Modulation of androgen receptor-dependent transcription by resveratrol and genistein in prostate cancer cells

Natural compounds targeting nuclear receptors for effective cancer therapy

Human nuclear receptors (NRs) are a family of forty-eight transcription factors that modulate gene expression both spatially and temporally. Numerous biochemical, physiological, and pathological processes including cell survival, proliferation, differentiation, metabolism, immune modulation, development, reproduction, and aging are extensively orchestrated by different NRs. The involvement of dysregulated NRs and NR-mediated signaling pathways in driving cancer cell hallmarks has been thoroughly investigated. Targeting NRs has been one of the major focuses of drug development strategies for cancer interventions. Interestingly, rapid progress in molecular biology and drug screening reveals that the naturally occurring compounds are promising modern oncology drugs which are free of potentially inevitable repercussions that are associated with synthetic compounds. Therefore, the purpose of this review is to draw our attention to the potential therapeutic effects of various classes of natural compounds that target NRs such as phytochemicals, dietary components, venom constituents, royal jelly-derived compounds, and microbial derivatives in the establishment of novel and safe medications for cancer treatment. This review also emphasizes molecular mechanisms and signaling pathways that are leveraged to promote the anti-cancer effects of these natural compounds. We have also critically reviewed and assessed the advantages and limitations of current preclinical and clinical studies on this subject for cancer prophylaxis. This might subsequently pave the way for new paradigms in the discovery of drugs that target specific cancer types.

Resveratrol Promotes Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stem Cells Through miR-193a/SIRT7 Axis

Resveratrol (RES) is a novel dietary phenol compound derived from plants and has been studied extensively for its health benefit and medical potential including osteoporosis. The purpose of this study is to investigate the role of resveratrol in osteoporosis in vivo and in vitro and explore the mechanism of osteogenic differentiation of BMSCs. RT-qPCR, ELISA, and Western blot were used to measure the expression level of miR-193a, SIRT7, and osteogenic markers proteins. The interaction between miR-193a and SIRT7 was validated by dual-luciferase reporter assay. Moreover, MTT assay was conducted to detect cell viability. Alizarin red s staining was used to examine bone formation and calcium deposits. The ovariectomized rat model was set up successfully and HE staining was used to examine femoral trabeculae tissue. Our results showed that miR-193a was overexpressed, while SIRT7 was downregulated in osteoporosis. RES suppressed miR-193a to promote osteogenic differentiation. Mechanically, miR-193a targeted and negative regulated SIRT7. Additionally, it was confirmed that SIRT7 promoted osteogenic differentiation of BMSCs through NF-κB signaling pathway. Further study indicated that RES exerted its beneficial function through miR-193a/SIRT7-mediated NF-κB signaling to alleviate osteoporosis in vivo. Our research suggested that the RES-modulated miR-193a inhibition is responsible for the activation of SIRT7/NF-κB signaling pathway in the process of osteogenic differentiation, providing a novel insight into diagnosis and treatment of osteoporosis.

Natural Compounds in Prostate Cancer Prevention and Treatment: Mechanisms of Action and Molecular Targets

Prostate cancer (PCa) represents a major cause of cancer mortality among men in developed countries. Patients with recurrent disease initially respond to androgen-deprivation therapy, but the tumor eventually progresses into castration-resistant PCa; in this condition, tumor cells acquire the ability to escape cell death and develop resistance to current therapies. Thus, new therapeutic approaches for PCa management are urgently needed. In this setting, natural products have been extensively studied for their anti-PCa activities, such as tumor growth suppression, cell death induction, and inhibition of metastasis and angiogenesis. Additionally, numerous studies have shown that phytochemicals can specifically target the androgen receptor (AR) signaling, as well as the PCa stem cells (PCSCs). Interestingly, many clinical trials have been conducted to test the efficacy of nutraceuticals in human subjects, and they have partially confirmed the promising results obtained in vitro and in preclinical models. This article summarizes the anti-cancer mechanisms and therapeutic potentials of different natural compounds in the context of PCa prevention and treatment.

Phytochemicals as Modulators of Long Non-Coding RNAs and Inhibitors of Cancer-Related Carbonic Anhydrases

Long non-coding RNAs (lncRNAs) are classified as a group of transcripts which regulate various biological processes, such as RNA processing, epigenetic control, and signaling pathways. According to recent studies, lncRNAs are dysregulated in cancer and play an important role in cancer incidence and spreading. There is also an association between lncRNAs and the overexpression of some tumor-associated proteins, including carbonic anhydrases II, IX, and XII (CA II, CA IX, and CA XII). Therefore, not only CA inhibition, but also lncRNA modulation, could represent an attractive strategy for cancer prevention and therapy. Experimental studies have suggested that herbal compounds regulate the expression of many lncRNAs involved in cancer, such as HOTAIR (HOX transcript antisense RNA), H19, MALAT1 (metastasis-associated lung adenocarcinoma transcript 1), PCGEM1 (Prostate cancer gene expression marker 1), PVT1, etc. These plant-derived drugs or phytochemicals include resveratrol, curcumin, genistein, quercetin, epigallocatechin-3-galate, camptothcin, and 3,3'-diindolylmethane. More comprehensive information about lncRNA modulation via phytochemicals would be helpful for the administration of new herbal derivatives in cancer therapy. In this review, we describe the state-of-the-art and potential of phytochemicals as modulators of lncRNAs in different types of cancers.

Steroid Receptor Signallings as Targets for Resveratrol Actions in Breast and Prostate Cancer

Extensive research over the past 25 years in hormone-dependent cancers, such as breast cancer and prostate cancer, has identified the molecular mechanisms driven by steroid receptors, elucidating the interplay between genomic and non-genomic steroid receptors mechanism of action. Altogether, these mechanisms create the specific gene expression programs that contribute to endocrine therapy resistance and cancer progression. These findings, on the bidirectional molecular crosstalk between steroid and growth factor receptors pathways in endocrine resistance, suggest the use of multi-target inhibitors together with endocrine therapies, for treating resistant disease. In this review we will discuss the novel understanding on the chemopreventive and anti-cancer activities of Resveratrol (3,5,4′-trihydroxy-stilbene) (RSV), a phytoalexin found in grapes acting on a plethora of targets. We will highlight Resveratrol effect on steroid receptors signalling and its potential use in the treatment of hormone-dependent cancer. Understanding the molecular mechanisms by which the bioactive compound influences cancer cell behaviour, by interfering with steroid receptors functional activity, will help to advance the design of combination strategies to increase the rate of complete and durable clinical response in patients.

