Chemoprevention of colon carcinogenesis by the synthetic organoselenium compound 1,4-phenylenebis(methylene)selenocyanate.

The chemopreventive effect of 40% and 80% maximum tolerated dose (MTD) levels of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) administered in the diet during the initiation phase (2 weeks before, during, and up to 3 days after carcinogen administration) and the post-initiation phase (3 days after carcinogen treatment until termination) of azoxymethane (AOM)-induced colon carcinogenesis was studied in male F344 rats. The MTD of p-XSC was determined in male F344 rats and found to be 50 ppm. Beginning at 5 weeks of age, all animals were divided into various experimental groups (42 rats/group) and fed the high-fat semipurified diet or diets containing 20 (40% MTD) and 40 (80% MTD) ppm p-XSC. At 7 weeks of age, all animals (30 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM (15 mg/kg body weight/week for 2 weeks). Three days after the second injection of AOM or vehicle (normal saline), groups of animals fed the p-XSC diets and control diet were transferred, respectively, to control diet and p-XSC diets and continued on these diets until the termination of the study. All animals were necropsied during the 36th week after AOM treatment. Colonic mucosal prostaglandin E2 and selenium-dependent glutathione peroxidase were measured in animals fed the control and p-XSC diets at the termination of the study. The results indicate that 40 ppm p-XSC administered during the initiation phase significantly inhibited the colon tumor incidence (percentage of animals with tumors). Dietary p-XSC administered at 20 and 40 ppm levels during the initiation phase significantly inhibited colon tumor multiplicity (tumors/animal and tumors/tumor-bearing animal). Colon tumor incidence and multiplicity were significantly reduced in groups fed 20 and 40 ppm p-XSC diets at the postinitiation phase of carcinogenesis. Colonic mucosal selenium-dependent glutathione peroxidase activity was increased, and prostaglandin E2 was reduced in animals fed the p-XSC diet compared to animals fed the control diet. Whereas the precise mechanisms of p-XSC-induced inhibition of colon carcinogenesis remain to be elucidated, it is likely that the effect during the initiation and postinitiation phases may be due to alteration in carcinogen metabolism and to modulation of prostaglandin synthesis and selenium-dependent glutathione peroxidase activity.     

Chemoprevention of colon cancer by a glutathione conjugate of 1,4-phenylenebis(methylene)selenocyanate, a novel organoselenium compound with low toxicity

We have consistently shown that several synthetic Organoselenium compounds are superior cancer chemopreventive agents and less toxic than selenite or certain naturally occurring selenoamino acids. 1,4-Phenylenebis(methylene)selenocyanate (p-XSC) is the lead Organoselenium compound in that it has been shown to be the most effective and the least toxic agent in several experimental cancer models. It is not known whether p-XSC or one of its metabolites is responsible for its chemopreventive efficacy. As an initial step, we synthesized one of its putative metabolites, i.e., the glutathione conjugate of p-XSC (p-XSe-SG), and determined its stability in the pH range from 2 to 8 and in the diet under normal feeding conditions. We also assessed its maximum tolerated dose and examined its chemopreventive efficacy against azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. p-XSe-SG proved to be very stable over the pH range tested. The maximum tolerated dose of p-XSe-SG determined in a 6-week subchronic toxicity study was found to be >210 ppm (>40 ppm selenium) when the compound was added to AIN-76A high-fat diet. To assess the efficacy of this agent in the postinitiation period of colon carcinogenesis, male F344 rats 6 weeks of age were fed the high-fat diet, and at beginning of weeks 7 and 8, all of the rats intended for carcinogen treatment were given AOM at a dose of 15 mg/kg body weight by s.c. injection. Two days after the carcinogen treatment, the groups of rats consuming the high-fat control diet began their respective high-fat experimental diet regimens with 0, 56, or 84 ppm p-XSe-SG (0.1, 10, and 15 ppm of selenium) supplementation. All animals continued on their respective diets for 38 weeks after the AOM-treatment and were then killed. Colon tumors were evaluated histologically using routine procedures and were also analyzed for cyclooxygenase (COX)-1 and COX-2 expression and enzymatic activities. The results indicate that p-XSeSG administered during the post-initiation stage significantly inhibited both the incidence (P < 0.05-0.01) and the multiplicity (P < 0.05-0.005) of AOM-induced colon adenocarcinomas. This agent also greatly suppressed the multiplicity (P < 0.01-0.001) of AOM-induced exophytic adenocarcinomas in a dose-dependent manner. Feeding of 56 or 84 ppm p-XSe-SG in the diet significantly suppressed total COX activity (P < 0.02 to -0.01) and COX-2 specific activity (P < 0.005-0.0005) but had minimal effect on the protein expression levels of COX-1 and COX-2. These results suggest that the newly developed synthetic Organoselenium compound, p-XSe-SG, is stable in the diet and at wide pH ranges, inhibits colon carcinogenesis when administered during the postinitiation stage, and inhibits COX activity. Compared with previous efficacy studies and considering the toxicity associated with selenium, p-XSe-SG seems to be the least toxic Organoselenium chemopreventive agent thus far tested in the experimental colon carcinogenesis. Studies are in progress to delineate whether p-XSe-SG is also effective when administered during the progression stage of colon carcinogenesis.     

