The mutant androgen receptor T877A mediates the proliferative but not the cytotoxic dose-dependent effects of genistein and quercetin on human LNCaP prostate cancer cells

Prostate as a target of endocrine disrupting chemicals: Relevance, pathways, assays

Prostate, the main accessory gland of the male reproductive system, is a critical but yet overlooked target for Endocrine Disruptors (EDs), affecting the male reproductive system. Prostate is essential for male fertility; indeed, the prostatic fluid is the main component of seminal fluid, which is essential for the activation and capacitation of sperm cells. Furthermore, the prostate is tightly regulated by androgen signaling and is an important site for endocrine-related tumorigenesis. The following systematic review assesses and discusses the available literature evidence regarding the use of the androgen-dependent human prostate cell line LNCaP, in which up- or down-regulation of androgen signaling is assessed by measuring a clinically relevant marker, the Prostate-Specific Antigen (PSA). The data set is still limited: 30 articles, mainly dealing on natural substances and plant extracts, met the eligibility criteria. However, the results support the potential of the PSA assay testing on LNCaP cells in evaluating endocrine-related effects on prostate function as well as to identifying substances that may affect androgen-regulated pathways. Overall, the findings encourage further investigations with a broader range of substances with different modes of action.

Identification of selective SWI/SNF dependencies in enzalutamide-resistant prostate cancer

Enzalutamide is a potent second-generation antiandrogen commonly used to treat hormone-sensitive and castration-resistant prostate cancer (CRPC) patients. While initially effective, the disease almost always develops resistance. Given that many enzalutamide-resistant tumors lack specific somatic mutations, there is strong evidence that epigenetic factors can cause enzalutamide resistance. To explore how resistance arises, we systematically test all epigenetic modifiers in several models of castration-resistant and enzalutamide-resistant prostate cancer with a custom epigenetic CRISPR library. From this, we identify and validate SMARCC2, a core component of the SWI/SNF complex, that is selectivity essential in enzalutamide-resistant models. We show that the chromatin occupancy of SMARCC2 and BRG1 is expanded in enzalutamide resistance at regions that overlap with CRPC-associated transcription factors that are accessible in CRPC clinical samples. Overall, our study reveals a regulatory role for SMARCC2 in enzalutamide-resistant prostate cancer and supports the feasibility of targeting the SWI/SNF complex in late-stage PCa.

The Metastasis Suppressor NDRG1 Directly Regulates Androgen Receptor Signaling in Prostate Cancer

N-myc-downregulated gene 1 (NDRG1) has potent anticancer effects and inhibits cell growth, survival, metastasis, and angiogenesis. Previous studies suggested that NDRG1 is linked to the androgen signaling network, but this mechanistic relationship is unclear. Considering the crucial role of the androgen receptor (AR) in prostate cancer (PCa) progression, here we examined for the first time the effect of NDRG1 on AR expression, activation, and downstream signaling in LNCaP, 22Rv1, and C4-2B PCa cell types. We demonstrate that NDRG1 effectively promotes interaction of AR with the chaperone HSP90, which in turn stabilizes the AR while decreasing its androgen-mediated activation. The expression of NDRG1 suppressed: (1) AR activation, as measured by p-AR^Ser213 and p-AR^Ser81; (2) expression of a major AR transcriptional target, prostate-specific antigen (PSA); and (3) AR transcriptional activity, probably via inhibiting the c-Jun-AR interaction by reducing c-Jun phosphorylation (p-c-Jun^Ser63). NDRG1 was also demonstrated to inhibit multiple key molecules involved in androgen-dependent and -independent signaling (namely EGFR, HER2, HER3, PI3K, STAT3, and NF-κB), which promote the development of castration-resistant prostate cancer. We also identified the cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) domain of NDRG1 as vital for inhibition of AR activity. Examining NDRG1 and p-NDRG1 in PCa patient specimens revealed a significant negative correlation between NDRG1 and PSA levels in prostatectomy patients that went on to develop metastasis. These results highlight a vital role for NDRG1 in androgen signaling and its potential as a key therapeutic target and biomarker in PCa.

Binding of Androgen- and Estrogen-Like Flavonoids to Their Cognate (Non)Nuclear Receptors: A Comparison by Computational Prediction

Flavonoids are plant bioactives that are recognized as hormone-like polyphenols because of their similarity to the endogenous sex steroids 17β-estradiol and testosterone, and to their estrogen- and androgen-like activity. Most efforts to verify flavonoid binding to nuclear receptors (NRs) and explain their action have been focused on ERα, while less attention has been paid to other nuclear and non-nuclear membrane androgen and estrogen receptors. Here, we investigate six flavonoids (apigenin, genistein, luteolin, naringenin, quercetin, and resveratrol) that are widely present in fruits and vegetables, and often used as replacement therapy in menopause. We performed comparative computational docking simulations to predict their capability of binding nuclear receptors ERα, ERβ, ERRβ, ERRγ, androgen receptor (AR), and its variant ART877A and membrane receptors for androgens, i.e., ZIP9, GPRC6A, OXER1, TRPM8, and estrogens, i.e., G Protein-Coupled Estrogen Receptor (GPER). In agreement with data reported in literature, our results suggest that these flavonoids show a relevant degree of complementarity with both estrogen and androgen NR binding sites, likely triggering genomic-mediated effects. It is noteworthy that reliable protein-ligand complexes and estimated interaction energies were also obtained for some suggested estrogen and androgen membrane receptors, indicating that flavonoids could also exert non-genomic actions. Further investigations are needed to clarify flavonoid multiple genomic and non-genomic effects. Caution in their administration could be necessary, until the safe assumption of these natural molecules that are largely present in food is assured.

