Effects of anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene on human small airway epithelial cells and the protective effects of myo-inositol

Biological Properties of Cyclitols and Their Derivatives

Cyclitols are polyhydroxy cycloalkanes, each containing at least three hydroxyls attached to a different ring carbon atom. The most important cyclitol derivatives are inositols, quercitols, conduritols and pinitols, which form a group of naturally occurring polyhydric alcohols and are widely found in plants. In addition, synthetic production of cyclitols has gained importance in recent years. Cylitols are molecules synthesized in plants as a precaution against salt or water stress. They have important functions in cell functioning as they exhibit important properties such as membrane biogenesis, ion channel physiology, signal transduction, osmoregulation, phosphate storage, cell wall formation and antioxidant activity. The biological activities of these very important molecules, obtained both synthetically and from the extraction of plants, are described in this review.

Myo-Inositol and Its Derivatives: Their Emerging Role in the Treatment of Human Diseases

Myo-inositol has been established as an important growth-promoting factor of mammalian cells and animals. The role of myo-inositol as a lipotropic factor has been proven, in addition to its involvement as co-factors of enzymes and as messenger molecules in signal transduction. Myo-inositol deficiency leads to intestinal lipodystrophy in animals and "inositol-less death" in some fungi. Of late, diverse uses of myo-inositol and its derivatives have been discovered in medicinal research. These compounds are used in the treatment of a variety of ailments from diabetes to cancer, and continued research in this direction promises a new future in therapeutics. In different diseases, inositols implement different strategies for therapeutic actions such as tissue specific increase or decrease in inositol products, production of inositol phosphoglycans (IPGs), conversion of myo-inositol (MI) to D-chiro-inositol (DCI), modulation of signal transduction, regulation of reactive oxygen species (ROS) production, etc. Though inositol pharmacology is a relatively lesser-known field, recent years of research has generated a critical mass of information on the subject. This review aims to summarize our current understanding on the role of inositol derivatives in ameliorating the symptoms of different diseases.

Cytotoxic potential of dispirooxindolo/acenaphthoquino andrographolide derivatives against MCF-7 cell line

Dispiro andrographolides induce a caspase-dependent apoptotic cell death pathway in breast cancer (MCF-7) cells.

Cytotoxic activity and apoptosis-inducing potential of di-spiropyrrolidino and di-spiropyrrolizidino oxindole andrographolide derivatives

Anticancer role of andrographolide is well documented. To find novel potent derivatives with improved cytotoxicity than andrographolide on cancer cells, two series of di-spiropyrrolidino- and di-spiropyrrolizidino oxindole andrographolide derivatives prepared by cyclo-addition of azomethine ylide along with sarcosine or proline (viz. sarcosine and proline series respectively) and substitution of different functional groups (-CH3, -OCH3 and halogens) were examined for their cytotoxic effect on a panel of six human cancer cell lines (colorectal carcinoma HCT116 cells, pancreatic carcinoma MiaPaCa-2 cells, hepatocarcinoma HepG2 cells, cervical carcinoma HeLa cells, lung carcinoma A549 and melanoma A375 cells). Except halogen substituted derivatives of proline series (viz. CY2, CY14 and CY15 for Br, Cl and I substitution respectively), none of the other derivatives showed improved cytotoxicity than andrographolide in the cancer cell lines examined. Order of cytotoxicity of the potent compounds is CY2>CY14>CY15>andrographolide. Higher toxicity was observed in HCT116, MiaPaCa-2 and HepG2 cells. CY2, induced death of HCT116 (GI50 10.5), MiaPaCa-2 (GI50 11.2) and HepG2 (GI50 16.6) cells were associated with cell rounding, nuclear fragmentation and increased percentage of apoptotic cells, cell cycle arrest at G1 phase, ROS generation, and involvement of mitochondrial pathway. Upregulation of Bax, Bad, p53, caspases-3,-9 and cleaved PARP; downregulation of Bcl-2, cytosolic NF-κB p65, PI3K and p-Akt; translocation of P53/P21, NF-κB p65 were seen in CY2 treated HCT116 cells. Thus, three halogenated di-spiropyrrolizidino oxindole derivatives of andrographolide are found to be more cytotoxic than andrographolide in some cancer cells. The most potent derivative, CY2 induced death of the cancer cells involves ROS dependent mitochondrial pathway like andrographolide.

Apoptosis and the airway epithelium

The airway epithelium functions as a barrier and front line of host defense in the lung. Apoptosis or programmed cell death can be elicited in the epithelium as a response to viral infection, exposure to allergen or to environmental toxins, or to drugs. While apoptosis can be induced via activation of death receptors on the cell surface or by disruption of mitochondrial polarity, epithelial cells compared to inflammatory cells are more resistant to apoptotic stimuli. This paper focuses on the response of airway epithelium to apoptosis in the normal state, apoptosis as a potential regulator of the number and types of epithelial cells in the airway, and the contribution of epithelial cell apoptosis in important airways diseases.

