Immediate consequences of cigarette smoking: rapid formation of polycyclic aromatic hydrocarbon diol epoxides

Polycyclic aromatic hydrocarbons (PAH) are among the likely major causative agents for lung cancer in smokers. PAH require metabolic activation to exert their carcinogenic effects, and one important pathway proceeds through a three-step sequence resulting in the formation of diol epoxides, which react with DNA to produce adducts that can cause mutations and initiate the carcinogenic process. However, no previous published studies have examined this critical pathway in humans specifically exposed to PAH by inhalation of cigarette smoke. This study used a unique approach employing a stable isotope derivative of phenanthrene, the simplest PAH with a bay region, a feature closely associated with PAH carcinogenicity. Twelve subjects each smoked a cigarette to which [D(10)]phenanthrene had been added. Plasma was analyzed for [D(10)]r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D(10)]PheT), the major end product of the diol epoxide metabolism pathway of phenanthrene. The analysis was performed by gas chromatography--negative ion chemical ionization--tandem mass spectrometry, using [(13)C(6)]PheT as internal standard. The results demonstrated that the three-step pathway resulting in the formation of diol epoxides, as monitored by [D(10)]PheT, occurred with remarkable rapidity. Levels of [D(10)]PheT in plasma of all subjects were maximal at the earliest time points examined, 15-30 min after smoking the cigarette containing [D(10)]phenanthrene, and decreased thereafter. These results demonstrate that the formation of a PAH diol epoxide occurs rapidly in smokers. Because PAH diol epoxides are mutagenic and carcinogenic, the results clearly demonstrate immediate negative health consequences of smoking, which should serve as a major warning to anyone contemplating initiating tobacco use.

Enhanced inhibition of lung adenocarcinoma by combinatorial treatment with indole-3-carbinol and silibinin in A/J mice

In earlier studies, we demonstrated the efficacy of indole-3-carbinol (I3C) against lung adenocarcinoma in A/J mice. However, these effects were accompanied by reductions in body weight gain. We therefore assessed if combinations of low doses of I3C with silibinin could inhibit lung tumorigenesis without causing undesirable side effects. In in vitro assays with A549 and H460 lung cancer cells, exposure of the cells to a mixture of low concentrations of I3C (50 μM) plus silibinin (50 μM) for 72 h caused inhibition of cell growth and extracellular signal-regulated kinase (ERK) and Akt activation and induction of apoptosis, whereas the individual agents did not have any effect. In mice pretreated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and given I3C (10 μmol/g diet) plus silibinin (7 μmol/g diet), multiplicities of tumors on the surface of the lung and adenocarcinoma were reduced by 60 and 95%, respectively. The individual effects of I3C and silibinin were relatively weaker: 43 and 36% reductions, respectively, in the multiplicity of tumors on the surface of the lung and 83 and 50% reductions, respectively, in the number of adenocarcinoma. Also, the expression of phospho-Akt, phospho-ERK and cyclin D1 and poly (ADP-ribose) polymerase cleavage were strongly modulated by I3C plus silibinin than by I3C or silibinin alone, suggesting that the chemopreventive activities of the mixture could be mediated, at least partly, via modulation of the level of these proteins. Taken together, our findings showed that mixtures of I3C and silibinin are more potent than the individual compounds for the chemoprevention of lung cancer in A/J mice.

Orbital rhabdomyosarcoma in an adult

INTRODUCTION

Rhabdomyosarcoma is the most common primary orbital malignant tumor in children. Orbital lesions represent about 10 % of all the cases of rhabdomyosarcoma. Rhabdomyosarcoma is a rare cause of proptosis in adults.

OBJECTIVE

To report a case of primary orbital rhabdomyosarcoma in a 45-year-old female.

DESIGN

Interventional case report. The main outcome measures are a rare cause ofproptosis in an adult, discussion on treatment options and prognosis ofrhabdomyosarcoma.

RESULT

The patient underwent total orbital exenteration and was referred for radiotherapy and chemotherapy.

CONCLUSION

Rhabdomyosarcoma is a rare cause of proptosis in adults. It should be suspected in a case of rapidly-progressive proptosis in adults.

Abstract CN07-02: Polycyclic aromatic hydrocarbon tetraols: Potential phenotypic indicators of lung cancer susceptibility in smokers

