Modulation of in vitro biomarkers of the carcinogenic process by chemopreventive agents

A structurally diverse group of chemopreventive agents was evaluated using in vitro biomarkers of the carcinogenesis process. With cultured human bronchial epithelia (BEAS-2B) cells, sulfur-containing compounds such as 1,2-dithiole-3-thione and sulforaphane, and phenolic compounds such as caffeic acid phenethyl ester and genistein, showed potent inhibition of benzo(a)pyrene [B(a)P] metabolite-DNA binding. Phenolic compounds also demonstrated strong antioxidant activity. Most of the test compounds did not inhibit 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ornithine decarboxylase (ODC) activity with cultured mouse epidermal ME 308 cells, with the exception of sulfur-containing compounds, 1,2-dithiole-3-thione and sulforaphane, and a selenium compound, 1,4-phenylenebis (methylene)selenocyanate. With cultured Hepa 1c1c7 cells, sulforaphane and 1,2-dithiole-3-thione mediated strong induction of quinone reductase, and genistein and ursolic acid were moderate inducers. Chalcone, 1,4-phenylenebis (methylene)selenocyanate and caffeic acid phenethyl ester induced HL-60 cell differentiation. Interestingly, sulforaphane and caffeic acid phenethyl ester inhibited the total metabolism of benzo(a)pyrene with cultured BEAS-2B cells, and the distribution pattern of water-soluble metabolites was altered in comparison with the control groups. These data are suggestive of pleiotropic mechanisms that should prove beneficial when considering the chemopreventive activity of these substances. As a result, of the group of 25 agents tested, four were judged as superior cancer chemopreventive agents: caffeic acid phenethyl ester, 1,2-dithiole-3-thione, genistein, and sulforaphane.