Selenomethionine induces p53 mediated cell cycle arrest and apoptosis in human colon cancer cells

Therapeutic Benefits of Selenium in Hematological Malignancies

Supplementing chemotherapy and radiotherapy with selenium has been shown to have benefits against various cancers. This approach has also been shown to alleviate the side effects associated with standard cancer therapies and improve the quality of life in patients. In addition, selenium levels in patients have been correlated with various cancers and have served as a diagnostic marker to track the efficiency of treatments or to determine whether these selenium levels cause or are a result of the disease. This concise review presents a survey of the selenium-based literature, with a focus on hematological malignancies, to demonstrate the significant impact of selenium in different cancers. The anti-cancer mechanisms and signaling pathways regulated by selenium, which impart its efficacious properties, are discussed. An outlook into the relationship between selenium and cancer is highlighted to guide future cancer therapy development.

Micronutrient Food Supplements in Patients with Gastro-Intestinal and Hepatic Cancers

Colorectal carcinogenesis is the second most common cause of mortality across all types of malignancies, followed by hepatic and stomach cancers. Chemotherapy and radiotherapy are key approaches to treating cancer patients, but these carry major concerns, such as a high risk of side effects, poor accessibility, and the non-selective nature of chemotherapeutics. A number of natural products have been identified as countering various forms of cancer with fewer side effects. The potential impact of vitamins and minerals on long-term health, cognition, healthy development, bone formation, and aging has been supported by experimental and epidemiological studies. Successful treatment may thus be highly influenced by the nutritional status of patients. An insufficient diet could lead to detrimental effects on immune status and tolerance to treatment, affecting the ability of chemotherapy to destroy cancerous cells. In recent decades, most cancer patients have been taking vitamins and minerals to improve standard therapy and/or to decrease the undesirable side effects of the treatment together with the underlying disease. On the other hand, taking dietary supplements during cancer therapy may affect the effectiveness of chemotherapy. Thus, micronutrients in complementary oncology must be selected appropriately and should be taken at the right time. Here, the potential impact of micronutrients on gastro-intestinal and hepatic cancers is explored and their molecular targets are laid down.

The Antitumor Activity of Sodium Selenite Alone and in Combination with Gemcitabine in Pancreatic Cancer: An In Vitro and In Vivo Study

Sodium selenite acts by depleting enzymes that protect against cellular oxidative stress. To determine its effect alone or in combination with gemcitabine (GMZ) in pancreatic cancer, we used PANC-1 and Pan02 cell lines and C57BL mice bearing a Pan02-generated tumor. Our results demonstrated a significant inhibition of pancreatic cancer cell viability with the use of sodium selenite alone and a synergistic effect when associated with GMZ. The molecular mechanisms of the antitumor effect of sodium selenite alone involved apoptosis-inducing factor (AIF) and the expression of phospho-p38 in the combined therapy. In addition, sodium selenite alone and in association with GMZ significantly decreased the migration capacity and colony-forming ability, reduced tumor activity in multicellular tumor spheroids (MTS) and decreased sphere formation of cancer stem cells. In vivo studies demonstrated that combined therapy not only inhibited tumor growth (65%) compared to the untreated group but also relative to sodium selenite or GMZ used as monotherapy (up to 40%), increasing mice survival. These results were supported by the analysis of C57BL/6 albino mice bearing a Pan02-generated tumor, using the IVIS system. In conclusion, our results showed that sodium selenite is a potential agent for the improvement in the treatment of pancreatic cancer and should be considered for future human clinical trials.

Molecular Mechanism for Selective Cytotoxicity towards Cancer Cells of Diselenide-Containing Paclitaxel Nanoparticles

Diselenide-containing paclitaxel nanoparticles (SePTX NPs) indicated selectivity of cytotoxicity between cancerous and normal cells in our previous work. Herein, the mechanism is revealed by molecular biology in detail. Cancer cells and normal cells were treated with the SePTX NPs and cell proliferation was measured using 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay and cell morphology. Measurement of reactive oxygen species (ROS) levels and biochemical parameters were employed to monitor oxidative stress of the cells. JC-1 assay was used to detect the mitochondrial dysfunction of the cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) analysis was used to detect apoptosis of the cells. Immunofluorescence analysis and western blotting were employed to monitor changes in signaling pathway-related proteins. Compared with PTX, SePTX NPs has a good selectivity to cancer cells and can obviously induce the proliferation damage of cancer cells, but has no significant toxicity to normal cells, indicating that SePTX NPs has a specific killing effect on cancer cells. The results of mechanism research show that SePTX NPs can successfully inhibit the depolymerization of microtubules and induce cell cycle arrest, which is related to the upregulation of p53 and CyclinB1. Simultaneously, SePTX NPs can successfully induce oxidative stress, cause mitochondrial dysfunction, resulting in mitochondrial pathway-mediated apoptosis, which is related to the upregulation of autophagy-related protein LC3-II. On the other hand, lewis lung cancer C57BL/6 mice were used to evaluate the anti-tumor effects of SePTX NPs in vivo. Our data show that SePTX NPs exhibited high inhibiting efficiency against the growth of tumors and were able to reduce the side effects. Collectively, these data indicate that the high antitumor effect and selective cytotoxicities of SePTX NPs is promising in future cancer therapy.

