Indole-3-carbinol inhibits 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone plus benzo(a)pyrene-induced lung tumorigenesis in A/J mice and modulates carcinogen-induced alterations in protein levels

We tested the chemopreventive efficacy of indole-3-carbinol (I3C), a constituent of Brassica vegetables, and its major condensation product, 3,3'-diindolylmethane (DIM), against lung tumorigenesis induced by a mixture of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (BaP) in A/J mice. The mixture of NNK plus BaP (2 micromol each) was administered by gavage as eight weekly doses, whereas I3C (112 micromol/g diet) and DIM (2 and 30 micromol/g diet in experiments 1 and 2, respectively) were given in the diet for 23 weeks beginning at 50% of carcinogen treatment. I3C reduced NNK plus BaP-induced tumor multiplicity by 78% in experiment 1 and 86% in experiment 2; the respective reductions in tumor multiplicity by DIM were 5% and 66%. Using a quantitative proteomics method, isobaric tags for relative and absolute quantitation (iTRAQ) coupled with mass spectrometry, we identified and quantified at least 250 proteins in lung tissues. Of these proteins, nine showed differences in relative abundance in lung tissues of carcinogen-treated versus untreated mice: fatty acid synthase, transketolase, pulmonary surfactant-associated protein C (SP-C), L-plastin, annexin A1, and haptoglobin increased, whereas transferrin, alpha-1-antitrypsin, and apolipoprotein A-1 decreased. Supplementation of the diet of carcinogen-treated mice with I3C reduced the level of SP-C, L-plastin, annexin A1, and haptoglobin to that of untreated controls. These results were verified using immunoblotting. We show here that tumor-associated signature proteins are increased during NNK plus BaP-induced lung carcinogenesis, and I3C inhibits this effect, suggesting that the lung tumor chemopreventive activity of I3C might be related to modulation of carcinogen-induced alterations in protein levels.

Investigation of the reaction of myosmine with sodium nitrite in vitro and in rats

Previous studies have shown that the minor tobacco alkaloid myosmine (5) reacts with NaNO2 in the presence of acid to yield 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB, 8) via 4-(3-pyridyl)-4-oxobutanediazohydroxide (7). Intermediate 7 is also formed in the metabolism of the tobacco-specific nitrosamines N'-nitrosonornicotine (NNN, 1) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 2), resulting in pyridyloxobutylation of DNA and Hb. These pyridyloxobutyl adducts can be quantified by analyzing HPB released upon acid treatment of DNA or base treatment of Hb. Quantitation of HPB-releasing DNA and Hb adducts has been used to assess the metabolic activation of NNN and NNK in smokers and smokeless tobacco users. Because myosmine is found in the diet as well as in tobacco products, it has been suggested that nitrosation of myosmine could lead to the formation of HPB-releasing adducts in people not exposed to tobacco products. We investigated the nitrosation of myosmine in vitro and in vivo in rats. The reaction of myosmine with NaNO2 under acidic conditions produced HPB, as previously reported. A new product was identified as 3'-oximinomyosmine (11) based on its spectral properties. NNN was not detected. Groups of rats were treated with NNN, NNK, myosmine, NaNO2, or combinations of myosmine and NaNO2. HPB-releasing Hb and DNA adducts were clearly detected in the rats treated with NNN or NNK, but we found no evidence for production of these adducts from the combination of myosmine plus NaNO2. The results of this study do not support the hypothesis that exposure to dietary myosmine could lead to HPB-releasing DNA or Hb adducts in humans.

Quantitation of N-acetyl-S-(9,10-dihydro-9-hydroxy-10-phenanthryl)-L-cysteine in human urine: comparison with glutathione-S-transferase genotypes in smokers

There are major interindividual differences in carcinogenic polycyclic aromatic hydrocarbon (PAH) metabolism in humans, and it has been hypothesized that these differences may be related to cancer risk in smokers and other exposed people. One important pathway of PAH metabolism involves the detoxification of the epoxide and diol epoxide metabolites by reaction with glutathione, catalyzed by glutathione-S-transferases (GSTs). Interindividual differences in these pathways have been examined by genotyping methods, investigating polymorphisms in GSTM1 and GSTP1. We are developing a phenotyping approach to assessing individual differences in PAH metabolism by quantifying human urinary metabolites of the ubiquitous PAH phenanthrene (1). In this study, we developed a method for quantitation of a mercapturic acid, N-acetyl-S-(9,10-dihydro-9-hydroxy-10-phenanthryl)-l-cysteine (PheO-NAC, 12), the end product of the reaction of phenanthrene-9,10-epoxide (11) with glutathione. [D(10)]PheO-NAC was added to the urine as internal standard, and the PheO-NAC fraction was enriched by solid-phase extraction. PheO-NAC was quantified by liquid chromatography electrospray ionization tandem mass spectrometry with selected reaction monitoring. The detection limit was approximately 4 fmol/mL of urine. PheO-NAC was detected in the urine of 46 of 104 smokers, mean (S.D.) 57.9 +/- 144 fmol/mL. PheO-NAC was detected significantly more frequently (P < 0.0001) in subjects who were GSTM1 positive than in those who were GSTM1 null, and the levels of PheO-NAC were significantly higher in the GSTM1 positive subjects, consistent with a role for GSTM1 in the detoxification of phenanthrene-9,10-epoxide. There were no significant relationships between PheO-NAC levels and the occurrence of two GSTP1 polymorphisms. The results of this study provide the first evidence for a PAH-derived mercapturic acid in human urine and should be useful in the development of a phenotyping approach to assess individual differences in PAH metabolism.

