Structural basis for androgen receptor interdomain and coactivator interactions suggests a transition in nuclear receptor activation function dominance

Structural Changes Due to Antagonist Binding in Ligand Binding Pocket of Androgen Receptor Elucidated Through Molecular Dynamics Simulations

When a small molecule binds to the androgen receptor (AR), a conformational change can occur which impacts subsequent binding of co-regulator proteins and DNA. In order to accurately study this mechanism, the scientific community needs a crystal structure of the Wild type AR (WT-AR) ligand binding domain, bound with antagonist. To address this open need, we leveraged molecular docking and molecular dynamics (MD) simulations to construct a structure of the WT-AR ligand binding domain bound with antagonist bicalutamide. The structure of mutant AR (Mut-AR) bound with this same antagonist informed this study. After molecular docking analysis pinpointed the suitable binding orientation of a ligand in AR, the model was further optimized through 1 μs of MD simulations. Using this approach, three molecular systems were studied: (1) WT-AR bound with agonist R1881, (2) WT-AR bound with antagonist bicalutamide, and (3) Mut-AR bound with bicalutamide. Our structures were very similar to the experimentally determined structures of both WT-AR with R1881 and Mut-AR with bicalutamide, demonstrating the trustworthiness of this approach. In our model, when WT-AR is bound with bicalutamide, Val716/Lys720/Gln733, or Met734/Gln738/Glu897 move and thus disturb the positive and negative charge clumps of the AF2 site. This disruption of the AF2 site is key for understanding the impact of antagonist binding on subsequent co-regulator binding. In conclusion, the antagonist induced structural changes in WT-AR detailed in this study will enable further AR research and will facilitate AR targeting drug discovery.

Evolution of Melanoma Antigen-A11 (MAGEA11) During Primate Phylogeny

Melanoma antigen-A11 (MAGE-A11) is an X-linked and primate-specific steroid hormone receptor transcriptional coregulator and proto-oncogenic protein whose increased expression promotes the growth of prostate cancer. The MAGEA11 gene is expressed at low levels in normal human testis, ovary, and endometrium, and at highest levels in castration-resistant prostate cancer. Annotated genome predictions throughout the surviving primate lineage show that MAGEA11 acquired three 5' coding exons unique within the MAGEA subfamily during the evolution of New World monkeys (NWM), Old World monkeys (OWM), and apes. MAGE-A11 in all primates has a conserved FXXIF coactivator-binding motif that suggests interaction with p160 coactivators contributed to its early evolution as a transcriptional coregulator. An ancestral form of MAGE-A11 in the more distantly related lemur has significant amino acid sequence identity with human MAGE-A11, but lacks coregulator activity based on the absence of the three 5' coding exons that include a nuclear localization signal (NLS). NWM MAGE-A11 has greater amino acid sequence identity than lemur to human MAGE-A11, but inframe premature stop codons suggest that MAGEA11 is a pseudogene in NWM. MAGE-A11 in OWM and apes has nearly identical 5' coding exon amino acid sequence and conserved interaction sites for p300 acetyltransferase and cyclin A. We conclude that the evolution of MAGEA11 within the lineage leading to OWM and apes resulted in steroid hormone receptor transcriptional coregulator activity through the acquisition of three 5' coding exons that include a NLS sequence and nonsynonymous substitutions required to interact with cell cycle regulatory proteins and transcription factors.

Drug-Discovery Pipeline for Novel Inhibitors of the Androgen Receptor

The androgen receptor (AR) is an important regulator of genes responsible for the development and recurrence of prostate cancer. Current therapies for this disease rely on small-molecule inhibitors that block the transcriptional activity of the AR. Recently, major advances in the development of novel AR inhibitors resulted from X-ray crystallographic information on the receptor and utilization of in silico drug design synergized with rigorous experimental testing.Herein, we describe a drug-discovery pipeline for in silico screening for small molecules that target an allosteric region on the AR termed the binding-function 3 (BF3) site. Following the identification of potential candidates, the compounds are tested in cell culture and biochemical assays for their ability to interact with and inhibit the AR. The described pipeline is readily accessible and could be applied in drug design efforts toward any surface-exposed region on the AR or other related steroid nuclear receptor.

Targeting AR Variant-Coactivator Interactions to Exploit Prostate Cancer Vulnerabilities

Castration-resistant prostate cancer (CRPC) progresses rapidly and is incurable. Constitutively active androgen receptor splice variants (AR-Vs) represent a well-established mechanism of therapeutic resistance and disease progression. These variants lack the AR ligand-binding domain and, as such, are not inhibited by androgen deprivation therapy (ADT), which is the standard systemic approach for advanced prostate cancer. Signaling by AR-Vs, including the clinically relevant AR-V7, is augmented by Vav3, an established AR coactivator in CRPC. Using mutational and biochemical studies, we demonstrated that the Vav3 Diffuse B-cell lymphoma homology (DH) domain interacted with the N-terminal region of AR-V7 (and full length AR). Expression of the Vav3 DH domain disrupted Vav3 interaction with and enhancement of AR-V7 activity. The Vav3 DH domain also disrupted AR-V7 interaction with other AR coactivators: Src1 and Vav2, which are overexpressed in PC. This Vav3 domain was used in proof-of-concept studies to evaluate the effects of disrupting the interaction between AR-V7 and its coactivators on CRPC cells. This disruption decreased CRPC cell proliferation and anchorage-independent growth, caused increased apoptosis, decreased migration, and resulted in the acquisition of morphological changes associated with a less aggressive phenotype. While disrupting the interaction between FL-AR and its coactivators decreased N-C terminal interaction, disrupting the interaction of AR-V7 with its coactivators decreased AR-V7 nuclear levels.Implications: This study demonstrates the potential therapeutic utility of inhibiting constitutively active AR-V signaling by disrupting coactivator binding. Such an approach is significant, as AR-Vs are emerging as important drivers of CRPC that are particularly recalcitrant to current therapies. Mol Cancer Res; 15(11); 1469-80. ©2017 AACR.

Identification of endocrine active disinfection by-products (DBPs) that bind to the androgen receptor

The formation of disinfection by-products (DBPs) in drinking water occurs when chemical disinfectants such as chlorine and chloramine react with natural organic matter and anthropogenic pollutants. Some DBPs have been linked to bladder cancer and infertility; however, the underlying mechanism of action is unknown. One possibility is disruption of the endocrine system, with DBPs binding to the androgen receptor and subsequently altering gene expression. Using the androgen receptor-binding assay and in silico molecular docking, the binding affinity of 21 suspected and known DBPs were tested individually at concentrations over the range 0.1 nM-2 mM. 14 DBPs were found to bind at IC₅₀ values ranging from 1.86 mM for 2,3-dichloropropionamide to 13.5 μM for 3,4,5,6-tetrachloro-benzoquinone as compared to the positive control, 4-n-nonylphenol which bound at 31.6 μM. Since DBPs are present in drinking waters as mixtures, the question of how IC₅₀ values for individual DBPs might be affected by the presence of other chemicals is addressed. Seven of the chemicals with the strongest binding affinities and one chemical with no binding affinity were tested in binary mixtures with 4-n-nonylphenol, a known androgenic chemical found in some surface waters. In these binary mixtures, concentration additive binding was observed. While typical levels of individual androgenic DBPs in drinking water are below their measured IC₅₀ values, their combined binding abilities in mixtures could be a source of androgen disruption.