Polycyclic aromatic hydrocarbons (PAH) are believed to be among the major causative agents for lung cancer in smokers. PAH require metabolic activation to exert their carcinogenic effects, and one important pathway proceeds through a three-step metabolic sequence resulting in the formation of diol epoxides which react with DNA producing adducts that can cause mutations and initiate the carcinogenic process. Many studies demonstrate wide interindividual differences in PAH metabolism. Our working hypothesis is that individuals who metabolically activate PAH by the diol epoxide pathway more extensively will be at higher risk for lung cancer than those who are less proficient. We have used a phenotyping approach to investigate this hypothesis. In this approach, we use gas chromatographytandem mass spectrometry to quantify PAH tetraols, the major end products of the diol epoxide metabolic activation pathway, in plasma or urine. In one recent nested case-control study of 475 lung cancer cases and 475 controls, all smokers, in the Shanghai Cohort Study of over 18,000 men, we demonstrated a significant relationship to lung cancer of urinary levels of r,1-t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene (PheT), the major end product of the diol epoxide pathway of phenanthrene, the simplest PAH with a bay region, a feature closely associated with carcinogenicity. With advances in mass spectrometry, we are now able to directly assess levels of tetraols resulting from diol epoxide formation from the prototypic carcinogenic PAH, benzo[a]pyrene. These studies demonstrated higher levels of this tetraol in the urine of smokers than non-smokers. Our approach to individual phenotyping of smokers uses a stable isotope labeled PAH, [D10]phenanthrene. Smokers either use cigarettes to which [D10]phenanthrene has been added, or take the substance orally. Plasma and urine are analyzed for the tetraol, [D10]PheT, the major end product of the diol epoxide metabolism pathway of phenanthrene. The results of these ongoing studies show a large interindividual variation in [D10]PheT production and demonstrate that this approach is feasible for identifying those individuals who extensively metabolize phenanthrene. These studies also showed for the first time that the three-step pathway resulting in formation of diol epoxides, as monitored by [D10]PheT, occurred with remarkable rapidity in all subjects. Levels of [D10]PheT in plasma of all subjects were maximal 15-30 min after smoking a cigarette containing [D10]phenanthrene, and decreased thereafter. These results demonstrate that the formation of a PAH diol epoxide occurs rapidly in smokers. Since PAH diol epoxides are mutagenic and carcinogenic, the results clearly demonstrate immediate negative health consequences of smoking which should serve as a major warning to anyone contemplating initiating tobacco use.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):CN07-02.

Preferential glutathione conjugation of a reverse diol epoxide compared with a bay region diol epoxide of benzo[a]pyrene in human hepatocytes

Many studies have examined the relationship between polymorphisms in glutathione S-transferase genes and cancer in people exposed to polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (BaP), but the results to date have been modest. Missing from these studies has been an exploration of the formation of the appropriate glutathione conjugates in humans. We incubated human hepatocytes from 10 donors with racemic anti-BaP-7,8-diol-9,10-epoxide (BPDE), believed to be a major ultimate carcinogen of BaP, or with the noncarcinogenic reverse diol epoxide, racemic anti-BaP-9,10-diol-7,8-epoxide (rev-BPDE). Incubations were carried out for 12 or 24 h. We used high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring at m/z 464 --> m/z 317 to analyze the incubation mixtures for the mercapturic acid products that would result from glutathione conjugation. The standard mercapturic acids were synthesized by reaction of BPDE or rev-BPDE with N-acetylcysteine. We obtained convincing evidence in human hepatocytes for mercapturic acid formation from rev-BPDE in all 10 samples, in amounts up to 17 pmol/ml. However, we could detect mercapturic acids from BPDE in only 1 of 10 samples (0.05 pmol/ml). Taken together with our similar previous results of analyses of phenanthrene metabolites in human hepatocytes and human urine, the results of this study indicate that conjugation of BPDE with glutathione is a minor pathway in humans, indicating that glutathione S-transferase genotyping is not an effective method for assessing risk of PAH-induced cancer in humans, at least with respect to the diol epoxide pathway of PAH carcinogenesis.

Inhibition of lung carcinogenesis and critical cancer-related signaling pathways by N-acetyl-S-(N-2-phenethylthiocarbamoyl)-l-cysteine, indole-3-carbinol and myo-inositol, alone and in combination

In an extension of our earlier studies, we examined the inhibitory effects of N-acetyl-S-(N-2-phenethylthiocarbamoyl)-l-cysteine (PEITC-NAC), myo-inositol (MI) and indole-3-carbinol (I3C) or 3,3'-diindolylmethane (DIM), alone and in combination, on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) plus benzo[a]pyrene (BaP)-induced A/J mouse lung tumorigenesis and proliferation of A549 cells and human bronchial epithelial cells (HBECs) and relevant potential mechanisms. Mice treated with NNK plus BaP and fed non-supplemented diet had 13.0 + or - 4.1 lung tumors per mouse. Dietary feeding of mice with PEITC-NAC (5 mumol/g diet), I3C (5 mumol/g diet) or MI (56 mumol/g diet), beginning at 50% in the carcinogen treatment phase, significantly reduced tumor multiplicity to 8.2 + or - 2.0, 8.4 + or - 1.5 and 6.8 + or - 1.7 tumors per mouse, respectively. In mice given combinations of the chemopreventive agents, lung tumor multiplicity was significantly reduced to 6.3 + or - 2.2, 4.9 + or - 1.8, 4.8 + or - 1.9 and 3.6 + or - 1.4 by PEITC-NAC plus I3C, PEITC-NAC plus MI, I3C plus MI or PEITC-NAC plus I3C plus MI, respectively. Post-carcinogen administration of combinations of the agents also caused significant but weaker effects. Assessment of the anti-proliferative effects of the individual agents or their combinations showed significant reductions in the proliferation of cigarette smoke condensate (CSC)-pretreated HBEC (reduction by 30-41% at 48 h and 41-58% at 72 h) and A549 cells (30-43% at 48 h and 40-59% at 72 h), but not in dimethyl sulfoxide-pretreated HBEC. Combinatorial treatment with the agents also caused marked reductions in the activation of Akt, extracellular signal-regulated kinase and nuclear factor-kappaB in lung tumor tissues, CSC-pretreated HBEC and A549 cells. In conclusion, our studies demonstrated the promise of combinations of PEITC-NAC, I3C/DIM and MI for the chemoprevention of lung carcinogenesis in current and former smokers.