Identification of adducts formed in the reaction of 5'-acetoxy-N'-nitrosonornicotine with deoxyguanosine and DNA

N'-Nitrosonornicotine (NNN) is believed to play an important role as a cause of cancer in people who use tobacco products and is considered to be a human carcinogen. NNN requires metabolism to form DNA adducts, which are absolutely critical to its carcinogenic properties. Previous studies have identified cytochrome P450-catalyzed 2'- and 5'-hydroxylation of NNN as potential DNA adduct forming metabolic pathways. 5'-Hydroxylation is the more prevalent of these in monkeys and humans and is known to generate mutagenic intermediates, but the DNA adducts formed by this pathway have never been characterized. In this study, we used 5'-acetoxyNNN as a stable precursor to 5'-hydroxyNNN and investigated its esterase-catalyzed reactions with deoxyguanosine (dGuo) and DNA. Adducts resulting from carbocation and oxonium ion intermediates, produced by the spontaneous decomposition of 5'-hydroxyNNN, were identified. The carbocation pathway resulted in the formation of 2-[2-hydroxy-5-(3-pyridyl)pyrrolidin-1-yl]deoxyinosine (12) which was characterized by comparison to an independently synthesized standard. Treatment of 12 with NaBH(3)CN produced two diastereomers of 2-[2-(3-pyridyl)pyrrolidin-1-yl]deoxyinosine (14), and their absolute configurations at the 2-position were determined by comparison to synthetic standards. The oxonium ion pathway produced diastereomers of N(2)[5-(3-pyridyl)tetrahydrofuran-2-yl]dGuo (16), identified by comparison to synthetic standards. The absolute configuration at the 5-position was determined by establishing the stereochemistry of the enantiomers of 5-(3-pyridyl)-2-hydroxytetrahydrofuran at the 5-position and allowing these to react individually with dGuo. Treatment of 16 with NaBH(3)CN produced N(2)[4-hydroxy-4-(3-pyridyl)but-1-yl]dGuo (18) which was also synthesized independently. Using liquid chromatography-electrospray ionization-tandem mass spectrometry with selected reaction monitoring, we identified adducts 12 and 16 as products of the reactions of 5'-acetoxyNNN with dGuo. Similarly, adducts 14 and 18 were identified as products of the reaction of 5'-acetoxyNNN with DNA followed by NaBH(3)CN treatment and enzymatic hydrolysis. These results provide the first structural characterization of DNA adducts that can be formed by 5'-hydroxylation of NNN.

Characterization of N-glucuronidation of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in human liver: importance of UDP-glucuronosyltransferase 1A4

The nicotine-derived tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is one of the most potent and abundant procarcinogens found in tobacco and tobacco smoke and is considered to be a causative agent for several tobacco-related cancers. Glucuronidation of the major metabolite of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), has been implicated as an important mechanism for NNK detoxification. To characterize NNAL metabolism by N-glucuronidation in humans, high-pressure liquid chromatography was used to detect glucuronide conjugates of NNAL formed in human liver microsomes in vitro. In addition to peaks corresponding to the O-glucuronides of NNAL (NNAL-O-Gluc), a second series of peaks were observed in human liver microsomes that were identified by liquid chromatography-mass spectrometry to be NNAL N-glucuronides (NNAL-N-Gluc). Microsomes prepared from liver specimens from individual subjects (n = 42) exhibited substantial variability in the levels of NNAL-N-Gluc (49-fold variability) and NNAL-O-Gluc (49-fold variability) formed in vitro. This variability was likely not due to differences in tissue quality, as substantial variability (5-fold) was also observed in the ratio of NNAL-N-Gluc/NNAL-O-Gluc formation, with a mean ratio of 1.7 in the 42 specimens. Liver microsomes from smokers (n = 14) exhibited no significant difference in the levels of either NNAL-N-Gluc or NNAL-O-Gluc formation, or in the ratio of NNAL-N-Gluc/NNAL-O-Gluc formation, as compared with liver microsomes from never smokers (n = 28). Overexpressed UDP-glucuronosyltransferase (UGT) 1A4 exhibited significant levels of N-glucuronidating activity (V(max)/K(m) = 3.11 microl. min(-1). g(-1)) in vitro; no NNAL-N-glucuronide formation was detected for the 11 other overexpressed UGT enzymes tested in these studies. These results demonstrate the importance of N-glucuronidation in the metabolism of NNAL and the role of UGT1A4 in this pathway.

Identification of O2-substituted pyrimidine adducts formed in reactions of 4-(acetoxymethylnitrosamino)- 1-(3-pyridyl)-1-butanone and 4-(acetoxymethylnitros- amino)-1-(3-pyridyl)-1-butanol with DNA

Metabolic hydroxylation of the methyl group of the tobacco specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) results in the formation of intermediates that can alkylate DNA. Similarly, metabolic hydroxylation of the 2'-position of the tobacco specific carcinogen N'-nitrosonornicotine gives DNA alkylating intermediates. The resulting pyridyloxobutyl and pyridylhydroxybutyl adducts with dGuo have been characterized, but there are no reports of pyrimidine adducts. Therefore, in this study, we investigated the reactions of 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKCH(2)OAc) and 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanol (NNALCH(2)OAc) with DNA, dCyd, and dThd. NNKCH(2)OAc and NNALCH(2)OAc are stable precursors to the products formed upon metabolic methyl hydroxylation of NNK and NNAL. Analysis by LC-ESI-SIM of enzyme hydrolysates of DNA that had been allowed to react with NNKCH(2)OAc and NNALCH(2)OAc demonstrated the presence of major adducts with dCyd and dThd. The dCyd adducts were thermally unstable, releasing 4-HPB (18) or 4-hydroxy-1-(3-pyridyl)-1-butanol (25) upon treatment at 100 degrees C, pH 7.0. The dThd adducts were stable under these conditions. The dCyd adduct of NNALCH(2)OAc was characterized by its MS and UV and by conversion upon neutral thermal hydrolysis to the corresponding Cyt adduct, which was identified by MS, UV, and NMR. The dCyd and Cyt adducts of NNKCH(2)OAc were similarly characterized. The dThd adduct of NNKCH(2)OAc was identified by MS, UV, and NMR. Treatment of this adduct with NaBH(4) gave material, which was identical to that produced upon reaction of NNALCH(2)OAc with DNA or dThd. These data demonstrate that the major pyrimidine adducts formed in the reactions of NNKCH(2)OAc with DNA are O(2)[4-(3-pyridyl)-4-oxobut-1-yl]dCyd (26) and O(2)[4-(3-pyridyl)-4-oxobut-1-yl]dThd (30) while those produced from NNALCH(2)OAc are O(2)[4-(3-pyridyl)-4-hydroxybut-1-yl]dCyd (28) andO(2)[4-(3-pyridyl)-4-hydroxybut-1-yl]dThd (31). Levels of these pyrimidine adducts of NNKCH(2)OAc in DNA were substantially greater than those of the dGuo adducts of NNKCH(2)OAc, based on MS peak area. Furthermore, 26 was identified as a major 4-HPB releasing adduct of NNKCH(2)OAc. These results suggest that pyrimidine adducts of tobacco specific nitrosamines may be important contributors to their mutagenic and carcinogenic activity.

