Drugs that Destabilize Microtubules

Microtubule-destabilizing drugs can prevent polymerization or promote depolymerization of microtubules. Examples include natural agents like vinblastine, vincristine, and colchicine and synthetic drugs like nocodazole.

Colchicine, a plant alkaloid, inhibits microtubule assembly and promotes disassembly of preformed microtubules; therefore it is used to treat tumors. Disassembly of  microtubules by colchicine prevents new blood vessel formation and destroys existing tumor blood vessels.

Colchicine acts by binding to the colchicine pockets present at the interface of free α- and β-tubulin subunits.

During mitosis, the tubulin-colchicine complex binds to the growing microtubule and prevents the complete polymerization of the spindle assembly. As a result, chromosomes remain fixed at metaphase plates and cannot segregate into single chromatids, resulting in the formation of tetraploid cells.