The Microtubule-Stabilizing Agent Discodermolide Competitively Inhibits the Binding of Paclitaxel (Taxol) to Tubulin Polymers, Enhances Tubulin Nucleation Reactions More Potently Than Paclitaxel, and Inhibits the Growth of Paclitaxel-Resistant Cells

The lactone-bearing polyhydroxylated alkatetraene (+)-discodermolide, which was isolated from the sponge Discodermia dissoluta, induces the polymerization of purified tubulin with and without microtubule-associated proteins or GTP, and the polymers formed are stable to cold and calcium. These effects are similar to those of paclitaxel (Taxol), but discodermolide is more potent. We confirmed that these properties represent hypernucleation phenomena; we obtained lower tubulin critical concentrations and shorter polymers with discodermolide than paclitaxel under a variety of reaction conditions. Furthermore, we demonstrated that discodermolide is a competitive inhibitor with [H-3]paclitaxel in binding to tubulin polymer, with an apparent K-i value of 0.4 mu M. Multidrug-resistant human colon and ovarian carcinoma cells overexpressing P-glycoprotein, which are 900- and 2800-fold resistant to paclitaxel, respectively, relative to the parental lines, retained significant sensitivity to discodermolide (25- and 89-fold more resistant relative to the parental lines). Ovarian carcinoma cells that are 20-30-fold more resistant to paclitaxel than the parental line on the basis of expression of altered beta-tubulin polypeptides retained nearly complete sensitivity to discodermolide. The effects of discodermolide on the reorganization of the microtubules of Potorous tridactylis kidney epithelial cells were examined at different times. Intracellular microtubules were reorganized into bundles in interphase cells much more rapidly after discodermolide treatment compared with paclitaxel treatment. A variety of spindle aberrations were observed after treatment with both drugs. The proportions of the different types of aberration were different for the two drugs and changed with the length of drug treatment. [References: 40]

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