Modulation of Human Sperm Mitochondrial Respiration Efficiency by Plant Polyphenols

Plant bioactives, such as polyphenols, can differentially affect (positively or negatively) sperm quality, depending on their concentration. These molecules have been proposed as natural scavengers of reactive oxygen species (ROS) for male infertility treatment. However, few data are available about their effects on the molecular mechanisms related to sperm quality and, in particular, to sperm mitochondrial function. We investigated the effects of quercetin, naringenin, genistein, apigenin, luteolin, and resveratrol at the concentration of 0.1-1000 nM on mitochondrial respiration efficiency. Upon chemical exposure, spermatozoa were swollen in a hypotonic solution and used for polarographic assays of mitochondrial respiration. All tested compounds, except for apigenin, caused a significant increase in the mitochondrial respiration efficiency at the concentration of 0.1 nM, and a significant decrease starting from concentrations of 10 nM. The analysis of oxygen consumption rate in the active and in the resting state of mitochondrial respiration suggested different mechanisms by which the tested compounds modulate mitochondrial function. Therefore, by virtue of their ability to stimulate the respiration active state, quercetin, genistein, and luteolin were found to improve mitochondrial function in asthenozoospermic samples. Our results are relevant to the debate on the promises and perils of natural antioxidants in nutraceutical supplementation.

Regulation of the neuroendocrine axis in male rats by soy-based diets is independent of age and due specifically to isoflavone action†

Soy-based foods are consumed for their health beneficial effects, implying that the population is exposed to soy isoflavones in the diet. Herein, male rats at 21, 35, and 75 days of age were maintained either on a casein control diet, soybean meal (SBM), or control diet supplemented with daidzin and genistin (G + D) for 14 days. Feeding of SBM and G + D diets decreased testicular testosterone (T) secretion regardless of age. Altered androgen secretion was due to decreased (P < 0.05) Star and Hsd17β protein in the testes and was associated with increased (P < 0.05) Lhβ and Fshβ subunit protein expression in pituitary glands. Second, male rats were fed either a casein control diet, control diet + daidzin, control diet + genistin, or control diet + genistin + daidzin (G + D). Compared to control, feeding of all isoflavone-containing diets decreased (P < 0.05) testicular T concentrations, and more so in the G + D diet group. Interestingly, Esr1 and androgen receptor protein and pituitary Fshβ with Lhβ subunit protein were increased (P < 0.05) by feeding of genistin and G + D diets, but not the daidzin diet. However, daidzein and genistein both caused a concentration dependent inhibition (P < 0.05) of T secretion by Leydig cells in vitro with IC50 of 184 ηM and 36 ηM, respectively. Results demonstrated that altered testicular steroidogenic capacity and pituitary FSHβ and LHβ subunit expression due to soy-based diets result from specific actions by genistein and daidzein. Experiments to assess effects of isoflavone regulation of intratesticular androgen concentrations on male fertility are warranted.

Effects of Isolated Isoflavones Intake on Health

BACKGROUND

Isoflavones are naturally occurring flavonoids, commonly found in the food consumed for centuries in the East-Asian population, characterized by a structure able to exert nonsteroidal estrogen-like activity on human cells. They have attracted researcher interest all around the word, following the results obtained in epidemiological and clinical studies. The involvement of isoflavones and their metabolites in various biological processes suggests that they can influence several metabolic pathways and can influence the gene expression at epigenetic level, involving effects that probably are due to early life exposure. They show positive health effects on several diseases, especially in the prevention of coronary heart and neurological diseases, hormone-related cancers, osteoporosis, and postmenopausal symptoms.

METHODS

We have performed a critical evaluation of available literature trough a structured search of bibliographic databases about isoflavones health promoting properties, risk assessment and mechanisms of action. In addition, we supplied useful information on their biochemical properties, sources and bioavailability.

RESULTS

Although these molecules have been the subjects of numerous researches, their role for the wellness of the human organism remains controversial. Moreover, there are substantial inconsistencies between the results obtained by epidemiologic studies conducted on Eastern population, which found high health promoting properties, and Western clinical trials, which found much less positive effects.

CONCLUSION

Further epidemiologic studies and well-designed prospective human studies are to determine the beneficial effects of isoflavones exposure, as well as establishing its safe therapeutic.

Androgen receptor and soy isoflavones in prostate cancer

Androgens and androgen receptor (AR) play a critical role not only in normal prostate development, but also in prostate cancer. For that reason, androgen deprivation therapy (ADT) is the primary treatment for prostate cancer. However, the majority of patients develop castration-resistant prostate cancer, which eventually leads to mortality. Novel therapeutic approaches, including dietary changes, have been explored. Soy isoflavones have become a focus of interest because of their positive health benefits on numerous diseases, particularly hormone-related cancers, including prostate and breast cancers. An important strategy for the prevention and/or treatment of prostate cancer might thus be the action of soy isoflavones on the AR signaling pathway. The current review article provides a detailed overview of the anticancer potential of soy isoflavones (genistein, daidzein and glycitein), as mediated by their effect on AR.