Stereoselective metabolism and tissue retention in rats of the individual enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), metabolites of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is reduced to its main metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in a reaction that is both stereoselective and reversible. (S)-NNAL has been shown to be equivalent to NNK in carcinogenic potency, and significantly more potent than (R)-NNAL. It was hypothesized that stereoselective differences in metabolism or tissue distribution contributed to the difference in carcinogenicity between the enantiomers. The individual NNAL enantiomers were therefore administered to bile duct-cannulated rats. Male Fisher F344 rats received i.v. doses of either (R)-NNAL (n = 10) or (S)-NNAL (n = 9) and bile, urine, blood and tissue samples were collected over 24 h. (R)/(S)-NNAL and metabolites were quantified by HPLC and radioflow detection. NNAL was also collected from the HPLC and silylated, and the two NNAL enantiomers were separated by chiral GC-TEA. (S)-NNAL had a much larger tissue distribution (Vss = 1792 +/- 570 ml) than did (R)-NNAL (Vss = 645 +/- 230 ml). Overall, (R)-NNAL tended to enter detoxification pathways, particularly glucuronidation, while reversible metabolism of (S)-NNAL to NNK was favored. For example, after (R)-NNAL administration, approximately 50% of the dose was excreted as (R)-NNAL-Gluc in bile and urine, and <5% was excreted as NNK or NNK metabolites. In contrast, only 10% of an (S)-NNAL dose was excreted as a glucuronide, while almost 20% of the (S)-NNAL dose was excreted as NNK or NNK metabolites. In tissues, particularly the lung, (S)-NNAL appeared to be stereoselectively retained. These findings suggest that the difference in carcinogenicity between the NNAL enantiomers may be attributed to stereoselective differences in tissue distribution and excretion.

Endogenous 5-methylcytosine protects neighboring guanines from N7 and O6-methylation and O6-pyridyloxobutylation by the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

All CG dinucleotides along exons 5-8 of the p53 tumor suppressor gene contain endogenous 5-methylcytosine (MeC). These same sites (e.g., codons 157, 158, 245, 248, and 273) are mutational hot spots in smoking-induced lung cancer. Several groups used the UvrABC endonuclease incision assay to demonstrate that methylated CG dinucleotides of the p53 gene are the preferred binding sites for the diol epoxides of bay region polycyclic aromatic hydrocarbons (PAH). In contrast, effects of endogenous cytosine methylation on the distribution of DNA lesions induced by tobacco-specific nitrosamines, e.g., 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), have not been elucidated. In the work presented here, a stable isotope labeling HPLC-ESI-MS/MS approach was employed to analyze the reactivity of the N7 and O6 positions of guanines within hemimethylated and fully methylated CG dinucleotides toward NNK-derived methylating and pyridyloxobutylating species. 15N3-labeled guanine bases were placed within synthetic DNA sequences representing endogenously methylated p53 codons 154, 157, and 248, followed by treatment with acetylated precursors to NNK diazohydroxides. HPLC-ESI-MS/MS analysis was used to determine the relative yields of N7- and O6-guanine adducts at the 15N3-labeled position. In all cases, the presence of MeC inhibited the formation of N7-methylguanine, O6-methylguanine, and O6-pyridyloxobutylguanine at a neighboring G, with the greatest decrease observed in fully methylated dinucleotides and at guanines preceded by MeC. Furthermore, the O6-Me-dG/N7-Me-G molar ratios were decreased in the presence of the 5'-neighboring MeC, suggesting that the observed decline in O6-alkylguanine adduct yields is, at least partially, a result of an altered reactivity pattern in methylated CG dinucleotides. These results indicate that, unlike N2-guanine adducts of PAH diol epoxides, NNK-induced N7- and O6-alkylguanine adducts are not preferentially formed at the endogenously methylated CG sites within the p53 tumor suppressor gene.

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

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

Conservative management of splenic trauma: history and current trends

Evolution of the present-day policy of conservative management of ruptured spleen has been hailed as one of the most notable advances in pediatric surgery. Until 1971, routine splenectomy used to be the sacrosanct treatment for splenic trauma. It was universally believed that non-operative management carried a high mortality of 90 to 100%. Sporadic reports of successful conservative treatment appeared in the early twentieth century, but regrettably, these were ignored. Likewise, experimental studies pointing to the danger of post-splenectomy sepsis were also disregarded. Dominant surgical opinion continued to practice removal of the injured spleen. In 1968, Upadhyaya and Simpson, based on a well-designed clinical analysis of 52 children made a convincing plea for conservative management. In 1971, Upadhyaya et al. presented results of a corroborative experimental study, which provided the conclusive evidence that isolated splenic tears are well tolerated and heal spontaneously by first intention. Seeing the surge of publications that followed this presentation, it becomes apparent that this study constituted the real turning point that changed the world opinion in favour of salvage of the ruptured spleen. By 1979, numerous authors had reported the safety of non-operative management in hundreds of children all over the world. Currently, the policy of routine splenectomy has been universally abandoned; and the reported salvage rate of ruptured spleen is more than 90%. This paper traces the historical perspectives in the management of injured spleen from the times of Aristotle to the present day.

