Monomethylated selenium inhibits growth of LNCaP human prostate cancer xenograft accompanied by a decrease in the expression of androgen receptor and prostate-specific antigen (PSA)

Detailed resume of S-methyltransferases: Categories, structures, biological functions and research advancements in related pathophysiology and pharmacotherapy

Methylation is a vital chemical reaction in the metabolism of many drugs, neurotransmitters, hormones, and exogenous compounds. Among them, S-methylation plays a significant role in the biotransformation of sulfur-containing compounds, particularly chemicals with sulfhydryl groups. Currently, only three S-methyltransferases have been reported: thiopurine methyltransferase (TPMT), thiol methyltransferase (TMT), and thioether methyltransferase (TEMT). These enzymes are involved in various biological processes such as gene regulation, signal transduction, protein repair, tumor progression, and biosynthesis and degradation reactions in animals, plants, and microorganisms. Furthermore, they play pivotal roles in the metabolic pathways of essential drugs and contribute to the advancement of diseases such as tumors. This paper reviews the research progress on relevant structural features, metabolic mechanisms, inhibitor development, and influencing factors (gene polymorphism, S-adenosylmethionine level, race, sex, age, and disease) of S-methyltransferases. We hope that a better comprehension of S-methyltransferases will help to provide a reference for the development of novel strategies for related disorders and improve long-term efficacy.

Selenium in Prostate Cancer: Prevention, Progression, and Treatment

Selenium, a trace mineral with various biological functions, has become a focal point in prostate cancer research. This review aims to present a comprehensive overview of selenium's involvement in prostate cancer, covering its impact on prevention, development, treatment, and underlying mechanisms. Observational studies have revealed a link between selenium levels and selenoproteins with prostate cancer progression. However, randomized controlled studies have shown that selenium supplementation does not prevent prostate cancer (HR: 0.95; 95% CI 0.80-1.13). This discrepancy might be attributed to selenoprotein single nucleotide polymorphisms. In the context of combinatorial therapy, selenium has demonstrated promising synergistic potential in the treatment of prostate cancer. Emerging evidence highlights the significant role of selenium and selenoproteins in prostate cancer, encompassing AR signaling, antioxidative properties, cell death, cell cycle regulation, angiogenesis, epigenetic regulation, immunoregulation, epithelial-mesenchymal transformation, and redox signal. In conclusion, selenium's diverse properties make it a promising trace mineral in prostate cancer prevention, development, and treatment and as a platform for exploring novel agents.

Enhanced selenocysteine biosynthesis for seleno-methylselenocysteine production in Bacillus subtilis

Seleno-methylselenocysteine (SeMCys) is an effective component for selenium supplementation with anti-carcinogenic potential and can ameliorate neuropathology and cognitive deficits. In this study, we aimed to engineer Bacillus subtilis 168 for the microbial production of SeMCys. First, the accumulation of intracellular selenocysteine (SeCys) as the precursor of SeMCys was enhanced through overexpression of serine O-acetyltransferase, which was desensitized against feedback inhibition by cysteine. Next, the S-adenosylmethionine (SAM) synthetic pathway was optimized to improve methyl donor availability through expression of S-adenosylmethionine synthetase. Further, SeMCys was successfully produced through expression of the selenocysteine methyltransferase in SeCys and SAM-producing strain. The increased expression level of selenocysteine methyltransferase benefited the SeMCys production. Finally, all the heterologous genes were integrated into the genome of B. subtilis, and the strain produced SeMCys at a titer of 18.4 μg/L in fed-batch culture. This is the first report on the metabolic engineering of B. subtilis for microbial production of SeMCys and provides a good starting point for future pathway engineering to achieve the industrial-grade production of SeMCys. KEY POINTS: • Expression of the feedback-insensitive serine O-acetyltransferase provided B. subtilis the ability of accumulating SeCys. • SAM production was enhanced through expressing S-adenosylmethionine synthetase in B. subtilis. • Expression of selenocysteine methyltransferase in SeCys and SAM-accumulating strain facilitated SeMCys production.

Effect of Dietary Methylseleninic Acid and Se-Methylselenocysteine on Carcinogen-Induced, Androgen-Promoted Prostate Carcinogenesis in Rats

Selenomethionine (SeMet) did not prevent prostate cancer in the SELECT trial and in two hormone-driven rat models. However, we have shown that daily oral bolus administration of next-generation selenium forms, methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) at 3 mg Se/kg body weight, inhibits prostate carcinogenesis in the TRAMP and pten-deficient mouse models and In Vivo growth of human prostate cancer cells. Here, we determined whether these Se forms prevent prostate cancer in a chemically induced-androgen promoted carcinogenesis rat model in which SeMet was not preventive. WU rats were treated with methylnitrosourea, and one week later, slow-release testosterone implants when they were randomized to groups fed AIN-93M diet supplemented with 3 ppm selenium as MSeA or MSeC or control diet. Mean survival, tumor incidence in all accessory sex glands combined (dorsolateral and anterior prostate plus seminal vesicle) and the incidence of tumors confined to dorsolateral and/or anterior prostate were not statistically significantly different among the groups. Thus, MSeA and MSeC feeding was not preventive in this model. The contrast with the inhibitory effects of MSeA and MSeC in mouse models may be due to differences in carcinogenic mechanisms, selenium dosage, delivery mode, and pharmacokinetics or fundamental rat-mouse differences in selenium metabolism.

The Effect of Organoselenium Compounds on Histone Deacetylase Inhibition and Their Potential for Cancer Therapy

Genetic and epigenetic changes alter gene expression, contributing to cancer. Epigenetic changes in cancer arise from alterations in DNA and histone modifications that lead to tumour suppressor gene silencing and the activation of oncogenes. The acetylation status of histones and non-histone proteins are determined by the histone deacetylases and histone acetyltransferases that control gene transcription. Organoselenium compounds have become promising contenders in cancer therapeutics. Apart from their anti-oxidative effects, several natural and synthetic organoselenium compounds and metabolites act as histone deacetylase inhibitors, which influence the acetylation status of histones and non-histone proteins, altering gene transcription. This review aims to summarise the effect of natural and synthetic organoselenium compounds on histone and non-histone protein acetylation/deacetylation in cancer therapy.

Targeting INMT and interrupting its methylation pathway for the treatment of castration resistant prostate cancer

Background

Castration-resistant prostate cancer (CRPC) is associated with a very poor prognosis, and the treatment of which remains a serious clinical challenge.

Methods

RNA-seq, qPCR, western blot and immunohistochemistry were employed to identify and confirm the high expression of indolethylamine N-methyltransferase (INMT) in CRPC and the clinical relevance. Chip assay was used to identify Histone-Lysine N-Methyltransferase (SMYD3) as a major epigenetic regulator of INMT. LC-MS/MS were used to identify new substrates of INMT methylation in CRPC tissues. Gene knockdown/overexpression, MTT and mouse cancer models were used to examine the role of INMT as well as the anticancer efficacy of INMT inhibitor N,N-dimethyltryptamine (DMT), the SMYD3 inhibitor BCl-12, the selenium compounds methaneseleninic acid (MSA) and Se-(Methyl)selenocysteine hydrochloride (MSC), and the newly identified endogenous INMT substrate Bis(7)-tacrine.