Novel selenylated imidazo[1,2-a]pyridines for breast cancer chemotherapy: Inhibition of cell proliferation by Akt-mediated regulation, DNA cleavage and apoptosis

A novel series of selenylated imidazo[1,2-a]pyridines were designed and synthesized with a view to a promising activity against breast cancer cell. The compounds, 7-methyl-3-(naphthalene-1-ylselanyl)-2-phenylimidazo[1,2-a]pyridine, named IP-Se-05, and 3-((2-methoxyphenyl)selanyl)-7-methyl-2-phenylimidazo[1,2-a]pyridine, named IP-Se-06, showed high cytotoxicity for MCF-7 cells (IC₅₀ = 26.0 μM and 12.5 μM, respectively). Both the compounds inhibited the cell proliferation and caused decrease in the number of cells in the G2/M phase of cell cycle. IP-Se-05 and IP-Se-06 were also evaluated for effects on CT-DNA and DNA of MCF-7 cells. The compounds intercalated into CT-DNA and both treatments caused cleavage of DNA in cells. In addition, the compounds induced cell death by apoptosis. However, the presence of (2-methoxyphenyl) selenyl moiety at the imidazo[1,2-a]pyridine (IP-Se-06) appears to have a better antitumor effect with higher cytotoxicity at a lower concentration and caused less necrosis. Overall, the current study established IP-Se-06 more than IP-Se-05 as a potential prototype compound to be employed as an antiproliferative agent for the treatment of breast cancer.

Emodin promotes the arrest of human lymphoma Raji cell proliferation through the UHRF1‑DNMT3A‑∆Np73 pathways

Emodin is an active constituent found in the roots and rhizomes of numerous Chinese medicinal herbs. It exerts antitumor activity against Dalton's lymphoma in vivo, although the detailed mechanisms by which emodin induces apoptosis remains to be elucidated. The present study aimed to analyze the mechanisms underlying the response to emodin treatment. Using lymphoma Raji cells, an emodin‑induced cell proliferating inhibition model was first established, then flow cytometry, western blotting, reverse transcription‑quantitative polymerase chain reaction and luciferase reporter assay were performed. It was found that emodin decreased the percentage of Raji cell viability, induced apoptosis, and increased the activation of caspase 3, caspase 9 and poly (ADP‑ribose) polymerase through the downregulation of ubiquitin‑like protein containing PHD and RING domains 1 (UHRF1). The emodin‑induced downregulation of UHRF1 led to an increase in the level of DNA methyltransferase 3A, which in turn inhibited the activity of p73 promoter 2 and decreased the levels of NH2‑terminally truncated dominant‑negative p73. The treatment of Raji cells with emodin combined with doxorubicin led increased cell death of Raji cells, indicating that emodin may sensitize Raji cells to doxorubicin‑induced apoptosis.

Biogenic selenium nanoparticles induce ROS-mediated necroptosis in PC-3 cancer cells through TNF activation

BACKGROUND

Selenium is well documented to inhibit cancer at higher doses; however, the mechanism behind this inhibition varies widely depending on the cell type and selenium species. Previously, we have demonstrated that Bacillus licheniformis JS2 derived biogenic selenium nanoparticles (SeNPs) induce non-apoptotic cell death in prostate adenocarcinoma cell line, PC-3, at a minimal concentration of 2 µg Se/ml, without causing toxicity to the primary cells. However, the mechanism behind its anticancer activity was elusive.

RESULTS

Our results have shown that these SeNPs at a concentration of 2 µg Se/ml were able to induce reactive oxygen species (ROS) mediated necroptosis in PC-3 cells by gaining cellular internalization. Real-time qPCR analysis showed increased expression of necroptosis associated tumor necrotic factor (TNF) and interferon regulatory factor 1 (IRF1). An increased expression of RIP1 protein was also observed at the translational level upon SeNP treatment. Moreover, the cell viability was significantly increased in the presence of necroptosis inhibitor, Necrostatin-1.

CONCLUSION

Data suggest that our biogenic SeNPs induce cell death in PC-3 cells by the ROS-mediated activation of necroptosis, independent to RIP3 and MLKL, regulated by a RIP1 kinase.

