A new type of phorbol ester, which has a macrocyclic dicarboxylic acid diester structure, was isolated from the seed oil of Jatropha curcas L. (Euphorbiaceae). Based on the results of spectroscopic analyses of the compound and its chemical degradation products, its structure is proposed to be an intramolecular 13,16-diester of 12-deoxy-16-hydroxyphorbol, 12-deoxy-16-hydroxyphorbol-4′-[12′,14′-butadienyl]-6′-[16′,18′,20′-nonatrienyl]-bicyclo[3.1.0]hexane-(13-O)-2′-[carboxylate]-(16-O)-3′-[8′-butenoic-10′]ate (DHPB). DHPB showed slightly weaker biological and biochemical activities than 12-O-tetradecanoylphorbol-13-acetate (TPA). DHPB induced ornithine decarboxylase in mouse skin (2.8 nmol CO2/30 min/mg protein/34 nmol application), inhibited the specific binding of [3H]-12-O-tetradecanoylphorbol-13-acetate to phorbol ester receptors (50% effective dose, 17.0 nm), and activated protein kinase C in vitro (50% effective dose, 36.0 nm). Also, a weak tumor-promoting activity of DHPB was found in a two-stage carcinogenesis experiment on mouse skin. One week after initiation of mice with 100 µg of 7,12-dimethylbenz(a)anthracene, topical application, twice a week, of 2 µg of DHPB until week 17, followed by application of 5 µg of DHPB until week 30 at the same rate, resulted in 46.7% incidence of tumors by week 30. The groups treated with 7,12-dimethylbenz(a)anthracene alone or DHPB alone did not produce significant numbers of tumors. These results indicate that the new phorbol ester, DHPB, is a tumor promoter with weaker activity than 12-O-tetradecanoylphorbol-13-acetate.
This work was supported in part by Grants-in-Aid for the Monbusho International Scientific Research Program from the Ministry of Education, Science and Culture, and for Cancer Research in the Comprehensive 10-Year Strategy for Cancer Control from the Ministry of Health and Welfare and by a grant from the Princess Takamatsu Cancer Research Fund.