Nutrition and cancer: essential elements for a roadmap.

Personalizing nutrition for cancer prevention and therapy will require a comprehensive understanding of "genotypes/phenotypes" in order to identify, evaluate, and prioritize appropriate points for dietary intervention. This nutritional preemption roadmap must begin with accurately assessing intakes/exposures of which bioactive food component(s) is needed to bring about a desired response in critical cellular processes (carcinogen metabolism, DNA repair, cell proliferation, apoptosis, inflammation, immunity, differentiation, angiogenesis, hormonal regulation and cellular energetic) within an individual. Understanding this "individuality" through a better understanding of the "omics" is fundamental to arriving at the correct destination and thus interpreting biological variables which establish the magnitude or direction of a response to bioactive food components.

Nutrition in the 'omics' era.

Consumers throughout the world are increasingly questioning the quality and safety of their diets and how the foods they eat are influencing their health. Much of this interest stems from mounting evidence that bioactive food components cannot only influence one's ability to achieve one's genetic potential, but can also have a significant influence on the quality of life as measured by both physical and cognitive performance, and modify the risk and/or severity of a variety of disease conditions. During the past century, a wealth of evidence has pointed to dietary habits as a determinant of premature death, including that associated with heart disease, stroke, diabetes, liver disease, atherosclerosis and cancer, although considerable variability in response is evident. Several factors may account for these discrepancies including individual variability due to genetic and epigenetic regulation of cellular proteins and associated small-molecular-weight compounds. This interrelationship between the food components and the 'omics' (genomics, epigenomics, transcriptomics, proteomics and metabolomics) will be briefly reviewed as a factor contributing to the variability among studies. Expanded knowledge about these omics interrelationships will not only define the molecular target for food components but will also assist in identifying those individuals who are likely to respond maximally.

Targets for indole-3-carbinol in cancer prevention.

Mounting preclinical and clinical evidence indicate that indole-3-carbinol (I3C), a key bioactive food component in cruciferous vegetables, has multiple anticarcinogenic and antitumorigenic properties. Evidence that p21, p27, cyclin-dependent kinases, retinoblastoma, Bax/Bcl-2, cytochrome P-450 1A1 and GADD153 are targets for I3C already exists. Modification of nuclear transcription factors including Sp1, estrogen receptor, nuclear factor kappaB and aryl hydrocarbon receptor may represent a common site of action to help explain downstream cellular responses to dietary I3C and, ultimately, to its anticancer properties. While the current information is intriguing, future I3C research needs to focus on why these changes in nuclear transcription factors occur and how they relate to phenotypic responses and the quantity and duration of exposure to I3C and its dimer 3,3'-diindolylmethane.

Molecular targets for bioactive food components.

Mounting evidence points to dietary habits as an important determinant of cancer risk and tumor behavior. Although the linkages with diet are intriguing, the literature is also laden with inconsistencies. The reasons for these inconsistencies are likely multi-factorial, but probably reflect variations in the ability of bioactive constituents to reach or affect critical molecular targets. Fluctuations in the foods consumed not only influence the intake of particular bioactive components, but may alter metabolism and potentially influence the sites of action of both essential and nonessential nutrients. Genetic polymorphisms are increasingly recognized as another factor that can alter the response to dietary components (nutritional transcriptomic effect) by influencing the absorption, metabolism, or sites of action. Likewise, variation in DNA methylation patterns and other epigenetic events that influence overall gene expression can be influenced by dietary intakes. Furthermore, variation in the ability of food components to increase or depress gene expression (nutrigenomic effect) may account for some of the observed inconsistencies in the response to dietary change. Because a host of food components are recognized to influence phosphorylation and other posttranslational events, it is also likely that these and other proteomic modifications account for at least part of the response and variation that is reported in the literature. Collectively, it is clear that bioactive food components can influence a number of key molecular events that are involved in health and disease resistance. As the era of molecular nutrition unfolds, a greater understanding of how these foods and components influence cancer will surely arise. Such information will be critical in the development of effective tailored strategies for reducing cancer burden. Just as important, however, is that as this information unfolds it is utilized within a responsible bioethical framework.

Diallyl disulfide induces ERK phosphorylation and alters gene expression profiles in human colon tumor cells.