Curcumin loading potentiates the chemotherapeutic efficacy of selenium nanoparticles in HCT116 cells and Ehrlich's ascites carcinoma bearing mice

The anticancer properties of selenium (Se) and curcumin nanoparticles in solo formulations as well as in combination with other therapeutic agents have been proved time and again. Exploiting this facet of the two, we clubbed their tumoricidal characteristics and designed curcumin loaded Se nanoparticles (Se-CurNPs) to achieve an enhanced therapeutic effect. We evaluated their therapeutic effects on different cancer cell lines and Ehrlich's ascites carcinoma mouse model. In vitro results showed that Se-CurNPs were most effective on colorectal carcinoma cells (HCT116) compared to the other cancer cell lines used and possessed pleiotropic anticancer effects. The therapeutic effect on HCT116 was primarily attributed to an elevated level of autophagy and apoptosis as evident from significant up-regulation of autophagy associated (LC3B-II) and pro-apoptotic (Bax) proteins, down-regulation of anti-apoptotic (Bcl-2) protein and Cytochrome c (cyt c) release from mitochondria along with reduced NFκB signaling and EMT based machineries marked by downregulation of inflammation (NFκB, phospho-NFκB) and epithelial-mesenchymal transition (CD44, N-cadherin) associated proteins. In vivo studies on Ehrlich's ascites carcinoma (EAC) mice model indicated that Se-CurNPs significantly reduced the tumor load and enhanced the mean survival time (days) of tumor-bearing EAC mice.

Site-selective installation of BASHY fluorescent dyes to Annexin V for targeted detection of apoptotic cells

Fluorophores are indispensable for imaging biological processes. We report the design and synthesis of azide-tagged boronic acid salicylidenehydrazone (BASHY) dyes and their use for site-selective labelling of Annexin V. The Annexin V-BASHY conjugate maintained function and fluorescence as demonstrated by the targeted detection of apoptotic cells.

In Vitro Investigation of Six Antioxidants for Pig Diets

Oxidative stress in the small intestinal epithelium can lead to barrier malfunction. In this study, the effect of rosmarinic acid (RA), quercetin (Que), gallic acid (GA), lipoic acid (LA), ethoxyquin (ETQ) and Se-methionine (SeMet) pre-treatments using 2 mM Trolox as a control on the viability and the generation of intracellular reactive oxygen species (iROS) of oxidatively (H₂O₂) stressed intestinal porcine epithelial cells (IPEC-J2) was investigated. A neutral red assay showed that RA (50-400 µM), Que (12.5-200 µM), GA (50-400 µM), ETQ (6.25-100 µM), and SeMet (125-1000 µM) pre-treatments but not LA significantly increased the viability of H₂O₂-stressed IPEC-J2 cells (p < 0.05). A 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) fluorescent probe showed that RA (100-600 µM), Que (25-800 µM), ETQ (3.125-100 µM) and SeMet (500-2000 µM) pre-treatments significantly reduced iROS in IPEC-J2 monolayers (p < 0.05). Moreover, RA and Que were most effective in reducing iROS. Therefore, the effects of RA and Que on barrier functioning in vitro were examined. RA and Que pre-treatments significantly decreased fluorescein isothiocyanate (FITC)-conjugated dextran-4 (4 kDa) permeability and transepithelial electrical resistance (TEER) of an IPEC-J2 cell monolayer (p < 0.05). These in vitro results of RA and Que hold promise for their use as antioxidants in pig feed.

Cancer chemoprevention research with selenium in the post-SELECT era: Promises and challenges

The negative efficacy outcomes of double-blinded, randomized, placebo-controlled Phase III human clinical trials with selenomethionine (SeMet) and SeMet-rich selenized-yeast (Se-yeast) for prostate cancer prevention and Se-yeast for prevention of nonsmall cell lung cancer (NSCLC) in North America lead to rejection of SeMet/Se-yeast for cancer prevention in Se-adequate populations. We identify 2 major lessons from the outcomes of these trials: 1) the antioxidant hypothesis was tested in wrong subjects or patient populations, and 2) the selection of Se agents was not supported by cell culture and preclinical animal efficacy data as is common in drug development. We propose that next-generation forms of Se (next-gen Se), such as methylselenol precursors, offer biologically appropriate approaches for cancer chemoprevention but these are faced with formidable challenges. Solid mechanism-based preclinical efficacy assessments and comprehensive safety studies with next-gen Se will be essential to revitalize the idea of cancer chemoprevention with Se in the post-SELECT era. We advocate smaller mechanism-driven Phase I/II trials with these next-gen Se to guide and justify future decisions for definitive Phase III chemoprevention efficacy trials.