Positive feedback loop mediated by protein phosphatase 1α mobilization of P-TEFb and basal CDK1 drives androgen receptor in prostate cancer

P-TEFb (CDK9/cyclin T) plays a central role in androgen receptor (AR)-mediated transactivation by phosphorylating both RNA polymerase 2 complex proteins and AR at S81. CDK9 dephosphorylation mobilizes P-TEFb from an inhibitory 7SK ribonucleoprotein complex, but mechanisms targeting phosphatases to P-TEFb are unclear. We show that AR recruits protein phosphatase 1α (PP1α), resulting in P-TEFb mobilization and CDK9-mediated AR S81 phosphorylation. This increased pS81 enhances p300 recruitment, histone acetylation, BRD4 binding and subsequent further recruitment of P-TEFb, generating a positive feedback loop that sustains transcription. AR S81 is also phosphorylated by CDK1, and blocking basal CDK1-mediated S81 phosphorylation markedly suppresses AR activity and initiation of this positive feedback loop. Finally, androgen-independent AR activity in castration-resistant prostate cancer (CRPC) cells is driven by increased CDK1-mediated S81 phosphorylation. Collectively these findings reveal a mechanism involving PP1α, CDK9 and CDK1 that is used by AR to initiate and sustain P-TEFb activity, which may be exploited to drive AR in CRPC.

Modulation of nongenomic activation of PI3K signalling by tetramerization of N-terminally-cleaved RXRα

Retinoid X receptor-alpha (RXRα) binds to DNA either as homodimers or heterodimers, but it also forms homotetramers whose function is poorly defined. We previously discovered that an N-terminally-cleaved form of RXRα (tRXRα), produced in tumour cells, activates phosphoinositide 3-kinase (PI3K) signalling by binding to the p85α subunit of PI3K and that K-80003, an anti-cancer agent, inhibits this process. Here, we report through crystallographic and biochemical studies that K-80003 binds to and stabilizes tRXRα tetramers via a ‘three-pronged’ combination of canonical and non-canonical mechanisms. K-80003 binding has no effect on tetramerization of RXRα, owing to the head–tail interaction that is absent in tRXRα. We also identify an LxxLL motif in p85α, which binds to the coactivator-binding groove on tRXRα and dissociates from tRXRα upon tRXRα tetramerization. These results identify conformational selection as the mechanism for inhibiting the nongenomic action of tRXRα and provide molecular insights into the development of RXRα cancer therapeutics.

The transcription factor retinoid X receptor-alpha (RXRα) can also form homotetramers. Here the authors show that the anti-cancer agent K-80003 selectively inhibits the nongenomic action of N-terminally-cleaved RXRα in tumour cells by stabilizing its tetramerization but not that of full-length RXRα.

An Amyloidogenic Sequence at the N-Terminus of the Androgen Receptor Impacts Polyglutamine Aggregation

The human androgen receptor (AR) is a ligand inducible transcription factor that harbors an amino terminal domain (AR-NTD) with a ligand-independent activation function. AR-NTD is intrinsically disordered and displays aggregation properties conferred by the presence of a poly-glutamine (polyQ) sequence. The length of the polyQ sequence as well as its adjacent sequence motifs modulate this aggregation property. AR-NTD also contains a conserved KELCKAVSVSM sequence motif that displays an intrinsic property to form amyloid fibrils under mild oxidative conditions. As peptide sequences with intrinsic oligomerization properties are reported to have an impact on the aggregation of polyQ tracts, we determined the effect of the KELCKAVSVSM on the polyQ stretch in the context of the AR-NTD using atomic force microscopy (AFM). Here, we present evidence for a crosstalk between the amyloidogenic properties of the KELCKAVSVSM motif and the polyQ stretch at the AR-NTD.

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

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

Unfoldomics of prostate cancer: on the abundance and roles of intrinsically disordered proteins in prostate cancer

Prostatic diseases such as prostate cancer and benign prostatic hyperplasia are highly prevalent among men. The number of studies focused on the abundance and roles of intrinsically disordered proteins in prostate cancer is rather limited. The goal of this study is to analyze the prevalence and degree of disorder in proteins that were previously associated with the prostate cancer pathogenesis and to compare these proteins to the entire human proteome. The analysis of these datasets provides means for drawing conclusions on the roles of disordered proteins in this common male disease. We also hope that the results of our analysis can potentially lead to future experimental studies of these proteins to find novel pathways associated with this disease.

Androgen receptor regulation by histone methyltransferase Suppressor of variegation 3-9 homolog 2 and Melanoma antigen-A11

Androgen receptor (AR) transcriptional activity depends on interactions between the AR NH₂-terminal region and transcriptional coregulators. A yeast two-hybrid screen of a human testis library using predicted α-helical NH₂-terminal fragment AR-(370-420) as bait identified suppressor of variegation 3-9 homolog 2 (SUV39H2) histone methyltransferase as an AR interacting protein. SUV39H2 interaction with AR and the AR coregulator, melanoma antigen-A11 (MAGE-A11), was verified in two-hybrid, in vitro glutathione S-transferase affinity matrix and coimmunoprecipitation assays. Fluorescent immunocytochemistry colocalized SUV39H2 and AR in the cytoplasm without androgen, in the nucleus with androgen, and with MAGE-A11 in the nucleus independent of androgen. Chromatin immunoprecipitation using antibodies raised against SUV39H2 demonstrated androgen-dependent recruitment of AR and SUV39H2 to the androgen-responsive upstream enhancer of the prostate-specific antigen gene. SUV39H2 functioned cooperatively with MAGE-A11 to increase androgen-dependent AR transcriptional activity. SUV39H2 histone methyltransferase is an AR coactivator that increases androgen-dependent transcriptional activity through interactions with AR and MAGE-A11.

Androgen dependent mechanisms of pro-angiogenic networks in placental and tumor development

The placenta and tumors share important characteristics, including a requirement to establish effective angiogenesis. In the case of the placenta, optimal angiogenesis is required to sustain the blood flow required to maintain a successful pregnancy, whereas in tumors establishing new blood supplies is considered a key step in supporting metastases. Therefore the development of novel angiogenesis inhibitors has been an area of active research in oncology. A subset of the molecular processes regulating angiogenesis are well understood in the context of both early placentation and tumorigenesis. In this review we focus on the well-established role of androgen regulation of angiogenesis in cancer and relate these mechanisms to placental angiogenesis. The physiological actions of androgens are mediated by the androgen receptor (AR), a ligand dependent transcription factor. Androgens and the AR are essential for normal male embryonic development, puberty and lifelong health. Defects in androgen signalling are associated with a diverse range of clinical disorders in men and women including disorders of sex development (DSD), polycystic ovary syndrome in women and many cancers. We summarize the diverse molecular mechanisms of androgen regulation of angiogenesis and infer the potential significance of these pathways to normal and pathogenic placental function. Finally, we offer potential research applications of androgen-targeting molecules developed to treat cancer as investigative tools to help further delineate the role of androgen signalling in placental function and maternal and offspring health in animal models.