Design, synthesis, and evaluation of the antiproliferative activity of hydantoin-derived antiandrogen-genistein conjugates

Androgen receptor (AR) signaling is vital to the viability of all forms of prostate cancer (PCa). With the goal of investigating the effect of simultaneous inhibition and depletion of AR on viability of PCa cells, we designed, synthesized and characterized the bioactivities of bifunctional agents which incorporate the independent cancer killing properties of an antiandrogen and genistein, and the AR downregulation effect of genistein within a single molecular template. We observed that a representative conjugate, 9b, is much more cytotoxic to both LNCaP and DU145 cells relative to the antiandrogen and genistein building blocks as single agents or their combination. Moreover, conjugate 9b more effectively down regulates cellular AR protein levels relative to genistein and induces S phase cell cycle arrest. The promising bioactivities of these conjugates warrant further investigation.

Bioactive natural products for chemoprevention and treatment of castration-resistant prostate cancer

Prostate cancer (PCa), a hormonally-driven cancer, ranks first in incidence and second in cancer related mortality in men in most Western industrialized countries. Androgen and androgen receptor (AR) are the dominant modulators of PCa growth. Over the last two decades multiple advancements in screening, treatment, surveillance and palliative care of PCa have significantly increased quality of life and survival following diagnosis. However, over 20% of patients initially diagnosed with PCa still develop an aggressive and treatment-refractory disease. Prevention or treatment for hormone-refractory PCa using bioactive compounds from marine sponges, mushrooms, and edible plants either as single agents or as adjuvants to existing therapy, has not been clinically successful. Major advancements have been made in the identification, testing and modification of the existing molecular structures of natural products. Additionally, conjugation of these compounds to novel matrices has enhanced their bio-availability; a big step towards bringing natural products to clinical trials. Natural products derived from edible plants (nutraceuticals), and common folk-medicines might offer advantages over synthetic compounds due to their broader range of targets, as compared to mostly single target synthetic anticancer compounds; e.g. kinase inhibitors. The use of synthetic inhibitors or antibodies that target a single aberrant molecule in cancer cells might be in part responsible for emergence of treatment refractory cancers. Nutraceuticals that target AR signaling (epigallocatechin gallate [EGCG], curcumin, and 5α-reductase inhibitors), AR synthesis (ericifolin, capsaicin and others) or AR degradation (betulinic acid, di-indolyl diamine, sulphoraphane, silibinin and others) are prime candidates for use as adjuvant or mono-therapies. Nutraceuticals target multiple pathophysiological mechanisms involved during cancer development and progression and thus have potential to simultaneously inhibit both prostate cancer growth and metastatic progression (e.g., inhibition of angiogenesis, epithelial-mesenchymal transition (EMT) and proliferation). Given their multi-targeting properties along with relatively lower systemic toxicity, these compounds offer significant therapeutic advantages for prevention and treatment of PCa. This review emphasizes the potential application of some of the well-researched natural compounds that target AR for prevention and therapy of PCa.

Synthesis and Anti-Proliferative Effects of Quercetin Derivatives

Prostate cancer is the most common diagnosed invasive cancer in American men and is the second leading cause of cancer-related deaths. Although there are several therapies successful in treating early, localized stage prostate cancer, current treatment of advanced metastatic castration-resistant prostate cancer remains ineffective due to inevitable progression of resistance to first-line treatment with docetaxel. The natural product quercetin (3,3′,4′,5,7-pentahydroxyflavone), a flavonoid compound ubiquitous in dietary plants, possesses evidenced potential in treating advanced metastatic castration-resistant prostate cancer. However, its poor bioavailability and moderate potency hinder its advancement into clinical therapy. In order to engineer quercetin derivatives with improved potency and pharmacokinetic profiles for the treatment of advanced metastatic prostate cancer, we started this study with creating a small library of alkylated derivatives of quercetin for in vitro evaluation. The biological data and chemical reactivity of quercetin and its derivatives reported in literature directed us to design 3,4′,7- O-trialkylquercetins as our first batch of targets. Consequently, nine 3,4′,7- O-trialkylquercetins, together with four 3,7- O-dialkylquercetins, four 3,3′,4′,7-tetraalkylquercetins, and one 3,3′,4′- O-trialkylquercetin, were prepared by one step O-alkylation of commercially available quercetin mediated by potassium carbonate. Their structures were determined by 1D and 2D NMR data, and HRMS. Their anti-proliferative activities towards both androgen-refractory and androgen-sensitive prostate cancer cells were evaluated using WST-1 cell proliferation assay. The acquired structure-activity relationships indicate that 3,7- O-dialkylquercetins rather than 3,4′,7- O-trialkylquercetins were much more potent than quercetin towards prostate cancer cells.

Anti-androgenic effects of flavonols in prostate cancer

Dietary-derived agents, such as the flavonoids, are of particular interest for prostate cancer (PCa) chemoprevention as they may offer a favourable safety and side-effect profile. An agent that demonstrates action on the androgen receptor (AR) axis may have value for preventing or treating castrate-resistant PCa. Four main flavonols - quercetin, myricetin, kaempferol, and fisetin - have been demonstrated in laboratory studies to have chemopreventive action in both castrate-resistant and castrate-sensitive PCa models. Mechanisms of flavonol action on the AR axis in PCa have been proposed to be inhibition of the 5α-reductase enzymes, direct androgen competition, suppression of the AR complex and transactivation by coregulators such as c-Jun, Sp1, and the PI3K/Akt pathway. It is, however, still unclear with current levels of evidence whether AR axis-mediated effects can fully account for the flavonols' chemopreventive action.