Selenocysteine derivative overcomes TRAIL resistance in melanoma cells: evidence for ROS-dependent synergism and signaling crosstalk

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), as one of the most promising targeted drug for new cancer therapeutics, is limited in clinical application by the evolution of resistance in many cancer cell lines, especially in malignant melanoma. Thus, it is urgently needed to identify chemosensitizers to enhance the apoptotic inducing efficacy of TRAIL and overcome resistance of malignant melanoma cells. Herein, we reported that 3,3'-diselenodipropionic acid (DSeA), a Selenocysteine derivative, could synergistically enhance the growth inhibitory effect of TRAIL on A375 melanoma cells though induction of ROS-dependent apoptosis with involvement of PTEN-mediated Akt inactivation and DNA damage-mediated p53 phosphorylation, which subsequently activated mitochondrial and death receptor apoptotic pathways. Moreover, silencing of p53 down-regulated the expression levels of p53-inducible genes, and effectively blocked the cell apoptosis. Suppression of PI3K significantly increased the apoptotic cell death. In contrast, antioxidants effectively reversed the cell apoptosis through regulation of Akt and p53 signaling pathways. Taken together, the combination of DSeA and TRAIL could be a novel strategy to overcome TRAIL resistance in malignant melanoma, and DSeA may be candidates for further evaluation as a chemosensitizer in clinical trails.

Selenocystine-induced cell apoptosis and S-phase arrest inhibit human triple-negative breast cancer cell proliferation

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited effective treatment options. New therapeutic approaches are urgently needed to improve the prognosis of TNBC. Here we demonstrated that a redox modulator, selenocystine (SeC), significantly inhibits TNBC cell proliferation in a dose- and time-dependent manner. Through cell apoptosis assays and cell cycle distribution analyses, we have shown that the in vitro inhibitory effect of SeC on TNBC cells can be attributed to the induction of apoptosis and the S-phase arrest in a dose-dependent manner. Therefore, this finding implies that SeC potentially is a novel therapeutic agent for TNBC.

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.

Tetrazolium violet induced apoptosis and cell cycle arrest in human lung cancer a549 cells

Tetrazolium violet is a tetrazolium salt and has been proposed as an antitumor agent. In this study, we reported for the first time that tetrazolium violet not only inhibited human lung cancer A549 cell proliferation but also induced apoptosis and blocked cell cycle progression in the G1 phase. The results showed that tetrazolium violet significantly decreased the viability of A549 cells at 5-15 μM. Tetrazolium violet -induced apoptosis in A549 cells was confirmed by H33258 staining assay. In A549, tetrazolium violet blocked the progression of the cell cycle at G1 phase by inducing p53 expression and further up-regulating p21/WAF1 expression. In addition, an enhancement in Fas/APO-1 and its two forms of ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), as well as caspase, were responsible for the apoptotic effect induced by tetrazolium violet. The conclusion of this study is that tetrazolium violet induced p53 expression which caused cell cycle arrest and apoptosis. These findings suggest that tetrazolium violet has strong potential for development as an agent for treatment lung cancer.

Selenoprotein W depletion induces a p53- and p21-dependent delay in cell cycle progression in RWPE-1 prostate epithelial cells

The anticancer activity of selenium (Se) has been demonstrated in myriad animal and in vitro studies, yet the mechanisms remain obscure. The main form of Se in animal tissues is selenocysteine in selenoproteins, but the relative importance of selenoproteins versus smaller Se compounds in cancer protection is unresolved. Selenoprotein W (SEPW1) is a highly conserved protein ubiquitously expressed in animals, bacteria, and archaea. SEPW1 depletion causes a delay in cell cycle progression at the G1/S transition of the cell cycle in breast and prostate epithelial cells. Tumor suppressor protein p53 is a master regulator of cell cycle progression and is the most frequently mutated gene in human cancers. p53 was increased in SEPW1 silenced cells and was inversely correlated with SEPW1 mRNA in cell lines with altered SEPW1 expression. Silencing SEPW1 decreased ubiquitination of p53 and increased p53 half-life. SEPW1 silencing increased p21(Cip1/WAF1/CDKN1A), while p27 (Kip1/CDKN1B) levels were unaffected. G1-phase arrest from SEPW1 knockdown was abolished by silencing p53 or p21. Cell cycle arrest from SEPW1 silencing was not associated with activation of ATM or phosphorylation of Ser-15 in p53, suggesting the DNA damage response pathway was not involved. Silencing GPX1 had no effect on cell cycle, suggesting that G1-phase arrest from SEPW1 silencing was not due to loss of antioxidant protection. More research is required to identify the function of SEPW1 and how it affects stability of p53.

