Comparison of the effects of an organic and an inorganic form of selenium on a mammary carcinoma cell line

Identification of altered metabolic functional components using metabolomics to analyze the different ages of fruiting bodies of Sanghuangporus vaninii cultivated on cut log substrates

Sanghuangporus vaninii is a profitable traditional and medicinal edible fungus with uncommon therapeutic properties and medicinal value. The accumulation of active ingredients in this fungus that is used in traditional Chinese medicine is affected by its years of growth, and their pharmacological activities are also affected. However, the effects of age on the medicinal value of fruiting bodies of S. vaninii cultivated on cut log substrate remain unclear. In this study, an untargeted liquid chromatography mass spectrometry (LC-MS)-based metabolomics approach was performed to characterize the profiles of metabolites from 1-, 2- and 3-year-old fruiting bodies of S. vaninii. A total of, 156 differentially accumulated metabolites (DAMs) were screened based on the criterion of a variable importance projection greater than 1.0 and p < 0.01, including 75% up regulated and 25% down regulated. The results of enrichment of metabolic pathways showed that the metabolites involved the biosynthesis of plant secondary metabolites, biosynthesis of amino acids, central carbon metabolism in cancer, steroid hormone biosynthesis, linoleic acid metabolism, prolactin signaling pathway, and arginine biosynthesis, and so on. The biosynthesis of plant secondary metabolites pathway was significantly activated. Five metabolites were significantly elevated within the growth of fruiting bodies, including 15-keto-prostaglandin F2a, (4S, 5R)-4,5,6-trihydroxy-2-iminohexanoate, adenylsuccinic acid, piplartine, and chenodeoxycholic acid. 15-keto-prostaglandin F2a is related to the pathway of arachidonic acid metabolism and was significantly increased up to 1,320- and 535-fold in the 2- and 3-year-old fruiting bodies, respectively, compared with those in the 1-year-old group. The presence of these bioactive natural products in S. vaninii is consistent with the traditional use of Sanghuang, which prompted an exploration of its use as a source of natural prostaglandin in the form of foods and nutraceuticals. These findings may provide insight into the functional components of S. vaninii to develop therapeutic strategies.

Increased Transglutaminase 2 and GLUT-1 Expression in Breast Tumors not Susceptible to Chemoprevention with Antioxidants

Goals

Expression of GLUT-1 and transglutaminase 2 is increased in aggressive breast cancer, whereas claudin-1, which is expressed in normal tissues, is absent in such tumors. This experimental study was undertaken to establish the aggressiveness and prognosis of DMBA-induced mammary tumors in female Wistar rats based on the assessment of these markers.

Materials and methods

The rats were divided into two groups, a control group (n = 70) and a chemoprevention group (n = 70). Breast tumors were induced in both groups by administration of 7,12-dimethylbenz[a]anthracene (DMBA). The chemoprevention group also received alpha-tocopherol and a solution of micronutrients containing ascorbic acid and selenium. Neoplastic lesions of both groups were randomly selected for immunohistochemical assessment of the expression of GLUT-1, transglutaminase 2 and claudin-1.

Results

A higher proportion of mammary tumors expressed GLUT-1 and transglutaminase 2 in the chemoprevention group. Claudin-1 expression was absent in all tumors of both groups.

Conclusions

These results are suggestive of increased aggressiveness of tumors not susceptible to chemoprevention by the agents used in this study.

Rational design and optimization of selenophenes with basic side chains as novel potent selective estrogen receptor modulators (SERMs) for breast cancer therapy

To increase the diversity of estrogen receptor (ER) ligands having novel structures and activities, series of selenophene derivatives with a basic side chain (BSC) were synthesized and their biological activity as subtype-selective antagonists for the ER was explored. Compared with the selenophenes without a BSC, most compounds showed an increase in binding affinity, and several compounds displayed enhanced antagonist potency and antiproliferative activity. Especially, compound 16c exhibited excellent transcriptional activity for ERα (IC50 = 13 nM) which made this compound the most potent antagonist for ERα of the whole series and is 66-fold better than the best selenophene compound without a BSC. Moreover, several compounds showed values of IC50 better than that of 4-hydroxytamoxifen in breast cancer MCF-7 cells. The modeling study indicated that the basic side chain might contribute to their increased antagonist potency and antiproliferative activity. These new ligands have the potential to be further developed as novel agents to improve therapeutics that target the estrogen receptor.

Biological Chemistry of Hydrogen Selenide

There are no two main-group elements that exhibit more similar physical and chemical properties than sulfur and selenium. Nonetheless, Nature has deemed both essential for life and has found a way to exploit the subtle unique properties of selenium to include it in biochemistry despite its congener sulfur being 10,000 times more abundant. Selenium is more easily oxidized and it is kinetically more labile, so all selenium compounds could be considered to be "Reactive Selenium Compounds" relative to their sulfur analogues. What is furthermore remarkable is that one of the most reactive forms of selenium, hydrogen selenide (HSe- at physiologic pH), is proposed to be the starting point for the biosynthesis of selenium-containing molecules. This review contrasts the chemical properties of sulfur and selenium and critically assesses the role of hydrogen selenide in biological chemistry.

Selenium Induces an Anti-tumor Effect Via Inhibiting Intratumoral Angiogenesis in a Mouse Model of Transplanted Canine Mammary Tumor Cells

Selenium (Se) has been widely reported to possess anti-tumor effects. Angiogenesis is the formation of new blood vessels and is required to supply oxygen, nutrients, and growth factors for tumor growth, progression, and metastasis. To explore whether the anti-tumor effect of Se was associated with angiogenesis in vivo, we studied the effects of sodium selenite (Sel) and methylseleninic acid (MSA) on tumors induced by canine mammary tumor cells (CMT1211) in mice; cyclophosphamide (CTX) served as a positive control. The results showed that the Se content was significantly increased in the Sel and MSA groups. Se significantly inhibited the tumor weights and volumes. Large necrotic areas and scattered and abnormal small necrotic areas were observed in the Se treatment group. Immunofluorescence double staining showed a reduction in the microvessel density (MVD) and increment in the vessel maturation index (VMI) compared with the untreated control group. As expected, the protein and mRNA levels of the angiogenesis factors angiopoietin-2 (Ang-2), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) were decreased in the Se-treated tumors by IHC, as shown by western blotting and RT-QPCR. We also found that organic Se MSA provided stronger inhibition of tumor growth compared with inorganic sodium selenite (Sel). Altogether, our results indicated that Se exerted anti-tumor effects in vivo at least partially by inhibiting angiogenic factors.

