Sixteen of the 22 poorly characterized compounds were predicted to be antitubulin drugs (Table ). Among them, a widely used laser dye, coumarin-30 (the 70 th in the top 200 list, Fig. ), attracted our attention due to the combination of its high Pearson correlation coefficient (r = 0.723) with colchicine, its low mean cancer growth inhibition index (GI50 = 0.4 μM) and its wellcharacterized fluorescence properties.