Abstract 3244: Supplementation with selenium-enriched yeast but not selenomethionine reduces oxidative stress in healthy men in a randomized clinical trial

Epidemiological and laboratory studies indicate that dietary selenium is protective against prostate cancer. Results from clinical trials suggest that selenium-enriched yeast (SY) but not selenomethionine (SeMet) may be effective at reducing prostate cancer risk. Our objectives were to directly compare for the first time the effects of SeMet and SY on prostate cancer relevant biomarkers in men. We performed a randomized double blind, placebo-controlled trial of SY (200 or 285 μg/day) and SeMet (200 μg/day) administered for 9 months in 69 healthy adult males. Biomarkers including blood selenium, glucose, PSA and glutathione (GSH) and urine 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-iso-prostaglandin-F2α (8-iso-PGF2α) were measured at baseline and various times thereafter. Compliance was high in all groups (>95%). Plasma selenium levels were increased 93%, 54%, and 86% after 9 months in the SeMet and low and high dose SY groups, respectively, and returned to baseline levels after a 3 month washout (P<0.05). Urinary biomarkers of oxidative stress, 8-OHdG and 8-iso-PGF2α, were decreased 34% and 28%, respectively, after 9 months in the high dose SY group (P<0.05). Decreases in oxidative stress biomarkers were greatest in individuals with low baseline plasma levels of selenium (<127 ng/ml). No changes in serum PSA or blood glucose and GSH were observed. We showed for the first time reductions in biomarkers of oxidative stress following supplementation with SY but not SeMet in healthy men. These findings suggest that selenium-containing compounds other than SeMet may be responsible for the decrease in oxidative stress and possibly cancer risk. This work was supported a National Cancer Institute grant (R01CA127729).

Citation Format: Matt G. Kaag, John P. Richie, Arun Das, Ana Calcagnotto, Raghu Sinha, Wanda Neidig, Jiangang Liao, Eugene J. Lengreich, Arthur Berg, Terryl J. Hartman, Amy Ciccarella, Aaron Baker, Telih Boyiri, Susan Goodin, Robert S. DiPaola, Karam El-Bayoumy. Supplementation with selenium-enriched yeast but not selenomethionine reduces oxidative stress in healthy men in a randomized clinical trial. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3244. doi:10.1158/1538-7445.AM2014-3244

Mechanisms underlying the varied mammary carcinogenicity of the environmental pollutant 6-nitrochrysene and its metabolites (-)-[R,R]- and (+)-[S,S]-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene in the rat

The mechanisms that can account for the remarkable mammary carcinogenicity of the environmental pollutant 6-nitrochrysene (6-NC) in the rat remain elusive. In our previous studies, we identified several 6-NC-derived DNA adducts in the rat mammary gland; one major adduct was derived from (±)-trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene (1,2-DHD-6-NC). In the present study, we resolved the racemic (±)-1,2-DHD-6-NC into (-)-[R,R]- and (+)-[S,S]-1,2-DHD-6-NC and compared their in vivo mutagenicity and carcinogenicity in the mammary glands of female transgenic (BigBlue F344 × Sprague-Dawley)F1 rats harboring lacI/cII and Sprague-Dawley rats, respectively. Both [R,R]- and [S,S]-isomers exerted similar mutagenicity and carcinogenicity but were less potent than 6-NC. Additional in vivo and in vitro studies were then performed to explore possible mechanisms that can explain the higher potency of 6-NC than 1,2-DHD-6-NC. Using ELISA, we found that neither 6-NC nor 1,2-DHD-6-NC increased the levels of several inflammatory cytokines in plasma obtained from rats 24 h after treatment. In MCF-7 cells, as determined by immunoblotting, the effects of 6-NC and 1,2-DHD-6-NC on protein expression (p53, Akt, p38, JNK, c-myc, bcl-2, PCNA, and ERβ) were comparable; however, the expressions of AhR and ERα proteins were decreased by 6-NC but not 1,2-DHD-6-NC. The expression of both receptors was decreased in mammary tissues of rats treated with 6-NC. Our findings suggest that the differential effects of 6-NC and 1,2-DHD-6-NC on AhR and ERα could potentially account for the higher carcinogenicity of 6-NC in the rat mammary gland.