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.

Selenized milk casein in the diet of BALB/c nude mice reduces growth of intramammary MCF-7 tumors

BACKGROUND

Dietary selenium has the potential to reduce growth of mammary tumors. Increasing the Se content of cows' milk proteins is a potentially effective means to increase Se intake in humans. We investigate the effects of selenized milk protein on human mammary tumor progression in immunodeficient BALB/c nude mice.

METHODS

Four isonitrogenous diets with selenium levels of 0.16, 0.51, 0.85 and 1.15 ppm were formulated by mixing low- and high-selenium milk casein isolates with a rodent premix. MCF-7 cells were inoculated into the mammary fat pad of female BALB/c nude mice implanted with slow-release 17 β-estradiol pellets. Mice with palpable tumors were randomly assigned to one of the four diets for 10 weeks, during which time weekly tumor caliper measurements were conducted. Individual growth curves were fit with the Gompertz equation. Apoptotic cells and Bcl-2, Bax, and Cyclin D1 protein levels in tumors were determined.

RESULTS

There was a linear decrease in mean tumor volume at 70 days with increasing Se intake (P < 0.05), where final tumor volume decreased 35% between 0.16 and 1.15 ppm Se. There was a linear decrease in mean predicted tumor volume at 56, 63 and 70 days, and the number of tumors with a final volume above 500 mm3, with increasing Se intake (P < 0.05). This tumor volume effect was associated with a decrease in the proportion of tumors with a maximum growth rate above 0.03 day-1. The predicted maximum volume of tumors (Vmax) and the number of tumors with a large Vmax, were not affected by Se-casein. Final tumor mass, Bcl-2, Bax, and Cyclin D1 protein levels in tumors were not significantly affected by Se-casein. There was a significantly higher number of apoptotic cells in high-Se tumors as compared to low-Se tumors.

CONCLUSIONS

Taken together, these results suggest that turnover of cells in the tumor, but not its nutrient supply, were affected by dairy Se. We have shown that 1.1 ppm dietary Se from selenized casein can effectively reduce tumor progression in an MCF-7 xenograft breast cancer model. These results show promise for selenized milk protein as an effective supplement during chemotherapy.

Long-term selenium supplementation in HaCaT cells: importance of chemical form for antagonist (protective versus toxic) activities

The beneficial effect of selenium (Se) on cancer is known to depend on the chemical form, the dose and the duration of the supplementation. The aim of this work was to explore long term antagonist (antioxidant versus toxic) effects of an inorganic (sodium selenite, Na2SeO3) and an organic (seleno-L-methionine, SeMet) forms in human immortalized keratinocytes HaCaT cells. HaCaT cells were supplemented with Na2SeO3 or SeMet at micromolar concentrations for 144 h, followed or not by UVA radiation. Se absorption, effects of UVA radiation, cell morphology, antioxidant profile, cell cycle processing, DNA fragmentation, cell death triggered and caspase-3 activity were determined. At non-toxic doses (10 μM SeMet and 1 μM Na2SeO3), SeMet was better absorbed than Na2SeO3. The protection of HaCaT from UVA-induced cell death was observed only with SeMet despite both forms increased glutathione peroxidase-1 (GPX1) activities and selenoprotein-1 (SEPW1) transcript expression. After UVA irradiation, malondialdehyde (MDA) and SH groups were not modulated whatever Se chemical form. At toxic doses (100 μM SeMet and 5 μM Na2SeO3), Na2SeO3 and SeMet inhibited cell proliferation associated with S-G2 blockage and DNA fragmentation leading to apoptosis caspase-3 dependant. SeMet only led to hydrogen peroxide production and to a decrease in mitochondrial transmembrane potential. Our study of the effects of selenium on HaCaT cells reaffirm the necessity to take into account the chemical form in experimental and intervention studies.

CONFORMATIONAL PROPERTIES AND INTRAMOLECULAR HYDROGEN BONDING OF 3-AMINO-PROPENESELENAL: AN AB INITIO AND DENSITY FUNCTIONAL THEORY STUDIES

In the present work a conformational analysis of 3-amino-propeneselenal (APS) was performed using several computational methods, including DFT (B3LYP), MP2 and G2MP2. Harmonic vibrational frequencies were estimated at the same levels to confirm the nature of the stationary points found and also to account for the zero point vibrational energy (ZPVE) correction. Two intramolecular hydrogen bonds (HBs) established between the polar groups were identified by the structural geometric parameters. The excited-state properties of intramolecular hydrogen bonding in hydrogen bonded systems have been investigated theoretically using the time dependent density functional theory (TDDFT) method. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the polarized continuum model (PCM), the self-consistent isodensity polarized continuum model (SCI-PCM) and the integral equation formalism-polarizable continuum model (IEF-PCM) methods. The "atoms in molecules" theory of Bader was used to analyze critical points and to study the nature of HB in these systems. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions. The calculated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occur within the molecule. Further verification of the obtained transition state structures were implemented via intrinsic reaction coordinate (IRC) analysis. Calculations of the 1 H NMR chemical shift at GIAO/B3LYP/6–311++G** level of theory are also presented.

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.