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.

Phytocompounds modulating Aquaporins: Clinical benefits are anticipated

A series of plant-derived bioactive compounds belonging to the class of polyphenols, terpenes and capsaicinoids, interact with important pathophysiological pathways at a molecular, cellular and systemic level. Mechanisms of action include altering cell growth and differentiation, apoptosis, autophagy, inflammation, redox balance and metabolic and energy homeostasis. These effects might also involve the expression and function of Aquaporins (AQPs), a family of membrane channel proteins, involved in several body functions. The ultimate translational beneficial effect of such phytocompounds on AQPs in health and disease is a matter of intensive research. Results might provide novel therapeutic approaches to a number of human diseases. Here, we give an updated overview of this fast growing and promising field, discussing a number of phytocompounds and their action on AQPs and related potential clinical achievements.

Aquaporins as Targets of Dietary Bioactive Phytocompounds

Plant-derived bioactive compounds have protective role for plants but may also modulate several physiological processes of plant consumers. In the last years, a wide spectrum of phytochemicals have been found to be beneficial to health interacting with molecular signaling pathways underlying critical functions such as cell growth and differentiation, apoptosis, autophagy, inflammation, redox balance, cell volume regulation, metabolic homeostasis, and energy balance. Hence, a large number of biologically active phytocompounds of foods have been isolated, characterized, and eventually modified representing a natural source of novel molecules to prevent, delay or cure several human diseases. Aquaporins (AQPs), a family of membrane channel proteins involved in many body functions, are emerging among the targets of bioactive phytochemicals in imparting their beneficial actions. Here, we provide a comprehensive review of this fast growing topic focusing especially on what it is known on the modulatory effects played by several edible plant and herbal compounds on AQPs, both in health and disease. Phytochemical modulation of AQP expression may provide new medical treatment options to improve the prognosis of several diseases.

Resveratrol, Potential Therapeutic Interest in Joint Disorders: A Critical Narrative Review

Trans-resveratrol (t-Res) is a natural compound of a family of hydroxystilbenes found in a variety of spermatophyte plants. Because of its effects on lipids and arachidonic acid metabolisms, and its antioxidant activity, t-Res is considered as the major cardioprotective component of red wine, leading to the “French Paradox” health concept. In the past decade, research on the effects of resveratrol on human health has developed considerably in diverse fields such as cancer, neurodegenerative and cardiovascular diseases, and metabolic disorders. In the field of rheumatic disorders, in vitro evidence suggest anti-inflammatory, anti-catabolic, anti-apoptotic and anti-oxidative properties of t-Res in various articular cell types, including chondrocytes and synoviocytes, along with immunomodulation properties on T and B lymphocytes. In preclinical models of osteoarthritis and rheumatoid arthritis, resveratrol has shown joint protective effects, mainly mediated by decreased production of pro-inflammatory and pro-degradative soluble factors, and modulation of cellular and humoral responses. Herein, we comprehensively reviewed evidence supporting a potential therapeutic interest of t-Res in treating symptoms related to rheumatic disorders.

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.

Rodent models for human diseases

One of the factors limiting the translation of knowledge from preclinical studies to the clinic has been the limitations of in vivo diseases models. Except in the case of highly controlled and regulated clinical trials, geneticists and scientists do not use humans for their experimental investigations because of the obvious risk to life. Instead, they use various animal, fungal, bacterial, and plant species as model organisms for their studies. Amongst these model organisms, rodent models are the most used due to the easiness for the experiments and the possibility to modify genetically these model animals. Nevertheless, due to the fact that animal models typically do not contract the same genetic diseases as people, so scientists must alter their genomes to induce human disease states and to know what kind of mutation causes the disease. In this brief review, we will discuss the interests of rodent models that have been developed to simulate human pathologies, focusing in models that employ xenografts and genetic modification. Within the framework of genetically engineered mouse (GEM) models, we will review some of the current genetic strategies for modeling diseases.

Regulation of GLUT transporters by flavonoids in androgen-sensitive and -insensitive prostate cancer cells

Cancer cells show different metabolic requirements from normal cells. In prostate cancer, particularly, glycolytic metabolism differs in androgen-responsive and nonresponsive cells. In addition, some natural compounds with antiproliferative activities are able to modify glucose entry into cells by either modulating glucose transporter (GLUT) expression or by altering glucose binding. The aim of this work was to study the regulation of some GLUTs (GLUT1 and GLUT4) in both androgen-sensitive (LNCaP) and -insensitive (PC-3) prostate cancer cells by 4 structurally different flavonoids (ie, genistein, phloretin, apigenin, and daidzein). Glucose uptake was measured using nonradiolabeled 2-deoxyglucose. The evaluation of protein levels as well as subcellular distribution of GLUT1/4 were analyzed by Western blot and immunocytochemistry, respectively. Androgen-insensitive LNCaP-R and androgen-sensitive PC-3-AR cells were used to study the effect of androgen signaling. Additionally, a docking simulation was employed to compare interactions between flavonoids and XylE, a bacterial homolog of GLUT1 to -4. Results show for the first time the presence of functionally relevant GLUT4 in prostate cancer cells. Furthermore, differences in GLUT1 and GLUT4 levels and glucose uptake were found, without differences on subcellular distribution, after incubation with flavonoids. Docking simulation showed that all compounds interact with the same location of transporters. More importantly, differences between androgen-sensitive and -insensitive prostate cancer cells were found in both GLUT protein levels and glucose uptake. Thus, phenotypic characteristics of prostate cancer cells are responsible for the different effects of these flavonoids in glucose uptake and in GLUT expression rather than their structural differences, with the most effective in reducing cell growth being the highest in modifying glucose uptake and GLUT levels.

