Inhibitory effects of topical application of low doses of curcumin on 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion and oxidized DNA bases in mouse epidermis.

The effects of topical applications of very low doses of curcumin (the major yellow pigment in turmeric and the Indian food curry) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced oxidation of DNA bases in the epidermis and on tumor promotion in mouse skin were investigated. CD-1 mice were treated topically with 200 nmol of 7,12-dimethylbenz[a]anthracene followed one week later by 5 nmol of TPA alone or together with 1, 10, 100 or 3000 nmol of curcumin twice a week for 20 weeks. Curcumin-mediated effects on TPA-induced formation of the oxidized DNA base 5-hydroxymethyl-2'-deoxyuridine (HMdU) and tumor formation were determined. All dose levels of curcumin inhibited the mean values of TPA-induced HMdU formation in epidermal DNA (62-77% inhibition), but only the two highest doses of curcumin strongly inhibited TPA-induced tumor promotion (62-79% inhibition of tumors per mouse and tumor volume per mouse). In a second experiment, topical application of 20 or 100 nmol (but not 10 nmol) of curcumin together with 5 nmol TPA twice a week for 18 weeks markedly inhibited TPA-induced tumor promotion. Curcumin had a strong inhibitory effect on DNA and RNA synthesis (IC50 = 0.5-1 microM) in cultured HeLa cells, but there was little or no effect on protein synthesis.