Whole blood selenium levels (WBSL) in patients with prostate cancer (PC), benign prostatic hyperplasia (BPH) and healthy male inhabitants (HMI) and prostatic tissue selenium levels (PTSL) in patients with PC and BPH

BACKGROUND

The aim of this exploratory study was to evaluate whether significant differences exist between whole blood selenium levels (WBSL) in patients with prostate cancer (PC), benign prostatic hyperplasia (BPH), healthy male inhabitants (HMI) in northern Bavaria and the normal value. Furthermore, we investigated whether differences exist between prostatic tissue selenium levels (PTSL) in patients with PC, BPH and the benign tissue surrounding the PC.

MATERIAL AND METHODS

We prospectively evaluated WBSL in 24 patients with PC, 21 patients with BPH, and 21 HMI. Measurements of PTSL were performed in 17 patients with PC and 22 patients with BPH. In 9 cases with PC, measurements were also done in the benign tissue surrounding the carcinoma. Measurements were performed using automated graphite furnace atomic absorption spectrophotometry.

RESULTS

In patients with PC, there is a significantly lower WBSL in comparison to HMI (p=0.04). There is no significant difference in WBSL between BPH-patients and HMI (p=0.13) and between PC- and BPH-patients (p=0.67). In all patients and the HMI, there is a significantly lower WBSL in comparison to the recommended normal value of 85-162 microg/l (p<0.01). There is no significant difference in PTSL between PC and BPH (p=0.49), and between PC and the tissue compartment surrounding the PC (p=0.56). PTSL seemed to be reduced in the compartment surrounding the PC in comparison to BPH (p=0.03). In PC-patients, there is no significant correlation between WBSL and prostate specific antigen (PSA) (? = -0.20; p=0.36), Gleason score (? = 0.32, p=0.13), and T-stage (? = 0.22; p=0.23).

CONCLUSION

Since the WBSL measured in all men with PC and BPH, and in HMI participating in our study were significantly lower than the recommended normal range, our findings may support the recommendation of selenium supplementation.

Genotoxicity of organoselenium compounds in human leukocytes in vitro

DNA damage and cell viability of human leukocytes cells were examined as simple tests for screening the potential toxicity of organoselenium compounds. Leukocytes were incubated with different organoselenium compounds at 4, 10, 40 and 100 microM or vehicle (DMSO) for 3h at 37 degrees C before of in vitro assays. Cell viability was determined by Trypan blue exclusion. DNA damage was assessed using the alkaline comet assay with silver staining. The exposure of leukocytes to (S)-tert-butyl 1-diselenide-3-methylbutan-2-ylcarbamate, (S)-tert-butyl 1-diselenide-3-phenylpropan-2-ylcarbamate, (S)-2-amino-1-diselenide-3-methylpropanyl, (S)-2-amino-1-diselenide-3-phenylpropanyl, 3',3-ditrifluoromethyl diphenyl diselenide, 4',4-dimethoxy diphenyl diselenide, 4',4-dichloro diphenyl diselenide and 2',2,4',4,6',6-hexamethyl diphenyl diselenide, in the range of 10-100muM, induced a significant increase in Damage Index (DI). The genotoxic effect of all compounds was associated with high frequencies of cells with damage level 4 and all compounds caused a decrease in cell viability. Our results suggest that the selenium compounds tested were genotoxic and cytotoxic to human leukocytes cells in vitro and that the organoselenium amino acid derivatives ((S)-tert-butyl 1-diselenide-3-methylbutan-2-ylcarbamate, (S)-tert-butyl 1-diselenide-3-phenylpropan-2-ylcarbamate, (S)-2-amino-1-diselenide-3-methylpropanyl and (S)-2-amino-1-diselenide-3-phenylpropanyl) were more genotoxic than aromatic derivatives (3',3-ditrifluoromethyl diphenyl diselenide, 4',4-dimethoxy diphenyl diselenide, 4',4-dichloro diphenyl diselenide and 2',2,4',4,6',6-hexamethyl diphenyl diselenide). These effects may be linked to the pro-oxidant activity exhibited by selenium compounds when used in relatively high concentrations.

Differential sensitivity of various human tumour-derived cell types to apoptosis by organic derivatives of selenium

Selenium is an important trace element with anti-cancer properties. In the present study, the apoptosis-inducing effects of organic selenium derivatives, namely methyl-L-selenocysteine and selenomethionine, were evaluated in vitro on human tumour-derived cell lines from breast, liver, colon, brain, skin and a non-tumorigenic line of epithelial origin. Apoptosis was assessed by cell-death detection immunoassay on cytoplasmic cell lysates. Breast carcinoma cells were highly sensitive to the organic selenium compounds, manifesting apoptosis at concentrations as low as 0.113 microm (0.0205 microg/ml) selenium. By contrast, non-tumorigenic mammary epithelial cells displayed poor sensitivity to selenium, requiring a substantially high concentration of the trace element of 87.9 microm (16.0 microg/ml). The cell lines derived from hepatoma and neuroblastoma showed intermediate sensitivity, with colon carcinoma cells manifesting the lowest sensitivity to the trace element. These results indicate intrinsic differences in the sensitivity of human tumour derivatives to selenium-mediated apoptosis, providing experimental support for the development of organic selenium compounds as anti-neoplastic agents against solid tumours displaying selective apoptotic sensitivity to these compounds.

Diphenyl diselenide supplementation delays the development of N-nitroso-N-methylurea-induced mammary tumors

The effect of dietary diphenyl diselenide (1 ppm) on N-nitroso-N-methylurea (NMU)-induced mammary carcinogenesis was examined in female Wistar rats. Beginning at 5 weeks of age, the animals were fed with either control or diphenyl-diselenide-supplied diets until the end of the study (210 days). At 50 days of age, mammary tumor was induced by the administration of three doses of NMU (50 mg/kg body wt, intraperitoneally) once a week for 3 weeks. In experimental trials, latency to tumor onset was extended in rats fed with diet supplemented with diphenyl diselenide (P < 0.05). The incidence and frequency of tumors were significantly small in animals supplemented with diphenyl diselenide. However, the multiplicity of tumors was not altered by dietary diphenyl diselenide. Diphenyl diselenide supplementation also restored superoxide dismutase (SOD) activity and vitamin C levels altered in the NMU group (P < 0.05). Our results suggest that diphenyl diselenide can be considered a chemopreventive agent, even when supplemented at a relatively low concentration.

