Inhibitors of microtubule dynamics are expected to arrest cells in mitosis, possibly further promoting apoptosis. To test whether this is true for compounds 2 and 3, we examined their effects on the proliferation of human cancer cells. First, we analyzed the effect of compounds 2 and 3 on cultured lung adenocarcinoma cells, A549, using the flow cytometry-based propidium iodide (PI) cell cycle assay (Fig. ). In the presence of compound 2a, accumulation of cells in G2/M stage was observed at 116 μM and more prominent -at 200 μM. For compounds 2c and 2d, no significant G2/M accumulation was observed at maximum concentrations. Compound 3a induced G2/M accumulation at concentrations above 22 μM and more prominently -at 66 μM. For compound 3b, no significant G2/M accumulation was observed at 66 μM, the maximum concentration we tested.