). Fluctuations in basal androgen levels can upset the delicate balance of genes that are sensitive to androgen levels, contributing to cognitive impairment. This detailed review dives into the various aspects of PCa aetiology and its relationship with cognitive decline. It investigates the discovery of particular biomarkers, as well as microRNAs (miRNAs), which play important roles in pathogenic progression. The review attempts to identify potential biomarkers associated with ADT-induced cerebral changes, including Aβ oligomer buildup, NFT formation, and tauopathy, which can contribute to early-onset dementia and cognitive impairment. Besides it further aims to provide insights into innovative diagnostic and therapeutic avenues for alleviating PCa and ADT-related cognitive sequelae by unravelling these complicated pathways and molecular mechanisms.

Integrative Molecular Analyses of the MD Anderson Prostate Cancer Patient-derived Xenograft (MDA PCa PDX) Series

PURPOSE

Develop and deploy a robust discovery platform that encompasses heterogeneity, clinical annotation, and molecular characterization and overcomes the limited availability of prostate cancer models. This initiative builds on the rich MD Anderson (MDA) prostate cancer (PCa) patient-derived xenograft (PDX) resource to complement existing publicly available databases by addressing gaps in clinically annotated models reflecting the heterogeneity of potentially lethal and lethal prostate cancer.

EXPERIMENTAL DESIGN

We performed whole-genome, targeted, and RNA sequencing in representative samples of the same tumor from 44 PDXs derived from 38 patients linked to donor tumor metadata and corresponding organoids. The cohort includes models derived from different morphologic groups, disease states, and involved organ sites (including circulating tumor cells), as well as paired samples representing heterogeneity or stages before and after therapy.

RESULTS

The cohort recapitulates clinically reported alterations in prostate cancer genes, providing a data resource for clinical and molecular interrogation of suitable experimental models. Paired samples displayed conserved molecular alteration profiles, suggesting the relevance of other regulatory mechanisms (e.g., epigenomic) influenced by the microenvironment and/or treatment. Transcriptomically, models were grouped on the basis of morphologic classification. DNA damage response-associated mechanisms emerged as differentially regulated between adenocarcinoma and neuroendocrine prostate cancer in a cross-interrogation of PDX/patient datasets.

CONCLUSIONS

We addressed the gap in clinically relevant prostate cancer models through comprehensive molecular characterization of MDA PCa PDXs, providing a discovery platform that integrates with patient data and benchmarked to therapeutically relevant consensus clinical groupings. This unique resource supports robust hypothesis generation and testing from basic, translational, and clinical perspectives.

Alternative splicing in prostate cancer progression and therapeutic resistance

Prostate cancer (CaP) remains the second leading cause of cancer deaths in western men. CaP mortality results from diverse molecular mechanisms that mediate resistance to the standard of care treatments for metastatic disease. Recently, alternative splicing has been recognized as a hallmark of CaP aggressiveness. Alternative splicing events cause treatment resistance and aggressive CaP behavior and are determinants of the emergence of the two major types of late-stage treatment-resistant CaP, namely castration-resistant CaP (CRPC) and neuroendocrine CaP (NEPC). Here, we review recent multi-omics data that are uncovering the complicated landscape of alternative splicing events during CaP progression and the impact that different gene transcript isoforms can have on CaP cell biology and behavior. We discuss renewed insights in the molecular machinery by which alternative splicing occurs and contributes to the failure of systemic CaP therapies. The potential for alternative splicing events to serve as diagnostic markers and/or therapeutic targets is explored. We conclude by considering current challenges and promises associated with splicing-modulating therapies, and their potential for clinical translation into CaP patient care.

Proliferation and migration of PC-3 prostate cancer cells is counteracted by PPARγ-cladosporol binding-mediated apoptosis and a decreased lipid biosynthesis and accumulation

OBJECTIVES

Chemoprevention, consisting of the administration of natural and/or synthetic compounds, appears to be an alternative way to common therapeutical approaches to preventing the occurrence of various cancers. Cladosporols, secondary metabolites from Cladosporium tenuissimum, showed a powerful ability in controlling human colon cancer cell proliferation through a peroxisome proliferator-activated receptor gamma (PPARγ)-mediated modulation of gene expression. Hence, we carried out experiments to verify the anticancer properties of cladosporols in human prostate cancer cells. Prostate cancer represents one of the most widespread tumors in which several risk factors play a role in determining its high mortality rate in men.

MATERIALS AND METHODS

We assessed, by viability assays, PPARγ silencing and overexpression experiments and western blotting analysis, the anticancer properties of cladosporols in cancer prostate cell lines.

RESULTS

Cladosporols A and B selectively inhibited the proliferation of human prostate PNT-1A, LNCaP and PC-3 cells and their most impactful antiproliferative ability towards PC-3 prostate cancer cells, was mediated by PPARγ modulation. Moreover, the anticancer ability of cladosporols implied a sustained apoptosis. Finally, cladosporols negatively regulated the expression of enzymes involved in the biosynthesis of fatty acids and cholesterol, thus enforcing the relationship between prostate cancer development and lipid metabolism dysregulation.

CONCLUSION

This is the first work, to our knowledge, in which the role of cladosporols A and B was disclosed in prostate cancer cells. Importantly, the present study highlighted the potential of cladosporols as new therapeutical tools, which, interfering with cell proliferation and lipid pathway dysregulation, may control prostate cancer initiation and progression.

New advances of the androgen receptor in prostate cancer: report from the 1st International Androgen Receptor Symposium

The androgen receptor (AR) is a crucial player in various aspects of male reproduction and has been associated with the development and progression of prostate cancer (PCa). Therefore, the protein is the linchpin of current PCa therapies. Despite great research efforts, the AR signaling pathway has still not been deciphered, and the emergence of resistance is still the biggest problem in PCa treatment. To discuss the latest developments in AR research, the "1st International Androgen Receptor Symposium" offered a forum for the exchange of clinical and scientific innovations around the role of the AR in prostate cancer (PCa) and to stimulate new collaborative interactions among leading scientists from basic, translational, and clinical research. The symposium included three sessions covering preclinical studies, prognostic and diagnostic biomarkers, and ongoing prostate cancer clinical trials. In addition, a panel discussion about the future direction of androgen deprivation therapy and anti-AR therapy in PCa was conducted. Therefore, the newest insights and developments in therapeutic strategies and biomarkers are discussed in this report.

Supraphysiological Androgens Promote the Tumor Suppressive Activity of the Androgen Receptor through cMYC Repression and Recruitment of the DREAM Complex

The androgen receptor (AR) pathway regulates key cell survival programs in prostate epithelium. The AR represents a near-universal driver and therapeutic vulnerability in metastatic prostate cancer, and targeting AR has a remarkable therapeutic index. Though most approaches directed toward AR focus on inhibiting AR signaling, laboratory and now clinical data have shown that high dose, supraphysiological androgen treatment (SPA) results in growth repression and improved outcomes in subsets of patients with prostate cancer. A better understanding of the mechanisms contributing to SPA response and resistance could help guide patient selection and combination therapies to improve efficacy. To characterize SPA signaling, we integrated metrics of gene expression changes induced by SPA together with cistrome data and protein-interactomes. These analyses indicated that the dimerization partner, RB-like, E2F, and multivulval class B (DREAM) complex mediates growth repression and downregulation of E2F targets in response to SPA. Notably, prostate cancers with complete genomic loss of RB1 responded to SPA treatment, whereas loss of DREAM complex components such as RBL1/2 promoted resistance. Overexpression of MYC resulted in complete resistance to SPA and attenuated the SPA/AR-mediated repression of E2F target genes. These findings support a model of SPA-mediated growth repression that relies on the negative regulation of MYC by AR leading to repression of E2F1 signaling via the DREAM complex. The integrity of MYC signaling and DREAM complex assembly may consequently serve as determinants of SPA responses and as pathways mediating SPA resistance.

SIGNIFICANCE

Determining the molecular pathways by which supraphysiological androgens promote growth arrest and treatment responses in prostate cancer provides opportunities for biomarker-selected clinical trials and the development of strategies to augment responses.

