Antitumor-promoting effects of gallotannins extracted from various sources in mouse skin in vivo.

Sumach leaf, Aleppo gall, Tara pod and commercial tannic acids (TAs) were tested topically for their ability to inhibit the biochemical and biological effects of 12-0-tetradecanoylphorbol-13-acetate (TPA) in mouse epidermis in vivo. These TAs all inhibit to various degrees ornithine decarboxylase (ODC) induction, hydroperoxide (HPx) production and the sequential stimulation of RNA, protein and DNA synthesis linked to TPA promotion. When applied before each promotion treatment, these TAs all inhibit complete tumor promotion by TPA. Sumach leaf TA is the most effective. TAs applied 24h after TPA inhibit HPx production but not tumor promotion, since ODC activity and DNA synthesis have already been stimulated. However, these TA post-treatments enhance the antioxidant and antitumor-promoting effects of TA pretreatments. TAs inhibit the 2nd rather than the 1st stage of tumor promotion. Plant TAs, therefore, may be valuable against tumor propagation but their efficacy may vary considerably depending on their origin.