Stereospecific deuterium substitution attenuates the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Stereochemical determinants of the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were investigated using the stereospecifically deuterated isotopomers (4R)-[4-(2)H(1)]NNK and (4S)-[4-(2)H(1)]NNK. Upon ip administration to groups of 20 female A/J mice, NNK and (4S)-[4-(2)H(1)]NNK exhibited similar lung tumorigenicity at three different doses, whereas (4R)-[4-(2)H(1)]NNK was 2-fold less tumorigenic at all three doses. In a parallel experiment, levels of O(6)-methylguanine and 7-methylguanine were 2-fold lower in lung DNA of mice treated with (4R)-[4-(2)H(1)]NNK than in mice treated with NNK or (4S)-[4-(2)H(1)]NNK. To corroborate these in vivo data, the in vitro metabolism of these compounds was investigated using A/J mouse lung microsomes and Spodoptera frugiperda (Sf9)-expressed mouse cytochrome p450s 2A4 and 2A5. Kinetic isotope effects on the apparent V(max) ((D)V) for the product of NNK 4-hydroxylation, OPB, were 2.7 +/- 0.2 and 2.8 +/- 0.4 when (4R)- and (4S)-[4-(2)H(1)]NNK were incubated with mouse lung microsomes, respectively. The (D)V values for OPB formation were 3.2 +/- 0.2 and 2.2 +/- 0.2 when (4R)-[4-(2)H(1)]NNK was the substrate for p2A4 and 2A5, respectively, whereas they were 1.3 +/- 0.1 and 1.1 +/- 0.1 when (4S)-[4-(2)H(1)]NNK was the substrate for these respective enzymes. Analysis of an OPB derivative (10) for deuterium content by LC/MS confirmed the results from the kinetic assays and indicated that p450s 2A4 and 2A5 preferentially abstract the pro-R 4-hydrogen of NNK. The results obtained using Sf9-expressed p450s provide a rationale for the differences observed in the lung tumor and DNA adduct experiments, namely, that the attenuated tumorigenicity of (4R)-[4-(2)H(1)]NNK relative to (4S)-[4-(2)H(1)]NNK is due to prochiral selectivity during p450-catalyzed metabolic activation.

Identification of adducts formed by pyridyloxobutylation of deoxyguanosine and DNA by 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone, a chemically activated form of tobacco specific carcinogens

The tobacco specific carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) are metabolically activated to 4-oxo-4-(3-pyridyl)-1-butanediazohydroxide (7), which is known to pyridyloxobutylate DNA. A substantial proportion of the adducts in this DNA releases 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB, 11) under various hydrolysis conditions, including neutral thermal hydrolysis. These HPB-releasing DNA adducts have been detected in target tissues of animals treated with NNK and NNN as well as in lung tissue from smokers. Although their presence in pyridyloxobutylated DNA was conclusively demonstrated 15 years ago, their structures have not been previously determined. We investigated this question in the present study by determining the structures of products formed in reactions with dGuo and DNA of 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKCH(2)OAc, 3), a stable precursor to 7. Reaction mixtures from NNKCH(2)OAc and dGuo were analyzed by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) with selected ion monitoring at m/z 415. A major peak was detected and identified as 7-[4-oxo-4-(3-pyridyl)but-1-yl]dGuo (37) by its ESI-MS fragmentation pattern and by neutral thermal hydrolysis, which converted it to 11 and 7-[4-oxo-4-(3-pyridyl)but-1-yl]Gua (26). The latter was identified by comparison to synthetic 26 using LC-ESI-MS with selected ion monitoring at m/z 299, M + 1 of 26. Further evidence was obtained by NaBH(4) reduction of 26 to 7-[4-hydroxy-4-(3-pyridyl)but-1-yl]Gua, which was also matched with a standard. Adduct 37 was similarly identified in enzyme hydrolysates of DNA reacted with NNKCH(2)OAc, accounting for 30-35% of the HPB-releasing adducts in this DNA. Several other adducts resulting from pyridyloxobutylation of the N(2)- and O(6)-positions of Gua were also identified as products in the dGuo or DNA reactions by comparison to standards; their concentrations were considerably less than that of 37. These adducts were N(2)-[4-oxo-4-(3-pyridyl)but-1-yl]dGuo (23), N(2)-[4-oxo-4-(3-pyridyl)but-2-yl]dGuo (25), N(2)-[2-(3-pyridyl)tetrahydrofuran-2-yl]dGuo (31a) (or its open chain tautomer 31b), and O(6)-[4-oxo-4-(3-pyridyl)but-1-yl]dGuo (10). Adducts 23, 25, and 10 did not release HPB upon neutral thermal hydrolysis. The results of this study provide the first structural identification of an HPB-releasing DNA adduct of the tobacco specific nitrosamines NNK and NNN.

Effects of benzyl isothiocyanate and 2-phenethyl isothiocyanate on benzo[a]pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone metabolism in F-344 rats