Beyond Prostate Cancer: An Androgen Receptor Splice Variant Expression in Multiple Malignancies, Non-Cancer Pathologies, and Development

Multiple studies have demonstrated the importance of androgen receptor (AR) splice variants (SVs) in the progression of prostate cancer to the castration-resistant phenotype and their utility as a diagnostic. However, studies on AR expression in non-prostatic malignancies uncovered that AR-SVs are expressed in glioblastoma, breast, salivary, bladder, kidney, and liver cancers, where they have diverse roles in tumorigenesis. AR-SVs also have roles in non-cancer pathologies. In granulosa cells from women with polycystic ovarian syndrome, unique AR-SVs lead to an increase in androgen production. In patients with nonobstructive azoospermia, testicular Sertoli cells exhibit differential expression of AR-SVs, which is associated with impaired spermatogenesis. Moreover, AR-SVs have been identified in normal cells, including blood mononuclear cells, neuronal lipid rafts, and the placenta. The detection and characterization of AR-SVs in mammalian and non-mammalian species argue that AR-SV expression is evolutionarily conserved and that AR-SV-dependent signaling is a fundamental regulatory feature in multiple cellular contexts. These discoveries argue that alternative splicing of the AR transcript is a commonly used mechanism that leads to an expansion in the repertoire of signaling molecules needed in certain tissues. Various malignancies appropriate this mechanism of alternative AR splicing to acquire a proliferative and survival advantage.

The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications

The discovery of the benefits of castration for prostate cancer treatment in 1941 led to androgen deprivation therapy, which remains a mainstay of the treatment of men with advanced prostate cancer. However, as early as this original publication, the inevitable development of castration-resistant prostate cancer was recognized. Resistance first manifests as a sustained rise in the androgen-responsive gene, PSA, consistent with reactivation of the androgen receptor axis. Evaluation of clinical specimens demonstrates that castration-resistant prostate cancer cells remain addicted to androgen signalling and adapt to chronic low-testosterone states. Paradoxically, results of several studies have suggested that treatment with supraphysiological levels of testosterone can retard prostate cancer growth. Insights from these studies have been used to investigate administration of supraphysiological testosterone to patients with prostate cancer for clinical benefits, a strategy that is termed bipolar androgen therapy (BAT). BAT involves rapid cycling from supraphysiological back to near-castration testosterone levels over a 4-week cycle. Understanding how BAT works at the molecular and cellular levels might help to rationalize combining BAT with other agents to achieve increased efficacy and tumour responses.

Androgen Receptor Upregulates Mucosa-Associated Lymphoid Tissue 1 to Induce NF-κB Activity via Androgen-Dependent and -Independent Pathways in Prostate Carcinoma Cells

The androgen-dependent or -independent pathways are regarded as primary therapeutic targets for the neoplasm of the prostate. Mucosa-associated lymphoid tissue 1 (MALT1) acting as a paracaspase in the regulation of nuclear factor κB (NF-κB) signal transduction plays a central role in inflammation and oncogenesis in cancers. This study confirmed the potential linkages between androgen and NF-κB activation by inducing MALT1 in the androgen receptor-full length (ARFL)-positive LNCaP and 22Rv1 prostate cancer cells. Although androgen did not stimulate MALT1 expression in AR-null or ectopic ARFL-overexpressed PC-3 cells, the ectopic overexpression of the AR splicing variant 7 (ARv7) upregulated MALT1 to activate NF-κB activities in 22Rv1 and PC-3 cells. Since the nuclear translocation of p50 and p65 was facilitated by ARv7 to motivate NF-κB activity, the expressions of MALT1, prostate-specific antigen (PSA), and N-myc downstream regulated 1 (NDRG1) were therefore induced in ectopic ARv7-overexpressed prostate cancer cells. Ectopic ARv7 overexpression not only enhanced 22Rv1 or PC-3 cell growth and invasion in vitro but also the tumor growth of PC-3 cells in vivo. These results indicate that an androgen receptor induces MALT1 expression androgen-dependently and -independently in ARFL- or ARv7-overexpressed prostate cancer cells, suggesting a novel ARv7/MALT1/NF-κB-signaling pathway may exist in the cells of prostate cancer.

Newly Developed Targeted Therapies Against the Androgen Receptor in Triple-Negative Breast Cancer: A Review

Among different types of breast cancers (BC), triple-negative BC (TNBC) amounts to 15% to 20% of breast malignancies. Three principal characteristics of TNBC cells are (i) extreme aggressiveness, (ii) absence of hormones, and (iii) growth factor receptors. Due to the lack or poor expression of the estrogen receptor, human epidermal growth factor receptor 2, and progesterone receptor, TNBC is resistant to hormones and endocrine therapies. Consequently, chemotherapy is currently used as the primary approach against TNBC. Expression of androgen receptor (AR) in carcinoma cells has been observed in a subset of patients with TNBC; therefore, inhibiting androgen signaling pathways holds promise for TNBC targeting. The new AR inhibitors have opened up new therapy possibilities for BC patients carrying AR-positive TNBC cells. Our group provides a comprehensive review of the structure and function of the AR and clinical evidence for targeting the cell's nuclear receptor in TNBC. We updated AR agonists, inhibitors, and antagonists. We also presented a new era of genetic manipulating CRISPR/Cas9 and nanotechnology as state-of-the-art approaches against AR to promote the efficiency of targeted therapy in TNBC. SIGNIFICANCE STATEMENT: The lack of effective treatment for triple-negative breast cancer is a health challenge. The main disadvantages of existing treatments are their side effects, due to their nonspecific targeting. Molecular targeting of cellular receptors, such as androgen receptors, increased expression in malignant tissues, significantly improving the survival rate of breast cancer patients.

Harnessing transcriptionally driven chromosomal instability adaptation to target therapy-refractory lethal prostate cancer

Metastatic prostate cancer (PCa) inevitably acquires resistance to standard therapy preceding lethality. Here, we unveil a chromosomal instability (CIN) tolerance mechanism as a therapeutic vulnerability of therapy-refractory lethal PCa. Through genomic and transcriptomic analysis of patient datasets, we find that castration and chemotherapy-resistant tumors display the highest CIN and mitotic kinase levels. Functional genomics screening coupled with quantitative phosphoproteomics identify MASTL kinase as a survival vulnerability specific of chemotherapy-resistant PCa cells. Mechanistically, MASTL upregulation is driven by transcriptional rewiring mechanisms involving the non-canonical transcription factors androgen receptor splice variant 7 and E2F7 in a circuitry that restrains deleterious CIN and prevents cell death selectively in metastatic therapy-resistant PCa cells. Notably, MASTL pharmacological inhibition re-sensitizes tumors to standard therapy and improves survival of pre-clinical models. These results uncover a targetable mechanism promoting high CIN adaptation and survival of lethal PCa.

YAP antagonizes TEAD-mediated AR signaling and prostate cancer growth

Hippo signaling restricts tumor growth by inhibiting the oncogenic potential of YAP/TAZ-TEAD transcriptional complex. Here, we uncover a context-dependent tumor suppressor function of YAP in androgen receptor (AR) positive prostate cancer (PCa) and show that YAP impedes AR+ PCa growth by antagonizing TEAD-mediated AR signaling. TEAD forms a complex with AR to enhance its promoter/enhancer occupancy and transcriptional activity. YAP and AR compete for TEAD binding and consequently, elevated YAP in the nucleus disrupts AR-TEAD interaction and prevents TEAD from promoting AR signaling. Pharmacological inhibition of MST1/2 or LATS1/2, or transgenic activation of YAP suppressed the growth of PCa expressing therapy resistant AR splicing variants. Our study uncovers an unanticipated crosstalk between Hippo and AR signaling pathways, reveals an antagonistic relationship between YAP and TEAD in AR+ PCa, and suggests that targeting the Hippo signaling pathway may provide a therapeutical opportunity to treat PCa driven by therapy resistant AR variants.

Multifocal glioblastoma and hormone replacement therapy in a transgender female

Background

Glioblastoma multiforme represents approximately 60% of all brain tumors in adults. This malignancy shows a high level of biological and genetic heterogeneity associated with exceptional aggressiveness, leading to poor patient survival. One of the less common presentations is the appearance of primary multifocal lesions, which are linked with a worse prognosis. Among the multiple triggering factors in glioma progression, the administration of sex steroids and their analogs has been studied, but their role remains unclear to date.

