mitotic inhibitor
Meaning of mitotic inhibitor: Chemotherapy drugs that jam the machinery pulling chromosomes apart, so a dividing cell stalls partway through and dies.
Definition of mitotic inhibitor
A mitotic inhibitor is a drug that interferes with the spindle, the scaffold of protein filaments a cell builds to drag its duplicated chromosomes into two sets. Cells caught in the act of dividing cannot finish the job and are triggered to destroy themselves. Most of these agents were originally isolated from plants, and they are used mainly against cancers whose cells divide rapidly.
How do they actually work?
The spindle is built from microtubules, hollow rods of protein that grow and shrink constantly as the cell adjusts them. Two opposite tricks disable it. One group binds the building block and prevents new rod from being added, so the spindle never forms. The other group glues the rods rigid so they cannot shorten, and a spindle that cannot shorten cannot pull anything. Either way the cell arrests in the middle of mitosis and, unable to resolve the problem, switches on its own self-destruction program.
How do the main groups differ?
| Group | Originally from | Effect on the filaments |
|---|---|---|
| Vinca alkaloids | Periwinkle plant | Block assembly, so the spindle cannot be built |
| Taxanes | Yew tree bark and needles | Lock filaments so they cannot come apart |
| Epothilones | Soil bacterium | Lock filaments, in the manner of taxanes |
| Halichondrin analogs | Marine sponge | Block growth at the filament tip |
Why do the side effects fall where they do?
Two patterns follow directly from the mechanism. Normal tissues that renew fastest are hit alongside the tumor, which is why low blood counts, mouth soreness, bowel upset and hair loss recur across this whole class of antimitotic agent. The second pattern is more specific. Microtubules are not only spindle material; in nerve cells they form the rails along which supplies travel down fibers that may run the length of a limb. Interfering with them starves the far ends of those fibers, producing numbness, tingling and clumsiness in the hands and feet that can outlast treatment and often sets the practical ceiling on dose.
Also known as
Used in a sentence
The regimen combined a mitotic inhibitor with a platinum agent.
Good to know
These drugs do not slow growth in general terms; they halt cells partway through division, and because microtubules also carry supplies along nerve fibers, damage to the longest nerves commonly limits how much can be given.
Word origin
Where “mitotic inhibitor” comes from
Mitosis comes from the Greek mitos, meaning thread, after the threadlike appearance of chromosomes during division; inhibitor comes from the Latin inhibere, to hold back.