Abdominal Wall Endometriosis

Endometriosis of abdominal wall scar following operation on uterus and tubes is extremely rare. The late onset of symptoms after surgery is the usual cause of misdiagnosis. Scar endometriosis is a rare disease which is difficult to diagnose and should always be considered as a differential diagnosis of painful abdominal masses in women. The diagnosis is made only after excision and histopathology of the lesion. Preoperative differentials include hernia, lipoma, suture granuloma or abscess. Hence an awareness of the entity avoids delay in diagnosis, helps clinicians to a more tailored treatment and also avoids unnecessary referrals. We report a case of abdominal endometriosis. The definitive diagnosis of which was established by histopathological studies. KEYWORDS: abdominal wall endometriosis, cesarean scar, cyclical symptoms.

Abstract 1696: Metabolism of (S)-NNAL and (R)-NNAL in the isolated perfused rat lung system

(S)-NNAL and (R)-NNAL are metabolites of NNK, a tobacco-specific pulmonary carcinogen. The purpose of the current study was to compare the pulmonary metabolism of the NNAL enantiomers to determine if differences in metabolism are responsible for the greater carcinogenicity of (S)-NNAL compared to (R)-NNAL.

The pulmonary metabolism of (S)-NNAL and (R)-NNAL was examined in the isolated perfused rat lung system (IPRL) to eliminate the contribution of other metabolizing organs, such as the liver. The lungs of F344 rats were perfused with [5-3H] (S)-NNAL and [5-3H] (R)-NNAL at an initial concentration of 1.2 µM in 50 mL of Ringer's buffer. The perfusions were conducted for 360 min at 37 °C with a perfusate flow rate of 8 mL/min.

The major perfusate metabolite for both enantiomers was NNAL-N-oxide, which accounted for approximately 40% of the final perfusate radioactivity. Unmetabolized NNAL contributed to roughly 20-30% of the final perfusate radioactivity. Hydroxy acid (∼10-15%) and diol (∼9%) were both observed in the perfusate, but NNK and its subsequent metabolites were not detected. NNAL-N-oxide was also the major metabolite in the tissue (∼70-80%), while NNAL contributed to less than 3% of the radioactivity in the tissue. Both (S)-NNAL and (R)-NNAL had apparent volumes of distribution similar to the volume of the reservoir, indicating that substantial partitioning of NNAL into the tissue did not occur. The apparent clearance, half-life, volume of distribution, and extraction ratio for each enantiomer was estimated, but no significant difference was observed for any of the pharmacokinetic parameters.

There was no significant difference in perfusate metabolite concentrations or apparent pharmacokinetic parameters between (S)-NNAL and (R)-NNAL in the IPRL system. These results contradict the hypothesis that differences in the lung metabolism of (S)-NNAL and (R)-NNAL may account for the difference in the lung carcinogenicity of the two enantiomers. This also contradicts previous in vitro metabolism studies in rat lung microsomes and in vivo pharmacokinetic studies in the rat. It is possible that the liver is responsible for the metabolic differences of (S)-NNAL and (R)-NNAL in vivo, a process which is absent in the IPRL. Alternatively, it may be that diffusional barriers exist in the intact lung, inhibiting the ability of preformed (S)-NNAL and (R)-NNAL to reach the site of metabolism. The microsomal studies would lack these diffusional barriers. The long perfusion time required for metabolism of the NNAL enantiomers and the low concentration of NNAL in the tissue support the existence of diffusional barriers to NNAL metabolism.

This work was supported by the Public Health Service [Grants NCI CA-81301 to SSH]; and University of Minnesota Fellowships [3M Science and Technology Fellowship, Ted Rowell Graduate Fellowship, and Edward Rippie Fellowship to LAM].

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1696.