Methylselenol generated from selenomethionine by methioninase downregulates integrin expression and induces caspase-mediated apoptosis of B16F10 melanoma cells

Melanoma is a highly metastatic cancer resistant to current chemotherapeutic and radiotherapeutic approaches. Several studies have shown that interactions between cancer cells and the extracellular matrix (ECM) are critical for the survival and invasion of metastatic cancer cells. In this study, we examine the effects of methylselenol generated from selenomethionine (SeMet) by methioninase (METase) on cell proliferation, adhesion, and expression of integrins in murine melanoma B16F10 cells, which are metastatic in the lungs of syngeneic C57BL/6J mice. Combined treatment with SeMet-METase decreased the expression of integrins alpha(4), beta(1), alpha(nu), and beta(3), and inhibited melanoma-ECM adhesion. Caspase-mediated apoptosis was induced following loss of cell adherence. Phosphorylation of focal adhesion kinase (FAK) and Akt, related to integrin-mediated survival, were decreased upon treatment with SeMet-METase while phosphorylation of p38, PKC-delta, and IkappaBalpha increased. In the presence of specific inhibitors of p38, PKC-delta, and NF-kappaB, expression of integrins and cell adhesion to ECM were maintained and cell apoptosis was prevented in SeMet-METase-treated melanoma cells. Treatment with caspase inhibitors restored cell viability and blocked poly (ADP-ribose) polymerase (PARP) cleavage, but did not restore integrin expression and cell adhesion to ECMs reduced by SeMet-METase. Based on these results, we propose that combined treatment with SeMet-METase induces caspase-mediated apoptosis in melanoma cells by altering integrin expression and adhesion. Furthermore, activation of p38, PKC-delta, and NF-kappaB is a prerequisite for the down-regulation of integrin expression, followed by detachment-mediated apoptosis.

Tumour plasticity and extravascular circulation in ECV304 human bladder carcinoma cells

BACKGROUND

The concepts of vasculogenic mimicry and mosaic vessels have been proposed as novel modes of tumour neovascularisation. However, the presence and significance of these types of neovascularisation remain unclear.

MATERIALS AND METHODS

ECV304 human bladder carcinoma cells were used to determine how tumour cells take part in tumour neovascularisation.

RESULTS

Subcutaneous ECV304 xenografts in mice showed various vessel types, including angiogenic vessels, tumour cell-related vessels and extracellular matrix networks. A tracer experiment demonstrated perfusion of beads in these structures. ECV304 cells, cultured on collagen I gels, formed tube networks with expressions of several endothelial-related markers. In coculture models of ECV304 cells and human umbilical vein endothelial cells, the two cells collaborated to form sprouts or networks.

CONCLUSION

ECV304 cells possess an endothelial character which confers the ability to mimic and collaborate with vascular endothelial cells and facilitates the acquisition of tumour microcirculation.

Selenium protects against toxicity induced by anticancer drugs and augments antitumor activity: a highly selective, new, and novel approach for the treatment of solid tumors

Limited therapeutic selectivity and tumor resistance are major obstacles to current chemotherapy. The development of new therapeutic modalities for solid tumor remains a challenge. The use of selenium, 5-methylselenocysteine (MSC), or seleno-L-methionine (SLM) as selective modulators of anticancer drugs is novel and has not been previously investigated. Selenium deficiency is associated with an increased risk of cancer and cancer death. Although low-dose selenium supplementation has been investigated in a large randomized prevention trial, its potential in chemotherapy toxicity prevention and enhancement of antitumor activity of anticancer drugs has not been evaluated. An ideal biomodulator of anticancer drugs would allow escalation of drug dose with the hope of enhancing antitumor activity and possibly reversing drug resistance. Results from this laboratory have demonstrated that MSC and SLM are highly effective modulators of irinotecan cure rates in de novo sensitive and resistant human tumor xenografts. Studies in mice have documented that the minimum effective dose of MSC when combined with irinotecan is 0.01 mg daily. The optimal schedule is to administer MSC orally for 7 days before and concurrently with irinotecan. The observed effects were not drug-specific, as similar results were obtained with taxanes, platinum agents, 5-fluorouracil, and anthracyclines; nor were they species-specific, as selective effects were obtained in mice and rats and are currently being confirmed in ongoing clinical trials.

Diphenylmethyl selenocyanate inhibits DMBA–croton oil induced two-stage mouse skin carcinogenesis by inducing apoptosis and inhibiting cutaneous cell proliferation

Numerous epidemiological and experimental studies have showed the inverse relationship between dietary selenium intake and different types of cancer. Continuous efforts are going on to develop suitable organoselenium compounds, which can be used as cancer chemopreventive agents for human. In the present study, a synthetic organoselenium compound diphenylmethyl selenocyanate was evaluated for its ability to arrest cell proliferation and to induce apoptosis against 7,12-dimethylbenz[a]anthracene-croton oil induced two-stage mouse skin carcinogenesis model. Reduction in the incidence and number of papilloma, the preneoplastic lesion, was considered to be the mean of assessment. Significant decrease in the level of cell proliferation (p<0.01) and significant enhancement in the level of apoptosis (p<0.01) were found. Caspase-3, which contribute a part in the process of cellular apoptosis to prevent further cellular differentiation was also elevated significantly (P<0.01) during the treatment with the Se compound. These observations seem to be correlated with the significant reduction in the corresponding number of skin papilloma formation after 12 weeks of experiment. Thus the compound, diphenylmethyl selenocyanate may be considered for further research to establish it as an effective cancer chemopreventive agent.

