Carcinogen-induced mutations in the mouse c-Ha-ras gene provide evidence of multiple pathways for tumor progression

Primary Prevention and Interception Studies in RAS-Mutated Tumor Models Employing Small Molecules or Vaccines

Therapeutic targeting of RAS-mutated cancers is difficult, whereas prevention or interception (treatment before or in the presence of preinvasive lesions) preclinically has proven easier. In the A/J mouse lung model, where different carcinogens induce tumors with different KRAS mutations, glucocorticoids and retinoid X receptor (RXR) agonists are effective agents in prevention and interception studies, irrespective of specific KRAS mutations. In rat azoxymethane-induced colon tumors (45% KRAS mutations), cyclooxygenase 1/2 inhibitors and difluoromethylornithine are effective in preventing or intercepting KRAS-mutated or wild-type tumors. In two KRAS-mutant pancreatic models multiple COX 1/2 inhibitors are effective. Furthermore, combining a COX and an EGFR inhibitor prevented the development of virtually all pancreatic tumors in transgenic mice. In the N-nitroso-N-methylurea-induced estrogen receptor-positive rat breast model (50% HRAS mutations) various selective estrogen receptor modulators, aromatase inhibitors, EGFR inhibitors, and RXR agonists are profoundly effective in prevention and interception of tumors with wild-type or mutant HRAS, while the farnesyltransferase inhibitor tipifarnib preferentially inhibits HRAS-mutant breast tumors. Thus, many agents not known to specifically inhibit the RAS pathway, are effective in an organ specific manner in preventing or intercepting RAS-mutated tumors. Finally, we discuss an alternative prevention and interception approach, employing vaccines to target KRAS.

Treatment with LEDs at a wavelength of 642 nm enhances skin tumor proliferation in a mouse model

Photobiomodulation (PBM) is attracting increased attention in the fields of dermatology and cosmetics. PBM with a variety of light parameters has been used widely in skin care, but can cause certain types of unwanted cells to proliferate in the skin; this can lead to skin tumors, such as papillomas and cancers. We constructed a mouse model of human skin tumors using DMBA as an initiator and TPA as a promoter, and confirmed that LEDs with a wavelength of 642 nm (red light) increased tumor size, epidermal thickness, and systemic proinflammatory cytokine levels. These results indicated that skin tumor cell proliferation may result from the use of 642 nm LEDs, suggesting the need for regulation of skin care based on LED light therapy.

Current status of targeted microbubbles in diagnostic molecular imaging of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is often associated with a poor prognosis due to silent onset, resistance to therapies, and rapid spreading. Most patients are ineligible for curable surgery as they present with advanced disease at the time of diagnosis. Present diagnostic methods relying on anatomical changes have various limitations including difficulty to discriminate between benign and malignant conditions, invasiveness, the ambiguity of imaging results, or the inability to detect molecular biomarkers of PDAC initiation and progression. Therefore, new imaging technologies with high sensitivity and specificity are critically needed for accurately detecting PDAC and noninvasively characterizing molecular features driving its pathogenesis. Contrast enhanced targeted ultrasound (CETUS) is an upcoming molecular imaging modality that specifically addresses these issues. Unlike anatomical imaging modalities such as CT and MRI, molecular imaging using CETUS is promising for early and accurate detection of PDAC. The use of molecularly targeted microbubbles that bind to neovascular targets can enhance the ultrasound signal specifically from malignant PDAC tissues. This review discusses the current state of diagnostic imaging modalities for pancreatic cancer and places a special focus on ultrasound targeted-microbubble technology together with its clinical translatability for PDAC detection.

Clues to the non-carcinogenicity of certain N-Nitroso compounds: Role of alkylated DNA bases

N-Nitroso compounds (NOC) are known for the carcinogenicity of most members. However, 13% of 332 NOC reviewed in 1984 were found to be non-carcinogenic. The non-carcinogenicity of all N-nitrosamines with even one tertiary alkyl group is notable. Clues to the lack of carcinogenicity include (a) inability to generate the reactive ultimate carcinogen which alkylates DNA bases, and (b) inability of the alkylated DNA base to mispair during DNA replication. This DFT study probes a three-stage process for the induction of mutations, including (a) N-deprotonation of O-alkylated DNA bases formed by attack of the carcinogen, (b) adoption of a conformer by the O-alkylated base conducive to mutagenic base mispairing, and (c) creation of the base mismatch involving the O-alkylated base. These three criteria are applied to the products of methylation, ethylation, isopropylation and tert-butylation at the N7-G, O6-G and O4-T sites. The N-deprotonation criterion differentiates the non-mutagenic N7-alkylguanines from the promutagenic O6-alkylguanines and O4-alkylthymines. All the O-alkylated bases except O4-tert-butylthymine are predicted as capable of adopting a conformer conducive to successful mispairing. O4-tert-butylthymine is predicted as incapable of creating a base mismatch by H-bonding with guanine, pointing to the non-mutagenic effects of tert-butylation of the O4-T site. By extrapolating to all tertiary alkyl groups, this explains why tert-alkylating N-nitrosamines are carcinogenically inactive. These results also highlight the carcinogenic role of alkylation at the O4-T site rather than at the O6-G site.

Calcium Fructoborate Prevents Skin Cancer Development in Balb-c Mice

Tumor microenvironment, genetic, and non-genetic factors are responsible for the atypical metabolic feature of cancer cells. Aberrant activity of PI3K/Akt pathway, increased glycolytic flux, and decreased intracellular pH gradient are the leading causes of this feature. Calcium Fructoborate (CaFB), a sugar-borate ester, has major benefits for human health. The aim of this study was to explore the implication of CaFB on experimentally induced skin cancer in vivo. According to the treatment, 92 female Balb-c mice are divided into six groups: control, CaFB (3 mg/kg/day), 7,12-Dimethylbenz(a)anthracene (DMBA)+12-O-tetradecanoylphorbol-13-acetate (TPA) (97.5 nmol DMBA, 6.5 nmol TPA), T1: CaFB+DMBA+TPA (3 mg/kg/day CaFB together with DMBA), T2: DMBA+CaFB+TPA (3 mg/kg/day CaFB together with TPA), T3: DMBA+TPA+CaFB (3 mg/kg/day CaFB after tumor formation). Topical DMBA and TPA application resulted in a significant increase in the protein levels, immunoreactivity, and mRNA expression of HRAS, HIF1α, Akt, and PTEN (p < 0.05). Moreover, an increase in the number of TUNEL-positive cells was observed in DMBA-TPA group compared with the control group (p < 0.05). CaFB application reduced the protein levels, immunoreactivity, and mRNA expressions of HRAS, HIF1α, Akt, and PTEN and also decreased the number of TUNEL-positive cells. Recent evidence obtained from our study validated that CaFB treatment may have skin cancer-preventing effect.

