7,12-dimethylbenz[a]anthracene induces oxidative DNA modification in vivo

NRF2, a crucial modulator of skin cells protection against vitiligo, psoriasis, and cancer

The skin represents a physical barrier between the organism and the environment that has evolved to confer protection against biological, chemical, and physical insults. The inner layer, known as dermis, is constituted by connective tissue and different types of immune cells whereas the outer layer, the epidermis, is composed by different layers of keratinocytes and an abundant number of melanocytes, localized in the stratum basale of the epidermis. Oxidative stress is a common alteration of inflammatory skin disorders such as vitiligo, dermatitis, or psoriasis but can also play a causal role in skin carcinogenesis and tumor progression. Nuclear factor (erythroid-derived 2)-like 2 (NRF2) has emerged as a crucial regulator of cell defense mechanisms activating complex transcriptional programs that facilitate reactive oxygen species detoxification, repair oxidative damage and prevent xenobiotic-induced toxicity. Accumulating evidence suggests that the keratinocytes, melanocytes, and other skin cell types express high levels of NRF2, which is known to play a pivotal role in the skin homeostasis, differentiation, and metabolism during normal and pathologic conditions. In the present review, we summarize the current evidence linking NRF2 to skin pathophysiology and we discuss some recent modulators of NRF2 activity that have shown a therapeutic efficacy in skin protection against tumor initiation and common inflammatory skin conditions such as vitiligo or psoriasis, with a particular emphasis on natural compounds.

A look beyond the priority: A systematic review of the genotoxic, mutagenic, and carcinogenic endpoints of non-priority PAHs

Knowledge of the toxic potential of polycyclic aromatic hydrocarbons (PAHs) has increased over time. Much of this knowledge is about the 16 United States - Environmental Protection Agency (US - EPA) priority PAHs; however, there are other US - EPA non-priority PAHs in the environment, whose toxic potential is underestimated. We conducted a systematic review of in vitro, in vivo, and in silico studies to assess the genotoxicity, mutagenicity, and carcinogenicity of 13 US - EPA non-priority parental PAHs present in the environment. Electronic databases, such as Science Direct, PubMed, Scopus, Google Scholar, and Web of Science, were used to search for research with selected terms without time restrictions. After analysis, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol, 249 articles, published between 1946 and 2020, were selected and the quality assessment of these studies was performed. The results showed that 5-methylchrysene (5-MC), 7,12-dimethylbenz[a]anthracene (7,12-DMBA), cyclopenta[cd]pyrene (CPP), and dibenzo[al]pyrene (Db[al]P) were the most studied PAHs. Moreover, 5-MC, 7,12-DMBA, benz[j]aceanthrylene (B[j]A), CPP, anthanthrene (ANT), dibenzo[ae]pyrene (Db[ae]P), and Db[al]P have been reported to cause mutagenic effects and have been being associated with a risk of carcinogenicity. Retene (RET) and benzo[c]fluorene (B[c]F), the least studied compounds, showed evidence of a strong influence on the mutagenicity and carcinogenicity endpoints. Overall, this systematic review provided evidence of the genotoxic, mutagenic, and carcinogenic endpoints of US - EPA non-priority PAHs. However, further studies are needed to improve the future protocols of environmental analysis and risk assessment in severely exposed populations.

Preventive Effect of Combined Zingiber officinale and Terminalia chebula against DMBA-Induced Breast Cancer Rats via mTOR Inhibition

Zingiber officinale (ZO) and Terminalia chebula (TC) are plants used for the treatment of diverse illnesses in traditional medicine. The present study investigates the preventive effect of Zingiber officinale-Terminalia chebula extract (ZOTC) against DMBA-induced breast cancer in a rat model. Bioactive compounds from ZO (6-gingerol, 6-shogaol) and TC (gallic acid, ellagic acid, corilagin, chebulinic acid, and chebulagic acid) were detected using high-performance liquid chromatography. Mammary carcinogenesis was induced in rats with a single subcutaneous injection of 7,12-Dimethylbenz[a]anthracene (DMBA). Oral administration of ZOTC ameliorated the antioxidant status in mammary tissues, serum lipid levels, and serum cytokines. Histological analysis of the mammary tissue (normal and tumor) was carried out to obtain pathological alterations due to ZOTC treatment. The effect of ZOTC on the mechanistic target of rapamycin (mTOR) gene and accumulation of corresponding gene product was also investigated. mTOR plays a central role in cell metabolism and proliferation in normal and cancer cells. Transcriptional and immunohistochemical analysis showed the downregulation of mTOR expression in the mammary tissues of ZOTC-treated rats. In conclusion, the results obtained suggest that ZOTC can suppress tumor progression in DMBA-induced breast cancer rats via inhibition of the mTOR pathway.

Restraint stress abates the antioxidant potential of melatonin on dimethyl benz (a) anthracene (DMBA) induced carcinogenesis

Free radical involvement in initiation, promotion and progression of carcinogenesis, implicates that scavengers of free radicals may act as inhibitors in the carcinogenic process. Melatonin, an antioxidant was used in the present study to evaluate its effectiveness on skin carcinogenesis induced by DMBA both with and without chronic restraint stress (CRS). Fifty Swiss albino young male rats were divided into five groups of 10 rats each as controls, topical DMB alone, Pre CRS-DMBA, melatonin DMBA and Pre-CRS-DMBA-melatonin treated groups. After 18 weeks blood was collected along with liver and skin samples. These were used for antioxidant enzyme assay, DNA damage and fluorescent spectra analysis. Melatonin showed antioxidant potential in combatting DMBA induced skin carcinogenesis measured by free radical scavenging enzymes and in vivo antioxidant status, DNA damage. Sensitive detection of the DMBA induced micro biochemical changes was possible by fluorescent spectroscopy from the transformed ratio of fluorescent intensity (F1 530 nm/630 nm) otherwise found constant for normal tissues. By melatonin treatment this ratio was similar to control values. The decreased antioxidant biochemical parameters depicting oxidative stress were comparable to comet assay and fluorescent studies, endorsing the chemo-preventive efficacy of melatonin against skin carcinogenesis caused by DMBA. CRS pre-exposure diminished the chemo-preventive/antioxidant ability of melatonin and the results were same as DMBA alone treatment, showing stress affected both cancer development and chemoprevention. CRS decreased the antioxidant potential of melatonin. Hence, managing stress could be perceived in cancer chemoprevention. Further studies focusing on stress reduction are needed.

Claudin-low-like mouse mammary tumors show distinct transcriptomic patterns uncoupled from genomic drivers

BACKGROUND

Claudin-low breast cancer is a molecular subtype associated with poor prognosis and without targeted treatment options. The claudin-low subtype is defined by certain biological characteristics, some of which may be clinically actionable, such as high immunogenicity. In mice, the medroxyprogesterone acetate (MPA) and 7,12-dimethylbenzanthracene (DMBA)-induced mammary tumor model yields a heterogeneous set of tumors, a subset of which display claudin-low features. Neither the genomic characteristics of MPA/DMBA-induced claudin-low tumors nor those of human claudin-low breast tumors have been thoroughly explored.

METHODS

The transcriptomic characteristics and subtypes of MPA/DMBA-induced mouse mammary tumors were determined using gene expression microarrays. Somatic mutations and copy number aberrations in MPA/DMBA-induced tumors were identified from whole exome sequencing data. A publicly available dataset was queried to explore the genomic characteristics of human claudin-low breast cancer and to validate findings in the murine tumors.

RESULTS

Half of MPA/DMBA-induced tumors showed a claudin-low-like subtype. All tumors carried mutations in known driver genes. While the specific genes carrying mutations varied between tumors, there was a consistent mutational signature with an overweight of T>A transversions in TG dinucleotides. Most tumors carried copy number aberrations with a potential oncogenic driver effect. Overall, several genomic events were observed recurrently; however, none accurately delineated claudin-low-like tumors. Human claudin-low breast cancers carried a distinct set of genomic characteristics, in particular a relatively low burden of mutations and copy number aberrations. The gene expression characteristics of claudin-low-like MPA/DMBA-induced tumors accurately reflected those of human claudin-low tumors, including epithelial-mesenchymal transition phenotype, high level of immune activation, and low degree of differentiation. There was an elevated expression of the immunosuppressive genes PTGS2 (encoding COX-2) and CD274 (encoding PD-L1) in human and murine claudin-low tumors.

CONCLUSIONS

Our findings show that the claudin-low breast cancer subtype is not demarcated by specific genomic aberrations, but carries potentially targetable characteristics warranting further research.

