Colchicine

Colchicine inhibits microtubule polymerization by binding to tubulin, which disrupts spindle formation during mitosis. Since increased rate of mitosis is associated with cancer cell proliferation, blocking microtubule function with colchicine has been used as an approach to anti-cancer therapy. Its mitosis-inhibiting function is also utilized to perform karyotypes in genetic studies.
Colchicine blocks chromosome segregation during meiosis. Therefore it is used to induce polyploidy (tetraploid) in plant cells.