Carotenoids and their role in cancer prevention

Approximately two of every five people will develop cancer in their lifetime. Dietary modifications are one of the most promising lifestyle changes that can adjust the risk of developing cancer by nearly 40%. Carotenoids are a diverse group of natural pigments and are present in many fruits and vegetables. The data surrounding carotenoids and their potential roles in carcinogenesis have been rapidly growing over the past two decades. This review summarizes the literature surrounding the associations between the most six common carotenoids in the diet and ten of the most commonly diagnosed cancers. In this study, preclinical, epidemiological, and toxicology data were reviewed. Data from these studies suggest that several carotenoids might provide a beneficial impact on reducing carcinogenesis. Further studies are needed to determine the causal relationships between individual carotenoids and cancer incidence and progression. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.     

Toll‐like receptor 4 regulates spontaneous intestinal tumorigenesis by up‐regulating IL‐6 and GM‐CSF

Inflammation is as an important component of intestinal tumorigenesis. The activation of Toll‐like receptor 4 (TLR4) signalling promotes inflammation in colitis of mice, but the role of TLR4 in intestinal tumorigenesis is not yet clear. About 80%–90% of colorectal tumours contain inactivating mutations in the adenomatous polyposis coli (Apc) tumour suppressor, and intestinal adenoma carcinogenesis in familial adenomatous polyposis (FAP) is also closely related to the germline mutations in Apc. The Apc^Min/+ (multiple intestinal neoplasia) model mouse is a well‐utilized model of FAP, an inherited form of intestinal cancer. In this study, Apc^Min/+ intestinal adenoma mice were generated on TLR4‐sufficient and TLR4‐deficient backgrounds to investigate the carcinogenic effect of TLR4 in mouse gut by comparing mice survival, peripheral blood cells, bone marrow haematopoietic precursor cells and numbers of polyps in the guts of Apc^Min/+ WT and Apc^Min/+ TLR4^?/? mice. The results revealed that TLR4 had a critical role in promoting spontaneous intestinal tumorigenesis. Significant differential genes were screened out by the high‐throughput RNA‐Seq method. After combining these results with KEGG enrichment data, it was determined that TLR4 might promote intestinal tumorigenesis by activating cytokine‐cytokine receptor interaction and pathways in cancer signalling pathways. After a series of validation experiments for the concerned genes, it was found that IL6, GM‐CSF (CSF2), IL11, CCL3, S100A8 and S100A9 were significantly decreased in gut tumours of Apc^Min/+ TLR4^?/? mice compared with Apc^Min/+ WT mice. In the functional study of core down‐regulation factors, it was found that IL6, GM‐CSF, IL11, CCL3 and S100A8/9 increased the viability of colon cancer cell lines and decreased the apoptosis rate of colon cancer cells with irradiation and chemical treatment.     

The tumor suppressor p53: Cancer and aging

Aging, like many other biological processes, is subject to regulation by genes that reside in pathways that have been conserved during evolution. The insulin/ IGF-1 pathway, mTOR pathway and p53 pathway are among those conserved pathways that impact upon longevity and aging-related diseases such as cancer. Most cancers arise in the last quarter of life span with the frequency increasing exponentially with time, and mutation accumulation in critical genes (e.g. p53) in individual cells over a lifetime is thought to be the reason. Recently, we found that the efficiency of the p53 response to stress decline significantly with age in mice, and the time of onset of this decreased p53 response correlates with the life span of mice. Given the crucial role of the p53 in tumor prevention, this decline in p53 activity at older ages in animals could contribute to the observed dramatic increases in cancer frequency, and provides a plausible explanation for the correlation between tumorigenesis and aging in addition to the accumulation of DNA mutations over lifetime. We discuss here the coordination and communication between the p53 pathway and the IGF-1-mTOR pathways, and their possible impact on cancer and longevity.     