Treatment of a human papillomavirus type 31b-positive cell line with benzo[a]pyrene increases viral titer through activation of the Erk1/2 signaling pathway

Numerous epidemiological studies have implicated cigarette smoking as a cofactor in the progression to cervical cancer. Tobacco-associated hydrocarbons have been found in cervical mucus, suggesting a possible interaction with human papillomavirus (HPV)-infected cells. The polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) is a major component of cigarette smoke condensate that has received significant attention due to its ability to induce carcinogenesis. We have previously demonstrated by conventional methods for determining viral titer that high concentrations of BaP increase HPV31b titers within the context of organotypic raft cultures compared with the level for vehicle controls. However, a definitive mechanism for explaining this increase in viral titer was lacking. Here, we show that BaP treatment activates the Ras-Raf-Mek1/2-Erk1/2 signaling pathway. The importance of Erk1/2 pathway activation to the BaP-mediated increase in viral titer was determined by Erk pathway inhibition with multiple Erk1/2 pathway inhibitors. Finally, BaP treatment activated p90RSK and its downstream target CDK1. These data indicate that the Erk1/2 signaling pathway plays an important role in mediating the response to BaP treatment that ultimately leads to increased viral titers.

Downregulation of Cdc2/CDK1 kinase activity induces the synthesis of noninfectious human papillomavirus type 31b virions in organotypic tissues exposed to benzo[a]pyrene

Epidemiological studies suggest that human papillomavirus (HPV)-infected women who smoke face an increased risk for developing cervical cancer. We have previously reported that exposure of HPV-positive organotypic cultures to benzo[a]pyrene (BaP), a major carcinogen in cigarette smoke, resulted in enhanced viral titers. Since BaP is known to deregulate multiple pathways of cellular proliferation, enhanced virion synthesis could result from carcinogen/host cell interaction. Here, we report that BaP-mediated upregulation of virus synthesis is correlated to an altered balance between cell cycle-specific cyclin-dependent kinase (CDK) activity profile compared with controls. Specifically, BaP treatment increased accumulation of hyperphosphorylated retinoblastoma protein (pRb) which coincided with increased cdc2/CDK1 kinase activity, but which further conflicted with the simultaneous upregulation of CDK inhibitors p16(INK4) and p27(KIP1), which normally mediate pRb hypophosphorylation. In contrast, p21(WAF1) and p53 levels remained unchanged. Under these conditions, CDK6 and CDK2 kinase activities were decreased, whereas CDK4 kinase activity remained unchanged. The addition of purvalanol A, a specific inhibitor of CDK1 kinase, to BaP-treated cultures, resulted in the production of noninfectious HPV type 31b (HPV31b) particles. In contrast, infectivity of control virus was unaffected by purvalanol A treatment. BaP targeting of CDK1 occurred independently of HPV status, since BaP treatment also increased CDK1 activity in tissues derived from primary keratinocytes. Our data indicate that HPV31b virions synthesized in the presence of BaP were dependent on BaP-mediated alteration in CDK1 kinase activity for maintaining their infectivity.

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.

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.

The role of repair protein Rad51 in synergistic cytotoxicity and mutagenicity induced by epidermal growth factor receptor inhibitor (Gefitinib, IressaR) and benzo[a]pyrene in human lung cancer

Rad51 protein is essential for homologous recombination repair of DNA damage, and is over-expressed in chemo- or radioresistant carcinomas. The polycyclic hydrocarbon carcinogen benzo[a]pyrene (B[a]P) affects MAPKs transduction pathways. Gefitinib (IressaR, ZD1839) is a selective epidermal growth factor receptor tyrosine kinase inhibitor that blocks growth factor-mediated cell proliferation and ERK1/2 activation. We hypothesized that gefitinib enhances B[a]P-mediated cytotoxicity by decreasing ERK1/2 activation. Exposure of human lung cancer cells to gefitinib decreased B[a]P-elicited ERK1/2 activation and induced Rad51 protein expression. Gefitinib and B[a]P co-treatment decreased Rad51 protein stability by triggering degradation via a 26S proteasome-dependent pathway. Expression of constitutive active MKK1/2 vectors (MKK1/2-CA) rescues the decreased ERK1/2 activity, and restores Rad51 protein level and stability under gefitinib and B[a]P co-treatment. Gefitinib enhances B[a]P-induced growth inhibition, cytotoxicity and mutagenicity. Co-treatment with gefitinib and B[a]P can further inhibit cell growth significantly after depletion of endogenous Rad51 by siRad51 RNA transfection. Enhancement of ERK1/2 activation by MKK1-CA expression decrease B[a]P- and gefitinib-induced cytotoxicity, and B[a]P-induced mutagenicity. Rad51 protein protects lung cancer cells from synergistic cytotoxic and mutagenic effects induced by gefitinib and B[a]P. Suppression of Rad51 protein expression may be a novel lung cancer therapeutic modality to overcome drug resistance to gefitinib.