Psychosocial Stress Exposure Disrupts Mammary Gland Development

Exposure to psychosocial stressors and ensuing stress physiology have been associated with spontaneous invasive mammary tumors in the Sprague-Dawley rat model of human breast cancer. Mammary gland (MG) development is a time when physiologic and environmental exposures influence breast cancer risk. However, the effect of psychosocial stress exposure on MG development remains unknown. Here, in the first comprehensive longitudinal study of MG development in nulliparous female rats (from puberty through young adulthood; 8-25 wks of age), we quantify the spatial gradient of differentiation within the MG of socially stressed (isolated) and control (grouped) rats. We then demonstrate that social isolation increased stress reactivity to everyday stressors, resulting in downregulation of glucocorticoid receptor (GR) expression in the MG epithelium. Surprisingly, given that chemical carcinogens increase MG cancer risk by preventing normal terminal end bud (TEB) differentiation, chronic isolation stress did not alter TEBs. Instead, isolation blunted MG growth and alveolobular differentiation and reduced epithelial cell proliferation in these structures. Social isolation also enhanced corpora luteal progesterone at all ages but reduced estrogenization only in early adulthood, a pattern that precludes modulated ovarian function as a sufficient mechanism for the effects of isolation on MG development. This longitudinal study of natural variation provides an integrated view of MG development and the importance of increased GR activation in nulliparous ductal growth and alveolobular differentiation. Thus, social isolation and its physiological sequelae disrupt MG growth and differentiation and suggest a contribution of stress exposure during puberty and young adulthood to the previously observed increase in invasive MG cancer observed in chronically socially-isolated adult Sprague-Dawley rats.

Deoxynivalenol induced mouse skin tumor initiation: Elucidation of molecular mechanisms in human HaCaT keratinocytes

Among food contaminants, mycotoxins are toxic to both human and animal health. Our prior studies suggest that Deoxynivalenol (DON), a mycotoxin, behaves as a tumor promoter by inducing edema, hyperplasia, ODC activity and activation of MAPK's in mouse skin. In this study, topical application of DON, 336 and 672 nmol significantly enhanced ROS levels, DNA damage and apoptosis with concomitant downregulation of Ki-67, cyclin D, cyclin E, cyclin A and cyclin-dependent kinases (CDK4 and CDK2) thereby resulting in tumor initiation in mouse skin. Further, the elucidation of molecular mechanisms of tumor initiation by DON (0.42-3.37 nmol/ml) in HaCaT keratinocytes, revealed (i) enhanced ROS generation with cell cycle phase arrest in G0/G1 phase, (ii) increase in levels of 8-OxoG (6-24 hr) and γH2AX protein, (iii) significant enhancement in oxidative stress marker enzymes LPO, GSH, GR with concomitant decrease in antioxidant enzymes catalase, GPx, GST, SOD and mitochondrial membrane potential after DON (1.68 nmol) treatment, (iv) suppression of Nrf2 translocation to nucleus, enhanced phosphorylation with subsequent activation ERK1/2, p38 and JNK MAPK's following DON (1.68 nmol) treatment, (v) overexpression of c-jun, c-fos proteins, upregulation of Bax along with downregulation of Bcl-2 proteins, (vi) increase in cytochrome-c, caspase-9, caspase-3 and poly ADP ribose polymerase levels leads to apoptosis. Pretreatment of superoxide dismutase, mannitol and ethanol to HaCaT cells resulted in significant reduction in ROS levels and apoptosis indicating the role of superoxide and hydroxyl radicals in DON induced apoptosis as an early event and skin tumor initiation as a late event.

Tangeretin ameliorates oxidative stress in the renal tissues of rats with experimental breast cancer induced by 7,12-dimethylbenz[a]anthracene

Tangeretin, a citrus polymethoxyflavone, is an antioxidant modulator which has been shown to exhibit a surfeit of pharmacological properties. The present study was hypothesized to explore the therapeutic activity of tangeretin against 7,12-dimethylbenz[a]anthracene (DMBA) induced kidney injury in mammary tumor bearing rats. Recently, we have reported the chemotherapeutic effect of tangeretin in the breast tissue of DMBA induced rats. Breast cancer was induced by "air pouch technique" with a single dose of 25mg/kg of DMBA. Tangeretin (50mg/kg/day) was administered orally for four weeks. The renoprotective nature of tangeretin was assessed by analyzing the markers of oxidative stress, proinflammatory cytokines and antioxidant competence in DMBA induced rats. Tangeretin treatment revealed a significant decline in the levels of lipid peroxides, inflammatory cytokines and markers of DNA damage, and a significant improvement in the levels of enzymatic and non-enzymatic antioxidants in the kidney tissue. Similarly, mRNA, protein and immunohistochemical analysis substantiated that tangeretin treatment notably normalizes the renal expression of Nrf2/Keap1, its downstream regulatory proteins and the inflammatory cytokines in the DMBA induced rats. Histological and ultrastructural observations also evidenced that the treatment with tangeretin effectively protects the kidney from DMBA-mediated oxidative damage, hence, proving its nephroprotective nature.

Effect of blueberries (BB) on micronuclei induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 7,12-dimethylbenz(a)anthracene (DMBA) in mammalian cells, assessed in in vitro and in vivo assays

The protective effect of blueberry (BB) on the clastogenic effects of MNNG and DMBA was evaluated with the induced micronucleus (MN) frequency as a biomarker, both in vitro and in vivo. Human hepatoma HepG2 cells, which contain most of the metabolic activating enzymes was used for the in vitro test. MN frequencies were determined in binucleated cells generated by blocking cytokinesis by use of cytochalasin-B. The MN frequency in vivo was determined in polychromatic erythrocytes (PCEs) from the bone marrow of treated mice. BB by itself was not toxic both in vivo and in vitro. There was no evidence of a potential physico-chemical interaction between BB and the test carcinogens in vitro. Pre-treatment with BB reduced the MN frequency induced by MNNG. But, simultaneous treatment and post-treatment with BB did not affect the frequency of MNNG-induced MN. BB did not affect the frequency of DMBA-induced MN in vitro under any test condition. Under in vivo conditions, BB reduced the frequencies of MNNG- and DMBA-induced MN in PCEs, but in the case of the protective effect of BB against DMBA a dramatic reduction in the percentage of PCEs was observed, suggesting increased cytotoxicity.

Pronounced cancer resistance in a subterranean rodent, the blind mole-rat, Spalax: in vivo and in vitro evidence

Background

Subterranean blind mole rats (Spalax) are hypoxia tolerant (down to 3% O₂), long lived (>20 years) rodents showing no clear signs of aging or aging related disorders. In 50 years of Spalax research, spontaneous tumors have never been recorded among thousands of individuals. Here we addressed the questions of (1) whether Spalax is resistant to chemically-induced tumorigenesis, and (2) whether normal fibroblasts isolated from Spalax possess tumor-suppressive activity.

Results

Treating animals with 3-Methylcholantrene (3MCA) and 7,12-Dimethylbenz(a) anthracene/12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA), two potent carcinogens, confirmed Spalax high resistance to chemically induced cancers. While all mice and rats developed the expected tumors following treatment with both carcinogens, among Spalax no tumors were observed after DMBA/TPA treatment, while 3MCA induced benign fibroblastic proliferation in 2 Spalax individuals out of12, and only a single animal from the advanced age group developed malignancy 18 months post-treatment. The remaining animals are still healthy 30 months post-treatment. In vitro experiments showed an extraordinary ability of normal Spalax cultured fibroblasts to restrict malignant behavior in a broad spectrum of human-derived and in newly isolated Spalax 3MCA-induced cancer cell lines. Growth of cancer cells was inhibited by either direct interaction with Spalax fibroblasts or with soluble factors released into culture media and soft agar. This was accompanied by decreased cancer cell viability, reduced colony formation in soft agar, disturbed cell cycle progression, chromatin condensation and mitochondrial fragmentation. Cells from another cancer resistant subterranean mammal, the naked mole rat, were also tested for direct effect on cancer cells and, similar to Spalax, demonstrated anti-cancer activity. No effect on cancer cells was observed using fibroblasts from mouse, rat or Acomys. Spalax fibroblast conditioned media had no effect on proliferation of noncancerous cells.

Conclusions

This report provides pioneering evidence that Spalax is not only resistant to spontaneous cancer but also to experimentally induced cancer, and shows the unique ability of Spalax normal fibroblasts to inhibit growth and kill cancer cells, but not normal cells, either through direct fibroblast-cancer cell interaction or via soluble factors. Obviously, along with adaptation to hypoxia, Spalax has evolved efficient anti-cancer mechanisms yet to be elucidated. Exploring the molecular mechanisms allowing Spalax to survive in extreme environments and to escape cancer as well as to kill homologous and heterologous cancer cells may hold the key for understanding the molecular nature of host resistance to cancer and identify new anti-cancer strategies for treating humans.