PP2A Deficiency Enhances Carcinogenesis of Lgr5+ Intestinal Stem Cells Both in Organoids and In Vivo

In most cancers, cellular origin and the contribution of intrinsic and extrinsic factors toward transformation remain elusive. Cell specific carcinogenesis models are currently unavailable. To investigate cellular origin in carcinogenesis, we developed a tumorigenesis model based on a combination of carcinogenesis and genetically engineered mouse models. We show in organoids that treatment of any of three carcinogens, DMBA, MNU, or PhIP, with protein phosphatase 2A (PP2A) knockout induced tumorigenesis in Lgr5⁺ intestinal lineage, but not in differentiated cells. These transformed cells increased in stem cell signature, were upregulated in EMT markers, and acquired tumorigenecity. A mechanistic approach demonstrated that tumorigenesis was dependent on Wnt, PI3K, and RAS-MAPK activation. In vivo combination with carcinogen and PP2A depletion also led to tumor formation. Using whole-exome sequencing, we demonstrate that these intestinal tumors display mutation landscape and core driver pathways resembling human intestinal tumor in The Cancer Genome Atlas (TCGA). These data provide a basis for understanding the interplay between extrinsic carcinogen and intrinsic genetic modification and suggest that PP2A functions as a tumor suppressor in intestine carcinogenesis.

Mouse-Derived Isograft (MDI) In Vivo Tumor Models II. Carcinogen-Induced cMDI Models: Characterization and Cancer Therapeutic Approaches

In this second study, we established syngeneic in vivo models named carcinogen-induced mouse-derived isografts (cMDIs). Carcinogen-induced tumors were obtained during short-term observation (3–9 months) of CBA/J mice treated with various administration routes with 3-methylcholanthrene (MCA) or N-methyl-N-nitrosourea (MNU) as carcinogens. During necropsy, primary tumors and suspicious tissues were assessed macroscopically and re-transplanted (in PDX-like manner) into sex-matched syngeneic animals. Outgrowing tumors were histologically characterized as either spinocellular carcinoma (1/8) or various differentiated sarcomas (7/8). Growth curves of four sarcomas showed striking heterogeneity. These cMDIs were further characterized by flow cytometry, RNA sequencing, or efficacy studies. A variable invasion of immune cells into the tumors, as well as varying expression of tyrosine kinase receptor, IFN-γ signature, or immune cell population marker genes could be observed. Immune checkpoint inhibitor treatment (anti-mPD-1, anti-mCTLA-4, or a combination thereof) showed different responses in the various cMDI models. In general, cMDI models are carcinogen-induced tumors of low passage number that were propagated as tissue pieces in mice without any tissue culturing. Therefore, the tumors contained conserved tumor characteristics and intratumoral immune cell populations. In contrast to the previously described spontaneous MDI, carcinogen induction resulted in a greater number of individual but histologically related tumors, which were preferentially sarcomas.

A Polymorphic Variant in p19Arf Confers Resistance to Chemically Induced Skin Tumors by Activating the p53 Pathway

Identification of the specific genetic variants responsible for the increased susceptibility to familial or sporadic cancers is important. Using a forward genetics approach to map such loci in a mouse skin cancer model, we previously identified a strong genetic locus, Stmm3, conferring resistance to chemically induced skin papillomas on chromosome 4. Here, we report the cyclin-dependent kinase inhibitor gene Cdkn2a/p19^Arf as a major responsible gene for the Stmm3 locus. We provide evidence that the function of Stmm3 is dependent on p53 and that p19^ArfMSM confers stronger resistance to papillomas than p16^Ink4aMSMin vivo. In addition, we found that genetic polymorphism in p19^Arf between a resistant strain, MSM/Ms (Val), and a susceptible strain, FVB/N (Leu), alters the susceptibility to papilloma development, malignant conversion, and the epithelial-mesenchymal transition. Moreover, we demonstrated that the p19^ArfMSM allele more efficiently activates the p53 pathway than the p19^ArfFVB allele in vitro and in vivo. Furthermore, we found polymorphisms in CDKN2A in the vicinity of a polymorphism in mouse Cdkn2a associated with the risk of human cancers in the Japanese population. Genetic polymorphisms in Cdkn2a and CDKN2A may affect the cancer risk in both mice and humans.

Time-Series Analysis of Tumorigenesis in a Murine Skin Carcinogenesis Model

Recent years have witnessed substantial progress in understanding tumor heterogeneity and the process of tumor progression; however, the entire process of the transition of tumors from a benign to metastatic state remains poorly understood. In the present study, we performed a prospective cancer genome-sequencing analysis by employing an experimental carcinogenesis mouse model of squamous cell carcinoma to systematically understand the evolutionary process of tumors. We surgically collected a part of a lesion of each tumor and followed the progression of these tumors in vivo over time. Comparative time-series analysis of the genomes of tumors with different fates, i.e., those that eventually metastasized and regressed, suggested that these tumors acquired and inherited different mutations. These findings suggest that despite the occurrence of an intra-tumor selection event for malignant alteration during the transformation from early- to late-stage papilloma, the fate determination of tumors might be determined at an even earlier stage.

Chemical Carcinogenesis Models of Cancer: Back to the Future

Over a century has elapsed since the first demonstration that exposure to chemicals in coal tar can cause cancer in animals. These observations provided an essential causal mechanistic link between environmental chemicals and increased risk of cancer in human populations. Mouse models of chemical carcinogenesis have since led to the concept of multistage tumor development through distinct stages of initiation, promotion, and progression and identified many of the genetic and biological events involved in these processes. Recent breakthroughs in DNA sequencing have now given us tools to dissect complete tumor genome architectures and revealed that chemically induced cancers in the mouse carry a high point mutation load and mutation signatures that reflect the causative agent used for tumor induction. Chemical carcinogenesis models may therefore provide a route to identify the causes of mutation signatures found in human cancers and further inform studies of therapeutic drug resistance and responses to immunotherapy, which are dependent on mutation load and genetic heterogeneity.

