Cancer Chemopreventive Efficacy Research Articles

Abstract B40: Chemoprevention potential of grape seed extract in azoxymethane-induced colon tumorigenesis in the A/J mouse model

Abstract Colorectal cancer (CRC) is the second leading cause of cancer-related deaths. Overall, CRC is the third most diagnosed cancer in the United States with 150,000 new cases per year. Traditional CRC therapies are associated with severe toxicity, and therefore, natural products are appealing alternatives. Grape seed extract (GSE) is a natural supplement, rich in proanthocyanidins; which attributes to its cancer chemopreventive and anti-cancer efficacy in both in-vitro and in-vivo models. Chemoprevention utilizes an agent, natural or synthetic, to delay or stop cancer progression. Most (∼75%) of CRC develops sporadically, and diet, lifestyle, and/or environmental factors could further contribute to CRC progression. Taken together the above discussion, the present study was designed to assess GSE efficacy as a chemoprevention agent against chemical carcinogen (azoxymethane, AOM)-induced colon tumorigenesis in the A/J mouse model. As a carcinogen, AOM is utilized to mimic sporadic CRC development in humans. AOM is metabolized to its active form and results in the development of neoplastic aberrant crypt foci (ACF), which progress to adenoma, then to malignant adenocarcinoma. AOM-induced tumors form primarily in the colon, with greater tumor burden in the distal region. In our study, 6-week old A/J mice were divided into 5 groups: Group 1 received control diet (CD), Group 2 received 0.5% GSE in diet, and the other 3 groups received i.p. injections of AOM (5mg/kg) weekly, for six weeks. Two weeks post AOM injections, one group continued on CD and the other two groups were supplemented with 0.25% and 0.5% GSE (w/w) in diet. Animals were sacrificed at 32 and 42 weeks of age, or 20 and 30 weeks after AOM injections. GSE feeding did not exhibit toxic side effects with long-term treatment, as indicated by diet consumption and body weight-gain profile. GSE treatment resulted in a 48% decrease in colon tumor multiplicity at 32 weeks, and a 55% decrease at 42 weeks with 0.5% GSE. This effect was dose-dependent, with 0.5% GSE exhibiting maximum efficacy. Also, the efficacy was regionally specific, where tumor burden dramatically reduced in the distal region of the colon. Furthermore, GSE treatment reduced overall tumor size; tumor burden ranging from 2–3mm was decrease 85% in AOM-GSE-fed animals (only 5 tumors) compared to AOM-CD group (41 tumors) and no tumors over 3mm were observed with GSE-fed groups. GSE treatment also resulted in a 50% decrease in tumor burden in small intestine. Next we analyzed colon tissue from control and GSE groups to study the mechanism of GSE effects in vivo, towards apoptotic cell death, proliferation, and inflammation. Compared to controls, colon mucosal tissue from GSE-treated mice showed a 2-fold increase in TUNEL positive apoptotic cells, 30% decrease in PCNA positive proliferative cells, and ∼50% decrease in COX2 and iNOS levels in IHC analysis. In addition, cytokine array of colon mucosal tissue revealed that compared to controls, GSE treatment upregulates IFN-γ, IP-10, TNF-α, IL-17, IL-1α, IL-1β and TIMP-1, and down regulates M-CSF and MCP-1. These results are consistence with our IHC observations, specifically IFN-γ and TNF-α have been shown to induce apoptotic death, and MCP-1 expression is associated with colon cancer staging; the lower the levels of MCP-1, the better the prognosis. In conclusion, our results indicated that GSE, a non-toxic agent already consumed by humans, exerts strong chemopreventive effect against sporadic colorectal cancer development, through modulation of apoptosis, proliferation, and inflammation pathways. Citation Information: Cancer Prev Res 2011;4(10 Suppl):B40.

Preclinical renal cancer chemopreventive efficacy of geraniol by modulation of multiple molecular pathways