Loss of GM130 in breast cancer cells and its effects on cell migration,invasion and polarity

Spatially distinct pools of the small GTPase Cdc42 were observed, but the major focus of research so far has been to investigate its signaling at the plasma membrane. We recently showed that the Golgi pool of Cdc42 is relevant for cell polarity and that it is regulated by GM130, a Golgi matrix protein. Loss of GM130 abrogated cell polarity and consistent with the notion that polarity is frequently impaired in cancer, we found that GM130 is downregulated in colorectal cancer. Whether the loss of GM130 solely affects polarity, or whether it affects other processes relevant for tumorigenesis remains unclear. In a panel of breast cancer cells lines, we investigated the consequences of GM130 depletion on traits of relevance for tumor progression, such as survival, proliferation, adhesion, migration and invasion. We show that cellular assays that depend on polarity, such as chemotaxis and wound scratch assays, are only of limited use to investigate the role of polarity modulators in cancer. Depletion of GM130 increases cellular velocity and increases the invasiveness of breast cancer cells, therefore supporting the view that alterations of polarity contribute to tumor progression.     

Regulation of EGFR signalling by palmitoylation and its role in tumorigenesis

The epidermal growth factor receptor (EGFR) is an essential driver of oncogenic signalling, and EGFR inhibitors are some of the earliest examples of successful targeted therapies in multiple types of cancer. The tractability of EGFR as a therapeutic target is overshadowed by the inevitable drug resistance that develops. Overcoming resistance mechanisms requires a deeper understanding of EGFR regulation in cancer cells. In this review, we discuss our recent discovery that the palmitoyltransferase DHHC20 palmitoylates EGFR on the C-terminal domain and plays a critical role in signal regulation during oncogenesis. Inhibiting DHHC20 expression or mutating the palmitoylation site on EGFR alters the EGF-induced signalling kinetics from a transient signal to a sustained signal. The change in signalling is accompanied by a decrease in cell proliferation in multiple human cancer cell lines. Our in vivo studies demonstrate that ablating the gene Zdhhc20 by CRISPR/Cas9-mediated inhibition in a mouse model of oncogenic Kras-driven lung adenocarcinoma potently inhibits tumorigenesis. The negative effect on tumorigenesis is mediated by EGFR since the expression of a palmitoylation-resistant mutant form of EGFR also inhibits Kras-driven lung adenocarcinoma. Finally, reducing EGFR palmitoylation increases the sensitivity of multiple cancer cell lines to existing inhibitors of EGFR and downstream signalling effector pathways. We will discuss the implications of these effects and strategies for targeting these new vulnerabilities.     

Tumorigenesis as a process of gradual loss of original cell identity and gain of properties of neural precursor/progenitor cells

Cancer is a complex disease without a unified explanation for its cause so far. Our recent work demonstrates that cancer cells share similar regulatory networks and characteristics with embryonic neural cells. Based on the study, I will address the relationship between tumor and neural cells in more details. I collected the evidence from various aspects of cancer development in many other studies, and integrated the information from studies on cancer cell properties, cell fate specification during embryonic development and evolution. Synthesis of the information strongly supports that cancer cells share much more similarities with neural progenitor/stem cells than with mesenchymal-type cells and that tumorigenesis represents a process of gradual loss of cell or lineage identity and gain of characteristics of neural cells. I also discuss cancer EMT, a concept having been under intense debate, and possibly the true meaning of EMT in cancer initiation and development. This synthesis provides fresh insights into a unified explanation for and a previously unrecognized nature of tumorigenesis, which might not be revealed by studies on individual molecular events. The review will also present some brief suggestions for cancer research based on the proposed model of tumorigenesis.     

CUL4B increases platinum‐based drug resistance in colorectal cancer through EMT: A study in its mechanism

Platinum‐based chemotherapy drugs play a very important role in the treatment of patients with advanced colorectal cancer, but the drug resistance of platinum‐based chemotherapy drugs is an important topic that puzzles us. If we can find mechanisms of resistance, it will be revolutionary for us. We analysed the differential genes, core genes and their enrichment pathways in platinum‐resistant and non‐resistant patients through a public database. Platinum‐resistant cell lines were cultured in vitro for in vitro colony and Transwell analysis. Tumorigenesis analysis of nude mice in vivo. Verify the function of core genes. Through differential gene and enrichment analysis, we found that CUL4B was the main factor affecting platinum drug resistance and EMT. Our hypothesis was further verified by in vitro drug‐resistant and wild‐type cell lines and in vivo tumorigenesis analysis of nude mice. CUL4B leads to platinum drug resistance in colorectal cancer by affecting tumour EMT.     