Carcinogen-specific mutations in preferred Ras-Raf pathway oncogenes directed by strand bias

Carcinogen exposures inscribe mutation patterns on cancer genomes and sometimes bias the acquisition of driver mutations toward preferred oncogenes, potentially dictating sensitivity to targeted agents. Whether and how carcinogen-specific mutation patterns direct activation of preferred oncogenes remains poorly understood. Here, mouse models of breast cancer were exploited to uncover a mechanistic link between strand-biased mutagenesis and oncogene preference. When chemical carcinogens were employed during Wnt1-initiated mammary tumorigenesis, exposure to either 7,12-dimethylbenz(a)anthracene (DMBA) or N-ethyl-N-nitrosourea (ENU) dramatically accelerated tumor onset. Mammary tumors that followed DMBA exposure nearly always activated the Ras pathway via somatic Hras(CAA61CTA) mutations. Surprisingly, mammary tumors that followed ENU exposure typically lacked Hras mutations, and instead activated the Ras pathway downstream via Braf(GTG636GAG) mutations. Hras(CAA61CTA) mutations involve an A-to-T change on the sense strand, whereas Braf(GTG636GAG) mutations involve an inverse T-to-A change, suggesting that strand-biased mutagenesis may determine oncogene preference. To examine this possibility further, we turned to an alternative Wnt-driven tumor model in which carcinogen exposures augment a latent mammary tumor predisposition in Apc(min) mice. DMBA and ENU each accelerated mammary tumor onset in Apc(min) mice by introducing somatic, "second-hit" Apc mutations. Consistent with our strand bias model, DMBA and ENU generated strikingly distinct Apc mutation patterns, including stringently strand-inverse mutation signatures at A:T sites. Crucially, these contrasting signatures precisely match those proposed to confer bias toward Hras(CAA61CTA) versus Braf(GTG636GAG) mutations in the original tumor sets. Our findings highlight a novel mechanism whereby exposure history acts through strand-biased mutagenesis to specify activation of preferred oncogenes.

Locally advanced rectal cancers with simultaneous occurrence of KRAS mutation and high VEGF expression show invasive characteristics

In this study, we investigated the mutation status of KRAS gene in pretherapeutic and preoperative biopsies in 63 specimens of locally advanced rectal cancers in order to evaluate its potential predictive and/or prognostic role. Regions of interest of KRAS exon 2 were amplified and visualized on 2% agarose gel. Obtained PCR products were subjected to direct sequencing. KRAS mutations were detected in 35% of patients, 91% of which were located in codon 12 and 9% in codon 13. In general, KRAS mutation status did not affect the response to neoadjuvant chemoradiotherapy (CRT). However, patients harboring mutated KRAS gene, simultaneously with high vascular endothelial growth factor (VEGF) expression, exhibited a worse response to CRT (p=0.030), a more frequent appearance of local recurrences and distant metastasis (p=0.003), and shorter overall survival (p=0.001) compared to all others. On the contrary, patients with GGT>GCT KRAS mutation exhibited a significantly better response to CRT than those with any other type of KRAS mutation (p=0.017). Moreover, the presence of GGT>GCT mutation was associated with low VEGF and Ki67 expression (p=0.012 in both cases), parameters related to less aggressiveness of the disease. Our results suggest that KRAS mutation status could have some predictive and prognostic importance in rectal cancer when analyzed together with other parameters, such as VEGF and Ki67 expression. In addition, it seems that not only the presence but the type of KRAS mutation is important for examining its impact on CRT response.

Animal Models of Chemical Carcinogenesis: Driving Breakthroughs in Cancer Research for 100 Years

The identification of carcinogens in the workplace, diet, and environment through chemical carcinogenesis studies in animals has directly contributed to a reduction of cancer burden in the human population. Reduced exposure to these carcinogens through lifestyle changes, government regulation, or change in industry practices has reduced cancer incidence in exposed populations. In addition to providing the first experimental evidence for cancer's relationship to chemical and radiation exposure, animal models of environmentally induced cancer have and will continue to provide important insight into the causes, mechanisms, and conceptual frameworks of cancer. More recently, combining chemical carcinogens with genetically engineered mouse models has emerged as an invaluable approach to study the complex interaction between genotype and environment that contributes to cancer development. In the future, animal models of environmentally induced cancer are likely to provide insight into areas such as the epigenetic basis of cancer, genetic modifiers of cancer susceptibility, the systems biology of cancer, inflammation and cancer, and cancer prevention.

Modeling cutaneous squamous carcinoma development in the mouse

Cutaneous squamous cell carcinoma (SCC) is one of the most common cancers in Caucasian populations and is associated with a significant risk of morbidity and mortality. The classic mouse model for studying SCC involves two-stage chemical carcinogenesis, which has been instrumental in the evolution of the concept of multistage carcinogenesis, as widely applied to both human and mouse cancers. Much is now known about the sequence of biological and genetic events that occur in this skin carcinogenesis model and the factors that can influence the course of tumor development, such as perturbations in the oncogene/tumor-suppressor signaling pathways involved, the nature of the target cell that acquires the first genetic hit, and the role of inflammation. Increasingly, studies of tumor-initiating cells, malignant progression, and metastasis in mouse skin cancer models will have the potential to inform future approaches to treatment and chemoprevention of human squamous malignancies.

The molecular etiology and prevention of estrogen-initiated cancers: Ockham's Razor: Pluralitas non est ponenda sine necessitate. Plurality should not be posited without necessity

Elucidation of estrogen carcinogenesis required a few fundamental discoveries made by studying the mechanism of carcinogenesis of polycyclic aromatic hydrocarbons (PAH). The two major mechanisms of metabolic activation of PAH involve formation of radical cations and diol epoxides as ultimate carcinogenic metabolites. These intermediates react with DNA to yield two types of adducts: stable adducts that remain in DNA unless removed by repair and depurinating adducts that are lost from DNA by cleavage of the glycosyl bond between the purine base and deoxyribose. The potent carcinogenic PAH benzo[a]pyrene, dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and 3-methylcholanthrene predominantly form depurinating DNA adducts, leaving apurinic sites in the DNA that generate cancer-initiating mutations. This was discovered by correlation between the depurinating adducts formed in mouse skin by treatment with benzo[a]pyrene, dibenzo[a,l]pyrene or 7,12-dimethylbenz[a]anthracene and the site of mutations in the Harvey-ras oncogene in mouse skin papillomas initiated by one of these PAH. By applying some of these fundamental discoveries in PAH studies to estrogen carcinogenesis, the natural estrogens estrone (E1) and estradiol (E2) were found to be mutagenic and carcinogenic through formation of the depurinating estrogen-DNA adducts 4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua. These adducts are generated by reaction of catechol estrogen quinones with DNA, analogously to the DNA adducts obtained from the catechol quinones of benzene, naphthalene, and the synthetic estrogens diethylstilbestrol and hexestrol. This is a weak mechanism of cancer initiation. Normally, estrogen metabolism is balanced and few estrogen-DNA adducts are formed. When estrogen metabolism becomes unbalanced, more catechol estrogen quinones are generated, resulting in higher levels of estrogen-DNA adducts, which can be used as biomarkers of unbalanced estrogen metabolism and, thus, cancer risk. The ratio of estrogen-DNA adducts to estrogen metabolites and conjugates has repeatedly been found to be significantly higher in women at high risk for breast cancer, compared to women at normal risk. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of breast cancer. Significantly higher adduct ratios have been observed in women with breast, thyroid or ovarian cancer. In the women with ovarian cancer, single nucleotide polymorphisms in the genes for two enzymes involved in estrogen metabolism indicate risk for ovarian cancer. When polymorphisms produce high activity cytochrome P450 1B1, an activating enzyme, and low activity catechol-O-methyltransferase, a protective enzyme, in the same woman, she is almost six times more likely to have ovarian cancer. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of ovarian cancer. Significantly higher ratios of estrogen-DNA adducts to estrogen metabolites and conjugates have also been observed in men with prostate cancer or non-Hodgkin lymphoma, compared to healthy men without cancer. These results also support a critical role of estrogen-DNA adducts in the initiation of cancer. Starting from the perspective that unbalanced estrogen metabolism can lead to increased formation of catechol estrogen quinones, their reaction with DNA to form adducts, and generation of cancer-initiating mutations, inhibition of estrogen-DNA adduct formation would be an effective approach to preventing a variety of human cancers. The dietary supplements resveratrol and N-acetylcysteine can act as preventing cancer agents by keeping estrogen metabolism balanced. These two compounds can reduce the formation of catechol estrogen quinones and/or their reaction with DNA. Therefore, resveratrol and N-acetylcysteine provide a widely applicable, inexpensive approach to preventing many of the prevalent types of human cancer.