Targeting the MEK1 cascade in lung epithelium inhibits proliferation and fibrogenesis by asbestos

The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are phosphorylated after inhalation of asbestos. The effect of blocking this signaling pathway in lung epithelium is unclear. Asbestos-exposed transgenic mice expressing a dominant-negative mitogen-activated protein kinase kinase-1 (dnMEK1) (i.e., the upstream kinase necessary for phosphorylation of ERK1/2) targeted to lung epithelium exhibited morphologic and molecular changes in lung. Transgene-positive (Tg+) (i.e., dnMEK1) and transgene-negative (Tg-) littermates were exposed to crocidolite asbestos for 2, 4, 9, and 32 days or maintained in clean air (sham controls). Distal bronchiolar epithelium was isolated using laser capture microdissection and mRNA analyzed for molecular markers of proliferation and Clara cell secretory protein (CCSP). Lungs and bronchoalveolar lavage fluids were analyzed for inflammatory and proliferative changes and molecular markers of fibrogenesis. Distal bronchiolar epithelium of asbestos-exposed wild-type mice showed increased expression of c-fos at 2 days. Elevated mRNA levels of histone H3 and numbers of Ki-67-labeled proliferating bronchiolar epithelial cells were decreased at 4 days in asbestos-exposed Tg+ mice. At 32 days, distal bronchioles normally composed of Clara cells in asbestos-exposed Tg+ mouse lungs exhibited nonreplicating ciliated and mucin-secreting cells as well as decreased mRNA levels of CCSP. Gene expression (procollagen 3-a-1, procollagen 1-a-1, and IL-6) linked to fibrogenesis was also increased in lung homogenates of asbestos-exposed Tg- mice, but reduced in asbestos-exposed Tg+ mice. These results suggest a critical role of MEK1 signaling in epithelial cell proliferation and lung remodeling after toxic injury.

The cigarette smoke carcinogen benzo[a]pyrene enhances human papillomavirus synthesis

Epidemiological studies suggest that cigarette smoke carcinogens are cofactors which synergize with human papillomavirus (HPV) to increase the risk of cervical cancer progression. Benzo[a]pyrene (BaP), a major carcinogen in cigarette smoke, is detected in the cervical mucus and may interact with HPV. Exposure of cervical cells to high concentrations of BaP resulted in a 10-fold increase in HPV type 31 (HPV31) viral titers, whereas treatment with low concentrations of BaP resulted in an increased number of HPV genome copies but not an increase in virion morphogenesis. BaP exposure also increased HPV16 and HPV18 viral titers. Overall, BaP modulation of the HPV life cycle could potentially enhance viral persistence, host tissue carcinogenesis, and permissiveness for cancer progression.

A phase I study of myo-inositol for lung cancer chemoprevention

INTRODUCTION

A phase I, open-label, multiple dose, dose-escalation clinical study was conducted to assess the safety, tolerability, maximum tolerated dose, and potential chemopreventive effect of myo-inositol in smokers with bronchial dysplasia.

MATERIALS AND METHODS

Smokers between 40 and 74 years of age with >or= 30 pack-years of smoking history and one or more sites of bronchial dysplasia were enrolled. A dose escalation study ranging from 12 to 30 g/d of myo-inositol for a month was first conducted in 16 subjects to determine the maximum tolerated dose. Ten new subjects were then enrolled to take the maximum tolerated dose for 3 months. The potential chemopreventive effect of myo-inositol was estimated by repeat autofluorescence bronchoscopy and biopsy.

RESULTS

The maximum tolerated dose was found to be 18 g/d. Side effects, when present, were mild and mainly gastrointestinal in nature. Using the regression rate of the placebo subjects from a recently completed clinical trial with the same inclusion/exclusion criteria as a comparison, a significant increase in the rate of regression of preexisting dysplastic lesions was observed (91% versus 48%; P = 0.014). A statistically significant reduction in the systolic and diastolic blood pressures by an average of 10 mm Hg was observed after taking 18 g/d of myo-inositol for a month or more.

CONCLUSION

myo-Inositol in a daily dose of 18 g p.o. for 3 months is safe and well tolerated. The potential chemopreventive effect as well as other health benefits such as reduction in blood pressure should be investigated further.

Effects of polycyclic aromatic hydrocarbons (PAHs) on vascular endothelial growth factor induction through phosphatidylinositol 3-kinase/AP-1-dependent, HIF-1alpha-independent pathway