Inhibition of thymidine kinase in cultured mammary tumor cells by the chemopreventive organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate

To identify mechanisms by which the organoselenium compound1,4-phenylenebis(methylene)selenocyanate (p-XSC) mediates itschemopreventive activities, we have examined its effects oncell lines derived from breast cancer of humans and rats. Whenlog-phase cells were treated with a dose of 1 µM p-XSC,we observed a significant decrease in thymidine kinase (TK)activity within 4 h, and reduced thymidine incorporation after24–48 h. When the dose of p-XSC was increased to 2 µM,the decrease in TK was accompanied by a modest, but significant,decrease in thymidine incorporation at 4 h, and a greater inhibitionafter 24–48 h. At a dose of     

Synthesis and excretion profile of 1,4- [14C]phenylenebis(methylene)selenocyanate in the rat

1,4-Phenylenebis(methylene)selenocyanate (p-XSC) inhibits chemically induced tumors in several laboratory animal models. To understand its mode of action, we synthesized p-[14C]XSC, examined its excretion pattern in female CD rats and also the nature of its metabolites. p- [14C]XSC was synthesized from alpha,alpha-dibromo-p-[ring-14C]xylene in 80% yield. The excretion profile of p-[14C]XSC (15.8 mg/kg body wt, 200 microCi/rat, oral administration, in 1 ml corn oil) in vivo was monitored by measuring radioactivity and selenium content. On the basis of radioactivity, approximately 20% of the dose was excreted in the urine and 68% in the feces over 3 days. The cumulative percentages of the dose excreted over 7 days were 24% in urine and 75% in feces, similar to excretion rates of selenium. According to selenium measurement, <1% of the dose was detected in exhaled air; radioactivity was not detected. Only 15% of the dose was extractable from the feces with EtOAc and was identified as tetraselenocyclophane (TSC). Most of the radioactivity remained tightly bound to the feces. Approximately 10% of this bound material converted to TSC on reduction with NaBH4. Organic soluble metabolites in urine did not exceed 2% of the dose; sulfate (9 % of urinary metabolites) and glucuronic acid (19.5% of urinary metabolites) conjugates were observed but their structural identification is still underway. Co-chromatography with a synthetic standard led to the detection of terephthalic acid (1,4- benzenedicarboxylic acid) as a minor metabolite. The major urinary conjugates contained selenium. Despite the low levels of selenium in the exhaled air, the reductive metabolism of p-XSC to H2Se cannot be ruled out. Identification of TSC in vivo indicates that a selenol may be a key intermediate responsible for the chemopreventive action of p- XSC.      

Morphodensitometric analysis of protein kinase C beta(II) expression in rat colon: modulation by diet and relation to in situ cell proliferation and apoptosis

