Androgen Receptor Downregulation Research Articles

Elucidation of the Multiple Activities of Abiraterone by a Synthetic Chemistry Approach

Objective: Novel agents to treat metastatic prostate cancer include a class of drugs which function primarily by inhibiting the action of the CYP17 enzyme, which results in decreased androgen synthesis. Abiraterone and related molecules have been shown to decrease expression of the androgen receptor (AR) and to inhibit its transcriptional activity in addition to CYP17 inhibition. The structure-activity relationships (SAR) governing AR down regulation are less well understood than CYP17 and AR inhibition, so we designed abiraterone derivatives with the goal of better understanding the SAR of AR down regulation. Methods: We synthesized 17 abiraterone derivatives with unsaturated, cyclic and acyclic substituents containing hydrogen bond acceptors at C16 and C17 positions. We examined the ability of these compounds to inhibit CYP17 and AR, and to decrease AR expression. Results: While abiraterone was the most potent AR down regulator, we found that a hydrogen bond acceptor on an unsaturated nitrogen or oxygen, 4 to 6 angstroms from C17 is required for AR down-regulation, but a heterocyclic ring is not necessary, as shown by the activity of compounds 4, 8, and 10. The size and shape of substituents on active AR down regulators indicates that the binding site near C17 is significantly larger than the pyridine ring in abiraterone. We found no correlation between the ability of a compound to down regulate AR and its ability to inhibit CYP17 or AR transcriptional activity. AR transcriptional activity was inhibited most potently by molecules with hydrogen bond donors 2-3 angstroms from C17. Molecules with C16 substituents could inhibit AR transcription but were inactive as AR down regulators, as indicated by compounds 5, 13, and 14. CYP17 inhibitors had an unsaturated nitrogen (pyridine or hydrazine) oriented away from the steroid backbone and perpendicular to the C16-C17 bond. Conclusion: We determined the SAR for AR down regulation. The complete lack of correlation between SARs for AR down regulation and AR or CYP17 inhibition suggests distinct mechanisms of actions for these activities. The SAR for AR down regulation suggests that additional hydrogen bond acceptor side chains 4-6 angstroms from C17 could enhance the activity of abiraterone.

Perinatal exposure to di-(2-ethylhexyl) phthalate affects anxiety- and depression-like behaviors in mice

Di-(2-ethylhexyl) phthalate (DEHP) is an environmental endocrine disrupter. The present study investigated the effect of DEHP on emotional behavior of mice following perinatal exposure (10, 50, and 200mgkg−1d−1) from gestation day 7 through postnatal day 21. The results showed that, in pubertal males (6-w-old), DEHP decreased the time spent in the open arms and the number of entries into them in elevated plus maze and decreased the time in the mirrored chamber and in the light-box; in pubertal females, DEHP decreased the time spent in the open arms and the number of entries into them, suggesting that DEHP exposure made a anxiogenic effect in pubertal offspring regardless of sex. While DEHP effect on anxiety of adult (12-w-old) displayed sex differences, with decreased time spent in the open arms in the adult females. Perinatal exposure to DEPH significantly extended the time of immobility in forced swim task of pubertal offspring and adulthood regardless of sex. Furthermore, DEHP down-regulated the expressions of androgen receptor (AR) in pubertal male hippocampus and of estrogen receptor (ER) β in pubertal female and adult hippocampus of both sexes and inhibited the phosphorylation of ERK1/2 of hippocampus in pubertal mice and adult males. These results suggest that exposure to DEHP early in life affected the anxiety- and depressive-like behaviors of pubertal offspring and even adult. The disruption of gonadal hormones’ modulation of behaviors due to down-regulation of AR or ERβ in the hippocampus may be associated with the aggravated anxiety- and depression-like status induced by DEHP.

