Emerging data on androgen receptor splice variants in prostate cancer

Advances in the understanding of androgen receptor structure and function and in the development of next-generation AR-targeted therapeutics

Androgen receptor (AR) and its ligand androgens are important for development and physiology of various tissues. AR and its ligands also play critical role in the development of various diseases, making it a valuable therapeutic target. AR ligands, both agonists and antagonists, are being widely used to treat pathological conditions, including prostate cancer and hypogonadism. Despite AR being studied widely over the last five decades, the last decade has seen striking advances in the knowledge on AR and discoveries that have the potential to translate to the clinic. This review provides an overview of the advances in AR biology, AR molecular mechanisms of action, and next generation molecules that are currently in development. Several of the areas described in the review are just unraveling and the next decade will bring more clarity on these developments that will put AR at the forefront of both basic biology and drug development.

Species variation in steroid hormone-related gene expression contributes to species diversity in sexually dimorphic communication in electric fishes

Sexually dimorphic behaviors are often regulated by gonadal steroid hormones. Species diversity in behavioral sex differences may arise as expression of genes mediating steroid action in brain regions controlling these behaviors evolves. The electric communication signals of apteronotid knifefishes are an excellent model for comparatively studying neuroendocrine regulation of sexually dimorphic behavior. These fish produce and detect weak electric organ discharges (EODs) for electrolocation and communication. EOD frequency (EODf), controlled by the medullary pacemaker nucleus (Pn), is sexually dimorphic and regulated by androgens and estrogens in some species, but is sexually monomorphic and unaffected by hormones in other species. We quantified expression of genes for steroid receptors, metabolizing enzymes, and cofactors in the Pn of two species with sexually dimorphic EODf (Apteronotus albifrons and Apteronotus leptorhynchus) and two species with sexually monomorphic EODf ("Apteronotus" bonapartii and Parapteronotus hasemani). The "A." bonapartii Pn expressed lower levels of androgen receptor (AR) genes than the Pn of species with sexually dimorphic EODf. In contrast, the P. hasemani Pn robustly expressed AR genes, but expressed lower levels of genes for 5α-reductases, which convert androgens to more potent metabolites, and higher levels of genes for 17β-hydroxysteroid dehydrogenases that oxidize androgens and estrogens to less potent forms. These findings suggest that sexual monomorphism of EODf arose convergently via two different mechanisms. In "A." bonapartii, reduced Pn expression of ARs likely results in insensitivity of EODf to androgens, whereas in P. hasemani, gonadal steroids may be metabolically inactivated in the Pn, reducing their potential to influence EODf.

Androgen receptor: Structure, signaling, function and potential drug discovery biomarker in different breast cancer subtypes

The Androgen Receptor (AR) is emerging as an important factor in the pathogenesis of breast cancer (BC), which is the most common malignancy worldwide. >70 % of AR expression in primary and metastatic breast tumors has been observed which suggests that AR may be a new marker and a potential therapeutic target among AR-positive BC patients. Biological insight into AR-positive breast cancer reveals that AR may cross-talk with several vital signaling pathways, including key molecules and receptors. Downstream signaling of AR might also affect many clinically important pathways that are emerging as clinical targets in BC. AR exhibits different behaviors depending on the breast cancer molecular subtype. Preliminary clinical research using AR-targeted drugs, which have already been FDA-approved for prostate cancer (PC), has given promising results for AR-positive breast cancer patients. However, since AR positivity's prognostic and predictive value remains uncertain, it is difficult to identify and stratify patients who would benefit from AR-targeted therapies alone. Thus, the need of the hour is to target the androgen receptor as a monotherapy or in combination with other conventional therapies which has proven to be an effective clinical strategy for the treatment of prostate cancer patients, and these therapeutic strategies are increasingly being investigated in breast cancer. Therefore, in this manuscript, we review the role of AR in various cellular processes that promote tumorigenesis and aggressiveness, in different subtypes of breast cancer, as well as discuss ongoing efforts to target AR for the more effective treatment and prevention of breast cancer.

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.

Loss of feedback regulation between FAM3B and androgen receptor driving prostate cancer progression

BACKGROUND

Although the fusion of the transmembrane serine protease 2 gene (TMPRSS2) with the erythroblast transformation-specific-related gene (ERG), or TMPRSS2-ERG, occurs frequently in prostate cancer, its impact on clinical outcomes remains controversial. Roughly half of TMPRSS2-ERG fusions occur through intrachromosomal deletion of interstitial genes and the remainder via insertional chromosomal rearrangements. Because prostate cancers with deletion-derived TMPRSS2-ERG fusions are more aggressive than those with insertional fusions, we investigated the impact of interstitial gene loss on prostate cancer progression.

METHODS

We conducted an unbiased analysis of transcriptome data from large collections of prostate cancer samples and employed diverse in vitro and in vivo models combined with genetic approaches to characterize the interstitial gene loss that imposes the most important impact on clinical outcome.

RESULTS

This analysis identified FAM3B as the top-ranked interstitial gene whose loss is associated with a poor prognosis. The association between FAM3B loss and poor clinical outcome extended to fusion-negative prostate cancers where FAM3B downregulation occurred through epigenetic imprinting. Importantly, FAM3B loss drives disease progression in prostate cancer. FAM3B acts as an intermediator of a self-governing androgen receptor feedback loop. Specifically, androgen receptor upregulates FAM3B expression by binding to an intronic enhancer to induce an enhancer RNA and facilitate enhancer-promoter looping. FAM3B, in turn, attenuates androgen receptor signaling.

CONCLUSION

Loss of FAM3B in prostate cancer, whether through the TMPRSS2-ERG translocation or epigenetic imprinting, causes an exit from this autoregulatory loop to unleash androgen receptor activity and prostate cancer progression. These findings establish FAM3B loss as a new driver of prostate cancer progression and support the utility of FAM3B loss as a biomarker to better define aggressive prostate cancer.

Emerging proteins involved in castration‑resistant prostate cancer via the AR‑dependent and AR‑independent pathways (Review)

Despite achieving optimal initial responses to androgen deprivation therapy, most patients with prostate cancer eventually progress to a poor prognosis state known as castration‑resistant prostate cancer (CRPC). Currently, there is a notable absence of reliable early warning biomarkers and effective treatment strategies for these patients. Although androgen receptor (AR)‑independent pathways have been discovered and acknowledged in recent years, the AR signaling pathway continues to play a pivotal role in the progression of CRPC. The present review focuses on newly identified proteins within human CRPC tissues. These proteins encompass both those involved in AR‑dependent and AR‑independent pathways. Specifically, the present review provides an in‑depth summary and analysis of the emerging proteins within AR bypass pathways. Furthermore, the significance of these proteins as potential biomarkers and therapeutic targets for treating CRPC is discussed. Therefore, the present review offers valuable theoretical insights and clinical perspectives to comprehensively enhance the understanding of CRPC.

