Colchicine is a water-soluble alkaloid found in the autumn crocus; it has
been used as an anticancer drug. It blocks or
suppresses cell division by inhibiting
mitosis, the division of a cell's nucleus. Specifically, it inhibits the
development of spindles as the nuclei are dividing. Normally, the cell would
use its spindle fibers to line up its chromosomes, make a copy of them, and
divide into two new cells with each daughter cell having a single set of
chromosomes. With colchicine present, the spindle fibers don't form, and so
the cell can't move its chromosomes around. The cell may end up copying some
or all of the chromosomes anyway, but can't parcel them out into new cells,
and so it never divides.
Because cancer cells divide much more rapidly than normal cells,
cancers are more susceptible to being poisoned by mitotic inhibitors such as
colchicine, paclitaxel, and the Vinca alkaloids.
However, colchicine has proven to have a fairly narrow range of
effectiveness as a chemotherapy agent, so its only FDA-approved use is to
treat gout (it is one of the active ingredients of ColBenemid, anti-gout
tablets marketed by Merck & Co.), though it is also occasionally used in
veterinary medicine to treat cancers in some animals. It is also used as an
antimitotic agent in cancer research involving cell cultures.
Researchers aren't sure exactly how colchicine works against gout,
but it does seem to reduce the frequency of severe attacks and relieves
residual pain.
As far as side effects go, colchicine can cause a temporary reduction
in the number of leukocytes (white blood cells) in the bloodstream;
afterward, the leukocyte count can rebound to abnormally high levels.
Colchicine also causes teratogenic birth defects in lab animals, and so
pregnant women with gout should not use colchicine-containing drugs.
Colchicine poisoning resembles arsenic poisoning; the symptoms (which,
because it is a mitotic poison, occur 2 to 5 hours after the toxic dose has
been ingested) include burning in the mouth and throat, diarrhea, stomach
pain, vomiting, and kidney failure. Death from respiratory failure often
follows. A specific antidote doesn't exist, so treatment typically involves
giving the victim activated charcoal or pumping the stomach.