Diallyl disulfide (DADS), a compound found in processed garlic, has been shown to arrest unsynchronized human colon tumor cells (HCT-15) in the G(2)/M phase of the cell cycle. The present studies were designed to examine whether this cell cycle block related to alterations in protein kinase C (PKC), Ca(2+)/calmodulin-dependent protein kinase II (CAMK II) or extracellular signal-regulated kinase (ERK) activity. Exposing double thymidine synchronized HCT-15 cells to DADS (25, 50 and 100 micromol/L) for 4 h increased the G(2)/M population by 30, 31 and 63%, respectively, compared with controls (P < 0.05). PKC and CAM KII activities were not influenced by increasing DADS exposure and thus did not correlate with the block of cells in the G(2)/M phase. Although ERK activity increased by 44 and 60% after treatment with 100 and 500 micromol/L DADS (P < 0.05), it was not influenced by exposure to 25 or 50 micromol/L DADS. Western blot analysis revealed that although DADS (25, 50, 100 and 500 micromol/L) did not influence the quantity of ERK protein expressed, it did increase its phosphorylation by 39, 52, 73 and 61%, respectively, compared with controls (P < 0.05). These studies provide evidence that early alterations in ERK pathway signaling may contribute to the G(2)/M arrest observed after DADS exposure. Preliminary data generated using the Clonetech Atlas Human Cancer cDNA Expression Array suggest that alterations in cell cycle, DNA repair and cellular adhesion factors accompany DADS exposure and may also be involved in mediating the block in G(2)/M progression.

Functional foods and health: a US perspective.

Linkages between diet habits and the quality of life continue to surface on numerous fronts. Collectively these epidemiological, pre-clinical and clinical studies provide rather compelling evidence that numerous essential and non-essential dietary components are capable of influencing growth, development and performance and disease prevention. Scientific discoveries and widespread interest in the potential medicinal benefits of foods and food components have fostered a variety of content, health and structure-function claims. Unfortunately, defining the ideal diet is complicated by the numerous and diverse components that may influence biological processes. Inconsistencies in the literature may reflect the multi-factorial nature of these processes and the specificity that individual dietary constituents have in modifying genetic and epigenetic events. New and emerging genomic and proteonomic approaches and technologies offer exciting opportunities for identifying molecular targets for dietary components and thus determining mechanisms by which they influence the quality of life. All cells have unique 'signatures' that are characterized by active and inactive genes and cellular products. It is plausible that bridging knowledge about unique cellular characteristics with molecular targets for nutrients can be used to develop strategies to optimize nutrition and minimize disease risk.

Strategies for cancer prevention: the role of diet.

Linkages between diet habits and cancer risk have surfaced from a multitude of epidemiological and preclinical studies. Collectively these studies provide rather compelling evidence that dietary components modify the incidence and biological behavior of tumors. While the risk of breast, prostate, colon, lung and liver cancers are frequently associated with dietary patterns, inconsistencies are not uncommon. These inconsistencies likely reflect the multi-factorial and complex nature of cancer and the specificity that individual dietary constituents have in modifying cancer related genetic pathways. The complexity of defining the role of diet is underscored by the numerous and diverse essential and non-essential components that may alter one or more phases of the cancer process. The explosive increase in the recognition of genes and pathways for regulating cell growth and development, and evaluating the response to hormones and other chemicals synthesized by the body, offers exciting opportunities for unraveling the molecular targets by which dietary components influence cancer prevention. It is recognized that all cells have unique 'signatures' that are characterized by active and inactive genes and cellular products. It is certainly plausible that bridging knowledge about these unique cellular characteristics with the molecular targets for nutrients can be used to assist in optimizing nutrition and minimizing cancer risk.

Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis.

Overall, a host of studies provides compelling evidence that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. These studies reveal that the benefits of garlic are not limited to a specific species, to a particular tissue, or to a specific carcinogen. Several mechanisms are likely to account for this protection. Notable among these is a depression in nitrosamine formation and a reduction in carcinogen bioactivation. The benefits provided by garlic must be viewed as part of the entire diet, since several dietary constituents can influence the degree of protection. More than one compound is responsible for the anticancer properties associated with garlic. Future research should focus on how genetic variability and daily environmental factors influence the anticancer benefits attributed to garlic and its allyl sulfur components.

Diet and cancer prevention.