Results

We found that the expression of INMT was highly increased in CRPC and was correlated with poor prognosis of clinical prostate cancer (PCa). INMT promoted PCa castration resistance via detoxification of anticancer metabolites. Knockdown of INMT or treatment with INMT inhibitor N,N-dimethyltryptamine (DMT) significantly suppressed CRPC development. Histone-Lysine N-Methyltransferase SMYD3 was a major epigenetic regulator of INMT expression, treatment with SMYD3 inhibitor BCl-121 suppressed INMT expression and inhibits CRPC development. Importantly, INMT knockdown significantly increased the anticancer effect of the exogenous selenium compounds methaneseleninic acid (MSA) and Se-(Methyl)selenocysteine hydrochloride (MSC) as well as the endogenous metabolite Bis(7)-tacrine.

Conclusions

Our study suggests that INMT drives PCa castration resistance through detoxification of anticancer metabolites, targeting INMT or its regulator SMYD3 or/and its methylation metabolites represents an effective therapeutic avenue for CRPC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02109-z.

EGFR-IL-6 Signaling Axis Mediated the Inhibitory Effect of Methylseleninic Acid on Esophageal Squamous Cell Carcinoma

Epidemiological and experimental evidence indicate that selenium is associated with a reduced risk of some cancers, including esophageal cancer. However, the exact mechanism is still unclear. In the present study, we used esophageal squamous cell carcinoma (ESCC) cell lines and animal models to explore the anti-cancer mechanism of methylseleninic acid (MSA). Firstly, MSA treatment dramatically attenuated Epidermal Growth Factor Receptor (EGFR) protein expression but did not alter mRNA levels in ESCC cells. On the contrary, EGFR overexpression partly abolished the inhibitory effect of MSA. With a microRNA-array, we found MSA up-regulated miR-146a which directly targeted EGFR, whereas miR-146a inhibitor antagonized MSA-induced decrease of EGFR protein. We further used 4-nitroquinoline-1-oxide (4NQO)-induced esophageal tumor mice model to evaluate the inhibitory effect of MSA in vivo. MSA treatment significantly decreased the tumor burden and EGFR protein expression in tumor specimens. Furthermore, MSA treatment inhibited EGFR pathway and subsequntly reduced Interleukin-6 (IL-6) secretion in the supernatant of cancer cell lines. MSA-induced IL-6 suppression was EGFR-dependent. To further evaluate the association of IL-6 and the anti-tumor effect of MSA on esophageal cancer, we established the 4NQO-induced esophageal tumor model in IL-6 knock-out (IL-6 KO) mice. The results showed that IL-6 deficiency did not affect esophageal tumorigenesis in mice, but the inhibitory effect of MSA was abolished in IL-6 KO mice. In conclusion, our study demonstrated that MSA upregulated miR-146a which directly targeted EGFR, and inhibited EGFR protein expression and pathway activity, subsequently decreased IL-6 secretion. The inhibitory effect of MSA on esophageal cancer was IL-6 dependent. These results suggested that MSA may serve as a potential drug treating esophageal cancer.

A Novel mRNA-Mediated and MicroRNA-Guided Approach to Specifically Eradicate Drug-Resistant Hepatocellular Carcinoma Cell Lines by Se-Methylselenocysteine

Despite progress in the treatment of non-visceral malignancies, the prognosis remains poor for malignancies of visceral organs and novel therapeutic approaches are urgently required. We evaluated a novel therapeutic regimen based on treatment with Se-methylselenocysteine (MSC) and concomitant tumor-specific induction of Kynurenine aminotransferase 1 (KYAT1) in hepatocellular carcinoma (HCC) cell lines, using either vector-based and/or lipid nanoparticle-mediated delivery of mRNA. Supplementation of MSC in KYAT1 overexpressed cells resulted in significantly increased cytotoxicity, due to ROS formation, as compared to MSC alone. Furthermore, microRNA antisense-targeted sites for miR122, known to be widely expressed in normal hepatocytes while downregulated in hepatocellular carcinoma, were added to specifically limit cytotoxicity in HCC cells, thereby limiting the off-target effects. KYAT1 expression was significantly reduced in cells with high levels of miR122 supporting the concept of miR-guided induction of tumor-specific cytotoxicity. The addition of alpha-ketoacid favored the production of methylselenol, enhancing the cytotoxic efficacy of MSC in HCC cells, with no effects on primary human hepatocytes. Altogether, the proposed regimen offers great potential to safely and specifically target hepatic tumors that are currently untreatable.

Methylselenol Produced In Vivo from Methylseleninic Acid or Dimethyl Diselenide Induces Toxic Protein Aggregation in Saccharomyces cerevisiae

Methylselenol (MeSeH) has been suggested to be a critical metabolite for anticancer activity of selenium, although the mechanisms underlying its activity remain to be fully established. The aim of this study was to identify metabolic pathways of MeSeH in Saccharomyces cerevisiae to decipher the mechanism of its toxicity. We first investigated in vitro the formation of MeSeH from methylseleninic acid (MSeA) or dimethyldiselenide. Determination of the equilibrium and rate constants of the reactions between glutathione (GSH) and these MeSeH precursors indicates that in the conditions that prevail in vivo, GSH can reduce the major part of MSeA or dimethyldiselenide into MeSeH. MeSeH can also be enzymatically produced by glutathione reductase or thioredoxin/thioredoxin reductase. Studies on the toxicity of MeSeH precursors (MSeA, dimethyldiselenide or a mixture of MSeA and GSH) in S.cerevisiae revealed that cytotoxicity and selenomethionine content were severely reduced in a met17 mutant devoid of O-acetylhomoserine sulfhydrylase. This suggests conversion of MeSeH into selenomethionine by this enzyme. Protein aggregation was observed in wild-type but not in met17 cells. Altogether, our findings support the view that MeSeH is toxic in S. cerevisiae because it is metabolized into selenomethionine which, in turn, induces toxic protein aggregation.

Role of GDF15 in methylseleninic acid-mediated inhibition of cell proliferation and induction of apoptosis in prostate cancer cells

The growth inhibitory efficacy of methylseleninic acid (MSA) in prostate cancer cells has been documented extensively. However, our understanding of the immediate targets that are key to the growth inhibitory effects of MSA remains limited. Here, using multiple preclinical prostate cancer models, we demonstrated in vitro and in vivo that GDF15 is a most highly induced, immediate target of MSA. We further showed that knockdown of GDF15 mitigates MSA inhibition of cell proliferation and induction of apoptosis. Analysis of gene expression data from over 1000 primary and 200 metastatic prostate cancer samples revealed that GDF15 expression is decreased in metastatic prostate cancers compared to primary tumors and that lower GDF15 levels in primary tumors are associated with higher Gleason scores and shorter survival of the patients. Additionally, pathways that are negatively correlated with GDF15 levels in clinical samples are also negatively correlated with MSA treatment in cultured cells. Since most, if not all, of these pathways have been implicated in prostate cancer progression, suppressing their activities by inducing GDF15 is consistent with the anticancer effects of MSA in prostate cancer. Overall, this study provides support for GDF15 as an immediate target of MSA in prostate cancer cells.

Selenium Species: Current Status and Potentials in Cancer Prevention and Therapy

Selenium (Se) acts as an essential trace element in the human body due to its unique biological functions, particularly in the oxidation-reduction system. Although several clinical trials indicated no significant benefit of Se in preventing cancer, researchers reported that some Se species exhibit superior anticancer properties. Therefore, a reassessment of the status of Se and Se compounds is necessary in order to provide clearer insights into the potentiality of Se in cancer prevention and therapy. In this review, we organize relevant forms of Se species based on the three main categories of Se-inorganic, organic, and Se-containing nanoparticles (SeNPs)-and overview their potential functions and applications in oncology. Here, we specifically focus on the SeNPs as they have tremendous potential in oncology and other fields. In general, to make better use of Se compounds in cancer prevention and therapy, extensive further study is still required to understand the underlying mechanisms of the Se compounds.

