Chemicals experimental tumor promoter

Plants and microorganisms produce unique and diverse chemical stmctures, some of which act as immunomodulators (18—28). Of specimens used in traditional medicine, approximately 450 plant species have shown antiviral activity out of 4000 plants screened (19). Several tannins (20) exhibit strong inhibition of tumor promotion experimentally. Pretreatment of mice with small amounts of tannins for several days strongly rejected transplanted tumors. This activity has been claimed to be effected through enhancement of host-mediated antitumor activity. 

Sivak, A., Mechanisms of Tumor Promotion and Cocarcinogenesis A Summary from One Point of View. In T.J. Slaga, A. Sivak, R.K. Boutwell, eds. "Carcinogenesis - A Comprehensive Survey - Volume 2", Raven Press, New York, N.Y., 1978, 553-564. Miller, E.C., Some Current Perspectives on Chemical Carcinogenesis in Humans and Experimental Animals Presidential Address, Cancer Research, 1978, 38 1479-1496. 

A literature review of animal experimental studies with tryptophan and carcinogenesis, particularly involving bladder and liver, indicates that tryptophan alone does not induce tumors but is capable of acting in many cases as a promoting agent in chemical carcinogenesis. Whether this effect is due to tryptophan alone or to tryptophan metabolites is not clear. In the induction of bladder cancer, tryptophan metabolites are clearly implicated. 

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