Research from several sources provides strong evidence that vegetables, fruits, and whole grains, dietary fibre, certain micronutrients, some fatty acids and physical activity protect against some cancers. In contrast, other factors, such as obesity, alcohol, some fatty acids and food preparation methods may increase risks. Unravelling the multitude of plausible mechanisms for the effects of dietary factors on cancer risk will likely necessitate that nutrition research moves beyond traditional epidemiological and metabolic studies. Nutritional sciences must build on recent advances in molecular biology and genetics to move the discipline from being largely 'observational' to focusing on 'cause and effect'. Such basic research is fundamental to cancer prevention strategies that incorporate effective dietary interventions for target populations.

A historical perspective on garlic and cancer.

Epidemiological and laboratory studies provide insight into the anticarcinogenic potential of garlic and its constituent compounds. Both water- and lipid-soluble allyl sulfur compounds are effective in blocking a myriad of chemically induced tumors. Part of the protection from these compounds probably relates to a block in nitrosamine formation and metabolism. However, blockage in the initiation and promotion phases of the carcinogenicity of various compounds, including polycyclic hydrocarbons, provide evidence that garlic and its constituents can alter several phase I and II enzymes. Their ability to block experimentally induced tumors in a variety of sites including skin, mammary and colon, suggests a general mechanism of action. Changes in DNA repair and in immunocompetence may also account for some of this protection. Some, but not all, allyl sulfur compounds can also effectively retard tumor proliferation and induce apoptosis. Changes in cellular thiol and phosphorylation stains may account for some of these antitumorigenic properties. The anticarcinogenic potential of garlic can be influenced by several dietary components including specific fatty acids, selenium, and vitamin A. Since garlic and its constituents can suppress carcinogen formation, carcinogen bioactivation, and tumor proliferation it is imperative that biomarkers be established to identify which individuals might benefit most and what intakes can occur with ill consequences.

The influence of heating on the anticancer properties of garlic.

Allyl sulfur compounds are the major active constituents found in crushed garlic. Research has revealed that garlic and its lipid- or water-soluble components have many pharmacologic properties; however, studies also demonstrate that heating has a negative influence on these beneficial effects. We recently conducted several studies to investigate the influence of microwave or oven heating on the anticarcinogenesis property of garlic. Our studies showed that as little as 60 s of microwave heating or 45 min of oven heating can block garlic's ability to inhibit in vivo binding of mammary carcinogen [7,12-dimethylbenzene(a)anthracene (DMBA)] metabolites to rat mammary epithelial cell DNA. Allowing crushed garlic to "stand" for 10 min before microwave heating for 60 s prevented the total loss of anticarcinogenic activity. Our studies demonstrated that this blocking of the ability of garlic was consistent with inactivation of alliinase. These studies suggest that heating destroyed garlic's active allyl sulfur compound formation, which may relate to its anticancer properties.

Possible mechanism by which allyl sulfides suppress neoplastic cell proliferation.

Both oil- and water-soluble allyl sulfur compounds from garlic have been found to possess antitumorigenic properties. These antitumorigenic properties increase as exposure increases both in vitro and in vivo. Generally, oil-soluble allyl sulfur compounds are more effective antiproliferative agents than their water-soluble counterparts. The ability of these compounds to suppress proliferation is associated with a depression in cell cycle progression and the induction of apoptosis. This depression in cell division coincides with an increase in the percentage of cells blocked in the G(2)/M phase of the cell cycle. A depression in p34(cdc2) kinase may account for this blockage in cell division.

Molecular targets for nutrients involved with cancer prevention.

Dietary nutrients can influence cancer risk by inhibiting or enhancing carcinogenesis through diverse mechanisms of action. The identification and elucidation of their sites of action have been a focus of nutrition and cancer research for more than four decades. Transforming nutrition and cancer research from a predominantly observational to a molecular approach offers exciting opportunities for truly identifying those who will and will not benefit from dietary intervention strategies. The emerging field of nutritional genomics, defined here as the study of any genetic or epigenetic interaction with a nutrient, will be key to this evolution. Unraveling which genetic upregulation or downregulation leads to subsequent phenotype changes will not be easy. There is evidence that genetic polymorphisms can influence the dynamics between nutrients and molecular targets and, thus, contribute to variation in response among individuals. Because many molecular targets will likely be identified, it may be necessary to credential nutrients, that is, to determine which specific nutrient-related genetic and epigenetic changes bring about phenotypic changes, to establish which interactions are the most important and under what circumstances. Vitamin D, calcium, folate, selenium, genistein, and resveratrol are highlighted, because they represent specific classes of nutrients and illustrate the need to credential various nutrients to understand their physiological significance in cancer prevention. As the science of nutrition unfolds, a clearer understanding will emerge about how nutrients can modulate cancer risk through molecular interactions and how foods might be changed by agronomic approaches and/or biotechnology. Undeniably, embracing new genomic technologies offers exciting opportunities for advances in the broad area of nutrition, especially those related to cancer prevention.