Abstract 4698: Preferential glutathione conjugation of a reverse diol epoxide compared to a bay region diol epoxide of benzo[a]pyrene in human hepatocytes: Relevance to glutathione-S-transferase genotyping in epidemiology studies

Many studies have examined the relationship between polymorphisms in glutathione-S-transferase genes and cancer in people exposed to polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (BaP), but results to date have been modest. Missing from these studies has been an exploration of the formation of the appropriate glutathione conjugates in humans. We previously addressed this question using the three ring bay region PAH phenanthrene as a model compound and found that, in human urine, the only detectable mercapturic acids which result from metabolic degradation of glutathione conjugates were formed from a reverse diol epoxide of phenanthrene (phenanthrene-3,4-diol-1,2-epoxide), not from the bay region diol epoxide (phenanthrene-1,2-diol-3,4-epoxide) which would be typical of those associated with PAH carcinogenicity. We obtained similar results when we incubated human hepatocytes with these diol epoxides of phenanthrene. In the study reported here, we extended our investigation to BaP, a prototypic PAH carcinogen. We incubated human hepatocytes from ten donors with 10 µM racemic BaP-7,8-diol-9,10-epoxide, believed to be a major ultimate carcinogen of BaP, or with the non-carcinogenic reverse diol epoxide, racemic BaP-9,10-diol-7,8-epoxide. Incubations were carried out for 12 or 24h. We used high performance liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring at m/z 464→317 to analyze the incubation mixtures for the mercapturic acid products which would result from glutathione conjugation followed by normal metabolic processing of the conjugates. The standard mercapturic acids were synthesized by reaction of racemic BaP-diol epoxides with N-acetylcysteine. Major products resulting from cis- and trans- addition to each diol epoxide were characterized by proton NMR and MS. A mercapturic acid derived from phenanthrene-3,4-diol-1,2-epoxide was used as an internal standard in the hepatocyte analyses. We obtained convincing evidence for time dependent mercapturic acid formation from the non-carcinogenic reverse diol epoxide BaP-9,10-diol-7,8-epoxide in all 10 samples. Levels ranged from 0.12 to 17 pmol/ml. However, we could detect mercapturic acids from the bay region diol epoxide BaP-7,8-diol-9,10-epoxide in only 1 of 10 samples (0.05 pmol/ml). Taken together with our similar previous results of analyses of phenanthrene metabolites in human hepatocytes and human urine, the results of this study indicate that conjugation of BaP-7,8-diol-9,10-epoxide with glutathione is a minor pathway in humans, suggesting that glutathione-S-transferase genotyping is not an effective method of assessing risk of PAH induced cancer in humans, at least with respect to the diol epoxide pathway of PAH carcinogenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4698.

Abdominal wall endometriosis

Endometriosis of abdominal wall scar following operation on uterus and tubes is extremely rare. The late onset of symptoms after surgery is the usual cause of misdiagnosis. Scar endometriosis is a rare disease which is difficult to diagnose and should always be considered as a differential diagnosis of painful abdominal masses in women. The diagnosis is made only after excision and histopathology of the lesion. Preoperative differentials include hernia, lipoma, suture granuloma or abscess. Hence an awareness of the entity avoids delay in diagnosis, helps clinicians to a more tailored treatment and also avoids unnecessary referrals. We report a case of abdominal endometriosis. The definitive diagnosis of which was established by histopathological studies.

Formation and distribution of NNK metabolites in an isolated perfused rat lung

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a lung-specific tobacco carcinogen. Metabolism is critical to its elimination given its lipophilic nature. Although NNK can be metabolized through detoxification pathways that safely eliminate it from the body, it can also be bioactivated, resulting in the formation of potentially carcinogenic DNA adducts. The isolated perfused rat lung (IPRL) system was used to determine the effect of NNK perfusate concentration (0.1 and 1.2 microM) on the formation and distribution of metabolites, the level of individual DNA adducts, and total covalent binding in the lung. Coadministration of the chemopreventive agent phenethyl isothiocyanate (PEITC; 20 microM) was also examined to determine its effect on NNK metabolism. NNK was readily metabolized in the IPRL system. In the 0.1 muM perfusions approximately 55% of metabolites formed were through detoxification pathways, whereas roughly 30% were the result of bioactivation pathways. An increase in NNK concentration increased the percentage of unmetabolized NNK and decreased the apparent metabolic clearance in the lung, but the metabolite profiles remained similar between concentrations. The addition of PEITC reduced the formation of oxidative metabolites and increased 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) formation and the percentage of unmetabolized NNK. PEITC also significantly decreased the formation of DNA adducts in the lung tissue. The level of O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O(2)-POB-dThd) and O(6)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O(6)-POB-dGuo) decreased by 70 to 75%, and that of O(6)-methylguanine (O(6)-methyl-Gua) and 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua) decreased by 40 to 45%. Pyridylhydroxybutyl-DNA adducts were not detected in any of the treatment groups. Thus, the IPRL system is useful in determining pulmonary metabolism and DNA adduct formation separate from other metabolizing organs.