Epigenomic Regulation of Androgen Receptor Signaling: Potential Role in Prostate Cancer Therapy

Androgen receptor (AR) signaling remains the major oncogenic pathway in prostate cancer (PCa). Androgen-deprivation therapy (ADT) is the principle treatment for locally advanced and metastatic disease. However, a significant number of patients acquire treatment resistance leading to castration resistant prostate cancer (CRPC). Epigenetics, the study of heritable and reversible changes in gene expression without alterations in DNA sequences, is a crucial regulatory step in AR signaling. We and others, recently described the technological advance Chem-seq, a method to identify the interaction between a drug and the genome. This has permitted better understanding of the underlying regulatory mechanisms of AR during carcinogenesis and revealed the importance of epigenetic modifiers. In screening for new epigenomic modifiying drugs, we identified SD-70, and found that this demethylase inhibitor is effective in CRPC cells in combination with current therapies. The aim of this review is to explore the role of epigenetic modifications as biomarkers for detection, prognosis, and risk evaluation of PCa. Furthermore, we also provide an update of the recent findings on the epigenetic key processes (DNA methylation, chromatin modifications and alterations in noncoding RNA profiles) involved in AR expression and their possible role as therapeutic targets.

Antagonizing the Androgen Receptor with a Biomimetic Acyltransferase

The Androgen Receptor (AR) remains the leading target of advanced prostate cancer therapies. Thiosalicylamide analogs have previously been shown to act in cells as acyltransfer catalysts that are capable of transferring cellular acetate, presumably from acetyl-CoA, to HIV NCp7. Here we explore if the cellular acetyl-transfer activity of thiosalicylamides can be redirected to other cellular targets guided by ligands for AR. We constructed conjugates of thiosalicylamides and the AR-binding small molecule tolfenamic acid, which binds the BF-3 site of AR, proximal to the coactivator "FXXLF" binding surface. The thiosalicylamide-tolfenamic acid conjugate, YZ03, but not the separate thiosalicylamide plus tolfenamic acid, significantly enhanced acetylation of endogenous AR in CWR22Rv1 cells. Further analysis confirms that Lys720, a residue critical to FXXLF coactivator peptide binding, is a site of acyl-YZ03 acetylation. Under acyl-transfer conditions, YZ03 significantly enhances the ability of BF-3 site binding ligands to inhibit AR-coactivator peptide association. These data suggest that biomimetic acyltransferases can enhance protein-protein interaction inhibitors through covalent modification of critical interfacial residues.

UGT2B17 Expedites Progression of Castration-Resistant Prostate Cancers by Promoting Ligand-Independent AR Signaling

Castration-resistant prostate cancer (CRPC) is characterized by a shift in androgen receptor (AR) signaling from androgen-dependent to androgen (ligand)-independent. UDP-glucuronosyltransferase 2B17 (UGT2B17) is a key enzyme that maintains androgen homeostasis by catabolizing AR agonists into inactive forms. Although enhanced UGT2B17 expression by antiandrogens has been reported in androgen-dependent prostate cancer, its roles in regulating AR signaling transformation and CRPC progression remain unknown. In this study, we show that higher UGT2B17 protein expression in prostate tumors is associated with higher Gleason score, metastasis, and CRPC progression. UGT2B17 expression and activity were higher in androgen-independent compared to androgen-dependent cell lines. UGT2B17 stimulated cancer cell proliferation, invasion, and xenograft progression to CRPC after prolonged androgen deprivation. Gene microarray analysis indicated that UGT2B17 suppressed androgen-dependent AR transcriptional activity and enhanced of ligand-independent transcriptional activity at genes associated with cell mitosis. These UGT2B17 actions were mainly mediated by activation of the c-Src kinase. In CRPC tumors, UGT2B17 expression was associated positively with c-Src activation. These results indicate that UGT2B17 expedites CRPC progression by enhancing ligand-independent AR signaling to activate cell mitosis in cancer cells. Cancer Res; 76(22); 6701-11. ©2016 AACR.

Multivalent Peptoid Conjugates Which Overcome Enzalutamide Resistance in Prostate Cancer Cells

Development of resistance to antiandrogens for treating advanced prostate cancer is a growing concern and extends to recently developed therapeutics, including enzalutamide. Therefore, new strategies to block androgen receptor (AR) function in prostate cancer are required. Here, we report the characterization of a multivalent conjugate presenting two bioactive ethisterone ligands arrayed as spatially defined pendant groups on a peptoid oligomer. The conjugate, named Multivalent Peptoid Conjugate 6 (MPC6), suppressed the proliferation of multiple AR-expressing prostate cancer cell lines including those that failed to respond to enzalutamide and ARN509. The structure-activity relationships of MPC6 variants were evaluated, revealing that increased spacing between ethisterone moieties and changes in peptoid topology eliminated its antiproliferative effect, suggesting that both ethisterone ligand presentation and scaffold characteristics contribute to MPC6 activity. Mechanistically, MPC6 blocked AR coactivator-peptide interaction and prevented AR intermolecular interactions. Protease sensitivity assays suggested that the MPC6-bound AR induced a receptor conformation distinct from that of dihydrotestosterone- or enzalutamide-bound AR. Pharmacologic studies revealed that MPC6 was metabolically stable and displayed a low plasma clearance rate. Notably, MPC6 treatment reduced tumor growth and decreased Ki67 and AR expression in mouse xenograft models of enzalutamide-resistant LNCaP-abl cells. Thus, MPC6 represents a new class of compounds with the potential to combat treatment-resistant prostate cancer. Cancer Res; 76(17); 5124-32. ©2016 AACR.

Recent progress in the development of protein-protein interaction inhibitors targeting androgen receptor-coactivator binding in prostate cancer

The androgen receptor (AR) is a key regulator for the growth, differentiation and survival of prostate cancer cells. Identified as a primary target for the treatment of prostate cancer, many therapeutic strategies have been developed to attenuate AR signaling in prostate cancer cells. While frontline androgen-deprivation therapies targeting either the production or action of androgens usually yield favorable responses in prostate cancer patients, a significant number acquire treatment resistance. Known as the castration-resistant prostate cancer (CRPC), the treatment options are limited for this advanced stage. It has been shown that AR signaling is restored in CRPC due to many aberrant mechanisms such as AR mutations, amplification or expression of constitutively active splice-variants. Coregulator recruitment is a crucial regulatory step in AR signaling and the direct blockade of coactivator binding to AR offers the opportunity to develop therapeutic agents that would remain effective in prostate cancer cells resistant to conventional endocrine therapies. Structural analyses of the AR have identified key surfaces involved in protein-protein interaction with coregulators that have been recently used to design and develop promising AR-coactivator binding inhibitors. In this review we will discuss the design and development of small-molecule inhibitors targeting the AR-coactivator interactions for the treatment of prostate cancer.

