Spindle inhibitors affect the structural process that allows cell division or mitosis, phases four and five. In order for the cell to divide, the newly formed DNA must split into two identical pieces. The splitting process is assisted by the development of spindle fibers that pull the copies apart into separate cells. Spindle inhibitors affect the creation of the spindle fiber mechanism, stopping cell division.
There are several types of spindle inhibiting drugs.
Plant alkaloids – In the early 1950s, research interests turned to naturally occurring substances. The Eli Lilly Company, while pursuing other research, discovered that alkaloids from the Madagascar periwinkle (Vinca Rosea) disrupted the development of spindle fibers, stopping cell division. These drugs, vincristine, vinblastine and vinorelbine, remain prominent as chemotherapeutic agents in the treatment of many types of cancer.
Other plants that have yielded mitosis–disrupting include the Chinese tree Camptotheca, also discovered in the 1950s. A derivative drug, irinotecan, was FDA-approved in 1996 for the treatment of colon cancer and later for use with lung and ovarian cancer.
Taxanes – In the 1960s, researchers discovered a new class of drugs called taxanes, that bind to spindle fibers, interfering with their function. Taxanes were isolated from the bark of the Yew tree. In 1992, the FDA approved Taxol (paclitaxel) for the treatment of ovarian cancer and the drug is now approved for use against many cancers including breast, lung, bladder, prostate, and gastrointestinal.
Taxatere (docetaxel) has been approved for the treatment of many different cancers, most recently head and neck cancer ion conjunction with other chemotherapeutic drugs.