Expression of NHERF1 in colonic tumors induced by 1,2-dimethylhydrazine in rats is independent of plasma ovarian steroids

In normal embryonic fibroblasts, the Na(+)/H(+) exchanger regulator factor 1 (NHERF1) stabilizes E-cadherin/β-catenin binding and the lack of NHERF1 expression promotes cell transformation thus acting as a tumor suppressor gene. We here tested the hypothesis that NHERF1 could act as a tumor suppressor gene in colon cancer as a mediator of estrogens' protective actions in colon carcinogenesis. We studied the expression and localization of NHERF1 and β-catenin by immunohistochemistry in colonic tumors induced by 1,2 dimethylhidrazine (DMH) in Sprague-Dawley rats. One group of the rats treated with the carcinogen was ovariectomized (OVX) in the middle of the tumor induction, simulating a human menopausal condition. We observed a protective role of estrogens in colon cancer, as non-ovariectomized rats (DMH) had a reduced tumor area compared with the ovariectomized group (DMH + OVX; mean ± SE) 28.98 ± 4.65 vs. 67.58 ± 8.69 (p < 0.00380). Despite the lack of plasma estrogen stimulation, we found abundant expression of NHERF1 in colon tumors from ovariectomized rats. NHERF1 was mainly localized in the cytoplasm of the adenocarcinoma cells and lost the apical localization previously reported in normal colon tissue. We also detected expression of NHERF1 by western blot in the SW48, CACO-2, and HT29 colon cancer cell lines. Non-estrogenic factors in plasma or the tumor microenvironment may regulate NHERF1 expression in transformed colon epithelial cells. Further studies are required to understand the regulation of NHERF1 expression in colon cancer tissue.

Effects of cadmium chloride and sodium selenite alone or in combination on the liver of male Sprague-Dawley rats assessed by different assays

This study assessed the impact of either cadmium chloride (Cd) or sodium selenite (Se) alone or in combination on male Sprague-Dawley rats. For this purpose, body and liver weights, comet and TUNEL assays, histological analysis and levels of lipid peroxidation and antioxidants in liver were determined in four groups of male Sprague-Dawley rats. The rats were given subcutaneous doses of 1 mg/kg body weight (BW) of either normal saline (control=Ct) or Cd or Se or Cd plus Se (Cd+Se) on alternate days for 4 weeks. The Cd group showed increased DNA damage, apoptosis and hepatic levels of lipid peroxidation and altered histology. Conversely, the antioxidant levels in this group were decreased as compared with the control group. The Se group also showed DNA damage, apoptosis and altered histology and reduced catalase activity, but it was less severe than the Cd group. In the Cd+Se group, ameliorating effects of Se on Cd-induced changes were observed. While the Se was able to curtail the toxic effect of Cd, the Cd or Se alone were genotoxic and cytotoxic for rats receiving a high pharmacological but non-fatal dose of 1 mg/kg BW.

Protective effects of selenocystine against γ-radiation-induced genotoxicity in Swiss albino mice

Selenocystine (CysSeSeCys), a diselenide aminoacid exhibiting glutathione peroxidase-like activity and selective antitumor effects, was examined for in vivo antigenotoxic and antioxidant activity in Swiss albino mice after exposure to a sublethal dose (5 Gy) of γ-radiation. For this, CysSeSeCys was administered intraperitoneally (i.p.) to mice at a dosage of 0.5 mg/kg body weight for 5 consecutive days prior to whole-body γ-irradiation. When examined in the hepatic tissue, CysSeSeCys administration reduced the DNA damage at 30 min after radiation exposure by increasing the rate of DNA repair. Since antigenotoxic agents could alter the expression of genes involved in cell cycle arrest and DNA repair, the transcriptional changes in p53, p21 and GADD45α were monitored in the hepatic tissue by real-time PCR. The results show that CysSeSeCys alone causes moderate induction of these three genes. However, CysSeSeCys pretreatment resulted in a suppression of radiation-induced enhancement of p21 and GADD45α expression, but did not affect p53 expression. Further analysis of radiation-induced oxidative stress markers in the same tissue indicated that CysSeSeCys significantly inhibits lipid peroxidation and prevents the depletion of antioxidant enzymes and glutathione (GSH) levels. Additionally, it also prevents radiation-induced DNA damage in other radiation sensitive cellular systems like peripheral leukocytes and bone marrow, which was evident by a decrease in comet parameters and micronucleated polychromatic erythrocytes (mn-PCEs) frequency, respectively. Based on these observations, it is concluded that CysSeSeCys exhibits antigenotoxic effects, reduces radiation-induced oxidative stress, and is a promising candidate for future exploration as a radioprotector.

The ameliorative and toxic effects of selenite on Caenorhabditis elegans

Selenium is an essential trace nutrient that has a narrow exposure window between its beneficial and detrimental effects. We investigated how selenium affected the development, fertility, and cholinergic signaling of the nematode, Caenorhabditis elegans. Our results showed that selenite supplementation at 0.01 and 0.05 μM accelerated development and increased the brood size, while the addition of 20 μM selenite retarded the developmental rate and decreased the brood size. We also showed that the 0.01 μM selenite-pretreated nematodes were more resistant to paralysis induced by an acetylcholinesterase inhibitor, aldicarb, and a nicotinic acetylcholine receptor agonist, levamisole, compared to untreated worms. In contrast, 20 μM selenite-pretreated animals were more sensitive to aldicarb- and levamisole-induced paralysis compared to untreated worms. We measured the internal selenium in supplemented worms using inductively coupled plasma atomic emission spectroscopy, and the data obtained suggested that selenite added to growth medium was taken up by the worms. Taken together, these results suggest that selenite exerts both ameliorative and toxic effects on C.elegans, depending on the amount. Our investigations here thus reinforce our understanding of the ameliorative and toxic effects of selenium on development, reproduction, and cholinergic signaling.