In the present study, we have evaluated the chemopreventive potential of geraniol (GOH), an acyclic monoterpene alcohol against ferric nitrilotriacetate (Fe-NTA) induced renal oxidative stress and carcinogenesis in Wistar rats. Chronic treatment of Fe-NTA induced oxidative stress, inflammation and cellular proliferation in Wistar rats. The chemopreventive efficacy of GOH was studied in terms of xenobiotic metabolizing enzyme activities, LPO, redox status, serum toxicity markers and the expression of putative nephrotoxicity biomarker Kim-1, tumor suppressor gene P53, inflammation, cell proliferation and apoptosis related genes in the kidney tissue. Oral administration of GOH at doses of 100 and 200 mg/kg b wt effectively suppressed renal oxidative stress and tumor incidence. Chemopreventive effects of GOH were associated with upregulation of xenobiotic metabolizing enzyme activities and down regulation of serum toxicity markers. GOH was able to down regulate expression of Kim-1, NFκB, PCNA, P53 along with induction of apoptosis. However, higher dose of GOH was more effective in modulating these multiple molecular targets both at transcriptional and protein level. These results provide a powerful evidence for the chemopreventive efficacy of GOH against renal carcinogenesis possibly by modulation of multiple molecular pathways.

Chemomodulatory potential of Asparagus adscendens against murine skin and forestomach papillomagenesis

We have evaluated the cancer chemopreventive efficacy of the roots of Asparagus adscendens, which have been used in the Indian traditional medicine system for a long time for the treatment of various ailments. For the first time, the effect of its different doses in a test diet was examined on 7,12-dimethylbenz(a)anthracene-induced skin and benzo(a)pyrene-induced forestomach papillomagenesis in mice. The effect of these test diets was also examined on drug-metabolizing phase I and phase II enzymes, antioxidant enzymes, reduced glutathione content, and peroxidative damage in mice. Results exhibited a significant reduction in the skin and the forestomach tumor incidence with respect to all the three (2, 4, and 6%, w/w) doses as compared with control. Among all the doses tested, 4% of test diet was most effective in protecting the animals against papillomagenesis. Further, the roots of A. adscendens inhibited phase I, and activated phase II system and antioxidant enzymes in the liver especially with 4% of test diet. The content of reduced glutathione was also significantly elevated whereas the peroxidative damage along with lactate dehydrogenase activity were reduced with all the three doses of the test diet. Together, these results suggest the cancer chemopreventive potential of A. adscendens, which could be mediated through drug-metabolizing phase I and phase II enzymes as well as free radical scavenging antioxidant enzymes.

Antiangiogenetic Effects of 4 Varieties of Grapes In Vitro

The purpose of this study was to investigate the inhibitory effects of grapes on the human umbilical vein endothelial (HUVE) cells' capillary tube formation and matrix metalloproteinase-2 (MMP-2) expression secreted into the medium. Four different grape varieties (Concord, Niagara, Chardonnay, and Pinot Noir) were extracted using 80% acetone and the extracts were stored at -80 degrees C. The total amount of phenolics and flavonoids for each of the 4 grape varieties were determined by spectrophotometry. Grape extracts were co-cultured with HUVE cells on Matrigel and inhibitory effects on tube formation were observed under a microscope. The inhibitory effects of grape extracts on MMP-2 expression were examined by zymogram. All 4 grape varieties inhibited the tube formation of HUVE cells in a dose-dependent manner on Matrigel. Except for Chardonnay, the other 3 grape varieties completely inhibited secretion of MMP-2 at 20 mg/mL. There was a significant positive relationship between the total phenolics and flavonoids and antiangiogenetic activities. The grapes tested have the potential to inhibit angiogenesis mainly by their phenolics and flavonoids contents, which partly contribute to their cancer chemopreventive efficacy.

Preclinical Colorectal Cancer Chemopreventive Efficacy and p53-Modulating Activity of 3′,4′,5′-Trimethoxyflavonol, a Quercetin Analogue

Some naturally occurring flavonols, exemplified by quercetin, seem to possess experimental cancer chemopreventive efficacy. Modulation of p53 is a mechanism thought to contribute to their activity. The hypothesis was tested that a synthetic flavonol, 3',4',5'-trimethoxyflavonol (TMFol), can interfere with tumor development and p53 expression in two models of colorectal carcinogenesis, Apc(Min) mice and human-derived HCT116 adenocarcinoma-bearing nude mice. Mice received TMFol with their diet (0.2%) from weaning to week 16 in the case of Apc(Min) or from either day 7 before ("TMFol early") or day 7 after ("TMFol late") tumor inoculation in HCT116 mice. The ability of TMFol to affect tumor proliferation or apoptosis, as reflected by staining for Ki-67 or cleaved caspase-3, respectively, was studied in HCT116 tumors. TMFol tumor levels were measured by high-performance liquid chromatography. Consumption of TMFol reduced small intestinal adenoma burden in Apc(Min) mice by 47%, compared with control mice (P < 0.002). The TMFol early regimen approximately halved HCT116 tumor size (P < 0.05), decreased tumor proliferation, and increased apoptosis, whereas the TMFol late regimen had no significant effect when compared with controls. In tumor tissues from mice, in which TMFol reduced tumor development, p53 expression was increased 3-fold in Apc(Min) and 1.5-fold in HCT116 tumor-bearing mice (P = 0.02). TMFol increased p53 also in cells derived from these tumors. TMFol was detected in HCT116 tumors, but levels did not correlate with tumor burden. TMFol was not mutagenic in the Ames test. The results suggest that chemical modification of the flavonol structure may generate safe and efficacious cancer chemopreventive agents.

