Discovery of N-(4-(Benzyloxy)-phenyl)-sulfonamide Derivatives as Novel Antagonists of the Human Androgen Receptor Targeting the Activation Function 2

Androgen receptor (AR) antagonists have been widely used for the treatment of prostate cancer (PCa). As a link between the AR and its transcriptional function, the activation function 2 (AF2) region has recently been revealed as a novel targeting site for developing AR antagonists. Here, we reported a series of N-(4-(benzyloxy)-phenyl)-sulfonamide derivatives as new-scaffold AR antagonists targeting the AR AF2. Therein, compound T1-12 showed excellent AR antagonistic activity (IC50 = 0.47 μM) and peptide displacement activity (IC50 = 18.05 μM). Furthermore, the in vivo LNCaP xenograft study confirmed that T1-12 offered effective inhibition on tumor growth when administered intratumorally. The study represents the first successful attempt to identify a small molecule targeting the AR AF2 with submicromolar AR antagonistic activity by structure-based virtual screening and provides important clues for the development of novel therapeutics for PCa treatment.

Design and synthesis of isothiocyanate-containing hybrid androgen receptor (AR) antagonist to downregulate AR and induce ferroptosis in GSH-Deficient prostate cancer cells

Sustained androgen receptor (AR) signaling and apoptosis evasion are among the main hurdles of castration-resistant prostate cancer (CRPC) treatment. We designed and synthesized isothiocyanate (ITC)-containing hybrid AR antagonist (ITC-ARi) and rationally combined ITC-ARi with GSH synthesis inhibitor buthionine sulfoximine (BSO) to efficiently downregulate AR/AR splice variant and induce ferroptosis in CRPC cells. The representative ITC-ARi 13 is an AR ligand that contains an N-acetyl cysteine-masked ITC moiety and gradually releases parental unconjugated ITC 12b in aqueous solution. The in vitro anti-PCa activities of 13, such as growth inhibition and AR downregulation, are significantly enhanced when combined with BSO. The drug combination caused notable lipid peroxidation and the cell viability was effectively rescued by iron chelator, antioxidants or the inhibitor of heme oxygenase-1, supporting the induction of ferroptosis. 13 and BSO cooperatively downregulate AR and induce ferroptosis likely through increasing the accessibility of 13/12b to cellular targets, escalating free intracellular ferrous iron and attenuating GSH-centered cellular defense and adaptation. Further studies on the combination of ITC-ARi and GSH synthesis inhibitor could result in a new modality against CRPC.

High Content Screening Using New U2OS Reporter Cell Models Identifies Harmol Hydrochloride as a Selective and Competitive Antagonist of the Androgen Receptor

Prostate cancer is the most commonly diagnosed malignancy in men. Its growth mainly relies on the activity of the androgen receptor (AR), justifying the use of androgen deprivation therapy as a gold standard treatment for the metastatic disease. Inhibition of the androgen axis using second generation antagonists has improved patients’ survival, but is systematically confronted to resistance mechanisms, leading to a median survival that does not exceed 5 years. Counteracting this resistance has been the object of a large number of investigations, with a particular emphasis towards the identification of new AR inhibitors, whether they antagonize the receptor by a competitive or a non-competitive binding. To this end, many high content screens have been performed, to identify new non-steroidal AR antagonists, using a variety of approaches, but reported somewhat controversial results, depending on the approach and on the cell model that was used for screening. In our study, we used the U2OS osteosarcoma cells stably transfected with AR or ARv7 and a luciferase reporter as a previously validated model to screen the Prestwick Phytochemical library. The results of our screen identified ellipticine, harmol, and harmine hydrochloride as confirmed hits. Surprisingly, we could demonstrate that harmol hydrochloride, previously identified as a non-competitive inhibitor of AR or a weak inhibitor of androgen signaling, was actually a competitive antagonist of AR, which inhibits the growth of VCaP prostate cancer line, at concentrations for which it did not affect the growth of the AR negative DU145 and PC3 cells. Interestingly, we also report for the first time that harmol hydrochloride was selective for AR, as it could not alter the activity of other nuclear receptors, such as the glucocorticoid receptor (GR), the progesterone receptor (PR), or the mineralocorticoid receptor (MR). Additionally, we demonstrate that, conversely to enzalutamide, harmol hydrochloride did not show any agonistic activity towards the pregnane X receptor (PXR), a master regulator of drug metabolism. Together, our results shed light on the importance of the cellular context for the screening of new AR antagonists. They further indicate that some of the potential hits that were previously identified may have been overlooked.