Wine polyphenols exert antineoplasic effect on androgen resistant PC-3 cell line through the inhibition of the transcriptional activity of COX-2 promoter mediated by NF-kβ

OBJECTIVE

Mediterranean diet may play a role in the prevention of prostate cancer (PCa) development and progression. Cyclooxygenase-2 (COX-2) expression is associated with increased cellular proliferation, prevents apoptosis and favors tumor invasion. We intend to clarify whether resveratrol and other polyphenols effectively inhibit COX-2 activity and induce apoptosis in hormone-resistant PC-3 cell line.

MATERIAL AND METHOD

PC-3 cells were cultured and treated with different concentrations of gallic acid, tannic acid, quercetin, and resveratrol in presence of phorbol myristate acetate (PMA; 50 μg/ml) that induces COX-2 expression. Total RNA was extracted and COX-2 expression was analyzed by relative quantification real-time PCR (ΔΔCt method). COX-2 activity was determined by PGE-2 detection using ELISA. Caspase 3/7 luminescence assay was used to disclose apoptosis. Transitory transfection with short human COX-2 (phPES2 -327/+59) and p5xNF-kβ-Luc plasmids determined COX-2 promoter activity and specifically that dependant of NF-kβ.

RESULTS

COX-2 expression was not modified in media devoid of PMA. However, under PMA induction tannic acid (2.08 ±.21), gallic acid (2.46 ±.16), quercetin (1.78 ±.14) and resveratrol (1.15 ±.16) significantly inhibited COX-2 mRNA with respect to control (3.14 ±.07), what means a 34%, 23%, 46% and 61% reduction, respectively. The inhibition in the levels of PGE-2 followed a similar pattern. All compounds studied induced apoptosis at 48 h, although at a different rate. PMA caused a rise in activity 7.4 ±.23 times phPES2 -327/+59 and 2.0 ±.1 times p5xNF-kβ-Luc at 6h compared to basal. Resveratrol suppressed these effects 17.1 ±.21 and 32.4 ±.18 times, respectively. Similarly, but to a lesser extent, the rest of evaluated polyphenols diminished PMA inductor effect on the activity of both promoters.

CONCLUSIONS

Polyphenols inhibit transcriptional activity of COX-2 promoter mediated by NF-kβ. This effect could explain, at least in part, the induction of apoptosis in vitro by these substances in castration resistant PCa.

P44/WDR77 restricts the sensitivity of proliferating cells to TGFβ signaling

We previously reported that a novel WD-40 domain-containing protein, p44/WDR77, drives quiescent epithelial cells to re-enter the cell cycle and plays an essential role for growth of lung and prostate cancer cells. Transforming growth factor beta (TGFβ) signaling is important in the maintenance of non-transformed cells in the quiescent or slowly cycling stage. However, both non-transformed proliferating cells and human cancer cells are non-responsive to endogenous TGFβ signaling. The mechanism by which proliferating cells become refractory to TGFβ inhibition is not well established. Here, we found that silencing p44/WDR77 increased cellular sensitivity to TGFβ signaling and that this was inversely correlated with decreased cell proliferation. Smad2 or 3 phosphorylation, TGFβ-mediated transcription, and TGFβ2 and TGFβ receptor type II (TβRII) expression were dramatically induced by silencing of p44/WDR77. These data support the hypothesis that p44/WDR77 down-regulates the expression of the TGFβ ligand and its receptor, thereby leading to a cellular non-response to TGFβ signaling. Finally, we found that p44/WDR77 expression was correlated with cell proliferation and decreased TGFβ signaling during lung tumorigenesis. Together, these results suggest that p44/WDR77 expression causes the non-sensitivity of proliferating cells to TGFβ signaling, thereby contributing to cellular proliferation during lung tumorigenesis.

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.

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.

cGMP-dependent protein kinase Iβ interacts with p44/WDR77 to regulate androgen receptor-driven gene expression

The androgen receptor (AR) pathway plays critical roles in controlling differentiation and proliferation of prostate epithelial cells. We previously identified a novel AR cofactor, p44/WDR77, which specifically enhances AR transcriptional activity in the prostate gland and prostate cancer. To further elucidate p44/WDR77's role in the AR signaling pathway, we conducted a yeast two-hybrid screening and identified cGMP-dependent protein kinase (PKG) as a p44/WDR77-interacting protein. Further investigation by lusiferase assay and kinase assay demonstrated that PKG-Iβ physically interacted with and phosphorylated both p44 and AR and enhanced AR transactivity in synergy with p44 in an androgen- and cGMP-dependent manner. Furthermore, PKG1β expression promoted p44/WDR77 nuclear translocation and inhibited prostate cancer cell growth via G1 cell cycle arrest. Our findings characterize PKG as a novel regulator of AR-mediated transcription by enhancing AR cofactor p44/WDR77's function, which provide a novel mechanism for the growth regulation of prostate cancer cells by the androgen signaling.

Regulation of the androgen receptor by post-translational modifications

The androgen receptor (AR) is a key molecule in prostate cancer and Kennedy's disease. Understanding the regulatory mechanisms of this steroid receptor is important in the development of potential therapies for these diseases. One layer of AR regulation is provided by post-translational modifications including phosphorylation, acetylation, sumoylation, ubiquitination and methylation. While these modifications have mostly been studied as individual events, it is becoming clear that these modifications can functionally interact with each other in a signalling pathway. In this review, the effects of all modifications are described with a focus on interplay between them and the functional consequences for the AR.