Previous studies have demonstrated that exposure to polycyclic aromatic hydrocarbons (PAHs) and its derivatives is associated with an increased risk of skin cancers, and the carcinogenic effect of PAHs is thought to involve both tumor initiation and promotion. Whereas PAH tumor initiation is well characterized, the mechanisms involved in the tumor promotion of PAHs remain elusive. In the present study, we investigated the effects of PAHs on vascular endothelial growth factor (VEGF) expression by comparison of its induction between the active metabolite and its parent compound (B[a]PDE versus B[a]P) or between active compound and its relatively inactive analog (5-MCDE versus CDE). We found that exposure of cells to (+/-)-anti-benzo-[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE) or (+/-)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) led to marked induction of VEGF in Cl41 cells, whereas benzo[a]pyrene (B[a]P) or chrysene-1,2-diol-3,4-epoxide (CDE) did not exhibit significant inductive effects. Exposure of cells to B[a]PDE and 5-MCDE did not induce HIF-1alpha activation, whereas AP-1 was significantly activated. Moreover, overexpression of TAM67 (a dominant-negative mutant c-Jun) dramatically blocked that VEGF induction. Electrophoretic mobility shift assay showed that AP-1 was only able to specifically recognize and bind to its AP-1 potential binding site within -1136 and -1115 of the VEGF promoter region. Site-directed mutation of this AP-1 binding site eliminated the VEGF transcriptional activity induced by B[a]PDE, suggesting that the AP-1 binding site between -1136 and -1115 in the VEGF promoter region is critical for VEGF induction by B[a]PDE. In addition, overexpression of Deltap85 (a dominant-negative mutant PI-3K) impaired B[a]PDE- and 5-MCDE-induced VEGF induction. Considering our previous findings that PI-3K is an upstream mediator for c-Jun/AP-1 activation, we conclude that the VEGF induction by B[a]PDE and 5-MCDE is through PI-3K/AP-1-dependent and HIF-1alpha-independent pathways. These findings may help us to understand the mechanisms involved in PAH carcinogenic effects.

Characterization of the biochemical effects of 1-nitronaphthalene in rats using global metabolic profiling by NMR spectroscopy and pattern recognition

Metabolic fingerprints, in the form of patterns of high-concentration endogenous metabolites, of 1-nitronaphthalene (NN)-induced lung toxicity have been elucidated in bronchoalveolar lavage fluid (BALF), urine, blood plasma, and intact lung and liver tissue using NMR spectroscopy-based metabolic profiling. A single dose of NN (75 mg kg(-1)) was administered orally to Sprague-Dawley rats. BALF and lung tissue were obtained 24 h after dosing from these animals and matched control rats post-mortem. High-resolution (1)H-NMR spectroscopy of BALF samples indicated that NN caused increases in concentrations of choline, amino acids (leucine, isoleucine and alanine) and lactate together with decreased concentrations of succinate, citrate, creatine, creatinine and glucose. In addition, the intact lung weights were higher in the NN-treated group (p<0.01), consistent with pulmonary oedema. The NMR-detected perturbations indicated that NN induces a perturbation in energy metabolism in both lung and liver tissue, as well as surfactant production and osmolyte levels in the lungs. As well as reporting the first NMR spectroscopic combined examination of BALF and intact lung, this study indicates that such holistic approaches to investigating mechanisms of lung toxicity may be of value in evaluating disease progression or the effects of therapeutic intervention in pulmonary conditions such as surfactant disorders or asthma.

Preferential induction of CYP1A1 and CYP1B1 in CCSP-positive cells

Both benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are potent ligands of aryl hydrocarbon receptors (AhR). Although animal studies indicate that both compounds induce pathological changes in the peripheral lung, the specific cell type involved remains unclear. Clara cells, expressing Clara cell specific protein (CCSP) and abundant in cytochrome P450, are nonciliated bronchiolar epithelial cells in the peripheral lung. Here we explore the hypothesis that CCSP-positive Clara cells are highly responsive to AhR ligands and are the primary cell type involved in BaP- and TCDD-induced toxicities. The responsiveness to AhR ligands was evaluated by measuring the respective mRNA and protein levels of cytochrome P450 1A1 (CYP1A1) and 1B1 (CYP1B1) using real-time RT-PCR and immunocytochemistry assays. Two in vitro models were used: primary cultures of human small airway epithelial (SAE) cells and rat lung slice cultures. In the presence of calcium, human SAE cells differentiated into CCSP-positive cells. BaP- and TCDD-induced mRNA and protein levels of CYP1A1 and CYP1B1 levels were significantly elevated in CCSP-positive cell cultures. Similarly, AhR mRNA and protein levels were increased in CCSP-positive cell cultures, as determined by real-time RT-PCR and Western blot analysis. When rat lung slice cultures were treated with BaP or TCDD for 24 h, CYP1A1 and CYP1B1 proteins were strongly induced in Clara cells. These results indicate that, in the peripheral lung of both rats and humans, CCSP-positive cells (Clara cells) may be more sensitive to AhR ligands than other cell types.