315 Biological characterization of TAS3681, a new type of androgen receptor antagonist with androgen receptor downregulating activity

Background: Recent evidence from both preclinical and clinical studies is consistent with the importance of reactivation of androgen receptor (AR) signaling in a majority of castration-resistant prostate cancer (CRPC). This knowledge has driven the clinical development of new inhibitors of androgen production (e.g., abiraterone) and AR signaling (e.g., enzalutamide). However, resistance to these new therapies has already been reported. Reactivation of AR signaling occurs by several mechanisms in CRPC. In the present study, we describe the biological characterization of TAS3681, which is a new AR antagonist with AR downregulation activity, and propose this concept as a potential new approach for the treatment of CRPC. Methods: For cell growth assay, prostate cancer cells were treated with androgen and TAS3681 in steroid depleted media for 3 days, and the living cells were determined by using wst-8 reagent. For assay of AR transactivation, COS-7 cells were transiently transfected with androgenresponsive reporter gene construct and expression vectors encoding wt or mu ARs. The transfected cells were treated with TAS3681 and androgen in steroid depleted media for 24 h, and luciferase activity was measured. For an in vivo pharmacodynamic (PD) assay to confirm AR downregulation in tumor, TAS3681 was orally dosed in CRPC tumor xenograft model. Tumor was isolated and AR level in tumor was determined by Western blot. Results: In cell growth assay, TAS3681 suppressed the growth of AR positive prostate cancer cells but did not affect that of AR-negative DU145 prostate cancer cells, indicating a dependency on AR for efficacy. TAS3681 did not stimulate AR nuclear translocation and suppressed wt and mu ARs (including F876L) transactivation in cells, indicative of its pure AR antagonist profile. In contrast to enzalutamide and bicalutamide, TAS3681 effectively suppressed androgen-independent AR transactivation by growth factors and cytokines via AR downregulation activity. Interestingly, in prostate cancer cells which express full-length and splice variant AR, TAS3681 reduced the expression of both ARs. Moreover, TAS3681 treatment effectively decreased AR level in CRPC tumors in vivo. Conclusion: Our findings suggest that TAS3681, a new type of AR antagonist with AR downregulation activity, has the potential to circumvent resistance to current and 2nd-generation therapies targeting AR signaling and could provide a new therapeutic strategy in the treatment of CRPC.

Antiandrogenic mechanisms of pesticides in human LNCaP prostate and H295R adrenocortical carcinoma cells.

Several pesticides suspected or known to have endocrine disrupting effects were screened for pro- or antiandrogenic properties by determining their effects on proliferation, prostatic-specific antigen (PSA) secretion and androgen receptor (AR) expression, and AR phosphorylation in androgen-dependent LNCaP human prostate cancer cells, as well as on the expression and catalytic activity of the enzyme CYP17 in H295R human adrenocortical carcinoma cells, an in vitro model of steroidogenesis. Effects on SRD5A gene expression were determined in both cell lines. Benomyl, vinclozolin, and prochloraz, but not atrazine, concentration dependently (1-30 μM) decreased dihydrotestosterone (DHT)-stimulated proliferation of LNCaP cells. All pesticides except atrazine decreased DHT-stimulated PSA secretion, AR nuclear accumulation, and AR phosphorylation on serines 81 and 213 in LNCaP cells. Benomyl and prochloraz, but not vinclozolin or atrazine, decreased levels of CYP17 gene and protein expression, as well as catalytic activity in H295R cells. In the case of prochloraz, some of these effects corresponded with cytotoxicity. H295R cells expressed AR protein and SRD5A1, but not SRD5A2 transcripts. SRD5A1 gene expression in H295R cells was increased by 10 nM DHT, whereas in LNCaP cells significant induction was observed by 0.1 nM DHT. AR protein expression in H295R cells was not increased by DHT. Vinclozolin decreased DHT-induced SRD5A1 gene expression in LNCaP, but not H295R cells, indicating a functional difference of AR between the cell lines. In conclusion, pesticides may exert antiandrogenic effects through several mechanisms that are cell type-specific, including AR antagonism and down-regulation or catalytic inhibition of androgen biosynthetic enzymes, such as CYP17 and SRD5A1.