Synergistic and Selective Cancer Cell Killing Mediated by the Oncolytic Adenoviral Mutant AdΔΔ and Dietary Phytochemicals in Prostate Cancer Models

AdΔΔ is an oncolytic adenoviral mutant that has been engineered to selectively target tumors with deregulated cell cycle and apoptosis pathways. AdΔΔ potentiates apoptotic cell death induced by drugs, including mitoxantrone and docetaxel, which are commonly used to treat prostate cancer. Here, we demonstrate that AdΔΔ can also interact synergistically with dietary phytochemicals known to have anti-cancer activities, without incurring the toxic side effects of chemodrugs. Curcumin, genistein, epigallocatechin-gallate, equol, and resveratrol efficiently killed both androgen-receptor positive (22Rv1) and negative cell lines (PC-3, DU145) in combination with adenoviral mutants. Synergistic cell killing was demonstrated with wild-type virus (Ad5) and AdΔΔ in combination with equol and resveratrol. EC(50) values for both phytochemicals and viruses were reduced three- to eightfold in all three combination-treated cell lines. The most potent efficacy was achieved in the cytotoxic drug- and virus-insensitive PC-3 cells, both in vitro and in vivo, while cell killing in normal bronchial epithelial cells was not enhanced. Although equol and resveratrol induced only low levels of apoptosis when administered alone, in combination with wild-type virus or AdΔΔ, the level of apoptotic cell death was significantly increased in PC-3 and DU145 cells. In vivo studies using suboptimal doses of AdΔΔ and equol or resveratrol, showed reduced tumor growth without toxicity to normal tissue. These findings identify novel functions for AdΔΔ and phytochemicals in promoting cancer cell killing and apoptosis, suggesting the use of these natural nontoxic compounds might be a feasible and currently unexploited anti-cancer strategy.

Complementary and alternative medicines in prostate cancer: from bench to bedside?

Complementary and alternative medicine (CAM) use is common among adults, and recent reports suggest that 25%-50% of prostate cancer (PCa) patients use at least one CAM modality. The most common CAM modalities used by PCa patients are vitamin and herbal preparations with purported antitumor effects despite only modest underlying preclinical or clinical evidence of efficacy. In this review we provide a brief overview of the basic scientific and clinical studies underlying the most common herbal and vitamin preparations including common antioxidants, pomegranate extract, green tea, turmeric, resveratrol, silibinin, and herbal combination preparations. When available, prostate cancer clinical trial data are reviewed. Importantly, we have compared the concentration of these agents used in in vitro experiments to that likely to be achievable in humans. From the available data we conclude that there is insufficient evidence to support the use of CAMs for the treatment of prostate cancer patients outside of a clinical trial. The purpose of this review is to more rigorously evaluate CAM therapy in prostate cancer and educate oncologists and patients. This review focuses on examples from the general classes of agents in common use.

Control of stability of cyclin D1 by quinone reductase 2 in CWR22Rv1 prostate cancer cells

Aberrant expression of cyclin D1, frequently observed in human malignant disorders, has been linked to the control of G(1)→S cell cycle phase transition and development and progression in carcinogenesis. Cyclin D1 level changes are partially controlled by GSK-3β-dependent phosphorylation at threonine-286 (Thr286), which targets cyclin D1 for ubiquitination and proteolytic degradation. In our continuing studies on the mechanism of prostate cancer prevention by resveratrol, focusing on the role of its recently discovered target protein, quinone reductase 2 (NQO2), we generated NQO2 knockdown CWR22Rv1 using short hairpin RNA (shRNA)-mediated gene silencing approach. We found that, compared with cells expressing NQO2 (shRNA08), NQO2 knockdown cells (shRNA25) displayed slower proliferation and G(1) phase cell accumulation. Immunoblot analyses revealed a significant decrease in phosphorylation of retinoblastoma Rb and cyclin D1 in shRNA25 compared with shRNA08. Moreover, shRNA25 cells showed a 37% decrease in chymotrypsin-like proteasome activity. An increase in AKT activity was also observed in shRNA25, supported by a ∼1.5-fold elevation in phosphorylation and ∼50% reduction/deactivation of GSK-3α/β at Ser21/9, which were accompanied by a decrease in phosphorylation of cyclin D1 at T286. NQO2 knockdown cells also showed attenuation of resveratrol-induced downregulation of cyclin D1. Our results indicate a hitherto unreported role of NQO2 in the control of AKT/GSK-3β/cyclin D1 and highlight the involvement of NQO2 in degradation of cyclin D1, as part of mechanism of chemoprevention by resveratrol.

The changing therapeutic landscape of castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) has a poor prognosis and remains a significant therapeutic challenge. Before 2010, only docetaxel-based chemotherapy improved survival in patients with CRPC compared with mitoxantrone. Our improved understanding of the underlying biology of CRPC has heralded a new era in molecular anticancer drug development, with a myriad of novel anticancer drugs for CRPC entering the clinic. These include the novel taxane cabazitaxel, the vaccine sipuleucel-T, the CYP17 inhibitor abiraterone, the novel androgen-receptor antagonist MDV-3100 and the radioisotope alpharadin. With these developments, the management of patients with CRPC is changing. In this Review, we discuss these promising therapies along with other novel agents that are demonstrating early signs of activity in CRPC. We propose a treatment pathway for patients with CRPC and consider strategies to optimize the use of these agents, including the incorporation of predictive and intermediate end point biomarkers, such as circulating tumor cells.

Nuclear transport signals control cellular localization and function of androgen receptor cofactor p44/WDR77

The androgen receptor (AR) cofactor p44/WDR77, which regulates expression of a set of androgen target genes, is required for differentiation of prostate epithelium. Aberrant localization of p44/WDR77 in the cytoplasm is associated with prostate tumorigenesis. Here, we describe studies that used the mouse prostate and human prostate cancer cells as model systems to investigate signals that control subcellular localization of p44/WDR77. We observed distinct subcellular location of p44/WDR77 during prostate development. p44/WDR77 localizes in the cytoplasm at the early stage of prostate development, when prostate epithelial cells are rapidly proliferating, and in the nucleus in adult prostate, when epithelial cells are fully differentiated. Subcellular localization assays designed to span the entire open-reading frame of p44/WDR77 protein revealed the presence of two nuclear exclusion signal (NES) and three nuclear localization signal (NLS) sequences in the p44/WDR77 protein. Site-directed mutagenesis of critical residues within an NLS led to loss of nuclear localization and transcriptional activity of p44/WDR77, suggesting that nuclear localization of p44/WDR77 is essential for its function as a transcriptional cofactor for AR. Three identified NLS were not functional in AR-positive prostate cancer (LNCaP and 22RV1) cells, which led to localization of p44/WDR77 in cytoplasm. The function of NLS in LNCaP cells could be restored by factor(s) from Cos 7 or PC3 cells. Mass spectrometric (MALDI-TOF/TOF) analysis identified proteins associated with an NLS and an NES in prostate cancer cells. These results provide a basis for understanding subcellular transport of p44/WDR77 during prostate development and tumorigenesis.