Dual role of the antioxidant enzyme peroxiredoxin 6 in skin carcinogenesis

The antioxidant enzyme peroxiredoxin 6 (Prdx6) is a key regulator of the cellular redox balance, particularly under stress conditions. We identified Prdx6 as an important player in different phases of skin carcinogenesis. Loss of Prdx6 in mice enhanced the susceptibility to skin tumorigenesis, whereas overexpression of Prdx6 in keratinocytes of transgenic mice had the opposite effect. The tumor-preventive effect of Prdx6, which was observed in a human papilloma virus 8-induced and a chemically induced tumor model, was not due to alterations in keratinocyte proliferation, apoptosis, or in the inflammatory response. Rather, endogenous and overexpressed Prdx6 reduced oxidative stress as reflected by the lower levels of oxidized phospholipids in the protumorigenic skin of Prdx6 transgenic mice and the higher levels in Prdx6-knockout mice than in control animals. In contrast to its beneficial effect in tumor prevention, overexpression of Prdx6 led to an acceleration of malignant progression of existing tumors, revealing a dual function of this enzyme in the pathogenesis of skin cancer. Finally, we found strong expression of PRDX6 in keratinocytes of normal human skin and in the tumor cells of squamous cell carcinomas, indicating a role of Prdx6 in human skin carcinogenesis. Taken together, our data point to the potential usefulness of Prdx6 activators or inhibitors for controlling different stages of skin carcinogenesis.

Topical application of ochratoxin A causes DNA damage and tumor initiation in mouse skin

Skin cancer is one of the most common forms of cancer and 2-3 million new cases are being diagnosed globally each year. Along with UV rays, environmental pollutants/chemicals including mycotoxins, contaminants of various foods and feed stuffs, could be one of the aetiological factors of skin cancer. In the present study, we evaluated the DNA damaging potential and dermal carcinogenicity of a mycotoxin, ochratoxin A (OTA), with the rationale that dermal exposure to OTA in workers may occur during their involvement in pre and post harvest stages of agriculture. A single topical application of OTA (20-80 µg/mouse) resulted in significant DNA damage along with elevated γ-H2AX level in skin. Alteration in oxidative stress markers such as lipid peroxidation, protein carbonyl, glutathione content and antioxidant enzymes was observed in a dose (20-80 µg/mouse) and time-dependent (12-72 h) manner. The oxidative stress was further emphasized by the suppression of Nrf2 translocation to nucleus following a single topical application of OTA (80 µg/mouse) after 24 h. OTA (80 µg/mouse) application for 12-72 h caused significant enhancement in- (a) reactive oxygen species generation, (b) activation of ERK1/2, p38 and JNK MAPKs, (c) cell cycle arrest at G0/G1 phase (37-67%), (d) induction of apoptosis (2.0-11.0 fold), (e) expression of p53, p21/waf1, (f) Bax/Bcl-2 ratio, (g) cytochrome c level, (h) activities of caspase 9 (1.2-1.8 fold) and 3 (1.7-2.2 fold) as well as poly ADP ribose polymerase cleavage. In a two-stage mouse skin tumorigenesis protocol, it was observed that a single topical application of OTA (80 µg/mouse) followed by twice weekly application of 12-O-tetradecanoylphorbol-13-acetate for 24 week leads to tumor formation. These results suggest that OTA has skin tumor initiating property which may be related to oxidative stress, MAPKs signaling and DNA damage.

The chemotherapeutic potential of Terminalia ferdinandiana: Phytochemistry and bioactivity

Plants contain a myriad of natural compounds which exhibit important bioactive properties. These compounds may provide alternatives to current medications and afford a significant avenue for new drug discovery. Despite this, little information is available in the literature regarding native Australian plants and their potential for medicinal and industrial uses. Recent studies have reported Terminalia ferdinandiana to be an extremely good source of antioxidants. Indeed, T. ferdinandiana has been reported to have ascorbic acid levels per gram of fruit more than 900 times higher than blueberries. T. ferdinandiana also has high levels of a variety of other antioxidants, including phenolic compounds and anthocyanins. Antioxidants have been associated with the prevention of cancer, cardiovascular diseases, and neurological degenerative disorders. They are also linked with antidiabetic bioactivities and have been associated with the reduction of obesity. Antioxidants can directly scavenge free radicals, protecting cells against oxidative stress-related damage to proteins, lipids, and nucleic acids. Therefore, T. ferdinandiana has potential in the treatment of a variety of diseases and disorders and its potential bioactivities warrant further investigation.

Chronic unpredictable stress exacerbates 7,12-dimethylbenz (a) anthracene induced hepatotoxicity and nephrotoxicity in Swiss albino mice

Oxidative stress, a pervasive condition induced by stress has been implicated and recognized to be a prominent feature of various pathological states including cancer and their progression. The present study sought to validate the effectiveness of chronic unpredictable stress (CUS) on hepatic and renal toxicity in terms of alterations of various in vivo biochemical parameters, oxidative stress markers and the extent of DNA damage in Swiss albino mice. Animals were randomized into different groups based on their exposure to CUS alone, 7,12-dimethylbenz (a) anthracene (DMBA) alone (topical), DMBA-12-O-tetradecanoylphorbol-13-acetate (TPA) (topical), and exposure to CUS prior to DMBA or DMBA-TPA treatment, and sacrificed after 16 weeks of treatment. Prior exposure to CUS increased the pro-oxidant effect of carcinogen as depicted by significantly compromised levels of antioxidants; superoxide dismutase, catalase, glutathione-S-transferase, glutathione reductase, reduced glutathione in hepatic and renal tissues accompanied by a significant elevation of thiobarbituric acid reactive species (TBARS) as compared to DMBA alone or DMBA-TPA treatments. Loss of structural integrity at the cellular level due to stress-induced oxidative damage was demonstrated by significant increases in the hepatic levels of intracellular marker enzymes such as glutamate oxaloacetate transaminase, glutamate pyruvate transaminase and alkaline phosphatase, and significantly reduced levels of uric acid in kidney tissues. The results of DNA damage studies further positively correlated with all the above biochemical measurements. Thus, exposure to physical or psychological stress may significantly enhance the hepatotoxic and nephrotoxic potential of carcinogens through enhanced oxidative stress even if the treatment is topical.

Estrogen action and prostate cancer

Early work on the hormonal basis of prostate cancer focused on the role of androgens, but more recently estrogens have been implicated as potential agents in the development and progression of prostate cancer. In this article, we review the epidemiological, laboratory and clinical evidence that estrogen may play a causative role in human prostate cancer, as well as rodent and grafted in vivo models. We then review recent literature highlighting potential mechanisms by which estrogen may contribute to prostate cancer, including estrogenic imprinting and epigenetic modifications, direct genotoxicity, hyperprolactinemia, inflammation and immunologic changes, and receptor-mediated actions. We discuss the work performed so far separating the actions of the different known estrogen receptors (ERs), ERα and ERβ, as well as G-protein-coupled receptor 30 and their specific roles in prostate disease. Finally, we predict that future work in this field will involve more investigations into epigenetic changes, experiments using new models of hormonal dysregulation in developing human prostate tissue, and continued delineation of the roles of the different ER subtypes, as well as their downstream signaling pathways that may serve as therapeutic targets.

Synergistic growth inhibition of mouse skin tumors by pomegranate fruit extract and diallyl sulfide: evidence for inhibition of activated MAPKs/NF-κB and reduced cell proliferation

Limited outcomes from earlier chemopreventive studies have necessitated that some modifications be made to get better efficacy. It is proposed that cancer prevention is more feasible than treatment, and this could be achieved effortlessly with use of multiple agents competent of targeting multiple targets. This study was initiated to examine the chemopreventive efficacy of pomegranate fruit extract (PFE) and diallyl sulfide (DAS), alone and in combination, using 2-stage mouse skin tumorigenesis model. PFE and DAS alone delayed onset and tumor incidence by ∼55% and ∼45%, respectively, while their combination at low doses synergistically decreased tumor incidence more potentially (∼84%, p<0.01). In addition, regression in tumor volume was seen with continuous combinatorial treatment (p<0.01). Mechanistic studies revealed that this inhibition was associated with decreased expression of phosphorylated ERK1/2, JNK1 and activated NF-κB/p65, IKKα, IκBα phosphorylation and degradation in skin tissue/tumor. Histological and cell death analysis also confirmed that combined PFE and DAS inhibit cellular proliferation and markedly induce apoptosis than the single agents. Altogether, our results suggest that PFE and DAS in combination impart better suppressive activity than either of these agents alone and provide support that development of novel combination therapies/chemoprevention using dietary agents will be more beneficial against cancer.

Effects of red mold dioscorea on oral carcinogenesis in DMBA-induced hamster animal model

Monascus-fermented products offer valuable therapeutic benefits and have been extensively used for centuries in East Asia. Dioscorea has been proved to have anti-cancer effect. The aim of this study is to investigate the anti-tumor ability of the ethanol extract of red mold dioscorea (RMDE) on 7,12-dimethyl-1,2-benz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. We induced oral squamous cell carcinoma (OSCC) in the buccal pouch of male Syrian golden hamsters by painting with 0.5% DMBA three times a week for 14 weeks. From 9 to 14 weeks, a dose of 50, 100, and 200 mg RMDE per kg body weight were painting with the hamsters for 6 weeks on days alternate to the DMBA application. The results demonstrated that RMDE decreased nitric oxide (NO), reactive oxygen species (ROS), and prostaglandin E(2) (PGE(2)) overexpression in hamster buccal pouches in the DMBA treatment group and increased p53, serum tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) to significantly stimulate caspase-8 and -3 activities, indicating that RMDE reduced oxidative damage causing by DMBA and induced apoptosis in oral cancer cells. Therefore, RMDE may have therapeutic potentials against OSCC.