Abstract 2704: Simultaneous targeting of androgen receptor (AR) and Eukaryotic Initiation Factor 4E (eIF4E) dependent translation initiation by RAMBA Retinamides promotes apoptosis and impedes cell growth, cell proliferation and matrix invasion in androgen sensitive and castration-resistant prostate cancers

Abstract Introduction: Prostate cancer (PCa) remains the second most leading cause of cancer-related death in Western male population. Although initially counteracted by androgen deprivation therapy (ADT), PCa cells eventually progress to a hormone-independent state thereby limiting treatment options and rendering the discovery of new therapeutic approaches a clinical priority. Direct targeting of translational machinery has gained enormous attention in recent years for treating castration resistant prostate cancers (CRPC). The present study aims to investigate the effect of our novel retinoic acid metabolism blocking agents (RAMBA) retinamides (RRs) on eukaryotic translation initiation factor 4E (eIF4E) translational machinery and androgen receptor (AR) signaling in prostate cancers. Methods: Androgen-sensitive (LNCaP), androgen-resistant (PC-3, C4-2B and CWR22Rv1), enzalutamide resistant (MR49F) prostate cancer cells and normal prostatic epithelial cells (PWR-1E) were used analyzing the effect of RRs on prostate cancers. Results: 24 h treatment of PCa cells to RRs resulted in substantial down-regulation of androgen receptor (AR), degradation of MAPK-interacting kinases (MNK), and attenuation of eukaryotic translation initiation factor 4E (eIF4E) cap dependent translation initiation. Down-regulation of AR and MNK mediated eIF4E translation initiation by RRs in PCa cells were in turn associated with inhibition of cell growth and proliferation, induction of cell cycle arrest, increased apoptosis, and inhibition of matrix invasion and metastasis. Most importantly, the effects of our RRs on AR degradation, eIF4E translation initiation and subsequent oncogenic program were far more potent than the clinically relevant retinoids, established MNK inhibitors (CGP 57380 and/or cercosporamide) and the FDA approved PCa drugs (Casodex, Enzalutamide and Abiraterone acetate). Conclusion: RAMBA retinamides which can exclusively target the degradation of both AR and MNK- the two divergent axes in PCa, at pharmacologically feasible concentrations are novel therapeutic compounds for treatment of both androgen-sensitive and androgen-resistant prostate cancers. Citation Format: Vidya priyadarsini Ramamurthy, Senthilmurugan Ramalingam, Lalji Gediya, Vincent C.O Njar. Simultaneous targeting of androgen receptor (AR) and Eukaryotic Initiation Factor 4E (eIF4E) dependent translation initiation by RAMBA Retinamides promotes apoptosis and impedes cell growth, cell proliferation and matrix invasion in androgen sensitive and castration-resistant prostate cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2704. doi:10.1158/1538-7445.AM2014-2704

Abstract 2121: Resveratrol regulates phospho-serine 81 androgen receptor and its stability to inhibit growth of prostate cancer cells

Abstract Resveratrol, a polyphenol, has been reported as a cell growth inhibitor of various types of cancer. The molecular mechanisms of resveratrol are involved in different cellular signal transductions such as anti-inflammation and anti-oxidation. Resveratrol inhibits growth of prostate cancer cells through regulating cyclin-dependent kinases, anti-apoptotic proteins, and pro-apoptotic proteins. Notably, resveratrol may down-regulate androgen receptor (AR) and its downstream gene to inhibit prostate cancer cell growth. In previous study, serine 81 phosphorylation of AR increases its protein stability and transcriptional activity, which promotes prostate cancer cell growth. The aim of this study is to investigate whether AR serine 81 phosphorylation would be a target of resveratrol in prostate cancer cells. Our data indicate that resveratrol inhibited the growth of prostate cancer cell line, LNCaP, with the decrease of AR phospho-serine 81 levels. Moreover, AR protein stability was declined by resveratrol without affecting AR mRNA expression. Indeed, resveratrol inhibited AR transcriptional activity in results of AR reporter assay and PSA level in LNCaP cells. In summary, the results suggest that resveratrol might inhibit growth of LNCaP cells, at least, via decreasing phospho-serine 81 of AR, AR protein stability, and AR transcriptional activity. Citation Format: Yu-Ting Peng, Tzu-Yin Chen, Mei-Chih Chen, Eugene Lin, Ho Lin. Resveratrol regulates phospho-serine 81 androgen receptor and its stability to inhibit growth of prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2121. doi:10.1158/1538-7445.AM2014-2121