We have recently demonstrated that overexpression of PKC beta(II) renders transgenic mice more susceptible to carcinogen-induced colonic hyperproliferation and aberrant crypt foci formation. In order to further investigate the ability of PKC beta(II) to modulate colonocyte cytokinetics, we determined the localization of PKC beta(II) with respect to cell proliferation and apoptosis along the entire colonic crypt axis following carcinogen and diet manipulation. Rats were provided diets containing either corn oil [containing n-6 polyunsaturated fatty acids (PUFA)] or fish oil (containing n-3 PUFA), cellulose (non-fermentable fiber) or pectin (fermentable fiber) and injected with azoxymethane (AOM) or saline. After 16 weeks, an intermediate time point when no macroscopic tumors are detected, colonic sections were utilized for immunohistochemical image analysis and immunoblotting. Cell proliferation was measured by incorporation of bromodeoxyuridine into DNA and apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling. In the distal colon, PKC beta(II) staining was localized to the upper portion of the crypt. In comparison, proximal crypts had more (P < 0.05) staining in the lower tertile. AOM enhanced (P < 0.05) PKC beta(II) expression in all regions of the distal colonic crypt (upper, middle and lower tertiles). There was also an interaction (P < 0.05) between dietary fat and fiber on PKC beta(II) expression (corn/pectin > fish/cellulose, fish/pectin > corn/cellulose) in all regions of the distal colonic crypt. With respect to colonic cell kinetics, proliferation paralleled the increase in PKC beta(II) expression in carcinogen-treated animals. In contrast, apoptosis at the lumenal surface was inversely proportional to PKC beta(II) expression in the upper tertile. These results suggest that an elevation in PKC beta(II) expression along the crypt axis in the distal colon is linked to enhancement of cell proliferation and suppression of apoptosis, predictive intermediate biomarkers of tumor development. Therefore, select dietary factors may confer protection against colon carcinogenesis in part by blocking carcinogen-induced PKC beta(II) expression.     

Remarkable inhibition of mTOR signaling by the combination of rapamycin and 1,4-phenylenebis(methylene)selenocyanate in human prostate cancer cells

Preclinical studies and clinical analyses have implicated the mammalian target of rapamycin (mTOR) pathway in the progression of prostate cancer, suggesting mTOR as a potential target for new therapies. mTOR, a serine/threonine kinase, belongs to two distinct signaling complexes: mTORC1 and mTORC2. We previously showed that the synthetic organoselenium compound, p-XSC, effectively inhibits viability and critical signaling molecules (e.g., androgen receptor, Akt) in androgen responsive (AR) and androgen independent (AI) human prostate cancer cells. On the basis of its inhibition of Akt, we hypothesized that p-XSC modulates mTORC2, an upstream regulator of the kinase. We further hypothesized that combining p-XSC with rapamycin, an mTORC1 inhibitor, would be an effective combinatory strategy for the inhibition of prostate cancer. The effects of p-XSC and rapamycin, alone or in combination, on viability and mTOR signaling were examined in AR LNCaP prostate cancer cells and AI C4-2 and DU145 cells. Phosphorylation of downstream targets of mTORC1 and mTORC2 was analyzed by immunoblotting. The interaction of mTORC1- and mTORC2-specific proteins with mTOR was probed through immunoprecipitation and immunoblotting. p-XSC inhibited phosphorylation of mTORC2 downstream targets, Akt and PCKα, and decreased the levels of rictor, an mTORC2-specific protein, coimmunoprecipitated with mTOR in C4-2 cells. The combination of p-XSC and rapamycin more effectively inhibited viability and mTOR signaling in C4-2, LNCaP and DU145 cells than either agent individually.     

Chemoprevention of familial adenomatous polyposis development in the APC(min) mouse model by 1,4-phenylene bis(methylene)selenocyanate

Epidemiological and experimental studies have suggested that dietary supplementation with selenium can inhibit the development of cancers at several organ sites. We have consistently shown that 1, 4-phenylene bis(methylene) selenocyanate (p-XSC) is a highly effective cancer chemopreventive agent against the development of chemically induced cancers in several laboratory animal species. This is the first report describing the preventive effects of p-XSC in an animal model of familial adenomatous polyposis (FAP) containing a germline mutation of the APC gene. Six-week old male (heterozygous) C57BL/6J-APC(min) or wild-type mice were fed high fat diets containing 0, 10 or 20 p.p.m. p-XSC. After 80 days, the mice were killed and their intestines were excised and evaluated for polyps. Multiple samples were also harvested from normal appearing small intestine and colon for molecular analysis. Both the mucosa and polyps from the intestine and colon were assayed for beta-catenin, cyclooxygenase (COX)-2 expression and COX isoform activities. Administration of p-XSC in the diet significantly decreased the rate of formation of small intestinal tumors (P < 0. 0001) and colon tumors (P < 0.002) in APC(min) mice. p-XSC produced a dose-dependent inhibition of tumors in both small intestine (P < 0. 0001) and colon (P < 0.035). Mice fed 20 p.p.m. p-XSC had significantly lower levels of beta-catenin expression and COX-2 activity in polyps. These observations demonstrate for the first time that the synthetic organoselenium compound p-XSC possesses antitumor activity against genetically predisposed neoplastic lesions, such as FAP. While the exact mechanism(s) for this antitumor activity of p-XSC remains to be elucidated, it appears that modulation of beta-catenin expression and COX-2 activity is associated with inhibition of intestinal polyps.     