Decreases in binding capacity of the mitochondrial 18 kda translocator protein accompany oxidative stress and pathological signs in rat liver after DMBA exposure

7,12-Dimethylbenz[a]anthracene (DMBA) presents a pollutant implicated in various toxicological effects. The aim of this experiment was to study the effects of DMBA administration on oxidative stress, histopathological signs, and 18 kDa translocator protein (TSPO) binding characteristics in rat liver. We also studied the effects of dose stoichiometry, dose frequency, and duration of protocol of DMBA administration. In this study, rats surviving eighteen weeks after DMBA exposure showed mild to moderate histopathological changes in the liver, mainly characterized by glossy appearance of hepatocytes, heterochromatic nuclei, and glycogen overload in the midzonal region of the hepatic lobe. These changes were accompanied by significant rises in oxidant levels, along with declines in nonenzymic antioxidants, indicating that DMBA induced oxidative stress in the liver. This finding correlated well with decreases in TSPO binding capacity in the liver of the rats in our study. Other studies have shown that TSPO can be affected by oxidative stress, as well as contribute to oxidative stress at mitochondrial levels. Further studies are needed to assay whether the decreases in TSPO density in the liver are part of the damaging effects caused by DMBA or a compensatory response to the oxidative stress induced by DMBA.

DIGE-based protein expression analysis of B[a]P-exposed hepatoma cells reveals a complex stress response including alterations in oxidative stress, cell cycle control, and cytoskeleton motility at toxic and subacute concentrations

Although the effects of high concentrations of the carcinogen benzo[a]pyrene (B[a]P) have been studied extensively, little is known about its effects at subacute toxic concentrations, which are typical for environmental pollutants. We exposed murine Hepa1c1c7 cells to a toxic concentration (5 μM) and a subacute concentration (50 nM) of B[a]P over a period of 2-24 h to differentiate between acute and pseudochronic effects and conducted a time-course analysis of B[a]P-influenced protein expression by DIGE. In total, a set of 120 spots were found to be significantly altered due to B[a]P exposure of which 112 were subsequently identified by mass spectrometry. Clustering and principal component analysis were conducted to identify sets of proteins responding in a concerted manner to the exposure. Our results indicate an immediate response to the contaminant at the protein level and demonstrate that B[a]P exposure alters the cellular response by disturbing proteins involved in oxidative stress, cell cycle regulation, apoptosis, and cytoskeleton organization. Furthermore, network analysis of protein-protein interactions revealed a complex network of interacting, B[a]P-regulated proteins mostly belonging to the cytoskeleton organization and several signal transduction pathways.

Saffron suppresses oxidative stress in DMBA-induced skin carcinoma: A histopathological study

Cancer chemoprevention is the use of natural, synthetic or biological substances to reverse or prevent the development of cancer. Saffron is a naturally derived plant product that acts as an antispasmodic, diaphoretic, carminative, emmenagogic and sedative. Our aim in this study was to investigate the chemopreventive effect of aqueous saffron on chemically induced skin carcinogenesis using a histopathological approach. Mice were divided into five groups: carcinogen control (CC), normal control (NC) and saffron-treated Groups A, B and C. Groups A, B, C and CC mice received three topical applications of 7,12 dimethylbenz[a]anthracene (DMBA) followed by croton oil on shaven dorsal skin for 8 weeks. NC mice received topical skin applications of the vehicle, acetone, only. Saffron infusion was fed orally to three groups of mice either before (Group A) or after (Group C) or both before and after (Group B) DMBA applications. The activities of antioxidant enzymes glutathione-S transferase (GST), glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) in liver tissue samples taken at 0, 6, 10 and 12 weeks from all groups were assessed. Standard histological examination of skin demonstrated a beneficial action of saffron in mice where saffron treatments were given both before and after the induction of skin carcinogenesis. Saffron ingestion inhibited the formation of skin papillomas in animals and simultaneously reduced their size. In conclusion, saffron inhibits DMBA-induced skin carcinoma in mice when treated early. This may be due, at least in part, to the induction of cellular defense systems.

ASK1 and ASK2 differentially regulate the counteracting roles of apoptosis and inflammation in tumorigenesis

Apoptosis and inflammation generally exert opposite effects on tumorigenesis: apoptosis serves as a barrier to tumour initiation, whereas inflammation promotes tumorigenesis. Although both events are induced by various common stressors, relatively little is known about the stress-induced signalling pathways regulating these events in tumorigenesis. Here, we show that stress-activated MAP3Ks, ASK1 and ASK2, which are involved in cellular responses to various stressors such as reactive oxygen species, differentially regulate the initiation and promotion of tumorigenesis. ASK2 in cooperation with ASK1 functioned as a tumour suppressor by exerting proapoptotic activity in epithelial cells, which was consistent with the reduction in ASK2 expression in human cancer cells and tissues. In contrast, ASK1-dependent cytokine production in inflammatory cells promoted tumorigenesis. Our findings suggest that ASK1 and ASK2 are critically involved in tumorigenesis by differentially regulating apoptosis and inflammation.

The role of polycyclic aromatic hydrocarbon-DNA adducts in inducing mutations in mouse skin

Polycyclic aromatic hydrocarbons (PAH) form stable and depurinating DNA adducts in mouse skin to induce preneoplastic mutations. Some mutations transform cells, which then clonally expand to establish tumors. Strong clues about the mutagenic mechanism can be obtained if the PAH-DNA adducts can be correlated with both preneoplastic and tumor mutations. To this end, we studied mutagenesis in PAH-treated early preneoplastic skin (1 day after exposure) and in the induced papillomas in SENCAR mice. Papillomas were studied by PCR amplification of the H-ras gene and sequencing. For benzo[a]pyrene (BP), BP-7,8-dihydrodiol (BPDHD), 7,12-dimethylbenz[a]anthracene (DMBA) and dibenzo[a,l]pyrene (DB[a,l]P), the codon 13 (GGC to GTC) and codon 61 (CAA to CTA) mutations in papillomas corresponded to the relative levels of Gua and Ade-depurinating adducts, despite BP and BPDHD forming significant amounts of stable DNA adducts. Such a relationship was expected for DMBA and DB[a,l]P, as they formed primarily depurinating adducts. These results suggest that depurinating adducts play a major role in forming the tumorigenic mutations. To validate this correlation, preneoplastic skin mutations were studied by cloning H-ras PCR products and sequencing individual clones. DMBA- and DB[a,l]P-treated skin showed primarily A.T to G.C mutations, which correlated with the high ratio of the Ade/Gua-depurinating adducts. Incubation of skin DNA with T.G-DNA glycosylase eliminated most of these A.T to G.C mutations, indicating that they existed as G.T heteroduplexes, as would be expected if they were formed by errors in the repair of abasic sites generated by the depurinating adducts. BP and its metabolites induced mainly G.C to T.A mutations in preneoplastic skin. However, PCR over unrepaired anti-BPDE-N(2)dG adducts can generate similar mutations as artifacts of the study protocol, making it difficult to establish an adduct-mutation correlation for determining which BP-DNA adducts induce the early preneoplastic mutations. In conclusion, this study suggests that depurinating adducts play a major role in PAH mutagenesis.

Inhibition of 7,12-Dimethylbenz(a)anthracene-Induced Skin Tumorigenesis in C57BL/6 Mice by Sulforaphane Is Mediated by Nuclear Factor E2–Related Factor 2

Sulforaphane, a dietary isothiocyanate, possesses potent chemopreventive effects through the induction of cellular detoxifying/antioxidant enzymes via the transcription factor nuclear factor E2-related factor 2 (Nrf2). To investigate carcinogenesis mechanisms related to the regulation of Nrf2, we examined the tumor incidence and tumor numbers per mouse in Nrf2 wild-type (+/+) and Nrf2 knockout (-/-) mice. 7,12-Dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate treatments resulted in an increase in the incidence of skin tumors and tumor numbers per mouse in both genotypes; however, both indices were markedly higher in Nrf2(-/-) mice as compared with Nrf2(+/+) mice. Western blot analysis revealed that Nrf2 as well as heme oxygenase-1, a protein regulated by Nrf2 were not expressed in skin tumors from mice of either genotype, whereas expression of heme oxygenase-1 in Nrf2(+/+) mice was much higher than that in Nrf2(-/-) mice in nontumor skin samples. Next, we examined the chemopreventive efficacy of sulforaphane in mice with both genotypes. Topical application of 100 nmol of sulforaphane once a day for 14 days prior to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate applications decreased the incidence of skin tumor in the Nrf2(+/+) mice when compared with the vehicle-treated group. Importantly, there was no chemoprotective effect elicited by sulforaphane pretreatment in the Nrf2(-/-) mice group. Taken together, our results show for the first time that Nrf2(-/-) mice are more susceptible to skin tumorigenesis and that the chemopreventive effects of sulforaphane are mediated, at least in part, through Nrf2.