PPARβ/δ promotes HRAS-induced senescence and tumor suppression by potentiating p-ERK and repressing p-AKT signaling

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) inhibits skin tumorigenesis through mechanisms that may be dependent on HRAS signaling. The present study examined the hypothesis that PPARβ/δ promotes HRAS-induced senescence resulting in suppression of tumorigenesis. PPARβ/δ expression increased p-ERK and decreased p-AKT activity. Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ. Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression. Decreased p-AKT activity in turn promotes cellular senescence through upregulation of p53 and p27 expression. Both over-expression of RASGRP1 and shRNA-mediated knockdown of ILK partially restore cellular senescence in Pparβ/δ-null cells. Higher PPARβ/δ expression is also correlated with increased senescence observed in human benign neurofibromas and colon adenoma lesions in vivo. These results demonstrate that PPARβ/δ promotes senescence to inhibit tumorigenesis and provide new mechanistic insights into HRAS-induced cellular senescence.

"The development tumor model" to study and monitor the entire progression of both primary and metastatic tumors

Glioblastoma multiforme and other malignant cancers resulting in solid tumors continue to be devastating diseases. In order to find more effective treatments, it is necessary to cultivate a better understanding of the dynamics of tumor development in relation to both primary and secondary tumors. Although hand-held or digital caliper methods can measure tumor growth in subcutaneous xenograft models, to date, the only way to follow and monitor the progression of growing tumors in orthotopic animal models is imaging. This is not enough. To improve our knowledge of the biological characteristics that take place during tumor progression at both primary and metastatic sites, it is indispensable to develop an in vivo model which enables us to reproduce, from the beginning to the end of the cancer's natural history, what really happens in a patient affected by a solid tumor. The ideal tumor model must allow us to monitor all the stages of the tumor's development, both in the primary bulk and in secondary locations, by obtaining cells, biopsies as well as performing stainings on sections. In this paper, "the development tumor model", already proposed by the author to monitor the whole progression of the glioblastoma, is also applied to the study of all solid malignancies. It is a xenogeneic orthotopic transplantation model using human tumor-derived cells from the pre-hypoxic phase as transplanted material, which will be cultured in a neurobasal serum-free medium. By transplanting the same material at the same time (time zero) into a number of immunodeficient and genetically identical mice or rats, the model can be used to create a pool of twin animal transplant candidates under the same testing conditions. By sacrificing one animal a week (or choosing other intervals as needed) and performing multiple biopsies and stainings on sections, we can monitor the entire development of both the primary and secondary tumors. This may shed light on which specific cells and particular markers need to be focused on in order to develop innovative, valid therapeutic strategies.

BRAF inhibitors suppress apoptosis through off-target inhibition of JNK signaling

Vemurafenib and dabrafenib selectively inhibit the v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) kinase, resulting in high response rates and increased survival in melanoma. Approximately 22% of individuals treated with vemurafenib develop cutaneous squamous cell carcinoma (cSCC) during therapy. The prevailing explanation for this is drug-induced paradoxical ERK activation, resulting in hyperproliferation. Here we show an unexpected and novel effect of vemurafenib/PLX4720 in suppressing apoptosis through the inhibition of multiple off-target kinases upstream of c-Jun N-terminal kinase (JNK), principally ZAK. JNK signaling is suppressed in multiple contexts, including in cSCC of vemurafenib-treated patients, as well as in mice. Expression of a mutant ZAK that cannot be inhibited reverses the suppression of JNK activation and apoptosis. Our results implicate suppression of JNK-dependent apoptosis as a significant, independent mechanism that cooperates with paradoxical ERK activation to induce cSCC, suggesting broad implications for understanding toxicities associated with BRAF inhibitors and for their use in combination therapies. DOI: http://dx.doi.org/10.7554/eLife.00969.001.

Adaptive immunity does not strongly suppress spontaneous tumors in a Sleeping Beauty model of cancer

The tumor immunosurveillance hypothesis describes a process by which the immune system recognizes and suppresses the growth of transformed cancer cells. A variety of epidemiological and experimental evidence supports this hypothesis. Nevertheless, there are a number of conflicting reports regarding the degree of immune protection conferred, the immune cell types responsible for protection, and the potential contributions of immunosuppressive therapies to tumor induction. The purpose of this study was to determine whether the adaptive immune system actively suppresses tumorigenesis in a Sleeping Beauty (SB) mouse model of cancer. SB transposon mutagenesis was performed in either a wild-type or immunocompromised (Rag2-null) background. Tumor latency and multiplicity were remarkably similar in both immune cohorts, suggesting that the adaptive immune system is not efficiently suppressing tumor formation in our model. Exceptions included skin tumors, which displayed increased multiplicity in wild-type animals, and leukemias, which developed with shorter latency in immune-deficient mice. Overall tumor distribution was also altered such that tumors affecting the gastrointestinal tract were more frequent and hemangiosarcomas were less frequent in immune-deficient mice compared with wild-type mice. Finally, genetic profiling of transposon-induced mutations identified significant differences in mutation prevalence for a number of genes, including Uba1. Taken together, these results indicate that B and T cells function to shape the genetic profile of tumors in various tumor types, despite being ineffective at clearing SB-induced tumors. To our knowledge, this study represents the first forward genetic screen designed to examine tumor immunosurveillance mechanisms.