Hemoglobin-ligand binding: understanding Hb function and allostery on atomic level

The major physiological function of hemoglobin (Hb) is to bind oxygen in the lungs and deliver it to the tissues. This function is regulated and/or made efficient by endogenous heterotropic effectors. A number of synthetic molecules also bind to Hb to alter its allosteric activity. Our purpose is to review the current state of Hb structure and function that involves ensemble of tense and relaxed hemoglobin states and the dynamic equilibrium of the multistate due to the binding of endogenous heterotropic or synthetic allosteric effectors. The review also discusses the atomic interactions of synthetic ligands with the function or altered allosteric function of Hb that could be potentially harnessed for the treatment of diseases. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.

Stereoselective metabolism of the environmental mammary carcinogen 6-nitrochrysene to trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene by aroclor 1254-treated rat liver microsomes and their comparative mutation profiles in a laci mammary epithelial cell line

The environmental pollutant 6-nitrochrysene (6-NC) is a powerful mammary carcinogen and mutagen in rats. Our previous studies have shown that 6-NC is metabolized to trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene (1,2-DHD-6-NC) in rats and in several in vitro systems, including human breast tissue, and the latter is the proximate carcinogenic form in the rat mammary gland. Because optically active enantiomers of numerous polynuclear aromatic hydrocarbon (PAH) metabolites including chrysene have different biological activities, we hypothesized that the stereochemical course of 6-NC metabolism might play a significant role in the carcinogenic/mutagenic activities of the parent 6-NC. The goal of this study is to evaluate the effect of stereochemistry on the mutagenicity of 1,2-DHD-6-NC using the cII gene of lacI mammary epithelial cells in vitro. Resolution of (+/-)-1,2-DHD-6-NC was obtained by either nonchiral or chiral stationary phase HPLC methods. We determined that the ratio of (-)-[R,R]- and (+)-[S,S]-1,2-DHD-6-NC formed in the metabolism of 6-NC by rat liver microsomes is 88:12. The mutation fractions and mutation spectra of [R,R] and [S,S]-enantiomers were examined. Our results showed that the [R,R]-isomer is a significantly (p < 0.01) more potent mutagen than the [S,S]-isomer. The major types of mutation induced by the [R,R]-enantiomer are AT > GC, AT > TA, and GC > TA substitutions, and these are similar to those obtained from 6-NC in vivo in the mammary glands of rats treated with 6-NC. The mutation spectra of the [S,S]-isomer were similar to the [R,R]-isomer, but a higher percentage of AT > GC substitutions in the [R,R]-isomer was noted. On the basis of the results of the present study, we hypothesize that [R,R]-1,2-DHD-6-NC is the proximate carcinogen of 6-NC in the rat mammary gland in vivo and will test this hypothesis in a future study.

Modulations of benzo[a]pyrene-induced DNA adduct, cyclin D1 and PCNA in oral tissue by 1,4-phenylenebis(methylene)selenocyanate

Tobacco smoking is an important cause of human oral squamous cell carcinoma (SCC). Tobacco smoke contains multiple carcinogens include polycyclic aromatic hydrocarbons typified by benzo[a]pyrene (B[a]P). Surgery is the conventional treatment approach for SCC, but it remains imperfect. However, chemoprevention is a plausible strategy and we had previously demonstrated that 1,4-phenylenebis(methylene)selenocyanate (p-XSC) significantly inhibited tongue tumors-induced by the synthetic 4-nitroquinoline-N-oxide (not present in tobacco smoke). In this study, we demonstrated that p-XSC is capable of inhibiting B[a]P-DNA adduct formation, cell proliferation, cyclin D1 expression in human oral cells in vitro. In addition, we showed that dietary p-XSC inhibits B[a]P-DNA adduct formation, cell proliferation and cyclin D1 protein expression in the mouse tongue in vivo. The results of this study are encouraging to further evaluate the chemopreventive efficacy of p-XSC initially against B[a]P-induced tongue tumors in mice and ultimately in the clinic.