Polycyclic aromatic hydrocarbon (PAH) o-quinones produced by the aldo-keto-reductases (AKRs) generate abasic sites, oxidized pyrimidines, and 8-oxo-dGuo via reactive oxygen species

Reactive and redox-active polycyclic aromatic hydrocarbon (PAH) o-quinones produced by Aldo-Keto Reductases (AKRs) have the potential to cause depurinating adducts leading to the formation of abasic sites and oxidative base lesions. The aldehyde reactive probe (ARP) was used to detect these lesions in calf thymus DNA treated with three PAH o-quinones (BP-7,8-dione, 7,12-DMBA-3,4-dione, and BA-3,4-dione) in the absence and presence of redox-cycling conditions. In the absence of redox-cycling, a modest amount of abasic sites were detected indicating the formation of a low level of covalent o-quinone depurinating adducts (>3.2 x 10(6) dNs). In the presence of NADPH and CuCl2, the three PAH o-quinones increased the formation of abasic sites due to ROS-derived lesions destabilizing the N-glycosidic bond. The predominant source of AP sites, however, was revealed by coupling the assay with human 8-oxoguanine glycosylase (hOGG1) treatment, showing that 8-oxo-dGuo was the major lesion caused by PAH o-quinones. The levels of 8-oxo-dGuo formation were independently validated by HPLC-ECD analysis. Apyrimidinic sites were also revealed by coupling the assay with Escherichia coli (Endo III) treatment showing that oxidized pyrimidines were formed, but to a lesser extent. Different mechanisms were responsible for the formation of the oxidative lesions depending on whether Cu(II) or Fe(III) was used in the redox-cycling conditions. In the presence of Cu(II)-mediated PAH o-quinone redox-cycling, catalase completely suppressed the formation of the lesions, but mannitol and sodium benzoate were without effect. By contrast, sodium azide, which acts as a *OH and 1O2 scavenger, inhibited the formation of all oxidative lesions, suggesting that the ROS responsible was 1O2. However, in the presence of Fe(III)-mediated PAH o-quinone redox-cycling, the *OH radical scavengers and sodium azide consistently attenuated their formation, indicating that the ROS responsible was *OH.

Prior exposure to restraint stress enhances 7,12-dimethylbenz(a)anthracene (DMBA) induced DNA damage in rats

Over the years, several lines of evidence have emerged supporting the role of stress in the development and progression of cancer. Stress can cause an increase in the production of reactive oxygen species (ROS) and decrease in the in vivo antioxidant defense systems. A ROS-induced DNA damage in peripheral lymphocytes, liver and skin cells may be revealed by Comet assay. To test whether DNA is damaged by stress/DMBA/stress and DMBA, rats were exposed to multiple doses of DMBA in the presence and absence of restraint stress, and DNA damage was evaluated. Insignificant differences were detected in all the three cells tested (peripheral lymphocytes, liver and skin cells) between control and stress treatment in terms of frequencies of damaged DNA. The extent of DNA migration was enhanced in DMBA treated rats in a dose dependent manner. Pre-stress DMBA treatment showed still higher frequencies of damage in comparison with control, stress alone or DMBA alone groups. Thus, prior exposure to stress clearly enhanced the DMBA induced DNA damage, especially so in the skin cells (target organ of the carcinogen application) than liver and peripheral lymphocytes as observed on the basis of the extent of DNA migration (tail DNA) during single cell gel electrophoresis.

Synthesis and evaluation of antioxidative properties of a series of organoselenium compounds

A series of organoselenocyanate compounds 4a-d were synthesized utilizing 1,8-naphthalic anhydride as the building unit. These compounds were evaluated for their antioxidative activities against DMBA-PMA-induced oxidative stress in a two-stage mouse skin carcinogenic model. Compound 4d was found to have the maximum antioxidative property in comparison with the other compounds. Also, the pretreatment group showed better results than the concomitant treatment groups.

Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) by PAH o-quinones: involvement of reactive oxygen species and copper(II)/copper(I) redox cycling

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants and procarcinogens that require activation by host metabolism. Metabolic activation of PAHs by aldo-keto reductases (AKRs) leads to formation of reactive and redox active o-quinones, which may cause oxidatively generated DNA damage. Spectrophotometric assays showed that NADPH caused PAH o-quinones to enter futile redox cycles, which result in the depletion of excess cofactor. Copper(II) amplified NADPH-dependent redox cycling of the o-quinones. Concurrent with NADPH oxidation, molecular oxygen was consumed, indicating the production of ROS. To determine whether PAH o-quinones can cause 8-oxo-dGuo formation in salmon testis DNA, three prerequisite experimental conditions were satisfied. Quantitative complete enzymatic hydrolysis of DNA was achieved, adventitious oxidation of dGuo was eliminated by the use of chelex and desferal, and basal levels of less than 2.0 8-oxo-dGuo/10(5) dGuo were obtained. The HPLC-ECD analytical method was validated by spiking the DNA with standard 8-oxo-dGuo and demonstrating quantitative recovery. HPLC-ECD analysis revealed that in the presence of NADPH and Cu(II), submicromolar concentrations of PAH o-quinones generated >60.0 8-oxo-dGuo adducts/10(5) dGuo. The rank order of 8-oxo-dGuo generated in isolated DNA was NP-1,2-dione > BA-3,4-dione > 7,12-DMBA-3,4-dione > BP-7,8-dione. The formation of 8-oxo-dGuo by PAH o-quinones was concentration-dependent. It was completely or partially inhibited when catalase, tiron, or a Cu(I) specific chelator, bathocuproine, was added, indicating the requirement for H(2)O(2), O(2)(-), and Cu(I), respectively. Methional, which is a copper-hydroperoxo complex [Cu(I)OOH] scavenger, also suppressed 8-oxo-dGuo formation. By contrast, mannitol, sodium benzoate, and sodium formate, which act as hydroxyl radical scavengers, did not block its formation. Sodium azide, which can act as both a hydroxyl radical and a (1)O(2) scavenger, abolished the formation of 8-oxo-dGuo. These data showed that the production of 8-oxo-dGuo was dependent on Cu(II)/Cu(I) catalyzed redox cycling of PAH o-quinones to produce ROS and that the immediate oxidant was not hydroxyl radical or Cu(I)OOH and that it is more likely (1)O(2), which can produce a 4,8-endoperoxide-dGuo intermediate.

Caffeic acid phenethyl ester (CAPE) prevents transformation of human cells by arsenite (As) and suppresses growth of As-transformed cells

Recent evidence suggests that inflammatory cytokines and growth factors contribute to arsenite (As)-induced human carcinogenesis. We investigated the expression of inflammatory cytokine mRNAs during the transformation process induced by chronic As exposure in non-tumorigenic human osteogenic sarcoma (N-HOS) cells using gene arrays, and results were confirmed by RT-PCR and protein arrays. Caffeic acid phenethyl ester (CAPE), a naturally occurring immunomodulating agent, was used to evaluate the role of inflammatory factors in the process of As-mediated N-HOS cell transformation and in As-transformed HOS (AsT-HOS) cells. We found that an 8-week continuous exposure of N-HOS to 0.3 microM arsenite resulted in HOS cell transformation. That exposure also caused substantial decreases in inflammatory cytokine mRNAs, such as interleukin (IL) IL-1alpha, IL-2, IL-8, IL-18, MCP-1, TGF-beta2, and TNF-alpha, while it increased c-jun mRNA in a time-dependent manner. Co-incubation of N-HOS with As and CAPE (0.5-2.5 microM) prevented As-mediated declines in cytokine mRNAs in the co-treated cells, as well as their transformation to anchorage independence, while it caused decreases in c-jun mRNA. CAPE (up to 10 microM) had no effect on growth of N-HOS cells. However, CAPE (1-10 microM) treatment of AsT-HOS cells inhibited cell growth, induced cell cycle G2/M arrest, and triggered apoptosis, accompanied by changes in cytokine gene expression, as well as decreases in cyclin B1 and cdc2 abundance. Resveratrol (RV) and (-)(.) epigallocatechin gallate (EGCG), preventive agents present in grapes and green tea, respectively, induced similar changes in AsT-HOS cell growth but required much higher doses than CAPE to cause 50% growth arrest (<2.5 microM CAPE versus 25 microM RV or 50 microM EGCG). Overall, our findings suggest that inflammatory cytokines play an important role in the suppressive effects of CAPE on As-induced cell transformation and in the selective cytotoxicity of CAPE to As-transformed HOS cells.