Effects of a combination of docosahexaenoic acid and 1,4-phenylene bis(methylene) selenocyanate on cyclooxygenase 2, inducible nitric oxide synthase and beta-catenin pathways in colon cancer cells

Epidemiological and preclinical studies suggest that diets that are rich in n-3 polyunsaturated fatty acids (PUFAs) and selenium (Se) reduce the risk of colon cancer. Studies conducted in our laboratory have indicated that synthetic organoselenium 1,4-phenylene bis(methylene) selenocyanate (p-XSC) is less toxic and more effective than inorganic Se and selenomethionine, the major Se compound in natural selenium yeast. Through cDNA microarray analysis, we have demonstrated earlier that the n-3 PUFA docosahexaenoic acid (DHA), modulated more than one signaling pathway by altering several genes involved in colon cancer growth. There is increasing interest in the use of combinations of low doses of chemopreventive agents that differ in their specific modes of action as this approach can minimize toxicity and increase efficacy in model assays. In the present study we assessed the efficacy of DHA and p-XSC individually and in combination at low doses in CaCo-2 colon cancer cells, using cell growth inhibition and apoptosis as measures of chemopreventive efficacy. On the basis of western blot and RT-PCR analysis, we also determined the effects of DHA and p-XSC on the levels of expression of cyclooxygenase-2, inducible nitric oxide synthase, cyclin D1, beta-catenin and nuclear factor kappaB, all of which presumably participate in colon carcinogenesis. A 48 h incubation of CaCo-2 cells with 5 microM each DHA or p-XSC induced cell growth inhibition and apoptosis and altered the expression of the above molecular parameters. Interestingly, the modulation of these cellular and molecular parameters was more pronounced in cells treated with low doses of DHA and p-XSC (2.5 microM each) in combination than in cells treated with these agents individually at higher concentrations (5.0 microM each). These findings are viewed as highly significant since they will provide the basis for the development of combinations of low dose regimens of DHA and p-XSC in preclinical models against colon carcinogenesis and, ultimately, in human clinical trials.     

Elevated activities of protein kinase C and tyrosine kinase correlate to leukemic cell aggressiveness.

We report a linkage between cell aggressiveness, protein kinase C (PKC) activity, tyrosine kinase (PTK) activity and serum requirement. We used 2 leukemic cell lines induced by Moloney murine leukemia virus (MLV). One line was highly aggressive (BS-24-1) and required low serum concentrations (3%) for optimal growth in comparison to the less aggressive line (RO2T) that needed 10% serum for optimal growth. The more malignant cells exhibited higher PKC and PTK activity. This activity was independent of serum concentration between 0.01-10%. In contrast, the weakly malignant cells need a high serum concentration (10%) for optimal PKC or PTK activity. Immunoblot analysis revealed a higher level of PKC protein in the BS-24-1 cells than in the RO2T cells. Serum induction of PKC activity did not change the amount of PKC protein in the cytosol or the membrane fractions, indicating post-translational mechanism regulation of PKC. We suggest that the aggressiveness of BS-24-1 resulted from its ability to become independent of growth regulation by serum factors, via autocrine stimulation of PKC and PTK.     