Glucuronidation of active tamoxifen metabolites by the human UDP glucuronosyltransferases

Tamoxifen (TAM) is an antiestrogen that has been widely used in the treatment and prevention of breast cancer in women. One of the major mechanisms of metabolism and elimination of TAM and its major active metabolites 4-hydroxytamoxifen (4-OH-TAM) and 4-OH-N-desmethyl-TAM (endoxifen; 4-hydroxy-N-desmethyl-tamoxifen) is via glucuronidation. Although limited studies have been performed characterizing the glucuronidation of 4-OH-TAM, no studies have been performed on endoxifen. In the present study, characterization of the glucuronidating activities of human UDP glucuronosyltransferases (UGTs) against isomers of 4-OH-TAM and endoxifen was performed. Using homogenates of individual UGT-overexpressing cell lines, UGTs 2B7 approximately 1A8 > UGT1A10 exhibited the highest overall O-glucuronidating activity against trans-4-OH-TAM as determined by Vmax/K(M), with the hepatic enzyme UGT2B7 exhibiting the highest binding affinity and lowest K(M) (3.7 microM). As determined by Vmax/K(M), UGT1A10 exhibited the highest overall O-glucuronidating activity against cis-4-OH-TAM, 10-fold higher than the next-most active UGTs 1A1 and 2B7, but with UGT1A7 exhibiting the lowest K(M). Although both N- and O-glucuronidation occurred for 4-OH-TAM in human liver microsomes, only O-glucuronidating activity was observed for endoxifen; no endoxifen-N-glucuronidation was observed for any UGT tested. UGTs 1A10 approximately 1A8 > UGT2B7 exhibited the highest overall glucuronidating activities as determined by Vmax/K(M) for trans-endoxifen, with the extrahepatic enzyme UGT1A10 exhibiting the highest binding affinity and lowest K(M) (39.9 microM). Similar to that observed for cis-4-OH-TAM, UGT1A10 also exhibited the highest activity for cis-endoxifen. These data suggest that several UGTs, including UGTs 1A10, 2B7, and 1A8 play an important role in the metabolism of 4-OH-TAM and endoxifen.

Human cytochromes P450 1A1 and 1B1 catalyze ring oxidation but not nitroreduction of environmental pollutant mononitropyrene isomers in primary cultures of human breast cells and cultured MCF-10A and MCF-7 cell lines

The position of the nitro group determines the relative carcinogenic activities of mono-nitropyrene isomers (mono-NPs) in the rat mammary gland. To determine whether the results obtained in rodents treated with these environmental pollutants can be applicable to humans, we examined their metabolic activation in primary cultures of human breast cells derived from reduction mammoplasty, as well as in the cultured human breast cancer cell line MCF-7 and the immortalized human mammary epithelial cell line MCF-10A. Primary cultures as well as cell lines were competent in metabolizing all three isomers via both ring oxidation and nitro reduction pathways. Qualitatively similar metabolic patterns were observed but quantitative differences were evident. On the basis of cochromatography with synthetic standards in two HPLC systems, metabolites of 1-NP were identified as 1-OH-Py, 3-, 6-, and 8-OH-1-NP and 1-AP. In the case of 2-NP, 6-OH-2-NP and 2-AP were identified. 4-NP was metabolized to 9,10-DHD-4-NP, Py-4,5-Q, 9,10-Q-4-NP, 9/10-OH-4-NP, 6/ 8-OH-4-NP, and 4-AP. Varying degrees of sulfate and glucuronide conjugation of mono-NP metabolites were detected. In MCF-7 cells, we found that 1-, 2-, and 4-NP bind to DNA at levels of 68, 17, and 132 pmol/mg DNA, respectively. Following HPLC analysis of the DNA hydrolysates, we detected multiple DNA adducts including those derived from nitro reduction of 2- and 4-NP; however, none was detected in the case of 1-NP. To determine the P450 enzymes responsible for the metabolic activation of these carcinogens, we incubated [(3)H]mono-NPs with recombinant human P450 1A1 or 1B1. Metabolites identified were primarily derived from ring oxidation; both P450s 1A1 and 1B1 yielded similar metabolic profiles. This is the first report demonstrating that human breast (target organ) cells, immortalized human mammary epithelial cell line MCF-10A, and breast cancer cell line MCF-7 are capable of activating mono-NPs to metabolites that can damage DNA.

Identification of 5-(Deoxyguanosin-N2-yl)- 1,2-dihydroxy-1,2-dihydro-6-aminochrysene as the Major DNA Lesion in the Mammary Gland of Rats Treated with the Environmental Pollutant 6-Nitrochrysene

