In vitro activity: Vincristine inhibits net addition of tubulin dimers at assembly ends of steady-state microtubules with Ki of 85 NM. At low concentrations, Vincristine stabilizes the spindle apparatus resulting in failure of the chromosomes to segregate leading to metaphase arrest and inhibition of mitosis. At higher concentrations, Vincristine may disrupt and induce total depolymerization of microtubules. Vincristine induces apoptosis in tumor cells and inhibits SH-SY5Y cell proliferation with IC50 of 0.1 μM. Vincristine induces mitotic arrest and promots the expression of caspase-3 and -9 and cyclin B, while decreasing the expression of cyclin D. Vincristine induced neurotoxicity is caused by interference with microtubule function, which results in blockage of axonal transport and thus in axonal degeneration.

Cell Assay: Cells are plated in 2 mL of medium in 35-mm plates at a concentration of about 5 × 104 cells/mL and grow for 24 h at 37 ℃ in an atmosphere of 5% CO2 and 95% air. Then medium is replaced with fresh medium lacking or containing 4 nM drug and proliferation is continued for 3 days. Cell counts are done each day in a Coulter Counter after detaching the cells with trypsin and EDTA.