PARP-1 regulates epithelial-mesenchymal transition (EMT) in prostate tumorigenesis

Poly (ADP-ribose) polymerase (PARP) is involved in key cellular processes such as DNA replication and repair, gene transcription, cell proliferation and apoptosis. The role of PARP-1 in prostate cancer development and progression is not fully understood. The present study investigated the function of PARP-1 in prostate growth and tumorigenesis in vivo. Functional inactivation of PARP-1 by gene-targeted deletion led to a significant reduction in the prostate gland size in young PARP-1-/- mice (6 weeks) compared with wild-type (WT) littermates. To determine the effect of PARP-1 functional loss on prostate cancer onset, PARP-1-/- mice were crossed with the transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Pathological assessment of prostate tumors revealed that TRAMP+/-, PARP-1-/- mice exhibited higher grade prostate tumors compared with TRAMP+/- PARP-1+/+ (16-28 weeks) that was associated with a significantly increased proliferative index and decreased apoptosis among the epithelial cells in TRAMP+/- PARP-1-/- prostate tumors. Furthermore tumors harboring PARP-1 loss, exhibited a downregulation of nuclear androgen receptor. Impairing PARP-1 led to increased levels of transforming growth factor-β (TGF-β) and Smads that correlated with induction of epithelial-mesenchymal transition (EMT), as established by loss of E-cadherin and β-catenin and upregulation of N-cadherin and ZEB-1. Our findings suggest that impaired PARP-1 function promotes prostate tumorigenesis in vivo via TGF-β-induced EMT. Defining the EMT control by PARP-1 during prostate cancer progression is of translational significance for optimizing PARP-1 therapeutic targeting and predicting response in metastatic castration-resistant prostate cancer.

PMA induces androgen receptor downregulation and cellular apoptosis in prostate cancer cells.

Phorbol 12-myristate 13-acetate (PMA) induces cellular apoptosis in prostate cancer cells, the growth of which is governed by androgen/androgen receptor (AR) signaling, but the mechanism by which PMA exerts this effect remains unknown. Therefore, in this study, we investigated the mechanistic action of PMA in prostate cancer cells with regard to AR. We showed that PMA decreased E2F1 as well as AR expression in androgen-dependent prostate cancer LNCaP cells. Furthermore, PMA activated JNK and p53 signaling, resulting in the induction of cellular apoptosis. In LNCaP cells, androgen deprivation and a novel anti-androgen enzalutamide (MDV3100) augmented cellular apoptosis induced by PMA. Moreover, castration-resistant prostate cancer (CRPC) C4-2 cells were more sensitive to PMA compared with LNCaP cells and were sensitized to PMA by enzalutamide. Finally, the expression of PKC, E2F1, and AR was diminished in PMA-resistant cells, indicating that the gain of independence from PKC, E2F1, and AR functions leads to PMA resistance. In conclusion, PMA exerted its anti-cancer effects via the activation of pro-apoptotic JNK/p53 and inhibition of pro-proliferative E2F1/AR in prostate cancer cells including CRPC cells. The therapeutic effects of PMA were augmented by androgen deletion and enzalutamide in androgen-dependent prostate cancer cells, as well as by enzalutamide in castration-resistant cells. Taken together, PMA derivatives may be promising therapeutic agents for treating prostate cancer patients including CRPC patients.