Towards a dietary prevention of hereditary breast cancer

Inheritance of a deleterious mutation in BRCA1 or BRCA2 confers a high lifetime risk of developing breast cancer. Variation in penetrance between individuals suggests that factors other than the gene mutation itself may influence the risk of cancer in susceptible women. Several risk factors have been identified which implicate estrogen-induced growth stimulation as a probable contributor to breast cancer pre-disposition. The protein products of both of these genes appear to help preserve genomic integrity via their participation in the DNA damage response and repair pathways. To date, the evidence for a cancer-protective role of dietary nutrients, for the most part those with antioxidant properties, has been based on women without any known genetic pre-disposition and it is important to identify and evaluate dietary factors which may modify the risk of cancer in BRCA carriers. Here we propose that diet modification may modulate the risk of hereditary breast cancer by decreasing DNA damage (possibly linked to estrogen exposure) or by enhancing DNA repair. The prevention of hereditary breast cancer through diet is an attractive complement to current management strategies and deserves exploration.

Can we prevent prostate cancer? Rationale and current status of prostate cancer chemoprevention

Prostate cancer has been one of the most frequent cancers among men in Western countries for the past decade. Investigation of prostate cancer prevention is very attractive, because prostate cancer has a high incidence, long-term natural history, regional difference in incidence, and is effected by sex steroids. Chemoprevention is defined as the use of specific agents to suppress or reverse carcinogenesis and to prevent the development of cancer. The development of chemoprevention strategies against prostate cancer would be of medical and economic importance. Basic and clinical research of chemoprevention of prostate cancer are under active investigation. This article aims to summarize and review the basic evidence and clinical trials on prostate cancer chemoprevention. Recent research has demonstrated that many agents, such as agents altering sex steroid signaling, drugs inducing antiproliferation/differentiation, retinoids, anti-inflammatory drugs, and antioxidants, could be potential preventatives for prostate cancer. Large-scale clinical trials have suggested that 5alpha-reductase inhibitor finasteride, selenium, and vitamin E can function as a chemopreventive agent. Although no definitely effective strategies of prostate cancer prevention have been identified yet, increasing evidence will provide effective and safe strategies that bring clinical benefits.

Irinotecan pharmacokinetic and pharmacogenomic alterations induced by methylselenocysteine in human head and neck xenograft tumors

The combination of methylselenocysteine and irinotecan (CPT-11) is synergistic against FaDu and A253 xenografts. Methylselenocysteine/CPT-11 increased tumor cure rate to 100% in FaDu and to 60% in A253. In this study, the effect of methylselenocysteine on pharmacokinetic and pharmacogenetic profiles of genes relevant to CPT-11 metabolic pathway was evaluated to identify possible mechanisms associated with the observed combinational synergy. Nude mice bearing tumors (FaDu and A253) were treated with methylselenocysteine, CPT-11, and a combination of methylselenocysteine/CPT-11. Samples were collected and analyzed for plasma and intratumor concentration of CPT-11 and 7-ethyl-10-hydroxyl-camptothecin (SN-38) by high-performance liquid chromatography. The intratumor relative expression of genes related to the CPT-11 metabolic pathway was measured by real-time PCR. After methylselenocysteine treatment, the intratumor area under the concentration-time curve of SN-38 increased to a significantly higher level in A253 than in FaDu and was associated with increased expression of CES1 in both tumors. Methylselenocysteine/CPT-11 treatment, compared with CPT-11 alone, resulted in a significant decrease in levels of ABCC1 and DRG1 in FaDu tumors and an increase in levels of CYP3A5 and TNFSF6 in A253 tumors. No statistically significant changes induced by methylselenocysteine/CPT-11 were observed in the levels of other investigated variables. In conclusion, the significant increase in the cure rate after methylselenocysteine/CPT-11 could be related to increased drug delivery into both tumors (CES1), reduced resistance to SN-38 (ABCC1 and DRG1) in FaDu, and induced Fas ligand apoptosis (TNFSF6) in A253. No correlation was observed between cure rate and other investigated variables (transporters, degradation enzymes, DNA repair, and cell survival/death genes) in either tumor.

Selective modulation of the therapeutic efficacy of anticancer drugs by selenium containing compounds against human tumor xenografts

PURPOSE

Studies were carried out in athymic nude mice bearing human squamous cell carcinoma of the head and neck (FaDu and A253) and colon carcinoma (HCT-8 and HT-29) xenografts to evaluate the potential role of selenium-containing compounds as selective modulators of the toxicity and antitumor activity of selected anticancer drugs with particular emphasis on irinotecan, a topoisomerase I poison.

EXPERIMENTAL DESIGN

Antitumor activity and toxicity were evaluated using nontoxic doses (0.2 mg/mouse/day) and schedule (14-28 days) of the selenium-containing compounds, 5-methylselenocysteine and seleno-L-methionine, administered orally to nude mice daily for 7 days before i.v. administration of anticancer drugs, with continued selenium treatment for 7-21 days, depending on anticancer drugs under evaluation. Several doses of anticancer drugs were used, including the maximum tolerated dose (MTD) and toxic doses. Although many chemotherapeutic agents were evaluated for toxicity protection by selenium, data on antitumor activity were primarily obtained using the MTD, 2 x MTD, and 3 x MTD of weekly x4 schedule of irinotecan.

RESULTS

Selenium was highly protective against toxicity induced by a variety of chemotherapeutic agents. Furthermore, selenium increased significantly the cure rate of xenografts bearing human tumors that are sensitive (HCT-8 and FaDu) and resistant (HT-29 and A253) to irinotecan. The high cure rate (100%) was achieved in nude mice bearing HCT-8 and FaDu xenografts treated with the MTD of irinotecan (100 mg/kg/week x 4) when combined with selenium. Administration of higher doses of irinotecan (200 and 300 mg/kg/week x 4) was required to achieve high cure rate for HT-29 and A253 xenografts. Administration of these higher doses was possible due to selective protection of normal tissues by selenium. Thus, the use of selenium as selective modulator of the therapeutic efficacy of anticancer drugs is new and novel.

