Transgenic mouse models for the prevention of breast cancer

Breast cancer prevention research has made remarkable progress in the past decade. Much of this progress has come from clinical trials. However, in the future to test the many promising agents that are now available, pre-clinical models of breast cancer are needed. Such models are now available. Useful models include rat and mouse models, particularly, the genetically engineered mice (GEM). Many transgenic mouse models have been generated by manipulating growth factors and their receptors, cell cycle regulators, signal transduction pathways, cellular differentiation, oncogenes and tumor suppressor genes. The transgenes are induced to express in the mouse mammary glands under the control of various transgenic promoters, which have respective characteristics in expression pattern and other biological attributes. These models are providing invaluable insight on the molecular mechanisms of breast tumorigenesis. In this review, we discuss the relative relevance of the most commonly used transgenic mouse models for breast cancer prevention studies, and provide examples of how these transgenic models can be used to conduct cancer prevention research. Due to the multi-factor, multi-step nature of breast cancer, many factors should be incorporated into a valid prevention study. However, many barriers to progress must be overcome, including access to and availability of new cancer preventive drugs, and difficulties in conducting studies of combinations of preventive agents.     

Vitamin D and prostate cancer.

Classically, the actions of vitamin D have been associated with bone and mineral metabolism. More recent studies have shown that vitamin D metabolites induce differentiation and/or inhibit cell proliferation of a number of malignant and nonmalignant cell types including prostate cancer cells. Epidemiological studies show correlations between the risk factors for prostate cancer and conditions that can result in decreased vitamin D levels. The active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 (calcitriol), inhibits growth of both primary cultures of human prostate cancer cells and cancer cell lines, but the mechanism by which the cells are growth-inhibited has not been clearly defined. Initial studies suggest that calcitriol alters cell cycle progression and may also initiate apoptosis. One of the disadvantages of using vitamin D in vivo is side-effects such as hypercalcemia at doses above physiological levels. Analogs of calcitriol have been developed that have comparable or more potent antiproliferative effects but are less calcemic. Further research into the mechanisms of vitamin D action in prostate and identification of suitable analogs for use in vivo may lead to its use in the treatment or prevention of prostate cancer.     

X-linked inhibitor of apoptosis deficiency in the TRAMP mouse prostate cancer model

Deregulation of apoptotic pathways plays a central role in cancer pathogenesis. X-linked inhibitor of apoptosis protein (XIAP), is an antiapoptotic molecule, whose elevated expression has been observed in tumor specimens from patients with prostate carcinoma. Studies in human cancer cell culture models and xenograft tumor models have demonstrated that loss of XIAP sensitizes cancer cells to apoptotic stimuli and abrogates tumor growth. In view of these findings, XIAP represents an attractive antiapoptotic therapeutic target for prostate cancer. To examine the role of XIAP in an immunocompetent mouse cancer model, we have generated transgenic adenocarcinoma of the mouse prostate (TRAMP) mice that lack XIAP. We did not observe a protective effect of Xiap deficiency in TRAMP mice as measured by tumor onset and overall survival. In fact, there was an unexpected trend toward more aggressive disease in the Xiap-deficient mice. These findings suggest that alternative mechanisms of apoptosis resistance are playing a significant oncogenic role in the setting of Xiap deficiency. Our study has implications for XIAP-targeting therapies currently in development. Greater understanding of these mechanisms will aid in combating resistance to XIAP-targeting treatment, in addition to optimizing selection of patients who are most likely to respond to such treatment.     

Prostate cancer and the genomic revolution: Advances using microarray analyses

The emerging technology of microarray analysis allows the establishment of molecular portraits of prostate cancer and the discovery of novel genes involved in the carcinogenesis process. Many novel genes have already been identified using this technique, and functional analyses of these genes are currently being tested. The combination of microarray analysis with other recently developed high-throughput techniques, such as proteomics, tissue arrays, and gene promoter-methylation, especially using tissue microdissection methods, will provide us with more comprehensive insights into how prostate cancer develops and responds to gene-targeted therapies. Animal models of prostate cancer are being characterized by high throughput techniques to better define the similarities and differences between those models and the human disease, and to determine whether particular models may be useful for specific targeted therapies in pre-clinical studies. Although profiling of mRNA expression provides important information of gene expression, the development of proteomic technologies will allow for an even more precise global insight into cellular signaling and structural alterations during prostate carcinogenesis. Not only will the "omic" revolution change basic science, but it will lead to a new era of molecular medicine.     

