Suppression of chemical carcinogenesis by water-soluble organosulfur compounds

The chemopreventive effects of five water-soluble organosulfur compounds, S -methylcysteine (SMC) and four analogs, were examined on the promotion stag e of diethylnitrosamine hepatocarcinogenesis in male F344 rats, using the m edium-term bioassay (Ito test), which is based on the two-step model of hep atocarcinogenesis. In addition, we investigated the modifying effects of SM C and cysteine on the initiation stage of rat hepatocarcinogenesis. Carcino genic potential was scored by comparing the numbers and areas of a putative neoplastic lesion, glutathione S-transferase placental form (GST-P)-positi ve hepatocellular foci. SMC and cysteine significantly decreased the number and area of GST-P-positive foci when given in the promotion stage of the I to test. When given during the initiation stage, these two organosulfur com pounds also significantly inhibited focus formation. Liver ornithine decarb oxylase activity after two thirds partial hepatectomy and the proportion of hepatocytes positive for proliferating cell nuclear antigen significantly decreased the number of aberrant crypt foci in the colon in a multiorgan ca rcinogenesis bioassay of rats. These results support SMC and cysteine as ch emopreventive agents for hepatocarcinogenesis and colon carcinogenesis. The ir intake may be of importance for cancer.