Case Description

A 43-year-old transgender woman who has a personal pathological history of receiving intramuscular (IM) hormone treatment for 27 years based on algestone/estradiol 150 mg/10 mg/mL. Three months ago, the patient suddenly experienced hemiplegia and hemiparesis in her right lower extremity, followed by a myoclonic focal epileptic seizure, vertigo, and a right frontal headache with a visual analog scale of 10/10. Magnetic resonance imaging images revealed an intra-axial mass with poorly defined, heterogeneous borders, and thick borders with perilesional edema in the left parietal lobe, as well as a rounded hypodense image with well-defined walls in the right internal capsule. The tumor was resected, and samples were sent to the pathology department, which confirmed the diagnosis of wild-type glioblastoma.

Conclusion

This report identifies prolonged use of steroid-based hormone replacement therapy as the only predisposing factor in the oncogenesis of multifocal glioblastoma. It is an example that highlights the importance for physicians not to consider pathologies related to the human immunodeficiency virus rather than neoplasms in transgender patients in view of progressive neurological deterioration.

Liquid biopsy-based targeted gene screening highlights tumor cell subtypes in patients with advanced prostate cancer

Prostate cancer (PCa) clinical heterogeneity underscores tumor heterogeneity, which may be best defined by cell subtypes. To test if cell subtypes contributing to progression can be assessed noninvasively, we investigated whether 14 genes representing luminal, neuroendocrine, and stem cells are detectable in whole blood RNA of patients with advanced PCa. For each gene, reverse transcription quantitative polymerase chain reaction assays were first validated using RNA from PCa cell lines, and their traceability in blood was assessed in cell spiking experiments. These were next tested in blood RNA of 40 advanced PCa cases and 40 healthy controls. Expression in controls, which was low or negative, was used to define stringent thresholds for gene overexpression in patients to account for normal variation in white blood cells. Thirty-five of 40 patients overexpressed at least one gene. Patients with more genes overexpressed had a higher risk of death (hazard ratio 1.42, range 1.12-1.77). Progression on androgen receptor inhibitors was associated with overexpression of stem (odds ratio [OR] 7.74, range 1.68-35.61) and neuroendocrine (OR 13.10, range 1.24-142.34) genes, while luminal genes were associated with taxanes (OR 2.7, range 1.07-6.82). Analyses in PCa transcriptomic datasets revealed that this gene panel was most prominent in metastases of advanced disease, with diversity among patients. Collectively, these findings support the contribution of the prostate cell subtypes to disease progression. Cell-subtype specific genes are traceable in blood RNA of patients with advanced PCa and are associated with clinically relevant end points. This opens the door to minimally invasive liquid biopsies for better management of this deadly disease.

Androgen receptor signaling and spatial chromatin organization in castration-resistant prostate cancer

Prostate cancer is one of the leading causes of cancer death and affects millions of men in the world. The American Cancer Society estimated about 34,500 deaths from prostate cancer in the United States in year 2022. The Androgen receptor (AR) signaling is a major pathway that sustains local and metastatic prostate tumor growth. Androgen-deprivation therapy (ADT) is the standard of care for metastatic prostate cancer patient and can suppress the tumor growth for a median of 2–3 years. Unfortunately, the malignancy inevitably progresses to castration-resistant prostate cancer (CRPC) which is more aggressive and no longer responsive to ADT. Surprisingly, for most of the CPRC patients, cancer growth still depends on androgen receptor signaling. Accumulating evidence suggests that CRPC cells have rewired their transcriptional program to retain AR signaling in the absence of androgens. Besides AR, other transcription factors also contribute to the resistance mechanism through multiple pathways including enhancing AR signaling pathway and activating other complementary signaling pathways for the favor of AR downstream genes expression. More recent studies have shown the role of transcription factors in reconfiguring chromatin 3D structure and regulating topologically associating domains (TADs). Pioneer factors, transcription factors and coactivators form liquid-liquid phase separation compartment that can modulate transcriptional events along with configuring TADs. The role of AR and other transcription factors on chromatin structure change and formation of condensate compartment in prostate cancer cells has only been recently investigated and appreciated. This review intends to provide an overview of transcription factors that contribute to AR signaling through activation of gene expression, governing 3D chromatin structure and establishing phase to phase separation. A more detailed understanding of the spatial role of transcription factors in CRPC might provide novel therapeutic targets for the treatment of CRPC.

A chemical probe for BAG1 targets androgen receptor-positive prostate cancer through oxidative stress signaling pathway

BAG1 is a family of polypeptides with a conserved C-terminal BAG domain that functions as a nucleotide exchange factor for the molecular chaperone HSP70. BAG1 proteins also control several signaling processes including proteostasis, apoptosis, and transcription. The largest isoform, BAG1L, controls the activity of the androgen receptor (AR) and is upregulated in prostate cancer. Here, we show that BAG1L regulates AR dynamics in the nucleus and its ablation attenuates AR target gene expression especially those involved in oxidative stress and metabolism. We show that a small molecule, A4B17, that targets the BAG domain downregulates AR target genes similar to a complete BAG1L knockout and upregulates the expression of oxidative stress-induced genes involved in cell death. Furthermore, A4B17 outperformed the clinically approved antagonist enzalutamide in inhibiting cell proliferation and prostate tumor development in a mouse xenograft model. BAG1 inhibitors therefore offer unique opportunities for antagonizing AR action and prostate cancer growth.

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BAG1L interacts with a sequence overlapping a polyalanine tract in the AR NTD

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Knockdown of BAG1L increase AR dynamics in the nucleus

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BAG1L uses ROS pathway to regulate AR⁺ prostate cancer cell proliferation

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A small molecule BAG1 inhibitor inhibits prostate tumor growth in mouse xenografts

Androgen receptor-mediated transcriptional repression targets cell plasticity in prostate cancer

Androgen receptor (AR) signaling remains the key therapeutic target in the management of hormone‐naïve‐advanced prostate cancer (PCa) and castration‐resistant PCa (CRPC). Recently, landmark molecular features have been reported for CRPC, including the expression of constitutively active AR variants that lack the ligand‐binding domain. Besides their role in CRPC, AR variants lead to the expression of genes involved in tumor progression. However, little is known about the specificity of their mode of action compared with that of wild‐type AR (AR‐WT). We performed AR transcriptome analyses in an androgen‐dependent PCa cell line as well as cross‐analyses with publicly available RNA‐seq datasets and established that transcriptional repression capacity that was marked for AR‐WT was pathologically lost by AR variants. Functional enrichment analyses allowed us to associate AR‐WT repressive function to a panel of genes involved in cell adhesion and epithelial‐to‐mesenchymal transition. So, we postulate that a less documented AR‐WT normal function in prostate epithelial cells could be the repression of a panel of genes linked to cell plasticity and that this repressive function could be pathologically abrogated by AR variants in PCa.

Development of a Benzothiazole Scaffold-Based Androgen Receptor N-Terminal Inhibitor for Treating Androgen-Responsive Prostate Cancer

All current clinically approved androgen deprivation therapies for prostate cancer target the C-terminal ligand-binding domain of the androgen receptor (AR). However, the main transactivation function of the receptor is localized at the AR N-terminal domain (NTD). Targeting the AR NTD directly is a challenge because of its intrinsically disordered structure and the lack of pockets for drugs to bind. Here, we have taken an alternative approach using the cochaperone BAG1L, which interacts with the NTD, to develop a novel AR inhibitor. We describe the identification of 2-(4-fluorophenyl)-5-(trifluoromethyl)-1,3-benzothiazole (A4B17), a small molecule that inhibits BAG1L-AR NTD interaction, attenuates BAG1L-mediated AR NTD activity, downregulates AR target gene expression, and inhibits proliferation of AR-positive prostate cancer cells. This compound represents a prototype of AR antagonists that could be key in the development of future prostate cancer therapeutics.