Animal models in carotenoids research and lung cancer prevention

Numerous epidemiological studies have consistently demonstrated that individuals who eat more fruits and vegetables (which are rich in carotenoids) and who have higher serum β-carotene levels have a lower risk of cancer, especially lung cancer. However, two human intervention trials conducted in Finland and in the United States have reported contrasting results with high doses of β-carotene supplementation increasing the risk of lung cancer among smokers. The failure of these trials to demonstrate actual efficacy has resulted in the initiation of animal studies to reproduce the findings of these two studies and to elucidate the mechanisms responsible for the harmful or protective effects of carotenoids in lung carcinogenesis. Although these studies have been limited by a lack of animal models that appropriately represent human lung cancer induced by cigarette smoke, ferrets and A/J mice are currently the most widely used models for these types of studies. There are several proposed mechanisms for the protective effects of carotenoids on cigarette smoke-induced lung carcinogenesis, and these include antioxidant/prooxidant effects, modulation of retinoic acid signaling pathway and metabolism, induction of cytochrome P450, and molecular signaling involved in cell proliferation and/or apoptosis. The technical challenges associated with animal models include strain-specific and diet-specific effects, differences in the absorption and distribution of carotenoids, and differences in the interactions of carotenoids with other antioxidants. Despite the problems associated with extrapolating from animal models to humans, the understanding and development of various animal models may provide useful information regarding the protective effects of carotenoids against lung carcinogenesis.     

Effects of tea polyphenols on signal transduction pathways related to cancer chemoprevention

The inhibition of carcinogenesis by tea and tea polyphenols has been demonstrated in different animal models by many investigators. The mechanisms of this inhibitory activity have also been investigated extensively, mostly in cell culture systems, but no clear conclusion can be reached concerning the cancer preventive mechanisms in vivo. In this article, we reviewed the possible mechanisms, which include the inhibition of specific protein kinase activities, blocking receptor-mediated functions, and inhibition of proteases. These events may lead to cell cycle regulation, growth inhibition, enhanced apoptosis, inhibition of angiogenesis, and inhibition of invasion and metastases. The possible complications of translating results obtained in cell culture studies to animals and humans are discussed. It is likely that multiple signal transduction pathways are involved in the inhibition of carcinogenesis by tea constituents. The relative importance of these pathways needs to be determined in vivo.     

Modeling cancer progression via pathway dependencies

Cancer is a heterogeneous disease often requiring a complexity of alterations to drive a normal cell to a malignancy and ultimately to a metastatic state. Certain genetic perturbations have been implicated for initiation and progression. However, to a great extent, underlying mechanisms often remain elusive. These genetic perturbations are most likely reflected by the altered expression of sets of genes or pathways, rather than individual genes, thus creating a need for models of deregulation of pathways to help provide an understanding of the mechanisms of tumorigenesis. We introduce an integrative hierarchical analysis of tumor progression that discovers which a priori defined pathways are relevant either throughout or in particular steps of progression. Pathway interaction networks are inferred for these relevant pathways over the steps in progression. This is followed by the refinement of the relevant pathways to those genes most differentially expressed in particular disease stages. The final analysis infers a gene interaction network for these refined pathways. We apply this approach to model progression in prostate cancer and melanoma, resulting in a deeper understanding of the mechanisms of tumorigenesis. Our analysis supports previous findings for the deregulation of several pathways involved in cell cycle control and proliferation in both cancer types. A novel finding of our analysis is a connection between ErbB4 and primary prostate cancer.     

实验小鼠在癌症研究中的应用及其进展

小鼠是生物医学研究中使用数量最多的哺乳类实验动物。人类利用小鼠模型进行癌症研究已有100多年的历史,小鼠大量的遗传变异可作为研究人类癌症的借鉴。特别是近年来,培育成功的转基因、基因敲除等遗传工程小鼠模型,使我们对人类癌症发生有了深刻的认识,为评估癌症的诊断方法,革新预防和治疗方案提供了一个很有价值的平台。本文着重介绍了癌症研究中常用的小鼠模型、GEM模型及取得的最新进展等,分析了小鼠肿瘤模型的局限性,并对其发展趋势进行展望。     

MET-dependent cancer invasion may be preprogrammed by early alterations of p53-regulated feedforward loop and triggered by stromal cell-derived HGF

