Michael J. Wargovich

Inhibition of carcinogenesis by tea: The evidence from experimental studies

In its various forms, tea is one of the most widely consumed beverages in the world. Elucidation of the chemical components of tea has revealed that the beverage is a rich repository of antioxidants. Among these are the polyphenolics, common to green tea, but also found in black teas together with oxidized polymers that in part account, for the darkened color. Consumption of tea on a regular basis has been associated with reduced risk of several forms of cancer in human populations, with the strongest evidence linking green tea use to reduction in cancer risk in parts of Asia. To understand how tea prevents cancer, studies in animal carcinogenesis models have been done with very encouraging results. This review examines the available data from animal studies on the effects of tea in the prevention of cancer.

Sphingosine kinase 1 is up-regulated in colon carcinogenesis

Sphingosine kinase 1 (SK1) phosphorylates sphingosine to form sphingosine 1‐phosphate (S1P), which has the ability to promote cell proliferation and survival and stimulate angiogenesis. The SK1/S1P pathway also plays a critical role in regulation of cyclooxygenase‐2 (COX‐2), a well‐established pathogenic factor in colon carcinogenesis. Therefore, we examined the expression of SK1 and COX‐2 in rat colon tumors induced by azoxymethane (AOM) and the relationship of these two proteins in normal and malignant intestinal epithelial cells. Strongly positive SK1 staining was found in 21/28 (75%) of rat colon adenocarcinomas induced by AOM, whereas no positive SK1 staining was observed in normal mucosa. The increase in SK1 and COX‐2 expression in AOM‐induced rat colon adenocarcinoma was confirmed at the level of mRNA by real‐time RT‐PCR. In addition, it was found that 1) down‐regulation of SK1 in HT‐29 human colon cancer cells by small interfering RNA (siRNA) decreases COX‐2 expression and PGE2 production; 2) overexpression of SK1 in RIE‐1 rat intestinal epithelial cells induces COX‐2 expression; and 3) S1P stimulates COX‐2 expression and PGE2 production in HT‐29 cells. These results suggest that the SK1/S1P pathway may play an important role in colon carcinogenesis, in part, by regulating COX‐2 expression and PGE2 production.

Herbals, Cancer Prevention and Health

The use of herbs for medical benefit has played an important role in nearly every culture on earth. Herbal medicine was practiced by ancient cultures in Asia, Africa, Europe and the Americas. The recent popularity in use of herbals can be tied to the belief that herbs can provide some benefit over and above allopathic medicine and allow users to feel that they have some control in their choice of medications. The widespread use of herbs, either directly or as dietary supplements, has raised many scientific questions. Are herbal preparations safe? Do herbs interact with pharmaceutical medications to enhance or reduce their efficacy? The first interaction can be shown by the effects of St. Johns Wort, a mild herbal antidepressant, and many commonly used medicines. St. Johns Wort can induce the CYP3A family of activation enzymes through which approximately 50% of drugs are metabolized. This poses some risk of inadvertently reducing the half-life of such drugs as indinavir, cyclosporin and cyclophosphamide. On the other hand, herbal products may act in a pathway similar to pharmaceuticals yet without side effects. Natural anti-inflammatory compounds abound in the herbal world and are found in green tea, the spices turmeric and rosemary, feverfew and others. Because the use of nonsteroidal anti-inflammatory drugs (NSAID) is associated with a reduced risk for several cancers, it is at least plausible that natural NSAID should be explored for possible use as cancer preventives.

Inflammation, Cancer, and Targets of Ginseng

Chronic inflammation is associated with a high cancer risk. At the molecular level, free radicals and aldehydes, produced during chronic inflammation, can induce deleterious gene mutation and posttranslational modifications of key cancer-related proteins. Other products of inflammation, including cytokines, growth factors, and transcription factors such as nuclear factor kappaB, control the expression of cancer genes (e.g., suppressor genes and oncogenes) and key inflammatory enzymes such as inducible nitric oxide synthase and cyclooxygenase-2. These enzymes in turn directly influence reactive oxygen species and eicosanoid levels. The procancerous outcome of chronic inflammation is increased DNA damage, increased DNA synthesis, cellular proliferation, disruption of DNA repair pathways and cellular milieu, inhibition of apoptosis, and promotion of angiogenesis and invasion. Chronic inflammation is also associated with immunosuppression, which is a risk factor for cancer. Current treatment strategies for reactive species overload diseases are frequently aimed at treating or preventing the cause of inflammation. Although these strategies have led to some progress in combating reactive species overload diseases and associated cancers, exposure often occurs again after eradication, treatment to eradicate the cause fails, or the treatment has long-term side effects. Therefore, the identification of molecules and pathways involved in chronic inflammation and cancer is critical to the design of agents that may help in preventing the progression of reactive species overload disease and cancer associated with disease progression. Here, we use ginseng as an example of an antiinflammatory molecule that targets many of the key players in the inflammation-to-cancer sequence.

