Qualitative and quantitative separation of a series of phorbol-ester tumor promoters by high-pressure liquid chromatography

Analysis and purification of phorbol esters using normal phase HPLC and photodiode-array detection

For the first time a normal-phase HPLC method using photodiode-array detection is described for the analysis and purification of phorbol esters. The use of the method is demonstrated with examples of 10 different tigliane and daphnane esters (TPA, DOPP, DOPPA, Sap A, Sap B, Sap C, Sap D, Thy A, Ro and Rx). Both analytical and semipreparative techniques were developed. The method has been used in the final purification of DOPP and Rx from plant extracts. The method can be employed in the areas of phytochemistry, biochemistry and pharmacology/toxicology, where small samples of the toxic materials are required for research.

Multistage carcinogenesis in mouse skin

The mouse skin model of multistage carcinogenesis has for many years provided a conceptual framework for studying carcinogenesis mechanisms and potential means for inhibiting specific stages of carcinogenesis. The process of skin carcinogenesis involves the stepwise accumulation of genetic change ultimately leading to malignancy. Initiation, the first step in multistage skin carcinogenesis involves carcinogen-induced genetic changes. A target gene identified for some skin tumor initiators is c-Ha-ras. The second step, the promotion stage, involves processes whereby initiated cells undergo selective clonal expansion to form visible premalignant lesions termed papillomas. The process of tumor promotion involves the production and maintenance of a specific and chronic hyperplasia characterized by a sustained cellular proliferation of epidermal cells. These changes are believed to result from epigenetic mechanisms such as activation of the cellular receptor, protein kinase C, by some classes of tumor promoters. The progression stage involves the conversion of papillomas to malignant tumors, squamous cell carcinomas. The accumulation of additional genetic changes in cells comprising papillomas has been correlated with tumor progression, including trisomies of chromosomes 6 and 7 and loss of heterozygosity. The current review focuses on the mechanisms involved in multistage skin carcinogenesis, a summary of known inhibitors of specific stages and their proposed mechanisms of action, and the relevance of this model system to human cancer.

Phorbol myristate acetate stimulates phagosome-lysosome fusion in mouse macrophages

The effect of the tumor promoter phorbol myristate acetate (PMA) on phagosome-lysosome (P-L) fusion in mouse macrophages has been studied using a previously described (10) fluorescence assay. Treatment with 0.1--1.0 microgram PMA/ml caused a striking increase in the rate and extent of P-L fusion. Exposure of cells to phorbol, free myristate, or the monoesters of PMA did not reproduce this effect. Macrophages required from 2 to 3 h of pretreatment to express maximal P-L fusion, and this was maintained for at least 20 h when cells were returned to PMA-free medium. Catalase, superoxide dismutase, indomethacin, and hydrocortisone, agents that are known to block the effect of PMA on H2O2, O2-, prostaglandins, or plasminogen activator, did not affect the stimulation of P-L fusion by PMA. The protein-synthesis inhibitors puromycin and cycloheximide did block the PMA effect under conditions in which the high fusion rate of 4-d cells was not affected. Labeled PMA was rapidly taken up by macrophages, with a plateau of uptake at approximately 3 h. When cells were returned to PMA-free medium, cel-associated label was rapidly released, returning to background level within 1 h. The released label was found to be a metabolite of PMA by thin-layer chromatography. This product migrated between the monoester phorbol-12-myristate and free phorbol. Rapid metabolism of PMA was also observed by a macrophage cell line, J774, and, to a lesser extent, by primary rat embryo fibroblasts.