Multifaceted approach to resveratrol bioactivity: Focus on antioxidant action, cell signaling and safety

Resveratrol (RVT) is a naturally occurring trihydroxy stilbene that displays a wide spectrum of physiological activity. Its ability to behave therapeutically as a component of red wine has attracted wide attention. The phenol acts as a protective agent involving various body constituents. Most attention has been given to beneficial effects in insults involving cancer, aging, cardiovascular system, inflammation and the central nervous system. One of the principal modes of action appears to be as antioxidant. Other mechanistic pathways entail cell signaling, apoptosis and gene expression. There is an intriguing dichotomy in relation to pro-oxidant property. Also discussed are metabolism, receptor binding, rationale for safety and suggestions for future work. This is the first comprehensive review of RVT based on a broad, unifying mechanism.

Clinical pharmacology of isoflavones and its relevance for potential prevention of prostate cancer

Isoflavones are phytoestrogens that have pleiotropic effects in a wide variety of cancer cell lines. Many of these biological effects involve key components of signal transduction pathways within cancer cells, including prostate cancer cells. Epidemiological studies have raised the hypothesis that isoflavones may play an important role in the prevention and modulation of prostate cancer growth. Since randomized phase III trials of isoflavones in prostate cancer prevention are currently lacking, the best evidence for this concept is presently provided by case control studies. However, in vitro data are much more convincing in regard to the activity of a number of isoflavones, and have led to the development of genistein and phenoxodiol in the clinic as potential treatments for cancer. In addition, the potential activity of isoflavones in combination with cytotoxics or radiotherapy warrants further investigation. This review focuses on the clinical pharmacology of isoflavones and its relevance to their development for use in the prevention of prostate cancer, and it evaluates some of the conflicting data in the literature.

Pharmacogenomics of metabotropic glutamate receptor subtype 1 and in vivo malignant melanoma formation

We have previously shown that ectopic expression of metabotropic glutamate receptor subtype 1 in melanocytes is essential for both development and in vivo growth of melanoma using newly developed transgenic mice which conditionally express metabotropic glutamate receptor subtype 1 (mGluR1). In this study, we developed conditional transgenic mice, which harbor melanocytes not only in the dermis and hair follicles but also in the epidermis using stem cell factor transgenic mice. Pigmented plaques on the backs, tails, ears or groins of the transgenic mice began to appear 13 weeks after activation of the mGluR1 transgene, and the transgenic mice produced melanomas at a frequency of 100% 36 weeks after transgene activation. Although this transgenic mouse harbors melanocytes in the epidermis, proliferation of melanoma cells took place in the dermis. To elucidate the signals involved in development and growth of melanoma, inhibitors to phospholipase C, protein kinase C and mitogen-activated protein kinase kinase 1/2, and antagonists to Ca(2+) and calmodulin were administrated to transgenic mice. Each signal inhibitor to phospholipase, protein kinase C, Ca(2+) release, calmodulin and mitogen-activated protein kinase kinase 1/2 inhibited melanoma development. However, once melanoma was developed, the growth of melanoma was dramatically inhibited only by the inhibitor to mitogen-activated protein kinase kinase 1/2 with partial inhibition by inhibitors to protein kinase C and phospholipase C. This inhibition of melanoma growth was well correlated with the expression of phosphorylated extracellular signal-regulated kinase 1/2 and Ki-67. These results indicate that for development of melanoma, activation of every signaling pathway from mGluR1 is required. However, for growth of melanoma, the extracellular signal-regulated kinase pathway plays a key role.

Xeno-oestrogens and phyto-oestrogens are alternative ligands for the androgen receptor

The androgen receptor (AR) plays a critical role in prostate cancer development and progression. This study aimed to use a computerized docking approach to examine the interactions between the human AR and phyto-oestrogens (genistein, daidzein, and flavone) and xeno-oestrogens (bisphenol A, 4-nonylphenol, dichlorodiphenyl trichloroethane [DDT], diethylstilbestrol [DES]). The predicted three-dimensional structure of AR and androgens was established using X-ray diffraction. The binding of four xeno-oestrogens and three phyto-oestrogens to AR was analysed. The steroids estradiol and dihydrotestosterone (DHT) were used as positive controls and thyroxine as negative control. All the ligands shared the same binding site except for thyroxine. The endogenous hormones DHT and 17beta-oestradiol showed the strongest binding with the lowest affinity energy (< -10 kcal mol(-1)). All three phyto-oestrogens and two xeno-oestrogens (bisphenol A and DES) showed strong binding to AR. The affinities of flavone, genistein, and daidzein were between -8.8 and -8.5 kcal mol(-1), while that of bisphenol A was -8.1 kcal mol(-1) and DES -8.3 kcal mol(-1). Another two xeno-oestrogens, 4-nonylphenol and DDT, although they fit within the binding domain of AR, showed weak affinity (-6.4 and -6.7 kcal mol(-1), respectively). The phyto-oestrogens genistein, daidzein and flavone, and the xeno-oestrogens bisphenol A and DES can be regarded as androgenic effectors. The xeno-oestrogens DDT and 4-nonylphenol bind only weakly to AR.

Structural and functional analysis of amino-terminal enhancer of split in androgen-receptor-driven transcription

We previously demonstrated that the Groucho protein AES (amino-terminal enhancer of split) functions as a co-repressor of the AR (androgen receptor). It physically interacts with the N-terminal domain of AR and inhibits AR-driven transcription, but the molecular mechanism of its action remained unclear. In the present paper we report that the AES protein contains one inhibitory domain, and one positive and one negative regulatory domain. The negative regulatory domain inhibits AES dimerization and AES-mediated inhibition of AR-driven transcription through an interaction with the inhibitory domain. The positive regulatory domain blocked this interaction and relieved the inhibitory effect. In addition, we discovered mechanisms by which AES regulates AR transcriptional activity, which included disruption of the interaction between the AR N-terminal and C-terminal domains, and inhibition of AR-DNA interaction. Although AES broadly inhibited the activity of androgen-dependent luciferase reporters in a transient transfection assay, it selectively regulated the expression of endogenous androgen-dependent genes in prostate cancer cells.