Abstract A70: Kava as a lung cancer chemopreventive agent

Lung cancer is a serious malignancy with high incidence and death. Chemoprevention is a complementary approach to smoking cessation to help control lung cancer. Recently, we reported that kava inhibits 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) plus benzo(a)pyrene (BaP)-induced lung tumorigenesis in A/J mice. In the present study, we examined the dose-dependent lung tumor inhibitory activities of kava and attempted to identify the active constituent(s). Carcinogen-treated mice, dosed eight times with a mixture of NNK plus BaP (2 µmol each) administered by gavage, had 12.2 ± 5.7 lung adenomas per mouse after 26 weeks. Carcinogen-treated mice given diets containing kava at dosages of 1.25, 2.5, 5, and 10 mg/g had 8.4 ± 3.5, 6.6 ± 3.5, 4.3 ± 2.4, and 3.8 ± 2.3 lung adenomas per mouse, corresponding to reductions of 31%, 46%, 64%, and 69%, respectively. All reductions were significant (P < 0.05). Flavokawains A, B, and C from kava demonstrated either no or much weaker chemopreventive efficacies, suggesting that they are unlikely to be responsible for the chemopreventive activity of kava. Western blot analyses of lung adenoma tissues and lung cancer cells reveal that kava modulates the NF-kB signaling pathway, a potential mechanism responsible for kava-induced lung cancer chemoprevention.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):A70.

Inhibition of vinyl carbamate-induced pulmonary adenocarcinoma by indole-3-carbinol and myo-inositol in A/J mice

In previous studies, we reported that indole-3-carbinol (I3C) and myo-inositol (MI) inhibit lung adenoma induced by tobacco smoke carcinogens in A/J mice. In this paper, we extended our work and examined the effects of I3C (70 or 30 micromol/g diet) and MI (56 micromol/g diet) against vinyl carbamate (VC)-induced lung adenocarcinoma by administering the agents from 1 week after the second of two injections of VC until termination of the study at week 18. The higher dose of I3C decreased multiplicities of tumors on the surface of the lung (26%, P = 0.0005), carcinoma incidence (38%), multiplicity (67%, P < 0.0001) and size (complete abolition of carcinoma with an area of >1.0 cm(2)) as well as adenoma with cellular pleomorphism (46%, P < 0.0001). The lower dose of I3C was less effective. MI decreased multiplicities of pulmonary surface tumors (20%, P = 0.0005), adenoma with cellular pleomorphism (40%, P < 0.0001) and lung adenoma (52%, P < 0.0001) and the proportion of the biggest carcinoma (carcinoma with an area of >1.0 cm(2), P < 0.05). Immunoblot analyses of lung tissues for potential target identification showed that I3C (70 micromol/g diet) inhibits IkappaBalpha degradation, nuclear factor-kappaB activation, expression of cyclooxygenase-2, phospho-Akt and fatty acid synthase (FAS) and activates caspase-3 and poly ADP ribose polymerase cleavage. The effect of MI was limited to inhibition of phospho-Akt and FAS expression. Our data show that I3C and MI inhibit lung carcinoma and provide a basis for future evaluation of these compounds in clinical trials as chemopreventive agents for current and former smokers.

Comparative levels of O6-methylguanine, pyridyloxobutyl-, and pyridylhydroxybutyl-DNA adducts in lung and liver of rats treated chronically with the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a lung carcinogen in rats and may be a cause of lung cancer in smokers. NNK is metabolized by cytochromes P450 to intermediates that react with DNA forming methyl, pyridyloxobutyl (POB), and pyridylhydroxybutyl (PHB) adducts, which are critical in carcinogenesis. The methyl adduct O(6)-methylguanine (O(6)-methyl-G) has miscoding properties, but there are no reports on levels of this adduct in rats treated chronically with NNK in the drinking water, nor has its levels been compared with those of POB- and PHB-DNA adducts. We used liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring to quantify O(6)-methyl-G in lung and liver DNA of rats treated with a carcinogenic dose of 10 ppm of NNK in the drinking water and sacrificed after 1, 2, 5, 10, 16, and 20 weeks. The maximal level of O(6)-methyl-G in lung DNA, 2550 +/- 263 fmol/mg DNA, was reached at 5 weeks and was significantly greater (P < 0.05) at that point than all other adducts (measured previously) except O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine. Overall levels of O(6)-methyl-G in lung were intermediate between those of total POB- and PHB-DNA adducts. In liver, the wave of O(6)-methyl-G peaked at 2 weeks while that of total POB-DNA adducts peaked at 10 weeks, and levels of total PHB-DNA adducts were low throughout. The results of this study demonstrate that substantial amounts of O(6)-methyl-G are formed at various time points in lung and liver DNA of rats treated chronically with NNK, supporting its role in carcinogenesis.