Yang-tonifying traditional Chinese medicinal plants and their potential phytoandrogenic activity

The concept of phytoandrogens, plants that contain androgens or those that stimulate androgenic activity in men, is relatively new. In traditional Chinese medicine a number of phytoandrogens are classified in medicinal plant restoratives for reinforcing yang, and they find their application in the treatment of the kidney yang deficiency diseases. In this review, the phytoandrogens used in traditional Chinese medicine are listed, and their proven applications in the treatment of kidney yang deficiency diseases, such as sexual disorders, cancer, and obesity and associated metabolic syndromes are presented. As a background, the mechanism of action of androgens, their synthesis and metabolism, the interrelations of androgens and estrogens, as well as the state of art methods to detect and analyze these hormonal activities in medicinal plants are discussed.

Design, Synthesis, and Evaluation of Genistein Analogues as Anti-Cancer Agents

Genistein is a bioactive isoflavone derived from soybeans. The tie-in between the intake of genistein and the decreased incidence of some solid tumors (including prostate cancer) has been demonstrated by epidemiological studies. The potential of genistein in treating prostate cancer has also been displayed by in vitro cell-based and in vivo animal experiments. Genistein has entered clinical trials for both chemoprevention and potential treatment of prostate cancer. Even though the low oral bioavailability has presented the major challenges to genistein's further clinical development, chemical modulation of genistein holds the promise to generate potential anti-prostate cancer agents with enhanced potency and/or better pharmacokinetic profiles than genistein. As part of our ongoing project to develop natural products-based anti-prostate cancer agents, the current study was undertaken to synthesize eight genistein analogues for cytotoxic evaluation in three prostate cancer cell lines (PC-3, DU-145, LNCaP; both androgen-sensitive and androgen-refractory cell lines), as well as one aggressive cervical cancer cell line (HeLa). Eight genistein analogues have been successfully synthesized with Suzuki-Miyaura coupling reaction as a key step. Their in vitro anti-cancer potential was evaluated by trypan blue exclusion assay and WST-1 cell proliferation assay against a panel of four human cancer cell lines. The acquired data suggest i) that the C-5 and C-7 hydroxyl groups in genistein are very important for the cytotoxicity and anti-proliferative activity; and ii) that 1-alkyl-1H-pyrazol-4-yl and pyridine-3-yl might act as good bioisosteres for the 4'-hydroxyphenyl moiety in genistein.

Soy isoflavones and prostate cancer: a review of molecular mechanisms

Soy isoflavones are dietary components for which an association has been demonstrated with reduced risk of prostate cancer (PCa) in Asian populations. However, the exact mechanism by which these isoflavones may prevent the development or progression of PCa is not completely understood. There are a growing number of animal and in vitro studies that have attempted to elucidate these mechanisms. The predominant and most biologically active isoflavones in soy products, genistein, daidzein, equol, and glycetin, inhibit prostate carcinogenesis in some animal models. Cell-based studies show that soy isoflavones regulate genes that control cell cycle and apoptosis. In this review, we discuss the literature relevant to the molecular events that may account for the benefit of soy isoflavones in PCa prevention or treatment. These reports show that although soy isoflavone-induced growth arrest and apoptosis of PCa cells are plausible mechanisms, other chemo protective mechanisms are also worthy of consideration. These possible mechanisms include antioxidant defense, DNA repair, inhibition of angiogenesis and metastasis, potentiation of radio- and chemotherapeutic agents, and antagonism of estrogen- and androgen-mediated signaling pathways. Moreover, other cells in the cancer milieu, such as the fibroblastic stromal cells, endothelial cells, and immune cells, may be targeted by soy isoflavones, which may contribute to soy-mediated prostate cancer prevention. In this review, these mechanisms are discussed along with considerations about the doses and the preclinical models that have been used.

The hurdle of antiandrogen drug resistance: drug design strategies

INTRODUCTION

Prostate cancer is the second most common cancer death in men after lung cancer, due to distant metastases. While distant prostate cancer is typically castrate resistant, it is not necessarily androgen independent. For this reason, a review of the literature regarding the pathways involved in androgen signaling and therapeutic regimens to treat distant metastases is beneficial to increasing the survival rate of prostate cancer patients.

AREAS COVERED

In this article, the author reviews the literature from the past decade covering metastatic hormone refractory prostate cancer with the aim to examine and identify pathways, therapeutic targets and current therapies for treating castrate-resistant disease. As this area is lacking, the author aims to provide the reader with knowledge of the molecular consequences of castrate resistant prostate cancer, the current treatment paradigms and future directions.

EXPERT OPINION

While there have been advances in the treatment of castrate resistant prostate cancer, only minimal advances have been made in overall survival rate. Due to aberrant mutations and activation in the androgen receptor gene, and the complexity of cell signaling within prostate cancer, the androgen receptor should remain a main target for drug discovery efforts. This author believes that designing compounds that will reduce the activation of the androgen receptor may hold the key to a cure in the future.

