aplysiatoxin and mezerein

Adherent bone marrow, spleen and peritoneal mouse macrophages, as well as human peripheral blood monocytes were exposed in vitro to the phorbol ester derivatives 12-O-tetradecanoyl-phorbol-13-acetate (TPA), phorbol 13-monoacetate (PA), phorbol 12-myristate (PM), phorbol 12,13-diacetate (PDA), phorbol 12,13 dibutyrate (PDBu), TPA-20 aldehyde (TPA-AL), phorbol 12-retinoate 13-acetate (PRA), 4-alpha TPA (alpha-TPA) and to mezerein (MEZ) and aplysiatoxin (APL). The triggered macrophages/monocytes were tested for the production of an IL 1-like activity by the thymocyte proliferation assay and for H2O2 generation in a quantitative method which is based on the H2O2-mediated and horseradish peroxidase-dependent oxidation of phenol red. The results showed that strong first stage and second stage tumor promoters such as TPA, PDBu, PRA, MEZ and APL are also strong stimulators of IL 1 and H2O2 generation, whereas weak tumor promoters exhibited a low, if any, effect at all. The afore-described findings lend support to the idea that chronic inflammatory phagocytes might play a role in the tumor promoting process by furnishing both carcinogenic and growth factors at the site of tumor origin.

Topics: Animals; Carcinogens; Diterpenes; Humans; Hydrogen Peroxide; In Vitro Techniques; Interleukin-1; Lyngbya Toxins; Mice; Mice, Inbred CBA; Phagocytes; Phorbol Esters; Terpenes

In the two-stage model of skin carcinogenesis, it is believed that initiators bind to DNA and that tumor promoters such as phorbol 12-tetradecanoate 13-acetate (TPA) bind noncovalently to membrane-associated high-affinity receptors, probably protein kinase C. Two other types of potent tumor-promoting substances, aplysiatoxin and teleocidin, appear to act also by binding to and activating protein kinase C, even though their chemical structures are quite different. Therefore, we have undertaken computer modeling of the special relationship of various functional groups in these three chemical classes of tumor promoters in an attempt to explain how these diverse structures bind to the same receptor molecule. We propose a stereochemical model in which the oxygens in TPA at C-3, C-4, C-9, and C-20 (O-3, O-4, O-9, and O-20) correspond to the O-11, N-13, N-1, and O-24 positions in teleocidin and the O-27, O-3, O-11, and O-30 oxygens in aplysiatoxin, respectively. In this model all distances with respect to overlap of the corresponding atoms are less than 1 A. In addition, all three types of molecules have their hydrophobic moieties oriented in a similar position. This model is further discussed with respect to other compounds showing various degrees of activity as tumor promoters, including mezerein, ingenol, and 4 alpha-TPA. The model explains how chemically diverse structures can have similar biological activity as tumor promoters and provides a basis for designing both agonists and antagonists of tumor promoters.

Topics: Carcinogens; Diterpenes; Lyngbya Toxins; Molecular Conformation; Phorbol Esters; Structure-Activity Relationship; Terpenes

Two polyacetates, aplysiatoxin and debromoaplysiatoxin, as well as 12-O-tetradecanoylphorbol-13-acetate (TPA), mezerein and teleocidin enhance nitroblue tetrazolium (NBT) reduction in mouse peritoneal macrophages in vitro. The ED50 values for NBT reduction of these 5 TPA-type tumor promoters were 4.2 ng/ml for TPA, 36 ng/ml for mezerein, 0.53 ng/ml for teleocidin, 1.5 ng/ml for aplysiatoxin and 108 ng/ml for debromoaplysiatoxin. The NBT reduction induced by the 5 tumor promoters is inhibited by 2 inhibitors of tumor promotion, retinoic acid and dibromoacetophenone. The possibility that tumor promotion by TPA-type tumor promoters involves similar mechanisms such as superoxide anion radicals release in cell membranes is discussed.

Topics: Acetophenones; Animals; Carcinogens; Cells, Cultured; Diterpenes; Female; Free Radicals; Lyngbya Toxins; Macrophages; Mice; Mice, Inbred Strains; Nitroblue Tetrazolium; Superoxides; Terpenes; Tetradecanoylphorbol Acetate; Tetrazolium Salts; Tretinoin

Tumor promoters such as phorbol 12-tetradecanoate 13-acetate (TPA), mezerein, teleocidin, aplysiatoxin, and benzoyl peroxide, although structurally unrelated, induce similar, profound changes in morphology in differentiated epithelial Madin-Darby canine kidney (MDCK) cell colonies. The alteration is evident in the organization of intermediate filaments in intact cells and in whole mounts of the nuclear matrix-intermediate filament (NM-IF) scaffold of the epithelial sheet. This substructure, obtained by salt extraction of the cytoskeletal framework, represents only 5% of the total cell protein but contains all of the intermediate filaments, nuclear matrix, and desmosomal core proteins arranged essentially as in the intact cell. The NM-IF is profoundly reorganized after exposure to TPA and retains the morphological changes observed in intact cells. These include bundling of the intermediate filaments, disruption of cell-cell borders, and marked deformation of the polygonal geometry of epithelia. Thus, TPA and all other complete or second-stage tumor promoters examined have a characteristic morphological signature that is not induced by mitogens, metabolic inhibitors, or agents known to disrupt microtubules or microfilaments. This signature, characteristic of tumor promoters, occurs in the absence of both protein and RNA synthesis. These results suggest that this response is prior to and independent of other biochemical markers for tumor promoters. Of the major filament systems, the cytokeratin network is implicated as an early or possibly primary site of tumor-promoter action because characteristics of the promoted cytoskeletal signature are observed in epithelial colonies after prior exposure to colchicine or cytochalasin D. Despite the massive reorganization of cytoskeletal morphology induced by TPA, the distribution of prelabeled proteins into structural fractions (i.e., cytoskeletal, chromatin, and the NM-IF) remains essentially unchanged. The sensitivity and specificity of the epithelial cell response suggest its possible use as a screen for promoting compounds.

Topics: Alkaloids; Animals; Benzoyl Peroxide; Carcinogens; Cell Line; Diterpenes; Dogs; Electrophoresis, Polyacrylamide Gel; Fluorescent Antibody Technique; Kidney; Lactones; Lyngbya Toxins; Microscopy, Electron; Terpenes; Tetradecanoylphorbol Acetate

Three potent tumor promoters of different classes, 12-O-tetradecanoylphorbol-13-acetate, dihydroteleocidin B, and aplysiatoxin, and two moderate tumor promoters, mezerein and debromoaplysiatoxin, enhanced the frequency of appearance of cadmium-resistant Chinese hamster lung cells when the cells were exposed to cytotoxic levels of CdCl2. With these compounds, the activity to induce cadmium-resistant cells correlated well with the potency of tumor-promoting activity. Cadmium resistance, which persisted after removal of the tumor promoters, was associated with the overproduction of metallothionein I messenger RNA. The amplified metallothionein I genes were shown by Southern blotting experiments. The relevance of the gene amplification caused by tumor promoters is discussed in relation to cancer development and progression.

Topics: Alkaloids; Animals; Cadmium; Carcinogens; Cell Line; Cricetinae; Cricetulus; Diterpenes; Gene Amplification; Genes; Lactones; Lung; Lyngbya Toxins; Metallothionein; Mollusk Venoms; Phorbol Esters; Terpenes; Tetradecanoylphorbol Acetate