Production of diacylglycerol, an activator of protein kinase C, by human intestinal microflora

Although dietary lipids have been implicated in colon cancer causation, the underlying mechanisms are not known. This paper indicates that when bacteria obtained from normal human feces are incubated with 14C-labeled phosphatidylcholine there is appreciable production of diacylglycerol (DAG), monoacylglycerol, and free fatty acid. Curiously, the production of DAG and monoacylglycerol, but not fatty acid, is strictly dependent on addition of certain bile acids to the incubation system. Among the bile acids tested deoxycholic acid is the most active. Assays of fecal specimens from 10 normal individuals demonstrate a 27-fold interindividual variation in the production of DAG in the in vitro assay system, and also in the absolute levels of DAG present in the same fecal samples. On the other hand, both parameters of DAG are quite constant in repeated fecal samples obtained from the same individual over a period of about 4 months. DAG is a normal physiological activator of protein kinase C, an enzyme that plays a key role in growth control and tumor promotion. We speculate, therefore, that DAG produced by the intestinal microflora might stimulate growth of colonic epithelial cells. Thus an interaction between dietary lipids, bile acids, and specific bacteria in the intestinal lumen could contribute to the risk of colon cancer development in humans.     

NO-releasing NSAIDs and colon cancer chemoprevention: a promising novel approach (Review)

The chemoprevention of colon cancer, the second leading cause of cancer-related deaths in the United States, has been pursued actively during the last two decades. Methodological problems and those stemming from the available agents per se have constrained this difficult task; to some extent, these problems persist to date. That NSAIDs decrease the incidence of and mortality from colon cancer has been a major advance in chemoprevention. These compounds are, however, limited by their significant side effects. NO-releasing NSAIDs (NO-NSAIDs) are a novel class of compounds, synthesized to overcome the limitations of NSAIDs. In general, they appear safer and much more effective than their traditional counterparts. We review their structural features, metabolism and pharmacological actions. In vitro and in vivo studies indicate that they are much more effective than traditional NSAIDs in modulating colonocyte kinetics and the formation of premalignant colon lesions. Their mechanism of action is complex and not fully understood, including modulation of NO synthesis, signaling mediated via NF-kappaB and likely other pathways. Current early findings indicate that NO-NSAIDs may play a highly promising role in the chemoprevention of colon cancer.     

Inhibition of 7,12-dimethylbenz(a)anthracene-induced tumors and DNA adduct formation in the mammary glands of female Sprague-Dawley rats by the synthetic organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate.

We synthesized a novel organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate (XSC), possessing low toxicity by comparison with inorganic Na2SeO3, and several other synthetic organoselenium compounds (K. El-Bayoumy, Cancer Res., 45: 3631-3636, 1985). We tested the effect of XSC treatment during the initiation phase on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma formation. A semipurified high-fat diet containing 80 ppm of XSC (40 ppm as selenium) was fed to 6-wk-old virgin female Sprague-Dawley rats for 2 wk, starting 1 wk before and ending 1 wk after carcinogen treatment. At 7 wk of age, rats were given a single dose of DMBA (5 mg) in 0.2 ml of olive oil by gastric intubation; the experiment was terminated 16 wk later. The development of mammary tumors in those rats that received XSC-supplemented diets was significantly inhibited when compared with the control group (fed the same diet without XSC supplements). This was evident from tumor incidence (percentage of tumor-bearing rats, 88 versus 20) and multiplicity of tumors (mean number of tumors/rats, 3.96 versus 0.28). The finding that XSC acts as a chemopreventive agent in the DMBA mammary tumor model prompted us to examine the effect of dietary XSC on DMBA-DNA binding in both the liver and mammary tissue under conditions identical to those described above for the bioassay. Rats (four/group) were killed 6, 24, 48, and 168 h after [3H]DMBA (5 mg/rat; specific activity, 51.2 mCi/mM) administration. Liver and mammary tissue were obtained and DNA was isolated. Dietary XSC was found to inhibit total DMBA-DNA binding in the mammary tissue, but not in the liver. The most profound effect was observed at early time points, i.e., 24 to 48 h after [3H]DMBA administration. The inhibition in total binding was attributed to a reduction in the formation of the three major adducts derived from bay-region diol-epoxides of DMBA; these were identified as anti-diol-epoxide:deoxyguanosine, syn-diol-epoxide:deoxyadenosine, and anti-diol-epoxide:deoxyadenosine adducts on the basis of their chromatographic characteristics on high-pressure liquid chromatography and on a boronate affinity column. The inhibition of the DMBA-DNA binding in the target tissue provides a plausible explanation for the chemopreventive effect of XSC during the initiation stage of carcinogenesis.     