Differential effects of genistein on prostate cancer cells depend on mutational status of the androgen receptor

Blocking the androgen receptor (AR) activity is the main goal of therapies for advanced prostate cancer (PCa). However, relapse with a more aggressive, hormone refractory PCa arises, which harbors restored AR activity. One mechanism of such reactivation occurs through acquisition of AR mutations that enable its activation by various steroidal and non-steroidal structures. Thus, natural and chemical compounds that contribute to inappropriate (androgen-independent) activation of the AR become an area of intensive research. Here, we demonstrate that genistein, a soy phytoestrogen binds to both the wild and the Thr877Ala (T877A) mutant types of AR competitively with androgen, nevertheless, it exerts a pleiotropic effect on PCa cell proliferation and AR activity depending on the mutational status of the AR. Genistein inhibited, in a dose-dependent way, cell proliferation and AR nuclear localization and expression in LAPC-4 cells that have wild AR. However, in LNCaP cells that express the T877A mutant AR, genistein induced a biphasic effect where physiological doses (0.5-5 µmol/L) stimulated cell growth and increased AR expression and transcriptional activity, and higher doses induced inhibitory effects. Similar biphasic results were achieved in PC-3 cells transfected with AR mutants; T877A, W741C and H874Y. These findings suggest that genistein, at physiological concentrations, potentially act as an agonist and activate the mutant AR that can be present in advanced PCa after androgen ablation therapy.

Aggressive prostate cancer is prevented in ERαKO mice and stimulated in ERβKO TRAMP mice

Previous evidence suggests soy genistein may be protective against prostate cancer, but whether this protection involves an estrogen receptor (ER)-dependent mechanism is unknown. To test the hypothesis that phytoestrogens may act through ERα or ERβ to play a protective role against prostate cancer, we bred transgenic mice lacking functional ERα or ERβ with transgenic adenocarcinoma of mouse prostate (TRAMP) mice. Dietary genistein reduced the incidence of cancer in ER wild-type (WT)/transgenic adenocarcinoma of mouse prostate mice but not in ERα knockout (KO) or ERβKO mice. Cancer incidence was 70% in ERWT mice fed the control diet compared with 47% in ERWT mice fed low-dose genistein (300 mg/kg) and 32% on the high-dose genistein (750 mg/kg). Surprisingly, genistein only affected the well differentiated carcinoma (WDC) incidence but had no effect on poorly differentiated carcinoma (PDC). No dietary effects have been observed in either of the ERKO animals. We observed a very strong genotypic influence on PDC incidence, a protective effect in ERαKO (only 5% developed PDC), compared with 19% in the ERWT, and an increase in the incidence of PDC in ERβKO mice to 41%. Interestingly, immunohistochemical analysis showed ERα expression changing from nonnuclear in WDC to nuclear in PDC, with little change in ERβ location or expression. In conclusion, genistein is able to inhibit WDC in the presence of both ERs, but the effect of estrogen signaling on PDC is dominant over any dietary treatment, suggesting that improved differential targeting of ERα vs. ERβ would result in prevention of advanced prostate cancer.

Preferential induction of G1 arrest in androgen-responsive human prostate cancer cells by androgen receptor signaling antagonists DL3 and antiandrogen bicalutamide

The purpose of this study was to further characterize cell growth-inhibitory effects of a recently identified androgen receptor (AR) signaling inhibitor 6-amino-2-[2-(4-tert-butyl-pnenoxy)-ethylsulfanyl]-1H-pyrimidin-4-one (DL3)(5) and antiandrogen bicalutamide (Bic). DL3 was more potent than Bic in induction of G1 arrest and reduction of G1-related cell cycle protein expression in AR-positive LNCaP cells. DL3, but not Bic, moderately inhibited growth of AR-negative PC-3 cells independent of G1 arrest. The data indicated that DL3 inhibit cell growth in both AR-dependent and -independent manners and is potentially a potent therapeutic agent for the management of advanced human prostate cancer.

Isoflavones and the prevention of breast and prostate cancer: new perspectives opened by nutrigenomics

Epidemiological evidence together with preclinical data from animal and in vitro studies strongly support a correlation between soy isoflavone consumption and protection towards breast and prostate cancers. The biological processes modulated by isoflavones, and especially by genistein, have been extensively studied, yet without leading to a clear understanding of the cellular and molecular mechanisms of action involved. This review discusses the existing gaps in our knowledge and evaluates the potential of the new nutrigenomic approaches to improve the study of the molecular effects of isoflavones. Several issues need to be taken into account for the proper interpretation of the results already published for isoflavones. Too often knowledge on isoflavone bioavailability is not taken into account; supra-physiological doses are frequently used. Characterization of the individual variability as defined by the gut microflora composition and gene polymorphisms may also help to explain the discrepancies observed so far in the clinical studies. Finally, the complex inter-relations existing between tissues and cell types as well as cross-talks between metabolic and signalling pathways have been insufficiently considered. By appraising critically the abundant literature with these considerations in mind, the mechanisms of action that are the more likely to play a role in the preventive effects of isoflavones towards breast and prostate cancers are reviewed. Furthermore, the new perspectives opened by the use of genetic, transcriptomic, proteomic and metabolomic approaches are highlighted.

Androgen receptor transactivation assay using green fluorescent protein as a reporter

For screening of a large number of samples for androgenic activity, a robust system with minimal handling is required. The coding sequence for human androgen receptor (AR) was inserted into expression plasmid YEpBUbi-FLAG1, resulting in the plasmid YEpBUbiFLAG-AR, and the estrogen response element (ERE) on the reporter vector YRpE2 was replaced by an androgen response element (ARE), resulting in the plasmid YRpE2-ARE. Thus, a fully functional transactivation assay system with beta-galactosidase as a reporter gene could be created. Furthermore, green fluorescent protein (GFP) was introduced as an alternative reporter gene that resulted in a simplification of the whole assay procedure. For evaluation of both reporter systems, seven steroidal compounds with known AR agonistic properties (5 alpha-dihydrotestosterone, testosterone, androstenedione, 17 alpha-methyltestosterone, progesterone, epitestosterone, and d-norgestrel) were tested, and their potencies obtained in the different assays were compared. Furthermore, potencies from the transactivation assays were compared with IC(50) values obtained in radioligand binding assays. The newly developed androgen receptor transactivation assay is a useful tool for characterizing compounds with androgenic activity.