Bitter Melon: Antagonist to Cancer

The incidence of cancer is increasing worldwide, in spite of substantial progress in the development of anti-cancer therapies. One approach to control cancer could be its prevention by diet, which inhibits one or more neoplastic events and reduces cancer risk. Dietary compounds offer great potential in the fight against cancer by inhibiting the carcinogenesis process through the regulation of cell homeostasis and cell-death machineries. For centuries, Ayurveda (Indian traditional medicine) has recommended the use of bitter melon (Momordica charantia) as a functional food to prevent and treat diabetes and associated complications. It is noteworthy to mention that bitter melon extract has no-to-low side effects in animals as well as in humans. The anti-tumor activity of bitter melon has recently begun to emerge. This review focuses on recent advancements in cancer chemopreventive and anti-cancer efficacy of bitter melon and its active constituents. Several groups of investigators have reported that treatment of bitter-melon-related products in a number of cancer cell lines induces cell cycle arrest and apoptosis without affecting normal cell growth. Therefore, the effect of bitter melon should be beneficial for health, and use of the non-modified dietary product is cost effective.

Abstract A53: Chemoprevention of colon cancer by PBIT, an iNOS-selective inhibitor, administered alone or in combination with low-doses of celecoxib, a COX-2 selective inhibitor

Abstract Clinical and preclinical studies suggest that NSAIDs and cyclooxygenase (COX)-2 inhibitors such as celecoxib, reduce the risk of colorectal cancer. However high doses of NSAIDs causes gastrointestinal toxicity and increased cardiovascular risk. Inducible nitric oxide synthase (iNOS), like COX-2, is overexpressed in colon tumors. Interestingly, nitric oxide stimulates COX-2 activity and contributes to the tumor growth. The present study examines the effects of S,S′-1,4-phenylenebis(1,2-ethanediyl)bisisothiourea (PBIT), an iNOS-selective inhibitor on 1) azoxymethane (AOM)-induced colon adenocarcinomas in F344 rats 2) evaluates the combined effects of a low-dose PBIT and celecoxib on chemopreventive efficacy in rats. Seven-week old male F344 rats (36/group) were fed control AIN-76A diet and one week later, AOM was administered s.c to induce colonic tumors. Four-weeks after the AOM treatment, groups of rats were fed experimental diets containing either 0, 50, 100 ppm of PBIT or 250 and 500 ppm of celecoxib or a combination of 50 ppm PBIT plus 250 ppm celecoxib. Forty-eight weeks after AOM treatment, rats were killed and the intestinal tumors were evaluated. Multiple samples of colonic tumors from each group were assayed for expression and activity of iNOS, COX-2 and markers of apoptosis and cell proliferation. We found that 50 and 100 ppm PBIT in diet suppressed colon adenocarcinoma incidence by 34.6% (p&amp;lt;0.01) and 43% (p&amp;lt;0.002), respectively. Similarly, dietary PBIT suppressed adenocarcinoma multiplicity by 40% (p&amp;lt;0.05, 50 ppm) and 60% (p&amp;lt;0.006, 100 ppm). Celecoxib at both 250 and 500 ppm significantly suppressed colon adenocarcinoma incidence (55–77%, p&amp;lt;0.002-0.0001) and multiplicity (66–82%, p&amp;lt;0.002 - 0.0002). A low-dose combination of 50 ppm PBIT and 250 ppm celecoxib significanlty suppressed colon adenocarcinoma incidence by 70% and multiplicity by 83% (p&amp;lt;0.0001). Interestingly, a combination of low-dose PBIT and celecoxib produced either equal or increased inhibitory effect when compared with high dose PBIT or celecoxib alone. Rats fed PBIT and/or a combination of PBIT plus celecoxib showed considerable suppression of iNOS (38–59%, p&amp;lt;0.01-0.0001 and COX-2 (44–67%, p&amp;lt;0.0001) activities and increased p21WAF1/CIP expression in colonic tumors. Administration of 100 ppm PBIT, 250 ppm or 500 ppm celecoxib and a combination of 50 ppm PBIT plus 250 ppm celecoxib suppressed tumor cell proliferation (BrdU index by 22–53%, p&amp;lt;0.05-0.0001) when compared with colon tumors from the control group. Significant levels of apoptotic cells were observed in the adenocarcinomas of celecoxib fed rats and also in rats fed with a combination of low-dose PBIT and celecoxib. These observations demonstrate, for the first time, that the iNOS-selective inhibitor possesses dose-dependent chemopreventive activity in well-established models of colon cancer and a combination of low-dose PBIT and celecoxib significantly enhanced colon cancer chemopreventive efficacy. [Supported by NIH grants R01-CA-102947] Citation Information: Cancer Prev Res 2010;3(1 Suppl):A53.

