First, we examined a series of compounds 1a-d, 2, 3 (Fig. ) that were synthesized and partially evaluated by our group recently (Fig. , Fig. ). Based on a combination of microtubule dynamics and cancer cell cycle assays, the activities of these compounds were expected to range from low micromolar to undetectable, providing a balanced selection for testing the sensitivity and specificity of the C-MST assay. The assay has correctly identified all potent tubulin binders and accurately sorted out the non-binders (Fig. , Fig. ).