A mixture of dietary benzyl isothiocyanate (BITC) and 2-phenethyl isothiocyanate (PEITC) inhibits lung tumorigenesis by a mixture of benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A/J mice. Previous studies indicated that inhibition of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) releasing DNA adducts of NNK by PEITC in the lung was responsible for inhibition of tumorigenicity. We have now extended these investigations to F-344 rats treated with 2 p.p.m. B[a]P in the diet and 2 p.p.m. NNK in the drinking water. The effects of BITC (1 micromol/g diet), PEITC (3 micromol/g diet), and a mixture of BITC plus PEITC (1 and 3 micromol/g diet) on DNA and hemoglobin (Hb) adducts of B[a]P and NNK, and on two urinary metabolites of NNK, were examined. DNA adducts were quantified after 8 and 16 weeks of treatment. Hb adducts were quantified in blood samples withdrawn every 2 weeks. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide NNAL-Gluc were measured in urine every 4 weeks. PEITC or BITC plus PEITC significantly reduced levels of HPB releasing DNA adducts of NNK in lung at 8 and 16 weeks, but there was no effect of BITC. There were no effects of any of the treatments on levels of HPB releasing DNA adducts of NNK in liver, or on DNA adducts of B[a]P in either lung or liver. PEITC or BITC plus PEITC significantly inhibited the formation of Hb adducts of NNK from 2-12 weeks of treatment while there were no effects on Hb adducts of B[a]P. There was a significant increase in levels of NNAL and NNAL-Gluc in the urine of the rats treated with PEITC or BITC plus PEITC. These results demonstrate that dietary PEITC, or a mixture of BITC plus PEITC, inhibit the formation of HPB releasing adducts of NNK in the rodent lung, leading to inhibition of tumorigenesis.

Identification of adducts produced by the reaction of 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanol with deoxyguanosine and DNA

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a metabolite of the tobacco specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNAL is present in the blood and urine of people exposed to tobacco products and has carcinogenic activity in rodents similar to that of NNK. DNA adducts specific to NNAL have not been previously identified. Metabolic activation of NNAL by alpha-methyl hydroxylation, a pathway known to occur in rodent and human microsomes, would produce pyridylhydroxybutylating agents that could react with DNA. We investigated this possibility in the present study by allowing 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNALCH(2)OAc) to react with dGuo and DNA. Products were identified by HPLC with UV detection, liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS) and LC/ESI-tandem mass spectrometry (LC/ESI-MS/MS). In the dGuo reactions, selected ion monitoring for m/z 417, corresponding to pyridylhydroxybutylated dGuo, showed several peaks. One adduct was identified as 7-[1-hydroxy-1-(3-pyridyl)but-4-yl]dGuo (21) by neutral thermal hydrolysis, which converted it to 7-[1-hydroxy-1-(3-pyridyl)but-4-yl]Gua (22) and 4-hydroxy-1-(3-pyridyl)-1-butanol (16). Adduct 22 was identified by comparison of its LC/ESI-MS and LC/ESI-MS/MS properties to those of standard 22. Two other adducts, O(6)-[1-hydroxy-1-(3-pyridyl)but-4-yl]dGuo (17) and N(2)-[1-hydroxy-1-(3-pyridyl)but-4-yl]dGuo (19), were identified by comparison of their LC/ESI-MS and LC/ESI-MS/MS properties to those of standard 17 and 19. Further evidence for the identity of 17 and 19 was obtained by mild acid hydrolysis, which converted them to the corresponding Gua bases 18 and 20, identified by comparison to synthetic standards. Neutral thermal hydrolysis of DNA that had been reacted with NNALCH(2)OAc produced 22, identified by comparison to a standard. Adducts 17 and 19 were identified in enzyme hydrolysates of this DNA by comparison to standards. Thus, DNA that had been allowed to react with NNALCH(2)OAc contained adducts 17, 19, and 21. The results of this study provide markers for investigating the role of specific NNAL-DNA adducts in carcinogenesis by NNAL and NNK.

Benzyl isothiocyanate: an effective inhibitor of polycyclic aromatic hydrocarbon tumorigenesis in A/J mouse lung

Polycyclic aromatic hydrocarbons (PAH) are an important group of carcinogens that are likely to be involved as one of the causes of lung cancer in smokers and occupationally exposed individuals. Previous studies have shown that benzyl isothiocyanate (BITC), administered by gavage, is a good inhibitor of lung tumorigenesis in A/J mice induced by benzo[a]pyrene (BaP), a typical PAH carcinogen. In this study, we evaluated the effects of BITC on lung tumor induction in A/J mice by two other carcinogenic PAH in cigarette smoke - 5-methylchrysene (5-MeC) and dibenz[a,h]anthracene (DBahA). We also compared the effects of BITC with two other well known chemopreventive agents - butylated hydroxyanisole (BHA) and sulforaphane. In experiment 1, groups of A/J mice were treated by gavage once weekly for 8 weeks with BaP (3 micromol) or 5-MeC (2 micromol) or DBahA (1 micromol) in 0.1 ml cottonseed oil. Fifteen minutes before each treatment, the mice were gavaged with 0.1 ml cottonseed oil or 0.1 ml cottonseed oil containing 13.4 micromol or 6.7 micromol of BITC. The experiment was terminated 19 weeks after the final carcinogen treatment. BITC significantly reduced lung tumor multiplicity in all PAH-treated groups by 63.5-90.6%. In experiment 2, groups of A/J mice were treated with BaP or BITC and BaP as in experiment 1, or with BHA or sulforaphane at doses equimolar to those of BITC. BITC was significantly more effective as an inhibitor of lung tumor induction than either BHA or sulforaphane. These results firmly establish gavaged BITC as a strong inhibitor of lung tumorigenesis induced in A/J mice by PAH, and support its further development for chemoprevention of smoking-induced lung cancer.