CONCLUSIONS

We demonstrated that selenium is a highly effective modulator of the therapeutic efficacy and selectivity of anticancer drugs in nude mice bearing human tumor xenografts of colon carcinoma and squamous cell carcinoma of the head and neck. The observed in vivo synergic interaction is highly dependent on the schedule of selenium.

Mechanisms of mammary cancer chemoprevention by organoselenium compounds

Searching for optimal diets and for naturally occurring agents in routinely consumed foods that may inhibit cancer development, although challenging, constitutes a valuable and plausible approach to finding ways to control and prevent cancer. To date, the use of the micronutrient selenium in human clinical trials is limited but the outcome of these investigations indicates that selenium is one of the most promising agents. Data presented in this mini-review indicate that the dose and the form (structure) in which selenium is used are the most critical determinants of success in future clinical trials. The focus of this mini-review is on the mechanisms of mammary cancer chemoprevention by organoselenium compounds. Among the naturally occurring organoselenium compounds, Se-Methylselenocysteine is more efficacious than the most extensively studied forms, such as selenomethionine. However, we showed that synthetic organoselenium compounds can be tailored to achieve greater chemopreventive efficacy with minimal side effects by structural modifications; it is evident that synthetic agents are superior to the inorganic selenite, naturally occurring selenium compounds and their sulfur-containing analogs. We have demonstrated that 1,4-phenylenebis (methylene) selenocyanate (p-XSC) and its putative metabolite glutathione conjugate (p-XSeSG) are highly promising agents in the chemoprevention of mammary carcinogenesis in the 7,12-dimethylbenz[a]anthracene (DMBA)-rat mammary tumor model system. Both compounds inhibit the initiation phase of carcinogenesis by inhibiting DMBA-DNA adduct formation in the target organ in vivo. cDNA microarray analysis indicates that both selenium compounds alter genes in a manner that leads to inhibition of cell proliferation and induction of apoptosis; modulation of apoptosis and cell proliferation can account for chemoprevention during the post-initiation phase of mammary carcinogenesis. Using a rat mammary cancer cell line, we compared p-XSC and p-XSeSG as inhibitors of cell proliferation; depending on the selenium dose and time point selected, p-XSC was comparable to or better than p-XSeSG. Collectively, the results described here, suggest that the molecular targets modulated by organoselenium compounds are highly useful indicators of success in clinical cancer chemoprevention trials.

Plasmodium falciparum: selenium-induced cytotoxicity to P. falciparum

The in vitro antimalarial activity of sodium selenite (NaSe) was investigated and the mechanism of its action was studied. NaSe had antimalarial activity against both the chloroquine-susceptible strain FCR-3 and chloroquine-resistant strain K-1 of Plasmodium falciparum. The shrunken cytoplasm of the parasite was observed in a smear 12 h after treatment with NaSe. Co-treatment with copper sulfate (CuSO(4)) in culture did not affect the antimalarial activity of NaSe, but NaSe cytotoxicity against the mammalian cell line Alexander was decreased significantly. The intracellular reduced glutathione level of parasitized red blood cells was decreased significantly by treatment with NaSe, and the decrease was consistent with their mortality. Treatment with NaSe had a strong inhibitory effect on plasmodial development, and NaSe cytotoxicity to human cells was decreased by co-treatment with CuSO(4). These results suggest that co-treatment with NaSe and CuSO(4) may be useful as a new antimalarial therapy.

Copper may interact with selenite extracellularly in cultured HT-29 cells

Previous studies have demonstrated that copper (15.7 micromol/L) can inhibit selenite (12.6 micromol/L)-induced cytotoxicity and apoptosis in HT-29 cells. However, the exact nature of the interactions between selenium and copper is not fully understood. In this study, the effect of copper on the cell cycle arrest induced by selenite or selenocystine was examined. Both selenite and selenocystine were effective in inhibition of cell growth and cell cycle progression. Cell cycle analysis revealed that selenite (3-5 micromol/L) caused a decrease in G1 phase cells that corresponded with an increase in S and G2 phase cells, and that 0.625 or 1.25 micromol/L copper sufficiently inhibited selenite-induced cell cycle arrest. In contrast, selenocystine caused an increase in G1 phase cells that corresponded with a decrease in S and G2 phase cells. Interestingly, 0.625 or 1.25 micromol/L copper did not inhibit selenocystine-induced cell cycle arrest. In addition, cell free gel shift assay demonstrated that selenite suppressed the inhibitory effect of copper on SP-1 DNA binding. Furthermore, although 5 micromol/L selenite in culture media significantly increased the intracellular selenium content, 1.25 micromol/L copper sulfate blocked this increase of the intracellular selenium content. Collectively, these data demonstrate that selenite and selenocystine cause cell cycle arrest via distinct mechanisms, and suggest that copper may interact with selenite extracellularly, which represents the basis of antagonism between copper sulfate and selenite.

Selenium: epidemiology and basic science

PURPOSE

The trace element selenium, a constituent of antioxidant enzymes, has been proposed as a chemopreventive agent for prostate and other cancers.

MATERIALS AND METHODS

Published epidemiological and scientific studies relating to the potential clinical and molecular role of selenium in preventing cancer are reviewed and summarized. A unifying hypothesis underlying observations on the effect of selenium on early events in carcinogenesis is presented.

RESULTS

A large body of epidemiological evidence, including observational, case-control, cohort and randomized controlled clinical trials, support the proposition that selenium may prevent prostate cancer in humans. The available data suggest a beneficial effect for men with low baseline serum or toenail selenium levels, without preexisting tumors, with serum prostate specific antigen less than 4 ng/ml and in current or former smokers. Molecular data demonstrate that selenium prevents clonal expansion of nascent tumors by causing cell cycle arrest, promoting apoptosis, and modulating p53 dependent DNA repair mechanisms.

CONCLUSIONS

These observations give strong scientific support to ongoing clinical trials testing the ability of selenium to prevent prostate cancer and the progression of high grade prostatic intraepithelial neoplasia to cancer.