Steroid Receptors in Breast Cancer: Understanding of Molecular Function as a Basis for Effective Therapy Development

Breast cancer remains one of the most important health problems worldwide. The family of steroid receptors (SRs), which comprise estrogen (ER), progesterone (PR), androgen (AR), glucocorticoid (GR) and mineralocorticoid (MR) receptors, along with a receptor for a secosteroid-vitamin D, play a crucial role in the pathogenesis of the disease. They function predominantly as nuclear receptors to regulate gene expression, however, their full spectrum of action reaches far beyond this basic mechanism. SRs are involved in a vast variety of interactions with other proteins, including extensive crosstalk with each other. How they affect the biology of a breast cell depends on such factors as post-translational modifications, expression of coregulators, or which SR isoform is predominantly synthesized in a given cellular context. Although ER has been successfully utilized as a breast cancer therapy target for years, research on therapeutic application of other SRs is still ongoing. Designing effective hormone therapies requires thorough understanding of the molecular function of the SRs. Over the past decades, huge amount of data was obtained in multiple studies exploring this field, therefore in this review we attempt to summarize the current knowledge in a comprehensive way.

Altered glucuronidation deregulates androgen dependent response profiles and signifies castration resistance in prostate cancer

Glucuronidation controls androgen levels in the prostate and the dysregulation of enzymes in this pathway is associated with castration resistant prostate cancer. UDP-glucose dehydrogenase (UGDH) produces UDP-glucuronate, the essential precursor for glucuronidation, and its expression is elevated in prostate cancer. We compared protein and metabolite levels relevant to the glucuronidation pathway in five prostate cancer patient-derived xenograft models paired with their isogenic counterparts that were selected in vivo for castration resistant (CR) recurrence. All pairs showed changes in UGDH and associated enzymes and metabolites that were consistent with those we found in an isogenic androgen dependent (AD) and CR LNCaP prostate cancer model. Ectopic overexpression of UGDH in LNCaP AD cells blunted androgen-dependent gene expression, increased proteoglycan synthesis, significantly increased cell growth compared to controls, and eliminated dose responsive growth suppression with enzalutamide treatment. In contrast, the knockdown of UGDH diminished proteoglycans, suppressed androgen dependent growth irrespective of androgens, and restored androgen sensitivity in CR cells. Importantly, the knockdown of UGDH in both LNCaP AD and CR cells dramatically sensitized these cells to enzalutamide. These results support a role for UGDH in androgen responsiveness and a target for therapeutic strategies in advanced prostate cancer.

Androgen receptor (AR) heterogeneity in prostate cancer and therapy resistance

Androgen receptor (AR), a ligand-dependent nuclear transcription factor and a member of steroid hormone receptor family, plays an important role in prostate organogenesis by regulating epithelial differentiation and restricting cell proliferation. Although rarely mutated or amplified in treatment-naïve prostate cancer (PCa), AR signaling drives tumor growth and as a result, therapies that aim to inhibit AR signaling, called ARSIs (AR signaling inhibitors), have been in clinical use for >70 years. Unfortunately, the clinical efficacy of ARSIs is short-lived and the majority of treated patients develop castration-resistant PCa (CRPC). Numerous molecular mechanisms have been proposed for castration resistance; however, the cellular basis for CRPC emergence has remained obscure. One under-appreciated cellular mechanism for CRPC development is the AR heterogeneity that pre-exists in treatment-naive primary tumors, i.e., although most PCa cells express AR (i.e., AR⁺), there is always a population of PCa cells that express no/low AR (i.e., AR^-/lo). Importantly, this AR heterogeneity becomes accentuated during ARSI treatment and highly prominent in established CRPC. Here, we provide a succinct summary of AR heterogeneity across the PCa continuum and discuss its impact on PCa response to treatments. While AR⁺ PCa cells/clones exhibit exquisite sensitivities to ARSIs, AR^-/lo PCa cells/clones, which are greatly enriched in stem cell signaling pathways, display de novo resistance to ARSIs. Finally, we offer several potential combinatorial strategies, e.g., ARSIs with stem cell targeting therapeutics, to co-target both AR⁺ and AR^-/lo PCa cells and metastatic clones.

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

Metastatic prostate cancer is the most common cancer in males and the fifth cause of cancer mortality worldwide. Despite the major progress in this field, leading to the approval of novel anti-androgens, the prognosis is still poor. A significant number of patients acquire an androgen receptor splice variant 7 (AR-V7), which is constitutively activated and lacks the ligand-binding domain (LBD) while maintaining the nuclear localization signal and DNA-binding domain (DBD). This conformational change, even in the absence of the ligand, allows its retention within the nucleus, where it acts as a transcription factor repressing crucial tumor suppressor genes. AR-V7 is an important oncogenic driver and plays a role as an early diagnostic and prognostic marker, as well as a therapeutic target for antagonists such as niclosamide and TAS3681. Anti-AR-V7 drugs have shown promise in recent clinical investigations on this subset of patients. This mini-review focuses on the relevance of AR-V7 in the clinical manifestations of castration-resistant prostate cancer (CRPC) and summarizes redemptive therapeutic strategies.

Dissecting the Hormonal Signaling Landscape in Castration-Resistant Prostate Cancer

Understanding the molecular mechanisms underlying prostate cancer (PCa) progression towards its most aggressive, castration-resistant (CRPC) stage is urgently needed to improve the therapeutic options for this almost incurable pathology. Interestingly, CRPC is known to be characterized by a peculiar hormonal landscape. It is now well established that the androgen/androgen receptor (AR) axis is still active in CRPC cells. The persistent activity of this axis in PCa progression has been shown to be related to different mechanisms, such as intratumoral androgen synthesis, AR amplification and mutations, AR mRNA alternative splicing, increased expression/activity of AR-related transcription factors and coregulators. The hypothalamic gonadotropin-releasing hormone (GnRH), by binding to its specific receptors (GnRH-Rs) at the pituitary level, plays a pivotal role in the regulation of the reproductive functions. GnRH and GnRH-R are also expressed in different types of tumors, including PCa. Specifically, it has been demonstrated that, in CRPC cells, the activation of GnRH-Rs is associated with a significant antiproliferative/proapoptotic, antimetastatic and antiangiogenic activity. This antitumor activity is mainly mediated by the GnRH-R-associated Gαi/cAMP signaling pathway. In this review, we dissect the molecular mechanisms underlying the role of the androgen/AR and GnRH/GnRH-R axes in CRPC progression and the possible therapeutic implications.

Inter- and intra-tumor heterogeneity of metastatic prostate cancer determined by digital spatial gene expression profiling

Metastatic prostate cancer (mPC) comprises a spectrum of diverse phenotypes. However, the extent of inter- and intra-tumor heterogeneity is not established. Here we use digital spatial profiling (DSP) technology to quantitate transcript and protein abundance in spatially-distinct regions of mPCs. By assessing multiple discrete areas across multiple metastases, we find a high level of intra-patient homogeneity with respect to tumor phenotype. However, there are notable exceptions including tumors comprised of regions with high and low androgen receptor (AR) and neuroendocrine activity. While the vast majority of metastases examined are devoid of significant inflammatory infiltrates and lack PD1, PD-L1 and CTLA4, the B7-H3/CD276 immune checkpoint protein is highly expressed, particularly in mPCs with high AR activity. Our results demonstrate the utility of DSP for accurately classifying tumor phenotype, assessing tumor heterogeneity, and identifying aspects of tumor biology involving the immunological composition of metastases.

The inter- and intra-tumor heterogeneity of metastatic prostate cancer (mPC) is underexplored. Here the authors use Digital Spatial Profiling to study gene and protein expression heterogeneity in 27 mPC patients, finding variation in associated pathways and potential immunotherapy targets.

Derivation and Application of Molecular Signatures to Prostate Cancer: Opportunities and Challenges

Prostate cancer is a high-incidence cancer that requires improved patient stratification to ensure accurate predictions of risk and treatment response. Due to the significant contributions of transcription factors and epigenetic regulators to prostate cancer progression, there has been considerable progress made in developing gene signatures that may achieve this. Some of these are aligned to activities of key drivers such as the androgen receptor, whilst others are more agnostic. In this review, we present an overview of these signatures, the strategies for their derivation, and future perspectives on their continued development and evolution.

Upregulation of potential regulatory signaling molecules correlate with androgen receptor splice variants AR-V7 and AR-V567es in prostate cancer metastasis

AIM

Androgen receptor splice variants (AR-Vs) produced by alternative splicing of the AR play an important role in the treatment resistance and progression of prostate cancer (PCa). In this study, two most common AR variants and how they associate with the inflammatory response (NF-Kβ) and regulatory transcriptional activity (HSP-27) genes were investigated in patients with PCa and metastatic PCa (Met-PCa).