Metabolism and pharmacokinetics of N'-nitrosonornicotine in the patas monkey

N'-Nitrosonornicotine (NNN) is present in significant quantities in tobacco and tobacco smoke and is believed to play an important role as a cause of cancer in people who use tobacco products. Biomarkers of NNN uptake in humans such as urinary metabolites would be useful for assessing cancer risk. Previous studies, carried out almost exclusively in rodents, have characterized urinary metabolites of NNN, but none of these would be suitable as a biomarkers of NNN uptake in humans. Therefore, we studied NNN metabolism in the patas monkey. Monkeys were treated intravenously with [5-(3)H]NNN, which has tritium in the pyridine ring. Blood and urine samples were collected at timed intervals. Six urinary metabolites were observed by high-performance liquid chromatography (HPLC) and were identified by their spectral properties and/or comparison to appropriate standards as follows: metabolite (% of radioactivity eluting from HPLC +/- S.D., n = 3 monkeys); 4-hydroxy-4-(3-pyridyl)butyric acid (43.8 +/- 4.0); 4-oxo-4-(3-pyridyl) butyric acid (2.7 +/- 0.66); norcotinine (13.1 +/- 2.7); norcotinine-1N-oxide (16.5 +/- 1.3); 3'-hydroxynorcotinine (16.9 +/- 2.0); 3'-(O-beta-D-glucopyranuronosyl)hydroxynorcotinine (5.4 +/- 1.0); and unchanged NNN (0.63 +/- 0.15). The two major metabolites in serum were 4-hydroxy-4-(3-pyridyl)butyric acid and norcotinine. NNN was rapidly metabolized to 4-hydroxy-4-(3-pyridyl)butyric acid, whereas the formation of norcotinine and 3'-hydroxynorcotinine were somewhat delayed. The results of this study demonstrate substantial differences between NNN metabolism in the rodent and patas monkey. Metabolism of NNN to norcotinine and its derivatives was far more prevalent in the patas monkey than in the rat. 3'-Hydroxynorcotinine and its O-glucuronide may be formed from NNN via alpha-oximinonornicotine or isomyosmine. There was no evidence that it was formed via norcotinine, although this pathway could not be excluded. 3'-Hydroxynorcotinine could potentially be a biomarker of NNN uptake in humans.

Effects of benzyl isothiocyanate and phenethyl isothiocyanate on DNA adduct formation by a mixture of benzo[a]pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in A/J mouse lung

Dietary phenethyl isothiocyanate (PEITC) and a mixture of dietary PEITC and benzyl isothiocyanate (BITC) inhibit lung tumorigenesis in A/J mice induced by a mixture of the tobacco smoke carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In this study, we tested the hypothesis that inhibition of tumorigenesis by these isothiocyanates was due to inhibition of DNA adduct formation. We quantified the following pulmonary DNA adducts: N2-[7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10-yl]deoxyguanosine (BPDE-N2-dG) from B[a]P; and O(6)-methylguanine (O(6)-mG) and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing adducts from NNK. Initial experiments demonstrated that there were no effects of B[a]P on NNK-DNA adduct formation, or vice versa, and established by way of a time course study the appropriate sacrifice intervals for the main experiment. Dietary PEITC, or dietary BITC plus PEITC, inhibited the formation of HPB-releasing DNA adducts of NNK at several of the time points examined. There were no effects of dietary isothiocyanates on levels of O(6)-mG or BPDE-N2-dG. These results, which are consistent with previous studies in rats and with tumor inhibition data in mice, support a role for inhibition of HPB-releasing DNA adducts of NNK as a mechanism of inhibition of tumorigenesis by dietary PEITC and BITC plus PEITC. However, the observed inhibition was modest, suggesting that other effects of isothiocyanates are also involved in chemoprevention in this model.

Inhibition of lung tumorigenesis in A/J mice by N-acetyl-S-(N-2-phenethylthiocarbamoyl)-L-cysteine and myo-inositol, individually and in combination

Isothiocyanates, their N-acetylcysteine conjugates, and myo-inositol (MI) are inhibitors of lung tumorigenesis in A/J mice. However, chemoprevention by combinations of these compounds in different temporal sequences has not been examined. This is important for developing practical approaches to lung cancer chemoprevention in smokers and ex-smokers. We used a tumor model in which A/J mice are treated with 8 weekly doses of benzo[a]pyrene (B[a]P) plus 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and killed 19 weeks after the final treatment. In Experiment 1, isothiocyanates or their N-acetylcysteine conjugates were added to the diet (1 or 3 micro mol/g) from 1 week before until 1 week after carcinogen treatment. The compounds were 2-phenethyl isothiocyanate (PEITC), 3-phenylpropyl isothiocyanate (PPITC), N-acetyl-S-(N-benzyl-thiocarbamoyl)-L-cysteine (BITC-NAC), N-acetyl-S-(N-2-phenethylthiocarbamoyl)-L-cysteine (PEITC-NAC), and N-acetyl-S-(N-3-phenylpropylthiocarbamoyl)-L-cysteine (PPITC-NAC). Significant reductions in lung tumor multiplicity were observed in mice treated with PEITC, PEITC-NAC, PPITC and PPITC-NAC. PEITC-NAC was chosen for combination studies with MI (Experiment 2). Mice were treated with B[a]P plus NNK without or with PEITC-NAC (3 micro mol/g diet), MI (55.5 micro mol/g diet), or PEITC-NAC plus MI (3 micro mol plus 55.5 micro mol/g diet). Different temporal sequences of dietary additions were investigated: carcinogen treatment phase; post-carcinogen treatment phase; entire experiment; 50% of carcinogen treatment phase until termination; and 75% of carcinogen treatment phase until termination. All treatments reduced lung tumor multiplicity except PEITC-NAC post-carcinogen or from 75% of the carcinogen treatment phase. Reduction of lung tumor multiplicity by PEITC-NAC plus MI was greater than that in the mice treated with the agents alone in all temporal sequences. When all results were combined, PEITC-NAC plus MI was significantly more effective than the agents alone. There was a significant trend for reduction in lung tumor multiplicity with increased duration of treatment by the chemopreventive agents. These results provide a basis for further development of mixtures of PEITC-NAC and MI for chemoprevention of lung cancer.