GCP-mediated growth inhibition and apoptosis of prostate cancer cells via androgen receptor-dependent and -independent mechanisms

BACKGROUND

Genistein combined polysaccharide (GCP) is a nutritional supplement that can inhibit prostate cancer growth experimentally and clinically. It is composed predominantly of the isoflavones genistein, daidzein, and glycitein, which have anti-cancer properties. Although genistein is well studied, the properties of GCP are not well defined. The goal of this work was to better characterize the signaling pathways impacted by GCP in an effort to optimize its efficacy.

METHODS

Cell growth and apoptosis were evaluated by MTS proliferation, caspase-based assays, and flow cytometry. Modulation of androgen receptor (AR) levels and activation status of signaling molecules were monitored by immunoblot analysis. AR function was measured by evaluating prostate-specific antigen (PSA) message and protein levels and by reporter assays.

RESULTS

GCP inhibited proliferation of androgen-dependent LNCaP and androgen-independent LNCaP-p53(GOF) and 22Rv1 cell lines in a dose-dependent manner and cells were more responsive in the presence of androgen. GCP markedly suppressed mTOR-p70S6K signaling while Akt and p53 were only modestly modulated. GCP significantly attenuated androgen signaling as evidenced by diminished AR protein levels and a consequent reduction in transcriptional activity and PSA expression. AR expression was enhanced by de-repression of translation with inhibitors of PI3K-Akt-mTOR signaling and by inhibition of proteasome-dependent degradation. Neither inhibitor could counteract GCP-mediated AR downregulation, suggesting the involvement of a mechanism(s) independent of these pathways.

CONCLUSIONS

Our results suggest that GCP mediates growth inhibition and apoptosis through multiple mechanisms including (1) molecular mimicry of androgen ablation (via AR downregulation) and (2) by providing an AR-independent, pro-apoptotic signal (mTOR inhibition).

17beta-Estradiol differentially regulates androgen-responsive genes through estrogen receptor-beta- and extracellular-signal regulated kinase-dependent pathways in LNCaP human prostate cancer cells

The molecular mechanism underlying the actions of estrogens in normal prostate physiology and prostate cancer development remains unclear. In the present study we tested the hypothesis that estrogens modulate androgen-dependent events in prostate cells by examining the effects of 17beta-estradiol (E2) on androgen-responsive genes (ARGs) in the androgenresponsive LNCaP cells. We found that LNCaP cells express estrogen receptor-beta (ER-beta) as the major form of ER and ER treatment with E2 led to an increase in cell growth. The proliferative effect of E2 correlated with induction of several ARGs by E2. Interestingly, some other ARGs did not respond to E2. Consistent with involvement of ER-beta, the induction of both cell growth and ARG mRNA levels by E2 was attenuated by the pure antiestrogen ICI 182,780. Moreover, we found ER-beta small interfering RNA attenuated induction of ARG mRNAs by E2. However, the effect of E2 on ARG mRNA appeared also to require the androgen receptor and to be mediated through activation of the extracellular-signal regulated kinase (ERK) pathway. These results provide mechanistic evidence supporting a direct effect of estrogen, mediated through ER-beta- and ERK-dependent pathways, on specific molecular targets in human prostate cancer cells.

Polyphenols and cancer cell growth

Polyphenols constitute an important group of phytochemicals that gained increased research attention since it was found that they could affect cancer cell growth. Initial evidence came from epidemiologic studies suggesting that a diet that includes regular consumption of fruits and vegetables (rich in polyphenols) significantly reduces the risk of many cancers. In the present work we briefly review the effects of polyphenols on cancer cell fate, leading towards growth, differentiation and apoptosis. Their action can be attributed not only to their ability to act as antioxidants but also to their ability to interact with basic cellular mechanisms. Such interactions include interference with membrane and intracellular receptors, modulation of signaling cascades, interaction with the basic enzymes involved in tumor promotion and metastasis, interaction with oncogenes and oncoproteins, and, finally, direct or indirect interactions with nucleic acids and nucleoproteins. These actions involve almost the whole spectrum of basic cellular machinery--from the cell membrane to signaling cytoplasmic molecules and to the major nuclear components--and provide insights into their beneficial health effects. In addition, the actions justify the scientific interest in this class of compounds, and provide clues about their possible pharmaceutical exploitation in the field of oncology.

BRCA1 and BRCA2 as molecular targets for phytochemicals indole-3-carbinol and genistein in breast and prostate cancer cells