The androgen receptor

The Androgen Receptor (AR) is a ligand (androgen) activated transcription factor and a member of the nuclear receptor (NR) superfamily. It is required for male sex hormone function. AR-FL (full-length) has the domain structure of NRs, an N-terminal domain (NTD) required for transactivation, a DNA-binding domain (DBD), a nuclear localization signal (NLS) and a ligand-binding domain (LBD). Paradoxes exist in that endogenous ligands testosterone (T) and 5α-dihydrotestosterone (DHT) have differential effects on male sexual development while binding to the same receptor and transcriptional specificity is achieved even though the androgen response elements (AREs) are identical to those seen for the progesterone, glucocorticoid and mineralocorticoid receptors. A high resolution 3-dimensional structure of AR-FL by either cryo-EM or X-ray crystallography has remained elusive largely due to the intrinsic disorder of the NTD. AR function is regulated by post-translational modification leading to a large number of proteoforms. The interaction of these proteoforms in multiprotein complexes with co-activators and co-repressors driven by interdomain coupling mediates the AR transcriptional output. The AR is a drug target for selective androgen receptor modulators (SARMS) that either have anabolic or androgenic effects. Protstate cancer is treated with androgen deprivation therapy or by the use of AR antagonists that bind to the LBD. Drug resistance occurs due to adaptive AR upregulation and the appearance of splice variants that lack the LBD and become constitutively active. Bipolar T treatment and NTD-antagonists could surmount these resistance mechanisms, respectively. These recent advances in AR signaling are described.

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.

Investigation of the regulatory effects of synthesized antisense oligonucleotides on androgen receptor (AR) exon 3 splicing in prostate cancer cells

The Androgen Receptor (AR) gene plays a key role in castration-resistant prostate cancer (CRPC). Controlling the progression of CRPC by inhibiting AR gene expression is one of the core directions for prostate cancer (Pca) drug development. A 23-amino acids retention, named exon 3a, into the DNA binding domain of the splice variant AR23 has been shown to prevent AR from entering the nucleus and restore the sensitivity of cancer cells to related therapies. In this study, we conducted a preliminary investigation of the splicing modulation of the AR gene in order to develop a splice-switching therapy for Pca by promoting exon 3a inclusion. Using mutagenesis-coupled RT-PCR with AR minigene and over-expression of certain splicing factors, we found that serine/arginine-rich (SR) proteins are key factors facilitating the recognition of the 3' splice site of exon 3a (L-3' SS), while the deletion or blocking of the polypyrimidine tract (PPT) region of the original 3' splice site of exon 3 (S-3' SS) could strongly enhance exon 3a splicing without affecting the function of any SR protein. Furthermore, we designed a series of antisense oligonucleotides (ASOs) to screen drug candidates, and ASOs targeting S-3' SS and its PPT region or the exonic region of exon 3 turned out to be most effective in rescuing exon 3a splicing. A dose-response test indicated ASO12 as the lead candidate drug significantly promoting the inclusion of exon 3a to more than 85%. MTT assay confirmed that the cell proliferation was significantly inhibited after ASO treatment. Our results provide the first glance to AR splicing regulation. With several promising therapeutic ASO candidates obtained here, further development of ASO drugs to treat CRPC is strongly encouraged.

Dual-Acting Peptides Target EZH2 and AR: A New Paradigm for Effective Treatment of Castration-Resistant Prostate Cancer

Prostate cancer starts as a treatable hormone-dependent disease, but often ends in a drug-resistant form called castration-resistant prostate cancer (CRPC). Despite the development of the antiandrogens enzalutamide and abiraterone for CRPC, which target the androgen receptor (AR), drug resistance usually develops within 6 months and metastatic CRPC (mCRPC) leads to lethality. EZH2, found with SUZ12, EED, and RbAP48 in Polycomb repressive complex 2 (PRC2), has emerged as an alternative target for the treatment of deadly mCRPC. Unfortunately, drugs targeting EZH2 have shown limited efficacy in mCRPC. To address these failures, we have developed novel, dual-acting peptide inhibitors of PRC2 that uniquely target the SUZ12 protein component, resulting in the inhibition of both PRC2 canonical and noncanonical functions in prostate cancer. These peptides were found to inhibit not only the EZH2 methylation activity, but also block its positive effect on AR gene expression in prostate cancer cells. Since the peptide effect on AR levels is transcriptional, the inhibitory peptides can block the expression of both full-length AR and its splicing variants including AR-V7, which plays a significant role in the development of drug resistance. This dual-mode action provides the peptides with the capability to kill enzalutamide-resistant CRPC cells. These peptides are also more cytotoxic to prostate cancer cells than the combination of enzalutamide and an EZH2 inhibitory drug, which was recently suggested to be an effective treatment of mCRPC disease. Our data show that such a dual-acting therapeutic approach can be more effective than the existing front-line drug therapies for treating deadly mCRPC.

The Crucial Role of AR-V7 in Enzalutamide-Resistance of Castration-Resistant Prostate Cancer

Simple Summary

Androgen receptor splice variant 7 (AR-V7) has always been considered a key driver for triggering enzalutamide resistance of castration-resistant prostate cancer (CRPC). In recent years, both the homeostasis of AR-V7 protein and AR-V7’s relationship with LncRNAs have gained great attention with in-depth studies. Starting from protein stability and LncRNA, the paper discusses and summarizes the mechanisms and drugs that affect the CRPC patients’ sensitivity to enzalutamide by regulating the protein or transcriptional stability of AR-V7, hoping to provide therapeutic ideas for subsequent research to break through the CRPC therapeutic bottleneck.

Abstract

Prostate cancer (PCa) has the second highest incidence of malignancies occurring in men worldwide. The first-line therapy of PCa is androgen deprivation therapy (ADT). Nonetheless, most patients progress to castration-resistant prostate cancer (CRPC) after being treated by ADT. As a second-generation androgen receptor (AR) antagonist, enzalutamide (ENZ) is the current mainstay of new endocrine therapies for CRPC in clinical use. However, almost all patients develop resistance during AR antagonist therapy due to various mechanisms. At present, ENZ resistance (ENZR) has become challenging in the clinical treatment of CRPC. AR splice variant 7 (AR-V7) refers to a ligand-independent and constitutively active variant of the AR and is considered a key driver of ENZR in CRPC. In this review, we summarize the mechanisms and biological behaviors of AR-V7 in ENZR of CRPC to contribute novel insights for CRPC therapy.

