A sensitive assay for taxol and other microtubule-stabilizing agents

The ability of taxol to protect microtubules in cultured human ovarian carcinoma cells from drug- and cold-induced depolymerization was characterized as a functional assay for microtubule stabilizing agents. Treatment of the cells with concentrations of vinblastine or colchicine of 50 nM or greater, or incubation at 4°C resulted in complete depolymerization of cytoplasmic microtubules. Pretreatment with taxol for 3 h enabled the cells to maintain substantial numbers of microtubules following the application of vinblastine or colchicine. This protective effect was easily observed at 50 nM taxol, whereas taxol-induced microtubule bundling was observed only at concentrations of 500 nM or greater. Concentrations of taxol as low as 10 nM stabilized microtubules against cold-induced depolymerization. Therefore, protection of microtubules from drug- and cold-induced depolymerization provides a sensitive functional assay for taxol. These systems should be similarly effective in identifying novel compounds which stabilize microtubules.