Anaerobic incubation of phorbol (1) from Croton tiglium with human intestinal bacteria afforded five metabolites: isophorbol (2), deoxyphorbol (3), 4beta,9alpha,20-trihydroxy-13,15-seco-1,6,15-tigliatriene-3,13-dione (4), 4beta,9alpha,20-trihydroxy-15,16,17-trinor-1,6-tigliadiene-3,13-dione (5) and 4beta,9a,20-trihydroxy-14(13-->12)-abeo-12alphaH-1,6-tigliadiene-3,13-dione (6). All these metabolites (2-6) were identified and characterized by spectroscopic means, including two-dimensional (2D)-NMR. Nine defined strains from the human intestine showed an ability to transform 1 to these metabolites.
12-O-tetradecanoylphorbol 13-acetate (I) & phorbol (II) incr the recovery of ouabain-resistant mutants in N-methyl-N'-nitro-N-nitrosoguanidine- and methylazoxyethanol acetate-treated V79 chinese hamster cell cultures. In both cases I was more effective than II in promoting the mutant recovery.
Studies on the mechanism of skin tumor promotion. Phorbol given simultaneously with 12-o-tetradecanoylphorbol 13-acetate after 7,12-dimethylbenz[a]anthracene (DMBA) initiation in female mice had no effect on promotion.
A single s.c. injection of 200 uCi ((3)H)-thymidine into pregnant BALB/c mice followed by i.p. injections of phorbol twice weekly for 25 wk, in the offspring, resulted in higher tumor development in the lungs and livers of male and, to a lesser extent, of female offspring, than in their untreated littermates. The difference in overall tumor incidence was statistically significant, but the increases of the individual tumor types were only of borderline significance. Slight carcinogenic activity of ((3)H)thymidine alone was observed in the mothers and in the offspring without phorbol treatment. ((3)H)-thymidine may be useful as a broad spectrum initiator for transplacental 2-stage carcinogenicity studies to determine the organ specificity of different promoting agents.
Twice-weekly i.p. injections of 4 mg phorbol for 10 wk, after a single feeding of 6 mg dimethylbenz(a)anthracene (DMBA) in female Wistar rats, led to a significant augmentation of mammary adenocarcinoma incidence and of lymphatic leukemia incidence as compared to 6 mg DMBA alone. In female Sprague-Dawley rats, using the same doses of DMBA and phorbol and the same injection schedule, phorbol given after DMBA did not augment mammary adenocarcinoma incidence or lymphatic leukemia incidence as compared to DMBA given alone. There is a strain-related sensitivity between Wistar and Sprague-Dawley rats with regard to the promoting activity of phorbol when phorbol treatment follows DMBA treatment, and mammary adenocarcinoma incidence and lymphatic leukemia incidence are studied. Phorbol did not promote mammary fibroadenoma incidence in DMBA-treated rats, mammary adenocarcinoma incidence in procarbazine-treated rats and mammary adenocarcinoma incidence or mammary fibroadenoma incidence in X-ray-treated rats. DMBA and procarbazine, with or without phorbol, tended to induce more mammary neoplasms in the anterior (thoracic) than in the posterior (abdominal) mammary glands. X-Irradiation tended to induce mammary neoplasms in approximately equal numbers in the anterior and posterior mammary glands. Regional differences in chemically induced mammary carcinogenesis were due to a difference in the transport and delivery of the chemical carcinogens to the regions rather than a difference in the amount of mammary gland tissue in the regions. An analysis of the numbers of Sprague-Dawley rats that developed either no mammary neoplasms, or only mammary adenocarcinomas, or only mammary fibroadenomas, or both mammary adenocarcinomas and mammary fibroadenomas in response to DMBA, procarbazine and X-ray, suggested that the development of a mammary adenocarcinoma or the development of a mammary fibroadenoma are independent processes.
IDENTIFICATION AND USE: Phorbol is a powder. It is used in biochemical and medical research. HUMAN EXPOSURE AND TOXICITY: Phorbol lacked the lymphocyte-activating inducing properties found in phorbol esters. Unlike phorbol esters, phorbol lacks tumor-promoting activity and it was either inactive or elicited poor response in inhibition of growth and stimulation of differentiated functions in human melanoma cells. ANIMAL STUDIES: Phorbol (20 ug/mL) was devoid of biological activity and had no effect on binding sites in prepn from mouse brain. Phorbol did not stimulate prostaglandin E2 synthesis in bone and bone resorption in neonatal mouse calvaria in organ culture. Phorbol showed no erythroid differentiation in Friend virus-transformed proerythroid C1 745 cells. Thus phorbol is inactive analog of phorbol esters.