Green tea polyphenol (−)-epigallocatechin-3-gallate inhibits cyclooxygenase-2 expression in colon carcinogenesis

Tea, one of the most widely consumed beverages worldwide, has been shown to have anti‐cancer activity in various cancers including colon cancer. It has been demonstrated that overexpression of the inducible isoform of cyclooxygenase (COX‐2) occurs during colon tumorigenesis and inhibition of COX‐2 by non‐steroidal anti‐inflammatory drugs (NSAIDs) is chemopreventive. To determine whether the anti‐cancer effect associated with green tea impacted COX‐2 expression levels, human colorectal cancer cell lines HT‐29 and HCA‐7, were treated with (−)‐epigallocatechin‐3‐gallate (EGCG), the most abundant and effective polyphenol of green tea. EGCG significantly inhibited constitutive COX‐2 mRNA and protein overexpression. The inhibitory effects of EGCG on signaling pathways controlling COX‐2 expression were examined. We observed that EGCG downregulated the ERK1/2 and Akt pathways in colon cancer cells. The effect of EGCG on COX‐2 expression resulted in decreased COX‐2 promoter activity via inhibition of nuclear factor κB (NF‐κB) activation. EGCG also promoted rapid mRNA decay mediated through the COX‐2 3′untranslated region (3′UTR). In conclusion, these data suggest that inhibition of COX‐2 is a mechanism for the anti‐proliferative effect of green tea and emphasizes the role that dietary factors have as anti‐cancer agents.

Initiation and post-initiation chemopreventive effects of diallyl sulfide in esophageal carcinogenesis

Diallyl sulfide (DAS), one of a number of organosulfur compounds accounting for the flavor and smell associated with garlic, has been shown to inhibit a number of chemically induced forms of cancer. In this study, DAS was examined for its chemopreventive effects in both the initiation and post-initiation phases of nitrosomethylbenzylamine-induced esophageal carcinogenesis in the Sprague-Dawley rat. Although highly inhibitory during initiation, DAS is ineffective when given after the carcinogen. DAS, though not effective as a preventive in post-initiation, was not found to promote esophageal carcinogenesis.

Resveratrol induces premature senescence in lung cancer cells via ROS-mediated DNA damage.

Resveratrol (RV) is a natural component of red wine and grapes that has been shown to be a potential chemopreventive and anticancer agent. However, the molecular mechanisms underlying RVs anticancer and chemopreventive effects are incompletely understood. Here we show that RV treatment inhibits the clonogenic growth of non-small cell lung cancer (NSCLC) cells in a dose-dependent manner. Interestingly, the tumor-suppressive effect of low dose RV was not associated with any significant changes in the expression of cleaved PARP and activated caspase-3, suggesting that low dose RV treatment may suppress tumor cell growth via an apoptosis-independent mechanism. Subsequent studies reveal that low dose RV treatment induces a significant increase in senescence-associated β–galactosidase (SA-β-gal) staining and elevated expression of p53 and p21 in NSCLC cells. Furthermore, we show that RV-induced suppression of lung cancer cell growth is associated with a decrease in the expression of EF1A. These results suggest that RV may exert its anticancer and chemopreventive effects through the induction of premature senescence. Mechanistically, RV-induced premature senescence correlates with increased DNA double strand breaks (DSBs) and reactive oxygen species (ROS) production in lung cancer cells. Inhibition of ROS production by N-acetylcysteine (NAC) attenuates RV-induced DNA DSBs and premature senescence. Furthermore, we show that RV treatment markedly induces NAPDH oxidase-5 (Nox5) expression in both A549 and H460 cells, suggesting that RV may increase ROS generation in lung cancer cells through upregulating Nox5 expression. Together, these findings demonstrate that low dose RV treatment inhibits lung cancer cell growth via a previously unappreciated mechanism, namely the induction of premature senescence through ROS-mediated DNA damage.

