Calyculins, potent antitumour metabolites from the marine sponge Discodermia calyx: biological activities.

Calyculins A-D, extraordinary metabolites of the Japanese marine sponge Discodermia calyx, showed marked cytotoxicity against murine leukaemia cells and echinoderm embryos. The major compound, calyculin A, also had potent antitumour activity, although it was highly toxic in mice. Its mode of action in L1210, rat fibroblasts and fertilized sea urchin eggs has been studied, which led the authors to predict that calyculins affect primarily a system other than macromolecular syntheses.