Chemomodulatory Effect of Trachyspermum ammi on Murine Skin and Forestomach Papillomagenesis

Trachyspermum ammi seed consumed worldwide as a spice ingredient is much valued for its medicinal properties. However, it has not been investigated for its cancer chemopreventive efficacy. Herein, the chemopreventive effect of different doses (2%, 4%, and 6%) of test diets of Trachyspermum ammi seeds were examined on DMBA-induced skin and B(a)P-induced forestomach papillomagenesis, inducibility of drug metabolizing phase I and phase II enzymes, antioxidant enzymes(catalase, superoxide dismutase, glutathione peroxidase, glyoxalase I), reduced glutathione content, and peroxidative damage. Results exhibited a significant reduction in the skin as well as the forestomach tumor multiplicity with respect to all doses of test diet as compared to the control group. Biochemical assays revealed a significant increase in the activities of phase I enzymes especially with 6% test diet. A concomitant increase in the activities of the phase II enzymes and antioxidant enzymes were observed in Trachyspermum ammi treated groups. The content of reduced glutathione was significantly elevated, whereas the peroxidative damage along with lactate dehydrogenase activity exhibited a significant reduction with all the three doses of test diet. These findings were indicative of chemopreventive potential of Trachyspermum ammi seeds against carcinogenesis.

Sulindac Sulfide Selectively Induces Apoptosis of Human Breast Tumor Cells by Inhibiting PDE5A, Elevating cGMP, and Activating PKG.

Abstract Nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX)-2 selective inhibitors display promising antineoplastic activity, but the gastrointestinal, renal, and cardiovascular toxicities that result from COX inhibition limit their clinical utility for cancer chemoprevention. Previous studies suggest that the pro-apoptotic activity of these drugs may be due to a COX-independent mechanism involving cyclic guanosine monophosphate (cGMP) phosphodiesterase (PDE) inhibition. However, the specific PDE isozyme(s) responsible has not yet been identified. Here we used the NSAID sulindac sulfide (SS) to further study cGMP PDE as a potential molecular target of the NSAIDs for breast cancer chemoprevention. SS inhibited growth and induced apoptosis of human SK-BR-3 and MDA-MB-231 breast tumor cells, while normal human mammary epithelial cells (HMEC) were less sensitive. SS also inhibited cGMP PDE activity from tumor cell lysates at concentrations comparable to those required for apoptosis, while appreciably higher concentrations were necessary to inhibit activity from HMEC lysates or cAMP PDE activity from any of the cell lysates. Additionally, SS increased intracellular cGMP concentrations and induced protein kinase G (PKG) activity in MDA-MB-231 cells as determined by ELISA and increased levels of phosphorylated VASP, a known PKG substrate, respectively. Moreover, pretreatment with the guanylyl cyclase inhibitor LY83583 desensitized the breast tumor cells to the growth-inhibitory activity of SS, likely by suppressing intracellular cGMP levels. The guanylyl cyclase activator NOR-3 and the cGMP PDE inhibitors MY5445 and trequinsin inhibited tumor cell growth, while the adenylyl cyclase activator forskolin and other PDE inhibitors had no effect. HMEC were found to express several cGMP hydrolyzing PDE isozymes (PDE1, 5, and 9), while the breast tumor cells expressed predominantly PDE5, which was confirmed to be sensitive to inhibition by SS using a recombinant enzyme. This work demonstrates that inhibition of PDE5A, elevation of cGMP, and activation of PKG are responsible for the pro-apoptotic effects of SS in human breast tumor cells and that differential expression of PDE isozymes between normal and tumor cells may explain the tumor selectivity of NSAIDs. These data also suggest that it may be feasible to develop NSAID derivatives with increased selectivity for inhibiting PDE5 and decreased COX-inhibitory activity, which would potentially improve safety and efficacy for breast cancer chemoprevention. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1041.