Advances in the Biology of Lung Cancer Chemoprevention

The heavy burden of lung cancer, which includes the highest worldwide mortality of any cancer, and its resistance to standard approaches (smoking cessation, screening, and therapy), have motivated an intense interest in chemoprevention of this disease. Randomized controlled trials of agents (including retinoids, beta-carotene, and vitamin E) to prevent lung cancer have produced only disappointing clinical results to date. New, molecular-targeted approaches are advancing rapidly, however, with many promising targets and interactive signaling pathways for developing novel agents and combinatorial approaches in this setting. This promise is illustrated by recent studies of 15-hydroxyprostaglandin dehydrogenase, which plays a critical role in polyunsaturated fatty acid metabolism and (like another important target, prostacyclin) is downstream of cyclooxygenase-2. 15-hydroxyprostaglandin dehydrogenase degrades prostaglandin E2, appears to have tumor suppressor activity, and can be induced both by peroxisome proliferator-activated receptor-gamma ligands and an epidermal growth factor receptor inhibitor. Other important targets/pathways include the insulin-like growth factor axis, phosphoinositide 3-kinase pathway, cyclin D and E family members, and epigenetic events. Defining highest lung cancer risk (eg, establishing molecular risk models through long-term analyses of high-risk cohorts) will facilitate the clinical development of molecular-targeted prevention that will potentially reduce the enormous burden of lung cancer.

Molecular interactions of the aryl hydrocarbon receptor and its biological and toxicological relevance for reproduction

The dioxin/aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor responsive to both natural and man-made environmental compounds. AhR and its nuclear partner ARNT are expressed in the female reproductive tract in a variety of species and several indications suggest that the AhR might play a pivotal role in the physiology of reproduction. Furthermore, it appears to be the mediator of most, if not all, the adverse effects on reproduction of a group of highly potent environmental pollutants collectively called aryl hydrocarbons (AHs), including the highly toxic compound 2,3,7,8-tetrachlor-odibenzo-p-dioxin (TCDD). Although a large body of recent literature has implicated AhR in multiple signal transduction pathways, the mechanisms of action resulting in a wide spectrum of effects on female reproduction are largely unknown. Here we summarize the major types of molecular cross-talks that have been identified for the AhR and linked cell signaling pathways and that are relevant for the understanding of the role of this transcription factor in female reproduction.

A novel in vitro system, the integrated discrete multiple organ cell culture (IdMOC) system, for the evaluation of human drug toxicity: comparative cytotoxicity of tamoxifen towards normal human cells from five major organs and MCF-7 adenocarcinoma breast cancer cells

In vitro assays involving primary cells are used routinely to evaluate organ-specific toxic effects, for instance, the use of primary hepatocytes to evaluate hepatotoxicity. A major drawback of an in vitro system is the lack of multiple organ interactions as observed in a whole organism. A novel cell culture system, the integrated discrete multiorgan cell culture system (IdMOC), is described here. The IdMOC is based on the "wells within a well" concept, consisting of a cell culture plate with larger, containing wells, within each of which are multiple smaller wells. Cells from multiple organs can be cultured initially in the small wells (one organ per well, each in its specialized medium). On the day of toxicity testing, a volume of drug-containing medium is added to the containing well to flood all inner wells, thereby interconnecting all the small wells. After testing, the overlying medium is removed and each cell type is evaluated for toxicity using appropriate endpoints. We report here the application of IdMOC in the evaluation of the cytotoxicity of tamoxifen, an anticancer agent with known human toxicity, on primary cells from multiple human organs: liver (hepatocytes), kidney (kidney cortical cells), lung (small airway epithelial cells), central nervous system (astrocytes), blood vessels (aortic endothelial cells) as well as the MCF-7 human breast adenocarcinoma cells. IdMOC produced results that can be used for the quantitative evaluation of its anticancer effects (i.e., cytotoxicity towards MCF-7 cells) versus its toxicity toward normal organs (i.e., liver, kidney, lung, CNS, blood vessels).

Differential requirement of signal pathways for benzo[ a ]pyrene (B[ a ]P)-induced nitric oxide synthase (iNOS) in rat esophageal epithelial cells

Overexpression of inducible nitric oxide synthase (iNOS) has been reported in several human cancers, including esophageal squamous cell carcinoma (SCC). Benzo[a]pyrene (B[a]P), a polycyclic hydrocarbon carcinogen found in tobacco smoke and in the environment, induces cancer in multiple organ sites in animals and may be a causative agent for certain human cancers, such as esophageal cancer. In the present study, the effects of B[a]P on the induction of iNOS and the signaling pathways that lead to the induction were investigated in cultured rat esophageal epithelial (RE-149) cells. Treatment of RE-149 cells with B[a]P led to a marked increase in the expression of iNOS. The induction of iNOS by B[a]P was found to occur through an extracellular signal-regulated protein kinases (ERKs)-dependent pathway, since inhibition of ERKs by either pretreatment of RE-149 cells with PD98059, an inhibitor of ERKs upstream kinase MEK1/2, or overexpression of DN-ERK2, blocked the induction of iNOS by B[a]P. Furthermore, impairing nuclear factor-kappaB (NFkappaB) activation by either NEMO-BDBP, an NFkappaB specific inhibitor, or overexpression of DN-IkappaBalpha or IKK-KM markedly inhibited the expression of B[a]P-induced iNOS, suggesting that the NFkappaB pathway is also required for the induction of iNOS by B[a]P. In addition, treatment of RE-149 cells with either SB202190, a p38 kinase inhibitor, or c-JunN-terminal kinase inhibitor II, resulted in an increased induction of iNOS. Pretreatment of RE-149 cells with wortmannin, a PI-3K inhibitor, or with rapamycin, an mTOR/p70S6K pathway inhibitor, had no effect on the expression of iNOS. These results suggest that B[a]P initiates the signaling pathways leading to the induction of iNOS in cultured rat esophageal epithelial cells. In view of the potential role of iNOS in the development of esophageal SCC in humans, we speculate that the induction of iNOS by B[a]P may be one mechanism by which B[a]P could produce carcinogenic effects in the human esophagus.