Analytical and compositional aspects of isoflavones in food and their biological effects

This paper provides an overview of analytical techniques used to determine isoflavones (IFs) in foods and biological fluids with main emphasis on sample preparation methods. Factors influencing the content of IFs in food including processing and natural variability are summarized and an insight into IF databases is given. Comparisons of dietary intake of IFs in Asian and Western populations, in special subgroups like vegetarians, vegans, and infants are made and our knowledge on their absorption, distribution, metabolism, and excretion by the human body is presented. The influences of the gut microflora, age, gender, background diet, food matrix, and the chemical nature of the IFs on the metabolism of IFs are described. Potential mechanisms by which IFs may exert their actions are reviewed, and genetic polymorphism as determinants of biological response to soy IFs is discussed. The effects of IFs on a range of health outcomes including atherosclerosis, breast, intestinal, and prostate cancers, menopausal symptoms, bone health, and cognition are reviewed on the basis of the available in vitro, in vivo animal and human data.

Repressive effects of resveratrol on androgen receptor transcriptional activity

Background

The chemopreventive effects of resveratrol (RSV) on prostate cancer have been well established; the androgen receptor (AR) plays pivotal roles in prostatic tumorigenesis. However, the exact underlying molecular mechanisms about the effects of RSV on AR have not been fully elucidated. A model system is needed to determine whether and how RSV represses AR transcriptional activity.

Methodology

The AR cDNA was first cloned into the retroviral vector pOZ-N and then integrated into the genome of AR-negative HeLa cells to generate the AR(+) cells. The constitutively expressed AR was characterized by monitoring hormone-stimulated nuclear translocation, DNA binding, and transcriptional activation, with the AR(-) cells serving as controls. AR(+) cells were treated with RSV, and both AR protein levels and AR transcriptional activity were measured simultaneously. Chromatin immunoprecipitation (ChIP) assays were used to detect the effects of RSV on the recruitment of AR to its cognate element (ARE).

Results

AR in the AR (+) stable cell line functions in a manner similar to that of endogenously expressed AR. Using this model system we clearly demonstrated that RSV represses AR transcriptional activity independently of any effects on AR protein levels. However, neither the hormone-mediated nucleus translocation nor the AR/ARE interaction was affected by RSV treatment.

Conclusion

We demonstrated unambiguously that RSV regulates AR target gene expression, at least in part, by repressing AR transcriptional activity. Repressive effects of RSV on AR activity result from mechanisms other than the affects of AR nuclear translocation or DNA binding.

Uptake of resveratrol and role of resveratrol-targeting protein, quinone reductase 2, in normally cultured human prostate cells

Resveratrol is a dietary polyphenol espoused to have chemopreventive activity against a variety of human cancer types. We first reported that resveratrol significantly decreases the proliferation of both androgen-dependent and hormone-refractory prostate cancer cells. However, the effects of resveratrol in normal prostate epithelial and stromal cells, particularly with regard to its uptake, subcellular distribution and intracellular targets, have not been investigated. To advance the knowledge on accessibility and cellular disposition of resveratrol in prostate cells, [(3)H] resveratrol, fractionation of cell extracts into subcellular compartments, Western blot analysis, resveratrol affinity column chromatography and flow cytometry were used to study the uptake and intracellular distribution of resveratrol in normally cultured prostate stromal (PrSCs) and epithelial cells (PrECs). Pretreatment of both PrSCs and PrECs for 2 days with resveratrol modulated its uptake and selectively increased its distribution to the membrane and organelle compartments. Resveratrol affinity column chromatography studies showed differential expression of a previously identified resveratrol-targeting protein, quinone reductase 2 (QR2), in PrSCs and PrECs. Flow cytometric analysis comparing resveratrol-treated and untreated PrSCs showed a large decrease in G(1)-phase and a concomitant increase in S and G(2)/M-phases of the cell cycle. These results suggest that resveratrol suppresses PrSC proliferation by affecting cell cycle phase distribution, which may involve the participation by QR2.

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.

Diets high in selenium and isoflavones decrease androgen-regulated gene expression in healthy rat dorsolateral prostate

BACKGROUND

High dietary intake of selenium or soybean isoflavones reduces prostate cancer risk. These components each affect androgen-regulated gene expression. The objective of this work was to determine the combined effects of selenium and isoflavones on androgen-regulated gene expression in rat prostate.

METHODS

Male Noble rats were exposed from conception until 200 days of age to diets containing an adequate (0.33-0.45 mg/kg diet) or high (3.33-3.45 mg/kg) concentration of selenium as Se-methylselenocysteine and a low (10 mg/kg) or high (600 mg/kg) level of isoflavones in a 2 x 2 factorial design. Gene expression in the dorsolateral prostate was determined for the androgen receptor, for androgen-regulated genes, and for Akr1c9, whose product catalyzes the reduction of dihydrotestosterone to 5alpha-androstane-3alpha, 17beta-diol. Activity of hepatic glutathione peroxidise 1 and of prostatic 5alpha reductase were also assayed.

RESULTS

There were no differences due to diet in activity of liver glutathione peroxidase activity. Total activity of 5alpha reductase in prostate was significantly lower (p = 0.007) in rats fed high selenium/high isoflavones than in rats consuming adequate selenium/low isoflavones. High selenium intake reduced expression of the androgen receptor, Dhcr24 (24-dehydrocholesterol reductase), and Abcc4 (ATP-binding cassette sub-family C member 4). High isoflavone intake decreased expression of Facl3 (fatty acid CoA ligase 3), Gucy1a3 (guanylate cyclase alpha 3), and Akr1c9. For Abcc4 the combination of high selenium/high isoflavones had a greater inhibitory effect than either treatment alone. The effects of selenium on gene expression were always in the direction of chemoprevention

CONCLUSION

These results suggest that combined intake of high selenium and high isoflavones may achieve a greater chemopreventive effect than either compound supplemented individually.

