Disruption of microtubule function in cultured human cells by a cytotoxic ruthenium(ii) polypyridyl complex.

Treatment of malignant and non-malignant cultured human cell lines with a cytotoxic IC dose of ∼2 μM tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(ii) chloride () retards or arrests microtubule motion as tracked by visualizing fluorescently-tagged microtubule plus end-tracking proteins. Immunofluorescent microscopic images of the microtubules in fixed cells show substantial changes to cellular microtubule network and to overall cell morphology upon treatment with . Flow cytometry with MCF7 and H358 cells reveals only minor elevations of the number of cells in G/M phase, suggesting that the observed cytotoxicity is not tied to mitotic arrest. studies with purified tubulin reveal that acts to promote tubulin polymerization and when imaged by electron microscopy, these microtubules look normal in appearance. Isothermal titration calorimetry measurements show an associative binding constant of 4.8 × 10 M for to preformed microtubules and support a 1 : 1 to tubulin dimer stoichiometry. Competition experiments show does not compete for the taxane binding site. Consistent with this tight binding, over 80% of the ruthenium in treated cells is co-localized with the cytoskeletal proteins. These data support acting as an microtubule stabilizing agent and sharing many similarities with cells treated with paclitaxel.