Analysis of pyridyloxobutyl and pyridylhydroxybutyl DNA adducts in extrahepatic tissues of F344 rats treated chronically with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) are potent pulmonary carcinogens in rats. NNK and NNAL require metabolic activation to express their carcinogenicity. Cytochrome P450-catalyzed alpha-hydroxylation at the methyl position of NNK or NNAL generates reactive intermediates, which alkylate DNA to form pyridyloxobutyl (POB)-DNA adducts or pyridylhydroxybutyl (PHB)-DNA adducts. NNK is metabolized to NNAL in a reversible and stereoselective manner, and the tissue-specific retention of (S)-NNAL is believed to be important to the carcinogenicity of NNK. In the present study, we investigated the formation of POB- and PHB-DNA adducts in extrahepatic tissues of F344 rats treated chronically with NNK and (R)- and (S)-NNAL (10 ppm in the drinking water, 1-20 weeks). POB- and PHB-DNA adducts were quantified in nasal olfactory mucosa, nasal respiratory mucosa, oral mucosa, and pancreas of treated rats. Adduct formation in the nasal respiratory mucosa exceeded that in the other tissues. O(2)-[4-(3-Pyridyl)-4-oxobut-1-yl]thymidine (O(2)-POB-dThd) or O(2)-[4-(3-pyridyl)-4-hydroxybut-1-yl]thymidine (O(2)-PHB-dThd) was the major adduct, followed by 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua) or 7-[4-(3-pyridyl)-4-hydroxybut-1-yl]guanine (7-PHB-Gua). There was a remarkable similarity in adduct formation between the NNK and the (S)-NNAL groups, both of which were distinctively different from that in the (R)-NNAL group. For example, in the nasal olfactory mucosa, POB-DNA adduct levels in the NNK and (S)-NNAL groups were not significantly different from each other, while (R)-NNAL treatment generated 6-33 times lower amounts of POB-DNA adducts than did NNK treatment. In contrast, (R)-NNAL treatment produced significantly higher levels of PHB-DNA adducts than did NNK or (S)-NNAL treatment. Similar trends were observed in the nasal respiratory mucosa, oral mucosa, and pancreas. These results suggest extensive retention of (S)-NNAL in various tissues of NNK-treated rats and support a mechanism in which the preferential metabolism of NNK to (S)-NNAL, followed by sequestration of (S)-NNAL in the target tissues and reoxidation to NNK, is important to NNK tumorigenesis.

Dose-dependent inhibition of tobacco smoke carcinogen-induced lung tumorigenesis in A/J mice by indole-3-carbinol

Recently, we reported inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) plus benzo(a)pyrene (BaP)-induced lung tumorigenesis in A/J mice by indole-3-carbinol (I3C; 112 micromol/g diet) administered beginning at 50% in the carcinogen treatment phase. In this study, we examined the dose-dependent and postcarcinogen tumor-inhibitory activities of I3C. A mixture of NNK plus BaP (2 micromol each) administered by gavage as eight biweekly doses caused 21.1 +/- 5.2 lung tumors per mouse. Carcinogen-treated mice given diets containing I3C at 1, 10, 30, 71, and 112 micromol/g, beginning at 50% in the carcinogen treatment phase, had 17.9 +/- 6.1, 10.4 +/- 3.7, 9.8 +/- 5.1, 5.2 +/- 4.0, and 2.5 +/- 2.4 lung tumors per mouse, corresponding to reductions by 15%, 51%, 53%, 75%, and 88%, respectively. All reductions, except at the lowest dose level (1 micromol I3C/g diet), were significant (P < 0.001). Similarly, administration of I3C (112 micromol/g diet) beginning 1 week after the last dose of the carcinogen significantly reduced NNK plus BaP-induced lung tumor multiplicity to 5.6 +/- 3.5, corresponding to a reduction by 74%. Analyses of cell proliferation and apoptosis markers revealed that I3C reduced the number of Ki-67-positive cells and expression of proliferating cell nuclear antigen, phospho-Akt, and phospho-BAD and increased cleavage of poly(ADP-ribose) polymerase, suggesting that the lung tumor inhibitory effects of I3C were mediated, at least partly, through inhibition of cell proliferation and induction of apoptosis. These results clearly show the efficacy of I3C in the prevention of tobacco carcinogen-induced lung tumorigenesis in A/J mice and provide a basis for future evaluation of this compound in clinical trials as a chemopreventive agent for current and former smokers.

Differential expression of microRNAs in early-stage neoplastic transformation in the lungs of F344 rats chronically treated with the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

While numerous microRNAs (miRNAs) have been reported to alter their expression levels in human lung cancer tissues compared with normal tissues, the function of these miRNAs and their contribution to the long process of lung cancer development remains largely unknown. We applied a tobacco-specific carcinogen-induced cancer model to investigate the involvement of miRNAs in early lung cancer development, which could also provide information on potential, early biomarkers of lung cancers. Male F344 rats were first chronically treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogen present in tobacco products, for up to 20 weeks. The expression profiles of miRNAs in rat lungs were then determined. As measured by miRNA microarrays and confirmed by Northern blot and real-time polymerase chain reaction analyses, NNK treatment reduced the expression of a number of miRNAs, such as miR-101, miR-126*, miR-199 and miR-34. Significantly, these miRNAs overlap with previously published reports on altered miRNA expression in human lung cancer samples. These miRNAs might, therefore, represent early-response miRNAs that signify the molecular changes associated with pulmonary tumorigenesis. Moreover, we identified cytochrome P450 (CYP) 2A3, a critical enzyme in rat lungs that activates NNK to render it carcinogenic, as a potential target of miR-126*. NNK treatment in rats repressed miR-126* but induced CYP2A3 expression, a mechanism that may potentiate the oncogenic effects of NNK.