Organic selenium compounds as potential chemotherapeutic agents for improved cancer treatment

Selenium(Se)-containing compounds have attracted a growing interest as anticancer agents over recent decades, with mounting reports demonstrating their high efficacy and selectivity against cancer cells. Typically, Se compounds exert their cytotoxic effects by acting as pro-oxidants that alter cellular redox homeostasis. However, the precise intracellular targets, signalling pathways affected and mechanisms of cell death engaged following treatment vary with the chemical properties of the selenocompound and its metabolites, as well as the cancer model that is used. Naturally occurring organic Se compounds, besides encompassing a significant antitumor activity with an apparent ability to prevent metastasis, also seem to have fewer side effects and less systemic effects as reported for many inorganic Se compounds. On this basis, many novel organoselenium compounds have also been synthesized and examined as potential chemotherapeutic agents. This review aims to summarize the most well studied natural and synthetic organoselenium compounds and provide the most recent developments in our understanding of the molecular mechanisms that underlie their potential anticancer effects.

Selenium Analysis and Speciation in Dietary Supplements Based on Next-Generation Selenium Ingredients

Selenium is essential for humans and the deficit of Se requires supplementation. In addition to traditional forms such as Se salts, amino acids, or selenium-enriched yeast supplements, next-generation selenium supplements, with lower risk for excess supplementation, are emerging. These are based on selenium forms with lower toxicity, higher bioavailability, and controlled release, such as zerovalent selenium nanoparticles (SeNPs) and selenized polysaccharides (SPs). This article aims to focus on the existing analytical systems for the next-generation Se dietary supplement, providing, at the same time, an overview of the analytical methods available for the traditional forms. The next-generation dietary supplements are evaluated in comparison with the conventional/traditional ones, as well as the analysis and speciation methods that are suitable to reveal which Se forms and species are present in a dietary supplement. Knowledge gaps and further research potential in this field are highlighted. The review indicates that the methods of analysis of next-generation selenium supplements should include a step related to chemical species separation. Such a step would allow a proper characterization of the selenium forms/species, including molecular mass/dimension, and substantiates the marketing claims related to the main advantages of these new selenium ingredients.

4-Hydroxybenzoic acid (4-HBA) enhances the sensitivity of human breast cancer cells to adriamycin as a specific HDAC6 inhibitor by promoting HIPK2/p53 pathway

Breast cancer is reported a very complex disease along with heterogeneous morphological characteristics and unrelated clinical behavior, and is a leading cancer among female. Nevertheless, chemo-resistance is frequently observed. Adriamycin (ADM) is a always employed drug to treat clinical breast cancer. However, strong resistance to ADM limited its clinical efficacy. Deregulation of HDAC6 activity is linked to various diseases including cancer resulting in accumulating interest for developing HDAC6 inhibitors. In the present study, for the first time, we found that 4-Hydroxybenzoic acid (4-HBA), as histone deacetylase 6 (HDAC6) inhibitor, could successfully reverse ADM resistance in human breast cancer cells. 4-HBA significantly promoted the anticancer effect of ADM on apoptosis induction, as evidenced by the increased expressions of Caspase-3 and PARP cleavage, which was associated with the promotion p53 and homeodomain interacting protein kinase-2 (HIPK2) expressions in ADM-resistant breast cancer cells. Furthermore, the suppressive effect of ADM on drug-resistant breast cancer cells was accelerated by 4-HBA through increasing the number of cells distributed in G2/M phase of cell cycle arrest. Inhibiting HIPK2/p53 pathway could abolish 4-HBA/ADM co-treatment-induced apoptosis and G2/M cell cycle arrest. Importantly, HDAC6 expressions were also significantly down-regulated in ADM-resistance breast cancer cells co-treated with ADM and 4-HBA. Additionally, 4-HBA clearly potentiated the anticancer role of ADM in the MCF-7 breast cancer animal model with low toxicity. Therefore, 4-HBA could be applied as an effective HDAC6 inhibitor to reverse human breast cancer resistance. Herein, the 4-HBA and ADM combination might represent as a useful therapeutic strategy to prevent human breast cancer.

Selenocompounds in Cancer Therapy: An Overview

In vitro and in vivo experimental models clearly demonstrate the efficacy of Se compounds as anticancer agents, contingent upon chemical structures and concentrations of test molecules, as well as on the experimental model under investigation that together influence cellular availability of compounds, their molecular dynamics and mechanism of action. The latter includes direct and indirect redox effects on cellular targets by the activation and altered compartmentalization of molecular oxygen, and the interaction with protein thiols and Se proteins. As such, Se compounds interfere with the redox homeostasis and signaling of cancer cells to produce anticancer effects that include alterations in key regulatory elements of energy metabolism and cell cycle checkpoints that ultimately influence differentiation, proliferation, senescence, and death pathways. Cys-containing proteins and Se proteins involved in the response to Se compounds as sensors and transducers of anticancer signals, i.e., the pharmacoproteome of Se compounds, are described and include critical elements in the different phases of cancer onset and progression from initiation and escape of immune surveillance to tumor growth, angiogenesis, and metastasis. The efficacy and mode of action on these compounds vary depending on the inorganic and organic form of Se used as either supplement or pharmacological agent. In this regard, differences in experimental/clinical protocols provide options for either chemoprevention or therapy in different human cancers.

Prostate Cancer Prevention: Concepts and Clinical Trials

Prevention is an important treatment strategy for diminishing prostate cancer morbidity and mortality and is applicable to both early- and late-stage disease. There are three basic classifications of cancer prevention: primary (prevention of incident disease), secondary (identification and treatment of preclinical disease), and tertiary (prevention of progression or recurrence). Based on level I evidence, 5-alpha reductase inhibitors (5-ARIs) should be considered in selected men to prevent incident prostate cancer. Level I evidence also supports the consideration of dutasteride, a 5-ARI, for tertiary prevention in active surveillance and biochemical recurrence patients. Vitamins and supplements, including selenium or vitamin E, have not been proven in clinical trials to prevent prostate cancer and in the case of Vitamin E has been found to increase the risk of incident prostate cancer. Ongoing and future trials may further elucidate the role of diet and immunotherapy for prevention of prostate cancer.

Methylselenocysteine preventing castration-resistant progression of prostate cancer

BACKGROUND

Castration-resistant progression of prostate cancer after androgen deprivation therapy remains a critical challenge in the clinical management of prostate cancer. Resurgent androgen receptor activity is an established driver of castration-resistant progression, and upregulation of androgen receptor expression has been implicated to contribute to the resurgent androgen receptor activity. We reported previously that methylselenocysteine can decrease the expression and activity of androgen receptor. Here we investigated the ability of methylselenocysteine to inhibit castration-resistant progression of prostate cancer.

METHODS

The regrowth of LNCaP prostate cancer xenografts after castration was monitored. The levels of prostate-specific antigen in mouse serum were measured by ELISA. Tumor cell proliferation and apoptosis were analyzed via Ki-67 immunohistochemistry and TUNEL assay, respectively. Intratumoral angiogenesis was assessed by immunohistochemistry staining of vascular endothelial growth factor and CD31.