MET, a receptor protein tyrosine kinase activated by hepatocyte growth factor (HGF), is a crucial determinant of metastatic progression. Recently, we have identified p53 as an important regulator of MET-dependent cell motility and invasion. This regulation occurs via feedforward loop suppressing MET expression by miR-34-dependent and -independent mechanisms. Here, by using Dicer conditional knockout, we provide further evidence for microRNA-independent MET regulation by p53. Furthermore, we show that while MET levels increase immediately after p53 inactivation, mutant cells do not contain active phosphorylated MET and remain non-invasive for a long latency period at contrary to cell culture observations. Evaluation of mouse models of ovarian and prostate carcinogenesis indicates that formation of desmoplastic stroma, associated production of HGF by stromal cells and coinciding MET phosphorylation precede cancer invasion. Thus, initiation mutation of p53 is sufficient for preprogramming motile and invasive properties of epithelial cells, but the stromal reaction may represent a critical step for their manifestation during cancer progression.     

N-Acetylcysteine enhances the lung cancer inhibitory effect of epigallocatechin-3-gallate and forms a new adduct

The major tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), inhibits carcinogenesis in many in vivo models. Many potential mechanisms of action have been proposed based on cell line studies, including prooxidant activity. In the present study, we studied the effect of N-acetylcysteine (NAC) on the inhibitory effects of EGCG on lung cancer cell growth. We found that NAC (0-2 mM) dose dependently enhanced the growth inhibitory activity of EGCG against murine and human lung cancer cells. The combination of NAC and EGCG caused an 8.8-fold increase in apoptosis in CL13 mouse lung cancer cells compared to treatment with either agent alone. Addition of 2 mM NAC increased the stability of EGCG in the presence of CL13 cells (t 1/2=8.5 h vs 22.7 h). Intracellular levels of EGCG were increased 5.5-fold by the addition of 2 mM NAC. HPLC and LC-MS analyses of cell culture medium from CL13 cells treated with EGCG and NAC for 24 h revealed that EGCG-2'-NAC was time dependently formed. This adduct was not formed in the absence of NAC. The present results show that under cell culture conditions, EGCG and NAC interact to form a previously unreported adduct, EGCG-2'-NAC, which may contribute to enhancement of EGCG-mediated cell killing.     

Inhibition of carcinogenesis by retinoids.

Experimental investigations of the antineoplastic effects of retinoids are reviewed in this paper. In vitro studies have shown that the hyperplastic and metaplastic response to chemical carcinogens of mouse prostate cultures is suppressed by the addition of retinoids to the culture medium, that retinoids can partially inhibit the morphologic transformation of 10T 1/2 cells by physical or chemical carcinogens, and that the growth of some non-neoplastic and some neoplastic cell lines can be inhibited by retinoids. In vivo studies have shown that retinoids can suppress papilloma and carcinoma development (the promotion phase) in the two-stage skin carcinogenesis assay, inhibit mammary and bladder carcinogenesis in mice and rats, and inhibit the growth of some transplantabletumor lines. So far it has not been possible to inhibit predictably tumour formation in the intestinal tract or the respiratory tract of rodents. Almost all the synthetic retinoids have a higher therapeutic index than the natural retinoids in the prevention or treatment of cancer.     

Green tea polyphenols for prostate cancer chemoprevention: A translational perspective

Every year nearly 200,000 men in the United States are diagnosed with prostate cancer (PCa), and another 29,000 men succumb to the disease. Within certain regions of the world population based studies have identified a possible role for green tea in the prevention of certain cancers, especially PCa. One constituent in particular, epigallocatechin-3-gallate also known as EGCG has been shown in cell culture models to decrease cell viability and promote apoptosis in multiple cancer cell lines including PCa with no effect on non-cancerous cell lines. In addition, animal models have consistently shown that standardized green tea polyphenols when administered in drinking water delay the development and progression of PCa. Altogether, three clinical trials have been performed in PCa patients and suggest that green tea may have a distinct role as a chemopreventive agent. This review will present the available data for standardized green tea polyphenols in regard to PCa chemoprevention that will include epidemiological, mechanism based studies, safety, pharmacokinetics, and applicable clinical trials. The data that has been collected so far suggests that green tea may be a promising agent for PCa chemoprevention and further clinical trials of participants at risk of PCa or early stage PCa are warranted.     

