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Antimitotic and Antitubulin Activity of the Tumor Inhibitor Steganacin¹

Departments of Biology [R. W-J. W., L. I. R.] and Chemistry [S. M. K.], University of Virginia, Charlottesville, Virginia 22901

Steganacin, a newly isolated tumor inhibitor, completely inhibits cleavage in sea urchin eggs at 3 x 10^–7 M by preventing the formation of the mitotic apparatus. Steganacin inhibits the polymerization of tubulin in vitro and also causes a slow depolymerization of preformed microtubules. Optical ultracentrifuge studies of steganacin-treated tubulin show a small reduction in 20 S and 30 S peaks at 0°. In electron microscope studies the ring structure of tubulin is seen at 0° but disappears if the temperature of tubulin incubated with steganacin is raised to 37°. Steganacin inhibits the binding of colchicine to tubulin and thus resembles podophyllotoxin, which also competitively inhibits colchicine binding. Steganacin has a trimethoxybenzene ring and probably interacts with that portion of the colchicinebinding site that recognizes the trimethoxybenzene ring of colchicine.

¹ This work was supported in part by Grant CA-12059 from the National Cancer Institute. A preliminary report of this work was presented at the First International Congress on Cell Biology (30).

² To whom requests for reprints should be addressed, at the Department of Biology, Gilmer Hall, University of Virginia, Charlottesville, Va. 22901. This work will be submitted to the Department of Biology, University of Virginia, in partial fulfillment of the requirements for the degree of Master of Science.

³ Recipient of Grant BMS-75-17790 from the National Science Foundation.

⁴ Recipient of Grant CI-102K from the American Cancer Society.

Received 1/14/77. Accepted 5/20/77.

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