induce tubulin polymerization polymerization was then monitored in a gilford spectrophotometer at 350 nm the final reaction mixtures 0 25 ml contained 1 5 mg ml tubulin 0 6 mg ml microtubule associated proteins maps 0 5 mm gtp 0 5 mlm mgcl 2 4 dmso and 0 1m 4 morpholineethanesulfonate buffer mes ph 6 4 ic50 is the amount of inhibitor needed to inhibit tubulin polymerization 50 with respect to the amount of inhibition that occurs in the absence of inhibitor newly prepared compounds were evaluated for cytotoxic activity against a variety of cell lines derived from human tumors using an assay system similar to the national cancer institute procedure previously described monks et al j natl cancer inst 1991 briefly the cell suspensions diluted according to the particular cell type and the expected target cell density 5 000 40 000 cells per well based on cell growth characteristics were added by pipet 100 ul to 96 well microtiter plates inoculates were allowed a preincubation time of 24 28 hours at 37 c for stabilization incubation with the inhibitor compounds lasted for 48 hours in 5 co 2 atmosphere and 100 humidity determination of cell growth was performed by in situ fixation of cells followed by staining with a protein binding dye sulforhodamine b srb which binds to the basic amino acids of cellular macromolecules the solubilized stain was measured spectrophotometrically several compounds were evaluated for cytotoxic activity against human p388 leukemia cell lines the effective dose or ed50 value defined as the effective dosage required for inhibition of 50 of cell growth was measured these and additional compounds were evaluated in terms of growth inhibitory activity against several other human cancer cell lines including central nervous system u201c cns u201d sf 268 pancreas bxpc 3 non small cell.