The environmental pollutant 6-nitrochrysene (6-NC) is a potent carcinogen in several animal models including the rat mammary gland. 6-NC can be activated to intermediates that can damage DNA by simple nitroreduction, ring oxidation, or a combination of ring oxidation and nitroreduction. Only the first pathway (nitroreduction) has been clearly established, and DNA adducts derived from this pathway have been fully characterized in in vitro systems. We also showed previously that the second pathway, ring oxidation leading to the formation of the bay region diol epoxide of 6-NC, is not responsible for the formation of the major DNA adduct in the mammary gland of rats treated with 6-NC. Therefore, in the present study, we explored the validity of the third pathway that involves the combination of both ring oxidation and nitroreduction of 6-NC to form trans-1,2-dihydroxy-1,2-dihydro-6-hydroxylaminochrysene (1,2-DHD-6-NHOH-C). During the course of this study, we synthesized for the first time 1,2-DHD-6-NHOH-C, N-(deoxyguanosin-8-yl)-6-aminochrysene, and N-(deoxyguanosin-8-yl)-1,2-dihydroxy-1,2-dihydro-6-aminochrysene. Incubation of 1,2-DHD-6-NHOH-C with calf thymus DNA resulted in the formation of three adducts. Upon LC/MS combined with 1H NMR analyses, the first eluting adduct was identified as 5-(deoxyguanosin-N2-yl)-1,2-dihydroxy-1,2-dihydro-6-aminochrysene [5-(dG-N2-yl)-1,2-DHD-6-AC], the second eluting adduct was identified as N-(deoxyguanosin-8-yl)-1,2-dihydroxy-1,2-dihydro-6-aminochrysene, and the last was identified as N-(deoxyinosin-8-yl)-1,2-dihydroxy-1,2-dihydro-6-aminochrysene. We also report here for the first time that among those adducts identified in vitro, only 5-(dG-N2-yl)-1,2-DHD-6-AC is the major DNA lesion detected in the mammary glands of rats treated with 6-NC.

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.

Mammary carcinogenesis and molecular analysis of in vivo cII gene mutations in the mammary tissue of female transgenic rats treated with the environmental pollutant 6-nitrochrysene

We determined the mutant fractions (MF) and mutational specificities in the cII gene in histologically confirmed normal, non-involved and tumor mammary tissues of female transgenic (Big Blue F344 x Sprague-Dawley)F1 rats treated with the environmental pollutant 6-nitrochrysene (6-NC). At 30 days of age, three groups were set up for oral treatment with 6-NC dissolved in trioctanoin, or trioctanoin alone once a week for 8 weeks. Two dose levels of 6-NC (100 and 200 micromol/rat) were selected on the basis of our previous carcinogenicity bioassays with CD rats. The rats were decapitated 32 weeks after the last carcinogen dose. Both incidence and multiplicity of mammary adenocarcinomas were significantly elevated in the high dose (36%, 0.57, P < 0.01) group but at the low dose these outcomes (16%, 0.23, P < 0.1) were not significantly different from those of control rats (3%, 0.03). The MF in normal, non-involved and tumor tissues from the mammary glands of 6-NC-treated rats were comparable. At the high and low doses, respectively (4.8 +/- 2.0, 3.2 +/- 2.1) the MF of 6-NC-treated rats, were significantly higher (P < 0.05) than that observed in control rats (1.2 +/- 0.6). Control mutants consisted primarily of GC --> AT transitions, whereas 6-NC-induced mutants were comprised of several major classes of mutations with GC --> TA, GC --> CG, AT --> GC and AT --> TA as the most prevalent. Further studies indicated that the structures of 6-NC-DNA adducts in the mammary tissue are consistent with the mutational specificities. This is the first report that defines the relationship between carcinogenesis and mutagenesis, as well as between structures of 6-NC-DNA adducts and mutation characteristics in the target organ in vivo.

Metabolism of benzo[c]chrysene and comparative mammary gland tumorigenesis of benzo[c]chrysene bay and fjord region diol epoxides in female CD rats