In situ reduction of oxidative damage, increased cell turnover, and delay of mitochondrial injury by overexpression of manganese superoxide dismutase in a multistage skin carcinogenesis model

To study early subcellular pathologic changes of tumorigenesis in mouse skin and possible modulation by overexpression of the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD), skin keratinocytes from nontransgenic (Ntg) and transgenic (TgH) mice overexpressing MnSOD topically treated with one dose of 7,12-dimethylbenz(a)anthracene (DMBA) and a subsequent dose of 12-O-tetradecanoylphorbol 13-acetate (TPA) were analyzed in situ for levels of MnSOD and the oxidative damage product 4-hydroxy-2-nonenal (4HNE)-modified proteins using specific antibodies and immunogold electron microscopy. At all selected time points analyzed after TPA treatment, there was more MnSOD immunoreactive protein in mitochondria of keratinocytes of TgH mice than Ntg mice. Compared with untreated groups, there was a large increase in 4HNE-modified proteins at 6-24 h after TPA treatment, and this increase was larger in Ntg than TgH mice. Indices of mitosis and apoptosis of keratinocytes were greater in DMBA/TPA-treated TgH than Ntg mouse skin. Mitochondrial injury detected by transmission electron microscopy was delayed in keratinocytes of TgH compared with Ntg mice. The present study demonstrated that overexpression of MnSOD not only protected cells from oxidative damage, but also affected cell turnover kinetics. Thus, previously identified reduction in papilloma formation observed in TgH mice is correlated with mitochondrial events.

Loss of tyrosinase activity confers increased skin tumor susceptibility in mice

The tyrosinase (Tyr) gene encodes the enzyme tyrosinase that catalyses the conversion of L-tyrosine into DOPA (3,4-dihydroxyphenylalanine)-quinone. The albino mutation abrogates functional activity of tyrosinase resulting in deficiency of melanin pigment production in skin and retina. Tyr maps to a region in the central position of Chromosome 7 that contains a skin tumor-modifier locus. We rescued the albino mutation in transgenic mice to assess a possible role of Tyr gene in two-stage skin carcinogenesis. Transgenic expression of the functional Tyr(Cys) allele in albino mice (Tyr(Ser)) caused a reduction in skin papilloma multiplicity, in four independent experiments and at three dose levels of DMBA (9,10-dimethyl-1,2-benzanthracene). In vitro mechanistic studies demonstrated that transfection of the Tyr(Cys) allele in a human squamous cell carcinoma cell line (NCI-H520) increases tyrosinase enzyme activity and confers resistance to hydrogen peroxide-induced oxidative DNA damage. These results provide direct evidence that the Tyr gene can act as a skin cancer-modifier gene, whose mechanism of action may involve modulation of oxidative DNA damage.

Metabolomics of plant saponins: bioprospecting triterpene glycoside diversity with respect to mammalian cell targets

One of the goals of cancer chemotherapy and prevention is the discovery of compounds that are relatively selective to tumor cells and, therefore, have reduced effects on normal cell growth. In previously published studies, it was shown that certain triterpene saponins (called avicins) from a desert tree, Acacia victoriae, are selectively toxic to tumor cells at very low doses (IC(50): 0.2 microg/mL for Jurkat cells). To extend this research to human clinical studies, we needed to find a reliable supply of avicins and have developed a transformed "hairy root" culture as a means of biomass production. Protocols were optimized for A. victoriae micropropagation; after a boiling water treatment, A. victoriae seeds were maintained under in vitro conditions on defined media. Embryo-axis explants from shoot tips were removed and infected with Agrobacterium rhizogenes Conn (R 1000) for hairy root induction. Plasmid integration was confirmed by PCR analysis with a primer set for a segment of the rol B gene. Culture conditions have been optimized for root biomass production, and various inducers have been investigated for enhancement of avicin production. Hairy root cultures were compared with intact pod tissue from field-grown sources for avicin content following partial purification of triterpene glycosides and HPLC separation of the secondary metabolites. From bioassays of the collected HPLC fractions, we have identified putative triterpene "metabolic clusters" with enhanced activity against tumor cells. This now provides a system for both production of clinical trial lots of active samples, but also a means to correlate structure of individual triterpene glycosides with specific cellular target activity in mammalian cells.

Comments on the history and importance of aromatic and heterocyclic amines in public health

The carcinogenic risk of aromatic amines in humans was first discovered when a physician related the occurrence of urinary bladder cancer to the occupation of his patients. They were employed in the dyestuff industry, chronically exposed to large amounts of intermediate arylamines. Laboratory investigations disclosed that rats and mice administered specific azo dyes arylamines or derivatives developed cancer, primarily in the liver. Also, at that time, a possible pesticide, 2-aminofluorene, was tested for chronic toxicity, revealing that it rapidly induced cancers in several organs of rodents. This led to investigations on the mode of action of this class of chemicals, including their metabolic conversion. Biochemical activation to more reactive N-hydroxy compounds was found to occur, mostly in the liver, through what is now known as the cytochrome p450 enzyme systems, and also through prostaglandin synthetases. There were species differences. Guinea pigs were resistant to carcinogenesis because of the low titer of the necessary activating enzymes. In target tissues, a second essential reaction was necessary, namely acylation or sulfate ester formation. The reactive compounds produced display attributes of genotoxicity in appropriate test systems. Interest in this class of compounds increased when of Sugimura and colleagues discovered the formation of mutagens at the surface of cooked meat or fish, that were identified as heterocyclic amines (HCAs). These compounds undergo the same type of activation reactions, as do other arylamines. Epidemiological data suggest that meat eaters may have a higher risk of breast and colon cancer. HCAs induced cancer in rats in these organs and also in the prostate and the pancreas. In addition, there is some evidence that they affect the vascular system. The formation of HCAs during cooking can be decreased by natural and synthetic antioxidants, by tryptophan or proline, or by removing the essential creatine through brief microwave cooking prior to frying or broiling. The amounts of HCAs in cooked foods are small, but other components in diet such as omega-6-polyunsaturated oils have powerful promoting effects in target organs of HCAs. On the other hand, the action of HCAs may be decreased by foods containing antioxidants, such as vegetables, soy, and tea. Some constituents in foods also induce phase II enzymes that detoxify reactive HCA metabolites. Additional mechanisms involved decreased growth of neoplasms by intake of protective foods. Possibly, the carcinogenic effect of HCAs is accompanied by the presence of reactive oxygen species (ROS), which are also inhibited by antioxidants. World-wide, there have been many contributors to knowledge in this field. Adequate information may permit now to adjust lifestyle and lower the risk of human disease stemming from this entire class of aryl and HCA.

Inhibition of 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral carcinogenesis in hamsters by tea and curcumin

Tea is one of the most popular beverages consumed in the world. Curcumin, the major yellow pigment in turmeric, is used widely as a spice and food-coloring agent. In this study, we studied the effects of tea and curcumin on 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral carcinogenesis in hamsters. DMBA solution (0.5% in mineral oil, 0.1 ml) was applied topically to the left cheek pouch of male Syrian golden hamsters 3 times/week for 6 weeks. Two days after the last treatment of DMBA, the animals received green tea (6 mg tea solids/ml) as drinking fluid, or 10 mmol curcumin applied topically 3 times/week, or the combination of green tea and curcumin treatment, or no treatment for 18 weeks. The combination of tea and curcumin significantly decreased the oral visible tumor incidence from 92.3% (24/26) to 69.2% (18/26) and the squamous cell carcinoma (SCC) incidence from 76.9% (20/26) to 42.3% (11/26). The combination of tea and curcumin also decreased the number of visible tumors and the tumor volume by 52.4 and 69.8%, as well as the numbers of SCC, dysplasic lesions and papillomas by 62.0, 37.5 and 48.7%, respectively. Green tea or curcumin treatment decreased the number of visible tumors by 35.1 or 39.6%, the tumor volume by 41.6 or 61.3% and the number of SCC by 53.3 or 51.3%, respectively. Green tea also decreased the number of dysplasic lesions. Curcumin also significantly decreased the SCC incidence. Tea and curcumin, singly or in combination, decreased the proliferation index in hyperplasia, dysplasia and papillomas. Only the combination treatment decreased the proliferation index in SCC. Tea alone and in combination with curcumin significantly increased the apoptotic index in dysplasia and SCC. Curcumin, alone and in combination with tea, significantly inhibited the angiogenesis in papilloma and SCC. The results suggested that green tea and curcumin had inhibitory effects against oral carcinogenesis at the post-initiation stage and such inhibition may be related to the suppression of cell proliferation, induction of apoptosis and inhibition of angiogenesis.