Comparative action of 1,4-phenylenebis(methylene)selenocyanate and its metabolites against 7,12-dimethylbenz[a]anthracene-DNA adduct formation in the rat and cell proliferation in rat mammary tumor cells

1,4-phenylenebis(methylene)selenocyanate (p-XSC) inhibits 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis and DMBA-DNA binding in the rat mammary gland. Tetraselenocyclophane (TSC) was identified in rat feces as a metabolite of p-XSC. This led us to postulate the metabolic pathway: p-XSC-->glutathione conjugate (p-XSeSG)-->aromatic selenol (p-XSeH)-->TSC. Whether p-XSC or one of its metabolites is responsible for cancer prevention is the focus of this study. We utilized the DMBA-DNA binding assay with p-XSC as a positive control to evaluate the chemopreventive potential of p-XSC metabolites at dietary selenium levels of 10 ppm. Rats were fed AIN-76A diet supplemented with various selenium compounds for 1 week prior to the oral administration of a single dose of [3H]DMBA (5 mg per rat, specific activity 51.3 mCi/mmol). The rats were sacrificed 24 h later and DNA was isolated from the mammary fat pads. Relative levels of total binding were: [pmol/mg DNA, mean +/- S.D., n=6]; DMBA [7.2 +/- 1.6]; DMBA+p-XSC [3.5 +/- 2.7]; DMBA+p-XSeSG [2.2 +/- 1.1]; DMBA+TSC [5.6 +/- 2.9]. All selenium compounds, except TSC, significantly inhibited DMBA-DNA adduct formation; however, the difference between p-XSC and p-XSeSG was not statistically significant. The inhibition of total binding was attributed to a reduction in the formation of the three major adducts derived from bay-region diol epoxides of DMBA. On the basis of their chromatographic characteristics, these were identified as anti-diol-epoxide:deoxyguanosine, syn-diol-epoxide:deoxyadenosine, and anti-diol-epoxide:deoxyadenosine. Our results suggest that p-XSeSG, but not TSC, is the likely inhibitor of mammary cancer. Selenium levels measured by atomic absorption spectroscopy in the target organ (mammary fat pads) and in plasma following the dietary administration of selenium compounds were in the order of p-XSeSG congruent with p-XSC>TSC. These results appear to be consistent with their order of inhibitory effects on total DMBA-DNA binding. Further in vitro studies of the effect of selenium compounds on cell proliferation suggest that, depending on the dose and time point selected, p-XSC is comparable to or better than p-XSeSG; but both are more effective than TSC. Collectively, our in vivo and in vitro results indicate that p-XSC and its conjugate are better candidates than TSC for future studies on mammary cancer chemoprevention.

Antiproliferative effect of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) on colonic epithelium of patients with adenomatous polyps in vitro

We have consistently shown that the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) is a superior cancer chemopreventive agent and less toxic than selenite or certain naturally-occurring selenoamino acids. To elucidate the effects of p-XSC on human colonic mucosa, biopsies from endoscopically normal sigmoid colon of 30 patients with adenomatous polyps were incubated with p-XSC at concentrations of 1, 2 and 5 micromol/l dissolved in dimethylsulphoxide (DMSO). Biopsies incubated with DMSO or pure culture medium served as a control. Proliferating cells were labelled by bromodeoxyuridine immunohistochemistry and the labelling index (LI) was computed. Upper crypt labelling index (LI of crypt compartments 4+5) and Phih value, which are both discriminators of the expansion of the proliferative zone, were significantly lower after incubation with 1 and 5 micromol/l p-XSC, respectively (LI 4+5: 0.8 and 1.0; Phih value: 2.1 and 2.4), as compared with DMSO (LI 4+5: 3.6 and 4.5; Phih value: 7.0 and 8.3) or culture medium (LI 4+5: 3.3 and 4.5; Phih value: 7.2 and 8.1) (P<0.005 and P<0.05 by Friedman's block test). A trend towards lower levels of LI 4+5 (P=0.059) and Phih value (P=0.075) were seen after 2 micromol/l p-XSC incubation compared with DMSO. Since hyperproliferation of colonic crypt cells with expansion of the proliferative zone is regarded as a biomarker of increased cancer risk, the antiproliferative effects of p-XSC especially on upper crypt LI and Phih value may indicate a possible protective effect of this organoselenium compound in the prevention of human colon cancer development.

New insights regarding pharmacologic approaches for ovarian cancer prevention

The pathogenesis of epithelial ovarian cancer is not completely understood, but it commonly is believed that the process of recurrent ovulation (incessant ovulation) causes genetic damage in ovarian epithelial cells and that sufficient genetic damage can lead to ovarian cancer in susceptible individuals. Under this model, it has been suggested that reproductive and hormonal factors, such as pregnancy and oral contraceptive use, decrease ovarian cancer risk mainly via their inhibitory effects on ovulation. There is mounting evidence that the ovarian epithelium is a hormonally responsive target organ whose biology can be impacted strongly by the local hormonal environment. Progestin-mediated apoptotic effects may be a major mechanism underlying the ovarian cancer protective effects of pregnancy (a high progestin state) and oral contraceptive pill use. Similarly, retinoids, vitamin D, and non-steroidal anti-inflammatory drugs may have biologic effects on the ovarian epithelium that are cancer preventive, whereas androgens may have stimulatory effects on the ovarian epithelium, leading to an increased ovarian cancer risk.

Presentation serum selenium predicts for overall survival, dose delivery, and first treatment response in aggressive non-Hodgkin's lymphoma

PURPOSE

This study was undertaken to test the hypothesis that serum selenium concentration at presentation correlates with dose delivery, first treatment response, and overall survival in patients with aggressive B-cell non-Hodgkin's lymphoma.

PATIENTS AND METHODS

The patients presented between July 1986 and March 1999 and received anthracycline-based chemotherapy, radiotherapy, or both. The total selenium content was retrospectively analyzed in 100 sera, frozen at presentation, using inductively coupled plasma mass spectrometry.