Benzo[c]chrysene (BcC), an environmental pollutant, is a unique polycyclic aromatic hydrocarbon that possesses both a bay region and a fjord region in the same molecule. We previously demonstrated that both bay region and fjord region terminal rings are involved in the in vitro metabolism of BcC. In the present investigation, we prepared [14-(3)H]BcC and tested the hypothesis that BcC can be activated to both bay region and fjord region diol epoxides in female CD rats. At 6 weeks of age, rats were gavaged with a single dose of [14-(3)H]BcC (5 mg/rat; specific activity, 6.7 Ci/mmol) in 0.5 mL of trioctanoin. During the first 48 h, 20.3% of the dose was eliminated in the feces and 2.8% was eliminated in the urine. After 1 week, cumulatively, 23.2 and 3.5%, respectively, were eliminated. 3-Hydroxybenzo[c]chrysene, 10-hydroxybenzo[c]chrysene, and trans-7,8-dihydroxy-7,8-dihydrobenzo[c]chrysene were the major fecal metabolites. In urine, trans-1,2-dihydroxy-1,2-dihydrobenzo[c]chrysene, 2-hydroxybenzo[c]chrysene, (+/-)-1,t-2,t-3,c-4-tetrahydroxy-1,2,3,4-tetrahydrobenzo[c]chrysene, and (+/-)-9,t-10,t-11,c-12-tetrahydroxy-9,10,11,12-tetrahydrobenzo[c]chrysene were detected, primarily as glucuronic acid and sulfate conjugates. The identification of the two tetraols clearly indicates that both bay region and fjord region diol epoxides are formed as intermediates in the metabolism of BcC in vivo. The second goal of this study was to test the hypothesis that the location of the epoxide moiety (fjord vs bay region) determines the carcinogenic activity. Thus, we compared the carcinogenicity of the bay region (+/-)-anti-1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydrobenzo[c]chrysene and the fjord region (+/-)-anti-9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydrobenzo[c]chrysene in the rat mammary gland. The results clearly showed that the fjord region diol epoxide is a potent mammary carcinogen, while the bay region diol epoxide lacks activity in this model assay. This is the first report on a comparison of mammary cancer induction by fjord and bay region diol epoxides derived from the same molecule. It further supports previous observations that fjord region diol epoxides are more carcinogenic than structurally related bay region diol epoxides.

Influence of selenium-enriched yeast supplementation on biomarkers of oxidative damage and hormone status in healthy adult males: a clinical pilot study

The mechanisms responsible for the protective role of selenium against the development of prostate cancer remain to be determined (L. C. Clark et al., J. Am. Med. Assoc., 276: 1957-1963, 1996). In the present study, we tested the hypothesis that selenium supplementation reduces oxidative stress. A secondary aim was to determine whether selenium-induced changes in testosterone (T) metabolism may also be involved. To this end, we conducted a double-blind, randomized, placebo-controlled trial of 247 micro g selenium/day administered p.o. in the form of Se-enriched yeast. Study subjects were 36 healthy adult males, 11 blacks and 25 whites, 19-43 years of age. Supplementation occurred over the first 9 months, after which all subjects were placed on placebo for an additional 3 months. Blood and urine were collected at baseline and after 3, 9, and 12 months. In the selenium group, plasma selenium levels were 2-fold higher than baseline values after 3 and 9 months and returned to 136% of baseline after 12 months (P < 0.0001), whereas in the placebo group, levels were unchanged. A 32% increase in blood glutathione (GSH) levels was observed after 9 months in the selenium group only (P < 0.05). This change coincided with a 26% decrease in protein-bound GSH (bGSH) and a 44% decrease in bGSH:GSH ratios (P < 0.05). The changes in GSH and bGSH were highly correlated with changes in plasma selenium concentrations and may reflect a decrease in oxidative stress. No changes were observed in either group for plasma T, dihydrotestosterone (DHT) or DHT:T ratios, suggesting that selenium had no effect on the alpha-reductase involved in the conversion of T to DHT. A small but significant decrease in prostate-specific antigen levels was observed after 3 and 9 months (P < 0.001), and this difference disappeared after 12 months. Future trials will test the above hypothesis in prostate cancer patients and in subjects at high risk for prostate cancer.

Metabolism and DNA binding of the environmental pollutant 6-nitrochrysene in primary culture of human breast cells and in cultured MCF-10A, MCF-7 and MDA-MB-435s cell lines