RESULTS

We showed that methylselenocysteine delayed castration-resistant regrowth of LNCaP xenograft tumors after androgen deprivation. This was accompanied by decreased serum levels of prostate-specific antigen, inhibition of prostate cancer cell proliferation and tumor angiogenesis, as well as downregulation of androgen receptor and induction of apoptosis in the relapsed tumors.

CONCLUSIONS

The present study represents the first to show the preclinical efficacy of methylselenocysteine in delaying castration-resistant progression of prostate cancer. The findings provide a rationale for evaluating the clinical application of combining methylselenocysteine with androgen deprivation therapy for the treatment of advanced prostate cancer.

The interaction between epigenetics, nutrition and the development of cancer

Unlike the genome, the epigenome can be modified and hence some epigenetic risk markers have the potential to be reversed. Such modifications take place by means of drugs, diet or environmental exposures. It is widely accepted that epigenetic modifications take place during early embryonic and primordial cell development, but it is also important that we gain an understanding of the potential for such changes later in life. These “later life” epigenetic modifications in response to dietary intervention are the focus of this paper. The epigenetic modifications investigated include DNA methylation, histone modifications and the influence of microRNAs. The epigenotype could be used not only to predict susceptibility to certain cancers but also to assess the effectiveness of dietary modifications to reduce such risk. The influence of diet or dietary components on epigenetic modifications and the impact on cancer initiation or progression has been assessed herein.

Selenium compounds as therapeutic agents in cancer

BACKGROUND

With cancer cells encompassing consistently higher production of reactive oxygen species (ROS) and with an induced antioxidant defense to counteract the increased basal ROS production, tumors have a limited reserve capacity resulting in an increased vulnerability of some cancer cells to ROS. Based on this, oxidative stress has been recognized as a tumor-specific target for the rational design of new anticancer agents. Among redox modulating compounds, selenium compounds have gained substantial attention due to their promising chemotherapeutic potential.

SCOPE OF REVIEW

This review aims in summarizing and providing the recent developments of our understanding of the molecular mechanisms that underlie the potential anticancer effects of selenium compounds.

MAJOR CONCLUSIONS

It is well established that selenium at higher doses readily can turn into a prooxidant and thereby exert its potential anticancer properties. However, the biological activity of selenium compounds and the mechanism behind these effects are highly dependent on its speciation and the specific metabolic pathways of cells and tissues. Conversely, the chemical properties and the main molecular mechanisms of the most relevant inorganic and organic selenium compounds as well as selenium-based nanoparticles must be taken into account and are discussed herein.

GENERAL SIGNIFICANCE

Elucidating and deepening our mechanistic knowledge of selenium compounds will help in designing and optimizing compounds with more specific antitumor properties for possible future application of selenium compounds in the treatment of cancer. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Beyond androgen deprivation: ancillary integrative strategies for targeting the androgen receptor addiction of prostate cancer

The large majority of clinical prostate cancers remain dependent on androgen receptor (AR) activity for proliferation even as they lose their responsiveness to androgen deprivation or antagonism. AR activity can be maintained in these circumstances by increased AR synthesis--often reflecting increased NF-κB activation; upregulation of signaling pathways that promote AR activity in the absence of androgens; and by emergence of AR mutations or splice variants lacking the ligand-binding domain, which render the AR constitutively active. Drugs targeting the N-terminal transactivating domain of the AR, some of which are now in preclinical development, can be expected to inhibit the activity not only of unmutated ARs but also of the mutant forms and splice variants selected for by androgen deprivation. Concurrent measures that suppress AR synthesis or boost AR turnover could be expected to complement the efficacy of such drugs. A number of nutraceuticals that show efficacy in prostate cancer xenograft models--including polyphenols from pomegranate, grape seed, and green tea, the crucifera metabolite diindolylmethane, and the hormone melatonin--have the potential to suppress AR synthesis via downregulation of NF-κB activity; clinical doses of salicylate may have analogous efficacy. The proteasomal turnover of the AR is abetted by diets with a high ratio of long-chain omega-3 to omega-6 fatty acids, which are beneficial in prostate cancer xenograft models; berberine and sulforaphane, by inhibiting AR's interaction with its chaperone Hsp90, likewise promote AR proteasomal degradation and retard growth of human prostate cancer in nude mice. Hinge region acetylation of the AR is required for optimal transactivational activity, and low micromolar concentrations of the catechin epigallocatechin-3-gallate (EGCG) can inhibit such acetylation--possibly explaining the ability of EGCG administration to suppress androgenic activity and cell proliferation in prostate cancer xenografts. Hence, it is proposed that regimens featuring an N-terminal domain-targeting drug, various nutraceuticals/drugs that downregulate NF-κB activity, and/or supplemental intakes of fish oil, berberine, sulforaphane, and EGCG have potential for blocking proliferation of prostate cancer by targeting its characteristic addiction to androgen receptor activity.

Combination effects of dietary soy and methylselenocysteine in a mouse model of prostate cancer

BACKGROUND

High dietary intake of soy or selenium (Se) is associated with decreased risk of prostate cancer. Soy constituents and various chemical forms of Se have each been shown to downregulate expression of the androgen receptor (AR) and AR-regulated genes in the prostate. We hypothesized that downregulation of AR and AR-regulated genes by the combination of these dietary components would inhibit tumorigenesis in the TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse.

METHODS

Male mice were exposed from conception to stock diets high or low in soy, with or without a supplement of Se-methylseleno-L-cysteine (MSC) in a 2 × 2 factorial design. Mice were sacrificed at 18 weeks. Prostate histopathology, urogenital tract (UGT) weight, hepatic activity of androgen-metabolizing enzymes, and expression of AR, AR-regulated, and AR-associated FOX family genes, in the dorsolateral prostate were examined.

RESULTS

High soy intake decreased activity of hepatic aromatase and 5α-reductase, expression of AR, AR-regulated genes, FOXA1, UGT weight, and tumor progression, and upregulated protective FOXO3. Supplemental MSC upregulated AKR1C14, which reduces 5α-dihydrotestosterone.

CONCLUSIONS

Soy is an effective pleiotropic dietary agent for prevention of prostate cancer. The finding of effects of soy on FOX family gene expression in animals is novel. Combination effects of supplemental MSC may depend upon the soy content of the basal diet to which it is added.

Methylselenol prodrug enhances MDV3100 efficacy for treatment of castration-resistant prostate cancer

The next-generation antiandrogen MDV3100 prolongs overall survival of patients with metastatic castration-resistant prostate cancer (CRPC). However, patient responses are variable, and survival benefit remains relatively small. Developing effective modality to improve MDV3100 efficacy is urgently needed. Recent evidence suggests that constitutively active androgen receptor splice variants (AR-Vs) drive resistance to MDV3100. In our study, we show that methylselenol prodrug downregulates the expression and activity of both the full-length AR (AR-FL) and AR-Vs. The downregulation is independent of androgen and could be attributable to repressed transcription of the AR gene. Cotreatment with methylselenol prodrug and MDV3100 suppresses AR signaling more dramatically than either agent alone, and synergistically inhibits the growth of CRPC cells in vitro. The combinatorial efficacy is observed in not only AR-V-expressing cells but also cells expressing predominantly AR-FL, likely owing to the ability of the two drugs to block the AR signaling cascade at distinct steps. Ectopic expression of AR-FL or AR-V7 attenuates the combinatorial efficacy, indicating that downregulating AR-FL and AR-V7 is importantly involved in mediating the combinatorial efficacy. Significantly, methylselenol prodrug also downregulates AR-FL and AR-Vs in vivo and substantially improves the antitumor efficacy of MDV3100. These findings support a potential combination therapy for improving MDV3100 efficacy, and provide a rationale for evaluating the clinical application of combining methylselenol prodrug with MDV3100 for the treatment of CRPC.