Role of estrogens in development of prostate cancer

Estrogens have previously been extensively used in prostate cancer treatment. Serious side effects, primarily in cardiovascular system have, however, limited their use. The therapeutic effect of estrogen in preventing prostate cancer growth was mainly obtained indirectly by feedback inhibition of the hypothalamic release of LRH leading to lowered serum androgen levels and castration like effects. Prostate tissue is also most probably a target for direct regulation by estrogens. Prostate contains estrogen receptor alpha (ERalpha) and beta (ERbeta), which are localized characteristically in stroma and epithelium, respectively. The physiological function of these receptors is not known but there is evidence of the role of estrogens in prostatic carcinogenesis. Developing prostate seems particularly sensitive to increased level of endogenous and/or exogenous estrogens. Perinatal or neonatal exposure of rats and mice to estrogens leads to "imprinting" of prostate associated with increased proliferation, inflammation and dysplastic epithelial changes later in life. Prolonged treatment of adult rodents with estrogens along with androgens also leads to epithelial metaplasia, PIN-like lesions and even adenocarcinoma of prostate speaking for the role of estrogen in prostate cancer development. Recent results concerning antiestrogen inhibition of prostate cancer development beyond PIN-type lesions in transgenic mouse models further suggests a role for estrogens in prostate cancer progression. These results also suggest that direct inhibition of estrogen action at the level of prostate tissue may provide an important novel principle of development of prostate cancer therapies.     

Use of transgenic mice as models for prostate cancer chemoprevention

Prostate cancer is a long latency type of tumor that usually develops in men older than 50 years of age. Prostate epithelial neoplasia (PIN), the initial malignant lesion, progresses to invasive carcinoma over the course of years. Because of the particular features of prostate carcinogenesis, this type of tumor may represent a paradigm for cancer prevention. Several clinical trials have evaluated the effect of different compounds on prostate tumor development, including finasteride, selenium, vitamin E, and carotenes. Although some results are promising, no conclusive data have been achieved as to recommend any of these compounds as preventive agents. Results from some trials, such as SELECT, where supplementation of selenium and/or vitamin-E was used, have been rather disappointing. However, many novel chemopreventive agents that target different cancer-related pathways are being developed lately. Appropriate animal models (in particular, genetically modified mice) are being used to assess the efficacy of these novel compounds. The transgenic adenocarcinoma of the mouse prostate (TRAMP) model has been validated as an accurate model to test a variety of preventive agents. Genistein, alpha-difluoromethylornithine, toremifene, R-flurbiprofen, celecoxib, and green tea polyphenols have been shown to prevent prostate cancer development in TRAMP mice. In conclusion, new chemopreventive compounds which are effective in animal models are likely to be tested soon in clinical trials, with the final goal of reducing prostate cancer incidence in men.     

Tumor models for prostate cancer exemplified by fibroblast growth factor 8-induced tumorigenesis and tumor progression

Prostate cancer is a very common malignancy among Western males. Although most tumors are indolent and grow slowly, some grow and metastasize aggressively. Because prostate cancer growth is usually androgen-dependent, androgen ablation offers a therapeutic option to treat post-resection tumor recurrence or primarily metastasized prostate cancer. However, patients often relapse after the primary response to androgen ablation therapy, and there is no effective cure for cases of castration-resistant prostate cancer (CRPC). The mechanisms of tumor growth in CRPC are poorly understood. Although the androgen receptors (ARs) remain functional in CRPC, other mechanisms are clearly activated (e.g., disturbed growth factor signaling). Results from our laboratory and others have shown that dysregulation of fibroblast growth factor (FGF) signaling, including FGF receptor 1 (FGFR1) activation and FGF8b overexpression, has an important role in prostate cancer growth and progression. Several experimental models have been developed for prostate tumorigenesis and various stages of tumor progression. These models include genetically engineered mice and rats, as well as induced tumors and xenografts in immunodeficient mice. The latter was created using parental and genetically modified cell lines. All of these models greatly helped to elucidate the roles of different genes in prostate carcinogenesis and tumor progression. Recently, patient-derived xenografts have been studied for possible use in testing individual, specific responses of tumor tissue to different treatment options. Feasible and functional CRPC models for drug responsiveness analysis and the development of effective therapies targeting the FGF signaling pathway and other pathways in prostate cancer are being actively investigated.     