METHODS

Our study was carried out with the whole blood obtained from 25 healthy control subjects, 25 PCa patients and 39 Met-PCa patients. We examined the expression levels of AR, AR-V7 and AR-V567es genes via Real-time PCR and those of HSP-27 and NF-Kβ via ELISA method.

RESULTS

AR, AR-V7 and AR-V567es expressions were observed in 84.61%, 64.1%, 23.07% of Met-PCa patients respectively. The expression levels of full-length AR and variants (AR-V7 and AR-V567es) were associated with the prostate cancer stage. In the Met-PCa, the expression levels of AR, AR-V7 and AR-V567es were associated with the Gleason Scores but not with the PSA levels. AR-V7 expression levels in stage T4 patients significantly increased. NF-Kβ and HSP-27 protein levels were significantly higher in Met-PCa patients.

DISCUSSION

Our findings highlight the targeting of the proteostasis and inflammation pathways through inhibiting HSP-27 and NF-Kβ. This might be a valuable strategy to overcome anti-androgen resistance and improve drug therapy in Met-PCa patients whose gene expression levels of AR-V7 and AR-V567es variants are high.

The Androgen Receptor in Prostate Cancer: Effect of Structure, Ligands and Spliced Variants on Therapy

The androgen receptor (AR) plays a predominant role in prostate cancer (PCa) pathology. It consists of an N-terminal domain (NTD), a DNA-binding domain (DBD), a hinge region (HR), and a ligand-binding domain (LBD) that binds androgens, including testosterone (T) and dihydrotestosterone (DHT). Ligand binding at the LBD promotes AR dimerization and translocation to the nucleus where the DBD binds target DNA. In PCa, AR signaling is perturbed by excessive androgen synthesis, AR amplification, mutation, or the formation of AR alternatively spliced variants (AR-V) that lack the LBD. Current therapies for advanced PCa include androgen synthesis inhibitors that suppress T and/or DHT synthesis, and AR inhibitors that prevent ligand binding at the LBD. However, AR mutations and AR-Vs render LBD-specific therapeutics ineffective. The DBD and NTD are novel targets for inhibition as both perform necessary roles in AR transcriptional activity and are less susceptible to AR alternative splicing compared to the LBD. DBD and NTD inhibition can potentially extend patient survival, improve quality of life, and overcome predominant mechanisms of resistance to current therapies. This review discusses various small molecule and other inhibitors developed against the DBD and NTD—and the current state of the available compounds in clinical development.

Isolation and characterization of castration-resistant prostate cancer LNCaP95 clones

The androgen receptor (AR) is a validated therapeutic target for prostate cancer and has been a focus for drug development for more than six decades. Currently approved therapies that inhibit AR signaling, such as enzalutamide, rely solely on targeting the AR ligand-binding domain and, therefore, have limited efficacy on prostate cancer cells that express truncated, constitutively active AR splice variants (AR-Vs). The LNCaP95 cell line is a human prostate cancer cell line that expresses both functional full-length AR and AR-V7. LNCaP95 is a heterogeneous cell population that is resistant to enzalutamide, with its proliferation dependent on transcriptionally active AR-V7. The purpose of this study was to identify a LNCaP95 clone that would be useful for evaluating therapies for their effectiveness against enzalutamide-resistant prostate cancer cells. Seven clones from the LNCaP95 cell line were isolated and characterized using morphology, in vitro growth rate, and response to ralaniten (AR N-terminal domain inhibitor) and enzalutamide (antiandrogen). In vivo growth of the clones as subcutaneous xenografts was evaluated in castrated immunodeficient mice. All of the clones maintained the expression of full-length AR and AR-V7. Cell proliferation of the clones was insensitive to androgen and enzalutamide but importantly was inhibited by ralaniten, which is consistent with AR-Vs driving the proliferation of parental LNCaP95 cells. In castrated immunodeficient animals, the growth of subcutaneous xenografts of the D3 clone was the most reproducible compared to the parental cell line and other clones. These data support that the enzalutamide-resistant LNCaP95-D3 subline may be suitable as a xenograft tumor model for preclinical drug development with improved reproducibility.

Structural Insights of Transcriptionally Active, Full-Length Androgen Receptor Coactivator Complexes

Steroid receptors activate gene transcription by recruiting coactivators to initiate transcription of their target genes. For most nuclear receptors, the ligand-dependent activation function domain-2 (AF-2) is a primary contributor to the nuclear receptor (NR) transcriptional activity. In contrast to other steroid receptors, such as ERα, the activation function of androgen receptor (AR) is largely dependent on its ligand-independent AF-1 located in its N-terminal domain (NTD). It remains unclear why AR utilizes a different AF domain from other receptors despite that NRs share similar domain organizations. Here, we present cryoelectron microscopy (cryo-EM) structures of DNA-bound full-length AR and its complex structure with key coactivators, SRC-3 and p300. AR dimerization follows a unique head-to-head and tail-to-tail manner. Unlike ERα, AR directly contacts a single SRC-3 and p300. The AR NTD is the primary site for coactivator recruitment. The structures provide a basis for understanding assembly of the AR:coactivator complex and its domain contributions for coactivator assembly and transcriptional regulation.

Androgen receptor variant-driven prostate cancer II: advances in laboratory investigations

Background:

The androgen receptor (AR) is a key prostate cancer drug target. Suppression of AR signaling mediated by the full-length AR (AR-FL) is the therapeutic goal of all existing AR-directed therapies. AR-targeting agents impart therapeutic benefit, but lead to AR aberrations that underlie disease progression and therapeutic resistance. Among the AR aberrations specific to castration-resistant prostate cancer (CRPC), AR variants (AR-Vs) have emerged as important indicators of disease progression and therapeutic resistance.

Methods:

We conducted a systemic review of the literature focusing on recent laboratory studies on AR-Vs following our last review article published in 2016. Topics ranged from measurement and detection, molecular origin, regulation, genomic function, and preclinical therapeutic targeting of AR-Vs. We provide expert opinions and perspectives on these topics.

Results:

Transcript sequences for 22 AR-Vs have been reported in the literature. Different AR-Vs may arise through different mechanisms, and can be regulated by splicing factors and dictated by genomic rearrangements, but a low-androgen environment is a prerequisite for generation of AR-Vs. The unique transcript structures allowed development of in-situ and in-solution measurement and detection methods, including mRNA and protein detection, in both tissue and blood specimens. AR variant-7 (AR-V7) remains the main measurement target and the most extensively characterized AR-V. Although AR-V7 co-exists with AR-FL, genomic functions mediated by AR-V7 do not require the presence of AR-FL. The distinct cistromes and transcriptional programs directed by AR-V7 and their co-regulators are consistent with genomic features of progressive disease in a low-androgen environment. Preclinical development of AR-V-directed agents currently focuses on suppression of mRNA expression and protein degradation as well as targeting of the amino-terminal domain.

Conclusions:

Current literature continues to support AR-Vs as biomarkers and therapeutic targets in prostate cancer. Laboratory investigations reveal both challenges and opportunities in targeting AR-Vs to overcome resistance to current AR-directed therapies.

Merging new-age biomarkers and nanodiagnostics for precision prostate cancer management

The accurate identification and stratified treatment of clinically significant early-stage prostate cancer have been ongoing concerns since the outcomes of large international prostate cancer screening trials were reported. The controversy surrounding clinical and cost benefits of prostate cancer screening has highlighted the lack of strategies for discriminating high-risk disease (that requires early treatment) from low-risk disease (that could be managed using watchful waiting or active surveillance). Advances in molecular subtyping and multiomics nanotechnology-based prostate cancer risk delineation can enable refinement of prostate cancer molecular taxonomy into clinically meaningful and treatable subtypes. Furthermore, the presence of intertumoural and intratumoural heterogeneity in prostate cancer warrants the development of novel nanodiagnostic technologies to identify clinically significant prostate cancer in a rapid, cost-effective and accurate manner. Circulating and urinary next-generation prostate cancer biomarkers for disease molecular subtyping and the newest complementary nanodiagnostic platforms for enhanced biomarker detection are promising tools for precision prostate cancer management. However, challenges in merging both aspects and clinical translation still need to be overcome.