The environmental pollutant 6-nitrochrysene (6-NC) is a potent mammary carcinogen in the rat. To determine if the results obtained in 6-NC-treated rodents can be applicable to humans, we examined its metabolic activation in primary cultures of human breast cells prepared from tissues obtained from reduction mammoplasty from 3 women and in a cultured, immortalized human mammary epithelial cell line (MCF-10A), as well as estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-435s) human breast cancer cell lines. Metabolites identified following 24 hr incubations of [(3)H]6-NC (2.5, 5.0 and 10 microM) with human breast cells were derived from ring-oxidation (trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene [1,2-DHD-6-NC]) and nitro-reduction (6-aminochrysene [6-AC]); chrysene-5,6-quinone (C-5,6-Q) was also detected. Levels of metabolites (pmol/mg protein) varied greatly depending on the concentration of 6-NC and the individual breast tissue used; 1,2-DHD-6-NC, ranged from not detected to 15.6 +/- 1.0; 6-AC, from 11.5 +/- 4.0 to 155 +/- 10.2; C-5,6-Q, from 18.3 +/- 10.8 to 196.7 +/- 15.4. Qualitatively similar metabolic profiles were obtained upon incubation of [(3)H]6-NC with MCF-10A, MCF-7 and MDA-MB-435s. We also detected 1,2-dihydroxy-6-aminochrysene (1,2-DH-6-AC; ranged from not detected to 50.4 +/- 9.8). Some of the metabolites identified in our study are known to be proximate carcinogenic forms of 6-NC in rodents. MCF-7 was the most efficient cell line in catalyzing 6-NC to genotoxic metabolites, and we demonstrated that the major DNA adduct is chromatographically identical to that found in the mammary gland of rats treated by gavage with 6-NC and that obtained from the incubation of [(3)H]1,2-DHD-6-NC with MCF7 cells or from nitro-reduction of 1,2-DHD-6-NC in the presence of 2'-deoxyguanosine 5'-monophosphate in vitro. This is the first report to demonstrate the ability of human breast cells, MCF-10A, and breast cancer cell lines to activate 6-NC to metabolites that can damage DNA.

Comparative tumorigenicity of the environmental pollutant 6-nitrochrysene and its metabolites in the rat mammary gland

Human exposure to the class of nitropolynuclear aromatic hydrocarbons is via inhalation and/or ingestion. Therefore, one of the goals of this study was to determine the propensity of the environmental contaminant 6-nitrochrysene (6-NC) for inducing mammary cancer following its oral administration to female CD rats. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), an established mammary carcinogen in the same animal model, was used as a positive control and trioctanoin as a negative control. Thirty-day-old female CD rats were gavaged once weekly for 8 weeks with 6-NC at 50, 25, or 12.5 micromol/rat or PhIP at 50 micromol/rat in 500 microL of trioctanoin. Twenty-three weeks after the last carcinogen administration, rats were decapitated, necropsied, and evaluated histologically. The most common mammary tumors were adenocarcinomas, followed by adenomas and fibroadenomas. The incidence and multiplicity (mean +/- standard deviation) of mammary adenocarcinomas induced by these two carcinogens at the highest dose (6-NC: 90%, 3.73 +/- 2.74; PhIP: 83%, 2.62 +/- 2.58) were significantly higher than those in control rats (10%, 0.10 +/- 0.31). However, there were no statistically significant differences between groups treated with 6-NC and PhIP or among groups receiving various doses of 6-NC. Following its metabolic activation, 6-NC is known to bind covalently to DNA; however, it remains to be determined whether it can also induce DNA base oxidation. Thus, employing the same route of administration, our studies revealed no effect of 6-NC on the basal level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the mammary gland in tests at 6, 24, and 48 h after 6-NC treatment and at termination of the carcinogenesis assay in the normal, noninvolved tissue and in mammary tumors. This result suggests that covalent DNA binding of 6-NC metabolites is important in the induction of mammary cancer in rats. Therefore, the other goal of this study was to compare the tumorigenic activities of 6-NC and its metabolites in the rat mammary gland by intramammary administration. This route has also been used in our laboratory to induce mammary cancer in the rat by 6-NC and is employed here to avoid systemic effects and to determine the role of the mammary gland in the metabolic activation of 6-NC and its metabolites. Toward this end, a new method was developed to obtain ample materials of trans-1,2-dihydroxy-1,2-dihydro-6-aminochrysene (1,2-DHD-6-AC); other metabolites were synthesized as reported previously. On the basis of the results, the carcinogenic potency toward the mammary gland is ranked in the following order: 6-NC > 1,2-DHD-6-NC > 6-AC > 6-NCDE > 1,2-DHD-6-AC. Among the metabolites tested, 1,2-DHD-6-NC was the most potent carcinogen. It was significantly more active than its reduced product 1,2-DHD-6-AC. However, the potency of 1,2-DHD-6-NC was not significantly different from 6-AC, a metabolite derived from simple nitroreduction, or from 6-NCDE. Collectively, these results suggest that metabolites derived from both ring-oxidation and nitroreduction contribute to the overall carcinogenicity of 6-NC in the rat mammary gland.

