Discodermolide, a cytotoxic marine agent that stabilizes microtubules more potently than taxol

Computer-assisted structure analysis indicated (+)-discodermolide, a polyhydroxylated alkatetraene lactone marine natural product, was an antimitotic compound, and we confirmed this prediction. Previous work had shown an accumulation of discodermolide-treated cells in the G(2)/M portion of the cell cycle, and we have now found that discodermolide arrests Burkitt lymphoma cells in mitosis. Discodermolide-treated breast carcinoma cells displayed spectacular rearrangement of the microtubule cytoskeleton, including extensive microtubule bundling. Microtubule rearrangement that occurred with 10 nM discodermolide required 1 mu M taxol. Discodermolide had equally impressive effects on tubulin assembly in vitro. Near-total polymerization occurred at 0 degrees C with tubulin plus microtubule-associated proteins (MAPs) under conditions in which taxol at an identical concentration was inactive. Without MAPs and/or without GTP, tubulin assembly was also more vigorous with discodermolide than with taxol under every reaction condition examined. Discodermolide-induced polymer differed from taxol-induced polymer in that it was completely stable at 0 degrees C in the presence of high concentrations of Ca2+. In a quantitative assay designed to select for agents more effective than taxol in inducing assembly, discodermolide had an EC(50) value of 3.2 mu M versus 23 mu M for taxol.