Rationale and Roadmap for Developing Panels of Hotspot Cancer Driver Gene Mutations as Biomarkers of Cancer Risk

Cancer driver mutations (CDMs) are necessary and causal for carcinogenesis and have advantages as reporters of carcinogenic risk. However, little progress has been made toward developing measurements of CDMs as biomarkers for use in cancer risk assessment. Impediments for using a CDM-based metric to inform cancer risk include the complexity and stochastic nature of carcinogenesis, technical difficulty in quantifying low-frequency CDMs, and lack of established relationships between cancer driver mutant fractions and tumor incidence. Through literature review and database analyses, this review identifies the most promising targets to investigate as biomarkers of cancer risk. Mutational hotspots were discerned within the 20 most mutated genes across the 10 deadliest cancers. Forty genes were identified that encompass 108 mutational hotspot codons overrepresented in the COSMIC database; 424 different mutations within these hotspot codons account for approximately 63,000 tumors and their prevalence across tumor types is described. The review summarizes literature on the prevalence of CDMs in normal tissues and suggests such mutations are direct and indirect substrates for chemical carcinogenesis, which occurs in a spatially stochastic manner. Evidence that hotspot CDMs (hCDMs) frequently occur as tumor subpopulations is presented, indicating COSMIC data may underestimate mutation prevalence. Analyses of online databases show that genes containing hCDMs are enriched in functions related to intercellular communication. In its totality, the review provides a roadmap for the development of tissue-specific, CDM-based biomarkers of carcinogenic potential, comprised of batteries of hCDMs and can be measured by error-correct next-generation sequencing. Environ. Mol. Mutagen. 61:152-175, 2020. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Prostate cancer androgen receptor splice variant 7 biomarker study - a multicentre randomised feasibility trial of biomarker-guided personalised treatment in patients with advanced prostate cancer (the VARIANT trial) study protocol

INTRODUCTION

Prostate cancer is the most common male cancer with one in four developing non-curable metastatic disease. Initial treatment responses to hormonal therapies are transient and further management options lie between (1) further hormone therapy or (2) a non-hormonal approach involving additional chemotherapy or molecular radiotherapy (radium-223). There is no clear rationale for choosing between these mechanistically different treatment approaches. The biology of hormone resistance is driven through abnormal androgen receptor activity and we can assay this through a blood test measuring androgen receptor variant 7 (AR-V7) expression in circulating tumour cells. Despite increasing evidence supporting AR-V7's role as a prognostic marker, the clinical utility of such measures remains unknown in helping personalise treatment decisions.

METHODS AND DESIGN

The VARIANT feasibility trial is a pragmatic design, to be run over 18 months with participants randomised into the intervention arm receiving biomarker (AR-V7) guided clinical treatment and participants randomised into the control arm with conventional standard management (no biomarker guidance). AR-V7 positive participants (likely to be insensitive to further hormone treatment) will receive chemotherapy or in other cases radium-223 (where routinely available). Seventy male ≥18 years old participants with metastatic castrate resistant prostate cancer clinically indicated to proceed to further hormone therapy or chemotherapy, will be recruited from three National Health Service Trusts based in England, Scotland and Wales. The feasibility primary outcome is willingness of patients to be randomised and clinicians to recruit to a biomarker-based treatment strategy, with trial data informing the basis of a definitive and appropriately powered randomised control trial.

ETHICS AND DISSEMINATION

Formal ethics review was undertaken with a favourable opinion, through Wales NRES Committee 2 18/WA/0419. Findings to be disseminated through patient and professional organisations that have expressed their support, media outlets and peer-reviewed journal publication.

TRIAL REGISTRATION NUMBER

ISRCTN10246848; pre-results.

Interaction between androgen receptor and coregulator SLIRP is regulated by Ack1 tyrosine kinase and androgen

Aberrant activation of the androgen receptor (AR) may play a critical role in castration resistant prostate cancer. After ligand binding, AR is recruited to the androgen responsive element (ARE) sequences on the DNA where AR interaction with coactivators and corepressors modulates transcription. We demonstrated that phosphorylation of AR at Tyr-267 by Ack1/TNK2 tyrosine kinase results in nuclear translocation, DNA binding, and androgen-dependent gene transcription in a low androgen environment. In order to dissect downstream mechanisms, we searched for proteins whose interaction with AR was regulated by Ack1. SLIRP (SRA stem-loop interacting RNA binding protein) was identified as a candidate protein. Interaction between AR and SLIRP was disrupted by Ack1 kinase activity as well as androgen or heregulin treatment. The noncoding RNA, SRA, was required for AR-SLIRP interaction. SLIRP was bound to ARE’s of AR target genes in the absence of androgen. Treatment with androgen or heregulin led to dissociation of SLIRP from the ARE. Whole transcriptome analysis of SLIRP knockdown in androgen responsive LNCaP cells showed that SLIRP affects a significant subset of androgen-regulated genes. Our data suggest that Ack1 kinase and androgen regulate interaction between AR and SLIRP and that SLIRP functions as a coregulator of AR with properties of a corepressor in a context-dependent manner.

Androgen receptor splicing variant 7: Beyond being a constitutively active variant

In prostate cancer development, the androgen receptor (AR) signaling plays a crucial role during both formation of early prostate lesions and progression to the lethal, incurable castration resistant stage. Accordingly, numerous approaches have been developed to inhibit AR activity including androgen deprivation therapy, application of the AR antagonists as well as the use of taxanes. However, these treatments, although effective initially, resistance inevitably occur for most of the patients within several years and limiting the therapeutic efficacy. Of note, alterations and reactivation of the AR signaling pathway have been demonstrated as the major reasons for the observed resistance. Accumulating evidences have suggested that synthesis of AR splicing variants, in particular, the constitutively active AR-V7, is one of the most important mechanisms that contribute to the abnormal AR signaling. In addition, clinical data also highlight the potential of using AR-V7 as a predictive biomarker and a therapeutic target in metastatic castration resistant prostate cancer (mCRPC). In this review, we summarize the recent findings concerning the specific role of AR-V7 in CRPC progression, drug resistance and its potential value in clinical assessment.

The androgen receptor antagonist enzalutamide induces apoptosis, dysregulates the heat shock protein system, and diminishes the androgen receptor and estrogen receptor β1 expression in prostate cancer cells

Enzalutamide's accepted mode of action is by targeting the androgen receptor's (AR) activity. In clinical practice, enzalutamide demonstrates a good benefit-risk profile for the treatment of advanced prostate cancer (PC), even after poor response to standard antihormonal treatment. However, since both, well-established antiandrogens and enzalutamide, target AR functionality, we hypothesized that additional unknown mechanisms might be responsible for enzalutamide's superior anticancer activity. In the current study, PC cells were incubated with enzalutamide and enzalutamide-dependent modulation of apoptotic mechanisms were assessed via Western blot analysis, TDT-mediated dUTP-biotin nick end-labeling assay, and nuclear morphology assay. Alterations of heat shock protein (HSP), AR, and estrogen receptor (ER) expression were examined by Western blot analysis. Enzalutamide attenuated the proliferation of PC cells in a time- and dose-dependent manner. In the presence of enzalutamide, apoptosis occurred which was shown by increased BAX expression, decreased Bcl-2 expression, nuclear pyknosis, and genomic DNA fragmentation. Moreover, enzalutamide inhibited the expression of HSPs primarily involved in steroid receptor stabilization and suppressed AR and ERβ1 expression. This study demonstrates for the first time that enzalutamide treatment of PC cells triggers varying molecular mechanisms resulting in antiproliferative effects of the drug. In addition to the well-characterized antagonistic inhibition of AR functionality, we have shown that enzalutamide also affects the intracellular synthesis of steroid receptor-associated HSPs, thereby diminishing the expression of AR and ERβ1 proteins and inducing apoptotic pathways. According to an indirect attenuation of HSP-associated factors such as steroid receptors, endometrial carcinoma, uterine leiomyosarcoma, and mamma carcinoma cells also demonstrated inhibited cell growth in the presence of enzalutamide. Our data, therefore, suggest that enzalutamide's high efficacy is at least partially independent of AR and p53 protein expression, which are frequently lost in advanced PC.