Influence of natural and synthetic histone deacetylase inhibitors on chromatin

SIGNIFICANCE

Histone deacetylase inhibitors (HDACIs) have emerged as a new class of anticancer therapeutics. The hydroxamic acid, suberoylanilide hydroxamic acid (Vorinostat, Zolinza™), and the cyclic peptide, depsipeptide (Romidepsin, Istodax™), were approved by the U.S. Food and Drug Administration (FDA) for the treatment of cutaneous T-cell lymphoma in 2006 and 2009, respectively. At least 15 HDACIs are currently undergoing clinical trials either alone or in combination with other therapeutic modalities for the treatment of numerous hematological and solid malignancies.

RECENT ADVANCES

The potential utility of HDACIs has been extended to nononcologic applications, including autoimmune disorders, inflammation, diseases of the central nervous system, and malaria.

CRITICAL ISSUES

Given the promise of HDACIs, there is growing interest in the potential of dietary compounds that possess HDAC inhibition activity. This review is focused on the identification of and recent findings with HDACIs from dietary, medicinal plant, and microbial sources. We discuss the mechanisms of action and clinical potential of natural HDACIs.

FUTURE DIRECTIONS

Apart from identification of further HDACI compounds from dietary sources, further research will be aimed at understanding the effects on gene regulation on lifetime exposure to these compounds. Another important issue that requires clarification.

Selenium and its' role in the maintenance of genomic stability

Selenium (Se) is an essential micronutrient for humans, acting as a component of the unusual amino acids, selenocysteine (Se-Cys) and selenomethionine (Se-Met). Where Se levels are low, the cell cannot synthesise selenoproteins, although some selenoproteins and some tissues are prioritised over others. Characterised functions of known selenoproteins, include selenium transport (selenoprotein P), antioxidant/redox properties (glutathione peroxidases (GPxs), thioredoxin reductases and selenoprotein P) and anti-inflammatory properties (selenoprotein S and GPx4). Various forms of Se are consumed as part of a normal diet, or as a dietary supplement. Supplementation of tissue culture media, animal or human diets with moderate levels of certain Se compounds may protect against the formation of DNA adducts, DNA or chromosome breakage, and chromosome gain or loss. Protective effects have also been shown on mitochondrial DNA, and on telomere length and function. Some of the effects of Se compounds on gene expression may relate to modulation of DNA methylation or inhibition of histone deacetylation. Despite a large number of positive effects of selenium and selenoproteins in various model systems, there have now been some human clinical trials that have shown adverse effects of Se supplementation, according to various endpoints. Too much Se is as harmful as too little, with animal models showing a "U"-shaped efficacy curve. Current recommended daily allowances differ among countries, but are generally based on the amount of Se necessary to saturate GPx enzymes. However, increasing evidence suggests that other enzymes may be more important than GPx for Se action, that optimal levels may depend upon the form of Se being ingested, and vary according to genotype. New paradigms, possibly involving nutrigenomic tools, will be necessary to optimise the forms and levels of Se desirable for maximum protection of genomic stability in all humans.

Soy content of basal diets determines the effects of supplemental selenium in male mice

The effects of supplemental Se in rodent models may depend upon composition of the basal diet to which it is added. Wild-type male littermates of Transgenic Adenocarcinoma of Mouse Prostate mice were fed until 18 wk of age 1 of 2 Se-adequate stock diets high in soy (HS) or low in phytoestrogens (LP) or the same diets supplemented with 3.0 mg Se/kg diet as seleno-methylselenocysteine. Body and abdominal fat pad weights were lower (P < 0.01) in mice fed the HS diet. Supplemental Se reduced fat pad weights in mice receiving the LP diet but increased body and fat pad weights in mice consuming the HS formulation (P-interaction < 0.005). Serum free triiodothyronine concentrations were unaffected by supplemental Se in mice fed the LP diet but were decreased by Se supplementation of mice given the HS feed (P-interaction < 0.02). Free thyroxine concentrations were higher in mice consuming the HS diet regardless of Se intake (P < 0.001). Hepatic mRNA for iodothyronine deiodinase I was lower (P < 0.001) in mice fed the HS diet. Supplementation of Se increased this mRNA (P < 0.001) in both diet groups. Results from this study show a significant interaction between the composition of basal diets and the effects of supplemental Se with respect to body composition. These findings have important implications for future studies in rodent models of the effects of supplemental Se on heart disease, cancer, diabetes, and other conditions related to body weight and composition.

Nutritional and supranutritional levels of selenate differentially suppress prostate tumor growth in adult but not young nude mice

The inhibitory effect of oral methylseleninic acid or methylselenocysteine administration on cancer cell xenograft development in nude mice is well characterized; however, less is known about the efficacy of selenate and age on selenium chemoprevention. In this study, we tested whether selenate and duration on diets would regulate prostate cancer xenograft in nude mice. Thirty-nine homozygous NU/J nude mice were fed a selenium-deficient, Torula yeast basal diet alone (Se-) or supplemented with 0.15 (Se) or 1.0 (Se+) mg selenium/kg (as Na₂SeO₄) for 6 months in Experiment 1 and for 4 weeks in Experiment 2, followed by a 47-day PC-3 prostate cancer cell xenograft on the designated diet. In Experiment 1, the Se- diet enhanced the initial tumor development on days 11-17, whereas the Se+ diet suppressed tumor growth on days 35-47 in adult nude mice. Tumors grown in Se- mice were loosely packed and showed increased necrosis and inflammation as compared to those in Se and Se+ mice. In Experiment 2, dietary selenium did not affect tumor development or histopathology throughout the time course. In both experiments, postmortem plasma selenium concentrations in Se and Se+ mice were comparable and were twofold greater than those in Se- mice. Taken together, dietary selenate at nutritional and supranutritional levels differentially inhibit tumor development in adult, but not young, nude mice engrafted with PC-3 prostate cancer cells.

Increased androgen receptor transcription: a cause of castration-resistant prostate cancer and a possible therapeutic target

Few effective therapies exist for the treatment of castration-resistant prostate cancer (CRPC). Recent evidence suggests that CRPC may be caused by augmented androgen/androgen receptor (AR) signaling, generally involving AR overexpression. Aberrant androgen/AR signaling associated with AR overexpression also plays a key role in prostate carcinogenesis. Although AR overexpression could be attributed to gene amplification, only 10-20% of CRPCs exhibit AR gene amplification, and aberrant AR expression in the remaining instances of CRPC is thought to be attributed to transcriptional, translational, and post-translational mechanisms. Overexpression of AR at the protein level, as well as the mRNA level, has been found in CRPC, suggesting a key role for transcriptional regulation of AR expression. Since the analysis of the AR promoter region in the 1990s, several transcription factors have been reported to regulate AR transcription. In this review, we discuss the molecules involved in the control of AR gene expression, with emphasis on its transcriptional control by transcription factors in prostate cancer. We also consider the therapeutic potential of targeting AR expression.