Endocrine Disrupting Chemicals Mediated through Binding Androgen Receptor Are Associated with Diabetes Mellitus

Endocrine disrupting chemicals (EDCs) can mimic natural hormone to interact with receptors in the endocrine system and thus disrupt the functions of the endocrine system, raising concerns on the public health. In addition to disruption of the endocrine system, some EDCs have been found associated with many diseases such as breast cancer, prostate cancer, infertility, asthma, stroke, Alzheimer’s disease, obesity, and diabetes mellitus. EDCs that binding androgen receptor have been reported associated with diabetes mellitus in in vitro, animal, and clinical studies. In this review, we summarize the structural basis and interactions between androgen receptor and EDCs as well as the associations of various types of diabetes mellitus with the EDCs mediated through androgen receptor binding. We also discuss the perspective research for further understanding the impact and mechanisms of EDCs on the risk of diabetes mellitus.

Development of Bag-1L as a therapeutic target in androgen receptor-dependent prostate cancer

Targeting the activation function-1 (AF-1) domain located in the N-terminus of the androgen receptor (AR) is an attractive therapeutic alternative to the current approaches to inhibit AR action in prostate cancer (PCa). Here we show that the AR AF-1 is bound by the cochaperone Bag-1L. Mutations in the AR interaction domain or loss of Bag-1L abrogate AR signaling and reduce PCa growth. Clinically, Bag-1L protein levels increase with progression to castration-resistant PCa (CRPC) and high levels of Bag-1L in primary PCa associate with a reduced clinical benefit from abiraterone when these tumors progress. Intriguingly, residues in Bag-1L important for its interaction with the AR AF-1 are within a potentially druggable pocket, implicating Bag-1L as a potential therapeutic target in PCa.

Androgen Receptor Splice Variants Are Not Substrates of Nonsense-Mediated Decay

BACKGROUND

Androgen receptor (AR) splice variants have been clinically associated with progressive cancer, castration-resistance, and resistance to AR antagonists and androgen synthesis inhibitors. AR variants can be generated by genomic alterations and alternative splicing, and their expression is androgen-regulated. There has been a suggestion that AR variants bearing premature termination codons and coding for truncated proteins should be regulated by the nonsense-mediated decay (NMD) mRNA surveillance pathway, suggesting that either the NMD pathway is dysfunctional in variant-expressing cell lines or that variants are somehow able to evade degradation by NMD.

METHODS

We first used siRNA knockdown of the NMD regulator, UPF1, in an NMD reporter assay to determine if this surveillance pathway is functioning normally in AR variant-expressing cell lines. We then used UPF1 knockdown to determine if expression of the AR variants ARV3 and ARV7 is affected by inhibition of NMD. Next, we analyzed androgen regulation of UPF1 and used transcript expression analysis to determine if there is any association between UPF1 expression, resistance, and ARV3 or ARV7 expression.

RESULTS

We found that the NMD pathway functions normally in the AR variant-expressing cell line 22Rv1 and that inhibition of NMD does not increase expression of ARV3 or ARV7. Furthermore, we found that expression of UPF1 is not androgen-regulated. We also found that UFP1 expression levels do not differentiate castration-sensitive from resistant cell line and that UPF1 expression does not correlate with expression of ARV3 or ARV7 in cells in which these variants are highly expressed.

CONCLUSION

This study eliminates a possible mechanism of regulation of certain AR variants. Future research into the regulation of AR variants should focus on other mechanisms to better understand the origin of these variants and to possibly inhibit their expression for the resensitization of resistant cancers. Prostate 77:829-837, 2017. © 2017 Wiley Periodicals, Inc.