Androgen receptor-modulatory microRNAs provide insight into therapy resistance and therapeutic targets in advanced prostate cancer

Androgen receptor (AR) signalling is a key prostate cancer (PC) driver, even in advanced 'castrate-resistant' disease (CRPC). To systematically identify microRNAs (miRs) modulating AR activity in lethal disease, hormone-responsive and -resistant PC cells expressing a luciferase-based AR reporter were transfected with a miR inhibitor library; 78 inhibitors significantly altered AR activity. Upon validation, miR-346, miR-361-3p and miR-197 inhibitors markedly reduced AR transcriptional activity, mRNA and protein levels, increased apoptosis, reduced proliferation, repressed EMT, and inhibited PC migration and invasion, demonstrating additive effects with AR inhibition. Corresponding miRs increased AR activity through a novel and anti-dogmatic mechanism of direct association with AR 6.9 kb 3'UTR and transcript stabilisation. In addition, miR-346 and miR-361-3p modulation altered levels of constitutively active AR variants, and inhibited variant-driven PC cell proliferation, so may contribute to persistent AR signalling in CRPC in the absence of circulating androgens. Pathway analysis of AGO-PAR-CLIP-identified miR targets revealed roles in DNA replication and repair, cell cycle, signal transduction and immune function. Silencing these targets, including tumour suppressors ARHGDIA and TAGLN2, phenocopied miR effects, demonstrating physiological relevance. MiR-346 additionally upregulated the oncogene, YWHAZ, which correlated with grade, biochemical relapse and metastasis in patients. These AR-modulatory miRs and targets correlated with AR activity in patient biopsies, and were elevated in response to long-term enzalutamide treatment of patient-derived CRPC xenografts. In summary, we identified miRs that modulate AR activity in PC and CRPC, via novel mechanisms, and may represent novel PC therapeutic targets.

Androgen receptor plasticity and its implications for prostate cancer therapy

Acquired resistance to a drug treatment is a common problem across many cancers including prostate cancer (PCa) - one of the major factors for male mortality. The androgen receptor (AR) continues to be the main therapeutic PCa target and despite the success of modern targeted therapies such as enzalutamide, resistance to these drugs eventually develops. The AR has found many ways to adapt to treatments including overexpression and production of functional, constitutively active splice variants. However, of particular importance are point mutations in the ligand binding domain of the protein that convert anti-androgens into potent AR agonists. This mechanism appears to be especially prevalent with the AR in spite of some distant similarities to other hormone nuclear receptors. Despite the AR being one of the most studied and attended targets in cancer, those gain-of-function mutations in the receptor remain a significant challenge for the development of PCa therapies. This drives the need to fully characterize such mutations and to consistently screen PCa patients for their occurrence to prevent adverse reactions to anti-androgen drugs. Novel treatments should also be developed to overcome this resistance mechanism and more attention should be given to the possibility of similar occurrences in other cancers.

BAG1L: a promising therapeutic target for androgen receptor-dependent prostate cancer

Androgens are important determinants of normal and malignant prostate growth. They function by binding to the C-terminal ligand-binding domain (LBD) of the androgen receptor (AR). All clinically approved AR-targeting antiandrogens for prostate cancer therapy function by competing with endogenous androgens. Despite initial robust responses to androgen deprivation therapy, nearly all patients with advanced prostate cancer relapse with lethal castration-resistant prostate cancer (CRPC). Progression to CRPC is associated with ongoing AR signaling, which in part, is due to the expression of constitutively active AR splice variants that contain the N-terminus of the receptor but lack the C-terminus. Currently, there are no approved therapies specifically targeting the AR N-terminus. Current pharmacologic targeting strategies for inhibiting the AR N-terminal region have proven difficult, due to its intrinsically unstructured nature and lack of enzymatic activity. An alternative approach is to target key molecules such as the cochaperone BAG1L that bind to and enhance the activity of the AR AF1. Here, we review recent literature that suggest Bag-1L is a promising target for AR-positive prostate cancer.

Cell-based evidence regarding the role of FSH in prostate cancer

INTRODUCTION

Conversion of androgen-responsive prostate cancer (CaP) to castration-resistant CaP is associated with an acceleration of the disease that often requires treatment modalities other than androgen deprivation therapy only. Recently, follicle-stimulating hormone (FSH) has been shown to play a role in CaP growth, and clinical data showed that high serum concentration of FSH in chemically castrated CaP patients was associated with a shorter time of progression to castration-resistant CaP. In this study, we sought to investigate if FSH could have direct effects on CaP cells, possibly through the androgen receptor and androgen receptor regulated genes, such as prostate-specific antigen (PSA).

MATERIALS AND METHODS

The human CaP cell lines PC-3, LNCaP and C4-2, and nonmalignant PNT1A cells, were utilized to investigate the effects of FSH. qPCR, Western blotting analysis, and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymetoxyphenyl)-2-(4-sulfophenyl)-2H tetrazolium assays were performed in order to analyze the FSH effects.

RESULTS

The FSH receptor was present in all cell lines except PNT1A. FSH significantly increased PSA mRNA (P < 0.01) and protein (P < 0.03) levels in C4-2 cells in a dose-dependent manner. In LNCaP cells, FSH also increased PSA protein level, although to a lesser extent than in C4-2 cells, and the expression was reduced by the antiandrogen enzalutamide. In PC-3 cells, FSH was shown to increase their proliferation (P < 0.03) and β-catenin expression.

CONCLUSION

These findings demonstrate that FSH may have a direct effect in CaP in an androgen-depleted environment. However, further research is needed to understand the significance of direct FSH action in the maintenance of CaP growth at the different phases of transition from androgen dependence to androgen independence.

Incidence of fatigue and low-dose corticosteroid use in prostate cancer patients receiving systemic treatment: a meta-analysis of randomized controlled trials

BACKGROUND

Cancer-related fatigue (CRF) is a complex condition that is reported in > 50% of cancer patients. In men with castration-resistant prostate cancer (CRPC), CRF was reported in 12-21% of patients. Approved systemic therapy against CRPC is commonly administered in combination with androgen-deprivation treatment (ADT) and, in some cases, with daily, low-dose corticosteroids. Importantly, the use of low-dose corticosteroids is associated with multiple negative effects, including reduced muscle mass. On these grounds, we hypothesized that the chronic use of corticosteroids may increase the incidence of fatigue in patients with prostate cancer.

METHODS

We reviewed all randomized trials published during the last 15 years conducted in patients with prostate cancer receiving systemic treatment and we performed a sub-group analysis to gather insights regarding the potential differences in the incidence of fatigue in patients receiving vs. not receiving daily corticosteroids as part of their systemic anti-neoplastic regimen.

RESULTS

Overall, 22,734 men enrolled in prospective randomized phase II and III trials were evaluable for fatigue. Estimated pooled incidence of grade 1-2 fatigue was 30.89% (95% CI = 25.34-36.74), while estimated pooled incidence of grade 3-4 fatigue was reported in 3.90% (95% CI = 2.91-5.02). Sub-group analysis showed that grade 3-4 fatigue was approximately double in patients who received daily corticosteroids as part of their anti-neoplastic treatment (5.58; 95% CI = 4.33-6.98) vs. those who did not (2.67%; 95% CI = 1.53-4.11).

CONCLUSION

Our findings highlight the need for ad hoc-designed prospective clinical trials to investigate whether the benefits associated with low-dose, daily corticosteroids outweigh the risks associated with corticosteroid-related adverse events such as fatigue.

Enzalutamide-resistant castration-resistant prostate cancer: challenges and solutions

The new-generation hormonal agent enzalutamide has been approved for the treatment of metastatic castration-resistant prostate cancer (CRPC), in both post- and predocetaxel setting, due to the significant improvement in overall survival. More recently, enzalutamide also showed impressive results in the treatment of men with nonmetastatic CRPC. Unfortunately, not all patients with CRPC are responsive to enzalutamide, and even in responders, benefits are limited by the development of drug resistance. Adaptive resistance of metastatic prostate cancer to enzalutamide treatment can be due to the activation of both androgen receptor (AR)-dependent pathways (expression of constitutively active AR splice variants, AR point mutations, gene amplification and overexpression) and mechanisms independent of AR signaling pathway (altered steroidogenesis, upregulation of the glucocorticoid receptor, epithelial–mesenchymal transition, neuroendocrine transformation, autophagy and activation of the immune system). In this review, we focus on resistance mechanisms to enzalutamide, exploring how we could overcome them through novel therapeutic options.