TR3 Enhances AR Variant Production and Transactivation, Promoting Androgen Independence of Prostate Cancer Cells

Simple Summary

Advanced prostate cancer development is associated with androgen-independent AR signaling. TR3 overexpression alters AR expression, splicing process, and transactivation towards increasing the androgen independence of AR signaling in prostate cancer cells. These results suggest that TR3 is a pivotal factor in the progression of prostate cancer to advanced form.

Abstract

The pro-oncogenic function of TR3, an orphan nuclear receptor, has been reported in prostate cancer. However, the roles of TR3 in androgen receptor (AR) expression and signaling in prostate cancer cells are poorly understood. Database analysis revealed that TR3 expression level is elevated in prostate tumors, and is positively, although weakly, correlated with that of AR. TR3 overexpression increased the production of AR splice variants in addition to general upregulation of AR expression. TR3 interacted with some spliceosomal complex components and AR precursor mRNA, altering the splice junction rates between exons. TR3 also enhanced androgen-independent AR function. Furthermore, TR3 overexpression increased cell proliferation and mobility of AR-positive prostate cancer cells and stimulated tumorigenesis of androgen-independent prostate cancer cells in mouse xenograft models. This is the first study to report that TR3 is a multifunctional regulator of AR signaling in prostate cancer cells. TR3 alters AR expression, splicing process, and activity in prostate cancer cells, increasing the androgen independence of AR signaling. Therefore, TR3 may play a crucial role in the progression of prostate cancer to an advanced castration-resistant form.

Poly-glutamine-dependent self-association as a potential mechanism for regulation of androgen receptor activity

The androgen receptor (AR) plays a central role in prostate cancer. Development of castration resistant prostate cancer (CRPC) requires androgen-independent activation of AR, which involves its large N-terminal domain (NTD) and entails extensive epigenetic changes depending in part on histone lysine demethylases (KDMs) that interact with AR. The AR-NTD is rich in low-complexity sequences, including a polyQ repeat. Longer polyQ sequences were reported to decrease transcriptional activity and to protect against prostate cancer, although they can lead to muscular atrophy. However, the molecular mechanisms underlying these observations are unclear. Using NMR spectroscopy, here we identify weak interactions between the AR-NTD and the KDM4A catalytic domain, and between the AR ligand-binding domain and a central KDM4A region that also contains low-complexity sequences. We also show that the AR-NTD can undergo liquid-liquid phase separation in vitro, with longer polyQ sequences phase separating more readily. Moreover, longer polyQ sequences hinder nuclear localization in the absence of hormone and increase the propensity for formation of AR-containing puncta in the nucleus of cells treated with dihydrotestosterone. These results lead us to hypothesize that polyQ-dependent liquid-liquid phase separation may provide a mechanism to decrease the transcriptional activity of AR, potentially opening new opportunities to design effective therapies against CRPC and muscular atrophy.

Gene therapy with AR isoform 2 rescues spinal and bulbar muscular atrophy phenotype by modulating AR transcriptional activity

Spinal and bulbar muscular atrophy (SBMA) is an X-linked, adult-onset neuromuscular condition caused by an abnormal polyglutamine (polyQ) tract expansion in androgen receptor (AR) protein. SBMA is a disease with high unmet clinical need. Recent studies have shown that mutant AR-altered transcriptional activity is key to disease pathogenesis. Restoring the transcriptional dysregulation without affecting other AR critical functions holds great promise for the treatment of SBMA and other AR-related conditions; however, how this targeted approach can be achieved and translated into a clinical application remains to be understood. Here, we characterized the role of AR isoform 2, a naturally occurring variant encoding a truncated AR lacking the polyQ-harboring domain, as a regulatory switch of AR genomic functions in androgen-responsive tissues. Delivery of this isoform using a recombinant adeno-associated virus vector type 9 resulted in amelioration of the disease phenotype in SBMA mice by restoring polyQ AR-dysregulated transcriptional activity.

The Role of Androgen Receptor Splicing Variant 7 in Predicting the Prognosis of Metastatic Castration-Resistant Prostate Cancer: Systematic Review and Meta-Analysis

OBJECTIVE

The purpose of this meta-analysis was to study the prognostic effects of androgen receptor splicing variant 7 (AR-V7) on metastatic castration-resistant prostate cancer (mCRPC) under different treatment options (chemotherapy, hormone therapy).

METHODS

We conducted a systematic search of PubMed, EMBASE and Cochrane databases for clinical studies up to June 4, 2021, and used prostate-specific antigen (PSA) progression free-survival (PSA-PFS), radiologic PFS (r-PFS), overall survival (OS) and PSA response rate (PSA RR) as the main endpoints. Subgroup analyses were conducted based on the source of the specimens. STATA v.15 software was used for data analysis.

RESULTS

Twenty-one studies were included in this meta-analysis, with a total of 1578 samples. In the abiraterone (AA)/enzalutamide (E) treatment group, AR-V7 positive patients had worse PSA-PFS (hazard ratio [HR] = 3.40; 95% confidence interval [95%CI] 2.56-4.51; P < 0.05) and worse r-PFS (HR = 2.69; 95%CI 1.70-4.24; P < 0.05) and OS (HR = 3.02; 95%CI 1.73-5.30; P < 0.05). Multivariate Cox regression results showed that AR-V7 positive status was an independent risk factor for OS in the AA/E treatment group. In the taxane treatment group, AR-V7-positive and negative patients had similar PSA-PFS (HR = 0.87; 95%CI 0.46-1.63; P = 0.657), r-PFS (HR = 1.01; 95%CI 0.53-1.96; P = 0.965) and OS (HR = 1.50; 95%CI 0.89-2.52; P = 0.127). For AR-V7-positive patients, the difference in OS between taxane and AA/E treatment was not statistically significant (HR = 1.03; 95%CI 0.52-2.06; P = 0.930). However, multivariate Cox regression results suggested that for AR-V7-positive patients, taxane therapy was a protective factor for OS (HR = 0.35; 95%CI 0.20-0.60; P < 0.05).

CONCLUSION

The expression of AR-V7 indicates a poor prognosis and is an independent risk factor for OS in AA/E-treated mCRPC patients. However, AR-V7 positive status does not play the same role in taxane-treated patients. In addition, compared to AA/E, taxane treatment is a protective factor for OS in AR-V7-positive patients. AR-V7 may thus be an effective biomarker for treatment prognosis in patients with mCRPC.