Pterostilbene-Isothiocyanate Conjugate Suppresses Growth of Prostate Cancer Cells Irrespective of Androgen Receptor Status

Chemotherapy and anti-hormonal therapies are the most common treatments for non-organ-confined prostate cancer (PCa). However, the effectiveness of these therapies is limited, thus necessitating the development of alternative approaches. The present study focused on analyzing the role of pterostilbene (PTER)-isothiocyanate (ITC) conjugate – a novel class of hybrid compound synthesized by appending an ITC moiety on PTER backbone – in regulating the functions of androgen receptor (AR), thereby causing apoptosis of PCa cells. The conjugate molecule caused 50% growth inhibition (IC50) at 40±1.12 and 45±1.50 μM in AR positive (LNCaP) and negative (PC-3) cells, respectively. The reduced proliferation of PC-3 as well as LNCaP cells by conjugate correlated with accumulation of cells in G2/M phase and induction of caspase dependent apoptosis. Both PI3K/Akt and MAPK/ERK pathways played an important and differential role in conjugate-induced apoptosis of these PCa cells. While the inhibitor of Akt (A6730) or Akt-specific small interference RNA (siRNA) greatly sensitized PC-3 cells to conjugate-induced apoptosis, on the contrary, apoptosis was accelerated by inhibition of ERK (by PD98059 or ERK siRNA) in case of LNCaP cells, both ultimately culminating in the expression of cleaved caspase-3 protein. Moreover, anti-androgenic activity of the conjugate was mediated by decreased expression of AR and its co-activators (SRC-1, GRIP-1), thus interfering in their interactions with AR. All these data suggests that conjugate-induced inhibition of cell proliferation and induction of apoptosis are partly mediated by the down regulation of AR, Akt, and ERK signaling. These observations provide a rationale for devising novel therapeutic approaches for treating PCa by using conjugate alone or in combination with other therapeutics.

Effects of triclocarban, N,N‐diethyl‐meta‐toluamide, and a mixture of pharmaceuticals and personal care products on fathead minnows (Pimephales promelas)

Pharmaceuticals and personal care products (PPCPs) have been detected widely in aquatic ecosystems, but little is known about their mechanisms of toxicity. We exposed adult fathead minnows (Pimephales promelas) for 48 h to triclocarban (1.4 µg/L), N,N-diethyl-meta-toluamide (DEET; 0.6 µg/L), or a mixture of PPCPs consisting of atenolol (1.5 µg/L), caffeine (0.25 µg/L), diphenhydramine (0.1 µg/L), gemfibrozil (1.5 µg/L), ibuprofen (0.4 µg/L), naproxen (1.6 µg/L), triclosan (2.3 µg/L), progesterone (0.2 µg/L), triclocarban (1.4 µg/L), and DEET (0.6 µg/L). Quantitative real-time polymerase chain reaction revealed an upregulation in vitellogenin (vtg) in livers of females and males exposed to triclocarban. Also, an upregulation of hepatic lipoprotein lipase (lpl) and a downregulation of androgen receptor (ar) and steroidogenic acute regulatory protein (star) were observed in testes. The group treated with DEET only showed a significant decrease in ar in females. In contrast, the PPCP mixture downregulated vtg in females and males and expression of estrogen receptor alpha (erα), star, and thyroid hormone receptor alpha 1 (thra1) in testes. The authors' results show that the molecular estrogenic effects of triclocarban are eliminated (males) or reversed (females) when dosed in conjunction with several other PPCP, once again demonstrating that results from single exposures could be vastly different from those observed with mixtures. Environ Toxicol Chem 2014;33:910-919. © 2013 SETAC.

The Interplay of AMP-Activated Protein Kinase and Androgen Receptor in Prostate Cancer Cells

AMP-activated protein kinase (AMPK) has recently emerged as a potential target for cancer therapy due to the observation that activation of AMPK inhibits tumor cell growth. It is well-known that androgen receptor (AR) signaling is a major driver for the development and progression of prostate cancer and that downregulation of AR is a critical step in the induction of apoptosis in prostate cancer cells. However, little is known about the potential interaction between AMPK and AR signaling pathways. In the current study, we showed that activation of AMPK by metformin caused decrease of AR protein level through suppression of AR mRNA expression and promotion of AR protein degradation, demonstrating that AMPK activation is upstream of AR downregulation. We also showed that inhibition of AR function by an anti-androgen or its siRNA enhanced AMPK activation and growth inhibition whereas overexpression of AR delayed AMPK activation and increased prostate cancer cellular resistance to metformin treatment, suggesting that AR suppresses AMPK signaling-mediated growth inhibition in a feedback mechanism. Our findings thus reveal a novel AMPK-AR regulatory loop in prostate cancer cells and should have a potential clinical significance.