RESULTS

The serum selenium concentration ranged from 0.33 to 1.51 micromol/L (mean, 0.92 micromol/L; United Kingdom adult reference range, 1.07 to 1.88 micromol/L). Serum selenium concentration correlated closely with performance status but with no other clinical variable. Multivariate analysis revealed that increased dose delivery, summarized by an area under the curve, correlated positively with younger age (P <.001), advanced stage (P =.001), and higher serum selenium concentration (P =.032). Selenium level also correlated positively with response (odds ratio, 0.62; 95% confidence interval [CI], 0.43 to 0.90; P =.011) and achievement of long-term remission after first treatment (log-rank test, 4.38; P =.036). On multivariate analysis, selenium concentration was positively predictive of overall survival (hazard ratio [HR], 0.76 for 0.2 micromol/L increase; 95% CI, 0.60 to 0.95; P =.018), whereas age indicated negative borderline significance (HR, 1.09; 95% CI, 0.99 to 1.18; P =.066).

CONCLUSION

Serum selenium concentration at presentation is a prognostic factor, predicting positively for dose delivery, treatment response, and long-term survival in aggressive non-Hodgkin's lymphoma. Unlike most existing prognostic factors in aggressive non-Hodgkin's lymphoma, selenium supplementation may offer a novel therapeutic strategy in this frequently curable malignancy.

The selenium and vitamin E cancer prevention trial

BACKGROUND

Evidence suggests that both selenium and vitamin E reduce the risk of prostate cancer. The Selenium and Vitamin E Cancer Prevention Trial (SELECT) is a randomized, prospective, double-blind study designed to determine whether selenium and vitamin E alone and in combination can reduce the risk of prostate cancer among healthy men.

MATERIALS AND METHODS

The preclinical and epidemiological evidence supporting a role for selenium and vitamin E as chemopreventive agents in prostate cancer are reviewed, and details of the trial design are presented. RESULTS. Preclinical, epidemiological, and phase III data from randomized, placebo-controlled clinical trials suggest that both selenium and vitamin E have potential efficacy in prostate cancer prevention. SELECT is a 2x2 factorial study with an accrual goal of 32,400 men with nonsuspicious DRE and serum PSA of 4 ng/ml or lower.

CONCLUSIONS

SELECT is the second large-scale study of chemoprevention for prostate cancer. Enrollment began in 2001 with final results anticipated in 2013.

Sodium selenite, dietary micronutrient, prevents the lymphocyte DNA damage induced by N-nitrosodiethylamine and phenobarbital promoted experimental hepatocarcinogenesis

Selenium (Se), a micronutrient, has a long history in chemoprevention of mammary and colon cancers in rodent models. Se is a current clinical trial, having shown promise in prevention of prostate and other human cancers. The mechanisms involved in the in vivo anti-carcinogenic activity of Se remain to be elucidated. In the present study, we examined the effect of sodium selenite supplementation in lymphocytes, obtained from hepatoma bearing rats on DNA damage in correlation with oxidative stress. In addition, this study examined the supplementation of Se at 4-ppm levels in the form of sodium selenite either before initiation or during initiation and/or promotion phase's increases lymphocyte Se concentrations. This in turn improves lymphocyte resistance to oxidative stress and protection against the lymphocytes DNA damage. Supplementation of Se increased lymphocyte Se concentration and reduced lymphocytes DNA damage as determined by single cell gel electrophoresis. The enzymatic antioxidants such as superoxide dismutase, glutathione peroxidase, and catalase were found to be decreased while the thiobarbituric acid reactive substances level was increased in the lymphocytes of hepatoma bearing rats. Furthermore, the reactive oxygen species such as superoxide radicals and hydroxyl radicals were also found to be high in lymphocytes. Our present results explain the understanding of unique association between anti-peroxidative effect of Se and ultimately the capability of Se to prevent cancer.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.

SELECT: the selenium and vitamin E cancer prevention trial

PURPOSE

Growing evidence suggests that both selenium and vitamin E may reduce the risk of prostate cancer. SELECT is a randomized, prospective, double-blind study designed to determine if selenium and vitamin E can reduce the risk of prostate cancer among healthy men.

MATERIALS AND METHODS

The preclinical and epidemiologic evidence regarding chemoprevention with selenium and vitamin E were reviewed. Secondary analyses from randomized trials of both agents were included in the analysis. Data from these analyses as well as evidence from the Prostate Cancer Prevention Trial were used to develop the schema of SELECT.

RESULTS

Preclinical, epidemiologic, and Phase III data suggest that both selenium and vitamin E have potential efficacy in prostate cancer prevention. The experience of the Prostate Cancer Prevention Trial and the rapid accrual of SELECT during its first year demonstrate the interest and dedication of healthy men to long-term studies of cancer prevention. A total of 32,400 men are planned to be randomized in SELECT.

CONCLUSIONS

SELECT is the second large-scale study of chemoprevention for prostate cancer. Enrollment began in 2001 with final results anticipated in 2013.

Multiorgan sensitivity to anticarcinogenesis by the organoselenium 1,4-phenylenebis(methylene)selenocyanate

The data in this report clearly indicate that the form (structure) in which selenium is used is the most critical determinant of success in future clinical trials. Synthetic organoselenium compounds can be tailored to achieve greater chemopreventive efficacy with minimal toxic side effects by structural modifications. We demonstrated that 1,4-phenylenebis(methylene)selenocyanate is a powerful chemopreventive agent against the development of experimental colon, mammary, lung, and oral carcinogenesis. On the basis of metabolism studies of organoselenium compounds and those reported in the literature, our working hypothesis is that aromatic selenol intermediates are important entities in cancer chemoprevention. In addition, we suggest that 1,4-phenylenebis(methylene)selenocyanate not only serves as a chemopreventive agent, but it may be valuable in preventing metastatic diseases in future studies in the clinic.