Palytoxin is a non-12-o-tetradecanoylphorbol-13-acetate type tumor promoter in two-stage mouse skin carcinogenesis

Palytoxin, which is a toxin with a molecular weight of 2681 daltons isolated from a marine coelenterate, is a potent skin irritant. However, it did not induce ornithine decarboxylase in mouse skin, or adhesion of human promyelocytic leukemia cells (HL-60). Moreover, it did not inhibit the specific binding of (³H)12-O-tetradecanoylphorbol-13-acetate (TPA) to a mouse skin particulate fraction or activate protein kinase C isolated from mouse brain in vitro. Since palytoxin showed strong irritation on mouse ear in one short-term screening test for a promoter, it was examined in a two-stage carcinogenesis experiment. The incidence of tumors in a group of mice treated with 7, 12-dimethylbenz(a)anthracene plus palytoxin was 62.5% in week 25. These tumors were identified histologically as seven papillonmas and one carcinoma. This paper reports the potent tumor-promoting activity of palytoxin, which is classified as a non-TPA-type tumor promoter.