FOXA1 promotes tumor cell proliferation through AR involving the Notch pathway in endometrial cancer

BackgroundIncreasing evidence suggests that forkhead box A1 (FOXA1) is frequently dysregulated in many types of human cancers. However, the exact function and mechanism of FOXA1 in human endometrial cancer (EC) remains unclear.MethodsFOXA1 expression, androgen receptor (AR) expression, and the relationships of these two markers with clinicopathological factors were determined by immunohistochemistry analysis. FOXA1 and AR were up-regulated by transient transfection with plasmids, and were down-regulated by transfection with siRNA or short hairpin RNA (shRNA). The effects of FOXA1 depletion and FOXA1 overexpression on AR-mediated transcription as well as Notch pathway and their impact on EC cell proliferation were examined by qRT-PCR, western blotting, co-immunoprecipitation, ChIP-PCR, MTT, colony-formation, and xenograft tumor–formation assays.ResultsWe found that the expression of FOXA1 and AR in ECs was significantly higher than that in a typical hyperplasia and normal tissues. FOXA1 expression was significantly correlated with AR expression in clinical tissues. High FOXA1 levels positively correlated with pathological grade and depth of myometrial invasion in EC. High AR levels also positively correlated with pathological grade in EC. Moreover, the expression of XBP1, MYC, ZBTB16, and UHRF1, which are downstream targets of AR, was promoted by FOXA1 up-regulation or inhibited by FOXA1 down-regulation. Co-immunoprecipitation showed that FOXA1 interacted with AR in EC cells. ChIP-PCR assays showed that FOXA1 and AR could directly bind to the promoter and enhancer regions upstream of MYC. Mechanistic investigation revealed that over-expression of Notch1 and Hes1 proteins by FOXA1 could be reversed by AR depletion. In addition, we showed that down-regulation of AR attenuated FOXA1-up-regulated cell proliferation. However, AR didn’t influence the promotion effect of FOXA1 on cell migration and invasion. In vivo xenograft model, FOXA1 knockdown reduced the rate of tumor growth.ConclusionsThese results suggest that FOXA1 promotes cell proliferation by AR and activates Notch pathway. It indicated that FOXA1 and AR may serve as potential gene therapy in EC.

RANK-mediated signaling network and cancer metastasis

Cancer metastasis is highly inefficient and complex. Common features of metastatic cancer cells have been observed using cancer cell lines and genetically reconstituted mouse and human tumor xenograft models. These include cancer cell interaction with the tumor microenvironment and the ability of cancer cells to sense extracellular stimuli and adapt to adverse growth conditions. This review summarizes the coordinated response of cancer cells to soluble growth factors, such as RANKL, by a unique feed forward mechanism employing coordinated upregulation of RANKL and c-Met with downregulation of androgen receptor. The RANK-mediated signal network was found to drive epithelial to mesenchymal transition in prostate cancer cells, promote osteomimicry and the ability of prostate cancer cells to assume stem cell and neuroendocrine phenotypes, and confer the ability of prostate cancer cells to home to bone. Prostate cancer cells with activated RANK-mediated signal network were observed to recruit and even transform the non-tumorigenic prostate cancer cells to participate in bone and soft tissue colonization. The coordinated regulation of cancer cell invasion and metastasis by the feed forward mechanism involving RANKL, c-Met, transcription factors, and VEGF-neuropilin could offer new therapeutic opportunities to target prostate cancer bone and soft tissue metastases.