Inhibition of the promotional phase of azoxymethane-induced colon carcinogenesis in the F344 rat by calcium lactate: effect of simulating two human nutrient density levels

The effects of 2 levels of dietary calcium and 2 types of dietary fat on the promotional phase phase of azoxymethane-induced colon cancer in the F344 rat were investigated. During the initiation phase of carcinogenesis all animals were fed a 5% corn oil AIN-76A diet containing 0.32% Ca in the form of calcium lactate. Rats were then injected with azoxymethane (AOM) weekly for 8 weeks. Thereafter, the rats were fed 1 of 3 diet formulations: a 5% corn oil diet or a 20% corn oil or 20% American Blend oil fat diet, with the level of Ca set at either 0.32% of the diet, a nutrient density simulating a daily human intake of approximately 1700 mg Ca/day, or at 0.04% of the diet, reflecting a human daily intake of approximately 200-250 mg of Ca/day, thus modeling 2 human nutrient density levels for calcium. Measurements of fecal pH during the experiment indicated an acidic adaptation of the large bowel to the lactate anion. Analysis of collected fecal samples showed more total fatty acids to be present in the colon when higher amounts of calcium were consumed. However, results of the tumorigenesis study indicated that calcium lactate fed at the 0.32% level significantly inhibited the development of colonic adenocarcinoma in all dietary groups. Taken together, this investigation supports the hypothesis that calcium supplementation can inhibit colon neoplasia in rats fed a high fat diet; however, under the conditions of this study, the 20% fat level did not significantly promote colon cancer as compared to a 5% fat level.

Epigenetic modulation of the retinoid X receptor α by green tea in the azoxymethane‐ApcMin/+ mouse model of intestinal cancer

We investigated the possible mechanisms of inhibition of colorectal carcinogenesis by green tea (GT) in azoxymethane‐treated (AOM) ApcMin/+ mice. Mice received water or a 0.6% (w/v) solution of GT as the only source of beverage. GT treatment commenced at the 8th week of age and lasted for 8 wk. The treatment caused a statistically significant reduction in the number of newly formed tumors (28%, P < 0.05). Immunohistochemical analysis showed that GT decreased the levels of β‐catenin and its downstream target cyclin D1. To probe a mechanism, we further investigated the expression of retinoic X receptor alpha (RXRα) in AOM/ApcMin/+ tumors. Our results show that RXRα is selectively downregulated in AOM/ApcMin/+ mouse intestinal tumors. In contrast, other retinoic receptors including retinoic acid receptor alpha (RARα), RARβ, RXRβ, and RXRγ were all expressed in ApcMin/+ adenomas. Furthermore, our results show that RXRα downregulation is an early event in colorectal carcinogenesis and is independent of β‐catenin expression. GT significantly increased the protein levels of RXRα. In addition, RT‐PCR analysis showed that GT induced a similar increase in the levels of RXRα mRNA. Genomic bisulfite treatment of colonic DNA followed by pyrosequencing of 24 CpG sites in the promoter region of RXRα gene showed a significant decrease in CpG methylation with GT treatment. The results suggest that a low concentration of GT is sufficient to desilence RXRα and inhibit intestinal tumorigenesis in the ApcMin/+ mouse. Mol. Carcinog.

The Role of Dietary Supplements during Cancer Therapy

This guide was compiled after recommendations by the American Institute for Cancer Research (AICR) Cancer Resource Advisory Council. It encompasses the AICR position on current issues in nutrition for cancer survivors during treatment and is intended to provide advice about dietary supplements for cancer survivors who are still being treated. Current scientific findings about the safety and effectiveness of some commonly used dietary antioxidants and nonantioxidant supplements during chemotherapy are presented and assessed. Use of dietary supplements during cancer treatment remains controversial. Patients are cautioned that vitamin and mineral supplements as therapies are not substitutes for established medicine. The current recommendation for cancer patients is to only take moderate doses of supplements because evidence from human clinical studies that confirm their safety and benefits is limited. A daily multivitamin containing supplements at the levels of the Dietary Reference Intakes can be used safely as part of a program of healthy nutrition. In addition, the AICR Cancer Resource Advisory Council concluded that further scientific research is needed to provide a set of firm guidelines for the use of vitamin and mineral supplements by cancer patients during treatment.