Aryl hydrocarbon receptor, cell cycle regulation, toxicity, and tumorigenesis

Most effects of exposure to halogenated and polycyclic aromatic hydrocarbons are mediated by the aryl hydrocarbon receptor (AHR). It has long been recognized that the AHR is a ligand-activated transcription factor that plays a central role in the induction of drug-metabolizing enzymes and hence in xenobiotic detoxification. Of late, it has become evident that outside this well-characterized role, the AHR also functions as a modulator of cellular signaling pathways. In this Prospect, we discuss the involvement of the AHR in pathways critical to cell cycle regulation, mitogen-activated protein kinase cascades, immediate-early gene induction, and the functions of the RB protein. Ultimately, the toxicity of AHR xenobiotic ligands may be intrinsically connected with the perturbation of these pathways and depend on the many critical signaling pathways and effectors with which the AHR itself interacts.

Aryl hydrocarbon receptor activation of an antitumor aminoflavone: Basis of selective toxicity for MCF-7 breast tumor cells

Aminoflavone (4H-1-benzopyran-4-one, 5-amino-2-(4-amino-3-fluorophenyl)-6,8-difluoro-7-methyl; NSC 686288) demonstrates differential antiproliferative activity in the National Cancer Institute's anticancer drug screen. We demonstrate here that MCF-7 human breast cancer cells are sensitive to aminoflavone both in vitro and when grown in vivo as xenografts in athymic mice. As previous work has indicated that aminoflavone requires metabolic activation by cytochrome P450 1A1 (CYP1A1), we investigated the effect of aminoflavone on CYP1A1 expression and on the aryl hydrocarbon receptor (AhR), a transcriptional regulator of CYP1A1. In aminoflavone-sensitive but not aminoflavone-resistant cells, the drug caused a 100-fold induction of CYP1A1 mRNA and a corresponding increase in ethoxyresorufin-O-deethylase activity. An AhR-deficient variant of the MCF-7 breast carcinoma, AHR100, with diminished CYP1A1 inducibility, exhibits cellular resistance to aminoflavone and is refractory to CYP1A1 mRNA induction by the drug. The increase in CYP1A1 mRNA in the aminoflavone-sensitive MCF-7 breast tumor cell results from transcriptional activation of xenobiotic-responsive element (XRE)–controlled transcription. Aminoflavone treatment causes a translocation of the AhR from the cytoplasm to the nucleus with subsequent formation of AhR-XRE protein DNA complexes. In contrast to the aminoflavone-sensitive MCF-7 cells, the resistant cell lines (MDA-MB-435, PC-3, and AHR100) demonstrated constitutive nuclear localization of AhR. Additionally, aminoflavone failed to induce ethoxyresorufin-O-deethylase activity, CYP1A1 transcription, AhR-XRE complex formation, and apoptosis in aminoflavone-resistant cells. These results suggest that the cytotoxicity of aminoflavone in a sensitive breast tumor cell line is the result of the engagement of AhR-mediated signal transduction.

Reduction of androgen receptor expression by benzo[a]pyrene and 7,8-dihydro-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene in human lung cells

5Alpha-dihydrotestosterone significantly increased cell growth of lung adenocarcinoma cell line H1355. Benzo[alpha]pyrene (BaP) was a pulmonary carcinogen found in cigarette smoke. Treatment with 1microM BaP tremendously reduced constitutive androgen receptor (AR) expression, as determined with Western immunoblotting and the real-time RT-PCR assay, as well as testosterone-induced AR protein levels in H1355 cells. Similarly, 1microM BaP significantly reduced AR mRNA levels in human bronchial epithelial cells BEAS-2B. Although BaP, 2,3,7,8-tetrachlorodibenzo-p-dixin and polychlorinated biphenyl 126 activated aryl hydrocarbon receptor (AhR), which subsequently induced cytochrome P4501A1 (CYP1A1) and P4501B1 (CYP1B1) expression in H1355 cells, unexpectedly, neither TCDD nor PCB126 reduced AR expression. Antagonizing AhR activation and cytochrome P4501 activity with alpha-naphthoflavone, or inhibiting CYP1B1 activity with 2,4,3',5'-tetramethoxystilbene, however, prevented BaP-induced AR reduction. Furthermore, 7,8-dihydro-9,10-epoxy-7,8,9,10-tetrahydrobenzo[alpha]pyrene, a BaP carcinogenic metabolite catalyzed by CYP1A1 and CYP1B1, significantly reduced AR expression in H1355 cells and human lung fibroblasts WI-38. This was the first study that reports that BaP and BPDE reduced endogenous AR expression. These data suggest that metabolically activated BaP may disrupt androgen function by reducing AR levels in androgen-responsive organs.