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

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

Synthesis and biological activity of two pregnane derivatives with a triazole or imidazole ring at C-21

Pregnane derivatives are studied as agents for the treatment of different hormone-dependent diseases. The biological importance of these steroids is based on their potential use against cancer. In this study, we report the synthesis, characterization and biological activity of two pregnane derivatives with a triazole (3β-hydroxy-21-(1H-1,2,4-triazol-1-yl)pregna-5,16-dien-20-one; T-OH) or imidazole (3β-hydroxy-21-(1H-imidazol-1-yl)pregna-5,16-dien-20-one; I-OH) moieties at C-21. These derivatives were synthesized from 16-dehydropregnenolone acetate. The activity on cell proliferation of the compounds was measured on three human cancer cells lines: prostate cancer (PC-3), breast cancer (MCF7) and lung cancer (SK-LU-1). The cytotoxic and antiproliferative effects of T-OH and I-OH were assessed by using SBR and XTT methods, respectively. The gene expressions were evaluated by real time PCR. In addition, results were complemented by docking studies and transactivation assays using an expression vector to progesterone and androgen receptor. Results show that the two compounds inhibited the three cell lines proliferation in a dose-dependent manner. Compound I-OH downregulated the gene expression of the cyclins D1 and E1 in PC-3 and MFC7 cells; however, effect upon Ki-67, EAG1, BIM or survivin genes was not observed. Docking studies show poor interaction with the steroid receptors. Nevertheless, the transactivation assays show a weak antagonist effect of I-OH on progesterone receptor but not androgenic or antiandrogenic actions. In conclusion, the synthesized compounds inhibited cell proliferation as well as genes key to cell cycle of PC-3 and MCF7 cell lines. Therefore, these compounds could be considered a good starting point for the development of novel therapeutic alternatives to treat cancer.

Functional analysis of androgen receptor mutations that confer anti-androgen resistance identified in circulating cell-free DNA from prostate cancer patients

BACKGROUND

The androgen receptor (AR) is a pivotal drug target for the treatment of prostate cancer, including its lethal castration-resistant (CRPC) form. All current non-steroidal AR antagonists, such as hydroxyflutamide, bicalutamide, and enzalutamide, target the androgen binding site of the receptor, competing with endogenous androgenic steroids. Several AR mutations in this binding site have been associated with poor prognosis and resistance to conventional prostate cancer drugs. In order to develop an effective CRPC therapy, it is crucial to understand the effects of these mutations on the functionality of the AR and its ability to interact with endogenous steroids and conventional AR inhibitors.

RESULTS

We previously utilized circulating cell-free DNA (cfDNA) sequencing technology to examine the AR gene for the presence of mutations in CRPC patients. By modifying our sequencing and data analysis approaches, we identify four additional single AR mutations and five mutation combinations associated with CRPC. Importantly, we conduct experimental functionalization of all the AR mutations identified by the current and previous cfDNA sequencing to reveal novel gain-of-function scenarios. Finally, we evaluate the effect of a novel class of AR inhibitors targeting the binding function 3 (BF3) site on the activity of CRPC-associated AR mutants.

CONCLUSIONS

This work demonstrates the feasibility of a prognostic and/or diagnostic platform combining the direct identification of AR mutants from patients' serum, and the functional characterization of these mutants in order to provide personalized recommendations regarding the best future therapy.

Preventing the Androgen Receptor N/C Interaction Delays Disease Onset in a Mouse Model of SBMA

Spinal and bulbar muscular atrophy (SBMA) is a neurodegenerative disease caused by a polyglutamine expansion in the androgen receptor (AR) and is associated with misfolding and aggregation of the mutant AR. We investigated the role of an interdomain interaction between the amino (N)-terminal FxxLF motif and carboxyl (C)-terminal AF-2 domain in a mouse model of SBMA. Male transgenic mice expressing polyQ-expanded AR with a mutation in the FxxLF motif (F23A) to prevent the N/C interaction displayed substantially improved motor function compared with N/C-intact AR-expressing mice and showed reduced pathological features of SBMA. Serine 16 phosphorylation was substantially enhanced by the F23A mutation; moreover, the protective effect of AR F23A was dependent on this phosphorylation. These results reveal an important role for the N/C interaction on disease onset in mice and suggest that targeting AR conformation could be a therapeutic strategy for patients with SBMA.

Ultrafast protein structure-based virtual screening with Panther

Molecular docking is by far the most common method used in protein structure-based virtual screening. This paper presents Panther, a novel ultrafast multipurpose docking tool. In Panther, a simple shape-electrostatic model of the ligand-binding area of the protein is created by utilizing the protein crystal structure. The features of the possible ligands are then compared to the model by using a similarity search algorithm. On average, one ligand can be processed in a few minutes by using classical docking methods, whereas using Panther processing takes <1 s. The presented Panther protocol can be used in several applications, such as speeding up the early phases of drug discovery projects, reducing the number of failures in the clinical phase of the drug development process, and estimating the environmental toxicity of chemicals. Panther-code is available in our web pages (http://www.jyu.fi/panther) free of charge after registration.

Splicing Factor Prp8 Interacts With NES(AR) and Regulates Androgen Receptor in Prostate Cancer Cells

Androgen receptor (AR) plays a pivotal role in the development of primary as well as advanced castration-resistant prostate cancer. Previous work in our lab identified a novel nuclear export signal (NES) (NES(AR)) in AR ligand-binding domain essential for AR nucleocytoplasmic trafficking. By characterizing the localization of green fluorescence protein (GFP)-tagged NES(AR), we designed and executed a yeast mutagenesis screen and isolated 7 yeast mutants that failed to display the NES(AR) export function. One of those mutants was identified as the splicing factor pre-mRNA processing factor 8 (Prp8). We further showed that Prp8 could regulate NES(AR) function using short hairpin RNA knockdown of Prp8 coupled with a rapamycin export assay in mammalian cells and knockdown of Prp8 could induce nuclear accumulation of GFP-tagged AR in PC3 cells. Prp8 expression was decreased in castration-resistant LuCaP35 xenograft tumors as compared with androgen-sensitive xenografts. Laser capture microdissection and quantitative PCR showed Prp8 mRNA levels were decreased in human prostate cancer specimens with high Gleason scores. In prostate cancer cells, coimmunoprecipitation and deletion mutagenesis revealed a physical interaction between Prp8 and AR mainly mediated by NES(AR). Luciferase assay with prostate specific antigen promoter-driven reporter demonstrated that Prp8 regulated AR transcription activity in prostate cancer cells. Interestingly, Prp8 knockdown also increased polyubiquitination of endogenous AR. This may be 1 possible mechanism by which it modulates AR activity. These results show that Prp8 is a novel AR cofactor that interacts with NES(AR) and regulates AR function in prostate cancer cells.

Nemo-like kinase is a novel regulator of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a progressive neuromuscular disease caused by polyglutamine expansion in the androgen receptor (AR) protein. Despite extensive research, the exact pathogenic mechanisms underlying SBMA remain elusive. In this study, we present evidence that Nemo-like kinase (NLK) promotes disease pathogenesis across multiple SBMA model systems. Most remarkably, loss of one copy of Nlk rescues SBMA phenotypes in mice, including extending lifespan. We also investigated the molecular mechanisms by which NLK exerts its effects in SBMA. Specifically, we have found that NLK can phosphorylate the mutant polyglutamine-expanded AR, enhance its aggregation, and promote AR-dependent gene transcription by regulating AR-cofactor interactions. Furthermore, NLK modulates the toxicity of a mutant AR fragment via a mechanism that is independent of AR-mediated gene transcription. Our findings uncover a crucial role for NLK in controlling SBMA toxicity and reveal a novel avenue for therapy development in SBMA.

DOI:http://dx.doi.org/10.7554/eLife.08493.001

Spinal and bulbar muscular atrophy (SBMA) is an inherited disease that eventually leads to degeneration in motor neurons and weakness in muscles. It is caused by a specific genetic mutation in the gene that encodes the androgen receptor protein, which leads to the production of a mutant protein that is larger than normal. Similar mutations in other genes can lead to the development of other so-called ‘polyglutamine’ diseases such as Huntington's disease and spinocerebellar ataxia. However, the precise details of how these mutations lead to disease symptoms are not known, and there are currently no effective ways of treating these conditions.

