Colorectal cancer is a major cause of cancer deaths in Western countries, but epidemiological data suggest that dietary modi®cation might reduce these by as much as 90%. Cyclo-oxygenase 2 (COX2), an inducible isoform of prostaglandin H synthase, which mediates prostaglandin synthesis during in¯ammation, and which is selectively overexpressed in colon tumours, is thought to play an important role in colon carcinogenesis. Curcumin, a constituent of turmeric, possesses potent anti-in¯amma-tory activity and prevents colon cancer in animal models. However, its mechanism of action is not fully understood. We found that in human colon epithelial cells, curcumin inhibits COX2 induction by the colon tumour promoters, tumour necrosis factor a or fecapentaene-12. Induction of COX2 by in¯ammatory cytokines or hypoxia-induced oxidative stress can be mediated by nuclear factor kappa B (NF-kB). Since curcumin inhibits NF-kB activation, we examined whether its chemopreventive activity is related to modulation of the signalling pathway which regulates the stability of the NF-kBsequestering protein, IkB. Recently components of this pathway, NF-kB-inducing kinase and IkB kinases, IKKa and b, which phosphorylate IkB to release NF-kB, have been characterised. Curcumin prevents phosphorylation of IkB by inhibiting the activity of the IKKs. This property, together with a long history of consumption without adverse health e ects, makes curcumin an important candidate for consideration in colon cancer prevention.

Indole-3-carbinol (I3C) and 3,3-diindolylmethane (DIM) are promising cancer chemopreventive agents in rodent models, but there is a paucity of data on their pharmacokinetics and tissue disposition. The disposition of I3C and its acid condensation products, DIM, [2-(indol-3-ylmethyl)-indol-3-yl]indol-3-ylmethane (LTr 1 ), indolo[3,2b]carbazole (ICZ) and 1-(3-hydroxymethyl)-indolyl-3-indolylmethane (HI-IM) was studied, after oral administration of I3C (250 mg/kg) to female CD-1 mice. Blood, liver, kidney, lung, heart, and brain were collected between 0.25 and 24 h after administration and the plasma and tissue concentrations of I3C and its derivatives determined by high-performance liquid chromotography. I3C was rapidly absorbed, distributed, and eliminated from plasma and tissues, falling below the limit of detection by 1 h. Highest concentrations of I3C were detected in the liver where levels were approximately 6-fold higher than those in the plasma. Levels of DIM, LTr 1 , and HI-IM were much lower, although they persisted in plasma and tissues for considerably longer. DIM and HI-IM were still present in the liver 24 h after I3C administration. Tissue levels of DIM and LTr 1 were found to be in equilibrium with plasma at almost every time point measured. In addition to acid condensation products of I3C, a major oxidative metabolite (indole-3-carboxylic acid) and a minor oxidative metabolite (indole-3-carboxaldehyde) were detected in plasma of mice after oral administration of I3C. ICZ was also tentatively identified in the liver of these mice. This study shows for the first time that, after oral administration to mice, I3C, in addition to its acid condensation products, is absorbed from the gut and distributed systemically into a number of well-perfused tissues, thus allowing the possibility for some pharmacological activity of the parent compound in vivo.

Consumption of fruits and vegetables has generally been associated with a decrease in cancer incidence and cardiovascular disease. Over the years, numerous bioactive compounds have been identified that contribute to these beneficial health effects. More recently, evidence is emerging that specific combinations of phytochemicals may be far more effective in protecting against cancer than isolated compounds. Combinatorial effects have been observed where any one of the single agents is inactive. Apart from interactions among dietary micronutrients, drug-phytochemical interactions have also been observed, indicating possibilities for improved cancer therapeutic strategies. Our understanding of the molecular mechanisms underlying such synergistic effects is still limited, but it appears that different combinations of complementary modes of actions are involved. In this review, we discuss the molecular mechanisms that are likely to be involved in cancer chemoprevention and summarize the most important findings of those studies that report synergistic chemopreventive effects of dietary compounds.

The highly inducible enzyme, hemeoxygenase-1 (HO-1), metabolizes heme, thereby protecting a variety of cells against oxidative stress and apoptosis. Up-regulation by cancer chemopreventive agents has been reported, but its regulation and function in transformed cells are unclear. We compared induction by two dietary polyphenols, curcumin and epigallocatechin-3-gallate (EGCG), with that by the endogenous substrate hemin in epithelial and endothelial cells and examined the relevance to apoptosis. Curcumin or hemin (20 M) induced HO-1 in breast cells from 5 to 24 h. Curcumin (5-40 M) or hemin (5-100 M) induced HO-1 and nuclear levels of nuclear factor (erythroid-derived 2)-related factor (Nrf2) in a dose-dependent manner. EGCG had no effect in breast cells, but at 30 M, it induced nuclear translocation of Nrf2 and HO-1 expression in B-lymphoblasts. In all cases, induction was inhibited by pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) or the p38 inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580). The nuclear factor-B (NF-B)-DNA binding inhibitor helenalin (20 M) also prevented induction. However, wortmannin had no effect, suggesting that PI3K was not involved. Curcumin and hemin also induced nuclear Nrf2 and HO-1 effectively in wild-type mouse embryo fibroblasts (wt MEFs) and in B-Raf Ϫ/Ϫ MEFs but not in Nrf2 Ϫ/Ϫ MEFs. However, EGCG (5-20 M) induced HO-1 only in wt MEFs. Results suggest that signaling through p38 mitogen-activated protein kinase, NF-B, and Nrf2 as well as other unidentified molecules is involved in HO-1 induction by hemin and both polyphenols, but cell-specific factors also play a role, particularly with respect to EGCG. Induction of HO-1 by curcumin, EGCG, or low concentrations (5-10 M) of helenalin did not protect MDA-MB468 breast cells or B-lymphoblasts from apoptosis.