Roussin red methyl ester, a tumor promoter isolated from pickled vegetables.

Roussin red methyl ester [RRME; Fe2(SMe)2(NO)4], has recently been isolated from pickled vegetables consumed in Linxian, China. In the present studies, the tumor-promoting effect of RRME was found in rats treated first with nitrosodiethylamine. A two-stage experiment was also carried out by application of RRME on BALB/c mouse skin subsequent to 7,12-dimethylbenz[a]anthracene treatment, and induction of ornithine decarboxylase (ODC) activity was observed in epidermal cells. After 37-week treatments with 150, 300 or 450 nmol of RRME, the skin developed precancerous lesions and squamous cell carcinomas. The epidermal ODC activity was increased rapidly following a single application of RRME, and the level of its activation was in proportion to the doses used, although the promoting effect of RRME was weaker than that of 12-O-tetradecanoyl-phorbol-13-acetate. Since pickled vegetables are staple food in high-risk areas for esophageal cancer, RRME, as a tumor promoter, may therefore play a role in the development of this malignant disease.