Risk factors and risk reduction of breast cancer

Because of its increasing incidence, breast cancer is a significant burden for women worldwide. In industrialized countries, breast cancer is the second-leading cause of cancer-related deaths among women, and it is estimated that 1 in every 8 women will develop the disease during her lifetime. Sufficient evidence indicates that a number of genetic, environmental and lifestyle risk exposures during life may play important roles in the etiology of this disease. The purpose of this paper is to review some etiologic factors and underlying mechanisms in relation to breast cancer risk. Based on the published literature, there is sufficient evidence that some established factors are associated with breast cancer risk. Age, early age at menarche, late menopause, height, post-menopausal obesity, family history of breast cancer, ionizing radiation, oral contraceptives, hormonal replacement therapy, mammographic density, some gene mutations and clinical conditions, such as benign breast disease, are associated with an increased risk of breast cancer. The risk decreases with early childbearing, high parity and physical activity, and breastfeeding. Alcohol increases the risk, while caloric restriction may confer protection from breast cancer. Epidemiological evidence for other nutritional factors is insufficient. These results suggest that breast cancer is a multifactorial disease where genetic susceptibility, environment, nutrition and other lifestyle risk factors interact. Better identification of modifiable risk factors and risk reduction of breast cancer may allow implementation of useful strategies for prevention.     

Transgenic models to study gonadotropin function: the role of follicle-stimulating hormone in gonadal growth and tumorigenesis.

The role of FSH in gonadal tumorigenesis and, in particular, in human ovarian cancer has been debated. It is also unclear what role the elevated FSH levels in the inhibin-deficient mouse play in the gonadal tumorigenesis. To directly assess the role of FSH in gonadal growth, differentiation, and gonadal tumorigenesis, we have generated both gain-of-function and loss-of-function transgenic mutant mice. In the gain-of-function model, we have generated transgenic mice that ectopically overexpress human FSH from multiple tissues using a mouse metallothionein-1 promoter, achieving levels far exceeding those seen in postmenopausal women. Male transgenic mice are infertile despite normal testicular development and demonstrate enlarged seminal vesicles secondary to elevated serum testosterone levels. Female transgenic mice develop highly hemorrhagic and cystic ovaries, have elevated serum estradiol and progesterone levels, and are infertile, mimicking the features of human ovarian hyperstimulation and polycystic ovarian syndromes. Furthermore, the female transgenic mice develop enlarged and cystic kidneys and die between 6-13 weeks as a result of urinary bladder obstruction. In a complementary loss-of-function approach, we have generated double-homozygous mutant mice that lack both inhibin and FSH by a genetic intercross. In contrast to male mice lacking inhibin alone, 95% of which die of a cancer cachexia-like syndrome by 12 weeks of age, only 30% of the double-mutant male mice lacking both FSH and inhibin die by 1 yr of age. The remaining double-mutant male mice develop slow-growing and less hemorrhagic testicular tumors, which are noted after 12 weeks of age, and have minimal cachexia. Similarly, the double-mutant female mice develop slow-growing, less hemorrhagic ovarian tumors, and 70% of these mice live beyond 17 weeks. The double-mutant mice demonstrate minimal cachexia in contrast to female mice lacking only inhibin, which develop highly hemorrhagic ovarian tumors, leading to cachexia and death by 17 weeks of age in 95% of the cases. The milder cachexia-like symptoms of the inhibin and FSH double-mutant mice are correlated with low levels of serum estradiol and activin A and reduced levels of aromatase mRNA in the gonadal tumors. Based on these and our previous genetic analyses, we conclude that elevated FSH levels do not directly cause gonadal tumors. However, these results suggest FSH is an important trophic modifier factor for gonadal tumorigenesis in inhibin-deficient mice.     