Identification of adducts formed in the reactions of 5'-acetoxy-N'-nitrosonornicotine with deoxyadenosine, thymidine, and DNA

N'-Nitrosonornicotine (NNN) is the most prevalent of the carcinogenic tobacco-specific nitrosamines found in all tobacco products. Previous studies have demonstrated that cytochrome P450-mediated 5'-hydroxylation of NNN is a major metabolic pathway leading to mutagenic products, but to date, DNA adducts formed by this pathway have been only partially characterized, and there have been no studies reported on adducts formed with bases other than dGuo. Because adducts with dAdo and dThd have been identified in the DNA of the livers of rats treated with the structurally related carcinogen N-nitrosopyrrolidine, we investigated dAdo and dThd adduct formation from 5'-acetoxyNNN (3), a stable precursor to 5'-hydroxyNNN (2). Reaction of 3 with dAdo gave diastereomeric products, which were identified by their spectral properties and LC-ESI-MS/MS-SRM analysis as N(6)-[5-(3-pyridyl)tetrahydrofuran-2-yl]dAdo (9). This adduct was further characterized by NaBH(3)CN reduction to N(6)-[4-hydroxy-4-(3-pyridyl)but-1-yl]dAdo (17). A second dAdo adduct was identified, after NaBH(3)CN treatment, as 6-[2-(3-pyridyl)pyrrolidin-1-yl]purine-2'-deoxyriboside (18). Reaction of 3 with dThd, followed by NaBH(3)CN reduction, gave O(2)-[4-(3-pyridyl)-4-hydroxybut-1-yl]thymidine (11). Adducts 9, 11, 17, and 18 were all identified by LC-ESI-MS/MS-SRM comparison to synthetic standards. The reaction of 3 with calf thymus DNA was then investigated. The DNA was enzymatically hydrolyzed to deoxyribonucleosides, and the resulting mixture was treated with NaBH(3)CN and analyzed by LC-ESI-MS/MS-SRM. Adducts 11, 17, and 18, as well as the previously identified dGuo adducts, were identified. The results of this study provide a more comprehensive picture of DNA adduct formation by the quantitatively important 5'-hydroxylation pathway of NNN and will facilitate investigation of the presence of these adducts in laboratory animals treated with NNN or in people who use tobacco products.

Combinations of N-Acetyl-S-(N-2-Phenethylthiocarbamoyl)-L-Cysteine and myo-inositol inhibit tobacco carcinogen-induced lung adenocarcinoma in mice

We have previously generated convincing evidence that combinations of N-acetyl-S-(N-2-phenethylthiocarbamoyl)-L-cysteine (PEITC-NAC; 3 micromol/g diet) and myo-inositol (MI; 56 micromol/g diet) were significantly more effective than the individual compounds as inhibitors of tobacco smoke carcinogen-induced lung tumorigenesis in A/J mice. In this study, we further investigated the efficacy of combinations of PEITC-NAC (9 or 15 micromol/g diet) and MI (56 micromol/g diet). Female A/J mice were treated with a mixture of the tobacco smoke carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and benzo[a]pyrene by gavage once weekly for 8 weeks. PEITC-NAC plus MI was given in the diet beginning at 1 day after the 4th of eight carcinogen treatments (temporal sequence A) or 1 week after the last carcinogen treatment (temporal sequence B). Regardless of the dose of carcinogen or PEITC-NAC plus MI, or temporal sequence, administration of PEITC-NAC plus MI significantly reduced the multiplicity of gross tumors and, in most instances, adenocarcinoma. PEITC-NAC plus MI was particularly effective against bigger tumors. The observed inhibition of lung tumorigenesis by PEITC-NAC plus MI was attributed, at least partly, to inhibition of cell proliferation and induction of apoptosis. These results clearly show the efficacy of PEITC-NAC plus MI in the prevention of tobacco carcinogen-induced lung adenocarcinoma in A/J mice and provide a basis for future evaluation of PEITC-NAC plus MI in clinical trials as a chemopreventive agent for current and former smokers.

Extensive metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in smokers

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung carcinogen present in both unburned tobacco and cigarette smoke. The sum of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides, referred to as total NNAL, is an established urinary biomarker of human NNK uptake. Metabolic activation of NNK to DNA adducts proceeds via alpha-hydroxylation pathways, and 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid) are the principal end products of these pathways in rodents and primates. The purpose of this study was to determine NNK metabolic activation in smokers, as measured by the sum of keto acid and hydroxy acid, relative to total NNAL. To specifically identify NNK-derived keto acid and hydroxy acid, which are also formed from nicotine, we added [pyridine-D(4)]NNK to cigarettes that were originally low in NNK, and measured the deuterium-labeled metabolites in the urine of people who smoked these cigarettes. The total amount of [pyridine-D(4)]keto acid plus [pyridine-D(4)]hydroxy acid averaged 4.00 +/- 2.49 nmol/24 h, whereas the average amount of total [pyridine-D(4)]NNAL was 0.511 +/- 0.368 nmol/24 h. The results of this study show for the first time that NNK metabolic activation is a quantitatively significant pathway in smokers, accounting for approximately 86% of total urinary excretion of NNK metabolites. The large interindividual variation in the excreted [pyridine-D(4)]keto acid and [pyridine-D(4)]hydroxy acid among 20 smokers strongly supports our hypothesis that some smokers activate NNK more extensively than others and that the ratio between biomarkers of metabolic activation and detoxification at a given dose of NNK could be a potential indicator of cancer risk.