MiR-185 attenuates androgen receptor function in prostate cancer indirectly by targeting bromodomain containing 8 isoform 2, an androgen receptor co-activator

OBJECTIVES

Aberrant androgen receptor (AR) signaling functions are implicated in prostate cancer (PCa) pathogenesis. Here, we studied interactions between miR-185 and the bromodomain containing 8 isoform 2 (BRD8 ISO2) to investigate indirect mechanisms of miR-185 with respect to AR function through BRD8 ISO2 in PCa.

METHODS

Putative miRNA response element (MRE) of miR-185 in 3'-untranslated region (3'-UTR) of BRD8 ISO2 mRNA was predicted by software and confirmed using dual-luciferase assays and Ago2 immunoprecipitation. BRD8 and AR expression were determined by qRT-PCR and Western blot in PCa cells and tissues. MMTV-Fluc reporter plasmids and dual-luciferase assays were used to evaluate AR activity.

RESULTS

MRE prediction, dual-luciferase assays and Ago2 immunoprecipitation confirmed that miR-185 is capable of binding the 3'-UTR of BRD8 ISO2 mRNA. QRT-PCR and Western blot indicated that BRD8 ISO2 expression is decreased by miR-185 mimic transfection while increased by miR-185 inhibitor transfection. MMTV-Fluc reporter assays revealed that miR-185 can attenuate AR function by suppressing BRD8 ISO2. Additionally, Pearson's correlation analyses confirmed that BRD8 ISO2 mRNA expression is inversely correlated with miR-185 expression in clinical specimens.

CONCLUSION

In addition to suppression of AR expression, miR-185 can attenuate AR function indirectly by suppressing BRD8 ISO2. MiR-185 and BRD8 ISO2 may be possible therapeutic targets for PCa treatment.

Causes of endocrine disrupting potencies in surface water in East China

Surface water is essential for human health and ecological diversity, but some endocrine disrupting chemicals are detectable. Both thyroid receptor (TR) and androgen receptor (AR) agonistic/antagonistic potencies in grade II surface water in East China were investigated using reporter gene assays. While none of the water exhibited agonistic potency, significant AR and TR antagonistic potencies were detectable. TR antagonistic equivalents (TR-AntEQ) and AR antagonistic equivalents (AR-AntEQ) ranged from 3.6 to 76.1 μg dibutyl phthalate/L and from 2.3 to 242.6 μg flutamide/L, respectively. The TR and AR antagonistic potencies in the Yangtze River watershed were highlighted, with equivalents greater than the lowest observable effect concentration (LOEC) of dibutyl phthalate and flutamide, respectively. Phthalate esters (PAEs) being the most abundant explained most of the TR antagonistic potency, contributing more than 65% of the TR-AntEQ and diisobutyl phthalate (DiBP) was the major contributor. In most surface waters studied, PAEs contributed little of the AR-AntEQ, but the frequently detected octylphenol, nonylphenol and benzo[a]pyrene might be responsible.

Toxic Identification and Evaluation of Androgen Receptor Antagonistic Activities in Acid-Treated Liver Extracts of High-Trophic Level Wild Animals from Japan

Sulfuric acid-treated liver extracts of representative high-trophic level Japanese animals were analyzed by toxic identification and evaluation (TIE) with chemically activated luciferase expression (CALUX) and chemical analysis to elucidate androgen receptor (AR) antagonistic activities and potential contributions of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). The activities were detected in striped dolphins (n = 5), Stejneger's beaked whales (n = 6), golden eagle (n = 1), and Steller's sea eagle (n = 1) with CALUX-flutamide equivalents (FluEQs) as follow: 38 (20-52), 47 (21-96), 5.0, and 80 μg FluEQ/g-lipid, respectively. The AR antagonism was detected in limited number of specimens at lower levels for finless porpoise, raccoon dog, and common cormorant. Theoretical activities (Theo-FluEQs) were calculated using the concentration of OCPs and PCBs and their IC25-based relative potency (REP) values. These total contribution to CALUX-FluEQ was 126%, 84%, 53%, 55%, and 44% for striped dolphin, Steller's sea eagle, Stejneger's beaked whale, finless porpoise, and golden eagle, respectively, and the main contributor was p,p'-DDE. However, most of the activities for raccoon dog (7.6%) and common cormorant (17%) could not be explained by OCPs and PCBs. This suggests other unknown compounds could function as AR antagonists in these terrestrial species.