Inhibition of azoxymethane-induced colorectal cancer by CP-31398, a TP53 modulator, alone or in combination with low doses of celecoxib in male F344 rats.

Tumor suppressor p53 plays a major role in colorectal cancer development. The present study explores the effects of p53-modulating agent CP-31398 alone and combined with celecoxib on azoxymethane-induced aberrant crypt foci (ACF) and colon adenocarcinomas in F344 rats. Maximum tolerated doses were 400 and 3,000 ppm for CP-31398 and celecoxib, respectively. ACF and tumor efficacy endpoints were carried out on azoxymethane-treated 7-week-old rats (48 per group) fed the control AIN-76A diet. Two weeks after carcinogen treatment, rats were fed the diets containing 0, 150, or 300 ppm CP-31398, 300 ppm celecoxib, or 150 ppm CP-31398 plus 300 ppm celecoxib. ACF and colon adenocarcinomas were determined at 8 and 48 weeks after azoxymethane treatment, respectively. Dietary CP-31398 was shown to suppress mean colonic total ACF by 43% and multicrypt ACF by 63%; dietary CP-31398 at 150 and 300 ppm suppressed adenocarcinoma incidence by 30.4% (P < 0.02) and 44% (P < 0.005), respectively, and adenocarcinoma multiplicity by 51% (P < 0.005) and 65% (P < 0.0001), respectively. Dietary celecoxib suppressed colon adenocarcinoma incidence (60%; P < 0.0003) and multiplicity (70%; P < 0.0001). Importantly, combination of low-dose CP-31398 and celecoxib suppressed colon adenocarcinoma incidence by 78% and multiplicity by 90%. Rats that were fed the high-dose CP-31398 or a combination of low-dose CP-31398 and celecoxib showed considerable enhancement of p53 and p21(WAF1/CIP) expression, apoptosis, and reduced tumor cell proliferation in colonic tumors. These observations show, for the first time, that CP-31398 possesses significant dose-dependent chemopreventive activity in a well-established colon cancer model and that a combination of low-dose CP-31398 and celecoxib significantly enhanced colon cancer chemopreventive efficacy.

Anticancer and Cancer Chemopreventive Potential of Grape Seed Extract and Other Grape-Based Products1–3

With emerging trends in the incidence of cancer of various organ sites, additional approaches are needed to control human malignancies. Intervention or prevention of cancer by dietary constituents, a strategy defined as chemoprevention, holds great promise in our conquest to control cancer, because it can be implemented on a broader population base with less economic burden. Consistent with this, several epidemiological studies have shown that populations that consume diets rich in fruits and vegetables have an overall lower cancer incidence. Based on these encouraging observations, research efforts from across the globe have focused on identifying, characterizing, and providing scientific basis to the efficacy of various phytonutrients in an effort to develop effective strategy to control various human malignancies. Cancer induction, growth, and progression are multi-step events and numerous studies have demonstrated that various dietary agents interfere with these stages of cancer, thus blocking malignancy. Fruits and vegetables represent untapped reservoir of various nutritive and nonnutritive phytochemicals with potential cancer chemopreventive activity. Grapes and grape-based products are one such class of dietary products that have shown cancer chemopreventive potential and are also known to improve overall human health. This review focuses on recent advancements in cancer chemopreventive and anticancer efficacy of grape seed extract and other grape-based products. Overall, completed studies from various scientific groups conclude that both grapes and grape-based products are excellent sources of various anticancer agents and their regular consumption should thus be beneficial to the general population.