Androgen receptor signaling in prostate cancer

The androgen receptor (AR), ligand-induced transcription factor, is expressed in primary prostate cancer and in metastases. AR regulates multiple cellular events, proliferation, apoptosis, migration, invasion, and differentiation. Its expression in prostate cancer cells is regulated by steroid and peptide hormones. AR downregulation by various compounds which are contained in fruits and vegetables is considered a chemopreventive strategy for prostate cancer. There is a bidirectional interaction between the AR and micro-RNA (miRNA) in prostate cancer; androgens may upregulate or downregulate the selected miRNA, whereas the AR itself is a target of miRNA. AR mutations have been discovered in prostate cancer, and their incidence may increase with tumor progression. AR mutations and increased expression of selected coactivators contribute to the acquisition of agonistic properties of anti-androgens. Expression of some of the coactivators is enhanced during androgen ablation. AR activity is regulated by peptides such as cytokines or growth factors which reduce the concentration of androgen required for maximal stimulation of the receptor. In prostate cancer, variant ARs which exhibit constitutive activity were detected. Novel therapies which interfere with intracrine synthesis of androgens or inhibit nuclear translocation of the AR have been introduced in the clinic.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

EP2 signaling mediates suppressive effects of celecoxib on androgen receptor expression and cell proliferation in prostate cancer

Non-steroidal anti-inflammatory drugs inhibit the activity of cyclooxygenases (COXs), and their usage reduces the risks associated with prostate cancer. Celecoxib is a selective COX-2 inhibitor and reported to prevent the progression of prostate cancer. However, the mechanisms involved remain unclear. In this study, we investigated the suppression of prostate cancer growth by celecoxib and elucidated the biological relevance of the inhibited pathway in prostate cancer cell lines. Western blotting, quantitative real-time PCR and cell proliferation assay were used to resolve the mechanism of celecoxib in prostate cancer cell line PC3, LNCaP and their derivatives. Celecoxib induced apoptosis and downregulated EP2, CREB and androgen receptor (AR). Moreover, EP2 antagonist downregulated CREB as well as COX-2 and AR, resulting in the suppression of cell proliferation. Furthermore, EP2 and CREB knockdown induced AR downregulation, indicating that AR suppression by celecoxib is mediated by EP2/CREB signaling. Celecoxib exerts antitumor activity through EP2 signaling regulating AR and COX-2 expression. Furthermore, in addition to celecoxib, therapeutics targeting EP2 may also be promising against prostate cancers.

Diabetes Protects from Prostate Cancer by Downregulating Androgen Receptor: New Insights from LNCaP Cells and PAC120 Mouse Model

Type 2 diabetes has been associated with decreased risk of prostate cancer in observational studies, and this inverse association has been recently confirmed in several large cohort studies. However the mechanisms involved in this protective effect remain to be elucidated. The aim of the present study was to explore whether different features of type 2 diabetes (hyperinsulinemia, hyperglycemia and tumor necrosis factor alpha [TNF-α]) protect against the development of prostate cancer. For this purpose LNCaP cells were used for in vitro experiments and nude mice in which PAC120 (hormone-dependent human prostate cancer) xenografts had been implanted were used for in vivo examinations. We provide evidence that increasing glucose concentrations downregulate androgen receptor (AR) mRNA and protein levels through NF-κB activation in LNCaP cells. Moreover, there was a synergic effect of glucose and TNFα in downregulating the AR in LNCaP cells. By contrast, insulin had no effect on AR regulation. In vivo experiments showed that streptozotocin-induced diabetes (STZ-DM) produces tumor growth retardation and a significant reduction in AR expression in PAC120 prostate cancer mice. In conclusion, our results suggest that hyperglycemia and TNF-α play an important role in protecting against prostate cancer by reducing androgen receptor levels via NF-κB.

