calyculin-a and Stomach-Neoplasms

Okadaic acid is functionally a potent tumor promoter working through inhibition of protein phosphatases 1 and 2A (PP1 and PP2A), resulting in sustained phosphorylation of proteins in cells. The mechanism of tumor promotion with okadaic acid is thus completely different from that of the classic tumor promoter phorbol ester. Other potent inhibitors of PP1 and PP2A - such as dinophysistoxin-1, calyculins A-H, microcystin-LR and its derivatives, and nodularin - were isolated from marine organisms, and their structural features including the crystal structure of the PP1-inhibitor complex, tumor promoting activities, and biochemical and biological effects, are here reviewed. The compounds induced tumor promoting activity in three different organs, including mouse skin, rat glandular stomach and rat liver, initiated with three different carcinogens. The results indicate that inhibition of PP1 and PP2A is a general mechanism of tumor promotion applicable to various organs. This study supports the concept of endogenous tumor promoters in human cancer development.

Topics: Animals; Carcinogens; Disease Progression; Enzyme Inhibitors; Humans; Marine Toxins; Mice; Models, Molecular; Neoplasms; Neoplasms, Experimental; Okadaic Acid; Oxazoles; Protein Phosphatase 1; Protein Phosphatase 2; Rats; Skin Neoplasms; Stomach Neoplasms; Tetradecanoylphorbol Acetate; Tumor Necrosis Factor-alpha

Topics: Animals; Antifungal Agents; Carcinogens; Ethers, Cyclic; Liver Neoplasms; Marine Toxins; Mice; Molecular Structure; Okadaic Acid; Oxazoles; Peptides, Cyclic; Pyrans; Rats; Skin Neoplasms; Spiro Compounds; Stomach Neoplasms; Structure-Activity Relationship