Indole-3-carbinol (I3C) and genistein are naturally occurring chemicals derived from cruciferous vegetables and soy, respectively, with potential cancer prevention activity for hormone-responsive tumours (e.g., breast and prostate cancers). Previously, we showed that I3C induces BRCA1 expression and that both I3C and BRCA1 inhibit oestrogen (E2)-stimulated oestrogen receptor (ER-α) activity in human breast cancer cells. We now report that both I3C and genistein induce the expression of both breast cancer susceptibility genes (BRCA1 and BRCA2) in breast (MCF-7 and T47D) and prostate (DU-145 and LNCaP) cancer cell types, in a time- and dose-dependent fashion. Induction of the BRCA genes occurred at low doses of I3C (20 μM) and genistein (0.5–1.0 μM), suggesting potential relevance to cancer prevention. A combination of I3C and genistein gave greater than expected induction of BRCA expression. Studies using small interfering RNAs (siRNAs) and BRCA expression vectors suggest that the phytochemical induction of BRCA2 is due, in part, to BRCA1. Functional studies suggest that I3C-mediated cytoxicity is, in part, dependent upon BRCA1 and BRCA2. Inhibition of E2-stimulated ER-α activity by I3C and genistein was dependent upon BRCA1; and inhibition of ligand-inducible androgen receptor (AR) activity by I3C and genistein was partially reversed by BRCA1-siRNA. Finally, we provide evidence suggesting that the phytochemical induction of BRCA1 expression is due, in part, to endoplasmic reticulum stress response signalling. These findings suggest that the BRCA genes are molecular targets for some of the activities of I3C and genistein.

Human reporter gene assays: Transcriptional activity of the androgen receptor is modulated by the cellular environment and promoter context

The androgen receptor (AR) is a member of the nuclear receptor superfamily and mediates the physiological effects of androgens. Androgens are essential for male development and disruption of androgen signaling may cause androgen-dependent developmental defects and/or tumors. Here we present a comparative analysis of various model systems for the investigation of endocrine active compounds in human cell lines. We generated reporter plasmids containing androgen response elements derived from the human secretory component or the rat probasin genes as well as the glucocorticoid consensus response element and compared their activities to that of the mouse mammary tumor virus promotor. Additionally, we generated an expression plasmid containing the AR cDNA derived from LNCaP cells. In 22Rv1 cells transiently transfected with human AR, all reporters displayed a dose-dependent, high activity when treated with androgens. Interestingly, the potency of testosterone and its metabolite dihydrotestosterone was very low in HepG2 but not in 22Rv1 cells, independent of the reporter used. The efficacies of the androgens tested were comparable in both cell lines but highly dependent on the reporter used. Based on these results, 22Rv1 cells provide a highly sensitive in vitro test system to analyze endocrine activities of xenobiotics. Furthermore, this study highlights the need to investigate the (anti-) androgenic activity of compounds in dependence of the cellular and promoter context.

Soy isoflavones and bone health: a double-edged sword?

Numerous publications and research studies on isoflavones have prompted a nationwide increase in the consumption of soy-based foods and supplements in the United States. Isoflavones are natural endocrine active compounds generally considered to promote health and prevent or slow the onset of certain chronic diseases such as osteoporosis. The beneficial effects of soy isoflavones on bone may, however, be life-stage specific and dependent on the estrogen receptor number and endogenous hormone milieu. Perimenopausal and early menopausal women may therefore be more receptive to the therapeutic effects of isoflavones on bone loss prior to the diminution of estrogen receptors that occurs in the postmenopausal years, whereas laboratory studies in developmental age range animals have demonstrated the potential for adverse effects following exposure to high levels of soy isoflavones. Clinical studies in developing humans that either support or refute findings in animal studies are lacking. The effects of chronic consumption of high levels of soy isoflavones at each life stage to assess risk-benefit ratios should be a high priority of research.

Effect of increasing ratio of estrogen: androgen on proliferation of normal human prostate stromal and epithelial cells, and the malignant cell line LNCaP

BACKGROUND

Changes in steroid ratios seen in the aging male are thought to promote prostate disease. The aims of this study were to compare the effects of varied ratios of steroids on growth of normal stromal and epithelial cell isolates, and the prostate cancer cell line, LNCaP.

METHODS

The effect of altered steroid ratios on cell proliferation of normal stromal (PrSC) and epithelial (PrEC) prostate cells, and the malignant cell line, LNCaP, were assessed.

RESULTS

Increasing the ratios of both estrogen:dihydrotestosterone (DHT) and DHT:estrogen, stimulated PrSC proliferation, with increasing estrogen:DHT having the greatest effect. LNCaP proliferation was increased significantly by both steroids, but altered ratios had no additional effect. PrEC proliferation was unaffected when cells were grown alone, despite presence of androgen receptors (AR) and estrogen receptors (ER). When grown in co-culture PrEC cell proliferation was significantly increased by treatments.

CONCLUSIONS

PrSC proliferation is stimulated by an increasing ratio of estrogen:androgen. Proliferation of normal epithelial cells is stimulated as a result of an indirect action of steroids mediated by stromal cells. Malignant prostate cancer cells have an altered response in comparison.

Endocrine disrupting compounds and prostate cancer

Prostate cancer is a major health concern and is treated based on its hormone dependence. Agents that alter hormone action can have substantial biological effects on prostate cancer development and progression. As such, there is significant interest in uncovering the potential effects of endocrine disrupting compound (EDC) exposure on prostate cancer. The present review is focused on agents that alter hormone action in the prostate and how they may impact cancer growth or treatment.