Genetic counselling and testing for susceptibility to breast,ovarian and colon cancer: where are we today?

Recent advances in our understanding of the genetic characteristics of cancer will change approaches to genetic screening and counselling. Cancer results from multiple, cumulative mutations in genes that regulate cell replication and differentiation. In familial cancer a germ-line mutation is passed on in an autosomal dominant pattern, but cancer will develop in people who inherit the defect only if other mutations also occur in susceptible somatic cells. The tumour-suppressor gene known as BRCA1 is thought to affect half of those families who have an inherited breast cancer syndrome and most families with a breast and ovarian cancer syndrome. Another gene, BRCA2, is thought to affect most of the remaining families with a breast-cancer-only syndrome. Hereditary nonpolyposis colon cancer (HNPCC) is caused by mutations in surveillance genes that protect DNA from the spontaneous errors that occur during cell division. Because there are no outcome data on which to base practice guidelines for genetic screening or management of asymptomatic carriers in families at risk, testing should be restricted to research settings.     

Commercializing genetically modified crops under EU regulations: objectives and barriers

Agriculture faces serious problems in feeding 9 billion people by 2050: production must be increased and ecosystem services maintained under conditions for growing crops that are predicted to worsen in many parts of the world. A proposed solution is sustainable intensification of agriculture, whereby yields are increased on land that is currently cultivated, so sparing land to deliver other ecosystem services. Genetically modified (GM) crops are already contributing to sustainable intensification through higher yields and lower environmental impacts, and have potential to deliver further significant improvements. Despite their widespread successful use elsewhere, the European Union (EU) has been slow to introduce GM crops: decisions on applications to import GM commodities are lengthy, and decision-making on applications to cultivate GM crops has virtually ceased. Delayed import approvals result in economic losses, particularly in the EU itself as a result of higher commodity prices. Failure to grant cultivation approvals costs EU farmers opportunities to reduce inputs, and results in loss of agricultural research and development from the EU to countries such as the United States and China. Delayed decision-making in the EU ostensibly results from scientific uncertainty about the effects of using GM crops; however, scientific uncertainty may be a means to justify a political decision to restrict cultivation of GM crops in the EU. The problems associated with delayed decision-making will not improve until there is clarity about the EU's agricultural policy objectives, and whether the use of GM crops will be permitted to contribute to achieving those objectives.     

A biomechanical analysis of skull form in gum-harvesting galagids

Among primates, some highly gummivorous species habitually gouge trees to elicit exudate flow whereas others scrape the hardened gums from trees. These foraging behaviors are thought to require high external forces at the anterior dentition. In this study, we test whether skull form in gouging and scraping galagids corresponds to this suggested need to produce these higher external forces and to resist increased internal loads in the jaws. We find few consistent morphological patterns linking skull form and the generation of high forces during gouging. However, there is some tendency for gougers and scrapers to show increased load resistance capabilities in their mandibles. Future research on the mechanical properties of trees exploited by these species and on jaw function during gouging and scraping will improve our understanding of the mechanical demands of gum feeding on the galagid skull form.     

The prevention of lung cancer induced by a tobacco-specific carcinogen in rodents by green and black Tea