Antigenotoxic potencies of a lichen species, Evernia prunastri

In this article, the genotoxic and antigenotoxic effects of methanol extract of Evernia prunastri (Huds.) Willd. (MEP) were studied using WP2, Ames (TA1535 and TA1537) and sister chromatid exchange (SCE) test systems. The results obtained from bacterial test systems demonstrated that MEP has strong antimutagenic potencies on TA1537 and WP2 strains. The highest inhibition rates for MEP on TA1537 and WP2 strains were 37.70% and 69.70%, respectively. According to the SCE test system, MEP reduced the genotoxic effects of aflatoxin. In order to clarify the mechanism underlying the antigenotoxic effects of MEP, the antioxidants were determined. Cotreatments of 5, 10 and 20 µg/mL concentrations of MEP with aflatoxin B1 decreased the frequencies of SCE and the malondialdehyde level and increased amount of superoxide dismutase, glutathione and glutathione peroxidase which were decreased by aflatoxin. The data obtained from this work have clearly shown that MEP has significant antigenotoxic effects which are thought to be partly due to the antioxidant activities and antioxidant inducing capability of MEP. This is the first report indicating the antigenotoxic activities of MEP against several mutagen agents such as N-methyl-N'-nitro-N-nitrosoguanidine, acridin and aflatoxin.

The environmental and human effects of ptaquiloside-induced enzootic bovine hematuria: a tumorous disease of cattle

In this review, we address the major aspects of enzootic bovine hematuria and have placed special emphasis on describing the etiology, human health implications, and advanced molecular diagnosis of the disease.Enzootic bovine hematuria (EBH) is a bovine disease characterized by the intermittent presence of blood in the urine and is caused by malignant lesions in the urinary bladder. This incurable disease is a serious malady in several countries across many continents. Accurate early-stage diagnosis of the disease is possible by applying advanced molecular techniques, e.g., detection of genetic mutations in the urine of cows from endemic areas. Use of such diagnostic approaches may help create an effective therapy against the disease.There is a consensus that EBH is caused primarily by animals consuming bracken fern (P. aquilinum) as they graze. The putative carcinogen in bracken is ptaquiloside(PT), a glycoside. However, other bracken constituents like quercetin, isoquercetin,ptesculentoside, caudatoside, astragalin, and tannins may also be carcinogenic.Studies are needed to identify the role of other metabolites in inducing urinary bladder carcinogenesis.The bovine papilloma virus is also thought to be an associated etiology in causing EBH in cattle. There is growing alarm that these fern toxins and their metabolites reach and contaminate the soil and water environment and that the carcinogen (PT)is transmitted via cow's milk to the human food chain, where it may now pose a threat to human health. An increased incidence of gastric and esophageal cancer has been recorded in humans consuming bracken ferns, and among those living for long periods in areas infested with bracken ferns.Although preliminary therapeutic vaccine trials with inactivated BPV-2 against EBH have been performed, further work is needed to standardize and validate vaccine doses for animals.

Non-melanoma skin cancer in mouse and man

As a frontier organ, skin is exposed to different environmental and/or occupational chemicals which cause cutaneous cancers in experimental animals. In mice, 7,12-dimethylbenz[a]anthrancene (DMBA) and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) are frequently used as skin model tumor initiator and promoter, respectively. The sequential administration of DMBA and TPA leads to the appearance of a large number of benign papillomas, of which some convert later into invasive squamous cell carcinomas (SCC). At the molecular level, initiation of carcinogenesis in mouse skin consists in the mutational activation of the Ha-ras oncoprotein. HA-RAS mutations are rare in human SCC, but HA-RAS-mutated tumors appear in melanoma patients treated with B-raf inhibitors, indicating that initiated, HA-RAS-mutated stem cells also reside in human skin. Similarly, UV-induced human SCC show footprint mutations in the tumor suppressor gene TP53 which are also observed in UV-induced mouse SCC. Strong species differences exist with respect to phorbol ester-mediated tumor promotion. While certain mouse strains are very susceptible, other rodent species are much less sensitive. Likewise, humans appear to be much more resistant to phorbol ester-mediated skin toxicity. Papilloma formation as a result of a chemical insult is uncommon in men, questioning the relevance of this preneoplastic lesion for humans. However, skin tumorigenesis in the experimental situation and in humans appears to follow common molecular mechanisms, even though there are species differences in the morphological correlates to the preneoplastic state. Therefore, we recommend not simply labeling them as irrelevant for human risk assessment.

Loss of integrin α3 prevents skin tumor formation by promoting epidermal turnover and depletion of slow-cycling cells

Progression through the various stages of skin tumorigenesis is correlated with an altered expression of the integrin α3β1, suggesting that it plays an important role in the tumorigenic process. Using epidermis-specific Itga3 KO mice subjected to the 7,12-dimethylbenzanthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate two-stage skin carcinogenesis protocol, we demonstrate that efficient tumor development is critically dependent on the presence of α3β1. In the absence of α3β1, tumor initiation is dramatically decreased because of increased epidermal turnover, leading to a loss of DMBA-initiated label-retaining keratinocytes. Lineage tracing revealed emigration of α3-deficient keratinocytes residing in the bulge of the hair follicle toward the interfollicular epidermis. Furthermore, tumor growth and cell proliferation were strongly reduced in mice with an epidermis-specific deletion of Itga3. However, the rate of progression of α3β1-null squamous cell carcinomas to undifferentiated, invasive carcinomas was increased. Therefore, α3β1 critically affects skin carcinogenesis with opposing effects early and late in tumorigenesis.

KLF10, transforming growth factor-β-inducible early gene 1, acts as a tumor suppressor

Krüppel-like factor 10 (KLF10) has been suggested to be a putative tumor suppressor. In the present study, we generated KLF10 deficient mice to explore this hypothesis in vivo. KLF10 deficient mice exhibited increased predisposition to skin tumorigenesis and markedly accelerated papilloma development after DMBA/TPA treatment. On the other hand, KLF10 deficient keratinocytes showed increased proliferation and apoptosis. In colony formation assays after oncogenic H-Ras transfection, KLF10 deficient mouse embryonic fibroblasts (MEFs) yielded more colonies than wild-type MEFs. Furthermore, KLF10 dose-dependently activated p21(WAF1/CIP1) transcription, which was independent of p53 and Sp1 binding sites in p21(WAF1/CIP1) promoter. This study demonstrates that KLF10 is a tumor suppressor and that it targets p21(WAF1/CIP1) transcription.