Diet diversity, diet composition, and risk of colon cancer (United States)

In this study, we evaluate diet diversity, diet composition, and risk of colon cancer in an incident population-based study of 1,993 cases and2,410 controls in the Kaiser Permanente Medical Care Program of Northern California, eight counties in Utah, and the Twin Cities area of Minnesota(United States). Ninety-one and one-half percent of the population were non-Hispanic White. Dietary intake was obtained using an adaptation of the CARDIA diet-history questionnaire. Diet diversity was defined as the number of unique food items reported; diversity also was explored within six major food groups. Composition of the diet was described by estimating the proportion of total number of food items contributed by major food groups. Younger individuals, higher educated individuals, and those who lived in larger households reported eating the most diverse diet. Total diet diversity was not associated with colon cancer. However, eating a diet with greater diversity of meats, poultry, fish, and eggs, was associated with a50 percent increase in risk among all men (95 percent confidence interval[CI] = 1.1-2.0; P trend = 0.01), with slightly stronger associations for younger men and men with distal tumors. A diet with a greater number of refined grain products also was associated with increased risk among men(odds ratio [OR] = 1.7, CI = 1.3-2.3). Women who ate a diet with a more diverse pattern of vegetables were at approximately a 20 percent lower risk than women who had the least diverse diet in vegetables. Assessment of diet composition showed that men who consumed a large proportion of their food items from meat, fish, poultry, and eggs were at an increased risk, with the most marked association being for distal tumors (OR = 1.7, CI = 1.2-2.5).Women who consumed the largest percentage of their food items in the form of plant foods (fruits, vegetables, or whole grains) were at a reduced risk of developing colon cancer (OR = 0.7, CI = 0.5-1.0). This revised version was published online in July 2006 with corrections to the Cover Date.     

MTHFR C677T and A1298C polymorphisms: diet, estrogen, and risk of colon cancer.

5,10-methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in folate metabolism, diverting metabolites toward methylation reactions or nucleotide synthesis. Using data from an incident case-control study (1608 cases and 1972 controls) we investigated two polymorphisms in the MTHFR gene, C677T and A1298C, and their associations with risk of colon cancer. All of the combined genotypes were evaluated separately, and the 1298AA/677CC (wild-type/wild-type) group was considered the reference group. Among both men and women, the 677TT/1298AA (variant/wild-type) genotype was associated with a small reduction in risk [men: odds ratio (OR), 0.7, 95% confidence interval (CI), 0.5-1.0; women: OR, 0.8, 95% CI, 0.5-1.2]. However, the 677CC/1298CC (wild-type/variant) genotype was associated with a statistically significant lower risk among women (OR, 0.6; 95% CI, 0.4-0.9) but not men. When the polymorphisms were considered individually, for A1298C a significant risk reduction associated with the homozygous variant CC genotype was seen among women only (OR, 0.6; 95% CI, 0.5-0.9), and nonstatistically significant reduced risks were observed for the variant 677 TT genotypes among both men and women. Stratification by nutrient intakes showed inverse associations with higher intakes of folate, vitamin B(2), B(6), B(12), and methionine among women with the MTHFR 677CC/1298AA genotypes, but not those with 677TT/1298AA. We observed opposite risk trends for both MTHFR variants, depending on whether women used hormone-replacement therapy or not (P for interaction = <.01). In summary, this study supports recent findings that the MTHFR A1298C polymorphism may be a predictor of colon cancer risk and have functional relevance. The possible interaction with hormone-replacement therapy warrants additional investigation.     

Inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-1butanone tumorigenicity in mouse lung by the synthetic organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate

The chemopreventive effect of 5, 10 and 15 p.p.m. (as selenium)of l, 4-phenylenebis(methylene)selenocyanate (p-XSC) on lungtumor induction by the tobacco-specific 4-(methylnitrosamino)-l-(3-pyridyI)-l-butanone(NNK) was examined in female A/J mice by administering p-XSCin the diet. Sodium selenite (5 p.p.m. selenium) was given inthe same manner for comparison with p-XSC. Mice were fed experimentaldiets containing the selenium compounds 1 week before i.p. injectionof 10 µunol NNK in 0.1 ml saline and throughout the experimentuntil termination, 16 weeks after carcinogen administration.Body weights of the mice in the different dietary groups didnot differ significantly. p-XSC significantly inhibited lungtumor multiplicity from 7.6 tumors per mouse in the controlgroup to 4.1, 3.3 and 1.8 tumors per mouse in animals given5, 10 and 15 p.p.m. of selenium respectively. In contrast, 5p.p.m. sodium selenite had no protective effect against lungtumor induction. The results of this study clearly indicatethat the structure of selenium-containing compounds is importantin determining their efficacy as chemopreventive agents.     

