Fig. 4. Immunofluorescence assay of plinabulin and compounds a–f inhibition of tubulin polymerization in vitro. (a) Confocal images of DKP derivatives (5 nM) disrupting the mitotic spindles in BxPC-3 cell. (i) Nuclear (blue); (ii) tubulin (red); (iii) (i) and (ii) were overlapped. Scale bar is 50 μm. (b) Semi-quantitative analysis of the inhibition of tubulin polymerization.