Previous research has shown that an enzyme called Nemo-like kinase (or NLK for short) regulates the normal androgen receptor in cancer cells. NLK has kinase activity, that is, it adds phosphate molecules to other proteins to regulate their activity. Todd et al. used human cells, fruit flies, and mice as model systems to investigate whether NLK is involved in the development of SBMA.

The experiments show that NLK promotes the development of features associated with SBMA in all three models. The kinase activity of NLK is required for these features to develop. Todd et al. also found that NLK can bind to and add phosphate molecules to the mutant version of the androgen receptor protein. This causes the mutant androgen receptor proteins to accumulate and increases the ability of the mutant proteins to activate particular genes.

Todd et al.'s findings suggest that NLK promotes the development of SBMA by interacting with the mutant androgen receptor. Previous studies have shown that NLK is able to modulate the development of spinocerebellar ataxia type 1, which suggests that NLK may also play an important role in other polyglutamine diseases. The next challenge will be to fully understand the role of NLK in these diseases, which may aid future efforts to develop new treatments.

DOI:http://dx.doi.org/10.7554/eLife.08493.002

Identification of a Novel Coregulator, SH3YL1, That Interacts With the Androgen Receptor N-Terminus

Nuclear receptor (NR)-mediated transcriptional activity is a dynamic process that is regulated by the binding of ligands that induce distinct conformational changes in the NR. These structural alterations lead to the differential recruitment of coregulators (coactivators or corepressors) that control the expression of NR-regulated genes. Here, we show that a stretch of proline residues located within the N-terminus of androgen receptor (AR) is a bona fide coregulator binding surface, the disruption of which reduces the androgen-dependent proliferation and migration of prostate cancer (PCa) cells. Using T7 phage display, we identified a novel AR-interacting protein, Src homology 3 (SH3)-domain containing, Ysc84-like 1 (SH3YL1), whose interaction with the receptor is dependent upon this polyproline domain. As with mutations within the AR polyproline domain, knockdown of SH3YL1 attenuated androgen-mediated cell growth and migration. RNA expression analysis revealed that SH3YL1 was required for the induction of a subset of AR-modulated genes. Notable was the observation that ubinuclein 1 (UBN1), a key member of a histone H3.3 chaperone complex, was a transcriptional target of the AR/SH3YL1 complex, correlated with aggressive PCa in patients, and was necessary for the maximal androgen-mediated proliferation and migration of PCa cells. Collectively, these data highlight the importance of an amino-terminal activation domain, its associated coregulator, and downstream transcriptional targets in regulating cellular processes of pathological importance in PCa.

Dichotomy in the Epigenetic Mark Lysine Acetylation is Critical for the Proliferation of Prostate Cancer Cells

The dynamics of lysine acetylation serve as a major epigenetic mark, which regulates cellular response to inflammation, DNA damage and hormonal changes. Microarray assays reveal changes in gene expression, but cannot predict regulation of a protein function by epigenetic modifications. The present study employs computational tools to inclusively analyze microarray data to understand the potential role of acetylation during development of androgen-independent PCa. The data revealed that the androgen receptor interacts with 333 proteins, out of which at least 92 proteins were acetylated. Notably, the number of cellular proteins undergoing acetylation in the androgen-dependent PCa was more as compared to the androgen-independent PCa. Specifically, the 32 lysine-acetylated proteins in the cellular models of androgen-dependent PCa were mainly involved in regulating stability as well as pre- and post-processing of mRNA. Collectively, the data demonstrate that protein lysine acetylation plays a crucial role during the transition of androgen-dependent to -independent PCa, which importantly, could also serve as a functional axis to unravel new therapeutic targets.

Androgen insensitivity syndrome

Androgen insensitivity syndrome (AIS) results from androgen receptor dysfunction and is a common cause of disorder of sex development. The AIS phenotype largely depends on the degree of residual androgen receptor (AR) activity. This review describes the molecular action of androgens and the range of androgen receptor gene mutations, essential knowledge to understand the pathogenesis of the complete and partial forms of this syndrome. A multidisciplinary approach is recommended for clinical management from infancy through to adulthood. Hormone replacement therapy is needed following gonadectomy. Patients who choose to retain the gonads are at risk of developing germ cell tumors for which sensitive circulating tumor markers may soon become available. Whilst the contribution of AR dysfunction to complete AIS is well understood, the involvement of the AR and associated proteins as contributors to partial AIS is an area of active research. Disorders of sex development such as AIS which are related to AR dysfunction offer a breadth of manifestations for the clinician to manage and opportunities for further research on the mechanism of androgen action.

Identification and Characterization of the Androgen Receptor From the American Alligator, Alligator mississippiensis

Androgens are essential for the development, reproduction, and health throughout the life span of vertebrates, particularly during the initiation and maintenance of male sexual characteristics. Androgen signaling is mediated by the androgen receptor (AR), a member of the steroid nuclear receptor superfamily. Mounting evidence suggests that environmental factors, such as exogenous hormones or contaminants that mimic hormones, can disrupt endocrine signaling and function. The American alligator (Alligator mississippiensis), a unique model for ecological research in that it exhibits environment-dependent sex determination, is oviparous and long lived. Alligators from a contaminated environment exhibit low reproductive success and morphological disorders of the testis and phallus in neonates and juveniles, both associated with androgen signaling; thus, the alterations are hypothesized to be related to disrupted androgen signaling. However, this line of research has been limited because of a lack of information on the alligator AR gene. Here, we isolated A mississippiensis AR homologs (AmAR) and evaluated receptor-hormone/chemical interactions using a transactivation assay. We showed that AmAR responded to all natural androgens and their effects were inhibited by cotreatment with antiandrogens, such as flutamide, p,p'-dichlorodiphenyldichloroethylene, and vinclozolin. Intriguingly, we found a spliced form of the AR from alligator cDNA, which lacks seven amino acids within the ligand-binding domain that shows no response to androgens. Finally, we have initial data on a possible dominant-negative function of the spliced form of the AR against androgen-induced AmAR.

Endostatin: A novel inhibitor of androgen receptor function in prostate cancer

Acquired resistance to androgen receptor (AR)-targeted therapies compels the development of novel treatment strategies for castration-resistant prostate cancer (CRPC). Here, we report a profound effect of endostatin on prostate cancer cells by efficient intracellular trafficking, direct interaction with AR, reduction of nuclear AR level, and down-regulation of AR-target gene transcription. Structural modeling followed by functional analyses further revealed that phenylalanine-rich α1-helix in endostatin-which shares structural similarity with noncanonical nuclear receptor box in AR-antagonizes AR transcriptional activity by occupying the activation function (AF)-2 binding interface for coactivators and N-terminal AR AF-1. Together, our data suggest that endostatin can be recognized as an endogenous AR inhibitor that impairs receptor function through protein-protein interaction. These findings provide new insights into endostatin whose antitumor effect is not limited to inhibiting angiogenesis, but can be translated to suppressing AR-mediated disease progression in CRPC.