Synthesis of dihydrotestosterone derivatives modified in the A-ring with (hetero)arylidene, pyrazolo[1,5-a]pyrimidine and triazolo[1,5-a]pyrimidine moieties and their targeting of the androgen receptor in prostate cancer

One of the main directions of steroid research is the preparation of modified derivatives in which, in addition to changes in physicochemical properties, receptor binding is significantly altered, thus a bioactivity different from that of the parent compound predominates. In the frame of this work, 2-arylidene derivatives were first synthesized by regioselective modification of the A-ring of natural sex hormone, 5α-dihydrotestosterone (DHT). After Claisen-Schmidt condensations of DHT with (hetero)aromatic aldehydes in alkaline EtOH, heterocyclizations of the α,β-enones were performed with 3-amino-1,2,4-triazole, 3-aminopyrazole and 3-amino-5-methylpyrazole in the presence of t-BuOK in DMF to afford 7'-epimeric mixtures of A-ring-fused azolo-dihydropyrimidines, respectively. Depending on the electronic demand of the substituents of the arylidene moiety, spontaneous or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)-induced oxidation of the heteroring led to triazolo[1,5-a]pyrimidines and pyrazolo[1,5-a]pyrimidines in good yields, while, using the Jones reagent as a strong oxidant, 17-oxidation also occurred. The crystal structures of an arylidene and a triazolopyrimidine product have been determined by single crystal X-ray diffraction and both were found to crystallize in the monoclinic crystal system at P2₁ space group. Most derivatives were found to diminish the transcriptional activity of androgen receptor (AR) in reporter cell line. The candidate compound (17β-hydroxy-2-(4-chloro)benzylidene-5α-androstan-3-one, 2f) showed to suppress androgen-mediated AR transactivation in a dose-dependent manner. We confirmed the cellular interaction of 2f with AR, described the binding in AR-binding cavity by the flexible docking and showed the ability of the compound to suppress the expression of AR-regulated genes in two prostate cancer cell lines.

Breaking androgen receptor addiction of prostate cancer by targeting different functional domains in the treatment of advanced disease

In the last decade, treatment for castration-resistant prostate cancer has changed markedly, impacting symptom control and longevity for patients. However, a large proportion of cases progress despite androgen deprivation therapy and chemotherapy, while still being fit enough for several more lines of treatment. Overstimulation of the androgen receptor (AR) activity is the main driver of this cancer. Targeting biological functions of the AR or its co-regulators has proven very effective in this disease and led to the development of several highly effective drugs targeting the AR signalling axis. Drugs such as enzalutamide demonstrated that the improvement in anti-tumour efficacy is closely correlated with an affinity for the AR and its activity and have established the paradigm that AR remains activity in aggressive disease. However, as importantly, key insights into mechanisms of resistance are guiding the development of the next generation of AR-targeted drugs. This review outlines the historical development of these highly specific agents, their mechanism of action in the context of defective AR activity, and explores the potential for the upcoming next-generation AR inhibitors (ARI) for prostate cancer by targeting the alternative domains of AR, rather than by the conventional ligand-binding domain approach. There is huge potential in these approaches to develop new drugs with high clinical activity and further improve the outlook for patients.

Increased transcription and high translation efficiency lead to accumulation of androgen receptor splice variant after androgen deprivation therapy

Upregulation of androgen receptor splice variants (AR-Vs), especially AR-V7, is associated with castration resistance of prostate cancer. At the RNA level, AR-V7 upregulation is generally coupled with increased full-length AR (AR-FL); consequently, AR-V7 and AR-Vs collectively constitute a minority of the AR population. However, Western blotting showed that the relative abundance of AR-V proteins is much higher in many castration-resistant prostate cancers (CRPCs). To address the mechanism underlying this discrepancy, we analyzed RNA-seq data from ~350 CRPC samples and found a positive correlation between all canonical and alternative AR splicing. This indicates that increased alternative splicing is not at the expense of canonical splicing. Instead, androgen deprivation releases AR-FL from repressing the transcription of the AR gene to induce coordinated increase of AR-FL and AR-V mRNAs. At the protein level, however, androgen deprivation induces AR-FL, but not AR-V, degradation. Moreover, AR-V7 is translated much faster than AR-FL. Thus, androgen-deprivation-induced AR-gene transcription and AR-FL protein decay, together with efficient AR-V7 translation, explain the discrepancy between the relative AR-V mRNA and protein abundances in many CRPCs, highlighting the inevitability of AR-V induction after endocrine therapy.

Roles of circRNAs in prostate cancer: Expression, mechanism, application and potential

Circular RNA (circRNA) is a member of the non-coding RNA family that is formed by trans-splicing. Because of its unique structure and characteristics, it has extraordinary value for the diagnosis, treatment, and prognosis of diseases, particularly for tumors. Study of the role of circRNAs in the occurrence and development of prostate cancer has made considerable progress, but many areas remain that require further exploration and improvement. This article describes research into sequencing expression profiles, expression regulation, potential value as biomarkers, mechanism in the occurrence and development, therapy resistance, relationship with clinicopathological features, and prognostic value of circRNAs in prostate cancer from the past few years.

Regulation of carcinogenesis and mediation through Wnt/β-catenin signaling by 3,3'-diindolylmethane in an enzalutamide-resistant prostate cancer cell line

Enzalutamide (ENZ) is an important drug used to treat castration-resistant prostate cancer (CRPC), which inhibits androgen receptor (AR) signaling. Previous study showed that 3,3′-diindolylmethane (DIM) is an AR antagonist that also inhibits Wnt signaling and epithelial-mesenchymal transition (EMT). To investigate whether combined treatment with ENZ and DIM can overcome ENZ resistance by regulating Wnt signaling to inhibit AR signaling and EMT in ENZ-resistant prostate cancer cells, 22Rv1 cells were cultured in normal medium and treated with ENZ, DIM, and DIM with ENZ. Exposure of ENZ-resistant cells to both DIM and ENZ significantly inhibited cell proliferation without cytotoxicity and invasion in comparison with the control. DIM significantly increased the E-cadherin expression and inhibited the expressions of Vimentin and Fibronectin, subsequently inhibiting EMT. Co-treatment with ENZ and DIM significantly increased the expressions of GSK3β and APC and decreased the β-catenin protein expression, causing inhibition of Wnt signaling and AR expression, it also significantly decreased the AR-v7 expression and down-regulated AR signaling. Via suppression of Wnt and AR signaling, co-treatment increased the E-cadherin and decreased the Vimentin and Fibronectin RNA and protein expressions, then inhibited EMT. Co-treatment with DIM and ENZ regulated Wnt signaling to reduce not only the AR expression, but also the AR-v7 expression, indicating suppression of EMT that inhibits cancer cell proliferation, invasion and migration to ameliorate ENZ resistance.

