ABSTRACT

Dihydroteleocidin B, which is a derivative of teleocidin from Streptomyces, showed potent tumor-promoting activity in vivo when painted on mouse skin. Although the chemical structure of dihydroteleocidin B is entirely different from those of phorbol esters, the tumor-promoting activity of dihydroteleocidin B was found to be comparable to that of 12-0-tetradecanoylphorbol 13-acetate (TPA) in vivo. Teleocidin from Streptomyces and lyngbyatoxin A and debromoaplysiatoxin from the marine blue-green alga Lyngbya majuscula induced ornithine decarboxylase activity when painted on mouse skin, their effects being similar to those of dihydroteleocidin B and TPA. 13-cis-Retinoic acid inhibited this ornithine decarboxylase induction when painted on theskin 1 hr before these natural products. These three compounds produced adhesion of human promyelocytic leukemia cells (HL-60) to the flasks and inhibited differentiation of Friend erythroleukemia cells induced by dimethyl sulfoxide. The in vitro biological potencies of teleocidin and lyngbyatoxin A were almost as great as those of dihydroteleocidin B and TPA, but that of debromoaplysiatoxin was much weaker.

Thapsigargin, a hexaoxygenated tetraacylated sesquiterpene lactone, induced irritation of mouse ear and histidine decarboxylase (HDC) activity in mouse skin, but it did not induce ornithine decarboxylase in mouse skin or adhesion of human promyelocytic leukemia (HL-60) cells. Although thapsigargin did not give consistent positive results in a short-term screening system for tumor promoters, it was tested in a two-stage carcinogenesis experiment on mouse skin. The potency of thapsigargin to induce HDC in mouse skin was used to determine the dose in this experiment. Application of 10 micrograms (17 nmol) thapsigargin induced HDC activity of 139 pmol CO2/mg protein per 60 min. Tumors were found in the skin of 53.5% of the mice treated with DMBA plus 5 micrograms (8.5 nmol) thapsigargin in week 22, in none of those treated with thapsigargin alone by week 30. One tumor appeared in 1 of 15 mice treated with DMBA alone in week 21. Thapsigargin cannot bind to the phorbol ester receptor in the particulate fraction of mouse skin and so is classified as a non-12-O-tetradecanoylphorbol-13-acetate (TPA) type tumor promoter. It is a new tumor promoter differing in many respects from the well-defined TPA type tumor promoters. Several naturally occurring analogues of thapsigargin, such as thapsigargicin and thapsitranstagin, might also be new non-TPA type tumor promoters, because thapsigargicin and thapsitranstagin induced irritation of mouse ear and HDC activity in mouse skin.

Palytoxon, 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 papillomas and one carcinoma. This paper reports the potent tumor-promoting activity of palytoxin, which is classified as a non-TPA-type tumor promoter.

Okadaic acid (OA)-resistant variants of Chinese hamster ovary cells, clones CHO/OAR6-6 and CHO/OAR2-3, were isolated from a CHO-K1 culture. These variant cells were 17-to 26-fold more i t to OA than the parental cells. The phosphorylase phosphatase activity of the variant cell extracts was 2-to 4-fold more resistant to OA than that ofthe parental cells in the presence of inhibitor 2, a specific inhibitor of type 1 protein serine/threonine phosphatase (PP1