Differential effects of polycyclic aromatic hydrocarbons on transactivation of AP-1 and NF-?B in mouse epidermal cl41 cells

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives, such as benzo[a]pyrene (B[a]P), (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), and 5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE), are complete carcinogens. However, the tumor promotion effects of PAHs remain unclear. We therefore investigated the possible activation of activator protein-1 (AP-1) and nuclear factor-kappaB (NFkappaB) in mouse epidermal Cl41 cells after different PAHs treatments, including B[a]P, B[a]PDE, chrysene-1,2-diol-3,4-epoxid (CDE), and 5-MCDE. The results showed that B[a]PDE and 5-MCDE were able to activate AP-1 and NF-kappaB, whereas B[a]P showed only marginal effect on AP-1 activation, and B[a]P and CDE had no effect on NF-kappaB activation. Treatment with either B[a]PDE or 5-MCDE also resulted in mitogen-activated protein kinases (MAPKs) activation as well as inhibitory subunit kappa-B (IkappaBalpha) phosphorylation and degradation, whereas B[a]P and CDE had no effect. Pretreatment with PD98059, a specific inhibitor for extracellular signal-regulated protein kinases (ERKs) upstream kinase MEK1/2, or SB202190, a p38 kinase inhibitor, resulted in a dramatic inhibition of B[a]PDE-induced AP-1 transactivation. In addition, B[a]PDE-induced AP-1 activation was also inhibited by overexpressing a dominant negative mutant of JNK1 in the cells. All these suggest ERKs, c-jun N-terminal kinases (JNKs), and p38 kinase signal transduction pathways are required for AP-1 induction by B[a]PDE. Taken together, B[a]PDE and 5-MCDE are the active compounds of PAHs to initiate signaling pathways. Considering the important roles of AP-1 and NF-kappaB in tumor promotion, we speculated the activation of AP-1 and NF-kappaB by B[a]PDE and 5-MCDE may involve in their or their parent compounds' tumor promotion effects. This study may help in better understanding the tumor promotion effects of PAHs.

Differential c-myc expression profiles in normal human bronchial epithelial cells following treatment with benzo[a]pyrene, benzo[a]pyrene-4,5 epoxide, and benzo[a]pyrene-7,8-9,10 diol epoxide

Bronchial epithelial cells are often exposed to airborne mutagens that have the potential to induce genetic changes involved in the development of lung cancer. Although lung tumors often display alterations in the expression of oncogenes and/or tumor suppressor genes, the role of specific chemicals and/or metabolites in causing these alterations is not well defined. The polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P), a by-product of combustion, is a prevalent airborne environmental mutagen and a constituent of cigarette smoke. The primary objective of this study was to compare the effect of B[a]P and two of its reactive metabolites, benzo[a]pyrene diol epoxide (BPDE or bay region epoxide) and benzo[a]pyrene-4,5-dihydroepoxide (BPE or K-region epoxide), on expression of the proto-oncogene c-myc in normal human bronchial epithelial (NHBE) cells using a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method. Changes in c-myc gene expression were compared with DNA adduct formation, growth inhibition, and cell-cycle progression as determined by (32)P-postlabelling, neutral red (NR), and flow cytometric analyses, respectively. None of the three test compounds altered the levels of 18S ribosomal RNA or beta-actin at the concentrations evaluated for c-myc expression, indicating that nonspecific changes in gene expression induced by cytotoxicity, for example, were not present at the concentrations evaluated. Cells exposed to B[a]P exhibited a dose-dependent increase in c-myc expression; conversely, a dose-dependent decrease in c-myc expression was observed following BPDE exposure. A marginal but concentration-dependent increase in c-myc mRNA levels was observed following exposure to the K-region epoxide. Our results demonstrated that, although B[a]P and its metabolites alter c-myc expression, the parent compound and its metabolites produce unequal and contrasting effects on the expression of this gene.

