Tumor promoters, retinoid effects

The tumor promoters as a class exhibit mitogenic activity and as already discussed, the ability of retinoids to oppose or to enhance that effect depends on the particular cell culture system employed and on experimental design. Kaneko... 

Chao W-R, Jong L, Costa E, Lehmann J, Pfahl M, Dawson MI (1993) Effects of retinoic acid receptor-specific and retinoid X receptor-specific retinoids on the induction of ornithine decarboxylase in mouse epidermis treated with the tumor promoter 12-0-tetradecanoylphorbol-13-acetate. American Association of Cancer Research Special Conference, Mechanism of Action of Retinoids, Vitamin D, and Steroid Hormones. Banff, Alberta, Canada... 

Ciubotariu, D., Grozav, A., Gogonea, V., Ciubotariu, C., Medeleanu, M., Dragos, D., Pasere, M. and Simon, Z. (2001) The effects of retinoids upon epithelial differentiation of hamster trachea, induction of ornithine decarboxylase and promotion of tumors in mouse epidermis. A QSAR study by MTD method. MATCH Commun. Math. Comput. Chem., 44, 65-92. 

Phorbol esters. Phorbol esters are an interesting class of compounds which are synthesized by plants of the Euphorbiaceae family. (See also the article by Berry and Helms in this vo1-ume.) They promote skin tumors and also affect the immune system. They stimulate some subpopulations of human T-lymphocytes to divide (Kaplan et al., 1982) and alter the activity of natural killer cells (Kolb et al., 1981). The effect may be adjuvantlike, since the phorbol esters have a macrophage-replacing activity in some culture systems (Koretzky et al., 1982). Vitamin A derivatives appear to inhibit the mitogenic activity of phorbols (Skinnider and Giesbrecht, 1981), but it is not clear whether this is related to the immunopharmacological effects of retinoids discussed above. 

Retinoids are well-known inhibitors of phorbol ester-mediated promotion of skin tumor formation (see Chapters 5 and 14). In one suggested explanation of this effect, the induction of terminal differentiation of normal epidermal cells by phorbol esters would allow compensatory expansion of a population of initiated... 

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