Quantitation of pyridylhydroxybutyl-DNA adducts in liver and lung of F-344 rats treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and enantiomers of its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen in rats and is believed to be one cause of lung cancer in smokers. NNK is metabolized to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is also a strong lung carcinogen in rats and has a chiral center at its 1-carbon. Previous studies have demonstrated that cytochrome P450-catalyzed alpha-hydroxylation of NNK in the lung leading to the formation of methyl and pyridyloxobutyl (POB)-DNA adducts is critical for its carcinogenicity. alpha-Hydroxylation of NNAL would similarly produce pyridylhydroxybutyl (PHB)-DNA adducts, but these have not been previously investigated in vivo. POB- and PHB-DNA adduct levels can indicate the amounts of pyridyloxobutylating and pyridylhydroxybutylating agents present in tissues of NNK- or NNAL-treated rats at any given point. Therefore, in this study, we developed a sensitive and quantitative liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring method to determine levels of the PHB-DNA adducts O(6)-[4-(3-pyridyl)-4-hydroxybut-1-yl]-2'-deoxyguanosine (O(6)-PHB-dGuo, 10b), O(2)-[4-(3-pyridyl)-4-hydroxybut-1-yl]thymidine (O(2)-PHB-dThd, 11b), and 7-[4-(3-pyridyl)-4-hydroxybut-1-yl]-2'-deoxyguanosine (7-PHB-dGuo, 12b), the latter as the corresponding base 7-[4-(3-pyridyl)-4-hydroxybut-1-yl]-Gua (7-PHB-Gua, 14b) in DNA isolated from liver and lung of rats treated with 10 ppm NNK, (S)-NNAL, or (R)-NNAL in the drinking water for 20 weeks and sacrificed at 1, 2, 5, 10, 16, and 20 weeks. PHB-DNA adduct levels were higher in lung than in liver at each time point, consistent with previous studies of POB-DNA adducts in rats treated with NNK and NNAL in the drinking water. The results showed that NNK and (S)-NNAL behaved in a similar fashion, while (R)-NNAL was strikingly different. In the rats treated with NNK or (S)-NNAL, levels of each adduct at each time point were remarkably similar in lung, and levels of O(2)-PHB-dThd were generally greater than 7-PHB-Gua > O(6)-PHB-dGuo. The highest PHB-DNA adduct levels were found in lung and liver of rats treated with (R)-NNAL, suggesting that there are cytochrome P450s that efficiently catalyze the alpha-methyl hydroxylation of this compound. The results of this study provide further support for our hypothesis that (S)-NNAL is rapidly formed from NNK, sequestered at an unknown site in the lung, and then released and reoxidized to NNK with consequent DNA adduct formation resulting in lung carcinogenicity.

Chemopreventive agents modulate the protein expression profile of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone plus benzo[a]pyrene-induced lung tumors in A/J mice

We used isobaric tag labeling coupled with mass spectrometry to compare the relative abundance of proteins in lung tumors from A/J mice treated with a mixture of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and benzo[a]pyrene versus normal mouse lung tissues. Levels of 59 proteins changed-30 increased and 29 decreased-in tumor tissues versus normal tissues. Among proteins that showed increased levels in tumor tissues versus normal tissues were glycolytic enzymes, ribosomal proteins, fatty acid synthase, cathepsins D and H and carbonic anhydrase 2. On the other hand, the levels of cytochrome P450 enzymes 2B10 and 2F2, glutathione S-transferases mu-1, procollagen VI, Clara cell 10 kDA (CC10) protein, histones, receptor advanced glycation end product, and lung carbonyl reductase were lower in tumor tissues versus normal lung tissues. Upon dietary administration of a combination of N-acetyl-S-(N-2-phenethylthiocarbamoyl)-L-cysteine plus myo-inositol or indole-3-carbinol to carcinogen-treated mice, the relative abundance of 60S ribosomal protein L4 and carbonic anhydrase in tumor tissues decreased whereas that of histones, glutathione S-transferases mu, receptor advanced glycation end product, transglutaminase, and procollagen VI increased. Western assays with lung tissue homogenates not only verified the proteomics results for selected proteins but also showed differential expression of hypoxia inducible factor-1alpha, a transcription factor for most of the proteins that showed changes in relative abundance. This is the first report on the application of quantitative proteomics to study the relative abundance of proteins in a mouse model of lung carcinogenesis. These proteins may have utility for development of candidate lung cancer biomarkers and as targets of chemopreventive/chemotherapeutic agents.