A nutrient approach to prostate cancer prevention: The Selenium and Vitamin E Cancer Prevention Trial (SELECT)

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) randomized 35,533 healthy men, >55 yr old (>50 yr if African American), with normal digital rectal exams and prostate specific antigens <4 ng/ml to 1) 200 μg/day l-selenomethionine, 2) 400 IU/day all-rac-alpha-tocopheryl acetate (vitamin E), 3) both supplements, or 4) placebo for 7 to 12 yr. The hypotheses underlying SELECT, that selenium and vitamin E individually and together decrease prostate cancer incidence, derived from epidemiologic and laboratory evidence and significant secondary endpoints in the Nutritional Prevention of Cancer (selenium) and Alpha-Tocopherol Beta-Carotene (vitamin E) trials. In SELECT, prostate cancer incidence did not differ among the 4 arms: hazard ratios [99% confidence intervals (CIs)] for prostate cancer were 1.13 (99% CI = 0.95-1.35, P = 0.06; n = 473) for vitamin E, 1.04 (99% CI = 0.87-1.24, P = 0.62; n = 432) for selenium, and 1.05 (99% CI = 0.88-1.25, P = 0.52; n = 437) for selenium + vitamin E vs. 1.00 (n = 416) for placebo. Statistically nonsignificant increased risks of prostate cancer with vitamin E alone [relative risk (RR) = 1.13, P = 0.06) and newly diagnosed Type 2 diabetes mellitus with selenium alone (RR = 1.07, P = 0.16) were observed. SELECT data show that neither selenium nor vitamin E, alone or together, in the doses and formulations used, prevented prostate cancer in this heterogeneous population of healthy men.

Se-methylselenocysteine inhibits lipopolysaccharide-induced NF-κB activation and iNOS induction in RAW 264.7 murine macrophages

SCOPE

Se-methyl-L-selenocysteine (MSC), a naturally occurring organoselenium compound, has shown cancer chemopreventive activity against several types of cancer. Herein, the effect of MSC on the inflammatory response in lipopolysaccharide (LPS)-activated murine RAW 264.7 macrophage cells was investigated.

METHODS AND RESULTS

The present results demonstrated that MSC markedly inhibited LPS-induced production of NO in a dose-dependent pattern with decreased mRNA and protein levels of inducible nitric oxide synthase (iNOS). MSC also reduced nuclear translocation of p65 and p50 subunits of nuclear factor-κB (NF-κB), a critical transcription factor necessary for iNOS expression, accompanied with downregulation of LPS-triggered NF-κB-dependent gene expression evaluating by a luciferase reporter. Inhibition of nuclear translocation by MSC might result from the prevention of the inhibitor of NF-κB from phosphorylation and consequent degradation via suppression inhibition of phosphorylation of IκB kinase α/β. Exploring the action mechanism involved, MSC can reduce the phosphorylation/activation of mitogen-activated protein kinases (MAPKs) related to NF-κB activation induced by LPS, including p38 MAPK and c-Jun N-terminal kinase in RAW 264.7 cells.

CONCLUSION

MSC might contribute to the potent anti-inflammatory effect in LPS-activated RAW 264.7 cells via downregulation of NF-κB activation and iNOS expression, suggesting that MSC may be considered as a therapeutic candidate for chronic inflammatory diseases.

beta-Catenin/TCF pathway plays a vital role in selenium induced-growth inhibition and apoptosis in esophageal squamous cell carcinoma (ESCC) cells

Epidemiological and experimental studies have indicated selenium could reduce the risk of some cancers. In our present study, growth inhibition and apoptosis were detected upon methylseleninic acid (MSA) treatment in human esophageal squamous cell carcinoma cell lines EC9706 and KYSE150. MSA reduced beta-catenin protein levels, while there was no significant change observed on transcriptional levels. Moreover, we found MSA accelerated the degradation of beta-catenin and activated glycogen synthase kinase 3beta (GSK-3beta). Some targets of beta-catenin/TCF pathway and apoptosis-related genes altered after MSA treatment. Notably, utilizing the inducible 293-TR/beta-catenin cell line, we found the apoptotic phenotypes induced by MSA were partially reversed by the overexpression of beta-catenin. Overall, our data indicate the effects induced by MSA in ESCC cells may act on the inhibition of beta-catenin/TCF pathway.

Selenium and vitamin E for prostate cancer: post-SELECT (Selenium and Vitamin E Cancer Prevention Trial) status

Various formulations of selenium and vitamin E, both essential human dietary components, have been shown to possess a therapeutic and preventive effect against prostate cancer. Fortuitous results of clinical trials also implied a risk-reduction effect of selenium and vitamin E supplements. The Selenium and Vitamin E Cancer Prevention Trial (SELECT), using oral selenium and vitamin E supplementation in disease-free volunteers, was designed to test a prostate cancer chemoprevention hypothesis. SELECT was terminated early because of both safety concerns and negative data for the formulations and doses given. Here, we review and discuss the studies done before and since the inception of SELECT, as well as the parameters of the trial itself. We believe that there is a lack of appropriate in vivo preclinical studies on selenium and vitamin E despite many promising in vitro studies on these agents. It seems that the most effective doses and formulations of these agents for prostate cancer chemoprevention have yet to be tested. Also, improved understanding of selenium and vitamin E biology may facilitate the discovery of these doses and formulations.

1,4-phenylenebis(methylene)selenocyanate, but not selenomethionine, inhibits androgen receptor and Akt signaling in human prostate cancer cells

The lack of treatment for worried-well patients with high-grade prostatic intraepithelial neoplasia combined with issues of recurrence and hormone resistance in prostate cancer survivors remains a major public health obstacle. The long latency of prostate cancer development provides an opportunity to intervene with agents of known mechanisms at various stages of disease progression. A number of signaling cascades have been shown to play important roles in prostate cancer development and progression, including the androgen receptor (AR) and phosphatidylinositol 3-kinase/Akt signaling pathways. Crosstalk between these two pathways is also thought to contribute to progression and hormone-refractory prostate disease. Our initial investigations show that the naturally occurring organoselenium compound selenomethionine (SM) and the synthetic 1,4-phenylenebis(methylene)selenocyanate (p-XSC) can inhibit human prostate cancer cell viability; however, in contrast to SM, p-XSC is active at physiologically relevant doses. In the current investigation, we show that p-XSC, but not an equivalent dose of SM, alters molecular targets and induces apoptosis in androgen-responsive LNCaP and androgen-independent LNCaP C4-2 human prostate cancer cells. p-XSC effectively inhibits AR expression and transcriptional activity in both cell lines. p-XSC also decreases Akt phosphorylation as well as Akt-specific phosphorylation of the AR. Inhibition of Akt, however, does not fully attenuate p-XSC-mediated downregulation of AR activity, suggesting that inhibition of AR signaling by p-XSC does not occur solely through alterations in the phosphatidylinositol 3-kinase/Akt survival pathway. Our data suggest that p-XSC inhibits multiple signaling pathways in prostate cancer, likely accounting for the downstream effects on proliferation and apoptosis.

