Proc Amer Assoc Cancer Res, Volume 45, 2004
1377
It is known that the sulfate metabolites of estrogens and bioflavoniods have relatively long half-lives and could still exert biological functions following their metabolic desulfation. Recent studies by us and others have shown that cultured human cells appear to have the ability to re-uptake sulfated estrogens and bioflavonoids. In the present study, we used quercetin and quercetin-3-sulfate as model compounds to probe the roles of cellular transporter activity and metabolic desulfation in modulating the actions of drug sulfates in human mammary cells. Experimentally, since quercetin is a growth inhibitor whereas quercetin-3-sulfate is inactive (unless desulfated), we thus have chosen to measure cell growth as a reliable parameter for their biologic activity. Our data showed that quercetin inhibited growth of normal human mammary epithelial cells (HMECs) and MDA-MB-231 breast cancer cells in a concentration-dependent manner. The IC50 values for quercetin in inhibiting the growth of HMECs and MDA-MB-231 cells were ∼20 and 50 uM, respectively. Quercetin also showed a higher efficacy in inhibiting the growth of HMECs than the growth of MDA-MB-231 cells. Interestingly, quercetin-3-sulfate, when tested under the same experimental conditions, displayed exactly the opposite potency and efficacy in inhibiting the growth of these two human cell lines. As part of our continuing effort to search for the underlying mechanisms, we systematically analyzed the expression of genes encoding various organic anion transporters (OATs) and organic anion-transporting polypeptides (OATPs) by using the real time RT-PCR assay. Our data showed that a number of the transporters (such as OATP-B, D, and E) were expressed in HMECs and MDA-MB-231 cells, and their levels of expression did not appear to differ markedly. Although more studies are needed, the results of our present study, along with our other data on the sulfatase activity, suggest that cellular desulfation activity plays a more important role than the drug sulfate transporter activity in determining the biologic activities of various sulfated endobiotics, xenobiotics, as well as sulfated metabolites of anticancer drugs in human mammary cells. [Supported by Special Coordination Funds from the Ministry of Education, Culture, Sports, Science, and Technology of the Japanese government.]
Polyphenols, a large group of natural antioxidants, are a versatile group of phytochemicals beneficial for disease prevention. In this study, we comprehensively analyzed polyphenols, catechins, procyanidins, simple polyphenols, anthocyanins and flavonoids, in fruits consumed in Japan by high performance liquid chromatography with photo-diode array and mass spectrometric detection to complete the database of food components.
3-Amino-1, 4-dimethyl-5H-pyrido[4, 3-b]indole (Trp-P-1) is a mutagen/carcinogen derived from cooked foods which enhances the induction of mutations and chromosome aberrations by UV without microsomal activation. These co-mutagenic effects are considered to arise from inhibition of DNA excision repair at the incision step. However, the inhibition mechanism has not been clarified. in this study we show, using agarose gel electrophoresis, thatTrp-P-1 inhibits incision by T4 endonuclease V, which cleaves DNA at the site of cyclobutane dimers. Trp-P-1 also inhibitsthe binding of this enzyme to UV-damaged DNA in a gel shift assay. In addition, the results of DNA unwinding assay with topoisomerase I suggest that Trp-P-1 intercalates into DNA molecules. The known intercalators ethidium bromide and acriflavine demonstrate similar effects in these experiments. However, 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP), which showed no co-mutagenic effects in our previous study, does not demonstrate such effects. These resultssuggest that Trp-P-1 changes DNA conformation by intercalation, causing inhibition of binding of repair enzymes to UV-damaged DNA, and this in turn leads to inhibition of DNA excision repair and to co-mutagenic effects.
