Inhibition of cancer growth by resveratrol (trans-3,5,4'-trihydroxystilbene; RESV), a phytoalexin present in many plant species, is limited by its low bioavailability. Pterostilbene (3,5-dimethoxy-4'-hydroxystilbene; PTER) and quercetin (3,3',4',5,6-pentahydroxyflavone; QUER), two structurally related and naturally occurring small polyphenols, show longer half-life in vivo. In vitro growth of highly malignant B16 melanoma F10 cells (B16M-F10) is inhibited (56%) by short-time exposure (60 min/day) to PTER (40 microm) and QUER (20 microm) (approximate mean values of plasma concentrations measured within the first hour after intravenous administration of 20 mg/kg each polyphenol). Intravenous administration of PTER and QUER (20 mg/kg per day) to mice inhibits (73%) metastatic growth of B16M-F10 cell in the liver, a common site for metastasis development. The anti-metastatic mechanism involves: 1) a PTER-induced inhibition of vascular adhesion molecule 1 expression in the hepatic sinusoidal endothelium, which consequently decreases B16M-F10 cell adhesion to the endothelium through very late activation antigen 4; and 2) a QUER- and PTER-induced inhibition of Bcl-2 expression in metastatic cells, which sensitizes them to vascular endothelium-induced cytotoxicity. Our findings demonstrate that the association of PTER and QUER inhibits metastatic melanoma growth and extends host survival.

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Highly metastatic B16 melanoma (B16M)-F10 cells, as compared with the low metastatic B16M-F1 line, have higher GSH content and preferentially overexpress BCL-2. In addition to its anti-apoptotic properties, BCL-2 inhibits efflux of GSH from B16M-F10 cells and thereby may facilitate metastatic cell resistance against endothelium-induced oxidative/nitrosative stress. Thus, we investigated in B16M-F10 cells which molecular mechanisms channel GSH release and whether their modulation may influence metastatic activity. GSH efflux was abolished in multidrug resistance protein 1 knock-out (MRP؊/؊1) B16M-F10 transfected with the Bcl-2 gene or in MRP؊/؊1 B16M-F10 cells incubated with L-methionine, which indicates that GSH release from B16M-F10 cells is channeled through MRP1 and a BCL-2-dependent system (likely related to an L-methionine-sensitive GSH carrier previously detected in hepatocytes). The BCL-2-dependent system was identified as the cystic fibrosis transmembrane conductance regulator, since monoclonal antibodies against this ion channel or H-89 (a protein kinase A-selective inhibitor)-induced inhibition of cystic fibrosis transmembrane conductance regulator gene expression completely blocked the BCL-2-sensitive GSH release. By using a perifusion system that mimics in vivo conditions, we found that GSH depletion in metastatic cells can be achieved by using Bcl-2 antisense oligodeoxynucleotide-and verapamil (an MRP1 activator)-induced acceleration of GSH efflux, in combination with acivicin-induced inhibition of ␥-glutamyltranspeptidase (which limits GSH synthesis by preventing cysteine generation from extracellular GSH). When applied under in vivo conditions, this strategy increased tumor cytotoxicity (up to ϳ90%) during B16M-F10 cell adhesion to the hepatic sinusoidal endothelium.B16 melanoma (B16M) 1 cells with high glutathione (GSH; ␥-glutamylcysteinylglycine) content show higher metastatic activity in the liver than those with low GSH content (1). The liver is a common site for metastasis development, and we demonstrated that GSH protects B16M cells against nitrosative and oxidative stress in the murine hepatic microvasculature (2, 3). The concept that high GSH content status is an important factor for metastasis progression was strongly supported by the fact that metastatic B16M cell survival and growth can be enhanced by directly increasing their GSH content with GSH ester, which readily enters the cell and delivers free GSH (4, 5). In consequence, the maintenance of high intracellular levels of GSH appears critical for metastatic cells to survive intravascularly and to progress extravascularly.Multidrug and/or radiation resistance, which are characteristic features of malignant tumors, frequently associate with high GSH content in the cancer cells (6). Efflux of GSH and GSH S-conjugates from different mammalian cells is mediated by multidrug resistance proteins (MRP), among which MRP1 and MRP2 have been characterized at the functional level as ATP-dependent pumps with broad specificity for GSH and glucuro...

a b s t r a c tThe aim of the present work was to evaluate the occurrence of trichothecenes toxins, deoxynivalenol (DON) and nivalenol (NIV) in samples of corn-based foods (breakfast cereals and snacks) consumed by the Spanish population. A total of 175 commercially available samples were randomly collected during 2005. Trichothecenes were determined by a gas chromatography-electron capture detector. The estimated limit of quantification was 25.4 mg/kg for DON and 15.9 mg/kg for NIV. DON was detected in 22 of the 55 samples of breakfast cereals, in 13 of the 57 samples of baked corn snacks and in 12 of the 63 samples of fried corn snacks. NIV was detected in 6 samples of breakfast cereals and 1 sample of snacks. The median concentrations of DON and NIV found in all samples were 53.9 and 60.2 mg/kg, respectively. The influence of different factors, such as the presence of additional ingredients and the type of commercial brand, on the toxin incidence and content levels were also studied. The values of both mycotoxin intake found in this study are lower than the proposed tolerable daily intake for the respective toxin (1 and 0.7 mg/kg bw/day for DON and NIV, respectively).

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