Involvement of retrotransposition of long interspersed nucleotide element-1 in skin tumorigenesis induced by 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate

Tumor development induced by 7,12-dimethylbenz[a]anthracene (DMBA) plus 12-O-tetradecanoylphorbol-13-acetate (TPA) is a well-characterized model of multistep carcinogenesis. DMBA mutates the Ha-ras gene, whereas TPA promotes the growth of transformed cells by activating cellular signaling molecules. It remains to be clarified how repeated TPA treatment endows transformed cells with autonomous cell growth. Long interspersed nucleotide element-1 (L1) is an endogenous retroelement, and 80-100 copies of L1 function as autonomous mobile elements. Although the L1 retrotransposition (RTP) has been found in various human tumors, implying the possible mobility of L1 during carcinogenesis, little is known about how L1-RTP arises in tumor cells, owing to a lack of experimental models. To dissect the mechanism of L1-RTP during carcinogenesis, we established a line of transgenic mice carrying human L1 and enhanced green fluorescent protein (hL1-EGFP mice) and subjected them to DMBA/TPA-induced skin tumorigenesis. Of 15 skin tumors examined, 13 were positive for L1-RTP; L1-RTP was not detected in normal skin tissues adjacent to the tumors. Moreover, nine L1-RTP-positive tumors were positive for activated Ha-ras, and immunohistochemical analysis revealed cells positive for both L1-RTP and phosphorylated Stat3, a marker of tumor cells. Additional in vivo experiments suggested that L1-RTP occurred during tumor promotion by TPA. This is the first report on the involvement of L1-RTP in chemical carcinogenesis. We propose hL1-EGFP mice as a versatile system for investigating the mode of L1-RTP in tumor development and discuss the possible role of L1-RTP in tumorigenesis.

Use of the in vivo skin comet assay to evaluate the DNA-damaging potential of chemicals applied to the skin

The aim of the present study was to evaluate both sensitivity and specificity of an in vivo skin comet assay using chemically treated, hairless mouse dorsal skin as a model. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 0.0125-0.2%), 4-nitroquinoline-1-oxide (4NQO, 0.01-0.25%), mitomycin C (MMC, 0.0125-0.05%), benzo[a]pyrene (B[a]P, 0.25-2%), and 7,12-dimethylbenz[a]anthracene (DMBA, 0.25-1%) were each applied once to the dorsal skin of hairless male mice; after 3h, epidermal skin cells were isolated, and the alkaline comet assay was performed. The assay was performed after 24h for only the B[a]P and DMBA. Furthermore, B[a]P and DMBA were evaluated by alkaline comet assay using liver cells after both 3 and 24h. The mean percent of DNA (%DNA) in tail in the 0.05-0.2% MNNG and 0.1-0.25% 4NQO treatment groups was markedly higher than in the control group at 3h post-application. Although the mean %DNA values in the tail in the B[a]P and DMBA groups were the same as the controls at 3h post-application, the 2% B[a]P and 1% DMBA groups showed significantly higher values versus controls 24h after application. No significant increases in the mean %DNA in the tail were observed in the MMC group. No clear increases in %DNA in the tail were observed in the B[a]P and DMBA groups at 3 or 24h after application in the liver. These results suggest that the in vivo skin comet assay is able to accurately identify DNA-damaging potential with a skin-specific response and is a useful method to detect the DNA-damaging potential of genotoxic chemicals on the skin.

Tumor formation initiated by nondividing epidermal cells via an inflammatory infiltrate

In mammalian epidermis, integrin expression is normally confined to the basal proliferative layer that contains stem cells. However, in epidermal hyperproliferative disorders and tumors, integrins are also expressed by suprabasal cells, with concomitant up-regulation of Erk mitogen-activated protein kinase (MAPK) signaling. In transgenic mice, expression of activated MAPK kinase 1 (MEK1) in the suprabasal, nondividing, differentiated cell layers (InvEE transgenics) results in epidermal hyperproliferation and skin inflammation. We now demonstrate that wounding induces benign tumors (papillomas and keratoacanthomas) in InvEE mice. By generating chimeras between InvEE mice and mice that lack the MEK1 transgene, we demonstrate that differentiating, nondividing cells that express MEK1 stimulate adjacent transgene-negative cells to divide and become incorporated into the tumor mass. Dexamethasone treatment inhibits tumor formation, suggesting that inflammation is involved. InvEE skin and tumors express high levels of IL1α; treatment with an IL1 receptor antagonist delays tumor onset and reduces incidence. Depletion of γδ T cells and macrophages also reduces tumor incidence. Because a hallmark of cancer is uncontrolled proliferation, it is widely assumed that tumors arise only from dividing cells. In contrast, our studies show that differentiated epidermal cells can initiate tumor formation without reacquiring the ability to divide and that they do so by triggering an inflammatory infiltrate.

Ablation of TAK1 upregulates reactive oxygen species and selectively kills tumor cells

TAK1 kinase activates multiple transcription factors and regulates the level of reactive oxygen species (ROS). We have previously reported that ablation of TAK1 in keratinocytes causes hypersensitivity to ROS-induced cell apoptosis. It is known that some tumor cells produce ROS at higher levels compared with normal cells. We used inducible epidermal-specific TAK1 knockout mice and examined whether ablation of TAK1 in preexisting skin tumors could cause an increase in ROS and result in tumor cell death. Deletion of tak1 gene in skin tumors caused the accumulation of ROS and increased apoptosis, and skin tumors totally regressed within 5 to 10 days. Normal skin did not exhibit any significant abnormality on tak1 gene deletion. Thus, TAK1 kinase could be a new and effective molecular target for ROS-based tumor killing.

A review of the molecular mechanisms of chemically induced neoplasia in rat and mouse models in National Toxicology Program bioassays and their relevance to human cancer

Tumor response in the B6C3F1 mouse, F344 rat, and other animal models following exposure to various compounds provides evidence that people exposed to these or similar compounds may be at risk for developing cancer. Although tumors in rodents and humans are often morphologically similar, underlying mechanisms of tumorigenesis are often unknown and may be different between the species. Therefore, the relevance of an animal tumor response to human health would be better determined if the molecular pathogenesis were understood. The underlying molecular mechanisms leading to carcinogenesis are complex and involve multiple genetic and epigenetic events and other factors. To address the molecular pathogenesis of environmental carcinogens, the authors examine rodent tumors (e.g., lung, colon, mammary gland, skin, brain, mesothelioma) for alterations in cancer genes and epigenetic events that are associated with human cancer. National Toxicology Program (NTP) studies have identified several genetic alterations in chemically induced rodent neoplasms that are important in human cancer. Identification of such alterations in rodent models of chemical carcinogenesis caused by exposure to environmental contaminants, occupational chemicals, and other compounds lends further support that they are of potential human health risk. These studies also emphasize the importance of molecular evaluation of chemically induced rodent tumors for providing greater public health significance for NTP evaluated compounds.