A growing body of evidence from studies in laboratory animals indicates that green tea protects against cancer development at various organ sites. We have previously shown that green tea, administered as drinking water, inhibits lung tumor development in A/J mice treated with 4-(methylnitrosamino)-1-(3-pyridyl)-l-butanone (NNK), a potent nicotine-derived lung carcinogen found in tobacco. The inhibitory effect of green tea has been attributed to its major polyphenolic compound, epigallocatechin gallate (EGCG), and, to a lesser extent, to caffeine. We have also demonstrated that while levels of O6-methylguanine, a critical lesion in NNK lung tumorigenesis, were not affected in lung DNA. However, the levels of 8-hydroxydeoxyguanosine (8-OH-dG), a marker of oxidative DNA damage, were significantly suppressed in mice treated with green tea or EGCG. These studies underscore the importance of the antioxidant activity of green tea and EGCG for their inhibitory activity against lung tumorigenesis. Unlike green tea, the effect of black tea on carcinogenesis has been scarcely studied, even though the worldwide production and consumption of black tea far exceeds that of green tea. The oxidation products found in black tea, thearubigins and theaflavins, also possess antioxidant activity, suggesting that black tea may also inhibit NNK-induced lung tumorigenesis. Indeed, bioassays in A/J mice have shown that black tea given as drinking water retarded the development of lung cancer caused by NNK. However, data on the relationship of black tea consumption with the lung cancer risk in humans are limited and inconclusive. There is a need for additional tumor bioassays in animal models to better examine the protective role of black tea against lung cancer. The development of adenocarcinomas and adenosquamous carcinomas in F344 rats upon chronic administration of NNK provides an important and relevant model for lung carcinogenesis in smokers. Thus far, no information was previously available regarding the effects of tea on this model. We conducted a 2-year lifetime bioassay in F344 rats to determine whether black tea and caffeine are protective against lung tumorigenesis induced by NNK. Our studies in both mice and rats have generated important new data that support green and black tea and caffeine as potential preventive agents against lung cancer, suggesting that a closer examination of the roles of tea and caffeine on lung cancer in smokers may be warranted.     

Introduction

Intrinsic and acquired resistance to chemotherapy is a serious problem for many cancer patients. Cancer cells appear to have the capacity to generate variants resistant to any anticancer drug. Tumours, and even individual cancer cells, can exhibit multiple mechanisms of resistance simultaneously. In order to overcome resistance it may be necessary to achieve a high rate of tumour cell kill before multiple resistance mechanisms can develop, and/or to develop therapies which simultaneously target several resistance mechanisms. Mechanisms of resistance described so far include ‘bulk’ mechanisms (e.g. related to blood and drug supply, and to oxygenation), mechanisms relating to population cell kinetics, and mechanisms at the cellular level including altered expression of drug target proteins, drug transporter proteins, drug metabolising enzymes, and proteins which regulate cell death pathways. This volume brings together up-to-date reviews on all of these aspects written by researchers actively involved in their topic. It is a completely new book, different from its predecessor Multiple Drug Resistance in Cancer – Cellular, Molecular and Clinical Approaches (Kluwer, 1994). Most of the topics and contributors are new, and chapters on the same topics are included only in cases where there have been significant research developments in the interim period. I hope that this volume will bring together different ideas and approaches, and help to encourage their integration to generate new treatments which will cure more cancer patients. This revised version was published online in August 2006 with corrections to the Cover Date.     

Epstein-Barr virus latent nuclear antigens can induce metastasis in a nude mouse model

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with the development of both lymphoid and epithelial tumors. The EBV critical latent antigens EBNA1 and EBNA3C interact with Nm23-H1, a known suppressor of cell migration and tumor metastasis. This interaction is critical for the regulation of downstream cellular genes involved in tumorigenesis and cell migration. The significance of these interactions was determined in nude mice using cancer cells expressing both EBV antigens and Nm23-H1. The EBV antigens promoted the growth of transformed cells in vivo, but their expression was less critical during the later stage of tumor development. The expression of Nm23-H1 affected the growth of cancer cells and suppressed their metastatic potential. This effect was effectively rescued by the expression of both EBV antigens. Interestingly, the prometastatic potential of EBNA3C was greater than that of EBNA1, which triggered a dramatic immune response, as indicated by increased spleen size and development of ascites in the mice. These studies now bridge the expression of the EBV antigens with tumorigenesis and metastasis and widen the range of potential targets for development of therapies for EBV-associated malignancies.     