Flavones as Colorectal Cancer Chemopreventive Agents—Phenol-O-Methylation Enhances Efficacy

Flavonoids occur ubiquitously in plants, and some possess preclinical cancer chemopreventive activity. Little is known about molecular features that mediate chemopreventive efficacy of flavonoids. Here, three related flavones, apigenin (4',5,7-trihydroxyflavone), tricin (4',5,7-trihydroxy-3',5'-dimethoxyflavone), and 3',4',5',5,7-pentamethoxyflavone (PMF), were compared in terms of their effects on (a) adenoma development in Apc(Min) mice, a model of human gastrointestinal malignancies; (b) growth of APC10.1 mouse adenoma cells in vitro; and (c) prostaglandin E-2 generation in HCA-7 human-derived colorectal cancer cells in vitro. Life-long consumption of PMF with the diet at 0.2% reduced Apc(Min) mouse adenoma number and burden by 43% and 61%, respectively, whereas apigenin was inactive. Tricin has previously shown activity in this model. IC50 values for murine adenoma cell growth inhibition by PMF, tricin, and apigenin were 6, 13, and 18 micromol/L, respectively. In Apc(Min) mice that received flavones (0.2%) for 4 weeks, adenoma cell proliferation as reflected by Ki-67 staining was reduced by PMF and tricin, but not by apigenin. On incubation with HCA-7 cells for 6 hours, PMF reduced prostaglandin E-2 generation with an IC50 of 0.8 micromol/L, a fraction of the respective values reported for tricin or apigenin. In silico PMF docked into the cyclooxygenase active site with greater affinity than tricin or apigenin. The results suggest that the rank order of cancer chemopreventive efficacy in Apc(Min) mice is PMF > tricin > apigenin, supporting the notion that the presence of O-methyl in the flavone molecular scaffold promotes gastrointestinal cancer chemopreventive efficacy.

Do anthocyanins and anthocyanidins, cancer chemopreventive pigments in the diet, merit development as potential drugs?

Anthocyanins, plant pigments in fruits and berries, have been shown to delay cancer development in rodent models of carcinogenesis, especially those of the colorectal tract. Anthocyanins and anthocyanidins, their aglycons, especially cyanidin and delphinidin, have been subjected to extensive mechanistic studies. In cells in vitro, both glycosides and aglycons engage an array of anti-oncogenic mechanisms including anti-proliferation, induction of apoptosis and inhibition of activities of oncogenic transcription factors and protein tyrosine kinases. Anthocyanins and anthocyanidins exist as four isomers, interconversion between which depends on pH, temperature and access to light. Anthocyanidins are much more prone to avid chemical decomposition than the glycosides, and they only survive for minutes in the biophase. These pharmaceutical issues are very important determinants of the suitability of these flavonoids for potential development as cancer chemopreventive drugs, and they have hitherto not received adequate attention. In the light of their robust cancer chemopreventive efficacy in experimental models and their superior stability as compared to that of the aglycons, the anthocyanins seem much more suitable for further drug development than their anthocyanidin counterparts.

Evaluation of the cancer chemopreventive efficacy of silibinin in genetic mouse models of prostate and intestinal carcinogenesis: Relationship with silibinin levels

Silibinin, a flavonolignan from milk thistle seeds, possesses cancer chemopreventive properties in rodent models of carcinogenesis. We tested the hypotheses that silibinin or silipide, silibinin formulated with phospholipids, delays tumour development in TRAMP or ApcMin mice, genetic models of prostate or intestinal malignancies, respectively. Mice received silibinin or silipide with their diet (0.2% silibinin equivalents) from weaning. Intervention with silipide reduced the size of well differentiated TRAMP adenocarcinomas by 31%. Silipide and silibinin decreased the incidence of poorly differentiated carcinomas by 61% compared to mice on control diet. Silipide decreased plasma levels of insulin-like growth factor (IGF)-1 by 36%. Levels of circulating IGF binding protein (IGFBP)-3 in mice on silipide or silibinin were 3.9- or 5.9-fold, respectively, elevated over those in control TRAMP mice. In ApcMin mice silibinin, but not silipide, had only a marginal adenoma number-reducing effect. The results cautiously support the advancement of silipide to the stage of clinical investigation in prostate cancer.

Azoxymethane-induced rat aberrant crypt foci: Relevance in studying chemoprevention of colon cancer

The pathogenesis of colon cancer involves sequential and multistep progression of epithelial cells initiated to a cancerous state with defined precancerous intermediaries. Aberrant crypt foci (ACF) represent the earliest identifiable intermediate precancerous lesions during colon carcinogenesis in both laboratory animals and humans. ACF are easily induced by colon-specific carcinogens in rodents and can be used to learn more about the process of colon carcinogenesis. For over two decades, since its first discovery, azoxymethane (AOM)-induced rodent ACF have served as surrogate biomarkers in the screening of various anticarcinogens and carcinogens. Several dietary constituents and phytochemicals have been tested for their colon cancer chemopreventive efficacy using the ACF system. There has been substantial effort in defining and refining ACF in terms of understanding their molecular make-up, and extensive research in this field is currently in progress. In chemoprevention studies, AOM-induced rat ACF have been very successful as biomarkers, and have provided several standardized analyses of data. There have been several studies that have reported that ACF data do not correlate to actual colon tumor outcome, however, and hence there has been an ambiguity about their role as biomarkers. The scope of this mini-review is to provide valuable insights and limitations of AOM-induced rat ACF as biomarkers in colon cancer chemoprevention studies. The role of the dynamics and biological heterogeneity of ACF is critical in understanding them as biomarkers in chemoprevention studies.