A genetic variant of Aurora kinase A promotes genomic instability leading to highly malignant skin tumors

Aurora kinase A (Aurora-A) belongs to a highly conserved family of mitotis-regulating serine/threonine kinases implicated in epithelial cancers. Initially we examined Aurora-A expression levels at different stages of human skin cancer. Nuclear Aurora-A was detected in benign lesions and became more diffused but broadly expressed in well and poorly differentiated squamous cell carcinomas (SCC), indicating that Aurora-A deregulation may contribute to SCC development. To mimic the overexpression of Aurora-A observed in human skin cancers, we established a gene-switch mouse model in which the human variant of Aurora-A (Phe31Ile) was expressed in the epidermis upon topical application of the inducer RU486 (Aurora-AGS). Overexpression of Aurora-A alone or in combination with the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA), did not result in SCC formation in Aurora-AGS mice. Moreover, Aurora-A overexpression in naive keratinocytes resulted in spindle defects in vitro and marked cell death in vivo, suggesting that the failure of Aurora-A to initiate tumorigenesis was due to induction of catastrophic cell death. However, Aurora-A overexpression combined with exposure to TPA and the mutagen 7,12-dimethylbenz(a)anthracene accelerated SCC development with greater metastatic activity than control mice, indicating that Aurora-A cannot initiate skin carcinogenesis but rather promotes the malignant conversion of skin papillomas. Further characterization of SCCs revealed centrosome amplification and genomic alterations by array CGH analysis, indicating that Aurora-A overexpression induces a high level of genomic instability that favors the development of aggressive and metastatic tumors. Our findings strongly implicate Aurora-A overexpression in the malignant progression of skin tumors and suggest that Aurora-A may be an important therapeutic target.

Multi-stage chemical carcinogenesis in mouse skin: fundamentals and applications

For more than 60 years, the chemical induction of tumors in mouse skin has been used to study mechanisms of epithelial carcinogenesis and evaluate modifying factors. In the traditional two-stage skin carcinogenesis model, the initiation phase is accomplished by the application of a sub-carcinogenic dose of a carcinogen. Subsequently, tumor development is elicited by repeated treatment with a tumor-promoting agent. The initiation protocol can be completed within 1-3 h depending on the number of mice used; whereas the promotion phase requires twice weekly treatments (1-2 h) and once weekly tumor palpation (1-2 h) for the duration of the study. Using the protocol described here, a highly reproducible papilloma burden is expected within 10-20 weeks with progression of a portion of the tumors to squamous cell carcinomas within 20-50 weeks. In contrast to complete skin carcinogenesis, the two-stage model allows for greater yield of premalignant lesions, as well as separation of the initiation and promotion phases.

Increased skin carcinogenesis in caspase-activated DNase knockout mice

Caspase-activated DNase (CAD), also called DNA fragmentation factor (DFF), is the enzyme responsible for DNA fragmentation during apoptosis, a hallmark of programmed cell death. CAD/DFF has been shown to suppress radiation-induced carcinogenesis by preventing genomic instability in cells. In this study, we have investigated the role of CAD in chemical carcinogenesis using CAD-null mice and two-stage model of skin carcinogenesis. After topical treatment of mouse skin with dimethylbenz[a]anthracene (DMBA) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoting agent, there was a 4-fold increase in the number of papillomas per mouse and 50.8% increase in the incidence of papilloma formation in the CAD knockout mice compared with wild-type littermates. The papillomas in CAD-null mice grew faster and reached larger sizes. These data indicate that loss of CAD function enhances tumorigenesis induced by a chemical carcinogen in the DMBA/TPA two-stage model of skin carcinogenesis in mice.

Coexistence of different tissue tumourigenesis in an N-methyl-N-nitrosourea-induced mammary carcinoma model: a histopathological report in Sprague-Dawley rats

N-methyl- N-nitrosourea (MNU), a highly potent carginogen, is widely used to generate mammary tumours in murine species. In a model of MNU-induced mammary carcinogenesis using immature female Sprague-Dawley rats, large mammary tumours (largest dimension ≥0.5 cm) were obtained within a very short period of time. In addition, in the rats bearing MNU-induced mammary carcinomas, there were a number of tumours whose origins were not from mammary tissue but from several different tissues and from mammary non-epithelial tissue. The tumours were of mesenchymal or epithelial origin and they were located in the inguinal region. These tumours were diagnosed as fibroadenoma, combined tubular adenoma and fibroadenoma, hyperkeratotic papilloma, keratinous cyst and malignant peripheral nerve sheath tumour (MPNST) with smooth muscle differentiation. The occurrence of these other tumours in addition to the development of the mammary carcinomas may be attributed to a direct local effect of the intraperitoneal administration of MNU during the sexual development of the immature rats. In the MNU-induced mammary tumour model, coexistence of tumourigenesis in various non-mammary tissues should be considered an important factor that may interfere with experimental procedures and results and also the quality of life of the tumour-bearing animals.

C/EBPbeta represses p53 to promote cell survival downstream of DNA damage independent of oncogenic Ras and p19(Arf)

CCAAT/enhancer-binding protein-beta (C/EBPbeta) is a mediator of cell survival and tumorigenesis. When C/EBPbeta(-/-) mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19(Arf) and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19(Arf) is dramatically elevated in C/EBPbeta(-/-) epidermis and that C/EBPbeta represses a p19(Arf) promoter reporter. To determine whether p19(Arf) is responsible for the proapoptotic phenotype in C/EBPbeta(-/-) mice, C/EBPbeta(-/-);p19(Arf-/-) mice were generated. C/EBPbeta(-/-);p19(Arf-/-) mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19(Arf) is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPbeta(-/-) epidermis, we generated K14-ER:Ras;C/EBPbeta(-/-) mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPbeta(-/-) mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPbeta represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPbeta may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.

A mouse model for Costello syndrome reveals an Ang II-mediated hypertensive condition

Germline activation of H-RAS oncogenes is the primary cause of Costello syndrome (CS), a neuro-cardio-facio-cutaneous developmental syndrome. Here we describe the generation of a mouse model of CS by introduction of an oncogenic Gly12Val mutation in the mouse H-Ras locus using homologous recombination in ES cells. Germline expression of the endogenous H-RasG12V oncogene, even in homozygosis, resulted in hyperplasia of the mammary gland. However, development of tumors in these mice was rare. H-RasG12V mutant mice closely phenocopied some of the abnormalities observed in patients with CS, including facial dysmorphia and cardiomyopathies. These mice also displayed alterations in the homeostasis of the cardiovascular system, including development of systemic hypertension, extensive vascular remodeling, and fibrosis in both the heart and the kidneys. This phenotype was age dependent and was a consequence of the abnormal upregulation of the renin-Ang II system. Treatment with captopril, an inhibitor of Ang II biosynthesis, prevented development of the hypertension condition, vascular remodeling, and heart and kidney fibrosis. In addition, it partially alleviated the observed cardiomyopathies. These mice should help in elucidating the etiology of CS symptoms, identifying additional defects, and evaluating potential therapeutic strategies.