Telomerase as an important target of androgen signaling blockade for prostate cancer treatment

As the mainstay treatment for advanced prostate cancer, androgen deprivation therapy (ADT) targets the action of androgen receptor (AR) by reducing androgen level and/or by using anti-androgen to compete with androgens for binding to AR. Albeit effective in extending survival, ADT is associated with dose-limiting toxicity and the development of castration-resistant prostate cancer (CRPC) after prolonged use. Because CRPC is lethal and incurable, developing effective strategies to enhance the efficacy of ADT and circumvent resistance becomes an urgent task. Continuous AR signaling constitutes one major mechanism underlying the development of CRPC. The present study showed that methylseleninic acid (MSA), an agent that effectively reduces AR abundance, could enhance the cancer-killing efficacy of the anti-androgen bicalutamide in androgen-dependent and CRPC cells. We found that the combination of MSA and bicalutamide produced a robust downregulation of prostate-specific antigen and a recently identified AR target, telomerase, and its catalytic subunit, human telomerase reverse transcriptase. The downregulation of hTERT occurs mainly at the transcriptional level, and reduced AR occupancy of the promoter contributes to downregulation. Furthermore, apoptosis induction by the two agents is significantly mitigated by the restoration of hTERT. Our findings thus indicate that MSA in combination with anti-androgen could represent a viable approach to improve the therapeutic outcome of ADT. Given the critical role of hTERT/telomerase downregulation in mediating the combination effect and the fact that hTERT/telomerase could be measured in blood and urine, hTERT/telomerase could serve as an ideal tumor-specific biomarker to monitor the efficacy of the combination therapy noninvasively.

Prostate cancer prevention: concepts and clinical recommendations

Prevention is an important strategy for limiting prostate cancer morbidity and mortality. Two major types of prevention are primary (reduction of incident cases) and tertiary (inhibition of disease progression and recurrence). Pharmacological and dietary interventions have potential functions in both the primary and tertiary prevention of prostate cancer. Five-α reductase inhibitors (5-ARIs) reduce the incidence of prostate cancer in both general and higher-risk populations and are currently under study for tertiary prevention in active surveillance and biochemical recurrence patients. Selenium, vitamin E, and vitamin C do not prevent incident prostate cancer in the general population; however, other promising diet-based interventions are currently under study for tertiary prevention. We recommend consideration of 5-ARIs for prostate cancer prevention in (1) asymptomatic men with a PSA ≤ 3.0 ng ml(-1) who are undergoing or anticipate undergoing PSA screening for early detection of prostate cancer and (2) asymptomatic men with PSA ≥ 2.5 and ≤ 10 ng ml(-1) and an earlier prostate biopsy negative for cancer. Men should be informed of the potential risks of 5-ARI therapy. Currently, there is neither clinical evidence to support the use of 5-ARIs for tertiary prevention in active surveillance or biochemical recurrence populations, nor micronutrients for prostate cancer prevention of any type.

Synthesis and antitumor properties of selenocoxib-1 against rat prostate adenocarcinoma cells

Hormone refractory prostate cancer poses a huge problem and standard of care chemotherapy has not been very successful. We used a novel strategy to combine properties of 2 well-studied class of compounds (selenium and COX-2 inhibitor) and examined the resulting effectiveness against prostate cancer. Bearing in mind that sulfonamide moiety and pyrazole ring is important for the proapoptotic activity of Celecoxib, we synthesized a selenium derivative, Selenocoxib-1, by modifying Celecoxib at position 3 of the pyrazole ring. The PAIII cells derived from a metastatic prostate tumor that arose spontaneously in a Lobund-Wistar (LW) rat were used to examine the efficacy of Selenocoxib-1 in vitro. In addition, human metastatic prostate cancer cells, PC-3M, were tested for antitumor effect of Selenocoxib-1 in vitro. The IC(50) in PAIII and PC-3M cells for Selenocoxib-1 was about 5 microM, while for Celecoxib it was more than 20 microM. Selenocoxib-1 induced apoptosis in a dose-dependent manner in the PAIII cells. COX-2 expression in PAIII cells was downregulated by Celecoxib and Selenocoxib-1 at 20 and 5 microM, respectively; the COX-2 activity was, however, not affected by Selenocoxib-1. Following treatment with Selenocoxib-1, PAIII cells resulted in dose-dependent decrease in HIF-1alpha, p-AKT and Bcl-2 levels. A reduction in weights was observed in subcutaneous tumors produced by PAIII cells pretreated with Selenocoxib-1 as compared to Celecoxib in LW rats. Further, following 1 week Selenocoxib-1 treatment of PAIII tumors resulted in significant reduction of tumor weights. This study demonstrates that Selenocoxib-1 is more effective against prostate cancer than Celecoxib.

Selenium, but not lycopene or vitamin E, decreases growth of transplantable dunning R3327-H rat prostate tumors

Background

Lycopene, selenium, and vitamin E are three micronutrients commonly consumed and supplemented by men diagnosed with prostate cancer. However, it is not clear whether consumption of these compounds, alone or in combination, results in improved outcomes.

Methodology/Principal Findings

We evaluated the effects of dietary lycopene (250 mg/kg diet), selenium (methylselenocysteine, 1 mg/kg diet), and vitamin E (γ-tocopherol, 200 mg/kg diet) alone and in combination on the growth of androgen-dependent Dunning R3327-H rat prostate adenocarcinomas in male, Copenhagen rats. AIN-93G diets containing these micronutrients were prefed for 4 to 6 weeks prior to tumor implantation by subcutaneous injection. Tumors were allowed to grow for ∼18 weeks. Across diet groups, methylselenocysteine consumption decreased final tumor area (P = 0.003), tumor weight (P = 0.003), and the tumor weight/body weight ratio (P = 0.003), but lycopene and γ-tocopherol consumption intake did not alter any of these measures. There were no significant interactions among nutrient combinations on tumor growth. Methylselenocysteine consumption also led to small, but significant decreases in body weight (P = 0.007), food intake (P = 0.012), and body weight gain/food intake ratio (P = 0.022). However, neither body weight nor gain/food intake ratio was correlated with tumor weight. Methylselenocysteine, lycopene, and γ-tocopherol consumed alone and in combination did not alter serum testosterone or dihydrotestosterone concentrations; tumor proliferation or apoptosis rates. In addition, the diets also did not alter tumor or prostate androgen receptor, probasin, selenoprotein 15, selenoprotein P, or selenium binding protein 2 mRNA expression. However, using castration and finasteride-treated tissues from a previous study, we found that androgen ablation altered expression of these selenium-associated proteins.

Conclusions

Of the three micronutrients tested, only methylselenocysteine consumption reduced growth of transplantable Dunning R3327-H prostate tumors, albeit through an unresolved mechanism.

Selenium decreases thyroid cancer cell growth by increasing expression of GADD153 and GADD34

Selenium (Se) supplementation is reported to decrease the incidence and total mortality of cancer. Whereas in vitro and in vivo studies have shown a decrease in prostate, lung, and liver cancers, this has not been shown in thyroid cancer. ARO (anaplastic), NPA (BRAF positive papillary), WRO (BRAF negative papillary), and FRO (follicular) cells treated with 150 microM seleno-l-methionine (SM) were assessed for viability at 24, 48, and 72 h. Treated FRO cells were examined for cell cycle using flow cytometry, for apoptosis using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, and for gene expression using microarray. Genes identified as upregulated were confirmed by real-time PCR (RT-PCR) and proteins by Western blot analysis. SM treatment significantly decreased the proliferation of all cell lines. TUNEL assay showed no evidence of apoptosis, and flow cytometry showed a significant cell-cycle arrest in S (271% increase, P = 0.006) and G2/M (61% increase, P = 0.002) compared to control. Microarray revealed 21 differentially expressed genes with greater than twofold change. A relative overexpression of growth arrest and DNA damage inducible (GADD)34 and GADD153 in treated cells was confirmed with RT-PCR and Western blot. SM inhibits thyroid cancer cell proliferation through a time dependent upregulation of the GADD family of genes and arrest in S and G2/M phases of the cell cycle. This is the first report of selenium induced inhibition of thyroid cancer cell growth.