Activation of polycyclic aromatic hydrocarbon trans-dihydrodiol proximate carcinogens by human aldo-keto reductase (AKR1C) enzymes and their functional overexpression in human lung carcinoma (A549) cells

Polycyclic aromatic hydrocarbons (PAH) are environmental pollutants and suspected human lung carcinogens. In patients with non-small cell lung carcinoma, differential display shows that aldo-keto reductase (AKR1C) transcripts are dramatically overexpressed. However, whether AKR1C isoforms contribute to the carcinogenic process and oxidize potent PAH trans-dihydrodiols (proximate carcinogens) to reactive and redox active o-quinones is unknown; nor is it known whether these reactions occur in human lungs. We now show that four homogeneous human recombinant aldo-keto reductases (AKR1C1-AKR1C4) are regioselective and oxidize only the relevant non-K region trans-dihydrodiols. However, these enzymes are not stereo-selective, since they oxidized 100% of these racemic substrates. The highest utilization ratios (V(max)/K(m)) were observed for some of the most potent proximate carcinogens known (e.g. 7,12-dimethylbenz[a]anthracene-3,4-diol (DMBA-3,4-diol) and benzo[g]chrysene-11,12-diol). In vitro, DMBA-3,4-diol was oxidized by AKR1C4 to the highly reactive 7,12-dimethylbenz[a]anthracene-3,4-dione (DMBA-3,4-dione), which was trapped in situ as its mono- and bis-thioether conjugates, which arise from the sequential 1,6- and 1,4-Michael addition of thiol nucleophiles. Human multiple tissue expression array analysis showed that AKR1C isoform transcripts were highly expressed in the human lung carcinoma cell line A549. Isoform-specific reverse transcriptase-PCR showed that AKR1C1, AKR1C2, and AKR1C3 transcripts were all expressed. Western blot analysis and functional assays confirmed high expression of AKR1C protein and enzyme activity in these lung cells. A549 cell lysates were found to convert DMBA-3,4-diol to the corresponding o-quinone. In trapping experiments, LC/MS analysis identified peaks in the cell lysates that corresponded to the synthetically prepared mono- and bis-thioether conjugates of DMBA-3,4-dione. This quinone is one of the most electrophilic and redox-active o-quinones produced by AKRs. Its unique ability to form bis-thioether conjugates parallels the formation of bis- and tris-glutathionyl conjugates of hydroquinone, which display end organ toxicity. The ability to measure DMBA-3,4-dione formation in A549 cells implicates the AKR pathway in the metabolic activation of PAH in human lung.

Analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine and DNA strand breaks in white blood cells of occupationally exposed workers: comparison with ambient monitoring, urinary metabolites and enzyme polymorphisms

The relationship between biomarkers of effect (8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo, HPLC system) and tail extent moment (comet assay)), markers of external and internal exposure, and biomarkers of susceptibility was evaluated for coke-oven and graphite-electrode-producing plant workers exposed to polycyclic aromatic hydrocarbons (PAHs). Mean 8-oxodGuo levels in white blood cells (WBC) of exposed workers were between 1.38 times (coke-oven, n = 20; P < 0.01) and 2.15 times (graphite-electrode-producing plant, n = 30; P < 0.01) higher than levels found in control samples (mean +/- SD 0.52 +/- 0.16 8-oxodGuo/10(5) dGuo, n = 47). The mean tail extent moment in lymphocytes was 1.38 times higher for coke-oven workers (n = 19; P = 0.09) and 3.13 times higher for graphite-electrode-producing plant workers (n = 29; P < 0.01) when compared with controls (mean plus minus SD 2.54 +/- 0.68, n = 32). Elevated tail extent moments (>3.73) were found in the majority (84%) of PAH-exposed workers showing increased DNA adduct levels (>0.78 8-oxodGuo/10(5) dGuo). However, no association (P > 0.05) was found between DNA damage (8-oxodGuo/10(5) dGuo or tail extent moment) in WBC of all PAH-exposed workers and either benzo[a]pyrene levels or the sum of 16 PAH levels in the air at work place. Furthermore, no relation (P > 0.05) could be established between DNA damage in WBC and biomarkers of internal exposure (1-hydroxypyrene (1-OHP) and sum of five hydroxyphenanthrenes (OHPHs)). Higher exposure to airborne pyrene and phenanthrene led to increasing concentrations of the metabolites 1-OHP (P < 0.01) and the sum of five OHPHs (P < 0.01) in the urine of PAH-exposed workers. The polymorphisms of genes CYP1A1, GSTM1, GSTT1 and GSTP1 (biomarkers of susceptibility) showed no association with biomarkers of effect. In conclusion, both biomarkers of effect may be appropriate for further surveillance studies of workers under PAH exposure.

Avicins, a family of triterpenoid saponins from Acacia victoriae (Bentham), suppress H-ras mutations and aneuploidy in a murine skin carcinogenesis model

We tested the ability of avicins, a family of triterpenoid saponins obtained from Acacia victoriae (Bentham) (Leguminosae: Mimosoideae), to inhibit chemically induced mouse skin carcinogenesis. Varying doses of avicins were applied to shaved dorsal skin of SENCAR mice 15 min before application of 100 nmol of 7,12-dimethylbenz[a]anthracene (DMBA) twice a week for 4 weeks (complete carcinogenesis model). The dorsal skin of a second group of mice was treated with one dose of 10 nmol of DMBA. Avicins were then applied 15 min before repetitive doses of 2 microg of phorbol 12-tetradecanoate 13-acetate (TPA) twice a week for 8 weeks (initiation/promotion model). At 12 weeks, avicins produced a 70% decrease in the number of mice with papillomas and a greater than 90% reduction in the number of papillomas per mouse in both protocols. We also observed a 62% and 74% reduction by avicins in H-ras mutations at codon 61 in the DMBA and DMBA/TPA models, respectively, as well as a significant inhibition of the modified DNA base formation (8-OH-dG) in both protocols. Marked suppression of aneuploidy occurred with treatment at 16 weeks in the initiation/promotion experiment. These findings, when combined with the proapoptotic property of these compounds and their ability to inhibit hydrogen peroxide (H(2)O(2)) generation, nuclear factor-kappaB (NF-kappaB) activation, and inducible nitric oxide synthase (iNOS) induction reported elsewhere, suggest that avicins could prove exciting in reducing oxidative and nitrosative stress and thereby suppressing the development of human skin cancer and other epithelial malignancies.

Comparison of iron-catalyzed DNA and lipid oxidation

Lipid and DNA oxidation catalyzed by iron(II) were compared in HEPES and phosphate buffers. Lipid peroxidation was examined in a sensitive liposome system constructed with a fluorescent probe that allowed us to examine the effects of both low and high iron concentrations. With liposomes made from synthetic 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine or from rat liver microsomal lipid, lipid peroxidation increased with iron concentration up to the range of 10--20 microM iron(II), but then rates decreased with further increases in iron concentration. This may be due to the limited amount of lipid peroxides available in liposomes for oxidation of iron(II) to generate equimolar iron(III), which is thought to be important for the initation of lipid peroxidation. Addition of hydrogen peroxide to incubations with 1--10 microM iron(II) decreased rates of lipid peroxidation, whereas addition of hydrogen peroxide to incubations with higher iron concentrations increased rates of lipid peroxidation. Thus, in this liposome system, sufficient peroxide from either within the lipid or from exogenous sources must be present to generate equimolar iron(II) and iron(III). With iron-catalyzed DNA oxidation, hydrogen peroxide always stimulated product formation. Phosphate buffer, which chelates iron but still allows for generation of hydroxyl radicals, inhibited lipid peroxidation but not DNA oxidation. HEPES buffer, which scavenges hydroxyl radicals, inhibited DNA oxidation, whereas lipid peroxidation was unaffected since presumably iron(II) and iron(III) were still available for reaction with liposomes in HEPES buffer.

The protective role of selenium on genetic damage and on cancer

Collectively, results from epidemiologic studies, laboratory bioassays, and human clinical intervention trials clearly support a protective role of selenium against cancer development. Several hypotheses have been proposed to explain these observations. Increased genomic instability, either inherent or induced by exogenous agents (mutagens or carcinogens), has been considered as a primary event leading to neoplastic transformation. This report deals specifically with the evidence for a role of selenium in the inhibition of carcinogen-induced covalent DNA adduct formation and retardation of oxidative damage to DNA, lipids and proteins, and for modulating cellular and molecular events that are critical in cell growth inhibition and in the multi-step carcinogenesis process. At present, the bulk of our knowledge on the role of selenium on genetic stability is based primarily on animal data and from studies conducted in in vitro systems. Studies performed in vitro showed that the dose and form of selenium compounds are critical factors with regard to cellular responses. Inorganic (at doses up to 10microM) and organic selenium compounds (at doses equal to or greater than 10microM) elicit distinctly different cellular responses. The recommended daily allowance (RDA) is 50-70 microgramSe per day for healthy adults; with 40 microgramSe as minimum requirement. Less than 11 microgramSe will definitely put people at risk of deficiency that would be expected to cause genetic damage. Daily doses of 100-200 microgramSe inhibited genetic damage and cancer development in humans. About 400 microgramSe per day is considered an upper limit. Clearly, doses above the RDA are needed to inhibit genetic damage and cancer. However, it has been hypothesized that the intake of excessive doses of selenium may cause oxidative damage, leading to genomic instability. The use of a cocktail consisting of selenium, and other vitamins and minerals appears to be a promising approach to inhibit genetic damage and the development of cancer. It is the author's recommendation that development of mechanism-based hypotheses that can be tested in pilot studies in different populations prior to a large-scale clinical trial in humans, is of paramount importance in order to better understand the role of selenium on genetic stability and cancer.