Antagonistic roles of CD4+ and CD8+ T-cells in 7,12-dimethylbenz(a)anthracene cutaneous carcinogenesis

The role that cell-mediated immune responses play during cutaneous carcinogenesis has received little attention. In this study, we evaluated the contribution of CD4(+) and CD8(+) T cells in C3H/HeN mice that were subjected to a two-stage 7,12-dimethylbenz(a)anthracene (DMBA) initiation, 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion skin carcinogenesis protocol. In CD8 knockout (CD8(-/-)) mice, allergic contact hypersensitivity to DMBA was reduced compared with wild-type (WT) C3H/HeN mice. On the other hand, CD4 knockout (CD4(-/-)) mice developed an exaggerated contact hypersensitivity response. CD4(+) T cells from DMBA contact-sensitized mice preferentially produced interleukin 4 (IL-4), IL-10, and IL-17; CD8(+) T cells, on the other hand, secreted IFN-gamma. When CD4(-/-), CD8(-/-), and WT mice were subjected to a standard two-stage DMBA/TPA cutaneous carcinogenesis protocol, the percentage of mice with tumors was much greater (P < 0.001) in CD8(-/-) mice than in WT mice. In contrast, the percentage of tumors was significantly less (P < 0.001) in CD4(-/-) mice than in WT mice. Similar results were obtained when the data were evaluated as the number of tumors per mouse. These findings indicate that (a) CD8(+) T cells are the predominant effector cells in allergic contact hypersensitivity to DMBA and that CD4(+) T cells have an inhibitory role and (b) the development of CD8(+) T cells plays a protective role in skin tumor development whereas CD4(+) T cells have the opposite effect. Manipulation of T-cell subpopulations that are induced by carcinogenic chemicals, like DMBA, could be a means of preventing skin cancers caused by these agents.

Glutathione transferase pi plays a critical role in the development of lung carcinogenesis following exposure to tobacco-related carcinogens and urethane

Human cancer is controlled by a complex interaction between genetic and environmental factors. Such environmental factors are well defined for smoking-induced lung cancer; however, the roles of specific genes have still to be elucidated. Glutathione transferase pi (GSTP) catalyzes the detoxification of electrophilic diol epoxides produced by the metabolism of polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP), a common constituent of tobacco smoke. Activity-altering polymorphisms in Gstp have therefore been speculated to be potential risk modifiers in lung cancer development. To clearly establish a role for GSTP in lung tumorigenesis, we investigated whether deletion of the murine Gstp genes (Gstp1 and Gstp2) alters susceptibility to chemically induced lung tumors following exposure to BaP, 3-methylcholanthrene (3-MC), and urethane. Gstp-null mice were found to have substantially increased numbers of adenomas relative to wild-type mice following exposure to all three compounds (8.3-, 4.3-, and 8.7-fold increase for BaP, 3-MC, and urethane, respectively). In Gstp-null mice, the capacity of pulmonary cytosol to catalyze conjugation of the BaP diol epoxide was significantly reduced. Concomitant with this, a significant increase in the level of BaP DNA adducts was measured in the lungs of null animals; however, no increase in DNA adducts was measured in the case of 3-MC exposure, suggesting that an alternative protective pathway exists. Indeed, significant differences in pulmonary gene expression profiles were also noted between wild-type and null mice. This is the first report to establish a clear correlation between Gstp status and lung cancer in vivo.

The high-risk benign tumor: evidence from the two-stage skin cancer model and relevance for human cancer

Benign tumors that form following chemical initiation and promotion in the mouse skin can be grouped into two classes. The majority of papillomas do not progress to squamous cell carcinoma (SCC), and these are designated as low-risk or terminally benign papillomas. In contrast, a much smaller group forms the true precursor to the SCC, and these have a significantly higher frequency and rate of malignant conversion than the bulk of low-risk papillomas. In standard two-stage carcinogenesis studies both tumor types are present, but grossly indistinguishable. Here we describe properties and potential origins of high-risk papillomas and discuss the relevance of this model for certain human cancers with defined premalignant states.

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.

Epidermal hyperplasia and oral carcinoma in mice overexpressing the transcription factor ATF3 in basal epithelial cells

ATF3 is a highly conserved eukaryotic transcription factor that is ubiquitously upregulated transcriptionally during cellular responses to a variety of stresses, in particular DNA damage. However, the role of ATF3 in the DNA damage response is unclear. Transgenic mice that overexpress human ATF3 in basal epithelial cells under the control of the bovine keratin 5 (K5) promoter were constructed and characterized for epidermal alterations. Strong, nuclear expression of the exogenous ATF3 protein was seen in basal cells of the epidermis, hair follicles, and oral mucosa. Hyperplastic changes in the K5-expressing, outer root sheath (ORS) cells of the hair follicle were observed in young mice, resulting in multiple layers of ORS cells in the mature follicle and large aberrantly shaped follicles. Mild hyperplasia of the interfollicular epidermis was also noted, increasing with age. However, no epidermal tumors were identified in BK5.ATF3 mice observed for 16 mo. At 16 mo of age, most transgenic mice exhibited multi-focal areas of hyperplasia and dysplasia in the oral mucosa, with cellular atypia and underlying acute inflammatory changes. Neoplastic lesions were also seen in the oral cavity of BK5.ATF3 mice, including oral squamous cell carcinoma (60% incidence) and basal cell tumors with follicular differentiation (70% incidence), but not in non-transgenic FVB/N littermates. Heterogeneous nuclear expression (or stabilization) of p53 protein was seen in some oral dysplasias, with a patchy distribution primarily in the least differentiated layers of the lesions. This represents the first indication that ATF3 may have oncogenic properties in epithelial cells.

HRAS and the Costello syndrome

Costello syndrome (CS) is a complex developmental disorder involving characteristic craniofacial features, failure to thrive, developmental delay, cardiac and skeletal anomalies and a predisposition to develop neoplasia, both benign and malignant. CS is caused by activating germline mutations in HRAS and belongs to an exciting class of genetic syndromes that are caused by perturbation of function through the Ras pathway. Some of these other syndromes include Noonan syndrome, LEOPARD syndrome, neurofibromatosis 1 and cardio-facio-cutaneous syndrome. Ras is a critical signaling hub in the cell and is activated by receptor tyrosine kinases, G-protein-coupled receptors, cytokine receptors and extracellular matrix receptors. The downstream effectors of Ras are many and control vital cellular functions including cell cycle progression, cell survival, motility, transcription, translation and membrane trafficking. Understanding the genetic etiology of CS is the first step in gaining insight to the role Ras plays in human development, cellular signaling and cancer pathogenesis.