The role of microRNAs 371 and 34a in androgen receptor control influencing prostate cancer behavior

BACKGROUND

The molecular mechanisms involved in androgen receptor (AR) signaling pathways are not completely understood, and deregulation of microRNAs (miRNAs) expression may play a role in prostate cancer (PC) development and progression.

METHODS

The expression levels of miRNA and AR were evaluated with quantitative real-time polymerase chain reaction using frozen tissue from the surgical specimens of 83 patients submitted to radical prostatectomy. The expression level of miRNAs was correlated with prognostic factors and biochemical recurrence during a follow-up period of 45 months. In vitro and in vivo experiments were performed to understand the effect of miRNAs over AR in the context of that seen in a PC model.

RESULTS

MiR-371 underexpression correlated with non-organ-confined (pT3) disease (P = 0.009). In vitro transfection of miR-371 reduced the levels of AR by 22% and 28% in LNCaP and PC3 cell lines, respectively, and in kallikrein 3, it was reduced by 51%. PC was induced in Balb/c mice using PC-3M-luc-C6 cells, and animals were treated with 3 local doses of miR-371. Tumor growth evaluated by in vivo imaging after luciferase injection was slower in animals treated with miR-371. To explore further the possible role of miRNAs in the AR pathway, LNCaP cell line was treated with 5α-dihydrotestosterone and flutamide showing alteration in miRNAs expression, especially miR-34a, which was significantly underexpressed after treatment with high doses of 5α-dihydrotestosterone.

CONCLUSION

Our data support a role for miRNAs, especially miR-371 and miR-34a, in the complex disarrangement of AR signaling pathway and in the behavior of PC.

Identification of a group of brominated flame retardants as novel androgen receptor antagonists and potential neuronal and endocrine disrupters

Brominated flame-retardants (BFRs) are used in industrial products to reduce the risk of fire. However, their continuous release into the environment is a concern as they are often persistent, bioaccumulating and toxic. Information on the impact these compounds have on human health and wildlife is limited and only a few of them have been identified to disrupt hormone receptor functions. In the present study we used in silico modeling to determine the interactions of selected BFRs with the human androgen receptor (AR). Three compounds were found to dock into the ligand-binding domain of the human AR and these were further tested using in vitro analysis. Allyl 2,4,6-tribromophenyl ether (ATE), 2-bromoallyl 2,4,6-tribromophenyl ether (BATE) and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE) were observed to act as AR antagonists. These BFRs have recently been detected in the environment, in house dust and in aquatic animals. The compounds have been detected at high concentrations in both blubber and brain of seals and we therefore also assessed their impact on the expression of L-type amino acid transporter system (LAT) genes, that are needed for amino acid uptake across the blood-brain barrier, as disruption of LAT gene function has been implicated in several brain disorders. The three BFRs down-regulated the expression of AR target genes that encode for prostate specific antigen (PSA), 5α-reductases and β-microseminoprotein. The potency of PSA inhibition was of the same magnitude as the common prostate cancer drugs, demonstrating that these compounds are strong AR antagonists. Western blot analysis of AR protein showed that ATE, BATE and DPTE decreased the 5α-dihydrotestosterone-induced AR protein levels, further confirming that these BFRs act as AR antagonists. The transcription of the LAT genes was altered by the three BFRs, indicating an effect on amino-acid uptake across cellular membranes and blood-brain barrier. This study demonstrated that ATE, BATE and DPTE are potent AR antagonists and the alterations in LAT gene transcription suggest that these compounds can affect neuronal functions and should be considered as potential neurotoxic and endocrine disrupting compounds.