Speciation analysis of selenium metabolites in urine and breath by HPLC- and GC-inductively coupled plasma-MS after administration of selenomethionine and methylselenocysteine to rats

Selenium is an essential trace element found in vegetables as selenomethionine (SeMet) and methylselenocysteine (MeSeCys). In the present study, we used stable isotopes of Se to investigate differences between how SeMet and MeSeCys are metabolized, using methylseleninic acid (MSA) as a reference methylselenol source. A mixture containing (76)Se-SeMet, (77)Se-MeSeCys, and (82)Se-MSA (each 25 microg Se/kg b.w.) was orally administered to rats, and then, speciation analyses of Se in urine and exhaled gas were conducted using HPLC-inductively coupled plasma (ICP)-MS and GC-ICP-MS, respectively. The proportions of (76)Se-, (77)Se-, and (82)Se-selenosugar (Se-sugar) to total urinary Se metabolites originating from each tracer were very similar, while the proportion of (77)Se-tirmethylselenonium (TMSe) was much less than that of(76)Se- and (82)Se-TMSe in urine, suggesting that(77)Se-SeMet is less efficiently metabolized to TMSe. Similarly, there was significantly less (77)Se-dimethylselenide (DMSe) originating from (77)Se-SeMet than(76)Se- and (82)Se-DMSe originating from (76)Se-MeSeCys and (82)Se-MSA in exhaled gas. It is generally accepted that DMSe and TMSe are metabolites of methylselenol, a putative metabolic intermediate in Se metabolism. Methylselenol is believed to be responsible for the cancer chemoprevention effects of Se. These results suggest that MeSeCys is converted to methylselenol more efficiently than is SeMet and that urinary TMSe and exhaled DMSe might be useful biomarkers for the generation of cancer chemopreventive forms of Se.

Selenium enrichment of broccoli sprout extract increases chemosensitivity and apoptosis of LNCaP prostate cancer cells

Background

Broccoli is a Brassica vegetable that is believed to possess chemopreventive properties. Selenium also shows promise as an anticancer agent. Thus, selenium enrichment of broccoli has the potential to enhance the anticancer properties of broccoli sprouts.

Method

Selenium-enriched broccoli sprouts were prepared using a sodium selenite solution. Their anticancer properties were evaluated in human prostate cancer cell lines and compared with those of a control broccoli sprout extract.

Results

Selenium-enriched broccoli sprouts were superior to normal broccoli sprouts in inhibiting cell proliferation, decreasing prostate-specific antigen secretion, and inducing apoptosis of prostate cancer cells. Furthermore, selenium-enriched broccoli sprouts but, not normal broccoli sprouts, induced a downregulation of the survival Akt/mTOR pathway.

Conclusion

Our results suggest that selenium-enriched broccoli sprouts could potentially be used as an alternative selenium source for prostate cancer prevention and therapy.

Alpha-keto acid metabolites of naturally occurring organoselenium compounds as inhibitors of histone deacetylase in human prostate cancer cells

Histone deacetylase (HDAC) inhibitors are gaining interest as cancer therapeutic agents. We tested the hypothesis that natural organoselenium compounds might be metabolized to HDAC inhibitors in human prostate cancer cells. Se-Methyl-L-selenocysteine (MSC) and selenomethionine are amino acid components of selenium-enriched yeast. In a cell-free system, glutamine transaminase K (GTK) and L-amino acid oxidase convert MSC to the corresponding alpha-keto acid, beta-methylselenopyruvate (MSP), and L-amino acid oxidase converts selenomethionine to its corresponding alpha-keto acid, alpha-keto-gamma-methylselenobutyrate (KMSB). Although methionine (sulfur analogue of selenomethionine) is an excellent substrate for GTK, selenomethionine is poorly metabolized. Structurally, MSP and KMSB resemble the known HDAC inhibitor butyrate. We examined androgen-responsive LNCaP cells and androgen-independent LNCaP C4-2, PC-3, and DU145 cells and found that these human prostate cancer cells exhibit endogenous GTK activities. In the corresponding cytosolic extracts, the metabolism of MSC was accompanied by the concomitant formation of MSP. In MSP-treated and KMSB-treated prostate cancer cell lines, acetylated histone 3 levels increased within 5 hours, and returned to essentially baseline levels by 24 hours, suggesting a rapid, transient induction of histone acetylation. In an in vitro HDAC activity assay, the selenoamino acids, MSC and selenomethionine, had no effect at concentrations up to 2.5 mmol/L, whereas MSP and KMSB both inhibited HDAC activity. We conclude that, in addition to targeting redox-sensitive signaling proteins and transcription factors, alpha-keto acid metabolites of MSC and selenomethionine can alter HDAC activity and histone acetylation status. These findings provide a potential new paradigm by which naturally occurring organoselenium might prevent the progression of human prostate cancer.

In vitro growth inhibition of mouse mammary epithelial tumor cells by methylseleninic acid: involvement of protein kinases

Methylseleninic acid (MSeA) is a synthetic organoselenium form known to be effective against mammary carcinogenesis in vivo. Using the synchronized mouse mammary epithelial tumor cell (TM6) model, we have previously shown that 5 microM MSeA significantly inhibits cell growth and induces a reversible growth arrest in the G1 phase. In the present study, we examined the effects of MSeA on Rb, cyclin dependent kinase 2 (cdk2), cdk4, cyclin E and cyclin D1. Growth arrest of cells was accompanied by a reduction in total cdk2 kinase and cyclin E-associated cdk2 kinase activities. The p27 levels associated with cdk2 were elevated during the cell cycle. In addition, growth inhibition correlated with a relative increase in the hypophosphorylated form of Rb in MSeA-treated cells and Egr1 was elevated in MSeA-treated cells. The Kinetworks Protein Kinase Screen (KPKS 1.0) was used to examine 75 protein kinases. MSeA treatment resulted in differential expression of several protein-serine/threonine kinases, protein-tyrosine kinases and protein-threonine/tyrosine kinases. Some of these kinases are being reported for the first time as being altered by MSeA. The outcome of these experiments will be of significance since these kinases are known to be involved in survival and/or apoptotic pathways of tumor cells.

Plasma selenium concentration and prostate cancer risk: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)

BACKGROUND

Some evidence indicates that a low selenium intake may be associated with an increased risk of prostate cancer.

OBJECTIVE

The aim of this study was to investigate the association of plasma selenium concentration with subsequent prostate cancer risk and to examine this association by stage and grade of disease and other factors.

DESIGN

A nested case-control study was performed among men in the European Prospective Investigation into Cancer and Nutrition (EPIC). The association between plasma selenium concentration and prostate cancer risk was assessed in 959 men with incident prostate cancer and 1059 matched controls.

RESULTS

Overall, plasma selenium concentration was not associated with prostate cancer risk; the multivariate relative risk for men in the highest fifth of selenium concentration compared with the lowest fifth was 0.96 (95% CI: 0.70, 1.31; P for trend = 0.25). There were no significant differences in the association of plasma selenium with risk when analyzed by stage or grade of disease. Similarly, the association of selenium with risk did not differ by smoking status or by plasma alpha- or gamma-tocopherol concentration.

CONCLUSION

Plasma selenium concentration was not associated with prostate cancer risk in this large cohort of European men.

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.