Selenium compounds activate ATM-dependent DNA damage response via the mismatch repair protein hMLH1 in colorectal cancer cells

Epidemiological and animal studies indicate that selenium supplementation suppresses risk of colorectal and other cancers. The majority of colorectal cancers are characterized by a defective DNA mismatch repair (MMR). Here, we have employed the MMR-deficient HCT 116 colorectal cancer cells and the MMR-proficient HCT 116 cells with hMLH1 complementation to investigate the role of hMLH1 in selenium-induced DNA damage response, a tumorigenesis barrier. The ATM (ataxia telangiectasia mutated) protein responds to clastogens and initiates DNA damage response. We show that hMLH1 complementation sensitizes HCT 116 cells to methylseleninic acid, methylselenocysteine, and sodium selenite via reactive oxygen species and facilitates the selenium-induced oxidative 8-oxoguanine damage, DNA breaks, G(2)/M checkpoint response, and ATM pathway activation. Pretreatment of the hMLH1-complemented HCT 116 cells with the antioxidant N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl or the ATM kinase inhibitor KU55933 suppresses hMLH1-dependent DNA damage response to selenium exposure. Selenium treatment stimulates the association between hMLH1 and hPMS2 proteins, a heterodimer critical for functional MMR, in a manner dependent on ATM and reactive oxygen species. Taken together, the results suggest a new role of selenium in mitigating tumorigenesis by targeting the MMR pathway, whereby the lack of hMLH1 renders the HCT 116 colorectal cancer cells resistant to selenium-induced DNA damage response.

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.

Primary prevention of colorectal cancer: are we closer to reality?

Colorectal cancer is one of the leading causes of morbidity and mortality worldwide. An early detection of colorectal cancer determines therapeutic outcomes, while primary prevention remains a challenge. Our aim was to review the dietary, geographical and genetic factors in the causation and their possible role in the primary prevention of colorectal cancer. Data from experimental and clinical studies and population screening programmes were analysed to determine the factors responsible for causation of colorectal cancer. The role of dietary constituents, including the consumption of fat, red meat, fibre content, alcohol consumption, and other lifestyle issues, including obesity, lack of exercise and geographical variations in cancer prevalence were reviewed. The role of genetic and lifestyle factors in causation of colorectal cancer is evident from the experimental, clinical and population-based studies. Dietary factors, including the consumption of fat, fibre, red meat and alcohol, seem to have a significant influence in this regard. The role of micronutrients, vitamins, calcium may be relevant but remain largely unclear. In conclusion, there is ample evidence favouring the role of various dietary and lifestyle factors in the aetiology of colorectal cancer. Modification of these factors is an attractive option, which is likely to help in the primary prevention and reduced disease burden.

Effects of selenite and genistein on G2/M cell cycle arrest and apoptosis in human prostate cancer cells

Combination of chemopreventive agents with distinct molecular mechanisms is considered to offer a potential for enhancing cancer prevention efficacy while minimizing toxicity. Here we report two chemopreventive agents, selenite and genistein, that have synergistic effects on apoptosis, cell cycle arrest, and associated signaling pathways in p53-expressing LNCaP and p53-null PC3 prostate cancer cells. We show that selenite induced apoptosis only, whereas genistein induced both apoptosis and G2/M cell cycle arrest. Combination of these two agents exhibited enhanced effects, which were slightly greater in LNCaP than PC3 cells. Selenite or genistein alone upregulated protein levels of p53 in LNCaP cells only and p21(waf1) and Bax in both cell lines. Additionally, genistein inhibited AKT phosphorylation. Downregulation of AKT by siRNA caused apoptosis and G2/M cell cycle arrest and masked the effects of genistein. Treatment with insulin-like growth factor I (IGF-I) elevated levels of total and phosphorylated AKT and suppressed the effects of genistein. Neither downregulation of AKT nor IGF-I treatment altered the cellular effects of selenite. Our study demonstrates that selenium and genistein act via different molecular mechanisms and exhibit enhanced anticancer effects, suggesting that a combination of selenium and genistein may offer better efficacy and reduction of toxicity in prostate cancer prevention.