In silico investigations of anti-androgen activity of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) have attracted great concern as global environmental pollutants and representative endocrine disruptors. In this work, a molecular model study combining three-dimensional quantitative structure-activity relationship (3D-QSAR), molecular docking, and molecular dynamics (MD) simulations was performed to explore the structural requirement for the anti-androgen activities of PCBs and to reveal the binding mode between the PCBs and androgen receptor (AR). The best comparative molecular similarity indices analysis (CoMSIA) model, obtained from receptor-based alignment, shows leave-one-out cross-validated correlation coefficient (q(2)) of 0.665 and conventional correlation coefficient (R(2)) of 0.945. The developed model has a highly predictive ability in both internal and external validation. Furthermore, the interaction mechanisms of PCBs to AR were analyzed by molecular docking and MD simulation. Molecular docking indicated that all the PCBs in the data set docked in a hydrophobic pocket. The Binding free energies calculated by Molecular mechanics-Poisson Boltzmann surface area (MM-PBSA) not only exhibited a good correlation with the experimental activity, but also could explain the activity difference of the studied compounds. The binding free energy decomposition analysis indicates that the van der Waals interaction is the major driving force for the binding process.

Steroid derivatives as pure antagonists of the androgen receptor

BACKGROUND

While the androgens of testicular origin (representing about 50% of total androgens in men over 50 years) can be completely eliminated by surgical or medical castration with GnRH (gonadotropin-releasing hormone) agonists or antagonists, the antiandrogens currently available as blockers of androgen binding to the androgen receptor (AR), namely bicalutamide (BICA), flutamide (FLU) and nilutamide have too weak affinity to completely neutralize the other 50% of androgens made locally from dehydroepiandrosterone (DHEA) in the prostate cancer tissue by the mechanisms of intracrinology.

MATERIALS AND METHODS

Series of steroid derivatives having pure and potent antagonistic activity on the human and rodent AR were synthesized. Assays of AR binding and activity in carcinoma mouse Shionogi and human LNCaP cells as well as in vivo bioavailability measurements and in vivo prostate weight assays in the rat were used.

RESULTS

The chosen lead steroidal compound, namely EM-5854, has a 3.7-fold higher affinity than BICA for the human AR while EM-5855, an important metabolite of EM-5854, has a 94-fold higher affinity for the human AR compared to BICA. EM-5854 and EM-5855 are 14 times more potent than BICA in inhibiting androgen (R1881)-stimulated prostatic specific antigen (PSA) secretion in human prostatic carcinoma LNCaP cells in vitro. MDV3100 has a potency comparable to bicalutamide in these assays. Depending upon the oral formulation, EM-5854 is 5- to 10-times more potent than BICA to inhibit dihydrotestosterone (DHT)-stimulated ventral prostatic weight in vivo in the rat while MDV3100 has lower activity than BICA in this in vivo model. These data are supported by respective 40-fold and 105-fold higher potencies of EM-5854 and EM-5855 compared to BICA to inhibit cell proliferation in the androgen-sensitive Shionogi carcinoma cell model.

CONCLUSIONS

Although the present preclinical results data need evaluation in clinical trials in men, combination of the data obtained in vitro in human LNCaP cells as indicator of potency in the human prostate and the data on metabolism evaluated in vivo on ventral prostate weight in the rat, could suggest the possibility of a 70- to 140-fold higher potency of EM-5854 compared to bicalutamide (Casodex) for the treatment of prostate cancer in men.

