To visualize the effects of coumarin-30 on microtubules and mitotic spindles in vivo, we fixed A549 cells after 24 hours of incubation with coumarin-30, DMSO, nocodazole, or paclitaxel and stained them with anti-tubulin antibodies (Fig. , Fig. , Fig. ). In contrast to treatment with DMSO, where normal microtubules and mitotic spindles were observed, treatment of the cells with paclitaxel led to bundled microtubules and aberrant spindles, while in cells treated with nocodazole or coumarin-30, the microtubules were completely disassembled (Fig. , Fig. ). Coumarin-30 and nocodazole were similarly effective on microtubules in mitotic and interphase cells (compare Figs. S1 and Fig. ). These observations confirmed that coumarin-30 acts as a potent microtubule destabilizer.