Androgen receptor: structure, role in prostate cancer and drug discovery

Androgens and androgen receptors (AR) play a pivotal role in expression of the male phenotype. Several diseases, such as androgen insensitivity syndrome (AIS) and prostate cancer, are associated with alterations in AR functions. Indeed, androgen blockade by drugs that prevent the production of androgens and/or block the action of the AR inhibits prostate cancer growth. However, resistance to these drugs often occurs after 2–3 years as the patients develop castration-resistant prostate cancer (CRPC). In CRPC, a functional AR remains a key regulator. Early studies focused on the functional domains of the AR and its crucial role in the pathology. The elucidation of the structures of the AR DNA binding domain (DBD) and ligand binding domain (LBD) provides a new framework for understanding the functions of this receptor and leads to the development of rational drug design for the treatment of prostate cancer. An overview of androgen receptor structure and activity, its actions in prostate cancer, and how structural information and high-throughput screening have been or can be used for drug discovery are provided herein.

Molecular determinants of the recognition of ulipristal acetate by oxo-steroid receptors

The human progesterone receptor (PR) plays a key role in reproductive function in women. PR antagonists have numerous applications in female health care including regular and emergency contraception, and treatment of hormone-related pathological conditions such as breast cancer, endometriosis, and leiomyoma. The main factor limiting their long-term administration is the fact that they cross-bind to other oxo-steroid receptors. Ulipristal acetate (UPA), a highly potent PR antagonist, has recently come onto the market and is much more selective for PR than the other oxo-steroid receptors (androgen, AR, glucocorticoid, GR, and mineralocorticoid, MR receptors) and, remarkably, it displays lower GR-inactivating potency than RU486. We adopted a structural approach to characterizing the binding of UPA to the oxo-steroid receptors at the molecular level. We solved the X-ray crystal structure of the ligand-binding domain (LBD) of the human PR complexed with UPA and a peptide from the transcriptional corepressor SMRT. We used the X-ray crystal structure of the GR in its antagonist conformation to dock UPA within its ligand-binding cavity. Finally, we generated three-dimensional models of the LBD of androgen and mineralocorticoid receptors (AR and MR) in an antagonist conformation and docked UPA within them. Comparing the structures revealed that the network of stabilizing contacts between the UPA C11 aryl group and the LBD is responsible for its high PR antagonist potency. It also showed that it is the inability of UPA to contact Gln642 in GR that explains why it has lower potency in inactivating GR than RU486. Finally, we found that the binding pockets of AR and MR are too small to accommodate UPA, and allowed us to propose that the extremely low sensitivity of MR to UPA is due to inappropriate interactions with the C11 substituent. All these findings open new avenues for designing new PR antagonist compounds displaying greater selectivity.

A comparative study of the androgenic properties of progesterone and the progestins, medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-A)

The importance of investigating the molecular mechanism of action of medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-A), two clinically important progestins used in hormone therapy (HT), has been highlighted by clinical evidence showing that MPA and norethisterone (NET) increase the risk of the development of breast cancer in HRT users, and that MPA may increase susceptibility to- and transmission of HIV-1. The aim of this study was to compare the molecular mechanisms of action of MPA, NET-A and progesterone (Prog) via the androgen receptor (AR) in a cell line model that can minimize confounding factors such as the presence of other steroid receptors. This study is the first to determine accurate apparent Ki values for Prog, MPA and NET-A toward the human AR in COS-1 cells. The results reveal that these ligands have a similar binding affinity for the AR to that of the natural androgen 5α-dihydrotestosterone (DHT) (Ki's for DHT, Prog, MPA and NET-A are 29.4, 36.6, 19.4 and 21.9 nM, respectively). Moreover, in both transactivation and transrepression transcriptional assays we demonstrate that, unlike Prog, MPA and NET-A are efficacious AR agonists, with activities comparable to DHT. One of the most novel findings of our study is that NET-A, like DHT, induces the ligand-dependent interaction between the NH2- and COOH-terminal domains (N/C-interaction) of the AR independent of promoter-context, while MPA does not induce the N/C interaction on a classical ARE and does so only weakly on an AR-selective ARE. This suggests that MPA and NET-A may exert differential promoter-specific actions via the AR in vivo. Consistent with this, molecular modeling suggests that MPA and NET-A induce subtle differences in the structure of the AR ligand binding domain. Taken together, the results from this study suggest that unlike Prog, both MPA and NET-A used in hormonal therapy are likely to compete with DHT and exert significant and promoter-specific off-target transcriptional effects via the AR, possibly contributing to some of the observed side-effects with the clinical use of MPA and NET-A.

Selectively targeting the DNA-binding domain of the androgen receptor as a prospective therapy for prostate cancer

The androgen receptor (AR) is a transcription factor that has a pivotal role in the occurrence and progression of prostate cancer. The AR is activated by androgens that bind to its ligand-binding domain (LBD), causing the transcription factor to enter the nucleus and interact with genes via its conserved DNA-binding domain (DBD). Treatment for prostate cancer involves reducing androgen production or using anti-androgen drugs to block the interaction of hormones with the AR-LBD. Eventually the disease changes into a castration-resistant form of PCa where LBD mutations render anti-androgens ineffective or where constitutively active AR splice variants, lacking the LBD, become overexpressed. Recently, we identified a surfaced exposed pocket on the AR-DBD as an alternative drug-target site for AR inhibition. Here, we demonstrate that small molecules designed to selectively bind the pocket effectively block transcriptional activity of full-length and splice variant AR forms at low to sub-micromolar concentrations. The inhibition is lost when residues involved in drug interactions are mutated. Furthermore, the compounds did not impede nuclear localization of the AR and blocked interactions with chromatin, indicating the interference of DNA binding with the nuclear form of the transcription factor. Finally, we demonstrate the inhibition of gene expression and tumor volume in mouse xenografts. Our results indicate that the AR-DBD has a surface site that can be targeted to inhibit all forms of the AR, including enzalutamide-resistant and constitutively active splice variants and thus may serve as a potential avenue for the treatment of recurrent and metastatic prostate cancer.

Androgen receptor functions in castration-resistant prostate cancer and mechanisms of resistance to new agents targeting the androgen axis

The metabolic functions of androgen receptor (AR) in normal prostate are circumvented in prostate cancer (PCa) to drive tumor growth, and the AR also can acquire new growth-promoting functions during PCa development and progression through genetic and epigenetic mechanisms. Androgen deprivation therapy (ADT, surgical or medical castration) is the standard treatment for metastatic PCa, but patients invariably relapse despite castrate androgen levels (castration-resistant PCa, CRPC). Early studies from many groups had shown that AR was highly expressed and transcriptionally active in CRPC, and indicated that steroids from the adrenal glands were contributing to this AR activity. More recent studies showed that CRPC cells had increased expression of enzymes mediating androgen synthesis from adrenal steroids, and could synthesize androgens de novo from cholesterol. Phase III clinical trials showing a survival advantage in CRPC for treatment with abiraterone (inhibitor of the enzyme CYP17A1 required for androgen synthesis that markedly reduces androgens and precursor steroids) and for enzalutamide (new AR antagonist) have now confirmed that AR activity driven by residual androgens makes a major contribution to CRPC, and led to the recent Food and Drug Administration approval of both agents. Unfortunately, patients treated with these agents for advanced CRPC generally relapse within a year and AR appears to be active in the relapsed tumors, but the molecular mechanisms mediating intrinsic or acquired resistance to these AR-targeted therapies remain to be defined. This review outlines AR functions that contribute to PCa development and progression, the roles of intratumoral androgen synthesis and AR structural alterations in driving AR activity in CRPC, mechanisms of action for abiraterone and enzalutamide, and possible mechanisms of resistance to these agents.