Chemoprevention of lung tumorigenesis induced by a mixture of benzo(a)pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate

We evaluated the chemopreventive efficacy of the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) against the development of tumors of the lung and forestomach induced by a mixture of benzo(a)pyrene (B(a)P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), two of the major lung carcinogens present in tobacco smoke. A/J mice (20 mice/group) were given intragastric doses of a mixture of B(a)P (3 micromol/mouse) and NNK (3 micromol/mouse) in cottonseed oil (0.1 ml) once a week for eight consecutive weeks. Mice were fed either AIN-76A control diet or control diet containing p-XSC (10 ppm selenium), either during or after carcinogen administration. Dietary p-XSC significantly reduced lung tumor multiplicity, regardless of whether it was given during or after carcinogen administration. p-XSC was also an effective inhibitor of tumor development in the forestomach. To provide some biochemical insights into the protective role of p-XSC, its effect on selected phase I and II enzyme activities involved in the metabolism of NNK and B(a)P was also examined in vivo in this animal model. Dietary p-XSC significantly inhibited the activities of the phase I enzymes, methoxyresorufin O-dealkylase (MROD) and N-nitrosodimethylamine N-demethylase (NDMAD), in mouse liver, but it had no effect on ethoxyresorufin O-dealkylase (EROD), pentoxyresorufin O-dealkylase (PROD), and erythromycin N-demethylase (ERYTD). Total glutathione S-transferase (GST) enzyme activity, as well as GST-pi and GST-mu enzyme activities, were significantly induced by dietary p-XSC in both the lung and liver. Glutathione peroxidase (GPX) activity was also induced by p-XSC in mouse lung, but not in the liver. Dietary p-XSC had no effect on selenium-dependent glutathione peroxidase (GPX(Se)), GST-alpha, and UDP-glucuronosyl transferase (UDPGT) enzyme activities in either the lung or the liver. These studies suggest that the chemopreventive efficacy of p-XSC, when fed during carcinogen administration, may be, in part, due to the inhibition of certain phase I enzymes involved in the metabolic activation of these carcinogens, and the induction of specific phase II enzymes involved in their detoxification. The mechanisms that account for the effect of p-XSC when fed after carcinogen administration remain to be determined.     

Suppressing effects of dietary supplementation of the organoselenium 1,4-phenylenebis(methylene)selenocyanate and the Citrus antioxidant auraptene on lung metastasis of melanoma cells in mice

The modifying effects of the organoselenium 1,4-phenylenebis(methylene)selenocyanate (p-XSC) and the Citrus antioxidant auraptene as dietary supplements on experimental pulmonary metastasis of B16BL6 murine melanoma cells were investigated in an i.v. injection model in mice. Seven groups of male C57BL/6 mice were fed a basal diet (control group) or the basal diet supplemented with p-XSC (4, 8, or 15 mg/kg) or auraptene (250, 500, or 1000 mg/kg). All mice were fed their respective diet for 2 weeks before and after i.v. injection of 1 x 10(5) viable melanoma cells. At termination of the study, the incidence of lung metastatic tumors was determined. Cross-sectional areas and tumor volumes were analyzed morphometrically. In addition, apoptotic indices of lung metastatic tumors of all groups were counted. The incidences of lung metastasis in mice fed the diet mixed with 8 or 15 mg p-XSC/kg were significantly smaller than that in mice fed the basal diet. The mean numbers of metastatic lung tumors were significantly lower in mice fed p-XSC (4, 8, and 15 mg/kg) and auraptene (500 and 1000 mg/kg) than in controls. Cross-sectional areas and volumes of the tumors were also significantly decreased in mice given p-XSC (8 or 15 mg/kg) and auraptene (500 mg/kg). Apoptotic indices in mice fed the diets mixed with p-XSC (4, 8, or 15 mg/kg) and auraptene (500 and 1000 mg/kg) were significantly greater than those in the control group. These results indicate that in mice, diet supplementation with p-XSC and auraptene reduces pulmonary metastasis of B16BL6 melanoma cells and inhibits the growth of these metastatic tumors in lung, in part, by inducing apoptosis. We suggest that these agents, especially p-XSC, may be valuable in preventing metastatic diseases in future studies in the clinic.     