Creating a new paradigm in nutrition research within the National Cancer Institute.

Almost two decades after Doll and Peto (1981) provided evidence that one third of cancer deaths are related to diet, it remains unclear which dietary components may be key in cancer prevention. Although the complexity of the diet can become overwhelming, the National Cancer Institute (NCI) of the National Institutes of Health (NIH) has remained steadfast in its commitment to defining the roles that diet and nutrition have in the development of cancer and has provided increased research and training support to assist in unraveling this interrelationship. Evidence for this sustained commitment is highlighted by a fourfold increase in NCI expenditures for nutrition research and training from 1983 to 1998; this substantial increase reflects a trend that is occurring in some universities and the private sector. More than one third of the nutrition-related NCI research is funded by the Division of Cancer Prevention. Supported investigations cover the gamut from basic mechanisms of action of dietary constituents, methodology development, human metabolic studies, clinical trials of dietary modification and the chemopreventive potential of individual nutrients to population-based studies.

Diallyl disulfide inhibits p34(cdc2) kinase activity through changes in complex formation and phosphorylation.

Previous studies from our laboratory demonstrated that diallyl disulfide (DADS), an oil-soluble allyl sulfur compound found in processed garlic, markedly suppressed p34(cdc2) kinase activity and induced a G(2)/M phase arrest in cultured human colon tumor (HCT-15) cells. The present studies reveal that suppression of p34(cdc2) kinase activity by DADS does not result from direct interactions with the protein, but through changes in factors influencing the formation and conversion of the enzyme to its active form. Flow cytometric analyses showed that the increased proportion of cells in the G(2)/M phase following DADS treatment was accompanied by an increase in cyclin B(1) protein expression. A temporal and dose-dependent response in cyclin B(1) expression was observed in cells treated with DADS. Western blot analysis revealed that 50 microM DADS did not influence the quantity of p34(cdc2) protein expressed, but did decrease the amount associated with cyclin B(1) by 26% (P < 0.05). Exposure of unsynchronized cells to 25 or 50 microM DADS caused a trend towards increased p34(cdc2) hyperphosphorylation (17 and 22%, respectively). Exposure of synchronized cells to 100 microM DADS increased p34(cdc2) hyperphosphorylation by 15% (P < 0.05). Consistent with its ability to slightly increase the quantity of hyperphosphorylated p34(cdc2), DADS, 25 or 50 microM, decreased cdc25C protein expression by 23 and 46%, respectively (P < 0.05). The present studies suggest that the ability of DADS to inhibit p34(cdc2) kinase activation occurs because of decreased p34(cdc2)/cyclin B(1) complex formation and modest p34(cdc2) hyperphosphorylation.

Functional foods: the US perspective.

Widespread interest in the possibility that selected foods might promote health has resulted in the coining of the term functional food, although agreement about what is and what is not a functional food is lacking. Public interest in functional foods is increasing because of higher health care costs; the passage of federal legislation affecting many food categories, including the expanded category of dietary supplements; and recent scientific discoveries linking dietary habits with the development of many diseases, including coronary heart disease and some cancers. A variety of foods have been proposed as providing health benefits by altering one or more physiologic processes. Biomarkers are needed to assess the ability of functional foods or their bioactive components to modify disease and to evaluate the ability of these foods to promote health, growth, and well-being. Evidence suggests that several biomarkers may be useful for distinguishing between diseased and nondiseased states and even for predicting future susceptibility to disease. A variety of biomarkers will probably be needed to develop a profile for an individual that reflects the impact of diet on performance and health. Another area of interest is the interaction of nutrients and their association with genetics. These interactions may account for the inconsistent interrelations observed between specific dietary constituents and the incidence of disease. Greater understanding of how diet influences a person's genetic potential, overall performance, and susceptibility to disease can have enormous implications for society. As new discoveries are made in this area, consumers will need access to this information so that they can make informed decisions.

Allyl sulfides modify cell growth.

