Colcemid

Used in cytogenetics, colcemid, also known as demecolcine, is related to colchicine but it is less toxic. It depolymerises microtubules and limits microtubule formation (inactivates spindle fibre formation), thus arresting cells in metaphase and allowing cell harvest and karyotyping to be performed.

Colcemid is a microtubule-depolymerizing drug like vinblastine. It acts by two distinct mechanisms. At very low concentration it binds to microtubule plus end to suppress microtubule dynamics. Recent study has found at higher concentration colcemid can promote microtubule detachment from microtubule organizing center. Detached microtubules with unprotected minus ends depolymerize with time. Cytotoxicity of the cells seems to correlate better with microtubule detachment. Lower concentrations affect microtubule dynamics and cell migration.

Colcemid is used primarily for scientific research in cells. It is used in a variety of ways, however, until recently, was used mostly for the study of mitosis in cells. For example, microtubules are necessary for the splitting of cells. More importantly, the movement of chromosomes during the M phase. Colcemid inhibition of microtubules causes aneuploidy in mitotic cells where the microtubules fall apart or are suppressed before they can complete their function of pulling chromosomes into the daughter cell, also known as nondisjunction of chromosomes. Colcemid, depending on dosage, has also been found to cause DNA fragmentation of chromosomes in micronuclei when nondisjunction occurs.

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