Tubulin inhibitor 15 (compound 6) (0-25 μM, 24 h followed by a 72 h compound-free incubation period) exhibits antiproliferative activity with IC 50 s of 1.60, 0.22, 1.40, 0.68, 0.47, 0.21, >25 μM for MCF7, MDA-MB-231, HepG2, SNU423, A549, HCT116, THLE-3 cells [1]. Cell Proliferation Assay [1] Cell Line: MCF7, MDA-MB-231, HepG2, SNU423, A549, HCT116 cells Concentration: 0-50 μM Incubation Time: 96 h Result: Exhibited antiproliferative activity with IC 50 s of 0.68, 0.21, 3.03, 0.60, 0.38, 0.19 μM for MCF7, MDA-MB-231, HepG2, SNU423, A549, HCT116 cells, respectively. Cell Cytotoxicity Assay [1] Cell Line: HepG2 cells Concentration: 0.5, 1 μM Incubation Time: 14 days Result: No colonies were evident when cells were treated with 0.5 or 1 μM.