A detailed characterization of stepwise activation of the androgen receptor variant 7 in prostate cancer cells

Expression of the andrgogen receptor splice variant 7 (AR-V7) is frequently detected in castrate resistant prostate cancer and associated with resistance to AR-targeted therapies. While we have previously noted that homodimerization is required for the transcriptional activity of AR-V7 and that AR-V7 can also form heterodimers with the full-length AR (AR-FL), there are still many gaps of knowledge in AR-V7 stepwise activation. In the present study, we show that neither AR-V7 homodimerization nor AR-V7/AR-FL heterodimerization requires cofactors or DNA binding. AR-V7 can enter the nucleus as a monomer and drive a transcriptional program and DNA-damage repair as a homodimer. While forming a heterodimer with AR-FL to induce nuclear localization of unliganded AR-FL, AR-V7 does not need to interact with AR-FL to drive gene transcription or DNA-damage repair in prostate cancer cells that co-express AR-V7 and AR-FL. These data indicate that AR-V7 can function independently of its interaction with AR-FL in the true castrate state or “absence of ligand”, providing support for the utility of targeting AR-V7 in improving outcomes of patients with castrate resistant prostate cancer.

Impact of taxanes on androgen receptor signaling

The development and progression of metastatic castration-resistant prostate cancer is the major challenge in the treatment of advanced prostate cancer. The androgen receptor signaling pathway remains active in metastatic castration-resistant prostate cancer. Docetaxel and cabazitaxel are the first- and second-line chemotherapy, respectively, for patients with metastatic castration-resistant prostate cancer. These two taxanes, in general, function by (i) inhibiting mitosis and inducing apoptosis and (ii) preventing microtubule-dependent cargo trafficking. In prostate cancer, taxanes have been reported to inhibit the nuclear translocation and activity of the androgen receptor. However, whether this is attainable or not clinically remains controversial. In this review, we will provide a comprehensive view of the effects of taxanes on androgen receptor signaling in prostate cancer.

Neddylation inactivation represses androgen receptor transcription and inhibits growth, survival and invasion of prostate cancer cells

Androgen receptor (AR) and its constitutively active variants (AR-Vs) have been extensively implicated in the progression and recurrence of prostate cancer, making them attractive targets in the treatment of this disease. Whether and how neddylation modification regulates AR, and the therapeutic implications of this potential regulation, are relatively unexplored areas of investigation. Here we report that neddylation inactivation by the pharmacological inhibitor MLN4924 or Lenti-shRNA-based genetic knockdown of neddylation activating enzyme (NAE) selectively suppressed growth and survival of prostate cancer cells with minor, if any, effect on normal prostate epithelial cells. MLN4924 also significantly suppressed the invasive capacity of prostate cancer cells. Furthermore, compared to monotherapy, the combination of MLN4924 with AR antagonist or castration significantly enhanced growth suppression of prostate cancer cells in vitro, and tumor growth in an in vivo xenograft model. Mechanistically, MLN4924 repressed the transcription of AR/AR-V7 and its downstream targets, and blocked MMP2 and MMP9 expression. Taken together, our study reveals that the neddylation pathway positively regulates AR/AR-V7 transcription, and that the neddylation inhibitor MLN4924 has therapeutic potential for the treatment of aggressive prostate cancers.

Shh Overexpression Is Correlated with GRP78 and AR Expression in Primary Prostate Cancer: Clinicopathological Features and Outcomes in a Chinese Cohort

Introduction

Shh plays an important role in prostate cancer progression, but its correlation with GRP78 and AR is elusive.

Methods

The study included 539 patients in total, of which 443 had primary prostate carcinoma and 96 patients had benign prostatic hyperplasia (BPH). The clinicopathologic features, histologic scores of protein expression, and correlations between protein and disease state were studied in this cohort. Kaplan–Meier and Pearson correlation analyses were used to compare measures between groups. We performed immunohistochemistry to evaluate the expression of the Shh protein in benign prostatic hyperplasia (n=96) and prostate cancer (Gleason scores ≤6 [n=399] or ≥7 [n=44]). We quantified the expression of Shh, AR, and GRP78 using the weighted histoscore method, studied the correlation between Shh expression and AR and GRP78, and evaluated the impact of Shh protein expression on patient survival.

Results

Shh expression was significantly higher in prostate cancer with Gleason scores ≥7 than in cancer with lower Gleason scores or benign hyperplasia and was much higher in AR-positive cancer than in AR-negative cancer. Shh is overexpressed in high-grade prostate cancer and is positively correlated with the expression of both GRP78 and AR.

Conclusion

Therefore, Shh may be a useful prognostic marker and therapeutic target for prostate cancer.

Advances of Zinc Signaling Studies in Prostate Cancer

Prostate cancer (PCa) is one of the most common cancers and the second leading cause of cancer-related death among men worldwide. Despite progresses in early diagnosis and therapeutic strategies, prognosis for patients with advanced PCa remains poor. Noteworthily, a unique feature of healthy prostate is its highest level of zinc content among all soft tissues in the human body, which dramatically decreases during prostate tumorigenesis. To date, several reviews have suggested antitumor activities of zinc and its potential as a therapeutic strategy of PCa. However, an overview about the role of zinc and its signaling in PCa is needed. Here, we review literature related to the content, biological function, compounds and clinical application of zinc in PCa. We first summarize zinc content in prostate tissue and sera of PCa patients with their clinical relevance. We then elaborate biological functions of zinc signaling in PCa on three main aspects, including cell proliferation, death and tumor metastasis. Finally, we discuss clinical applications of zinc-containing compounds and proteins involved in PCa signaling pathways. Based on currently available studies, we conclude that zinc plays a tumor suppressive role and can serve as a biomarker in PCa diagnosis and therapies.

Improved Androgen Receptor Splice Variant 7 Detection Using a Highly Sensitive Assay to Predict Resistance to Abiraterone or Enzalutamide in Metastatic Prostate Cancer Patients

BACKGROUND

In metastatic castration-resistant prostate cancer (mCRPC), androgen receptor splice variant 7 (AR-V7) expression is associated with a low response to androgen receptor signaling (ARS) inhibitors such as abiraterone or enzalutamide.

OBJECTIVE

To perform a highly sensitive assay for detecting AR-V7 (hsAR-V7) in circulating tumor cells (CTCs) and evaluate its ability to predict response to ARS inhibitors.