Castration-Resistant Prostate Cancer Refractory to Second-Generation Androgen Receptor Axis-Targeted Agents: Opportunities and Challenges

Second-generation androgen receptor axis-targeted (ARAT) agents, namely abiraterone and enzalutamide, enable stronger blockade of the androgen receptor (AR) axis and longer survival of men with castration-resistant prostate cancer (CRPC). However, the extent of the improved survival remains insufficient and the majority of patients eventually develop resistance to these novel agents. Some patients develop resistance against ARAT treatment through mechanisms termed “complete AR independence” or “AR indifference”, and no longer require activation of the AR axis. However, a considerable proportion of CRPC patients remain persistently dependent on AR or its downstream signaling pathways. Ligand-independent activation of the AR, an AR axis-dependent mechanism, is mediated by truncated forms of ARs that lack the ligand-binding domain (LBD), arising as products of AR splicing variants or nonsense mutations of AR. Post-translational modifications of ARs can also contribute to ligand-independent transactivation of the AR. Other mechanisms for AR axis activation are mediated by pathways that bypass the AR. Recent studies revealed that the glucocorticoid receptor can upregulate a similar transcription program to that of the AR, thus bypassing the AR. ARAT agents are essentially ineffective for CRPC driven by these AR-independent mechanisms. This review article describes recent efforts to overcome these refractory machineries for the development of next-generation AR axis blockade in CRPC.

BMX-Mediated Regulation of Multiple Tyrosine Kinases Contributes to Castration Resistance in Prostate Cancer

Prostate cancer responds to therapies that suppress androgen receptor (AR) activity (androgen deprivation therapy, ADT) but invariably progresses to castration-resistant prostate cancer (CRPC). The Tec family nonreceptor tyrosine kinase BMX is activated downstream of PI3K and has been implicated in regulation of multiple pathways and in the development of cancers including prostate cancer. However, its precise mechanisms of action, and particularly its endogenous substrates, remain to be established. Here, we demonstrate that BMX expression in prostate cancer is suppressed directly by AR via binding to the BMX gene and that BMX expression is subsequently rapidly increased in response to ADT. BMX contributed to CRPC development in cell line and xenograft models by positively regulating the activities of multiple receptor tyrosine kinases through phosphorylation of a phosphotyrosine-tyrosine (pYY) motif in their activation loop, generating pYpY that is required for full kinase activity. To assess BMX activity in vivo, we generated a BMX substrate-specific antibody (anti-pYpY) and found that its reactivity correlated with BMX expression in clinical samples, supporting pYY as an in vivo substrate. Inhibition of BMX with ibrutinib (developed as an inhibitor of the related Tec kinase BTK) or another BMX inhibitor BMX-IN-1 markedly enhanced the response to castration in a prostate cancer xenograft model. These data indicate that increased BMX in response to ADT contributes to enhanced tyrosine kinase signaling and the subsequent emergence of CRPC, and that combination therapies targeting AR and BMX may be effective in a subset of patients.Significance: The tyrosine kinase BMX is negatively regulated by androgen and contributes to castration-resistant prostate cancer by enhancing the phosphorylation and activation of multiple receptor tyrosine kinases following ADT. Cancer Res; 78(18); 5203-15. ©2018 AACR.

Targeting Bromodomain and Extra-Terminal (BET) Family Proteins in Castration-Resistant Prostate Cancer (CRPC)

Purpose: Persistent androgen receptor (AR) signaling drives castration-resistant prostate cancer (CRPC) and confers resistance to AR-targeting therapies. Novel therapeutic strategies to overcome this are urgently required. We evaluated how bromodomain and extra-terminal (BET) protein inhibitors (BETi) abrogate aberrant AR signaling in CRPC.Experimental Design: We determined associations between BET expression, AR-driven transcription, and patient outcome; and the effect and mechanism by which chemical BETi (JQ1 and GSK1210151A; I-BET151) and BET family protein knockdown regulates AR-V7 expression and AR signaling in prostate cancer models.Results: Nuclear BRD4 protein expression increases significantly (P ≤ 0.01) with castration resistance in same patient treatment-naïve (median H-score; interquartile range: 100; 100-170) and CRPC (150; 110-200) biopsies, with higher expression at diagnosis associating with worse outcome (HR, 3.25; 95% CI, 1.50-7.01; P ≤ 0.001). BRD2, BRD3, and BRD4 RNA expression in CRPC biopsies correlates with AR-driven transcription (all P ≤ 0.001). Chemical BETi, and combined BET family protein knockdown, reduce AR-V7 expression and AR signaling. This was not recapitulated by C-MYC knockdown. In addition, we show that BETi regulates RNA processing thereby reducing alternative splicing and AR-V7 expression. Furthermore, BETi reduce growth of prostate cancer cells and patient-derived organoids with known AR mutations, AR amplification and AR-V7 expression. Finally, BETi, unlike enzalutamide, decreases persistent AR signaling and growth (P ≤ 0.001) of a patient-derived xenograft model of CRPC with AR amplification and AR-V7 expression.Conclusions: BETi merit clinical evaluation as inhibitors of AR splicing and function, with trials demonstrating their blockade in proof-of-mechanism pharmacodynamic studies. Clin Cancer Res; 24(13); 3149-62. ©2018 AACR.

Molecular and cellular mechanisms of castration resistant prostate cancer

With increases in the mortality rate and number of patients with prostate cancer (PCa), PCa, particularly the advanced and metastatic disease, has been the focus of a number of studies globally. Over the past seven decades, androgen deprivation therapy has been the primary therapeutic option for patients with advanced PCa; however, the majority of patients developed a poor prognosis stage of castration resistant prostate cancer (CRPC), which eventually led to mortality. Due to CRPC being incurable, laboratory investigations and clinical studies focusing on CRPC have been conducted worldwide. Clarification of the molecular pathways that may lead to CRPC is important for discovering novel therapeutic strategies to delay or reverse the progression of disease. A sustained androgen receptor (AR) signal is still regarded as the main cause of CRPC. Increasing number of studies have proposed different potential mechanisms that cause CRPC, and this has led to the development of novel agents targeting the AR-dependent pathway or AR-independent signaling. In the present review, the major underlying mechanisms causing CRPC, including several major categories of AR-dependent mechanisms, AR bypass signaling, AR-independent mechanisms and other important hypotheses (including the functions of autophagy, PCa stem cell and microRNAs in CRPC progression), are summarized with retrospective pre-clinical or clinical trials to guide future research and therapy.

Non-canonical activation of hedgehog in prostate cancer cells mediated by the interaction of transcriptionally active androgen receptor proteins with Gli3

Hedgehog (Hh) is an oncogenic signaling pathway that regulates the activity of Gli transcription factors. Canonical Hh is a Smoothened- (Smo-) driven process that alters the post-translational processing of Gli2/Gli3 proteins. Though evidence supports a role for Gli action in prostate cancer (PCa) cell growth and progression, there is little indication that Smo is involved. Here we describe a non-canonical means for activation of Gli transcription in PCa cells mediated by the binding of transcriptionally-active androgen receptors (ARs) to Gli3. Androgens stimulated reporter expression from a Gli-dependent promoter in a variety of AR + PCa cells and this activity was suppressed by an anti-androgen, Enz, or by AR knockdown. Androgens also upregulated expression of endogenous Gli-dependent genes. This activity was associated with increased intranuclear binding of Gli3 to AR that was antagonized by Enz. Fine mapping of the AR binding domain on Gli2 showed that AR recognizes the Gli protein processing domain (PPD) in the C-terminus. Mutations in the arginine-/serine repeat elements of the Gli2 PPD involved in phosphorylation and ubiquitinylation blocked the binding to AR. β-TrCP, a ubiquitin ligase that recognizes the Gli PPD, competed with AR for binding to this site. AR binding to Gli3 suppressed its proteolytic processing to the Gli3 repressor form (Gli3R) whereas AR knockdown increased Gli3R. Both full-length and truncated ARs were able to activate Gli transcription. Finally, we found that an ARbinding decoy polypeptide derived from the Gli2 C-terminus can compete with Gli3 for binding to AR. Exogenous overexpression of this decoy suppressed Gli transcriptional activity in PCa cells. Collectively, this work identifies a novel pathway for non-canonical activation of Hh signaling in PCa cells and identifies a means for interference that may have clinical relevance for PCa patients.