Resveratrol down-regulates the androgen receptor at the post-translational level in prostate cancer cells

Androgen receptor (AR) functions as a transcriptional factor for the development and progression of prostate cancer. Resveratrol is known to inhibit the function of AR and to repress AR expression at the transcriptional level. This study focuses on the effects of resveratrol on the AR function and the post-translational AR level. Resveratrol repressed the transcriptional activities of a mutant AR lacking the ligand-binding domain, a constitutive active form of AR, and wild-type AR in a concentration-dependent manner in human prostate cancer PC-3 cells, indicating that resveratrol does not inhibit the transcriptional activity of AR through binding to the ligand-binding domain of AR. Furthermore, the half-life of AR protein was approximately 4 h in resveratrol-treated AR-positive prostate cancer LNCaP cells, compared to approximately 13 h in control cells, as determined by cycloheximide chase. These results indicate that resveratrol down-regulates AR protein through a post-translational mechanism and suggest that the inhibitory effect of resveratrol on AR function is partly attributable to a decrease in the post-translational AR level.

Glycitein activates extracellular signal-regulated kinase via vascular endothelial growth factor receptor signaling in nontumorigenic (RWPE-1) prostate epithelial cells

Increased consumption of soy is associated with a decreased risk for prostate cancer; however, the specific cellular mechanisms responsible for this anticancer activity are unknown. Dietary modulation of signaling cascades controlling cellular growth, proliferation and differentiation has emerged as a potential chemopreventive mechanism. The present study examined the effects of four soy isoflavones (genistein, daidzein, glycitein and equol) on extracellularsignal-regulated kinase (ERK1/2) activity in a nontumorigenic prostate epithelial cell line (RWPE-1). All four isoflavones (10 micromol/L) significantly increased ERK1/2 activity in RWPE-1 cells, as determined by immunoblotting. Isoflavone-induced ERK1/2 activation was rapid and sustained for approximately 2 h posttreatment. Glycitein, the most potent activator of ERK1/2, decreased RWPE-1 cell proliferation by 40% (P<.01). Glycitein-induced ERK1/2 activation was dependent, in part, on tyrosine kinase activity associated with vascular endothelial growth factor receptor (VEGFR). The presence of both VEGFR1 and VEGFR2 in the RWPE-1 cell line was confirmed by immunocytochemistry. Treatment of RWPE-1 cells with VEGF(165) resulted in transient ERK1/2 activation and increased cellular proliferation. The ability of isoflavones to modulate ERK1/2 signaling cascade via VEGFR signaling in the prostate may be responsible, in part, for the anticancer activity of soy.

Non-genomic action of resveratrol on androgen and oestrogen receptors in prostate cancer: modulation of the phosphoinositide 3-kinase pathway

Prostate cancer represents a major concern in human oncology and the phytoalexin resveratrol (RES) inhibits growth and proliferation of prostate cancer cells through the induction of apoptosis. In addition, previous data indicate that in oestrogen-responsive human breast cancer cells, RES induces apoptosis by inhibition of the phosphoinositide-3-kinase (PI3K) pathway. Here, using androgen receptor (AR)-positive LNCaP and oestrogen receptor alpha (ERα)-expressing PC-3 prostate tumour cells, we have analysed whether the antiproliferative activity of RES takes place by inhibition of the AR- or ERα-dependent PI3K pathway. Although RES treatment (up to 150 μM) decreased AR and ERα protein levels, it did not affect AR and ERα interaction with p85-PI3K. Immunoprecipitation and kinase assays showed that RES inhibited AR- and ERα-dependent PI3K activities in LNCaP and PC-3, respectively. Consistently, lower PI3K activities correlated with decreased phosphorylation of downstream targets protein kinase B/AKT (PKB/AKT) and glycogen synthase kinase-3 (GSK-3). GSK-3 dephosphorylation could be responsible for the decreased cyclin D1 levels observed in both cell lines. Importantly, RES markedly decreased PKB/AKT phosphorylation in primary cultures from human prostate tumours, suggesting that the mechanism proposed here could take place in vivo. Thus, RES could have antitumoral activity in androgen-sensitive and androgen-non-sensitive human prostate tumours by inhibiting survival pathways such as that mediated by PI3K.

The prevention of prostate cancer

From our better understanding of the natural history of prostate cancer, it is not unreasonable to believe that the disease is preventable. Prostate cancer has become a major healthcare problem worldwide, as life expectancy increases. Moreover, the cancer is slow growing, with a period of about 20-25 years from initiation to the stage when the clinically detectable phenotype can be identified. This review provides a simple overview of the endocrinology of prostate cancer and discusses some of the pharmaceutical agents that have been or are being tested to restrain, possibly arrest, the progression of this slowly growing cancer. Also discussed are many of the dietary factors that may influence the molecular or endocrine events implicated in its development. Dietary factors are considered responsible for the geographical differences in prostate cancer incidence and mortality. Since about 50% of all men worldwide, from both East and West, show evidence of microscopic cancer by 50 years of age, growth restraint would appear to be the pragmatic option to the possibility of preventing initiation.

Estrogen and resveratrol regulate Rac and Cdc42 signaling to the actin cytoskeleton of metastatic breast cancer cells

Estrogen and structurally related molecules play critical roles in breast cancer. We reported that resveratrol (50 microM), an estrogen-like phytosterol from grapes, acts in an antiestrogenic manner in breast cancer cells to reduce cell migration and to induce a global and sustained extension of actin structures called filopodia. Herein, we report that resveratrol-induced filopodia formation is time-dependent and concentration-dependent. In contrast to resveratrol at 50 microM, resveratrol at 5 microM acts in a manner similar to estrogen by increasing lamellipodia, as well as cell migration and invasion. Because Rho GTPases regulate the extension of actin structures, we investigated a role for Rac and Cdc42 in estrogen and resveratrol signaling. Our results demonstrate that 50 microM resveratrol decreases Rac and Cdc42 activity, whereas estrogen and 5 microM resveratrol increase Rac activity in breast cancer cells. MDA-MB-231 cells expressing dominant-negative Cdc42 or dominant-negative Rac retain filopodia response to 50 microM resveratrol. Lamellipodia response to 5 microM resveratrol, estrogen, or epidermal growth factor is inhibited in cells expressing dominant-negative Rac, indicating that Rac regulates estrogen and resveratrol (5 microM) signaling to the actin cytoskeleton. These results indicate that signaling to the actin cytoskeleton by low and high concentrations of resveratrol may be differentially regulated by Rac and Cdc42.