Identification of major dioxin-like compounds and androgen receptor antagonist in acid-treated tissue extracts of high trophic-level animals

We evaluated the applicability of combining in vitro bioassays with instrument analyses to identify potential endocrine disrupting pollutants in sulfuric acid-treated extracts of liver and/or blubber of high trophic-level animals. Dioxin-like and androgen receptor (AR) antagonistic activities were observed in Baikal seals, common cormorants, raccoon dogs, and finless porpoises by using a panel of rat and human cell-based chemical-activated luciferase gene expression (CALUX) reporter gene bioassays. On the other hand, no activity was detected in estrogen receptor α (ERα)-, glucocorticoid receptor (GR)-, progesterone receptor (PR)-, and peroxisome proliferator-activated receptor γ2 (PPARγ2)-CALUX assays with the sample amount applied. All individual samples (n = 66) showed dioxin-like activity, with values ranging from 21 to 5500 pg CALUX-2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent (TEQ)/g-lipid. Because dioxins are expected to be strong contributors to CALUX-TEQs, the median theoretical contribution of dioxins calculated from the result of chemical analysis to the experimental CALUX-TEQs was estimated to explain up to 130% for all the tested samples (n = 54). Baikal seal extracts (n = 31), but not other extracts, induced AR antagonistic activities that were 8-150 μg CALUX-flutamide equivalent (FluEQ)/g-lipid. p,p'-DDE was identified as an important causative compound for the activity, and its median theoretical contribution to the experimental CALUX-FluEQs was 59% for the tested Baikal seal tissues (n = 25). Our results demonstrate that combining in vitro CALUX assays with instrument analysis is useful for identifying persistent organic pollutant-like compounds in the tissue of wild animals on the basis of in vitro endocrine disruption toxicity.

Corepressor effect on androgen receptor activity varies with the length of the CAG encoded polyglutamine repeat and is dependent on receptor/corepressor ratio in prostate cancer cells

The response of prostate cells to androgens reflects a combination of androgen receptor (AR) transactivation and transrepression, but how these two processes differ mechanistically and influence prostate cancer risk and disease outcome remain elusive. Given recent interest in targeting AR transrepressive processes, a better understanding of AR/corepressor interaction and responses is warranted. Here, we used transactivation and interaction assays with wild-type and mutant ARs, and deletion AR fragments, to dissect the relationship between AR and the corepressor, silencing mediator for retinoic acid and thyroid hormone receptors (SMRT). We additionally tested how these processes are influenced by AR agonist and antagonist ligands, as well as by variation in the polyglutamine tract in the AR amino terminal domain (NTD), which is encoded by a polymorphic CAG repeat in the gene. SMRT was recruited to the AR ligand binding domain by agonist ligand, and as determined by the effect of strategic mutations in activation function 2 (AF-2), requires a precise conformation of that domain. A distinct region of SMRT also mediated interaction with the AR-NTD via the transactivation unit 5 (TAU5; residues 315-538) region. The degree to which SMRT was able to repress AR increased from 17% to 56% as the AR polyglutamine repeat length was increased from 9 to 42 residues, but critically this effect could be abolished by increasing the SMRT:AR molar ratio. These data suggest that the extent to which the CAG encoded polyglutamine repeat influences AR activity represents a balance between corepressor and coactivator occupancy of the same ligand-dependent and independent AR interaction surfaces. Changes in the homeostatic relationship of AR to these molecules, including SMRT, may explain the variable penetrance of the CAG repeat and the loss of AR signaling flexibility in prostate cancer progression.

Androgen receptor as a therapeutic target

Androgens function as sex hormone primarily via activation of a single androgen receptor (AR, or NR3C4). AR is an important therapeutic target for the treatment of diseases such as hypogonadism and prostate cancer. AR ligands of different chemical structures and/or pharmacological properties are widely used for these therapeutic applications, and all of the AR ligands currently available for therapy modulate AR function via direct binding to the ligand-binding pocket (LBP) of the receptor. In the past ten years, our understanding of AR structure and molecular mechanism of action has progressed extensively, which has encouraged the rapid development of newer generation of AR ligands, particularly tissue-selective AR ligands. With improved tissue selectivity, future generations of AR ligands are expected to greatly expand the therapeutic applications of this class of drugs. This review will provide an overview of the common therapeutic applications of currently available AR ligands, and discussion of the major challenges as well as novel therapeutic strategies proposed for future drug development.