Factors critical to the design and execution of epidemiologic studies and description of an innovative technology to follow the progression from normal to cancer tissue

The results obtained from experimental studies of estrogen carcinogenesis need validation in epidemiologic studies. Such studies present additional challenges, however, because variations in human populations are much greater than those in experimental systems and in animal models. Because epidemiologic studies are often used to evaluate modest differences in risk factors, it is essential to minimize sources of errors and to maximize sensitivity, reproducibility, and specificity. In the first part of this chapter, critical factors in designing and executing epidemiologic studies, as well as the influence of sample collection, processing, and storage on data reliability, are discussed. One of the most important requirements is attaining sufficient statistical power to assess small genetic effects and to evaluate interactions between genetic and environmental factors. The second part of this chapter describes innovative technology, namely, Fourier transform-infrared (FT-IR) spectra of DNA that reveal major structural differences at various stages of the progression from normal to cancer tissue. The structural differences become evident from wavenumber-by-wavenumber statistical comparisons of the mean FT-IR spectra of DNA from normal to cancer tissues. This analysis has allowed distinguishing benign tissues from cancer and metastatic tissues in human breast, prostate, and ovarian cancers. This analysis, which requires less than 1 microg of DNA, is predicted to be used for detecting early cancer-related changes at the level of DNA, rather than at the cellular level.

Estrogens as endogenous genotoxic agents--DNA adducts and mutations

Estrogens induce tumors in laboratory animals and have been associated with breast and uterine cancers in humans. In relation to the role of estrogens in the induction of cancer, we examine formation of DNA adducts by reactive electrophilic estrogen metabolites, formation of reactive oxygen species by estrogens and the resulting indirect DNA damage by these oxidants, and, finally, genomic and gene mutations induced by estrogens. Quinone intermediates derived by oxidation of the catechol estrogens 4-hydroxyestradiol or 4-hydroxyestrone may react with purine bases of DNA to form depurinating adducts that generate highly mutagenic apurinic sites. In contrast, quinones of 2-hydroxylated estrogens produce less harmful, stable DNA adducts. The catechol estrogen metabolites may also generate potentially mutagenic oxygen radicals by metabolic redox cycling or other mechanisms. Several types of indirect DNA damage are caused by estrogen-induced oxidants, such as oxidized DNA bases, DNA strand breakage, and adduct formation by reactive aldehydes derived from lipid hydroperoxides. Estradiol and the synthetic estrogen diethylstilbestrol also induce numerical and structural chromosomal aberrations and several types of gene mutations in cells in culture and in vivo. In conclusion, estrogens, including the natural hormones estradiol and estrone, must be considered genotoxic carcinogens on the basis of the evidence outlined in this chapter.

Developmental, cellular, and molecular basis of human breast cancer

Breast cancer, which is the most common neoplastic disease in females and accounts for up to one third of all new cases of women's cancer in North America, continues to rise in incidence. In addition, the mortality caused by this disease has remained almost unchanged for the past 5 decades, becoming only second to lung cancer as a cause of cancer-related death. The failure in eradicating this disease is largely due to the lack of identification of a specific etiologic agent, the precise time of initiation, and the molecular mechanisms responsible for cancer initiation and progression. Despite the numerous uncertainties surrounding the origin of cancer, there is substantial evidence that breast cancer risk relates to endocrinologic and reproductive factors. The development of breast cancer strongly depends on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. However, the specific hormone or hormone combinations responsible for cancer initiation have not been identified, and their role as protective or risk factors is still incompletely understood. A highly significant female hormone is estrogen, which is involved in the development of a variety of cancers, but it is still unclear whether estrogens are carcinogenic to the human breast. An understanding of whether estrogens cause mutations, and, if so, whether they act through hormonal effects activated by receptor binding, cytochrome P450-mediated metabolic activation, or compromise the DNA repair system, is essential for determining whether this steroid hormone is involved in the initiation or progression of breast cancer. This knowledge has to be based on a multidisciplinary approach encompassing studies of the development of the breast, influence of hormones on the differentiation of individual structures, and their interrelations in the pathogenesis of breast cancer. The analysis of the mechanisms involved would require confirmation in the adequate in vitro models and determination of the role played by genomic alterations in both cancer initiation and progression.

Cancer risk related to mammary gland structure and development

The breast undergoes dramatic changes in size, shape, and function in association with growth, reproduction, and post-menopausal regression. Those changes impact women's lifetime breast cancer risk. An early first full-term pregnancy exerts a protective effect, emphasizing the need for understanding the role of reproductive influences on breast development and on cancer initiation and progression, and providing a paradigm for developing preventive strategies based on physiological principles. Even though the cause of breast cancer and the ultimate mechanisms through which an early pregnancy protects from cancer development remain largely unknown, a likely explanation for this protection has been provided by experimental in vivo and in vitro models. These studies have led to the conclusions that cancer initiation requires the interaction of a carcinogen with an undifferentiated and highly proliferating mammary epithelium, whereas differentiation of the mammary gland inhibits carcinogenic initiation. The process of mammary gland differentiation is the result of complex interactions of ovarian, pituitary, and placental hormones, which in turn induce inhibition of cell proliferation, downregulation of estrogen and progesterone receptors, activation of specific genes, such as inhibin, mammary derived growth factor inhibitor and a serpin-like gene, and expression of extracellular matrix proteins in the normal breast. Cell immortalization and transformation are associated with the expression of ferritin H and S100P protein, which serve as markers of cancer initiation. Comparative studies of normal and neoplastic breast development have unraveled similarities with experimental models that validate the extrapolation of findings for testing hypotheses on the initiation and progression of breast cancer.

Evidence that error-prone DNA repair converts dibenzo[a,l]pyrene-induced depurinating lesions into mutations: formation, clonal proliferation and regression of initiated cells carrying H-ras oncogene mutations in early preneoplasia

Initiation of skin tumors in mice is associated with the formation of oncogenic mutations in the H-ras gene. Mice treated on the dorsal skin with the potent polycyclic aromatic hydrocarbon (PAH) carcinogen dibenzo[a,l]pyrene (DB[a,l]P) form papillomas carrying the H-ras codon 61 (CAA to CTA) mutations. These mutations are induced in early preneoplastic skin within 1 day after DB[a,l]P treatment (Oncogene 16 (1998) 3203-3210) and appear to be related to DB[a,l]P-Ade-depurinating adducts (Proc. Natl. Acad. Sci. U. S. A. 92 (1995) 10422-10426). The rapid kinetics of mutation induction suggests that abasic sites generated from base depurination may undergo error-prone excision repair in pre-S-phase cells to induce these mutations. Analysis of mutations in the H-ras exon 1 and 2 region in DB[a,l]P-treated early preneoplastic skin indicated great changes in mutation spectra in the preneoplastic period. The initial spectra contained abundant A-->G mutations, which frequently occurred 3' to a putative conserved sequence (TGN-doublet). These mutations appeared to be induced initially as mismatched (G.T) heteroduplexes and then converted into double-stranded mutations by one round of replication. Unlike the A-->G mutations found in DB[a, l]P-treated skin (which forms 99% depurinating adducts), A-->G mutations found in anti-DB[a,l]P-diol epoxide-treated skin (forms 97% stable adducts) did not appear to be G.T heteroduplexes. These results, therefore, suggest that under these conditions, the repair errors occurred only from abasic sites but not from stable adducts. Initiated cells carrying specific oncogenic mutations, formed presumably by misrepair, underwent rapid clonal expansion and regression (transient clonoplasia). The multiplication of initiated stem cells during transient clonoplasia may be a factor determining the tumor-initiating potential of some PAH carcinogens.

Single 8-oxo-guanine and 8-oxo-adenine lesions induce marked changes in the backbone structure of a 25-base DNA strand

Structural changes in a 25-base DNA strand, induced by single 8-oxo-guanine or 8-oxo-adenine substitutions, were shown by using Fourier transform-infrared spectroscopy with multivariate statistics. Pronounced differences were demonstrated between the parent and derivatives with respect to base interactions and changes in the phospho-deoxyribose backbone. The greatest degree of change in the backbone likely occurred immediately adjacent to the 8-oxo group, potentially altering the stereochemistry at a distance. The 8-oxo lesions, formed from reactive oxygen species (e.g., hydroxyl radicals), may appreciably alter the conformational properties of strands at the replication fork, thus affecting the selectivity of polymerases, the proofreading capability of repair enzymes, and the fidelity of the transcriptional machinery.