Xenoestrogen Action in Prostate Cancer: Pleiotropic Effects Dependent on Androgen Receptor Status

Androgen is critical for prostate development, growth, and survival. Therapies for advanced prostate cancer aim to block androgen receptor (AR) action. However, recurrent tumors ultimately arise, which harbor restored AR activity. One mechanism of such reactivation occurs through AR mutations, rendering the receptor responsive to noncanonical ligands. We have shown previously that a known xenoestrogen, bisphenol A (BPA), activates a tumor-derived AR mutant (T877A), leading to androgen-independent prostate cancer cell proliferation. Here, we show that BPA cooperates with androgen to activate AR-T877A as shown by both reporter assays and increased levels of prostate-specific antigen expression. Further investigations using both yeast and mammalian model systems revealed that multiple AR alleles are responsive to BPA, thus expanding the potential influence of xenoestrogens on prostate cancer. Moreover, in vitro radioligand binding assay revealed that BPA alters 5α-dihydrotestosterone binding to AR-T877A likely through noncompetitive inhibition. We also show that higher concentrations of BPA block proliferation of AR-positive, androgen-dependent prostate adenocarcinoma cells (LNCaP and LAPC-4), with a more modest inhibitory effect on androgen-independent cells (22Rv-1). By contrast, AR-negative prostate cancer cells failed to show growth inhibition after exposure to high BPA dose. Together, these data show that BPA can serve as a potential “hormone sensitizer” of the mutant ARs present in advanced prostate adenocarcinomas, thereby possibly contributing toward therapeutic relapse in advanced prostate cancer patients and supporting the notion that nonsteroidal environmental compounds can alter the function of nuclear receptor complexes.

Phytoestrogens in Common Herbs Regulate Prostate Cancer Cell Growth in Vitro

Prostate cancer is an important public health problem in the United States. Seven phytoestrogens found in common herbal products were screened for estrogen receptor binding and growth inhibition of androgen-insensitive (PC-3) and androgen-sensitive (LNCaP) human prostate tumor cells. In a competitive 3H-estradiol ligand binding assay using mouse uterine cytosol, 2.5 M quercetin, baicalein, genistein, epigallocatechin gallate (EGCG), and curcumin displaced > 85% of estradiol binding, whereas apigenin and resveratrol displaced > 40%. From growth inhibition studies in LNCaP cells, apigenin and curcumin were the most potent inhibitors of cell growth, and EGCG and baicalein were the least potent. In PC-3 cells, curcumin was the most potent inhibitor of cell growth, and EGCG was the least potent. In both cell lines, significant arrest of the cell cycle in S phase was induced by resveratrol and EGCG and in G2M phase by quercetin, baicalein, apigenin, genistein, and curcumin. Induction of apoptosis was induced by all of the 7 compounds in the 2 cell lines as shown by TUNEL and DNA fragmentation assays. Androgen responsiveness of the cell lines did not correlate with cellular response to the phytoestrogens. In conclusion, these 7 phytoestrogens, through different mechanisms, are effective inhibitors of prostate tumor cell growth.

Androgen receptor regulation by physiological concentrations of the isoflavonoid genistein in androgen-dependent LNCaP cells is mediated by estrogen receptor beta

OBJECTIVES

Isoflavonoids are discussed for use in chemoprevention and treatment of prostate cancer. We investigated the potential of genistein to modulate androgen receptor (AR) expression and transcriptional activity in the human androgen-sensitive prostate cancer cell line LNCaP.

MATERIALS AND METHODS

AR expression at mRNA and protein level was analyzed by real-time RT-PCR and immunoblot, respectively. In conditioned media PSA was measured by a microparticle enzyme immunoassay (MEIA). Binding of genistein to the AR was tested in a radioligand-binding assay and reporter gene co-transfection assay was employed to investigate AR activity.

RESULTS

Using concentrations of genistein that have been detected in sera of Asian men on regular soy-diet we found down-regulation of androgen receptor at both mRNA and protein level. The relative binding affinity to the AR was below 4% when compared to methyltrienologe (R1881) and there was no modulation of AR transcriptional activity by genistein concentrations up to 1 microM. We also demonstrated inhibition of PSA secretion after genistein treatment. As the anti-estrogen ICI 164 384 abolished the inhibitory effect of genistein and ER-beta, but not ER-alpha is expressed in LNCaP cells we postulate that the mechanism of genistein action on androgen receptor is mediated through ER-beta.

CONCLUSION

Using physiological concentrations of genistein we showed AR down-regulation by genistein in prostate cancer cells occurring via ER-beta. This likely results in a modified response to hormonal stimuli and may help to explain the low incidence of prostate cancer in the Asian population.

Phyto-oestrogens, their mechanism of action: current evidence for a role in breast and prostate cancer

The incidence of hormone-dependent cancers, such as those of the breast and prostate, is much lower in Eastern countries such as China and Japan in comparison with the Western world. Diet is believed to have a major effect on disease risk and one group of compounds, the phyto-oestrogens, which are consumed in large amounts in Asian populations, have been implicated in cancer protection. This view follows the finding that plasma and urinary levels of phyto-oestrogens are much higher in areas where cancer incidence is low in comparison with areas of high cancer incidence. The phyto-oestrogens are comprised of two main groups; the isoflavones and lignans. Of the isoflavones, genistein and daidzein have been the most widely studied. These compounds have been shown to possess anticancer properties; however their precise mechanism of action remains to be elucidated. In comparison, few studies have investigated the effects of lignans in breast and prostate cancer. In vitro studies have shown that genistein exerts biphasic effects on cancer cell growth, stimulating growth at low concentrations (<10 microm) and inhibiting growth at high concentrations (>10 microm), which suggests that low phyto-oestrogen levels may stimulate cancer growth in vivo. Plasma phyto-oestrogen concentrations of >10 microm cannot be achieved by dietary intake and therefore the timing of exposure to phyto-oestrogens may be of the utmost importance in determining their chemopreventive effects. The present paper reviews the effects of phyto-oestrogens on breast and prostate cancer in vivo and in vitro and discusses possible mechanisms of action via which these compounds may exert their effects.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.