Cytoprotection Against Oxidative Damage by Nrf2-regulated Genes

Chronic oxidative stress produced by exposure to environmental chemicals or pathophysiological states can lead animals to aging, carcinogenesis and degenerative diseases. Indirect antioxidative mechanisms, in which natural or synthetic agents are used to coordinately induce the expression of cellular antioxidant capacity, have been shown to protect cells and organisms from oxidative damages. Electrophile and free radical detoxifying enzymes, which were originally identified as the products of genes induced by cancer chemopreventive agents, are members of this protective system. The NFE2 family transcription factor Nrf2 was found to govern expression of these detoxifying enzymes, and screening for Nrf2-regulated genes has identified many gene categories involved in maintaining cellular redox potential and protection from oxidative damage as Nrf2 downstream genes. Further, studies using nrf2-deficient mice revealed that these mutant mice showed more susceptible phenotypes towards exposure to environmental chemicals/carcinogens and in oxidative stress related disease models. With the finding that cancer chemopreventive efficacy of indirect antioxidants (enzyme inducers) is lost in the absence of Nrf2, a central role of Nrf2 in the antioxidative protective system has been firmly established. Promising results from cancer prevention clinical trials using enzyme inducers propose that pharmacological interventions that modulate Nrf2 can be an effective strategy to protect tissues from oxidative damage.

Cancer chemoprevention by phytochemicals: potential molecular targets, biomarkers and animal models

Recent studies have strongly indicated that certain daily-consumed dietary phytochemicals could have cancer protective effects against transgenic mice cancer models and cancers mediated by carcinogens, irradiations and carcinogenic metabolites derived from exogenous or endogenous sources. The cancer-protective effects elicited by these dietary compounds are believed to be due at least in part to the induction of cellular defense systems including the detoxifying and antioxidant enzymes system, as well as the inhibition of anti-inflammatory and anti-cell growth signaling pathways culminating in cell cycle arrest and/or celldeath. In this review, we summarize the potential mechanisms including the modulation of nuclear factor kappaB (NF-kappaB), cyclooxygenases-2 (COX-2), activator protein-1 (AP-1), mitogen-activated protein kinases (MAPKs) and the induction of phase II cellular detoxifying and antioxidant enzymes mediated mainly by the antioxidant response elements (ARE) within the promoter regions of these genes through nuclear factor-erythroid 2-related factor 2 (Nrf2), a member of the Cap "n" collar (CNC) family of the basic region-leucine zipper transcription factor. In addition, we also review several animal models of carcinogenesis and cancer chemopreventive efficacy studies of these animal models using dietary chemopreventive compounds. Finally, we discuss the cellular signaling cascades mediated by Nrf2, NF-kappaB, AP-1, MAPKs and COX-2, which have been considered to play pivotal roles in tumor initiation, promotion and progression processes, and could be promising molecular targets for the design of drugs targeting cancer prevention and therapy.

Phase I Dose Escalation Pharmacokinetic Study in Healthy Volunteers of Resveratrol, a Potential Cancer Chemopreventive Agent

The red grape constituent resveratrol possesses cancer chemopreventive properties in rodents. The hypothesis was tested that, in healthy humans, p.o. administration of resveratrol is safe and results in measurable plasma levels of resveratrol. A phase I study of oral resveratrol (single doses of 0.5, 1, 2.5, or 5 g) was conducted in 10 healthy volunteers per dose level. Resveratrol and its metabolites were identified in plasma and urine by high-performance liquid chromatography-tandem mass spectrometry and quantitated by high-performance liquid chromatography-UV. Consumption of resveratrol did not cause serious adverse events. Resveratrol and six metabolites were recovered from plasma and urine. Peak plasma levels of resveratrol at the highest dose were 539 +/- 384 ng/mL (2.4 micromol/L, mean +/- SD; n = 10), which occurred 1.5 h post-dose. Peak levels of two monoglucuronides and resveratrol-3-sulfate were 3- to 8-fold higher. The area under the plasma concentration curve (AUC) values for resveratrol-3-sulfate and resveratrol monoglucuronides were up to 23 times greater than those of resveratrol. Urinary excretion of resveratrol and its metabolites was rapid, with 77% of all urinary agent-derived species excreted within 4 h after the lowest dose. Cancer chemopreventive effects of resveratrol in cells in vitro require levels of at least 5 micromol/L. The results presented here intimate that consumption of high-dose resveratrol might be insufficient to elicit systemic levels commensurate with cancer chemopreventive efficacy. However, the high systemic levels of resveratrol conjugate metabolites suggest that their cancer chemopreventive properties warrant investigation.