Analysis of N- and O-glucuronides of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in human urine

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a tobacco-specific lung carcinogen which may play an important role as a cause of lung cancer in smokers. NNK is extensively metabolized to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which like NNK is a potent pulmonary carcinogen. NNAL in turn is glucuronidated, and both NNAL and its glucuronides are excreted in human urine. Previous studies have clearly demonstrated the presence in human urine of 4-(methylnitrosamino)-1-(3-pyridyl)-1-(O-beta-D-glucopyranuronosyl)butane (NNAL-O-Gluc), but did not exclude the presence of 4-(methylnitrosamino)-1-(3-pyridyl-N-beta-D-glucopyranuronosyl)-1-butanolonium inner salt (NNAL-N-Gluc). In this study, we quantified NNAL, NNAL-N-Gluc, and NNAL-O-Gluc in the urine of smokers, snuff-dippers, and people who used the oral tobacco product "toombak". The presence of NNAL-N-Gluc in the urine of toombak users was confirmed by LC-ESI-MS/MS. In smokers' urine, NNAL-N-Gluc, NNAL-O-Gluc, and NNAL comprised (mean +/- SD) 26.5 +/- 6.2, 32.1 +/- 17.6, and 41.4 +/- 16.6%, respectively, of total NNAL. In snuff-dippers' urine, the corresponding figures were 13.6 +/- 5.1, 46.6 +/- 11.7, and 36.6 +/- 9.3%. NNAL-N-Gluc comprised 50 +/- 25% of total glucuronidated NNAL in smokers and 24 +/- 12% in snuff-dippers. This difference was significant (P = 0.01), suggesting that smoking induces glucuronidation of NNAL. The results of this study demonstrate that NNAL-N-Gluc contributes substantially to NNAL-glucuronides in human urine. These results are important for a clearer understanding of mechanisms of detoxification of NNK in humans.

Disposition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in bile duct-cannulated rats: stereoselective metabolism and tissue distribution

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a chiral compound, and the primary metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major carcinogen in tobacco smoke. The goal of the present work was to study the pharmacokinetics and stereoselective metabolism and tissue retention of NNK and NNAL in the rat. Groups of rats were dosed with [5-(3)H]NNK (n = 3) or racemic [5-(3)H]NNAL (n = 3) at a target dose of 8.45 micromol/kg and were killed at selected time points for tissue collection. Separate groups of rats (n =5 per group) received the same dose of either NNK or NNAL and serial sampling of blood, bile and urine was carried out over 24 h. All samples were analyzed by C(18) reversed-phase HPLC with gradient elution and radioflow detection. A gas chromatograph-thermal energy analyzer (GC-TEA) was used to separate the (R)-/(S)-NNAL enantiomers. Racemic NNAL and NNK had large volumes of distribution (321 +/- 137 ml for NNK and 2772 +/- 1423 ml for NNAL) and similar total body clearances (12.8 +/- 2.0 ml/min for NNK and 8.6 +/- 2.6 ml/min for NNAL). The results indicated that the enantiomers of NNAL are stereoselectively metabolized and excreted. The glucuronide of (R)-NNAL, ((R)-NNAL-Gluc) was identified as the major metabolite in the bile after administration of either NNK or NNAL. (R)-NNAL was the major NNAL enantiomer in the bile or urine samples. At 24 h after racemic NNAL administration, NNAL comprised an average of 75.4% of total radioactivity in the lung with an (S)-/(R)-ratio of >20. The stereoselective localization of (S)-NNAL to lung tissue may contribute to the lung selectivity of NNK carcinogenesis. The present studies suggest a need to look beyond metabolic activation as the sole mechanism for lung carcinogenesis.

Reactions of alpha-acetoxy-N-nitrosopyrrolidine with deoxyguanosine and DNA

We investigated the reactions of alpha-acetoxy-N-nitrosopyrrolidine (alpha-acetoxyNPYR) with dGuo and DNA. Alpha-acetoxyNPYR is a stable precursor to the major proximate carcinogen of NPYR, alpha-hydroxyNPYR (3). Our goal was to develop appropriate conditions for the analysis of DNA adducts of NPYR formed in vivo. Products of the alpha-acetoxyNPYR-dGuo reactions were analyzed directly by HPLC or after treatment of the reaction mixtures with NaBH3CN. Products of the alpha-acetoxyNPYR-DNA reactions were released by enzymatic or neutral thermal hydrolysis of the DNA, then analyzed by HPLC. Alternatively, the DNA was treated with NaBH3CN prior to hydrolysis and HPLC analysis. The reactions of alpha-acetoxyNPYR with dGuo and DNA were complex. We have identified 13 products of the dGuo reaction-6 of these were characterized in this reaction for the first time. They were four diastereomers of N2-(3-hydroxybutylidene)dGuo (20, 21), 7-(N-nitrosopyrrolidin-2-yl)Gua (2), and 2-(2-hydroxypyrrolidin-1-yl)deoxyinosine (12). Adducts 20 and 21 were identified by comparison to standards produced in the reaction of 3-hydroxybutanal with dGuo. Adduct 2 was identified by its spectral properties while adduct 12 was characterized by comparison to an independently synthesized standard. With the exception of adduct 2, all products of the dGuo reactions were also observed in the DNA reactions. The major product in both the dGuo and DNA reactions was N2-(tetrahydrofuran-2-yl)dGuo (10), consistent with previous studies. Several other previously identified adducts were also observed in this study. HPLC analysis of reaction mixtures treated with NaBH3CN provided improved conditions for adduct identification, which should be useful for in vivo studies of DNA adduct formation by NPYR.

Dose-response study of myo-inositol as an inhibitor of lung tumorigenesis induced in A/J mice by benzo

Dietary myo-inositol is an effective inhibitor of lung tumor induction in mice, but no dose-response studies have been reported. We assessed the ability of various doses of dietary myo-inositol to inhibit lung tumor induction in female A/J mice treated with eight weekly doses of benzo[a]pyrene (BaP) plus 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) (3 micromol of each by gavage), then killed 18 weeks later. In Expt. 1, groups of 20 mice each were treated with myo-inositol at concentrations of 1, 0.5, 0.25, 0.125, 0.0625, 0.03125, and 0% in AIN-93 diet for 1 week prior to, during, and for 1 week after the carcinogen administration period. In Expt. 2, groups of 20 mice each were treated with the same concentrations of myo-inositol in the diet as in Expt. 1, except this diet was administered from 1 week after carcinogen administration until termination. There were no effects of myo-inositol on lung tumor incidence, which was 100% in all groups treated with BaP plus NNK. However, myo-inositol significantly decreased lung tumor multiplicity in both experiments. In Expt. 1, significant reductions of 28.9 and 33.0% were observed at the 1 and 0.5% doses of myo-inositol, but not at the lower doses. In Expt. 2, a significant reduction of 48.4% was observed at the 1% dose. In both Expts. 1 and 2, there was a significant dose trend for inhibition (P<0.0001). No toxicity was observed at any dose. These results firmly establish myo-inositol as a chemopreventive agent against lung tumor induction in A/J mice, at doses that can be envisioned for human use.