Prostate cancer chemoprevention: models, limitations and potential (Review)

The silent course of prostate cancer and its fatal outcome have hindered the development of treatment options for this disease. There is a need for new options in the management of prostate cancer. Chemoprevention is a relatively new and promising strategy, employing natural or synthetic agents to delay, halt or even reverse the process of carcinogenesis. Numerous synthetic and naturally occurring compounds have been evaluated in cell culture systems and in vivo models of prostate cancer for possible use in cancer chemopreventive programs. Here, I provide a review of studies of chemopreventive/therapeutic agents in various models of prostate cancer.     

Apigenin and cancer chemoprevention: progress, potential and promise (review)

Cancer is one of the major public health burdens in the United States and in other developed countries, causing approximately 7 million deaths every year worldwide. Cancer rates vary dramatically in different regions and populations around the globe, especially between developing and developed nations. Changes in cancer prevalence patterns occur within regions as their populations age or become progressively urbanized. Migration has also contributed to such variations as changes in dietary habits influence cancer rates. These epidemiologic findings strongly suggest that cancer rates are influenced by environmental factors including diet, which is largely preventable. Approaches to prevent cancer include overlapping strategies viz. chemoprevention or dietary cancer prevention. Chemoprevention aims at prevention or reversal of the initiation phase of carcinogenesis or arrest at progression of carcinogenesis through the administration of naturally occurring constituents or pharmacological agents. Cancer prevention through diet may be largely achievable by increased consumption of fruits and vegetables. Considerable attention has been devoted to identifying plant-derived dietary agents which could be developed as promising chemopreventives. One such agent is apigenin. A naturally occurring plant flavone (4', 5, 7,-trihydroxyflavone) abundantly present in common fruits and vegetables including parsley, onions, oranges, tea, chamomile, wheat sprouts and some seasonings. Apigenin has been shown to possess remarkable anti-inflammatory, antioxidant and anti-carcinogenic properties. In the last few years, significant progress has been made in studying the biological effects of apigenin at cellular and molecular levels. This review examines the cancer chemopreventive effects of apigenin in an organ-specificity format, evaluating its limitations and its considerable potential for development as a cancer chemopreventive agent.     

Non-invasive detection of fecal protein kinase C betaII and zeta messenger RNA: putative biomarkers for colon cancer

We have developed a non-invasive method utilizing feces, containing sloughed colonocytes, as a sensitive technique for detecting diagnostic colonic biomarkers. In this study, we used the rat colon carcinogenesis model to determine if changes in fecal protein kinase C (PKC) expression have predictive value in monitoring the neoplastic process. Weanling rats were injected with saline or azoxymethane (AOM) and 36 weeks later fecal samples and mucosa were collected, poly A+ RNA isolated, and quantitative RT-PCR performed using primers to PKC betaII and zeta. Fecal PKC betaII and zeta mRNA levels were altered by the presence of a tumor, with tumor-bearing animals having a 3-fold higher (P < 0.05) PKC betaII expression as compared with animals without tumors. In addition, AOM-injection increased mucosal PKC betaII mRNA expression compared with saline controls. No effect of tumor incidence on mucosal PKC betaII expression was observed. In contrast, fecal PKC zeta expression was 2.5-fold lower (P < 0.05) in animals injected with azoxymethane versus saline. Since tumor incidence exerts a reciprocal effect on fecal PKC betaII and zeta mRNA expression, data were also expressed as the ratio between PKC betaII and zeta. The isozyme ratio was strongly related to tumor incidence, i.e. ratio for animals with tumors was 2.18 +/- 1.25, animals without tumors was 0.50 +/- 0.16, P = 0.025. We demonstrate that the expression of fecal PKC betaII and zeta may serve as a noninvasive marker for development of colon tumors. A sensitive technique for the detection of colon cancer is of importance since early diagnosis can substantially reduce mortality.