DESIGN, SETTING, AND PARTICIPANTS

From 41 mCRPC patients, CTCs were prospectively enriched using AdnaTest platform and analyzed for AR-V7 with and without the highly sensitive assay.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The first objective of the study was to compare AR-V7 detection rates with and without the highly sensitive assay. Next, we investigated how AR-V7 (detected without the highly sensitive assay) and hsAR-V7 status influenced prostate-specific antigen (PSA) response and long-term clinical outcomes (PSA progression-free survival [PFS] and radiological PFS) after ARS-inhibitor treatment. Finally, discriminatory abilities of the assays were assessed by C-index to compare their impact on long-term clinical outcomes.

RESULTS AND LIMITATIONS

AR-V7 detection rates increased from 22% to 56% when the highly sensitive assay was used. The discriminatory abilities of hsAR-V7 for PSA PFS (C-index, 0.74; 95% confidence interval [CI], 0.60-0.88) and radiological PFS (0.70; 95% CI, 0.55-0.85) were higher than those of AR-V7 detected without the highly sensitive assay (0.60, 0.51-0.72, and 0.56, 0.44-0.67, respectively). After ARS-inhibitor treatment, PSA response was lower in hsAR-V7⁺ (53%) than in hsAR-V7^- (93%) patients (p = 0.016). AR-V7⁺ patients had shorter median PSA PFS (3.0 vs 10.6 mo, p = 0.032) and nonsignificantly shorter median radiological PFS (6.0 vs 14.8 mo, p = 0.24) compared with AR-V7^- patients. The hsAR-V7⁺ status was associated with shorter median PSA PFS (3.0 mo vs not reached, p = 0.0001) and radiological PFS (median, 6.0 mo vs not reached, p = 0.0026).

CONCLUSIONS

The hsAR-V7 assay achieved the highest AR-V7 detection rates among those reported in mCRPC. Discriminatory abilities for long-term clinical outcomes were better with hsAR-V7 assay.

PATIENT SUMMARY

We prospectively analyzed circulating tumor cells from men with metastatic castration-resistant prostate cancer for androgen receptor splice variant 7 (AR-V7) status using a highly sensitive assay. It yielded higher AR-V7 detection rates and predicted resistance to androgen receptor signaling inhibitors with better discriminatory abilities for long-term clinical outcomes.

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.

Circular RNAs add diversity to androgen receptor isoform repertoire in castration-resistant prostate cancer

Deregulated expression of circular RNAs (circRNAs) is associated with various human diseases, including many types of cancer. Despite their growing links to cancer, there has been limited characterization of circRNAs in metastatic castration-resistant prostate cancer, the major cause of prostate cancer mortality. Here, through the analysis of an exome-capture RNA-seq dataset from 47 metastatic castration-resistant prostate cancer samples and ribodepletion and RNase R RNA-sequencing of patient-derived xenografts (PDXs) and cell models, we identified 13 circRNAs generated from the key prostate cancer driver gene-androgen receptor (AR). We validated and characterized the top four most abundant, clinically relevant AR circRNAs. Expression of these AR circRNAs was upregulated during castration-resistant progression of PDXs. The upregulation was not due to global increase of circRNA formation in these tumors. Instead, the levels of AR circRNAs correlated strongly with that of the linear AR transcripts (both AR and AR-variants) in clinical samples and PDXs, indicating a transcriptional mechanism of regulation. In cultured cells, androgen suppressed the expression of these AR circRNAs and the linear AR transcripts, and the suppression was attenuated by an antiandrogen. Using nuclear/cytoplasmic fractionation and RNA in-situ hybridization assays, we demonstrated predominant cytoplasmic localization of these AR circRNAs, indicating likely cytoplasmic functions. Overall, this is the first comprehensive characterization of circRNAs arising from the AR gene. With greater resistance to exoribonuclease compared to the linear AR transcripts and detectability of AR circRNAs in patient plasma, these AR circRNAs may serve as surrogate circulating markers for AR/AR-variant expression and castration-resistant prostate cancer progression.

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.

Raddeanin A down-regulates androgen receptor and its splice variants in prostate cancer

Castration-resistant progression of prostate cancer is a major cause of prostate cancer mortality, and increased expression and activity of the full-length and the splice variants of androgen receptor (AR) have been indicated to drive castration resistance. Consequently, there is an urgent need to develop agents that can target both the full-length and the splice variants of AR for more effective treatment of prostate cancer. In the present study, we showed that raddeanin A (RA), an oleanane-type triterpenoid saponin, suppresses the transcriptional activities of both the full-length and the splice variants of AR. This is attributable to their decreased expression as a result of RA induction of proteasome-mediated degradation and inhibition of the transcription of the AR gene. We further showed the potential of using RA to enhance the growth inhibitory efficacy of docetaxel, the first-line chemotherapy for prostate cancer. This study identifies RA as a new agent to target both the full-length and the splice variants of AR and provides a rationale for further developing RA for prostate cancer treatment.

Molecules targeting the androgen receptor (AR) signaling axis beyond the AR-Ligand binding domain

Prostate cancer (PCa) is the second most common cause of cancer-related mortality in men in the United States. The androgen receptor (AR) and the physiological pathways it regulates are central to the initiation and progression of PCa. As a member of the nuclear steroid receptor family, it is a transcription factor with three distinct functional domains (ligand-binding domain [LBD], DNA-binding domain [DBD], and transactivation domain [TAD]) in its structure. All clinically approved drugs for PCa ultimately target the AR-LBD. Clinically active drugs that target the DBD and TAD have not yet been developed due to multiple factors. Despite these limitations, the last several years have seen a rise in the discovery of molecules that could successfully target these domains. This review aims to present and comprehensively discuss such molecules that affect AR signaling through direct or indirect interactions with the AR-TAD or the DBD. The compounds discussed here include hairpin polyamides, niclosamide, marine sponge-derived small molecules (eg, EPI compounds), mahanine, VPC compounds, JN compounds, and bromodomain and extraterminal domain inhibitors. We highlight the significant in vitro and in vivo data found for each compound and the apparent limitations and/or potential for further development of these agents as PCa therapies.