Transport of the beta -O-glucuronide conjugate of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by the multidrug resistance protein 1 (MRP1). Requirement for glutathione or a non-sulfur-containing analog

Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) play a crucial role in the induction of lung cancer, and NNAL-O-glucuronide formation and elimination are important steps in detoxification of these compounds. In the present study, we investigated the ATP-binding cassette (ABC) protein, MRP1 (ABCC1), as a candidate transporter responsible for NNAL-O-glucuronide export. MRP1 mediates the active transport of numerous GSH-, sulfate-, and glucuronide-conjugated organic anions and can transport certain xenobiotics by a mechanism that may involve co-transport with GSH. Using membrane vesicles prepared from transfected cells, we found that MRP1 transports [3H]NNAL-O-glucuronide but is dependent on the presence of GSH (Km 39 microm, Vmax 48 pmol x mg(-1) x min(-1)). We also found that the sulfur atom in GSH was dispensable because transport was supported by the GSH analog, gamma-glutamyl-alpha-aminobutyryl-glycine. Despite stimulation of NNAL-O-glucuronide transport by GSH, there was no detectable reciprocal stimulation of [3H]GSH transport. Moreover, whereas the MRP1 substrates leukotriene C4 (LTC4) and 17beta-estradiol 17beta-(d-glucuronide) (E(2)17betaG) inhibited GSH-dependent uptake of [3H]NNAL-O-glucuronide, only [3H]LTC4 transport was inhibited by NNAL-O-glucuronide (+GSH) and the kinetics of inhibition were complex. A mutant form of MRP1, which transports LTC4 but not E(2)17betaG, also did not transport NNAL-O-glucuronide suggesting a commonality in the binding elements for these two glucuronidated substrates, despite their lack of reciprocal transport inhibition. Finally, the related MRP2 transported NNAL-O-glucuronide with higher efficiency than MRP1 and unexpectedly, GSH inhibited rather than stimulated uptake. These studies provide further insight into the complex interactions of the MRP-related proteins with GSH and their conjugated organic anion substrates, and extend the range of xenotoxins transported by MRP1 and MRP2 to include metabolites of known carcinogens involved in the etiology of lung and other cancers.

Preparation of pyridine-N-glucuronides of tobacco-specific nitrosamines

Nicotine and cotinine are metabolized to pyridine-N-glucuronides in humans. This suggests that the analogous metabolites of the carcinogenic nicotine-related nitrosamines N'-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) should also be formed in people exposed to these compounds via tobacco products. We describe the synthesis of the appropriate pyridine-N-glucuronides: pyridyl-N-beta-D-glucopyranuronosyl-N'-nitrosonornicotinium inner salt (NNN-N-Gluc, 8), 4-(methylnitrosamino)-1-(3-pyridyl-N-beta-D-glucopyranuronosyl)-1-butanonium inner salt (NNK-N-Gluc, 9), and 4-(methylnitrosamino)-1-(3-pyridyl-N-beta-D-glucopyranuronosyl)-1-butanolonium inner salt (NNAL-N-Gluc, 10). The starting material, methyl 2,3,4-tri-O-acetyl-1-bromo-1-deoxy-alpha-D-glucopyranuronate (1), is prepared in two steps from glucuronolactone. Reactions of 1 with racemic NNN (2), NNK (3), or racemic NNAL (4) are carried out with no solvent and the crude products are deprotected by treatment with base, giving the desired N-glucuronides 8-10 in 5-7% overall yield after HPLC purification. The N-glucuronides were characterized by (1)H NMR, including COSY and NOESY spectra, and by MS and MS/MS. NNN-N-Gluc exists as a 52:48 ratio of (E)- and (Z)-rotamers, which were partially separated by HPLC. This ratio was surprisingly similar to the (E):(Z) ratio for NNN itself suggesting hydrogen bonding of the (Z)-nitroso oxygen atom to the 2' '-hydroxyl group of the glucuronide moiety. Partial HPLC separations of the (E)- and (Z)-rotamers of NNK-N-Gluc and the (E)- and (Z)-rotamers as well as the (R)- and (S)-diastereomers of NNAL-N-Gluc were also achieved. The standards prepared in this study as well as the HPLC conditions developed for their separation will be important for analysis of these compounds in human urine.

Inhibition of vascular endothelial cells by 1,4-phenylenebis (methylene)selenocyanate--a novel chemopreventive organoselenium compound

Organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) was investigated for its effects on endothelial cell proliferation in vitro and angiogenesis in vivo. The organoselenium compound, p-XSC, has been shown to prevent carcinogen-induced tumorigenesis in murine model systems with low toxicity. Since tumor growth and metastasis are dependent on angiogenesis, we investigated the effects of the organoselenium compound on this process. Human umbilical vein endothelial cells treated with p-XSC showed concentration dependent inhibition of protein synthesis and cell viability in vitro with a TCID50 value of 6 microM. Subsequently, we studied the effects of p-XSC on experimental angiogenesis. Addition of p-XSC to three-dimensional cultures inhibited endothelial cell tube formation. Furthermore, p-XSC treatment inhibited growth factor induced angiogenesis in chick chorioallantoic membrane assays and i.p. administration of p-XSC inhibited neovascularization induced by tumor cells implanted subcutaneously into athymic mice. These studies suggest that vascular endothelium is an additional target for the chemopreventive organoselenium compound p-XSC.