Control of the allosteric equilibrium of hemoglobin by cross-linking agents

The kinetics of ligand rebinding have been studied for modified or cross-linked hemoglobins (Hbs). Several compounds were tested that interact with alpha Val 1 or involve a cross-link between alpha Val 1 and alpha Lys 99 of the opposite dimer. By varying the length of certain cross-linking molecules, a wide range in the allosteric equilibrium could be obtained. Several of the mono-aldehyde modified Hbs show a shift toward the high affinity conformation of Hb. At the other extreme, for certain di-aldehyde cross-linked Hbs, the CO kinetics are typical of binding to deoxy Hb, even at low photodissociation levels, with which the dominant photoproduct is the triply liganded species; in these cases the hemoglobin does not switch from the low to high affinity state until after the fourth ligand is bound. Although each modified Hb shows only two distinct rates, the kinetic data as a function of dissociation level cannot be simulated with a simple two-state model. A critical length is observed for the maximum shift toward the low affinity T-state. Longer or shorter lengths of the cross-linker yielded more high affinity R-state. Unlike native Hb, which is in equilibrium with free dimers, the cross-linked Hbs maintain the fraction slow kinetics, which is unique to Hb tetramers, even at 0.5 microM (total heme). Addition of HbCN to unmodified HbCO solutions results in dimer exchange, which decreases the relative fraction of slow bimolecular kinetics; the cross-linked Hbs did not show such an effect, indicating that they do not participate in dimer exchange.

Identification of tobacco-derived compounds in human pancreatic juice

Cancer of the pancreas is the fourth leading cause of cancer mortality in the USA with an estimated 28 900 deaths in 2001. Several factors have been implicated in the etiology of this disease. However, at present, only cigarette smoking has been positively associated with pancreatic cancer. It is our working hypothesis that tobacco-derived compounds can be delivered to the pancreas where, upon metabolic activation, they can initiate carcinogenesis. Our current investigation was conducted to determine whether cotinine and tobacco-specific nitrosamines (TSNA) are present in human pancreatic juice. Smoking status was assessed by the determination of levels of urinary cotinine and was further supported by quantifying nicotine in hair. The TSNA were extracted from the pancreatic juice of 18 smokers and 9 nonsmokers by supercritical carbon dioxide that contained 10% methanol. The extracts were analyzed for TSNA, namely, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN), by gas chromatography with mass spectrometric detection using a selected ion monitoring technique (GC-SIM-MS). Twenty-three extracts of human pancreatic juice were also analyzed for the presence of the NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by GC-SIM-MS and by gas chromatography interfaced wit a thermal energy analyzer (GC-TEA; TEA, a nitrosamine-specific detector). Cotinine was detected in all analyzed samples of pancreatic juice from smokers (129 +/- 150 ng/mL juice; mean +/- standard deviation) and was present in only two of the nine samples of pancreatic juice from nonsmokers. Its levels in these two samples were 7 and 9 ng/mL juice. NNK was detected in 15 of 18 samples (83%) from smokers at levels from 1.37 to 604 ng/mL pancreatic juice. In nine samples of pancreatic juice from nonsmokers, NNK ranged from not detected (in three samples) to 96.8 ng/mL juice. In pancreatic juice from smokers the mean level of NNK (88.7 +/- 161 ng/mL juice) was significantly higher (p < 0.04) than in that from nonsmokers (12.4 +/- 31.7 ng/mL juice). In addition to NNK, NNN was found in two samples of pancreatic juice of smokers at levels of 68.1 and 242 ng/mL juice; NNN was not detected in any other sample. NNAL was present in 8 of 14 pancreatic juice samples (57%) from smokers and in three of nine samples (33%) from nonsmokers. This research presents preliminary data that supports the hypothesis that pancreatic tissue is exposed to TSNA and that they may be important contributors to pancreatic carcinogenesis in humans.