Pilot Study of Oral Silibinin, a Putative Chemopreventive Agent, in Colorectal Cancer Patients: Silibinin Levels in Plasma, Colorectum, and Liver and Their Pharmacodynamic Consequences

Silibinin, a flavonolignan from milk thistle, has intestinal cancer chemopreventive efficacy in rodents. It is a strong antioxidant and modulates the insulin-like growth factor (IGF) system by increasing circulating levels of IGF-binding protein 3 (IGFBP-3) and decreasing levels of IGF-I. Here, the hypothesis was tested that administration of oral silibinin generates agent levels in human blood and colorectal and hepatic tissues consistent with pharmacologic activity. Patients with confirmed colorectal adenocarcinoma received silibinin formulated with phosphatidylcholine (silipide) at dosages of 360, 720, or 1,440 mg silibinin daily for 7 days. Blood and biopsy samples of normal and malignant colorectum or liver were obtained before dosing, and blood and colorectal or hepatic tissues were collected at resection surgery after the final silipide dose. Levels of silibinin were quantified by high-pressure liquid chromatography-UV, and plasma metabolites were identified by liquid chromatography-mass spectrometry. Blood levels of IGFBP-3, IGF-I, and the oxidative DNA damage pyrimidopurinone adduct of deoxyguanosine (M1dG) were determined. Repeated administration of silipide was safe and achieved levels of silibinin of 0.3 to 4 micromol/L in the plasma, 0.3 to 2.5 nmol/g tissue in the liver, and 20 to 141 nmol/g tissue in colorectal tissue. Silibinin monoglucuronide, silibinin diglucuronide, silibinin monosulfate, and silibinin glucuronide sulfate were identified in the plasma. Intervention with silipide did not affect circulating levels of IGFBP-3, IGF-I, or M1dG. The high silibinin levels achieved in the human colorectal mucosa after consumption of safe silibinin doses support its further exploration as a potential human colorectal cancer chemopreventive agent.

Differential modulation of cyclooxygenase-mediated prostaglandin production by the putative cancer chemopreventive flavonoids tricin, apigenin and quercetin

Diet-derived flavonoids possess cancer chemopreventive properties in preclinical models. The knowledge of the pharmacology of most flavonoids is insufficient to warrant their advancement to clinical evaluation. Here the three flavonoids tricin from rice bran, apigenin from leafy vegetables, and quercetin from onions and apples, were compared in terms of their ability to modulate cyclooxygenase- (COX-) catalyzed prostaglandin E-2 (PGE-2) generation. Specifically their effects on the following parameters were studied: (1) COX enzyme activity, (2) COX-2 expression in human-derived colon cancer cells HCA-7, which express COX-2 constitutively, (3) phorbol ester-mediated COX-2 induction in human colon epithelial cells (HCEC), and (4) PGE-2 levels in cellular incubations. Tricin and quercetin inhibited enzyme activity in purified COX-1 and -2 preparations with IC50 values of near 1 (tricin) and 5 microM (quercetin). Apigenin at up to 25 microM did not affect COX enzyme activity. Flavonoids were incubated with cells for 6 or 24 h and COX-2 protein expression and PGE-2 levels were assessed by Western blot and competitive immunoassay, respectively. None of the agents affected constitutive COX-2 expression in HCA-7 cells. Apigenin, but not tricin or quercetin, down-regulated inducible COX-2 expression in HCEC cells on 6 h incubation. All three flavonoids reduced cellular levels of PGE-2 in the supernatant of HCA-7 cells at both time points and of HCEC cells at 6 h. The results demonstrate that these structurally similar flavonoids regulate COX-mediated PGE-2 production in different fashions. Their ability to attenuate prostanoid levels may contribute to their cancer chemopreventive efficacy.