The role of the Ah receptor and p38 in benzo[a]pyrene-7,8-dihydrodiol and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide-induced apoptosis

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in the environment. Benzo[a]pyrene (B[a]P), a prototypical member of this class of chemicals, affects cellular signal transduction pathways and induces apoptosis. In this study, the proximate carcinogen of B[a]P metabolism, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-dihydrodiol) and the ultimate carcinogen, B[a]P-r-7,t-8-dihydrodiol-t-9,10-epoxide(+/-) (BPDE-2) were found to induce apoptosis in human HepG2 cells. Apoptosis initiated by B[a]P-7,8-dihydrodiol was linked to activation of the Ah receptor and induction of CYP1A1, an event that can lead to the formation of BPDE-2. With both B[a]P-7,8-dihydrodiol and BPDE-2 treatment, changes in anti- and pro-apoptotic events in the Bcl-2 family of proteins correlated with the release of mitochondrial cytochrome c and caspase activation. The onset of apoptosis as monitored by caspase activation was linked to mitogen-activated protein (MAP) kinases. Utilizing mouse hepa1c1c7 cells and the Arnt-deficient BPRc1 cells, activation of MAP kinase p38 by B[a]P-7,8-dihydrodiol was shown to be Ah receptor-dependent, indicating that metabolic activation by CYP1A1 was required. This was in contrast to p38 activation by BPDE-2, an event that was independent of Ah receptor function. Confirmation that MAP kinases play a critical role in BPDE-2-induced apoptosis was shown by inhibiting caspase activation of poly(ADP-ribose)polymerase 1 (PARP-1) by chemical inhibitors of p38 and ERK1/2. Furthermore, mouse embryo p38-/- fibroblasts were shown to be resistant to the actions of BPDE-2-induced apoptosis as determined by annexin V analysis, cytochrome c release, and cleavage of PARP-1. These results confirm that the Ah receptor plays a critical role in B[a]P-7,8-dihydrodiol-induced apoptosis while p38 MAP kinase links the actions of an electrophilic metabolite like BPDE-2 to the regulation of programmed cell death.

Role of the aryl hydrocarbon receptor in cell cycle regulation

Traditionally, the aryl hydrocarbon receptor (AHR) is considered to be a ligand-activated receptor and transcription factor responsible for the induction of drug-metabolizing enzymes. Its role in the combinatorial matrix of cell functions was neatly established long before the first report of an AHR cDNA sequence was published. Only recently, other functions of this protein have begun to be recognized. This review addresses novel findings relating to AHR functions that have resulted from experimental approaches markedly outside traditional receptor analyses. Here we examine the aspects of AHR biology relevant to its role in cell cycle regulation, from the activation of mitogen-activated protein kinases to the cross-talk between AHR and the RAS pathway and the functional significance of the interaction between AHR and the retinoblastoma protein. We have attempted to provide the reader with a balanced interpretation of the evidence, highlighting areas of consensus as well as areas still being contested.

Polycyclic aromatic hydrocarbon diol epoxides increase cytosolic Ca(2+) of airway epithelial cells

Polycyclic aromatic hydrocarbons (PAHs) increase cytosolic Ca(2+) concentration ([Ca(2+)](i)) in lymphocytes and mammary epithelial cells, but little is known regarding their effects on [Ca(2+)](i) in airway epithelium. We hypothesized that benzo[a]pyrene (BP) and/or anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), a carcinogenic BP metabolite, increases [Ca(2+)](i) in untransformed human small airway epithelial (SAE) cells and that their effects on [Ca(2+)](i) are directly proportional to carcinogenicity. SAE [Ca(2+)](i) was determined by a ratiometric digital Ca(2+) imaging system. BPDE increased SAE [Ca(2+)](i) within 20 s in media with high (1 mM) and low (10 nM) Ca(2+) at a threshold concentration of 0.2 nM. Elevation of [Ca(2+)](i) persisted longer with high Ca(2+). Neither BP nor solvent altered [Ca(2+)](i). Thapsigargin and inositol 1,4,5- phosphate receptor (InsP(3)R) antagonists inhibited this BPDE action with low Ca(2+). We conclude that BPDE but not BP increases [Ca(2+)](i) partly by mobilizing Ca(2+) from cytosolic stores through an InsP(3)R. The most potent carcinogenic PAH diol epoxide increased in SAE [Ca(2+)](i) at the lowest threshold concentration, suggesting that carcinogenicity is directly proportional to the action of PAHs on SAE [Ca(2+)](i). Short-term exposure to BPDE 36 to 48 h before the study rendered SAE cells less sensitive to BPDE, suggesting that BPDE may also induce persistent changes in Ca(2+) signaling pathways.

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.

Dietary factors in human colorectal cancer

Colorectal cancer is a significant cause of mortality in Western societies. The progression of the disease from normal colonic epithelium to the acquisition of the malignant phenotype is accompanied by numerous genetic and epigenetic alterations. Compelling experimental and epidemiological evidence indicates that diet and nutrition are key factors in the modulation of colorectal cancer. A salient case in point is the recent observation that a dietary regimen based on a Western-style diet provokes in the rodent colon the appearance of preneoplastic lesions in the absence of any genotoxic insult. This review mainly describes dietary factors that inhibit the development and progression of colorectal cancer. Much is unknown about the precise mechanisms of action of chemically disparate nutrients and how they interfere with the development and progression of this disease. Current knowledge about this important issue is summarized. We believe that continuing scrutiny and precise assessment of the benefits (and potential risks) of nutrients in the treatment and prevention of colorectal cancer will prove significant to controlling this devastating disease.