A positive role of c-Myc in regulating androgen receptor and its splice variants in prostate cancer

Increased expression of the full-length androgen receptor (AR-FL) and AR splice variants (AR-Vs) drives the progression of castration-resistant prostate cancer (CRPC). The levels of AR-FL and AR-V transcripts are often tightly correlated in individual CRPC samples, yet our understanding of how their expression is co-regulated is limited. Here, we report a role of c-Myc in accounting for coordinated AR-FL and AR-V expression. Analysis of gene expression data from 159 metastatic CRPC samples and 2142 primary prostate tumors showed that the level of c-Myc is positively correlated with that of individual AR isoforms. A striking positive correlation also exists between the activity of the c-Myc pathway and the level of individual AR isoforms, between the level of c-Myc and the activity of the AR pathway, and between the activities of the two pathways. Moreover, the c-Myc signature is highly enriched in tumors expressing high levels of AR, as is the AR signature in c-Myc-high-expressing tumors. Using shRNA knockdown, we confirmed c-Myc regulation of expression and activity of AR-FL and AR-Vs in cell models and a patient-derived xenograft model. Mechanistically, c-Myc promotes the transcription of the AR gene and enhances the stability of the AR-FL and AR-V proteins without altering AR RNA splicing. Importantly, inhibiting c-Myc sensitizes enzalutamide-resistant cells to growth inhibition by enzalutamide. Overall, this study highlights a critical role of c-Myc in regulating the coordinated expression of AR-FL and AR-Vs that is commonly observed in CRPC and suggests the utility of targeting c-Myc as an adjuvant to AR-directed therapy.

Computer-Aided Discovery of Small Molecules Targeting the RNA Splicing Activity of hnRNP A1 in Castration-Resistant Prostate Cancer

The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is a versatile RNA-binding protein playing a critical role in alternative pre-mRNA splicing regulation in cancer. Emerging data have implicated hnRNP A1 as a central player in a splicing regulatory circuit involving its direct transcriptional control by c-Myc oncoprotein and the production of the constitutively active ligand-independent alternative splice variant of androgen receptor, AR-V7, which promotes castration-resistant prostate cancer (CRPC). As there is an urgent need for effective CRPC drugs, targeting hnRNP A1 could, therefore, serve a dual purpose of preventing AR-V7 generation as well as reducing c-Myc transcriptional output. Herein, we report compound VPC-80051 as the first small molecule inhibitor of hnRNP A1 splicing activity discovered to date by using a computer-aided drug discovery approach. The inhibitor was developed to target the RNA-binding domain (RBD) of hnRNP A1. Further experimental evaluation demonstrated that VPC-80051 interacts directly with hnRNP A1 RBD and reduces AR-V7 messenger levels in 22Rv1 CRPC cell line. This study lays the groundwork for future structure-based development of more potent and selective small molecule inhibitors of hnRNP A1–RNA interactions aimed at altering the production of cancer-specific alternative splice isoforms.

Down-regulation of AR splice variants through XPO1 suppression contributes to the inhibition of prostate cancer progression

Emerging studies have shown that the expression of AR splice variants (ARv) lacking ligand-binding domain is associated with castrate-resistant prostate cancer (CRPC) and higher risk of tumor metastasis and recurrence. Nuclear export protein XPO1 regulates the nuclear localization of many proteins including tumor suppressor proteins. Increased XPO1 in prostate cancer is associated with a high Gleason score and bone metastasis. In this study, we found that high expression of AR splice variant 7 (AR-v7) was correlated with increased XPO1 expression. Silencing of XPO1 by RNAi or treatment with Selective Inhibitor of Nuclear Export (SINE) compounds selinexor and eltanexor (KPT-8602) down-regulated the expression of AR, AR-v7 and ARv567es at mRNA and protein levels. XPO1 silencing also inhibited the expression of AR and ARv regulators including FOXA1, Src, Vav3, MED1 and Sam68, leading to the suppression of ARv and AR target genes, UBE2C and PSA. By targeting XPO1/ARv signaling, SINE suppressed prostate cancer (PCa) growth in vitro and in vivo and potentiated the anti-cancer activity of anti-AR agents, enzalutamide and abiraterone. Therefore, XPO1 inhibition could be a novel promising agent used in combination with conventional chemotherapeutics and AR-targeted therapy for the better treatment of PCa, especially CRPC.

Androgen Receptor and Ki67 Expression and Survival Outcomes in Non-small Cell Lung Cancer

Lung cancer is the most common cause of cancer-related deaths worldwide with non-small cell lung cancer (NSCLC) making up most of these cases. Males have poorer overall survival compared to women following a lung cancer diagnosis. Many studies have focused on the effects of estrogen to explain higher survival rates among women, but few have looked at the effects of androgens. We describe the expression of the androgen receptor (AR) and Ki67 in lung cancer specimens in the Manitoba Tumor Bank (MTB) and correlate these factors with patient outcome. Using the MTB, we performed immunohistochemistry on lung cancer tissue to determine expression of the AR and Ki67. These were then correlated with patient outcome. Of the 136 cases, 55% were female and 55% were adenocarcinoma. AR expression was not independently associated with outcome. Ki67 was associated with a significantly higher hazard ratio for death and recurrence (HR 2.19, 95% CI 1.30-3.70; HR 1.92, 95% CI 1.07-3.46, respectively). AR expression modified the effect of Ki67 on outcome, such that when both were expressed, there was no association with recurrence or survival (HR 2.39, 95% CI 1.31-4.36 for AR- Ki67+ vs HR 1.54, 95% CI 0.44-5.37 for AR+ Ki67+). Ki67 was associated with poorer outcomes alone. AR status alone was not associated with outcome. Although the mechanism remains unclear, AR status seems to negate the association of a high Ki67 and poor outcome.

The potential of AR-V7 as a therapeutic target

INTRODUCTION

The androgen receptor variant AR-V7 is gaining attention as a potential predictive marker for as well as one of the resistance mechanisms to the most current anti-androgen receptor (AR) therapies in castration-resistant prostate cancer (CRPC). Accordingly, development of next-generation drugs that directly or indirectly target AR-V7 signaling is urgently needed. Areas covered: We review proposed mechanisms of drug resistance in relation to AR-V7 status, the mechanisms of generation of AR-V7, and its transcriptome, cistrome, and interactome. Pharmacological agents that interfere with these processes are being developed to counteract pan AR and AR-V7-specific signaling. Also, we address the current status of the preclinical and clinical studies targeting AR-V7 signaling. Expert opinion: AR-V7 is considered a true therapeutic target, however, it remains to be determined if AR-V7 is a principal driver or merely a bystander requiring heterodimerization with co-expressed full-length AR or other variants to drive CRPC progression. While untangling AR-V7 biology, multiple strategies are being developed to counteract drug resistance, including selective blockade of AR-V7 signaling as well as inhibition of pan-AR signaling. Ideally anti-AR therapies will be combined with agents preventing activation and enrichment of AR negative tumor cells that are otherwise depressed by AR activity axis.