Autophagy and cancer cell metabolism

Autophagy is a catabolic process involving lysosomal turnover of proteins and organelles for maintenance of cellular homeostasis and mitigation of metabolic stress. Autophagy defects are linked to diseases, such as liver failure, neurodegeneration, inflammatory bowel disease, aging and cancer. The role of autophagy in tumorigenesis is complex and likely context-dependent. Human breast, ovarian and prostate cancers have allelic deletions of the essential autophagy regulator BECN1 and Becn1(+/-) and other autophagy-deficient transgenic mice are tumor-prone, whereas tumors with constitutive Ras activation, including human pancreatic cancers, upregulate basal autophagy and are commonly addicted to this pathway for survival and growth; furthermore, autophagy suppression by Fip200 deletion compromises PyMT-induced mammary tumorigenesis. The double-edged sword function of autophagy in cancer has been attributed to both cell- and non-cell-autonomous mechanisms, as autophagy defects promote cancer progression in association with oxidative and ER stress, DNA damage accumulation, genomic instability and persistence of inflammation, while functional autophagy enables cancer cell survival under stress and likely contributes to treatment resistance. In this review, we will focus on the intimate link between autophagy and cancer cell metabolism, a topic of growing interest in recent years, which has been recognized as highly clinically relevant and has become the focus of intense investigation in translational cancer research. Many tumor-associated conditions, including intermittent oxygen and nutrient deprivation, oxidative stress, fast growth and cell death suppression, modulate, in parallel and in interconnected ways, both cellular metabolism and autophagy to enable cancer cells to rapidly adapt to environmental stressors, maintain uncontrolled proliferation and evade the toxic effects of radiation and/or chemotherapy. Elucidating the interplay between autophagy and tumor cell metabolism will provide unique opportunities to identify new therapeutic targets and develop synthetically lethal treatment strategies that preferentially target cancer cells, while sparing normal tissues.     

mTOR Inhibition Elicits a Dramatic Response in PI3K-Dependent Colon Cancers

The phosphatidylinositide-3-kinase (PI3K) signaling pathway is critical for multiple cellular functions including metabolism, proliferation, angiogenesis, and apoptosis, and is the most commonly altered pathway in human cancers. Recently, we developed a novel mouse model of colon cancer in which tumors are initiated by a dominant active PI3K (FC PIK3ca*). The cancers in these mice are moderately differentiated invasive mucinous adenocarcinomas of the proximal colon that develop by 50 days of age. Interestingly, these cancers form without a benign intermediary or aberrant WNT signaling, indicating a non-canonical mechanism of tumorigenesis. Since these tumors are dependent upon the PI3K pathway, we investigated the potential for tumor response by the targeting of this pathway with rapamycin, an mTOR inhibitor. A cohort of FC PIK3ca* mice were treated with rapamycin at a dose of 6 mg/kg/day or placebo for 14 days. FDG dual hybrid PET/CT imaging demonstrated a dramatic tumor response in the rapamycin arm and this was confirmed on necropsy. The tumor tissue remaining after treatment with rapamycin demonstrated increased pERK1/2 or persistent phosphorylated ribosomal protein S6 (pS6), indicating potential resistance mechanisms. This unique model will further our understanding of human disease and facilitate the development of therapeutics through pharmacologic screening and biomarker identification.     

Genes in food--why the furore?

Although unprecedented and perhaps unique in its irrationality, the recent furore over genetically modified (GM) food holds extremely important lessons for scientists. Some sections of the media undoubtedly bear a heavy responsibility for giving the expression 'GM' threatening connotations that are quite unwarranted. However, influential contributions to the hysteria have come from a surprising range of other sources, including some scientists. The research community has failed in its responsibility to society in three ways. Firstly, plant scientists did not appreciate that certain techniques (such as the use of antibiotic resistance genes as markers during plant transformation) would inevitably provoke public consternation. As a result, they took no steps to address such concerns. Secondly, researchers overlooked, minimized or in some cases simply dismissed the significance of public fears that they were 'interfering with Nature' or 'playing God'. Thirdly, plant breeders apparently saw no need to take pro-active measures with regard to the media and public in placing potential environmental and nutritional benefits of GM crops on the agenda in a positive fashion. Partly because of this failure, GM food is now firmly established in the public mind as wholly objectionable. One measure of how far we have travelled down that road is that it hardly matters any more whether objections are based on alleged environmental risks of cultivating GM crops or alleged toxicological hazards of eating them. 'Genetically modified organism', like 'radioactivity', has become an odious, generic shibboleth. Given that millions of people throughout the world are already benefiting from pharmaceuticals made by GM organisms, this is bizarre.