RhoGDIα downregulates androgen receptor signaling in prostate cancer cells

Treatment of primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state due to aberrant activation of androgen receptor (AR). Understanding the mechanisms leading to the aberrant activation of AR is critical to develop effective therapy. We have previously identified Rho GDP Dissociation Inhibitor alpha (GDIα) as a novel suppressor in prostate cancer. In this study, we examine the effect of GDIα on AR signaling in prostate cancer cells. GDIα was transiently or stably transfected into several prostate cancer cell lines including LNCaP, C4-2, CWR22Rv1, and DU145. The regulation of AR expression by GDIα was analyzed by qRT-PCR and Western blot. AR activity was measured by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Immunofluorescence assay was performed to study AR nuclear translocation. The interaction between GDIα and AR was examined by co-immunoprecipitation assays. In this study, we have identified GDIα as a negative regulator of AR signaling pathway. Overexpression of GDIα downregulates AR expression at both mRNA and protein levels. Overexpression of GDIα is able to prevent AR nuclear translocation and inhibit transactivation of AR target genes. Co-immunoprecipitation assays showed that GDIα physically interacts with the N-terminal domain of AR. GDIα suppresses AR signaling through inhibition of AR expression, nuclear translocation, and recruitment to androgen-responsive genes. GDIα regulatory pathway may play a critical role in regulating AR signaling and prostate cancer growth and progression.

Experimental varicocoele in rats affects mechanisms that control expression and function of the androgen receptor

Varicocoele is an important cause of male infertility. Normal male reproductive function and fertility depends on a delicate balance between androgen receptor (AR) and the classic oestrogen receptors ESR1 (ERα) and ESR2 (ERβ). Using a model of surgically induced varicocoele in rats, this study aimed to investigate the effects of varicocoele on the expression of AR, ESR1, ESR2 and G-protein coupled oestrogen receptor (GPER). Varicocoele did not affect the mRNA and protein expression of ESR1 and ESR2 in both testes. Varicocoele did not affect the mRNA and protein expression of GPER in the right testis, but slightly reduced the mRNA and increased the protein levels in the left testis. Varicocoele did not affect the mRNA for AR, but reduced the protein levels in both testes. A proteomic approach was used in an attempt to find differentially expressed targets with possible correlation with AR downregulation. Varicocoele caused the differential expression of 29 proteins. Six proteins were upregulated, including the receptor for activated C kinase 1 (RACK1), and 23 were downregulated, including dihydrolipoamide dehydrogenase, alpha-enolase and pyrophosphatase 1. Western blot analysis confirmed that varicocoele upregulated the expression of RACK1, a protein involved with tyrosine phosphorylation and regulation of AR transcriptional activity, AR metabolism and dynamics of the blood-testis barrier. In conclusion, this study suggests that varicocoele affects mechanisms that control AR expression and function. This regulation of AR may play an important role in the varicocoele-induced testicular dysfunction. Furthermore, varicocoele downregulates several other proteins in the testis that may be useful markers of spermatozoa function and male infertility.

Infiltrating bone marrow mesenchymal stem cells increase prostate cancer stem cell population and metastatic ability via secreting cytokines to suppress androgen receptor signaling

Although the contribution of the bone marrow mesenchymal stem cells (BM-MSCs) in cancer progression is emerging, their potential roles in prostate cancer (PCa) remain unclear. Here, we showed that PCa cells could recruit BM-MSCs and consequently the metastatic ability of PCa cells was increased. We also found that the increased metastatic ability of PCa cells could be due to the increased PCa stem cell population. Mechanism dissection studies found that the upregulation of Chemokine ligand 5 (CCL5) expression in BM-MSCs and PCa cells, after MSCs infiltrated into the PCa cells, subsequently downregulated androgen receptor (AR) signaling, which was due to inhibition of AR nuclear translocation. Interruption of such signaling led to suppression of the BM-MSCs-induced PCa stem cell population increase and thereby inhibited the metastatic ability of PCa cells. The PCa stem cell increase then led to the upregulation of matrix metalloproteinase 9, ZEB-1, CD133 and CXCR4 molecules, and enhanced the metastatic ability of PCa cells. Therefore, we conclude that the BM-MSCs-mediated increased metastatic ability of PCa cells can be due to the PCa stem cell increase via alteration of the CCL5-AR signaling pathway. Together, these results uncover the important roles of BM-MSCs as key components in the prostate tumor microenvironment to promote PCa metastasis and may provide a new potential target to suppress PCa metastasis by blocking BM-MSCs infiltration into PCa.