Molecular and structural basis of androgen receptor responses to dihydrotestosterone, medroxyprogesterone acetate and Δ(4)-tibolone

Medroxyprogesterone acetate (MPA) has widely been used in hormone replacement therapy (HRT), and is associated with an increased risk of breast cancer, possibly due to disruption of androgen receptor (AR) signaling. In contrast, the synthetic HRT Tibolone does not increase breast density, and is rapidly metabolized to estrogenic 3α-OH-tibolone and 3β-OH-tibolone, and a delta-4 isomer (Δ(4)-TIB) that has both androgenic and progestagenic properties. Here, we show that 5α-dihydrotestosterone (DHT) and Δ(4)-TIB, but not MPA, stabilize AR protein levels, initiate specific AR intramolecular interactions critical for AR transcriptional regulation, and increase proliferation of AR positive MDA-MB-453 breast cancer cells. Structural modeling and molecular dynamic simulation indicate that Δ(4)-TIB induces a more stable AR structure than does DHT, and MPA a less stable one. Microarray expression analyses confirms that the molecular actions of Δ(4)-TIB more closely resembles DHT in breast cancer cells than either ligand does to MPA.

Coregulator control of androgen receptor action by a novel nuclear receptor-binding motif

The androgen receptor (AR) is a ligand-activated transcription factor that is essential for prostate cancer development. It is activated by androgens through its ligand-binding domain (LBD), which consists predominantly of 11 α-helices. Upon ligand binding, the last helix is reorganized to an agonist conformation termed activator function-2 (AF-2) for coactivator binding. Several coactivators bind to the AF-2 pocket through conserved LXXLL or FXXLF sequences to enhance the activity of the receptor. Recently, a small compound-binding surface adjacent to AF-2 has been identified as an allosteric modulator of the AF-2 activity and is termed binding function-3 (BF-3). However, the role of BF-3 in vivo is currently unknown, and little is understood about what proteins can bind to it. Here we demonstrate that a duplicated GARRPR motif at the N terminus of the cochaperone Bag-1L functions through the BF-3 pocket. These findings are supported by the fact that a selective BF-3 inhibitor or mutations within the BF-3 pocket abolish the interaction between the GARRPR motif(s) and the BF-3. Conversely, amino acid exchanges in the two GARRPR motifs of Bag-1L can impair the interaction between Bag-1L and AR without altering the ability of Bag-1L to bind to chromatin. Furthermore, the mutant Bag-1L increases androgen-dependent activation of a subset of AR targets in a genome-wide transcriptome analysis, demonstrating a repressive function of the GARRPR/BF-3 interaction. We have therefore identified GARRPR as a novel BF-3 regulatory sequence important for fine-tuning the activity of the AR.

Androgen receptor gene rearrangements: new perspectives on prostate cancer progression

The androgen receptor (AR) is a master regulator transcription factor in normal and cancerous prostate cells. Canonical AR activation requires binding of androgen ligand to the AR ligand binding domain, translocation to the nucleus, and transcriptional activation of AR target genes. This regulatory axis is targeted for systemic therapy of advanced prostate cancer. However, a new paradigm for AR activation in castration-resistant prostate cancer (CRPC) has emerged wherein alternative splicing of AR mRNA promotes synthesis of constitutively active AR variants that lack the AR ligand binding domain (LBD). Recent work has indicated that structural alteration of the AR gene locus represents a key mechanism by which alterations in AR mRNA splicing arise. In this review, we examine the role of truncated AR variants (ARVs) and their corresponding genomic origins in models of prostate cancer progression, as well as the challenges they pose to the current standard of prostate cancer therapies targeting the AR ligand binding domain. Since ARVs lack the COOH-terminal LBD, the genesis of these AR gene rearrangements and their resulting ARVs provides strong rationale for the pursuit of new avenues of therapeutic intervention targeted at the AR NH2-terminal domain. We further suggest that genomic events leading to ARV expression could act as novel biomarkers of disease progression that may guide the optimal use of current and next-generation AR-targeted therapy.

Mechanism of androgen receptor corepression by CKβBP2/CRIF1, a multifunctional transcription factor coregulator expressed in prostate cancer

The transcription factor coregulator Casein kinase IIβ-binding protein 2 or CR6-interacting factor 1 (CKβBP2/CRIF1) binds the androgen receptor (AR) in prostate cancer cells and in response to dihydrotestosterone localizes with AR on the prostate-specific antigen gene enhancer, but does not bind DNA suggesting CKβBP2/CRIF1 localization in chromatin is determined by AR. In this study we show also that CKβBP2/CRIF1 inhibits wild-type AR and AR N-terminal transcriptional activity, binds to the AR C-terminal region, inhibits interaction of the AR N- and C-terminal domains (N/C interaction) and competes with p160 coactivator binding to the AR C-terminal domain, suggesting CKβBP2/CRIF1 interferes with AR activation functions 1 and 2. CKβBP2/CRIF1 is expressed mainly in stromal cells of benign prostatic hyperplasia and in stroma and epithelium of prostate cancer. CKβBP2/CRIF1 protein is increased in epithelium of androgen-dependent prostate cancer compared to benign prostatic hyperplasia and decreased slightly in castration recurrent epithelium compared to androgen-dependent prostate cancer. The multifunctional CKβBP2/CRIF1 is a STAT3 interacting protein and reported to be a coactivator of STAT3. CKβBP2/CRIF1 is expressed with STAT3 in prostate cancer where STAT3 may help to offset the AR repressor effect of CKβBP2/CRIF1 and allow AR regulation of prostate cancer growth.

Constitutive activity of the androgen receptor

Prostate cancer (PCa) is the most frequently diagnosed cancer in the United States. The androgen receptor (AR) signaling axis is central to all stages of PCa pathophysiology and serves as the main target for endocrine-based therapy. The most advanced stage of the disease, castration-resistant prostate cancer (CRPC), is presently incurable and accounts for most PCa mortality. In this chapter, we highlight the mechanisms by which the AR signaling axis can bypass endocrine-targeted therapies and drive progression of CRPC. These mechanisms include alterations in growth factor, cytokine, and inflammatory signaling pathways, altered expression or activity of transcriptional coregulators, AR point mutations, and AR gene amplification leading to AR protein overexpression. Additionally, we will discuss the mechanisms underlying the synthesis of constitutively active AR splice variants (AR-Vs) lacking the COOH-terminal ligand-binding domain, as well as the role and regulation of AR-Vs in supporting therapeutic resistance in CRPC. Finally, we summarize the ongoing development of inhibitors targeting discrete AR functional domains as well as the status of new biomarkers for monitoring the AR signaling axis in patients.