A cancer chemopreventive agent silibinin, targets mitogenic and survival signaling in prostate cancer

There are many epigenetic variables that affect the biological responses of autocrine, paracrine and endocrine regulatory molecules, which determine the growth and development of different cancers including prostate cancer (PCA). One of the focuses of the current cancer chemoprevention studies is the search for non-toxic chemopreventive agents that inhibit mitogenic and cell survival signaling in cancer cells. In general, advanced stage cancer cells harbor many constitutively active mitogenic signaling and anti-apoptotic mechanisms, which make them less dependent on external growth factors as well as resistant to chemotherapeutic agents. In this regard, silibinin (a naturally occurring flavanone) has shown the pleiotropic anticancer effects in different cancer cells. Our extensive studies with PCA have shown that inhibition of mitogenic and cell survival signaling, such as epidermal growth factor receptor, insulin-like growth factor receptor type I and nuclear factor kappa B signaling are the most likely molecular targets of silibinin's efficacy in PCA. We have observed that silibinin inhibits prostate tumor growth in animal models without any apparent signs of toxicity. At the same time, silibinin is also physiologically available in different organs of the body including plasma and prostate, which is generally required for the pharmacological dosing and translational mechanistic studies of the compound. There are substantial amount of data to support the inhibitory effect of silibinin on mitogenic and cell survival signaling in PCA, which are reviewed in the present communication.     

The carcinogenic effect of H. pylori on the gastric epithelial cell.

The recent demonstration in animal models that H. pylori alone may be capable of inducing intestinal-type gastric cancer, and that H. felis can accelerate gastrin-induced gastric neoplasia has stimulated research on examining the mechanisms of H. pylori-associated carcinogenesis in humans. Several mechanisms are currently under investigation, including the dysregulation of the gastric epithelial cell cycle, the formation of DNA adducts, the generation of free radicals, alterations in growth factor secretion and cytokines, and the effects of decreased gastric acid secretion. This review will examine the relevant evidence acquired from human tissue studies, animal models and cell culture systems in an attempt to explore these pathways, and to evaluate the mechanisms by which H. pylori may cause gastric cancer.     

A review of epidemiologic studies of tomatoes,lycopene, and prostate cancer

Prostate cancer is the most common cancer in American men. Preventable measures for this malignancy are not well established. Among potentially beneficial natural compounds is the carotenoid lycopene, which is derived largely from tomato-based products. Recent epidemiologic studies have suggested a potential benefit of this carotenoid against the risk of prostate cancer, particularly the more lethal forms of this cancer. Five studies support a 30% to 40% reduction in risk associated with high tomato or lycopene consumption, three are consistent with a 30% reduction in risk, but the results were not statistically significant, and seven were not supportive of an association. The largest relevant dietary study, a prospective study in male health professionals found that consumption of two to four servings of tomato sauce per week was associated with about a 35% risk reduction of total prostate cancer and a 50% reduction of advanced (extraprostatic) prostate cancer. Tomato sauce was by far the strongest predictor of plasma lycopene levels in this study. In the largest plasma-based study, very similar risk reductions were observed for total and advanced prostate cancer for the highest versus lowest quintile of lycopene. Other studies, mostly dietary case-control studies, have not been as supportive of this hypothesis. The reasons for these inconsistencies are unclear, but in three of the seven null studies, tomato consumption or serum lycopene level may have been too low to observe an effect. Because the concentration and bioavailability of lycopene vary greatly across the various food items, dietary questionnaires vary markedly in their usefulness of estimating the true variation in tissue lycopene concentrations across individuals. To optimize the interpretation of future findings, the usefulness of the questionnaire to measure lycopene levels in a population should be directly assessed. Although not definitive, the available data suggest that increased consumption of tomatoes and tomato-based products may be prudent.     

Tailoring cancer chemoprevention regimens to the individual

The present article, which is a tribute to the memory of Dr. Edward Bresnick, emphasizes the importance of environmental and life-style factors for cancer causation in the human population and points out approaches to cancer prevention. These approaches include vaccinations for the prevention of cancers that are caused by infectious agents as well as the use of cancer chemopreventive agents. The use of tamoxifen and letrozole to prevent breast cancer, finasteride to prevent prostate cancer, sunscreens or topical applications of 5-fluorouracil to prevent sunlight-induced skin cancer, and aspirin or calcium to prevent colon cancer are a few examples of cancer chemoprevention in high risk individuals and in the general population. An underdeveloped area of cancer chemoprevention is the use of combinations of agents that work by different mechanisms. It was pointed out that animal studies indicate that many cancer chemopreventive agents inhibit carcinogenesis under one set of experimental conditions but enhance carcinogenesis under another set of experimental conditions. These observations suggest that tailoring the chemopreventive regimen to the individual or to groups of individuals living under different environmental conditions or with different mechanisms of carcinogenesis may be an important aspect of cancer chemoprevention in human populations. How to tailor cancer chemoprevention regimens to the individual is an important challenge for the future.