Extensive evidence points to the ability of allyl sulfides from garlic to suppress tumor proliferation both in vitro and in vivo. This antineoplastic effect is generally greater for lipid-soluble than water-soluble allyl sulfides. Both concentration and duration of exposure can increase the antiproliferative effects of lipid- and water-soluble allyl sulfides. Part of their antiproliferative effects may relate to an increase in membrane fluidity and a suppression of integrin glycoprotein IIb-IIIa mediated adhesion. Alterations in cholesterol, arachidonic acid, phospholipids and/or thiols may account for these changes in membrane function. Allyl sulfides are also recognized for their ability to suppress cellular proliferation by blocking cells in the G2/M phase and by the induction of apoptosis. This increase in the G2/M and apoptotic cell populations correlates with depressed p34cdc2 kinase activity, increased histone acetylation, increased intracellular calcium and elevated cellular peroxide production. While impressive pre-clinical data exist about the antineoplastic effects of allyl sulfur compounds, considerably more attention needs to be given to their effects in humans. The composition of the entire diet and a host of genetic/epigenetic factors will likely determine the true benefits that might arise from allyl sulfur compounds from garlic and other Allium foods.

Flavonoids suppress androgen-independent human prostate tumor proliferation.

The present studies compared the effects of selected bioflavonoids on the proliferation of androgen-independent human prostatic tumor cells (PC-3). Complete growth retardation was observed in PC-3 cells treated with 100 microM quercetin, kaempferol, and luteolin, while isomolar genistein, apigenin, and myricetin suppressed PC-3 proliferation by 73%, 70%, and 59%, respectively (p < 0.05). Naringenin and rutin were not as effective and inhibited growth by < 25%. Exposure to increasing concentrations of quercetin and kaempferol led to a dose-dependent decrease in proliferation. Refeeding kaempferol-treated cells (50 microM) complete medium without the flavonoid resulted in a return toward control growth rates. Similar growth recovery was not observed in quercetin-treated cells. The antiproliferative response of PC-3 cells to quercetin and kaempferol was additive when supplemented to the medium at 25 microM. A block in G2-to-M phase progression was observed after the addition of 25 microM kaempferol. When quercetin reached 100 microM, an increase in the proportion of cells in the S phase became apparent within 24 hours. Apoptosis was not evident, even when concentrations of quercetin or kaempferol were raised to 100 microM. The present studies suggest that alterations in cell cycle progression contribute significantly to the antiproliferative effects of quercetin and kaempferol in PC-3 cells.

Functional foods and health promotion.

Statements about the ability of selected foods to reduce the risk of diseases and to enhance the quality of life continue to captivate, and at times polarize, opinions. Interests in these "functional" foods and their active components are being propelled by increasing health care cost, recent legislative events and mounting scientific evidence. Increasingly, scientists are being asked to clarify the precise role that foods have in maintaining and promoting health. Accepting this movement as an opportunity to "optimize nutrition" rather than as a way in which to endorse good or bad foods or as a marketing gimmick will surely make it more acceptable to many scientists. However, the response to functional foods depends on several factors, including genetics, physiologic state and the composition of the entire diet. Although evaluation of the benefits or risks of foods normally does not entail the same extensive examination as that required of drugs, this does not negate the need for sound scientific information for making recommendations to the consumer. Identification of sensitive and reliable biomarkers will be key to adequate assessment of the true effect of foods and their components. Inulin and oligofructose are components of the diet that deserve added attention for their potential health benefits. Evidence that oligofructose and inulin alter several biomarkers, including gastrointestinal transit time, experimentally induced neoplasia and colonic microflora, suggests that these nondigestible carbohydrates are naturally occurring dietary constituents that may improve the quality of life and increase disease resistance in both humans and animals.

Selenium-enriched Agaricus bisporus mushrooms suppress 7,12-dimethlybenz[a]anthracene bioactivation in mammary tissue.

The present studies compared dietary Se (1.0 microg/g) when provided as either fortified Agaricus bisporus mushrooms, or sodium selenite on the in vivo metabolism of 7,12-dimethylbenz(a)anthracene (DMBA). Dietary addition of Se unenriched A. bisporus mushrooms at 2% did not alter the occurrence of DMBA induced DNA adducts or the activity of glutathione S-transferase (GST). However, the addition of Se as enriched mushrooms, or as selenite, significantly increased both liver and mammary GST activity. Providing sodium selenite, or enriched mushrooms also significantly reduced total and anti-3,4-dihydrodiol-1,2-epoxide-deoxyguanosine adducts compared to feeding the basal diet (P < 0.05). These investigations provide evidence that Se enriched mushrooms can be used as an effective method to retard chemically induced tumors.