Molecular Pharmacology, Vol 20, 614-620, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

Inhibition of Cell Division and of Microtubule Assembly by Elatone, a Halogenated Sesquiterpene

¹ Marine Science Institute and Department of Biological Sciences, University of California, Santa Barbara, California 93106

Elatone, the 9-keto derivative of the marine natural product elatol, produces an irreversible dose-dependent inhibition of cell cleavage in synchronously dividing Strongylocentrotus purpuratus sea urchin embryos. When added early in the cell cycle, elatone produces a significant and progressive inhibition of [³H]thymidine uptake within 45 min after fertilization, and nearly complete inhibition of [³H]thymidine incorporation during both the S1 and S2 replicative periods. Incorporation studies using eggs preloaded with [³H]thymidine demonstrate that elatone blocks incorporation during S2, a DNA replication period which partially overlaps mitosis. By utilizing the inherent synchrony of this cell-culture system we examined the time course of elatone inhibition. We found that inhibition of cell division and S2-DNA synthesis dropped precipitously if exposure to elatone was withheld until the onset of mitosis, suggesting that the events immediately prior to and/or at the beginning of the M-phase are critical to elatone’s mode of action. By using purified beef brain microtubules we have further demonstrated that elatone inhibits the rate of initiation of microtubule assembly in vitro, with consequent reduction in the steady-state levels of polymerized microtubules. Although the possibility for other modes of action certainly exists, these results are consistent with the hypothesis that elatone inhibits egg cleavage through inhibition of mitosis.

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ACKNOWLEDGMENTS We wish to thank Aileen Morse for demonstration of the beef brain preparation, Amy Kossoff for technical assistance during the incorporation studies, Paul Culver for critical review of the manuscript, and Dr. Leslie Wilson for helpful discussions, from which we gained a deeper understanding and appreciation of the dynamics of microtubule polymerization. Finally, the authors are especially grateful to Dr. William Fenical (Scripps Institution of Oceanography) for his generous supplies of purified elatol, elatone, and various other derivatives.