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).

Resveratrol: a review of preclinical studies for human cancer prevention

The search for novel and effective cancer chemopreventive agents has led to the identification of various naturally occurring compounds one of which is resveratrol (trans-3,4',5-trihydroxystilbene), a phytoalexin derived from the skin of grapes and other fruits. Resveratrol is known to have potent anti-inflammatory and antioxidant effects and to inhibit platelet aggregation and the growth of a variety of cancer cells. Its potential chemopreventive and chemotherapeutic activities have been demonstrated in all three stages of carcinogenesis (initiation, promotion, and progression), in both chemically and UVB-induced skin carcinogenesis in mice, as well as in various murine models of human cancers. Evidence from numerous in vitro and in vivo studies has confirmed its ability to modulate various targets and signaling pathways. This review discusses the current preclinical and mechanistic data available and assesses resveratrol's anticancer effects to support its potential as an anticancer agent in human populations.

A novel function of caspase-8 in the regulation of androgen-receptor-driven gene expression

Transcriptional regulation by the androgen receptor (AR) is critical for male sexual development and prostate cancer. In this study, we used an expression cloning strategy to identify molecules that regulate AR-driven transcription. Screening of a human cDNA library resulted in isolation of caspase-8 (Casp8), an initiator caspase that mediates death-receptor-induced apoptosis. Casp8 repressed AR-dependent gene expression independently of its apoptotic protease activity by disrupting AR amino-terminal and carboxy-terminal (N/C) interaction and inhibiting androgen-induced AR nuclear localization. Protein-protein interaction analysis revealed that three motifs in Casp8 specifically interacted with the motifs that are known to be involved in AR N/C interaction. Substitutions of the amino-acid residues critical for AR-Casp8 interactions abolished the Casp8-mediated inhibition of AR transactivation. In addition, knockdown of Casp8 by RNA interference specifically affected the androgen-dependent expression of AR-targeting genes in LNCaP cells. These results indicate that Casp8 has a novel function beyond its known role in the mediation of apoptosis.

[Pharmacological potential of phytoestrogens in the treatment of prostate cancer]

INTRODUCTION

Phytoestrogenes are plant-derived compounds that have been shown to exert an antiproliferative potential on prostate cancer cells, although the exact mechanisms are still unclear. In prostate cancer cells proliferation is regulated by modulation of the IGF-1 receptor (IGF-R-1) by the androgen receptor (AR) and its co-activator prostate derived Ets factor (PDEF). Phytooestrogenes interact with these mechanisms as demonstrated exemplarily in the presented study with the isoflavone tectorigenin derived from Belamcanda chinensis.

MATERIAL AND METHODS

Cultured androgen-sensitive LNCaP prostate cancer cells were treated with tectorigenin of 100 microM for 24 hours. The mRNA-expression of AR, PSA, PDEF, hTERT, TIMP-3 and IGF-R-1 were quantified by real-time RT-PCR. Furthermore, the expression or activity of PSA, telomerase and IGF-R-1 was measured on the protein level. In addition, we investigated in nude mice the influence of a diet of extracts of Belamcanda chinensis on the growth of subcutaneously injected LNCaP cells versus a control group of animals fed with a soy-free diet.

RESULTS

In cultured LNCaP cells treatment with tectorigenin resulted in a significant down-regulation of the gene expression of AR, PDEF, PSA, IGF-R-1 and hTERT. On the protein level PSA secretion and the activity of telomerase and IGF-R-1 expression was also decreased. The gene expression of TIMP-3 was distinctly up-regulated by tectorigenin. Nude mice fed with Belamcanda chinensis extract showed a significantly decreased incidence and tumor growth compared to controls.

CONCLUSIONS

Tectorigenin shows an inhibition of the IGF-1-R modulated cell proliferation of PCa-Cells, due to modulation of the activity the co-activator PDEF independently from the AR. Furthermore, tectorigenin has pro-apoptotic effects and decreases tissue invasion by up-regulation of TIMP-3. Therefore, phytooestrogenes are an interesting option in the therapy of prostate especially advanced prostate cancer.

Specific Plasma Membrane Binding Sites for Polyphenols, Including Resveratrol, in the Rat Brain

Using [3H]resveratrol (3,5,4'-trihydroxy-trans-stilbene) as radioligand, we investigated the possible existence of specific polyphenol binding sites at the level of the cellular plasma membrane in rat brain. Specific [3H]resveratrol binding sites were found to be enriched in the plasma membrane pellet with lower levels in the nuclear and cell debris fraction. Specific [3H]resveratrol binding to the plasma membrane fraction was sensitive to trypsin digestion and protein denaturation but not to DNase and RNase treatment. Saturation binding experiments revealed that specific [3H]resveratrol recognized a single class of sites with an apparent affinity (KD) of 220+/-45 nM and a maximal capacity (Bmax) of 1060+/-120 fmol/mg protein. Various polyphenols and resveratrol derivatives competed against specific [3H]resveratrol binding in rat brain plasma membrane homogenates with the tea catechin gallates (epigallocatechin gallate and epicatechin gallate) displaying the highest affinities (Ki=25-45 nM) followed by resveratrol (Ki=102 nM). Quantitative autoradiographic studies revealed that specific [3H]resveratrol binding sites are broadly distributed in the rat brain, with highest levels of labeling seen in the choroid plexus and subfornical organ. Finally, the potency of various polyphenols and resveratrol analogs in protecting hippocampal cells against beta-amyloid-induced toxicity correlated well (r=0.74) with their apparent affinity in the [3H]resveratrol binding assay. Taken together, these results suggest that the neuroprotective action of various polyphenols and resveratrol analogs could be mediated by the activation of common "receptor" binding sites particularly enriched at the level of the cellular plasma membrane in the rat brain.

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.

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.