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

Abstract

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 [3H]paclitaxel in binding to tubulin polymer, with an apparent Ki value of 0.4 microM. 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.

Peloruside A Does Not Bind to the Taxoid Site on β-Tubulin and Retains Its Activity in Multidrug-Resistant Cell Lines

“…The paclitaxel-resistant cell lines PTX10, PTX22, and A8 showed high resistance ratios (133-, 18-, and 9-fold, respectively) for paclitaxel compared with the parental cell line 1A9 (P Ͻ 0.01; Kruskal-Wallis nonparametric test). Although these resistances are less than those seen with cells that overexpress P-gp (312-and 1417-fold; Table 1), the values are similar to those measured by others in these cell lines (8,9,11,13). As reported previously by Pryor et al (11) and as seen in our study, A8 and B10 cells are more resistant to epothilone B than PTX10 and PTX22 cells.…”

“…Discodermolide is also insensitive to mutations at amino acids ␤270 (PTX10 cells) and ␤364 (PTX22 cells; Ref. 13). Thus, discodermolide is unaffected by a number of ␤-tubulin mutations that increase resistance of cells to paclitaxel and/or epothilone, despite the fact that discodermolide competes with paclitaxel for binding to microtubules (11,13).…”

“…It is therefore important to identify drugs that have similar or improved pharmacological properties to paclitaxel that are also effective in paclitaxel-resistant cancer cells. Most of the microtubule-stabilizing agents have been examined for their susceptibility to MDR, and three look particularly promising because of their lack of interaction with the P-gp pump: epothilone (9 -12); discodermolide (13); and laulimalide (11,14). Recently, it was shown that laulimalide is not only more toxic than paclitaxel in cells with a MDR phenotype, but it also binds to a different site on tubulin to paclitaxel, epothilone, and discodermolide (11).…”

2-Methoxyestradiol suppresses microtubule dynamics and arrests mitosis without depolymerizing microtubules

“…Mitotic arrest that is associated with suppression of microtubule dynamics by many drugs, including the Vinca alkaloids and paclitaxel, is characterized by spindle abnormalities including uncongressed chromosomes, multipolar spindles, and other aberrant spindle morphologies (14,22,23). In addition to its effects on microtubule dynamics and polymer mass, 2ME2 also induced spindle abnormalities.…”

Understanding tubulin–Taxol interactions: Mutations that impart Taxol binding to yeast tubulin

“…However, there has been no direct experimental evidence supporting any of the putative binding interactions. Other recently discovered, potent, microtubule-stabilizing compounds such as the epothilones, discodermolide, and eleutherobins compete with Taxol for binding to mammalian microtubules (18)(19)(20). Therefore, despite a lack of structural similarity, these compounds seem to share an overlapping binding site with Taxol.…”