Alpha-keto acid metabolites of organoselenium compounds inhibit histone deacetylase activity in human colon cancer cells

Methylselenocysteine (MSC) and selenomethionine (SM) are two organoselenium compounds receiving interest for their potential anticancer properties. These compounds can be converted to beta-methylselenopyruvate (MSP) and alpha-keto-gamma-methylselenobutyrate (KMSB), alpha-keto acid metabolites that share structural features with the histone deacetylase (HDAC) inhibitor butyrate. We tested the organoselenium compounds in an in vitro assay with human HDAC1 and HDAC8; whereas SM and MSC had little or no activity up to 2 mM, MSP and KMSB caused dose-dependent inhibition of HDAC activity. Subsequent experiments identified MSP as a competitive inhibitor of HDAC8, and computational modeling supported a mechanism involving reversible interaction with the active site zinc atom. In human colon cancer cells, acetylated histone H3 levels were increased during the period 0.5-48 h after treatment with MSP and KMSB, and there was dose-dependent inhibition of HDAC activity. The proportion of cells occupying G(2)/M of the cell cycle was increased at 10-50 microM MSP and KMSB, and apoptosis was induced, as evidenced by morphological changes, Annexin V staining and increased cleaved caspase-3, -6, -7, -9 and poly(adenosine diphosphate-ribose)polymerase. P21WAF1, a well-established target gene of clinically used HDAC inhibitors, was increased in MSP- and KMSB-treated colon cancer cells at both the messenger RNA and protein level, and there was enhanced P21WAF1 promoter activity. These studies confirm that in addition to targeting redox-sensitive signaling molecules, alpha-keto acid metabolites of organoselenium compounds alter HDAC activity and histone acetylation status in colon cancer cells, as recently observed in human prostate cancer cells.

Selenium and risk of bladder cancer: a population-based case-control study

Emerging evidence indicates a potential role of selenium in the prevention of several types of cancer, including bladder cancer. We investigated the association between toenail selenium concentrations and bladder cancer risk in a population-based case-control study in New Hampshire. We analyzed data from 857 incidence cases diagnosed between July 1, 1994 and June 30, 2001 and 1,191 general population controls. Newly diagnosed cases of bladder cancer were identified from the New Hampshire State Cancer Registry, which operates a rapid reporting system. Controls were selected from population lists (driver's license and Medicare enrollment). We used logistic regression analyses to generate odds ratios (OR) and 95% confidence intervals (95% CI), controlling for age, sex, and pack-years of smoking and conducted separate analyses according to the intensity of p53 immunohistochemical staining of the tumor. Overall, toenail selenium concentrations were not significantly related to bladder cancer [OR Q4 versus Q1, 0.90 (95% CI, 0.68-1.19); P(trend) = 0.15]. However, within specific subgroups there were inverse associations, i.e., among moderate smokers [OR, 0.61 (95% CI, 0.39-0.96); P(trend) = 0.004], women [OR, 0.66 (95% CI, 0.40-1.10); P(trend) = 0.11], and those with p53-positive cancers [OR Q4 versus Q1, 0.57 (95% CI, 0.34-0.94); P(trend) = 0.01]. Our results indicate that selenium is not inversely related to risk of bladder cancer overall; however, they raise the possibility that selenium may be preventive in certain molecular phenotypes of tumors (e.g., p53 positive) or within certain subsets of a population (e.g., women or moderate smokers).

Selenocystine induces S-phase arrest and apoptosis in human breast adenocarcinoma MCF-7 cells by modulating ERK and Akt phosphorylation

Selenocystine (SeC) is a nutritionally available selenoamino acid with selective anticancer effects on a number of human cancer cell lines. The present study shows that SeC inhibited the proliferation of human breast adenocarcinoma MCF-7 cells in a time- and dose-dependent manner, through the induction of cell cycle arrest and apoptotic cell death. SeC-induced S-phase arrest was associated with a marked decrease in the protein expression of cyclins A, D1, and D3 and cyclin-dependent kinases (CDKs) 4 and 6, with concomitant induction of p21waf1/Cip1, p27Kip1, and p53. Exposure of MCF-7 cells to SeC resulted in apoptosis as evidenced by caspase activation, PARP cleavage, and DNA fragmentation. SeC treatment also triggered the activation of JNK, p38 MAPK, ERK, and Akt. Inhibitors of ERK (U0126) and Akt (LY294002), but not JNK (SP600125) and p38 MAPK (SB203580), suppressed SeC-induced S-phase arrest and apoptosis in MCF-7 cells. The findings establish a mechanistic link between the PI3K/Akt pathway, MAPK pathway, and SeC-induced cell cycle arrest and apoptosis in MCF-7 cells.