Peptidomimetic targeting of critical androgen receptor-coregulator interactions in prostate cancer

The growth of advanced prostate cancer depends on androgen receptor signalling, however treatment options are limited. Here we report the disruption of specific protein-protein interactions involving LXXLL motifs in androgen receptor-coregulator proteins such as PELP1 using a novel, small molecule peptidomimetic (D2). D2 is stable, non-toxic and efficiently taken up by prostate cancer cells. Importantly, D2 blocks androgen-induced nuclear uptake and genomic activity of the androgen receptor. Furthermore, D2 abrogates androgen-induced proliferation of prostate cancer cells in vitro with an IC50 of 40 nM, and inhibits tumour growth in a mouse xenograft model. D2 also disrupts androgen receptor-coregulator interactions in ex vivo cultures of primary human prostate tumours. These findings provide evidence that targeting androgen receptor-coregulator interactions using peptidomimetics may be a viable therapeutic approach for patients with advanced prostate cancer.

Fragment-based Shape Signatures: a new tool for virtual screening and drug discovery

Since its introduction in 2003, the Shape Signatures method has been successfully applied in a number of drug design projects. Because it uses a ray-tracing approach to directly measure molecular shape and properties (as opposed to relying on chemical structure), it excels at scaffold hopping, and is extraordinarily easy to use. Despite its advantages, a significant drawback of the method has hampered its application to certain classes of problems; namely, when the chemical structures considered are large and contain heterogeneous ring-systems, the method produces descriptors that tend to merely measure the overall size of the molecule, and begin to lose selective power. To remedy this, the approach has been reformulated to automatically decompose compounds into fragments using ring systems as anchors, and to likewise partition the ray-trace in accordance with the fragment assignments. Subsequently, descriptors are generated that are fragment-based, and query and target molecules are compared by mapping query fragments onto target fragments in all ways consistent with the underlying chemical connectivity. This has proven to greatly extend the selective power of the method, while maintaining the ease of use and scaffold-hopping capabilities that characterized the original implementation. In this work, we provide a full conceptual description of the next generation Shape Signatures, and we underline the advantages of the method by discussing its practical applications to ligand-based virtual screening. The new approach can also be applied in receptor-based mode, where protein-binding sites (partitioned into subsites) can be matched against the new fragment-based Shape Signatures descriptors of library compounds.

TALEN-engineered AR gene rearrangements reveal endocrine uncoupling of androgen receptor in prostate cancer

Androgen receptor (AR) target genes direct development and survival of the prostate epithelial lineage, including prostate cancer (PCa). Thus, endocrine therapies that inhibit the AR ligand-binding domain (LBD) are effective in treating PCa. AR transcriptional reactivation is central to resistance, as evidenced by the efficacy of AR retargeting in castration-resistant PCa (CRPC) with next-generation endocrine therapies abiraterone and enzalutamide. However, resistance to abiraterone and enzalutamide limits this efficacy in most men, and PCa remains the second-leading cause of male cancer deaths. Here we show that AR gene rearrangements in CRPC tissues underlie a completely androgen-independent, yet AR-dependent, resistance mechanism. We discovered intragenic AR gene rearrangements in CRPC tissues, which we modeled using transcription activator-like effector nuclease (TALEN)-mediated genome engineering. This modeling revealed that these AR gene rearrangements blocked full-length AR synthesis, but promoted expression of truncated AR variant proteins lacking the AR ligand-binding domain. Furthermore, these AR variant proteins maintained the constitutive activity of the AR transcriptional program and a CRPC growth phenotype independent of full-length AR or androgens. These findings demonstrate that AR gene rearrangements are a unique resistance mechanism by which AR transcriptional activity can be uncoupled from endocrine regulation in CRPC.

Characterization of a new class of androgen receptor antagonists with potential therapeutic application in advanced prostate cancer

The human androgen receptor plays a major role in the development and progression of prostate cancer and represents a well-established drug target. All clinically approved androgen receptor antagonists possess similar chemical structures and exhibit the same mode of action on the androgen receptor. Although initially effective, resistance to these androgen receptor antagonists usually develops and the cancer quickly progresses to castration-resistant and metastatic states. Yet even in these late-stage patients, the androgen receptor is critical for the progression of the disease. Thus, there is a continuing need for novel chemical classes of androgen receptor antagonists that could help overcome the problem of resistance. In this study, we implemented and used the synergetic combination of virtual and experimental screening to discover a number of new 10-benzylidene-10H-anthracen-9-ones that not only effectively inhibit androgen receptor transcriptional activity, but also induce almost complete degradation of the androgen receptor. Of these 10-benzylidene-10H-anthracen-9-one analogues, a lead compound (VPC-3033) was identified that showed strong androgen displacement potency, effectively inhibited androgen receptor transcriptional activity, and possesses a profound ability to cause degradation of androgen receptor. Notably, VPC-3033 exhibited significant activity against prostate cancer cells that have already developed resistance to the second-generation antiandrogen enzalutamide (formerly known as MDV3100). VPC-3033 also showed strong antiandrogen receptor activity in the LNCaP in vivo xenograft model. These results provide a foundation for the development of a new class of androgen receptor antagonists that can help address the problem of antiandrogen resistance in prostate cancer.

Posttranslational modification of the androgen receptor in prostate cancer

The androgen receptor (AR) is important in the development of the prostate by regulating transcription, cellular proliferation, and apoptosis. AR undergoes posttranslational modifications that alter its transcription activity, translocation to the nucleus and stability. The posttranslational modifications that regulate these events are of utmost importance to understand the functional role of AR and its activity. The majority of these modifications occur in the activation function-1 (AF1) region of the AR, which contains the transcriptional activation unit 1 (TAU1) and 5 (TAU5). Identification of the modifications that occur to these regions may increase our understanding of AR activation in prostate cancer and the role of AR in the progression from androgen-dependent to castration-resistant prostate cancer (CRPC). Most of the posttranslational modifications identified to date have been determined using the full-length AR in androgen dependent cells. Further investigations into the role of posttranslational modifications in androgen-independent activation of full-length AR and constitutively active splicing variants are warranted, findings from which may provide new therapeutic options for CRPC.

Proto-oncogene activity of melanoma antigen-A11 (MAGE-A11) regulates retinoblastoma-related p107 and E2F1 proteins

Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract that is expressed at higher levels in prostate cancer. Increased expression of MAGE-A11 enhances androgen receptor transcriptional activity and promotes prostate cancer cell growth. Further investigation into the mechanisms of MAGE-A11 function in prostate cancer demonstrated interactions with the retinoblastoma-related protein p107 and Rb tumor suppressor but no interaction with p130 of the Rb family. MAGE-A11 interaction with p107 was associated with transcriptional repression in cells with low MAGE-A11 and transcriptional activation in cells with higher MAGE-A11. Selective interaction of MAGE-A11 with retinoblastoma family members suggested the regulation of E2F transcription factors. MAGE-A11 stabilized p107 by inhibition of ubiquitination and linked p107 to hypophosphorylated E2F1 in association with the stabilization and activation of E2F1. The androgen receptor and MAGE-A11 modulated endogenous expression of the E2F1-regulated cyclin-dependent kinase inhibitor p27(Kip1). The ability of MAGE-A11 to increase E2F1 transcriptional activity was similar to the activity of adenovirus early oncoprotein E1A and depended on MAGE-A11 interactions with p107 and p300. The immunoreactivity of p107 and MAGE-A11 was greater in advanced prostate cancer than in benign prostate, and knockdown with small inhibitory RNA showed that p107 is a transcriptional activator in prostate cancer cells. These results suggest that MAGE-A11 is a proto-oncogene whose increased expression in prostate cancer reverses retinoblastoma-related protein p107 from a transcriptional repressor to a transcriptional activator of the androgen receptor and E2F1.