X-ray crystallographic analyses of symmetrical allosteric effectors of hemoglobin: compounds designed to link primary and secondary binding sites

The rational design and X-ray crystallographic analyses of two symmetrical allosteric effectors of hemoglobin (Hb) are reported. Compound design was directed by the previously solved co-crystal structure of one of the most potent allosteric effectors of Hb, 2-[4-[(3,5-dichlorophenylcarbamoyl)-methyl]-phenoxy]-2-methylpropionic acid (RSR4), which revealed two distinct binding sites for this compound in the Hb central water cavity. The primary binding site has been observed for all compounds of this structural class, which stabilize deoxy Hb by engaging in inter-dimer contacts with three of the four protein subunits. Interactions at the secondary binding site of RSR4 occur primarily between the beta(1) and beta(2) subunits and serve to further constrain the deoxy state. Based on these observations, it was hypothesized that compounds with the ability to simultaneously span and link both of these sites would possess increased potency, but at a lower molar concentration than RSR4. Two symmetrical compounds were designed and synthesized based on this hypothesis. The symmetrical effector approach was taken to minimize the number of compound orientations needed to successfully bind at either of the distinct allosteric sites. X-ray crystallographic analyses of these two effectors in complex with Hb revealed that they successfully spanned the RSR4 primary and secondary binding sites. However, the designed compounds interacted with the secondary binding site in such a way that intra-dimer, as opposed to inter-dimer, interactions were generated. In agreement with these observations, in vitro evaluation of the symmetrical effectors in Hb solution indicated that neither compound possessed the potency of RSR4. A detailed analysis of symmetrical effector-Hb contacts and comparisons with the binding contacts of RSR4 are discussed.

Bisaldehyde allosteric effectors as molecular ratchets and probes

Four new series of monoaldehyde bisacids and bisaldehyde bisacids with varying chain lengths have been synthesized and evaluated as allosteric effectors of hemoglobin. Molecular modeling, oxygen equilibrium, and crystallographic studies were combined for structure/function studies. Crystallographic analyses of the bisaldehydes reveal that Schiff base interaction occurred exclusively between Val 1 alpha and Lys 99 alpha of the opposite alpha chain even though the two terminal Val 1 alpha nitrogens are ideally spaced to also form cross-links. The reason for the observed mode of binding appears to be the influence of chain direction set by key substitutions on the bisaldehyde molecule. Even longer chain derivatives that could overcome the direction set by the key functional groups bind in the same manner. These studies support the general conclusion that long flexible molecules prefer to bind along cavity walls, like double-sided molecular sticky tape, rather than span large open spaces with few chances for interaction. The cross-linked bisaldehydes bind at the same site when incubated under both allosteric states and exhibit reduced cooperativity with a significant decrease in oxygen affinity. The chain length acts as a molecular ratchet and dictates the degree of allosteric effect observed. The tighter the cross-link, the greater the constraint on the tense- (T-) state and the stronger the allosteric effect that is produced. The monoaldehyde bisacids bind in the same fashion with Schiff base formation at Val 1 alpha while the acid that replaces the second aldehyde moiety forms a salt bridge with Lys 99 alpha of the opposite subunit. This class of molecules has weaker allosteric effector activity as would be expected with replacement of one covalent bond by a salt bridge. The importance of Lys 99 alpha on the allosteric equilibrium is confirmed.

How allosteric effectors can bind to the same protein residue and produce opposite shifts in the allosteric equilibrium

Monoaldehyde allosteric effectors of hemoglobin were designed, using molecular modeling software (GRID), to form a Schiff base adduct with the Val 1 alpha N-terminal nitrogens and interact via a salt bridge with Arg 141 alpha of the opposite subunit. The designed molecules were synthesized if not available. It was envisioned that the molecules, which are aldehyde acids, would produce a high-affinity hemoglobin with potential interest as antisickling agents similar to other aldehyde acids reported earlier. X-ray crystallographic analysis indicated that the aldehyde acids did bind as modeled de novo in symmetry-related pairs to the alpha subunit N-terminal nitrogens. However, oxygen equilibrium curves run on solutions obtained from T- (tense) state hemoglobin crystals of reacted effector molecules produced low-affinity hemoglobins. The shift in the allosteric equilibrium was opposite to that expected. We conclude that the observed shift in allosteric equilibrium was due to the acid group on the monoaldehyde aromatic ring that forms a salt bridge with the guanidinium ion of Arg 141 alpha on the opposite subunit. This added constraint to the T-state structure that ties two subunits across the molecular symmetry axis shifts the equilibrium further toward the T-state. We tested this idea by comparing aldehydes that form Schiff base interactions with the same Val 1 alpha residues but do not interact across the dimer subunit symmetry axis (a new one in this study with no acid group and others that have had determined crystal structures). The latter aldehydes shift the allosteric equilibrium toward the R-state. A hypothesis to predict the direction in shift of the allosteric equilibrium is made and indicates that it is not exclusively where the molecule binds but how it interacts with the protein to stabilize or destabilize the T- (tense) allosteric state.