Tetrazolium violet inhibits cell growth and induces cell death in C127 mouse breast tumor cells

Tetrazolium violet (TV), a tetrazolium salt, has been applied in several fields, including estimating respiration rate, as a redox indicator of microbial growth, and for estimating the number of viable animal cells. It has recently been found that TV is capable of inducing apoptosis in rat glioblastoma cells by way of an elusive mechanism. In this study, we demonstrated that TV also induced apoptosis in mouse breast tumor C127 cells as evidenced by nucleus condensation and nucleus fragmentation. Our data showed that TV caused activation of caspase-3 and caspase-8, but not caspase-9. An enhancement in Fas and its two ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), might be responsible for the apoptotic effect induced by TV. Also, the results first reported that TV not only inhibited C127 cells proliferation but also blocked cell cycle progression in the G1 and G2 phase, determined by MTT assay and flow cytometry analysis. Immunofluorescence assay demonstrated that TV significantly increased the expression of p53 protein, which caused cell cycle arrest. Taken together, p53, Fas/FasL, and the caspase apoptotic system may participate in the antiproliferative activity of TV in C127 cells.

Subchronic oral toxicity studies of Se-methylselenocysteine, an organoselenium compound for breast cancer prevention

Se-methylselenocysteine (MSC) is an organoselenium compound being developed for breast cancer chemoprevention. To characterize MSC toxicity, CD rats received daily gavage doses of 0, 0.5, 1.0, or 2.0 mg/kg/day (0, 3, 6, or 12 mg/m(2)/day), and beagle dogs received daily gavage doses of 0, 0.15, 0.3, or 0.6 mg/kg/day (0, 3, 6, or 12 mg/m(2)/day) for 28 days. In rats, MSC induced dose-related hepatomegaly in both sexes; mild anemia, thrombocytopenia, and elevated liver enzymes were observed in high dose females only. Microscopic pathology included hepatocellular degeneration (high dose males, all doses in females); arrested spermatogenesis (high dose males); and atrophy of corpora lutea (middle and high dose females). In dogs, MSC induced mild anemia in middle and high dose males, and in high dose females. Toxicologically significant microscopic lesions in dogs were seen only in the liver (peliosis and vacuolar degeneration in high dose males, midzonal necrosis in males in all dose groups). Based on liver pathology seen in female rats in all dose groups, the no observed adverse effect level (NOAEL) for MSC in rats is <0.5mg/kg/day. Based on alterations in hematology parameters and liver morphology in male dogs in all dose groups, the NOAEL for MSC in dogs is <0.15 mg/kg/day.

Novel potent organoselenium compounds as cytotoxic agents in prostate cancer cells

A series of 17 symmetrical substituted imidothiocarbamate and imidoselenocarbamate derivatives has been synthesized by reacting appropriately substituted acyl chlorides with alkyl imidothiocarbamates and alkyl imidoselenocarbamates. The antitumoral activities of the compounds were evaluated in vitro by examining their cytotoxic effects against human prostate cancer cells (PC-3). Five compounds showed interesting activity levels and 3p (IC(50)=1.85 microM) was 7.3 times more active than the standard etoposide used in the treatment of prostate cancer and emerges as the most interesting compound.

Colonic adenocarcinoma in a 13-year-old with cystic fibrosis

The increase in longevity among patients with cystic fibrosis has brought to light comorbidities associated with the disease that are less acutely fatal than its pulmonary manifestations. Modern retrospective analysis has demonstrated an increased risk of gastrointestinal malignancy in patients with cystic fibrosis, with a marked elevation in malignancy rates among patients in their 20s and 30s. Here we report a case of colonic adenocarcinoma presenting as pneumaturia in a 13-year-old patient with cystic fibrosis.

Chemotherapeutic selectivity conferred by selenium: a role for p53-dependent DNA repair

Selenium in various chemical forms has been the subject of cancer chemoprevention trials, but, more recently, selenium has been used in combination with DNA-damaging chemotherapeutics. Specifically, selenium protected tissues from dose-limiting toxicity and, in fact, allowed delivery of higher chemotherapeutic doses. At the same time, selenium did not protect cancer cells. Therefore, we seek to define the genetic basis for the observed selectivity of selenium in combination chemotherapeutics. The tumor suppressor p53 is mutated in the vast majority of cancers, but is by definition wild-type in nontarget tissues such as bone marrow and gut epithelium, tissues that are often dose-limiting due to DNA damage. We used primary, low-passage mouse embryonic fibroblasts that are wild-type or null for p53 genes to test differential effects of selenium. Seleno-l-methionine, nontoxic by itself, was used to pretreat cell cultures before exposure to UV radiation or UV-mimetic cancer chemotherapy drugs. Seleno-l-methionine pretreatment caused a DNA repair response, which protected from subsequent challenge with DNA-damaging agents. The observed DNA repair response and subsequent DNA damage protection were p53 dependent as neither was observed in p53-null cells. The data suggest that (a) p53 may be an important genetic determinant that distinguishes normal cells from cancer cells, and (b) combinatorial chemotherapeutics that act by p53-dependent mechanisms may enhance chemotherapeutic efficacy by increasing the chemotherapeutic window distinguishing cancer cells from normal cells.