Circulating steroid hormone variations throughout different stages of prostate cancer

Steroid hormones play a central role in the maintenance and progression of prostate cancer. The androgen receptor is the primary driver of tumor cell proliferation and is activated by the androgens testosterone and 5α-dihydrotestosterone. Inhibition of this pathway through medical or surgical castration improves survival in the majority of advanced prostate cancer patients. However, conversion of adrenal androgen precursors and alternative steroidogenic pathways have been found to contribute to tumor progression and resistance to treatment. The emergence of highly accurate detection methods allows us to study steroidogenic mechanisms in more detail, even after treatment with potent steroidogenic inhibitors such as the CYP17A1 inhibitor abiraterone. A clear overview of steroid hormone levels in patients throughout the local, metastatic and castration-resistant stages of prostate cancer and treatment modalities is key toward a better understanding of their role in tumor progression and treatment resistance. In this review, we summarize the currently available data on steroid hormones that have been implicated in the various stages of prostate cancer. Additionally, this review addresses the implications of these findings, highlights important studies in this field and identifies current gaps in literature.

Clinical relevance of androgen receptor alterations in prostate cancer

Prostate cancer (PC) remains a leading cause of cancer-related deaths among men worldwide, despite continuously improved treatment strategies. Patients with metastatic disease are treated by androgen deprivation therapy (ADT) that with time results in the development of castration-resistant prostate cancer (CRPC) usually established as metastases within bone tissue. The androgen receptor (AR) transcription factor is the main driver of CRPC development and of acquired resistance to drugs given for treatment of CRPC, while a minority of patients have CRPC that is non-AR driven. Molecular mechanisms behind epithelial AR reactivation in CRPC include AR gene amplification and overexpression, AR mutations, expression of constitutively active AR variants, intra-tumoural and adrenal androgen synthesis and promiscuous AR activation by other factors. This review will summarize AR alterations of clinical relevance for patients with CRPC, with focus on constitutively active AR variants, their possible association with AR amplification and structural rearrangements as well as their ability to predict patient resistance to AR targeting drugs. The review will also discuss AR signalling in the tumour microenvironment and its possible relevance for metastatic growth and therapy.

Novel galeterone analogs act independently of AR and AR-V7 for the activation of the unfolded protein response and induction of apoptosis in the CWR22Rv1 prostate cancer cell model

The androgen receptor (AR) has long been the primary target for the treatment of prostate cancer (PC). Despite continuous efforts to block AR activity through ligand depletion, AR antagonism, AR depletion and combinations thereof, advanced PC tumors remain resilient. Herein, we evaluate two galeterone analogs, VNPT-178 and VNLG-74A, in PC cell models of diverse androgen and AR dependence attempting to delineate their mechanisms of action and potential clinical utility. Employing basic biochemical techniques, we determined that both analogs have improved antiproliferative and anti-AR activities compared to FDA-approved abiraterone and enzalutamide. However, induction of apoptosis in these models is independent of the AR and its truncated variant, AR-V7, and instead likely results from sustained endoplasmic reticulum stress and deregulated calcium homeostasis. Using in silico molecular docking, we predict VNPT-178 and VNLG-74A bind the ATPase domain of BiP/Grp78 and Hsp70-1A with greater affinity than the AR. Disruption of 70 kDa heat shock protein function may be the underlying mechanism of action for these galeterone analogs. Therefore, despite simultaneously antagonizing AR activity, AR and/or AR-V7 expression alone may inadequately predict a patient's response to treatment with VNPT-178 or VNLG-74A. Future studies evaluating the context-specific limitations of these compounds may provide clarity for their clinical application.

A Standardized Wedelia chinensis Extract Overcomes the Feedback Activation of HER2/3 Signaling upon Androgen-Ablation in Prostate Cancer

Crosstalk between the androgen receptor (AR) and other signaling pathways in prostate cancer (PCa) severely affects the therapeutic outcome of hormonal therapy. Although anti-androgen therapy prolongs overall survival in PCa patients, resistance rapidly develops and is often associated with increased AR expression and upregulation of the HER2/3-AKT signaling pathway. However, single agent therapy targeting AR, HER2/3 or AKT usually fails due to the reciprocal feedback loop. Previously, we reported that wedelolactone, apigenin, and luteolin are the active compounds in Wedelia chinensis herbal extract, and act synergistically to inhibit the AR activity in PCa. Here, we further demonstrated that an herbal extract of W. chinensis (WCE) effectively disrupted the AR, HER2/3, and AKT signaling networks and therefore enhanced the therapeutic efficacy of androgen ablation in PCa. Furthermore, WCE remained effective in suppressing AR and HER2/3 signaling in an in vivo adapted castration-resistant PCa (CRPC) LNCaP cell model that was insensitive to androgen withdrawal and second-line antiandrogen, enzalutamide. This study provides preclinical evidence that the use of a defined, single plant-derived extract can augment the therapeutic efficacy of castration with significantly prolonged progression-free survival. These data also establish a solid basis for using WCE as a candidate agent in clinical studies.

Allosteric alterations in the androgen receptor and activity in prostate cancer

Organisms have evolved to generate biological complexity in their proteome and transcriptome from a limited number of genes. This concept holds true for the androgen receptor, which displays a diversity of inclusion/exclusion events in its structural motifs as a mechanism of resistance to the most forefront anti-androgen therapies. More than 20 androgen receptor variants that lack various portions of ligand-binding domain have been identified in human prostate cancer (PCa) samples. Most of the variants are inactive on their own, with a few exceptions displaying constitutive activity. The full-length receptor and one or more variants can be co-expressed in the same cell under many circumstances, which raises the question of how these variants physically and functionally interact with the full-length receptor or one another in the course of PCa progression. To address this issue, in this review, we will characterize and discuss androgen receptor variants, including the novel variants discovered in the last couple of years (i) individually, (ii) with respect to their physical and functional interaction with one another and (iii) in clinical relevance. Here, we also introduce the very recent understanding of AR-Vs obtained through successful development of some AR-V-specific antibodies as well as identification of novel AR-Vs by data mining approaches.

Glycosylation is a global target for androgen control in prostate cancer cells

Changes in glycan composition are common in cancer and can play important roles in all of the recognised hallmarks of cancer. We recently identified glycosylation as a global target for androgen control in prostate cancer cells and further defined a set of 8 glycosylation enzymes (GALNT7, ST6GalNAc1, GCNT1, UAP1, PGM3, CSGALNACT1, ST6GAL1 and EDEM3), which are also significantly upregulated in prostate cancer tissue. These 8 enzymes are under direct control of the androgen receptor (AR) and are linked to the synthesis of important cancer-associated glycans such as sialyl-Tn (sTn), sialyl LewisX (SLeX), O-GlcNAc and chondroitin sulfate. Glycosylation has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism. Our results suggest that alterations in patterns of glycosylation via androgen control might modify some or all of these processes in prostate cancer. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Emerging data on these often overlooked glycan modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.